Cell Division

Define Mitosis

Define Mitosis

nuclear division in which one nucleus divides to form two identical (daughter) nuclei.

Each cell contains the same no. of chromosomes with identical genes.

Mitosis takes place in… cells

somatic (non reproductive)

What are the stages of mitosis?

1.Prophase

2.Metaphase

3.Anaphase

4.Telophase

What is the first stage of mitosis?

Prophase

What occurs during prophase?

• Chromosomes become visible as double-stranded structures

• Nuclear membrane breaks down

• Spindle fibres form in the cytoplasm

Explain the term diploid

-A cell containing two copies of each chromosome is referred to as a 'diploid cell'; human somatic cells are diploid: they contain 46 chromosomes, 22 pairs of autosomes and a pair of sex chromosomes.

What is the diploid number of a cell?

• how many pairs of two?

• ex. in diagram. The diploid number is 4

Outline one function of mitosis in humans

mitosis helps in the production of identical copies of cells and thus helps in repairing the damaged tissue or replacing the worn-out cells.

Name human cell not produced by mitosis

Red blood cells or gut lining cells cannot undergo mitosis, egg, sperm

Give two observable events that happen during prophase

1. Nuclear membrane breaks down

2. Chromosomes become visible double structures

After mitosis, the cell divides in two. This happens differently in plant and animal cells. What happens?

1. animal- cleavage furrow

2. plant- cell plate

Define meiosis

• Form of nuclear division in which the daughter nuclei contain half the number of chromosomes of the parent nucleus.

• Meiosis occurs during formation of egg and sperm cells in mammals.

State 3 ways in which meiosis differs from mitosis

Mitosis

1. Two daughter cells produced

2. Identical to parent cell

3. Same number of chromosomes produced as the parent cell.

Meiosis

1. Four daughter cells produced

2. Variations to parent cell

3. Daughter cells will be haploid (half the no. of chromosomes of parent) Think: Meiosis is the process by which a haploid cell is formed from a diploid cell.

Define the term cancer

Cancer- cells have lost the ability to control the rate of mitosis, causing a group of disorders.

What is the function of mitosis in:

1. single celled organisms

2. multi-celled organisms

1. in single-celled organisms, the act of mitosis is asexual reproduction. Single-celled organisms use mitosis to reproduce and distribute their DNA

2. multicellular organisms because it provides new cells for growth and for replacement of worn-out cells, such as skin cells.

(T/F) Meiosis is an important source of variation

T

(T/F) Mitosis occurs in mature blood cells in humans

F

(T/F) During mitosis the nuclear membrane temporarily disappears

T

(T/F) Meiosis gives rise to the haploid condition

T

(T/F) In multicellular organisms mitosis functions primarily in growth

T

(T/F) In plants, the cell plate forms during telophase of mitosis

T

(T/F) The human zygote divides by meiosis

F. mitosis

What occurs during metaphase?

1. Nuclear membrane is gone

2. Chromosomes line up at the equator of cell

3. Spindle fibres attach to chromosomes

What occurs during anaphase?

1. Shortest phase

2. Spindle fibres contract, causing the centromeres to split

3. Chromosomes are pulled to either side of the cell

What occurs during telophase?

1. Chromosomes elongate and form chromatin

2. Nuclear membranes reform around each clump of chromatin

3. Mitosis is complete

   -Now cell begins to split:

   Animal cells=cleavage furrow

   Plant cells= cell plate (cell wall is too though to form c.f)

The human zygote is a …. and divides by….

diploid, mitosis

What is the difference between a haploid and diploid cells?

• haploid cells contain one complete set of chromosomes

• diploid cells contain two complete sets of chromosomes.

Draw a quick sketch of a diploid and a haploid cell

How many:

1. Diploid cells are present

2. Haploid cells are present

1. Diploid 2n=4

2. Haploid n=8

Define cancer

• cells have lost the ability to control the rate of mitosis, causing a group of disorders

Malignant cancer

life threatening ex. lung cancer

Benign cancer

harmless cancer ex. warts

Carcinogens

Cancer causing agents ex. sun and cigarettes

Is mitosis involved in sexual reproduction?

