sexual reproduction in flowering plants

What does the Embryo Sac produce in a plant?

The Egg Cell 2 Polar Nuclei

Describe in detail the development of the embryo sac from a megaspore mother-cell

Diploid megaspore mother-cell divides by meiosis/ giving 4 haploid daughter cells/ Only one survive, 3 die/ This becomes the embryo sac/ The embryo sac nucleus divides by mitosis to give 8 haploid nuceli/ Two of the haploid nuclei become the polar nuclei/ One haploid nucleus becomes the egg

Describe the formation of a pollen grain

Microspore undergoes meiosis to produce 4 haploid cells The 4 haploid cells undergo mitosis 2 haploid nuclei

Where are male gametes produced in a plant?

Generative Nucleus divides by Mitosis forming 2 male gametes

What is meant by self-pollination?

Transfer of pollen from anther to stigma on same plant

What is meant by Cross-pollination

Transfer of pollen from anther to stigma on different plant but same species

What are two methods by which pollination can occur?

Wind pollination Animal pollination

Describe the main events that occur immediately after pollination?

Pollen grain germinates and /produces pollen tube/ The tube nucleus digests through the style/ and reaches the ovary/ Generative nucleus divides by mitosis /to form two male nuclei /which enter the embryo sac/ One haploid male nucleus fuses with the haploid egg to form the diploid zygote/ The second male nucleus fuses with the two haploid polar nuclei to form a triploid endosperm

What is Dormancy?

period of low metabolism when seed does not germinate

What are two advantages of dormancy?

Seeds germinate when conditions are suitable Allows time for greater dispersal Survive unsuitable conditions

Why does the dry mass of a seed decrease?

respiration

Why does a seed remain dormant?

presence of Growth Inhibitors Tough testa (not allowing oxygen & water to enter)

As the seed forms following fertilisation, a food store develops. Name this structure

Endosperm

Define Germination

Growth of seed into a new plant

Define Dispersal

Carrying of seed away from the parent plant

Define Dormancy

Period of no growth and low metabolism

Give two roles of water in the proces of germination

Soften testa Activate enzymes Transport nutrients

What are two modes of Germination?

Epigeal Hypogeal

What happens in Epigeal Germination?

Cotyledons rise above the soil They become photosynthetic

What happens in Hypogeal Germination?

Cotyledons stay below the soil They shrivel and plumule sprouts leaves

Ouline the main events in the development of the pollen grain in the anther

Diploid microspore mother cell/ divides by meiosis/ to produce four haploid nuclei/ These halpoid nuclei divide by mitosis/ to form a pollen grain with two haploid nuclei/; the generative nucleus and the tube nucleus

"What is meant by the term ""pollination""?"

Transfer of pollen from the anther to the stigma

Describe the roles of digestion in germination

Produce soluble nutrients

What are adaptations of wind-pollinated flowers?

Anthers outside flower Pollen grain is light

State two advantages of sexual reproduction over asecual reproduction in plants

Variation Less competition

What happens during each double fertilisation in the embryo sac?

One male gamete fuses with the egg One male gametes fuses with the two polar nuclei

State what is produced during each double fertilisation in the embryo sac?

A diploid zygote A triploid endosperm

What does the Ovule develop into after fertilisation?

Seed

Following fertilisation, from precisely which part of the flower is the seed formed?

Ovule

Why is the measurement of dry mass prefered in experiments?

Water could vary between seeds

Explain why the dry mass of the endosperm tissue decreases over the 3 weeks

Food is transferred to the embryo

What occurs at A

Photosynthesis

Name the site of production of a pollen grain

Anther

Name the structure on which a pollen grain must land on to complete pollination

Stigma

What is the role of an anther in in flowering plant reproduction

Site of pollen release

What is the role of an Stigma in in flowering plant reproduction

Pollen lands on it

What is the role of digestion in germination?

Provides soluble nutrients

What is the role of respiration in germination?

Provides realease of energy for growth

Why is there an inital decrease in mass shortly after germination?

Respiration

Why is there an increase in mass over a period of time after germination?

Photosynthesis (food being made)

Why is it recommended to sterilise the seeds in the experiment to show digestive activity during seed germination?

To kill all microorganisms

Why were split seeds placed open-side on the starch agar in the experiment to show digestive activity during seed germination?

so that Enzyme is exposed to the substrate

How did you know that digestive activity had occured on one of you investiation plates in the experiment to show digestive activity during seed germination?

Flooded plates with iodine Clear areas around seeds

Whywas the iodine not cleared in one of the plates in the experiment to show digestive activity during seed germination?

as enzymes had been denatured

Why were seeds soaked in water prior to the investigation in the experiment to show digestive activity during seed germination?

To activate enzymes

Describe how you further prepared the seeds and added them to the agar plates in the experiment to show digestive activity during seed germination?

Cut the seeds Sterile the seeds using disinfectant Place flat side onto agar Repeat experiment for dead (boiled) seeds

Under what conditions did you store the plate containing the seeds to allow germination to occur?

Incubator for 6-7 days

When considering conditions necessary for seed germination describe how you provided an oxygen-free environment

Placed them in (cool) boiled water with a layer of oil on top

What is the role of Sepals in a flower?

protect flower

What is the role of anther in a flower?

produce pollen

What is the role of Stigma in a flower?

traps pollen

Name the substance that is used as a medium on which to germinate the seeds

Agar

Give two ways in which plants protect themselves from adverse external environments

Dormancy Heat Shock Proteins

Suggest in which way a knowledge of dormancy is useful to farmers and gardeners?

Optimum storage conditions

Why do plants need oxygen for the process of germination

for aerobic respiration

What is an agar plate?

Petri dish containing a jelly

Name the next stage of development following the formation of the zygote in flowering plants

Embryo

State the precise location of production of female gametes of flowering plants

Embryo sac

How are Wind-pollinated flowers adapted to carry out it's function

Eposed stamens Feathery stigma light pollen

Label

A - Stigma/Style B - Ovary C - Embryo Sac D - polar nucleli E - Ovule

What happens to the polar nuceli following fertilisation?

Fuse to form endosperm nucleus

Give one way in which a knowledge of seed dormancy is useful to humans

Correct environment for storage

When investigating the conditions necessary for germination, how did you deprive the seeds of correct temperature?

Fridge

When investigating the conditions necessary for germination, how did you deprive the seeds of water?

dry cotton wool

List the contents of a mature pollen grain

One generative nucleus One tube nucleus

What is the eventual fate of the ovule after double fertilisation?

Zygote develops into an embryo plant

Explain why having Stigma outside flower is beneficial

Catch pollen easily

State one way in which the pollen produced by an insect pollinated plant would diff er from the pollen produced by a wind pollinated plant.

Pollen produced by insect pollinated flowers is heavier while pollen produced by wind pollinated flowers is lighter

Suggest why cross-pollination is more common than self-pollination

greater diversity so better able to adapt to changing environment