1.2.2 - Transport in Animals (Circulatory Systems & Cardiac Cycle) Part 5, 6, 7 & 8

Question 1

Explain why the walls of the atria are thinner than the walls of the ventricles.

Answer 1

During atriole systole, a lot of pressure is not need to push the blood to the ventricles. This is because the distance is short as well as the fact that gravity helps the blood flow down to the ventricles. It also follows the pressure gradient.

However, the walls of the ventricles are thicker because they must generate enough pressure in the blood to flow upwards, into the arteries. From there, the blood must flow to the lungs / the rest of the body which is a much larger distance.

Question 2

Explain why a single circulatory system is suited for fish but not for mammals.

Answer 2

• Fish are not as active as mammals and therefore do not need as much energy.
• Their single circulatory system provides the oxygen and nutrients quickly enough for their needs.
• For mammals, the single circulatory system has a lower blood pressure and will not flow very quickly to the rest of the body.
• This means the supply of oxygen and nutrients will not be efficient for them to keep the body warm and to move.

Question 2

Explain why the walls of the left ventricle is much thicker than the walls of the right ventricle.

Answer 2

The right ventricle must pump the deoxygenated blood to the lungs whilst the left ventricle must pump the blood along a longer distance; it must pump blood around the whole body. This means the left ventricle needs a thicker wall of muscle to be able to generate enough pressure to overcome the resistance of the systemic circulation.

Question 3

Explain why there is a flat line in the PR segment:

Answer 3

The flat line represents the delay after the wave of excitation spreads over the atria.

Question 4

Explain the need for transport systems in multicellular animals in terms of size, level of activity anf surface area to volume ratio.

Answer 4

• Size - An animal with several layers of cells will have the oxygen used up by the outer layers of cell as it diffuses in.
• Level of activity - If an animal is very active, it needs a bigger supply of oxygen and nutrients for respiration.
• Surface area : volume ratio - In larger animals, the surface area to volume ratio is relatively small compare to a small oraganism. This means a large organism’s surface area is not large enough to supply all the oxygen it needs.

Question 4

Here is an ECG, where the S wave is very deep. Suggest what this could indicate.

Answer 4

This could indicate abnormal ventricular hypertrophy (increase in muscle thickness). The walls of the ventricle have become stiff making diastole difficult.

Question 5

Describe what happens during ‘ventricular systole’.

Answer 5

Ventricular systole - Ventricular contractions:

• For a short period of time, all the valves are closed.
• The ventricles contract, raising the pressure quickly.
• Contractions star in the apex (base), pushing the blood upwards.
• Blood flows upwards and the semi-lunar valves open.
• The contraction is strong, but very short. This allows more blood to enter the ventricles afterwards.

Question 5

Suggest what could be happening during the T wave:

Answer 5

During the T wave, the heart is going through the diastole phase. The wave of electrical activity represents repolarisation of the ventricles where the ventricle recovers and resets itself.

Question 6

The heart is myogenic. This means is can initiate its own contractions. Describe how the heart action is co-ordinated.

Answer 6

• At the top of the right atrium is the sinoatrial node (SAN). This is a small patch of tissue that generates electrical activity in waves across the atria. After it passes, the atria contract.
• At the base of the atria is a disc of non-conducting tissue which prevents this wave from spreading to the ventricles. There is a delay before the atrioventricular node (AVN) on top of this tissue carries the wave of excitation down the bundle of His to the Purkyne tissue. This is to ensure all the blood is in the ventricles.
• The waves spread upwards at the apex, causing the blood to be pushed upwards.

Question 7

Describe what happens during ‘diastole’.

Answer 7

Diastole - known as the ‘filling phase’:

• Both atria and ventricles are relaxed.
• The internal volume and pressure on the walls of the atria increase as blood flows into the atria.
• The atrio-ventricular valves are open, allowing some blood to flow into the ventricles.

Question 9

Rearrange the order of the terms below so that it describes the path blood takes in a closed circulatory system of a fish. The first two have been done for you.

• Heart
• Arteries
• Heart
• Veins
• Gills
• Body tissues
• Veins

Answer 9

• Heart
• Arteries
• Gills
• Veins
• Body tissues
• Veins
• Heart

Question 11

Define the term ‘single circulatory system’ and give an example of an organism that has this circulatory system.

Answer 11

Single circulatory system - Blood flows in one circuit. For example in a fish, the blood flows from the heart to the gills and then to the body, before returning to the heart again:

HEART —> GILLS —> BODY —> HEART

Question 12

Explain what is happening during the QRS complex:

Answer 12

• From Q—>R: a huge rise in electrical activity signifies the message from the AVN down the septum.
• From R—>S: a dip indicates the waves travelling upwards from the apex.

Question 13

Describe what is happening at the P wave:

Answer 13

The P wave represents the message for contracting the atria where the SAN generates a wave of excitation over the atria.

Question 15

Explain the term ‘open circulatory system’ and describe how this system works in insects such as a locust.

Answer 15

• Open circulatory system - Blood are not enclosed within blood vessels and are therefore free to flow.
• There is a long muscular tube under the dorsal that acts like a heart. It pumps blood to the head by peristalsis.
• From the head, the blood pours into the body cavity.
• Blood enters the heart again through pores (ostia).
• For locusts, there are open ended tubes attached to the heart, directing the blood towards the legs and wings.

Question 16

The P wave on an ECG represents the message for contracting atria. If the P wave on an ECG is unclear, suggest what this could mean.

Answer 16

An unclear P wave could mean atrial fibrilation - where the atria do not contract sufficiently leading to irregular ventricular contractions.

Question 17

Here is an ECG. Looking at the second ECG, the ST segment is elevated. Suggest what could be happening and give a reason for your answer.

Answer 17

Elevation of the ST segment - could be a heart attack.

This shows there is a premature ending of ventricular systole. This means the heart muscles are not retrieving enough blood.

Question 18

Label the diagram:

Answer 18

1. Aorta
2. Vena Cava
3. Pulmonary artery
4. Pulmonary vein
5. Right atrium
6. Right atrio-ventricular valve (tricuspid valve)
7. Right ventricle
8. Inferior vena cava
9. Pulmonary artery
10. Pulmonary vein
11. Left atrium
12. Left atrio-ventricular valve (biscupid)
13. Aortic semi-lunar valve
14. Left ventricle
15. Aorta

Question 19

Define what a ‘double circulatory system’ is and give an example of an organism that has this circulatory system.

Answer 19

Double circulatory system - This involes two separate circuits where blood flows through the heart twice. For example, this is seen in mammals, where:

• One circuit carries blood to the lungs to pick up oxygen - known as the pulmonary circulation.
• And another circuit carries oxygen and nutrients around the body - known as systemic circulation.

Question 20

Describe what happens during ‘atrial systole’.

Answer 20

Atriole systole - atrial contractions:

• Both left and right atria contract at the same time.
• Small pressure pushes all the blood into the ventricles.
• The pressure in the walls of ventricles increase as it fills.
• The atrio-ventricular vavles close.

Question 21

1. Explain the term ‘closed circulatory system’.
2. Why do larger organisms need a closed circulatory system?

Answer 21

1. Close circulatory system - Blood flows within vessels at all times. Instead, a separate fluid (tissue fluid) bathes the cells.
2. Larger organisms need a closed circulatory system because blood remains at a low pressure and flows at a slow rate in an open circulatory system. This means the system will not be sufficient enough to supply the oxygen a large, active organism needs. The blood will also not be able to reach all parts of the body so a closed circulatory system is needed.