the ovary develops into the fruit, the ovule into the seed. the fruit develops from the following...
TRANSCRIPT
• 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 a1. 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
DICOTYLEDONLorraine 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 change3.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
ecosystems2. re-introduce extinct, endangered or
threatened species3. provide research material
Lorraine Kuun, July 2011
SEED BANKS ...
CONFUSION ABOUT FRUIT AND VEGETABLES, AND SEED
Lorraine Kuun, July 2011