B4- Photosynthesis

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  • Created by: Lauren
  • Created on: 08-03-13 20:38


Green plants make their own food (glucose and starch) using sunlight; this is called photosynthesis. It produces glucose for biomass and energy. Oxygen is released as a by-product. The equation is:

6CO₂ + 6H₂O + C₆H₁₂O₆ + 6O₂

Understanding Photosynthesis

How we understand photosynthesis has changed and evolved over time. The Greek scientists thouht the plants gained mass only by taking in minerals from the soil. Van Helmont carried out many experiments and concluded that plany growth cannot be due only to the nutrients in the soil Joseph Priestley put a plant in a jar of air, and a plant in a jar with a mouse in it. He changed the combinations of plants and mouse and concluded that oxygen is produced by plants.

Using and Storing Food

The glucose produced in photosynthesis can be used immediately to produce energy through respiration, or it can be converted into other substances that the plant needs. Gluscose and starch can be converted into :

-energy (during respiration)

-proteins for growth and repair

-starch, fats or oils that can be stored in seeds

-cellulose, which is needed for plant cell walls.

Glucose is soluble. It can be transported arouned the plant as soluble suger but it must be converted into starch, which is insoluble, in order to be stored. 

Starch is a very useful storage molecule. It is insoluble so it doesnt affect the water concentration inside the cells where its stored. It also doesnt move away in solution from storage areas. If the cells stored soluble glucose, the inside of the cells would become very concentrated and water would constantly move in through osmoses, which would make the cell swell.

The Chemistry of Photosynthesis

Using radioactive oxygen-18, scientists discovered that the oxygen produed as a by-product in photosynthesis comes from the water and not from the carbon dioxide. You only get radioactive waste product of oxygen when radioactive oxygen-18 is introduced via water. This shows that photosynthesis is a 2 stage process. Firstly light energy splits the water, releasing oxygen gas and hydrogen ions. Secondly, the Carbon dioxide gas combines with the hydrogen ions to make glucose.

Increasing Photosynthesis

Plants need light and warmth to grow. This is why they grow faster in the summer.

Photosynthesis can be increased by increasing:

-the temperature- using heaters in greenhouses

-thelight intensity- using lamps in a greenhouse

-the carbon dioxide concentration-using…


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