CBSE Class 9 Science The Fundamental Unit of Life Sure Shot Questions Set 02

Question. Mitochondria stores energy in from of
(A) Heat energy
(B) ATP
(C) light energy
(D) none of the above
Answer : B

Question. Which of the following is called as ‘Suicidal bags’ ?
(A) Centrosome
(B) Lysosome
(C) Microsome
(D) Mesosomes
Answer : B

Question. Which of the following organelle is the site of Kreb cycle?
(A) Ribosome’s
(B) Lysosomes
(C) eukaryotic cells
(D) Nucleus
Answer : C

Question. Mitochondria are absent in
(A) Prokaryotic cells
(B) RBC of mammals
(C) eukaryotic cells
(D) (A) and (B) Both
Answer : D

Question. Eukaryotic ribosomes are
(A) 30s
(B) 50s
(C) 80s
(D) 70s
Answer : C

Question. Tonoplast is the membrane surrounding the
(A) cytoplasm
(B) vacuole
(C) nucleus
(D) mitochondria
Answer : B

Question. The ATP synthesizing units of Mitochondria are
(A) Oxysomes
(B) peroxysomes
(C) glyoxysomes
(D) lysosomes
Answer : A

Question. What is more abundant in smooth endoplasmic reticulum?
(A) Cistemae and vesicle
(B) Tubules
(B) Tubules and vesicles
(C) Cistemae
Answer : B

Question. Mitochondria are concerned with
(A) Kreb cycle
(B) C, cycle
(C) glycolysis
(D) none of the above
Answer : A

Question. Lipid synthesis is performed by
(A) Rough ER
(B) smooth ER
(C) both of above
(D) none of the above
Answer : B

Question. Who observed Mitochondria at first?
(A) Porter
(B) Palade
(C) Koliker
(D) Camilo Golgi
Answer : C

Question. Striking difference between a plant cell and an animal cell is due to the presence
(A) mitochondria
(B) plasma membrane
(C) cell wall
(D) ribosome
Answer : C

Question. In prokaryotic cell
(A) nucleus is developed
(B) membrane bounded organelles are present
(C) double membrane bounded organelles are absent
(D) none of these
Answer : C

Question. Lysosomes are responsible for
(A) protein synthesis
(B) digestion of organic molecules
(C) fat synthesis
(D) fat emulsification
Answer : B

Question. Plastids that are white in colour (Pigment free)
(A) chloroplast
(B) lysosome
(C) leucoplast
(D) Chromoplast
Answer : C

Question. A typical plant cell contains
(A) cell well
(B) plastids
(C) large vacuole
(D) all of the above
Answer : D

1. Who expanded cell theory by suggesting that all cells arise from pre-existing cells? [1 Mark]

Answer:
1. Rudolf Virchow expanded the cell theory in 1855.
2. He suggested that all cells arise from pre-existing cells (Omnis cellula e cellula).

Teacher's Note:
a) Rudolf Virchow added the third tenet to the original cell theory proposed by Schleiden and Schwann.
b) This principle is fundamental in understanding cell division and continuity of life.

2. In which year electron microscope was invented? [1 Mark]

Answer:
1. The electron microscope was invented in the year 1931.
2. It was designed by Max Knoll and Ernst Ruska.

Teacher's Note:
a) The invention of the electron microscope revolutionized cell biology by allowing high-resolution imaging of subcellular structures.
b) It uses a beam of electrons instead of light.

3. Name the book in which Robert Hooke published his observations about cork cells. [1 Mark]

Answer:
1. Robert Hooke published his observations in his book titled Micrographia.
2. The book was published in the year 1665.

Teacher's Note:
a) Robert Hooke coined the term 'cell' while observing thin slices of cork under a primitive microscope.
b) Micrographia contains drawings and descriptions of various microscopic observations.

4. Who discovered nucleus in the cell? [1 Mark]

Answer:
1. The nucleus in the cell was discovered by Robert Brown.
2. He made this discovery in the year 1831.

