Eduqas A Level Biology: Component 2: "Sexual Reproduction in Plants"

What occurs inside a pollen grain before it is ready to be germinated?

The haploid undergoes mitosis to form a pollen tube nucleus and a generative nucleus. the GN becomes 2 male nuclei

How is the exine of the pollen grain adapted for protection?

Resists desiccation
Tough
chemically resistant
resistant to UV radiation

Why is it important that pollen grains are resistant to UV radiation?

at high altitudes, theyre exposed more but UV can cause DNA mutation

Define pollination

The transfer of pollen grains from the anther to the stigma

What is the name for flowering plants?

Angiosperms

What are the names for the sepals and for the petals?

Sepals: calyx
Petals: corolla

State what comprises the stamen and their individual functions

1. Anther: male gamete which produces pollen
2. Filament: thin and contains vascular tissue to provide anther with nutrients

State the structures that make up the carpel and their functions.

Stigma: trap pollen
Style: hold the stigma to come into contact with insects
Ovule: female gamete
Ovary: protects ovule

How is the pollen produced by insect pollinated plants different to that of wind pollinated?

Wind pollinated produce a large quantity of pollen since theres a low probability of success. Small and lightweight to be carried by the wind.

Insect pollinated makes a small quantity of pollen with barbs and hooks to attach to insect

Outline the structure of a pollen sac

Fibrous layer, tapetum and pollen mother cells

Outline the steps to form pollen grains

Diploid pollen mother cells undergo meiosis to form a tetrad of pollen which seperates into pollen grains

Outline the process of dehiscence

1. Outer layers dry out causing tension in lateral grooves
2. Tensions pulls the walls of the anther apart
3. Edges of pollen sacs curl away
4. An opening exposes the pollen grains for insects or the wind

What is the opening for the pollen in dehiscence called?

Stomium

Outline the steps for the fornation of the ovule

1. Megaspore undergoes meiosis to form 4 haploid cells
2. 3 cells degenerate
3. One cell undergoes mitotic divisions
4. An embryo sac with 2 polar bodies, 2 synergids, 3 antipodals and egg cell is formed

Define self pollination

Pollination that occurs on the same flower or another flower on the same plant

What are the male parts of the plant called?

Stamen

What are the female parts of the plant called?

Carpel

What is the name of the part of the stalk where the flower is attached?

Receptacle

Describe the petals of insect and wind pollinated plants and why they are different

Insect: bright petals that produce scent and nectar for attraction
Wind; dull, scentless petals since they rely on wind

Describe the stigma of insect and wind pollinated plants and why they are different.

Insect: sticky to trap pollen and secrete chemicals to stimulate pollen tube growth
Wind; large and feathery so they have a large s.a to catch pollen grains in the wind

Why are the anthers of an insect pollinated plant inside the flower unlike the wind pollinated?

Inside the flower makes it more likely to brush against insects whereas wind pollinated just needs the pollen to be blown away

State the structures found inside the anther

Lateral groove, filament, pollen sac, epidermis

What provides the nutrients to a pollen sac?

Tapetum

What causes variation in self pollinated plants?

Mutation in DNA replication during Interphase, independent assortment and crossing over in meiosis

What are the advantages of self pollination?

Beneficial characteristics are likely to be passed on i.e farming
Preserves good genomes which is suited to a stable environment

What are the disadvantages of self pollination?

Lacking genetic diversity
Interbreeding results in a greater chance of 2 recessibe alleles being combined at fertilisation

Define cross pollination

Pollination that occurs with different plants of the same species

Why is it beneficial for genetic variability to be introduced in cross pollination?

The best adapted due to the variability will survive intraspecific competition

What are the sources of genetic variation in cross pollination?

mutations, crossing over, independent assortment, random fusion of haploid nuclei during fertilisation

What is dichogamy and what is its purpose?

the stamen and stigma ripen at different times
to stop self pollination

Name and differntiate the two types of dichogamy

1. Protandry: stamen ripens first so the stigma cant germinate the pollen
2. Protogyny; the stigma ripens first but no pollen is being produced

Apart from dichogamy, describe other ways to stop self pollination

1. Anther is below the stigma so the pollen cant fall onto the stigma with gravity
2. Genetic incompatibility so the pollen cant germinate on the stigma of the same plant
3. Seperate male and female parts of the plant

Outline the steps of fertilisation briefly

1. a compatible pollen grain lands on the stigma which releases a sugary solution
2. pollen grain germinates and pollen tube nucleus forms a pollen tube
3. The pollen tube goes down the style into the embryo sac through the micropyle
4. The pollen tube nucleus disintegrates and the two male nuclei are released into the sac

What is the micropyle?

