IGCSE BIOLOGY SECTION 3 LESSON 1

Content Section 3 Reproduction and Inheritance a)Reproduction - Flowering plants - Humans b) Inheritance

Content Lesson 1 a) Reproduction – flowering plants a) Reproduction 3.1 understand the differences between sexual and asexual reproduction 3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo Flowering plants 3.3 describe the structures of an insect-pollinated and a wind-pollinated flower and explain how each is adapted for pollination 3.4 understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit formation 3.5 understand the conditions needed for seed germination 3.6 understand how germinating seeds utilise food reserves until the seedling can carry out photosynthesis 3.7 understand that plants can reproduce asexually by natural methods (illustrated by runners) and by artificial methods (illustrated by cuttings)

Reproduction “ Understand the differences between sexual and asexual reproduction.”

Reproduction Reproduction is the production of new organisms. It may be sexual or asexual.

Reproduction In either case, reproduction involves passing genetic information from parent to offspring

Reproduction In either case, reproduction involves passing genetic information from parent to offspring Genetic material – contained in genes carried by chromosomes in the nucleus

Reproduction Sexual reproduction produces offspring that resemble their parents, but they are not identical to them.

Reproduction Sexual reproduction produces offspring that resemble their parents, but they are not identical to them. In asexual reproduction, the offspring, called clones, are genetically identical to their parents

Reproduction Sexual reproduction involves the fusion of gametes.

Reproduction Gametes are the sex cells. In animals, the male sex cell is the sperm, and the female eggs or ova.

Reproduction Gametes are the sex cells. In plants, the male sex cell is the pollen, and the female eggs.

Reproduction Sexual reproduction involves the fusion of gametes. SPERM EGG

Reproduction Sexual reproduction involves the fusion of gametes. SPERM EGG ZYGOTE

Reproduction Sexual reproduction involves the fusion of gametes. SPERM EGG ZYGOTEEMBRYO

Reproduction Zygotes are formed when the male gamete fertilises the female gamete.

Reproduction Following fertilisation, the zygote divides into 2, then 4, then 8, and so on.

Reproduction In animals, when the zygote becomes implanted in the womb it is known as the embryo.

Reproduction In animals, after about eight weeks of development, the embryo becomes known as the foetus

Reproduction 3.1 understand the differences between sexual and asexual reproduction 3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo

Reproduction in flowering plants Wind pollinated. The pollen is carried by the wind between flowers Insect pollinated. The pollen is carried by insects between flowers

Insect pollination Sepal – green, protects the flower whilst in the bud.

Insect pollination Petal – colourful, scented. Attracts insects to the flower

Insect pollination Anther – contains pollen sacs, in which are the pollen grains (male gametes)

Insect pollination Filament – holds the anther so that insects will brush against it and collect pollen

Insect pollination Together, the anther and the filament make up the stamen, the male part of the flower

Insect pollination Stigma – sticky, collects the pollen from insects visiting the flower.

Insect pollination Style – the pollen tube grows through this on its way to the ovary

Insect pollination Ovary – contains the ovules, the female parts of the flower

Insect pollination Ovule – this will develop into the seed when the egg cell (female gamete) is fertilised

Insect pollination Together, the stigma, style and ovary make up the carpel, the female reproductive structure in the flower

Insect pollination Insects visit flowers to collect nectar, a sugary substance produced in nectaries at the base of the petals.

Insect pollination Insects visit flowers to collect nectar, a sugary substance produced in nectaries at the base of the petals. As the insect climbs inside the flower in search of nectar, so it brushes against the pollen on the outside of the anthers.

Insect pollination Insects visit flowers to collect nectar, a sugary substance produced in nectaries at the base of the petals. As the insect climbs inside the flower in search of nectar, so it brushes against the pollen on the outside of the anthers. As the insect visits other flowers, so it transfers pollen to the stigma.

Insect pollination As the bee enters the flower, it brushes against the anther As the bee enters the next flower, pollen sticks to the stigma

Wind pollination In wind-pollinated flowers the petals are much reduced and are not colourful.

Wind pollination Stamens have anthers that hang outside of the flower, so they are exposed to the wind.

