1. Sexual reproduction in flowering plants

2. Lesson objectives By the end of this lesson you should be able to:
Distinguish between sexual and asexual reproduction with respect to plants
Describe the structures and functions of the parts of a flower
Discuss the formation male and female gametes

3. Introduction
The ability to produce offspring is one of the characteristics of life
Reproduction ensures that parental traits are transmitted to successive generations
Reproduction has 2 main functions
Replacing organisms that die
Allows for an increases in numbers when conditions are favourable

4. Asexual and sexual reproduction
Asexual reproduction involves 1 parent and requires no gametes – does not require meiosis – offspring are clones of parent (genetically identical)
Sexual reproduction involves 2 parents – fusion of gametes (fertilisation) – offspring show variations as they are a mixture of genes from both parents (driving force of evolution)

5. Structures and functions of a flower

6. Male gamete formation

7. Female gamete formation

8. What have you learned? Can you. . .
Distinguish between sexual and asexual reproduction with respect to plants?
Describe the structures and functions of the parts of a flower?
Discuss the formation male and female gametes?

9. Lesson objectives By the end of this lesson you should be able to:
Distinguish between self and cross pollination
Discuss methods of pollination
Discuss the causes, effects and treatments for hay fever
Discuss fertilisation and seed formation I flowering plants

10. Pollination
“Pollination is the transfer of pollen from an anther to a stigma of a flower from the same species”
There are 2 types of pollination:
Self pollination
Cross pollination

11. Methods of pollination – 2 types
Animal pollination
Wind pollination

13. Adaptations of flowers to wind or animal pollination
Wind pollination
Animal pollination
Petals: small or absent, not brightly coloured, no scent, no nectaries
Petals: large, brightly coloured, have nectaries
Pollen: large amounts, light, small, dry, smooth
Pollen: small amounts, large, heavy, sticky, spiny
Anthers: large, outside petals, loosely attached to filament
Anthers: usually small, inside petals, firmly attached to filament
Stigmas: large and feathery, outside petals
Stigmas: usually small and sticky, inside petals

14. Hay fever
Is an allergic reaction to the inhalation of particles of certain harmless substances
The substance that triggers the reaction is known as the allergen
The most common allergens are pollen grains but include fungal spores, animal skin or scales and house dust
The symptoms of hay fever include the inflammation of the mucous membranes of the nose, sneezing, a blocked and runny nose along with watery and irritated eyes
It affects 10% of the population and can be reduced by limiting contact with the allergen
Treatment include anti – histamine drugs and other drugs that partially inhibit the allergic response

15. Fertilisation
“Fertilisation is the union of male and female gametes to form a diploid zygote”
Growth of a pollen tube

16. Double fertilisation
Flowering plants are unique in having a double fertilisation:
1st sperm nucleus (n) joins with the egg nucleus (n) to form a diploid (2n) zygote) – develops into the embryo
2nd sperm nucleus (n) joins with the 2 polar nuclei (both n) to form a triploid (3n) endosperm nucleus

17. Seed development

18. Presence or absence of endosperm
Types of seeds
Number of cotyledons
Plants that form a seed with a single cotyledon are called monocots, while plants with 2 cotyledons are called dicots
Presence or absence of endosperm
In monocots the cotyledon absorbs food from the endosperm and normally passes it onto the embryo (i.e. the cotyledons do not store food) – at maturity monocot seeds have an endosperm – endospermic (grasses, cereals and maize)
In dicots the cotyledons absorb food from the endosperm and act as food stores – at maturity dicot seeds do not have an endosperm – non - endospermic

19. A non – endospermic seed (broadbean)

20. An endospermic dicot seed (castor oil bean)

21. LS of a monocot seed (maize). Note that maize
is not a typical monocot seed in that it stores food in
the cotyledon, as shown above.

22. What have you learned? Can you. . .
Distinguish between self and cross pollination?
Discuss methods of pollination?
Discuss the causes, effects and treatments for hay fever?
Discuss fertilisation and seed formation I flowering plants?

23. Lesson objectives By the end of this lesson you should be able to:
Discuss fruit formation
Distinguish between true and false fruits
Discuss the development of seedless fruit
Discuss fruit and seed dispersal
Discuss seed dormancy

24. Development of a fruit

25. Two types of fruit

26. Changes in a flower after fertilisation
Before fertilisation
After fertilisation
1 Ovule
Seed
2 Integumants
Testa (seed coat)
3 Nucellus
Endosperm→Cotyledons
4 Egg
Zygote→Embryo
5 Polar nuclei
Endosperm
6 Ovary
Fruit
7 Ovary wall
Pericarp (fruit coat/wall)

27. Seedless fruit
The development of a fruit without a seed is called parthenocarpy (or parthenocarpic fruiting) – it can be formed in 2 ways
Genetically, either naturally or through special breeding programmes – bananas, grapefruit, pineapples, oranges and grapes
To spray plants with growth regulators e.g. auxins – grapes, peppers, cherries and some types of seedless tomatoes

28. Fruit and seed dispersal
“Dispersal is the transfer of a seed or a fruit away from the parent plant”
Dispersal is necessary to :
Avoid large numbers of seeds competing with each other and the parent plant
Increase the chance of survival for the plant
Find new areas for growth
Increase the numbers of species
The main methods of dispersal are wind, water, animal and self - dispersal

