Section 3 - Unit 7: Mass Transport Flashcards
Explain how oxygen is loaded, transported and unloaded in the blood (6 marks)
- Haemoglobin carries oxygen
- Uptake in lungs;
- At high p.O2;
- Releases to respiring cells
- At low p.O2;
- Unloading linked to higher carbon dioxide concentration
Describe the path by which oxygen goes from an alveolus to the blood (2 marks)
- Through alveolar epithelium
- Through capillary epithelium
Describe how ventilation helps to maintain a difference in oxygen concentration in the lungs (2 marks)
- Brings in air containing a higher oxygen concentration
- Removes air with a lower oxygen concentration
Suggest why blood returning to the heart from the lungs contains some carbon dioxide (2 marks)
- Concentrations reach equilibrium
- Diffusion occurs when there is a concentration gradient
State two ways in which blood plasma is different from tissue fluid (2 marks)
- Larger proteins
- More glucose
Explain how the left ventricle causes the blood to be at high pressure (1 mark)
- It contracts
Explain why blood pressure decreases along the length of the capillary (2 marks)
- Loss of fluid/volume
- Friction/resistance of capillary wall
Explain how the shape of a red blood cell allows it to take up a large amount of oxygen in a short time (2 marks)
- Large surface area to volume ratio
- For diffusion
Explain why producing a much higher ventricular blood pressure than normal can cause tissue fluid to build up outside the blood capillaries (2 marks)
- More fluid forced out of blood/capillary
- Less fluid returns back to the capillary (due to high blood pressure)
Suggest how widening of blood vessels can reduce ventricular blood pressure (2 marks)
- Larger lumen
- This reduces blood pressure (less friction)
State which blood vessel carries oxygenated blood away from the heart (1 mark)
- Aorta
State which blood vessel carries deoxygenated blood to the heart (1 mark)
- Vena Cava
Explain how the highest blood pressure is produced in the left ventricle (1 mark)
- Strongest/stronger contractions
Suggest why having a hole between the right and the left ventricles means that sufficient oxygen doesn’t reach the rest of the body tissues (2 marks)
- Oxygenated and deoxygenated blood mix
- So a lower volume of oxygenated blood leaves left ventricle
Describe the role of haemoglobin in supplying oxygen to the tissues of the body (2 marks)
- Oxyhaemoglobin formed/haemoglobin is loaded/associates with oxygen in area of higher ppO2
- Oxygen is unloaded in an area of lower ppO2 (in tissues)
Explain how tissue fluid is formed (2 marks)
- Outward pressure of 3.2 kPa
- Forces small molecules out of capillary
Explain how high blood pressure leads to an accumulation of tissue fluid (3 marks)
- High blood pressure = high hydrostatic pressure
- This increases outward pressure from (arterial) end of capillary
- So more tissue fluid formed/less tissue fluid is reabsorbed
Explain why the water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary (3 marks)
- Water has left the capillary
- Proteins in blood are too large to leave capillary
- Increasing concentration of blood proteins (and thus water potential)
Explain the function of the coronary arteries (2 marks)
- Carries oxygen/glucose
- To heart muscle/tissues/cells
Explain why although the speed of blood flow in an arteriole is greater than the speed of blood flow in a capillary, blood does not accumulate in the arterioles (1 mark)
- Area of capillaries is much larger than arterioles
Other than causing slow blood flow, explain one advantage of capillaries being narrow (1 mark)
- Fast diffusion
What factor limits the minimum internal diameter of the lumen of a capillary (1 mark)
- Diameter of blood cell
Explain why the volume of blood leaving the capillary network into the veins is less than the volume of blood entering from the arteries (1 mark)
- Fluid in tissue fluid
Explain the importance of maintaining a constant blood pH (3 marks)
- Haemoglobin protein in blood is sensitive to pH
- Resultant change of tertiary structure
- So less oxygen binds to haemoglobin
Explain the advantage of the oxygen dissociation curve for haemoglobin shifting to the right during vigorous exercise (3 marks)
- Lower affinity for oxygen
- Faster unloading to muscles/tissues/cells
- For rapid respiration
Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta (5 marks)
- Atrium has higher pressure than ventricle causing atrioventricular valves to open
- Ventricle has higher pressure than atrium causing atrioventricular valves to close
