Sexual Reproduction of the Flowering Plant Learning objectives

Sexual Reproduction of the Flowering Plant Learning objectives

(1/4) State the structure & function of the floral parts including: Sepal, petal,stamen,carpel) State that the Pollen grain produces male gamete. State that the Embryo sac produces an egg cell & polar nuclei.

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

(2/4) 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. Outline fruit formation. Outline seedless fruit production Learning objectives

(3/4) Outline fruit & seed dispersal and give with examples of wind/water/animal/self dispersal Explain & emphasise the need for dispersal

Define the term dormancy. State advantages of dormancy. Explain dormancy in agricultural & horticultural practice. Define the term: Germination. Explain the factors necessary for and role of digestion and respiration in germination. Outline the stages of seed development Learning objectives

(4/4) State that vegetative propagation is asexual reproduction

Give 1 example of vegetative propagation from stem, root, leaf, bud Compare reproduction by seed and by vegetative reproduction Outline 4 methods of artificial propagation in flowering plants Reproduction in Flowering Plants Two Types of Reproduction: 1.

2. Asexual Reproduction Sexual Reproduction Asexual Reproduction Asexual Reproduction involve only one parent The offspring are genetically identical to the parent i.e. a clone Strawberry plants

Sexual Reproduction Sexual Reproduction involves the union of two sex cells called gametes. Gametes are haploid cells capable of fusion A zygote is formed when two haploid gametes fuse (join) together. The offspring of sexual reproduction are not genetically identical to the parents Structure of the flower

Structure of the flower Petal Structure of the flower Stigma Style Anther Ovary

Stamen Filament Sepal Ovule Carpel Function of floral parts

Sepal : To protect the flower (and to prevent it from drying out Petals : To attract insects to the flower for pollination

Function of floral parts Stamen : To produce the pollen grains in the anthers. (Each pollen grain produces two male gametes, one of which can fertilise an egg cell)

Function of floral parts Stamen Anther Produces pollen Filament Holds the anther in place Function of floral parts Carpel : To produce the

ovules (Each ovule contains an egg cell inside an embryo sac) Function of floral parts Carpel Stigma Where pollen lands after pollination Style Pollen travels down this

Ovary Contains ovules Function of each part of flower Part of Flower Function Receptacle Sepals Petals

Nectaries Stamens Carpels Pollination Pollination Transfer of pollen from the anther to the stigma of a flower of the same species

Pollination Self pollination Transfer of pollen from an anther to a stigma of the same plant Cross pollination

Transfer of pollen from the anther to the stigma of a different plant of the same species Methods of pollination Animal Pollination Wind Pollination

Adaptations for animal (insect) pollination Petals brightly

coloured, scented with nectaries Small amounts of sticky pollen Anthers inside petals Stigmas sticky, inside petals Adaptations for wind pollination

Petals small, not coloured brightly Anthers outside petals Stigmas large, feathery and outside petals

Pollen Large numbers, light, dry and small Adaptations for wind pollination Fertilisation Fertilisation

Fertilisation is the fusion of the male (n) and female (n) gametes to produce a zygote (2n) The pollen grain produces the male gametes Embryo sac produces an egg cell and polar nuclei

The pollen grain produces the male gametes Embryo sac produces polar nuclei and an egg cell Embryo sac

Polar nuclei Egg cell Stigma Style Ovary Embryo Sac

Polar nuclei Egg Cell Pollen Grain Pollen Tube Generative Nucleus Tube Nucleus

Mitotic division of generative nucleus to form 2 male gametes Tube nucleus disintegrates 1 male gamete fuses with the egg nucleus to form the

diploid zygote 1 Male gamete fuses with the 2 polar nuclei to form the triploid endosperm nucleus 3N endosperm nucleus Double fertilisation

2N Zygote Seed formation Endospermic & Non-Endospermic Monocots & Dicots Seed Formation

The zygote grows repeatedly by mitosis to form an embryo An embryo consists of a plumule (future shoot), a radical (future root) and cotyledons (food stores needed for

germination) 3N endosperm nucleus 2N Zygote 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 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. bean 3N

endosperm nucleus 2N Zygote Seed Formation Endosperm Food store for developing embryo

Embryo Plumule, radicle, cotyledons Integuments, becomes the seed coat Seed Formation If all the endosperm is absorbed by

the developing embryo the seed is a non endospermic seed e.g. broad bean Seed Formation If all the endosperm is

not absorbed by the developing embryo the seed is an endospermic seed e.g. Maize Seed types and structure Plumule (immature shoot)

embryo All seeds Seed Radicle (immature root) Cotyledon (food supply or seed leaf) In some seeds

endosperm Food store Endospermic Seed e.g. Maize Seed coat (testa) Endosperm Cotyledon

