2.1 Cell division

What causes cancer at the cellular level?

Cancer occurs when cells begin to divide uncontrollably and more quickly than normal.

Why do researchers studying cancer focus on cell division?

Because cancer involves uncontrolled cell division, scientists aim to understand and interrupt the steps of cell division.

What food was found to slow cancer cell growth in research?

Raw garlic.

Do all cells in the body divide?

No. Some cells, like brain neurons, stop dividing and remain in a resting state.

What happens when non-dividing cells like neurons are damaged?

They can't regenerate, which can lead to issues like memory loss.

What is the main goal of a cell?

To divide, creating two identical daughter cells.

What is meant by 'like produces like' in cell division?

A specific type of cell (like a cheek cell) only divides into more of the same type of cell.

Why is cell division important for humans and animals?

It's necessary for growth, repair, and regeneration of tissues.

How do humans grow from one cell to trillions?

Through constant cell division starting from a zygote.

How do some animals like lizards regrow lost body parts?

Through cell division, which regenerates tissue.

How does a wound heal on the skin?

New cells replace dead or damaged cells through rapid cell division.

What are the main phases of the cell cycle?

G0, G1, S, G2, and M (Mitosis + Cytokinesis).

What is the G0 phase?

A resting phase where cells are inactive or permanently stop dividing.

What would happen if cells didn’t have a G0 phase?

They would divide constantly, causing chaos and cellular exhaustion.

What happens during G1 phase?

The cell grows and collects materials needed for DNA replication.

What is the key event of the S phase?

DNA replication—each chromosome forms an identical copy (sister chromatid).

How many chromatids are present after S phase in a human cell?

92 chromatids (46 pairs of sister chromatids).

What happens during G2 phase?

The cell produces proteins and prepares for mitosis.

What is interphase?

A combination of G1, S, and G2—where the cell prepares to divide (about 23 hours).

What is mitosis?

The process of nuclear division that ensures equal chromosome distribution to daughter cells.

What is cytokinesis?

The division of the cytoplasm, forming two separate cells.

How long does the M phase usually take in a cheek cell?

About 1 hour.

What happens during prophase?

Chromosomes condense; sister chromatids become visible in an X shape; spindle begins to form.

What happens during prometaphase?

The nuclear envelope breaks down; spindle fibers attach to chromatids.

What occurs in metaphase?

Chromosomes align at the center of the cell; lasts about 20 minutes.

What happens during anaphase?

Sister chromatids separate and move to opposite ends; takes about 2 minutes.

What occurs in telophase?

Two new nuclei form at opposite ends; mitosis ends here.

What happens during cytokinesis in animal cells?

A cleavage furrow forms and pinches the cell into two daughter cells.

How does cytokinesis differ in plant cells?

A cell plate forms instead of a cleavage furrow.

What are sister chromatids?

Identical DNA copies of a chromosome, joined together in an X-shape.

What is the mitotic spindle?

Microtubule fibers that pull chromatids apart during mitosis.

What are centrosomes?

Organelles that organize spindle fibers during mitosis.

What ensures daughter cells are identical after mitosis?

Equal distribution of sister chromatids.

Who first observed chromosomes and coined the term mitosis?

Walther Flemming in 1882.

Why are onion root tips ideal for studying mitosis?

Because the root tips grow rapidly, they contain many cells actively undergoing division.