In human body a type of amoeba is found through polluted water which is called
Emtamoeba histolytica which causes dysentery.
Hydra Tentacle
Classification Mouth
Kingdom : Animalia
Sub-kingdom : Invertebrates
Phylum : Coelentarata Bud
Type : Hydra
Basal disc
Hydra are simple fresh-water animals possessing Fig : Hydra
radial symmentry. They are multi-cellular organism
attached with substrata or objects.
They body of hydra has two layers ciz: outer epidermis and the inner layer is called
gastrodermis, which are separated by gel called mesoglea. The body is elongated
tubular which is closed at one end and other end is open with a small pore. At the side
of closed end there is foot or basal disc which contain a gland. This gland secretes
sticky substance which helps them to attach on the substratum. The open end which
has a small pore called mouth surrounded by 6-10 slender, hollow tentacles.
Tentacles bear stinging cells called nematocysts which help to paralyse and catch the
prey. Other function of tentacles is locomotion.
Reproduction and Life Cycle
Asexual Reproduction
Budding: When food is plentiful, many hydras reproduce asexually by producing
buds in the body wall, which grow to be miniature adults and simply break away when
they are mature.The hydra may regenerate when injured.
Sexual Reproduction
When condition are harsh, often before winter or in poor feeding conditions sexual
reproduction occurs in some hydras. Swelling ovary or testes. The testes release free-
swimming gametes into the water and these can fertilize the egg in the ovary of another
individual. The fertilized eggs secrete a tough outer coating and as the adult dies these
resting eggs fall to the bottom of the lake or pond to await better conditions where
upon they often hatch into nymph hydras. Hydras are hermaphrodites i.e. they may
produce both testes and ovary at the same time.
Blooming Science & Environment Book 7 201
Many members of the hydrozoa go through a body change from a polyp (body having
tentacles) to an adult form called a medusa (body is umbrella shaped). However, all
hydras, deposite being hydrozoans, remains as polyps, throughout their lives.
Feeding
Hydras mainly feed on small aquatic invertebrates such as Daphnia and Cyclops
when feeding, hydras extend their body to maximum length and then slowly extend
their tentacles. Once fully extended, the tentacles are slowly move around waiting for
contact with a suitable prey animal. Upon contact nematocysts on the tentacles fire into
the prey and tentacles surround and move the prey into the mouth.
Some species of hydra exists in natural relationship with various types of unicellular
algae. The algae are protected from predators by the hydra and in return photosynthetic
products from the algae are beneficial as a food source to the hydra.
Main Points to Remember
1. A cell is the basic unit of life in the plants and animals.
2. In plant cells, there is a definite wall of cellulose enclosing the protoplasm.
3. In animal cells, the cell wall is absent. Hence, plasma membrane functions as an
outer protective layer.
4. In plant cells, there are prominent vacuoles, cell wall and plastids.
5. A cell wall consists of non-living material called cellulose.
6. The nucleus is one of the most important cell organelles which controls the
metabolic activity of the cell.
7. Animal cell contains centrosome and small temporary vacuoles.
8. Chloroplast, chromoplast and leucoplast are three types of plastids found in plant
cells.
9. Amoeba is unicellular and Hydra is multicellular organisms.
10. The group of cells form tissue.
PRO J ECTWORK
Prepare a model of animal cell / plant cell in a thick sheet by using various materials
availabe in your locality.
202 Blooming Science & Environment Book 7
Exercises
1. Fill in the blanks.
a. A cell is the basic unit of .................................
b. The outer covering of the plant cell is called .................................
c. The jelly like fluid found between the plasma membrane and the nucleus is
called .................................
d. ................................ are fluid-filled spaces.
e. Plastids are absent in ................................ cell.
f. Lysosomes are found in ................................ Cells only.
2. Tick () the correct and cross (×) the incorrect statements.
a. Animal cells are fixed in shape.
b. Major functions of cells are conducted inside the nucleus.
c. Plant cells contain centrosome.
d. An egg is a cell.
e. Some organisms are unicellular.
3. Draw the followings.
a. Amoeba b. Hydra
4. Answer the following questions.
a. What is a cell?
b. Where is the plasma membrane found?
c. Why are the cells of different shapes and sizes?
d. What is the function of the cell membrane?
e. What is the function of the centrosome?
f. What is the importance of a cell?
g. List any four differences between the plant and the animal cells.
h. Why is the cell considered as a functional unit of life?
i. What are the functions of different type of plastids in a plant cell?
j. What is the function of mitochondria? It is called powerhouse of cell, why?
k. Classify plastids and mention where they are found.
l. Write the function of the following:
Nucleus, plastid, vacuoles, cellwall, mitochondria, cell membrane.
o. What are the two body layers of hydra? What separates these two layers?
q. Define looping and somersaulting with neat figures.
Blooming Science & Environment Book 7 203
r. How does reproduction take place when they have plentiful of food and
goos with neat figure that takes place in hydra?
s. In what condition hydra reproduce sexually?
t. Describe the feeding habit of hydra.
5. Study the given diagram and answer the questions asked.
a. Label ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’.
b. Write the function of ‘D’ and ‘A’.
c. Which one of them is called powerhouse of a cell?
d. What is shown in the diagram?
6. Study the given diagram and answer the question asked.
a. Label ‘A’, ‘B’, ‘C’, ‘D’ and ‘E’.
b. Write the function of ‘D’ and ‘A’.
c. Which one of them helps in photosynthesis?
d. What is shown in the diagram?
7. Sketch neat and labeled diagrams of a plant cell and an animal cell.
8. Distinguish:
a. Cell wall and cell membrane
b. Unicellular and multicellular organisms
Glossary
Nerve Cell: a long cell which works as unit of nervous system
Safranin : a chemical used to stain the materials before observing under
microscope
Compartments : small boxes like structures
Rigid: solid, firm
Cellulose: a type of carbohydrate
Organelles: the living structure found inside cells
Chromatin: the substance of which chromosomes are composed.
204 Blooming Science & Environment Book 7
17Chapter Life Process in Plant
Learning Outcomes Estimated Period-10+2
On the completion of this unit, students will be able to:
• introduce respiration and explain respiratory organs of animals and plants.
• describe the mechanism of respiration in animals and plants in brief.
• introduce and explain human digestive system.
• introduce and describe excretion in animals and plants.
A. Respiration
We need energy to do different types of work and to conduct other life processes.
Food taken by us supplies energy to our body. Different types of organisms get food
by different methods. They are autotropic and heterotropic nutrition. The food taken
is broken down to release energy by a process called respiration. Thus, respiration is a
process by which the energy of the food is made available to the cells.
Oxygen is used in the process of respiration. The process of taking in oxygen and
giving out carbon dioxide is called breathing. It consists of inspiration and expiration.
Inspiration is the process of taking air in (breathe in) and expiration is the process of
throwing air out (breathe out). Oxygen reacts with food inside cells for the liberation
of energy which is called cellular respiration. Cellular respiration is essentially a
catabolic process which involves biological oxidation of organic molecules and result
in the release of energy. Therefore, respiration includes both breathing and oxidation.
Therefore, breathing is a combined form of inspiration and expiration. In inspiration,
oxygen is taken in with air. In expiration, carbon-dioxide with water vapour and
remaining air is thrown out. The combustion of food and releasing energy in the
presence of oxygen is called oxidation. The total process of cellular respiration and the
breakdown of glucose takes place into two steps: They are anaerobic respiration and
aerobic respiration.
Anaerobic Respiration
It takes place in the absence of oxygen, and results in incomplete oxidation of the
food. Carbon dioxide and organic compounds like ethyl alcohol, lactic acid, etc. are
produced in this process. During this process some energy is also released, whereas
water is not produced in this reaction. It is expressed in the form of following equation:
Blooming Science & Environment Book 7 205
C6H2O6 2C2H5OH + 2CO2 + Energy
(Glucose) (Ethylalcohol) (Carbondioxide) + Energy
Usually, anaerobic respiration takes place in the deep-seated tissue of plants, in
germinating seeds, in fruits and among many micro-organisms like yeast and
bacteria.
Aerobic Respiration
It takes place in the presence of oxygen. Complete oxidation of the food results in the
formation of carbon dioxide and water with the release of energy.
Glucose + Oxygen Carbon dioxide + Water + Energy
C6H12O6 + 6O2 6CO2 + 6H2O + Energy
Breathing Mechanism in Animals
There are different mechanisms for inhalation of oxygen and exhalation of carbon
dioxide in animals and plants. Animals contain some specific organs for respiration to
perform different mechanisms as requirements.
1. Gas Exchange in Algae and Protozoans (Body surface)
Insubmergedwaterplants,algae(Spirogyra)andprotozoans(Amoeba,Paramecium)
air diffuses through the body surface.
Nucleus
Vacuole Cell membrance
Cytoplasm Pseudopodia
Amoeba
2. Gas Exchange or Breathing in Insects (Trachea)
In most insects gas exchange or breathing take place through a system of
internal air-filled tubes called trachea. The tracheas usually open outside
through minute pores called spiracles, which are located on either side of the
body.
The respiration through trachea is called tracheal respiration. Tracheal
respiration is characteristics of insects like butterfly, cockroach, grasshopper etc.
In insects (e.g. cockroach), there occurs no respiratory pigment in blood since
blood has no role in oxygen transport.
206 Blooming Science & Environment Book 7
3. Breathing or Gas Exchange in Fishes (Gills)
Fishes have gills as a respiratory organ.
