Topic 7 - Mass transport

Question 1

Why are mass transport systems needed

Answer 1

In large multicellular organisms, mass transport systems needed to carry substances between exchange surfaces and rest of body
- Most cells too far away from exchange surfaces/each other for diffusion alone to maintain composition of tissue fluid within suitable metabolic range
- Mass transport maintains final diffusion gradients bringing substances to and from cells
- Mass transport helps maintain relatively stable immediate environment of cells that is tissue fluid

Question 2

Circulatory system

Answer 2

Question 3

Features of circulatory system: Closed double circulatory system - two circuits

Answer 3

• Blood passes through heart twice for each complete circulation of the body

Pulmonary circulation:
- Deoxygenated blood in left side of heart pumped to lungs –> oxygenated blood return to left side of heart

Systemic circulation:
- Oxygenated blood in left side of heart pumped to tissues . organs of body –> deoxygenated blood returns to right side

Important for mammals because:
- Prevents mixing of oxygenated and deoxygenated blood –> so blood pumped to body is fully saturated with oxygen –> efficient delivery of oxygen and glucose for respiration
-Blood can be pumped at higher pressure (after being lower from lungs) –> substances taken to and removed from body cells quicker and more efficiently

Question 4

Features of the circulatory system: Coronary arteries

Answer 4

• Deliver oxygenated blood to cardiac muscle

Question 5

Features of the circulatory system: Blood vessels entering and leaving heart

Answer 5

• Aorta - takes oxygenated blood from heart –> respiring tissues
• Vena cava - takes oxygenated blood from respiring tissues –> heart

Question 6

Features of the circulatory system: Pulmonary artery and vein

Answer 6

Pulmonary artery: takes deoxygenated blood from the heart –> lungs
Pulmonary vein: takes oxygenated blood from the lungs –> heart

Question 7

Features of the circulatory system: Blood vessels entering and leaving kidneys

Answer 7

• Renal arteries - take deoxygenated blood –> kidneys
• Renal veins –> take deoxygenated blood to vena cava from the kidneys

Question 8

Gross structure of the human heart

Answer 8

How the structure of the heart relates to its function:
- Atrioventricular valves = prevent back flow of blood from ventricles to atria
- Semilunar valves = generates higher blood pressure, for oxygenated blood has to travel greater distance around the body
- Right has thinner muscular wall = generates low blood pressure, for deoxygenated blood to travel a small distance to the lungs where high pressure would damage alveoli

Question 9

The structure of arteries is relation to their function

Answer 9

Arteries = carry blood from heart to rest of body at high pressure

Thick smooth muscle layer:
- Contract pushing blood along
- Control/maintain blood flow/pressure

Elastic tissue layer:
- Stretch as ventricle contracts (when under high pressure) and recoil as ventricle relaxes (when under low pressure)
- Reduces pressure surges / even out blood pressure and maintain high pressure

Thick wall:
- Withstands high pressure and presents artery bursting

Smooth (and thin) endothelium:
- Reduces friction

Narrow lumen:
- Increases and maintain high blood pressure

Question 10

The structure of arterioles in relation to their function

Answer 10

Arterioles = division of arteries to smaller vessels which can direct blood to different capillaries / areas

• Note: Similar to that of the arteries

Thicker muscle layer than arteries:
- Constricts to reduce blood flow by narrowing lumen
- Dilates to increase blood flow by enlarging lumen

Question 11

the structure of veins in relation to their function

Answer 11

Veins - carry blood back to the heart under low pressure

Wider lumen than arteries

Very little elastic and muscle tissue

Valves:
- Prevent back flow of blood

Contraction of skeletal muscles squeezes veins, maintaining blood flow

Question 12

Structure of capillaries and the importance of capillary beds as exchange surfaces

Answer 12

• Capillaries allow the efficient exchange of gases and nutrient between blood and tissue fluid
• Capillary wall is once cell thick so there is a short diffusion pathway and so rapid diffusion can occur
• Capillary bed is made of a large network of (branched) capillaries so there is an increased surface area which leads to rapid diffusion
• Narrow lumen reduces the flow rate so more time for diffusion
• No cell is far away form a capillary so there is a short diffusion pathway
• Pores in walls between cells allows substances to escape e.g. white blood cell to deal with infection

Question 13

The formation of tissue fluid and its return to the circulatory system

Answer 13

Tissue fluid = the fluid surrounding cells/tissues
- Provides respiring cells with e.g. water, oxygen, glucose, amino acids
- Enables (waste) substances to move back into the blood e.g. urea, lactic acid, carbon dioxide

The formation of tissue fluid = at arteriole end of capillaries
- Higher blood/hydrostatic pressure inside capillaries than inside tissue fluid
- Forces fluid/water out of capillaries into spaces around cells
- Large plasma proteins remain in capillary (too large to leave)

The return of tissue fluid to the circulatory system - towards venue end of capillaries
- Hydrostatic pressure reduces as fluid leaves capillary
- (Due to water loss,) an increasing concentration of plasma proteins (too large to leave capillaries) lowers the water potential in the capillary below the water the potation of the tissue fluid
- Water (re)enters the capillaries from the tissue fluid by osmosis down a water potential gradient
- Excess water taken up by lymph system (lymph capillaries) and is returned to the circulatory system

Question 14

Pressure and volume changes and associated valve movements during the cardiac cycle that maintain an unidirectional flow of blood

