4.1 sexual reproduction in plants Flashcards
What are 5 features of insect pollinated flowers?
Receptacle, calyx, corolla, stamen, carpel, nectaries.
What’s the function of the receptacle?
The top of the flower stalk from which the different parts of the flower develop.
What’s the function of the calyx?
The first set of modified leaves called the sepals - these protect the flower while it’s still forming and before the flower bud opens.
What’s the function of the corolla?
This is the layer of modified leaves called petals - these are often large, coloured and patterned to attract insects; some of the colours, e.g. UV are not visible to humans - only to insects.
What’s the function of the stamen?
This is made of the filament and anther. This is the male reproductive organ of a flower - the site of meiosis and mitosis to produce the male gametes.
What’s the carpel?
Composed of the ovary, style and stigma, this is the female reproductive organ of a flower. The ovary is the site of meiosis to produce the female gametes contained within the ovules.
What’s the function of the nectaries?
These secrete a sweet substance - nectar - that attracts many insects and other animals that carry pollen from one flower to another.
What are other features that distinguish an insect pollinated flower?
- A smell may be produced to attract insects,
- anthers and stigma are generally enclosed within the petals,
- pollen is often large and sticky/spiky, - only a small quantity of pollen is produced.
What are features of a wind pollinated flower?
-Petals are absent,
- no scent is produced,
- nectaries are absent,
- anthers and stigma hang outside the flower,
- anther is loosely attached,
- stigma is usually feathery,
- pollen is small and light, and very large quantities of pollen are produced.
Define self pollination.
Self-pollination occurs when a plant’s own pollen lands on the stigma of the same flower.
What are advantages of self pollination?
- Rapid pollination with a high chance of success.
- Reduced genetic variation.
- Good genomes are preserved.
What are disadvantages of self pollination?
Reduced genetic variation makes plants equally susceptible to diseases and environmental changes.
Define cross pollination.
Cross-pollination occurs when a stigma receives pollen from a different plant of the same species.
What’s the main advantage of cross pollination?
Increased genetic variation, enhancing the chance of species survival.
What are the disadvantages of cross pollination?
Good combinations of alleles can be lost due to crossing over and random fertilisation.
What are some adaptations of plants to ensure cross pollination occurs?
-Chemical self-incompatibility,
-flower structure,
-development of anther and stigma, separate male and female flowers.
How does chemical incompatibility increase cross pollination?
Stigma chemicals inhibit pollen from the same plant, promoting cross-pollination.
How does flower structure promote cross pollination?
Irregular structures force insects to enter and leave the flower in a way that reduces self-pollination.
How does the development of anthers/stigmas promote cross pollination?
Either the anthers mature before the stigmas or vice versa, preventing simultaneous presence.
What do pollen grains contain?
Pollen grains contain the male gametes of flowering plants.
What is the tapetum?
A specialised layer of nutritive cells found within the anther, important for the nutrition and development of pollen grains.
Describe the development of pollen.
Pollen mother cells develop
by mitosis.
- Meiosis occurs to produce
a tetrad of 4 haploid cells.
-In each haploid, pollen
grain mitotic division of the
nucleus forms a generative
nucleus (that mitotically
divides to produce 2 male
nuclei) and a tube nucleus.
Describe the development of an ovule.
- Diploid Megaspore mother cell undergoes meiosis to form 4 haploid megaspores
- Three megaspores disintegrate.
- The 1 functional megaspore develops into the embryo sac.
- It undergoes 3 mitotic divisions producing eight haploid nuclei.
- 2 nuclei move to centre of cell (polar nuclei), 3 antipodal cells and 2 synergids
What is double fertilisation?
Fertilisation of female gamete to form a diploid zygote and fertilisation of polar nuclei to form triploid endosperm nucleus.
What occurs during double fertilisation?
- Pollen grain lands on stigma.
- Pollen tube grows down the style.
- Generative nucleus divides to form two male gametes.
- Pollen tube enters through micropyle.
- Fertilization occurs.
What forms when the zygote divides by mitosis?
Forms the embryo which contains the embryo root (radicle) and embryo shoot (plumule).
What does the primary endosperm nucleus form?
Divides by mitosis to form food storage tissue.
What do the integuments form?
Fuse to form testa and seed coat.
What does the ovary form?
Forms fruit wall and encloses the seeds.
What do ovules form?
Seeds.
Describe the role of organelles in the passage of the pollen tubes through the style.
- Secretory vesicle releases enzymes.
- Enzymes digest a path through the style.
- Mitochondria provide ATP.
- Rough ER synthesizes enzymes.
- Golgi bodies process and package proteins.
What is a dicotyledonous plant?
A plant with 2 seed leaves or cotyledons which act as food stores.
What is a monocotyledon?
A plant with one seed leaf or cotyledon, where the main food store is the endosperm.
What are the requirements of germination?
Seeds absorb water and oxygen, require a warm temperature, and some need light to trigger germination.
What’s an endospermic seed?
Seeds which use endosperm as their food store, e.g., maize.
Describe the process of germination in endospermic seeds.
- Water is absorbed. 2. Gibberellins are mobilised. 3. DNA is transcribed into mRNA. 4. Hydrolytic enzymes are produced. 5. Amylase hydrolyses starch to glucose.
What’s a non-endospermic seed?
Seeds which don’t use endosperm as their food store, e.g., broad bean.
Describe the process of germination in non-endospermic seeds.
- Water is imbibed. 2. Cotyledon swells and testa splits. 3. Food reserves from cotyledons are mobilised.