Gills are the breathing organs of aquatic
animals and are found in fishes, tadpoles Gills arch
and in some mollusca. Gills are covered
with operculum. Gills are filamentous
structures richly supplied with blood
capillaries. Each gill filament consists
of numerous gill lamella through which
dissolved oxygen from the surrounding Water flow
water diffuses inside and carbon dioxide into mouth Water emerges through gills slits
is expelled out.
4. Gas Exchange Through Body Surface (Skin)
There are many animals such as sponges, coelenterates, earthworm, amphibians
(e.g. frog) in which integument or skin functions as a respiratory organ. The
skin of these animals remains moist all the time so that oxygen from the
surrounding environment can pass into the blood through simple diffusion.
Anus Capital
papillae
13th segment
Female gential pore
Setae Male gential pore
5. Breathing in Human Beings (Lungs)
Animals like reptiles, birds and mammals have lungs as the chief respiratory
Blooming Science & Environment Book 7 207
organs. Human breathe through their nostrils and lungs. A pair of lungs is located
in the air-tight thoracic cavity that is bounded by a muscular and elastic sheet
called diaphragm. The lungs are situated next to the heart in thoracic cavity.
Twelve pairs of bond ribs surround and protect the lungs and heart.
Lungs are like rubber balloons. Air enters through the nostrils. Nostrils possess
hairs, which trap dust particles and filter them out of the system. Air passes from
the nasal passage, through the pharynx, larynx, and into the trachea.
The trachea is also called windpipe. At its lower end, the trachea divided into
two bronchi (right and left bronchus). Within the lungs each bronchus subdivided
many times into much smaller tubes called bronchioles. These bronchioles later
give rise to alveolar sacs, which appear as a cluster of grapes. They give sponges
like texture to the lungs.
Nasal cavity Pulmonary venule
Nostrill Pulmonary arteriole
Oral cavity Alveolus
Larynx Pharynx Capillary network
Right main Trachea
(primary)
bronchus Alveoli
Right lung
Left main
(primary)
bronchus
Base of
left lung
Diaphragm
Respiratory system
Each lung is covered externally by a pleural membrane. Blood capillaries form
an extensive network around the alveoli. Rapid gaseous exchange take place
between blood capillaries and air-sacs. Oxygen contained in alveoli is absorbed
by blood whereas carbon dioxide from the blood is given out in alveoli. In this
way oxygen passes from the air into the blood, while carbon dioxide from the
blood into the air. Guard cell
Gas Exchange in Plants Stomatal pore
Chloroplast
Unicellular algae employ the whole
surface of the cell for gaseous exchange. Stomata open Stomata closed
In flowering plants gases pass through
208 Blooming Science & Environment Book 7
small pores in the leaves and green stems. These pores are the stomata. Woody plants
still have stomata in the leaves but the stem have small areas of loosely packed bark
cells called lenticels. Gases diffuse through the stomata and lenticels. Roots also
absorb oxygen and eliminate carbon dioxide into soil. Exchange of gases takes place
by diffusion across the surface of living cells surrounding the root.
Mechanism of Gas Exchange
Gaseous exchange, i.e., intake of oxygen and output of carbon dioxide, always takes
place at the respiratory surface. The respiratory surface may be a skin, a gill or lung.
Usually gaseous exchange takes place by simple diffusion. Diffusion is the movement
of molecules from higher concentration to lower concentration, leading finally to
uniform concentration.
Activity
To demonstrate that carbon
dioxide is released during
respiration.
Perform the following Boiles bean seeds Wet bean seeds Lime water turns milky
experiment with the help of
your teacher
a. Take two flasks and put wet cotton in both. Take few seeds of bean in flask
‘B’ and put the flask in suitable temperature and light for few days until the
seeds germinate. Similarly, take few seeds of boiled bean in flask ‘A’ and keep
it in the same condition as flask ‘B’. Both the flasks should be covered.
b. Put limewater in two different test tubes. Transfer the gas collected in flask B
and A into two test tubes B and A. Shake both the tubes. What do you observe?
Why there is colour change in test tube B? Why not in test tube A?
c. Put limewater in test tubes. Take plastic pipe and blow air through your mouth
in the test tubes. What is the colour of limewater?
When limewater come in contact with carbon dioxide, the colourless limewater
changes into milky white colour. We expel out carbon dioxide and the air which we
blow into the test tube, contain carbon dioxide. The carbon dioxide and limewater
give milky appearance in the test tube. Now, with this logic, find out the cause of
colour appearance in test tube B.
Conclusion: This activity proves the release of carbon dioxide during repiration.
Blooming Science & Environment Book 7 209
Importance of Respiration
All systems, from cells to ecosystem require energy so that they can work. The energy
stored in food is made available to cells because of respiration. Complex organic
molecules are broken down into simpler form with the release of energy. The released
energy is captured by molecules in the form of adenosine triphosphate (ATP). ATP is
energy carrier of the cells. The rest of the energy is lost as heat.
All living cells respire so as to live. Growing plant organs namely floral and vegetative
buds, germinating seeds, stem and root tips respire actively. Due to respiration, there
is a balance of gases in the atmosphere.
Main Points to Remember
1. Respiration is a process by which the energy of the food is made available to
cells.
2. The biochemical process, which occurs within cells, is called cell respiration.
3. Respiration is a destructive process.
4. Aerobic respiration takes place in the presence of free oxygen.
5. Anaerobic respiration takes place in the absence of free oxygen.
6. Glycolysis or breaking of glucose molecule takes place in cytoplasm.
7. Unicellular organism like amoeba respire through their general body surface.
8. Animals like earthworm, respire by their skin.
9. Insects like butterfly, moths and cockroach have tracheal respiration system.
10. Fishes have aquatic breathing organs called gills.
11. Most of the land animals have lungs to respire.
12. Gases diffuse through the stomata and lenticels of plants.
13. Gaseous exchange takes place in plants and animals because of diffusion.
14. Molecules move from higher concentration to lower in diffusion.
15. In most of the insects, there is no respiratory pigment in blood.
16. ATP is the energy carrier of the cells.
PRO J ECTWORK
You can learn about lungs from observing the lungs of slaughtered animals. Go to
a butcher’s shop and observe the location of the respiratory system. Observe the
windpipe, lungs and other parts of the lungs from the slaughtered animal and note
your findings in your notebook.
210 Blooming Science & Environment Book 7
Exercises
1. Fill in the blanks.
a. The full form of ATP is .................................
b. Carbon dioxide and ..............are the by-products of anaerobic respiration.
c. ................................ respiration takes place in the presence of oxygen.
d. Trachea divides in two .................................
e. ................................respire through skin.
2. Write down 'True' or 'False' and correct the false statements.
a. ATP is not the energy carrier of a cell.
b. Diffusion is a mechanism by which molecules in the lower concentration
move to higher concentration.
c. Whales have gills as a respiratory organ.
d. Frogs respire through skin.
e. Earthworms have a pair of lungs.
f. Glycolysis occurs in aerobic condition only.
g. Ethyl alcohol is the by-product of aerobic respiration.
h. Gas exchange in algae takes place through body surface.
i. Operculum is found in gills.
3. Choose the correct answer.
a. Which of the following is not involved in respiration process?
i. Glucose b. Respiratory enzyme
iii. Oxygen d. Carbon dioxide
b. Ethyl alcohol is produced in
i. Aerobic respiration b. Anaerobic respiration
iii. Photosynthesis d. Protein synthesis
c. Gas exchange in insects occurs by
i. Lungs b. Skin
iii. Hearts d. Tracheae
d. Each lungs of human is covered by
i. Dura matter b. Pleural membrane
iii. Plasma membrane d. Cell wall
Blooming Science & Environment Book 7 211
e. The trachea of human is divided into
i. Two larynx b. Two bronchi
iii. Two alveolar sacs d. Two bronchioles
f. Lime water changes its colour to ……………… when it comes in contact
with carbon dioxide.
i. Blue b. Milky white
iii. Yellow d. Colourless
4. Define the following terms.
a. Respiration b. External and internal respiration.
c. Breathing d. Tracheal respiration.
e. Diffusion
5. Answer the following questions.
a. How do amoeba respire?
b. What is respiration? Why should we respire continuously?
c. What are the by-products of anaerobic respiration? Show its reaction.
d. Give in brief the importance of respiration.
e. “Respiration is destructive process”. Explain.
f. What is the function of ATP?
g. How does gas exchange take place in insects?
h. What is the function of ribs in humans?
i. What is the function of diaphragm?
j. “Breathing through nostril is beneficial than breathing through mouth”.
Give reasons.
k. How do plants respire?
l. What happens when carbon dioxide is dissolved in limewater?
m. How fishes respire in water?
n. What is the role of skin in earthworm?
o. Why insects don’t have respiratory pigments?
p. Describe about the lungs of human.
q. Draw the respiratory organs of human
r. What is aerobic respiration? Write its reaction.
212 Blooming Science & Environment Book 7
6. Distinguish between.
a. Aerobic and anaerobic respiration. b. Inspiration and expiration.
c. Gills and lungs. d. Internal and external respiration.
7. Label the diagram.
Glossary
Accumulation : process of collecting things
Waste: unwanted, unsual remains
Toxic: poisonous, causing serious harm
Diffusion: spreading, scattering
Excess: extra, additional
Nephridia: simple tube-shaped organs for releasing waste
Resin: semi-solid substance from plants
Malphigian tubules: insects’ excretory organs
Adhesive: sticky substance, glue
Latex: milky white substance produced by plants
Waist: body part between ribs and limbs
Blooming Science & Environment Book 7 213
B. Digestion
In our body, damaged cells and tissues are replaced by new cells and tissues, the
nutrients which are consumed in our body are used up in the growth of body and some
of the nutrients are transformed into energy.
