SCIENCE | Class 9 | Question Bank Solutions; Chapter 5: The Fundamental Unit of Life, NCERT Book Inside Questions.

Use this Question Bank to write comfortably.

1. Assertion (A): All plants and animals are made up of cells.

Reason (R): According to the cell theory, a cell is the basic unit of an organism.
Options:
(a) ✅ Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

2. Assertion (A): The cells in different parts of the human body are different.

Reason (R): Different types of functions require cells of different structures.
Options:
(a) ✅ Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

3. Assertion (A): Osmosis is a special type of diffusion through the semipermeable membrane of a cell.

Reason (R): When the concentration of the liquid medium outside the cell is higher than the concentration of the liquid inside the cell, water leaves the cell by osmosis.
Options:
(a) ✅ Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

4. Assertion (A): Mitochondria can make their own proteins.

Reason (R): One of the characteristics of mitochondria is that they have their own DNA and ribosomes.
Options:
(a) ✅ Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

5. Assertion (A): Plastids exist only in plant cells.

Reason (R): Chlorophylls in plastids are essential for photosynthesis.
Options:
(a) ✅ Both (A) and (R) are true and (R) is the correct explanation of (A).
(b) Both (A) and (R) are true, but (R) is not the correct explanation of (A).
(c) (A) is true but (R) is false.
(d) (A) is false but (R) is true.

1. Select the correct alternatives:

(i) The term ‘cell’ was given by –
(a) Robert Brown
(b) Flemming
(c) Robert Hooke ✅
(d) Leeuwenhoek

(ii) The largest cell in the human body –
(a) liver cell
(b) kidney cell
(c) nerve cell ✅
(d) muscle cell

(iii) The cell theory was proposed by –
(a) Watson and Crick
(b) Darwin and Wallace
(c) Mendel and Morgan
(d) Schleiden and Schwann ✅

(iv) In eukaryotic cell the genetic material is found in –
(a) nucleus ✅
(b) nucleolus
(c) nucleoid
(d) nucleoplasm

(v) Plasma membrane is –
(a) semipermeable ✅
(b) selective permeable
(c) impermeable
(d) permeable

(vi) Nucleolus is a site of –
(a) enzyme synthesis
(b) protein synthesis ✅
(c) ribosome synthesis
(d) mRNA synthesis

(vii) A cell placed in hypotonic solution, bursts up. It is –
(a) plant cell
(b) fungal cell
(c) bacterial cell
(d) animal cell ✅

(viii) A cell placed in solution swells up. The solution is –
(a) hypotonic ✅
(b) hypertonic
(c) isotonic
(d) animal cell

(ix) Protein storing plastid is –
(a) elaioplast
(b) aleuroplast ✅
(c) amyloplast
(d) both (b) and (a)

(x) The site of protein synthesis –
(a) chloroplast
(b) chromoplast
(c) leucoplast
(d) ribosome ✅

(xi) Lysosomes are also called –
(a) digestive bags
(b) suicide bags ✅
(c) respiratory bag
(d) none of these

(xii) Centrosome occurs in –
(a) plant cells
(b) animal cells ✅
(c) respiratory bag
(d) none of these

(xiii) Main difference between animal and plant cell is –
(a) growth ✅
(b) movement
(c) respiration
(d) nutrition

(xiv) Cell wall of plant cell is chiefly composed of –
(a) proteins
(b) hemicellulose
(c) phospholipids
(d) cellulose ✅

(xv) Well defined nucleus is absent in –
(a) prokaryotic cell ✅
(b) eukaryotic cell
(c) plant cell
(d) animal cell

(xvi) Intercellular connections in plant cells are called –
(a) plasmodesmata ✅
(b) matrix
(c) microfibrils
(d) middle lamella

(xvii) The only cell organelle seen in prokaryotic cell –
(a) lysosomes
(b) plastids
(c) mitochondria
(d) ribosomes ✅

(xviii) First living cells were observed by –
(a) Robert Hooke
(b) Robert Brown
(c) A.V. Leeuwenhoek ✅
(d) R. Virchow

(xix) Which of the following is known as “physical basis of life”? –
(a) nucleus
(b) proteins
(c) gene
(d) protoplasm ✅

(xx) Plasmolysis occurs due to –
(a) exosmosis
(b) osmosis
(c) endosmosis
(d) absorption ✅

(Note: The scientifically correct answer should be (a) exosmosis) – it seems there's a printing error.

