Plant Reproduction (9.4) Flashcards
Give the ways in which plants can reproduce.
1) Vegetative propagation (asexual reproduction from plant cuttings).
2) Spore formation (eg. moulds).
3) Pollen transfer (in flowering plants).
Describe the stages in the sexual reproduction of flowering plants.
1) Pollination
The transfer of pollen grains from an anther to a stigma.
2) Fertilisation
The fusion of the male gamete nuclei (pollen) with the female gamete nuclei (ovule) to form a zygote.
3) Seed dispersal
The fertilisation of gametes results in the formation of a seed, which moves away from the parental plant. This seed dispersal reduces competition for resources between the germinating seed and the parental plant. Methods of seed dispersal include wind, fruits and animals.
Why is cross pollination in flowering plants preferred?
Because it improves genetic diversity. However, many plants possess both male and female structures and can self-pollinate.
Describe the differences between insect pollinated flowers and wind pollinated flowers.
Insect pollinated flowers are large and colourful, they produce scent and nectar and their pollen grains are spiked or sticky to attract insects.
Wind pollinated flowers are small and usually white. They have no scent or nectar and their stigma is feathery and exposed to the wind.
Where are the male and female gametes in flowering plants?
The male gametes are inside the pollen grains which develop in the anther of the flower. The female gametes develop inside the ovules which are enclosed in the ovary at the base of the carpal.
What causes flowering?
Changes in the gene expression trigger the enlargement of the shoot apical meristem. The tissue then differentiates to form the different flower structures - sepals, petals, stamen and pistil. The activation of genes responsible for flowering is influenced by abiotic factors, most commonly photoperiodism.
What is the purpose of flowering?
To enable the plant to sexually reproduce via pollination, fertilisation and seed dispersal. So flowers need to bloom when pollinators are at their most abundant.
Define phytochromes.
Leaf pigments which are used by the plant to detect periods of light and darkness. They exist in two forms: the inactive form of phytochrome (Pr) and the active form of phytochrome (Pfr). When Pr absorbs red light it changes to Pfr. Sunlight contains mostly red light so during the day there is high levels of Pfr. At night, Pfr is converted to Pr.
Explain short-day and long-day plants.
Only the active form of phytochrome (Pfr) is capable of causing flowering so the critical factor of determining plants activity is night length.
Short-day plants flower when the days are short – hence require the night period to exceed a critical length. Here, Pfr inhibits flowering and hence flowering requires low levels of Pfr (i.e. resulting from long nights).
Long-day plants flower when the days are long – hence require the night period to be less than a critical length. Here, Pfr activates flowering and hence flowering requires high levels of Pfr (i.e. resulting from short nights).
What are day-neutral plants?
Plants whose flowering is relatively unaffected by the amount of daylight.
How can the flowering of short-day and long-day plants be manipulated?
The critical night length required for a flowering response must be uninterrupted in order to be effective. So horticulturalists can manipulate the flowering of plants by controlling the exposure of light.
Eg. Long-day plants will traditionally not flower in winter or autumn when nights are long so during this time they are exposed to light during the night. Short-day plants will traditionally not flower in sumner when nights are short so during this time they are covered in a black cloth during the day.
Describe the structure of a bean seed.
Testa - outer seed coating for protection.
Cotyledon - contains the food stores.
Plumule/epicotyl - the embryonic shoot.
Radicle - the embryonic root.
Micropyle - a small pore which allows the passage of water.
Define germination.
The process by which a seed emerges from a period of dormancy and begins to sprout.
What are the conditions required for the germination of a typical seed?
- Water (to metabolically activate the cell - needed for the synthesis of gibberellin).
- Oxygen (for aerobic respiration to produce ATP for growth).
- Suitable temperature (for optimal function of enzymes).
- Suitable pH (for optimal function of enzymes).
Describe the metabolic events of germination.
Germination begins with the absorption of water, which causes gibberellin to be produced. Gibberellin stimulates the production of amylase which converts starch into simple sugars. The glucose is then used in aerobic respiration to produce the ATP needed for growth.
