Development of organisms and continuity of life flashcards

Topic 16: Development of organisms and continuity of life

Mitosis v meiosis

Same number and identical v halved and different.

Roles of mitosis and of meiosis

Mitosis: growth, repair, replacing dying cells, asexual reproduction. Meiosis: making gametes.

Stem cells

Unspecialised cells that divide by mitosis to give daughter cells that can become specialised.

Diploid nucleus

Two sets of chromosomes; a pair of each type. Human diploid cells: 23 pairs.

Asexual vs sexual reproduction: one advantage of each

Asexual: no mate or pollinator needed; fast; good features kept. Sexual: variation, so the population can respond to environmental change.

Pollination v fertilisation

Moving pollen v fusing nuclei.

Insect- vs wind-pollinated flowers (O Level)

Insect: large coloured scented petals, nectar; anthers and sticky stigma inside; larger sticky or spiky pollen. Wind: small dull petals; anthers on long filaments and feathery stigmas outside; small light smooth pollen in huge amounts.

From pollen to seed

Pollen lands on the stigma; a pollen tube grows down the style and enters an ovule through the micropyle; the male nucleus fuses with the female nucleus. The ovule becomes the seed; the ovary becomes the fruit.

Germination: conditions and what water does

Water, oxygen and a suitable temperature (not light). Water activates enzymes: amylase breaks starch to maltose and proteases break protein to amino acids, for respiration and growth of the embryo.

Sperm

Flagellum (swims); mitochondria (energy for swimming); acrosome enzymes (digest jelly coat).

Menstrual cycle hormones: FSH, LH, oestrogen and progesterone

FSH (pituitary): egg develops; ovary makes oestrogen. Oestrogen: rebuilds lining; inhibits FSH; triggers LH. LH (pituitary): ovulation. Progesterone (empty follicle): keeps lining thick; inhibits FSH and LH.

Placenta

O₂ and dissolved nutrients to fetus; CO₂ and urea to mother. Bloods do not mix.