Metabolism has two categories i.e. anabolism and catabolism. The catabolism and
anabolism are closely related with each other. The reaction in which simpler molecules
are synthesized to form complex molecules inside the body is called anabolism.
The reaction in which complex molecules are broken down into simpler molecules
with release of energy is called catabolism.
The collective process of construction and breaking down of molecules with
liberation of energy is known as metabolism. Metabolism includes both anabolism and
catabolism.
Nutrients like carbohydrates, fats, oils, proteins, minerals and vitamins are converted
into some useful components in the body with the release of energy. This can be studied
in digestive process.
The process of breaking down of the complex food molecules into simpler molecules
and then absorbed by the cells in known as digestion.
The digestion in human takes place outside the cells i.e. in the digestive tube or
alimentary canal. Thus, the digestion which takes place outside the cell is called extra
cellular digestion.
The digestion of unicellular organisms like amoeba is inside the cells and is called
intracellular digestion.
Human Digestive System
Mouth, pharynx, esophagus, stomach, small Esophagus
intestine, large intestine, rectum and anus are the
main organs of the digestive process of human. Liver
The digestive glands present in these organs Stomach
produce several enzymes which help to change Gall Pancreas
Bladder
the complex food into simpler molecules.
In mouth, the food is chewed with the help of Large Small
teeth and is converted into small pieces. These Intestine Intestine
foods mix with saliva secreted by the salivary
glands and then swallowed. Saliva contains an Appendix
enzyme ptyalin which coverts starch into a simpler
compound called maltose. Saliva also lubricates Rectum
Fig: Human digestive system
the food, making it easier to swallow.
214 Blooming Science & Environment Book 7
The tongue helps in rolling and pushing the food into the pharynx. Then food enters in
the esophagus and moves towards the stomach by the periodic relaxation and contraction
of the inner wall muscles of the esophagus. This is known as peristalsis.
In the stomach, the food is mixed with the gastric juice secreted by the gastric glands
present in the inner lining of the stomach. Gastric juice contains enzymes like pepsin,
rennin and hydrochloric acid.
Pepsin breaks proteins into peptones and amino acids. Rennin helps to emulsify fats
from milk. Hydrochloric acid dissolves minerals and also prevents bacterial growth.
The food remains in the stomach for 1-4 hours, depending upon the type of food. Then
it moves to the duodenum. Here the food is mixed with bile secreted from liver and
pancreatic juice secreted from the pancreas. Bile helps in digestion of fat. Pancreatic
juice contains several enzymes such as,
Trypsin - It changes protein into peptones.
Amylase - It changes starch into mattose
Lipase - It changes fat into glycerol and fatty acids.
From the duodenum, the food passes into ileum and acted by several enzymes like,
Erepsin - It change peptones into amino acids
Invertage - It changes sugar into glucose and fructose
Maltase - It changes milk and sugar into glucose
The food is finally converted into glucose, fructose, amino acids, fatty acids and
glycerol. These are soluble in water and absorbed by illeum second part of small
intestine. Inner surface of illeum contains tiny projections called villi. Villi contain
blood capillaries. Simple sugars and amino acids are absorbed by blood capillaries.
Fatty acids and glycerol enter the lymph vessels and pass into blood vessels then it
transports to different parts of the body.
The undigested residue which mainly contains cellulose move into large intestine.
Here water is absorbed and the solid residue is lubricated with mucus to form the
faeces. The faeces passes to the rectum and is then expelled from the body through the
anus.
Blooming Science & Environment Book 7 215
Digestive glands and their functions
The table below shows the process of digestion and the enzymes involved in it.
Organ Digestive Digestive Enzyme Food the End
gland juice enzyme product
1. Mouth Salivary Saliva Ptyalin acts on Maltose
2. Stomach glands Starch
Gastric Gastric Pepsin Peptone
glands juices, Rennin Protein Casein
HCl - Milk kill germs
3. Duodenum Liver Bile No - -
Pancreas Pancreatic Trypsin - Peptone
juice Amylase Protein Maltose
Lipase Starch Fatty acid &
Fat glycerol
4. Small Intestinal Intestinal Erepsin Peptone Amino acid
Intestine glands juice Maltase Maltose Glucose
Sucrase Sucrose Glucose
Lactase Lactose Glucose
Function of nutrients: The function of the nutrients are given below.
Carbohydrates: Carbohydrate provides energy. Deficiency of carbohydrates in diet
leads to imbalance in body.
Fats and oils: It increases the energy and maintain the body temperature.
Proteins: It helps to repair damaged cells or tissue and also helps in growth of cells
or tissues.
Minerals: The minerals like Iron, calcium, Phosphorus, etc. help in formation of blood
and makes teeth, bones strong.
Main Points to Remember
1. The building activities are called anabolism whereas the destructive activities
are called catabolism.
2. The digestion process is necessary to get the essential simpler component from
the complex food.
3. Several juices from different digestive organs are responsible for digestion of
food, which converts complex food into the simpler form of food.
4. The process of breaking down of complex food molecules into simpler form and
absorbed by the cells to get energy with the help of oxygen is called
digestion.
216 Blooming Science & Environment Book 7
5. The undigested material is sent into the rectum where water is absorbed and the
residue is thrown out through anus.
6. Carbohydrates, proteins, vitamins, minerals and fats are nutrients found in a
balanced diet.
PRO J ECTWORK
Study the digestive system of a goat by observing in butcher’s shop and sketch in a
chart paper.
Exercises
1. Fill in the blanks.
a. The building activities is ....... and destructive is......... .
b. The compounds such as ........... and ........... produced with liberation of
energy due to oxidation of glucose.
c. The tongue helps in ........... and ........... the food into the pharynx.
d. The undigested residue move on to........... intestine.
2. Write 'True' for true and 'False' for false statements.
a. Lungs are richly supplied with blood capillaries.
b. Digestion process begins in the mouth.
c. Fats help in the formation of blood.
d. Bile helps in digestion of protein.
3. Answer the following questions.
a. What is digestion?
b. Describe the function of villi.
c. How does the digested food is absorbed in our body?
d. Write the names of different glands and the juice secreted from these glands
in the alimentary canal.
e. What is the relationship between circulatory and digestive system?
Blooming Science & Environment Book 7 217
f. Draw a well labeled diagram of human digestive system.
g. What is called digestive system?
h. Write the functions of nutrients.
4. Write in short.
a. Cotabolism b. Anabolism c. Oxidation d. Enzymes
Glossary
Anabolism : the constructive or building up phase of metabolism.
Catabolism : the destructive or oxidative phase of metabolism.
Deficiency : lack of
Metabolism : sumofchemicalchangeconstructiveanddestructiveoccurringinthe
living organism.
Intercellular : occurring inside the cell.
Extra cellular : occurring outside the cell.
Enzyme : a protein catalyst.
Digestion : the process, which makes food soluble.
Starch : glucose substance in food that gives major energy
Diffusion : process of spreading something
Tracheae : breathng pipes
Inhalation : intake of or through the nose or mouth
Nostrill : nose holes
Release : let out something
Tiny : very small
Moist : damp, slightly wet
218 Blooming Science & Environment Book 7
C. Excretion
Introduction
In all living organisms, various life processes (metabolism) take place in order to
conduct daily life activities. Such activities not only produce useful materials but
also form some waste substances. The waste materials produced are called excreta.
Carbon dioxide, urea, uric acid, ammonia, excess water etc. are some of the excreta
produced by the complete digestion of carbohydrates, proteins and fats. Such
products are poisonous in nature and thus have to be removed from a living body. A
living body has several organs to remove such excreta.
The process of removing the waste materials produced during various activities of a
body through some special organs is called excretion.
Excretion in Animals
The lower aquatic organisms like amoeba, paramecium, hydra, sponges etc do not
have any special organs for excretion. They excrete the waste products from general
body surface into water by the process of diffusion.
In higher organisms, distinct organism and systems are present for excretion. Skin,
nose, mouth, lungs, liver, large intestine, kidneys etc are the main excretory organs.
Excretion in Human Beings
The main excretory organs in human beings are the kidneys. However, there are
some other organs meant for excretion. They are as follows:
a. Skin: Many sweat glands are present in the skin. These sweat glands remove
excess water, mineral salts and urea in the form of sweat.
b. Liver: It removes dead and worn out red blood cells and
excess amino acid.
Liver
c. Lungs: The lungs remove carbon dioxide produced during
breathing.
Lungs
d. Large Intestine: The undigested food passes out in the form of
faeces (stool) through large intestine, rectum and anus.
Large intestine
Blooming Science & Environment Book 7 219
e. Kidneys: These are reddish brown, Aorta
bean shaped structure found at the dorsal Ureter
abdominal cavity one on each Renal artery
side of the vertebral column. Each Bladder
kidney consists of millions of Renal vein Urethra
functional structures each called a Kidney Urinary system
nephron. It filters nitrogenous
waste materials like urea, uric acid and
excess water from the blood. These
materials are removed in the form of
urine through urinary system. The organs
of the urinary system are kidneys, a pair
of ureter, urinary bladder and urethra.
Two kidneys, right and left: They secrete
urine.
