1
A group of students observed two cells under a microscope. Cell A had a rigid, box-like structure with a thick outer layer, while Cell B had an irregular shape and a thin outer boundary.(i) Identify Cell A and Cell B and justify your answer. [2 marks](ii) What would happen to Cell B if placed in a solution of 20% sugar? Explain the process involved. [3 marks](iii) What function does the thick outer layer of Cell A perform that is absent in Cell B? 1mark
2
Assertion (A): Mitochondria are called the powerhouses of the cell.Reason (R): Mitochondria release energy stored in glucose and other molecules through cellular respiration.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
3
A researcher is studying the process of osmosis. They have three beakers containing different solutions: Beaker X (pure water), Beaker Y (5% salt solution), and Beaker Z (25% salt solution). They place identical red blood cells in each beaker.(i) Describe what will happen to the red blood cells in Beaker X. [1 mark](ii) Describe what will happen to the red blood cells in Beaker Y and explain the reason. [2 marks](iii) Describe what will happen to the red blood cells in Beaker Z and explain the reason. 2marks
4
Assertion (A): Lysosomes are known as the 'suicidal bags' of the cell.Reason (R): Lysosomes contain powerful digestive enzymes that can break down worn-out cell organelles and foreign materials.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
5
Observe the given diagrams of a bacterial cell and a plant cell.(i) Identify the labelled parts A and B. [1 mark](ii) Which of these cells is prokaryotic and why? [2 marks](iii) State one function of part A. [1 mark](iv) Name an organelle present in the plant cell but absent in the bacterial cell, which is responsible for photosynthesis. 1mark
(Diagrams of a bacterial cell with a nucleoid (A) and a plant cell with a nucleus and chloroplasts would be shown here)
6
A scientist is investigating the role of the nucleus in cell function. They observe that mature red blood cells in humans lack a nucleus, while actively dividing cells have a prominent nucleus.(i) Explain the advantage of mature red blood cells lacking a nucleus. [2 marks](ii) What would be the consequence for a cell if its nucleus were removed? [1 mark](iii) How does the nucleus contain genetic information? 1mark
7
Assertion (A): Smooth Endoplasmic Reticulum (SER) is primarily involved in protein synthesis.Reason (R): SER lacks ribosomes on its surface, whereas Rough Endoplasmic Reticulum (RER) has ribosomes attached to its surface.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
8
A student prepares a temporary mount of onion peel and observes it under a light microscope. They notice that the cells are regularly shaped and have a distinct outer boundary and a central dark-staining region.(i) What is the function of the outer boundary of the plant cell? [1 mark](ii) What is the central dark-staining region likely to be, and what is its main function? [2 marks](iii) If the student had observed cheek cells instead, how would the structure differ from the onion peel cells? 1mark
9
A farmer notices that his amla and lemon produce are perishing quickly. He decides to preserve them by making pickles and sharbats using salt and sugar.(i) Which scientific principle is being applied here for preservation? Explain how it works. [2 marks](ii) How does the high concentration of salt and sugar prevent the growth of microorganisms? [2 marks](iii) What value is demonstrated by the farmer's actions? 1mark
10
Assertion (A): Cell culture is a vital technique for studying diseases and developing medicines.Reason (R): Cells grown in culture outside the body can be used to test the effects of drugs and to produce vaccines.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
11
A large central vacuole is a prominent organelle in a mature plant cell, but typically absent or small in animal cells.(i) Explain the primary role of the large central vacuole in maintaining plant cell turgidity. [2 marks](ii) What would happen to a plant cell if its vacuole lost a significant amount of water? [1 mark](iii) Why are vacuoles generally smaller and less prominent in animal cells? 1mark
12
In the process of cell division, mitosis and meiosis are two distinct types.(i) Differentiate between mitosis and meiosis in terms of the number of daughter cells produced and their genetic makeup. [3 marks](ii) Where does meiosis primarily occur in the human body? 1mark
13
Assertion (A): Prokaryotic cells are less complex than eukaryotic cells.Reason (R): Prokaryotic cells lack a well-defined nucleus and membrane-bound organelles.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
14
A scientist is experimenting with a cell and finds that its plasma membrane is fluid, with proteins embedded in a lipid bilayer.(i) What model of the cell membrane structure does this description refer to? [1 mark](ii) Explain the role of proteins in this model. [2 marks](iii) Why is the term "fluid" used to describe this model? 1mark
15
