6. Exam Q

Question 1

Answer 1

Question 2

Answer 2

Question 3

Answer 3

Question 4

Answer 4

Question 5

Identify from the diagram the stages of mitosis labelled A to D.

Answer 5

Question 6

One stage of the cell cycle shown on the diagram is present in greater numbers than the
others. Name this stage and explain this observation. State three events that happen in
the phase. [2]

Answer 6

Question 7

Answer 7

Question 8

Answer 8

Question 9

Answer 9

Question 10

Answer 10

Question 11

Answer 11

Question 12

Answer 12

Question 13

Answer 13

Question 14

Answer 14

Question 15

Answer 15

GPT
1. Photomicrograph Observations
(i) Structure A has just completed meiosis I because homologous chromosomes are separated, while structure G has completed meiosis II as sister chromatids have been separated. [1]
(ii) Some cells in interphase do not show visible nuclei due to varying focal planes or different stages of interphase. Nuclei appear different sizes because cells may be in different growth phases (G1, S, or G2). [2]

Question 16

GPT

Answer 16

2. Anaphase Determination
   To determine whether a cell is in anaphase of mitosis, anaphase I, or anaphase II:

In mitosis: Sister chromatids separate.
In anaphase I of meiosis: Homologous chromosomes separate.
In anaphase II of meiosis: Sister chromatids separate, similar to mitosis but in haploid cells.
The answer depends on whether the chromosomes are single or paired and whether homologous chromosomes are separating. [3]

Question 17

GPT

Answer 17

3. Chromosome Visibility
   (i) Tissues must be stained with a DNA-specific dye (e.g., acetic orcein) and observed under a microscope to visualize chromosomes. [1]

Question 18

GPT

Answer 18

4. Mitotic Index and Growth Rate
   (ii) The mitotic index decreases as the distance from the root tip increases, indicating that cell division occurs mainly near the root tip, where growth is most active. [2]
   (iii) The reliability of data can be improved by increasing the number of fields of view observed or analyzing multiple samples. [1]

Question 19

GPT

Answer 19

The mitotic index measures the proportion of cells undergoing mitosis, but it does not fully explain the overall growth of garlic roots because:

Cell Enlargement Contributes to Growth

The drawings show that cells at 1.8 mm from the root tip are much longer (300 µm) than those at 0.2 mm (90 µm).
This indicates that after mitosis, cells elongate, which contributes significantly to root growth.
Cell Differentiation Also Plays a Role

The root cap and mature root cells undergo differentiation rather than mitosis.
Specialized cells form, contributing to overall root function and structure.
Variation in Mitosis Rate Across the Root

The mitotic index is highest near the root tip (0.2 mm), where rapid cell division occurs.
However, further from the tip, mitosis decreases while cell elongation and differentiation increase.
Mitosis Alone Does Not Account for All Growth

Although cell division produces new cells, it does not directly lead to a significant increase in root length.
Cell expansion is a major factor in the overall increase in root size.
Conclusion:
While mitosis is important for producing new cells, the main contributors to overall root growth are cell expansion and differentiation, which occur after mitosis.

Question 20

gpt

Answer 20

Answer to Question 2(e):
It would be difficult for the student to calculate a valid mitotic index from the image because:

Poor Clarity and Overlapping Cells

The cells are not clearly separated, making it difficult to distinguish individual cells and their stages of mitosis.
Some cells appear clumped together, preventing an accurate count.
Uneven Staining

The stain should highlight chromosomes clearly, but in this image, the staining is inconsistent.
This makes it hard to identify cells in mitotic stages like prophase, metaphase, anaphase, and telophase.
Squash Technique Not Performed Correctly

The root tip squash technique should spread cells into a single layer.
Here, the sample seems too thick, making it difficult to see individual nuclei and count cells in mitosis accurately.
Conclusion:
Even with higher magnification, the overlapping cells, poor staining, and thick preparation make it challenging to accurately determine the mitotic index.

(3 Marks)

Question 21

gpt

Answer 21

A = Centromere
B = Chromatid

Question 22

gpt

Answer 22

(i) The SRY gene can be transferred from the Y chromosome to the X chromosome through unequal crossing over during meiosis. [2]
(ii) Four different haploid sperm are produced due to independent assortment and crossing over, which generate genetic variation during meiosis. [2]
(iii) The low percentage (0.23%) of female athletes possessing the SRY gene is likely due to rare chromosomal abnormalities such as XX males (due to SRY translocation) or Androgen Insensitivity Syndrome, which are uncommon conditions. [2]

Question 23

what is the stage between successive cell divisions called

Answer 23

interphase

Question 24

Answer 24

Question 25

Answer 25

Question 26

Answer 26

Question 27

Answer 27

Question 28

Answer 28

Question 29

meiosis

Answer 29

Question 30

Answer 30

Question 31

Answer 31

Question 32

Answer 32

Question 33

Answer 33

Question 34

Answer 34

Question 35

Answer 35

Question 36

Answer 36

Question 37

Answer 37

Question 38

Answer 38

Question 39

Answer 39

Question 40

DNA polymerase

Answer 40

amplify - making copies

Question 41

Answer 41

Question 42

Answer 42

Question 43

Answer 43

20

Question 44

Answer 44