Optional Science Book Class 10

Internal nares: These are the posterior openings of the nasal chambers that lead to the
pharynx.

Pharynx: The pharynx is the passage Right caudal lobe
for both food and air. It is divided
into the nasopharynx above the palate fig: Respiratory system in rat
and the oropharynx behind the buccal
cavity. The edge of the soft palate
acts as a valve to prevent food from
passing into the nasopharynx during
swallowing.

Larynx or voice box: The pharynx leads to both the larynx and oesophagus. The larynx
consistsof cartilage and has vocal cords. The opening of the pharynx into the larynx, or
voice box, is called the glottis. The glottis is closed when food is swallowed to prevent
the passage of food into the larynx and lower respiratory passages. The vocal cords
help in the production of sound, but it is not well marked in a rat.

Trachea (wind pipe): The trachea is a tube, in the upper portion of the rat’s chest that
connects the pharynx and nasal cavities to the lung. It runs ventral to the oesophagus.
The trachea divides to form two main branches called primary bronchi. Each bronchus
enters a lung. Both the trachea and bronchi have cartilaginous rings embedded in their
walls to prevent the tube from collapsing. As they enter the lungs, each bronchus divides
into secondary branches, or bronchial tubes. Each secondary branch or bronchial tube
divides to form tertiary branches or bronchioles. These are again subdivided into
respiratory bronchioles.

From each respiratory bronchiole, several alveolar ducts arise, leading into subdivisions
called air sacs. The wall of the air sacs is folded to form tiny alveoli. Alveoli are richly
supplied with blood. Exchange of gases takes place in the alveoli.

Lungs: A pair of lungs is present. Each lies one on either side of the rat’s heart in the
thoracic cavity. Left lung of the rat contains only one lobe whereas right lung contains
four lobes. Each lung is composed of numerous branches of bronchiole and each
bronchiole ends with a microscopic unit called alveoli. Alveoli is the unit where the
actual exchange of inhaled oxygen gas and released carbon dioxide gas takes place.

Lungs are lined by two thin membranes, called pleura for their protection. A space
called pleural cavity is present between the two pleura. The pleural cavity is filled with
a pleural fluid. It protects the lungs from mechanical injury and friction during the
contraction and relaxation of lungs. Lungs are protected inside the rib cage.

Respiration in rat

Rats inhale and exhale through their nostrils. Air is brought in through the nasal cavities and
passed into the pharynx, then into the trachea and lungs. When rat is inhaling, the glottis closes
to prevent food particles from entering the pharynx. This prevents the rats from choking on
food particles.

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The inhaled air comes to the alveoli travels through the respiratory tract (trachea, bronchi,
bronchioles). In alveoli there is carbon dioxide gas carried by the blood which is produced
from the oxidation of food. Oxygen and carbondioxide gases get exchanged in alveoli. Red
blood cells in the blood absorb oxygen and circulate it to different parts of the rat’s body with
the pumping of heart. Carbon dioxide is exhaled through the same tract.

The trachea connects the pharynx and nasal cavities to the lung. The diaphragm sits just below
the lungs and looks like a sheet of muscle. The diaphragm helps the movement of the lungs
as the rats breathes.

Activity 2

With the help of your teacher, dissect a rat carefully. Observe the respiratory tract of the
rat. Draw the observed respiratory tract of the rat, label it and discuss itsrespiratory system.

Urinogenital system of rat

The urinogenital system of a rat includes the organs concerned with reproduction and urinary
excretion. Although the functions of the organs involved in excretion and reproduction are
unrelated, the organs are morphologically associated and often used as common ducts.

The major structures of the urinary system in a rat are a pair of kidneys, ureters, urinary
bladder and urethra. The principal function of the urinary system is the maintenance of water
and electrolyte homeostasis. The major structures of the reproductive system in the male are
a pair of testes, epididymis, vasa deferens, urethra, and penis. The major structures of the
reproductive system in the female are the ovaries, a pair of fallopian tubes, uterus and vagina.

Excretory organs (urinary system)

Kidneys: The primary organs of the excretory system are the kidneys. These are large
bean shaped structures located toward the back of the abdominal cavity and made up
of millions of nephrons (structural and functional unit of kidney). A rat’s body has a
pair of kidneys, one on the left and one on the right. The right kidney is slightly higher
in position. The kidney consists of an outer cortex and an inner medulla. Bowman’s
Capsule, proximal tubules and distal tubules are located in the cortex. The loop of
Henle and the collecting tubules are located in the medulla. In the center, there is a
spherical structure with a coiled mass of capillaries, called glomerulus.

Kidneys help in the removal of nitrogenous waste products of protein like creatinine,
uric acid, urea, ammonia and controlled amount of water and salts. The function of
kidney occurs in the nephron. At the top of the kidneys, there are small yellowish
glands embedded in the fat called adrenal glands.

Ureters: The ureter is a long tube coming out of each kidney. Ureters carry urine from
the kidney to the urinary bladder.

Urinary bladder: It is a muscular sac-like structure in which two ureters open. The
urinary bladder stores urine temporarily.

Urethra: It is a tubular structure, which extends from the urinary bladder. The urethra
carries urine from the bladder to the urethral orifice. In the male, it carries both urine
and semen.

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Reproductive organs of male rat

Testes (singular: testis): Testes are oval shaped organs located in the scrotal sac. The
scrotal sacs are found in the form of pouches lying in front of the anus, between the
hind limbs. Spermatogenesis occurs in epithelial lining within the testes. Testes also
help in the secretion of steroidal hormone like testosterone and progesterone. The
urethra carries the sperm though the penis out of the body.

Epididymis: On the surface of the testis (lying along the inner edge of the testis), there
is a coiled tube called the epididymis. It collects and stores sperm cells.

Vasa deference: The vasa deferens is a straight tube which carries sperm from the
epididymis to the urethra. It lies on the inner side of the testis and opens into the
urethra.

Seminal vesicles: These are the lumpy brown ) I
glands located to the left and right of the I
urinary bladder. The gland below the bladder
is the prostate gland. It is partially wrapped Uterine Hom
around the penis. The seminal vesicles and the
prostate gland secrete alkaline materials called Urinary Bladde
seminal fluid (semen).

Penis: It is a long, narrow and cylindrical
copulatory organ. It is covered by a loose
sheath called the prepuce. The penis of the rat
has a bony process called the os-penis.

Accessory sex organs: The accessory sex organs fig: Genital organ of the female rat
in male rat are the seminal vesicles, prostate
and coagulating gland.

Reproductive organs of female rat

Ovaries: Ovaries are small and compact )
yellowis pea sized bodies (lumpy glands)
present at the tip of the uterine horns. They
are normally covered by a large amount of fat.
In mature ovaries, ovarian follicles are found.
Ovaries produce ova and female sex hormones.

Fallopian tubes: The fallopian tubes are

narrow coiled and convoluted tubes which

receive ova from the ovary.
Uterus: The uterus is a hollow muscular structure. Thefigu:tGeerniintael ohrogarnnosf athreefefmuaslee dratn.penagr the

vagina. Embryonic development takes place in the uterus. The embryo gets attached to

the uterine wall through the placenta.

Vagina: It is a short muscular tube which extends from the uterus and opens outside
as a vaginal opening (vulva). The vagina divides into two uterine horns that extend
toward the kidneys.

Clitoris: It is a small rod like organ lying at the anterior end of the vulva.

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Accessory sex organs: The accessory sex organs in female rat are bulbovrethral gland
and prenuptial gland.

Memory Plus

The duplex uterus (two uterine horns), present in rat, has multiple chambers for the
development of multiple embryos. Whereas only one uterus (simplex uterus) is present
in human.
A female rat delivers 6-8 young ones in a litter. The new born are hairless, blind and
deaf. The gestation period is about 22-23 days.

Activity 3

With the help of your teacher, dissect a rat carefully. Observe the urogenital tract of the
rat. Draw the observed uro-gential tract of the rat, label it and discuss its urinary and
reproductive system.

Life cycle of a rice plant (Oryza sativa)

Introduction

The rice plant is an annual grass that produces an edible seed, which is called rice. Rice is
a staple food in the diet of many cultures worldwide. The rice plant comes from the family
Gramineae (Grass family).

The rice plant grows rapidly. The rice plant usually takes 3-6 months from germination to
maturity, depending on the variety and the environment. It is not a water plant, but substantial
amount of water is required for planting. It is commonly grown in flooded fields. Cultivated
species of rice are considered to be semi-aquatic plants.

General information of the plant Classification
Kingdom: Plantae
Habitat: Semi-aquatic plant, cosmopolitan in distribution. The Division: Tracheophyta
rice plants are commonly found in temperate regions and also in Sub-division: Angiosperm
tropical and sub-tropical regions. Class: Monocot
Genus: Oryza
Habit: Annual or perennial shrubs cultivated as a crop. Species: sativa
Type: Rice
Root: Adventitious, fibrous

Stem: Erect, herbaceous, solid, cylindrical presence of distinct
nodes and internodes, branching from base, the stem is called
culm.

Leaf: Simple, alternate, exstipulate, sessile, leaf blade long and narrow with the leaf sheath
surrounding the innternode completely, hairy or rough, linear, parallel venation.

Flower:

i. It is Bracteate. Which means flower has a bract (i.e. a modified leaf growing just below
a flower which protects the flower in the bud condition).

ii. It is Zygomorphic. Which means flowers can be divided by only a single plane into
two mirror-image halves.

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iii. The perianth (i.e., the non-reproductive part of the flower
consisting of the calyx and the corolla) has two lodicules
(i.e., small scales below the ovary)

iv. Androecium (A) has six stamen and Gynoecium (G) has
one carpel.

Floral formula: Br%P2 A G6 (1)

Note: Br-Bracteate %- Zygomorphic
P- Perianth A- Androecium

G- Gynoecium

Floral diagram:

whorl 1- one palea and one lemma

whorl 2- two lodicules

whorl 3- six stamens Flornl Diag.-a m
whorl 4- one carpel

Fruit: It is caryopsis. Which means ovary wall (pericarp) is completely fused with the seed
coat.

Seed: Endospermic, with a single cotyledon.

Life cycle of a rice plant

~rlowerint

'I J''

H!I1-----Y------ept1tlw phase --- - - Reproduct ion - -1------------
Ylfllbt. - - - ----------~
----phase -
~------------
-----
fig: Life cycle of rice plant

Rice varieties can be categorized into two groups: the short-duration varieties, which mature

in 105-120 days, and the long-duration varieties, which mature in 150 days. A 120-day variety,

when planted in a tropical environment, remains around 60 days in the vegetative stage, 30

days in the reproductive stage, and 30 days in the ripening stage.

The growth of the rice plant is divided into three stages:

1. Vegetative stage (germination to panicle initiation)
2. Reproductive stage (panicle initiation to flowering) and
3. Ripening stage (flowering to mature grain)

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1. Vegetative Stage

i. Germination: The life cycle of rice begins with a seed. The rice

seed consists of the hull and the endosperm. The hull is an outer

protective coat of the embryo, which forms the actual plant.

The endosperm is the starchy part that provides food for the

seed when it begins to grow. When the seed is sown in watery

conditions, such as a flooded rice field, it will sprout. Cultivated

rice is sown in the spring. fig: Rice seed

ii. Early vegetative stage: As the seed grows, roots will grow down into the soil

beneath the water. The roots anchor and support the plant. It also absorbs nutrients

from the soil. Leaves will also begin to grow toward the surface of the water. In

cultivated rice, the young seedlings are harvested in bunches. These are then

separated into individual plants and are then replanted in the flooded rice fields in

evenly spaced rows to allow the plant to grow to full size. This improves the yield

of the seeds of the plant.

iii. Late vegetative stage: Late vegetative stage is also referred to as the tillering stage.
When the plant is mature and has reached a height of 3 to 4 feet, it will produce a
reproductive stem called a tiller. This usually occurs around 40 days after sowing.
The stem will continue to grow, eventually producing a flower head.

2. Reproductive stage
The flower head, also known as a spike, will then produce 100 to 150 tiny flowers. Each
flower is small and forms several long, thin stems that radiate upward from the tiller.
These flowers, once pollinated, will then form seeds. This usually takes around 30 days
to complete.

