Reproduction in Plants (part 1): Asexual and Sexual Reproduction in plants

1. Reproduction in plants Chapter 20 Content • Asexual Reproduction • Sexual Reproduction in Plants

2. Learning Objectives Candidates should be able to: (a) define asexual reproduction as the process resulting in the production of genetically identical offspring from one parent (b) define sexual reproduction as the process involving the fusion of nuclei to form a zygote and the production of genetically dissimilar offspring (c) identify and draw, using a hand lens if necessary, the sepals, petals, stamens and carpels of one, locally available, named, insect-pollinated, dicotyledonous flower, and examine the pollen grains under a microscope (d) state the functions of the sepals, petals, anthers and carpels

3. Learning Objectives (e) use a hand lens to identify and describe the stamens and stigmas of one, locally available, named, wind- pollinated flower, and examine the pollen grains under a microscope (f) outline the process of pollination and distinguish between self-pollination and cross pollination (g) compare, using fresh specimens, an insect-pollinated and a wind-pollinated flower (h) describe the growth of the pollen tube and its entry into the ovule followed by fertilisation (production of endosperm and details of development are not required)

4. Asexual or Sexual? 2 types of reproduction: 1. Asexual reproduction 2. Sexual reproduction Difference? Asexual reproduction is the formation of new individuals that does not involve fertilization (no fusion of gametes) Sexual reproduction involves the fusion of 2 gametes.

5. Asexual reproduction Methods of asexual reproduction 1. Vegetative propagation 2. Spore formation 3. Budding no male and female structures (Recall: No gametes involved) produces offspring that are genetically identical to parents (clones) through mitosis (covered in Chapter 18 Cell Division) • • •

6. Mitosis

7. Vegetative propagation • Involves the growth of a new part of a plant, usually a bud or stem, which eventually becomes separated from the parent plant to form a new individual • e.g. by means of underground storage organ 1) rhizomes 2) bulbs 3) corms/tubers 4) runners Note: Food stored in underground storage organ enables the plant to survive through unfavourable conditions

8. Rhizome • Horizontal underground stem • Possesses dry scale leaves and buds • May have adventitious roots (roots arising from the nodes at the base of the plant) • e.g. Canna, lallang and ginger

9. Bulbs • Modified shoot • Consists of flattened disc-like stem bearing buds, fleshy and dry scale leaves • e.g. onion, garlic

10. Corms • Thick short underground stem swollen with food reserves (mainly starch) • e.g. water chestnut

11. Tubers • Swollen underground stem bearing a number of reduced stem leaves and buds • Food reserve is mainly starch and proteins (found just beneath the skin) • e.g. potato

12. Summary http://www.tiscali.co.uk/reference/encyclopaedia/hutchinson/m0030820.html

13. ***Advantages of vegetative propagation (asexual reproduction) 1. Does not rely on external agencies (insects/wind) for pollination & dispersal 2. Food present in vegetative structures (buds can develop rapidly into daughter plants) 3. Beneficial traits are passed on directly to daughter plants 4. Involves only one parent (no fertilization!) 5. Can colonise area quickly (already in suitable habitat)

14. ***Disadvantages of vegetative propagation (asexual reproduction) 1. Overcrowding (because there is no dispersal mechanism) 2. Less variation in offspring (less adaptable to changes in environmental conditions)

15. Sexual Reproduction in flowering plants

16. Facts about sexual reproduction in flowering plants • involves fusion of gametes • Flowers = organs of sexual reproduction • Pollination + fertilisation = mechanisms to ensure the male and female gametes meet

17. Parts of a flower

18. Label the parts of the flower

19. Worksheet 4 5 1 6 2 7 8 pedicel 3

20. Worksheet

21. Parts of a flower - male part of flower - consists of filament bearing an anther (that produces pollen grains) - female part of flower -consists of carpels - each carpel consist of ovary + style (above the ovary) + one or more stigmas -modified leaves forming conspicuous part of flower - modified leaves (enclose & protect other parts of flower in bud stage) pedicel - flower stalk - brightly coloured (attract insects for pollination) - enlarged end of flower stalk on which other parts of flower are borne - landing platform

22. General parts of a flower 5. 4. 3. 6. 2. 1.

23. Anther • usually made up of two lobes • each lobe has 2 pollen sacs containing pollen grains (produced by meiosis → haploid number of chromosomes) • each pollen grain gives rise to two haploid male gametes • when anther matures, the two lobes split → setting free the pollen grains

24. Which structure is the stigma?

25. Stigma • swollen structure at end of style • receives the pollen grains

26. Ovary • consists of one or more ovules • within each mature ovule is a female gamete (egg cell / ovum) • region where ovules are attached in the ovary is called the placenta