Biology Module 2.6 Cell Division, Diversity And Differentiation

1. Different stages in Interphase- G1, G0, S, G2

G1- growth, organelles are duplicating, biosynthesis, S- DNA replication (SYNTHESIS), chromatid forms, rapid process to prevent chances of mutation which is possible due to exposed bases G2- growth and preparation for mitosis

2. Checkpoints- is replication correct, detect and repair DNA damage, prevents uncontrollable division, checking if cell is ready for the next stage

3. where? G1/S(restriction point) to check if ready for next stage and G2/M

1. Mitosis: type of nuclear division that maintains the chromosome number producing daughter cells identical to parent cells (diploid)

2. Cytokinesis: division of cytoplasm following mitosis

3. Chromatids: replicates of chromosomes

1. Prophase: two identical sister chromatids thicken and shorten. Nuclear envelope breaks down. Centrioles divide forming two new daughter centrioles. cytoskeleton protein spindles form

2. Metaphase: Chromatids align at equator. Spindle attaches to chromosomes at centromere

3. Anaphase: Chromatids pulled to opposite poles by motor proteins. centromere splits, now chromosome

4. Telephase and cytokinesis: Nuclear envelope forms and plasma membrane folds inwards

Importance of mitosis:

1. Assexual reproduction: e.g. Amoeba divide by mitosis to produce new individuals

2. Growth: multicellular organisms grow producing somatic cells

3. Tissue Repair:

Importance of Meiosis

1. Sexual Reproduction: fertilisation can only occur when there is half the number of chromosomes- Gametes in order to produce a zygote with full set of chromosomes

Prophase 1: Chromatids shorten and thicken. Nuclear envelope breaks down. Centriole and spindles form. chromatids come together in their homologous pairs. Crossing over occurs and alleles can be shuffled

Metaphase 1 : homologous chromosomes (crossed over) line up along the equator of the spindle. spindle and centromere. independent assortment- the homologous pairs are arranged randomly.

Anaphase 1: homologous pairs are pulled apart by motor proteins along spindle. Centromere does NOT divide. There is a random distribution

Telephase 1 : Nuclear envelope reforms. Plasma membrane folds inwards.

Prophase 2: Nuclear envelope break down again. Chromatids- coil, condence and shorten. Spindles form

Metaphase 2: Chromosomes attach by centromere to equator of the spindle. chromatid arrangement is random.

Anaphase 2: centromeres divide. Motor proteins pull chromosomes to opposite ends. Random segregation

Telophase 2: nuclear envelope reforms and plasma membrane folds in 4 haploid in animals and tetrad of four haploid cells is formed.

Multicellular organisms are larger therefore have a smaller SA/V ratio which means they do not have contact with external environment. This then means that processes such as diffusion take long.

Erythrocytes: red blood cells. carry O2 from lungss to cells. small, no nucleus, and bioconcave increases SA/V ratio which means they can carry a lot of haemglobin and diffuse O2 very quickly

Neutrophils: white blood cells and ingest pathogens. large, multilobed nucleus, attracted and travel towards infection sites by chemotaxis

Spermatozoa: many mitochondria for ATP energy to move to ovum. small, long thin- can move fast. can release enzymes in order to enter the ovum digesting the outer part. head contains nucleus.

Epithelial Cells: Flattened into shape (squamous) have cillia. It is a lining tissue found inside and outside body (lining of intestines)

Palisade cells:

Guard cells;

Root hair cells:

Xylem and Phloem:

epethelial tissue