Plant reproduction D3.1.8- D3.1.12

• What are pollinators?


  Insects- bees, hoverflies, wasps, beetles, butterflies and moths- are all pollinators. Flowering plants are therefore adapted to attract pollinators.
• What are petals?


  brightly coloured structures around the flower.
• What are the function of petals?

  attract insects with colour, scent, and sometimes nectar guides.
• What are sepals?

  green leaf-like structures at the base of the flower
• What are the function of sepals?

  protect the developing flower bud.
• What is the male part of the plant?

  Stamen (male part) - made up of:

  - Anthers - contain pollen sacs (produce pollen).

  - Filament - stalk holding up the anther.

  - Pollen - male gametes.
• What is the function of the anthers?

  produce and release pollen grains (male gametes).
• What is the function of the filament?

  positions the anther so insects can brush against it.
• What is the function of the pollen?

  carries sperm cells to fertilize ovules.
• What is female part of the plant?

  Carpel (female part) - made up of:

  - Stigma - sticky tip that catches pollen.

  - Style - tube connecting stigma to ovary.

  - Ovary - contains ovules.

  - Ovule - contains female gametes (eggs).
• What is the function of the stigma?

  sticky surface to catch and hold pollen.
• What is the function of the style?

  provides a pathway for pollen tubes to grow to the ovary.
• What is the function of the ovary?

  holds ovules, develops into fruit after fertilization.
• What is the function of the ovule?

  develop into seeds once fertilized.
• What is male gametogenesis in a plant?

  Diploid cells in the anther divide by meiosis to produce four haploid cells. Each of these haploid cells develops into a pollen grain.

  Inside each pollen grain, the nucleus divides by mitosis, to produce three haploid nuclei. Two of the nuclei are male gametes, the third is expressed during pollen development and fertilisation.
• What is female gametogenesis in a plant?

  The ovary contains one or more ovules, in which one cell in the centre grows especially large and then divides via meiosis to produce four haploid nuclei. One of these nuclei divide three times via mitosis, to produce eight haploid nuclei. One of these eight is the female gametes, the others assist in fertilisation.
• What are the stages of sexual reproduction in flowering plants?

  - pollination

  - fertilisation

  - embryo development
• What is pollination?

  Pollination is the transfer of pollen from an anther to a stigma. This usually occurs through the wind or animals.
• What is fertilisation?


  Fertilisation happens inside an ovule. From each pollen grain on the stigma, a tube grows down the style to the ovary. This pollen tube carries male gametes to the ovary. Once in the ovary, the pollen tube grows towards one ovule and into one end of it. When it reaches the centre of the ovule where the female gamete is located, the male gametes are released and fertilisation occurs.
• What is cross pollination, and why is it important?

  Cross pollination is the transfer of pollen from an anther in a flower on one plant to a stigma of a flower on another plant. It leads to the fusion of male and female gametes from different plants, so promotes genetic variation and therefore evolution.

  Cross pollination also promotes hybrid vigour- where the offspring of crosses between genetically unrelated plants tend to be healthy and grow strong.
• What is inbreeding/self pollination, and what are its implications?

  Most plants are hermaphrodites, meaning that they produce pollen containing male gametes and ovules containing female gametes. This makes self pollination- the transfer of pollen from an anther to a stigma on the same plant- possible. Inbreeding in this way increases the chance of a rare recessive allele in one ancestor being inherited twice by an individual, causing a genetic disorder. Inbreeding death is common among inbreeds- the general trend for premature death, failure to thrive and infertility among offspring. To prevent inbreeding in flowering plants, mechanisms have evolved to prevent self pollination.
• What are some mechanisms that prevent self-pollination?

  - Adaptations to facilitate transfer of pollen from one plant to another via an outside agent (e.g. madake by wind)

  - Separation of anthers and stigmas in separate male and female flowers of the same plant (monoecious) (e.g. maize)

  - Separation of anthers and stigmas in separate male and female flowers of different plants (dioecious) (e.g. stinging nettle)

  - Anthers and stigmas maturing at different times (dichogamy), with protandry being anthers first, and protogyny being stigmas first (e.g. foxglove as protandrous and sacred lotus as protogynous)
• What is self incompatibility?

  Self-incompatibility (SI) is a genetic mechanism that prevents self-fertilization and encourages cross-pollination. It is controlled by S-genes (self-incompatibility genes).
• What is Gametophytic Self-Incompatibility (GSI)?


  - Based on the genes in the pollen (male gamete).

  - If the pollen has the same S-allele as the style (female part), it is rejected.

  - The pollen tube doesn't grow, so fertilization doesn't happen.

  - Example: Tomato family (Solanaceae)
• What is Saprophytic Self-Incompatibility (SSI)?


  - Based on the genes in the parent plant that made the pollen.

  - If the S-alleles match, the pollen can't stick or grow on the stigma.

  - Rejection happens before the pollen tube forms.

  - Example: Cabbage family (Brassicaceae)
• What are s genes?

  - Special genes that control self-incompatibility.

  - Found in both the pollen and the stigma.

  - If the S-genes match, the plant blocks fertilization
• What are the functions of seeds?

  - To protect the embryo

  - To store nutrients

  - To allow delayed growth

  - To aid in dispersal
• What is germination?

  Germination is the process by which a seed develops into a new plant under suitable conditions.
• Why is water required for germination?

  - Activates enzymes

  - Softens the seed coat

  - Allows the seed to swell and begin metabolism
• Why is oxygen required for germination?

  Allows aerobic respiration to occur, which then provides ATP for division and growth
• Why is warmth required for germination?

  Provides the optimal enzymatic temperature
• How does the embryo grow and develop?

  - The embryo in the seed begins to grow after water uptake.

  - Food reserves (stored in endosperm or cotyledons) are mobilized to provide energy and materials for growth.

  - Root (radicle) emerges first to anchor and absorb water.

  - Shoot (plumule) grows upwards toward light.
• What is the role of gibberellin?

  Gibberellin is a plant hormone produced by the embryo.

  It stimulates the production of enzymes, especially amylase, in the aleurone layer of cereal grains. Amylase breaks down starch in the endosperm into maltose/glucose. These sugars provide energy for the growing embryo during germination.