(xxi) A cell placed in hypotonic solution will –
(a) no change in shape or size
(b) swell up ✅
(c) show plasmolysis
(d) shrink

(xxii) Solute concentration is higher in the external solution –
(a) isotonic
(b) hypotonic
(c) hypertonic ✅
(d) none

(xxiii) Which of the following is colourless plastid –
(a) chloroplasts
(b) chromoplast
(c) leucoplast ✅
(d) None of above

(xxiv) Chlorophyll is present in –
(a) thylakoid ✅
(b) stroma
(c) matrix
(d) cristae

(xxv) Which of the following is incorrect pair –
(a) nucleus – brain of the cell
(b) lysosome – secretory granules
(c) mitochondria – power house of the cell
(d) chloroplast – kitchen of the cell
Answer: (b) lysosome – secretory granules ✅

(xxvi) The infoldings in mitochondria are known as –
(a) grana
(b) cristae ✅
(c) stroma
(d) matrix

(xxvii) Mitochondria are the site of –
(a) kreb’s cycle ✅
(b) calvin cycle
(c) trapping of sunlight
(d) anaerobic respiration

(xxviii) Cell arise from pre-existing cell was stated by –
(a) Haeckel
(b) Hooke
(c) Virchow ✅
(d) Schleiden

(xxix) Cell organelle without a membrane is –
(a) nucleus
(b) ribosome ✅
(c) mitochondria
(d) chloroplast

(xxx) Silver nitrate solution is used to study –
(a) nucleus
(b) Golgi apparatus
(c) mitochondria
(d) endoplasmic reticulum ✅

(xxxi) In cells, the lipids are synthesized by –
(a) Golgi apparatus
(b) plastids
(c) rough endoplasmic reticulum
(d) smooth endoplasmic reticulum ✅

(xxxii) The proteins and lipids, essential for building the cell membrane, are manufactured by –
(a) mitochondria
(b) peroxisomes
(c) Golgi apparatus
(d) endoplasmic reticulum ✅

(xxxiii) Lysosomes arise from –
(a) Golgi apparatus ✅
(b) nucleus
(c) plastids
(d) ribosome

(xxxiv) Chromosomes are made up of –
(a) DNA
(b) protein
(c) DNA and protein ✅
(d) RNA

(xxxv) Plasmolysis in a plant cell is defined as –
(a) shrinkage of nucleoplasm
(b) breakdown of plasma membrane in hypotonic medium
(c) shrinkage of cytoplasm in hypertonic medium ✅
(d) None above

(xxxvi) Human cheek cells are commonly stained with –
(a) methylene blue ✅
(b) safranin
(c) eosine
(d) aceta carmine

(xxxvii) Safranin is a reagent that is used to stain –
(a) plasmodesmata
(b) cell wall ✅
(c) cytoplasm
(d) nucleus

(xxxviii) Coverslip is put on the mounted material on a slide very gently to –
(a) avoid oozing of glycerine
(b) avoid oozing of stain
(c) avoid entry of air bubble
(d) avoid crushing of mounted material ✅

(xxxix) The outermost layer of human cheek cells is –
(a) cell wall ✅
(b) nuclear membrane
(c) plasma membrane
(d) cytoplasm

(Note: Human cheek cells do not have a cell wall; correct answer should be (c) plasma membrane) – possible misprint.

