Plant Reproduction Flashcards Preview

A2 Biology > Plant Reproduction > Flashcards

Flashcards in Plant Reproduction Deck (21):

What are the adaptations of insect pollinated flowers?

•Brightly coloured petals, nectar and a scent
•Sticky pollen
•Anthers and stigma are inside the flower


What are the adaptations of wind pollinated flowers?

•Small flowers, no scent and dull petals
•Anthers hand outside the flower
•Large feathery stigma
•Large volumes of pollen produced


Explain self-pollination

When pollen lands on the stigma from the same flower or plant


Why is self-pollination not favourable?

•Reduces genetic variation
•Increases interbreeding depression (negative recessive alleles being expressed)


What is a benefit of self-pollination?

Lack of variation to preserve successful phenotypes


Explain cross-pollination

Where pollen is transferred from the anther to the stigma of another plant of the same species


Why is cross-pollination favourable?

Increases genetic variation due to meiosis forming gametes and random fertilisation of the gametes


Name three ways of reducing the chances of self-pollination

•male and female parts mature at different times (dichogamy)
• stigma higher than the anther
• have male flowers or female flowers


How are pollen grains developed?

•first, mitosis occurs to produce pollen mother cell
• meiosis occurs and produces tetrad haploid cells
• the tapetum provides the cells with pollen
• pollen grains contain a non reproductive cell and a generative cell
•generative cell contains a generative nucleus and a tube nucleus
• generative nucleus divided to form male gametes
• tube nucleus forms the pollen tube


What is a pollen grain composed of?

•inner layer (intine), made of cellulose
•outer later (exine) tough layer to prevent dessication (drying out)


What is dehiscence?

When pollen grains are mature, the anther dries out and splits along lines of weakness


Explain the development of an ovule

•meiosis of a megaspore mother cell in the nucellus to give 4 haploid megaspores
•three megaspores disintegrate
•one megaspore develops and undergoes 3 mitotic divisions
•produces 8 haploid nuclei within the embryo sac
-3 antipodals
-2 synergids
-2 polar nuclei
-1 egg cell


Explain the process of pollination and double fertilisation

1. Pollen grain takes in water and germinates in the sucrose solution secreted by the style
2. The tube nucleus begins to form the pollen tube
3. Hydrolase enzymes in the pollen tube digest through the style. In the pollen tube, the male generative nucleus divides by mitosis to produce two haploid gametes
4. Pollen tube enters the embryo sac through the micropyle
5. Male nuclei enters the ovule ( 1 haploid nucleus fuses with haploid female nucleus to for a diploid zygote)
6. Other male nucleus fuses with both polar nuclei to form a triploid primary endosperm nucleus
7. Seed and fruit develop


Explain the development of the seed and fruit ( what makes what )

• zygote becomes embryo
• integuments form testa / seed coat
• ovule forms the seed
• surrounding ovary forms the fruit
• ovary wall becomes the wall of the fruit
• triploid endosperm cell forms endosperm tissue


What is the endosperm useful for?

Food storage tissue in cereal grains


Explain the difference between monocots and dicots

Mono- single cotyledon (maize)
Di- double cotyledon (broad bean)


What is the name for a shoot and a root?

Plumule (shoot)
Radical (root)


What are the conditions required for germination?

•suitable temp- close to optimum for enzymes
• water- to mobilise enzymes, to form vacuoles and transport
• oxygen- production if ATP by aerobic respiration


What happens during germination?

•Seed imbibes water through the micropyle
•Cotyledons swell and testa splits so oxygen can enter for aerobic respiration
•Enzymes mobilise and break down energy storage molecules
•Plumule grows upwards, and radicle grows downwards


What is gibberellin?

Plant hormone involved in germination of endospermic seeds such as maize


How does gibberellins work?

•After the imbibition of water, gibberellins released by the embryo and diffuse through the aleurone layer
•Stimulates the production of hydrolytic enzymes such as amylase
•Product of the digestion diffuse to the embryo where they are used for respiration