Haemoglobin & oxygen transport

21

Describe three ways fish gills are adapted for efficient gas exchange.

Explain why insects can function with open circulatory systems.

The largest fish is the whale shark. Whale sharks have an average mass of 20 tonnes.

The largest marine mammal is the blue whale. Blue whales have an average mass of 150 tonnes.

Use your knowledge of gas exchange and circulatory systems to suggest why marine mammals can grow to a much larger size than fish.

Explain how the structure of haemoglobin allows it to transport oxygen from the lungs to the tissues.

During pregnancy the mother’s body undergoes several physiological changes to support the developing fetus. These changes affect every organ system in the body.

Changes to the heart and circulatory system begin in the first few weeks of pregnancy.

Fig. 16.1 shows the changes in stroke volume and heart rate that occur during pregnancy.

Fig. 16.1

Use the data in Fig. 16.1 to calculate the cardiac output in week 20.

Suggest an advantage of the increase in cardiac output.

Fig. 16.2 shows how blood pressure varies throughout pregnancy.

Fig. 16.2

A student looked at the data in Fig. 16.1 and Fig. 16.2 and drew the following conclusion:

‘As cardiac output increased blood pressure dropped so there must have been a decrease in vascular resistance.’

Evaluate this conclusion.

* Describe the flow of blood through the left side of the heart during the cardiac cycle and explain the role of valves and pressure differences in this process.

Additional answer space if required.

Another change that occurs in pregnancy is an increase in oxygen uptake by the mother. This is partly due to an increase in the mother’s metabolic rate and partly to supply the developing fetus.

Fig. 16.3 shows the oxygen dissociation curve for the mother’s haemoglobin.

Fig. 16.3

Sketch the oxygen dissociation curve for fetal haemoglobin.

Answer on Fig. 16.3.

Explain how the different affinities of maternal and fetal haemoglobin enable transfer of oxygen from the maternal circulation to the fetus.

Changes to kidney function during pregnancy can be confused with some diseases, such as chronic kidney disease or kidney failure.

The estimated glomerular filtration rate (eGFR) in a healthy 30–39-year-old is 107 cm³ min The eGFR usually decreases with age but in pregnancy, can increase by between 50 and 85%.

The table shows the results of some of the physiological measurements that a clinic carried out on two 35-year-old women. One of the patients was pregnant.

A doctor concluded that patient A was undergoing a normal pregnancy whereas patient B was suffering from kidney failure.

Explain the doctor’s conclusion.

Haemoglobin is an important protein in many animals, including humans.

Sickle cell disease (SCD) is a disease caused by the production of abnormal haemoglobin.

A treatment for SCD is based on a technique called CRISPR gene editing and allows SCD patients to begin production of fetal haemoglobin.

The treatment has the following steps:

• Bone marrow stem cells are removed from the patient with SCD.

• An enzyme called Cas9 is added to the stem cells.

• Cas9 deletes bases from the BCL11A gene.

• The BCL11A gene usually switches off the fetal haemoglobin gene in adults.

• The gene-edited stem cells are placed back in the patient.

• The patient can now produce fetal haemoglobin.

This CRISPR gene editing method is different from traditional genetic engineering, which uses restriction enzymes and plasmids.

Describe the similarities and other differences between CRISPR gene editing and traditional genetic engineering methods.

Haemoglobin plays a crucial role in transporting oxygen in animals. Several ions also have roles in oxygen transport.

Three ions are listed in the table below.

Place ticks (✓) in the correct boxes to indicate which properties and features are true for each ion.

The oxygen dissociation curves for adult haemoglobin and fetal haemoglobin are shown in Fig. 6.1.

Outline why it is important that fetal haemoglobin has a higher oxygen affinity than adult haemoglobin.

Myoglobin is a protein found in muscles. Oxygen binds to myoglobin.

A student described the oxygen dissociation curve for myoglobin as follows:

• When oxygen first becomes available, myoglobin saturation increases at a constant rate of 8% per mmHg of oxygen.

• When there is a slightly higher partial pressure of oxygen, the rate of oxygen binding slows gradually until the myoglobin is 100% saturated.

• The partial pressure at which myoglobin reaches 100% saturation is the partial pressure at which adult haemoglobin is 80% saturated.

Sketch an oxygen dissociation curve for myoglobin on Fig. 6.1 based on the description provided above.

........ Answer on Fig. 6.1........

Haemocyanin is an oxygen‑binding pigment that is found in many invertebrate animals, including lobsters.

Fig. 6.2 shows the oxygen dissociation curves for haemoglobin and haemocyanin.

What can you conclude about the habitat of a lobster?

When old red blood cells are broken down, each haem group is converted to a molecule called bilirubin. Bilirubin passes through the digestive system. Bilirubin gives faeces their characteristic colour.

Explain why bilirubin production and processing is an example of excretion.

Myoglobin is a protein found in muscle. Myoglobin has a very high affinity for oxygen at most partial pressures of oxygen.

The figure below shows dissociation curves for

• adult haemoglobin

• fetal haemoglobin

• myoglobin.

Which of the following rows, A to D, shows the correct labels for the lines on the graph?

Your answer

Mammals and fish both need circulatory systems to transport oxygen to respiring tissues. They have different circulatory systems because they have different oxygen requirements.

Acetylcholine (ACh) is a neurotransmitter in mammals. Studies have suggested that it also functions as a hormone in some invertebrate species, such as squid.

When ACh comes into contact with specialised cells in squid skin, it causes them to change colour. These colour changes allow the squid to communicate and to camouflage itself.

ACh is made by cells in the centre of the squid’s body.

Explain how it is possible for ACh to have an effect on cells in the skin of the squid.

Squid blood contains a blue oxygen-carrying protein called haemocyanin.

High partial pressures of carbon dioxide reduce the affinity for oxygen of haemocyanin.

Suggest a mechanism by which carbon dioxide could reduce the affinity for oxygen of haemocyanin.