(xl) Nucleus was discovered by –
(a) Robert Brown ✅
(b) Robert Hooke
(c) Schleiden
(d) Virchow

(xli) Which of the following is not a function of vacuole?
(a) locomotion ✅
(b) waste excretion
(c) storage
(d) providing turgidity and rigidity to the cell

(xlii) Cell wall in plant cells is made of –
(a) glycogen
(b) starch
(c) chitin
(d) cellulose ✅

(xliii) The structural and functional unit of life is –
(a) cell ✅
(b) tissue
(c) organ
(d) organ system

(xliv) Plant cells generally have –
(a) all equal sized vacuole
(b) no vacuole at all
(c) small but large number of vacuoles ✅
(d) big but less number of vacuoles

(xlv) The organelle not present in human cheek cells is –
(a) chloroplast ✅
(b) nucleus
(c) plasma membrane
(d) mitochondria

(xlvi) Iodine solution is used to –
(a) stain human cheek cells
(b) mount human cheek cells
(c) stain onion fed cells ✅
(d) mount onion peel cells

(xlvii) Who coined the term protoplasm –
(a) Robert Brown
(b) J.E. Purkinje ✅
(c) Robert Hooke
(d) W. Flemming

(xlviii) Ribosome are the site for –
(a) protein synthesis ✅
(b) sugar synthesis
(c) fat synthesis
(d) starch synthesis

(xlix) ATP stands for –
(a) amino tri phosphate
(b) adenine triphosphogly oxide
(c) adenosine triphosphate ✅
(d) amino triglycerophosphate

(l) Proteins are formed in –
(a) nucleus
(b) ribosome ✅
(c) Golgi bodies
(d) plastids

(li) The root hair absorb water by the process called –
(a) osmosis ✅
(b) plasmolysis
(c) diffusion
(d) endocytosis

(lii) While preparing a temporary mount of cheek cells, the reason behind staining the cell is –
(a) to prevent the cells from drying quickly
(b) to prevent them from decaying
(c) to disinfect them
(d) to make the organelles clearly visible ✅

(liii) Cells are stained to –
(a) make the cell turgid
(b) nourish the cell
(c) help in cell multiplication
(d) highlight the cell organelles ✅

(liv) Cell wall of plant is made up of –
(a) cellulose ✅
(b) pectine
(c) chitin
(d) lignin

2. Fill in the blanks:

(i) For preparing temporary mount of the onion peel, we stain the peel with safranin solution.

(ii) Cells are enclosed by a plasma membrane composed of lipoproteins.

(iii) In plant cell, a cell wall is present outside the cell membrane. It is composed of mainly cellulose.

(iv) Chromoplast that contain chlorophyll are called chloroplast.

(v) The primary function of leucoplast is storage.

(vi) The large central vacuole of plant cells helps to maintain the turgidity of the cell.

(vii) Due to loss of water through osmosis there is shrinkage of contents of a living plant cell. This phenomenon is known as plasmolysis.

(viii) The organelles which have their own DNA are mitochondria and plastids.

(ix) The virus are an exception of cell theory.

(x) The nuclear region of prokaryotic cells is called nucleoid.

(xi) An ostrich egg is the largest animal cell.

(xii) The movement of cytoplasm in prokaryotic cell is known as cyclosis.

(xiii) Plasmodesmata communicates two adjacent plant cells.

(xiv) The minute pores of cell wall is known as pit.

(xv) The minute pores of nuclear membrane is known as nuclear pore.

(xvi) Nucleus is known as brain of a cell.

(xvii) Cytoskeleton is called skeleton of a cell.

(xviii) 1 Å (Angstrom) = 0.1 mµ.

(xix) The Golgi bodies of plant cell is called dictyosome.

(xx) The smallest unit of chromosome is known as gene.

(xxi) Nucleosome is formed by DNA and histone.

(xxii) The disc-like structure of chromosome is called centromere.

(xxiii) The circular naked DNA of prokaryotes is known as nucleoid.

(xxiv) Mitochondria is the site of cellular respiration.

(xxv) Plastid containing the pigment chlorophyll are known as chloroplast.

