Ecology

Radiation

The emission of electromagnetic energy by a surface.

Heat gain- the sun on your skin

Heat loss- cold surroundings

Conduction

The transfer of the kinetic energy of heat between substances that are in contact with one another.

Heat gain- organism sitting on a warm rock

Heat loss- touching ice

What three factors determine the rate at which heat moves by conduction between Ann organism and its surroundings?

1. Surface area

2. Resistance to heat transfer

3. Difference between the organism and its surroundings

How does an organisms surface area help determine its rate of heat conduction?

A greater amount of exposed surface allows a greater surface for the energy transfer to take place.

Convection

The transfer of heat by the movement of liquids and gases. Molecules of air or water next to a warm surface gain enery and move away from the surface.

Heat gain- warm water surrounding an organism

Heat loss- swimming in cold water or wind blowing on the skin

Evaporation

The transformation of water from a liquid to a gaseous state with the input of heat energy.

Heat loss- sweat, dog panting, water leaving your skin

Thermoregulagion

The ability of an organism to control the temperature of its body.

Homeotherms

Maintain constant temperature conditions within the cells.

Dogs, humans, cats, birds

Poikiotherms

Do not have constant body temperature.

Lizards, snakes, frogs, fish, turtles

Ectotherms

Have body temperatures that are determined by their environment.

Lizards, snakes, turtles, frogs, fish

Endotherms

Organisms that can generate metabolic heat to raise body temperatures higher than their environment.

Humans, dogs, cats, birds, mice

Heat flux

The RATE at which heat moves from one place to another.

Positive heat flux- heat is moving into an organism

Negative heat flux- heat is moving out of an organism

How do you find the balance between heat gain and heat loss?

Gain=loss+stored

What happens when heat gain>heat loss?

Heat is stored → organism cools → heat stored < 0

Gain > loss = warm

What happens when heat loss > heat gain?

Stored heat is lost → organism cools → heat stored < 0

Loss > gain = cool

Qmet?

Heat produced by the organisms metabolism.

How body heat is produced when you exercise.

Qrad-absorbed

Heat gained by absorbing radiation.

Sun warming your skin

Qrad-emitted

Heat lost by emitting radiation.

Your body radiating heat in a cold room

Qcond

Heat gained through direct contact.

A lizard sitting on a warm rock

Qconv

Heat gained or lost through moving air or water.

Qevap

Heat lost when water evaporates.

Sweat evaporating from your skin

What is heat balance?

The relationship between heat gained, heat lost, and heat stored by an organism.

What equation is used for heat balance?

Qmet + Qrad-absorbed = Qrad-emitted + Qcond + Qconv + Qevap + Qstored

What do photons have to do with radiation?

Kinetic energy if molecules converts to electromagnetic energy (photons).

Photons travel outward until striking other molecules.

What happens when a molecule absorbs photons?

Its molecular motion increases.

How do you calculate heat lost by emitting radiation?

AeT^4(sigma)

A= surface area of the object emitting radiation

E= defines how effectively the object radiates energy (0-1)

T= temperature in kelvin (C° + 273.15)

Sigma= Stefan Boltzman constant (5.67 × 10^8 W/m² x K^4)

When does an organism lose heat by convection?

When it is exposed to cold air or water.

What determines how much heat is lost by convection?

The temperature difference between the organisms surface and the surrounding air/water, surface area, and convection coefficient.

What is the equation for heat transfer by convection?

Qconv = h x A x (Tb - Ta)

H = convection coefficient (larger h = greater heat transfer

A = surface area of the

Tb = temperature of the organisms body

Ta = temperature of the surrounding air/water

What happens to to convection when h increases?

Heat transfer be convection increases.

What happens to convection when A increases?

Heat transfer by convection increases.

What happens to convection when (Tb - Ta) increases?

Heat transfer by convection increases.

How does wind or moving water affect convection?

Can increase the convection coefficient (h), causing faster heat transfer.

What is the equation for heat transfer by conduction?

Qcond = k x A x (Tb - Tg) / L

K= thermal conductivity (how well a material transfers heat)

A = surface area of contact between the organism and the environment

Tb = body surface temperature

Tg = ground (or other solid)

L = length/distance of heat transfer

What happens to conduction when k, a, (Tb - Tg) increases?

Heat transfer increases.

What happens to conduction when L increases?

Heat transfer decreases.

How does insulation affect conduction?

Insulation increases L, which decreases heat transfer.

What type of materials have high thermal conductivity?

Metals

What mist happen for a water molecule to evaporate?

Must have enough kinetic energy to break its hydrogen bonds and escape into the air.

Which water molecules are most likely to evaporate?

The molecules with the highest kinetic energy (highest temperature).

When does evaporation occur more easily?

When the body has a higher water vapor pressure in the air.

What is the equation for heat loss by evaporation?

Qevap = cA (ew-ea)

C = A constant that converts water loss into heat loss

A = surface area

Ew = vapor pressure of water in the body

Ea = vapor pressure of water in the air

What happens to evaporated heat loss when surface area increases?

Evaporative heat loss increases.

What happens to evaporation when the vapor pressure difference (ew - ea) increases?

Evaporation increases, causing more cooling.