Teacher's Note:
a) Robert Brown was a Scottish botanist who studied orchid cells.
b) Do not confuse Robert Brown (discoverer of nucleus) with Robert Hooke (discoverer of cells).

5. Name the two postulates of the cell theory. [2 Marks]

Answer:
1. All plants and animals are composed of cells, and the cell is the basic unit of life.
2. All cells arise from pre-existing cells.

Teacher's Note:
a) Originally proposed by Matthias Schleiden and Theodor Schwann, and later expanded by Rudolf Virchow.
b) It forms the foundational principle of modern biology.

6. Who coined the term 'protoplasm'? [1 Mark]

Answer:
1. The term 'protoplasm' was coined by Johannes Evangelista Purkinje.
2. He coined this term in the year 1839 for the fluid substance of the cell.

Teacher's Note:
a) Protoplasm refers to the living content of a cell surrounded by the plasma membrane.
b) It comprises cytoplasm and nucleoplasm.

7. Name the largest cell? [1 Mark]

Answer:
1. The largest isolated single cell is the egg of an ostrich.

Teacher's Note:
a) Cell size varies greatly depending on the function.
b) Ostrich egg serves as a classic example of a massive single cell visible to the naked eye.

8. Name the world's smallest cell. [1 Mark]

Answer:
1. The world's smallest cells are Mycoplasma (also known as PPLO - Pleuropneumonia-like organisms).

Teacher's Note:
a) Mycoplasmas are bacteria that completely lack a cell wall.
b) Their size can be as small as 0.1 micrometer.

9. Name the smallest cell in human body. [1 Mark]

Answer:
1. The smallest cell in the human body is the sperm cell.

Teacher's Note:
a) Sperm cells are highly compact male gametes designed for motility.
b) Red blood cells are also extremely small, but sperm cells represent the absolute minimum volume.

10. Name the biggest cell in human body. [1 Mark]

Answer:
1. The biggest (or largest) cell in the human body is the female ovum (egg cell).

Teacher's Note:
a) Ovum contains stored nutrients to support early embryonic development.
b) It is visible without a microscope.

11. Name the longest cell in human body. [1 Mark]

Answer:
1. The longest cell in the human body is the nerve cell or neuron.

Teacher's Note:
a) Neurons can reach lengths of over a meter in human beings.
b) They are specialized for transmitting nerve impulses across long distances.

12. Name the cell in human body which cannot reproduce. [1 Mark]

Answer:
1. Mature mammalian red blood cells (erythrocytes) cannot reproduce (divide).

Teacher's Note:
a) Mature mammalian RBCs lose their nucleus and other organelles to accommodate more hemoglobin.
b) Without a nucleus, they cannot undergo cell division.

13. Give an example of anucleate cell i.e. cell without nucleus. [1 Mark]

Answer:
1. A mature mammalian red blood cell (RBC) or a plant sieve tube cell.

Teacher's Note:
a) Anucleate cells lack a true nucleus at maturity.
b) Sieve tube elements rely on adjacent companion cells for metabolic regulation.

14. Give an example of cells containing two nuclei (Binucleate). [1 Mark]

Answer:
1. Paramecium (which typically has a macronucleus and a micronucleus) is a classic example.

Teacher's Note:
a) Binucleate cells contain two distinct nuclei within a single cell body.
b) Certain liver cells (hepatocytes) can also be binucleate.

15. Give examples of cells which are muti-nucleate (i.e. having many nuclei). [1 Mark]

Answer:
1. Striated muscle cells (skeletal muscle fibers) and Opalina are examples of multinucleate cells (syncytium).

Teacher's Note:
a) Multinucleate cells are formed either by the fusion of multiple cells or nuclear division without cytokinesis.
b) They are also known as syncytia or coenocytes.

16. What is the plasma membrane composed of? [1 Mark]

Answer:
1. The plasma membrane is primarily composed of lipids (phospholipids) and proteins.

