The ovary develops into the fruit, the ovule into the seed. 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

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 Significant features of seeds

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 Why is dormancy important?

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 Agents for seed dispersal

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

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 Seeds as a source of food

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 Use of seed banks to maintain biodiversity

Offer protection against loss of species in wild due to: 1.Habitat loss – agriculture, development of cities, building of dams, large-scale ecological disasters etc. 2.Climate change 3.Over-exploitation of certain species Lorraine Kuun, July 2011 How do seed banks contribute to maintain biodiversity?

Can be used to 1.re-establish damaged, lost habitats and ecosystems 2.re-introduce extinct, endangered or threatened species 3.provide research material Lorraine Kuun, July 2011 SEED BANKS...

CONFUSION ABOUT FRUIT AND VEGETABLES, AND SEED Lorraine Kuun, July 2011