✨Module 3: Transport in animals

Question 1

How does a single celled organism gain the oxygen and glucose needed for aerobic respiration?

Answer 1

Oxygen diffuses through cell membrane from high to low conc. This process is passive and doesn’t require energy.
Glucose passes through by facilitated diffusion or active transport.

Question 2

Why do multicellular organisms require a transport system?

Answer 2

As organisms get larger, diffusion alone cannot supply the body with enough O2 and nutrients. CO2 also cannot be removed quick enough.

Question 3

Open vs closed circulatory system.

Answer 3

Open - blood flows freely through body cavities.
Closed - blood flows through vessels such as arteries and veins.

Question 4

Define body cavity.

Answer 4

A fluid-filled space inside the body that holds and protects internal organs.

Question 5

Cons of having an open circulatory system?

Answer 5

=> Blood pressure is much lower so slower delivery of oxygen and nutrients to tissues.
=> Difficult to regulate blood flow to specific tissues or organs.

Question 6

Compare single closed and double closed circulatory system.

Answer 6

Single - blood passes through heart once in one circuit, blood passes through 2 capillary networks before returning to the heart.

Double - blood passes through heart twice in one circuit, blood passes through 1 capillary network before returning to the heart. This system maintains higher blood pressure and average speed flow, as when blood enters a capillary network the pressure and speed drop a lot. This maintains a steeper concentration gradient which allows efficient exchange of nutrients and waste with surrounding tissues.

Double circulatory system keeps oxygenated blood and deoxygenated blood separate.

Question 7

How does the single closed circulatory system in fish work?

Answer 7

The heart pumps deoxygenated blood to gills. The gills are the exchange site for O2 and CO2 with the environment. Oxygenated blood flows from the gills to the rest of the body. The heart only has one atrium and one ventricle.

Question 8

Open circulatory system in insects?

Answer 8

The tubular heart in the abdomen pumps haemolymph (insect blood) into the dorsal vessel running along the back of the insect.
The dorsal vessel delivers the haemolymph into the haemocoel (body cavity). Haemolymph surrounds the organs and eventually re-enters the heart via one-way valves called ostia.

Question 9

Describe the structure and function of arteries.

Answer 9

=> Transports blood away from the heart.
=> They carry oxygenated blood apart from the pulmonary artery.
=> Arteries have a narrow lumen to carry blood at high pressure.
=> Artery walls consist of three layers: tunica externa, tunica media, tunica intima.
=> Artery walls contain elastic fibres (stretch and recoil to provide flexibility), smooth muscle (contracts and relaxes to change the size of lumen), collagen (provides structural support).
=> Arteries have a pulse.

=> Tunica intima is made up of an endothelial layer, a layer of connective tissue and a layer of elastic fibres. The endothelium is one cell thick and lines the lumen of all blood vessels. It is very smooth and reduces friction for free blood flow.
=> Tunica media is made up of smooth muscle, elastic tissue.

Question 10

What are arterioles?

Answer 10

Arterioles connect the arteries and capillaries.
Unlike arteries, arterioles have less elastic fibres and lots of smooth muscle, which contracts and closes the lumen to prevent blood flow to capillary bed (vasoconstriction).

Question 11

Describe the structure and function of veins.
Adaptations of veins?

Answer 11

=> Carries deoxygenated blood apart from pulmonary vein.
=> Transports blood to heart at low pressure.
=> Large lumen reduces friction between blood and endothelial layer.
=> Veins have valves to prevent backflow.
=> Wall has lots of collagen.

Question 12

Structure of capillaries and adaptations.

Answer 12

=> They link the arterioles to venules.
=> Capillaries have a very small lumen, forcing blood to travel slowly which allows more diffusion.
=> White blood cells can combat infection in affected tissues by squeezing through pores in the capillary walls.

=> Capillaries have a large SA for diffusion of substances in and out of the blood.
=> Capillary wall is only 1 cell thick so substances can diffuse between blood and cells quickly.

Question 13

Route of blood travel.

Answer 13

Arteries -> Arterioles -> Capillaries -> Venules -> Veins

Question 14

Describe what blood is and its function.

Answer 14

A tissue that consists of a yellow liquid called plasma that carries lots of components. Blood transports:
=> O2 and CO2
=> Chemical messengers like hormones
=> Platelets to damaged areas
=> Antibodies in the immune response

Question 15

What is tissue fluid and why is it important?

