Sexual Reproduction in flowering plants:

Flower structure diagram:

Male parts: Filament + Anther.

Female Parts: Stigma, Style + Ovary.

Receptacle:

Supports the flowering plants.

Sepals:

Protects the flower when it is in a bud.

Petals:

• Animal pollinated plants = Brightly coloured to attract insects (Bees)

• Wind pollinated plants: Very small or absent.

Stamen:

Collective name for the Male parts of a flower.

EG: Filament & Anther.

Filament:

Contains vascular bundles (Xylem + Phloem)

Anther:

Produces pollen grains by meiosis. (Sperm of plant)

Carpel:

Female parts of a flower.

EG: Stigma, style & ovary.

Stigma:

Where pollen lands - Catches the pollen.

Style:

Where pollen tube grows.

Ovary:

Contains ovules.

Sexual reproduction of plants:

• Involves 2 parents (One plant)

• Gametes formed in male & female parts of plant via meiosis.

• Two haploid gametes fuse to form diploid zygote

• Offspring show variation.

Variation:

Genetic differences between individuals of the same species.

Advantages of sexual reproduction in plants:

• Variation

• Dispersal

• Less competiton

Types of reproduction in plants (Formation of gamete)

• Male - pollen grain development = Occurs in anther.

• Female - occurs in ovule.

Pollen grain development (Males)

• Diploid microspore mother cell divides by meiosis to produce 4 haploid cells called a tetrad.

• This tetrad splits up to form 4 separate haploid cells called microspores.

• Microspores carry out mitosis, forming a tube nucleus and a generative nucleus.

• The generative nucleus divides by mitosis to produce 2 haploid sperm nuclei.

Contents of a matured pollen grain =

Tube nucleus & generative nucleus.

Female Gametes:

• Diploid megaspore mother cell divides by meiosis to produce 4 haploid cells.

• 3 degenerate and die.

• The remaining cell = megaspore or embryonic sac.

• This megaspore divides by mitosis 3 times to produce 8 haploid nuclei.

• Of the 8 haploid nuclei, 5 will degenerate and die.

• The remaining 3 nuclei form the female gametes:

- Two polar nuclei.

- Egg Cell.

Pollination:

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

Self-Pollination:

Transfer of pollen from the anther to the stigma on the same plant.

Results of self-pollination:

• Less variation

• Offspring are more susceptible to disease.

Cross pollination:

Transfer of pollen from the anther to the stigma on another plant.

Methods of pollination:

• Wind - Wind blows pollen from anther - stigma.

• Animal - Animal carries pollen from anther to stigma. EG: birds carry pollen for daisies.

Adaptations of petals:

• Wind pollinated: Small, no scent, not brightly coloured, absent.

• Animal pollinated: large, scented, brightly coloured.

Adaptations of pollen:

• Wind pollinated: Large amounts of pollen grain & pollen grains light.

• Animal pollinated: Small amounts of pollen grain, heavy, large, sticky.

Adaptations of anther:

• Wind pollinated: Large, outside petals, & loosely attached to filament.

• Animal pollinated: Small, inside petals, firmly attached to filament.

Adaptations of stigma:

• Wind pollinated: Large, outside petals, feathery.

• Animal pollinated: Small, inside petals, not feathery.

Wind pollinated flowers...

• Anther outside petals/flower.

• Feathery stigma

What happens after pollenation?

Fertilization.

Fertilization:

Fusion of the male & female gametes to produce a diploid zygote.

Process of fertilization in plants:

• Pollen grain lands on stigma.

• Tube nucleus causes pollen to grow through style towards ovule.

• When it arrives @ ovule, the tube denigrate and dies.

• The two haploid male sperm nuclei move through the tube.

-> DOUBLE FERTILIZATION NOW OCCURS:

• One sperm nucleus (n) joins with the egg nucleus (n) to form a diploid (2n) zygote. This develops into the embryo.

• The other sperm nucleus (n) joins with the 2 polar nuclei (both n) to form a triploid (3n) endosperm nucleus.

Precise location of fertilization:

The ovule.

What is a triploid?

A cell that contains 3 sets of chromosomes.

What does a fertilized ovule become?

A seed.

Seed formation process:

• Fertilized ovule becomes a seed.

• The zygote grows by mitosis to form an embryo.

• Embryo has a future root (radicle) & future shoot (Plumble)

• Some embryo cells develop to form one/two leaves.

• These a cotyledons (a seed leaf)

• Triploid endosperm acts as food store.

Radicle:

Part of embryo that develops into root.

Pumble:

Part of the embryo that develops into a shoot.

Testa (seed coat) function

Protects embryo

Embryo:

Develops into a new plant.

cotyledons function...

Food storage.

If cotyledons absorb all the endosperm...

The seed is non-endospermic (EG: Broad bean) - Dicots.

If cotyledons absorb some endosperm...

The seed is endospermic (Corn) - Monocots.

How is food stored in a monocot?

Endosperm.

How is food stored in dicot?

