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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
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:
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
SEED BANKS ...
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
CONFUSION ABOUT FRUIT AND
VEGETABLES, AND SEED
Lorraine Kuun, July 2011