Biology - Cell Division

Cell Continuity

all cells develop from pre-existing cells

Chromosomes

• coiled threads of DNA (which forms genes) and protein that become visible in the nucleus at cell division

• chromatin in elongated form

Haploid Cell

• (n)

• has one set of chromosomes - i.e. only one type of each chromosome in the nucleus

Diploid Cell

• (2n)

• has two sets of chromosomes - i.e. has two of each type of chromosome in the nucleus

Homologous Pair

two chromosomes of similar size with the same sequence of genes

Cell Cycle

• the changes that take place in a cell during the period between one cell division and the next

• interphase is when the cell is not dividing

• cell division (mitosis or meiosis)

Interphase

• phase in the cell cycle when it’s not dividing

• an active phase where new organelles are formed, and single-stranded chromosomes form double-stranded copies of themselves

Mitosis

a form of nuclear division in which one nucleus divides to form two nuclei, each containing the same number of chromosomes with identical genes

Meiosis

a form of nuclear division in which the four daughter nuclei contain half the chromosome number of the parent nucleus

Centromere

the point at which the chromosomes are attached in a double-stranded chromosome

Gene

a short-section of DNA that controls the formation of a protein

Stage 1

prophase

Stage 2

metaphase

Stage 3

anaphase

Stage 4

telophase

Functions of MItosis

• allows single-celled organisms to reproduce

• allows for growth and repair in multi-cellular organisms

Tumour

forms when one or more cells lose the ability to control the rate of mitosis

Benign

tumour that is not life-threatening

Malignant

life-threatening tumours

Oncogenes

cancer causing genes

Cancer

occurs when cells lose the ability to control the rate and the number of times mitosis takes place

Carcinogens

cancers are cause by these agents

Gametes

haploid cells that are able to fuse with another gamete of the opposite sex

Functions of Meiosis

• to halve the number of chromosomes so that the normal number may be restored at fertilisation (to allow for sexual reproduction)

• to produce chromosomes with genetic variations that will result in variations in the organisms produced by sexual reproduction

Prophase

• chromatin contracts

• chromosomes are seen as two strands held together at the centromere

• the nucleus disappears

• spindle fibres appear

• the nuclear membrane starts to break down

Metaphase

• the nuclear membrane is broken down

• two spindle fibres attach to each centromere

• the chromosomes line up along the equator of the cell

Anaphase

• the spindle fibres contract

• an equal number of identical chromosomes is pulled to each pole

Telophase

• the chromosomes elongate to form chromatin

• the spindle fibres break down

• nucleoli re-form

• two nuclear membranes form

Animal Cells

(cell division)

a cleavage furrow forms and deepens to produce two new cells

Plant Cells

(cell division)

vesicles gather to form a cell plate, which forms the cell walls and middle lamella