The first sign that the rice plant is getting ready to enter its reproductive phase is a
bulging of the leaf stem that conceals the developing panicle, called the ‘booting’ stage.
Then the tip of the developing panicle emerges from the stem and continues to grow.
Rice is said to be at the ‘heading’ stage when the panicle is fully visible. Flowering
begins a day after heading has completed. As the flowers open they shed their pollen
on each other so that pollination can occur. Flowering can continue for about 7 days.

3. Ripening stage

During the next 30 days, the rice seeds will eventually ripen, turning golden brown
when fully ripe. The ripening process can be affected by the temperature and change in
climate. A cool, rainy weather can lengthen the process, while warm, sunny conditions
can shorten it. Once completely ripe, the seeds can then be harvested for food.

Memory Plus

When rice is harvested, it is called ‘paddy’. Each paddy grain has many layers with the
outermost layer forming the husk. Each husk protects one half of the paddy. The husk
is composed of silica and cellulose. The next layer is bran. Bran is mainly composed of
fiber, Vitamin B complex, protein and fat, and forms the most nutritious part. The inner
part of the grain is the rice kernel, which is composed of mainly starch.

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Endocrine System

There are glands in our body that secrete hormones and regulate cellular metabolism,
reproduction, sexual development, heart rate, sugar level, digestion etc. The endocrine system
is a chemical messenger system of an organism consisting of hormones, the group of glands
that secrete those hormones directly into blood to regulate the function of distant target
organs. The branch of science that deals with the study of the structure, secretion and functions
of different endocrine glands is called Endocrinology. There are two types of glands found in
the human body:

i. Exocrine glands: Exocrine glands
pour their secretions into a duct. For
example: sweat glands, tear glands,
etc. These glands are present near
from the site of action and secrete
enzymes.

ii. Endocrineglands:Endocrineglands
are richly supplied with blood
vessels and pour their secretions
(hormones) directly into the blood
vessels. These glands are often
called ductless glands. Example:
thyroid gland, adrenal gland. The
secretions of the endocrine glands
are called hormones.

Hormones

Hormones are chemical messengers that fig: Endocrine glands
are released into the blood stream by
the endocrine glands. Hormones control
or regulate many biological processes.

Although hormones reach all parts of the

body, only target cells respond to them

and regulate many biological processes.

Fact with reason

Hormones are called chemical messengers, why?

Hormones are secreted by endocrine glands. They are secreted in one part of the body and
carried by the blood to another part where they stimulate or inhibit specific physiological
processes. So, hormones are called chemical messengers.

Characteristics of hormones

1. Hormones may be protein or non-proteinaceous. They are composed of amino acids,
steroids, etc.

2. They are secreted as per the need but are neither excreted nor stored.
3. Hormones are transported by blood.

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4. Hormones act either by stimulating or inhibiting the target organs.
5. They regulate long-term effects like growth, change in behavior, etc.
6. They are soluble in water and blood.

Functions of hormone

Hormones have following functions:
1. Hormones regulate metabolic activities, glandular secretion, etc.
2. They control Growth and development of body.
3. They control reproduction by regulating the activities like gametogenesis, development

of the sexual characteristics, etc.
4. Hormones conserve water and minerals in the body.

Memory Plus

Thomas Addison is considered as the ‘father of endocrinology’. He was the first who
reported a disease due to malfunction of adrenal gland known as Addison disease.

Major Glands of Endocrine System

Following are the major glands in human endocrine system:

1. Pituitary 2. Thyroid

3. Parathyroid 4. Adrenal

5. Pancreas 6. Gonads (Testes and Ovaries)

7. Pineal Hypothalamus

1. Pituitary gland: The pituitary Bone

gland is a small pea-sized gland

connected to the inferior portion of

the hypothalamus of the brain. The

pituitary gland is actually made up of

three completely separate structures:

the posterior, intermediate and Anterior
anterior pituitary lobes. lobeol
pituitary
i. Anterior pituitary lobe:
Posteri or Anterior Posterior
lobe of pituitary pituitary
pituitary

fig: Pituitary gland

The anterior pituitary gland is controlled by the releasing and inhibiting hormones of

the hypothalamus. It produces six important hormones:

i. Thyroid stimulating hormone (TSH): It stimulates the thyroid gland to produce
thyroxine hormone (T4) and triiodothyronine (T3).

ii. Adrenocorticotropic hormones (ACTH): It stimulates the adrenal gland to
produce corticosteroids hormone.

iii. Gonadotropins: Gonadotropins are hormones secreted by gonadotrope cells of
the anterior pituitary which regulate the functions of the gonads in both sexes.
These are:

Follicle stimulating hormone (FSH): It stimulates the follicle cells of the gonads
to produce gamates- ova in females and sperm in males.

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Luteinizing hormone (LH): It stimulates the gonads to produce sex hormones-
estrogen in females and testerone in males.
v. Human growth hormone (HGH): It acts on many target cells throughout the body by
stimulating their growth, repair and reproduction. It also stimulates cellular metabolism,
protein synthesis, mobilizes fats and inhibits glucose uptake. It is very important for
normal physical growth in children.
Effects due to hyposecretion: Deficiency of this hormone leads to dwarfism(small height
and sexual immaturity) and simmond's diseases (loss of body weight)occur
Effects of hypersecretion: Hyper-secretion leads to gigantism and abnormal size of the
hand, feet or face.
vi. Prolactin (PRL): It stimulates the mammary glands to produce milk after child birth.

ii. Intermediate pituitary lobe:

The intermediate pituitary gland produces melanocyte stimulating hormone (MSH). It
stimulates the production and release of melanin pigment (melanocytes).

Adrenal Breast
cortex
-......:.._ Prolactin . /
Skin -Oxytocin

--ADH~

.--- \Bone /

GH

Thyroid Testicle

fig: Hormones from pituitary gland

iii. Posterior pituitary lobe:

The posterior pituitary gland is a small extension of the hypothalamus. This gland
releases the following hormones:

Oxytocin hormone:

i. It is responsible for uterine contractions during child birth. Therefore, it is also
known as birth hormone.

ii. It helps in the release of milk during breast feeding.
iii. In males, it helps in the transportation and ejection of sperms.

Antidiuretic hormone (ADH): It helps in preventing water loss in the body by

increasing the absorption of water in the Kidneys and reducing blood flow to sweat

glands.

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Fact with reason

Pituitary gland is called the 'master gland', why?

Pituitary gland takes messages from the brain through hypothalamus and uses these
messages to produce hormones. These hormones stimulate all the other hormone-producing
glands to produce their own hormones. So, pituitary gland is called the ‘master gland’.

2. Thyroid gland: The thyroid gland is a butterfly-shaped gland located in the anterior
throat below larynx. It is found wrapped around the lateral sides of the trachea. The
thyroid gland produces three major hormones:

i. Thyroxine or tetra-iodothyronine (T4): Its functions are:

a. Thyroxine hormone regulates the metabolic rate.

b. It regulates physical and mental development of the body.

c. It controls absorption of glucose from the intestine.

d. It regulates heat generation in humans by regulating respiration.

Effects due to Hyposecretion: Hypothyroidism

a. Cretinism: It is a condition characterized by retarded physical, mental and sexual

growth, slow heart beat, low blood pressure, decrease in body temperature, etc.

b. Myxoedema or Gull’s disease: It is the t; ~ -- (
condition of swelling of the skin and underlying I
tissues. Person becomes fatty and sluggish. \
Other effects are slow heart beat, low body Thyroid gland
temperature and retarded sexual growth. \

c. Goitre (Simple goiter): It is an abnormal '"'"'~
enlargement thyroid gland, thus swelling in
neck. --I

Cartilage

c. Hashimoto disease: It is an autoimmune Trachea
disease in which the thyroid gland is gradually (windpipe)
destroyed.
fig: Location of thyroid gland

Effects due to Hypersecretion: Hyperthyroidism

Grave’s disease (Exopthalmic goiter or Parry’s disease): The over secretion of

thyroxin causes exophthalmic goitre or grave’s disease. Its symptoms are higher

metabolism, restlessness, decrease in body weight, bulging of the eyes, insomnia,

nervousness, high heart rate and high body temperature.

ii. Calcitonin: Calcitonin gets released when there is a rise in calcium ion levels in the
blood. Its functions is to reduces the concentration of calcium ions in the blood by
helping the absorption of calcium into the bones.

Deficiency of calcitonin leads to the decrease of calcium level in bone by the
deposition of calcium in blood. It results in weakening of bones.

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iii. Tri-iodothyronine (T3): Tri-iodothyronine hormone regulates the body’s
metabolic rate. Increased level of T3 hormone leads to increased cellular activity
and energy usage in the body.

3. Parathyroid glands: Parathyroid glands ~Th ·

are four glands found on the posterior Thyroid (back vi.ew)

side of either lobe of the thyroid gland. It ~)
produces parathyroid hormone (PTH).

Function: Its function is just antagonistic ~

Ca~r(opposite in nature) to calcitonin. It is
~Trach-;;----
released when calcium ion levels in the
blood drop down. It stimulates the bone (windpipe)_..,..---
cells to break down the calcium to release

free calcium ions into the bloodstream. fig: Location of parathyroid gland

Effects due to Hyposecretion: Hypoparathyroidism

It causes less concentration of calcium ions in the blood and tissues. The person will
suffer from painful jerking of muscles of neck, face, hands and feet. This condition is
called tetany.

Effects due to Hypersecretion: Hyperparathyroidism

It leads to more extraction of calcium from the bones and causes softening, bending
and fracture of the bones. This condition is called osteoporosis. Similarly, it can lead to
kidney stones due to excess deposition of calcium in kidney tubules and ureter. It also
leads to tumours.

4. Adrenal glands (Suprarenal glands): The adrenal glands are a pair of roughly triangular
glands found above the kidneys. The adrenal glands are made up of two distinct layers:
the outer adrenal cortex and inner adrenal medulla.

i. Adrenal cortex: The adrenal cortex produces three hormones:

a. Glucocorticoids: Glucocorticoids hormone is involved in the breakdown of

proteins and lipids to produce glucose. This increases the glucose level in blood.

It also aids in reducing inflammation and immune response. In case of excessive
bleeding, glucocorticoids hormone constrict blood vessels and balance the blood

pressure due to blood loss.

b. Mineralocorticoids (Aldosterone): Mineralocorticoids hormone increases the

reabsorption of sodium from urine, saliva, bile and sweat to reduce its loss from

the body. Thus, it regulates the concentration of minerals, such as sodium and
potassium ions, in the body. It also increases the reabsorption of water from the

urine by raising the osmotic pressure of the blood through reabsorption of Na+ in

to it.

c. Sex-corticoids: Sex-corticoids hormone secretes androgen hormone in the male.

In the female, it secretes oestrogen and progesterone hormones. These hormones
stimulate the development of secondary sexual characters like body hairs, menstrual

cycle, enlargement of the breast, change of voice in the male child.

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Memory Plus

In adult males, the amount of androgens produced by the testis is many
times greater than the amount produced by the adrenal cortex, leading to the
appearance of male secondary sex characteristics.

Effects due to Hyposecretion

a. Addisons disease: It is caused due to deficiency of mineralocorticoids. The
symptoms of this disorder are low blood sugar, low sodium ion concentration,
high potassium ion concentration, loss of weight, nausea, vomiting, etc.
b. Conn’s disease: It is caused by the deficiency of mineralocorticoids. It is related
with neural disorder, which can lead to convulsions and death.

Effects due to Hypersecretion

a. Cushings syndrome: It is caused by hypersecretion of glucocorticoides in
blood. The major symptoms of this syndrome are increase in blood sugar, blood
pressure, obesity, wasting of limb muscles, etc.

b. Aldosteronism: It is caused by hyper secretion of aldosterone, and its symptoms
are high sodium ion concentration and low potassium ion concentration in the
plasma, increase in blood volume, blood pressure, etc.

c. Adrenal virilism: It is caused by hyper
secretion of sex corticoids. In females, excess
androgen production leads to the development
of male secondary sexual characters, such as a
beard, moustache and hoarse voice.

ii. Adrenal medulla:

The adrenal medulla produces two hormones: I
Adrenaline (epinephrine) and nor-adrenaline (nor-
epinephrine). Both these hormones help to increase kidney
the flow of blood to the brain and muscles to fight fig: Adrenal gland and adrenal medulla
stress. These hormones are responsible for increasing
the heart rate, breathing rate and blood pressure when
there is decrease in the flow of blood.

