Biology - Section C - Plant Physiology

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Plants and Food


Plants make food through the process of photosynthesis. 

carbon dioxide + water ----> gluscose + oxygen

The leaves of a plant make glucose from carbon dioxide and water using light energy from thr Sun. This energy is captured by the chlorophyll in the chlorplasts of leaves and is then converted to chemical energy in the glucose. Oxygen is produced as a waste product.Glucose is converted into sucrose to be transported around the pant and into starch to be stored. The rate of photosynthesis is affected by the concentration of carbon dioxide, light intensity and temperature.

Adaptations of the leaves

  • They are thin and flat which increases the surface area of a leaf which allows more light to be absorbed and makes the distance for gases to diffuse very short.
  • The leaf has lots of chlorplasts which contain chlorophyll
  • They have a leaf stalk which allows the blade of the leaf to be angeled to recieve the maximum amount of sunlight.
  • Inside the leaf there is a thin, waxy layer of material covering the upper and lower epidermis which reduces the amount of water lost through evaporation. It also acts as a barrier to the entry of disease-causing micro-organisms
  • The stomata allows carbon dioxide to diffuse into the leave to reach the photosynthetic tissues

Limiting Factors

A limiting factor is a component of a reaction that is in short supply. This means it limits the rate at which the reaction takes place. The main limiting factors for photosynthesis are the intesnsity of light, the concentration of carbon dioxide and the temperature.

Mineral nutrition in plants

Plants cannot survive on only the food they produce from photosynthesis. They also need minerals and ions which they take from the soil. This involves active transport as the mineral ions are taken up against a concentration gradient. Plants need nutrients to make amino acids, which are built up into proteins and magnesium to make chlorophyll.

Transport in Plants

Osmosis in Plant Cells

Diffusion is the movement of molecules from a region of high concentration to a region of low concentration, down a concentration gradient. Osmosis is a specialised form of diffusion.

Osmosis is the movement of water molecules…


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