This programme uses everyday examples, laboratory demonstrations and graphics to illustrate and explain the details of chemical reactions such as photosynthesis and respiration which happen in cells, and the role of enzymes. There is particular emphasis on investigating the conditions which affect the rate of these reactions and enzyme activity. Some of the demonstrations could be duplicated in a school laboratory and used in conjunction with the programme.

The programme is divided into three sequences:

1. Photosynthesis
2. Respiration
3. Enzymes

Each section of this programme could be used to introduce these topics or as a valuable revision aid. Before attempting practical coursework, some general points about the methodology involved in science investigations could be introduced using this programme.

Photosynthesis

00.00 Introduction to photosynthesis

Photosynthesis is responsible for growth in plants. The raw materials are carbon dioxide and water, and light is the energy source transformed by chlorophyll. The products are glucose and oxygen. The rate of photosynthesis can be maximised in a greenhouse by using artificial light and supplying carbon dioxide.

01.25 How does light intensity affect the rate of photosynthesis?

The amount of CO₂ used (measured by a gas analyser) indicates the rate of photosynthesis. If the light intensity increases, so does the uptake of CO₂ and the rate of photosynthesis.

03.31 How does the supply of carbon dioxide affect the rate of photosynthesis?

This sequence starts with a demonstration of pondweed photosynthesising in water. The amount of oxygen produced (measured in capillary tubing) indicates the rate of photosynthesis. Next a solution of sodium hydrogen carbonate is used to supply CO₂. As the supply of CO₂ increases so do the production of O₂ and the rate of photosynthesis. Data are displayed.

Respiration

05.21 Life processes require energy

Respiration releases energy from food for the processes of life.

05.50 Food is our energy source

Here we see respiration releasing energy from food for humans. For most living things, including humans, this process requires oxygen and is therefore aerobic.

06.06 An equation for respiration

This graphical sequence builds up the equation for respiration and shows the energy released. Respiration happens in every cell.

06.23 Monitoring the rate of respiration

Sequences show the use of a gas analyser linked to a data-logger to record information on production of CO₂ and uptake of O₂ during respiration. The rates of respiration are compared for an athlete at rest, walking, jogging, and running. Graphs show how exercise demands a greater rate of respiration. The rates of O₂ uptake and CO₂ release both increase with the rate of respiration.

08.26 Anaerobic respiration

Breathing rate increases with exercise, to supply the necessary oxygen. What happens when breathing can't keep up with oxygen demand? Respiration becomes anaerobic, as happens in the leg muscles of sprinters. Lactic acid builds up and less energy is released when respiration is anaerobic. A test kit can be used to show lactic acid levels.

Enzymes

10.01 Introduction to enzymes

Enzymes are present in all cells and are secreted by some of them. They speed up or catalyse reactions. Using amylase as an example, sequences model how an enzyme acts.

10.20 Enzyme activity

Enzyme activity is affected by temperature. An experiment which is commonly carried out in schools is demonstrated here: the digestion of starch by amylase at several temperatures. The amount of starch and enzyme is controlled, while the temperature is varied. Iodine solution is used as an indicator of the end-point (when the starch has disappeared).

The higher the temperature, the greater the rate of enzyme action.

10.38 What is the optimum temperature for enzyme activity?

Animated sequences model how enzyme molecules can be denatured (at 600°C), causing a change in shape so that the substrate does not fit.

12.46 Catalase in plant and animal tissue

The equation for the breakdown of hydrogen peroxide is shown, and the production of oxygen demonstrated through experiments with liver and potato tissue.

13.24 Does pH affect enzyme activity?

This demonstration could be duplicated in school, and adapted as an investigation for students. The amount of living tissue and hydrogen peroxide solution is constant, while the pH is altered. pH 9 is the optimum for catalase activity.