AQA Biology - Topic 1.2: Cell Division

Define the term chromosome.

Chromosomes are structures formed by the coiling of DNA double helices in the nucleus, visible during cell division, and containing genetic information in the form of genes.

True or False? Each chromosome carries a large number of genes.

True
Each chromosome carries many genes coding for different proteins.

How many chromosomes do human body cells contain?

Human body cells contain 23 pairs of chromosomes (46 total) in diploid cells (2n).

Why are chromosomes found in pairs in human body cells?

They occur as homologous pairs:

• One chromosome inherited from each parent
• Carry corresponding genes (may have different alleles)

How is the chromosome number in gametes different from that of body cells?

Gametes contain the haploid number (n), half the diploid number found in body cells.

True or False? Chromosomes are only visible during cell division.

True
Chromosomes condense and become visible during division (mitosis or meiosis).

Define the term mitosis.

Mitosis is nuclear division producing genetically identical cells, used for growth, repair, and asexual reproduction.

True or False? Mitosis results in genetically diverse cells.

False
Mitosis results in genetically identical cells.

What happens to chromosomes before mitosis?

Each chromosome replicates, forming two identical copies (one for each daughter cell).

Why is mitosis important in the body?

Mitosis produces new cells for:

• Growth
• Repair of damaged tissues
• Replacement of cells

What is the outcome of a mitotic division?

Two genetically identical daughter cells, identical to each other and the parent cell.

What cells are not produced by mitosis in animals and plants?

Gametes (sperm, egg, pollen, ovules) are produced by meiosis, not mitosis.

How many chromosomes are present in a human cell produced by mitosis?

46 chromosomes (23 pairs) are present after mitosis.

True or False? Mitosis is another name for the cell cycle.

False
Mitosis is part of the cell cycle. Most of the cycle involves growth and DNA replication.

Name the three stages of the cell cycle.

1. Cell growth, DNA replication, organelle replication

2. Mitosis (nuclear division)

3. Cytokinesis (cytoplasm splitting)

True or False? Ribosome numbers increase in cells before mitosis occurs.

True
Cells replicate ribosomes and other organelles (e.g. mitochondria) before division.

Define the term stem cell.

A stem cell is an undifferentiated cell that can divide to form many more of the same type and differentiate into other types.

True or False? Embryonic stem cells can differentiate to produce most cell types.

True
They can differentiate into most or all cell types, forming tissues and organs.

How can stem cells be used to treat diseases such as diabetes?

By replacing damaged cells with healthy stem cells, which can divide and form new cells.

What is the potential benefit of using a patient's own stem cells in treatment?

They would not be rejected by the patient’s immune system.

True or False? There is risk of infection when transferring lab-cultured stem cells into a patient.

True
Lab-grown stem cells can become infected, passing infection to patients.

True or False? There are ethical issues associated with the use of embryonic stem cells in medicine.

True
Concerns include:

• Destruction of embryos
• Embryos cannot give consent
• Treating embryos as a commodity

True or False? Adult stem cells have a limited capacity to differentiate.

True
Adult stem cells can only form a few cell types.

Name the tissue type in plants where stem cells are located.

Meristem tissue in growing roots and shoots.

Where are human stem cells that differentiate into red blood cells located?

They are found in the bone marrow.

How can meristem cells be used with cloning to aid plant conservation and crop development?

Meristem stem cells can be cloned to produce large numbers of:

• Endangered species
• Crop plants with desirable traits (e.g. disease resista