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REPRODUCTION

REPRODUCTION. 1. SEXUAL AND ASEXUAL 2. LIFE CYCLES OF PLANTS AND INSECTS 3. FLOWERS AS REPRODUCTIVE STRUCTURES 4. REPRODUCTIVE STRATEGIES IN ANIMALS. Definition of asexual reproduction: No fertilisation Only one parent No genetic variation as opposed to. SEXUAL REPRODUCTION.

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REPRODUCTION

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  1. REPRODUCTION 1. SEXUAL AND ASEXUAL 2. LIFE CYCLES OF PLANTS AND INSECTS 3. FLOWERS AS REPRODUCTIVE STRUCTURES 4. REPRODUCTIVE STRATEGIES IN ANIMALS

  2. Definition of asexual reproduction: • No fertilisation • Only one parent • No genetic variation as opposed to ... Lorraine Kuun, July 2011

  3. SEXUAL REPRODUCTION • Fertilization • Two parents • Genetic variation • Gametes fuse to form zygote, containing genes from both parents. • Further variation brought about by: • Crossing over during meiosis, prophase I • Random assortment and segregation of chromosomes • Random fertilisation • Mutations Lorraine Kuun, July 2011

  4. 1. Binary fission – “splitting in two” – mitosis, e.g. bacterium: Escherichia coli Lorraine Kuun, July 2011

  5. 2. Budding – new individual develops as outgrowth on parent organisms e.g. Yeast cells. Lorraine Kuun, July 2011

  6. 3. Spore production – spores produced during favourable conditions e.g. Fungi Lorraine Kuun, July 2011

  7. 4. Vegetative reproduction – vegetative part of plant, i.e. root, stem of leaf develops into new plant; can be natural or artificial. Buds on leaf margins e.g. Kalanchoe Lorraine Kuun, July 2011

  8. Bulbs Tubers

  9. Large number of offspring • Reproduction process is fast • Energy expenditure low – no mates needed, no gametes produced • Offspring well-adapted to environment in which parent lives ONE CONDITION: environment must be FAVOURABLE Lorraine Kuun, July 2011

  10. DISADVANTAGES OF ASEXUAL REPRODUCTION • No genetic variation – adaptation may be difficult • All share same “weak characteristics” – may die out when environmental conditions change/become unfavourable • Mass reproduction can threaten environment – carrying capacity Lorraine Kuun, July 2011

  11. ADVANTAGES OF SEXUAL REPRODUCTION • Genetic variation • Possible better adaptations to changing environment • Role in natural selection • Better chances of survival Lorraine Kuun, July 2011

  12. DISADVANTAGES OF SEXUAL REPRODUCTION • High energy cost – gametes to be produced, gestation, parental care etc. • Needs two parents • Slower, longer process • Young can be vulnerable to predators • Extended periods of parental care • Plants may need pollinators Lorraine Kuun, July 2011

  13. LIFE CYCLES OF PLANTS ALTERNATION OF GENERATIONS

  14. DEFINITIONS OF THE FOLLOWING: 1. Alternation of generations: haploid (n) stage (gametophyte generation) that produces gametesfollowed by diploid (2n) stage (sporophyte generation) producing spores. 2. Haploid: gametes; half the number of chromosomes in somatic cell, indicated by n, result of meiosis. 3. Diploid: somatic cells; double number of chromosomes in gametes, indicated by 2n; result of fertilisation.

  15. More terminology ... 1. Gametophyte: generation producing gametes in gametangium/ gametangia sexual stage. 2. Sporophyte: generation producing spores in sporangium/ sporangia – asexual stage. NB: In higher plants the generations alternate in the life cycle of a plant; in lower plants reproduction is either through gametes (sexual) or spores etc. (asexual).

  16. All terrestrial plants have two phases in their life cycles ... 1. A haploid gametophyte generation that produces gametes (n) by mitosis ... the gametes (n) fuse to form zygote (2n), the start of ... 2. A diploid sporophyte generation that produces spores (n) by meiosis.

  17. MOSSES Leaf-like structures of moss gametophyte Sporangium of moss sporophyte

  18. Flowering plants

  19. LYFE CYCLES IN ANIMALS INSECT METAMORPHOSIS

  20. METAMORPHOSIS • Physical changes from one stage in life cycle to another. • TWO TYPES OF METAMORPHOSIS: • 1. Complete metamorphosis • 2. Incomplete metamorphosis

  21. Comparison of metamorphosis • COMPLETE • Four stages: • 1. egg • 2. larva • 3. pupa • 4. adult • E.g. Butterflies, bees, housefly • INCOMPLETE • Three stages: • 1. egg • 2. nymph • 3. adult • E.g. Locust, cricket, cockroach 88 % of all insects 12 % of insects

  22. Complete metamorphosis

  23. Incomplete metamorphosis

  24. Advantages and disadvantages of complete metamorphosis • Advantages: • Larva and adult occupy different habitats and niches – not in competition. • Carrying capacity of ecosystem increased. • Egg and pupa stages allow insect to survive unfavourable conditions. • Disadvantages: • Larval forms vulnerable to predators. • Suitable habitat for laying of eggs needed. • Change from pupa to adult requires high energy-input.

