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FLOWERS AS REPRODUCTIVE STRUCTURES. The Angiosperm flower. Male and female whorls. The stamens are the male organs and produce pollen that contain the male gametes The pistil with the stigma, style and ovary is the female organ of the plant. The ovulums are found in the ovule.
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FLOWERS AS REPRODUCTIVE STRUCTURES Lorraine Kuun, July 2011
The Angiosperm flower Lorraine Kuun, July 2011
Male and female whorls • The stamens are the male organs and produce pollen that contain the male gametes • The pistil with the stigma, style and ovary is the female organ of the plant. The ovulums are found in the ovule. Lorraine Kuun, July 2011
POLLEN, BEARERS OF MALE GAMETES • Stamens consist of an anther with a filament. • The anther produces pollen in the pollen sac. • The pollen grains contain the male gametes. Lorraine Kuun, July 2011
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
Self pollination 2. Geitonogamy 3.Cross-pollination Lorraine Kuun, July 2011
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
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
Adaptations of Salvia for insect pollination by bees Pistil overhanging landing platform Stamens form “lever” Tubular shape, contains nectar Nectar guides Landing platform Bees attracted to blue and yellow flowers Lorraine Kuun, July 2011
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
Adaptations of Strelitzia for pollination by birds Stigma close to pollen Stamens fused in tube to fit beak Bright colours Nectaries Sturdy landing platform Lorraine Kuun, July 2011
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
The pollen grain germinates • Meiosis occurs in the pollen grain. • The male gametes are haploid. • When the ripe pollen grain lands on a receptive stigma, it will germinate. • The pollen grain germinates and form a pollen tube. Lorraine Kuun, July 2011
The germinated pollen grain is the male gametophyte Lorraine Kuun, July 2011
The female pistil • The ovary contains the ovule(s) with female gametes (n). • The pollen tube grows down the style, through the micropyle and into the embryo sac. • Double fertilisation occurs. Lorraine Kuun, July 2011
The female gametophyte: germ sac with 8 nuclei Lorraine Kuun, July 2011
The fruit develops from the following layers: • Fruit wall from ovary wall. • Seed from ovule. Lorraine Kuun, July 2011
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
A SEED … Endosperm– result of double fertilization. Endosperm is food for embryo– also why we eat seeds for food. Lorraine Kuun, July 2011
When a seed germinates • The cotyledons contain food for the embryo in some seeds. • In beans the cotyledons are responsible for photosynthesis after germination before first leaves are formed. Lorraine Kuun, July 2011
Plants can be dicots or monocots MONOCOTYLEDON Lorraine Kuun, July 2011
Plants can be dicots or monocots DICOTYLEDON Lorraine Kuun, July 2011
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
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
Agents for seed dispersal • Wind – seeds are light with plumes or wings. • Animals – hooks and thorns – cling to wool, stick in paws. • Animals – 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
SEEDS NEED TO BE DISTRIBUTED BY DIFFERENT AGENTS Lorraine Kuun, July 2011
SEEDS NEED TO BE DISTRIBUTED BY DIFFERENT AGENTS COCO DE MER drifts along ocean currents Lorraine Kuun, July 2011
SEEDS AND FRUIT PROVIDE US WITH FOOD Lorraine Kuun, July 2011
Seeds as a source of food • Most important plant source of food for humans. • Practical form of food – easy to transport and store for long periods of time. • Grains – wheat, maize (mealies), sorghum, rice, oats; mainly starch • Pulses (legumes) – beans, peas, soy beans, peanuts, lentils, plant proteins • Nuts – oily seeds in hard shells e.g. walnuts, cashews, pecans etc. Lorraine Kuun, July 2011
Use of seed banks to maintain biodiversity • Many plant species under threat. • Seed bank stores seeds of wild plants and crops. • UK – conserves seeds of about 10% of wild plant species at Kew – Millennium Seed Bank Project. • Swedish International Seed Vault – reinforced concrete tunnel – 4,5 million seed samples – will remain viable for 1000’s of years. • MSBP working with SA National Biodiversity Institute – contributing 2500 indigenous species – endangered, endemic, over-exploited Lorraine Kuun, July 2011
How do seed banks contribute to maintain biodiversity? • Offer protection against loss of species in wild due to: • Habitat loss – agriculture, development of cities, building of dams, large-scale ecological disasters etc. • Climate change • Over-exploitation of certain species Lorraine Kuun, July 2011
SEED BANKS ... Can be used to • re-establish damaged, lost habitats and ecosystems • re-introduce extinct, endangered or threatened species • provide research material Lorraine Kuun, July 2011
CONFUSION ABOUT FRUIT AND VEGETABLES, AND SEED Lorraine Kuun, July 2011
