Photosynthesis

What is Photosynthesis?

Uses of Glucose in Plants

The glucose made in photosynthesis is used by the plant in many ways.

• Glucose is used to produce energy in respiration. 
• Lots of glucose molecules are joined together to form cellulose which provides strength to cell walls.
• Glucose can be combined with nitrate ions that are absorbed from the soil to produce amino acids. Amino acids join together to make proteins in a process called protein synthesis. 
• Glucose can be stored as insoluble starch in the plants leaves, stems and roots. This means the plant will have glucose available in times where it cannot photosynthesise such as during winter. 
• Glucose can also be stored in seeds as fats and oils.

Limiting Factors of Photosynthesis

Light intensity, carbon dioxide (CO₂) concentration, temperature and amount of chlorophyll have a combined affect on the rate of photosynthesis. 

If there is a shortage of these factors, they can limit the rate of photosynthesis – they become the limiting factor:

• At night, it is dark, so light becomes the limiting factor. If there was more light, photosynthesis would happen quicker.
• In winter, it is cold, so temperature becomes the limiting factor. If the temperature was warmer, photosynthesis would happen quicker. 
• On sunny and warm days, light intensity and temperature levels are both high so CO₂ concentration becomes the limiting factor. Increasing CO₂ concentration would increase the rate of photosynthesis. 
• Diseased plants may have less chlorophyll so will not be able to absorb as much light for photosynthesis. This means the amount of chlorophyll is the limiting factor.

Creating an Ideal Environment for Plant Growth

An ideal environment for plant growth can be created artificially in a greenhouse. Factors that affect photosynthesis can be controlled easily and prevented from being limited:

Heat:

• Glass structure traps heat from the sun to keep the plants warm.
• Windows can be opened to provide ventilation if it gets too hot.
• Heaters can be used in winter to keep the inside of the greenhouse warm.

Light:

• Glass panes allow lots of light in for photosynthesis. 
• At night, artificial lamps can be used to enable plants to continue photosynthesising when there is no natural light.

Carbon dioxide concentration:

• Paraffin heaters can be used that increase the temperature and the amount of carbon dioxide.

Keeping plants in a greenhouse prevents diseases and pest infestations and therefore promotes healthy growth. 

Water and fertiliser can be controlled more easily in a greenhouse so plants can receive everything they need to grow. 

 

Farmers use these techniques to make their crops grow faster and stronger, increasing their crop yields and making more money. However, controlling all of the factors on a large scale can be very expensive.  It is important that the increase in crop yield is enough cover the costs of the greenhouse while also making a profit. Farmers will provide their crops with the optimum amounts of heat, light etc. but no more than that, as this would be wasting money.