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Topic 9.4 Source: Bioninja - Coggle Diagram
Topic 9.4 Source: Bioninja
Understanding 1: Flowering involves a change in gene expression in the shoot apex
Flowers are the reproductive organs of angiospermophytes (flowering plants) and develop from the shoot apex
Changes in gene expression trigger the enlargement of the shoot apical meristem
This tissue then differentiates to form the different flower structures – sepals, petals, stamen and pistil
activation of genes responsible for flowering is influenced by abiotic factors - usually linked with seasons
Most commonly, it is activated by night and day (photoperiodism)
Flower Diagram
Male parts
Anther – pollen producing organ of the flower (pollen is the male gamete of a flowering plant)
Filament – slender stalk supporting the anther (makes the anther accessible to pollinators)
Female parts
Stigma – the sticky, receptive tip of the pistil that is responsible for catching the pollen
Style – the tube-shaped connection between the stigma and ovule (it elevates the stigma to help catch pollen)
Ovule – the structure that contains the female reproductive cells (after fertilisation, it will develop into a seed)
Support parts
Petals – brightly coloured modified leaves, which function to attract pollinators
Sepal – Outer covering which protects the flower when in bud
Peduncle – Stalk of the flower
Understanding 2: The switch to flowering is a response to the length of light and dark periods in many plants
Red light (sunlight) will quickly convert Pf to Pfr
Infrared light will quickly convert Pfr to Pf
Darkness will slowly convert Pfr to Pf
Long day: high levels of P fr to flower
Short day: high levels of Pr to flower
link to bionija for the flowering controls in a diagram format
Pfr/Pf flower control diagram thing
Understanding 3: Success in plant reproduction depends on pollination, fertilization and seed dispersal
Plants can reproduce through:
Vegetative propagation (asexual reproduction from a plant cutting)
Spore formations (e.g. moulds, ferns)
Pollen transfer (flowering plants – angiospermophytes)
Pollination
The transfer of pollen grains from an anther (male plant structure) to a stigma (female plant structure)
Many plants possess both male and female structures (monoecious) and can potentially self-pollinate
From an evolutionary perspective, cross-pollination is preferable as it improves genetic diversity
Fertilisation:
Fusion of a male gamete nuclei with a female gamete nuclei to form a zygote
In plants, the male gamete is stored in the pollen grain and the female gamete is found in the ovule
Seed dispersal:
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
There are a variety of seed dispersal mechanisms, including wind, water, fruits and animals
Seed structure will vary depending on the mechanism of dispersal employed by the plant
Germination
Other possible factors, that are specific to species
Fire – some seeds will only sprout after exposure to intense heat (e.g. after bushfires remove established flora)
Freezing – some seeds will only sprout after periods of intense cold (e.g. in spring, following the winter snows)
Digestion – some seeds require prior animal digestion to erode the seed coat before the seed will sprout
Washing – some seeds may be covered with inhibitors and will only sprout after being washed to remove the inhibitors
Scarification – seeds are more likely to germinate if the seed coat is weakened from physical damage
Factors affecting it
Oxygen – for aerobic respiration (the seed requires large amounts of ATP in order to develop)
Water – to metabolically activate the seed (triggers the synthesis of gibberellin)
Temperature – seeds require certain temperature conditions in order to sprout (for optimal function of enzymes)
pH – seeds require a suitable soil pH in order to sprout (for optimal function of enzymes)
Understanding 4: Most flowering plants use mutualistic relationships with pollinators in sexual reproduction
Cross-pollination involves transferring pollen grains from one plant to the ovule of a different plant
Pollen can be transferred by wind or water, but is commonly transferred by animals (called pollinators)
Pollinators
Pollinators are involved in a mutualistic relationship with the flowering plant – whereby both species benefit from the interaction
The flowering plant gains a means of sexual reproduction (via the transference of pollen between plants)
The animal gains a source of nutrition (plants secrete a sugar-rich substance called nectar to attract pollinators
examples: birds, bats and insects (including bees and butterflies)
Skill: Drawing internal structure of seeds
Testa – an outer seed coat that protects the embryonic plant
Micropyle – a small pore in the outer covering of the seed, that allows for the passage of water
Cotyledon – contains the food stores for the seed and forms the embryonic leaves
Plumule – the embryonic shoot (also called the epicotyl)
Radicle – the embryonic root
Bean Diagram