Plant Reproduction Flashcards
What is an angiosperm?
A flowering plant.
Describe asexual reproduction and what types of plants are involved.
No sex, no seed, results in clones
E.g tubers (potatoes), suckers, runners, budding, fragmentation/shedding (cacti)
Describe the angiosperm life cycle in steps.
- alternating generations between the haploid (n) stage and diploid (2n) stage.
1. Meiosis produces haploid microspores in pollen sac (male) and megaspores in the ovary (female).
2. The male pollen sac microspores then undergo mitosis to produce microgametophytes in the form of pollen grains (male). Meanwhile, the female ovary megaspores undergo mitosis to produce megagametophytes in embryo sacs.
3. POLLINATION then occurs with male pollen grains entering pollen tube and female embryo sacs entering ovary.
4. FERTILISATION then occurs with sperm fusing with embryo sac, producing zygote within parent ovary.
5. Mitosis then produces embryo within seed, which then produces independent sporophyte.
6. Independent sporophyte then produces flower.
What is the dominant generation in flowering plants?
The diploid stage
Describe the general structure of a flower.
- flower grows in 4 whorls around the tip of the flower stalk (receptacle)
- whorl 1 contains the sepal which is a leaf like structure on top of the stem
- whorl 2 contains the petal, some of which may contain honey guides that guide pollinators to the nectary glands
- nectary glands are not part of any whorl
- whorl 3 is the stamen which is the male reproductive organs and contains anthers on top of filaments
- whorl 4 is the carpel which is the female reproductive organs and contains the ovary, ovule, style and stigma
Where do ovules develop?
In the ovary
What is an embryo sac and what does it contain?
It is the female gametophyte and contains an egg cell
What gender are stamens and what do they consist of?
Stamens are male and consist of anther on top of filaments.
What is produced in the anther?
Male gametophytes which are pollen grain
What gender are carpels and what do they consist of?
Carpels are female and consist of an ovary containing ovules, and a style stemming from the ovary with a stigma on top of the style.
What is a gynoecium?
Several carpels fused together.
What is the stigma covered in? Why is this substance important?
Covered in papillae. It increases surface area.
What is the function of the stigma?
Captures pollen grains
Why is pollen size important?
Must be the right size in order to stick between papillae
How do the sperm reach egg cells?
- pollen must be transported from the anther to the female stigma by air, water or animal vectors.
- pollen that arrives on a stigma germinates to produce a pollen tube that grows down the style to the ovary.
- in this way, male gametes are transferred to the egg cell in the embryo sac, lying within the ovule
- fertilisation takes place and an embryo is formed, the new diploid generation
What is a seed?
An embryo, together with some food reserved and an outer coat. Also known as the unit of dispersal.
What is the product of fertilisation?
A seed containing an embryo
Describe what happens as a pollen tube approaches an ovule involving synergid cells.
- one synergid cell degenerates
- once the pollen tube reaches the embryo sac, it enters the degenerated synergid
- tube tip ruptures and releases pair of sperm cells and tube nucleus
What does double fertilisation involve? Explain the steps.
It involves true fertilisation (fusion of sperm and egg) and an accessory fusion (between sperm and central cell).
One sperm cell released form the pollen tube fuses with the egg cell to form the diploid zygote, the first cell of the new sporophyte generation.
The other sperm cell fuses with a central cell containing two nuclei to produce a triple fusion nucleus. This nucleus divides mitotically to produce a nutritive triploid tissue called endosperm that supports growth of the embryo and the young seedling.
What is formed in the first fertilisation event?
What is formed in the second fertilisation event?
- Embryo
2. Endosperm
What is apomixis?
Meiosis does not occur and embryos develop asexually.
What do ovules develop into?
What does carpel wall develop into?
- Seeds
2. Fruit
What do flowering plants use to select appropriate mates?
This selection takes place on the stigma or in the style.
What are abiotic methods of seed dispersal?
- wind e.g dandelion, sycamore seed
- gravity
- water (buoyancy) e.g coconut floating
What are biotic methods of seed dispersal?
- fleshy fruits to attract frugivores
- sticky seeds to catch on animals
- cap on seed as reward for ants that provides them with nutrients
Why do plants control mate choice?
To avoid mating with relatives.
What is inbreeding?
Mating within a single individual (can still be between different flowers on the same plant)
What are the advantages and disadvantages of inbreeding?
Advantages:
- preserves well-adapted genotypes
- ensures seed set in absence of pollinators
- single colonising individual possible
Disadvantages:
- decreases genetic variability
- offspring with deleterious (harmful) mutations
What is outbreeding?
Mating between two different individuals.
What are the advantages and disadvantages of outbreeding?
Advantages:
- increased genetic variability
- strong evolutionary potential
- adaptation to changing conditions
Disadvantages:
- can destroy well-adapted genotypes
- relies on effective pollination vectors
What is cross-pollination?
The transfer of pollen from one plant to the stigma of a different plant of the same species.
What is self-pollination?
Transfer of pollen to a stigma of a flower on the same plant.
What are the ways in which self-pollination is prevented?
Dioecy: unisexual flowers on different plants (separate plants have male or female organs)
Protandry: male organs mature first.
Protygyny: female organs mature first
(Therefore temporal separation of male and female function)
Self-incompatibility: genetic control of pollen compatibility. Plant will possess same genotypes alleles in all flowers, therefore cannot be pollinated (self incompatible alleles)
What are the ways in which self-pollination is encouraged?
Cleistogamy: flowers that don’t open and therefore self-pollinate
Apomixis: egg cells form mitotically and develop into clone embryos without fertilisation
What is generalist pollination?
Many kinds of flower visitors that act as couriers to transport pollen = anyone
What is specialist pollination?
Exclusive set of flower visitors that act as couriers to transport pollen, often one species.
Why is specialist pollination advantageous?
Bc pollen is less likely to be wasted on a different species of flower.
How has evolutionary feedback worked with pollination?
Flower adapts to sensory system of the pollinator.
Describe examples of co-evolution between pollinators and flowers.
Bird pollination: bird pollinated flowers are almost always red because birds are visually driven.
Moth pollination: pale nocturnal flowers with deep nectar tubes. Emit aromatic hydrocarbons
Carrion fly pollination: flower emits rotting smell which is irresistable to carrion flies
Buzz pollination: “poricidal anthers” only release pollen when vibrated at a fundamental frequency. Pollen is therefore only accessible to the bee who can produce that frequency. E.g tomato