Two ureters, right and left: They drain urine from the kidneys to the urinary
bladder.
The urinary bladder: It functions as the urinary reservoir. It is where urine is collected
and stored for a short time.
Urethra: It is a canal through which the urine is eliminated from the urinary bladder
to exterior.
Excretion in Plants water vapour
Plants have different
physiology than animals. Co2 during respiration
Plants do not have special
organs for excretion. Plants O2 during respiration
are producers and they
synthesize all their organic
requirements according to
demand. Three of the waste
products produced by certain
metabolic activities in plants,
that is oxygen, carbon dioxide
and water, are raw materials Excretion in plants
for other reactions, and excess
of carbon dioxide and water are used up in this way. The main nitrogenous end product
of protein metabolism is ammonia, which is utilized by the plants to synthesize new
compounds.
220 Blooming Science & Environment Book 7
The only major gaseous excretory product of plants is oxygen. During light periods,
the rate of production of oxygen is far greater than the plant’s demand for oxygen in
respiration and this escapes from plants into the environment by diffusion.
Many organic waste products of plants are stored within dead permanent tissues or
within leaves or bark, which are removed periodically.
Aquatic plants lose most of their metabolic wastes by diffusion directly into the water
surrounding them.
The loss of water in the form of vapours from the aerial parts of the plants is called
transpiration. Since the plants absorb far more amounts of water than is actually used
by plants, transpiration helps in the removal of excess of water.
Stomata are the pores through which majority of gaseous exchange takes place.
Some waste materials of plants like gums, resins, and latex are stored in different parts
of a plant. These are useful to mankind in various ways.
Importance of Excretion
The excretory process plays a most important role maintaining the relative consistency
of the body’s internal environment without which life is impossible. Excretion helps
the body to remove toxic waste, regulate water content of the body and regulate ionic
concentration and pH of the body fluids.
Main Points to Remember
1. Excretion is the removal of the toxic waste products of metabolism from the
body.
2. Osmo-regulation is the maintenance of constant osmotic conditions in the
body.
3. Excretion and osmo-regulation are two important homeostatic processes
occurring in living organism.
4. The regulation of the chemical composition of its body fluids and other aspects
of its internal environment by an organism is called homeostasis.
5. Malphigian tubules are the chief excretory organs of most insects.
6. Water, urea and salts are excreted from skin.
7. Carbondioxide and water vapour diffuse from lungs.
8. Bile pigments from old red blood cells and urea from excess amino acids are the
major excretory products of liver.
9. Kidneys excrete urea and other substances as urine.
10. Urination is the process of eliminating urine from the body.
11. Egestion is the removal of undigested food from gut.
12. The urinary system consists of two kidneys each linked to the bladder by a
ureter.
13. Excretion in plants occurs through diffusion.
14. Transpiration helps in the removal of excess of water.
Blooming Science & Environment Book 7 221
PRO J ECTWORK
1. Observe the urinary system of slaughtered animal in a butcher’s shop. You
can also bring kidney at your home and dissect the kidney with the help of a
sharp blade. Observe the internal part of the kidney and note your observation
in the copy.
2. Take a potted plant, which is given sufficient water before the experiment.
Cover the plant tightly with a plastic bag and keep it in sunlight for some time.
You will observe the water vapour condensing to the internal surface of a
plastic bag. This is because of transpiration process.
Exercises
1. Fill in the blanks.
a. Kidney excretes .................................
b. ................................ have millions of nephrons.
c. The functional unit of kidney is .................................
d. The ................................ functions as urinary reservoir.
e. Lungs help in the diffusion of ............................ and .................................
2. State True or False and correct the false statements.
a. Human have two urinary bladder.
b. Kidneys have small numbers of nephron.
c. Malphigian tubules are the chief excretory organs of fishes.
d. Toxic waste is useful for us.
e. Plants have various excretory organs.
f. Gas exchange takes place through stomata in plants.
3. Match the following.
Column A Column B
Skin Bile pigments
Malpighian tubules Loss of water
Kidney Sweat
Transpiration Nephron
Liver Excretion in insects
4. Choose the correct answer.
a. Which of the following is the chief excretory organs of insects?
i. Lungs b. Flame cells
iii. Kidney d. Malpighian tubules
222 Blooming Science & Environment Book 7
b. Formation of urea occurs in ................................
i. Lungs b. Urethra c. Liver d. Stomata
c. Which of the following statement is correct?
i. The number of urethra is double.
ii. There are two ureters.
iii. The urinary bladder filters waste product from blood.
d. Which of the following contains nephron?
i. Urinary bladder ii. Ureter iii. Urethra iv. Kidney
5. Define the following terms.
a. Excretion b. Urinary system c. Homeostasis
d. Urination e. Osmoregulation f. Transportation
g. Transpiration h. Egestion
6. Answer the following questions.
a. Define excretion. What is excretory system?
b. What is the importance of excretion in human body?
c. Describe about human urinary system with a labeled diagram.
d. What is the function of liver in excretion?
e. Write about the organs of excretion on human body.
f. What is the function of stomata?
g. What are the functions of kidney?
h. What are the excretory products of plants?
i. Which part of plant store waste products?
j. Draw the diagram of kidneys and label the figures.
Glossary
Byproducts : substances that are produced during the process of making or
destroying something
Toxic : poisonous, containing poison
Eliminate : to remove or get rid of something
Vartebral column : backbone
Blooming Science & Environment Book 7 223
Chapter Structure of the Earth
18
Learning Outcomes
On the completion of this unit, students will be able to: Estimated Periods-5+1
• describe about the layers of the earth in short.
• define rocks and describe the structure and physical properties of rocks.
• describe about rocks, types of rocks and uses of rocks.
• describe about some important rocks found in Nepal.
About 4600 million years ago, the earth was like a huge hot ball. After a long time,
the earth began to cool. As the earth cooled, it gets contracted and the heavier liquid
materials settled towards the earth’s centre and the lighter materials came towards the
surface. The simple elements of the surface combined to form water vapour. The water
vapour formed cloud and covered the earth. The clouds causes heavy rainfall, which
cooled the earth more. As the result, the water remained on the earth in the form of
oceans, lakes and ponds. At present, about 70% of the earth’s surface is covered with
water and only about 30% is land.
The earth completes one rotation on its axis in about 24 hours and one revolution around
the sun in about 365 days, i.e., one year. The shape of the earth is not completely
round but it is orange shaped, its diameter at the equator is 12, 756 km and that at the
poles is 12,713 km. On the surface of the earth several types of structures like plains,
hill, plateaus and oceans are found.
Interior of the Earth
It is very difficult to study about the interior of the earth. The deepest mine, the Morro
Vehlo Mine of Brazil gives us samples of direct views of rocks down to the depths
of 2100 m only. The deepest bore hole in search of petroleum now penetrates about
6 km. But these depth mentioned about are very Crush
less in the comparison of the radius of the earth. Mantle
Volcanoes and lava flows bring magma to the
surface from about 64 km deep of the earth. You Outer core
may surprise that how scientists were able to know Inner core
about the inner parts of the earth, which has the
radius of about 6400 km. Depth and component of
the earth’s interior is known by studying the nature
and speed of earthquake waves. The interior of
the earth is divided into the following four layers: Interior of the earth
224 Blooming Science & Environment Book 7
1. Crust 2. Mantle 3. Outer core 4. Inner core
Crust
It is the outermost layer of the earth. It is also the thinnest layer. Its thickness is about
5-50 km. This layer is made up of solid rocks containing the maximum amount of
granite and basalt. Beneath the ocean, somewhere it is only about 5km thick. The
crust holds many useful gases (fuel), liquids like petroleum and water, solids like coal,
metals, etc. Although there are at least 90 elements present in the crust, five elements
of them cover 90% part of it. They are oxygen, silicon, aluminium, iron and calcium
(O, Si, Al, Fe, Ca). Temperature and pressure inside the crust increase as its depth
increases.
Mantle
The boundary of the crust and the mantle is called Moho, below which the layer of
mantle is found. It is the thickest layer, which is about 3000 km thick. Temperature of
this layer varies between about 800oC and 2500oC. Materials in this layer are about 2-3
times heavier than that of the crust. The main elements of this layer are magnesium
(Mg), iron (Fe), silicon (Si) and oxygen (O).
Outer Core
It is the third but the second thickest layer of the earth. Its thickness is about 2100 km.
It is believed that materials in this layer are in the liquid state. The main elements of
this layer are iron (Fe), cobalt (Co) and nickel (Ni). In this layer pressure is about 1.5
million atmospheric pressure and temperature is about 2500oC-3000oC.
Inner Core
It is the central layer of the earth. Its radius is about 1300 km. This layer also consists
of iron (Fe), cobalt (Co) and nickel (Ni), but the materials are in the solid state due
to the maximum pressure at that layer. The pressure at that layer is about 35 million
atmospheric pressure and temperature is believed to be 3000oC-5000oC.
S. Layers' Thickness Temperature Pressure Composition State
N. name
1. Crust 5-50 km Maximum 800oC One atmospheric O, Si, Al, Fe, Solid
3000 km at bottom Plastic
2. Mantle pressure at surface Ca Liquid
800oC-2500oC Solid
2-3 times more Fe, Mg, Si, O
than in the crust
3. Outer core 2100 km 2500oC-3000oC 1.5 million atm. Fe, Co, Ni
Pressure
4. Inner core 1300 km 3000oC-5000oC 3-5 million atm. Fe, Co, Ni
Pressure
Blooming Science & Environment Book 7 225
Rock
Rock is a naturally occurring solid material consisting of one or more minerals. Rock is
any consolidated material such as granite or limestone that forms, the hard structure of
the earth. Rocks are everywhere, in the ground, forming mountains, and at the bottom
of the oceans. Earth’s outer layer, or crust, is made mostly of rocks. Some common
rocks include granite and basalt.
