ICSE Class 9 Biology Solutions Chapter 2 Cell: The Unit of Life

Class 9th ICSE Biology Solutions Chapter 2 Cell: The Unit of Life

Progress Check

Question 1.
Name the following :-
(i) The kind of microscope that consists of a single biconvex lens ………………..
(ii) The kind of mirror used for throwing light on the object in Hooke’s microscope ……………….
Answer:
(i) Simple microscope
(ii) Concave mirror.

Question 2.
What is the maximum magnification that can usually be achieved by
(i) a compound microscope,………………..
(ii) an electron microscope? ………………
Answer:
(i) 2,000 times
(ii) 200,000 times.

Progress Check

Question 1.
Name the following :
(i) Any two, one-celled organisms ………………
(ii) The longest cells in animals …………………..
(iii) Amoeboid cells in humans ……………….
(iv) Outermost layer in plant cells ………………….
(v) A cell component which is visible only in cell division stages. …………………
Answer:
(i) yeast, amoeba
(ii) nerve cells
(iii) white blood cells
(iv) cell wall
(v) chromosomes.

Question 2.
List three categories of substances which are ensured greater diffusion due to large surface/volume ratio of the cells.
(i) ……………
(ii) ………….
(iii) ……………….
Answer:
(i) Nutrients into the cell
(ii) Metabolic wastes from the interior to the outside of the cell
(iii) Respiratory gases.

Progress Check

Question 1.
Name the part of a cell in which
(i) many chemical reactions occur with the help of enzymes ………………
(ii) a network of chromatin fibres occurs …………………..
(iii) cellulose forms the main component ……………..
Answer:
(i) present in Golgi apparatus
(ii) Nucleus
(iii) Cell wall

Question 2.
Differentiate between
(i) an organ and an organelle …………………
(ii) A plant cell and an animal cell pertaining to the presence of plastids
Answer:
(i) Organ – part of body having a definite shape, structure and function.
Organelles – Parts of cells having a definite shape, structure and function.

(ii) Plant Cells – Plastids present
Animal Cells – Plastids absent

Question 3.
Name the cell organelles concerned with
(i) Secretion of enzymes ………………….
(ii) Trapping of solar energy ……………..
(iii) Synthesis of proteins …………………
(iv) Intracellular digestion …………………
(v) Production of ATP …………….
Answer:
(i) Golgi apparatus
(ii) Plastids (chloroplasts)
(iii) Ribosomes
(iv) Lysosomes
(v) Mitochondria

Question 4.
Name the cell part which is
(i) composed of cellulose……………….
(ii) formed of an irregular network of tubular double membranes ………………..
(iii) a clear space with water or other substances in solution …………………
Answer:
(i) Cell wall
(ii) Endoplasmic reticulum
(iii) Vacuoles

Question 5.
Mention if the following statements are true or false. If false, suggest the change in the information underlined.
(i) Prokaryotic cells have larger ribosomes.
(ii) Eukaryotic cells have mitochondria.
(iii) Amoeba is an example of Prokaryotes.
(iv) Bacteria have no nuclear membrane but possess chromatin fibres.
Answer:
(i) It is false :
Prokaryotic cells have smaller ribosomes.
(ii) True
(iii) It is false. Amoeba is an example of Eukaryotic.
(iv) It is false : Organelles like endoplasmic reticulum, chloroplasts, mitochondria absent. Foods are absorbed in solution form.

Progress Check

Question 1.
Column I lists a few activities of living organisms and column II the activity of cells related to them. Match the items in the two columns.

Column I (Activity of organism)	column II (Activity of cells)
(i) Repair	(a) Contractility of cells
(ii) Cooling of body	(b) Cells devour germs
(iii) Movement	(c) Cell division
(iv) Protection from diseases	(d) Gland cells give out sweat for evaporation

Answer:
(i) Repair- (c) Cell division
(ii) Cooling of body – (d) Gland cells give out sweat for evaporation
(iii) Movement- (a) Contractility of cells
(iv) Protection from diseases – (b) Cells devour germs

Question 2.
Which cell organelle is the key to the life of the cell?
Answer:
Nucleus (Protoplasm)

Question 3.
How do you say that a cell also has a life span and death like an organism? Give one example. ……………….
Answer:
Cell also has life span, like all living Organisms exhibit a definite cycle consisting of birth, growth, reproduction and death. This life cycle of an organism can vary from a period of few days to hundreds of years. Every organ in human body is made of hundreds of thousands of cell. Similarly every part of a plant such as the leaf, the flower, the roots and even wood are made of cells.

