1. Sexual Reproduction In Flowering Plants Chapter 40

2. Chpt.40: Sexual Reproduction in flowering plants 2 Types of sexual reproduction AsexualSexual a ) Only requires one parent a) Involves 2 parents b) Mitosis – cell division b) 2 gametes (haploid cells) c) Offspring genetically identical to parent fuse to form a diploid cell called a zygote. c) Meiosis is essential for sexual reproduction. d) Offspring show variations i.e. not identical to parent.

3. Structures and functions of a flower

4. Receptacle: function is to support the flower. It is a swelling at the base of the flower. Sepals: function is to protect the flower when it is a bud (usually green, leaf like structures). Petals: function is to attract insects. animal pollinated plants – petals large, brightly coloured Wind pollinated plants – petals small or absent and green in colour

5. Structures and functions of a flower Stamens: male part of flower. Consists of filament and anther. a)Stalk that supports the anther.a) makes pollen grains (meiosis) b) contains vascular bundle tob) produces male bring food and water up to gametes in pollen anther. grains Filament:Anther:

6. Structures and functions of flower Carpel: female part of flower. Consists of stigma, style and ovary.

7. Structures and Functions of a flower Carpel: Stigma: place where pollen grains land. Style: connects stigma to ovary and pollen travels down this. Ovary: contains one or more ovules which produces an egg (embryo sac) due to meiosis.

8. Structures and Functions of a Flower

9. Formation of sex cells Male Gamete Formation: Pollen grain produces male gametes called sperm nuclei.

10. Pollen Development HIGHER LEVEL Anther consists of four chambers – pollen sacs. Inside each pollen sac are a number of diploid microspore mother cells (pollen mother cells). Mother cells divide by meiosis to produce a cluster of four haploid cells called a tetrad. Each tetrad breaks up to form four separate haploid pollen grains. Each pollen grain divides by mitosis to form two haploid nuclei: the tube nucleus and the generative nucleus Forms a tube from the stigma to the ovary Forms male gametes

11. Pollen Development HIGHER LEVEL Once pollen grains have matured walls of anther become dry and shrivel. As a result anther walls split exposing pollen grains on outside of anther.

12. Formation of sex cells Female gamete formation: The embryo sac produces female gametes called the egg cell and two polar nuclei.

13. Embryo Sac Development HIGHER LEVEL Each ovary contains one or more ovules. Each ovule has two walls called integuments. These contain a small opening called the micropyle through which a pollen tube can enter. One cell in ovule is called the megaspore mother cell (embryo sac mother cell), which is a diploid cell. Meiosis of megaspore produces 4 haploid cells, 3 die. The remaining cell is called the embryo sac (megaspore).

14. Embryo Sac Development HIGHER LEVEL Haploid nucleus of embryo sac divides 3 times by mitosis resulting in 8 haploid nuclei: five nuclei die 2 form polar nuclei 1 form egg cell gametes Embryo sac Polar nuclei Egg cell

15. Pollination Pollination: is the transfer of pollen from an anther to a carpel Two types of pollination Self-pollinationCross-pollination

16. Pollination Self-pollination: involves the transfer of pollen from an anther to a stigma on the same plant. leads to self-fertilisation (inbreeding) which produces offspring that are weaker e.g. some cereals. Cross-pollination: involves the transfer of pollen from an anther to a stigma on a different plant of the same species. Leads to cross-fertilisation which produces stronger and healthier offspring. Many methods of cross-pollination.

17. Pollination Methods of cross-pollination In cross-pollination in order to get the male gametes to reach the female gametes plants use either wind or animals. Wind Pollination: Original form of plant pollination Very wasteful of pollen Examples – conifers, grasses, oak, hazel, alder

18. Pollination Wind Pollination: Characteristics of wind pollinated plants: Petals: small, green, no scent or nectar Pollen: large amounts, small, light, dry, smooth Anthers: large and feathery, outside petals Stigma: large and feathery, outside petals

19. Pollination Animal Pollination: More advanced form of pollination Less pollen wasted Insects – most common animal pollinators Examples – orchids, dandelions, primroses, daisies, buttercups

20. Pollination Animal Pollination: Characteristics of animal pollinated plants: Petals: large, brightly coloured, scent, nectar Pollen: small amounts, heavy, large, sticky Anthers: usually small, inside petals Stigmas: usually small, sticky, inside petals, rounded

21. Cross-Pollination

22. Hay Fever Hay Fever: is an allergic reaction to the inhalation of particles of certain harmless substances.

23. Hay Fever Allergen: substance that triggers an allergic reaction e.g. pollen grains, fungus spores, animal skin/scales, house dust, house dust mites. Symptoms: - inflammation of the mucous membranes in the nose. - sneezing - blocked and runny nose - watery irritated eyes Treatment: - decongestant drugs - antihistamines

24. Fertilisation Fertilisation is the fusion of the male (n) and female (n) gametes to produce a zygote (2n) Remember: The pollen grain produces the male gametes Embryo sac produces an egg cell and polar nuclei

25. Pollen grain lands on the stigma Fertilisation Pollen Grain

26. Fertilisation Pollen Tube Tube nucleus causes the pollen tube to grow down through the style and into the ovule Generative Nucleus Tube Nucleus

