# IB DP Biology D2.1 Cell and nuclear division-FA 2025- IB Style Question For SL Paper 1

### Question

The micrograph shows some onion (Allium cepa) cells undergoing mitosis.

What is the mitotic index, taking into account all visible nuclei?
A. 0.1

B. 0.2

C. 0.4

D. 0.6

Ans:B

The mitotic index is a measure of the fraction of cells undergoing mitosis. It is calculated by dividing the total cells undergoing mitosis by the total cells visible
Mitotic index = number of cells with visible chromosomes ÷ total number of cells
Mitotic index = (prophase + metaphase + anaphase + telophase) ÷ total number of cell

Here 10 nuclei are visible and 2 of those are dividing, so mitotic index as per as given data will be (2 ÷10 = 0.2) or 20%.

### Question

A tissue sample was examined under the microscope in order to determine a mitotic index. The number of cells in each stage of the cell cycle was determined and the data were entered into a table.

 Stage of life cycle Interphase Prophase Metaphase Anaphase Telophase Total Number of cells 120 20 10 8 2 160

What is the mitotic index?

A. 0.125

B. 0.25

C. 0.75

D. 1.00

Ans B

The mitotic index is a measure of the fraction of cells undergoing mitosis. It is calculated by dividing the total cells undergoing mitosis by the total cells visible
Mitotic index = number of cells with visible chromosomes ÷ total number of cells
Mitotic index = (prophase + metaphase + anaphase + telophase) ÷ total number of cells

Here in this question, Mitotic index = [(20+10+8+2)÷(120)] = 0.25 or 25%

Question

Which diagram(s) represent(s) processes used in asexual reproduction?

A. I only

B. I and II only

C. II only

D. I, II and III

## Markscheme

C

Asexual reproduction is a type of reproduction that does not involve the fusion of gametes or change in the number of chromosomes. The offspring that arise by asexual reproduction from either unicellular or multicellular organisms inherit the full set of genes of their single parent and thus the newly created individual is genetically and physically similar to the parent or an exact clone of the parent. When prokaryotes and eukaryotes reproduce asexually, they transfer a nearly identical copy of their genetic material to their offspring through vertical gene transfer. Although asexual reproduction produces more offspring more quickly, any benefits of diversity among those offspring are lost.

Here in option B, gene pool of parent and offspring in identical.

Question

What occurs during meiosis but not mitosis?

A. Spindles are formed from microtubules.

B. Chromosome number is conserved.

C. Homologous chromosomes pair up.

D. Centromeres split.

## Markscheme

C

Homologous chromosomes are present in both mitosis and meiosis, but they don’t form pairs in mitosis. Rather they will form homologous chromosome pairs during meiosis, which allows for crossing over to occur. Crossing over is a cellular process that happens during meiosis when chromosomes of the same type are lined up. This can happen between multiple chromosomes or different segments of the same chromosome.  Crossing over is important because it ensures genetic variability and contributes to genetic reassortment which are the key factors to genetic diversity among offspring that would otherwise lead to lot of abnormalities, genetic disorders.

Question

In which stage of mitosis is the cell labelled X?

A. Anaphase
B. Interphase
C. Metaphase
D. Prophase

## Markscheme

A

The correct answer to the question “In which stage of mitosis is the cell labelled X?” is A, Anaphase. During anaphase, the sister chromatids separate and move towards opposite poles of the cell. In the image, the chromosomes are clearly separated and moving towards opposite poles, indicating that the cell is in anaphase.

Question

A two-cell sea urchin (Echinoidea) embryo was physically separated by scientists into two cells. Each cell, through further embryonic development, became an adult sea urchin.

What is the relationship between the two adult sea urchins?

A. They are equivalent to non-identical twins.

B. Half of the genes would be the same.

C. Both adults would have haploid cells.

D. They are clones.

D

Question

Which process occurs in meiosis but not in mitosis?

A. Attachment of spindle fibres to the centromeres of each chromosome

B. Movement of homologous chromosomes to opposite ends

C. Replication of DNA prior to the start of cell division

D. Separation of sister chromatids during anaphase

B

Question

When does DNA replication occur?

A. S phase of interphase

B. Early prophase

C. G phase of interphase

D. Late prophase

A

Question

What is a function of histones?

A.  Supercoiling of DNA during binary fission in prokaryotes

B.  Synthesis of proteins

C.  Formation of microtubules during mitosis

D.  Condensation of DNA

D

Question

The image shows a micrograph of a cell.

What explains the appearance of the cell in the micrograph?

A. The cell is dying.

B. The DNA is replicating.

C. The cell is in metaphase.

D. The cell is in telophase.

C

Question

The diagram shows a stage in cell division.

What is the stage shown?

A. Anaphase I of mitosis

B. Anaphase II of mitosis

C. Anaphase I of meiosis

D. Anaphase II of meiosis

D

Question

The image shows a cell from the root tip of an onion (Allium cepa) (2n = 16) during late prophase of mitosis.

How many chromatids are present in the cell?

A.  8

B.  16

C.  32

D.  64

C

Question

In the micrograph, which letter points to a cell in anaphase?

B

Question

The micrograph shows a cross section of a lily (Lilium longiflorum) anther.

What can be found in X?
A.  Haploid nuclei produced by meiosis

B.  Diploid nuclei produced by fertilization

C.  Haploid nuclei produced by mitosis

D.  Diploid nuclei produced by pollination

A

Question

The karyogram shown belongs to a human being.

What can be deduced from this karyogram?

A. The person is a male with Down syndrome.

B. The person is a female with Down syndrome.

C. The person is a male with a genetic disorder.

D. The person is a female with a missing chromosome.