Every cell has its own life. Old and weak cells in the body continually die and are replaced by new cells.
Example – Tearing of old skin from the body.

Question 4.
All organisms excrete. Does an individual cell also do it? Give one example. ………………. …………………..
Answer:
Individual cell excretes, whose collection leads to excretion by an organism e.g., metabolic wastes from the interior to the outside of the cell.

Question 5.
Every organism needs food. Does a cell also need it? Explain very briefly. …………………… ……………….
Answer:
Food is digested by the enzymes which the cells of the digestive glands secrete, digested food is absorbed by the cells and absorbed food is used up in cells for various metabolic activities.

Review Questions

A. Multiple Choice Type :

Question 1.
Which one of the following cell organelles is correctly matched with its function?
(a) Ribosomes – Synthesis of proteins
(b) Mitochondria – Secretion of enzymes
(c) Plasma membrane – Freely permeable
(d) Centrosome – Carries genes
Answer:
(a) Ribosomes – Synthesis of proteins

Question 2.
All life starts as
(a) an egg
(b) a single cell
(c) a gene
(d) a chromosome
Answer:
(b) a single cell

Question 3.
Which one of the following is found both in the cells of a mango plant and a monkey?
(a) chloroplasts
(b) centrioles
(c) cell wall
(d) cell membrane
Answer:
(d) cell membrane

Question 4.
A plant cell can be identified from an animal cell by the :
(a) absence of centrosome
(b) presence of cell membrane
(c) presence of vacuoles
(d) none of the above
Answer:
(a) absence of centrosome

Question 5.
Plant cell has a cell wall made of :
(a) Protein
(b) Fructose
(c) Cellulose
(d) Fatty acids
Answer:
(c) Cellulose

Question 6.
The cell organelle that helps in respiration of the cell is :
(a) Mitochondria
(b) Lysosome
(c) Ribosome
(d) Centrosome
Answer:
(a) Mitochondria

B. Very Short Answer Type

Question 1.
Name the part of the cell concerned with the following?
(a) Liberation of energy,
(b) Synthesis of proteins,
(c) Transmission of hereditary characters from parents to offspring.
(d) Initiation of cell division
(e) Hydrolytic in function
(f) Entry of only certain substances into and out of the cell.
Answer:
(a) Mitochondria
(b) Nucleolus
(c) Chromatin fibres.
(d) Centrosome
(e) Vacuoles
(f) cell membrane

Question 2.
State whether the following statements are true (T) or false (F):
(a) All animal cells contain a cell wall. T/F
(b) The cell wall is made of protein. T/F
(c) Centrosome occurs in animal cells. T/F
(d) Plant cells contain large vacuoles. T/F
(e) Protoplasm is the part of the cell which surrounds the nucleus. T/F
(f) Genes are located in chromosomes. T/F
(g) Anthocyanins are the pigments of flowers, which are dissolved in cell-sap. T/F
Answer:
(a) – F
(b) – F
(c) – T
(d) – T
(e) – F
(f) – T
(g) – T

Question 3.
How many chromosome pairs are found in human cells?
Answer:
23 chromosome pairs.

Question 4.
What is the name of the chemical substance which constitutes the genes?
Answer:
DNA (deoxyribonucleic acid)

Question 5.
Match the items in Column ‘A’ with those in Column ‘B’

Column A	Column b
(a) Vacuoles	(i) Intracellular digestion
(b) Nucleolus	(ii) Respiratory enzymes.
(c) Lysosomes	(iii) Covered by tonoplast
(d) Anthocyanin	(iv) Dissolved in the cytoplasm
(e) Cristae	(v) Forms RNA

Answer:
(a) Vacuoles- (iii) Covered by tonoplast
(b) Nucleolus- (v) Forms RNA
(c) Lysosomes- (i) Intracellular digestion
(d) Anthocyanin- (iv) Dissolved in the cytoplasm
(e) Cristae- (ii) Respiratory enzymes.