3. Find out the correct answer:

(i) The circular DNA strand of prokaryotic cell is known as plasmid / nucleoid
➡️ nucleoid

(ii) In mitochondria of eukaryotic cell, protein synthesis / cellular respiration is performed in mitochondria / nucleus
➡️ cellular respiration is performed in mitochondria

(iii) All the metabolic activities of a cell are controlled by nucleus / ribosome
➡️ nucleus

(iv) Mitochondria is known as power house of a cell / protein factory of a cell
➡️ power house of a cell

(v) Golgi bodies help in cellular secretion / synthesis
➡️ secretion

(vi) The germ cell contains haploid / diploid number of chromosomes
➡️ haploid

(vii) n/2n is used to express the number of body chromosomes of an organism
➡️ 2n

(viii) The membrane of animal cell is called cell wall / plasma membrane
➡️ plasma membrane

4. Determine True / False

(i) The centrally located naked DNA and RNA of prokaryotic cell is called nucleoid.
➡️ True

(ii) The cytoplasm of prokaryotic cell is static.
➡️ False (Cytoplasm shows cyclosis or streaming)

(iii) The genetic material of eukaryotic cell is RNA.
➡️ False (It is DNA in most eukaryotes)

(iv) The ribosome is known as skeleton of a cell.
➡️ False (Cytoskeleton is the skeleton, not ribosomes)

(v) Chemically the chromosome constitute DNA and histone protein.
➡️ True

(vi) Quantasome are found in chloroplast.
➡️ True

(vii) 'Cristae' is a component of chloroplast.
➡️ False (Cristae are part of mitochondria)

✏️ Short Answer Questions

5. What is cell?
➡️ The cell is the structural and functional unit of life.

6. Define cell biology.
➡️ Cell biology is the branch of biology that studies the structure, function, and behavior of cells.

7. What is called eukaryotic cell?
➡️ Cells having a well-defined nucleus and membrane-bound organelles are called eukaryotic cells.

8. What is called prokaryotic cell?
➡️ Cells lacking a true nucleus and membrane-bound organelles are called prokaryotic cells.

9. Name the scientist who first studied living cell.
➡️ Anton van Leeuwenhoek

10. Name the smallest and largest cell.
➡️ Smallest: Mycoplasma
➡️ Largest: Ostrich egg

11. Who proposed cell theory?
➡️ Schleiden and Schwann

12. What is electron microscope?
➡️ An electron microscope uses electron beams instead of light to view ultrastructure of cells with higher magnification.

13. Is plasma membrane living or dead?
➡️ Living

14. What is called protoplasm?
➡️ The living content of a cell surrounded by the plasma membrane is called protoplasm.

15. What is called diffusion?
➡️ The movement of molecules from higher concentration to lower concentration.

16. Define osmosis.
➡️ The movement of water molecules through a semipermeable membrane from low solute to high solute concentration.

17. What is endosmosis?
➡️ Entry of water into the cell through osmosis.

18. What is exosmosis?
➡️ The exit of water from a cell through osmosis.

19. Define the following:
(i) Hypertonic solution – Solution with higher solute concentration than the cell.
(ii) Hypotonic solution – Solution with lower solute concentration than the cell.
(iii) Isotonic solution – Solution with equal solute concentration as that inside the cell.

20. What is endocytosis?
➡️ The process by which a cell takes in material by engulfing it with its membrane.

21. What is exocytosis?
➡️ The process by which a cell expels materials through the cell membrane.

22. Write the names of three types of endocytosis.
➡️ (i) Phagocytosis
➡️ (ii) Pinocytosis
➡️ (iii) Receptor-mediated endocytosis

23. What is active transport?
➡️ The movement of molecules against the concentration gradient using energy (ATP).

24. Is the plant cell wall living or dead?
➡️ Dead (non-living rigid structure)

25. Name the nucleic acids that are present in an animal cell.
➡️ DNA and RNA

26. Do the plant cell contain centriole?
➡️ No, generally centrioles are absent in plant cells.

27. Write two differences between plant cell and animal cell.
➡️ (i) Plant cells have a cell wall; animal cells do not.
➡️ (ii) Plant cells have chloroplasts; animal cells do not.

28. Two fluids in the vacuole of a plant cell:
➡️ Water, cell sap (also contains sugars, amino acids, and salts)

29. What is cytosol?
➡️ The fluid part of the cytoplasm excluding organelles.

30. What is dictyosome?
➡️ A dictyosome is a stack of flat, membrane-bound cisternae, part of the Golgi apparatus in plant cells.

