Sexual reproduction in plants

1. Sexual reproduction in plants • A 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.

2. Insect-pollinated flower

3. Diagram of an insect-pollinated flower Petal Stigma Anther Filament Style Ovary Ovule Nectar Sepal

5. Wind-pollinated flower

6. Diagram of a wind-pollinated flower Bract Anther Filament Ovary Stigma

7. Functions of parts of the flower • sepals • petals • Anthers • filament • Stigma • style • ovaries • Protects the flower during the bud stage • Attracts insect pollinators by colourand scent • produce 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

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

9. 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 scent • Light & smooth pollen that can be blown in the wind

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

11. 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.

12. Photomicrograph of pollen grains: Note the spikes that attach pollen grains to insect’s body.

13. What happens after pollination? • pollen grains germinates forming pollen tube • the pollen tube grows down style digesting the style tissue • the e pollen tube enters ovule through micropyle • male nucleus moves into ovule • male nucleus (male gamete) fuses with the ovum or egg cell (female gamete) i.e. fertilisation occurs • ovule becomes seed • ovule wall becomes seed coat or testa • ovary becomes fruit • stigma and the style weathers and dry up

14. 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: • animals • wind • water • self dispersal

15. Seed and fruit dispersal by Wind • 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 Sycamore seed Dandelion seeds

16. 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, hookedspines which catch onto the animals’ fur to be carried long distance before dropping off

17. Advantages of seed dispersal • There 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

18. Structure of a Seed plumule radicle micropyle cotyledon testa (seed coat)

20. 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

21. Conditions for seed germination • Seed germinationis the process in which a plant emerges from a seed &begins grow • Conditions needed for seeds germination are: • Suitable temperature; for enzymes to work effectively • Oxygen; 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

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

23. I am willing to answer questions on sexual reproduction in plants. Thank you folks! You are such a wonderful group of students.