Question 6.
Fill in the blanks :
(a) ………………… consists of membranous sacs and secretes 40 types of digestive enzymes.
(b) ………………. is surrounded by microtubules, located near the nucleus.
(c) Very thin flexible, living membrane which is differentially permeable, is called ………………..
(d) More than 1000 chromosomes are found in the nucleus of certain ………………….
(e) ……………… are hereditary units.
(f) ………………. is a plastid which stores starch.
Answer:
(a) lysosomes
(b) centrioles
(c) plasma membrane
(d) insects
(e) genes
(f) leucoplasts

C. Short Answer Type

Question 1.
It is said that the protoplasm cannot be analysed chemically. Why?
Answer:
It is impossible to make an accurate chemical analysis of protoplasm because it ceases to be protoplasm as soon as it is removed from the organism. It is the living matter.

Question 2.
What is the difference between an organ and an organelle?
Answer:
Organ
1. These are the parts of a body.
2. Each organ has a specific function in the body.
Organelle
1. These are a part of the cell.
2. Organelle has a specific function in a cell.

Question 3.
Do you think the cells of an elephant would be larger than the cells of a rat? Explain briefly.
Answer:
The cells of an elephant would be large in number and not in size, as larger is an organism greater the number of cells is.

Question 4.
Differentiate between the following pairs of terms :
(a) Protoplasm and cytoplasm
(b) Nucleolus and nucleus
(c) Centrosome and chromosome.
(d) Cell wall and cell membrane
(e) Plant cell and animal cell
(f) Prokaryotes and eukaryotes
Answer:
(a) Protoplasm – It is the living matter, the total substance of a living cell, that is the cytoplasm and nucleus. Cytoplasm – All parts inside the plasma membrane excluding nucleus.

(b) Nucleus – Largest cell organelle contains thread-like
structures called chromatin which contain DNA. Nucleolus – One or more round-shaped nucleoli inside the ^ nucleus.

(c) Centrosome – Present in animal cells only. Initiates and regulates cell division.
Chromosomes – Made up of DNA threads carry hereditary information of the genes.
(d)

Cell wall	Cell Membrane
1. It is the non-living boundry wall.	1. It is a living membrane.
2. It it present outside the cell membrane.	2. It is a thin outer boundry of cytoplasm.
3. It is mainly composed of cellulose.	3. It is composed of lipids and protiens.
4 It is permeable.	4. It is semi-permeable.

(e)

Plant Cell	Animal Cell
1. A definite cell wall made up of cellulose is present.	1. Cell wall absent.
2. Cytoplasm in the form of a thin lining against the cell wall.	2. Cytoplasm is denser and more granular, occupies most of the space of the cell.
3. Vacuoles are large and prominent may be one or more.	3.Vacuoles absent. If present,are small and temporary.
4. Usually contain plastids.	4. Plastids are absent.

(e)

Prokaryotes	Eukaryotes
1. Cells are generally small.	1. Cells are comparitively larger.
2. No definite Nucleus is present.	2. Distinct nucleus bounded by a membrane is present.
3. Well defined cell organelles are absent in the cytoplasm.	3. Well defined organelles such as mitochondria, endoplasmic reticulum, golgi bodies and lysosomes are present.

Question 5.
Mention three features found only in plant cells and one found only in animal cells.
Answer:
Three features found only in plant cells are

1. Cell wall
2. Plastids
3. Chloroplast

One feature found only in animals cells :
Centrosome

Question 6.
Why are the cells generally of a small size?
Answer:
Cells are generally small in size so that these have a larger surface area.

D. Long Answer Type

Question 1.
What is the cell theory? Who propounded it and when?
Answer:
Cell theory – All animals and plants are made up of cells which serve as the units of structure and function. It states three main points.

