Sexual reproduction in plantsA flower is a leafy shoot containing the sexual organs of a flowering plant.

It is adapted for sexual reproduction.

It is a modified terminal bud typically composed of four sets of modified leaves.

Insect-pollinated flower

Floral structures

Diagram of an insect-pollinated flowerPetal

Stigma

Sepal

Anther

NectarOvuleOvary

StyleFilament

Wind-pollinated flower

Diagram of a wind-pollinated flowerBract

Anther

Filament

Ovary

Stigma

Functions of parts of the flowersepals petals

Anthers

filament

Stigma

style

ovaries

Protects the flower during the bud stageAttracts insect pollinators by colour and

scentproduce and release pollen grains

positions the anther for effective pickup of pollen by the pollinating agent

collects the pollen from the pollinating agent

positions the stigma for pollen collection

site of fertilisation, protects the developing seeds, aids in seed dispersal

In a form of a table, compare the different structural adaptations of insect-pollinated and wind-pollinated flowers. [6]

. . . . thinking

of you!

structural adaptations of insect-pollinated and wind-pollinated flowers

Insect-pollinated flowers

Wind-pollinated flowers

Petals large & brightly coloured to attract insects

Stigma located inside the flower where the insects have to brush past it

Anthers inside the flower where the insects have to brush past them

Stigma usually small & sticky so that pollen grains can attach from insect body

Flower often strongly scented

Large sticky or spiky pollen grains which stick to insects

Petals small or absent, if present, not brightly coloured

Stigma exposed to catch pollen grains blowing in the wind

Anthers exposed outside the flower so that wind can easily blow the pollen grains away

Stigma large & feathery to catch pollen grains blowing in the wind

Flowers have no scentLight & smooth pollen that

can be blown in the wind

Pollination the transfer of pollen grains from the male part of the plant (anther of stamen) to the female part of the plant (stigma).

Agents of pollination

. . . the means that moves the pollen grains from the anther to the stigma.

Agents of pollination include: wind; insects; birds; water & rodents.

Photomicrograph of pollen grains:

Note the spikes that attach pollen grains to insect’s body.

What happens after pollination?pollen grains germinates

forming pollen tubethe pollen tube grows down

style digesting the style tissuethe e pollen tube enters ovule

through micropylemale nucleus moves into ovulemale nucleus (male gamete)

fuses with the ovum or egg cell (female gamete) i.e. fertilisation occurs

ovule becomes seedovule wall becomes seed coat or

testaovary becomes fruitstigma and the style weathers

and dry up

Seed and fruit dispersal This is spread of seeds &

fruits some distance away from the parent plant

Dispersal allow seeds to spread out to colonise new areas so that the new plants do not compete with parent plant for light, water and mineral salts

means of seeds & fruits are: animalswindwaterself dispersal

Seed and fruit dispersal by Wind

Sycamore seed

Dandelion seeds

Wind dispersed seeds such as sycamore & dandelion:

are light so that they can easily be blown by wind

have wing –like outgrowth or feathery hair projections which increase the surface area so that the seeds can ‘float’ in air for some time so they are carried over long distance from the parent plant

Seed and fruit dispersal by Animals Animal dispersed seeds

includes: tomato & burr grass.Tomato fruits:

they are fleshy (succulent), brightly coloured & scented to attract animals

Have tough seed coat to protect the seeds from being digested in the animals' gut

Burr grass:Are covered with stiff,

hooked spines which catch onto the animals’ fur to be carried long distance before dropping off

Advantages of seed dispersalThere is less

competition, with parent plant & among seedlings for same resources such as; light, water , nutrients & space

Dispersal allow plants to colonise new areas since plants are stationary i.e. don’t move from place to place

External structure of a Seed

Internal structure of a Seed

plumule

radicle

micropyle

cotyledon

testa (seed coat)

Testa; protects the embryo from physical damage & attack from pathogens

Micropyle; a hole in the testa that allow water & oxygen to enter into the seed

Cotyledons; stores nutrients (starch, protein & lipids) required during germination

Plumule; grows into shoot after germination

Radicle; grows into root after germination

Conditions for seed germination Seed germination is the

process in which a plant emerges from a seed & begins grow

Conditions needed for seeds germination are:Suitable temperature; for

enzymes to work effectivelyOxygen; for aerobic

respiration to provide energy to growing embryo

Water; for chemical reactions to occur in solution, dissolve nutrients for transportation, activate enzymes & soak testa

Design & carry out an experiment to investigate the conditions necessary for germination of mung bean seeds.

I am willing to answer questions on sexual reproduction in plants.

Thank you folks!

You are such a wonderful group of students.