Homeostasis

HBS3A

Organisms need nutrients

Nutrients provide

• Energy for cellular and body activity eg movement, growth, active transport, etc

• Matter for building cell components and body structures eg cell membranes, enzymes, muscle, bone, etc

• Essential compounds eg cofactors, minerals, vitamins, for healthy functioning

Cells need energyEnergy in the cell is transported as ATP

Cells can get energy by: Respiration• Glycolysis glucose pyruvate + 2 ATP• Fermentation pyruvate lactic acid• These all occur in the cytoplasm• Transition reaction pyruvate enters

mitochondrion and the Krebs cycle • Krebs cycle – series of reactions that generates

ATP, H2O & CO2 and uses electron transport chain to generate large amounts of ATP (34 – 36 ATP)

Factors affecting rate of respiration

• Temperature as temperature increases, respiration increases, until temperature gets too high enzymes denature

• Concentration of glucose as glucose increases, respiration increases, until maximum level reached

• Concentration of oxygen as oxygen increases, respiration increases, until maximum level reached

• Concentration of wastes (eg CO2) as wastes increase, respiration decreases

Cells need to remove wastes

Most have damaging effects on the cell:

• Carbon dioxide - toxic, decreases pH

• Ammonia - toxic, increases pH

• Excess salts alters osmotic pressure – drags in water

• Excess water alters osmotic pressure – can burst cells

• Waste heat – raises body temperature

Homeostasis

Maintenance of constant internal environmentThis involves continually replacing substances as they are used up (eg glucose, oxygen) or continually removing substances as they build up (eg wastes)

Negative feedback systems

• Stimulus

• Receptor

• Modulator

• Effector

• Response

• Negative feedback

Negative feedback systems

• Stimulus change in conditions• Receptor detects the change• Modulator decides what to do about the

change• Effector part of the body that carries out

the response• Response change in activity• Negative feedback response alters the

stimulus in the opposite direction

An example of negative feedback

Stimulus

Negative feedback Receptor

Response Modulator

Effector

Exercise causes increasedtemperature

An example of negative feedbackStimulus

Negative feedback Receptor

Response Modulator

Effector

Exercise causes increasedtemperature

Brain - hypothalamus

Brain sympathetic system

Sweat glands

Sweating increases

Decreased temperature

Simple negative feedback loops

Positive and negative feedback

Cyclic control