Answer 15

Colourless fluid that surrounds body cells and tissues. It’s derived from blood plasma and contains water, ions, nutrients, and waste products. Tissue fluid plays a crucial role in delivering nutrients and oxygen to cells, and collecting waste products for removal.

Blood → Tissue fluid → Cells

Question 16

What is oncotic pressure?

Answer 16

Substances in plasma can pass into the capillaries. This gives capillaries a high solute conc, so water moves from blood into the capillaries by osmosis. This is oncotic pressure.

Question 17

What happens at the arterial end of the capillary?

Answer 17

As blood flows from arterioles into capillaries, it’s under high hydrostatic pressure from contraction of heart, forcing fluid out of the capillaries => tissue fluid. Tissue fluid has the same composition as plasma except RBC’s and plasma proteins (too big to pass through pores in capillary walls). The increased protein content creates a water potential gradient between the capillary and the tissue fluid.

Hydrostatic pressure > Oncotic pressure
Net outflow of water/plasma out of the capillary to form tissue fluid, taking with it oxygen, amino acids, glucose, fatty acids.

Question 18

What happens at the venous end of the capillary?

Answer 18

The hydrostatic pressure within the capillary is reduced due to increased distance from the heart and the slowing of blood flow as it passes through the capillaries.

Hydrostatic pressure < Oncotic pressure
Net inflow of water/plasma into capillary with O2 and urea.

Roughly 90 % of the fluid lost at the arterial end of the capillary is reabsorbed at the venous end. The other 10 % remains as tissue fluid and is eventually collected by lymph vessels and returned to the circulatory system/heart.

Question 19

Higher blood pressure means …

Answer 19

Pressure at the arterial end is even greater. This pushes more fluid out of the capillary and fluid begins to accumulate around the tissues. This is called oedema.

Question 20

What is the lymph and the function of the lymphatic system?

Answer 20

Most tissue fluid re-enters the capillaries, but some enters the lymph vessels. Lymph has similar composition to plasma and tissue fluid but has less oxygen and nutrients. It also contains fatty acids that have been absorbed from the villi of the small intestine.

Larger molecules that are not able to enter the capillary enter the lymphatic system. If plasma proteins were not removed from tissue fluid they could lower the water potential (of the tissue fluid) and prevent the reabsorption of water back into capillaries.

Functions:
=> Home for lymphocytes.
=>The lymphatic system collects excess fluid that leaks from blood capillaries and returns it to the bloodstream, preventing fluid build up in tissues (oedema),.

Question 21

Describe three ways in which the composition of tissue fluid is different to the composition of plasma.

Answer 21

In plasma there is:
A higher concentration of glucose, glycerol + fatty acids, plasma proteins, oxygen. A lower water potential.

In tissue fluid there is:
A higher concentration of CO2, urea, water, white blood cells.

Question 22

Role of valves in the heart?

Answer 22

Open when the pressure of blood behind them is greater than the pressure in front of them.
Close when the pressure of blood in front of them is greater than the pressure behind them.

Question 23

Coronary arteries?

Answer 23

Coronary arteries supply cardiac muscle cells with nutrients/glucose/O2 and remove waste products.
It’s important that these arteries don’t have plaques, as this could lead to angina or a heart attack (myocardial infarction).

Question 24

What are the symptoms of liver disease?

Answer 24

1. Ascites - fluid building up in abdomen.
2. Jaundice - yellowing of skin and eyes due to the yellow pigment bilirubin.
3. Oesophageal varices - vomiting blood.
4. Edema - swelling in legs and feet.

Question 25

Describe the cardiac cycle.

Answer 25

Systole - contraction of heart. Atria contract, closely followed by ventricles. Pressure in arteries is at max. Diastole - relaxing of heart. Atria fill with blood. Arteries pressure is at minimum.

Question 26

Atrial systole

Answer 26

Walls of the atria contract: Atrial volume decreases Atrial pressure increases The pressure in the atria rises above that in the ventricles, forcing the atrioventricular (AV) valves open. Blood is forced into the ventricles.. The ventricles are relaxed at this point.

Question 27

Ventricular systole.

Answer 27

Walls of the ventricles contract: Ventricular volume decreases Ventricular pressure increases The pressure in the ventricles rises above that in the atria, so AV valves shut. The pressure in the ventricles rises above that in the aorta and pulmonary artery, so aortic valve and pulmonary valve opens and blood is forced into aorta and pulmonary artery. Aortic valve and pulmonary valve are semi-lunar valves. During this period, the atria are relaxing. Relaxed atria begin to fill with blood again.

