Biology Unit 4.2 - Sexual Reproduction in Plants Flashcards
What is the flower?
Organ of reproduction in plants containing both male and femal gametes
Top-bottom:
* Petal
* Stigma
* Stamen consisting of the anther and filament
* Sepal
* Style
* Ovar containing one or more ovules
What is the function of the petal?
Brightly coloured, which may have a scent and produce nectar to attract insects
What is teh function of the stigma?
Receptive surface that receives pollen during pollination when matured
What is the function of the anther?
Structure that produces pollen grains and contains the male haploid gamete
What is the function of the filament?
Supports the anther, and has vascular tissue that transports food (phloem) and water (xylem)
What is the function of the sepal?
Usually green and protect the flower in bud
What is the function of the style?
Stalk like structure that supports the stigma
What is the function of the ovary?
Surrounds the ovules is the lower part of the carpel, and contains the femal haploid gamete
What is pollination?
Transfer of pollen grains from the anther to the mature stigma, so they can be brought into contact with the female part of the flower
What is self-pollination?
Pollen is transferred to the stigma of the same flower, or another flower on the same plant
What is cross-pollination?
Transfer of pollen from the anthers of one flower to the stigma of another flower on a different plant of the same species
What is insect pollination?
Bees feed on sugary nectar using long tongues to reach the nectaries, where anthers brush against the back of the bee, leaving behind sticky pollen, which burhs against a ripe stigma
What is wind pollination?
Petals are absent or small and insignificant
Anthers hang outside the flower; allow wind to blow away the small, smooth and light pollen
Feathery stigmas hang outside the flowers; provide a large surface area
Compare insects pollinated and wind pollinated flowers…
Insect pollinated:
* Colorful petals with nectar guides
* Scent and nectar - mainly sucrose
* Anther and stigma within the flower
* Small quantities of sticky sculptured pollen
* Produces large pollen grains
Wind pollinated:
* Petals ususally absent or small, green or insconspicuous
* No scent or nectar
* Anthers hanging outside the flower
* Large, feathery stigma hang outside the flower
* Large quantities of smooth pollen
* Produces smaller pollen grains
What are the genetic consequences of self-pollination?
- Leads to self-fertilisatio; results in inbreeding
- Variation can only be achieved by mutation by crossing over during prophase I and the random assortment of chromosomes/chromatids
- Less genetic variation
- Inbreeding can preserve good genomes suitable to a stable environment
What are the genetic consequences of cross-pollination?
- Leads to cross-fertilisation; results in outbreeding
- Variation achieved by fusion of gametes from diffeent plants of the same species in addition to mutation: crossing over during prophase I and random assortment of chromosomes/chromatids
- More genetic variation
- Outbreeding has evolutionary significance as some genomes are more successful than others; allow species to survive better in a changing environment
What are the anthers?
Contain male haploid gametes produced by meiosis
Explain pollen production…
- Diploid pollen mother cells divide by meiosis, where each forms a tetrad, containing haploid cells
- Haploid nucleus divides by mitosis forming two haploid nuclei per pollen grain
- One is the tube nucleus, while the other is generative nucleus
- As pollen matures tension in the lateral grooves occurs
- Dehiscence occurs, causing tension to pull the walls of the anther apart, while the edges of the pollen sacs curl away
- Opening called the stomium exposes the pollen grains and are carried away by insects or wind
Explain ovule development…
- Ovules develop in the ovary
- In each ovule a megaspore mother cell undergoes meiosis to form four haploid cells
- Three degenerate, while the remaining haploid cells divides by mitosis three times, producing eight haploid nuclei
- Two polar nuclei fuse forming a mature embryo sac
- Oosphere is the haploid female gamete
Explain double fertilisation…
- Male gamete is delivered by a pollen tube
- When a compatible pollen grain reaches a ripe stigma pollination occurs
- Pollen absorbs water, germinating it, producing a pollen tube, which grows out of the pollen grain through a gap in the cell wall called a pit
- Tube pushes down through the tissues of the style up a gradient of chemo-attractents
- Pollen tube nucleus produces hydrolases which digest through the style tissues
- Generative nucleus divides into two male nuclei
- Tio of the pollen tube enerts the ovule via the micropyle and releases the two male gametes into the embryo sac
- One fuses with the oosphere, forming a zygote which divides by mitosis
- Other male nucleus fuses with the diploid polar nucleus forming a triploid nucleus called the endosperm nucleus
Where do different fruit/seed structures develop from?
