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 energy Energy 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, H 2 O & CO 2 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 CO 2 ) 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 environment This 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 feedbackReceptor ResponseModulator Effector Exercise causes increased temperature

An example of negative feedback Stimulus Negative feedbackReceptor ResponseModulator Effector Exercise causes increased temperature Brain - hypothalamus Brain  sympathetic system Sweat glands Sweating increases Decreased temperature

Simple negative feedback loops

Positive and negative feedback

Cyclic control