Structure of rocks
Rocks are formed by different types of elements. They are found in different shapes
and colours. Most rocks are not uniform, they are composed of individual mineral
grains that vary in size, shape and compositions. Such verities in the features of rocks
are called structures of rocks.
Physical properties of Rocks
Rocks are made up of minerals and have different properties. Some of the important
physical properties of rocks include texture, hardness, colour etc.
a) Texture
The texture of rocks is the size, shape and arrangement of the grains or crystals. Some
rocks are composed of bigger granules while some rocks are composed of smaller
granules. Some are found in layers and some are found scattered. The rocks with
bigger granules are rough whereas rocks with smaller granules are smooth in nature.
Different size of rocks
b) Hardness
Both types of rocks i.e. hard and soft rocks are found in nature. The
hardness of rocks can be identified by scratching them. The rock
which can be scratched easily is soft and that cannot be scratched is
hard. For example; diamond is the hardest in nature while a mineral
talk is very soft.
226 Blooming Science & Environment Book 7
c) Colours
Rocks are found in different colours. None of the two rocks are found in
same colour. It is one of the contrasting characters of the rocks. Generally the
presence of iron staining gives the different colours to the rocks. For example,
a form of iron (feric iron) red, purple and yellow colours to the rocks where
as another form of iron (ferrous iron) makes greenish colour.
Types of Rock
Rocks are commonly divided into three major classes according to the process that
resulted in their formation. The different types of rocks are:
1. Igneous rocks 2. Sedimentary rocks 3. Metamorphic rocks
1. Igneous Rocks
Igneous rocks are formed from the solidification
of magma. Magma is the molten rock deep within Basalt Pumice
the earth. Magma migrates either at depth or to the
earth’s surface and is ejected as lava. During volcanic eruption, magma comes out
from inside the earth and it cools and solidifies to become igneous rocks. Examples of
igneous rock are basalt, granite, pumice stone, quartz, mica etc.
2. Sedimentary Rocks
Sedimentary rocks are formed due to the deposition
and lithification of soil, sand and other organic
and inorganic materials at the earth’s surface, with Conglomerate
the assistance of running water, wind, ice or living Sand stone
organisms. During the course of time, accumulation and deposition of material forms
different layers, which are pressed together and harden to form sedimentary rock.
Examples of sedimentary rocks are shale, sandstone, limestone, chalk, dolomite,
conglomerate etc.
Sedimentary rocks are generally stratified, i.e. they have layering. Layers may
be distinguished by differences in colour, particle size and internal arrangement.
Sedimentary rocks are important because they may contain fossil of plants and animals.
3. Metamorphic Rock
Metamorphic rocks are those which are formed
by changes in pre-existing rocks (sedimentary
rock or igneous rock) under the influence of high
temperature, pressure and chemically active Gneiss Marble
solutions. Forces within the earth create large amounts of heat and pressure, these
Blooming Science & Environment Book 7 227
factors change igneous and sedimentary rocks into metamorphic rocks. The word
metamorphism is taken from the Greek word that means “change of form”. Examples
of metamorphic rock are quartzite, marble, slate, etc.
S.N. Original rocks Metamorphic rocks
1. Silica Quartzite
2. Limestone, Dolomite Marble
3. Coal Graphite
4. Graphite (again) Diamond
5. Granite, Diorite Gneiss, Schist
6. Shale Slate
Uses of Rocks
Some of the important uses of rocks are given below:
1. Rocks are used in construction of roads, buildings and monuments.
2. Rocks are used to make sculptures and tiles for roof.
3. Marble is used in flooring and to decorate the houses.
4. Granite is used to make temples.
5. Slates are used for writing purposes by children and also for roofing purpose.
6. Valuable gems are obtained from rocks.
Difference between Igneous and Sedimentary Rocks.
Igneous Rock Sedimentary Rock
All materials are in molten state. The various layers can be found on it.
Fossils are not found. Fossils may be found on it.
Graphite, pumice, obsidian etc are the Conglomerate, sandstone, limestone etc
examples of it. are the examples of it.
Composition of Rocks
According to the geologists, the rocks are made of 92 elements. Of course, various
elements are found in the rock. Different elements are combined in different proportion
to constitute rocks. The elements present in the rock are listed below.
228 Blooming Science & Environment Book 7
Elements found in the Rock
S. No. Element Symbol Percentage
1. Oxygen O 46.6
2. Silicon Si 27.7
3. Aluminium Al 8.1
4. Iron Fe 5.0
5. Calcium Ca 3.6
6. Sodium Na 2.8
7. Potassium K 2.6
8. Magnesium Mg 2.1
9. Other elements - 1.5
Total 100
Minerals and Rocks
Minerals
Take a handful of sand on a white paper and observe it. What type of substances do you
see in it? You get some colourless, white, or coloured substances, but it is a mixture
of many substances and most of them are minerals and rocks. You also may see fine
sheets of shiny substances in it. They are different minerals. The granular fine particles
are silica or quartz, the sheets are mica. Silica and mica are examples of mineral.
Minerals are those chemical substances [element or compound] which are found
naturally in the earth’s crust. They are solid and crystalline. Minerals are not made
artificially and they do not come from living things.
Some examples of minerals are talc, gypsum, quartz, diamond, ruby, emerald, graphite,
garnet, sapphire, calcite, clay and topaz. Minerals are components of rocks.
Minerals differ in colour, lustre, hardness and cleavage. The minerals may cleave
in blocks or sheets. About 3000 minerals are found on the earth but only about 100
minerals of them are common and useful to us.
A pearl is a chemical compound but not considered as mineral, because a living being
oyster produces it. Coal is also not considered as a true mineral because it is formed
from dead parts of the plants.
Coal, petroleum and natural gases are considered as fuel minerals by economists, but
geologists do not considered them mineral.
Blooming Science & Environment Book 7 229
Important Rocks found in Nepal
The following are the important rocks found in Nepal:
1) Conglomerate: Conglomerate is a coarsed grained concrete rock.
It is a sedimentary rock formed by combining the small pieces of
stone, gravel, Sand,etc. It is found in the river banks of Nepal.
2) Sandstone: Sandstone is a sedimentary rock composed of sand size
grains of mineral, rock or organic material. It may contain silica and
clay soil. It is found in different parts of Nepal
3) Limestone: Limestone is a carbonate sedimentary rock that is
often composed skeletal fragments of marine organisms. It is
mainly made by calcium carbonate. It is found in different
colours and used as raw material in cement industries. It is found
in various part of Nepal like chobhar, Godawari, Bhaise, Udayapur, Jogimara, etc.
4) Marble: Marble is a metamorphic rock formed by the
metamorphosis of limestone. It is used in construction of temples,
buildings etc. It is found in godawari of lalitpur district.
5) Slate: Slate is another metamorphic rock formed by shale. It
is generally used for rooting. It is extensively mined in
different parts of Nepal such as Dhankuta, sindhupalchowk,
Nuwakot, Ramchhap, Dhing, Jahahun, Baglung, syangja,
kaski, Parbat, palpa, Jajarkot, Achham,Doti, Baitadi, Bajura and
many other districts also.
Main Points to Remember
1. It is believed that the earth evolved about 4.6 billion years ago.
2. 70% of the earth surface is water and 30% is land.
3. The rotational period of the earth is about 24 hr and the revolutional period is
about 365 days.
4. The equatorial diameter of the earth is 12,756 km and the polar diameter is
12713 km.
5. The earth is the third planet in order from the sun and the only planet known to
have life.
6. Earth science includes the sciences used to study the lithosphere, the atmosphere,
the hydrosphere, the biosphere, and space beyond the atmosphere.
7. Earth is not a perfect sphere but is lightly flattened at the poles.
8. Scientists have learned about Earth’s interior by studying rocks that formed in
230 Blooming Science & Environment Book 7
the interior and rose to the surface as well as from seismic waves.
9. The interior of the earth can be divided into four layers. They are crust, mantle,
outer core and inner core.
10. The solid miniral material forming part of the surface of the earth, exposed on the
surface or underlying the soil is called rock
11. The rocks have different proterties like texture, colour, hardness, etc.
12. There ae thre important types of rocks; igneous, sedimentary and metamorphic
13. The igneous rocks are made by moleten mass present inside the earth sedimentary
rocks are formed by deposition of various layers and metamorphic rocks are made
by changing igneous and sedimentary rocks.
PRO J ECTWORK
Collect different types of rocks from your surroundings. Observe their physical
properties. Try to identity their types and discuss with your friends in your class.
Exercises
1. Fill in the blanks.
a. The ................................ core has highest temperature.
b. The second abundant element found in earth crust is .................................
c. Average density of earth is .................................
d. The earthquake generates ................................ waves.
e. The thickness of mantle is about .................................
f. The earth has ................................ moon.
g. The inner core is in ................................ state.
2. Write down 'True' or 'False' and correct the false statements.
a. Earth is a perfect sphere but is slightly flattened at the poles.
b. The earth was cold at first and it gradually got heated over time.
c. Scientists have learned about Earth’s interior structure with the help of
rockets.
d. Oxygen is by far the dominate element in Earth’s crust.
e. Density of materials in mantle is 2-3 times greater than that of the crust.
f. The majority of elements like iron, cobalt and nickel are found in liquid state
in the inner core.
g. The outer core has thickness of about 2100 km.
