sees for survival
plants must make sure enough of the necxt generation will survive. they do this by packaging a minature plantin a protective coat with its own food supply: we call them seeds.
inside the seed the embryo remains dormant untill the conditions are suitbale for restarting growth.
seeds are vital to plants, they are adapted to ensure that they:
- protect the embryo
- aid dispersal
- provide nutrition for the new plant
in flowering plants the ovule is fertilised by the nucleus from a pollen grain and develops into a seed. the outer layers of the ovule are lignified creating a tough seed coat which protects the embryo within the seed. the surrounding ovary develops into a fruit which can help seed dispersal.
in some species the stored food remains outside the seed in storage tissue called endosperm. seeds of this type are called endospermic.
seeds come in many shapes and sizes most of which are apporpriate for wide dispersal which means offspring are less likely to have to compete for nutrients with other plants.
when conditions are suitable the seed begins taking in water through a small pore in the seed coat, which triggers metabolic changes in the seed. production of plant growth substances is switched on and these let out enzymes which mobilise stored food. maltase and amylase break down starch into glucose which is converted to sucrose for transport to the radicle and plumule. proteases break down proteins in the food store to give amino acids. lipases break down stored lipids to give glycerol and fatty acids.
starch from seeds
starch has many uses.
starch can be used for thickening substances. this is because when starch is heated in water its granules swell, absorb water and thicken the liquid. an example of this is the production of custard. this process is called 'gelatinisation'
starch can also be used to stiffen fabrics. the stiffening of cloth or paper is known as 'sizing'. large amounts of starch are added to paper coating which is frist geltinised and then cooled allowing bonds to form between starch molecules. adding water is the reverse of this and is called 'plasticisation'.
starch can be very useful as absorbents which take up large amounts of water.
uses for vegetable oils.
seeds are a good source of oils which can be used for cooking and many other uses.
one is the major uses for these oils are in fuels however the use of oil based plastics and fuels are not sustainable. there are three reasos why
- burning oil based fuels releases carbon dioxide into the atmospere contributing to global warming.
- oil supplies will eventually run out.
- plastics generate non biodegradable waste creating watse issues.