Home / A level Biology 5.2 Chromosome behaviour in mitosis – Exam style question – Paper 1

A level Biology 5.2 Chromosome behaviour in mitosis – Exam style question – Paper 1

Question

What occurs during metaphase of mitosis?

A chromosomes attach to the equator of the spindle
B chromosomes become shorter and thicker
C chromatids reach the poles of the spindle
D each chromosome forms two chromatids

Answer/Explanation

Answer     A

During metaphase of mitosis, chromosomes attach to the equator of the spindle. Therefore, the correct answer is A. Chromosomes are made up of two identical sister chromatids that are held together by a centromere. During metaphase, the spindle fibers attach to the centromeres of the chromosomes and align the chromosomes along the equator of the spindle, also known as the metaphase plate. This alignment ensures that each daughter cell will receive an identical copy of the genetic material during cell division. Chromosomes do not become shorter and thicker during metaphase (B), chromatids do not reach the poles of the spindle during metaphase (C), and each chromosome does not form two chromatids during metaphase (D).

Question

What are the conditions in a human cell just before the cell enters prophase?

           

Answer/Explanation

Answer     D

After mitosis, the chromosome number of a daughter cell is doubled compared to that of parent cells. The parent cell has 23pairs of chromosomes (one set from mother and one set from father) i.e., 46 chromosomes. During the S phase, the replication of the DNA occurs and the cell forms complementary DNA to the parent DNA template and a copy of the parent chromosomes is prepared and forms sister chromatids attached to the centromere. The prophase and metaphase of mitosis have 92 chromatids. At anaphase each chromatid is considered a single chromosome thus at the end of telophase, 92 chromosomes are present (double of 46 chromosomes of parent cell). After cytokinesis and karyokinesis, the cell divides into two each daughter cell having the 46 chromosomes forming a total of 92 chromosomes in two cells divided.
The mitotic spindle begins to self-assemble in the cytoplasm during prophase. 
Nuclear envelope is present before the cell enters the prophase of mitosis. During prophase, the chromosomes condense, the nucleolus disappears, and the nuclear envelope breaks down. 
Thus, the correct option is D.

Question

The diagram shows a human cell (2n = 46) at the end of prophase of mitosis (cell 1) and the daughter cells just after telophase (cells 2 and 3).

How many DNA molecules are there in the nucleus of cell 1 and cell 2?

Answer/Explanation

Ans:

D

A chromosome is formed from a single, enormously long DNA molecule that contains a linear array of many genes.
In the given human cell, 2n = 46 or 46 chromosomes and 46 DNA molecules in each cell.
Prior to mitosis, in S-phase, the DNA gets replicated, thus each chromosome now contains two DNA molecules i.e., 92 DNA molecules and 46 chromosomes.
After Telophase of mitosis, the duplicated genetic material is separated and carried from the nucleus of a parent cell into two identical daughter cells. Thus, each daughter cell receives 46 chromosomes i.e., 46 DNA molecules in each cell.
Thus, the correct option is D.

Question

Which statement about a diploid cell is not correct?

  1. It can undergo a mitotic division to allow growth to occur.
  2. It can undergo a mitotic division to repair a cell.
  3. It can undergo a reduction division to form haploid cells.
  4. It is one that possesses two complete sets of chromosomes.
Answer/Explanation

Ans:

B

Option B is the correct answer. A diploid cell can undergo mitotic division to repair a cell. Mitotic division allows for the repair and regeneration of damaged tissues, and it occurs in somatic cells of the body. Option C is incorrect because a diploid cell cannot undergo a reduction division to form haploid cells. Meiosis is the specialized cell division process that results in the formation of haploid cells. Option A is also correct because diploid cells can undergo mitotic division to allow growth to occur. Option D is also correct because a diploid cell has two complete sets of chromosomes, one from each parent. I apologize for any confusion.

Question

The graphs show various measurements taken from metaphase of mitosis onwards. The graphs are to scale when compared to one another.

Which row correctly identifies each graph?

Answer/Explanation

Ans:

C

In metaphase, chromosomes are aligned on the spindle with sister kinetochores facing toward the opposite poles. As anaphase approaches, the sister chromatids separate from each other and start moving towards the opposite poles. This is what we see in graph X, as chromosomes are aligned on plate, the distance between poles and chromosomes is constant, after metaphase this distance gradually decreased to zero.
At Telophase, the distance between poles of spindle is maximum in a cell, after which at cytokinesis, this distance is increased a bit. This is what we se in graph Y.
Graph Z depicts the distance between sister chromatids, it was zero initially at metaphase, then the distance increases as sister chromatids move towards the spindle poles during anaphase.
Thus, the correct option is C.

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