How does varying temperature affect the speed of woodlice?

Temp (oC) Distance travelled (cm)

Time taken (s)

Speed (m/s)

0 10 16

20 10 5

40 10 23

Temp (oC) Distance travelled (cm)

Time taken (s)

Speed (m/s)

0 10 17

20 10 12

40 10 8

Sarah, Eliza and Lydia

Pip, Jack and Lewis

Calculate the speed for each set of results. (2) Describe and suggest reasons to the trends with each set of results (5)

Temperature RegulationTemperature RegulationBy the end of the lesson you will be able to:(d) define the terms negative feedback, positive feedback and homeostasis;

(e) explain the principles of homeostasis in terms of receptors, effectors and negative feedback;

(f) describe the physiological and behavioural responses that maintain a constant core body temperature in ectotherms and endotherms, with reference to peripheral temperature receptors, the hypothalamus and effectors in skin and muscles.

Feedback Mechanisms

Feedback Mechanisms examplesnegative feedback,

(in physiology) a decrease in function in response to a stimulus. For example, the secretion of follicle-stimulating hormone decreases as the amount of circulating oestrogen increases.

positive feedback,

(in physiology) an increase in function in response to a stimulus. For example, micturition increases after the flow of urine has started, and the uterus contracts more frequently and with greater strength after it has begun to contract in labour.

Positive Feedback Mechanisms

Homeostatic systems utilising positive feedback exhibit two primary characteristics:

1. Time limitation – Processes in the body that must be completed within a constrained time frame are usually modified by positive feedback.

2. Intensification of stress – During a positive feedback process, the initial imbalance or stress is intensified rather than reduced as it is in negative feedback.

Typical Positive Feedback Process

Stress Sensor Control Center

EffectorIntensifies

Homeostatic Regulation of Child Birth through Positive Feedback

Pressure of Fetus on the Uterine Wall

Nerve endings in the uterine wall carry afferent messages

to the Hypothalamus

Production and Release of Oxytocin into the

BloodIncreasing strength of uterine contractions

Intensifies

The birth of the child will bring this process to a close. Other examples of positive feedback regulation occur during milk letdown and blood clotting.

Glossary

Maintain – keep up. Constant – the same. Internal – inside the body. Environment – surroundings of the body.

What is Homeostasis?

Body cells work best if they have the correct– Temperature– Water levels– Glucose concentration

Your body has mechanisms to keep the cells in a constant environment.

What is Homeostasis?

The maintenance of a constant environment in the body is called

Homeostasis

Controlling body temperature

All mammals maintain a constant body temperature.

Human beings have a body temperature of about 37ºC.– E.g. If your body is in a hot environment your

body temperature is 37ºC– If your body is in a cold environment your body

temperature is still 37ºC

The Transfer of thermal energy

Controlling body temperature Animals with a large surface area compared to

their volume will lose heat faster than animals with a small surface area.

Volume = _______

Surface area = ______

Volume : Surface area ratio = ___________

Volume = _______

Surface area = ______

Volume : Surface area ratio = ___________

Controlling body temperature

Volume : Surface area ratio = 1:6

Volume : Surface area ratio = 1:5

For every 1 unit of heat made, heat is lost out of 6 sides

For every 1 unit of heat made, heat is lost out of 5 sides

Controlling body temperature

Volume : Surface area ratio = 1:6

Volume : Surface area ratio = 1:5

The bigger the Volume : Surface Area

ratio is, the faster heat will

be lost.

Penguins huddling to keep warm

To provide the optimum conditions for enzyme-catalysed reactions to be carried out.

Why do we need to Why do we need to regulate:regulate:Internal body Internal body temperaturetemperature

Body TemperatureBody TemperatureNormal internal body

temperature is 370C.Temperatures above this:

denature enzymes and block metabolic pathways

Temperatures below this:slow down metabolism and affect the brain.

Water Bath

Temperature set on thermostatToo cool? Heater kicks on and temperature goes upToo warm? Heater stays off until bath cools down

Constant checking and turning on and off

Control of homeostasis Control of homeostasis through feedbackthrough feedback

Feedback system- cycle of events in which the status of a body condition is continually monitored, evaluated, changed, re-monitored, re-evaluated, etc.

1) receptor– sensor that responds to changes (stimuli)

2) control centre– sets range of values, evaluates input and

sends output 3) effector

– receives output from control centre and produces a response

3 basic components of a feedback system

Body Temperature Control

The hypothalamus acts as a thermostat and receives nerve impulses from heat and cold thermoreceptors in the skin.

There are also receptors in the hypothalamus- called central thermoreceptors. These detect changes in

blood temperature.

Vasoconstriction and Vasoconstriction and VasodilatationVasodilatation

Correction of Correction of overheatingoverheating

1. Detected by thermoreceptors in the hypothalamus.

2. Causes vasodilation.3. Sweating

Cooling downCooling down

When it's hot and you need to cool down, muscles at each hair relax.

Hairs lie close to the skin.

Air does not act as an insulating layer.

SweatingSweating

How does it work?

Heat energy in the body is used to convert the water in sweat to vapour cooling down the body.

What mechanisms are there to cool the body down?

1. Sweating When your body is hot, sweat glands are

stimulated to release sweat. The liquid sweat turns into a gas (it

evaporates) To do this, it needs heat. It gets that heat from your skin. As your skin loses heat, it cools down.

Sweating

The skin

What mechanisms are there to What mechanisms are there to coolcool the body down? the body down?

2.2. VasodilationVasodilation Your blood carries most of the heat energy Your blood carries most of the heat energy

around your body.around your body. There are capillaries underneath your skin There are capillaries underneath your skin

that can be filled with blood if you get too that can be filled with blood if you get too hot.hot.

This brings the blood closer to the surface This brings the blood closer to the surface of the skin so more heat can be lost.of the skin so more heat can be lost.

This is why you look red when you are This is why you look red when you are hot!hot!

If the temperature rises, the blood vessel dilates (gets bigger).

This means more heat is lost from the surface of the skin

Correction of overcooling

1. Detected by thermoreceptors in the hypothalamus.

2. Causes vasoconstriction.3. Decreased sweating4. Shivering

Keeping warmKeeping warm

When it's cold, the muscle contracts pulls the hair up.

A layer of warm air accumulates around the hair and insulates the organism.

Heat retained

Shivering

How does it work?

What mechanisms are there to warm the body up?

1.1. VasoconstrictionVasoconstriction This is the opposite of vasodilationThis is the opposite of vasodilation The capillaries underneath your skin get The capillaries underneath your skin get

constricted (shut off).constricted (shut off). This takes the blood away from the This takes the blood away from the

surface of the skin so less heat can be surface of the skin so less heat can be lost.lost.

If the temperature falls, the blood vessel constricts (gets shut off).

This means less heat is lost from the surface of the skin

What mechanisms are there to warm the body up?

2.2. PiloerectionPiloerection This is when the hairs on your skin “stand This is when the hairs on your skin “stand

up” .up” . It is sometimes called “goose bumps” or It is sometimes called “goose bumps” or

“chicken skin” if you are a bit weird like “chicken skin” if you are a bit weird like Americans!Americans!

The hairs trap a layer of air next to the skin The hairs trap a layer of air next to the skin which is then warmed by the body heatwhich is then warmed by the body heat

The air becomes an insulating layer.The air becomes an insulating layer.

Voluntary responsesVoluntary responses In humans the cerebrum “makes”

people feel cold or hot. They can then e.g. put on more

clothes, eat a hot meal, exercise etc as appropriate.