Teacher's Note:
a) Carbohydrates are also attached to lipids and proteins on the outer surface.
b) It provides flexibility and structural integrity to the cell.

17. Who proposed fluid-mosaic model of cell or plasma membrane? [1 Mark]

Answer:
1. The fluid-mosaic model of the plasma membrane was proposed by S.J. Singer and G.L. Nicolson in 1972.

Teacher's Note:
a) This model describes the plasma membrane as a fluid phospholipid bilayer with mosaic proteins embedded in it.
b) It is the most widely accepted model of membrane structure.

18. Is plasma membrane permeable or selectively permeable? [1 Mark]

Answer:
1. The plasma membrane is selectively permeable.

Teacher's Note:
a) It allows the entry and exit of only selected substances while preventing others.
b) This property helps maintain the internal cellular environment (homeostasis).

19. What are different types transport of components across cell membrane? [2 Marks]

Answer:
1. Passive transport (movement without energy expenditure, e.g., diffusion and osmosis).
2. Active transport (movement requiring cellular energy in the form of ATP against concentration gradient).

Teacher's Note:
a) Passive transport occurs along the concentration gradient.
b) Active transport utilizes carrier proteins and energy.

20. Define Passive Transport. [1 Mark]

Answer:
1. Passive transport is the movement of molecules across the cell membrane along the concentration gradient without the use of cellular energy (ATP).

Teacher's Note:
a) It includes simple diffusion, facilitated diffusion, and osmosis.
b) Molecules move from a region of higher concentration to a region of lower concentration.

21. What is diffusion? [1 Mark]

Answer:
1. Diffusion is the spontaneous movement of a substance from a region of higher concentration to a region of lower concentration until it is evenly distributed.

Teacher's Note:
a) It can occur across a membrane or freely in gases and liquids.
b) No metabolic energy is expended during diffusion.

22. Define Osmosis. What are different types of osmosis? Give examples of osmosis. [3 Marks]

Answer:
1. Osmosis is the movement of water molecules from a region of higher water concentration (dilute solution) to a region of lower water concentration (concentrated solution) through a semi-permeable membrane.
2. The two main types of osmosis are Endosmosis (movement of water into the cell) and Exosmosis (movement of water out of the cell).
3. Examples include absorption of water by plant roots from the soil and swelling of dried raisins when placed in water.

Teacher's Note:
a) Osmosis is a special case of diffusion involving water molecules.
b) It plays a crucial role in maintaining water balance in plant and animal cells.

23. What is plasmolysis? [1 Mark]

Answer:
1. Plasmolysis is the shrinkage or contraction of the protoplasm of a plant cell away from its cell wall due to loss of water via exosmosis when placed in a hypertonic solution.

Teacher's Note:
a) It occurs exclusively in plant cells due to the presence of a rigid cell wall.
b) It demonstrates the semi-permeable nature of the plant cell membrane.

24. What would happen if the plasma membrane ruptures or breaks down? [2 Marks]

Answer:
1. The cell will lose its structural integrity and organization.
2. Cellular contents will spill out, leading to cell death and lysis.

Teacher's Note:
a) The plasma membrane is vital for separating internal cellular machinery from the external environment.
b) Its breakdown disrupts all metabolic processes.

25. What do you mean by Endocytosis? How does an Amoeba obtain its food? [2 Marks]

Answer:
1. Endocytosis is the process by which a cell engulfs extracellular material using its flexible plasma membrane.
2. Amoeba obtains its food through a type of endocytosis called phagocytosis, extending pseudopodia around the food particle to form a food vacuole.

Teacher's Note:
a) The flexibility of the cell membrane enables unicellular organisms like Amoeba to capture food.
b) It is an active process requiring energy.

26. Define Exocytosis. [1 Mark]

Answer:
1. Exocytosis is the process by which a cell expels waste materials or secretory products by fusion of vesicles with the plasma membrane.