31. What is tonoplast?
➡️ The membrane surrounding the central vacuole in plant cells.

32. Two structures found only in animal cells:
➡️ Centrosome, lysosomes

33. One organelle with no membrane:
➡️ Ribosome

34. What happens when:
(a) Plasma membrane breaks down ➝ Cell dies or becomes non-functional.
(b) Golgi apparatus removed ➝ Protein packaging & secretion stops.
(c) Red blood cell in concentrated salt ➝ Shrinks (crenation due to osmosis).
(d) Dry grapes in water then sugar ➝ Swell first (endosmosis), shrink later (exosmosis).

35. Why is plasma membrane selectively permeable?
➡️ Because it allows only certain substances to pass through.

36. Molecules in chromatin:
➡️ DNA and histone proteins

37. Function of cell wall:
➡️ Provides structure, protection, and support.

38. Function of plasma membrane:
➡️ Regulates movement of substances in and out of the cell.

39. Process for O₂ movement:
➡️ Diffusion

40. What are genes?
➡️ Units of heredity made of DNA that carry genetic information.

41. What is nucleoid?
➡️ Region in prokaryotic cells where DNA is located.

42. Site of photosynthesis:
➡️ Chloroplast

43. Why viruses don’t show life characteristics?
➡️ Because they lack cellular structure and only reproduce inside hosts.

44. Function of rough ER:
➡️ Protein synthesis and transport.

45. Function of smooth ER:
➡️ Synthesis of lipids and detoxification.

46. Organelle functions:
(a) Lysosome – Suicidal bag
(b) Mitochondria – Power house
(c) Nucleus – Brain of the cell
(d) Ribosome – Kitchen of the cell

47. Proteins are synthesized:
➡️ In ribosomes

48. Two features of prokaryotic cells:
➡️ No membrane-bound nucleus, circular DNA

49. Name the following:
(a) Nucleic acid in nucleus ➝ DNA
(b) Organelle with chlorophyll ➝ Chloroplast
(c) Rich in digestive enzymes ➝ Lysosome
(d) Own genetic material ➝ Mitochondria

50. Suicidal bag of the cell:
➡️ Lysosome

51. What if no Golgi apparatus?
➡️ No protein packaging, secretion, or lysosome formation – cell won’t function properly.

52. Described Golgi apparatus:
➡️ Camillo Golgi

53. Functional unit of DNA:
➡️ Gene

B. Short Type Questions (Marks: 2/3 each)

1. Why are lysosomes known as suicide bags?
➡️ Lysosomes contain powerful digestive enzymes. When they burst, these enzymes digest the cell itself, hence they are called "suicide bags."

2. How is a prokaryotic cell different from a eukaryotic cell?
➡️ Prokaryotic cell lacks a true nucleus and membrane-bound organelles, while eukaryotic cells have both.

3. Which organelle is known as power house of the cell? Why?
➡️ Mitochondria, because they produce energy in the form of ATP during respiration.

4. Distinguish between plant cell and animal cell.
➡️

Plant Cell

Has a cell wall made of cellulose.
Fixed, rectangular shape.
Contains chloroplasts for photosynthesis.
Has one large central vacuole.
Plastids (like chloroplasts) are present.
Stores energy as starch.
Centrioles are usually absent.
Lysosomes are rare.

Animal Cell

No cell wall, only a cell membrane.
Irregular or round shape.
No chloroplasts.
Has small, many vacuoles (or absent).
Plastids are absent.
Stores energy as glycogen.
Centrioles are present.
Lysosomes are common.

5. State two conditions required for osmosis.
➡️ (i) Presence of a semipermeable membrane
➡️ (ii) Difference in concentration of solvent (water) on both sides

6. What are the functions of three types of plastids in plants?
➡️

Chloroplasts: Photosynthesis
Chromoplasts: Give color to fruits and flowers
Leucoplasts: Store food like starch, protein, fats

7. Draw an animal cell and label the following: (a) Nucleus
(b) Cell membrane
(c) Golgi apparatus
(d) Mitochondria
Ans:

Correction: Mitochondria in place of Su10th ER.