These hormones help our body to act in emergency
situations like fear, fligh, fight, anger, etc. Therefore
adrenal glands are also called emergency glands.

5. Pancreas: The pancreas is a large gland located in the abdominal cavity behind the
stomach. The pancreas is a heterocrine gland as it contains both endocrine and exocrine
tissues. The islets of Langerhans of the pancreas act as the endocrine cell. It secretes
insulin, glucagon and somatostatin hormones directly into the bloodstream. Insulin
lowers the blood sugar level while glucagon raises the blood sugar.

There are three types of cells within islets of Langerhans: alpha cells, beta cells and delta
cells.

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i. Alpha cell: It produces glucagon hormone. This hormone is responsible for raising
blood glucose levels. Glucagon triggers muscle and liver cells to break down the
polysaccharide glycogen to release glucose into the bloodstream.

ii. Beta cell: It produces insulin hormone. Pancreatic islets
When the blood level of glucose rises,
beta cells secrete insulin, which increases
the rate of glucose uptake and cellular
metabolism. It alos increases the protein
metabolism. Insuline also stimulates
deposition of extra glucose in the form
of glycogen in liver and muscle.

iii. Gamma cell: It produces somatostatin Normal islet
hormone. It is responsible for controlling
the activity of insulin as well as of beta cells destroyed
glucagon.
fig: Pancreas cells
Effects due to Hyposecretion

Hyposecretion of insulin results in diabetes mellitus (DM). It is caused due to high
level of glucose in blood (hyperglycaemia). It affects several organs like kidney,
eye, brain, etc. The symptoms of DM are: frequent urination, intense thirst,
weakness, loss of weight, slow healing of wounds, or even diabetic coma, etc.

Effects due to Hypersecretion

Hypersecretion of insulin or deficiency of glucagon results in hypoglycemia (low
blood glucose level) and eventually insulin shock. Its symptoms include dizziness,
fainting, convulsions, diabetic coma due to low glucose, brain damage and even
death.

6. Gonads (Testes and Ovaries): The gonads are the ovaries in females and testes in males.
They are responsible for producing the sex hormones of the body.

a. Testes: (singular: testis): The testes are the two ball-

like glands present on the either side of the scrotum.

They have tubules in them called seminiferous Spermatocele---.,;;...-
tubules in which sperms develop. The seminiferous Epididymis---;~~ 111!!1''.r
tubules secrete testosterone and androgen hormone.

The testosterone stimulates spermatogenesis Testicle --_,_~
and production of sperms. It also controls the Scrotum-- -+,.__

development of secondary sexual characteristics fig: Testicle

like growth of penis and scrotum, beard, moustache,

hoarse voice, pubic hair, etc.

b. Ovaries (singular: ovary): Ovaries are the two fig: Ovaries
gonads on either side of the lower abdomen near
the fallopian tubes in females. They produce eggs
and also many female sex hormones like oestrogen
and progesterone.

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The oestrogen stimulates the maturation of eggs, development of secondary
sexual characteristics like shrill voice, pubic hair, enlargement of breasts, soft
skin, etc. Similarly, the progesterone helps in the formation of the placenta during
pregnancy, releases egg during ovulation, prepares the uterus for the delivery of
a baby and controls the development of mammary gland buds.

7. Pineal gland: Pineal gland is a small pine-cone shaped gland. It is found posterior to the
thalamus of the brain. It produces melatonin hormone. This hormone helps to regulate the
sleep-wake cycle of humans (circadian rhythm).This hormone is only produced in low light
or darkness. Hyper-secretion of this hormone causes humans to feel drowsy at night.

Answer writing skill

1. Write the scientific name of the rat.
The scientific name of the rat is Rattus rattus.

2. What is alimentary canal?
Alimentary canal is a pathway by which food enters the body and solid wastes are
thrown out. It is a tube running from the mouth to the anus.

3. What is insulin?
Insulin is a hormone secreted by the pancreas, which converts glucose in the liver and
muscles.

4. Give the scientific name of the rice plant.
The scientific name of the rice plant is Oryza sativa.

5. Write the differences between endocrine and exocrine glands.
The differences between endocrine and exocrine glands are as follows:

Exocrine gland Endocrine gland

Exocrine gland pours its secretions into a Endocrine gland pours its secretions

duct. directly into the blood vessels.

It is called a duct gland. These glands are often called ductless

glands.

The secretions of the exocrine gland are The secretions of the endocrine glands are

called enzymes. called hormones.

6. Write the function of bile.
The functions of bile are as follows:

a) It helps in the digestion of fats
b) It eliminates waste products from the blood.

0314 Optional Science - 10 BIOLOGY

7. What is the function of thyroid stimulating hormone (TSH)?
Thyroid stimulating hormone stimulates the thyroid gland to produce thyroxine
hormone (T4) and triiodothyronine (T3).

8. Write short notes on thyroxine hormone.
Thyroxine hormone is secreted by the thyroid gland. It is also known as tetra-
iodothyronine (T4) hormone. The hyposecretion (hypothyroidism) of thyroxine leads
to goitre and hypersecretion (hyperthyroidism) causes Graves’s disease.

The functions of thyroxine hormone are:

a) It regulates the metabolic rate of a body.
b) It plays a significant role in the mental and physical development of a body.

c) It also plays a role in the absorption of glucose from the intestine.

9. What are the characteristics of a hormone?

The characteristics of hormones are:

a) Hormones may be protein or non proteinaceous.
b) Hormones act either by stimulating or inhibiting the target organs.

c) They regulate long-term effects like growth, change in behavior, etc.

10. What are gonads? Which hormone is secreted by them? Write its function.
The gonads are the ovaries in females and testes in males. They are responsible for
producing the sex hormones of the body.
In the female, the ovaries secrete oestrogen and progesterone hormones and in the
male, the testis secrete testosterone and androgen hormone.
The functions of these sex hormones are:
a) These sex hormones determine the secondary sex characteristics of adult females
and adult males.
b) Progesterone maintains the menstrual cycle. It promotes maturation of the female
reproductive organ. It thickens the uterine wall during pregnancy.
c) Testosterone promotes maturation of the male reproductive organs, stimulates
spermatogenesis and production of sperm.

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Exercise

Section "A"

1. What is digestive system?

2. What is alimentary canal?

3. Define digestion.

4. What do you understand by coprophagy?

5. What is the function of the glottis?

6. What is the function of the ureter?

7. What is spermatic cord?

8. Write the function of:

a. Thyroid gland b. Adrenal glands c. Pineal gland

d. Parathyroid gland e. Gonads f. Pancreas

9. What do seminal vesicles secrete?

10. Give the family of the rice plant.

11. What is tillering stage?

12. Define endocrine system.

13. Where is pituitary gland located?

14. What is endocrinology?

15. What is a hormone? Section "B"

1. List the organs present in the alimentary canal.
2. What are the organs associated with the respiratory system of a rat?
3. What are the organs of the urinary system in a rat?
4. List the organs of the male reproductive system.
5. List the organs of the female reproductive system.
6. What are the stages of the life cycle of a rice plant?
7. What do you mean by booting stage?
8. List the glands associated with the endocrine system.
9. List the major parts of pituitary gland with two hormones secreted by each.
10. Pituitary gland is often called as the “master gland”, why?
11. Why is endocrine glands also called ductless gland?

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12. Pancreas is a heterocrine gland. Give reason.
13. Write the secretion of gastric glands.
14. What is the role of gastric glands in digestion?
15. What are secreted by the intestinal glands?
16. What is the role of pleural fluid?

Section "C"

1. Write short notes on the liver of a rat.
2. Write about the secretion of the pancreas.
3. Write the function of insulin.
4. Write the function of the salivary glands in digestion.
5. Give a short account of a rat’s kidney.
6. Give a short account ofthe adrenal gland and its secretion.
7. Write the functions of progesterone and testosterone hormones.
8. Write the difference between exocrine and endocrine glands.
9. What are the differences between the alpha and beta cells of the pancreas?
10. Write short notes on the pineal gland.

Section "D"

1. Describe the external features of a rat.
2. Explain the process of digestion in a rat.
3. What are the roles of organs of excretory system of rats?
4. Give a short account in male and female reproductive

organs in rats.
5. Explain the process of respiration in a rat.
6. What do you understand by urogenital system?
7. Explain the stages of the life cycle of a rice plant.
8. Describe the structure of rice plant.
9. Write the hormones secreted by the thyroid gland and the

function.
10. Which hormone is secreted by the parathyroid gland? Give

the function.
11. Name the glands in the the given figure alongside.
12. How pancreas helps to maintain the blood glucose level? Explain.
13. Complete the following table.

Pituitary gland Hormone functions

Anterior pituitary gland

Posterior pituitary gland

Intermediate pituitary gland

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Multiple choice questions

1. The reproductive stem is called

a. Spike b. Hull c. Tiller d. Embryo

2. The outer protective coat of rice is

a. Hull b. Tiller c. Spike d. Pellicle

3. Hormones that stimulates the follicle cells of the gonads to produce gametes- ova in
females and sperm in males:

a. Adrenocorticotropic hormones b. Follicle stimulating hormones

c. Luteinizing hormones d. Prolactin hormones

4. Hyposecretion of thyroxin leads to

a. Goitre b. Graves’s disease. c. Calcitonin d. Softening of bones

5. Hypersecretion of parathyroid hormone cause

a. Hyperparathyroidism b. Hyperthyroidism

c. Hypoparathyroidism d. Hypothyroidism

6. The islets of Langerhans of pancreas act as the

a. Heterocrine gland b. Homocrine gland c. Exocrine gland d. Endocrine gland
7. The hormone produced by the ovaries:

a. Oestrogens b. Androgens c. Testosterone d. Melatonin

8. The cells of a liver are called

a. Hepatocytes b. Oestocytes c. Chondrocytes d. Melanocytes

9. Exchange of gases takes place in

a. Alveoli b. Bronchioles c. Lungs d. Trachea

10. The functional unit of the kidneys

a. Nephrons b. Capsule c. Glomerulus d. Adrenal

11. Saliva contains the enzyme …… that helps to digest the starch present in the food.

a. Amylase b. Trypsin c. Ptyalin d. All

12. The condition of softening, bending and fracture of bone.

a. Osteoporosis b. Decalcification c. Bone deformation d. Oesteocytes

Project Work

1. Pay a visit to a field. Collect some ideas about rice plantation, the month and method
for doing so, ripening time, transplantation of seedlings and ways to protect the rice
plants. Prepare a report on it and submit it to your teacher.

2. Make a model showing the digestive, respiratory, urinary and reproductive parts of a rat.

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UNIT

16 HEREDITY

Hugo Marie de Vries (1848-1935) was born on February 16, 1848 in Haarlem, the
Netherlands. He was a Dutch botanist and one of the first geneticists. He is famous for
suggesting the concept of genes and rediscovering the laws of heredity in the 1890s. He is
the one who introduced mutation and developed the mutation theory.

·······························································••••••••••••••••••••······················································

Syllabus issued by CDC Learning objectives:

Theory 6 At the end of this unit, the students will be able to:
Practical 2
• describe Mendel’s dihybrid cross and
Mendel’s law along with the diagram.

Atomic mass, molecular mass and • define chromosome, sex-linked inheritance
mole concept and twins.

• describe the process of sex-linked inheritance
and formation of twins.

Key terms and terminologies of the unit

Heredity: This phenomenon of transmitting parental characteristics to the offspring is called
heredity.

Variation: The difference between parents and the offspring or between individuals in a species is
called variation

Genetics: The branch of science which deals with the study of heredity and variation is called
genetics.