Question 28

Diastole

Answer 28

The ventricles and atria are both relaxed. Pressure in ventricles drops below that in the aorta and pulmonary artery, so SL valve closes. Beginning of diastole - Left ventricle has been emptied of blood Muscles in the walls of the left ventricle relax and pressure falls below that in the newly filled aorta Early diastole - The ventricle remains relaxed and ventricular pressure continues to decrease In the meantime, blood is flowing into the relaxed atrium from the pulmonary vein, causing an increase in pressure Aortic valve closes The atria continue to fill with blood Blood returns to the heart via the vena cava and pulmonary vein Pressure in the atria rises above that in the ventricles, forcing the AV valves open. Blood flows passively into the ventricles without need of atrial systole. Late diastole - There is a short period of time during which the left ventricle expands due to relaxing muscles This increases the internal volume of the left ventricle and decreases the ventricular pressure At the same time, blood is flowing slowly through the newly opened AV valve into the left ventricle, causing a brief decrease in pressure in the left atrium The pressure in both the atrium and ventricle then increases slowly as they continue to fill with blood The cycle then begins again with atrial systole.

Question 29

Define cardiac output.

Answer 29

Volume of blood pumped out of the left ventricle per minute. Fitter people have higher cardiac outputs as they have stronger ventricular muscles.

Question 30

Define heart rate.

Answer 30

Number of times the heart beats per minute.

Question 31

Define stroke volume.

Answer 31

Volume of blood pumped out of the left ventricle in one cardiac cycle.

Question 32

How to calculate cardiac output?

Answer 32

Heart rate x stroke volume

Question 33

Why is heartbeat control described as myogenic?

Answer 33

The heart will beat without any external stimulus.

Question 34

How are heartbeat sounds made?

Answer 34

Blood pressure closing the heart valves. It sounds like 'lub-dub'. The first sound is due to AV valves closing due to ventricular systole. The second sound is due to the closing of the semi-lunar valves and aortic valves due to diastole.

Question 35

Explain the roles of the sinoatrial node, the atrioventricular node and the Purkinje fibres in a heartbeat.

Answer 35

=> SAN is the pacemaker area located in upper wall of the right atrium that initiates a wave of excitation, causing both atria to contract, causing atrial systole. => Non-conducting tissue called the Annulus fibrosus prevents the excitation/depolarisation from spreading to the ventricles and so this ensures that atria and ventricles don’t contract at the same time. => The atrioventricular node (a region of conducting tissue) receives the electrical activity and then sends the wave of excitation along the Bundle of His (conducting tissue) to the ventricles after a short delay, ensuring that the atria have time to empty their blood into the ventricles. => The bundle of His divides into two conducting fibres, called Purkinje tissue. The Purkinje fibres spread around the ventricles and conduct the excitation down the septum of the heart to the apex (bottom). This makes the ventricles contract and blood is forced upwards and out of the pulmonary artery and aorta. If Purkinje fibres are blocked, it would lead to atrial fibrillation => irregular heartbeat.

Question 36

How is oxygen and CO2 transported around the body?

Answer 36

Each haemoglobin contains 4 haem groups, each bonded with 1 molecule of oxygen. Oxygen + haemoglobin = Oxyhaemoglobin (reversible reaction) The binding of the first O2 molecules results in a change in structure of haemoglobin, making it easier for each successive O2 to bind. This is coorperate binding. When haemoglobin is mostly saturated with oxygen, it is harder for more oxygen to bind CO2 diffuses from the tissues into the blood. After that, CO2 can bind to haemoglobin to form carbaminohaemoglobin. Or CO2 is transported in the form of hydrogen carbonate ions.

Question 37

Describe how these hydrogen carbonate ions are formed from CO2. NEED TO REMEMEBER.

Answer 37

1. CO2 diffuses from plasma into red blood cells. 2. Inside RBC's: CO2 + H2O = H2CO3. Enzyme carbonic anhydrase present in RBC's catalyses this. Plasma contains a small proportion of carbonic anhydrase so H2CO3 forms more slowly in plasma than in the cytoplasm of RBC's. 3. Carbonic acid (H2CO3) readily dissociates into H+ and HCO3- ions. 4. H+ ions can combine with haemoglobin, forming haemoglobinic acid and preventing H+ ions from lowering the pH of the red blood cell. Haemoglobin is said to act as a buffer here. 5. The hydrogen carbonate ions diffuse out of the red blood cell into the blood plasma where they are transported in solution. By removing CO2 and converting it to hydrogen carbonate ions, the erythrocytes maintain a steep concentration gradient for CO2 to diffuse from respiring tissues into the erythrocytes. Haemoglobin in erythrocytes act as a buffer int his process by accepting free H+ ions in a reversible reaction to form haemoglobinic acid.