8. Explain the structure and function of Golgi bodies.
➡️ Structure: Stack of membrane-bound sacs (cisternae).
➡️ Function: Modifies, sorts, and packages proteins and lipids for secretion or delivery.

9. What are ribosomes? Where are they located? What is their function?
➡️ Ribosomes are small granules made of RNA and proteins.
➡️ Found free in cytoplasm or attached to rough ER.
➡️ Function: Protein synthesis.

10. Draw a neat labelled diagram of plant cell and label its following parts:
Ans:

11. A few dried raisins are kept in water for a few hours. Answer the following –
(a) What changes could be observed in raisins?
→ Raisins swell up.
(b) Name the process involved.
→ Endosmosis
(c) Define the process involved.
→ Endosmosis is the movement of water into the cell when it is placed in a hypotonic solution, causing the cell to swell.

12. Write at least four significance of plant cell wall.
→ (i) Provides structural support and protection
→ (ii) Maintains cell shape
→ (iii) Prevents bursting of cell in hypotonic solutions
→ (iv) Helps in the transport of substances between cells

13. What are the main points of cell theory which was proposed by Schleiden and Schwann?
→ (i) All living organisms are composed of cells.
→ (ii) The cell is the basic unit of structure and function in living organisms.

14. What is the function of centrosome? Name the structure found in plant cell to do the same function.
→ Function: Centrosome helps in spindle formation during cell division.
→ In plant cells, spindle fibres are formed without centrosomes (anastral spindle), using microtubule organizing centers.

15. Briefly describe the structure and function of peroxisome.
→ Structure: It is small, membrane-bound organelles.
→ Function:It is involved in the breakdown of fatty acids and detoxification of hydrogen peroxide.

16. Why is nucleus called brain of the cell?
→ Because it controls all cellular activities and contains genetic material (DNA) responsible for inheritance and protein synthesis.

17. Describe briefly the structure of mitochondria and mention the function of it.
→ Structure: It is double membrane, inner membrane folded into cristae, has its own DNA and ribosomes.
→ Function: It is powerhouse of the cell and also site of cellular respiration and energy (ATP) production.

18. What are plastids? How many types of plastids are found in plant cell and mention the colour of different plastids.
→ Plastids are double-membrane organelles found in plant cells.
→ Types:
(i) Chloroplast – green (contains chlorophyll)
(ii) Chromoplast – red, yellow, orange (contains carotenoids)
(iii) Leucoplast – colourless (stores starch, oils, proteins)

19. Write down three living and three non-living parts of cell.
→ Living: Nucleus, cytoplasm, mitochondria
→ Non-living: Cell wall, vacuole (sap), stored food (like starch granules)

20. What are the advantages of selectively permeable membrane?
→ Allows essential substances in and waste out
→ Maintains internal environment
→ Prevents entry of harmful substances

21. Differentiate between active transport and diffusion (point-wise):

Active Transport

Requires energy (ATP) to occur.
Molecules move against the concentration gradient (from low to high concentration).
Specific carrier proteins are involved.
Example: Sodium-potassium pump in cells.

Diffusion

Does not require energy.
Molecules move along the concentration gradient (from high to low concentration).
No special carriers are needed.
Example: Oxygen or carbon dioxide exchange in lungs.

22. Differentiate between osmosis and diffusion (point-wise):

Osmosis

Involves movement of water molecules only.
Occurs through a semipermeable membrane.
Water moves from a dilute to a concentrated solution.
Essential for maintaining cell turgidity in plants.

Diffusion

Involves movement of any gas or solute (not just water).
Can occur with or without a membrane.
Moves from high to low concentration.
Helps in exchange of gases like O₂ and CO₂.

23. Main differences between endocytosis and exocytosis (point-wise):

Endocytosis

The process of taking materials into the cell.
The cell membrane folds inward to form a vesicle.
Includes phagocytosis (solids) and pinocytosis (liquids).
Example: White blood cells engulfing bacteria.

Exocytosis

The process of expelling materials out of the cell.
Vesicles fuse with the cell membrane to release contents.
Common in secretion of enzymes or hormones.
Example: Salivary glands releasing saliva.

