9.4 Plant Reproduction Flashcards
In what 3 ways can plants reproduce?
Vegetative propagation (asexual reproduction from a plant cutting)
Spore formations (e.g. moulds, ferns)
Pollen transfer (flowering plants – angiospermophytes)
What does sexual reproduction in flowering points involve?
Sexual reproduction in flowering plants involves the transfer of pollen (male gamete) to an ova (female gamete)
What 3 phases are involved in the sexual reproduction of flowering plants?
involves three distinct phases – pollination, fertilization and seed dispersal
What is pollination?
The transfer of pollen grains from an anther (male plant structure) to a stigma (female plant structure)
Can plants self-pollinate?
YES
Many plants possess both male and female structures (monoecious) and can potentially self-pollinate
Why do plants tend to not self-pollinate?
From an evolutionary perspective, cross-pollination is preferable as it improves genetic diversity
What is fertilisation?
Fusion of a male gamete nuclei with a female gamete nuclei to form a zygote
Where are the male and female gametes stored in a plant?
In plants, the male gamete is stored in the pollen grain and the female gamete is found in the ovule
What is seed dispersal?
Fertilisation of gametes results in the formation of a seed, which moves away from the parental plant
Why is seed dispersal useful?
This seed dispersal reduces competition for resources between the germinating seed and the parental plant
What varieties of seed dispersal are there?
There are a variety of seed dispersal mechanisms, including wind, water, fruits and animals
Will seed structures be the same for different methods of seed dispersal?
NO
Seed structure will vary depending on the mechanism of dispersal employed by the plant
What does cross-pollination involve?
Cross-pollination involves transferring pollen grains from one plant to the ovule of a different plant
In what ways can pollen be transfered?
Pollen can be transferred by wind or water, but is commonly transferred by animals (called pollinators)
What type of relationship do plants have with pollinators?
Pollinators are involved in a mutualistic relationship with the flowering plant – whereby both species benefit from the interaction
How do plants benefit from pollination?
The flowering plant gains a means of sexual reproduction (via the transference of pollen between plants)
How do pollinators benefit from pollination?
The animal gains a source of nutrition (plants secrete a sugar-rich substance called nectar to attract pollinators
What are common example of pollinators?
Common examples of pollinators include birds, bats and insects (including bees and butterflies)
How may a plant structurally adapt for birds (as pollinators)?
Flowers may be structured to optimise access for certain pollinators (e.g. tube-shaped flowers for birds with long beaks)
How may a plant structurally adapt for birds (as pollinators)?
Flowers may be structured to optimise access for certain pollinators (e.g. tube-shaped flowers for birds with long beaks)
What are flowers?
Flowers are the reproductive organs of angiospermophytes (flowering plants) and develop from the shoot apex
What causes the enlargement of shoot apical meristems?
Changes in gene expression trigger the enlargement of the shoot apical meristem
What does the tissue do in the shoot apical meristem?
This tissue then differentiates to form the different flower structures – sepals, petals, stamen and pistil
What is the activation of genes responsible for flowering influenced by? (basic)
abiotic factors - typically linked to seasons
When will flowering plants most likely bloom?
Flowering plants will typically come into bloom when a suitable pollinator is most abundant - this is dependent on seasons
What is the most common trigger for a change in gene expression?
The most common trigger for a change in gene expression is day/night length (photoperiodism)
Do flowers always contain both male and female structures?
NO
Most flowers possess both male and female structures (monoecious), but some may only possess one structure (dioecious)
What is the male part of the flower called?
stamen
What is the stamen composed of?
anther
filament
What is the anther?
pollen producing organ of the flower
What is the male gamete of a flowering plant?
pollen is the male gamete of a flowering plant
What is the filament?
slender stalk supporting the anther (makes the anther accessible to pollinators)
What is the female part of the flower called?
pistil/carpel
What is the carpel composed of?
- stigma
- style
- ovule & ovary
What is the stigma?
the sticky, receptive tip of the carpel that is responsible for catching the pollen
What is the style?
the tube-shaped connection between the stigma and ovule (it elevates the stigma to help catch pollen)
What is the ovule?
the structure that contains the female reproductive cells
What happens to the ovule after fertilisation?
after fertilisation, it will develop into a seed
What 3 support structures do flowers possess?
- petals
- sepal
- peduncle
What are the petals?
brightly coloured modified leaves, which function to attract pollinators
What is the sepal?
Outer covering which protects the flower when in bud
What is the peduncle?
The stalk of the flower
What is the purpose of flowering?
The purpose of flowering is to enable the plant to sexually reproduce via pollination, fertilisation and seed dispersal
What 2 types of flowering plants are there? (depending on when they bloom)
Some plants bloom in long day conditions (summer), whereas other plants bloom in short day conditions (autumn / winter)
What is the critical factor responsible for flowering?
