B4.1. How do chemical reactions take place in living things?

Why is photosynthesis important?

1. Plants capture energy from sunlight and use it to make the molecules they need for growth. 2. These molecules feed other organisms long the food chain, so photosynthesis supplies food for life on Earth.

Lock-and-key model

1. An enzyme has an active site. 2. Substrates fit into the active site of the enzyme, which have a specific shape. 3. Reactions take place in the active site. Only the correct molecule with the correct shape fits into the active site. 4. The product leaves the active site, and the enzyme can be used again.

How does temperature affect enzymes?

1. Enzymes work at an *optimum temperature.* 2. Enzyme reactions get faster if the temperature is increased. At low temperature, the rate of reaction is slow. 3. Above a certain temperature the reaction stops, because the enzymes are proteins and the active site *denatures* so molecules no longer fit into the enzyme. The active site doesn't go back to its original shape.

How does pH affect enzymes?

1. Proteins can be damaged by acids and alkalis. 2. The enzyme's active site will be changed if bonds holding protein chains together are broken. 3. Substrates no longer fit into the active site, so the enzyme denatures. 4. There is an optimum pH for each enzyme.

What are the different types of enzymes?

1. They break down large molecules into smaller ones. 2. They join small molecules together.

Enzymes in humans: optimum temperature

37 degrees C

Photosynthesis

A series of chemical reactions that use energy from sunlight to build large food molecules in plant cells and some microorganisms (e.g. phytoplankton)

How do cells make enzymes?

According to the instructions carried in genes; the sequence of amino acids is determined by these instructions.

Growth

Bacteria divide to form new bacteria; plants and animals grow from a single fertilised egg cell.

What are living things made up of?

Cells

What do basic processes of life carried out by all living things depend on?

Chemical reactions within cells that require energy released by respiration.

Respiration

Energy is needed to carry out cell processes. Respiration is a series of chemical reactions that release energy from food molecules; enzymes allow respiration to happen.

How are enzymes harvested?

Fermenters grow bacteria so that their enzymes can be harvested. These fermenters contain a nutrient solution, and conditions like temperature, pH and oxygen levels are controlled for optimum growth.

Proteins

Large molecules made up of long chains of amino acids, which are different in each protein and fold to make different shapes.

Excretion

Living cells make wastes that become toxic as they build up; these are removed by excretion. An example is carbon dioxide.

Nutrition

Living things need a supply of energy, and they get this from food. Plants make their own food by photosynthesis.

What are the basic life processes?

Movement Respiration Sense Growth Reproduction Excretion Nutrition

Sense

Organisms are able to sense and respond to their surroundings e.g. plants grow towards light, woodlice run away from it.

Movement

Organisms may move to find food, escape from predators or find better conditions to grow.

Why do we need enzymes?

Our body temperature at 37 degrees means that chemical reactions in our body happen too slowly to keep us alive. Higher body temperatures would speed up these reactions, but they would damage our cells and would also need a lot more food. Enzymes increase the rates of reaction for us.

Enzymes

Proteins that speed up chemical reactions in living organisms (biological catalyst).

Reproduction

Reproduction makes new generations that keep a species alive.

How are life processes carried out?

The biological chemical factory in the cytoplasm of cells takes small molecules and builds them into large molecules. These reactions are catalysed by *enzymes*; each cell has genes with instructions for making these.