A groove in the embryo sac which allows the entry of the pollen tube

What is the role of the integuments?

Physical protection

How does the pollen tube go from the stigma to the embryo sac?

The pollen tube nucleus produces hydrolytic enzymes which digests the style tissue on the path. it absorbs the products. The path is guided by chemioattractants secreted by the egg cell

Describe the process of double fertilisation

One male nuclei+ egg= diploid zygote
one male nuclei + 2 polar bodies = triploid endosperm nucleus

List some similarities between fertilisation in plants and humans

1. internal fertilisation in humans
2. chemotrophism of male gamete towards female gametes
3. fusion of haploid gametes to form a zygote
4. secretion of digestive enzymes to let male gamete reach the female gamete

List some differences between fertilisation in plants and humans

1. double fertilisation in plants
2. triploid nucleus formed in plants
3. human male gametes can swim and dont need a tube
4. acrosome reaction in humans, pollen tube in plants

What is the endosperm tissue?

food storage tissue in plants

What structures are found in the diploid embryo?

plumule, radicle, cotyledons

What forms the fruit and what forms the seed?

Fruit; fertilised ovary
seed; ovule

What is the function of the fruit and how is it adapted for this?

Protection
To distribute the seed so its sweet smelling and tasty for animals to eat and discard the seeds

What does the integuments become, and how is it adapted for its function?

Testa; chemically resistant for its role

What is a cotyledon?

A seed leaf

Differentiate a monocotyledon and a dicotyledon

Di; nonendospermic, cotyledon absorbs endosperm and photosynthesizes itself to obtain nutrients
Mono; endospermic as it remains as a food source, one seed as the testa fuses with ovary wall

What role does the endosperm or the cotyledon play in maintaining a terrestrial life for seeds?

Supplies nutrienrs until true leaves develop and photosynthesise

How are dormant seeds adapted to terrestrial life?

low metabolic rate so they can survive the cold and low water content

Why is seed dispersal beneficial?

Spreads the plants over a large area so it reduces intra specific competition and colonises new areas

Describe 3 methods of seed dispersal

1. water; seeds are able to float e.g. coconut
2 wind: seeds are lightweight e.g. dandelion
3. animals; spikes that attach to fur or feathers

When does germination occur?

environmental factors are favourable;
enough oxygen for aerobic respiration, optimum temperature for enzymes and water for the mobilisation of enzymes

Outline the process of germination

1. Water is imbibed through the micropyle
2. tissues swell so the testa splits and oxygen enters for aerobic respiration
3. food reserves from cotyledons are hydrolysed to soluble forms
4. the soluble products are transported to the growing points of the embryo as energy sources for growth and respiration
5. the plumule grows upwards with a hooked tip to avoud soil erosion, and leaves unfurl
6. radicle grows downwards into roots

What are the food reserves that are hydrolysed in germination and what do they become?

starch- maltose
maltose- alpha glucose
a glucose- b glucose
proteins- amino acids

In terms of phototrophism, describe the change in plumule and radicle in germination

plumule; positive
radicle; negative

in terms of geotrophism, describe the change in plumule and radicle in germination

plumule; negative
radicle; positive

What is the name of the hormone for germination control?

Gibberellins

Explain how gibberellins works.

1. after imbibition, G is released by the embryo to the aleurone layer
2. G stimulates the aleurone cells to produce hydrolytic enzymes
3. proteins in the aleurone layer are hydrolysed into amino acids
4. enzyme synthesis from these amino acids occurs to make amylase
5. amylase diffuses into endosperm and hydrolyses starch
6. these diffuse to embryo for aerobic respiration and growth

How does gibberelline stimulate the production of proteases,

By triggering transcription and translation in aleurone cells