Plumule will develop into a new shoot Radicle will develop into a new root Non-Endospermic seed e.g. Broad Bean Seed coat (testa) Cotyledon

Plumule Radicle Nonendospermic and Endospermic seed Endosperm Cotyledon Plumule Radicle

e.g. Broad Bean e.g. Maize Classification of seeds Classified according to two features: 1. Number of cotyledons (Seed leaves)

Monocotyledon one cotyledon E.g. Maize Dicotyledon - Two cotyledons E.g. Broad bean

Presence of endosperm 2. Present Endospermic e.g. maize Absent Non-endospermic e.g. broad bean Broad Bean Non-Endospermic

Dicot Testa 2 Cotyledons Differences between monocots and dicots Feature Monocot Dicot

Number of cotyledons 1 2 Venation Parallel

Reticulate (Net) Vascular Bundle arrangement Scattered In a ring

Number of petals Usually in multiples of 3 Usually in multiples of 4 or 5 Fruit

Fruit formation Seedless fruits Fruit and seed dispersal Fruit Formation The ovule becomes the seed The ovary becomes the fruit

Fruit Formation A fruit is a mature ovary that may contain seeds The process of fruit formation is stimulated

by growth regulators produced by the seeds Seedless Fruits Can be formed in two ways 1. Genetically

Either naturally or by special breeding programmes e.g. seedless oranges Seedless Fruits 2. Growth regulators e.g. auxins If large amounts of

growth regulators are sprayed on flowers fruits may form without fertilisation e.g. seedless grapes Fruit and seed dispersal

Need for dispersal Minimises competition for light, water etc. Avoids overcrowding Colonises new areas Increases chances of survival Types of dispersal 1. 2.

3. 4. Wind Water Animal Self Methods of dispersal 1.

Wind Sycamore and ash produce fruit with wings Dandelions and thistles produce fruit with

parachute devices Both help the disperse the seeds more widely using wind Methods of dispersal 2.

Water Light, air filled fruits that float away on water E.g. coconuts, water lilies Methods of dispersal 3. Animal

Edible fruit Animals attracted to bright colours, smells and food Seed passes through digestive system unharmed E.g. strawberries, blackberries, nuts Methods of dispersal

3. Animal Sticky fruit Fruits with hooks that can cling to the hair of an animal and be carried away E.g. burdock, goose grass

Methods of dispersal 4. Self Some fruits explode open when they dry out and flick the seed away E.g. peas and beans Dormancy and germination

Dormancy (definition) A resting period when seeds undergo no growth and have reduced cell activity or metabolism Dormancy (advantages)

Plant avoids harsh winter conditions Gives the embryo time to develop Provides time for dispersal

What brings about dormancy? 1. 2. 3. Growth inhibitors e.g. abscisic acid may be present in the seed and it prevents germination until it is broken down by cold,

water or decay The testa (seed coat) might be impermeable to water or oxygen and it might take time for the testa to break down The testa might be too tough for the embryo to emerge. It will take time for the testa to soften. Application in agriculture and horticulture

Some seeds need a period of cold before they germinate It may be necessary to break dormancy in some seeds before they are planted for agricultural or horticultural purposes This can be done by placing them in the

fridge before they are planted Germination The re-growth of the embryo after a period of dormancy, if the environmental conditions are suitable

Germination Factors necessary Water Oxygen Suitable temperature

Dormancy must be complete Germination Factors necessary Water

Activates the enzymes Medium for germination reactions e.g. digestion Transport medium for digested products

Germination Factors necessary Oxygen Needed for aerobic

respiration Suitable temperature Allows maximum enzyme activity Events in Germination

Digestion Of stored food in endosperm and cotyledon Respiration To produce ATP to drive cell division

Events in germination cease when the plants leaves have developed and the plant has started to photosynthesise Events in Germination (detail)

Water is absorbed Food reserves are digested Digested food is moved to the embryo New cells are produced using amino acids Glucose is turned into ATP to drive cell division Radicle breaks through the testa

Plumule emerges above ground New leaves begin to photosynthesise Events in Germination Plumule Radicle Cotyledon Events in Germination

Plumule Radicle Dry mass of seed (g) Changes in dry weight of seeds during germination Time (days) Mass drops initially due to respiration of stored food, but then

begins to increase due to photosynthesis Dry mass of seed (g) Changes in dry weight of seeds during germination Embryo Endosperm Time (days)

Food reserves in endosperm are transferred to the growing embryo Germination of broad bean (hypogeal) Germination of broad bean (hypogeal) Germination of broad bean Ground

Seed water is absorbed through the micropyle Germination of broad bean The testa splits Radicle emerges Germination of broad bean

Plumule emerges Radicle continues to grow Germination of broad bean The plumule is hooked to protect the leaves at the tip Epicotyl