Wind pollination The stigmas are feathery and exposed, so that they can catch pollen grains blown by the wind

Comparison of insect and wind pollinated flowers

Wind pollinated flowersInsect pollinated flowers Flowers are small and do not have brightly coloured petals (if at all) Flowers are large and have brightly coloured petals

Comparison of insect and wind pollinated flowers Wind pollinated flowersInsect pollinated flowers Flowers are small and do not have brightly coloured petals (if at all) Flowers are large and have brightly coloured petals Large amounts of small, very light pollen grains produced. Sticky pollen is produced in small amounts.

Comparison of insect and wind pollinated flowers Wind pollinated flowersInsect pollinated flowers Flowers are small and do not have brightly coloured petals (if at all) Flowers are large and have brightly coloured petals Large amounts of small, very light pollen grains produced. Sticky pollen is produced in small amounts. Stigmas are long and feathery and held outside of the flower Stigmas are positioned inside the flower so insects brush against them

Comparison of insect and wind pollinated flowers Wind pollinated flowersInsect pollinated flowers Flowers are small and do not have brightly coloured petals (if at all) Flowers are large and have brightly coloured petals Large amounts of small, very light pollen grains produced. Sticky pollen is produced in small amounts. Stigmas are long and feathery and held outside of the flower Stigmas are positioned inside the flower so insects brush against them Anthers are held outside of the flower by long filaments Anthers are positioned inside the flower so that insects will brush against them.

Comparison of insect and wind pollinated flowers Wind pollinated flowersInsect pollinated flowers Flowers are small and do not have brightly coloured petals (if at all) Flowers are large and have brightly coloured petals Large amounts of small, very light pollen grains produced. Sticky pollen is produced in small amounts. Stigmas are long and feathery and held outside of the flower Stigmas are positioned inside the flower so insects brush against them Anthers are held outside of the flower by long filaments Anthers are positioned inside the flower so that insects will brush against them. Wind pollinated flowers do not produce nectar Insect pollinated flowers produce nectar in nectaries.

Comparison of insect and wind pollinated flowers Wind pollinated flowersInsect pollinated flowers Flowers are small and do not have brightly coloured petals (if at all) Flowers are large and have brightly coloured petals Large amounts of small, very light pollen grains produced. Sticky pollen is produced in small amounts. Stigmas are long and feathery and held outside of the flower Stigmas are positioned inside the flower so insects brush against them Anthers are held outside of the flower by long filaments Anthers are positioned inside the flower so that insects will brush against them. Wind pollinated flowers do not produce nectar Insect pollinated flowers produce nectar in nectaries. Eg. the grasses, cerealsEg. orchids, foxgloves

Fertilisation Understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit formation STIGMA STYLE OVARY

Fertilisation STIGMA STYLE OVARY The pollen grain lands on the sticky stigma, and produces a pollen tube.

Fertilisation STIGMA STYLE OVARY The pollen tube, containing the male nuclei, grows down through the style

Fertilisation STIGMA STYLE OVARY The pollen tube continues until it reaches the embryo sac of the ovule in the ovary

Fertilisation STIGMA STYLE OVARY The male nucleus in the pollen tube fuses with the egg nucleus in the embryo sac. EMBRYO SAC EGG NUCLEUS

Fertilisation STIGMA STYLE OVARY The male nucleus in the pollen tube fuses with the egg nucleus in the embryo sac. EMBRYO SAC EGG NUCLEUS The fertilized egg then divides by mitosis and grows into a seed which will become a new plant.

Fertilisation STIGMA STYLE OVARY The male nucleus in the pollen tube fuses with the egg nucleus in the embryo sac. EMBRYO SAC EGG NUCLEUS The fertilized egg then divides by mitosis and grows into a seed which will become a new plant. The layers around the ovule harden and become the seed coat.

Fertilisation STIGMA STYLE OVARY The male nucleus in the pollen tube fuses with the egg nucleus in the embryo sac. EMBRYO SAC EGG NUCLEUS The fertilized egg then divides by mitosis and grows into a seed which will become a new plant. The layers around the ovule harden and become the seed coat. In some plants the ovary grows into a fruit to help with seed dispersal.

