9.4 Reproduction in plants Flashcards
What happens when a seed germinates?
a young plant is formed that grows roots, stems and leaves (its vegetative structures grow)
What are vegetative structures?
roots, stems and leaves
How can a plant change into the reproductive phase?
the vegetation phase can last for weeks, months or years, until a trigger causes the plant to change into the reproductive phase and produce flowers
When does the change from the vegetative to reproductive phase happen?
happens when meristems in the shoot start to produce parts of flowers instead of leaves
What do the structure of flowers allow for?
sexual reproduction, thereby increasing variety
What are flowers produced by?
by the shoot apiocal meristem
What does flower being produced by the shoot apical meristem say about the shoot?
is is a reproductive shoot
What are the 2 factors that play a role in trnasforming a leaf-producing shoot into a flower-producing shoot? Which is the main one?
Temperature
Day length (main)
* more specifically the length of the dark period
How do seasons affect flowering?
Autumn and winter - more darkness, shorter day
Spring and summer - less darkness, longer day
What does it mean to categorized a plant as short-day plants?
they flower when the dark period becomes longer than a critical length
i.e. Poinsettia
What does it mean to categorized a plant as a long-day plant?
they flower during the long days of early summer when nights are short, night must be less than critical length
What seasons if good for short day and long day plants?
Short day - winter autumn when nights have become long enough
Long day - spring, summer when nights have become short enough
What seasons if good for short day and long day plants?
Short day - winter autumn
Long day - spring, summer
How does light play a role in controlling flowering?
plays a role in the production of either inhibitors or activators of genes that control flowering
Describe the details of how light plays a role in the production of activators of genes that contorl flowering.
- in long day plants, the active form of the pigment phytochrome leads to the transcription of a flowering time (FT) gene
- The FT mRNA is transported in the phloem to the shoot apical meristem where it is translated into FT protein
- the FT protein binds to a transcription factor
- this leads to the activation of many flowering genes which transform the leaf-producing apical meristem into a reproductive meristem
What leads to the tanscription of a flowering time (FT) gene?
the active form of the pigment phytochrome
What is the particular day length that triggers flowering in plants?
the length of darkness is what matters not the length of daylight
What pigment was discovered in leaves that plants use to measure the length of dark periods?
phytochrome
What two forms can phytochrome switch between?
P_r and P_fr
What does P_r absorb?
red light of wavelength 660nm
What does P_fr absorb?
far-red right, of wavelength 730nm
What do P_r and P_fr do when absorbing their respective wavelength?
P_r is converted dinto P_fr
P_fr is converted into P_r
Why is the conversion of P_fr to P_r not of great importance?
As sunlight contains more light of wavelength 660nk than 730nm so in normal suhnlight phytochome is rapidly converted to P_fr
Which form of phytochrome is active?
P_fr
What do P_fr bind to but not P_r?
receptor proteins present in the cytoplasm
Which form of phytochrome is more stable?
P_r
Since P_r is more stable, what happens in the darkness?
In darkness P_fr very gradually changes into P_r
How does P_fr affect flowering in long-day plants?
- large enough amounts of P_fr remain at the end of short nights to bind to the receptor
- then promotes transcription of genes needed for flowering
How does P_fr affect flowering in short-day plants?
- the receptor inhibits the transcription of genes needed for flowering gene when P_fr binds to it
- However at the end of long nights, very little P-fr remains
- so inhibition fails and the plant flowers
What is photoperiods?
the response of plants to relative light and dark period
Which form of phytochrome determines whether plants flower or not?
P_fr
What is flower forcing?
- a procedure designed to get flowers to bloom out of season or at a specific time such as during holiday time
- Growers can manipulate the length of the days and nights to force flowering
What is an example of flower forcing?
- Siamp tulip
- normally produces flowers seasonally during the rainy season where long-day conditions apply
- so its a long-day plant
- providing additional light in the middle of the night leads to flowering
How to induce flowering in short-day plants?
increase the time they are exposed to darkness e.g. by covering them up
How to induce flowering in long-day plants?
expose them to longer periods of light during the night-time
What is the relationship between short and long day plants with their critical night length?
