Study Note for Class Eight Science || Unit 3 Living Beings and Their Structure

Unit 3

Living Beings and Their Structure

Exercise

1. Select the correct option from the followings:

a. What is called the branch of science that deals with the study of the cell?

i) Histology ii) Cytology iii) Cytogenetics iv) Anatomy

Ans: ii) Cytology

b. In which form is the energy generated in a cell stored before it is distributed to organelles?

i) DNA ii) RNA iii) RBC iv) ATP

Ans: iv) ATP

c. What is the common feature of the nuclear membrane and cell membrane?

i. they help in internal transportation

ii. they are composed of Pectin

iii. they are non-elastic in nature

iv. they inherit heredity to offspring

Ans: iii. they are non-elastic in nature

d. What is indicated by 'R' in the given figure?

i) Nucleus ii) Chloroplast iii) Mitochondrion iv) Vacuole

Ans: iv) Vacuole

e. Which of the following function is done by both plant and animal cells?

i. Photosynthesis ii) Cellular respiration iii) Transpiration iv) Guttation

Ans: iv) Guttation

f. What would happen if there was no cell membrane,

i. Cell organelles would be lost ii) Cell would die iii) Cell couldn't conduct metabolism iv) Nucleus would be lost

Ans: iii) Cell couldn't conduct metabolism

g. Which of the following is a function of the nucleus for the growth and development of the body?

i) to synthesize protein ii) internal transportation of cell iii) to take part in cell division iv) to control and coordinate all the functions of cell

Ans: iv) to control and coordinate all the functions of cell

2. Differentiate:

a)Cytoplasm and Nucleoplasm

Cytoplasm

i. It is a gel-like substance filling the cell between the nucleus and the cell membrane.

ii. It contains various organelles like mitochondria, endoplasmic reticulum, and ribosomes.

iv. It is the site of many cellular activities including metabolism and protein synthesis.

Nucleoplasm

i. It is a gel-like substance enclosed within the nucleus.

ii. It contains the cell's genetic material, including DNA and RNA.

iii. It is the site of transcription, where messenger RNA is synthesized from DNA templates.

b) Chloroplast and Chromoplast

Chloroplast

i. It is the site of photosynthesis in plant cells, containing chlorophyll pigments.

ii. It converts light energy into chemical energy (glucose).

iii. It is green in colour due to the presence of chlorophyll.

Chromoplast

i. It is plastids responsible for storing pigments other than chlorophyll, giving fruits and flowers their distinctive colours.

ii. It contain pigments like carotenoids, which produce red, orange, and yellow hues.

iii. It plays a role in attracting pollinators and seed dispersers.

c) Cell wall and Cell membrane

Cell wall

i. It is a rigid, protective outer layer found in plant cells.

ii. It is composed mainly of cellulose in plants, providing structural support and protection.

iii. It allows plants to maintain shape and resist mechanical stress.

Cell membrane

i. It is a thin, flexible barrier surrounding the cell's cytoplasm.

ii. It is composed of a phospholipid bilayer embedded with proteins.

iii. It regulates the passage of substances in and out of the cell.

d) Cell organelles and Cell inclusions

Cell organelles

i. Cell organelles are membrane-bound structures within the cell that have specific functions.

ii. They carry out specialized tasks necessary for cellular function and survival.

ii. Examples include the nucleus, mitochondria, endoplasmic reticulum, Golgi apparatus, lysosomes, and chloroplasts.

Cell inclusions

i. Cell inclusions are non-membrane-bound substances suspended in the cytoplasm.

ii. Serve various temporary or specialized functions but are not considered organelles.

iii. Examples include stored nutrients, pigments, and waste products.

3. Give reason:

a) Ribosomes are also called 'protein factories.

Ribosomes are called "protein factories" because they are where proteins are made in the cell. They read the instructions from the DNA and assemble amino acids into proteins.

b) Cell wall provides a fixed shape to plant cells.

The cell wall gives plant cells a fixed shape because it's like a rigid outer shell. It helps the plant stand up straight and protects it from damage.

c) Metabolism occurs in the cytoplasm

Metabolism happens in the cytoplasm because it's like the cell's kitchen. All the chemical reactions that keep the cell alive and functioning, like breaking down food to make energy, happen there.

d) Cells are considered the basic unit of life.