- Ventricle has higher pressure than aorta causing semilunar valve to open
- Higher pressure in aorta than ventricle causing semilunar valve to close
- Contraction causes increase in pressure
The oxygen dissociation curve of the fetus is to the left of that for its mother - explain the advantage of this for the fetus (2 marks)
- Higher affinity/partial pressure
- So oxygen moves from mother to fetus
Name the blood vessel to which an artificial heart is connected (1 mark)
- Aorta
Suggest why the artificial heart mainly helps the left ventricle and not the right ventricle (2 marks)
- Left ventricle pumps to whole body
- So it does most work/produces a greater pressure
Suggest why the pulse felt can be used to measure heart rate (2 marks)
- The pulse is caused by pressure
- From one contraction
Explain why an arteriole is described as an organ (1 mark)
- Made up of more than one tissue
Explain how muscle fibres in an arteriole reduce blood flow to capillaries (2 marks)
- The muscle contracts
- And narrows the capillaries
Give the advantage of blood flow in capillaries being slow (1 mark)
- More time for exchange of substances
Explain why a lack of protein in the blood causes a build up of tissue fluid (3 marks)
- Water potential in capillary not as low
- So no water removed into capillary
- By osmosis, causing the build up of tissue fluid
Explain why the values for the pressure in the xylem are negative (1 mark)
- Inside xylem lower than atmospheric pressure
Explain the difference in thickness between the pulmonary artery and the pulmonary vein (2 marks)
- Artery is thicker
- Higher pressure/more muscle
Explain why the thickness of the aorta wall changes all the time during each cardiac cycle (3 marks)
- Aorta wall stretches when heart contracts/systole
- Aorta wall recoils when heart relaxes/diastole
- Maintains smooth pressure
Describe how tissue fluid is formed and how it is returned to the circulatory system (6 marks)
Formation:
- Hydrostatic pressure
- Forces water/fluid out
- Large proteins remain in capillary
Return:
- Low water potential in capillary/blood
- Due to (plasma) proteins
- Water enters capillary/blood
- By osmosis
- Correct reference to lymph
In which one of the four chambers of the human heart does pressure reach the highest value (1 mark)
- Left ventricle
Explain how the structure of the left ventricle causes high pressure (1 mark)
- Thick walls
Explain what causes the maximum pressure in the ventricle to be much higher than that in the atrium (2 marks)
- Ventricle has thicker muscle
- So the contractions are stronger
Explain how tissue fluid is returned to the circulatory system (3 marks)
- Hydrostatic pressure lower in capillary/blood
- Water returns
- By osmosis
- Water potential lower in blood/capillary
- Due to protein in blood
- Returns via lymph system/vessels
When a wave of electrical activity reaches the AVN, there is a short delay before a new wave leaves the AVN. Explain the importance of this short delay (2 marks)
- Allows atria to empty/contract
- Before ventricles contract
Explain how the structures of the walls of arteries and arterioles are related to their functions (6 marks)
Elastic tissue:
- Stretches under pressure then recoils
- Evens out pressure/flow
Muscle:
- Contracts to reduce diameter of lumen
- Changes flow/pressure
Epithelium:
- Smooth
- Reduces friction/blood clots
Explain the importance of elastic fibres in the wall of the aorta (2 marks)
- Stretches under high pressure/during systole and recoils under low pressure/during diastole
Explain the importance of muscle fibres in the wall of an arteriole (2 marks)
- Muscle contracts
- Arteriole narrows
Explain the relationship between the surface area to volume ratio of mammals and the oxygen dissociation curves of their haemoglobins (4 marks)
- Smaller mammal has greater surface area to volume ratio
- Smaller mammal has more heat lost
- Smaller mammal has greater rate of respiration
- Oxygen required for respiration so haemoglobin releases more oxygen
Describe how the cardiac cycle is controlled by the sinoatrial node (SAN) and the atrioventricular node (AVN) (5 marks)
- SAN initiates heartbeat/acts as a pacemaker/
- SAN sends wave of electrical activity/impulses across atria causing atrial contraction
- AVN delays electrical activity/impulses
- Allowing atria to empty before ventricles contract
- AVN sends wave of electrical activity/impulses down
- Causing ventricles to contract from base up/ventricular systole
Describe and explain how an increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin (2 marks)
