Plant Reproduction

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Insect Pollinated Fower

-          Stigma = sticky to trap the pollen on its surface

-          Petal = brightly coloured and scented to attract insects

-          Style = holds the stigma where it can come in contact with insect

-          Ovule = contains the female gamete

-          Ovary = protects the ovule

-          Anther = pollen with the male gamete

-          Filament = contains vascular tissue that provides the anther with nutrients

-          Stigma can secrete chemicals to stimulate pollen growth

-          Small quantity of pollen that las hooks on the surface to attach to the insect

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Wind Pollinated Flower

-          Dull coloured petals that are small and contain no scent or nectar

-          Anthers hang outside the flower

-          Stigma is large and feathery

-          Stigma has a large surface area to catch the pollen grain on its surface

-          Stigma is outside the flower

-          Large quantity of pollen = lower chance of successful pollination

-          Pollen is small, smooth and lightweight

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Pollen Formation

-          Pollen mother cells undergo mitosis to produce diploid megaspore mother cells

-          Diploid megaspore mother cells divide by Meiosis 1 and 2 to form a tetrad of four haploid cells

-          The tetrad separates to form the pollen grain

-          In the pollen grain, the haploid nucleus divides by mitosis to form a generative nucleus and a pollen tube nucleus

-          The exine is tough and resistant to chemicals to prevent desiccation and makes the pollen resistant to UV Radiation in high altitudes

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Ovule Production

-          The diploid megaspore mother cell divides by meiosis to form 4 haploid megaspores

-          3 of the haploid megaspores degenerate

-          The megaspore undergoes 3 mitotic divisions to produce 8 haploid nuclei

-          3 antipodal cells and 2 synergids degenerate leaving the central cell with the polar nuclei and the egg cell

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Self Pollination

  • Transfer of pollen from the anther to the mature stigma in the same flower or a different flower
  • on the same plant
  • Mutation of DNA Meiosis 1 Meiosis 2
  • Crossing over at Prophase 1 Independent Assortment of bivalents at Metaphase 1
  • and sister chromatids in Metaphase 2
  • Preserves successful genomes = better chance of survival
  • Beneficial characteristics likely to be passed = Higher probability of successful pollination Reduction in genetic variation = no mixing of genotypes
  • Inbreeding = greater chance of 2 recessive alleles being brought together = increases homozygosity
  • Genetic variation will depend on only mutation, crossing over and independent assortment
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Cross Pollination

  • Transfer of pollen from the anther to the mature stigma in a flower from a different plant
  • Mutation of DNA, Meiosis 1 and Meiosis 2
  • Combination of alleles from 2 different individuals
  • Crossing over at Prophase 1
  • Independent Assortment of bivalents at Metaphase 1 and sister chromatids in Metaphase 2
  • Random fusion of gametes from different organisms
  • Promotes outbreeding = combines gametes from 2 different individuals
  • More genetic variation
  • Reduces chances of producing harmful allele combination
  • May allow species to survive in a changing environment = combination of genotypes
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Cross Pollination

-          Dichogamy = the stamens and stigma ripen at different times

-          Protandry = stamen ripens first so the pollen will not germinate and the stigma in the flower is not fully mature

-          Protogyny = stigma ripens so no pollen will fall on the ripe stigma and pollen is not being produced at the right time.

-          Anter is below the stigma = pollen cannot fall from the anter into the stigma as the anther is below

-          Genetic incompatibility = pollen is unable to germinate on the stigma of the flower which produced it

-          Separate male and female plants = (Dioecious) plants does not have both male and female sex organs

-          Separate male and female flowers in the same plant = flowers do not have both male and female sex organs as the carpel flowers are above the stamen flowers

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Fertillisation

-  when a compatible pollen grain lands on the stigma = stigma releases a sugary solution

pollen grain germinates and pollen tube nucleus produces the pollen tube

pollen tube nucleus is at the tip of the pollen tube with the two male nuclei behind

pollen tube nucleus codes for hydrolytic enzymes that digest the style tissue. the products are used by the pollen tube

the pollen tube enters the micropyle to the embryo sac

pollen tube nucleus disintegrates and the tip of the pollen tube opens releasing 2 male nuclei into the embryo sac