Cells are considered the basic unit of life because they are the smallest parts of living things that can carry out all the activities needed for life, like growth, reproduction, and responding to the environment.

e) There should be proper coordination among cells, tissues and organs to conduct the life process.

There should be proper coordination among cells, tissues and organs to conduct the life process to keep the organism alive and healthy. Each part has its job to do, and they need to communicate and cooperate to make sure everything runs smoothly.

4. Answer the following questions:

a) What is a cell?

A cell is the basic unit of every life. All the mechanisms of life processes like digestion, respiration, reproduction, internal transportation, photosynthesis, etc. are accomplished inside or by the action of these cells through biochemical reactions and contraction-relaxation motion. Because of these reasons, cells are also called the functional unit of life.

c) Where are the mitochondria located in a cell? Write their functions.

In a cell, mitochondria are found within the cytoplasm

Their functions are:

i. The main function of mitochondria is to generate energy for the survival of the cell.

ii. Mitochondria also contain some DNA molecules which transfer hereditary character.

d) Which organelle of the cell undergoes self-digestion and Why?

The organelle that undergoes self-digestion is the lysosome.

e) Make a list of cell organelles and cell inclusions found in a cell.

Cell Organelles:

i. Mitochondria

ii. Plastid

iii. Ribosome

iv. Golgi body

Cell Inclusions:

i. droplets of free water

ii. crystals of salts and minerals

iii. enzymes

iv. hormones

v. vitamins

vi. waste materials

f) Mention the function of plastids in a plant cell.

The function of plastids in a plant cell:

i. Chloroplasts, a type of plastid, are responsible for photosynthesis.

ii. Plastids store starch, which serves as a reserve energy source for the plant.

iii. They produce pigments like chlorophyll, which give plants their green color and are essential for photosynthesis.

iv. Other plastids, like chromoplasts, store pigments responsible for the colors of fruits, flowers, and other plant parts.

h) Mention the role of the Golgi body and Vacuole in a cell.

The Role of the Golgi body:

i. It helps to secrete gum, mucus, sweat, saliva, tear etc.

ii. During cell division, the Golgi body contributes to making new cell membranes in animal cells and new cell-plate in plant cells.

iii. It also helps in the internal transportation of cells and sorting of proteins.

The Role of Vacuole:

i. It balances the amount of water and salts in the cytoplasm.

ii. It collects metabolic wastes of organelles before they are excreted out of the cell membrane.

i) Study the given figure carefully and answer the following questions:

i) Copy this figure in your exercise book and label A, B, C and D.

A- Nucleus

B- Nucleoplasm

C- Chromatin Fibre

D- Nuclear Membrane

ii) What is the function of B?

It assists the nucleus by balancing the amount of water, providing enzymes and synthesizing DNA and RNA molecules.

iii) What happens if there is no nucleus in a cell?

If there's no nucleus in a cell, it wouldn't be able to control its activities. It is like the cell's brain as it holds all the instructions for making proteins and managing the cell's functions. Without it, the cell wouldn't know what to do and couldn't survive or reproduce.

j) Among various organelles of a cell, which one is the most important in your opinion and why?

In my opinion, the nucleus is the most important organelle in a cell. It's like the cell's control center. Just like how our brain controls our bodies, the nucleus controls everything happening inside the cell. Without it, the cell wouldn't know what to do, and it wouldn't be able to survive or reproduce.

k) What would happen in the plants' life processes if there were no chloroplasts in them?

If there were no chloroplasts in the plants, they could not perform photosynthesis. As a result, plants would be unable to produce their own food, leading to their inability to grow, develop, and ultimately survive.

l) What is the reason that the nucleus is also called 'the brain of cells'? Clarify.

The nucleus is the central part of a cell. It controls and coordinates the function of every cell organelle, so it is also called 'the brain of a cell'.

m) If there were no metabolic processes in a cell, what effect would occur in the life processes of the organism?

Without metabolic processes in a cell, the organism would not obtain energy from nutrients, break down molecules for building blocks, or carry out essential biochemical reactions necessary for life. The organism would be unable to perform any vital functions required for survival