plant reproduction

• structure of a flower? female, male and general

  female- stigma, ovule, style, ovary

  male- filament, anther

  general- petal, nectary, sepal, receptacle
• Forensic palynology is the study of pollen, spores and other acid-resistant microscopic plant bodies to prove or disprove a relationship between objects, people and places in criminal and civil cases
• Forensic palynology is particularly useful in cases where there is suspected movement of evidence or where a crime has occurred in a location with distinct plant species
• Flowering plants are known as angiosperms
• Insect-Pollinated Flower:

  • Presence of petals, scent, nectar
  • Colourful petals, scent, nectar
  • Anthers within flower
  • Stigma within flower
  • Small quantities of larger, sticky sculpted pollen
• Formation of a Pollen Grain (Male Gamete):

  • Pollen grains are formed in the anther by mitosis and meiosis
  • The tapetum provides nutrients to the developing pollen grains and produces a waterproof coat for the pollen grain
  • Inside each pollen grain, the haploid nucleus undergoes mitosis to produce two nuclei: a generative nucleus and a pollen tube nucleus
  • The pollen cell wall (exine) is tough and resistant to chemicals
  • Pollen is resistant to UV radiation, important for wind pollination
• Female gamete (n):

  • The ovule contains the female gamete and is formed in the ovary by mitosis and meiosis
  • The megaspore mother cell in the nucellus undergoes meiosis to produce four haploid megaspores
  • One megaspore undergoes three mitotic divisions to produce eight haploid nuclei within the embryo sac of the ovule
• Embryo Sac Development:

  • The 8 haploid nuclei inside each embryo sac include one female gamete, two polar nuclei, two synergids and three antipodal cells
• Pollination:

  • Pollination is the transfer of pollen grains from the anther to the stigma
  • Self-pollination: transfer of pollen grains from an anther to a stigma of the same plant
  • Cross-pollination: transfer of pollen grains from an anther to a stigma of a different plant of the same species
  • Advantages of self-pollination: only one parent needed, can help maintain well-adapted genotypes
  • Disadvantages of self-pollination: reduces genetic variation, increases the chance of genetic diseases
  • Advantages of cross-pollination: increases genetic variation for species adaptation
• Cross Pollination:

  • Stamen and stigma ripen at different times
  • The anther is below the stigma
  • Genetic/chemical incompatibility
  • Separate male and female plants
  • Preventing cross-pollination during plant reproduction experiments: enclose or isolate the flower in a bag
• Fertilisation:

  • When a compatible pollen grain lands on a stigma, the stigma secretes a sugary solution
  • The pollen tube enters the embryo sac through the micropyle
  • Both male gametes are involved in separate fertilisation events
• Double Fertilisation:

  • One male gamete fuses with the female gamete to produce a diploid zygote
  • The second male gamete fuses with the two polar nuclei to form a triploid primary endosperm nucleus
• Internal fertilisation in the female involves the secretion of digestive enzymes to digest a path for the male gamete to reach the female gamete
• Double fertilisation occurs in plants
• Pollen tube formation in plants / acrosome reaction in humans
• Male gamete is able to swim in humans / pollen seed
• Mitosis forms a diploid embryo, consisting of plumule (developing shoot), radicle (developing root) and one or two cotyledons
• Endosperm tissue is an important food storage tissue in cereal grains like wheat & maize
• The testa develops into a fruit wall enclosing the seeds
• Seeds with one cotyledon are called monocotyledons, e.g. maize & wheat
• Seeds with two cotyledons are called dicotyledons, e.g. broad beans
• Maize is a monocotyledon so only has one cotyledon
• Broad beans are dicotyledons, they have two cotyledons, with the embryo lying between them
• Broad bean seeds use the cotyledons as food storage tissue and are non-endospermic
• Maize is endospermic
• Seeds have evolved as a survival strategy for a terrestrial mode of life (living on land)
• The testa is chemically resistant and provides physical protection for seeds
• Endosperm / cotyledons provide a supply of nutrients until photosynthesis can occur
• Dormant seeds have a low metabolic rate to survive over winter and germinate in spring/summer
• Seeds with low water content can survive dry conditions
• Fruits are important in seed dispersal as they are eaten by animals and the seeds pass through the digestive system for dispersal
• Seeds can be dispersed by water, wind, or animals
• Germination requires water, suitable temperature, and oxygen
• In endospermic seeds like maize, gibberellin is involved in germination
• Starch and proteins in seeds are broken down into soluble products by enzymes like amylase and proteases
• Soluble products are transported in the plumule and radicle via phloem
• Plumule grows towards light and against gravity, radicle grows away from light and towards gravity
• Tapetum provides nutrients and regulatory molecules to developing pollen grains
• Pollen tube nucleus contains genetic information for digesting a path through the style
• Generative nucleus undergoes mitosis to form two male nuclei (gametes)