Home / IB DP Biology- D2.1 Cell and nuclear division-IB Style Questions For HL Paper 1A

IB DP Biology- D2.1 Cell and nuclear division-IB Style Questions For HL Paper 1A -New Syllabus

IBDP Biology HL Paper 1 -All Chapters

Question

The image below shows cells in the root tip of an onion (Allium cepa) undergoing cell division by mitosis.

The cell labeled \( Z \) is currently in which stage of mitosis?

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

▶️ Answer/Explanation
In the micrograph, the chromosomes in cell \( Z \) are being pulled toward opposite poles of the cell.
This separation of sister chromatids is characteristic of anaphase, when spindle fibers shorten and move the chromatids apart.
✅ Answer: (D) Anaphase

Question

The micrograph shows cells in an onion root (Allium cepa) undergoing mitosis.

What is happening at X?

(A) Unequal cytokinesis by budding
(B) Assembly of cell membrane and cell wall by vesicles
(C) Contraction of a ring of actin and myosin proteins
(D) Movement of chromosomes by microtubules
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{B}} \)

The labelled cell is undergoing cytokinesis. During this stage, Golgi vesicles fuse at the centre of the cell to form a cell plate, which develops into the new cell membrane and cell wall, separating the parent cell into two genetically identical daughter cells.

Question

In which order do the following steps occur in a cell that divides by meiosis?

1. Separation of homologous chromosomes
2. DNA replication
3. Crossing over
4. Pairing of homologous chromosomes
(A) 2 → 4 → 3 → 1
(B) 2 → 3 → 4 → 1
(C) 4 → 3 → 2 → 1
(D) 4 → 2 → 3 → 1
▶️ Answer/Explanation

Correct Answer: \( \boxed{\mathbf{A}} \)

Before meiosis begins, DNA replicates during interphase. In prophase I, homologous chromosomes pair (synapsis) and then undergo crossing over. Finally, during anaphase I, homologous chromosomes separate and move to opposite poles. Therefore, the correct sequence is 2 → 4 → 3 → 1.

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