Dihybrid cross: A cross between the two individuals that differ in gene by considering two pairs
of contrasting characteristics is called dihybrid cross.

Hybrids: Hybrids are the organisms produced when two genetically different organisms are
crossed.

Hybridization: The process of crossing two alternating characteristics is called hybridization. It can
also be defined as the process by which hybrids are formed.

Genotype: The genetic composition of an organism is called genotype.

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Phenotype: The characteristics which appear externally are called phenotype.

Linkage: Linkage can be defined as the phenomenon of association between two or more genes
present in the same chromosome that were inherited together from one generation to another
transmitting the characteristics as an inseparable unit.

Autosomes: The chromosomes which are responsible for all the characteristics except sex
determination.

Allosomes: The chromosomes which determine the sex of the offspring are called allosomes.

Sex-linked gene: Genes that are carried by sex chromosome (X or Y) are called sex linked gene.

Sed-linked characteristics: The characteristics which inherit due to sex linked gene are called sex-
linked characteristics.

Sex-linkage: The inheritance of non-sex determining characteristics along with sex chromosomes
is called sex linked inheritance or sex linkage.

X-linked inheritance: The inheritance of genes for non-sexual characteristics through X sex
chromosome is called X-linked inheritance

Y-linked inheritance: The inheritance of genes for non-sexual characteristics through the Y-sex
chromosome is called Y-linked inheritance.

Colour blindness: Color blindness is a disorder in which a person cannot distinguish red, green,
or both colors from other colors.

Haemophilia: Haemophilia is a sex-linked disease in which blood loses its ability to clot on
exposure to air.

Multiple birth: This process of giving birth to more than one baby is called multiple births.

Twins: Twins are two babies reproduced by the same pregnancy.

Identical twins: If twins are developed from the same ovum then they are called identical twins or
monozygotic twins.

Fraternal twins: The twins which are formed by the fertilization of two different ova by two
different sperms are called fraternal or dizygotic twins.

Introduction

All organisms have characteristics of their parents. These characteristics are transmitted
from the parents to the offspring during the formation of gametes and then to the zygote.
This phenomenon of transmitting parental characteristics to the offspring is called heredity.
Besides the phenomenon of heredity, all the organisms look different. This is possible due to
some new characteristics developed in an individual. And this difference between parents and
the offspring or between individuals in a species is called variation.

Variatin is caused by the environmental factors too. Organisms when adjust with their
environment, there is development of some special features in the body of organisms.
Thus, variation is an essential phenomenon for adaptation. Both the genetic variation and
environmental variation play an important role in the development of a body. The branch
of science which deals with the study of heredity and variation is called genetics. Due to the
phenomenon of variation, each and every individual is different in this world.

Mendel performed experiments by crossing pea plants to give his laws of heredity. In this

unit, we will learn about dihybrid cross, Mendel’s law of inheritance, chromosome, sex-linked

inheritance and how twins are formed. BIOLOGY

0320 Optional Science - 10

Mendel’s Experiment

An Austrian monk, Gregor Johann Mendel (1822-1884), studied how characteristics are
transmitted from the parents to the offspring. Since the offspring contain half the chromosomes
from the mother and half from the father, which characteristicswill they actually show? And
why? To solve these questions, he conducted many experiments on the garden pea plant
(Pisum sativum). On the basis of his experiments on the pea, he explained the term genetics
and the pattern of transmitting hereditary characteristics, and gave the laws of heredity. For
this contribution, Mendel is also called the 'Father of Genetics'.

Fact with reason

Mendel is called the 'father of genetics', why?
Mendel was the first to perform scientific experiments in pea plants for the study of transfer
of genetic character in offspring. He recognized the dominant and recessive genetic traits
through his experiments. Mendel discovered that the genetic characteristics are passed
from parent to offspring in a measurable and predictable way. He was the first to give laws
of heredity in a systematic way. So, Mendel is called ‘father of genetics’.

Contrasting Characteristics in Pea Plants

The pair of alternate characteristics in an organism are called contrasting characteristics.
Mendel selected 7 pairs of contrasting characteristics of the pea plant for his experiment.
These characteristics are as follows:

Size of the plant: tall and dwarf
Position of flowers: axial and terminal
Shape of mature seeds: round and wrinkled
Color of the flower: purple and white
Color of the seed: green and yellow
Shape of the mature pods: inflated and constricted
Color of the mature pods: yellow and green

Fact with reason

Why did Mendel select garden pea plants for his experiment?

The following characteristics of the pea plant made Mendel to choose it for his experiment:

1. Short life cycle: Pea plants have a short life cycle. So many generations can be studied
in a single year.

2. Bisexual plant: Pea plants are bisexual plants. So plants can easily self-pollinate or
cross-pollinate to obtain successive generations.

3. Productivity: A large number of offspring plants are produced in each generation.
4. Easy to cultivate
5. Variety of characteristics: Pea plants have varieties of pairs of contrasting

characteristics.

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The table given below shows the seven paris of contrasting characteristics in parental pea
plants (P). It also shows the results of mendel's experiment in which pea plants were crossed
by considering one pair of contrasting characteristics (monohybrid cross). The expressed
characteristics in the first filial generation (F1) are the dominant characteristics.

Podcolot

Purple Yellow Round lnfi11ed Green

pX 1,1X X

While Tc,m,nal G,ecn W11nklcd Const1ic1cd Yellow Dwa,f
Axial
I- ) J1

Pu,pte Yellow Round l t.

fig: Mendel's experiment on the basis of seven pairs of contrasting characteristics in pea plant

Mendel’s Dihybrid Cross

We have already learnt about monohybrid cross, Mendel's law of dominance, and Mendel's
law of purity of gametes (or law of segregation). Here we will learn about dihybrid cross and
Mendel's law of inheritance (law of independent assortment) in this unit.

A cross between the two individuals that differ in gene by considering two pairs of contrasting
characteristics is called dihybrid cross. For a dihybrid cross, Mendel selected two pairs of
characteristics in pure pea plant as: the shape of the seed and seed colour. He first carried
out self-pollination followed by cross-pollination and observed the results of the consecutive
generations.

Mendel chose two homozygous pea plants, one having round seeds with yellow colour
(RRYY) and another having wrinkled seeds with green colour (rryy). Then he cross-pollinated
these two plants and got the F1-generation. In the F1-generation, he found that all the plants
had round seeds with yellow colour, but their genotype was heterozygous (i.e. RrYy). With
this result, he concluded that the round seed was dominant over the wrinkled seed. Similarly,
the yellow colour was dominant over the green colour.

According to Mendel’s law of purity of gametes, genes in heterozygous plants separate at the
time of gamete formation in their reproductive parts (androecium and gynoecium). The four
possible gametes (male and female) from the heterozygous plant (RrYy) are RY, Ry, rY and ry
for F₂-generation. Then for the F2-generation, he allowed the offspring of the F1-generation to
self-pollinate and observed the results of the F2-generation. The entire process can be studied
in the following phylogenetic chart:

0322 Optional Science - 10 BIOLOGY

Parents Round seed with yellow colour Wrinkled seed with green colour
Genotypes
RRYY ! •rryy
Gametes
! ry

RY

Cross-pollination Hybrid plants with round
and yellow coloured seed

Gametes ! RrYy
(for F2-generation)
RY l lIRy rY
l

ry

Self-pollination

F2-generation (in Punnett square): •Ry rY ry
RY

RY RRYY 0 RRYy J RrYY 0
Ry RRYy 0 RrYy \)
rY RrYY 0 RRyy rrYY
ry RrYy 0 rrYy 0
• •RrYy ,J
Specification: Round Yellow
• •Rryy
RrYy ~
Rryy
rrYy
rryy

Wrinkled green
•• • ••Round green
Wrinkled yellow

The phenotypic and genotypic results in F2-generation of the dihybrid cross were as follows:

Phenotype Form Genotype Number of individuals

Round seed with Homozygous (pure) RRYY 1
yellow colour

Heterozygous RRYy 2

(Hybrid) RrYY 2

RrYy 4

Total: 9

Round seed with Pure RRyy 1
green colour Hybrid Rryy 2

Total: 3 rrYY 1
Wrinkled seed with Pure rrYy 2
yellow colour Hybrid rryy 1
3
Total: Pure Genotypic ratio: 1:2:2:4:1:2:1:2:1
Wrinkled seed with
green colour 1
Total: 9:3:3:1
Phenotypic ratio:

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Result: As a result of Mendel’s dihybrid cross, he found the phenotypic ratio as

Round yellow seeded: Round green seeded: wrinkled yellow seeded: wrinkled green seeded
= 9:3:3:1

The genotypic ratio is 1:2:2:4:1:2:1:2:1.

Conclusion: In the F1-generation, Mendel found all round seeds with yellow colour, but their
genotype was heterozygous (i.e. RrYy). In the F₂-generation, he found four different types
of pea plants - round seeds with yellow colour, round seeds with green colour, wrinkled
seeds with yellow colour and wrinkled seeds with green colour in the ratio of 9:3:3:1. This
result shows that the pair of alleles(alternative forms of a gene) segregate from each other and
combine with another allele independently, forming a new set of characteristics. On the basis
of this result, Mendel formulated the law of independent assortment.

Mendel’s law of independent assortment (law of free recombination)

It states that the different characteristics in a hybrid union are inherited independently and
when two pairs of traits are followed in the same cross, they assort/combine independently”.
For example, in the above dihybrid cross:

Total round seeded = 9+3=12 Total yellow seeded = 9+3=12

Total wrinkled seeded = 3+1 =4 Total green seeded = 3+1 =4

Round seeded: wrinkled seeded = 3:1 Yellow seeded: green seeded = 3:1

He also suggested that the genes responsible for different characteristics can separate from
each other and form a new combination of genes in the offspring. This concept has been
implemented in the agricultural field to develop new and advantageous characteristics in
crops as well as in animals to improve their productivity.

Limitation of Mendel’s law of Independent Assortment

According to Mendel’s law of independent assortment, every gene assorts with another gene
independently. But this phenomenon is only true when those genes are present in two different
chromosomes not when those genes are present in the same chromosome. As we know that a
single chromosome contains many genes, those genes are linked with each other and
transmitted as a single unit. These genes, which are transmitted together, are called linked
genes, and this phenomenon is called linkage. Hence, linkage can be defined as the phenomenon
of association between two or more genes present in the same chromosome that were inherited
together from one generation to another transmitting the characteristics as an inseparable unit.

Genes that are located on the same chromosome are not free to
participate in independent assortment. Thus, Mendel's law of
independent assortment cannot be applied in case of linked genes.

Sex-linked Inheritance Linked Not Linked

Sex chromosomes (X and Y) not only carry the genes that determine male and female traits but
also those for some other characteristics as well. Genes that are carried by sex chromosome (X
or Y) are called sex linked gene. Among the two sex chromosomes (X and Y), X-linked genes
are much more common than Y-linked genes. These genes of non-sexual characteristics are
transmitted from one generation to another generation along with the sex chromosome. The
characteristics which inherit due to sex linked gene are called sex-linked characteristics.

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The inheritance of non-sex determining characteristics along with sex chromosomes is called sex
linked inheritance or sex linkage. Sex-linked inheritance can also be defined as the inheritance
of non-sexual characteristics determined by a gene present on either of the sex chromosome. It
was first explained by Bateson and Punnet in 1906.

Sex-linked Inheritance in Human

As other organisms, a human also develops from a single cell, called a zygote. A zygote is
formed by the fusion of the male gamete (sperm) and female gamete (ovum). Both the gametes
are formed by the gametogenesis process, where meiosis cell division reduces the number of
chromosomes to half (23) of the number of chromosomes present in the diploid cell (23pairs).
In case of a male gamete, out of 23 chromosomes present in the sperm, 22 are autosomes and
one is a sex chromosome(allosome) - either an X or a Y. But in case of a female gamete, out of
23 chromosomes present in the ovum, 22 are autosomes and the sex chromosome is always an
X. When these gametes are fertilized, the following process occurs:

1. X from the father and X from the mother fertilize to form a girl.

2. Y from the father and X from the mother fertilize to form a boy.

3. X chromosome is never transferred from the father to a boy.

4. Y chromosome is always transferred from the father to a boy.

Mother Father
(XX) (XY)

XX XY

XX XY XX XY
(Girl) (Boy) (Girl) (Boy)

In human beings, sex-linked characteristics can be transmitted from either the X or Y
chromosomes. Both the men and women have the probability to get sex-linked gene. In case
of Y-linked gene, only men can inherit it. But X-linked gene can get inherited in both men and
women since both inherit X chromosomes.