Content Lesson 1 a) Reproduction – flowering plants a) Reproduction 3.1 understand the differences between sexual and asexual reproduction 3.2 understand that fertilisation involves the fusion of a male and female gamete to produce a zygote that undergoes cell division and develops into an embryo Flowering plants 3.3 describe the structures of an insect-pollinated and a wind-pollinated flower and explain how each is adapted for pollination 3.4 understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit formation 3.5 understand the conditions needed for seed germination 3.6 understand how germinating seeds utilise food reserves until the seedling can carry out photosynthesis 3.7 understand that plants can reproduce asexually by natural methods (illustrated by runners) and by artificial methods (illustrated by cuttings)

Germination What’s needed?

Germination What’s needed? Water - to hydrate the protoplasm, to mobilise enzymes, to hydrolyse stored food (starch)

Germination What’s needed? Water - to hydrate the protoplasm, to mobilise enzymes, to hydrolyse stored food (starch) Warmth – to enable enzymes to work

Germination What’s needed? Water - to hydrate the protoplasm, to mobilise enzymes, to hydrolyse stored food (starch) Warmth – to enable enzymes to work Oxygen - For aerobic respiration to supply energy for growth

Germination What’s needed? Water - to hydrate the protoplasm, to mobilise enzymes, to hydrolyse stored food (starch) Warmth – to enable enzymes to work Oxygen - For aerobic respiration to supply energy for growth Some seeds require light, others dark, for germination, but most are indifferent

Germination A: No water D: Water, oxygen, warmth C: No warmth B: No oxygen Seeds Dry cotton wool Wet cotton wool NaOH and pyrogallol to absorb oxygen NaOH Put in refrigerator All tubes except C put in a warm place

Germination A: No water D: Water, oxygen, warmth C: No warmth B: No oxygen Seeds Dry cotton wool Wet cotton wool NaOH and pyrogallol to absorb oxygen NaOH Put in refrigerator All tubes except C put in a warm place Result: only seeds in tube D germinate! So seeds need water, oxygen and warmth

Seed germination 1. The seed germinates and the first growth is seen. The stored food is utilised. 1

Seed germination 2. The first roots and shoot begin to grow. Food stores in the seed are still being used. 1 2

Seed germination 3. The first leaves begin to uncurl and photosynthesise. The food store in the seed is used up

Seed germination 4. The leaves are now fully photosynthesising and providing all the nourishment that the plant needs

Understand that plants can reproduce asexually by natural methods (illustrated by runners) and by artificial methods (illustrated by cuttings)

Asexual reproduction All the offspring from one asexually-reproducing parent are known as a clone, and are all genetically identical.

Asexual reproduction Natural method – eg. strawberry runner Strawberry runners are more correctly called “stolons”. They are horizontal stems that run above the ground and produce new clone plants at “nodes” spaced at varying intervals

Asexual reproduction Natural method – eg. strawberry runner Strawberry runners are more correctly called “stolons”. They are horizontal stems that run above the ground and produce new clone plants at “nodes” spaced at varying intervals Under favourable conditions (warm, sufficient water), most strawberry plants produce lots of runners. It is not uncommon for a single plant to produce between 30 and 50 runners.

Asexual reproduction Artificial method – eg. cuttings When a cutting is taken, a short length of a young stem is cut just below a node.

Asexual reproduction Artificial method – eg. cuttings The cut end is then dipped in rooting powder. – this contains plant hormones that encourage the growth of roots. The cutting will then be planted in aerated damp soil. Some leaves may be removed to lessen transpiration

Reproduction in flowering plants 3.3 describe the structures of an insect-pollinated and a wind-pollinated flower and explain how each is adapted for pollination 3.4 understand that the growth of the pollen tube followed by fertilisation leads to seed and fruit formation 3.5 understand the conditions needed for seed germination 3.6 understand how germinating seeds utilise food reserves until the seedling can carry out photosynthesis 3.7 understand that plants can reproduce asexually by natural methods (illustrated by runners) and by artificial methods (illustrated by cuttings)

End of Section 3 Lesson 1 In this lesson we have covered: Sexual and asexual reproduction Fertilisation Reproduction in flowering plants Germination