SEXUAL REPRODUCTION IN FLOWERING PLANTS

1. SEXUAL REPRODUCTION IN FLOWERING PLANTS Group members: Tamara Wong Paula Ellington Kadene Freckleton

2. PARTS OF A FLOWERING PLANT

3. FEMALE PART (GYNOECIUM) • Gynoecium – this is the female part the flower and is a collection of carpels. A carpel consists of a stigma, style and ovary. Stigma – receives pollen grains during pollination. Style – bears the stigma in a suitable position in the flower to receive the pollen. Ovary – swollen, hollow base of the carpel and contains one or more ovules. Ovules are the structures in which the embryo sacs develop and which, after fertilisation, become seeds.

4. MALES PART (ANDROECIUM) • Androecium - this is the male reproductive part of the flower and is a collection of stamens. Each stamen consists of an anther and a filament. Anther - contains pollen sacs in which pollen is made. Filament – contains a vascular bundle that carries food & water to the anther.

5. REMAINING PARTS • Pedicel - the stalk. • Receptacle – the top of the flower stalk (pedicel) from which the flower parts arise.  • Perianth – consists of two whorl structures called Perianth segments. In monocot, the whorls are similar. In dicot, the whorls are usually different. It consists of an outer part: Calyx – which is a collection of sepals. And an inner part: Corolla – which is a collection of petals

6. PARTS OF A FLOWERING PLANT

7. TERMS USED TO DESCRIBE THE RECEPTACLE OF A FLOWER

8. Terms used to describe the receptacle and flower • Hypogynous – if the stamens and perianth are inserted below the gynoecium. • Epigynous - if the stamens and perianth are located above the ovary. • Perigynous – if the receptacle is flattened or cup-shaped, with the gynoecium in the centre and the stamens and perianth are attached round the rim.

9. The nectaries are glandular structures, that secret nectar, a sugary fluid that attracts animals for pollination. The following terms are applied to whole plants and flowers: • Hermaphrodite- male and female organs borne on the same plant. • Dioecious – male and female organs borne on different plants. • Monoecious – separate male and female flowers borne on the same plant.

10. DEVELOPMENT OF POLLEN GRAINS

11. The anther has four pollen sacs which contain mother cells. • These mother cells undergo meiosis to form four pollen grains (groups of four- Tetrad). • The pollen grains develop a thick outer wall (exine) which is made of a waterproof substance (sporopollenin). • It is said to be one of the most resistance and long lasting substances in nature. • The pollen grain nucleus divides into two by mitosis to form a generative nucleus and a pollen tube nucleus.

12. DEVELOPMENT OF POLLEN GRAINS

13. DEVELOPMENT OF OVULES

14. DEVELOPMENT OF OVULES • Ovules develop inside the ovary, they are attached to the ovary by a point of attachment called the placenta, by a short stalk, the funicle. • The main body of the ovule (nucellus) is enclosed and protected by two sheaths or integuments. • A small pore is left in the integuments at one end of the ovule, the micropyle.

15. Inside the nucellus, at the end nearest the micropyle, one spore mother cell develops, known as the embryo sac mother cell. • This diploid undergoes meiosis to produce four haploid cells, only one of which develops. • This forms the embryo sac. • The embryo sac grows and its nucleus undergoes repeated meiosis until eight nuclei are produced. – one of these nuclei are the female gamete.

16. Two nuclei migrate to the centre of the embryo sac and fuse to form a single diploid nucleus. • The remaining six nuclei, become separated by thin cells walls and only one of these, the female gamete, appears to serve any other function. • The rest disintegrate

17. FEMALE PARTS

18. POLLINATION

19. This is the transfer of pollen grains from an anther to a stigma. • The transfer of pollen grains from an anther to a stigma of the same flower, or a different flower on the same plant is called self-pollination. • The transfer of pollen from the anther of one plant to the stigma of another plant is called cross-pollination.

20. Both types of pollination have advantages and disadvantages. • Cross-pollination increases the amount of genetic variation. It is dependent on external factors. • Self-pollination increases reliability, especially where members of the same species are uncommon and distant. It results in less vigorous off-spring.

21. DIOECIOUS AND MONOECIOUS PLANTS

22. Dioecious plant species have separate male and female plant. Therefore self-pollination does not occur. • Monoecious plants have separate male and female flowers on the same plant (hermaphrodite), self-pollination occurs.

23. PROTANDRY AND PROTOGYNY

24. Anthers and stigmas sometimes mature at different times. • If the anthers mature first then it is described as protandry (eg. Dandelion). • If the stigmas mature first then it is protogyny (eg. Bluebell). • In most cases of protandry and protogyny there is an overlapping period when both anthers and stigmas are ripe.

25. DANDELION BLUEBELL

26. SELF-INCOMPATIBILITY • Even if self-pollination does occur, the pollen grain often does not develop, or develops very slowly, so preventing or reducing the chances of self-fertilisation. • In all such cases there is a specific inhibition of pollen penetration of the stigma, or of pollen tube growth down the style, and this is genetically determined by self-incompatibility genes. • When self-incompatibility occurs, some cross-pollination is also incompatible. The most efficient use of the pollen will occur when a high proportion of cross-pollinations are compatibility occurs between less than one in 22000 pairs.

27. INSECT POLLINATION • Insects specialised for flower feeding appear in the fossil record at the same time as flowering plants, and include bees, wasps, butterflies and moths. • This suggests that once flowers evolved, insect-pollination also rapidly evolved. The insect is a much more precise dispersal agent than wind.

28. It can carry a small amount of pollen from the anthers of one flower and deposit it precisely on the stigma of another flower. • As a result special relationships between flowers and insects have evolved.

30. The reward the insects receive from the flowers is food in the form of nectar or pollen. In few cases insects and the plant it pollinates can live with one another. Eg. Yucca and moth. • In order to attract insects, flowers are usually large, brightly coloured, or if small, grouped in inflorescences. There are often lines on the petals which guide the insects to the nectaries. Scents produced by flowers also attract insects. Recognition is also helped by flower shape.

32. CROSS POLLINATION