Teacher's Note:
a) It is also known as cell vomiting or reverse pinocytosis.
b) It helps in waste removal and secretion of hormones or enzymes.

27. Why are lysosomes known as suicide bags? [2 Marks]

Answer:
1. Lysosomes contain powerful digestive enzymes capable of breaking down all organic material.
2. When the cell gets damaged or disturbed, lysosomes may burst, and their digestive enzymes digest their own cellular components, leading to cell destruction.

Teacher's Note:
a) They are membrane-bound sacs filled with digestive enzymes made by RER.
b) This autolysis mechanism helps in clearing out damaged cells during development or injury.

28. What happens to a cell (plant cell or animal cell) when placed in the following solutions:
(a) Hypotonic solution
(b) Isotonic solution
(c) Hypertonic solution [3 Marks]

Answer:
1. (a) Hypotonic solution: Water enters the cell by endosmosis, causing the cell to swell and potentially burst (animal cell) or become turgid (plant cell).
2. (b) Isotonic solution: There is no net movement of water; the cell retains its original size and shape.
3. (c) Hypertonic solution: Water leaves the cell by exosmosis, causing the cell to shrink (crenation in animal cells, plasmolysis in plant cells).

Teacher's Note:
a) Hypotonic solutions have lower solute concentration than the cell interior.
b) Isotonic solutions have equal solute concentration, while hypertonic solutions have higher solute concentration.
c) Plant cell walls prevent bursting in hypotonic solutions due to turgor pressure.

29. Place a de-shelled egg in water for five minutes. What do you observe? (Note: De-shelled egg means, the shell of an egg is removed by dissolving it in dilute hydrochloric acid. The shell is mostly calcium carbonate. A thin outer skin now encloses the egg.)
What will happen if a de-shelled egg in a concentrated salt solution for 5 minutes? [3 Marks]

Answer:
1. When a de-shelled egg is placed in water, water enters the egg by endosmosis because the concentration of water is higher outside than inside, causing the egg to swell.
2. When the swollen egg is placed in a concentrated salt solution, water moves out of the egg by exosmosis due to the higher solute concentration outside, causing the egg to shrink.
3. This demonstrates the process of osmosis across the semi-permeable cell membrane of the egg.

Teacher's Note:
a) Endosmosis occurs when water molecules move into a cell placed in a hypotonic solution.
b) Exosmosis occurs when water molecules move out of a cell placed in a hypertonic solution.
c) A common student mistake is confusing the direction of water movement based on solute versus solvent concentrations.

30. Put dried raisins in plain water and leave them for some time. Then place them in concentrated solution of sugar or salt. What do you observe in both cases? [3 Marks]

Answer:
1. When dried raisins are placed in plain water, they absorb water through endosmosis and swell up, becoming plump.
2. When these swollen raisins are subsequently placed in a concentrated sugar or salt solution, they lose water via exosmosis and shrink or shrivel.
3. This happens because water moves from a region of higher water concentration to a region of lower water concentration through a semi-permeable membrane.

Teacher's Note:
a) Raisins act as an ideal model for demonstrating plant cell osmosis due to their semi-permeable skin.
b) Students often forget to specify that the surrounding solution concentration dictates the direction of osmosis.
c) Always mention both endosmosis and exosmosis clearly when explaining the two phases of this experiment.

31. Viruses are [1 Mark]
(A) Uni cellular micro-organisms
(B) Bi-Cellular micro-organisms
(C) Multi-cellular micro-organisms
(D) Non-cellular micro-organisms

Answer: (D) Non-cellular micro-organisms

1. Viruses lack cellular structure, cytoplasm, and organelles.
2. They consist only of genetic material surrounded by a protein coat.
3. Hence, the correct option is (D).

Teacher's Note:
a) Viruses are considered a border line between living and non-living things as they show no life characteristics outside a host body.
b) They cannot be classified as unicellular since they lack a true cell membrane and cellular machinery.