The critical factor responsible for flowering is the length of light and dark periods, which is detected by phytochromes
What are phytochromes?
Phytochromes are leaf pigments which are used by the plant to detect periods of light and darkness
What is photoperiodism?
Phytochromes are leaf pigments which are used by the plant to detect periods of light and darkness
What are the 2 forms of phytochromes?
Pr -inactive form
Pfr - active form
When is the inactive form of phytochrome converted?
The inactive form of phytochrome (Pr) is converted into the active form when it absorbs red light (~660 nm)
When is the active form of phytochrome broken down?
The active form of phytochrome (Pfr) is broken down into the inactive form when it absorbs far red light (~725 nm)
Can the active form of phytochrome be converted into the inactive form?
YES
the active form will gradually revert to the inactive form in the absence of light (darkness reversion)
Which form of phytochrome is predominant during the day? Why?
Because sunlight contains more red light than moonlight, the active form is predominant during the day
Which form of phytochrome is predominant during the night? Why?
as the active form is reverted in darkness, the inactive form is predominant during the night
How can plants be classified into long/short day plants?
Plants can be classed as short-day or long-day plants, however the critical factor in determining their activity is NIGHT LENGTH
When do short-day plants flower? (length…)
Short-day plants flower when the days are short – hence require the night period to exceed a critical length
How does phytochrome play a role in short-day plants?
In short-day plants, Pfr INHIBITS flowering and hence flowering requires low levels of Pfr (i.e. resulting from long night
When do long-day plants flower? (length…)
Long-day plants flower when the days are long – hence require the night period to be less than a critical length
How does phytochrome play a role in long-day plants?
In long-day plants, Pfr activates flowering and hence flowering requires high levels of Pfr (i.e. resulting from short nights)
How can horticulturalists manipulate flowering?
Horticulturalists can manipulate the flowering of short-day and long-day plants by controlling the exposure of light
What must be uninterrupted/maintained to control plant flowering?
The critical night length required for a flowering response must be uninterrupted in order to be effective
In what seasons will long-day plants typically not flower?
These plants will traditionally not flower during the winter and autumn months when night lengths are long
How can horticulturalists manipulate long-day plants to bloom?
Horticulturalists can trigger flowering in these plants by exposing the plant to a light source during the night
What is an example of a long-day plant?
Carnations are an example of a long-day plant
When will short-day plants typically not flower?
These plants will traditionally not flower during the summer months when night lengths are short
How can horticulturalists manipulate short-day plants to bloom?
Horticulturalists can trigger flowering in these plants by covering the plant with an opaque black cloth for ~12 hours a day
What is an example of a short-day plant?
Crysanthemums are an example of a short-day plant
In, for example, a greenhouse, what length of darkness do long-day plants require?
Long-day plants require periods of darkness to be less than an uninterrupted critical length
In, for example, a greenhouse, what length of darkness do short-day plants require?
Short-day plants require periods of darkness to be greater than an uninterrupted critical length
What does germination create?
The seed will be dispersed from the parental plant and will then germinate, giving rise to a new plant
What 5 features does a typical seed possess?
- testa
- micropyle
- cotyledon
- plumule
- radicle
What is the testa?
an outer seed coat that protects the embryonic plant
What is the micropyle?
a small pore in the outer covering of the seed, that allows for the passage of water
What is the cotyledon?
contains the food stores for the seed and forms the embryonic leaves
What is the plumule?
the embryonic shoot (also called the epicotyl)
What is the radicle?
the embryonic root
What is germination?
Germination is the process by which a seed emerges from a period of dormancy and begins to sprout
What 4 basic factors does a seed require to germinate?
- oxygen
- water
- temperature
- pH
Why does a seed require oxygen for germination?
or aerobic respiration (the seed requires large amounts of ATP in order to develop)
Why does a seed require water for germination?
to metabolically activate the seed (triggers the synthesis of gibberellin)
Why does a seed require temperature for germination?
seeds require certain temperature conditions in order to sprout (for optimal function of enzymes)
Why does a seed require pH for germination?
seeds require a suitable soil pH in order to sprout (for optimal function of enzymes)
Why might some plant species require fire as a condition for germination?
some seeds will only sprout after exposure to intense heat (e.g. after bushfires remove established flora)
Why might some plant species require freezing as a condition for germination?
some seeds will only sprout after periods of intense cold (e.g. in spring, following the winter snows)
Why might some plant species require digestion as a condition for germination?
some seeds require prior animal digestion to erode the seed coat before the seed will sprout
Why might some plant species require washing as a condition for germination?
some seeds may be covered with inhibitors and will only sprout after being washed to remove the inhibitors
Why might some plant species require scarification as a condition for germination?
seeds are more likely to germinate if the seed coat is weakened from physical damage
How can experiments be developed to test germination?
Experiments can be developed using any of these factors as an independent variable
How can germination be measured?
Germination can be measured by the rate of seed growth over a set period of time
