16.1 - 16.3 Reproduction in plants Flashcards
asexual reproduction
a process of resulting in the production of genetically identical offspring from one parent
binary fission
when bacteria produce exact genetic copies of themselves in a type of asexual reproduction
state and explain types of asexual reproduction in plants
- Bulbs and tubers - these are food storage organs from whcih budding can occur and produce new plants that are genetically identical to parent plant
- Runners - some plants grow shoots that contain tiny plantelets on them (e.g. strawberries). These will grow roots and develop into seperate plants that are genetically identical to parent plant.
Advantages of ASEXUAL reproduction
- pop can be increased rapidly when conditions are right
- can exploit suitable environments quickly
- more time and energy efficient
- reproduction is completed much faster than sexual
Disadvantages of ASEXUAL repoduction
- Limited genetic variation in pop
- pop is vulnerable to changes in conditions - only suited for one habitat
- disease more likely to affect the whole pop bcs no genetic variation
Advantages and Disadvantages of ASEXUAL reproduction for CROPS
+) varieties with useful features can be cloned in large numbers
-) all clone plants are susceptible to the same disease
Sexual reproduction
a process involving the fusion of the nuclei of two gametes to form a zygote and the production of genetically different offspring
fertilisation
fusion of the nuclei of gametes
whats special about the nuclei of gametes?
they are haploid nuclei - contains only one set of chromosomes (23, no pairs)
Advantages of SEXUAL reproduction
- Increases genetic variation
- species can adapt to new environment bcs variation, giving them a survival advantage
- disease less likely to affect pop (due to variation)
Disadvantages of SEXUAL reproduction
- takes time and energy to find mates
- difficult for isolated members of the species to reproduce
Advantages and disadvantages of SEXUAL reproduction in CROPS
(+) speed up natural selection through selective breeding - increasing yield
(-) takes a long time to grow new crops. Is dependent on sucessful pollination.
sepal
protects the unopened flower
petal
may be brightly coloured to attract insects
anther
produces and releases the male gamete (pollen grain)
stigma
top of female part of the flower - collects pollen grains
ovary
produces the female gamete (ovum)
ovule
contains the female gamete (found inside the ovary)
difference between pollen produced by wind and insect pollinated flowers
INSECT: produce smaller amounts of larger, heavier pollen grains that often contains spikes or hooks on outside to stick to insects better
WIND: large amounts of small, lightweight pollen that are usually smooth
difference between flowers on wind and insect pollinated flowers
INSECT: large and brightly coloured to attract insects
WIND: small and dull (often green or brown)
difference between scent/nectar in wind and insect pollinated flowers
INSECT: present - entices insects to visit the flower and push past stamen to get nectar
WIND: absent - no need to waste energy
difference between anthers and stigmas in wind and insect pollinated flowers
INSECT: Anthers are inside the flower, stiff and firmly attached to brush against insects. Stigmas are sticky so pollen grains can stick when insect brushes past.
WIND: Anthers are outside flower, swiming loose on long filaments to release pollen grains easily. Stigmas are outside flower, feathery to catch drifting pollen grains
Cross pollination
occurs when the pollen from one plant is transferred to the stigma of another plant of the same species
- improves genetic variation
- relies completely on pollinators, if pollinators gone (reduction in bees) then no pollination.
Self pollination
when the pollen from a flower lands on its own stigma or on the stigma of another flower on the same plant
- reduces genetic variation. less likely that any offspring will have adaptations that suit the new conditions well.
how does fertilisation occur in flowers. starting from how the pollen gets to the ovum.
- pollen grain lands on the stigma
- the pollen grain grows a tubule down the style using digestive enzymes. Acting as a channel to deliver the male gamete to the female gamete in the ovule.
- fertilisation occurs when the haploid male and female gametes nuclei fuse and form a diploid zygote. Divides to become embryo, which become seed. the fertilised ovary is a fruit.
germination
start of growth in the seed
factors required for sucessful germination and why
WATER - allows the seed to swell up and the enzymes in the embryo to start working so that growth can occur
OXYGEN - so that energy can be released for germination
WARMTH - germination improves as temp rises as the reactions which take place are controlled by enzymes
Experiment to investigate germination
- Set up 4 boiling tubes each containing 10 cress seeds on cotton wool
- Set each test tube as shown in diagram below
- Leave tubes in set environment for a period of time: A, B and C incubated at 20°C; D placed in a fridge at 4°C
- Compare results and see which tube has the greatest number of germinated seeds