27. Fertilisation Mitotic division of generative nucleus to form 2 male gametes (haploid) Tube nucleus disintegrates

28. Double Fertilisation 1 male gamete fuses with the egg nucleus to form the diploid zygote (2n) 1 Male gamete fuses with the 2 polar nuclei to form the triploid endosperm nucleus (3n)

29. Double Fertilisation Double fertilisation 3N endosperm nucleus 2N Zygote

30. Notes on: Fertilisation, Seed Formation, Monocot and Dicot Seeds, Fruit Formation, False Fruits and Seedless Fruits on handout

31. Dispersal of Fruit: Dispersal is the scattering of seeds or fruit away from the parent plant. Benefits of dispersal: 1.Avoids competition 2.Increase in chances of survival for plant 3.Find new areas for growth 4.Increase in the numbers of species

32. Dispersal of Fruit Four methods of dispersal: 1. Wind 2. Water 3. Animal 4. Self Wind dispersal: in general seeds adapt so they can be blown various distances by the wind: Orichids - small, light seeds – easily dispersed Dandelions – feathery parachute – disperse seeds more widely

33. Wind Dispersal: Sycamore, Ash – winged fruits – increase distance over which seeds may be dispersed. Water Dispersal: Water lily, Coconuts etc. – light air filled fruits – can float away (disperse) from parent. Animal Dispersal: Two main types of animal dispersed seeds Sticky fruits Edible Fruits

34. Animal Dispersal: Sticky Fruits – attach to animal and fall off some time later e.g. burdock, buttercup. Edible Fruits – the animal eats and digests fruit, however, seeds are not digested and pass out of animals intestines some time later e.g. blackberries, raspberries, strawberries. Self Dispersal: Plants such as peas and beans have dry fruits called pods. These pods shrivel and burst to expel the seeds.

35. Dormancy Dormancy: is a resting period when seeds stop growing and stop metabolic functions. Causes of Dormancy: Growth inhibitors – prevent embryo from growing. Testa may not allow water or oxygen ( both necessary for germination) to enter seed. Testa may be too tough to allow embryo to emerge. Growth promoters needed to stimulate growth may take time to produce.

36. Advantages of Dormancy: 1.Allows seedling to avoid harsh conditions of winter. 2.Allows time for seed to be dispersed. 3.Gives embryo time to develop fully. 4.Helps survival of the species – different lengths of dormancy mean that there are always some seeds in the soil. 5.Allows long growing season for seedlings.

37. Dormancy in Agriculture and Horticulture: Dormancy means that seeds remain viable for long periods of time. This allows seeds to be stored and sold in packets. However, before planting it may be necessary to treat seeds to break dormancy: This may involve: 1. soaking seeds in water 2. placing them in a cold place over night 3. scraping their surface to break the tough testa.

38. Use of Dormancy in Agriculture and Horticulture: 1.It allows for the safe storage of seeds during winter. 2.It allows farmers to predict when plants will grow.

39. Germination Germination: is the end of dormancy and the re-growth of the embryo into a new plant. Conditions Needed for Germination: 1.Dormancy: - must be completed. 2.Water: - needed to allow enzyme action. 3.Oxygen: - needed to allow respiration to occur (aerobic). 4.Suitable Temperature (5 0 -30 0 C): - is needed to allow enzyme action to proceed. 5.Light: - may be required as some seeds need light for germination.

40. Events in germination: Digestion Of stored food in endosperm and cotyledon Respiration To produce ATP to drive cell division Events in germination cease when the plants leaves have developed and the plant has started to photosynthesise

41. Events in Germination (Detail) Germination begins when seed absorbs water. This water allows enzymes to be activated in the seed. Food reserves are digested: - oils digested to fatty acids, glycerol - starch digested to glucose - proteins digested to amino acids. Digested food is moved to the embryo New cell walls and enzymes are produced using glucose and amino acids Fats and some of the glucose is turned into ATP to drive cell division. Dry Weight (mass) of seed falls as a result of respiration.

42. Events in Germination (Detail) As the weight of the food stores falls the weight of the embryo increases. Radicle breaks through the testa Plumule emerges above ground New leaves begin to photosynthesise – dry weight of seedlings increase once again.

43. Events in Germination Plumule Radicle Cotyledon

44. Events in Germination Plumule Radicle

45. Changes in dry weights of Germinating seeds When weighing plant material, dry weight is normally used. This is the weight without water. Dry weight is measured by placing the plant in an oven at 100 o C until the weight remains constant.

46. Changes in dry weight of seeds during germination Dry mass of seed (g) Time (days) Mass drops initially due to respiration of stored food, but then begins to increase due to photosynthesis

47. Changes in dry weight of seeds during germination Dry mass of seed (g) Time (days) Embryo Endosperm Food reserves in endosperm are transferred to the growing embryo

48. Types of germination Broad bean germination The cotyledons stay below the ground Sunflower germination The cotyledons move above the ground to form the first leaves

49. Mandatory Experiments 1.) To investigate the effect of water, oxygen and temperature on germination 2.) To use starch agar or skimmed milk plates to show activity during germination

50. To investigate the effect of water, oxygen and temperature on germination Main Points: Conclusion: To use starch agar or skimmed milk plates to show digestive activity during germination Main Points: Conclusion:

51. Plant Reproduction