Learning about Photosynthesis – Biology Revision

The plant cells are different from animal cells as they contain chloroplast which contains chlorophyll. All green plants have chlorophyll in their leaves and with the help of the chlorophyll, they are able to trap the light energy from the sun and convert it into chemical energy in the form of food. They use light energy to react carbon dioxide and water to form glucose. The glucose is utilised in respiration, or is stored in the form of starch if present in excess. In this process, oxygen is formed as a by product and is released into the atmosphere. This entire process is called photosynthesis. Hence, we can describe photosynthesis as the process of forming glucose with carbon dioxide and water in presence of sunlight and chlorophyll. Plants use this process to synthesis their food which is glucose, and which is further utilised in respiration.


Photosynthesis takes place in the leaves of the plant containing chloroplast which are tiny organelles containing chlorophyll. The first step for synthesising food is photosynthesis and it is not just for plants themselves but for animals as well as this food forms the part of a food chain.

Image source : BBC.co.uk – Structure of a photosynthetic leaf

Equation of Photosynthesis:

Image source: biology4u.com

Carbon dioxide is absorbed by the leaves of the plant and water is absorbed by the roots. They react in presence of sunlight and chlorophyll which is trapped by chlorophyll present in chloroplast of the leaf. They give glucose as a product which is used in respiration and excess is stored in the form of starch. Stored starch can again be converted into glucose to be used in respiration. Oxygen is also formed as a by product which is released into the atmosphere.

Factors limiting the rate of photosynthesis


How temperature affects rate of photosynthesis

If the temperature is too hot or too cold the rate of photosynthesis certainly decreases. Plants cannot photosynthesise at at very high or at a very low temperature. It requires an optimum temperature to accelerate the process. At low temperature, the kinetic energy of the particles is too low to initiate a reaction, and high temperature denatures the enzymes making them non functional.

Carbon dioxide

How carbon dioxide affects the rate of photosynthesis

Concentration of carbon dioxide is an important parameter for the process of photosynthesis to take place. Even if there is sufficient amount of light energy present in the atmosphere and the carbon dioxide concentration is less, then photosynthesis will not take place successfully.

Light intensity / sunlight.

How light intensity affects the rate of photosynthesis

Increasing the light intensity always boosts the photosynthesis. Presence of light is very important, along with carbon dioxide and temperature. In night time or dim light, photosynthesis either stops or slows down.

Green House

To maximise the process of photosynthesis farmers can use, the knowledge of limiting factors, and provide artificial lights in the green house in order to increase the rate of photosynthesis. They can also use paraffin lights as they release carbon dioxide and maximises the process of photosynthesis. In the green house, farmers can also control the other limiting factors like presence of light, water, temperature and minerals.

Mineral requirements

In addition to the limiting factors listed above plants need certain more minerals and ions which are equally important for the growth and nutrition of the plants.

  • Carbon
  • Hydrogen
  • Oxygen
  • Nitrate
  • Magnesium

Plants fulfil the requirements of carbon and oxygen from carbon dioxide and oxygen in the atmosphere and the requirement of hydrogen and oxygen by water absorbed by the plants.
Carbon dioxide and water are used to synthesise food by the plant and oxygen is used to release energy from the food . In addition to these two, more mineral ion required by the plant are nitrate, which helps in making amino acids which make protein and magnesium to synthesise chlorophyll. Where there is deficiency of these two minerals, plants can suffer from stunted growth and yellowing of leaves.

Mahima Laroyia, is an Oxford Postgraduate in Integrative Biosciences who has more than 8 years of tutoring experience in tutoring students Maths and Sciences from KS2 up to A-levels. She specializes in providing custom and tailor made study materials to school students to make Maths and Sciences easier and fun.Find me at: www.expertguidance.co.uk

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