		24. What would happen when eukaryotic cells are placed in hypotonic, hypertonic and isotonic solution?

→ Hypotonic: Cell swells due to water intake (may burst in animal cells).
→ Hypertonic: Cell shrinks due to water loss (plasmolysis in plant cells).
→ Isotonic: No net water movement; cell remains unchanged.

25. Describe briefly the structure of nucleus and write at least two important functions of it.
→ Structure: It is double membrane-bound, contains nucleoplasm, chromatin, and nucleolus.
→ Functions:

Controls all cell activities.
Carries genetic material (DNA) for inheritance and protein synthesis.

26. What will happen in a cell if its nucleus is removed? Give reasons in support of your answer.
→ The cell will lose control of all its activities and will eventually die, as the nucleus controls metabolism and reproduction.

27. Explain why do spinach look green, ripe papaya yellow and edible part of watermelon red?
→ Due to presence of different pigments:

Spinach: Chlorophyll (green)
Papaya: Carotenoids (yellow/orange)
Watermelon: Lycopene (red)

28. Draw a neat labelled diagram of typical prokaryotic cell.
Ans:

29. Plasma membrane is permeable to water. How does a cell show endosmosis or exosmosis?
→ Endosmosis: When a cell is placed in a hypotonic solution, water enters the cell through osmosis.
→ Exosmosis: When placed in a hypertonic solution, water exits the cell causing shrinkage.

30. Why does the skin of your fingers shrink when you wash clothes for a long time?
Answer:
When you wash clothes for a long time, your fingers are soaked in water. Due to osmosis, water moves into the skin cells, and the outer layer of the skin absorbs water and swells. However, the underlying layers do not swell equally, causing the skin to wrinkle or shrink.

31. Why is endocytosis found in animals only?
Answer:
Endocytosis is found only in animals because they do not have a rigid cell wall like plants. The flexible plasma membrane of animal cells can invaginate to form vesicles for the intake of materials through endocytosis. Plant cells cannot perform endocytosis efficiently due to their rigid cell walls.

32. A person takes concentrated solution of salt. After some time he starts vomiting. What is the phenomenon responsible for such a situation? Explain.
Answer:
The phenomenon is osmosis.
When a person takes a concentrated salt solution, the high salt concentration in the stomach draws water out of the surrounding cells by osmosis. This sudden change in the osmotic balance irritates the stomach lining and can cause vomiting as a defensive mechanism to remove the excess salt.

33. If you are provided with some vegetables to cook, you generally add salt into vegetables during cooking process. After adding salt, vegetables release water. What mechanism is responsible for this?
Answer:
The mechanism responsible is osmosis.
When salt is added to vegetables, it creates a hypertonic environment outside the vegetable cells. As a result, water from inside the cells moves out through the semi-permeable membrane by osmosis, making the vegetables release water.

34. What are consequences of the following conditions?
(a) A cell having higher water concentration than the surrounding medium.
Answer: Water will move out of the cell (exosmosis), and the cell will shrink or become plasmolysed.

(b) A cell having low water concentration than the surrounding medium.
Answer: Water will move into the cell (endosmosis), and the cell may swell or even burst if excess water enters.

(c) A cell having equal water concentration than the surrounding medium.
Answer: There is no net movement of water. The cell remains in equilibrium and retains its shape.

35. Give two differences between Prokaryotic and Eukaryotic cell.
Answer:

Prokaryotic Cell	Eukaryotic Cell
• No well-defined nucleus	• Has a well-defined nucleus
• No membrane-bound organelles	• Has membrane-bound organelles

36. Which organelle is known as the powerhouse of the cell? Why?
Answer:
Mitochondria are known as the powerhouse of the cell because they produce energy in the form of ATP (adenosine triphosphate) through the process of cellular respiration.

37. Why are mitochondria known as the powerhouses of the cell?
Answer:
Mitochondria are called the powerhouses of the cell because they convert glucose and oxygen into ATP during cellular respiration. This energy is used by the cell to perform various functions.