• Both sexual and asexual organisms go through the process of mitosis. It happens in the cells of the body known as the somatic cells and produces cells related to growth and repair.

• It is not however involved in sexual reproduction.

• Meiosis does not occur during asexual reproduction. Meiosis is the process of producing gametes (eggs and sperm). Mitosis, on the other hand, is simply the process of cell division.

What does the letter ‘n’ represent?

Are gametes and zygotes haploids?

• it represents haploid cells

• the sperm and egg are haploid cells, they each contain 23 chromosomes

• fertilisation causes these two haploid cell to form 46 chromosomes

• Hence, a Zygote is diploid. Each chromosome is present in two homologous, or comparable, copies in almost all human body cells. Due to the presence of both of its parents' genes, the zygote is diploid (carrying two sets of chromosomes).

Which diagram represents:

1. haploid cells

2. diploid cells

Also state the ‘n’ or ‘2n’

Top diagram is haploid- n=3 and n=4

Bottom is diploid- 2n=6 and 2n=8

• Remember: n represents haploid cells, 2n represents diploid

What does ‘2n’ represent

diploid cells, 2 sets of chromosomes

Chromosomes are paired in diploid cells called… genes

Chromosomes are paired in diploid cells called homologous genes

What is a homologous pair?

• two chromosomes that both have genes for the same features

What is the function of interphase?

• The phase of the cell cycle during which no division is occurring.

• 90% of cell cycle

• Function:

  1. Chromosome duplication

  2. Cell organelle replication (mitochondria, chloroplasts etc.)

  3. Production of enzymes

  4. Transcription and uncoiling

  5. Biomolecules produced; protein, fats, carbs

Define cell continuity and explain why it is useful:

° Cell continuity= all cells develop from pre-existing cells.

° Cell continuity is useful for the following reasons:

• It produces all needed materials

• It allows organisms to grow larger

• It replaces new cells

Chromosomes

Chromosomes are coiled threads of DNA and proteins that combine genetic materials up in the form of genes.

What occurs during interphase?

° During interphase:

• A cell isn’t dividing

• Chromosomes appear as thin threads called chromatin

• Cell is producing new organelles and enzymes

• Chromosomes duplicate and become double stranded

Somatic cells divide by … to produce … cells

Somatic cells divide by mitosis to produce diploid cells

Sex cells divide by … to produce … cells

Sex cells divide by meiosis to produce haploid cells

Define ‘metastasis’

Metastasis is the movement or spread of malignant tumours

Define ‘oncogenes’

a mutated gene that has the potential to cause cancer

(T/F) In plants, a cell plate forms during telophase of mitosis

T

(T/F) The human zygote divides by meiosis

False

Name two types biomolecules that are produced during interphase

1. protein

2. fats

or nucleic acid (RNA/DNA) or carbs

Name one organelle that is replicated during interphase

ribosome/mitochondria/chloroplast

Give any two changes that will have occurred in the cell by the end of interphase, a stage of the cell cycle

1. Chromosomes visible

2. Nuclear membrane disappears

End of Interphase is the start of Prophase

Suggest why mature human red blood cells do not undergo cell division

they don’t have a nucleus

Give a cellular process that occurs when the cell is in interphase

1. protein synthesis

2. photosynthesis

3. respiration

4. growth

Draw a diagram of a 2n=6 nucleus during metaphase

2n=6, so 6 chromosomes

Give one location where mitosis occurs in flowering plants

buds/ovule/embryo/sac/pollen

For the convenience of study, mitosis is divided into 4 stages. List these starting at A.

Prophase, Metaphase, Anaphase, Telophase

• by start at A they didn’t meant start at Anaphase

Give the names of the two processes involving DNA which take place during interphase

1. uncoiling

2. transcription

What is the role of chromosomes?

Carry genetic material, code for protein

Some cells in the body undergo meiosis. Give one function of meiosis

to produce gametes