What are the conditions necessary for seed germination? Seeds can easily be destroyed by unfavourable conditions such as excessive heat, cold or animals. Seeds need certain conditions to germinate and grow.
Some of these conditions are external, for example water, oxygen and suitable temperature while others are internal such as enzymes, hormones and viability of the seeds themselves.
Water
A non-germinating seed contains very little water. Without water a seed cannot germinate. Water activates the enzymes and provides the medium for enzymes to act and break down the stored food into soluble form.
Water hydrolyses and dissolves the food materials and is also the medium of transport of dissolved food substances through the various cells to the growing region of the radical and plumule. Besides, water softens the seed coat which can subsequently burst and facilitate the emergence of the radicle.
Oxygen
Germinating seeds require energy for cell division and growth. This energy is obtained from the oxidation of food substances stored in the seed through respiration thus making oxygen an important factor in seed germination. Seed in water logged soil or seed buried deep into the soil will not germinate due to lack of oxygen.
Temperature
Most seeds require suitable temperature before they can germinate. Seeds will not germinate below 0°C or above 47° C. The optimum temperature for seeds to germinate is 30°C. At higher temperature the protoplasm is killed and the enzymes in the seed are denatured.
At very low temperatures the enzymes become inactive. Therefore, the protoplasm and the enzymes work best within the optimum temperature range. The rate of germination increases with temperature until it reaches an optimum. This varies from plant to plant.
Enzymes
Enzymes play a vital role during germination in the breakdown and subsequent oxidation of food. Food is stored in seeds in form of carbohydrates, fats and proteins which are in insoluble form. The insoluble food is converted into a soluble form by the enzymes.
Carbohydrates are broken down into glucose by the diastase enzyme, fats into fatty acids and glycerol by lipase, and proteins into amino acids by protease.
Enzymes are also necessary for the conversion of hydrolysed products to new plant tissues.
Hormones
Several hormones play a vital role in germination since they act as growth stimulators. These include gibberellins and cytokinins. These hormones also counteract the effect of germination inhibitors.
Viability
Only seeds whose embryos are alive and healthy will be able to germinate and grow.
Seeds stored for long periods usually lose their viability due to depletion of their food reserves and destruction of their embryo by pests and diseases.
Practical Activity
To investigate conditions necessary for seed germination
Requirements
Cotton wool, seeds, water, six fiat bottomed flasks, 2 corks, 2 test-tubes, blotting paper, incubator, refrigerator, thermometer, pyrogallic acid and sodium hydroxide.
Procedure
- Prepare three set-ups
- Leave the set-ups to stand for five days.
- Record all the observable changes that have taken place in the flasks hi each set¬ up in a table form as shown
Evaluation
- What are the conditions required for seed germination?
- What are 3 factors that affect seed germination?
- What are the conditions a seed need to sprout?
- Is sunlight needed for germination?
- How does air affect seed germination?
- Can seeds germinate without air?