Reproduction And Growth Flashcards
Features of sexual reproduction
- gametes produced
- fertilisation takes place
- genetic variation in offspring
- has survival value in changing environments
Features of asexual reproduction
- no gametes produced
- no fertilisation takes place
- no genetic variation
- has survival value in stable environments
Diploid number in humans
46
Haploid number in humans
23
Why does sexual reproduction produce genetic variation?
- variation amongst gametes
- random nature in which fertilisation takes place
What does sexual reproduction involve
Fusion of male and female gamete to produce a zygote that undergoes cell division and develops into an embryo.
What are the male gametes in plants?
Pollen grains
Where are the pollen grains produce in plants?
Anthers of the stamens
Where are the egg cell produced in plants
Ovules of the ovaries
Insect pollinated flower structure adaptations
- stamen and stigma is enclosed - so insect has to come into contact with it
- stigma is sticky - pollen grains stick to it from insect
- large, brightly coloured petals - attract insects
- nectar - attract insects
- pollen grains are large and sticky - stick to insect bodies
Two sexual ways to pollinate flowers
Wind pollinated
Insect pollinated
Wind pollinated flower structure adaptations
- stamen is exposed - wind can blow pollen grains away
- stigma is exposed and feathery - catch pollen grains easily
- small, not brightly coloured petals
- no nectar
- Pollen grains a re smaller and smoother - travel further in wind
Advantages of sexual and asexual reproduction
Sexual
- offspring are genetically varied
Asexual
- only one parent needed
- offspring are clones
Natural asexual ways to reproduce a plant
Runners - part of plant touches ground and forms new plant
Tubers - form at end of branches. Food store fro new plant whilst it develops
Bulbs - acts as food store where new buds can develop
Artificial ways to asexually reproduce plant
cutting - branch from parent cell is cut off with a few leaves. Stem placed in damp compost with hormones to promote new root development
Grafting - plant cutting placed onto the stem of another and they grow together. Used when plant grows poorly but has desirable traits (large fruits, disease resistance)
3 main conditions needed for seed to germinate
Water ( enzyme reactions)
Warmth ( metabolic reactions)
Oxygen ( respiration)
Signs a seed has germinated
- small root ( radicle) and a shoot (plumule) show
- seed splits
What happens to the ovary and ovule after fertilisation?
Ovary wall - becomes fruit coat
Ovule wall - Becomes seed coat
Steps for germination
- Seed coat absorbs water and expands
- Seed coat swells and splits
- Shots grow upwards and roots grow downwards
- First leaf develops - producing food by photosynthesis
- More leaves develop
What is the role of placenta
Allows embryo to obtain nutrients from mothers blood and get rid of waste products ( urea and carbon dioxide)
Anchors embryo in uterus
Examples of what the placenta passes through mother’s blood
- Oxygen, glucose, amino acids ( to make proteins), fatty acids and glycerol ( to make lipids). Secretes progesterone
- carbon dioxide, urea
- prevents mixing of mother and embryo’s blood
What does amnion secrete and what does it do?
- Secretes amniotic fluid which protects the embryo from shock and sudden movement (amniotic sac)
- Maintains constant temperature around foetus
Role of umbilical cord
Transports foetus blood to the placenta and back to allow exchange of materials with mother’s blood
Role of cervix
-Stays closed during pregnancy forming a barrier to pathogens
- softens and dilates during labour
