1. Most organisms are active in a limited temperature range

1.1 identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates

Metabolism- all the chemical reactions that occur within an organism that are necessary to maintain life e.g. photosynthesis and respiration

Enzymes- large protein molecules which maintain the rate of chemical activity and regulation of an organism without being affected themselves. Each enzyme is specific for a specific substrate, hence a specific reaction.

Lock and Key model (Emil Fischer)

Lock and key model shows enzyme specificity. The enzyme has a specific shape which fits a specific substrate to form an enzyme-substrate complex.

Induced Fit Model

The induced fit model is a modification of the Lock and Key model. This model shows that the enzyme can alter its shape to better accommodate the substrate, it will return to its normal shape after the reaction has occurred.

Enzymes can be affected by:
-temperature
-pH
-substrate concentration

1.2 identify the pH as a way of describing the acidity of a substance pH (per hydrogen) is a measurement of the concentration of hydrogen ions released by an acid hence how acidic or basic the substance is pH 7 is neutral e.g blood and water compounds are acidic if they have a pH lower than 7 e.g HCl and lemon juice compounds are basic/alkaline if they have a pH higher than 7 e.g. bleach

1.3 explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency
Enzymes have a narrow range of temperature and pH under which they can function, these optimum conditions need to be maintained to achieve a constant internal environment. A constant internal environment allows cells to operate at their highest level of efficiency.

1.4 describe homeostasis as the process by which organisms maintain a relatively stable internal environment
Homeostasis is the process by which organisms maintain an internal environment despite changes in the external environment. For example, organisms need to control:
-body temperature
-metabolic rate
-input and output of water
-concentration of nutrients in the blood

1.5 explain that homeostasis consists of two stages:
A feedback mechanism is a self-regulating system which maintains homeostasis, information about something is continually fed back to a central control region. detecting changes from the stable state – e.g. skin receptors detect when there is an increase in the external temperature and increase their activity to send nerve impulses to the hypothalamus. counteracting changes from the stable state – e.g.the hypothalamus stimulates heat loss by increasing blood circulation through the skin to cause sweating. Heat is released via sweat, hence the body’s