Enzymes, Plant nutrition summary and key terms.

• • All the chemical reactions in cells are controlled by enzymes. Enzymes are biological catalysts which increase the rate of reactions.
• • Enzyme activity is affected by environmental conditions, such as pH and temperature.
• • Investigations can be carried out to observe the effects of temperature and pH on enzyme-controlled reactions.
• • Enzymes have a conformational shape which compliments the shape of the substrate which attaches at the active site of the enzyme. Enzymes and substrates fit together, similar to a lock and a key.
• • Enzymes have an ideal temperature and/or pH value where its activity is at its highest point, this is known as the optimum.
• • The enzyme and substrate have a complementary or matching shape, forming enzyme–substrate complexes.
• • Temperature affects the speed of molecular movement and rate of collisions between the substrate and enzyme. Raising the temperature will result in more collisions, increasing the reaction rate.
• • Changes in pH affect the the bonds holding the enzyme molecule in its shape, this causes the active site to change shape.
• • Photosynthesis is the process by which green plants make carbohydrates using carbon dioxide and water using light as a source of energy.
• The equation for photosynthesis is as given:

  carbon dioxide + water → glucose + oxygen
• • Light energy and chlorophyll are required for photosynthesis.
• • Chlorophyll is a green pigment found in chloroplasts.
• • The glucose produced during photosynthesis is either broken down to release energy or converted into other substances like sucrose, starch, cellulose, and nectar.
• • Essential mineral ions in plants include nitrate ions for making amino acids and magnesium ions for synthesising chlorophyll.
• • Varying the carbon dioxide concentration, light intensity and the temperature affects the rate of photosynthesis.
• • An increase in the carbon dioxide concentration/intensity of light increases the rate of photosynthesis up to a certain level after which it remains constant.
• • An increase in the temperature increases the rate of photosynthesis up to a certain level after which the rate decreases. This is because the enzyme is denatured.
• • Unlike respiration, photosynthesis happens only during the day. The carbon dioxide levels are hence higher in the night as photosynthesis does not take place. The varying levels of carbon dioxide at different intensities of light are detected using hydrogen carbonate as an indicator.
• Glucose is highly reactive and may cause unwanted reactions in the plant if transported in this form. Therefore, for transport glucose is converted into sucrose, which is more stable.
• All conditions that could affect enzyme activity, except the temperature, should be standardised. The temperature is the independent variable.
• Some amino acids form the shape of the enzyme's active site, which determines the enzyme's specificity, function and behaviour.
• The palisade mesophyll cells contain the highest concentration of chloroplasts and so have the highest rate of photosynthesis. They therefore have the highest rate of carbon dioxide uptake.