- Increase in/more carbon dioxide
- Curve moves to the right
Describe the role of the sinoatrial node (2 marks)
- Sends out electrical activity/impulses
- Initiates the heartbeat/acts as a pacemaker
Explain how blood in a vein in the leg is returned to the heart (6 marks)
- Muscles surrounding veins contract and press on walls of vein and squeezes blood along veins
- Valves prevent backflow
- Systole/contraction of heart pumps blood through arteries into veins
- Recoil of heart muscle during diastole
- Draws blood from veins into atria
- Wide lumen little resistance/friction
Explain how oxygen in a red blood cell is made available for respiration in active tissues (3 marks)
- Respiration increases carbon dioxide concentration
- So it increases the rate at which oxygen is dissociated
- There’s a low partial pressure of oxygen in tissues
- So oxygen diffuses from rbc to tissues
Give one way in which the structure of the wall of an artery is similar to the structure of the wall of a capillary (1 mark)
- Both have epithelium
Explain what is meant by the term partial pressure (1 mark)
- Measure of the concentration of a gas
Give two ways in which the total oxygen supplied to muscles during exercise is increased (2 marks)
- Increased heart rate
- Vasodilation of arterioles
Describe and explain how water is exchanged between the blood and tissue fluid as blood flows along the capillary (4 marks)
- HP forces water out
- HP is “higher” than WP
- Proteins remain in blood and this increases WP
- WP is now “higher” than HP
- So water returns by osmosis
- Water moves out at arteriole end and back in (at venule end)
Suggest and explain some xerophytic features that leaves of a plant may have (4 marks)
- Hairs so ‘trap’ water vapour so water potential gradient decreased
- Stomata grooves to ‘trap’ water vapour so water potential gradient decreased
- Thick waxy layer so diffusion distance increased
- Waxy cuticle reduces evaporation/transpiration
- Curled leaves to ‘trap’ water vapour and so water potential gradient decreased
- Needles to reduces surface area to volume ratio
Suggest two reasons why the rate of water uptake by a plant might not be the same as the rate of transpiration (2 marks)
- Water used for support
- Water used in photosynthesis
- Water used in hydrolysis
- Water produced during respiration
Describe the processes involved in the transport of sugars in plant stems (5 marks)
- At source sucrose is actively transported into the phloem/sieve element/tube
- By companion cells
- Lowers water potential in phloem/sieve element/tube and water enters by osmosis
- Produces high hydrostatic pressure
- Mass flow towards sink/roots
- At sink/roots sugars are removed
Describe how a high pressure is produced in the leaves (3 marks)
- Water potential becomes lower
- So water enters phloem by osmosis
- Increased volume of water causes increased pressure
Describe the mass flow hypothesis for the mechanism of translocation in plants (4 marks)
- In source/leaf sugars actively transported into phloem
- By companion cells
- This lowers water potential of sieve cell/tube and water enters by osmosis
- Increase in pressure causes mass movement towards sink/root
- Sugars used/converted in root for respiration for storage
Explain one way in which sieve cells are adapted for mass transport (2 marks)
- Few organelles
- So more flow
Explain why the transpiration rate increases when the temperature increases (2 marks)
- Molecules have more kinetic energy
- So faster diffusion of water
Give two precautions when setting up the potometer to obtain reliable measurements of water uptake by the plant shoot (2 marks)
- Cut shoot under water
- Ensure no air bubbles are present
Give two reasons why the potometer does not truly measure the rate of transpiration (2 marks)
- Water used in photosynthesis
- Water produced in respiration
- Water used to provide turgidity
Explain why the diameter of the trunk is smallest at midday (6 marks)
- Diameter of trunk minimal at warmest time of day
- Stomata open in light → so more water loss
- Water evaporates more when warm / more heat energy for water evaporation
- Hydrogen-bonding between water molecules/cohesion
- Adhesion between water molecules and walls of xylem vessels
- Xylem pulled inwards by faster flow of water/pulled in by tension
Explain how xylem tissue is adapted for its function (4 marks)
- Long cells/tubes with no end walls
- continuous water columns
- No cytoplasm / no organelles
- To obstruct flow