Types of Sex-linked Inheritance

There are three types of sex-linked inheritance:

1. X-linked inheritance: The inheritance of genes for non-sexual characteristics through
X sex chromosome is called X-linked inheritance. Such characteristics are transmitted
to the male where females are the carriers. Examples of X-linked inheritance are
haemophilia, congenital night blindness, baldness in males, Duchenne muscular
dystrophy, red-green color blindness.

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2. Y-linked inheritance: The inheritance of genes for non-sexual characteristics through
the Y-sex chromosome is called Y-linked inheritance. This inheritance only occurs in
male from male. Hypertrichosis (hairy ear), TDS (testis determining region), etc. are
examples of Y-linked inheritance.

3. X-Y linked inheritance: It is the inheritance of genes for non-sexual characteristics
through both homologous chromosomes X and Y. Examples of this type of inheritance
are complete color blindness, skin cancer, etc. This type of sex linkage is also called
incomplete sex linkage because for a characteristic to occur in the offspring, both the
chromosomes - X as well as Y - must contain the same gene. If anyone of them lacks that
gene, then the characteristic won’t be observed in the offspring.

Memory Plus

Disorders caused by sex-linked inheritance are called sex-linked disease. Eg.
Haemophilia, color blindness, hypertrochosis, etc.

There are about 120 sex linked genetic disorders have been identified till now. Among
those the most common sex linked traits are colour blindness and haemophilia.

Fact with reason

X-linked human genetic disorders are much more common in males than in females, why?

X-linked genetic disorders are due to inheritance of X-linked gene. Males only have one X
chromosome. The inherited X-linked gene gets expressed in males and shows its effect. On
the other hand, females have two X-chromosomes. There is a probability of being X-linked
gene as a recessive which gets suppressed by the genes in a normal X chromosome. So,
X-linked human genetic disorders are much more common in males than in females

Characteristic features of inheritance for a sex- linked trait

The characteristic features of the transmission of sex-linked traits to the offspring are:

1. The gene responsible for sex-linked characteristics (X-linked gene) is never transmitted
from the father to a son because the son not only receives the Y-chromosome from the
father but also receives the X-chromosome from the mother.

2. A male with X-linked, dominant allele (Affected father) 0 ""1f1ected mot.hoc
d~::::,'1•thectransmits his sex-linked genes (i.e., X-linked genes) to Xlioked.
Iall his daughters, since females receive one of their two - Recessive
allele allele
------
XX
X-chromosomes from father. These daughters, in turn, XY

transmit this gene to half of their male progeny. Thus, □ cefA t e d
a X-linked dominant gene is transmitted from a male Ou,affected ~

to its female progeny, and thereafter to half of the male wl\ 11 w,i 1II
progeny of such females. All X-linked genes therefore
pass from male to female and then come back to a male

of F₂ generation (grand-children generation). Unaffected Affected Unaffected Affected
son daugther son daugt her

Father (affected) Pass trait from female progeny Grandson (affected)

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3. A female with X-linked, recessive allele (Unaffected carrier Oo.ffec<edfa<hv• I -"ca"rr'i"er"m"o't·her
X•"°'"·rece5siveallele
mother) transmits her sex-linked genes (i.e., X-linked genes) XX

to the half of male progeny (sons) in the F1-generation and Doamllmeloeo<- 11
to the half of female progeny(daughters). Sons get affected
XY
but the unaffected daughters will become carriers like their □ efAtcd

Ounaffe<:ted

oc,rr;e, ~

mother. These sons, in turn, transmit this gene to the female tQIQ ~ II
progeny in the F2-generation.

Pass trait from male progeny Unaffected Unaffected Affected Unaffected.
Mother (carrier)
Granddaughter (affected)son daugther son carrierdaugther

4. A female with X-linked, dominant allele (Affected mother) transmits her sex-linked
genes (i.e., X-linked genes) to the half of male progeny (sons) and to the half of female
progeny(daughters) in the F1-generation. All of these sons and daughters get affected.

Cause of Sex Linkage

If we study the structural features of the sex chromosomes in a ~homNoloong-ous { • l
human cell, then we will find that there are two parts in between part ,
in X and Y chromosomes. They are homologous segment and non- Homologou:{- : - : -
homologous segment. The long arm of the Y-chromosome and
the short arm of the X-chromosome are the homologous segments part • •
whereas the remaining segments are non-homologous.
I~ :
Genes located in the homologous segment of the X chromosome M at ern1I Patcnial
do not show sex-linked inheritance because it is a recessive gene
segment. Any gene present in the non-homologous segment causes fig: Male sex chromosomes
a different sex-linked inheritance. (XY) with homologous and

non-homologous parts

If a few genes are found in the non-homologous segment of the Y-chromosome, which have
no allele in X-chromosome then a different pattern of inheritance is shown, called Y-linked
inheritance. For example, hypertrichosis, TDS, etc. Similary, if a gene is present on the X-
chromosome, but no allele in Y-chromosome then it is said to be X-linked inheritance.

Thus, the two causes of sex linkage are:

1. The location of a gene in the X chromosome and the absence of its allele in the Y
chromosome (X-linked inheritance)

2. The location of a gene in the non-homologous region of the Y chromosome and the
absence of its allele in the X chromosome (Y-linked inheritance)

Color Blindness in Human

Color blindness is a disorder in which a person cannot distinguish red, green, or both colors
from other colors. The human eye actually detects only three colors; red, green and blue, which
are mixed by the brain to form different colors. Among these three pigments, red and green
lie close together in the X-chromosome, and hence the most common type of color blindness
in humans is caused by the red and green pigments, which is called red-green color blindness.
Since both these pigments are located in the X-chromosomes, this defect is a recessive and
X-linked defect.

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We can study the pattern of transmitting this defect with the help of the crisscross method.
Let us assume that the genotype for a normal female is XX, color blind female is XcXc, carrier
female XcX, color blind male (XcY) and normal male (XY).

If a color blind male (XcY) marries a normal woman (XX), then all male progenies will be
normal (XY) and all female progenies will be carriers in the F1-generation. If the carrier female
(XcX) marries a normal male (XY), then there will be four possibilities - one a carrier female
(XcX), one a normal female (XX), one a normal male (XY) and the other a color blind male (XcY)
in the F2-generation.

Colour blind Male Normal Female
(XCY) (XX)

XC Y X X (F1-_generat)ion

XCX XCX XY XY
(Carrier Female) (Carrier Female) (Normal Male) (Normal Male)

Carrier Female Normal Male
(XCX) XY

XC X X Y (F2-_generation,)

XCX XCY XX XY
(Carrier Female) (Colour blind male (Normal Female) (Normal Male)

Result of theF₂-generation: Among the female anormal •
progenies, half of them will be carriers and half oolor ff
of them will be normal. Similarly among the vision
males, half of them will be normal and half will
suffer from color blindness. •female 4ff'

carrier

If a color blind female (XcXc) marries a normal male

(XY), then there is a 50% chance of getting a carrier

female (XcX) and 50% chance of getting a color blind

male (XcY) in the F1-generation. fig: Red-Green colour Blindness inheritance pattern

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Colour blind Female Normal Male
(XCXC) ( XY)

I\ XY

XC XC

XCXC XCY XCX XCY
(Carrier Female) (Colour blind Male)
(Colour blind male (Carrier Female)

If a carrier female (XcX) marries a color blind male, then there is a 25% probability of each of a
color blind female, color blind male, carrier female and normal male.

Carrier Female Colour blind male
(XCX) (XCY)

I\ XC Y

XC X

XCXC XCY XCX XY
(Normal Male)
(Colour blind Female) (Colour blind male) (Carrier Female)

If a colour blind female (XcXc) marries a color blind male (XcY), then all the offspring will suffer
from color blindness in the upcoming generation.

Colour blind Female Colour blind male
(XCXC) (XCY)

XC XC XC Y

XCXC XCY XCXC XCY

(Colour blind Female) (Colour blind male) (Colour blind female (Colour blind Male)

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Haemophilia in Humans

Haemophilia is a sex-linked disease in which blood loses its ability to clot on exposure to
air. This disorder leads to prolonged bleeding and ultimately excessive loss of blood. This
disorder is also called the royal disease as it was first observed in Queen Victoria. One of her
sons, Leopold, suffered from haemophilia and died of it at the age of 31 years. This trait is also
an X-linked recessive trait. The pattern of this disease can also be discussed with the help of
the crisscross method.

Let us assume that the genotype for a normal female is XX, hemophilic female is XhXh, carrier
female is XhX, hemophilic male is (XhY) and normal male is (XY).

If a hemophilic male (XhY) marries a normal woman (XX), then all male progenies will be
normal (XY) and all female progenies will be carriers in the F1-generation. If a carrier female
(XhX) marries a normal male (XY), then there will be four possibilities - one a carrier female
(XhX), one a normal female (XX), one a normal male (XY) and the other a hemophilic male
(XhY) in the F2-generation.

Homophilic Male Normal Female
(XhY) (XX)

Xh Y ~ ( lX X F1-generation

XhX XhX XY XY
(Carrier Female) (Carrier Female) (Normal Male) (Normal Male)

Carrier Female Normal Male
(XhX) (XY)

Xh X ~ ( lX Y F2-generation

XhX XhY XX XY
(Carrier Female) (Homophilic Male) (Normal Female) (Normal Male)

0330 Optional Science - 10 BIOLOGY

Result of the F₂-generation: Among the female progenies, half of them will be carriers and
half of them will be normal. Similarly among the males, half of them will be normal and half
will suffer from haemophilia.

Fact with reason

Haemophilia is called a sex-linked disease, why?

The genes associated with haemophiliac conditions are located on the X-chromosome,
which is one of the two sex chromosomes. Haemophilia is transmitted along with the sex
chromosome. A hemophilia female is the carrier of the gene responsible for the disease.
So, haemophilia is called a sex-linked disease.

Activity

Draw a crisscross diagram upto the F1-generation and find out the result of that
cross when a carrier female marries a normal male, hemophilic female marries a
normal male, hemophilic female marries a hemophilic male, carrier female marries a
hemophilic male.

Twins

Sometimes a mother gives birth to more than one baby, mostly two at a time. Sometime even
three or more at the same time from the same pregnancy. This process of giving birth to more
than one baby is called multiple births. Twins, triplets are examples of multiple births. Twins
are two babies reproduced by the same pregnancy.

Two types of twins

Twins can develop either from the fertilization of an ovum by a sperm or fertilization of two
different ova by different sperms. On the basis of fertilization, the two types of twins are:
identical twins and fraternal twins.

1. Identical Twins (Monozygotic twins) r

If twins are developed from the same ovum then wJadsauo.<q
they are called identical twins or monozygotic
twins. They are called identical twins because they pas m1JaJpueAle.-.owoJJ0\
look similar and possess similar characteristics.
Idetical twins share exactly the same genes. So, pase.11aJ 6 6ila uo
they look alike, although it may get changed with
increasing age due to environmental variation. ...______,f.....----------'
s 11 1(1sua 11 1 p o e
A qWOMu! nue1dw1 Jlll!jSl!ldsua111 pue
qwOM. u1 nue1dw!
'f.(ffj1 o.<Jqwa.<1ie3
qwo111u1 o..t,qwa.<1a 3
6u11ue1dw! IJOJitqSl!ldS @) t [Fa]
t
o..t,qwa..< 1a 3 ®
a
t
'f.(:Jjl

Formation of identical twins ttt

First of all, fertilization occurs between the sperm S>H JiJUU!lltJeda,pue S)H JIUU!lltJed1spu, )H JI UU! fMJV'\{S pue
and mature ovum to form a zygote. During the se1ua,ef(la1titdas eiua,el(lp.JtljS eiua,et(lp.JtljS
development of the embryo, the dividing zygote
splits into two and develop separately as two fig: formation of identical twins
different cells, forming two babies with identical
characteristics.

