Class 6 - Biology - Cell - The Structure And Function - Exercise And Solutions

EXERCISE

Multiple Choice questions:

1. Tick (√) the appropriate answer.

(i) Identify the part which contains pigment.

(a)    Cell membrane                      (b)    Plastid

(c)    Centrosome                           (d)    Cell wall

(ii) The organelle that controls all activities in a cell

(a)    Nucleus                                 (b)    Vacuole

(c)    Plastids                                  (d)    Cytoplasm

(iii) A cell that is spherical in shape is

(a)    White blood cell                    (b)    Nerve cell

(c)    Red blood cell                       (d)    Amoeba

(iv) The vacuole contains

(a)    Water                                     (b)    Cell sap

(c)    Salts                                       (d)    Food

Short Answer questions

1. Name the scientist who invented the first microscope.

Antonie Van Leeuwenhoek developed the first microscope.

2. Who coined the term cell?

Robert Hooke coined the term cell.

3. Briefly describe the three essential parts of a cell.

The three essential parts of a cell are

i) Cell membrane: This is the outer most part of a cell. It is also called as

plasma membrane. It is very thin, delicate and flexible. It is presented

both in animals and plants. It has fine pores in it, through which only

certain substances can pass in and out.

ii) Cytoplasm: It is a semi-liquid substance, which is colourless and

translucent. It is found between the nucleus and the cell membrane.

iii) Nucleus: It is a small spherical mass mostly located towards the

centre of the cytoplasm. It is the most important part of the cell. It

regulates and coordinates various life processes of the cell and

plays an important role in cell division.

4. The cell membrane is called selectively permeable. Why?

The cell membrane is called selectively permeable because it allows the

entry of certain molecules only, while holding back the others

5. State the difference between:

(i) Nucleus and Nucleolus  (ii) Cytoplasm and Protoplasm

(iii) Cell wall and Cell membrane

(i) Nucleus and Nucleolus

Nucleus	Nucleolus
It is the central organelle of a cell.	It is a component of nucleus
It is surrounded by cytoplasm and the cell membrane.	It is surrounded by nucleoplasm and nuclear membrane.
It is the most important part of the cell.	It is an important part of the nucleus.

(ii) Cytoplasm and Protoplasm

Cytoplasm	Protoplasm
It is found between the nucleus and the cell membrane. It has many parts like Golgi bodies, mitochondria and plasma membrane.	It is the living substance of the cell which includes cytoplasm and nucleus and nuclear membrane.
It is a colourless and translucent semi liquid substance.	It is a jelly like substance.

(iii) Cell wall and Cell membrane

Cell wall	Cell Membrane
It is a nonliving structure.	It is a living structure.
It is present only in the plant cell and lies outside the cell membrane.	It is present in both plant and animal cells.
It is made up of cellulose.	It is very thin delicate and flexible.
It is selectively permeable and allows the entry of certain molecules only.	It is freely permeable and allows substances to enter and leave the cell without any hindrance.

6. List the measure difference between a plant cell and an animal cell.

Plant cell	Animal cell
Size is usually larger	Size is usually smaller.
Plant cell has a definite cell wall.	It has no cell wall.
Cytoplasm is not so dense. Only a thin layer of cytoplasm.	Cytoplasm is denser and more granular. It fills almost the entire cell.
Vacuoles are prominent, fewer in number.	Vacuoles are small, numerous and concerned with excretion or secretion.
Contains plastids.	Does not contain plastids.

7. Briefly discuss the importance of chromosomes in an organism.

Chromosomes are contained in the nucleoplasm. In the chromosomes

there are units called genes. These genes are responsible for

transmitting characteristics from parents to offsprings. The number of

chromosomes are defined for each species. Every cell of a human

body contains 46 chromosomes which occur in 23 pairs.

8. Fill up the blanks with the terms given below in the box. 

(i) The ___________ is the structural unit of all living things.

(ii) All cells arise from __________ cells.

(iii)Animal cells have no cell ____________.

(iv)Plastids contain ___________.

(v) _________ are filled with water and dissolved substance.