Blooming Science & Environment Book 7 231
3. Match the following.
Column A Column B
Mantle Crust
Earth Information of earth’s interior parts
Sun Core
Thinnest layer 2900 km
Inner layer Planet
Seismic waves Star
4. Answer the following questions.
a. How old is our earth?
b. Why is earth important for us?
c. What are the different layers of the earth?
d. Why is our earth not totally spherical?
e. What are the major elements found in crust, mantle, outer core and inner
core?
f. Mention the thickness of different layers of the earth?
g. What is the difference between outer core and inner core?
h. What is the temperature range of each layer?
i. How do scientists know about the interior of the earth?
j. Sketch a well-labelled diagram of earth showing different layers.
k. Define igneous, sedimentary and metamorphic rocks with examples.
l. Name the rocks found in Nepal.
Glossary
Rock: hard solid mass containing some minerals.
Igneous rock : the rock formed by cooling of molten mass which comes out
from the inner layers.
Sedimentary rock : the rock formed by hardening of the deposited layers in the
bottom of ocean.
Metamorphic : rock formed by the action of heat and pressure.
Lava: the molten mass that comes out.
Magma : the molten mass.
Volcano : the mountain which erupt fire, ash and molten mass.
Soil : soft surface where plants grow.
232 Blooming Science & Environment Book 7
19Chapter Weather and Climate
Learning Outcomes
On the completion of this unit, students will be able to: Estimated Period -5+1
• describe various layers of atmosphere.
• explain and demonstrate movement of air, its causes and effects.
• introduce clouds, snow and frost.
• introduce instruments to determine weather.
• describe about prediction of weather.
• describe about of prediction of weather.
Introduction
We are familiar with rainy days in summer, hot sunny day, very cold climate of winter,
etc. Why does it so happen? The clouds of the morning vanish as the sun rises up
and may even rain on the same day. Sometimes it is very dry and windy, whereas
sometimes it is very hot and humid. These changes in the atmosphere are called weather
changes. We should know the direction of the wind, humidity of the air, maximum and
minimum temperature, possibility of the rain, etc. to know about the weather. These
factors generally constitute of weather.
Atmosphere Above 720 km
The earth has water, land and air. The air is a Thermosphere
mixture of gases. The earth is covered by thick 80-720 km
portion of air. This layer of air surrounding the Mesosphere
earth is called atmosphere. The atmosphere has 50-80 km
different gases, water vapour and dust particles.
The layer of the air becomes thinner as we go Stratosphere
up above the surface of the earth. There is a 16-50 km
change in the temperature, humidity and the
composition of air. According to altitude, the Troposphere
atmosphere of the earth can be divided into five 16 km
layers which are discussed below:
(a) Troposphere (b) Stratosphere
(c) Mesosphere (d) Thermosphere
(e) Exosphere
Blooming Science & Environment Book 7 233
Troposphere
This is the lowermost layer of the atmosphere. It extends upto 16 km from the surface of
the earth. The part of this layer nearest to the surface of the earth is very hot. It becomes
cool in winter as the temperature changes with season. This layer of atmosphere
contains heavy gases, water vapour and dust particles in abundant. Different activities
related to weather such as cloud, rain, frost, hail, storm, fog, thunder, lightning etc.
occur in this layer.
Stratosphere
The layer above the troposphere is called stratosphere. This layer of atmosphere
extends from 16 km to 50 km. The temperature of this layer increases with the increase
in altitude. There is a negligible amount of humidity in this layer. The upper part of this
stratosphere has a thin layer of ozene gas called ozone layer. This ozone layer absorbs
about 99% of the ultraviolet rays and thus prevents the living beings from this harmful
ultraviolet rays.
Mesosphere
This layer of atmosphere lies above the stratosphere. It extends from 50-80 km from
the surface of the earth. The temperature of this layer decreases with altitude. Strong
wind blows in this layer.
Thermosphere
The layer of atmosphere above the mesosphere is called thermosphere. This layer
extends from 80 km to 720 km above the surface of the earth. The layer is very thin
due to less air. Due to the more effect of solar radiation in this layer, the temperature is
high. Wind blow is very low in this layer.
Exosphere
The layer of atmosphere above the thermosphere is called exosphere. This layer extends
above 720 km from the surface of the earth. It is the topmost layer of the atmosphere.
In this layer, air is negligible. The molecules and atoms of gases are less.
Weather
Weather is the state of the atmosphere at a particulaer place and time as regards heat,
cloudness, dryness, sunshine, wind, rain, etc. We have experienced hot, windy, moist,
dry and rainy weathers. When the rain falls, the air becomes humid. When there is no
rain, the air becomes dry. Presence of water vapour in the air increases humidity. Thus,
different types of weather are seen.
The science of the study of weather is called meteorology. While studying the
meteorological factors such as the minimum temperature, maximum temperature,
direction of wind or rain, humidity, formation of clouds, rainfall, etc we make a survey.
Let us discuss briefly about the factors that affect the weather.
Movement of Air
The movement of air is one of the most important factors in the weather change.
234 Blooming Science & Environment Book 7
How does the air move? What factor plays the role in the movement of air? Let us
experiment.
Activity
Convection current
Make a rectangular box with the two projected holes on the upperside as shown
in the figure. The front side is made of glass. Put a candle or lamp just below one
projection and allow the smouldering taper to pass from the other. You will see
that the smouldering taper passes and comes out from the other. This is due to the
fact that the hot air comes up because it becomes lighter. The cooler air takes the
place of hot air. Thus a current is setup of movement of air takes place.
Smoke Cold air
Hot air
Candle Glass box
Hot Air is Lighter
In the experiment given above you have noticed that hot air goes up and cool air
occupies the space left by hot air. This can be proved with the help of the following
experiment also.
Activity
Hot air is lighter
Suspend two paper cups upside
down with the help of a stick and
thread so that it looks like a balance.
See that they are equally balanced.
Bring a burning flame below one Hot air
of the paper cups. You will notice
that the cup moves up and the other Cold air
comes down. This is due to the fact
that heated air molecules become lighter and they go up. As they go up, the air
molecules push the cup and hence it rises up. The cup with cool air comes down.
Blooming Science & Environment Book 7 235
Similar phenomenon takes place
in the nature also. Due to the sun,
the heated molecules of air go up
and cool air molecules come to the
space left by hot molecules. Thus
air current moves. Such a current
in the nature is called convectional
current.
Wind
Warm air is lighter while the cold air is heavier.
When the air becomes warm, it rises and its place is
taken by a cool air and thus the air starts blowing.
This movement of air is called convection.
Convection is one of the main reason to cause
breeze.
A common example of convection in nature is land breeze and sea breeze. During day
time, the sun shines equally on land and sea. Land gets hot quick due to the sun. The
air above the land gets heated. The hot air expands and rises up. The sea is less hot and
so, to fill up this place, the cold air from the sea starts blowing towards the land and
forms sea breeeze.
At night, the land and the sea both lose heat. During the day time, sea warms slowly
and during night time, it loses heat slowly. The land cools quickly. The air above the
land becomes colder than sea. The warm air above the sea expands and rises up. To
fill up this space, the cold air from the land starts blowing towards sea and forms land
breeze.
Clouds
We see clouds in the sky. The atmosphere contains
air in it. When the air is cooled, the water vapour
in it condenses into tiny droplets of water. It forms
clouds. When the temperature of the air lowers
down below the freezing point of water, the water
vapour condenses directly into tiny crystals of ice.
The droplets of water or ice crystal in the clouds
are heavier than air, but they are so small and fall
so slowly that the slightest air movement is enough to keep them floating in the air.
When the clouds come at cold region they rain.
236 Blooming Science & Environment Book 7
Rain
Rain is the water that falls from clouds. The tiny
droplets of water in clouds join together and form larger
droplets. When the larger droplets come together to
form even a larger drop, they fall down to the earth as
rain. Rain is the main source of a water on the earth.
Dew and Frost
At night, the surface of the earth gets cold. When the
air comes in contract with the cold surface, it also
cools down. If the air cools down below its freezing
point, the water vapour in the air condenses into water
droplets called dew. If the dew point is below the
freezing point, the water vapour condenses directly
into crystals of ice. It is called frost.
Snow
When the temperature of the air lowers down below the
freezing point, snow is formed. Snow is frozen vapour.
Snow falls in polar regions and at very high peaks of
the mountains. It is because of very low temperature at
these places. Snow is the most common form of solid
precipitation.
Humidity
Humidity is the measure of moisture content of the Simple
atmosphere. The actual amount of water vapour present thermometers
in the unit volume of the air is called absolute humidity.
It is expressed in gram of water vapour per cubic meter. Plastic bottle
In meteorology, the relative humidity is used, which is Water
the ratio of the actual amount of the water vapour in
the air to the total amount of the water air can hold at a
given temperature. It is expressed in percentage. Warm
air has more humidity than cold air.
The relative humidity is measured by using a hygrometer. It is also known as dry and
wet thermometer. Hygrometer is a pair of simple thermometers. The bulb of one of
them is placed in water or wicked with water. It is called wet thermometer. The bulb
of the other thermometer is left in air. It is called dry thermometer. The difference of
readings between these two thermometers is used to calculate relative humidity. When
Blooming Science & Environment Book 7 237
the both thermometers show the same reading, it is said that the relative humidity is
100%.