- See - The ovule
- Embryo plant - Diploid zygote
- Endosperm - Triploid endosperm nucleus
- Test - Integument
- Fruit - Ovary
Explain the embryo plants, cotyledons, and endosperm…
- Embryo consists of a plumule, radicle, and one or two cotyledons
- Flowering plants are either monocotyledons (Maize) and dicotyledons (Broad bean)
- In the broad bean the endosperm is absorbed into the cotyledons
- In maize the endosperm surrounds the cotyledon
What is seed dispersal?
Movement of seeds away from the parent plant, where if germination occurs close to the parent the parent will be more successful
These methods are subject to natural selection
How evolutionary developments led to the success of Angiosperms?
- Dormant seeds have low metabolic rate to survive in very cold weather
- Testa is chemically resistant
- Water content of dormant seeds is reduced to 10% to survive in very dry conditions
- Test physically protect the embryo
- Endosperm and cotyledons supply nutrients
- Seeds can be dispersed great distances, allowing colinisation of new habitats
- Inhibitors only allow germination at suitable times of year
What is germination?
Process in which the plant grows from a seed, where the dormant seed will undergo vigorous biochemical and developmental activity, which lasts until the first photosynthesising leaves are produced
What are the optimum conditions for germination?
- Temperature - optimum for enzyme activity, usually between 5 and 30 degrees celsius
- Water - needed to mobilise enzymes, for transport in the xylem and phloem
- Oxygen - needed for aerobic respiration for ATP production, fueling metabolism and growth
Explain mobilisation of food reserves and germination…
- Begins with rapid absorption of water
- Tissues swell providing suitable conditions for enzyme activity
- Insoluble food stores must be hydrolysed, using amylase and proteases
- Products are transported to the embryo and carried in the phloem to the apical meristems
- Swelling causes the testa to split, causing the radicle and plumule to emerge
- Plumule elongates rapidly and pushes its way up through the soil
- Plumule emerges, hook straightens, leaves unfurl and photosynthesis begins while food reserves have been depleted
How does dry mass change during germination?
Dry mass of the seed and embryo increases, while the dry mass of the cotyledon decreases
Describe germination a broad bean…
- Endosperm has been absorbed by the cotyledon
- Amylase digests starch into maltose
- Proteins are broken down into amino acids
- Fats are broken down into fatty acids and glycerol
- Products are transported to the embryo for mitosis
Describe germination in barley seed…
- Endosperm is present (not within the cotyledon)
- Starch, proteins, and fats are present in the endosperm
- The embryo produces gibberellic acid, which diffuses into the aleurone layer causing the break down of proteins into amino acids
- Amino acids used to synthesis enzymes e.g., amylase to break down starch into maltose
- Maltose is transported to the embryo
What is the effect of gibberellin?
Speeds up germination so seeds need to be kept warm for less time, so more malted barley can be produced
What is gibberellic acid?
Plant growth regulator which triggers the processes necessary for germination
Summarise germination using gibberellic acid…
- Embryo produces GA which diffuses into the aleurone layer
- Enzymes hydrolyse proteins into amino acids
- Amino acids form the enzyme amylase
- Amylase diffuses into the endosperm, where starch is hydrolsyed into maltose
- Maltose is transported to the embryo
- Maltose is hydrolysed into glucose for respiration, while ATP provides energy for mitosis
How is wind used as a dispersal method?
Different species have mechanisms which enable pollen/spores to be dispersed by the wind
How is transport used as a dispersal method?
Organisms eat seeds which pass through the digestive system, where carification weakens the testa by the actions of enzymes and stomach acid
How is rolling used as a dispersal method?
Seeds of plants roll away from the parent tree
How is bursting used as a dispersal method?
Seeds scatter after the plant dries and splits
How is water used as a dispersal method?
Seeds float in the water due to air cavities making them buoyant, where they can be carried away
How is carrying used as a dispersal method?
Seeds attach to animal coats and are carried away
What is chemical incompatibility?
Gametes from the same parent plant fail to fuse to form a zygotre, or the embryo plant does no develop if the zygote is formed
What is irregular flower sturcture?
Stigmas and anthers are at different levels, within the flower, which makes it less likely self-pollination can occur
What is dichogamy?
Anthers and stigmans mature at different times
What are monoecious plants?
Plants which have seperate male and female flowers on the same plant
What are dioecious plants?
Plants that have seperate male and female plants
