maintaining a constant envioronment

homeostasis

maintenance of a constant internal temperature

what do cellular activities rely on

• the action of enzymes

• any change in external conditions eg temp, ph can result in enzyme denaturation

• environment of a cell or organism can be considered in terms of external and internal factors

stimulus

change in the environment

why do changes occur in cell and tissues

• bathed in tissue fluid

• they occur when cells carry out metabolic activities

managing blood and tissue fluid

• composition of tissue fluid is maintained by the blood

• waste substances can then be excreted

• composition of blood is constantly monitored

stimulus of increased concentration of urea

response= increased urine production

stimulus of decreased blood ph

response= increase hr and breathing rate

stimulus of increased glucose

response= release of insulin to convert glucose to glycogen

why are communication systems important

• in multicellular orgs, cells that detect stimulus and cells that bring about response can be in diff parts of body

• communication systems are therefore important to ensure the cells work together effectively

negative feedback

• detects a stimulus and issue a response to bring the value back to normal

positive feedback

• detects a stimulus a brings about a response that moves the factor away from normal level

• eg oxytocin when contractions are detected, more is secreted to increase strength of contractions