Answer 14

Atrial systole
- Atria contact - decreasing volume and increasing pressure inside atria
- Atrioventricular valves forced open: when pressure inside atria > pressure inside ventricles, atrioventricular valves open
- Blood pushed into ventricles
- Note: semilunar valves are shut

Ventricular systole
- Ventricles contract from the bottom up –> decreasing volume and increasing pressure inside ventricles
- Semilunar valves forced open: when pressure inside ventricles > pressure inside arteries
- Atrioventricular valves shut: When pressure inside ventricles > pressure inside atria
- Blood pushed out of heart through arteries

Diastole
- Atria and ventricles relax –> increasing volume and decreasing pressure inside chambers
- Blood from veins fills atria and flows passively to ventricles
- Atrioventricular valves open: when pressure inside ventricles blood flows passively to ventricles
- Semilunar valves shut: when pressure inside arteries > pressure inside ventricles

Question 15

Cardiac output equation

Answer 15

Cardiac output = stroke volume x heart rate

Cardiac output = amount of blood pumped out the heart per minute

Stroke volume = volume of blood pumped by the ventricles in each heart beat

Heart rate = number of beats per minute

Question 16

Cardiovascular disease and risk factors

Answer 16

Example of cardiovascular disease = coronary heart disease

Often associated with atherosclerosis and atheroma formation

How an atheroma can result in a heart attack
- Atheroma causes narrowing of coronary arteries
- Restricts blood flow to heart muscles supplying glucose, oxygen etc.
- Heart anaerobically respires –> less ATP produced –> not enough energy for heart to contract –> lactate produced –> damages heart tissue / muscle

Risk factors: increases probability of getting disease
- Age
- Diet high in salt or saturated fat
- High consumption of alcohol
- Stressful lifestyle
- Smoking cigarettes
- Genetic factors

High blood pressure increases risk of damage to endothelium of artery wall which increases risk of atheroma which can cause blood clots (thrombus)

Question 17

Haemoglobin

Answer 17

The haemoglobins are a group of chemically similar molecules found in many different organisms:
- Chemical structure may differ between organisms e.g. sequence of amino acids in the primary structure

Found in red blood cells (erythrocytes)
- No nucleus - contain more haemoglobin
- Biconcave shape - increases surface area for rapid diffusion/absorbtion of oxygen

Structure
- Quaternary structure protein - made of 4 polypeptide chains
- Each polypeptide chain contains a Haem group containing an iron ion (Fe2+) which combines with oxygen

Question 18

How oxygen is loaded, transported and unloaded in the blood

Answer 18

Haemoglobin in red blood cells carries/transports oxygen (as oxyhemoglobin)
- Haemoglobin can carry 4 oxygen molecules - one at each haem group

In the lungs, at high pO2, haemoglobin has a high affinity for oxygen –> oxygen readily loads / associates with haemoglobin

At respiring tissues, at a low pO2, oxygen readily unloads / dissociates from haemoglobin
- Also, concentration of CO2 is high, increasing the rate of unloading (Bohr effect - see further on)

Question 19

The loading, transport and unloading of oxygen can be seen in relation to the oxyhaemoglobin dissociation curve

Answer 19

The cooperative nature of oxygen binding - why the graph is ‘s’ shaped

• Haemoglobin has a low affinity for oxygen as the 1st oxygen molecule binds –> so from 0% saturation, an increase in pO2 results in a slow increase in saturation (shallow gradient)
• After the 1st oxygen molecule binds, the shape of haemoglobin changes in a way that makes it easier for the 2nd and 3rd oxygen molecules to bind too, so the haemoglobin now has a higher affinity for oxygen –> the rate of increase in % saturation increases as pO2 further increases (steep gradient)
• After the 3rd molecule binds, and haemoglobin starts to become saturated, the shape of haemoglobin changes in a way that makes it harder for other molecules to bind too –> at high pO2, the rate increase in % saturation decreases

Question 20

The effect of carbon dioxide concentration on the disassociation of oxyhaemoglobin - the Bohr effect

Answer 20

• When rate of respiration is high e.g. during exercise –> releases CO2
• High pCO2 lowers ph and reduces haemoglobin’s affinity for oxygen as haemoglobin changes shape so this increases the rate of oxygen unloading
• Advantageous because provides more oxygen for muscles/tissues for aerobic respiration
• Oxygen disassociation curve for haemoglobin shifts to the right

Question 21

Organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties –> enables organisms to survive better in their environment

Answer 21

Curve shifted left –> haemoglobin has a higher affinity for oxygen
- More oxygen associated with haemoglobin more readily as the lower p02 but dissociates less readily
- Advantageous to organism such as those living in high altitudes, underground

Curve shifted right –> haemoglobin has a lower affinity for oxygen
- Oxygen dissociates from haemoglobin more readily to respiring cells at a higher pO2 but associates less readily
- Advantageous to organisms such as those with a high rate of respiration (metabolic rate) e.g. small/ active organisms

Question 22

The cohesion tension theory of water transport in the xylem

Answer 22

• Cohesion tension theory = How water moves up the xylem against gravity via the transpiration stream
• Water evaporates from the leaves via the open stomata due to transpiration
• Reducing water potential I. the cell and increasing water potential gradient
• Water drawn out of xylem
• Creating tension
• Cohesive forces between water molecules pull water up as a column
• Water loss enter the roots via osmosis
• Water is moving up, against gravity
• Water is also cohesive so sticks to the edges of the column