Instruments used to Determine Weather
There are different kinds of instruments used to study the weather at a particular place.
Some of them are discussed below.
Maximum and Minimum Thermometer:
This thermometer consists of two indicators. One indicator shows the minimum
temperature of the day and the next column shows the maximum temperature. One
tube of the thermometer is filled with alcohol and the other is filled with mercury.
As the temperature in the atmosphere varies, two indicators show the maximum and
minimum limits respectively.
Rain Gauze
This is the device to find the rain in a day. One cylindrical vessel and a
cone or funnel are fitted and kept in the open space. As the rain falls, the
water is collected in the cylindrical flask and the amount of rain water
is measured to determine the rainfall on that day.
Hygrometer
Hygrometer is the instrument used to measure the humidity in the
air. The humidity means the percentage of water vapour in the
air. The humidity device consists of the parts which are highly
affected by the change in the humidity of the air. For example, the
clean dry hair becomes long or short due to humidity of the air.
On the same principle the components of a hygrometer is made.
Anemometer
This is the device which is used to measure the direction of wind.
From which direction to which direction the air is blowing can be
found out with the help of anemometer. This also finds the speed of
the air with the help of rotation speed of the cup shaped structures
on the top of rotating part.
238 Blooming Science & Environment Book 7
The anemometer and rain gauze are placed on the open air space while the barometer
hygrometer and maximum and minimum thermometer are placed in the shade. Using
the devices discussed in the section, we can find the following things.
a. Maximum and minimum temperature of the day
b. Content of the water vapour in the air (humidity)
c. Direction of the movement of the air
d. Speed of the air in the direction of the air.
Barometer
It is an instrument used to measure the atrnospheric pressure of a place. Atmospheric
pressure also determines the weather. In general when the atmospheric pressure
increases weather can be clear and when the atmospheric pressure decreases weather
can be cloudy and stormy. There are two types of barometers used to measure
atmospheric pressure; Mercury barometer and aneroid barometer
Mecury barometer Aneroid barometer
Weather Forcasting
Weather forecasting is the application of science and technology to predict the
conditions of the atmosphere for a given location and time. Meteorological stations
are established in different parts of our country to record the different conditions
of weather. Weather forecasts are made by collecting quantitative data about the
current state of the atmosphere at a given place and using meteorology to project how
the atmosphere will change. Now, weather is forecasted on the basis of the record
obtained by satellite i.e. weather forecasting now relies on computer based models that
take many atmospheric factors into account which is found more reliable.
Main Points to Remember
1. The layer of air around the earth is called atmosphere.
2. There are five layers of atmosphere.
3. Weather constitutes direction of the sun, direction of wind, water vapour in the
air, temperature, etc.
Blooming Science & Environment Book 7 239
4. The sun, air and water are some of the important elements of the weather.
5. Hot air moves up and the space is occupied by the cool air. Thus setup air currents
are called convectional current.
6 Water turns into vapour. It goes high up, cools and becomes clouds. After moving
a certain distance, it comes down in the form of rain.
7. Thermometer, rain gauze, anemometer, hygrometer are the instruments that help
in finding the changes in the weather. They help in finding temperature, rainfall,
direction of air and humidity.
8. The percentage of water vapour in the atmosphere is called humidity.
PRO J ECTWORK
To make your own rain gauge
Take a plastic bottle and cut it from little below its neck. Make scale on lower part
of the bottle. Keep the mouth of bottle upside down and fix it with the help of glue or
tape. Keep it on a table or stool in an open place to measure the rain fall.
Exercises
1. Fill in the blanks.
a. The direction of air can be found out with the help of ………………
b. Hot air is ………………….. than cool air.
c. The movement of air from hot and cold sets up a current called ………………
d. Thermometer can be used to measure …………….. and ……………………
temperature called maximum and minimum thermometer.
e. …………………….. is used to measure the rain on the day.
f. Percentage of water vapour in the atmosphere is called ……………..
g. Humidity is found out with the help of a device is called ………………..
h. Anemometer is used to find ………………….. and ………………….
2. Write short notes on:
a. Anemometer b. Hygrometer c. Maximum and Minimum thermometer
240 Blooming Science & Environment Book 7
3. Answer the following questions.
a. What is atmosphere? Which is the most dense layer of the atmosphere?
b. Why is stratosphere very important to the earth?
c. Write down important features of troposphere.
d. Is there any air in exposphere?Why?
e. What is meteorology? Define weather.
f. What kinds of instruments are used in finding weather?
g. Why do we need to study about the weather?
h. In nature, the air moves and a current is setup. What do you call it?
i. Draw the layers of atmosphere.
j. What do we call weather science technically?
k. What instrument is used to find the speed and direction of wind?
l. Using anemometer, hygrometer, thermometer and rain gauze what kind of
information do you get about weather?
m. What should be done to find the weather?
n. Give an experiment that shows the movement of air.
m. Give an experiment to show that hot air is lighter.
o. How do the clouds form?
p. How does the rainfall take place?
q. What is a rain gauze? How do you measure the rainfall in a day?
r. What is meant by humidity? What is the instrument used to measure
humidity?
Glossary
Atmosphere : the mixture of gases which surrounds some planets such as
earth.
Troposphere : the lower most layer of the earth surface.
Stratosphere : the layer just above troposphere.
Blooming Science & Environment Book 7 241
Mesosphere : the layer just above stratosphere.
Thermosphere : the layer just above mesosphere.
Exosphere : the outer most layer of atmosphere.
Wind : moving air.
Air pollution : mixing of undesirable and harmful substances.
Land breeze : the movement of air from land towards land during night.
Sea breeze : the movement of air from sea towards sea during day time.
Green house effects : rising of temperature has to trapping of solar energy.
Acid rain : weak acid which reacts with the water vapour in atmosphere
and comes back to the earth as rain.
Humidity : percentage of water vapour in the atmosphere
Weather : the condition of atmosphere of a place at a time
Cloud : water vapour along with dust in the sky
Rain : water droplets showering on the earth due to cooling of cloud
Meteorology : branch of science dealing with weather
Barometer : an instrument to measure atmospheric pressure
Hygrometer : an instrument to measure humidity
Anemometer : an instrument to measure to measure direction and speed of
wind
Weather forecasting : to predict before the weather conditions
242 Blooming Science & Environment Book 7
20Chapter The Earth and Space
Learning Outcomes
On the completion of this unit, students will be able to: Estimated Period-6+2
• introduce solar system and its members
• understand the movements of the Earth that cause day and night and create
changes in the seasons.
• find out the structure of the eight planets, their average distance from the sun,
their diameter and their time of revolution.
• introduce stars and to differentiate stars and planets
• introduce some common costellations.
We can see many heavenly bodies in the sky. What we see is an extremely large,
extended area that includes everything that exists (billion) of stars, planets, satellites,
clouds of dust and gases and all of this is known as the universe. Our solar system is
a small part of the universe. The sun in our solar system is the closest star to the Earth.
The sun is about 150 million kilometers away from the Earth. We can see twinkling
bodies in the sky at night. We call them stars .The main bodies that circle the sun are
known as planets. Planets do not produce their own light; they reflect the light of the
sun that falls on them.
The million and million of stars and planets, arranged together to form one huge group,
are known as a galaxy. Our Earth is in the Milky way galaxy. All the stars and planets
in a galaxy are held together by a force of attraction that exists between them.
The Earth
Earth is the planet on which we live. The sun is the closest star to Earth and the Earth
is about 150 million kilometers away from the sun. It has all the components of air,
temperature and water that are essential for all the living organisms to survive. The
average of the Earth’s diameter is 12,700km. Earth shows two types of movements; it
rotates on its own axis and it revolves around the sun in an elliptical orbit.
Day and Night
The Earth, when rotating on its own axis, has some parts of its surface facing the sun,
whilst other parts are not. The part of the Earth that faces the sun is in daytime and the
opposite face (hidden from the sun) is in night-time. It takes Earth 24 hours to rotate
once on its own axis.
Sometimes the Earth is near the sun and sometimes it is far away from it. The Earth
Blooming Science & Environment Book 7 243
rotates from west to east and the part of Earth Day
that emerges from the darkness into the rays
the sun experiences the sunrise. of
Solar System Sun rays
The sun is the closest star to the Earth. It Night
is about 150 million kilometers away from Earth
Earth. The solar system consists of a large
family of heavenly bodies that move around the sun. All of the planets move around
the sun in certain paths, called orbits. There are also many small objects that move
around the sun; they are called asteroids and comets. The sun, the planets and their
satellites and the asteroids and comets that move around the sun, are called the solar
system. There are eight planets including the Earth, Mercury, Venus, Mars, Jupiter,
Saturn, Uranus and Neptune. Pluto is no longer considered a planet. Planets move
around the sun in elliptical (oval shaped) orbits.
The planets do not fall away into space, because of the strong gravitational pull of
the sun. The Sun pulls all the heavenly bodies towards itself. There is also a force of
attraction between the planets that pulls them towards each other. Planets do not have
their own light; they shine when the light of the sun falls on them and is reflected. They
become bright only because of the sun’s light.
The nearest planets to the sun is Mercury. Mercury takes 88 days to complete revolution
around the sun. Jupiter is the largest planet. Venus is the brightest and the hottest planet.
244 Blooming Science & Environment Book 7
Planets According to their Distance from the Sun
Mercury:
Mercury is the nearest planet to the sun. In daytime, it is very hot and at night it is
very cold. This planet is without atmosphere and has no moon. It is the smallest planet
amongst the eight.
