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12.3 Reproduction in Flowering Plants. Vegetative structures : stems, roots and leaves Reproductive structures : flowers Vegetative Propagation : reproduction of vegetative structures. Sexual reproduction : introduce variation through meiosis by

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slide2
Vegetative structures:

stems, roots and leaves

  • Reproductive structures:

flowers

  • Vegetative Propagation:

reproduction of vegetative structures

slide3
Sexual reproduction:

introduce variation through meiosis by

  • 1. Independent assortment chromosomes

during metaphase

  • 2. Recombination of genes by

crossing over between homologous

chromosomes at prophase I

slide4
12.3.1 Floral Structure
  • Both self-fertilization and cross-fertilization

introduce variation.

  • External agents, e.g. insects , help in transfer

of genetic material when they assist in pollination

of flowers.

This, however, exposes the vulnerable gametes to

desiccation. Spermatophytes thus have evolved

their male gamete within a spore, the microspore

or pollen grain.

structures of a typical flower
Structures of a typical flower:

Angiosperms reproduce sexually by producing flowers

slide9

stomium

liberated pollen grain

slide13
The floweris the organ of sexual

reproduction in flowering plants

  • Flowers are usually hermaphrodite or
  • bisexual but sometimes unisexual

sepals: outermost whorl; form the calyx; green in colour; Function -

1 Protect the flower bud

2 Carry out photosynthesis

slide14
Petals: form the corolla; often brightly coloured & attractive;

with insect guides which guide insects to the base of the petals for nectar secreted by

the nectary;

  • In some flowers, the calyx & corolla are undistinguishable and are collectively called theperianth
slide15
Stamens: male reproductive parts or
  • androecium;
  • Each stamen consists of an antherand a long filament;
  • Each anther contains four pollen sacs with pollen grains inside;
  • The pollen grains contain the male gametes
slide16

stomium

liberated pollen grain

slide17
Carpels: female reproductive parts or

gynoecium (or pistil);

Each carpel consists of an ovary which

contains ovules withova inside;

At the top of the ovary is the style, with a

stigma at the tip to receive pollen grains for

fertilization

slide18
Actinophmorphic (regular): flowers with

petals & sepals of similar size and shape

exhibiting radial symmetry

  • Zygomorphic (irregular): flowers with

unequal sepals & petals of different shapes

and arranged in bilateral symmetry

slide20
12.3.2 Pollination
  • - meiosis occurs inside the pollen sacs of

anther;

  • When mature, pollen sacs split open

expose their pollen grains

  • - female gametes (egg nuclei) are inside ovules
  • funicle: ovule stalk
  • integuments: protective layer
  • micropyle: a small opening through

which pollen tube grows into ovule

slide21
Development of the pollen grain(for reference):
  • pollen mother cells (2n)
  • meiosis
  •  tetrad (4) haploid (n) cells
  •  microspores (pollen grains)
  • mitosis
  •  generative nucleus & tube nucleus
  • mitosis
  • 2 male nuclei & tube nucleus
slide22
Development of the ovule (for reference):
  • nucellus
  •  megaspore mother cell (2n)
  • meiosis
  •  4 megaspores (n)
  •  3 degenerated, 1
  •  embryo sac mitosis 3 times
  •  8 nuclei (3 antipodal cells,
  • 2 polar nuclei, 2 synergids with 1 egg cell)
slide23
Pollination: the transfer of pollen grains from anthers to the stigmas;
  • external agents are needed –
  • (1) by insect
  • (2) by wind
slide27
Comparison of anemophilous (wind-pollinated)

and entomorphilous (insect-pollinated) flowers

slide28
Comparison of anemophilous (wind-pollinated)

and entomorphilous (insect-pollinated) flowers

slide29
Comparison of anemophilous (wind-pollinated)

and entomorphilous (insect-pollinated) flowers

slide30
Comparison of anemophilous (wind-pollinated)

and entomorphilous (insect-pollinated) flowers

slide31
Comparison of anemophilous (wind-pollinated)

and entomorphilous (insect-pollinated) flowers

slide39
12.4.1 Fertilization &

Development in Flowering Plants

  • pollen grains send out pollen tubes which grows

down the style & ovary, towards the micropyle

  • pollen grains are attracted by sugars in stigma

and secrete enzymes to digest a pathway through

the style

slide41
Double Fertilization:
  • male gamete goes into the ovule and fertilizes with the egg cell
  • the other male gamete fuses with the polar nuclei to form the triploid endosperm
slide43

12.4.2 Methods of Preventing Inbreeding

Self-pollination: the transfer of pollen from the

anther to the stigma of the same flower,

or of another flower of the same plant

Cross-pollination: the transfer of pollen to a flower

on a different plant of the same species

*If pollen lands on the stigma of a plant of a different species, it usually dies.