Short day plants flower when a period of darkness (uninterrupted) exceeds a critical night length
Long day plants flower when a period of darkness is less than a critical night length threshold
proves that it is the length of darkness, rather than light that controls flowering
What is the stamen?
the male reproductive organ
What is the carpel?
the female reproductive organ
What is the male and female reproductive organ called in plants?
male - stamen
female - carpel
What makes up the stamen?
Anther and filament
What makes up the carpel?
stigma, style, ovary, and ovules
What are the part of the flower that is shared between both male and female reproductive systems?
petal, sepal, nectary, peduncle
Function of stigma?
sticky tip; recieves pollen during pollination
Function of the anther?
Part of the stamen that makes pollen grains (the male gamete)
Function of ovary?
produces ovules (female gametes). Will develop into the fruit when the plant is fertilised
What is the ovules?
female gametes. will become the seed when the plant is fertilised
Function of nectary?
contains and secretes sweet nectar (sugary liquid) to attract insects
Function of petal?
usually colourful and ented to attract pollinators. may provide a landing site for insects
What is the stamen?
Male reproductive organ - make up of anther and filment
What is the style?
slender tube that supports the stigma; pollen tube grows down from the stigma to the ovary
Function of the filament?
Part of the stamen that supports the anther
Function of the sepal?
encloses and protects flower before it blooms (when it is a bud)
What is the carpel?
female reproductive organ - made up of stigma, style ovary and ovules
What is the peduncle?
the stalk of the flower
What are 3 ways in which plants can reproduce?
- vegetative propagation (asexual reproduction) - runners, bulbs and tubers
- spore formation (e.g. moulds, ferns)
- Pollen transfer (flowering plants - angiospermophytes)
How can pollen be transferred between plants? (3)
- wind
- water
- pollinators (animals)
What does sexual reproduction of flowering plants depend on?
transfer of pollen from the stamen to a stigma of another plant
What are examples of pollinators?
birds bats and insects such as butterflies and bees
What is mutualism?
a close association betwen two organisms where both organisms benefit from the relationship
How do pollinators have a mutualistic relationship with a flowering plant?
- pollinators gain good in the form of nectar
- plant gains a means to transfer pollen to another plant
What are the 3 distinct phases of sexual reproduction of plants?
- pollination - transfer of pollen from anther to stigma
- fertilisation - fusion of a male gamete nuclei with a female gamete nuclei to form a zygote
- seed dispersal - seed moves away from parent plant
What is self pollination?
the pollen is transferred from the anther to the stigma of the same plant
What is cross pollination?
the pollen is transferred from the anther of one plant to the stigma of another plant of the same species
Why is cross-pollination an advantage over self-pollination?
- provides genetic variation
- if there is change in the environment e.g. disease, drought, it is more likely for the plants to be able to adapt and overcome
- reproducing to maintain the population
What happens to each pollen grain on the stigma?
- a tube grows down the style to the ovary
- the pollen tube carries male gametes to fertilize the ovary
What is the process of fertilisation in plants?
- pollen from the anther (parrt of the stamen) of one plant must land on the stigma (part of the carpel) of another plant - cross pollination
- If pollen grain is from the same species as the flower it has landed on, it will grow a pollen tube
- digestive enzymes are produced by the tip of the pollen tube, enabling it to grow through the tissues in the style
- the pollen tube follows a chemical trail down the style towards the ovary
- pollen tube enters the ovule though the micropyle (small gap in ovule wall)
- ovule contains an egg cell
- the nucleus of the pollen grain and the nucleus of the egg cell in the ovule fuse
Where is the ovary located in?
inside a small rounded structure called an ovule
What does the fertilized ovule, ovule wall and ovary develop into?
fertilised ovule - a seed
ovule wall - testa (seed coat)
ovary - (swells to form) a fruit
What does seed dispersal help?
reduces competition between offspring and parent and helps to spread the species
How does the type of seed dispersal depend on the structure of the fruit? (3)
- dry and explosive, fleshy and attractive for animals to eat
- feathery or winged to catch the wind
- covered in hooks that catch onto the coats of animals
How do bats act as a pollinator for a cactus?
they have elongated snouts to reach into the flowers for nectar, covering their heads with pollen that they then transfer from flower to flower as they fly from cactus to cactus thoughout the night
What does a seed contain?
an embryo plant and food reserves, all inside a protective seed coat
What does the embryo plant consist of?
