2 1 3 Explain Why The Maintenance Of A Constant Internal Env

Living organisms are made of cells which, in order to function effectively, must have well co-ordinated chemical reactions. The internal environment consists of the interstitial fluid and the cytoplasm in cells; cells are very sensitive to changes in the internal environment and changes adversely affect its functioning.

The internal environment must remain within a narrow band of conditions; examples include, temperature, volume of blood or cells or cytoplasm. The chemical content must also remain within a specific range to allow the proper functioning of enzymes and the high level of metabolic efficiency. Cells cannot tolerate any build up of waste products, such as carbon dioxide or other metabolic wastes.

Metabolic efficiency relies on the constant or almost constant variables in the internal environment; these variables include; temperature and pH, concentrations of metabolites (reactants), water and salt concentration (osmotic pressure) – this determines the volume of cells, and the absence of toxins.

Importance of maintaining the variables

Temperature and pH
All the chemical reactions in cells require enzymes, enzymes only function within a narrow range of temperature and pH, outside of this range results in the denaturing of the enzymes – which greatly reduces its efficiency.
Other problems include
- in very low temperatures the water in cells can freeze: this alters the concentration of solutes in the cytoplasm, which affects the pH and osmotic balance of the cell. Also since water expands as it freezes the cell could rupture, or organelles could burst.
- in very high temperatures the enzymes and other proteins can denature, disrupting cell function and metabolic activity.

Metabolites are chemicals that participate in the chemical reactions in cells. Some are taken into the cell (such as oxygen or glucose) others are products of metabolic pathways (such as ATP). Many metabolic reactions rely on the ATP energy in cells, if a cell cannot produce enough ATP energy or if it cannot gather other metabolites from the outside environment (glucose, oxygen) – the cell is unable to perform the chemical reactions required for its growth and development. Hence a lack of metabolites can slow down or stop chemical respiration, which reduces metabolic efficiency.

Water and Salt Concentration (Osmotic Pressure)
All chemical reactions in living organisms take place in water. In order for the reactions to proceed, the reactants must be dissolved in water – hence the water concentration of cells and the surrounding fluid is vital. Dissolved substances such as salts, affect the osmotic balance of these fluids – these concentrations levels of water and salt must be kept within a narrow range in order to maintain metabolic efficiency.

Absence of toxins
A buildup of carbon dioxide or other waste products can be toxic to the cell, either directly or indirectly affecting its enzymes. They can directly affect enzymes by blocking the active sites – or indirectly by altering the optimal conditions for enzyme reactions. In both cases, enzyme activity is reduced, which reduces metabolic efficiency.