Communication & Homeostasis (OCR A Level Biology)

Fig. 2.1 shows a naked mole rat, Heterocephalus glaber.

Fig. 2.1

The naked mole rat is a mammal. However, it has several features that are unusual for mammals.

Naked mole rats regulate their temperature in a way that is different from most mammals.

(i)

Some features of thermoregulation in naked mole rats are listed below:

• They live in complex underground tunnel systems, which tend to have a stable temperature of 30–32 °C. However, sometimes the environmental temperature can increase or decrease outside this range.
• In experiments that examine environmental temperature changes, the core body temperature of naked mole rats remains close to that of the environmental temperature.
• When tunnel temperature increases they often move to cooler parts of the tunnel system.
• When tunnel temperature decreases they often lie together in large groups.

Outline two ways in which thermoregulation in naked mole rats is different from thermoregulation in most mammals.

[2]

(ii)

In humans, when core body temperature falls below 35 °C, positive feedback causes this decrease in core body temperature to continue. This process is known as hypothermia.

Explain how positive feedback could accelerate the process of hypothermia.

[4]

(iii)

Mammals, including naked mole rats, have temperature receptors that play a role in thermoregulation.

The table below lists four statements about mammalian temperature receptors.

Write either ‘true’ or ‘false’ in the empty boxes to indicate whether each statement is true or false.

[2]

An unusual characteristic of naked mole rats is their tolerance of pain.

Acid causes pain responses in most mammals. Naked mole rats are tolerant of the pain caused by acid.

This tolerance can be explained by the type of pain receptor found in naked mole rats.

Fig. 2.2 shows a representation of the ion channels present in the pain receptors of naked mole rats and other mammals.

Fig. 2.2

Use the information in Fig. 2.2 to suggest why naked mole rats do not feel pain when exposed to acid.

 [2]

(ii)

Explain how a pain receptor is an example of a transducer.

 [1]

Fig. 2.3 shows the relationship between body mass and lifespan in a range of mammal species.

Fig. 2.3

Describe the relationship between body mass and lifespan shown in Fig. 2.3.

 [1]

(ii)

What conclusion can you draw from Fig. 2.3 about the lifespan of naked mole rats in comparison to other mammals?

 [1]

Naked mole rats can survive without oxygen for up to 18 minutes. This is several times longer than other mammals of a similar size.

The following information might help to explain how naked mole rats can survive without oxygen for a long time:

• In normal glycolysis, the enzymes needed to convert glucose to triose phosphate may be inhibited by lactate.
• Naked mole rats can use fructose as a respiratory substrate.
• Fructose is converted to triose phosphate.
• Triose phosphate can then enter the glycolysis pathway.

Suggest why the use of fructose allows naked mole rats to survive without oxygen for a long time.

[2]

(ii)

Suggest one other aspect of the physiology of naked mole rats that explains how they are able to survive without oxygen for a long time.

 [1]

Many insects such as moths are insulated with scales and hair, and are known as facultative endotherms.

Their metabolism during flight can cause the temperature of the flight muscles to increase 20–30 °C above the external temperature.

(i)

Using the information provided, explain why many moths are described as endothermic.

[1]

(ii)

It is more difficult for moths to maintain their body temperature than for mammals and birds to maintain their body temperature.

The control of water and glucose levels in the body involves negative feedback loops.

Give an example of a mechanism which involves positive feedback.

Positive feedback could include:                                                        

Another control mechanism in the body involves the control of blood pH.

Suggest why it is important that an organism maintains a stable blood pH.

Homeostasis depends heavily on the action of negative feedback in the body.

Explain why homeostasis is controlled by negative feedback and not positive feedback mechanisms.

Explain how the maintenance of a constant body temperature in humans allows metabolic reactions within cells to proceed at maximum efficiency.

Hypothermia is a condition in which the body's core temperature is lowered. Hypothermia can affect people who take part in outdoor activities in winter without wearing suitable clothing.

Some people believe that consuming alcohol helps to keep warm, as it can give a feeling of warmth. Alcohol causes vasodilation.

Explain why it is not a good idea to give alcohol to someone with hypothermia.

Fig. 1 shows the heat flow through the skin of an athlete during vigorous exercise.

Exercise starts at 400 seconds.

Fig. 1

Blood flow can be directed to those parts of the body that make the greatest demands.

Describe and explain the events that are occurring at points R and S.

Bees, such as Apis mellifera, are able to alter the temperature of their nests depending on factors such as external temperature. 

When a pathogen infects a colony the bees can raise the temperature of the nest; this is similar in function to humans getting a fever as part of the immune response. 

Explain how this behaviour benefits the colony. 

If the temperature of the colony becomes too high newly hatched bees may have malformations in their mouthparts and wings, and a shortened lifespan.

Suggest the cause of these malformations.

Another mechanism that can be used for thermoregulation in bee colonies is a behaviour where adult bees can crawl into cells adjacent to brood cells (containing eggs, larvae or pupae). This is shown in Fig. 1 below. 

Fig. 1

Explain the benefit of this behaviour to the development of the bees in the brood cells. 

Colonies of bees can go through a system of swarming, where a large group of bees relocates to a new area. 

The image in Fig. 2 shows an example of a bee swarm. 

Mark Osgatharp, CC BY-SA 3.0 <https://creativecommons.org/licenses/by-sa/3.0>, via Wikimedia Commons

Fig. 2

During the process of swarming the bees cooperate to allow for thermoregulation. 

The bees on the inside regularly swap places with the bees on the outside of the swarm. 

Suggest how this helps the colony to thermoregulate. 

The polar bear, Ursus maritimus, is a large bear native to the Arctic and nearby areas. They have unique adaptations that allow them to thermoregulate effectively, some of which are shown in the image below.

Identify two adaptations shown in the image, and explain how they help the polar bear to thermoregulate.

Polar bears also have a specialised, countercurrent circulatory system.

Suggest how this adaptation helps polar bears to regulate their body temperature.

A recent study found that polar bears have evolved genes that produce more nitric acid than other bear species. Nitric acid controls whether cells use their available nutrients to produce metabolic energy, or convert it into body heat.

[2]

The series of stages below outline the events that occur when blood volume decreases due to a significant blood loss.

As the action of aldosterone takes effect, this is detected by receptors in the body and the secretion of aldosterone decreases.

Name and describe the mechanism that results in this decrease.

Suggest and explain the effect of blood loss on heart rate.

Suggest how the opening of stomata can contribute towards homeostatic mechanisms in plants.

Explain why the homeostatic control of gas exchange in plants is important in maximising the growth rate of plants.

The image below shows stomata viewed using a light microscope. The image magnification is x60.

The measured length of one stoma in the image is 4 mm.

Calculate the actual size of the stoma, giving the answer in µm and to three significant figures.

[2]

A second cell signalling molecule related to the immune system is histamine which is produced by mast cells when an allergen is detected.

[3]

The table below shows varying levels of plasma histamine and associated severity of symptoms.

[2]

[2]

In colder weather, some birds are able to drop their body temperature by between 5 and 7OC and enter a regulated hypothermia.

Suggest how this is beneficial to the bird in cold weather.

Hypothermia in humans occurs when core body temperature in humans falls below 35^oC, and positive feedback causes this decrease in temperature to continue.

Explain how positive feedback could accelerate the process of hypothermia.