Sexual reproduction in flowering plants

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

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

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)

Structures and functions of a flower

Male gamete formation

Female gamete formation

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?

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

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

Methods of pollination – 2 types Animal pollination Wind pollination

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

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

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

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

Seed development

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

A non – endospermic seed (broadbean)

An endospermic dicot seed (castor oil bean)

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.

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?

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

Development of a fruit

Two types of fruit

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)

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

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

Wind dispersal

Water dispersal

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

Self - dispersal Examples include peas, beans and gorse

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

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

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

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?

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

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

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

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

Changes in dry weights of germinating seed parts

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

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

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

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

Male gamete formation

Pollen grain development

Formation of a pollen grain

Development of the embryo sac

Female gamete formation

LS of a carpal with mature embryo sac

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

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?