Cancer is a disease characterized by uncontrolled cell division.(i) What cellular process, if faulty, can lead to uncontrolled cell division and tumor formation? [1 mark](ii) How does the concept of 'contact inhibition' relate to the difference between normal cells and cancer cells? [2 marks](iii) What might happen if the process of programmed cell death (PCD) fails in normal cells? 1mark
16
Observe the given diagram of a mitochondrion.(i) Identify the labelled parts A and B. [1 mark](ii) What is the main function of the structure labelled B in energy production? [2 marks](iii) Why are mitochondria referred to as the 'powerhouses' of the cell? 1mark
(Diagram of a mitochondrion with inner and outer membranes, and cristae labelled would be shown here)
17
Assertion (A): The cell wall provides structural support and protection to plant cells.Reason (R): The cell wall is a rigid layer made primarily of cellulose, which allows water and dissolved minerals to pass through.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
18
A biologist is studying the differences between plant and animal cells. They note that plant cells often contain chloroplasts, while animal cells do not.(i) Explain the function of chloroplasts in plant cells. [2 marks](ii) What is the chemical pigment present in chloroplasts that is essential for this function? [1 mark](iii) How does the absence of chloroplasts in animal cells affect their mode of nutrition? 1mark
19
Two students are discussing the continuity of life. One student states that life's continuity is ensured by the formation of new cells from pre-existing cells. The other student adds that cell division is the fundamental process responsible for this.(i) Which classical cell theory principle are they referring to? [1 mark](ii) Explain the importance of cell division in the growth of an organism. [2 marks](iii) Name the two main types of cell division. 1mark
20
Assertion (A): Ribosomes are responsible for protein synthesis.Reason (R): Ribosomes are found freely in the cytoplasm and also attached to the endoplasmic reticulum.(a) Both assertion and reason are true and reason is the correct explanation of assertion.(b) Both assertion and reason are true but reason is not the correct explanation of assertion.(c) Assertion is true but reason is false.(d) Assertion is false but reason is true. 1mark
Answers
1
(i) Cell A is a plant cell, and Cell B is an animal cell. The rigid, box-like structure with a thick outer layer is characteristic of a plant cell's cell wall, while the irregular shape of Cell B indicates the absence of a cell wall, typical of animal cells. 2marks(ii) If Cell B (animal cell) is placed in a 20% sugar solution, it will shrink. This is because the external solution is hypertonic (has a higher solute concentration and lower water concentration) compared to the cytoplasm of the cell. Water will move out of the cell by osmosis, causing the cell to lose water and shrink. [3 marks](iii) The thick outer layer of Cell A (cell wall) provides structural rigidity, protection, and prevents the cell from bursting in hypotonic solutions. This rigid structure is absent in Cell B. [1 mark]
2
(a) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark
3
(i) In Beaker X (pure water), the external solution is hypotonic. Water will move into the red blood cells by osmosis, causing them to swell and potentially burst (hemolysis). 1mark(ii) In Beaker Y (5% salt solution), the solution is likely isotonic or slightly hypertonic to the red blood cells. If isotonic, there will be little net movement of water, and the cells will retain their normal shape. If slightly hypertonic, some water might move out, causing slight shrinkage. Assuming it's close to isotonic, there will be minimal change. [2 marks](iii) In Beaker Z (25% salt solution), the external solution is hypertonic. Water will move out of the red blood cells by osmosis, causing them to shrink and become crenated (shriveled). [2 marks]
4
(a) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark
5
(i) A: Nucleoid (region containing genetic material)B: Nucleus (containing genetic material enclosed by a membrane) [1 mark](ii) The bacterial cell is prokaryotic because it lacks a well-defined nucleus (has a nucleoid instead) and membrane-bound organelles. [2 marks](iii) Part A (Nucleoid) contains the genetic material (DNA) of the bacterial cell. [1 mark](iv) Chloroplast. 1mark
6
(i) The absence of a nucleus in mature red blood cells provides more space for haemoglobin. This allows the cell to carry a larger amount of oxygen to all parts of the body. 2marks(ii) If the nucleus were removed from a cell, it would lose control over its activities, including growth, division, and protein synthesis. The cell would eventually die. [1 mark](iii) The nucleus contains chromosomes, which are made of DNA. DNA molecules contain the genetic information in the form of genes, which are passed from parents to offspring. [1 mark]
7
(d) Assertion is false but reason is true. 1mark
8
