Sexual Reproduction in Flowering Plants

b) Pollination & Fertilisation

Learning objectives• Define the terms: pollination, self-pollination• Outline methods of pollination including:

cross-pollination & self pollination• Define the term: fertilisation.• Outline seed structure & function of following:

testa, plumule, radicle, embryo, cotyledon • Explain embryo & food supply (endosperm or

seed leaves)• Classify plants as monocotyledon or

dicotyledon & distinguish between them.• Make reference to non-endospermic seed. 2

Sexual reproduction in flowers

Sexual reproduction in flowers

Can you answer the following from your JC Science

• Pollination involves the transfer of pollen from the _______________ to the __________________

• Self-pollination: _________________________ • Cross-pollination: ___________________________ Put these stages of sexual reproduction in order

(a) Germination(b) Seed and fruit formation (c) Pollination(d) Seed dispersal(e) Fertilisation

• http://www.youtube.com/watch?v=RuYrFwDuYn0&feature=fvw

Answer the questions on the following video

1. What method is used to transfer pollen in daffodils?Insect

2. What type of pollination occurs in daffodils?Cross

3. Name 1 feature found in flowers involved in insect pollinationLanding strips to guide insects into flower, nectar, colourful petals

4. Describe the appearance of the pollen of flowers involved in wind pollination

Smooth, produced in large amounts

5. What happens in some flowers if cross pollination doesn’t occursSelf pollination

6. How do plants prevent self fertilisationRelease chemicals that favours pollen from other plants

7. How do imperfect flowers prevent fertilisationMale and female parts are out of sync

Pollination

Pollination

Transfer of pollen from the anther to the stigma of a flower of the same species

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Pollination

Pollination

PollinationSelf pollination

• Transfer of pollen from an anther to a stigma of the same plant to form zygotes

Cross pollination• Transfer of pollen from

the anther to the stigma of a different plant of the same species to form zygotes. Most common. Cross pollination increases variation.

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Methods of pollination

• Insect Pollination

• Wind Pollination

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Pollination by Insects

What do flowers, that are involved in insect pollination look like? 1. Petals: Large & coloured2. Scented3. Nectaries to produce nectar4. Anthers and Stigmas inside the flower5. Pollen: Spikey E.g. : tulip, buttercup

Adaptations for wind pollination

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Pollination by Wind

What do flowers, that are involved in wind pollination look like? Petals: small and greenNo scentNo nectaries or nectarAnthers and feathery stigmas hanging outside the flowerPollen: Large amounts & smoothE.g.: grass, oak

Learning Check

1. What is pollination2. Name 2 types of pollination and explain each3. Name 2 methods of pollination4. For each method, explain the appearance of

the flower.

Fertilisation

Fertilisation

• Fertilisation is the fusion of the nuclei of the male (n) and female (n) gametes to produce a zygote (2n)

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Fertilisation

• The pollen grain produces the male gametes

• Embryo sac produces an egg cell and 2 polar nuclei

Polar nuclei

Embryo sac

Egg cell

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Stigma

Style

Ovary

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Embryo Sac

Polar nuclei

Egg Cell 21

Pollen Grain

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Pollen Tube

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Tube Nucleus

Generative Nucleus

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Tube nucleus disintegrates

Mitotic division of generative nucleus to form 2 male gametes

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One Male gamete fuses with the two polar nuclei to form the triploid endosperm nucleus

One male gamete fuses with the egg nucleus to form the diploid zygote

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3n Endosperm nucleus

2n Zygote

Double fertilisation

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Learning Check

1. What is fertilisation2. Name the 2 types of nuclei in the ovule that

are involved in fertilisation3. Explain the method of fertilisation in 3 steps4. What is double fertilisation

Sexual Reproduction in Flowering Plants

c) Seed Formation

Seed formation

Endospermic & Non-EndospermicMonocots & Dicots

3n Endosperm nucleus

2n Zygote

Seed Formation: A seed develops from a fertilised ovule

• The zygote grows repeatedly by mitosis to form an embryo

• Embryo: (part of seed that) becomes the new plant

• An embryo consists of a• plumule (shoot)

• a radical (root)

• cotyledons (food stores needed for germination)

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Seed Formation

• The endosperm nucleus (3N) divides repeatedly to form the endosperm in endospermic seeds. This endosperm acts as a food store for the developing seed

• e.g. maize

3n Endosperm nucleus

2n Zygote

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Seed Formation

• In non-endospermic seeds the endosperm is used up in the early stages of seed development so the food is stored in the cotyledons

• e.g. broad bean 3n Endosperm nucleus

2n Zygote

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EndospermFood store for developing embryo

EmbryoPlumule, radicle, cotyledons

Integuments, becomes the seed coat

Seed Formation

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If all the endosperm is absorbed by the developing embryo the seed is a non-endospermic seed e.g. broad bean

Seed Formation

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If all the endosperm is not absorbed by the developing embryo the seed is an endospermic seed e.g. Maize

Seed Formation

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Cotyledon:

- Seed leaf specialised for food storage. - Stores food such as starch and sugar

Testa:- Seed coat.

Seed types and structure

Seed

embryo

Plumule (immature shoot)

Radicle (immature root)

Cotyledon (food supply or seed leaf)

endosperm Food store

All seeds

In some seeds

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Endosperm

Seed coat (testa)

Cotyledon

Plumule – will develop into a new shoot

Radicle – will develop into a new root

Endospermic Seed e.g. Maize

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Endospermic seed: contains endosperm when fully developed

• Moncotyledons (one cotyledon)• Small, food is stored in the endosperm• Cotyledon absorbs food from endosperm and

passes it onto embryoE.g. Maize

Seed coat (testa)

Cotyledon

Plumule

Radicle

Non-Endospermic seed e.g. Broad Bean

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Non-endospermic seed: Has no endosperm when fully formed

• Dicotyledons (2 cotyledons)• Food is stored in the cotyledons• No longer has endosperm as it is used upE.g. broad beans

e.g. Broad Bean e.g. Maize

Plumule

Radicle

Cotyledon

Endosperm

Non–endospermic and Endospermic seed

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Classification of seedsClassified according to two features:1. Number of cotyledons (Seed leaves)

Monocotyledon Dicotyledon

2. Presence of endosperm Present – Endospermic Absent – Non-endospermic

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Broad Bean – Non-Endospermic DicotTesta 2 Cotyledons

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48Stems are herbaceous Stems can be herbaceous

or woody

Grass Barley

DaisyRose

Example of Monocot and Dicot

Monocot Dicot

Grass Buttercup

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Learning Check

1. What method of division occurs in a zygote to form the embryo

2. Name the 3 parts of the embryo3. What 2 ways are seeds classified4. Explain endospermic and non-endospermic5. Give an example of each of the above6. Name 3 features of a monocot and 3 features of

a dicot7. State 2 places food is stored in a seed?

Can you…….• Define the terms: pollination, self-pollination• Outline methods of pollination including:

cross-pollination & self pollination• Define the term: fertilisation.• Outline seed structure & function of following:

testa, plumule, radicle, embryo, cotyledon • Explain embryo & food supply (endosperm or

seed leaves)• Classify plants as monocotyledon or

dicotyledon & distinguish between them.• Make reference to non-endospermic seed. 53