Ans. (i) cell, (ii) pre-existing   (iii) wall, (iv) pigments, (v) vacuoles

9. Try to find the names of four cell organelles hidden in this maze.

(Hint: The hidden words can appear horizontally or vertically; forward

or backward or even mixed up). Write them in the lines provided. For

example: “NUCLEUS” in the last row, seven backward letters.

(i) Vacuole  (ii) Chromoplast  (iii) Plastid  (iv)Leucoplast

Long Answer questions

1. Briefly describe the structure of nucleus and mention it’s any two

function.

Nucleus is a small spherical mass mostly located towards the centre of

the cytoplasm. It is the most important part of the cell.

It has the following structure.

(i) A delicate porous nuclear membrane which encloses the nucleoplasm

(ii) Inside the nucleoplasm there is a small darker body known as nucleolus. The nucleoplasm contains chromosomes and the chromosomes contain genes which are responsible for transmitting characteristics from the parents to offsprings.

The two functions of nucleus are

(i) It regulates and coordinates various life process of the cell.

(ii) It plays and important part during cell division.

2. Name the scientist who coined the term “cell”. How many lenses did he

use in his microscope? What did he observe under his microscope?

In 1665 Robert Hooke coined the term “cell”. He used two lenses

in his microscope. While examining a very thin slice of a dead cork, he

observed a cluster of box like cubicles piles up together. This reminded

him of “cells” of monks living in a monastery. So he named them cells.

3. Name the three essential parts of a cell. Briefly describe the structure of

cell membrane.

The three essential parts of a cell are:

(a) The outermost cell membrane or the plasma membrane.

(b) The cytoplasm

(c) The nucleus

Structure of cell membrane:

(i) It is a living structure present in both plant and animal cells.

(ii) It is very thin, delicate and flexible.

(iii) It has very fine pores in it, through which only certain substance can

Pass in and out. The cell membrane is selectively permeable.

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Extra Questions and Answers

A. Objective Questions

1. Fill in the blanks:

a) Nucleus was discovered by Antonie Van Leeuwenhoek.

b) Robert Hooke first coined the term cell.

c) A cell is the basic structural and functional unit of all living things.

d) The word cell is derived from the Latin word cella.

e) The branch of biology which deals with the study of cells is called

cytology.

f) The type of microscope we use in our school laboratory is known as

compound microscope.

g) A cell is called living when it contains a jelly like substance called

protoplasm.

h) On the basis of the number of cells, the organisms have been

categorized as unicellular and multicellular.

i) The red blood cells are spherical or disc shaped.

J) The smooth muscles of the heart are cylindrical in shape for easy

contraction and relaxation.

k) Paramecium is a single celled organism whose shape is like a slipper.

l) Spirogyra is a multicellular green algae, whose cells are cylindrical in

shape.

m) Chlamydomonas is a unicellular green algae, whose cells are oval in

shape.

n) Three scientists Schleiden, Schwann and Virchow formulated the cell

theory.

o) Nerve cells conduct the messages in the form of impulses.

p) The gland sells secrete enzymes that digest food.

q) Skin cells helps in regulating the body temperature.

r) Each cell is surrounded by a cell membrane, also called

plasma Membrane.

s) The cell membrane is called selectively permeable.

t) The cell wall is made up of cellulose.

u) Cytoplasm is found between the nucleus and the cell membrane.

v) The human body has 46 chromosomes which appear in 23 pairs.

w) Vacuoles are the non-living inclusions in the cytoplasm bound by a

membrane.

x) In animal cells the vacuoles are larger in number and smaller in size

and in plant cell the vacuoles are fewer in number but quite larger in

size.

y) The cell wall is freely permeable.

z) The cell shape is determined by the function of the cell.

