bio assignment draft 1

PENANG MATRICULATION COLLEGE
BIOLOGY
SB 015

SEMESTER 1, SESSION 2022/2023

MOLECULES OF LIFE & CELL
STRUCTURES AND FUNCTIONS

NAME : NUR NADIAH BINTI RADZI
MATRIC NUMBER : MS2113172738
PRACTICUM : H8T04A
LECTURER’S NAME : IFRIZAMUNIRAH BINTI IBRIM@IBRAHIM

Main types of molecules of life

3

Classify carbohydrates into three main classes based on
their structure and characteristics.

4-7

INDEX Human are unable to digest vegetables, but herbivors
are able but, herbivors are able to do so. Explain this
statement by focusing on a significant structure of the
plant cell.

8

Name the organelle which synthesizes carbohydrates in
plant cells. Describe how the organelles structures are
involved in the synthesis of carbohydrates.

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Reference 10

WATER

CARBOHYDRATES

PROTEINS

MAIN TYPES
OF

MOLECULES
OF LIFE

DNA and RNA molecules LIPIDS

3

Classify carbohydrates into three main classes based
on their structure and characteristics.

CARBOHYDRATES

MONOSACCHARIDES DISACCHARIDES POLYSACCHARIDES

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MONOSACCHARIDES

1. Characteristics
• Sweet-tasting
• Soluble in water
• Can be crystallised
• Reducing agent: has a free ketone or aldehyde group, can denotes electrons

to other molecules
2. Structure
• Straight-chain form, ring form in aqueous
• A sugar has : i) a carbonyl group ( C=O )

ii) many hydroxyl groups ( -OH )

eg: glucose (C6H12O6)

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DISACCHARIDES

1. Characteristics
• Sweet
• Water soluble
• Can be crystallised
• Reducing agent : depend on free functional group (aldehyde & ketone) at sugar structure

2. Structure
• A double sugar molecule : consists of monosaccharides
- Linked by glycosidic linkage / bond
- Glycosidic linkage: covalent bond formed between two

monosaccharides by a condensation reaction

eg: maltose (a-glucose + a-glucose)

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POLYSACCHARIDES

1. Characteristics eg: Cellulose ( polymers of B-glucose)
• Large/ macromolecule / complex
• Not sweet
• Insoluble in water
• Cannot be crystallised

2. Structure
• Polymers formed when hundreds of monosaccharides joined by glycosidic linkages

(through condensation)
• Breakdown by hydrolysis
• The chain formed by:

i. Variable in length

ii. Branched or unbranched

iii. Folded : ideal for energy storage

iv. Straight or coiled

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HUMAN ARE UNABLE TO DIGEST VEGETABLES, BUT HERBIVORS ARE ABLE BUT, HERBIVORS ARE ABLE TO DO SO. EXPLAIN THIS
STATEMENT BY FOCUSING ON A SIGNIFICANT STRUCTURE OF THE PLANT CELL.

• Cellulose is a complex organic compound that occurs abundantly in nature. It is a polymeric carbohydrate molecule consisting of a
linear chain having thousands of glycosidic linkages.

• It consists of unbranched chains of glucose (linked D-Glucopyranose). They are straight chains linked by hydrogen bonds producing
a substance that is inert and insoluble in water, in its pure form.

• Modified cellulose and pure cellulose are different in their chemical compositions. They are components of the plant cell wall and
have no odour or taste. It is crystalline in nature and does not dissolve water and other solvents. Termites and herbivorous animals
lack the enzyme for cellulose digestion.

Digestion of Cellulose in Humans
• Cellulose is a fibre which is not digestible by the human digestive system. It, however, helps in the smooth functioning of the

intestinal tract.
• The presence of beta acetal linkages in cellulose makes it different from starch and is a deciding factor in its digestibility. Humans

lack the enzyme required to break down the linkages. Furthermore, it forms a major part of the human diet from plant foods.
• Fruits and vegetables contain cellulose in small amounts which are easily digestible. Fibres contain cellulose which acts as roughage,

adding bulk to consumed food and helping in the smooth passage of the food efficiently and at a much faster pace. A high-fibre diet
reduces the risk of colon cancer as fibre in the diet helps reduce the time the faeces stay in the colon wall.
• Since it is insoluble in water it binds with other components adding bulk helping to move through the intestines by aiding bowel
movements. Consuming food that does not contain cellulose over a period of time results in the bowel becoming weak leading to
constipation.
• These fibres aid in the growth of bacteria in the gut which feeds on sugars and fibres. They maintain the health of the gut and check
for bacteria causing illness. Fibres also prevent weight gain and aid in weight loss.

