Temperature regulation

Some people keep rabbits as pets.

Figure 8 shows two types of rabbit.

The Himalayan fur pattern is controlled by a dominant allele.

A heterozygous male Himalayan rabbit was crossed many times with each of two female Himalayan rabbits, A and B.

The results of the two types of cross were different.

• Crosses with female A: all of the 210 offspring were Himalayan rabbits.

• Crosses with female B: some of the 240 offspring were Himalayan rabbits and some were white rabbits.

In Questions 08.1 and 08.2, use the following symbols to represent alleles: H = dominant allele for Himalayan fur h = recessive allele for white fur.

What is the genotype of female Himalayan rabbit A ?

Give the reason for your answer.

Determine the probability that one of the offspring from a cross with female Himalayan rabbit B will be white.

You should:

• draw a Punnett square diagram

• use the symbols H and h

• identify the phenotype of each offspring genotype.

Probability of offspring being white =

Adult Himalayan rabbits have:

• white fur over most of the body

• black fur on the nose, ears and feet.

The black colour is caused by production of a substance called melanin.

Figure 9 shows how melanin is made from another substance called tyrosine.

Figure 9

White rabbits have one base change in the gene that codes for the enzyme tyrosinase.

Explain how a change of one base in the DNA of the gene coding for tyrosinase could stop the tyrosinase working.

For the first four weeks of life, Himalayan rabbits produce white fur over the whole body.

The black areas of fur start to develop after four weeks.

In the first four weeks, young rabbits stay in the nest with their mother.

A rabbit’s body temperature is 39 °C.

The tyrosinase in Himalayan rabbits is:

• most active between 15 °C and 25 °C

• not active above 35 °C.

The fur on the nose, ears and feet of Himalayan rabbits is white for the first four weeks of life.

Explain what causes the fur to be white in the first four weeks of life.

From the age of four weeks, young rabbits move from the nest to the outside environment.

Explain why a Himalayan rabbit develops black nose, ears and feet from the age of four weeks.

Melanin is also produced in human skin.

Melanin absorbs ultraviolet (UV) radiation from sunlight and prevents the radiation reaching deep into the skin.

UV radiation is a type of ionising radiation.

Explain the advantage of producing melanin in human skin when exposed to bright sunlight.

The echidna is a mammal that lives in Australia. Figure 8 shows an echidna.

Figure 9 shows how the body temperature of the echidna varies during the cold winter months.

Give the lowest and highest body temperatures for the echidna shown in Figure 9.

In the cold winter months, the echidna hibernates. Figure 9 shows that the echidna woke up from hibernation several times. The echidna’s body temperature increased to over 30 C each time the echidna woke up.

How many times did the echidna wake up? Use information from Figure 9.

Each time the echidna wakes up, it hunts for food. Suggest why the echidna needs to eat food several times during hibernation.

During hibernation:

• the echidna sleeps

• the echidna’s body temperature decreases to below 5 °C

• the echidna uses food stored in its body cells to provide energy.

What process releases energy from stored food? Tick (✓) one box.

Most mammals use a lot of energy to evaporate sweat. The echidna does not sweat. Suggest one use of energy in the echidna’s body.

The control of body temperature is important in the human body. An athlete trained in a hot climate.

On one day, the athlete lost 3 200 cm³ of water in sweat. Evaporation of 1 cm³ of sweat requires 2.5 kJ of energy. Calculate the energy the athlete used for evaporation of sweat.

On a different day the athlete used 6 000 kJ of energy to evaporate sweat. The athlete’s energy intake was 24 000 kJ. Calculate the percentage of the athlete’s energy intake used for evaporation of sweat.

Some days the athlete did not do any training and rested at home. What effect would resting have on the volume of sweat produced each day?

An echidna is a mammal that lives in Australia. Figure 10 shows an echidna.

Figure 11 shows how the body temperature of the echidna varies in warm weather and in cold weather.

Figure 12 shows how human body temperature varies.

Compare the variation in body temperature of the echidna in warm weather with the variation in body temperature of the human. Use data from Figure 11 and Figure 12.

In the cold winter months, the echidna hibernates. During hibernation:

• the echidna’s body temperature decreases to below 5 °C

• the echidna sleeps for up to 17 days at a time

• the echidna’s rate of metabolism slows down.

Explain why the decrease in body temperature is an advantage to the echidna during hibernation.

During hibernation the echidna wakes up several times. Each time the echidna wakes up it becomes active and its body temperature

Explain why the echidna has a higher body temperature when it is active.

An echidna can dilate and constrict blood vessels in its skin. Explain how the dilation of blood vessels in the skin can help to decrease body temperature.

An athlete trained in a hot climate.

The athlete lost a large volume of water each day in sweat.

The athlete’s energy intake each day from food was 20 000 kJ. Evaporation of 1 cm³ of sweat requires 2.5 kJ of energy. 40% of the athlete’s daily energy intake was used to evaporate sweat. Calculate the volume of sweat the athlete lost each day. Give your answer in dm³

Suggest why the athlete was advised to take salt tablets each day.

Human body temperature is controlled within very narrow limits. Scientists investigated the effect of drinking ice-cold water on:

• internal body temperature

• the rate of sweating.

This is the method used.

1. Sit a person inside a room kept at a constant temperature of 25 C.

2. Measure the person’s internal body temperature near the brain.

3. Measure the person’s rate of sweating.

4. After 20 minutes, give the person 500 cm³ of ice-cold water to drink.

5. Continue to measure the person’s internal body temperature and sweating rate for a further 50 minutes.

Give the reason why the person should not move during the investigation.

Figure 17 and Figure 18 show the scientists’ results.

What is this person’s normal internal body temperature?

Tick (✓) one box.

The results show that when the ice-cold water was drunk, the temperature near the brain decreased.

Explain why the temperature near the brain decreased.

The thermoregulatory centre in the brain responds to the decrease in temperature. How does the thermoregulatory centre send information to sweat glands in the skin?

The rate of sweating changes between 24 minutes and 36 minutes. Explain how this change helps to maintain the person’s normal body temperature.

During exercise, the skin appears red. What causes the skin to appear red?

Tick (✓) one box.

Human body temperature is controlled within very narrow limits. Scientists investigated the effect of drinking ice-cold water on:

• internal body temperature

• the rate of sweating.

This is the method used.

1. Sit a person inside a room kept at a constant temperature of 25 C.

2. Measure the person’s internal body temperature near the brain.

3. Measure the person’s rate of sweating.

4. After 20 minutes, give the person 500 cm³ of ice-cold water to drink.

5. Continue to measure the person’s internal body temperature and sweating rate for a further 50 minutes.

Give the reason why the person should not move during the investigation.

Figure 5 and Figure 6 show the scientists’ results.

What is this person’s normal internal body temperature? Tick (✓) one box.

The results show that when the ice-cold water was drunk, the temperature near the brain decreased.

Explain why the temperature near the brain decreased.

The thermoregulatory centre in the brain responds to the decrease in temperature. How does the thermoregulatory centre send information to sweat glands in the skin?

The rate of sweating changes between 24 minutes and 36 minutes. Explain how this change helps to maintain the person’s normal body temperature.

During exercise, the skin appears red. What causes the skin to appear red? Tick (✓) one box.