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.