2. Give one word for the following.

a) Rounded body inside nucleus– Nucleolus.

b) A small darker body inside the nucleoplasm – Nucleolus.

c) The transparent substance in the nucleus is  – Nucleoplasm.

d) The cavity of vacuoles are filled with – Water.

e) The unit for measuring cells – Micrometer.

f) The longest cell – Nerve cells.

g) The largest cells – Ostrich eggs

h) The smallest cells are found in – Bacteria

i) The shape of the cells of onion peel – Rectangular.

j) The smooth muscles in our body is – Spindle shaped.

k) Slipper shaped animalcule – Paramecium

l) The structural and functional unit of all living organism – Cell

m) It protects the cell from the entry disease causing agents – Cell wall

n) Green plastids that trap the solar energy for photosynthesis – Chloroplast

o) They impart varied colours to flowers and fruits – Chromoplast

p) Colourless plastids which occur in seeds – Leukoplasts

q) Covering of the vacuole – Vacuolar membrane or Tonoplast

B. Short Questions And Answers.

1. Why cell wall is called freely permeable?

Cell wall is called freely permeable because it allows substances in

solution to enter and leave the cell without any hindrance.

2. Differentiate between Chloroplast and Chromoplast.

Chloroplast	Chromoplast
These are green plastids.	Contain yellow and red pigments.
Traps the solar energy for photosynthesis.	Responsible for varied colours to fruits and flowers as well as causing pollination by attracting insects.

  

3. What are the functions of a cell wall?

The main function of cell wall are

i) It gives shape and rigidity to plant cell.

ii) It protects the cell from the entry of diseases causing agents.

iii) It protects the plasma membrane and protoplasm against mechanical

injury.

4. Define cell. When a cell is called a living cell?

A cell can be defined as the basic structural and functional unit of an

organism. A cell is said to be living when it contains a jelly like substance

called protoplasm.

5. Define protoplasm.

Protoplasm is the living substance of a cell. It is made up of cytoplasm and

nucleus.

6. Define unicellular organisms with example.

The organisms having just a single cell are called unicellular organism.

Example: Bacteria, Yeast, Amoeba and Paramecium etc.

7. Define multicellular organisms with example.

Multicellular organism are made up of millions and billions of cells.

Example: All organism we can see around us like, Rose, Peepal, fish,

lion and human beings etc.

8. Why cell division is so important?

Cell division is necessary for replacement, repair, reproduction and

growth of the cells. It is necessary for the existence of all living beings

including the plants.

9. Define vacuole.

Vacuoles are the non-living inclusions in the cytoplasm. These are filled

with water and other substances in solution form called cell sap. These

are present both in animal and plant cells. Vacuoles are fewer and

quite large in size in plant cells and in animal cells vacuoles are large in

numbers but smaller in size.

C. Long Questions And Answers.

Answer the following:

1. Define the cell theory. Name the scientists who formulated it.

Three scientists, Schleiden, Schwann and Virchow formulated the cell

theory. The cell theory is described as follows.

i) Every living organism is made up of one or many cells.

ii) The cell is the structural unit of all living organism.

iii) The cell is the functional unit of all living organism.

iv) All cells arise from the pre-existing cells.

2. Classify and define the different cells according to their size.

According to their size the cells are classified as largest cells, longest

cells and smallest cells.

Largest cells: The ostrich eggs are example of largest cell.

Longest cells: The nerve cells are the longest cells, which are up

to 3 metre of length.

Smallest cells: The smallest cells are between 0.2 – 0.5 micrometre

And found in bacteria,

3. Define the different cells present in animals.

The different cells present in the animals are

i) Muscle cells: Muscle cells has the ability to contract and relax. It helps

in the movement of different body parts.

ii) Nerve cells: It helps in conducting the messages in the form of

impulses.

iii) Gland cells: These are present in the various glands and secret

enzymes that digest the food.

iv) Skin cells: It is present in the skin, which is the outermost covering of the

body and protects from various external factors like germs

and ultraviolet rays. It also helps in regulating the body

temperature.

4. What are plastids ? State its different types.

Plastids are organelles which are present only in the plant cells. These

are mainly three types depending upon the pigment they contain.

These are Chloroplasts, Chromoplasts and Leukoplasts.

Chloroplasts: These are green plastids that trap the solar energy for

photosynthesis.

Chromoplasts: These contains yellow and red pigments. They impart

colours to flowers and fruits. They also attracts the insects

for pollination.

Leukoplasts: These are colourless plastids which are present in the seeds.

They store starch, fat and proteins.

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