EQ's

Question 1

Explain how the alveoli create a surface for efficient gas exchange

[5 marks]

Answer 1

• The large number of alveoli means that they have a large surface area which means that the rate of diffusion is fast enough to supply enough oxygen and to remove carbon dioxide to prevent build-up
• The alveoli are covered in a thin layer of lung surfactant which prevents the alveoli from collapsing
• The alveoli are made up of a thin layer of squamous epithelial tissue which provides a short diffusion pathway which increases the rate and efficiency of gas exchange
• The alveoli contain elastic fibres which STRETCH and recoil to help with the ventilation of the alveoli and move air out of them
• The alveoli have a good blood supply which maintains a steep concentration gradient of carbon dioxide and oxygen for gas exchange

[5 marks]

Question 2

In a condition known as supraventricular tachycardia, electrical signals leak from the atrial
walls directly to the** top of the ventricles**. This causes the ventricle walls to contract twice for every atrial contraction.
Explain the effect that supraventricular tachycardia may have on blood flow from the heart

[2 marks]

Answer 2

• It will reduce the amount of blood flowing from the heart
• As the ventricles aren’t full before contracting

Question 3

The blood circulatory system of a mammal undergoes changes at, or soon after, birth.
One of these changes is that the foramen ovale, a hole in the septum between the right and left atria, closes. In the fetus, the foramen ovale allows blood to flow directly from the right atrium to the left atrium.
Suggest why the foramen ovale is open in the fetus before birth

Answer 3

• The lungs in the foetus are not functioning
• The foetus has a single circulatory system

[2 marks]

Question 4

Another change occurring after birth is that fetal haemoglobin is replaced with adult
haemoglobin.
State one difference between fetal haemoglobin and adult haemoglobin and give one
reason why this difference is essential to the fetus.

[2 marks]

Answer 4

• The foetal Hb has a higher affinity for oxygen
• It needs to able to bind to oxygen in the lowER partial pressure of the placenta

Question 5

Deinf health

[2 marks]

Answer 5

• Physical and metal wellbeing
• The absence of disease

Question 5

High concentrations of carbon dioxide in the blood reduce the amount of oxygen transported by haemoglobin.
Name this effect and explain why it occurs.

[3 marks]

Answer 5

• Bohr effect
• A high concentration of carbon dioxide lowers the oxygen affinity of Hb
• And so it releases more oxygen where it’s needed

Question 6

Sickle cell anaemia is an inherited disorder in which haemoglobin crystallises when the
partial pressure of oxygen (pO2) is low. The red blood cells change shape and oxygen
transport is disrupted.

Treatment with drugs, such as hydroxyurea, can stimulate adults to produce fetal
haemoglobin rather than adult haemoglobin.
Suggest why this treatment might be of benefit to adults with sickle cell anaemia

[2 marks]

Answer 6

• The foetal Hb will not crystalise as much
• As it has a higher affinity for oxygen and will pick up and bind to more oxygen than sickle cell Hb

Question 7

Describe and explain how substances that are dissolved in the blood plasma, such as oxygen
or glucose, enter the tissue fluid from the capillaries.

[4 marks]

Answer 7

• There is a higher concentration of these substances in the blood plasma than in the tissue fluid and so they diffuse out
• of the blood plasma from a high concentration to a low concentration
• The hydrostatic pressure in the capillaries is higher than in the tissue fluid and so the fluid in the capillaries is forced out of the capillaries, down the pressure gradient