8 - Sexual Reproduction in Plants (C2) Flashcards
What do the haploid spores contain?
Gametes
What are the male spores and where are they produced?
Pollen grains, produced in the anther
What is the female spore and where is it produced?
The embryo sac, produced in the ovule in the ovary
What is the outermost structure of a plant called which contains the sepals?
The calyx
What is the male part of the flower called and what does it contain?
The stamen - contains the anther and filament
What is the female part of the flower called and what does it contain?
The carpel - contains the stigma, style and ovary
What does the filament contain?
Vascular tissue
What does the vascular tissue in the plant do?
Transports sucrose, mineral ions and water to the developing pollen grains
What is the main function of the sepals?
To protect the flower while they bud
What are the features of insect-pollinated flowers?
- Colourful flowers
- Scent and nectar
- Anthers and stigma are within plant
- Small quantities of sticky, sculptured pollen
- Larger pollen grains
What are the features of wind-pollinated flowers?
- Petals absent or small and green
- No scent or nectar
- Anthers and stigma hang outside plant
- Large quantities of smooth pollen
- Smaller pollen grains
Why do the anthers of wind-pollinated plants hang outside the flower?
So the wind can blow away the small, smooth and light pollen
Why do the stigmas of wind-pollinated plants hang outside the flower?
To provide a large SA for catching pollen grains that are blown into their path
What is the tapetum?
A layer of cells around the pollen sac
What is the function of the tapetum?
Provides nutrients and regulatory molecules to the developing pollen grains
What are features of the pollen cell wall?
- Tough
- Resistant to chemicals
- Resistant to desiccation (drying out)
- UV light can’t penetrate it
Why can’t UV light penetrate the pollen cell wall?
To protect the DNA in pollen from mutation
What does the haploid nucleus in the pollen grain undergo mitosis to produce?
Two nuclei:
- Generative nucleus (which produces 2 male nuclei by mitosis)
- Tube nucleus
What is dehiscence?
The opening of the anther, releasing pollen grains
What is the process of the development of the female gamete?
- Megaspore mother cell undergoes meiosis, producing 4 haploid cells
- 3 disintegrate
- Remaining cell undergoes mitosis X3, producing 8 haploid nuclei, 1 of which is the female gamete
- 2 of the haploid nuclei fuse to make a diploid nucleus called the polar nucleus
What is the nucellus?
A layer of cells surrounding the nuclei in embryo sac which provides nutrients
What is the name of the two layers of cells that surround the nucellus?
The integuments
What is the gap in the integuments called?
The micropyle
What does the embryo sac in a mature ovule contain?
- 3 antipodals (haploid)
- 2 synergids (haploid)
- 1 oosphere (haploid)
- 1 polar nucleus (diploid)
What is the definition of pollination?
The transfer of pollen grains from the anther to the mature stigma of a plant of the same species
What is self-pollination?
When pollen from the anthers of a flower is transferred to the mature stigma of the same flower or another flower on the same plant
What is cross-pollination?
When pollen from the anthers of a flower is transferred to the mature stigma of another flower on another plant of the same species
What are advantages and disadvantages of self-pollination?
+ Preserves successful genomes
- Less genetic variation
- Greater chance of 2 potentially harmful recessive alleles being brought together at fertilisation
What are advantages of cross-pollination?
+ Genetic variation
+ Allows species to adapt and survive environmental changes
+ Reduces the chances of harmful allele combinations
How is cross-pollination ensured?
- Protandry
- Anther is below stigma so pollen can’t fall onto it
- Genetic incompatibility, so pollen can’t germinate on the stigma of the flower which produced it
- Separate male and female flowers on the same plant
- Separate male and female plants
What is the definition of fertilisation?
The fusion of a female and male gamete, producing a zygote
How is the male gamete delivered to the female gamete in plants?
By a pollen tube
What is the process of double fertilisation?
- When a compatible pollen grain lands on the stigma, it germinates in the sucrose solution secreted by stigma and produces a pollen tube
- Pollen tube grows out of the pollen grain through a gap in the cell wall, called a pit, down the style and digests its way through the tissues of the style
- Pollen tube grows through the micropyle into the embryo sac
- Pollen tube nucleus disintegrates
- Tip of pollen tube opens, releasing the 2 male gametes into the embryo sac
- 1 of the male gametes fuses with the female gamete (oosphere) forming a zygote
- 1 of the male gametes fuses with the diploid polar nucleus forming a triploid nucleus (endosperm nucleus)
What is the definition of a fruit?
A structure developing from the ovary wall, containing 1 or more seeds
What is the definition of a seed?
Structure developed from a fertilised ovule containing an embryo and food store enclosed within a testa
What is the plumule?
The developing shoot
What is the radicle?
The developing root
What are the cotyledons?
Seed leaves
How do seeds and fruit develop?
- Diploid zygote divides by mitosis, becoming an embryo that consists of a plumule, radicle and 1 or 2 cotyledons
- Triploid endosperm nucleus develops into a food store
- Outer integument dries out, hardens and becomes the seed coat / testa
- Ovule becomes the seed
- Funicle / stalk, of ovule becomes funicle of seed
- Ovary becomes the fruit
Why does the broad bean have a ‘non-endospermic’ seed?
