study questions topic 13

Question 1

Describe in detail the stages of mitosis: prophase, metaphase, anaphase, and
telophase. Be able to draw a cell in any of the stages of mitosis as well as
recognize the stage of mitosis from a diagram.

Answer 1

1. Prophase

Chromatin condenses into visible chromosomes, each consisting of two sister chromatids joined at a centromere.
The nucleolus disappears and the nuclear envelope begins to break down.
Centrosomes (in animal cells) migrate to opposite poles of the cell and begin forming the mitotic spindle, composed of microtubules.
The spindle fibers begin to attach to the kinetochores of the chromosomes.

2. Metaphase

Chromosomes are aligned at the metaphase plate (the equatorial plane of the cell).
The mitotic spindle is fully formed, with microtubules attached to the kinetochores of each chromosome.
This alignment ensures that each daughter cell will receive an equal set of chromosomes.

3. Anaphase

The sister chromatids separate as the spindle fibers shorten, pulling them toward opposite poles of the cell.
Each chromatid is now considered an individual chromosome.
The cell begins to elongate as non-kinetochore microtubules push against each other.

4. Telophase

The chromosomes decondense back into chromatin.
The nuclear envelope re-forms around each set of chromosomes, creating two distinct nuclei.
The nucleolus reappears, and the mitotic spindle disassembles.
This marks the end of nuclear division, though the cell is not fully divided until cytokinesis occurs.

Recognizing and Drawing Mitosis Stages
Prophase: Chromosomes are condensed, spindle fibers form, and nuclear envelope breaks down.
Metaphase: Chromosomes align in the middle of the cell at the metaphase plate.
Anaphase: Sister chromatids are pulled apart toward opposite poles.
Telophase: Chromosomes decondense, and two new nuclei form.

Question 2

Explain where in the human body meiosis occurs. Describe what cells are
produced by meiosis and their chromosome number in humans before and after
meiosis

Answer 2

Meiosis occurs in the gonads (reproductive organs) of humans:

In males, meiosis takes place in the testes, producing sperm cells through spermatogenesis.
In females, meiosis occurs in the ovaries, producing egg cells (ova) through oogenesis.

Before Meiosis (Diploid Cells - 2n)
Human body cells (somatic cells) contain 46 chromosomes (2n)—23 pairs (one set from each parent).
The precursor cells that undergo meiosis, called germ cells, also start as diploid (2n = 46 chromosomes).

After Meiosis (Haploid Gametes - n)
Meiosis produces four genetically unique haploid (n) gametes.
Each gamete (sperm or egg) contains 23 chromosomes (n)—one chromosome from each homologous pair.
This ensures that when fertilization occurs (sperm + egg), the resulting zygote will have the full diploid number (2n = 46 chromosomes), restoring the correct chromosome number in the offspring.

Question 3

Define the following: somatic cell and gamete cell. Identify which type of cell is
diploid in humans and which is haploid

Answer 3

Somatic Cell: A body cell that makes up most of an organism’s tissues and organs (e.g., skin, muscle, and nerve cells). Somatic cells do not participate in reproduction.
Gamete Cell: A reproductive cell (sperm or egg) that is involved in sexual reproduction. Gametes fuse during fertilization to form a zygote.
Diploid vs. Haploid Cells in Humans:
Diploid (2n) Cells: Somatic cells contain 46 chromosomes (23 pairs)—one set from each parent.
Haploid (n) Cells: Gamete cells (sperm and egg) contain 23 chromosomes, ensuring that fertilization restores the diploid number (2n = 46) in the zygote.