  • Since cross-pollination results in a great

variability of more adaptable offspring,

many plants prefer cross-pollination

slide49
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide50
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide51
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide52
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide53
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide54
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide55
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide56
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide57
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide58
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide59
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide60
12.4.3 Development of Fruits and Seeds

Fate of floral parts after fertilization

slide61
The most common food stores in seeds is

carbohydrates (in the form of starch).

  • Many young seeds store sugar but this

changes to starch as they mature.

  • Lipid are often stored in the cotyledons and

may form a high percentage of the dry

weight,

e.g. peanuts. Proteins are found to a lesser

extent in seeds but wheat has an aleurone layer

and protein is stored in the cotyledons of

legumes and nuts.

slide62
A fruit is an ovary after fertilization and it contains seeds
  • Functions:
  • Fruits: protect & disperse the embryo
  • Seeds: protect the embryo
  • Provide food for the embryo
  • Help in dispersal of the plant
slide63
Fruits and Seeds Dispersal
  • Dispersal of seeds by fruits –
  • (1) by wind,
  • (2) by animals,
  • (3) by water,
  • (4) by mechanical force,
  • (5) Censor mechanism, and
  • (6) Casual mechanism.

Significance of fruits & seeds dispersal

  • It prevents overcrowding & competition for

limited resources.

  • It allows the plants to have their seeds to

land on suitable places for germination, thus

increases the chance for the plants to

colonize new areas.

slide64

Acer劍葉槭

Clematis甘草藤

slide65

With hooks: Burdock牛旁

By animal: juice fruits

With hooks stick onto our clothes

With hooks: Bur-marigold鬼針草

slide66
1. Wind Dispersal

- fruits are light and have a large surface area to catch wind

  • examples: sycamore (pericarp extended to form a wing), dandelion (hairy parachute)

2. Animal Dispersal

  • fruits possess hooks or spines to cling to animals

bodies

  • fruits as food for animals: 'stoned seeds' remain

intact & pass out with the animals' faeces,

e.g. apple, cherry

slide67
3. Water Dispersal

- fruits like coconut contain air space which makes the fruit buoyant

- seed is covered in a spongy or fibrous layer

4. Mechanical Dispersal

- pods with a leathery skin which splits open to throw seeds away over a fairly wide area, e.g. pea

slide68
5. Censer Mechanisms
  • fruits are borne at the ends of long stalks with holes through which seeds are shaken
  • as they blow in the wind; pores are closed in wet conditions, e.g. poppy

6. Casual Mechanisms

  • taking opportunities & using any available

means of dispersal,

e.g. acorns (from oak tree) may be rolled

along the ground by wind or carried

about by squirrels or float downstream

in rivers

slide70
12.4.4 Dormancy

The water content of seeds is very low (5-10%

weight) and is the major factor in preventing

germination.

Periods of dormancy may last for a number of years.

Some seeds fail to germinate for one reason or another:

1. Light is necessary for germination of certain

seeds

2. A sustained period of cold is needed to make

some seeds of temperate climates germinate to

ensure their seeds do not germinate in dry

autumn & cold winter

3. Some seeds need the heat of a flash-fire for

germination

slide71
4. Time is needed for maturity / internal chemical

changes to complete before germination

5. Seed coat impermeable to water &/or gases;

time for decay of seed coat;

some seeds need physical abrasion or partial digestion in intestine to break dormancy

6. Presence of natural chemical inhibitors

slide72
12.4.5 Germination & Early Growth

in Flowering Plants

Conditions necessary for seed germination

1. Water - taken up through the micropyle;

softens seed coat;

cotyledons swell up & burst through seed coat;

enzymes are activated to break down starch to

simple sugars and proteins to amino acids;

fats are converted into fatty acids & glycerol;

these dissolve in water & are transported to the

growing points of the embryo

slide73
Glucose, fatty acids & glycerol provide

respiratory substrates from energy for

growth is released;

  • Glucose is also used in the formation of

cellulose cell walls;

  • Amino acids are used to form new

enzymes and structural proteins within new cells.

slide74
2. Temperature –
  • warmer temperatures enable enzymes
  • to work
  • 3. Oxygen - enables seeds to respire
  • aerobically to supply energy for growth
slide75

Epigeal: growth of the cotyledon above soil

Hypogeal: growth of the cotyledon below soil