Question 38

What is the chloride shift? How is this produced?

Answer 38

Movement of chloride ions into red blood cells when hydrogen carbonate ions are formed. Negatively charged hydrogen carbonate ions formed from the dissociation of carbonic acid are transported out of red blood cells via a transport protein in the membrane To prevent an electrical imbalance, negatively charged chloride ions are transported into the red blood cells via the same transport protein If this did not occur then red blood cells would become positively charged as a result of a build-up of hydrogen ions formed from the dissociation of carbonic acid.

Question 39

What is the Bohr shift?

Answer 39

Occurs when a high partial pressure of carbon dioxide causes haemoglobin to release oxygen into respiring tissues, as haemoglobin loses affinity for oxygen. When carbon dioxide levels rise or the pH drops, the hemoglobin molecule undergoes a conformational change, making it less likely to bind to oxygen. This shift in the oxygen-hemoglobin dissociation curve to the right means that at any given partial pressure of oxygen, the percentage saturation of hemoglobin is lower at higher CO2 levels.

Question 40

What is the oxygen dissociation curve?

Answer 40

Shows the rate at which oxygen associates, and also dissociates, with haemoglobin at different partial pressures of oxygen (pO2). The graph shows the affinity of haemoglobin to oxygen. Partial pressure of oxygen refers to the pressure exerted by oxygen within a mixture of gases; it is a measure of oxygen concentration. Haemoglobin is referred to as being saturated when all of its oxygen binding sites are taken up with oxygen; so when it contains four oxygen molecules. The ease with which haemoglobin binds and dissociates with oxygen can be described as its affinity for oxygen. => When haemoglobin has a high affinity it binds easily and dissociates slowly. => When haemoglobin has a low affinity for oxygen it binds slowly and dissociates easily. In other liquids, such as water, we would expect oxygen to becomes associated with water, or to dissolve, at a constant rate, providing a straight line on a graph, but with haemoglobin oxygen binds at different rates as the pO2 changes; hence the resulting curve. It can be said that haemoglobin's affinity for oxygen changes at different partial pressures of oxygen. Higher pO2 - Haemoglobin has a high affinity for oxygen and binds with it (e.g. in the lungs). Lower pO2/higher pCO2 - Haemoglobin has a low affinity for oxygen and releases it (e.g. at respiring body cells).

Question 41

Explain the shape of the oxygen dissociation curve. Draw curve in notes.

Answer 41

1. Due to the shape of the haemoglobin molecule it is difficult for the first oxygen molecule to bind to haemoglobin; this means that binding of the first oxygen occurs slowly, resulting in a shallow curve at the bottom left corner of the graph. 2. After the first O2 binds to haemoglobin, haemoglobin changes shape to make it easier for next O2 to bind. Results in a steeper part of the curve in the middle of the graph. This is known as cooperative binding. 3. As the haemoglobin molecule approaches saturation it takes longer for the fourth oxygen molecule to bind due to the shortage of remaining binding sites, explaining the levelling off of the curve in the top right corner of the graph. haemoglobin is saturated.

Question 42

What is fetal haemoglobin?

Answer 42

-> Has a higher affinity for oxygen than adult haemoglobin, so allows a foetus to obtain oxygen from its mother's blood at the placenta. -> Foetal haemoglobin can bind to oxygen at low pO2. At this low pO2 the mother's haemoglobin is dissociating with oxygen. Fetus removes oxygen from the maternal blood as the oxygenated blood of mother and deoxygenated blood of fetus move past each other. -> On a dissociation curve graph, the curve for foetal haemoglobin shifts to the left of that for adult haemoglobin. This means that at any given partial pressure of oxygen, foetal haemoglobin has a higher percentage saturation than adult haemoglobin. -> After birth, a baby begins to produce adult haemoglobin which gradually replaces foetal haemoglobin.

Question 43

Effect of altitude on the type and shape of haemoglobin. (may not need to know).

Answer 43

The partial pressure of oxygen is lower at higher altitude. Species living at high altitudes have haemoglobin that is adapted to these conditions. For example, llamas have haemoglobin that binds very readily to oxygen. This is beneficial as it allows them to obtain a sufficient level of oxygen saturation in their blood when the partial pressure of oxygen in the air is low.