• Cell is the unit of structure of all living things.
• All cells develop from pre-existing cells.
• The cell is the unit of function of all living things.
  It was propounded by Theodor Schwann and Matthias Schleiden in 1839.

Question 2.
Mention any three differences between a living cell and a brick in a wall.
Answer:

Cell Wall	Brick Wall
1. Non-rigid structure which is living.	1. Rigid structure which is non-living.
2. Mainly composed of cellulose.	2. Composed of bricks.
3. Freely permeable.	3. Non permeable.

Question 3.
Name the plastid and pigement likely to be found in the cells of:
(a) petals of sunflower
(b) ripe tomato
(c) skin of green mango
(d) cells of potato.
Answer:
(a) XANTHOPHYLL (Yellow)
(b) CAROTENE (Orange-Red)
(c) CHLOROPLASTS (Green)
(d) LEUCOPLASTS (White) and they have no pigment.

Question 4.
State the major functions of the following :
(a) Plasma membrane
(b) Ribosome
(c) Lysosome
(d) Mitochondria
(e) Golgi apparatus
(g) Asters of centrosome
(h) Chromosomes
(i) Glycogen granule
(j) Vacuoles
Answer:
Major functions of the following parts in a cell are as follows :
(a) Plasma membrane –

• Regulates the entry of certain solutes and ions
• Maintains shape of the cell.

(b) Mitochondria –

• Release of energy from food in form of ATP
• Syntheses respiratory enzymes.

(c) Golgi apparatus –

• Synthesis and secretion of enzymes, hormones etc.
• Formation of acrosome of sperm.

(d) Ribosome -Protein synthesis

(e) LysoSomes –

• Intra-cellular digestion
• Destroy foreign substances
• Destroy old or injured organelles
• Formation of bones by digesting cartilages.

(f) Cytoplasm-
It is viscous, like the white portion of an egg and more or less semi- liquid substance. It is just below the cell membrane and occupies a large part of the cell. Many reactions takes place in the cytoplasm.

Cytoplasm undergoes clockwise or anticlockwise movements in the cell. Endoplasmic reticulum, ribosomes, mitochondria, Golgi apparatus, lysosomes, certtrosome, plastids (only in plants) granules, vacuoles are present in the cytoplasm. The dense part of the cytoplasm has the nucleus.
Streaming movements are carried in the cytoplasm.

(g) Asters of Centrosomes –
The role of the asters is to shift the centriole pair to the opposite, ends of the cell. In these locations the centriole pairs will pass into separate daughter cells. When cytokinesis occurs.

(h) Chromosomes –
Nucleus is lodged in the denser portion of the cytoplasm. Nucleus is covered with nudlear membrane and it has ,dense nucleoplasm. In the nucleoplasm are thread like structures called chromatin fibres. During cell division these chromatin fibres become thick and ribbon like. These fibres are called chromosomes.

The number of chromosomes is definite in each species. Human body has 46 chromosomes (23 pairs) Maize has 20 chromosomes,
Lion has – 38 chromosomes.
Mouse – 40 chromosomes
Wheat – 42 chromosomes
Monkey – 54 chromosomes
Chimpanzee – 48 chromosomes
Chromosomes carry genetic characters from parents to the ‘ offspring through the union of the sperm and the egg. Genes lie on the chromosomes lie in linear order. Genes are made up of complex chemical substance DNA (Deoxyribonucleic acid).
Genes determine the characteristics of a species.

(i) Glycogen Granules :
These are spherical or rosette shaped polysaccharide particles stored in the liver and muscle cells of animals. It serves as food for the cell.

(j) Vacuoles :
These are rounded structures present in the cell. Each vacuole is bounded by tonoplast. These vacuoles have cell- sap. They carry on various functions in the cells. The cell- sap has water and various substances in solution form. In the plants the vacuoles are large and the solution is called cell- sap.
Vacuoles are few in the animals. They do not have prominent vacuoles.

Question 5.
List any six features found both in plant and animal cells.
Answer:
Six common features in plant and animal cells are :

1. Mitochondria
2. Cell
3. Nucleus
4. Cytoplasm
5. Endoplasmic reticulum
6. Ribosomes

E. Structured / Application / Skill Type

Question 1.
Given below are the sketches of two types of cells A and B.

