16. Reproduction Flashcards
(16 cards)
Describe asexual reproduction
A process resulting in the production of genetically identical offspring from 1 parent
Discuss the advantages and disadvantages of asexual reproduction:
(a) to a population of a species in the wild
(b) to crop production
a) Wild Species
Advantages:
1. Rapid population growth
2. Exploits suitable environments quickly
3. More time and energy-efficient
4. Reproduction is completed much faster
Disadvantages:
1. Limited genetic variation in population
2. Vulnerability to habitat changes
3. Disease is likely to affect the whole population (as no genetic variation)
4. Slow evolution (no recombination of genes)
b) Crop Plants
Advantages:
1. Reproduced with desired characteristics
2. Reproduced with uniform characteristics for commercial sale
3. Production can be fast
4. Cost of production will be less than investing in seeds
Disadvantages:
1. Won’t adapt to changes in climate
2. Process of asexual reproduction in crops requires human input and management
3. Disease is passed on to the offspring if parent plant used is affected
4. Vulnerability to disease or pests may result in big financial losses for farmer
Describe sexual reproduction
A process involving the fusion of the nuclei of two gametes to form a zygote and the production of offspring that are genetically different from each other
Describe fertilisation
The fusion of the nuclei of gametes
Discuss the advantages and disadvantages of sexual reproduction:
(a) to a population of a species in the wild
(b) to crop production
a) Wild species
- Advantages:
1. Increases genetic variation
2. Species can adapt to new environments due to variation, giving them a survival advantage
3. Disease is less likely to affect the population due to variation
- Disadvantages:
1. Takes time and energy to find mates
2. Difficult for isolated members of the species to reproduce
b) Crop production
- Advantages: Like above. But in addition to: Variation is increased, so a genetic variant may be produced. Allowing them to cope with weather changes, and produce significantly higher yield
- Disadvantages: Like above. But in addition to: Variation may lead to offspring that are less successful than the parent plant at growing well or producing a good harvest
State the functions of the structures in an insect-pollinated flower: sepals, petals, stamens, filaments, anthers, carpels, style, stigma, ovary and ovules
- Sepal: Protects unopened flowers
- Petals: Brightly coloured in insect-pollinated flowers to attract insects
- Anther: Produces and releases pollens
- Filaments: Provides support to the anther
- Stigma: Sticky top to collect pollen grains
- Style: Connects the stigma and ovary
- Ovary: Contains the ovules
- Ovule: Contains the female gametes
Describe the anthers and stigmas of a wind-pollinated flower
For wind to easily catch pollen grains and carry them to the stigmas of other flowers, the anthers and stigmas of wind-pollinated flowers hang outside the flower. So that pollens can:
1. Easily be blown away by the wind
2. Easily be caught by the stigmas of other flowers
How to distinguish between the pollen grains of insect-pollinated and wind-pollinated flowers
- Insect-pollinated: Produces larger, heavier pollen grains. Often containing spikes or hooks (able to stick to insect)
- Wind-pollinated flowers: Produces small, lightweight pollen grains (to easily be caught and carried by the wind)
Describe pollination
The transfer of pollen grains from an anther to a stigma
Describe self-pollination
The transfer of pollen grains from the anther of a flower to the stigma of the same flower or a different flower on the same plant
Describe cross-pollination
The transfer of pollen grains from the anther of a flower to the stigma of a flower on a different plant of the same species
Discuss the potential effects of self-pollination and cross-pollination on a population
a) Self-pollination:
- All gametes come from the same parent. Therefore, offsprings are genetically identical and have a reduced genetic variety
- If environmental conditions change, offsprings are less likely to have adaptations that suit the new conditions
b) Cross-pollination:
- Carried out by most plants. Improving genetic variation
- Relies completely on pollinators. If those pollinators go missing, problems may arise
Describe the growth of the pollen tube and its entry into the ovule followed by fertilisation
- Pollen tubes: Grow down the style until it reaches the ovary, and enters the ovule through micropyle
- Pollen nucleus: Travels down the tube
- Fertilisation: Nuclei enters the ovule and fuse with the nucleus of the female gamete within the ovum
- Seeds and fruits: After fertilisation, the ovary wall develops into a fruit. While the ovule eventually develops into a seed
Describe the structural adaptations of insect-pollinated and wind-pollinated flowers
- Petals:
- Insect-pollinated: Large and brightly coloured to attract insects
- Wind-pollinated: Small and dull, often green or brown in colour - Scent and nectar:
- Insect-pollinated: Produced to encourage insects to visit the flower and push past stamen to get nectar
- Wind-pollinated: Not produced; would be a waste of energy - Anthers:
- Insect-pollinated: Held on stiff filaments within the flower so that they brush against insects
- Wind-pollinated: Held on long filaments outside the flower to release pollen grains easily into the wind - Stigma:
- Insect-pollinated: Sticky stigmas within the flowers catch pollen grains when insects brush past
- Wind-pollinated: Feathery stigmas outside the flower catch airborne pollen grain
Investigate the environmental conditions that affect germination of seeds, limited to the requirement for: water, oxygen and a suitable temperature
- Set up: Like (check online notes). Put 10 cress seeds on cotton wool
- Placing: Test tube A, B and C incubated at 20°C, D in a fridge at 4°C. Leave them for a period of time
- Observations and results: Proves that all three factors are required for a successful germination. If any one factor is missing, the seeds cannot germinate
Describe the environmental conditions that affect germination of seeds
- Water: Swells up the seed for enzymes in the embryo to start working so that growth can occur
- Oxygen: Allows energy to be released for germination
- Warmth: Germination improves as temperature rises (until max) as the reactions are controlled by enzymes
