Topic 16 Flashcards
Asexual reproduction
Process used to produce genetically identical offspring from one parent
. Example: strawberry plants using runners, tulips using bulbs and bacteria by splitting in two
Asexual reproduction advantages
- Lots of offspring can be prodcuced very quickly
- Less energy required
- Offspring are genetically identical -> beneficial features will be inherited
- Offspring reach maturity quicker
Asexual reproduction disadvantages
- No genetic variation -> unlikely to adapt to changes in the environment
- Overpopulation
Sexual reproduction
Process used to produce offspring that are genetically distinct from each other -> involves the fusion of the nuclei of two gametes, which are haploids (fertilisation) to form a zygote, which is diploid
Sexual reproduction advantages
- Genetic variation -> likely to adapt to changes in the environment
- Diversity can lead to natural selection and evolution
- Selective breeding can be used to improve crop production and quality
Sexual reproduction disadvantages
- Takes more time and energy than sexual reproduction
- Two parents are needed
Stamen
Produces male gametes -> consits of anther and filament
Anther
Contains pollen grains which produce male gametes
Filament
Holds up anther
Petals
Brightly colored in insect-pollinated flowers to attract insects for pollination
Sepals
Protect flower in bud
Carpel
Produces female gametes -> consist of stigma, style and ovary
Stigma
End bit that pollen grains attatch to
Style
Supports stigma and connects it to ovary
Sexual reproduction in plants
Plants that reproduce sexually have both male and femal gametes in flower
Pollination
Transfer of pollen from an anther to a stigma
Self-pollination
Self-pollination: pollen is transferred from anther to a stigma on either same flower or a different flower on same plant
. Don’t rely on pollinators -> easier for them to spread to locations where there’s no pollinators
. Produces less variation (gene pool smaller) -> less likely to adapt to stimuli in environment
Cross-pollination
Pollen is transferred from anther to stigma on a flower from a different plant of same species
. Rely on pollinators to transfer pollen grains elsewhere -> If pollinator population declines = harder for flowers to reproduce
. Produces more variation -> more likely to adapt to stimuli in environment
Plant pollination: adaptations for insect pollination
. Large, brightly coloured petals to attract insects
. Scented flowers and nectaries (glands that secrete nectar) to attract insects
. Sticky stigma so pollen picked up by insects on other plants will stick to stigma
. Make big, sticky pollen grains which stick to insects as they go from plant to plant
Plant pollination: adaptations for wind pollination
. Small, dull petals
. No nectaries or strong scents
. Long filaments that hand anthers outside of flower so a lot of pollen fets blown away by wind
. Large and feathery stigma which hangs outside flower to catch pollen as it’s carried past by wind
Fertilisation in plants
Nucleus from pollen grain (male gamete) fuses with nucleus of female gamete in ovule -> happens in ovule
Steps of fertilisation in plants
- Pollen grains lands on stigma of flower -> with help from insects or wind
- Pollen tube grows out of a pollen grain and down through style to ovary and into ovule
- A nucleus from male gamete moves down tube to join with a female gamete in ovule and fertilisation occurs forming a zygote -> zygote divides by mitosis to form an embryo
- Each ovule containing fertilised female gamete forms a seed, which can grow into a new plant
Germination
After a seed is formed it will often lie dormant until conditions around it are right for germination (growth into a plant)
. Water: to activate enzymes that break down food reserves in seed
. Oxygen: for respiration -> transfers energy from food to growth
. Suitable temperature: for enzymes inside seed to work -> depends on type of seed
Urethra
Tube that carries sperm through penis during ejaculation and urine also passes through it to exit body