(a) Which one of these is a plant cell ? Give reason is support of your answer.
(b) List the cell structures which are common to both the types.
(c) Name the structures found only in plant cells and those found only in animal cells.
Answer:
(a) Fig. B is the plant cell. The presence of vacuole in Fig. B confirms the plant cell.
(b) Features common in plant and animal cells.

• Both contains the cell membrane.
• In both cell is the fundamental structural and functional i unit of life.
• the new cells are developed from a pre-existing cell.
• Both cells require nutrition for growth, repair and other activities of life.
• Nucleus is the key performer or brain of both cells.
• The structures within a cell i.e., cell organelles are concerned with different functions of both the cells.
• Both are microscopic.

(c) Structures found only in :
(i) Plant cell :

1. A definite cell wall, made up of cellulose.
2. Vacuoles prominent , one or more,
3. Usually contain plastids.
4. Centrosome is not present.

(ii) Animal cell :

1.  No cell wall.
2. Vacuoles, if any, are small and temporary.
3. Do not contain plastids.
4. Centrosome is present.

Additional Questions

A. Very Short Answer Type

Question 1.
Name the following :
(a) The organelle most vital for the survival of a cell. ………………
(b) The cell organelle concerned with transmission of hereditary characters from parents to offspring. ………………..
(c) The kind of carbohydrate particularly found in the plant cell wall ……………….
(d) Any one cytoplasmic structure found only in animal cells. …………………..
(e) Any structure other than cell wall, which is found only in plant cells. ………………..
(f) The plastids found in the cells of yellow coloured petals.
(g) The process by which living organisms obtain energy for their life activities.
(h) Cytoplasmic parts usually much larger than those, if any, in animal cells.
(i) The part of the cell which forms its supportive framework.
(j) The cell organelle that holds the key to the life of a cell.
Answer:
(a) Nucleus
(b) Nucleus
(c) Cellulose
(d) Centrosome
(e) Plastid
(f) Chromoplast
(g) Respiration
(h) vacuoles
(i) endoplasmic reticulum
(J) Nucleus

Question 2.
Fill in the blanks :
(a) The largest cell in the living world is the ……………… of ……………..
(b) Small size of cells presents a larger …………………
(c) ……………. is the part of the cell inside the cell membrane excluding the ………………
(d) The key performer or the master of a cell is it’s ……………………
Answer:
(a) egg, ostrich
(b) surface-volume
(c) cytoplasm, nucleus
(d) nucleus.

Question 3.
Given below are three statements (a, b, and c). Choose the correct alternative from those given within brackets.
(a) The additional outermost non-living layer of a plant cell is called (cell membrane/cell wall).
(b) The chromatin fibres are found in (cytoplasm/ nucleoplasm).
(c) Animal cells do not contain (centrosome/plastids).
Answer:
(a) cell wall
(b) nucleoplasm
(c) plastids.

Question 4.
The two statements (a and b) given below, are followed by four options. Select the most appropriate option in each case :
(a) A cell is best defined as
(i) the smallest part of a living being.
(ii) the body part that can be seen only under a microscope.
(iii) the starting point in the life of all organisms.
(iv) the structural and functional unit of life.
Answer:
(iv) the structural and functional unit of life.

(b) The pair correctly matched in regard to a cell organelle and it’s function, is
(i) Ribosome-Synthesis of protein
(ii) Endoplasmic reticulum-Production of ATP
(iii) Golgi body-Carries hereditary information
(iv) Mitochondria-Destroy foreign substances.
Answer:
(i) Ribosome-Synthesis of protein

(c) A cell organelle found only in plant cells is
(i) centrosome
(ii) plastid
(iii) mitochondria
(iv) ribosomes
Answer:
(ii) plastid