32. Who is known as Father of Biology? [1 Mark]

Answer: Aristotle is known as the Father of Biology.

Teacher's Note:
a) Aristotle made pioneering contributions to the classification and study of living organisms.
b) Remember to distinguish between the father of biology, botany (Theophrastus), and zoology (Aristotle).

33. Who discovered Golgi apparatus? [1 Mark]

Answer: Camillo Golgi discovered the Golgi apparatus.

Teacher's Note:
a) Camillo Golgi observed this cellular structure using the black reaction staining method.
b) It is named directly after its discoverer.

34. Which cell organelle is known as "protein factory"? [1 Mark]

Answer: Ribosome is known as the protein factory of the cell.

Teacher's Note:
a) Ribosomes are the primary sites for protein synthesis in both prokaryotic and eukaryotic cells.
b) They can be found floating freely in the cytoplasm or attached to the rough endoplasmic reticulum.

35. What is the energy currency of the cell called? [1 Mark]

Answer: Adenosine triphosphate (ATP) is called the energy currency of the cell.

Teacher's Note:
a) ATP is synthesized in the mitochondria during cellular respiration.
b) The cell uses stored energy in ATP to carry out various chemical and mechanical life processes.

36. When chromosomes are visible in the nucleus? [1 Mark]

Answer: Chromosomes are visible only when the cell is about to divide.

Teacher's Note:
a) During interphase, genetic material exists in the form of thread-like chromatin material.
b) Chromatin condenses into distinct, rod-shaped chromosomes only during cell division.

37. Which of the following is NOT involved in the synthesis of proteins? [1 Mark]
(A) rough ER
(B) smooth ER
(C) Golgi body
(D) ribosomes

Answer: (B) smooth ER

1. Smooth endoplasmic reticulum is primarily involved in the synthesis of lipids, fats, and steroid hormones.
2. Rough ER, ribosomes, and Golgi bodies are directly involved in protein synthesis and modification.
3. Hence, the correct option is (B).

Teacher's Note:
a) Smooth ER lacks ribosomes on its surface, distinguishing it from rough ER.
b) Pay close attention to the word NOT in the question stem to avoid misinterpretation.

38. Are plastids present in all cells? What are its types? [2 Marks]

Answer:
1. No, plastids are present only in plant cells and Euglenoids, and are absent in animal cells.
2. Plastids are of three main types: Chloroplasts (containing chlorophyll), Chromoplasts (containing colored pigments other than chlorophyll), and Leucoplasts (colorless plastids).

Teacher's Note:
a) Chloroplasts are essential for photosynthesis in plants.
b) Leucoplasts primarily store materials such as starch, oils, and proteins in plant cells.

39. Name the sac like structure which form the grana? [1 Mark]

Answer: Thylakoids are the sac-like structures that stack together to form the grana inside chloroplasts.

Teacher's Note:
a) Grana are interconnected stacks of membrane-bound thylakoid sacs.
b) The light-dependent reactions of photosynthesis take place on the thylakoid membranes.

40. What are the conditions for osmosis? [2 Marks]

Answer:
1. There must be two solutions of different concentrations separated by a semi-permeable membrane.
2. There must be a difference in the concentration of water molecules (solvent potential) between the two sides of the membrane.

Teacher's Note:
a) Osmosis is a special case of diffusion involving the movement of solvent molecules.
b) A semi-permeable membrane is compulsory for osmosis to take place.

41. Will the temperature have any effect on the process of the osmosis? [1 Mark]

Answer: Yes, an increase in temperature increases the rate of osmosis by increasing the kinetic energy of water molecules.

Teacher's Note:
a) Higher kinetic energy causes faster molecular movement across the semi-permeable membrane.
b) Extreme temperatures can damage membrane proteins, stopping osmosis entirely.