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v - 0The twins which are formed by the fertilization
2. Fraternal Twins (Dizygotic twins)

~Two egg H eleased 0
from ovaries

of two different ova by two different sperms are G) ! 0 /Eachegg fertilised0
called fraternal or dizygotic twins. They are called
fraternal twins because they are not similar with by separate sperm Q

each other and are unique. They are the most ,.--/
common type of twins.
!
Fraternal twins do not share the same genes as in
Each embryo

implants in womb

separately

case of the identical twins. The genes from parents

tranfer independently to such twins. So, fraternal

twins are not exactly alike. !
Formation of Fraternal Twins

In the female, multiple ova can mature at the same Sepa rate placentas
time. If two sperms fertilize two different ova, and separate inner sacs
then both the fertilized ova undergo cell division
to develop into an embryo and later on into two fig: formation of fraternal twins
different babies, which are called fraternal twins.
They are called twins, but they have unique
individual characteristics.

Fact with reason

Identical twins are also called monozygotic, why?

Monozygotic means single fertilized egg (zygote). Identical twins develop from one zygote,
which splits and forms two embryos. So, they are also called monozygotic twins.
Fraternal twins are also called dizygotic, why?

Dizygotic means two fertilized eggs (zygotes). Fraternal twins are developed from the
fertilization of two different zygotes at the same time. So, they are also called dizygotic.

Differences between identical twins and fraternal twins:

Identical twins Fraternal twins

In case of identical twins, one zygote splits In case of fraternal twins, two different eggs

and forms two embryos. are fertilized by two different sperm cells.

Identical twins always have the same gender. Fracternal twins usually have different gender.

Their appearance is extremely similar, Their appearance is as similar as any other

although it may get changed with the sibling.

increasing age due to environmental factors.

Their blood group is the same. Their blood group may be different.

Factors that increase the probability of having twins

According to articles published, multiple births are becoming common nowadays, which can be
fraternal, identical or a combination of both. Among multiple births, twins are the most common
type. Twins may be both boys, both girls or one boy and one girl. The reasons behind the formation
of twins are:

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1. Advancing age of the mother: Nowadays women marry in their 30s and some in their
40s. At this age,womensecrete higher levels of oestrogen (which helps in ovulation). So
multiple ova mature at the same time.

2. Number of pregnancies: Multiple pregnancies also trigger multiple births, especially
twins.

3. Heredity: If the mother herself is also a twin sister, either identical or fraternal, then she
can also conceive twins.

4. Race: According to a study, African women have the highest incidence of twins.

5. Assisted reproductive techniques: Nowadays techniques like stimulating the ovaries
with fertility drugs increase the number of ovulations at a given time.

Answer writing skill

1. What isa hybrid?

A hybrid is an organism produced by crossing two pure parents.

2. Define twins.
Twins are two babies produced by the same pregnancy.

3. Write why twins are formed.

Nowadays women marry in their 30s or 40s. At this age,a woman’s body secreteshigher
levels of oestrogen (which helps in ovulation). So multiple ova mature at the same time.
Multiple pregnancies also trigger multiple births, especially twins.

4. Write the differences between X-linked inheritance and Y-linked inheritance.

X-linked inheritance Y-linked inheritance

1. It is the inheritance of genes for non- 1. It is the inheritance of genes for non-

sexual characteristics through X sex sexual characteristics through Y sex

chromosome . chromosome .

2. Usually, the characteristics are 2. This inheritance only occurs in male

transmitted to the male where from male.

females are the carriers.

5. Write any two functions of chromosomes.

a) Chromosomes are the genetic materials which help in transmitting parental

characteristics to the offspring.

b) Sex chromosome determines the sex of the offspring.

6. Write short notes on haemophilia.

Haemophilia is a sex-linked disease, in which blood loses its ability to clot on exposure
to air. This disorder leads to prolonged bleeding and ultimately excessive loss of blood.
This disorder is also called royal disease as it was first observed in Queen Victoria, who
carried the gene responsible for the disease. One of her sons, Leopold, suffered from
haemophilia and died of it at the age of 31 years. This is also an X-linked recessive trait.
The pattern of this disease can also be discussed with the help of the crisscross method.

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_Exe_rcis_e J__Q_ - --------

Section "A"

1. What is heredity?
2. Define dihybrid cross.
3. Define haemophilia.
4. What happens in color blindness?
5. What is sex chromosome?
6. Write the number of each of autosomes and allosomes in a normal human cell.
7. What does sex linkage mean?
8. Write any two examples of sex-linked disease.
9. Write the names of three types of sex linked inheritance.
10. State Mendel's law of independent assortment.
11. On which experiment was Mendel's law of independent assortment formulated?
12. Write down the genotypic and phenotypic ratio of the dihybrid cross in the F2 generation.

Section "B"

1. Differentiate between autosome and allosome.
2. What is the major difference between identical and fraternal twins?
3. Write Mendel's law of independent assortment and also write its limitation.
4. Why did Mendel choose the pea plant for his experiment?
5. When a woman with normal color vision (but her father is color blind) gets married to a

color blind man, then what are their chances of having color blind children?
6. What is the genotypic and phenotypic ratio of Mendel’s dihybrid cross?

Section "C"

1. Write short notes on Mendel's dihybrid cross.
2. What conclusion can you draw from the result obtained in the dihybrid cross of Mendel’s

experiment?
3. Write in short about the methods used to show sex-linked inheritance.
4. Explain the process of formation of identical and non-identical twins in humans.
5. Write any three reasons behind the formation of twins.
6. What happens when a hybrid plant with round seeds and inflated pods is allowed to

self-pollinate? Draw a chart and show the result in a ratio.

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Section "D"

1. What happens if a man with normal vision marries a color blind woman? Show the
phenotype and genotype of their children.

2. What is sex-linked disease? How does it get transmitted to the offspring? Explain with
a suitable diagram.

3. A homozygous plant having round seeds and inflated pods is first cross-pollinated
with a homozygous plant having wrinkled seeds and constricted pods and then self-
pollinated. What result will be obtained in the 2nd generation? Show your result up to
the F2 generation with a proper chart.

4. A pure tall plant bearing red color flowers was crossed with a pure dwarf plant with
white flowers.

i. Draw a phylogenetic chart showing the above mentioned cross upto the F2 generation.

ii. What type of offspring will be produced in the F1 generation?

iii. Which law does it illustrate? State the law.

1. Explain the process how haemophilia gets transmitted from the parents to the offspring.

2. Explain the process how color blindness get transmitted from the parents to the offspring.

Multiple choices Question

1. What is the phenotypic ratio of the result observed in the F2 generation of a dihybrid cross?

a. 9:3:2:1 b. 3:1 c. 1:2:2:4:1:2:1:2:1 d. 9:3:3:1

2. What is the genotypic ratio of the result observed in F2 generation of a dihybrid cross?

a. 9:3:2:1 b. 3:1 c. 1:2:2:4:1:2:1:2:1 d. 9:3:3:1

3. Why did Mendel choose the pea plant for his experiment?

a. It has a very short life cycle. b. It is a bisexual plant.

c. It is easy to cultivate. d. All of the above.

4. Who is the carrier of the hemophillic gene?

a. mother b. father c. both d. none

5. Which one is an example of a sex-linked disease?

a. Baldness b. HIV/AIDS c. Cancer d. Syphilis

6. Which one is not a sex-linked disease?

a. Haemophilia b. Color blindness

c. Male pattern baldness d. Malaria

7. Identical twins are formed from

a. single zygote b. two different zygotse

c. two different mothers d. none

Project Work

Collect information about a sex-linked disease like baldness or hemophilia or color
blindness from different sources. Study your family history if any member has the linkage
or not. If yes, then collect the pattern, present it in a report.

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UNIT

17 ECOLOGY

Eugen Warming (1841-1924) He was a Danish botanist. He was the first to figure out the
scientific discipline of ecology. He wrote the first textbook in 1895 on plant ecology and
taught the first university course on ecology and gave the concept in its meaning and
content. He wrote a number of textbooks on botany, plant geography and ecology.

Syllabus issued by CDC Learning objectives:

Theory 5 At the end of this unit, the students will be able to:
Practical • describe the simsar ecosystem.
I I2 • explain different bio-geochemical cycles like

Atomic mass, molecular mass and the nitrogen cycle, oxygen cycle and carbon
mole concept cycle.

Key terms and terminologies of the unit

Ecology: Ecology can be defined as the study of the distribution and relations of organisms
and their interactions with the environment.
Wetland: A wetland is a place where land is permanently or seasonally covered with water.
Abiotic components: Abiotic components are the non-living components of an ecosystem.
Biotic components: Biotic components are all of the living organisms within an ecosystem.
Biogeochemical cycle: The biogeochemical cycle can be defined as a pathway by which a
chemical compound moves through the biotic and the abiotic components of an ecosystem.
Nitrogen fixation: The process of converting atmospheric nitrogen into organic nitrogen
compounds is called nitrogen fixation.
Biological fixation: Biological fixation is the process of conversion of atmospheric nitrogen
into nitrates by some symbiotic bacteria, free living soil bacteria and blue green algae.
Nitrogen assimilation: nitrogen assimilation is the formation of organic nitrogen compounds
like amino acids from inorganic nitrogen compounds present in the environment.

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Ammonification: The decomposition with production of ammonia or ammonium
compounds by the action of bacteria on nitrogenous organic matter is called ammonification.

Nitrification: The conversion of ammonia into nitrites (NO2 —)and then into nitrates (NO3—)
by the action of soil bacteria is called nitrification

Denitrification: Denitrification is the process of reduction of unused nitrates into free
nitrogen by the action of soil bacteria to return nitrogen back into the atmosphere.

Introduction

The word ecology is a combination of two different Greek words, oikos- house and logos-
study of. Therefore, Ecology can be defined as the study of the distribution and relations
of organisms and their interactions with the environment. According to Earnest Haeckel,
“ Ecology is the study of the reciprocal relationship between living organisms and their
environment.” In simple words, it is the scientific study of how living things interact with
each other and their natural environment. It includes the study of the population of plants and
animals as well as their communities and ecosystems.

Ecosystem is the interrelationship between living and non-living components in the
environment. It is the structural and functional unit of the environment. An ecosystem is
composed of organisms (biotic component), the communities they make up and non-living
components (abiotic components) of their environments. In this unit we will learn about
wetland ecosystem and some of the bio-geochemical cycles, namely carbon cycle, oxygen
cycle and nitrogen cycle.

Branches of Ecology

Autecology and Synecology are two main branches of ecology.

Autecology: Autecology is the study of an individual organism or its population throughout
their life in relation to their habitat in the environment. It is also known as
population ecology.

Syncecology: Syncecology is the branch of ecology that deals with the study of the connections
of group of organisms of different species which are associated together as a
unit in form of a community to their common environment.

Importance of ecology

1. The study of ecology helps to conserve and protect nature and natural sources.

2. It helps to understand the connections between plants and animals and their environment
and prevent the extinction of species.

3. Ecology provides information about the benefits of ecosystems.

4. It provides information for natural resource management.

Wetland ecosystem

A wetland is a place where land is permanently or seasonally covered with water. The water
can be fresh, salty or brackish. A common example of a wetland is the edge of a lake or ocean,
the delta at the mouth of a river, lowland areas that frequently flood. The main types of
wetlands are swamps (marshes, bogs and fens) and and sub-types include mangrove, carrum,
pocosin, and varzea.

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Eventhough the wetlands are important environmental assets, they occupy only 6% of the
earth's surface. Conservation of wetlands is important because they are the most productive
habitats of aquatic plants and animals, including mammals, birds, fish and invertebrates.
Wetlands are also a habitat for migratory birds and waterfowl, including ducks, egrets, and
geese.

Memory Plus

The largest wetlands in the world include the swamp forests of the Amazon and the Peat
lands of Siberia.

