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Chapter 2

Cell: The Unit of Life

Class 9 - Concise Biology Selina


Multiple Choice Type

Question 1

Which one of the following cell organelles is correctly matched with its function?

  1. Ribosomes- Synthesis of proteins ✓
  2. Mitochondria- Secretion of enzymes
  3. Plasma Membrane- Freely permeable
  4. Centrosome- – Carries genes

Question 2

All life starts as-

  1. an egg
  2. a single cell ✓
  3. a gene
  4. a chromosome

Question 3

Which one of the following is found both in cells of a mango plant and a monkey?

  1. chloroplasts
  2. centrioles
  3. cell wall
  4. cell membrane ✓

Question 4

A plant cell can be identified from an animal cell by the-

  1. Absence of centrosome ✓
  2. Presence of cell membrane
  3. Presence of vacuoles
  4. None of the above

Question 5

Plant cell has a cell wall made of-

  1. Protein
  2. Fructose
  3. Cellulose ✓
  4. Fatty acids

Question 6

The cell organelle that helps in respiration of the cell is-

  1. Mitochondria ✓
  2. Lysosome
  3. Ribosome
  4. Centrosome

Very Short Answer Type

Question 1

Name the part of the cell concerned with the following?

  1. Liberation of energy
  2. Synthesis of proteins
  3. Transmission of heredity characters from parents to offspring
  4. Initiation of cell division
  5. Hydrolytic in function
  6. Entry of only certain substances into and out of the cell.

Answer

  1. Mitochondria
  2. Ribosomes
  3. Chromosomes
  4. Centrosome
  5. Lysosomes
  6. Plasma membrane/cell membrane

Question 2

State whether the following statements are true(T) or false(F):

(a) All animal cells contain a cell wall
     False

(b) The cell wall is made of protein
     False

(c) Centrosome occurs in animal cells
     True

(d) Plant cells contain large vacuoles
     True

(e) Protoplasm is the part of the cell which surrounds the nucleus
     False

(f) Genes are located in chromosomes
     True

(g) Anthocyanins are the pigments of flowers, which are dissolved in cell-sap
     True

Question 3

How many chromosome pairs are found in human cells?

Answer

Normal human body cells contain 46 chromosomes, consisting of a pair of 23, one from each parent. Out of this, 22 pairs of chromosomes are autosomes – same in both males and females. The last pair of chromosomes is the sex chromosome and differs in males (XY) and females (xx).

Question 4

What is the name of the chemical substance which constitutes the genes?

Answer

The chemical substance constituting the genes is DNA. It stands for de-oxy ribonucleic acid.

Question 5

Match the items in column ‘A’ with those in column ‘B’

Column AColumn B
VacuolesIntracellular digestion
Nucleolusrespiratory enzymes
LysosomesCovered by tonoplast
AnthocyaninDissolved in the cytoplasm
CristaeForms RNA

Answer

Column AColumn B
VacuolesCovered by tonoplast
Nucleolusforms RNA
LysosomesIntracellular digestion
AnthocyaninDissolved in the cytoplasm
CristaeRespiratory enzymes

Fill in the blanks

Question 1

Lysosomes consists of membranous sacs and secretes 40 types of digestive enzymes.

Question 2

Centriole is surrounded by microtubules, located near the nucleus.

Question 3

Very thin flexible, living membranes which is differently permeable, is called Plasma membrane.

Question 4

More than 1000 chromosomes are found in the nucleus of certain Insects

Question 5

Genes are heredity units.

Question 6

Leucoplast is a plastid which stores starch.

Short Answer Type

Question 1

It is said that the protoplasm cannot be analysed chemically. Why?

Answer

The protoplasm cannot be analysed chemically because it has complex organic and living cell organelles which can disintegrate if chemicals are added to analyse. Also due to complexity of physical and chemical properties the ultimate chemical nature of protoplasm cannot be determined.