Question 5.
Match the organelles in Column I with the functions in Column II

Column I (Organelle)	Column II (Function)
(a) Mitochondria	(i) Rigidity to the cell
(b) Plasma membrane	(ii) Synthesis of proteins
(c) Cell wall	(iii) Intracellular digestion
(d) Chloroplasts	(iv) Differential absorption
(e) Ribosomes	(v) Trap solar energy
(f) Golgi apparatus	(vi) Production of ATP
(g) Lysosomes	(vii) Secretion of enzymes
(h) Nucleus	(viii) Division of cells

Answer:

Column I (Organelle)	Column II (Function)
(a) Mitochondria	(vi) Production of ATP
(b) Plasma membrane	(iv) Differential absorption
(c) Cell wall	(i) Rigidity to the cell
(d) Chloroplasts	(v) Trap solar energy
(e) Ribosomes	(ii) Synthesis of protein
(f) Golgi apparatus	(vii) Secretion of enzymes
(g) Lysosomes	(iii) Intracellular digestion
(h) Nucleus	(viii) Division of cells

Question 6.
Differentiate between the following pairs :
(a) Ribosomes and mitochondria
(b) Organ and organism.
(c) Organ and organelle
Answer:
(a) Ribosomes
1. The main function of ribosomes is protein synthesis to release energy in the form
Mitochondria
The main function of mitochondria is of ATP.

(b) Organ and Organism.
An organism contains a number of – organs. These organisms collectively perform the activities to keep the organism active. A number of tissues collectively perform a function in the form of an organ.

(c) Organ
1. These are the parts of a body.
2. Each organ has a specific function in the body.
Organelle
1. These are a part of the cell.
2. Organelle has a specific function in a cell.

Question 7.
Given below is an example of a certain structure and it’s special functional activity, e.g., kidney and excretion. Write similarly the functions of the following :
(a) Chloroplast and. ……………… (1998)
(b) Chromatin and …………………
(c) Nucleolus and ……………….
(d) Ribosomes and ……………… (1998, 2001)
(e) Cell wall and ……………….
Answer:
(a) Chloroplast and photosynthesis.
(b) Chromatin and hereditary information.
(c) Nucleolus and formation and storing R.N.A.
(d) Ribosomes and protein synthesis.
(e) Cell wall and protection.

Question 8.
Mention which of the following Statements are true or false. Give reason in support of your answer.
(a) Chromatin fibres and chromosomes are one and the same thing.
(b) Both cell membrane and cell wall in a plant cell are semipermeable.
(c) Bacterial cells have nuclear membrane and these are categorised as eukaryotes.
(d) Chromosomes carry genes.
(e) Larger cells have larger surface area-volume ratio.
(f) The cell wall is absent in most animal cells.
(g) Lysosomes may be considered as power houses of the cells.
Answer:
(a) False – Nucleoplasm contains chromatin fibres and they condense into short thick chromosomes.

(b) False – Cell membrane is semi-permeable whereas cell wall in a plant cell is freely permeable.

(c) False – Bacterial cells have no nuclear membrane and these are categorised as prokaryotes.

(d) True

(e) Smaller cells have larger surface area – volume ratio.

(f) False – The cell wall is absent in all animal cells.

(g) False – Mitochondria may be considered as power houses of the cells.

Question 9.
State any one aspect of cells which applies to all cells without exception.
Answer:
The new cells arise from the pre-existing cells.

Question 10.
Choose the odd one in each of the following :
Example :
Calyx, Corolla, Style, Androecium
Answer :
Style (Hint. Style is not a floral whorl)

(a) Cell wall, Plastids, Large vacuole, Centrosome (1998)
(b) Fat droplet, Glycogen, Cell membrane, Starch.
Answer:
(a) Centrosome
(b) Starch.

Question 11.
List any six features found in both plant and animal cells.
Answer:
Features common in plant and animal cells.

• The cell is the structural unit of life.
• In both cell is the functional unit of life functional cell is the functional unit of life.
• The new cells are developed from a pre-existing cell.
• Both cells require nutrition for growth, repair and other activities of life.
• Nucleus is the key performer or brain of both cells.
• The structures within a cell i.e., cell organelles are concerned with different functions of both the cells.
• Both are microscopic.

