Cell Division

What is cell division?

The process by which a cell divides to form new cells

Why is cell division important?

Growth, tissue repair, and asexual reproduction

What is the cell cycle?

The sequence of events a cell goes through from formation to division

What are the three main stages of the cell cycle?

Interphase, mitosis, cytokinesis

What happens during interphase?

Cell grows, replicates DNA, and prepares for division

What are the three stages of interphase?

G1, S, G2

What happens in the G1 phase?

Cell grows and synthesises proteins and organelles

What happens in the S phase?

DNA is replicated

What happens in the G2 phase?

Cell continues to grow and prepares for mitosis

Why is interphase important?

Ensures DNA is accurately copied before division

What is mitosis?

Division of the nucleus to produce two genetically identical nuclei

What type of cells divide by mitosis?

Somatic (body) cells

How many daughter cells are produced by mitosis?

Two

What is the chromosome number after mitosis?

Diploid (same as parent cell)

Why is mitosis important?

Growth, repair, and asexual reproduction

What is prophase?

Chromosomes condense and become visible; nuclear envelope breaks down

What happens to spindle fibres in prophase?

They form and begin to attach to chromosomes

What is metaphase?

Chromosomes line up at the equator of the cell

Why is metaphase important?

Ensures equal separation of chromosomes

What is anaphase?

Sister chromatids are pulled apart to opposite poles

What causes chromatids to separate in anaphase?

Contraction of spindle fibres

What is telophase?

Chromatids reach poles and nuclear envelopes reform

What is cytokinesis?

Division of the cytoplasm

What happens during cytokinesis in animal cells?

Cell membrane pinches inward

What happens during cytokinesis in plant cells?

Cell plate forms down the middle

What is a chromosome?

A DNA molecule wrapped around histone proteins

What is a chromatid?

One of two identical copies of a replicated chromosome

What joins sister chromatids together?

The centromere

When do chromatids become chromosomes?

When they separate during anaphase

What is meiosis?

Division of a nucleus to produce genetically different haploid cells

What is the purpose of meiosis?

To produce gametes for sexual reproduction

How many divisions occur in meiosis?

Two (meiosis I and meiosis II)

How many daughter cells are produced by meiosis?

Four

What is the chromosome number after meiosis?

Haploid

What happens in prophase I?

Homologous chromosomes pair up and crossing over occurs

What is crossing over?

Exchange of genetic material between homologous chromosomes

Why is crossing over important?

Increases genetic variation

What happens in metaphase I?

Homologous chromosome pairs line up at the equator

What happens in anaphase I?

Homologous chromosomes separate

Why is meiosis I called a reduction division?

Chromosome number is halved

How is meiosis II similar to mitosis?

Sister chromatids separate

What happens in anaphase II?

Chromatids are pulled to opposite poles

What is the outcome of meiosis II?

Four genetically different haploid cells

How does meiosis create genetic variation?

Crossing over and independent assortment

What is independent assortment?

Random orientation of chromosome pairs in metaphase I

Why is genetic variation important?

Allows adaptation and evolution

How does mitosis differ from meiosis?

Mitosis produces identical diploid cells; meiosis produces different haploid cells

Which process produces gametes?

Meiosis

Which process is used for growth and repair?

Mitosis

Why must DNA replicate before mitosis?

So each daughter cell receives a full set of genetic information

What would happen if mitosis was uncontrolled?

Tumour formation

What is a tumour?

A mass of cells caused by uncontrolled cell division

What is osmosis?

The movement of water molecules from a region of higher water potential to a region of lower water potential across a partially permeable membrane.

What is water potential?

A measure of the tendency of water to move out of a solution.

What causes osmosis to occur?

A water potential gradient across a partially permeable membrane.

What is a water potential gradient?

A difference in water potential between two areas.

Why must a membrane be partially permeable for osmosis?

So water can pass through but solutes cannot.

What happens to an animal cell in a hypotonic solution?

Water enters and the cell may burst (lysis).

What happens to an animal cell in a hypertonic solution?

Water leaves and the cell shrinks (crenation).

What happens to an animal cell in an isotonic solution?

No net movement of water.

What happens to a plant cell in a hypotonic solution?

It becomes turgid.

What happens to a plant cell in a hypertonic solution?

It becomes plasmolysed.

What is plasmolysis?

When the cell membrane pulls away from the cell wall due to water loss.

Why do plant cells not burst in hypotonic solutions?

The cell wall resists further expansion.

What plant tissue is used to investigate osmosis?

Potato cylinders.

What is measured in the potato osmosis experiment?

Change in mass or length.

Why are different concentrations of solution used?

To create different water potentials.

What does no change in mass show?

The solution has the same water potential as the potato tissue.

How is water potential of the tissue found?

By finding the solution where there is no net change in mass.

What is cell specialisation?

When cells are adapted to carry out a particular function.

How are erythrocytes specialised?

They have no nucleus and contain haemoglobin to carry oxygen.

How are neutrophils specialised?

They can engulf and digest pathogens.

How are squamous epithelial cells specialised?

They are thin to allow rapid diffusion.

How are ciliated epithelial cells specialised?

They have cilia to move substances such as mucus.

How are sperm cells specialised?

They have a tail for swimming and many mitochondria for energy.

How are palisade cells specialised?

They contain many chloroplasts for photosynthesis.

How are root hair cells specialised?

They have a large surface area for absorbing water and minerals.

How are guard cells specialised?

They change shape to open and close stomata.

What is a tissue?

A group of similar cells performing a particular function.

What is an organ?

A group of tissues working together.

What is an organ system?

A group of organs working together to perform a major function.

What is squamous epithelium?

Tissue made of flat cells for diffusion.

What is ciliated epithelium?

Tissue with cilia to move substances.

What is cartilage?

Tissue that provides support and flexibility.

What is muscle tissue?

Tissue that contracts to cause movement.

What is xylem?

Tissue that transports water and supports plants.

What is phloem?

Tissue that transports sugars.

What is a stem cell?

An undifferentiated cell that can divide and become specialised.

What does undifferentiated mean?

Not yet adapted to a specific function.

What is differentiation?

The process by which a cell becomes specialised.

Where are animal stem cells found?

Bone marrow.

Where are plant stem cells found?

Meristems.

What do bone marrow stem cells produce?

Erythrocytes and neutrophils.

What do meristem cells produce?

Xylem vessels and phloem sieve tubes.

How can stem cells be used in medicine?

To repair damaged tissues.

How can stem cells help neurological conditions?

They can replace damaged nerve cells.

How can stem cells be used in research?

To study how cells develop and specialise.