Question 2

What is the difference between an organ and an organelle?

Answer

AttributesOrganOrganelle
SizeVisible to the naked eyes, larger in sizeMicroscopic
LocationThey are present throughout the bodyKnown as little organs, are found within the cell.
FunctionCarry out functions of the entire bodyCarry out functions within the cell
ExampleHeart, Lungs, LiverRibosomes, Endoplasmic reticulum,Golgi complex

Question 3

Do you think the cells of an elephant would be larger than the cells of a rat? Explain

Answer

Cell is the basic unit of life. Cells aggregates to form tissue, organ, organ system and ultimately organism. Elephant has more cells compared to rat. The cell size is independent of the size of the entity. The cell size of a rat and that of an elephant are the same. Within the entity, the cell size is the same, it does not differ. However, what varies is the number of cells. Number of cells in a large entity such as elephant is much more compared to a smaller entity such as a rat.

Question 4

Differentiate between the following pairs of terms-

  1. Protoplasm and cytoplasm
  2. Nucleolus and nucleus
  3. Centrosome and chromosome
  4. Cell wall and cell membrane
  5. Plant cell and animal cell
  6. Prokaryotes and eukaryotes

Answer

The differences are as follows-

Protoplasm and cytoplasm

ProtoplasmCytoplasm
Protoplasm is the living matter of the cell. The total substance of a living cell-nucleus and cytoplasmMixture of insoluble and soluble organic compounds and water wherein different cell organelles are implanted.

Nucleolus and nucleus

NucleolusNucleus
It is present in the nucleus and is round-shaped nucleoli.It is present in the cell and is a dense spherical structure. It comprises a network of thread-like structures known as chromatin fibres.

Centrosome and chromosome

CentrosomeChromosome
Cytoplasm is close to the nucleus and it is a clear are. Here spindle fibres emerge during the process of cell divisionThey contain genes or hereditary data that transfer genetic traits from parents to offspring.
Found in animal cell onlyThey are found in the nucleus of both plant and animal cell

Cell wall and cell membrane

Cell wallCell membrane
Non-living rigid layerLiving, flexible membrane and thin
Composed of celluloseComposed of lipoproteins
Permeable freelySemi-permeable

Plant cell and animal cell

Plant cellAnimal cell
Cell wall is definite and made of celluloseNo cell wall
Centrosome is absentCentrosome is present
Plastids usually presentPlastids absent

Prokaryotes and eukaryotes

ProkaryotesEukaryotes
Cells contain primitive and undefined nucleusHave a well-defined nucleus along with a nuclear membrane
Other than ribosomes, they do not contain any other cell organellePossess other cell organelles
Possess smaller ribosomesLarger ribosomes
Example – Blue-green algaeExample – Humans

Question 5

Mention three features found only in plant cells and one found only in animal cells.

Answer

Given below are features found only in plant cell-

  1. Cell wall
  2. Plastids
  3. Large vacuoles

Following are the features that are observed in animal cells only:

  1. Centrosome is observed in animal cells only. Plants do not have centrosomes.

Question 6

Why are the cells generally of a small size?

Answer

Cells are generally so little so that they can maximize their ratio of area to volume. They have to be ready to get the nutrients in and therefore the waste out quickly.The important point is that the area to the volume ratio gets smaller as the cell gets larger. Thus, if the cell grows beyond a particular limit, not enough material is going to be ready to cross the membrane fast enough to accommodate the increased cellular volume. That's why cells are so small.

Long Answer Type

Question 1

What is the cell theory? Who propounded it and when?

Answer

The Cell Theory states three major points -

  1. The cell is the smallest unit of structure of all living thing
  2. The cell is the unit of function of all living things
  3. All cells arise from pre-existing cells.

The theory was propounded in 1839 by Schwann and Schleiden. Rudolf Virchow in 1858 made an additon to the cell theory by saying that all cells arise from pre-existing cells.