Digestion of Cellulose in Animals
• Termites have mastigophorans (microbes) in their gut which brings about the digestion of cellulose. Herbivorous animals, on the

other hand, are ruminants. They have different compartments in their stomach to carry out digestion.
• The rumen is the first compartment where ingested food containing cellulose is stored temporarily and later regurgitated to chew

their cud. They are able to digest cellulose because of the presence of bacteria and enzymes in the rumen where anaerobic
bacterial digestion occurs. A by-product of this type of digestion releases methane which is foul-smelling and causes the destruction
of the ozone layer of the Earth.

8

Name the organelle which synthesizes carbohydrates in plant cells. Describe
how the organelles structures are involved in the synthesis of carbohydrates.

• Organelle that synthesizes carbohydrates in plant cells are plastids.
• Plastid is a double membrane-bound organelle involved in the synthesis and storage of food, commonly found within

the cells of photosynthetic plants.
• They are necessary for essential life processes, like photosynthesis and food storage.
• A plastid containing green pigment (chlorophyll) is called chloroplast whereas a plastid containing pigments apart from

green is called a chromoplast. A plastid that lacks pigments is called a leucoplast and is involved mainly in food storage.

Structure of plastids
• The majority of chloroplasts of green plants exist in the leaf mesophyll cells. Their shape resembles a lens

and is discoid, oval, spherical, or ribbon-like organelles. Their length varies from 5-10 µm and their width
varies from 2-4 µm.
• These organelles are encircled by double membrane-like mitochondria. The inner membrane of chloroplast
is comparatively less permeable. Stroma is the space surrounded by the internal membrane of the
chloroplast. This internal space is filled with fluid that surrounds the grana, thylakoids. It also contains
ribosomes, starch, and DNA
• A number of flattened membranous sacs are organized and are called the thylakoid. These are located in the
stroma. Light-dependent reactions of photosynthesis occur in these thylakoids. There are packets of
chlorophyll pigments in the thylakoid membrane, these are termed quantasomes. There are 230-250
chlorophyll molecules present in every single quantasome.
• Space surrounded by the membrane of the thylakoids is called a lumen. This lumen is the site for the
phosphorylation process of photosynthesis. During light reactions of photosynthesis, the pH of the lumen
becomes acidic due to the inward pumping of protons.
• These Thylakoids are arranged in a bunch that resembles the heaps of coins known as grana. A single
chloroplast contains 10-100 grana enclosed in it.
• Along with these grana, there are membranous flattened tubules called the stroma lamellae. These stroma
lamellae interlink the thylakoids of the various grana.

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REFERENCE

1. Sushil Humagain( 17 October 2018 ) Amino acids: General properties and classification
o https://onlinesciencenotes.com/amino-acids-general-properties-and-classification/

2. PSIBERG Team (2 January 2022) Alpha(α) and Beta(β) Glucose: Comparison, Structures
o https://psiberg.com/alpha-and-beta-glucose/

3. Allison Soult (22 February 2022) Lipids and Triglycerides
o https://chem.libretexts.org/Courses/University_of_Kentucky/UK%3A_CHE_103_-

_Chemistry_for_Allied_Health_%28Soult%29/Chapters/Chapter_14%3A_Biological_Molecules/14.2%3A_Lipids_and_Triglyceri
des

4. NutrientsReview(2016) Glucose
o https://www.nutrientsreview.com/carbs/monosaccharides-glucose.html

5. Sagar Aryal ( 11 May 2021 ) Plastids- Definition, Structure, Types, Functions And Diagram
o https://microbenotes.com/plastids-types-structure-and-functions/

6. BYJU’S (2022) Cellulose In Digestion
o https://byjus.com/biology/cellulose-in-

digestion/#:~:text=Why%20can't%20humans%20digest,functioning%20of%20the%20intestinal%20tract

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