  25. Advantages and disadvantages of incomplete metamorphosis • Advantages: • Vulnerable pupa stage avoided. • Less energy is needed – no drastic changes from pupa to adult. • All stages can eat same food. • Disadvantages: • Nymph and adult often compete for same food. • Insect vulnerable to dehydration and predators when moulting. • Entire insect population could be threatened by environmental changes.

  26. Amphibian metamorphosis

  27. FLOWERS AS REPRODUCTIVE STRUCTURES Lorraine Kuun, July 2011

  28. The Angiosperm flower Lorraine Kuun, July 2011

  29. Male and female whorls • The STAMENSare the male organs (anther + filaments) and produce pollen that contain the male gametes • The PISTILwith the (stigma +style + ovary) is the female organ of the plant. The ovums/ova are found IN the ovule. Lorraine Kuun, July 2011

  30. POLLINATION is the transfer of RIPE POLLEN from the anther to a RECEPTIVE STIGMA of a flower of the same species Lorraine Kuun, July 2011

  31. Lorraine Kuun, July 2011

  32. How is cross-pollination ensured? • 1. Male (no pistil) or female (no anthers) flowers on different plants – dioecious. • 2. Protandry – pollen ripe before stigma is receptive. • 3. Protogyny – stigma receptive, but pollen not ripe yet. • i.e. self-pollination is prevented. Lorraine Kuun, July 2011

  33. POLLINATORS • Most pollinators are insects e.g. Bees, moths, butterflies, beetles. • Some vertebrates also pollinate flowers e.g. Bats, mice, birds (mainly). • Many flowers are pollinated by wind. Lorraine Kuun, July 2011

  34. Flower adapted for insect pollination • Bright colours (bees cannot see red), white for night pollinators e.g. moths • Often sweet scent (attracts moths and butterflies) • Reward of nectar and pollen • Contrasting markings on petals to locate centre of flower (usually not visible to human eye – ultraviolet) • Pollen cling to hair on insect bodies Lorraine Kuun, July 2011

  35. Adaptations of flowers for bird pollination • High yield of dilute nectar • Bigger than most insect-pollinated flowers • Open in daytime, often red • Sturdy against rough feeding of birds • Little or no scent – birds have poor sense of smell • Protect ovary against beaks by being inferior or by partition • Pollen sticks together in clumps • Often erect or with landing platform for birds that do not hover Lorraine Kuun, July 2011

  36. Adaptations for wind pollination • Flowers do not have scent, nectar or brightly coloured petals – no need to attract pollinators. • Flowers high on plant to be exposed to wind. • Flowers usually small and reduced, lacking calyx or corolla (sepals and petals). • Anthers large and well-exposed. • Masses of light, non-sticky pollen produced. • Stigmas long and feathery with large area for trapping pollen. Lorraine Kuun, July 2011

  37. Lorraine Kuun, July 2011

  38. Lorraine Kuun, July 2011

  39. The female gametophyte: germ sac with 8 nuclei Lorraine Kuun, July 2011

  40. The fruit develops from the following layers: • Fruit wall from ovary wall. • Seed from ovule. Lorraine Kuun, July 2011

  41. A SEED … • A seed consists of a 1. Seed coat – outer layer of ovule (pericarp). 2. Embryo – from fertilisized egg cell (zygote undergoes mitosis). Lorraine Kuun, July 2011

  42. A SEED … Endosperm– result of double fertilization. Endosperm is food for embryo– also why we eat seeds for food. Lorraine Kuun, July 2011

  43. Significant features of seeds • Resistant to unfavourable conditions as they have seed coat. • Can be dispersed effectively (see later). • Can remain viable in dormant state for long periods. • Seeds have stored food reserve in endosperm or cotyledons; includes starch, oils and or protein. • Important to man as they are cheap form of plant propagation, way to store plants and are a store of food. Lorraine Kuun, July 2011

  44. Why is dormancy important? • Dormancy is a state of rest. Embryo inactive, seed will not germinate. • Some plants have obligatory period of dormancy – seed will not germinate even if conditions are favourable. • Dormancy prevents seeds from hatching in wrong season when seedlings would be exposed to unfavourable conditions. Allows seeds to survive unfavourable conditions. • Allows for seed dispersal agents to act. Lorraine Kuun, July 2011

  45. Wind – seeds are light with plumes or wings. • Animals – hooks and thorns – cling to wool, stick in paws. • Humans – edible fruit – seeds egested in different position. • Water – seeds contain oil or air bubbles – float away. • Self-dispersed – fruit dry, dehiscent. Lorraine Kuun, July 2011

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