Why mitosis and meiosis occur? (CELL CYCLE Part 2)

Complete Exam & Conceptual Notes

" The Cell Cycle is called cycle because it Proceed slowly"

Definition:

"The period from the time a cell is produced until it completes mitosis/meiosis is called cell cycle"

Occurs during: Growth and repair processes

Why do mitosis and meiosis occur in the cell cycle? This is one of the most common questions students ask when studying the cell cycle for the first time.  In simple words, in this notes, we will know exactly why the mitosis and meiosis happens.

Does Mitosis Happen Every Day in Our Body?

Yes, mitosis happens in our body every day.

Even if you are an adult, your body is constantly making new cells. Old cells die and new cells are formed to replace them.

Why Does This Happen?

• To replace dead cells
• To repair damaged tissues
• To keep the body working properly

Scientists say that millions of cells die every minute in our body, and they must be replaced by new ones through mitosis.

Examples

• Skin cells are constantly replaced
• Blood cells are continuously made
• Cells in the intestine renew very fast

Some cells divide all the time, but some divide very slowly or not at all.

Important Point

Mitosis does NOT happen in all cells.

• Skin and blood cells → divide frequently
• Liver cells → divide when needed
• Nerve and heart cells → rarely divide

In adults, most cell division is for repair and maintenance, not for growth.

Mitosis is a continuous process in the body that helps in replacing old cells and repairing tissues, keeping us alive and healthy.

What is Meiosis and When Does It Happen?

Meiosis is a special type of cell division that makes sex cells (sperm and eggs).

It does not happen every day like mitosis. It only happens when the body is making reproductive cells.

Why Does Meiosis Happen?

• To produce sperm in males
• To produce eggs in females
• To help in reproduction

Meiosis is important because it reduces the number of chromosomes to half. 

Where Does Meiosis Occur?

• In males → testes
• In females → ovaries

It occurs only in special cells called germ cells inside these organs.

When Does It Occur?

• Starts at puberty in males
• In females, it begins before birth but continues later
• Happens only during formation of sperm and eggs

What Happens in Meiosis?

• One cell divides two times
• Produces 4 cells
• Each cell has half the chromosomes
• All cells are genetically different

Meiosis produces four different haploid cells (sex cells), each having half the chromosomes of the original cell.

Important Point

Meiosis does NOT happen in all body cells.

• It only happens in reproductive organs
• It is not used for growth or repair

Meiosis is a special process that helps in reproduction by producing sperm and eggs with half the genetic information, so a new life can be formed after fertilization.

Mitosis vs Meiosis (Quick Comparison)

Aspect	Mitosis	Meiosis
Main Purpose	Growth, repair, and maintenance of the body	Production of gametes (sperm and eggs)
Why It Occurs	To increase cell number and replace damaged cells	To maintain chromosome number and enable reproduction
Type of Cells	Somatic (body) cells	Germ cells (reproductive cells)
When It Occurs	Throughout life (growth, healing, replacement)	During gamete formation (after puberty)
Number of Divisions	One division	Two divisions (Meiosis I & II)
Daughter Cells	2 identical cells	4 different cells
Chromosome Number	Diploid (same as parent)	Haploid (half of parent)
Genetic Variation	No variation	High variation
Overall Role	Survival of the individual	Survival of the species

In simple words:
Mitosis Happens during growth, maintenance of body

CELL CYCLE NOTES

Cell Cycle, Mitosis and Meiosis - Complete Exam & Conceptual Notes

Click to read more...