Because the endosperm is absorbed into the cotyledons and is no longer the food store
Why are maize seeds ‘endospermic’?
The endosperm remains as the food store
Why does maize have a one-seeded fruit?
Because the testa fuses with the ovary wall
What does it mean when seeds are dormant?
The active growth of seeds is suspended as germination will only occur under specific conditions
What is seed dispersal?
The movement of seeds away from the parent plant
Why do seeds disperse?
- Ensures the parent plant doesn’t obtain most of the water and nutrients from the soil
- Ensures seedling isn’t shaded by parent plant, as this would prevent it photosynthesising
What is the dispersal method of bursting?
When legume pods split and scatter seeds
What is the dispersal method of transport?
When seeds are passed through the digestive system of birds and dispersed in the faeces
What is the dispersal method of water?
When seeds fall into water, float and are carried away
What are the names of the dispersal methods?
- Wind
- Transport
- Rolling
- Bursting
- Water
- Carrying
What is the definition of germination?
The biochemical and physiological processes through which a seed becomes a photosynthesising plant
What are the 3 main requirements for germination?
- Suitable temperature
- Water (to mobilise enzymes for transport in xylem and phloem, and to vacuolate cells, making them turgid)
- Oxygen (aerobic respiration releases energy which fuels metabolism and growth)
During germination why is the plumule bent over in the shape of a hook?
To protect the tip from damage by soil abrasion
What is the plant growth regulator secreted by the barley embryo?
Gibberellic acid
What does gibberellic acid do?
Switches on genes in the cells of the aleurone layer, resulting in transcription and translation, producing protease and amylase
What does the protease produced by gibberellic acid do?
Hydrolyses protein in the aleurone layer to amino acids, which are used to make amylase
What does the amylase produced by the gibberellic acid do?
Diffuses out of the aleurone layer and hydrolyses the starch stored in the endosperm cells
What does the maltose and glucose produced from gibberellin acid do?
- They diffuse back through the endosperm to the plumule and radicle of the embryo
- Are respired for energy, fuelling biosynthesis and cell division which brings the seeds out of dormancy
What is protandry?
When the stamens of a flower ripen before the stigmas
What are pollinators such as bees attracted to plants by?
- Large, coloured petals
- Scent and nectar
What are angiosperms?
Plants that have flowers and produce seeds enclosed within a carpel
When the male gamete fuses with the diploid polar nucleus it forms a triploid nucleus (endosperm nucleus). What does this do?
Divides repeatedly by mitosis, generating the endosperm tissue, which takes over from the nucellus in providing nutrition for the developing embryo
What is the definition of double fertilisation?
- Fusion of male and female gamete, forming a zygote
- Fusion of male gamete and polar nucleus, forming endosperm
- Unique process to flowering plants
What are features of monocots?
- 1 cotyledon in seed
- Leaf veins are parallel
- Sepals, petals and stamens in multiples of 3
- Vascular bundles scattered in stems and roots
What are features of dicots?
- 2 cotyledons in seed
- Leaf veins form a network
- Sepals, petals and stamens in multiples of 4 or 5
- Vascular bundles in a ring in stems
- Vascular bundle in centre of roots
What is the dispersal method of wind?
When seeds are blown off and transported
What is the dispersal method of rolling?
When the fruit breaks open and the seed falls to the ground and rolls away from the parent tree
What is the dispersal method of carrying?
When hooked seeds attach to animals coats and are carried away
How can dormant seeds survive very cold weather?
Due to their low metabolic rate
How can seeds survive adverse chemical conditions?
Their testa is chemically resistant
How can dormant seeds survive very dry conditions?
As the water content of a dormant seed is reduced below 10%
Until what point does the endosperm or cotyledons provide nutrients to the seed?
Until it can photosynthesise adequately
What may seed inhibitors do?
Only allow germination at a suitable time of year
What is the germination sequence?
- Seed imbibes water
- Testa splits
- Radicle emerges
- Plumule emerges
- Elongation pushes shoot above ground
Why must food reserves in seeds be broken into soluble molecules?
As the food reserves are insoluble in water and can’t be transported to the embryo until they’re hydrolysed
In what way does the plumule grow if it is positively phototrophic and negatively geotrophic?
Upwards
What is the aleurone layer in the endosperm?
A layer of cells towards the outside of the seed, which has a high protein content
What is the process of the effect of gibberellin?
- Barley embryo secretes gibberellic acid, which diffuses through endosperm to aleurone layer
- Gibberellic acid switches on genes in cells of aleurone layer, resulting in transcription and translation, producing enzymes
- Proteases hydrolyse protein in aleurone layer to amino acids, which are used to make amylase
- Amylase diffuses out of aleurone layer and hydrolyse starch stored in endosperm cells
- Maltose and glucose produced diffuse back through endosperm to plumule and radicle of embryo
- They’re respired for energy, which fuels biosynthesis and cell division, and brings the seed out of dormancy