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Double Fertillisation

one male gamete fuses with the female gamete to produce a diploid zygote

second male gamete fuses with the two polar nuclei to form a triploid endosperm nucleus

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Differences between flowering plants and humans

Humans :

  • single fertilisation
  • acrosome reaction
  • make gamete has a flagellum to swim to the 2 oocyte

Flowering Plants:

  • double fertilisation
  • pollen tube formation
  • pollen grain must form a pollen tube through which the male gamete nuclei move

Both :

  • fusion of haploid gametes to form zygote
  • internal fertilisation
  • secretion of hydrolytic enzymes to digest a path for the male gamete
  • chemotropism of spermatozoa and pollen tube to the ovule
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Formation of seed and fruits

  • Diploid Zygote = mitosis to form the diploid embryo, plumule, radicle and one or two cotyledons
  • Triploid central cell = mitosis to form the endosperm tissue which stores starch
  • Fertilised Ovule = seed
  • Ovary = develops into fruit wall enclosing the seeds
  • Integuments = develop into the testa ( exine prevents drying out)
  • Micropyle = remains as a pore in the testa to allow water for the germination
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Monocotyledons and Dicotyledons

Dicotyledons

  • have two seeds leaves with the embryo in between
  • endosperm is absorbed into the cotyledons
  • non-endospermic

Monocotyledons

  • only one cotyledon
  • endosperm remains as a food store
  • endospermic
  • testa is fused with the ovary wall so has one-seeded fruit
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Seeds and Survival

How are seeds are adapted

  • Testa is chemically resistant to survive adverse chemical conditions and physical protection
  • endosperm = glucose and amino acids and lipids
  • Dormant seeds = low metabolic rate and survive cold weather
  • low weather content to survive very dry conditions

Seed Dispersal Important

  • reduces interspecific competition
  • colonisation of new areas

Fruit important in seed dispersal

  • fruits are eaten by animals, seeds pass through the digestive system then egested
  • fruit may be adapted for a specific mode of dispersal
  • Water = float on water to be distributed
  • Wind = lightweight seeds are easily carried
  • Animals = spikes so seeds are attached to animals
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Requirements For Successful Germination

1.Oxygen = aerobic respiration in cells of embryo to produce ATP
2.Suitable temperature = optimum temperature for enzymes (e.g. amylase, maltase, protease) involved in germination 3.Water = mobilise enzymes for transport, enters cells by osmosis (down a water potential gradient) to make them turgid = important in growth

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Gemination

Water is taken in through the micropyle

tissues swell, splitting the testa and allowing entry of more oxygen for aerobic respiration

food reserves from the cotyledons are hydrolysed into soluble forms of transport

soluble products are transported to the growing points of the embryo to provide the source of energy for respiration and growth

plumule grows upwards, the tip is hooked to prevent damage from the soil abrasion. radicle grows downwards

once the plumule emerges from the soil, the leaves unfurl and begin to photosynthesise

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Germination

Starchhydrolysed tomaltose(2x α-glucose ) by amylase;  maltose is then hydrolysed to α-glucoseby maltase;

Phloem tissuethe soluble products transported in the plumule and radicle?

Maltoseis hydrolysed toα-glucoseforrespirationor it is converted to β-glucose to formcelluloseto make cell walls Amino acids for protein synthesis Plumule grows towards light and against gravity Radicle grows away from light and towards gravity

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Gibberelins

Entry of water activates release of GA from embryo which diffuses to aleurone layer

GA stimulates aleurone cells to make proteases = hydrolyses protein stores (releases amino acids)

Amino acids from protein break down now used in translation for making newenzymes

Amylaseconvertsstarchinto sugars such as maltose and a glucose which is absorbed bytheembryo

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