Germination of broad bean The plumule grows above the surface of the soil Lateral roots develop Germination of broad bean

Plumule straightens and the leaves open out Throughout Hypogeal germination the cotyledons remain below the ground Germination of sunflower

(Epigael) Seed water is absorbed through the micropyle Germination of sunflower Radicle emerges

Germination of sunflower Hypocotyl Hook Seed coat discarded Germination of sunflower Cotyledons Radicle grows downwards

Germination of sunflower Leaves emerge Cotyledons wither In Epigeal germination the cotyledons rise above the ground Learning Check

Outline the main stages of sexual reproduction in plants Review the plant life cycle After fertilization flower withers pollen is transferred

2 3 1 seeds disperse and germinate into new plant 4 seeds develop

in ovary Asexual Reproduction in Plants Vegetative Propagation Definition

Asexual reproduction does not involve the manufacture or union of sex cells or gametes e.g. binary fission, fragmentation, spore formation and budding It involves only one parent and offspring are genetically identical (have the same genetic content) to the parent Vegetative Propagation

A form of asexual reproduction in plants Does not involve gametes, flowers, seeds or fruits Offspring are produced by a single plant (genetically identical to parent) Can happen naturally or it can be done

artificially Vegetative Propagation Natural e.g. runners, tubers, plantlets, bulbs What happens?

Part of the plant becomes separated from the parent plant and divides by mitosis to grow into a new plant As a result the offspring are genetically identical to the parent Parts of the parent plant may be specially modified for this purpose: 1. 2.

3. 4. Stem Root Leaf Bud 1. Modified Stems Runners

horizontal, running over the soil surface terminal bud of the runner sends up new shoots e.g. strawberry,

creeping buttercup. Creeping buttercup Modified Stem (continued)

Stem Tubers swollen underground stem tips buds (eyes) produce new shoots e.g. potato

2. Modified Roots Root Tuber swollen fibrous roots the tuber stores food, but the new plant develops from a side bud at the base of the old stem e.g. dahlia, lesser

celandine Note: Tap Roots e.g. carrot and turnip, are swollen roots for food storage in biennial plants they are not reproductive organs 3.

Modified Leaves Plantlets Some plants produce

plantlets along the edges of the leaves Plantlets reach a certain size, fall off and grow into new plants e.g. Lily, kalanchoe (mother of thousands) 4.

Modified Buds Bulbs A bulb contains an underground stem, reduced in size Leaves are swollen

with stored food e.g. onion, daffodil, tulip 4. Modified Buds

Bulbs The main bud (apical bud) will grow into a new shoot) The side buds (lateral buds) will also grow into new shoots Comparison of

reproduction by seed (sexual) and by vegetative propagation (asexual) Advantage to seed formation Sexual (seed) Asexual (vegetative) Cross pollination ensures

variation (allows evolution) No variations can be advantage in commercial horticulture More resistant to disease All plants are of same species susceptible to disease

Dispersal reduces competition Overcrowding and competition Seeds can remain dormant and No seeds formed no survive unfavourable conditions dormancy Advantage to vegetative propagation Sexual (seed) Complex process

Asexual (vegetative) Simple process Depends on outside No outside agents agents for seed dispersal needed Slow growth of young plants to maturity Rapid growth

Wasteful e.g. petals, pollen, fruit No waste Vegetative propagation Artificial used by gardeners to propagate plants e.g. cuttings, layering, grafting and budding

Cuttings Parts of a plant (usually shoots) removed from plant allowed to form

new roots and leaves rooted in water, wellwatered compost, or rooting powder e.g. busy lizzie, geranium Grafting

Part of one plant (scion) is removed and attached to a healthy, rooted part of a second plant (stock) Useful qualities from both plants combined into one e.g. rose flower and thorn-less stem

e.g. apple trees Layering A branch of a plant is bent over and pinned to

the earth at a node When roots develop the branch is separated from the parent plant. Useful for the propagation of woody plants e.g. blackberry, gooseberry. Micropropagation (Tissue Culture) (1/3)

Cells removed from plant and grown as a tissue culture in a special medium Growth regulators and nutrients added so that growing cells form a group of similar cells

called a callus Micropropagation (Tissue Culture) (2/3)

Different growth regulators are then added so that this tissue develops into a plantlet Plantlet can be divided up again to produce many identical plants Entire plant can be grown from a small piece of stem, leaf or root tissue Used in mass production of house plants and crops such as bananas and strawberries

Micropropagation (Tissue Culture) (3/3) Provides a larger number of plants more

quickly than cuttings. Can be used to check cells for a particular feature e.g. resistance to chemicals or a particular disease Cloning

All offspring genetically identical - produced asexually Clones are produced by mitosis All the offspring from the various methods of vegetative reproduction (both natural and artificial) mentioned are examples of clones END

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