Biology 12

Metabolism and temperatureMetabolism refers to all reactions occurring in the

bodyMetabolic rate refers to the amount or speed of

reactions in the body. It can be measured by measuring temperature, rate of oxygen consumption or rate of carbon dioxide production

Reactions produce waste heat.The more reactions that occur, the greater the

temperatureReactions rely on enzymes

Enzyme activity and temperature

Enzyme activity

Temperature

Metabolic rate and temperature

As temperature increases, metabolic rate increases

As metabolic rate increases, temperature increases

Size and metabolic rateSmaller animals have a larger surface area

to volume ratio than larger animals

Animals lose heat from body surfaces, so smaller animals will lose more heat than larger ones

Metabolic rate is usually higher in smaller animals

Body temperaturePoikilotherms have changing body

temperatures - the same as their environment

eg fish, amphibians, reptilesHomeotherms have constant body

temperatures regardless of the environment

eg birds, mammalsEctotherms control body temperature

by behavioureg fish, amphibians, reptilesEndotherms control body temperature

by internal mechanisms eg birds, mammals

Environmental temperature

Bodytemperature

Metabolic rate

Environmental temperature

Poikilotherms

Endotherms

Homeotherms

Ectotherms

Endothermy vs Ectothermy

Endothermy Ectothermy

Advantages Can survive in a wide range of conditions and habitats eg Antarctica, winter

Don’t need a constant food supply to drive metabolism

Have simple control mechanisms

Disadvantages Must have a constant food supply to drive metabolism

Have complex control mechanisms

Can not survive in as wide a range of conditions and habitats eg Antarctica, winter

Heat production

Heat can be produced by:• Metabolism eg respiration

• Movement

Voluntary eg exercise Involuntary eg shivering

Heat loss or gain

Occurs from body surfaces

Uses the processes of:

• Radiation

• Conduction

• Convection

• Evaporation

Radiation

Loss without contact

Most important in terrestrial organisms.

Can be increased by

Increasing surface area exposure eg basking, big ears, vasodilation, bare skin/reduced fur

Can be decreased by

Decreasing surface area exposure eg huddling, small ears, vasoconstriction, fur or feathers

Conduction

Loss by contactMost important in aquatic organismsCan be increased byIncreasing surface area exposure eg larger

extremities, reduced fur, reducing insulation

Can be decreased byDecreasing surface area exposure eg smaller

extremities, increased fur, increased insulation (eg blubber)

Convection

Loss by air movements

Most important in land animals

Can be increased by

Increasing surface area exposure to wind eg sprawling, decreased fur

Can be decreased by

Decreasing surface area exposure to wind eg huddling, fluffing feathers, increased fur

Evaporation

Loss of heat due to liquid turning to gas

Most important in terrestrial organisms

Can be increased by sweating, panting or wetting skin or fur

Can be decreased by reducing sweating or panting, keeping surface dry or covered with thick fur or feathers

Control of body temperature

Control of heat production

Increasing or decreasing metabolic activity or movement (shivering or exercise)

Control of heat loss

Increasing or decreasing loss of heat from external or respiratory surfaces

An example of negative feedback

Stimulus

Negative feedback Receptor

Response Modulator

Effector

Heat

Thermoreceptors

Hypothalamus in brain

Sweat glands

Increased sweating

Cool down

An example of negative feedback

Stimulus

Negative feedback Receptor

Response Modulator

Effector

Thermoreceptors

Hypothalamus in brain

Cold

Muscles

Shivering

Warm up

Structural adaptations

Bare skin orreduced fur

Large ears/extremities Small ears/extremities

Small body size

Large body size

Dark extremities

Fur orfeathers

blubber

Counter current exchange

Physiological adaptationsSweating

Aestivation

Panting

Vasodilation Vasoconstriction

Hibernation

Fluffing feather or fur

Behavioural adaptationsLicking fur

Seeking shadeResting during heat

Dipping feet in water

Burrowing

Nocturnal

Basking

Migration

Huddling

Clothes