Question 12.
Do you think the cells of an elephant would be larger than the cells of a rat? Explain briefly.
Answer:
No, the cell is the basic unit of structure and function in all the living organisms. They generally remain small in size. They divide and redivide to produce more cells. It is the number of cells, not the size of the cell that serves the function of growth.

More for you Why are the cells generally small in size?
Answer:
The cells are generally of small size so that they have a larger surface area for greater diffusion of nutrients, respiratory gases and metabolic wastes.

Question 13.
Describe the gross structure of a generalised animal cell as seen under a compound microscope.
Answer:
Structure of a generalised animal cell.
Cell is the structural and functional unit of the body. All the living beings are made up of cells. These cells perform activities which contribute to the overall activities of an individual. Every organism starts it’s life as a single cell and the same cell undergoes divisions repeatedly to give ‘ rise to a large mass of cells.

The structure of an animal cell is given below :
The cell consist of two main parts i.e., cell membrane and the protoplasm.
(1) Cell membrane.
This membrane encircles the cell. It is a living membrane, having fine pores. It is semi-permeable membrane which allows only certain substances to pass through it, while preventing others. It is made up of lipo¬proteins. It also maintains the shape of the cell.

(2) Protoplasm.
It is the actual living substance, which is enclosed by the cell membrane. It is in the form of colloidal solution of organic substances and inorganic ions. The protoplasm can be differentiated into two important parts :
(a) Cytoplasm
(b) Nucleus.

(a) Cytoplasm.
It is a part of the cell inside the cell membrane and outside the nucleus. It is a semi-liquid substance. Many chemical reactions catalyzed by enzymes occur in it. The cytoplasm contains several organelles, each concerned with some specific functions. The part of cytoplasm other than the organelles is called CYTOSOL. It constitutes mainly the liquid medium. The various cell organelles present ip the animal cell are as ahead :-

(i) Endoplasmic reticulum.
It is a network complex of membranes continuous with the outer membrane of the nuclear envelop. It is found in the form of tubules, vesicles, tubules or cistenae. It may have smooth or rough surface. It provides larger surface area for a number of biochemical reactions. If provides supportive frame-work for the cell and helps in the synthesis and transport of proteins and fats.

(ii) Mitochondria.
It is a granular or filamentous body surrounded by an envelope of two membranes. Each membrane is about 60 to 80 A in thickness. The outer membrane appears to be smooth, whereas the inner is folded to form cristae. Cristae are the sites, where respiratory enzymes are produced which are responsible for the release of energy. This energy is released in the form of ATP. The released energy is used by the cell for carrying out the various cellular functions. That is why the mitochondria are called the POWER HOUSE OF THE CELL.

(iii) Golgi Apparatus.
It consists of stacks of flattened membrane bound sacs called cisternae, with a system of associated vesicles called golgi vesicles. It is involved in the synthesis and secretion of enzymes and hormones etc. It also helps in the formation of acrosome of the sperm.

(iv) Ribosomes.
They are minute, granular and spherical bodies. These are found either attached to the endoplasmic reticulum or dispersed freely in the cytoplasm. These are made up of RNA and protein. They are involved in protein synthesis with the help of three types of ribonucleic acid. There are also many types of ribosomes such as 60 S and 80 S types.

(v) Lysosomes.
These are membranous sacs bounded off from golgi bodies. They contain 40 different type of enzymes.They help in intracellular digestion. They also destroy foreign substances. When cell is old or injured, they rapidly i destroy organelles..Therefore, they are also called SUICIDE BAGS, they also help in the formation of bones by digesting cartilages.

(vi) Centrosomes.
These are located near nucleus and surrounded by microtubular or centrosphere. The centrosomes initiate and regulate cell division. They form spindle fibres with the help of asters.

(vii) Granules.
These are small particles, crystals or droplets. These are glycogen particles which serve as food for the cell.

(b) Nucleus.
It is a dense spherical body bounded by a membrane, called nuclear membrane. The space enclosed by the nuclear membrane is filled up with a transparent fluid, the nucleoplasm. Embedded within the nucleoplasm are found a number of thread- like structures called , chromosomes with genes on them.

