biology 4

Photosynthesis

photosynthesis is the chemical change which happens in the leaves of green plants. It is the first step towards making food - not just for plants but ultimately every animal on the planet.

During this reaction, carbon dioxide and water are converted into glucose and oxygen. The reaction requires light energy, which is absorbed by a green substance called chlorophyll.

Photosynthesis takes place in leaf cells. These contain chloroplasts, which are tiny objects containing chlorophyll.

Plants absorb water through their roots, and carbon dioxide through their leaves. Some glucose is used for respiration, while some is converted into insoluble starch for storage. The stored starch can later be turned back into glucose and used in respiration. Oxygen is released as a by-product of photosynthesis.

Enzymes

Enzymes are chemicals that speed up the rate of chemical reaction.

 Enzymes are protiens, They conist of long chains of amino acids joined tegother.

The chemicals that enzymes work on are called substrates.

Part of the enzyme called the active site has a special shape that the subutrate fits neatly into, like a key in a lock.

Glucose

Glucose is needed by cells for respiration. However, it is not produced at night when it is too dark for photosynthesis to happen. Plants and algae store glucose as insoluble products. These include:

• Starch
• Fats and oils

Uses

Some glucose is used for respiration to release energy. Some is used to produce:

• Cellulose - which strengthens the cell wall
• Proteins - such as enzymes and chlorophyll

Plants also need nitrates to make proteins. These are absorbed from the soil as nitrate ions.

The tomato plant on the left is healthy, the one on the right is growing in conditions where mineral ions are deficient.

All living things are made up of cells. The structures of different types of cells are related to their functions.

Animal cells…