42. What is osmoregulation? [1 Mark]

Answer: Osmoregulation is the active regulation of the osmotic pressure of body fluids and cells to maintain the homeostasis of water and salt concentrations.

Teacher's Note:
a) It prevents body fluids from becoming too diluted or too concentrated.
b) Organisms living in freshwater and marine environments rely heavily on osmoregulation.

43. Which organ of the plant body helps in osmoregulation? [1 Mark]

Answer: Roots and leaves (via stomata) help in plant osmoregulation and water balance.

Teacher's Note:
a) Roots absorb water and minerals from the soil according to osmotic needs.
b) Stomata regulate transpiration to prevent excessive water loss.

44. Which organelle of the cell in animals helps in osmoregulation? [1 Mark]

Answer: The contractile vacuole helps in osmoregulation in freshwater unicellular animals.

Teacher's Note:
a) Contractile vacuoles collect excess water from the cell and expel it outside.
b) This prevents the cell from bursting due to excessive water intake via endosmosis.

45. What are centrosomes? What functions do they perform? [2 Marks]

Answer:
1. Centrosomes are non-membrane-bound organelles found near the nucleus in animal cells, containing a pair of centrioles.
2. They help in organizing microtubules and form the spindle fibers during cell division.

Teacher's Note:
a) Centrosomes play a critical role in equitable chromosome distribution during mitosis and meiosis.
b) Plant cells lack centrosomes but still form spindle fibers through other mechanisms.

46. Who is known as 'Father of Microscopy'? [1 Mark]

Answer: Antonie van Leeuwenhoek is known as the Father of Microscopy.

Teacher's Note:
a) Leeuwenhoek constructed high-magnification single-lens microscopes.
b) He was the first to observe and describe living single-celled organisms like bacteria and protozoa.

47. Are Viruses Prokaryotic or Eukaryotic? [1 Mark]

Answer: Viruses are neither prokaryotic nor eukaryotic because they are non-cellular entities lacking cell structures.

Teacher's Note:
a) Prokaryotes and eukaryotes are classifications strictly reserved for cellular life forms.
b) Viruses do not possess a plasma membrane, cytoplasm, or ribosomes.

48. Which of the following often distinguishes plant cells from animal cells? [1 Mark]
(A) centrioles
(B) nucleus
(C) chromatin

Answer: (A) centrioles

1. Centrioles are typically present in animal cells and lower plant cells, but are absent in most higher plant cells.
2. Nucleus and chromatin are common to both plant and animal eukaryotic cells.
3. Hence, the correct option is (A).

Teacher's Note:
a) Plant cells are uniquely distinguished by cell walls and plastids.
b) Centrioles are characteristic features of animal cell centrosomes.

49. Which cell organelle is called "kitchen of plant"? [1 Mark]

Answer:
1. Plastids, specifically chloroplasts, are known as the kitchen of the plant.
2. They contain chlorophyll which helps in synthesizing food through photosynthesis.

Teacher's Note:
a) Chloroplasts trap solar energy to convert carbon dioxide and water into glucose.
b) Non-green plastids like leucoplasts serve different storage functions.

50. Which cell organelle is called 'control center'? [1 Mark]

Answer:
1. The nucleus is called the control center of the cell.
2. It regulates all cellular activities and contains hereditary material (DNA).

Teacher's Note:
a) It directs protein synthesis and cellular reproduction.
b) Prokaryotes lack a true, membrane-bound nucleus.

51. Which cell organelle is called 'transport system'? [1 Mark]

Answer:
1. Endoplasmic Reticulum (ER) is called the intracellular transport system of the cell.
2. It forms a network of membrane tubules that transport materials across the cytoplasm.

Teacher's Note:
a) Rough ER transports proteins, while smooth ER transports lipids.
b) It also provides mechanical support to the cytoplasm.

52. What is Endoplasmic Reticulum(ER)? Name its types? [2 Marks]

Answer:
1. Endoplasmic Reticulum is a large network of membrane-bound tubes and sheets.
2. It is of two types: Rough Endoplasmic Reticulum (RER) and Smooth Endoplasmic Reticulum (SER).