The chromosomes are made of deoxynucleic acid (DNA), the basic hereditary material. Nucleus also contains one or more rounded bodies called nucleoli. The nucleus controls various metabolic activities 6f the cell, besides, its role in transmissions of hereditary characters from parents to offspring.
Structure of nucleus.

Question 14.
Describe any five activities of an organism which are the outcome of the cell activities.
Answer:
The following are the activities of an organism which are the outcome of the cell activities :

1. All organisms grow due to the growth in size and increase in number of cells.
2. The movement of an organism is due to contraction and relaxation of the cells.
3. The regeneration and repair of an injured part of an organism is due to cell division.
4. The organism protects itself from disease-spreading germs through certain cells like W.B.C. etc.

Question 15.
How was it proved in the case of Amoeba that the key to life of a cell is it’s nucleus?
Answer:
When an amoeba was denucleated, it was not able to control or perform the activities necessary for life and hence, died, proving that the key to life of a cell is it’s nucleus.

Question 16.
Give one main function of each of the following :
(a) Cell wall – (1990)
(b) Rbosomes – (1979, 1990, 1991, 1998)
(c) Mitochondria – (1997, 1998, 2000)
(d) Cell membrane – (1982)
(e) Golgi bodies
Answer:
(a) Cell wall – Gives shape and protection to the cell.
(b) Ribosomes – Synthesize protein.
(c) Mitochondria – Power House of the Cell (Release of Energy).
(d) Cell membrane – Regulates the entry of solutes and ions.
(e) Golgi bodies – Synthesis and secretion of enzymes and hormones.

Question 17.
Mention any three differences between a living cell and a brick in a wall, based on considering them as units of structure and function. (Hint. Growth, Cell Division, etc.)
Answer:

Living cell	Brick in a wall
1. It shows growth.	1. It can’t grow.
2. The living cell divides and redivides to give birth to new cells i.e., shows cell division.	2. It can’t show cell division.
3. Living cells require nutrition for growth, repair and different activities of life.	3. It does not require nutrition and doesn’t show any life activities.

Question 18.
Recollect colours in plants. Name the plant and it’s part where the particular colour is found. Name the organelles which contain pigments.
Answer:
The plant cells contain PLASTIDS which gives colour to different parts of the plant.
(a) The green ‘colour plastids i.e., chloroplast gives green colour to the plant parts like leaves.
(b) The chromoplast gives different colour shades like red, blue, yellow etc. i.e., to the flowers.

Question 19.
Name the following :
(a) The plastids found in the cells of yellow coloured petals.(2001)
(b) The process by which living organisms obtain energy for their life activities. (2001)
(c) A cytoplasmic organelle found only in an animal cell.(2001)
(d) The structure that initiates cell division in animal cells. (2002)
(e) The parts which act as bearers of hereditary units.(2002)
(f) The cell organelle that holds the key to the life of a cell.
Answer:
Name the following :
(a) Xanthophyll
(b) Cellular respiration
(c) Lysosomes
(d) Centrosome
(e) Chromatin fibres
(f) Nucleus

Question 20.
Complete the following statements by Ailing in the blanks with the appropriate words from the choices given in the brackets. You must rewrite the complete statement :
(a) The part of the cell associated with heredity is ………………..
(Centrosome, Chromosome, Nucleolus) (2001)
(b) The organelle concerned with the secretions of the cells such as enzymes and hormones.
(mitochondria, plastids, golgi bodies, vacuoles).
(c) The organelle which destroys foreign particles or digests worn-out cells.
(Dictyosomes, nucleus, endoplasmic reticulum, lysosomes).
(d) The organelle that produces energy by oxidation of food. (Ribosomes, chloroplast, mitochondria, centrosome).
Answer:
(a) Chromosome is the part of nucleus which is associated with heredity.

(b) Golgi bodies are the cell organelle which are concerned with the secretions of enzymes and hormones.

(c) Lysosomes are the organelles which destroy foreign particles or digest worn-out cells.

(d) Mitochondria are the organelles that produce energy by the oxidation of food.

ICSE Class 9 Biology Solutions