About 5% of the total surface area of Nepal is wetland area. In Nepal, Koshitappu,
Beeshazar lake and associated lakes, ghodaghodi lake area and Jagadishpur reser-voir
have been designated as wetland areas.

Importance of wetland ecosystem

Wetlands play a number of roles in the environment. The importance of wetlands is:
1. Wetlands collect and hold flood water.
2. Wetlands play a significant role in carbon sink and shoreline stability.
3. Wetlands filter and clean water. They recharge groundwater aquifers.
4. Wetlands serve as a home to a wide range of plants and animal life.
5. Wetlands can improve tourism.
6. Wetlands provide us with many products, such as fishes, sea salt, animal fodder, fuel

wood, medicinal herbs.

Fact with reason

Wetlands are valuable habitats for wildlife. Give reason.

Wetlands are valuable habitats for wildlife because the surrounding uplands of the
wetlands provide a home for a large number of species, including plants, mammals, birds,
amphibians, reptiles, fish and invertebrates. These animals use wetlands for food, water,
nesting grounds, breeding and for shelter.
Wetlands are important to protect against erosion, Give reason.

Wetlands protect against erosion because there are many plants and types of vegetation
found in the wetlands that help to stabilize the soil and are able to hold the soil in place
against erosive forces, such as waves and currents. Also, wetland plants trap sediments that
are found in the water, which helps to reinforce the soil against erosion.

Components of wetland ecosystem

The components of wetlands vary widely due to local and regional differences in topography,
hydrology, vegetation and human involvement. The components of a wetland ecosystem can
be divided into two factors: Biotic and abiotic.

Abiotic components

Abiotic components are the non-living components of an ecosystem. These components are:
Water, soil, factors climate and temperature, rainfall.

0338 Optional Science - 10 BIOLOGY

1. Water: The wetlands contain surface water and ground water in its reservoirs. It is also
associated with streams, lakes and reservoirs as water sources. Most of the wetlands
have high concentration of dissolved nutrients and mineral ions, except bogs. Bogs
receive their water from the atmosphere, therefore have low mineral ion composition.

2. Soil: Most nutrients like calcium, phosphorus, sulfur and nitrogen are found in the soil
of wetlands. Carbon is the major nutrient.

3. Climate and temperature: The temperature of the wetlands varies greatly,depending
on the location of the wetland. Many of the world’s wetlands are in temperate zones.
Therefore, summers are warm and winters are cold, but the temperature is not extreme.
The wetlands found in the tropic zones are warm throughout the year.

4. Rainfall: The amount of rainfall also varies widely according to the area. Wetlands in
southeast Asia receive heavy rainfall. The wetlands of the northern areas of North
America receive little rainfall.

fig: Wetland ecosystem

Biotic Components

Biotic components are all of the living organisms within an ecosystem. In wetland ecosystem

,biotic components are the flora (plants) and fauna (animals).

Plants found in wetlands (flora)

Submerged plants, floating plants, emergent plants and aquatic trees are the four main

groups of hydrophytes found in the wetlands.

a. Algae: Algae are photosynthetic, non-vascular thalloid aquatic plants. They are

usually covered with mucilage that protects them form drying and decaying. They

are food sources for some animals, fish and invertebrates. Algae found in wetlands

are planktons. These are microscopic aquatic plants (algae). These are the primary
producers. They are filamentous algae, Chara and Nitulla.

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b. Submerged plants can grow in saline and fresh water. These plants are a source
of food for many animals. They help in the filtration of water within the wetlands.
Examples: hydrilla, sea grasses and eel grass.

c. Floating plants float freely on the surface of water. Example: green-algae, duckweed,
wolfia, water hyacinth, pistia.

d. Emergent plants have roots that are fixed in the mud at the bottom of the wetlands.
The stems are hollow and have plate-like leaves that float on the surface of water.
Example: water-lily, lotus, etc.

Some shrubs or small trees are also found in forested wetlands. They have a woody
stem and can grow 20 feet tall. Example: buttonbush and alder.

Animals found in wetlands (fauna)

Many species of frogs, different kinds of reptiles like turtles, alligators, crocodiles,
snakes, lizards and fishes are found in the wetlands. Among them, fishes are more
dependent on the wetland ecosystem to survive. Amphibians reproduce and feed on
the wetlands. Snapping turtles are one of the many kinds of turtles found in wetlands.
Tadpoles control the algal population and adult frogs feed on insects. The mammals
found in the wetlands include the beaver, swamp rabbit, Florida panther. Different
species of insects and invertebrates can be seen throughout the wetlands.

Memory Plus

A patch of land that develops pools of water after a rain is not considered a wetland.
Wetlands are characterized as having a water table that stands at or near the land
surface for a long period each year to support aquatic plants.

Biogeochemical cycle

Many elements cycle through an ecosystem, organisms, air, water and soil. They are passed
from one form to another and from one part of the biosphere to another through cycles known
as the biogeochemical cycle. Thus, the biogeochemical cycle can be defined as a pathway by
which a chemical compound moves through the biotic and the abiotic components of an
ecosystem. The cycle involves a biological, geological and chemical process. A biogeochemical
cycle connects living things to the earth. There are four chemicals that make up 95 % of living
things. They are carbon, oxygen, hydrogen and nitrogen. These chemicals are constantly being
cycled through living and non-living matter.

Importance of biogeochemical cycle

1. The biogeochemical cycle enables the transformation of matter from one form to another
for its utilisation. For example: We utilize water in liquid form, though water is also
found in vapor form or solid form as ice.

2. The biogeochemical cycle enables the transfer of chemical molecules from one locality
to another. For example: Nitrogen from the atmosphere is transported to the soil in
nitrate form.

3. The biogeochemical cycle helps in the storage of elements in natural reservoirs and are
released to organisms in small consumable amounts.

4. The biogeochemical cycle helps to balance the ecosystem by recycling the chemical
elements.

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Types of biogeochemical cycle

The biogeochemical cycle are classified into three types. They are water cycle, gaseous cycle
and sedimentary cycle(mineral cycle).

1. Water cycle: It involves the movement of water across various spheres of the earth
through different processes such as precipitation, evaporation, sublimation, condensation,
snowmelt and infiltration. The water cycle is also termed as hydrological cycle.

2. Gaseous cycle: It includes the continuous circulation of carbon, nitrogen, oxygen and
hydrogen gases in the atmosphere of the earth.

3. Sedimentary cycle: It includes the cycling of minerals like iron, calcium, phosphorous,
sulfur that are essential nutrients for living organisms. The sedimentary cycle is also
known as mineral cycle.

In this unit we will learn about gaseous cycles (carbon cycle, oxygen cycle and nitrogen cycle).

Carbon cycle

Carbon dioxide in
/ ; <he a<mosphm

Anim a l

~--/----, (I ~~:l~.~, O rganic
Fossil fuel Pl a n t carbon compo unds I -W--- - - -- i compo unds
com bustion respi ratio n in d ead organic in animals Pho tosyn thesis

m atter

Foss1hzat1o n \ Death

~ I

O rganic com po un ds
m green plants

fig: Carbon cycle

Carbon is the main component of living things. The main source of carbon is carbon dioxide.
Carbonates derived from rocks, volcanic eruption, fossil fuels like coal and petroleum products
give rise to carbon dioxide in the earth’s atmosphere.

The main process that brings carbon from the atmosphere to the biosphere is photosynthesis,
where producers utilize atmospheric carbon dioxide and convert it into carbon compounds.
Carbon dioxide is released back to the environment by the process of respiration, decomposition
of organic wastes and dead bodies, burning of wood and fossil fuels, volcanic eruption and
weathering of carbonate rocks.
The carbon cycle takes place by various processes:

1. Photosynthesis: The first step in the carbon cycle is the conversion of inorganic
atmospheric carbon into biological form. Producers absorb the atmospheric carbon as
carbondioxide by the process called photosynthesis. In photosynthesis, carbondioxide
combines with water in the presence of sunlight to make carbohydrates.

2. Respiration and combustion: Animals feed on plants passing carbon compounds along
the food chain. The carbondioxide is exhaled during respiration.

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Carbondioxide is also released in the atmosphere by burning fuels like coal, log and
petroleum products. Volcanic eruption and weathering of carbonate rocks by chemicals
also release carbondioxide in the atmosphere.
3. Decomposition: When plants and animals die, the dead organisms are eaten by the
decomposers. The carbon in their bodies is returned to the atmosphere as carbondioxide.
If decomposition is not completed, the remaining materials may then be available as
fossil fuel in the future for combustion.

Memory Plus

Since carbondioxide is a primary greenhouse gas, many studies argue that increase in
atmospheric carbondioxide from human activities has increased the greenhouse effect.
This can change our global climate, resulting in higher global temperatures.

The carbon cycle is mainly balanced by the process of photosynthesis and respiration.

Oxygen Cycle

: Ulrav+ O, -Oro••l•Jor(O.,J

01+0 O t+ UV n•v~_0_+_0_ _

Plants, Animals & = I Green Planls
Decomoosers
i
i

.s '---- ~
Fuels

fig: Oxygen cycle

All living things need oxygen to survive. It is necessary for respiration. Living cells need
oxygen to create energy. Plants take in oxygen and give out carbondioxide for synthesis during
the process of photosynthesis. We take in oxygen to break carbohydrates into energy and give
out carbondioxide by the process of respiration. The oxygen cycle helps in the movement of
oxygen in the three main regions of the earth: atmosphere, biosphere and lithosphere.

Steps in Oxygen Cycle

1. In the atmosphere, the energy in the sunlight breaks the oxygen molecule to produce
free oxygen. This process is called photolysis.

2. In the biosphere, plants and animals use oxygen for respiration and return it to the air
and water as carbondioxide. Plants use this carbondioxide in the presence of sunlight
to form carbohydrates and water. This process is called photosynthesis. In this process,
oxygen is produced as a byproduct. Water is the main source of oxygen.

3. In the lithosphere, oxygen is fixed in minerals like silicates and oxides. When the
mineral bearing oxygen is exposed to chemical reaction, the minerals wear down, and
free oxygen is produced. This process is called chemical weathering.

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Nitrogen cycle

Atmospheric L. lenin
~ itrogeo Physical fixation
(l<: gas)
lnduslrialfintion
Bk>l02ical fi:ution
Plants Ammonia liquor

Nitrates in soil ~ itrificatk>n ~ ilric add in soil

fig: Nitrogen cycle

Nitrogen is the most abundant element in the atmosphere. There is about 78% of nitrogen in
the air. It is essential for the formation of amino acids in proteins. It is also the building block
of nucleic acids (DNA and RNA). As nitrogen is not so reactive, it cannot be used directly by
plants to make proteins. Nitrogen is converted into various forms that can be utilized by living
organisms. Such forms of nitrogen are organic nitrogen, ammonium salt, nigrous oxide, nitrate,
nitrate, nitric oxide, etc.

The nitrogen cycle is a complex biogeochemical cycle. It completes in five stages: nitrogen
fixatation, nitrogen assimilation, ammonification, nitrification and denitrification.

1. Nitrogen fixation: The process of converting atmospheric nitrogen into organic nitrogen
compounds is called nitrogen fixation. It occurs in three ways:

a. Biological fixation of nitrogen

b. Atmospheric fixation of nitrogen

c. Industrial fixation of nitrogen

a. Biological fixation of nitrogen

Most atmospheric nitrogen is fixed through biological processes. Biological fixation
is the process of conversion of atmospheric nitrogen into nitrates by some symbiotic
bacteria, free living soil bacteria and blue green algae. The symbiotic bacteria host on
the root nodules of leguminous plants. The bacteria which convert atmospheric nitrogen
into nitrates are called nitrogen fixing bacteria. For example: free-living nitrogen fixing
bacteria(azotobacter, clostridium), symbiotic bacteria (rhizobium), cyanobacteria (blue-
green algae), etc. Algae like nostoc can also fix atmospheric nitrogen.

b. Atmospheric fixation of nitrogen

Nitrogen fixation also occurs by the physical or non-biological process. A small amount

of nitrogen is converted into ammonia and nitrates by the energy produced during

lightning in the air. When lightning occurs, atmospheric nitrogen reacts with oxygen

in the air and form nitric oxide and nitrogen dioxide. These oxides combine with water

vapor to form nitrous or nitric acids. These acids then combine with salts and produce

nitrate ions.