Cotyledon

As the seed develops what becomes the fruit of the plant:

Ovary

Why do plants form fruit?

To protect seeds. - surrounds.

What is the growth of fruit stimulated by...

= by auxins produced in seeds.

Seedless fruit:

Fruit formed via virgin birth - Egg not fertilized.

Can develop in 2 ways:

• Genetics - Naturally/by breeding programmes.

• Sprayed with growth regulators - prevents fertilization, EG: Ethene.

EG of a growth regulator:

Ethene - commercially ripens fruit.

Dispersal:

The transfer of a seed or fruit away from the parent plant.

Effects of dispersal:

• Increased chance of survival.

• Colonies in new areas

• Prevents competition of seeds - overcrowding.

Methods of seed & fruit dispersal:

• Wind

• Animal

• Water

Methods of seed & fruit dispersal: Wind

• Small, light seeds - easy for wind to carry (orchids)

• Parachute devices - travel in wind - Dandelion.

• Fruit wings - spread across distance & then spiral to ground. EG: Sycamore.

Methods of seed & fruit dispersal: Animal

• Sticky fruits - cling to animals hair & travel - goosegrass.

• Edible fruits - animals eat fruit & disperse seeds via faeces - Blackberries.

Methods of seed & fruit dispersal: Water

• Light - air filled fruits

• Allows the fruit to shoot.

• Dispersed by rivers, streams or ocean.

Dormancy:

Resting period when seeds undergo no growth & have reduced cell activity/metabolism.

Growth inhibitor...

= abscisic acid (ABA)

• Testa is impermeable - water cannot enter.

• Lack of suitable growth regulators to stimulate growth.

Breaking Dormancy & allowing growth:

Seeds need to be cold to break dormancy as cold breaks down growth inhibitors & activate growth promoters - Auxins.

Before seeds are planted they must...

• Be soaked in water.

• Placed in a cold tempeture, EG: Fridge.

Advantages of dormancy:

• Helps survival of species.

• Plants avoid harsh winter conditions

• Allows time for seed dispersal.

Germination:

The regrowth of the embryo, after a period of dormancy, if the environmental conditions are suitable.

Conditions needed for germination:

• Water - Enzyme function

• Oxygen - Aerobic respiration

• Suitable tempeture - Enzyme function.

Events of germination:

• Seed absorbs water via testa (Coating of seed)

• Digestion: Oils - fatty acids & glycerol, starch - glucose & protein - Amino acids.

• These digested products move to the embryo.

• Glucose & amino acids used to make plant structures.

• Mass of food stores fall (Endosperm/cotyledons - food being used)

• Weight of embryo increases.

• Radicle bursts through testa.

• Pumble emerages above group & leaves produced.

• Photosynthesis begins, increasing dry weight (Mass) of seedlings again.

Role of respiration in germination:

The release of energy from food.

Role of digestion in germination:

Make nutrients available.

EG: Protein broken down amino acids.

Role of water in germination:

• Softens testa

• Dissolve nutrients, making them available.

Dry weight:

Weight without water.

Vegetative propagation:

The asexual reproduction of plants.

Features of vegetative propagation:

• No gametes.

• No variation.

• Requires one parent.

Natural vegetative propagation:

Involves forming new plants from stem, leaf, root, or bud.

Methods of natural vegetative propagation =

• Stem

• Root

• Leaf

• Bud

Methods of natural vegetative propagation...Stem

EG: Runners - Horizontal stems that run above ground & from which new plants grow - strawberry plants.

Methods of natural vegetative propagation...Root

EG: Root Tuber - swollen underground root that remains dormant during winter & from which new plants may grow - Dahlia.

Methods of natural vegetative propagation...Leaf

EG: Some plants can produce new plants from the leaves of the parent - Cacti.

Methods of natural vegetative propagation...Bud

EG: Bulb - A modified bud - onion.

- Lateral bud produce new plant.

Methods of artificial vegetative propagation:

• Cutting

• Grafting

• Layering

• Micropropagation

Methods of artificial vegetative propagation: Cutting

Portion of a plant that is removed from the parent plant & grown into a new independent plant.

- MB mam - Aunt caroline.

How is cutting carried out?

Shoot of parent plant is cut @ an angle & is removed from parent plant & placed in rooting powder to grow new plant.

Methods of artificial vegetative propagation...Grafting

Joining & uniting of part of one plant with a second plant.

- Takes good qualities of two plants & combines.

- Roses

Methods of artificial vegetative propagation...Layering

Growth of a new plant from a stem that is still attached to parent plant - Blackberry plant.

Methods of artificial vegetative propagation...Micropropagation

Growth of small plants from small pieces of tissue under sterile conditions on a specially selected medium.

EG: Carrots.

Advantages of artificial vegetative propagation:

• New plants - fast

• New plants are genetically identical to parent.

Disadvantages of artificial propagation:

• No variation - No variation = desirable traits maintained.

• High risk of Diseases passed on.

Will structures produced by vegetative propagation be haploid (n) or diploid (2n)?

Diploid.