Biology 4.2 - Seed Dispersal and the Germination of Seeds.

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Seed dispersal

This refers to the movement of seeds away from the paernt plant. Plants have devekoped different characteristics for seed dispersal in order to reduce competition and increase the chances of the seed growing into a photosynthesising plant. There are several options, for example:

  • Wind - such as a dandelion seed, which has a parachute of stiff hairs.
  • Transport by birds - birds will eat berries that are indigestible. They are therefore dispersed through faeces. 
  • Rolling - horse chesnut fruits release conkors (seed).
  • Bursting - pea pods split open.
  • Water - coconuts are seeds that float on water due to their large air spaces. 
  • Carrying by other animals - burdock seeds attach to animals fur. Germination

Germination is a series of biochemical and physiological processes by which a seed becomes a photosynthesising plant. 

Seeds will remain dormant until suitable conditions are present:

  • Suitable temperature - this will vary depending on the enzymes used, but is usually between 5-30'C.
  • Oxygen - aerobic respiration releases a large amount of energy used for metabolism and growth.
  • Water - to mobilise enzymes so they can be transported through the xylem and phloem, and to make cells turgid.

Light is another factor but varies greatly. 

Stages of germination in a non-endospermic seed, e.g. broad bean

  • Water is taken up (IMBIBED) through the micropyle. This causes the tissues to swell and the enzymes become mobilised. 
  • The food reserves in seeds are insoluble and so need to be broken down into soluble molecules…

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