- an embryo root
- embryo shoot
- one or two cotyledons (depending if the plant is monocotyledonous or dicotyledonous)
What does the number of cotyledons an embryo plant have depend on?
depending if the plant is monocotyledonous or dicotyledonous)
What are the cotyledons?
the embryo leaves
What do the cotyledons contain?
food reserves of the seed
What is an endosperm?
a special food storage tissue
What is a testa?
the scientific name for the seed coat
What is the micropyle?
the small hole though the testa
located next toa scar where the seed was attached to the parent plant
What is germination?
the development of a root (radicle) and shoot (plumule) from a embryo in a seed
the early growth of a seed
What is dormancy?
when the seeds do not immediately germinate even if given the conditions normally required
What does dormancy allow for?
- time for seeds to be dispersed
- avoid germination at an unfavourable time
Why do all seeds need water to germinate?
- Water to rehydrate their cells (most seeds are dry)
- softens the testa to allow plumule and radicle to grow
- activates enzymes (amylase, maltase) and hormones (giberellin)
- some seeds contain a hormone that inhibits germination and water is needed to wash it out of the seed
What is the metabolic rate of a dry and dormant seed?
close to zero
What begins after absorption of water?
Metabolic proceses including enrgy release by aerobic cell respiration
Besides water, what 3 other things are required for germination?
Oxygen and warmth and pH
Why is warmth and right pH needed for germination?
because germination involves enzyme-catalysed metabolic reactions
Labell
What is gibberellin?
a plant hormone
What is another metabolic process occurring at the start of germination?
synthesis of gibberellin
What does gibberellin stimulate?
mitosis and cell division in the embryo
In starchy seeds, what does gibberellin also stimulate?
production of amylase
How is glucose obtained to be used for respiration. ina germinating seed?
- amylase is produced stmulated by gibberellin
- amylase break down the starch in the foood reserves into maltose
- other enzymes convert maltose into sucrose of glucose (i.e. maltase)
What is a benefit of enzymes converting starch into surcrose and glucose?
Starch is insoluble and immobile
Sucrose and glucose can be transported from the food reserves to where they are needed in the germinating seed
What does the embryo root and shoot need for growth?
- sugar
- amino acids
- and other substances released from the food stores
What do all parts of the embryo need glucose for?
aerobic cell respiration
What can maltose be polumerised to build?
polymerised to cellulose to build cell walls
What are some additional conditions required for germination? (5)
- fire - after exposure to intense heat
- freezing - after periods of intense cold
- digestion - prior animal digestion to erode the seed coat
- washing - may be covered with inhibitors and only sprout after being washed to remove the inhibitors
- scarification - seed coat weakened from physical damage
What is the process of germination including the metabolic activation. ofa dormant seed?
Metabolic activation of a dormant seed:
1. absorption of water
2. causes gibberellin to be produced
3. gibberellin triggers the synthesis of amylase, which breaks down starch into maltose
4. maltose is either hydrolysed (to glucose) for energy, or polymerised (to cellulose) for cell wall formation
5. this energy and cellular building blocks is used to promote cell division and the growth of a nascent shoot
Once seed is metabolically activated, germination proceeds:
1. seed coat (testa) ruptures and the embryonic root (radicle) grows into the ground to extract key nutrients and minerals
2. cotyledon emerges and produces the growing shoot’s first leaves
What can a growing plant be divided into?
- epicotyle (embryonic shoot)
- hypocotyl (embryonic stem)
- developing roots