(i) The outer boundary of the plant cell is the cell wall. Its function is to provide structural support, rigidity, and protection to the cell. 1mark(ii) The central dark-staining region is the nucleus. Its main function is to control all the activities of the cell and to store genetic information. [2 marks](iii) Cheek cells are animal cells and lack a cell wall. Therefore, they would have an irregular shape with only a cell membrane as the outer boundary, unlike the regular, box-like shape of onion peel cells. [1 mark]
9
(i) The scientific principle applied is osmosis and preservation by high solute concentration. High concentrations of salt and sugar create a hypertonic environment. Microorganisms need water to survive and reproduce. In a hypertonic environment, water moves out of the microbial cells by osmosis, dehydrating them and preventing their growth. 2marks(ii) High concentrations of salt and sugar draw water out of the spoilage-causing bacteria and fungi through osmosis, thus inhibiting their growth and preventing the food from spoiling. [2 marks](iii) Values like resourcefulness, scientific application in daily life, waste reduction, and economic benefit are demonstrated. [1 mark]
10
(a) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark
11
(i) The large central vacuole stores water. When the vacuole is full of water, it exerts turgor pressure against the cell wall. This pressure keeps the plant cell firm and rigid, preventing wilting and helping to maintain the plant's shape. 2marks(ii) If the vacuole lost a significant amount of water, the turgor pressure would decrease. The cell membrane would pull away from the cell wall, and the plant cell would become flaccid, leading to wilting. [1 mark](iii) Animal cells generally do not require the same level of structural support as plant cells. Their vacuoles, if present, are smaller and mainly involved in temporary storage or transport of substances, rather than maintaining turgidity. [1 mark]
12
(i) Mitosis: Produces two daughter cells that are genetically identical to the parent cell. Each daughter cell has the same number of chromosomes as the parent cell.Meiosis: Produces four daughter cells. Each daughter cell has half the number of chromosomes as the parent cell and is genetically different from the parent cell and from each other. [3 marks](ii) Meiosis primarily occurs in the reproductive organs (testes in males and ovaries in females) in humans. 1mark
13
(a) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark
14
(i) Fluid mosaic model. 1mark(ii) Proteins in the cell membrane act as channels or carriers for specific substances to pass through the membrane, acting as 'gatekeepers'. They are also involved in cell recognition and signaling. [2 marks](iii) The term "fluid" is used because the lipid molecules and proteins within the membrane can move sideways, flip, and rotate, giving the membrane a dynamic and fluid consistency. [1 mark]
15
(i) Errors in mitosis, particularly if it leads to uncontrolled cell division, can result in tumor formation. 1mark(ii) Normal cells exhibit contact inhibition, meaning they stop dividing when they come into contact with neighbouring cells. Cancer cells have lost this control and continue to divide even when crowded, leading to the formation of tumors. [2 marks](iii) If programmed cell death (PCD) fails, cells that should die might survive and continue to divide, potentially leading to uncontrolled growth or developmental abnormalities. [1 mark]
16
(i) A: Inner membraneB: Cristae [1 mark](ii) The inner membrane is folded into cristae, which significantly increase the surface area available for the chemical reactions of cellular respiration, leading to more efficient energy (ATP) production. [2 marks](iii) Mitochondria are called 'powerhouses' because they are the sites where glucose and other molecules are broken down through cellular respiration to release energy, which is then stored in the form of ATP. This ATP provides the energy required for most cellular activities. 1mark
17
(a) Both assertion and reason are true and reason is the correct explanation of assertion. 1mark
18
(i) Chloroplasts are the sites of photosynthesis in plant cells. They capture light energy from the sun and convert it into chemical energy in the form of glucose, which serves as food for the plant. 2marks(ii) The chemical pigment present in chloroplasts is chlorophyll. [1 mark](iii) The absence of chloroplasts in animal cells means they cannot perform photosynthesis. Therefore, animals must obtain their nutrition by consuming other organisms (heterotrophic nutrition). [1 mark]
19
(i) The principle they are referring to is: "All cells arise from pre-existing cells." 1mark(ii) Cell division is essential for growth because it increases the number of cells in an organism. This increase in cell number allows the organism to grow larger and develop. [2 marks](iii) The two main types of cell division are mitosis and meiosis. [1 mark]
20
(b) Both assertion and reason are true but reason is not the correct explanation of assertion. 1mark