C. Essay Type Questions

1. Draw a well labelled diagram of animal cell and mention one function of the main cell organelles.
Ans:

Correction: Mitochondria in place of Su10th ER

2. Answer the following questions:

(a) Present only in plant cell, provide strength and rigidity to the cell.
→ Cell wall

(b) It is site for lipids synthesis and helps in detoxification of drugs.
→ Smooth Endoplasmic Reticulum (SER)

(d) It helps in the formation of lysosomes.
→ Golgi apparatus

(e) It imparts colour to the fruit and flowers.
→ Chromoplast

Q.3: Carry out the following osmosis experiment:

[Try to do the experiment practically at home]

🔬 Osmosis Experiment Using Potato Cups

Materials Needed:

4 peeled potato halves
Knife or scooper (to hollow them)
Water
Sugar
Salt
One boiled potato half

Procedure:

Scoop out the center of each peeled potato half to make potato cups.
Take one of the potato cups and boil it. (Label it as Cup D.)
Place all four cups in a tray containing water.
Set up the cups as follows:
- Cup A – Leave it empty
- Cup B – Add 1 teaspoon of sugar
- Cup C – Add 1 teaspoon of salt
- Cup D – Add 1 teaspoon of sugar (but this cup is made from a boiled potato)
Leave the setup undisturbed for two hours.

Observation:

After 2 hours, observe the water collected inside the hollowed parts of the potato cups.

Conclusion:

You will observe that:

Water gathers in Cups B and C.
No water gathers in Cups A and D.

This demonstrates the process of osmosis.

(i) Explain why water gathers in the hollowed portion of B and C cup?

Answer:
Water gathers in the hollowed portions of potato cups B and C because osmosis occurs. In these cups:

Cup B has sugar and Cup C has salt.
These substances create a hypertonic solution inside the cups.
Water from the surrounding container (hypotonic solution) moves through the semi-permeable membrane (potato cells) into the cup to balance the concentration.

(ii) Why is potato A necessary for this experiment?

Answer:
Potato A (kept empty) acts as a control. It helps to:

Show that water does not gather in the hollowed part without any solute.
Compare the effect of solutes (sugar/salt) on water movement.
Confirm that osmosis requires a concentration difference.

(iii) Explain why water doesn’t gather in the hollowed-out portions of A and D.

Answer:

Cup A: It contains no solute, so no concentration gradient is created. Hence, no osmosis occurs.
Cup D: Although it has sugar, it is made from boiled potato. Boiling kills the cells and destroys the semi-permeable membrane, which is essential for osmosis. So water doesn't move inside.

Case Study Based Questions

1. A cell is a mass of cytoplasm...

(i) What is a cell?

Answer:
A cell is the structural and functional unit of life. It is a mass of cytoplasm surrounded by a cell membrane and carries out all life processes.

(ii) What is the smallest structural unit of living matter?

Answer:
The cell is the smallest structural and functional unit of living matter.

(iii) Which are the main constituents of a cell?

Answer:
The main constituents of a cell are:

Cell membrane
Cytoplasm
Nucleus
Cell organelles (like mitochondria, plastids, etc.)

2. Mitochondria are membrane-bound cell organelles...

(i) What are mitochondria?

Answer:
Mitochondria are double membrane-bound organelles present in most eukaryotic cells that generate energy through cellular respiration.

(ii) Where is the energy, produced by mitochondria, stored?

Answer:
The energy is stored in a molecule called Adenosine Triphosphate (ATP).

(iii) What is called the ‘Powerhouse of the cell’?

Answer:
Mitochondria are called the Powerhouse of the cell because they produce most of the cell’s energy.

3. Plastids are double-membrane organelles...

(i) What are plastids?

Answer:
Plastids are double membrane-bound organelles found in plant cells and algae. They are involved in functions like photosynthesis and food storage.

(ii) Can plastids exist in animal’s cells?

Answer:
No, plastids are not found in animal cells. They are present only in plant cells and algae.

(iii) What are the main functions of plastids?

Answer:

Chloroplasts: Photosynthesis
Chromoplasts: Pigment synthesis and color to flowers/fruits
Leucoplasts: Storage of starch, oils, and proteins

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