Question 2

Mention the three differences between a living cell and a brick in a wall

Answer

Following are the differences between a living cell and a brick in a wall-

Living cellBrick
The living structure is non-rigidLiving structure is rigid
Contains cellulose chieflyContains soil primarily
Is functional in nature, performs critical functions pertaining to life processesNon-functional
Generously permeableImpermeable

Question 3

Name the plastid and pigment likely to be found in the cells of:

  1. Petals of sunflower
  2. Ripe tomato
  3. Skin of green tomato
  4. Cells of potato.

Answer

The following are the pigments and plastids that are found in these cells-

  1. Pigment — Xanthophyll
    Plastid — Chromoplasts
  2. Pigment — Carotene
    Plastid — Chromoplasts
  3. Pigment — Chlorophyll
    Plastid — Chloroplasts
  4. Pigment — No pigment
    Plastid — Leucoplasts

Question 4

State the major functions of the following-

  1. Plasma membrane
  2. Ribosome
  3. Lysosome
  4. Mitochondria
  5. Golgi apparatus
  6. Cytoplasm
  7. Asters of centrosome
  8. Chromosomes
  9. Glycogen granule
  10. Vacuoles

Answer

The major functions are as follows-

  1. Plasma membrane —
    (a) Separates contents of cell from its surroundings.
    (b) Regulates the entry of certain solutes and ions.
    (c) Maintains shape of the cell in animal cells.

  2. Ribosome —
    (a) Protein synthesis

  3. Lysosome —
    (a) Intracellular digestion.
    (b) Destroy foreign substances.
    (c) They are referred to as ‘suicidal bags’ as they destroy cell organelles when they turn old or are damaged.

  4. Mitochondria —
    (a) Controls the cell functions.
    (b) Referred to as ‘power house of the cell’, as energy is stored in the form of ATP.
    (c) Involved in cellular respiration to release energy.
    (d) Bearers of genes.

  5. Golgi apparatus(in animal cells) —
    (a) Synthesis and secretion of enzymes, hormones,etc.
    (b) Acrosomes of sperms are formed.

  6. Cytoplasm —
    (a) Contains organelles perform multitude of functions.
    (b) Performs all metabolic activities.

  7. Asters of centrosome —
    (a) Cell division – regulation and initiation.
    (b) Spindle fibre formation.

  8. Chromosomes —
    (a) Passes genetic characteristics from parents to offspring.

  9. Glycogen granule —
    (a) Food for cells.

  10. Vacuoles —
    (a) Stores food, water, pigments and waste products.
    (b) Renders turgidity to the plant cell.

Question 5

List any six features found both in plant and animal cells.

Answer

Given below are the following six features found both in plant and animal cells

  1. Cell membrane is present.
  2. Golgi body is present.
  3. Liquid matrix known as cytoplasm is observed in the cell.
  4. Mitochondria generates energy, is found in the cells.
  5. Ribosomes are found. They are responsible for protein synthesis.
  6. A prominent nucleus is observed.

Structured/Application/Skill Type

Question 1

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

Which one of these is a plant cell? Give reason in support of your answer. Cell the unit of life, Concise Biology ICSE Class 9.
  1. Which one of these is a plant cell? Give reason in support of your answer.
  2. List the cell structures which are common to both the types.
  3. Name the structures found only in plant cells and those found only in animal cells.

Answer

  1. Figure B is a plant cell because in Figure B, the cell has a cell wall, a large vacuole and the vacuole is seen pushing the nucleus to the periphery.

  2. Cell structures common to both the types in the figure are:
    (a) Nucleus
    (b) Mitochondria
    (c) Ribosome
    (d) Cell membrane
    (e) Lysosome
    (f) Endoplasmic reticulum
    (g) Golgi body

  3. The structures found only in plant cells are:
    (a) cell wall
    (b) Plastid
    The structures found only in animal cells are:
    (a) Centrosome

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