Maintaining a Balance summary

Enzymes
The role of enzymes
Enzymes are organic catalysts. A catalyst is anything that speeds up a reaction or chemical change without being used up. As well as speeding up reactions, enzymes enable reactions to occur at lower a temperature, which means body temperatures do not have to be so high. Enzymes control all the chemical processes of living systems. They are produced within living cells.
The chemical composition of enzymes
Enzymes are proteins. They are made up of amino acids that are linked and then folded to produce a three dimensional protein structure. The folded shape is related to enzyme specificity. There are a large number of metabolic processes occurring in living organisms. Most metabolic processes would not occur at an efficient rate without enzymes.
A simple model of enzymes
Specificity means that only one compound can react with a particular enzyme. Each enzyme catalyses a distinct chemical reaction in which the compounds called the substrate are changed into other compounds. Enzymes are unique to one substrate. The enzyme combines with the substrate to form an enzyme-substrate molecule. This somehow alters the substrate so that a chemical reaction can take place. The substrate is altered and no longer ‘fits’ the enzyme. The enzyme is then released.
Effect of temperature on enzymes
Enzymes each have an optimum temperature for activity. Enzymes can be denatured by high temperatures.
Effect of pH on enzymes
Enzymes each have an optimum pH for activity. For example, digestive enzymes in the stomach work best under conditions with a pH of 6.
Effect of substrate concentration on enzymes
Substrate concentration means the amount of compound present that the enzyme catalyses. Beyond certain substrate concentrations, the rate of reaction is limited by the amount of enzyme.

pH pH is a measure of the concentration of hydrogen ions that are released by acids. It is therefore a way of describing the acidity of a substance. A pH of 7 is neutral. This means it is neither acidic nor alkaline. High acidity is shown by a low pH level.
Maintenance of an optimal internal environment
On a regular basis, living things may take in nutrients and water or change their level of activity. They are also exposed to frequent changes in their external environment. Organisms need to maintain a constant internal environment for optimal metabolic efficiency. If the internal environment is relatively stable, e.g. enzymes having their optimum temperature and pH conditions, a high level of efficiency for the running of cells is possible.
Definition of homeostasis
Homeostasis is the process by which organisms maintain their internal environment within tolerable limits, despite changes in their behaviour and the external environment. Through homeostasis organisms maintain an internal equilibrium by adjusting their physiological processes.
Living organisms need to control:
Body temperature and metabolic rate
Concentrations of dissolved salts and minerals
Concentrations of nutrients, such as glucose in the blood
Input and output of water
Quantities of nitrogenous wastes
Oxygen and carbon dioxide concentrations
Removal of malfunctioning cells or foreign substances
Homeostasis ensures that the organism operates at maximum performance.
Homeostasis as a two stage process
Coordination in animals is controlled by two systems:
The nervous system
The endocrine system
A feedback mechanism is a self-regulating mechanism that maintains balance or homeostasis. It is any circular situation where information about something is continually fed back to a central control region. For example, the human body operates feedback mechanisms to deal with changes in body temperature.
Detecting changes from the stable state
If our body temperature rises, the temperature rise in the blood stimulates the brain’s anterior hypothalamus. Alternatively, when a mammal is exposed to cold, skin receptors increase their activity, sending nerve