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N2 + O2 2NO

2NO+ O2 2NO2
N2O5
NO2 + O2 2HNO3
Ca(NO3)2 + CO2 + H2O
N2O5 + H2O

HNO3 + CaCO3

c. Industrial fixation of nitrogen

In industrial fixation, nitrogen is made to combine with hydrogen to form ammonia
by Haber process. The ammonia thus formed is converted into nitrate to use as a
nitrogenous fertilizer.

N2 + 3H2 (200-600) atm., 500oC 2NH3

Fe/Mo

2. Nitrogen assimilation

Plants absorb nitrates from the soil and use them to build up proteins. These plants are
eaten by herbivores and get the nitrogen containing nutrients. Again the carnivores eat
these herbivores and get animal proteins. Thus, nitrogen assimilation is the formation
of organic nitrogen compounds like amino acids from inorganic nitrogen compounds
present in the environment.

3. Ammonification

Some of the plant protein and animal protein are utilized by the individual organisms.
Animals excrete the unused nitrogen compounds in the soil. The remains of plants and
animals and their waste products are decomposed by the microorganism in the soil
to produce ammonia. This ammonia is dissolved in the soil in the form of ammonium
ions. The decomposition with production of ammonia or ammonium compounds by
the action of bacteria on nitrogenous organic matter is called ammonification. The
bacteria that cause ammonification are Bacillus, Proteus, Clostridium, Pseudomonas,
Streptomyces etc.

4. Nitrification

The conversion of ammonia into nitrites (NO2—) and then into nitrates (NO3—) by the
action of soil bacteria is called nitrification. These bacteria are called nitrifying bacteria.
For example, Nitrosomonas, Nitrobacter, Nitrosococcus, etc. are nitrifying bacteria. In
a more specific way, the bacteria that oxidizes ammonia into nitrites are called 'nitrite
bacteria' and that oxidize nitrites into nitrates are called 'nitrate bacteria'.

Nitrosomonas 2HNO2 + 2H2O
2NH3 + 3O2

Nitrosomonas 2HNO3
2HNO3 + O2

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5. Denitrification

Denitrification is the process of reduction of unused nitrates into free nitrogen by the
action of soil bacteria to return nitrogen back into the atmosphere. Bacteria involved
in denitrification are called denitrifying bacteria. For example, Agrobacterium,
micrococcus denitrificans, pseudomonas, bacillus, etc. are some denitrifying bacteria.
Denitrification completes the nitrogen cycle.

Answer writing skill

1. Define ecology.
Ecology can be defined as the study of the distribution and relations of organisms and
their interactions with the environment.

2. What is ammonification?
When plants and animals die, the microorganisms present in the soil or air breaks
down the organic matter of the dead bodies into ammonia. This process is called
ammonification.

3. Give the name of some nitifying bacteria.
Nitrosomonas, nitrobacter, nitrosococcus are some nitrifying bacteria.

4. Write the components of the wetland ecosystem.
The components of a wetland ecosystem can be divided into two factors:

Biotic components: animals like reptiles, amphibians, aquatic plants and algae, and

Abiotic components: Water, soil, temperature, rainfall

5. Write some common examples of wetlands.
Common examples of wetlands are the edge of a lake or ocean, the delta at the mouth
of a river, low land areas that frequently flood.

6. Write short notes on nitrogen fixation.
The process of converting atmospheric nitrogen into organic nitrogen compounds is
called nitrogen fixation. Atmospheric nitrogen is fixed through biological and non-
biological (physical) processes. Atmospheric nitrogen is deposited in the soil mainly
through precipitation. Then the nitrogen fixing bacteria and blue green algae in the soil
converts it into ammonia. Bacteria like azotobacter, clostridium, rhizobium, nostoc are
present in the root nodules of leguminous plants and loosely dug soil.

When lightning occurs, atmospheric nitrogen reacts with oxygen in the air and form
nitric oxide and nitrogen dioxide. These oxides combine with water vapou to form
nitrous or nitric acids. These acids then combine with salts and produce nitrate ions.

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N2 + O2 2NO

2NO+ O2 2NO2
N2O5
NO2 + O2 2HNO3
Ca(NO3)2 + CO2 + H2O
N2O5 + H2O

HNO3 + CaCO3

7. What are the important sources of carbon?
The main source of carbon is carbon dioxide. Other sources of carbon are rocks, volcanic
eruption, fossil fuels like coal and petroleum products that gives rise to carbon dioxide
in the earth’s atmosphere.

8. How does the study of ecology help to conserve natural resources?
The study of ecology helps to conserve natural resources by:

i. Providing information about the benefits of ecosystems.

ii. Providing information for natural resource management.

iii. Providing information about the different types of natural sources.

9. Why is conservation of wetlands important?
Conservation of wetlands is important because they are the most productive habitats of
aquatic plants and animals, including mammals, birds, fishes and invertebrates.

10. Explain the steps involved in the oxygen cycle.
Photolysis: In the atmosphere, the energy in the sunlight breaks the oxygen molecule to
produce free oxygen. This process is called photolysis.

1. Photosynthesis: In the biosphere, plants use this carbondioxide in the presence of
sunlight to form carbohydrates and water. This process is called photosynthesis. In
this process, oxygen is produced as a byproduct.

2. Chemical weathering: In the lithosphere, oxygen is fixed in minerals like silicates
and oxides. When the mineral bearing oxygen is exposed to chemical reaction, the
minerals wears down, and free oxygen is produced. This process is called chemical
weathering.

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Exercise

Section "A"

1. Define ecology.
2. What is a wetland?
3. Define biogeochemical cycle.
4. What are the types of biogeochemical cycle found in atmosphere?
5. What is the main source of carbon?
6. Write any two main sources of oxygen.
7. What is nitrogen fixation?
8. What is nitrogen assimilation?
9. What is ammonification?
10. Name any two ammonifying bacteria.
11. What is nitrification?
12. Give name of two nitrogen fixing bacteria.
13. What is denitrification?
14. What are denitrifying bacteria?
15. Give the name of two denitrifying bacteria.

Section "B"

1. List the biotic and abiotic components of wetland ecosystem.
2. Give the names of the main type of biogeochemical cycle.
3. Explain the importance of the biogeochemical cycle.
4. Differentiate between gaseous cycle and sedimentary cycle.
5. Write the difference between nitrification and denitrification process of the nitrogen

cycle.

Section "C"

1. Mention the importance of ecology.
2. Differentiate between autecology and syncecology.
3. Write the importance of algae in wetland ecosystem.
4. Why is a wetland ecosystem important?
5. Why is carbon cycle important?

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Section "D"

1. Describe the abiotic components of a wetland ecosystem in brief.
2. What are the biotic components of a wetland ecosystem? Explain.
3. Describe the carbon cycle in brief.
4. Give a short account of the nitrogen cycle.
5. Describe the oxygen cycle in brief.

Multiple choice questions

1. The water in a wetland can be

a) Fresh b) Salty c) Brackish d) All of the
above

2. Hydrilla is an example of

a. Submerged plants b. Floating plants c. Emergent plants d.Terrestrial plants

3. Rhizobium is an example of

a. Nitrifying bacteria b. Nitrogen fixating bacteria

c. Denitrifying bacteria d. Ammonification bacteria

4. The process of converting atmospheric nitrogen into organic nitrogen compounds.

a. nitrogen fixation b. nitrification c. ammonification d. denitrification

5. Example ofdenitrifying bacteria is

a. Rhizobium b. Nitrosomonas

c. Micrococcus denitrificans d. Nitrobacter

6. The main source of oxygen is

a. Water b. Soil c. Minerals d. Air

7. There is about ……. of nitrogen in the air.

a. 78% b. 72% c. 71% d. 74%

8. Water cycle is also known as

a. Sedimentary cycle b. Hydrologic cycle

c. Gaseous cycle d. Liquid cycle

Project Work

1. Study the wetlands found in Nepal. Prepare a report on any one of the wetlands and
show it to your teacher.
In your report include the abiotic factors and biotic factors of that wetland.

2. On a chart paper, present any one of the biogeochemical cycles and display it in
your classroom.

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UNIT

18 BEHAVIORAL
BIOLOGY

Karl Landsteriner (1868-1943) He was an Austrian biologist, physician and immunologist.
He developed the modern system of classification of blood groups from his identification
of the presence of agglutinins in the blood and identified the Rhesus factor in 1937.
He discovered the polio virus in 1909, and for this he was awarded the Nobel Prize in
Physiology, or Medicine. He is also known as the “father of transfusion medicine”.

Syllabus issued by CDC Learning objectives:

Theory 6 At the end of this unit, the students will be able to:
Practical • define organ transplantation.
I2 I • explain the method of organ transplantation.

Atomic mass, molecular mass and • state the effects and control measures for high
mole concept blood pressure, high cholesterol and high uric
acid.

• define and explain antibiotics.

• explain the method to distinguish blood

group.

Key terms and terminologies of the unit

Organ transplantation: An organ transplantation is the process of transferring an organ
from the body of donor to the body of recipient, to replace a damaged or missing organ

Transplant or graft: The tissue or organ which gets transplanted is called a transplant or
graft.

Blood pressure: Blood pressure is the pressure exerted on the walls of the arteries as blood
flows through them.

Systolic blood pressure: Systolic blood pressure is the pressure in the arteries as the
ventricles of the heart contract.

Diastolic blood pressure: Diastolic blood pressure is the pressure in the arteries as the
ventricles of the heart relax.

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Cholesterol: Cholesterol is an oil based substance (lipid) that does not mix with blood and
distributed throughout the body.

Uric acid: Uric acid is a waste product obtained during the breakdown of purines found in
foods such as liver, mushrooms, dried beans, etc.

Gout: Urate crystals when accumulate around the joints and soft tissues to cause
inflammation and pain. This is known as gout.

Antibiotic: Antibiotic is defined as a chemical substance produced by some microorganisms
that have the capacity to deactivate or kill other microorganisms

Blood group: A blood group is a classification of blood based on the presence or absence of
antigens on the surface of red blood cells (RBCs) and antibodies in blood plasma

Rh factor: Rh factor is the protein known as RhD antigen that is present on the surface of
RBC

Introduction

Biology is the science of life and of living organisms. It includes numerous fields like botany,
zoology, mycology, microbiology, biochemistry, etc. The practical uses of biological knowledge
come under applied biology. Applied Biology is the application of knowledge of Biology in
development of tools and methods specific to biological research needs. It is important for the
technologies and applications relevant to biology-based industries and institutions. In this
unit we will learn about organ transplantation, blood studies-blood group and its grouping,
cholesterol, high blood pressure, hypertension, uric acid. We will also learn about antibiotics
that destroy or inhibit the growth of microorganisms.

Organ Transplantation

Some damaged organs in the body can be replaced by transplantation. There are many
examples of tissue or organ transplantation on human beings such as skin grafting, heart
transplantation, kidney transplantation etc. Organs that can be transplanted include bone
marrow, lungs, heart, liver, cornea and kidneys. The person who receives the organ is the
recipient, and the person from whose body the organ was taken is the donor.

An organ transplantation is the process of transferring an organ from the body of donor to the
body of recipient, to replace a damaged or missing organ. It involves the removal of damaged
or injured tissues or organs from the body of receipient and replacing them by similar
tissues/organs from the body of donor. The tissue or organ which gets transplanted is called
a transplant or graft. It is essential to perform tissue matching and blood group matching
tests before undertaking any graft/ transplant. Transplantation may result in the rejection of
transplanted organs due to production of antibodies by patient’s immune system against the
transplanted organ. Therefore, the success rate of an organ transplant is very low. Organs
that have been successfully transplanted include the heart, kidneys, liver, lungs, pancreas,
intestine, and thymus. Some organs, like the brain, cannot be transplanted.

Memory Plus

The world’s first successful organ transplant was a kidney transplantation in 1954. It was
undertaken by David Hume and Joseph Kelly at the Peter Brigham Hospital in Boston.

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