Venus:
Venus is the brightest and closest planet to Earth. Its surface is covered by a thick layer
of cloud. It is not easily visible from Earth, but is commonly seen in the morning and
evening. The size of this planet is quite similar to Earth. It is a very hot planet and its
atmosphere consists of carbon dioxide. It is also called morning and evening star. It
has no moon.
Earth:
Earth is the planet on which we live. It has a suitable environment with plenty of water
and oxygen and a suitable temperature. It also has an atmosphere that enables living
organisms to survive. It is the fifth largest planet among the eight and it has one natural
satellite (moon). The Earth’s atmosphere consist of nitrogen, oxygen, argon, carbon
dioxide and water vapour.
Mars:
Mars looked red in the sky due to the presence of iron oxide on its surface and is
commonly known as the red planet. It has a thin layer of atmosphere consisting of
carbon dioxide, nitrogen, argon and a little water. Mars has two moons. Both of its poles
are covered with snow and they are known as icecaps. Some scientists believe that this
planet contains some simple living organisms. Scientists are currently investigating
this planet in detail.
Jupiter:
Jupiter is the largest planet. It is about 319 times bigger than the earth. Its outer surface
is covered with clouds. A red spot has been detected in the central portion of the planet
and its atmosphere consist of hydrogen gas. It has 67 moons. This planet can also be
seen in the sky as it is bright.
Saturn:
Saturn is the second largest planet in the solar system. It is quite similar to Jupiter
and is surrounded by rings. It has 62 moons, the biggest of which is named Titan. Its
density is less than water so, it floats in water.
Uranus:
Uranus is very far from the sun and from the Earth. It is a cold planet. Its atmosphere
consists of hydrogen and helium. It is nearly 15 times heavier than the Earth and it has
27 moons.
Blooming Science & Environment Book 7 245
Neptune:
Neptune is also very far away from the sun. It is the coldest planet. It has thick hydrogen
in the atmosphere. It has 13 moons.
The table below shows the eight planets, their average distance from the sun, their
diameter and their times of revolution.
Name Average Average Average Average Average Number
of distance diameter Daily annual Temperature of
planet (in lakh (in km) Speed Speed (In on the surface Satellite
km) Earth's
Mercury 58 5000 58.65 day) 0
88 Days Max 427oC
Venus 107 12100 Days Min 173oC 0
243 225 Days Max 482oC
Days
Earth 150 12700 24 365 Days Max 58oC 1
Hours min-88.29
Mars 226 6750 24 Hours 687 Days -23oC overall, - 2
37 min 150oC at poles
Jupiter 768 139040 9 Hours 12 -160oC 67
Saturn 1440 55 min Years -150oC 62
116000 10 Hours 29.5
Uranus 2880 50440 30 min Years -220oC 27
17 Hours 84
Neptune 4500 49000 14 min Years -213oC 14
16 Hours 165
6 min years
Source: IAU, WGPSN(2019)
Star
A star is an astronomical object consisting of a
luminous spheroid of plasma held together by
its own gravily. The stars are the gaseous masses
mainly formed by hydrogen and helium. Heat and
light energy nuclear fusion reaction.
There are millions of stars in the universe. Although Star in the sky
246 Blooming Science & Environment Book 7
the stars are very big in size, they are seen very small from the earth as they are at a
great distance away from the earth. Sun is also a type of star. It is considered as the
nearest star from the earth. The earth gets heat and light energy from the sun.
Brilliance of stars
There are different stars with different brilliance. The brilliancy of stars depend upon
the surface temperature, size and distance from the earth. The stars which are nearer
and larger in size are more brilliant. Similarly the stars having high temperature are
more brilliant.
Colours of stars
The stars are seen in different colours. The sun is the medium sized yellow colour star.
The temperature of the star determines the colours of stars. The stars with minimum
temperature are red in colours, average temperature is yellow in colour and maximum
temperature is blue in colour. The following table shows the average temperature and
colour of the stars.
Colours Red Ornge Yellow White Blue
4000oC 6000oC 11000oC 25000oC
Temperature 3000oC
Distance of Stars
The stars are very far from the earth. It is very difficult to measure the distance between
the star and the earth by using kilometre. So that the distance between the heavenly
bodies can be measured by using following biggar units.
1. Light year 2. Astronomical unit (A.U.)
Light Year:
It is defined as the distance travelled by light in one year. Its value is about 9.5 ×1012
km. The velocity of light is 3,00,000 km/s (3 × 105 km/s), so that light can travel
9.5 × 1012 km. in one year. Light year is used to measure the distance between two
heavenly bodies in the universe.
1 year = 365 days
= 365 × 24 hours
= 365 × 24 × 60 minutes
= 365 × 24 × 60 × 60 seconds
= 3,15,36,000 seconds
In 1 second, light can travel 3 × 105 km.
In 1 year (3,15,36,000 sec.), light can travel 3 × 105 × 3,15,36,000 km
Blooming Science & Environment Book 7 247
= 94,60,80,00,00,000 km
= 9.46 × 1012 km
= approx. 9.5 × 1012 km = 9.5 × 1015 m
There are 55 stars which lie at a distance of 16 light years. The nearest star from the
solar system is Alpha century which is at a distance of 4.3 light year.
Astronomical Unit
It is defined as the distance between the sun and the earth. Its value is about 150,000,000
km (1.5 × 108 km). Astronomical unit is used to measure the distance between the
heavenly bodies within the solar system.
Differences between Stars and Planets
Planet Stars
Planets do not have their own light. Stars have their own light.
Planets do not twinkle. Stars twinkle at night.
Planets revolve round the sun in their Stars are stationary.
own orbit.
There are billions of stars.
There are only nine planets in the solar Stars are very big in size they are very far
system. from us.
Planets are very small in size as
compared to stars.
Their surfaces are of different types. Their surfaces are covered by gases.
They have specific colours like blue, They have different colours.
white, yellow, red and orange.
Their temperature vary from 3,000 ºC to
Their temperature very from - 220ºC to 25,000 ºC
420ºC
Constellations Pole star
If you see in the sky at night you will find that some of Pole star
the groups of stars are arranged in a definite pattern. Ursa minor
Such groups of stars are called constellations. A group
of stars arranged in a fixed pattern in such a way that
it resembles some imaginary figure is known as a Ursa major
constellation. The position of all the members of a
constellation is relatively fixed to other members and
therefore their shape remains the same.
They appear to move in the sky from east to west. There are 88 constellations in the
248 Blooming Science & Environment Book 7
sky. Among them 12 constellations are considered as signs of zodiac such as Aries,
Taurus, Gemini, Cancer, Leo, Virgo, Libra, Scorpio, Sagittarius, Capricorn, Aquarius
and Pisces. Some of the constellations are:
Big Dipper (Ursa Major or Great Bear or Saptarishi)
It is a group of seven bright stars arranged in the form of a big spoon. So that it is called
the Big dipper. The word derived from ‘dipper’ which means the big spoon. It is also
called the Great Bear because it is made up seven bright stars along with many fainter
stars which are arranged in the form of Bear. The word Ursa is a Latin word, which
means bear. Hence, it is also called Ursa Major. The Nepali name of Big Dipper is
Saptarishi because of the seven stars present in it.
With the help of Big Dipper you can locate the position
of the pole star which is also known as 'Dhurba Tara'. It
always appears in the same position in the sky directly
above the north pole. This is visible during summer. It is
used to find direction.
Cassiopia
The Cassiopia looks like the English alphabet ‘W’. The
Saptarishi and Cassiopia lie at about equal distance from
the pole star.
The Orion
Orion is called the hunter because the stars are arranged in the form of hunter with a
belt and a sward. The three bright stars in the middle represent the belt of the hunter.
There are some faint stars below the belt forming sword of the hunter. It is a brightest
constellation that is seen in the north in winter and in the south in summer.
Blooming Science & Environment Book 7 249
Galaxy
A galaxy is a very large group of stars containing billions in numbers. There are many
galaxies in the sky. Our earth as well as the sun belongs to the galaxy called Milky Way.
It has a spiral shape. Andromeda is neighbouring galaxy. Other galaxies are elliptical
and irregular galaxies.
Differences between Constellations and Galaxy
Constellations Galaxies
1. They have few stars. 1. They have billions of stars.
2. They have a definite shape. 2. They don't have definite shape
3. There are 88 constellations in the 3. There are many galaxies (1011)in the
universe. universe.
Main Points to Remember
1. Life on Earth is possible due to water, oxygen and a suitable temperature.
2. Due to the rotation of the Earth on its own axis, day and night are caused.
3. The revolution of the planet around the sun, combined with the tilt of the Earth’s
axis, cause the seasons.
4. The sun, planets, satellites, asteroids, comets, and meteors are known as the solar
system.
5. There are eight planets in our solar system. Pluto is no longer considered as a
planet.
6. The moon is the only natural satellite of the Earth.
7. Earth is only the planet of the solar system whose surface environment is suitable
for the existence for the life.
8. Planets are the heavenly bodies, which revolve around the sun in the circular and
elliptical orbit.
9. All the planets except Venus move in the anticlockwise direction around the sun.
10. Sun is the major source of heat and light for the planets, which carries the 99%
of the mass of the solar system.
11. Moon is the natural satellite of the earth which takes 29.5 days to revolve around
the earth.
250 Blooming Science & Environment Book 7
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