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.

• 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).


A SEED …Endosperm – result of double fertilization. Endosperm is food for embryo – also why we eat seeds for food.


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.


Plants can be dicots or monocots

MONOCOTYLEDON


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.


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.


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.


Agents for seed dispersal

SEEDS NEED TO BE DISTRIBUTED BY DIFFERENT AGENTS


SEEDS NEED TO BE DISTRIBUTED BY DIFFERENT AGENTS

COCO DE MER drifts along ocean currents


SEEDS AND FRUIT PROVIDE US WITH 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.


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


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


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


SEED BANKS ...

CONFUSION ABOUT FRUIT AND VEGETABLES, AND SEED


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.

Documents

seed dispersallorraine

biodiversitylorraine

different agentslorraine

source of foodlorraine

seed samples

ocean currentslorraine

overexploitedlorraine

water seeds