Biology HSC Notes - Maintaining a Balance

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(HSC Course)

Topic 1: Maintaining a Balance


The Role of Enzymes

Enzymes role is to maintain the rate of chemical activity in an organism. They are biological catalysts, increasing the rate of reaction in metabolic processes. They also enable reactions to occur at lower temperatures, which means that body temperatures do not have to be so high.

Chemical Composition

Enzymes are specialised large proteins, which are composed of chains of amino acids, which are folded, to produce a 3-D protein structure. (3D: can be denatured).

Lock-and-key Mechanism (model)

Enzymes control specific reactions, therefore only one compound can react with a particular enzyme. The model used describes how the enzyme closely fits into the shape of the substrate (compound). The active site is where the enzyme catalyses the reaction.


Acidity of a substance

PH levels describe the acidity of a substance. pH ranges from 1-14, where lower levels are acidic, higher levels are basic and 7 is neutral.

Maintenance of a constant internal environment

The maintenance of a constant internal environment is important for optimal metabolic efficiency. This is because enzymes require specific temperatures, substrate concentration and pH levels to be able to function thereby maintaining optimal metabolic efficiency. There is only a very small temp range and pH range in which enzymes can work.

Temp: 36-40

pH: 7.35-7.45

Specific concentrations of hormones, salts, glucose, water


Homeostasis is the process by which organisms maintain a relatively stable internal environment.

The 2 Stages of Homeostasis

The organism detects changes from the stable state e.g. change in body temp.

The organism responds and counteracts the changes to bring the body back to its stable state.

The role of the Nervous System

The body detects changes via the nervous system, which along with the endocrine system, co-ordinates and controls the...