Teacher's Note:
a) RER appears rough due to the presence of ribosomes on its surface.
b) SER lacks ribosomes and helps in lipid manufacture.

53. What are the functions of Endoplasmic Reticulum (ER)? [3 Marks]

Answer:
1. RER helps in the synthesis and transport of proteins.
2. SER helps in the synthesis of lipids, fats, and steroid hormones.
3. It acts as a cytoplasmic framework providing structural support and detoxifies poisons and drugs in liver cells.

Teacher's Note:
a) Membrane biogenesis relies heavily on lipids and proteins synthesized by ER.
b) Students often forget the detoxification role of smooth ER.
c) ER connects the nuclear membrane with the cell membrane.

54. What are the components nucleus? [2 Marks]

Answer:
1. Nuclear membrane (nuclear envelope), nucleoplasm, and nucleolus.
2. Chromatin material (or chromosomes).

Teacher's Note:
a) The nuclear membrane has pores for material exchange with the cytoplasm.
b) Nucleolus is rich in RNA and proteins and is the site of ribosome biogenesis.

55. What is the function of nucleoplasm? [1 Mark]

Answer:
1. Nucleoplasm provides a medium for the suspension of nuclear components like chromatin and nucleolus.
2. It facilitates the exchange of materials between the nucleolus, chromatin, and the cytoplasm.

Teacher's Note:
a) It contains enzymes and nucleotides necessary for DNA and RNA synthesis.

56. How chromatic network is related to chromosomes? [2 Marks]

Answer:
1. Chromatin network is a tangle of fine DNA and protein threads present in a non-dividing cell.
2. When the cell is about to divide, the chromatin network condenses and organizes into distinct, rod-like structures called chromosomes.

Teacher's Note:
a) Both are chemically identical, consisting of DNA and histone proteins.
b) Chromatin is the relaxed, active form; chromosomes are the condensed, transportable form.

57. What are chromosomes? [1 Mark]

Answer:
1. Chromosomes are thread-like structures composed of DNA and proteins found in the nucleus.
2. They carry hereditary information from parents to offspring in the form of genes.

Teacher's Note:
a) The number of chromosomes is constant for a particular species.

58. What is the full form of DNA and RNA? [1 Mark]

Answer:
1. DNA: Deoxyribonucleic Acid.
2. RNA: Ribonucleic Acid.

Teacher's Note:
a) Spelling of Deoxyribonucleic must be exact without omissions.

59. Who discovered Virus? [1 Mark]

Answer:
1. Viruses were discovered by Dmitry Ivanovsky in 1892, and later Martinus Beijerinck gave the name virus.

Teacher's Note:
a) Ivanovsky discovered them while studying tobacco mosaic disease.

60. What are the function of nucleus? [3 Marks]

Answer:
1. It controls all metabolic activities of the cell.
2. It plays a central role in cellular reproduction by transmitting genetic traits from one generation to the next.
3. It regulates gene expression and protein synthesis through transcription.

Teacher's Note:
a) It contains the genetic blueprint of the organism.
b) Damage to the nucleus usually leads to cell death.
c) Often referred to as the brain of the cell.

61. Why can't single cells grow very large? Or Big organisms like human beings are multi-cellular? Why can't such big organisms be a single large cell? [3 Marks]

Answer:
1. As a cell grows larger, its volume increases at a much faster rate than its surface area.
2. A large cell cannot efficiently absorb sufficient nutrients and oxygen or eliminate wastes across its limited plasma membrane.
3. Therefore, multicellularity allows division of labor and efficient transport across smaller individual cells.

Answer:
1. Sprinkling water creates a high water potential environment around the vegetables.
2. This prevents water loss through evaporation and maintains turgidity, keeping vegetables fresh and crisp.