- Lignin
- Withstands tension/waterproof
- Pits in walls
- Allow lateral movement
Describe how water is moved through a plant according to the cohesion-tension hypothesis (4 marks)
- Water evaporates from leaves
- Reduces water potential in cell/water potential gradient across cells
- Water is drawn out of xylem
- Water creates tension
- Cohesive forces between water molecules
- Water pulled up as a column
Explain why a transpiration stream will still continue even if the cells are killed (2 marks)
- Xylem is non-living tissue
- No energy is needed/passive process
Explain the advantage of xerophytic plants having sunken stomata (2 marks)
- Reduces water loss/transpiration
- Reduced water potential gradient
Explain why binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind (2 mark)
- Binding of first oxygen changes tertiary structure of haemoglobin
- Uncovers another binding site
Explain the Bohr effect (5)
- the higher the rate of respiration, the more CO₂ produced
- this lowers ppO₂
- due to increase in carbonic acid, Hb’s tertiary structure changes (due to more H+) so there is a lower affinity for O₂
- this means that Hb’s shape is more loose so oxygen can be unloaded quickly at respiring muscles
- therefore the curve shifts to the right
Equation for cardiac output (1)
CO = stroke volume x heart rate
Give three reasons why organisms need a transport system (3)
- Larger animals have a smaller SA:V ratio so gas exchange via diffusion through skin is not very effective
- Most cells are far away from exchange surfaces
- Maintains diffusion gradient, bringing substances to and from cells
Explain why mammals have a double circulatory system (4)
- Blood flows through heart twice
- When it goes to the lungs, pressure drops and so circulation is slow
- Pumping through heart twice maintains pressure and prevents mix up of oxygenated and deoxygenated blood
- High pressure vital for effective transportation of blood around the body
Describe and explain four ways in which the structure of a capillary adapts it for the exchange of substances between blood and the surrounding tissue (4 marks)
- Permeable membrane
- Thin / single cell thick walls which reduce diffusion distance
- Flattened endothelial cells which reduce diffusion distance
- Small diameter increase SA:V
- Narrow lumen reduces flow rate, increasing diffusion time
Explain how the structures of the walls of arteries, veins and capillaries are related to their functions (6 marks)
Artery:
- Thickest wall, enabling it to carry blood at high pressure
- Most elastic tissue which maintains pressure
- Muscle to control blood flow
Vein:
- Thin wall as it does not need to withstand high pressure
Capillary:
- Thin wall allowing diffusion
- Only endothelium present, allowing short diffusion pathway
All vessels:
- Have endothelium which reduces friction
Mammals such as a mouse and a horse are able to maintain a constant body temperature. Use your knowledge of surface area to volume ratio to explain the higher metabolic rate of a mouse compared to a horse (3 marks)
Mouse
- Larger surface area to volume ratio
- More/faster heat loss
- Faster rate of respiration/metabolism releases heat (to replace heat loss)
Suggest why the transpiration rate increases when the air is moving as opposed to when the air is still (2 marks)
- Removes water vapour / moisture / saturated air
- Increases water potential gradient / more diffusion / more evaporation
Suggest why the transpiration rate increases with a higher temperature (2 marks)
- Increases kinetic energy so water molecules move faster
- Increases diffusion / evaporation
Explain why the rate of water movement through the xylem increases between 06.00 and 12.00 hours (2 marks)
- Stomata open and photosynthesis increases / transpiration increases
- More water pulled up due to cohesion between water molecules / by cohesion tension
Suggest why the diameter of a tree trunk is less at 12.00 hours than at 15:00 hours (2 marks)
- Water pulled up trunk / moves up at fast rate under tension
- Sticking / adhesion (between water and) walls / pulls xylem in
Explain the importance of elastic fibres in the wall of the aorta (2 marks)
- Stretches under high pressure / when ventricle contracts / springs back’ under low pressure / when ventricle relaxes
- Smooths blood flow / maintains blood pressure / reduces pressure surges
Explain the importance of muscle fibres in the wall of an arteriole (2 marks)
- (Muscle) contracts
- (Arteriole) constricts / narrows / reduces blood flow (to capillaries)