29. Wind dispersal

30. Water dispersal

31. Animal dispersal Edible, fleshy or succulent fruits
Sticky fruits - goosegrass

32. Self - dispersal
Examples include peas, beans and gorse

33. Dormancy
“Dormancy is a resting period when seeds undergo no growth and have reduced cell activity or metabolism”
Dormancy is brought about by a number of ways:
Growth inhibitors (e.g. abscisic acid) may be present in the outer part of the seed
The testa may be impermeable to water or oxygen
The testa may be to tough to allow the embryo to emerge
There may be a lack of suitable growth regulator present to stimulate growth

34. Dormancy in agriculture or horticulture
Many seeds need a cold break to break dormancy – cause the breakdown of growth inhibitors or the production of growth promoters such as auxins
Special conditions are necessary to break dormancy in seeds before they are planted for agricultural or horticultural use
These conditions include:
Soaking seeds in water
Physical damage
Exposure to light or dark
Exposure to cold temperatures

35. Advantages of dormancy
Allows the plant to avoid the harsh conditions of winter
Gives the embryo time to develop fully
Provides time for the seed to be dispersed
Maximises the growing season for the young seedling, i.e. by starting growth in the spring the plant is well developed by the autumn
Helps survival of the species because the duration of the dormancy varies

36. What do you know? Can you. . . Discuss fruit formation?
Distinguish between true and false fruits?
Discuss the development of seedless fruit?
Discuss fruit and seed dispersal?
Discuss seed dormancy?

37. Lesson objectives By the end of this lesson you should be able to:
Discuss the conditions necessary for seed germination
Discuss the events in seed germination
Account for changes in dry weights of germinating seeds
Discuss the stages in seedling growth
MA: To investigate the effect of water, oxygen and temperature on seed germination
MA: To use starch agar or skimmed milk plates to show digestive activity during germination

38. Germination
“Germination is the re - growth of the embryo after a period of dormancy if the environmental conditions are suitable”

39. Conditions for germination
Water is needed to allow enzyme reactions to occur – the seeds absorb water from the soil
Oxygen is needed for aerobic respiration
A suitable temperature is needed to allow enzyme reactions to take place
Dormancy must be complete
Light may be required

40. Events in germination
Seeds store food in the form of oils, starch (especially in cereals and grasses) and protein (especially in legumes such as peas and beans)
Germination begins when seeds absorb water through a tiny hole called the micropyle allowing enzymes to be activated
Oils are digested to fatty acids and glycerol, starch to glucose and proteins to amino acids
Dry weight (mass) of the seed falls due to the food used in respiration
Weight of food stores falls, the weight of the embryo increases
Radicle bursts through the testa
Products of digestion are moved to the embryo
Glucose and amino acids are used to make new structures such as cell walls and enzymes
Fats and some of the glucose are used in respiration
The plumule emerge above the ground and leaves form
Once the first leaves start to photosynthesize the dry weight of the seedling increases again

41. Changes in dry weights of germinating seed parts

42. The stages in seedling growth Cotyledons remain below the soil – Broad beans
In this type of germination the seed absorbs water, enzymes become active and the seed begins to grow
Radicle bursts out through the testa and grows down
Plumule emerges and the region between the plumule and cotyledon (epicotyl) grows
The radicle develops into the primary or tap root which forms many lateral roots
Once above the ground the plumule straightens up and produces the first true leaves which become green and start to photosynthesize
The plumule grows up through the soil and its delicate leaves are protected by the plumule being hooked over
The cotyledons (and endosperm, if present) shrivel as food is transferred from them

43. The stages in seedling growth Cotyledons move above the soil – Sunflower seeds
This form of germination is similar to the previous form with the following differences:
The region between the emerging radicle and the cotyledons (hypocotyl) grows causing the emerging cotyledons to be carried above the soil
Once above the soil, the fruit wall (pericarp) falls to the ground, the cotyledons open out and become green and photosynthetic. The plumule emerges from between the cotyledons and forms the first foliage leaves

44. What do you know?
Can you . . .
Discuss the conditions necessary for seed germination?
Discuss the events in seed germination?
Account for changes in dry weights of germinating seeds?
Discuss the stages in seedling growth?
MA: Describe an investigation of the effect of water, oxygen and temperature on seed germination
MA: Describe an investigation to use starch agar or skimmed milk plates to show digestive activity during germination

45. Lesson Objectives - HL
By the end of this lesson you should know how to:
Discuss male gamete formation and pollen grain development in detail
Discuss female gamete formation and the development of the embryo sac in detail
Discuss the events of fertilisation in detail

46. Male gamete formation

47. Pollen grain development

48. Formation of a pollen grain

49. Development of the embryo sac

50. Female gamete formation

51. LS of a carpal with mature embryo sac

52. Fertilisation
“Fertilisation is the union of male and female gametes to form a diploid zygote”
Growth of a pollen tube

53. What have you learned? Can you. . .
Discuss male gamete formation and pollen grain development in detail?
Discuss female gamete formation and the development of the embryo sac in detail?
Discuss the events of fertilisation in detail?