Teacher's Note:
a) Water enters plant cells via osmosis, maintaining cell turgor pressure.
b) It prevents wilting of leafy vegetables in open air.

63. Why do we stain cells while observing under microscope? List commonly used stains. [3 Marks]

Answer:
1. Cells are mostly transparent and colorless, making their internal structures difficult to distinguish under a microscope.
2. Staining provides contrast to different cell organelles so they become clearly visible.
3. Commonly used stains include Methylene blue, Safranin, Iodine, and Acetocarmine.

Teacher's Note:
a) Different stains bind preferentially to specific cell components like nuclei or cell walls.
b) Iodine stains starch, while safranin stains lignified tissues pink/red.
c) Methylene blue is commonly used for animal cells like cheek cells.

64. Are there any exceptions to cell theory proposed by Schleiden & Schwann and Virchow? If yes, what are those? [2 Marks]

Answer:
1. Yes, viruses are a major exception to the cell theory.
2. Viruses are non-cellular entities that lack cellular machinery and do not reproduce independently outside a host body.

Teacher's Note:
a) Cell theory states all living things are made of cells, which viruses violate.
b) Coenocytic fungi (multinucleated cytoplasm without cell boundaries) are also considered partial exceptions.

65. What is the thickness of cell membrane? [1 Mark]

Answer:
1. The plasma membrane is extremely thin, approximately \(7\) to \(10\) nanometers (\(70\) to \(100\) Ångströms) in thickness.

Teacher's Note:
a) It can only be observed clearly using an electron microscope.

66. Why is mitochondria absent in red blood cells? [2 Marks]

Answer:
1. Mammalian red blood cells (RBCs) lack mitochondria to maximize space for carrying hemoglobin.
2. Absence of mitochondria ensures that RBCs do not consume the oxygen they transport, performing anaerobic respiration instead.

Teacher's Note:
a) Maximizing oxygen-carrying capacity is the primary evolutionary adaptation of RBCs.
b) They also lack a nucleus for the same spatial reason.

67. Name the cell organelles which their own DNA and Ribosomes. [2 Marks]

Answer:
1. Mitochondria.
2. Plastids (such as chloroplasts).

Teacher's Note:
a) These are semi-autonomous organelles capable of synthesizing some of their own proteins.
b) This supports the endosymbiotic theory of their bacterial origin.

68. What is cytoskeleton? [2 Marks]

Answer:
1. Cytoskeleton is an intricate network of protein filaments and microtubules present in the cytoplasm.
2. It provides structural support, maintains cell shape, and assists in cell motility and intracellular transport.

Teacher's Note:
a) It consists of microfilaments, intermediate filaments, and microtubules.
b) It acts as both muscles and skeleton for the cell.

69. Name the cell organelles involved in synthesis, packaging and movement of protein (or other macromolecules) inside a cell. [3 Marks]

Answer:
1. Synthesis: Ribosomes and Rough Endoplasmic Reticulum (RER) synthesize proteins.
2. Packaging: Golgi apparatus modifies, sorts, and packages these proteins into vesicles.
3. Movement: Endoplasmic Reticulum, Golgi vesicles, and cytoskeleton help transport them inside the cell.

Teacher's Note:
a) This sequence represents the secretory pathway of proteins in a cell.
b) Golgi apparatus acts as the post office of the cell.
c) Ribosomes are the sites of actual polypeptide assembly.

70. Which of the following is an example of a single cell that does not function as a full fledged organism? [1 Mark]
(A) White blood cells (WBC)
(B) Amoeba
(C) WBC and Amoeba
(D) Paramecium

Answer: (A) White blood cells (WBC)

1. White blood cells are single cells found in multicellular organisms and cannot survive independently as a complete organism.
2. Amoeba and Paramecium are unicellular organisms capable of independent existence.
3. Hence, the correct option is (A).

Teacher's Note:
a) Unicellular organisms perform all life processes independently, unlike specialized somatic cells.