exchange of substances

Question 1

what is the equation for diffusion rate?

Answer 1

SA x conc. gradient/ diffusion pathway

Question 2

how can you maximise diffusion rate using the equation?

Answer 2

1) maximise SA and conc. gradient
2) minimise diffusion pathway

Question 3

why and how are fish adapted for gas exchange? (6)

Answer 3

1) need a specialised gas exchange surface as they have a small SA:V ratio
2) along each gill arch there are multiple gill filaments which are lined with gill lamellae (where gas exchange occurs)- this provides a large SA
4) blood and water flow across the lamellae in a counter current direction meaning they flow in the opposite direction to one another
5) this ensures that a steep diffusion gradient is maintained so that the maximum amount of oxygen is diffusing into the deoxygenated blood from the water
6) short diffusion pathway as gas exchange only happens on gill lamellae which are very thin

Question 4

what is the counter-current principle?

Answer 4

1) blood and water flow across the lamellae low in the opposite direction to one another
2) this ensures that a steep diffusion gradient is maintained across the entire width of the gill lamellae so that the maximum amount of oxygen is diffusing into the deoxygenated blood from the water
3) ensures equilibrium is not reached

Question 5

why does the volume of water passing over the gills increase if the temperature of the water increases?

Answer 5

At higher temperatures, less oxygen dissolves in the water so fish need to respire faster by absorbing more oxygen from the water

Question 6

why is counter current flow useful to a fish? (2)

Answer 6

1) higher rate of oxygen uptake for respiration so faster respiration rate
2) faster swimming speed

Question 7

what is the relationship between the size of an organism and
its surface area to volume ratio? (2)

Answer 7

1) as the size of an organism increases, its surface area to volume ratio decreases.
2) because its volume increases faster than its surface area, meaning the no. of cells respiring and using the O2 becomes greater than that of the area available to diffuse O2

Question 8

what is the physiological significance of surface area to volume ratio? (3)

Answer 8

1) small organisms with a higher SA:V lose heat energy more quickly per kg of bodyweight
2) so they have to respire fast to replace the body heat they are losing
3) large organisms with a lower SA:V have specialised gas exchange surfaces (gills, lungs, leaves) to increase the surface area for O2 diffusion/

Question 9

what adaptations do single-celled organisms have for gas exchange? (4)

Answer 9

1) small and have a large SA:V ratio
2) oxygen is absorbed by diffusion across their body surface which is only covered by a cell-surface membrane
3) Carbon dioxide from respiration diffuses out across their body surface
4) if organism has a cell wall, it doesn’t act as an additional barrier to the diffusion of gases

Question 10

what adaptations do insects have for gas exchange? (5)

Answer 10

1) tracheal system made up of tracheae which branch out to form additional tracheoles which increase surface area.
2) large number of tracheoles which have thin walls so there is a short diffusion distance to cells
3) O2 and CO2 conc. gradient is maintained by body movement and muscle contraction which moves air
4) tracheae provide tubes full of air so fast diffusion into insect tissues
5) fluid in the ends of the tracheoles moves out into tissues during exercise so faster diffusion through the air to the gas exchange surface

Question 11

how does the production of lactic acid during exercise speed up oxygen diffusion in insects? (3)

Answer 11

1) ends of the tracheoles are filled with water- during intense activity, muscles around the tracheoles carry out anaerobic respiration producing lactic acid.
2) This lowers the water potential of muscle cells so water moves into them from the tracheoles by osmosis
3) The volume of water in the ends of the tracheoles decreases and in doing so draws air further into them, speeding up diffusion of oxygen.

Question 12

what is the function of spiracles in insects? (2)

Answer 12

1) gases enter and leave the tracheae via spiracles which can open and close by a valve
2) periodically open to allow gas exchange

Question 13

how are the leaves of dicotyledonous plants adapted for gas exchange? (4)

Answer 13

1) large number of stomata which allow gas exchange found in the leaf’s bottom surface means no cell is far from the stomata, reducing the diffusion distance.
2) air spaces in the spongy mesophyll tissue provide a large surface area to allow gases to enter and move around the leaf and easily come into contact with photosynthesising mesophyll cells
3) CO2 concentration gradient is maintained from the air to the leaf cells as there is a low conc at the palisade cells due to it being used in photosynthesis
4) short diffusion pathway is also provided through the thin flat surface of the leaf

Question 14

what are the structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by terrestrial insects? (3)

Answer 14

1) gas exchange causes water loss because when spiracles open to allow gas exchange, water evaporates out
2) If insects are losing too much water, they close their spiracles using muscles.
3) insects have a waterproof, waxy cuticle all over their body and tiny hairs around their spiracles, both of which reduce evaporation.

Question 15

what are structural and functional compromises between the opposing needs for efficient gas exchange and the limitation of water loss shown by xerophytic plants? (5)

Answer 15

1) for optimal growth stomata would stay open at all times to allow maximum gas exchange so maximum rate of carbon dioxide uptake and maximum rate of photosynthesis however gas exchange causes water loss because when stomata open to allow gas exchange, water evaporates out
2) however as well as allowing gas exchange, stomata will also allow water loss. This must be minimised therefore stomata close under low light conditions (when less carbon dioxide is required for photosynthesis)
3) plant stomata open in day to allow gas exchange
4) waxy cuticle reduces evaporation
5) Xerophytes -> plants specially adapted to living in dry conditions (e.g. cacti and marram grass)

Question 16

how does gas exchange in leaves occur? (3)

Answer 16

1) carbon dioxide/oxygen diffuse through the stomata, which are opened by guard cells becoming turgid
2) carbon dioxide/oxygen diffuse into mesophyll layer into air spaces
3) carbon dioxide/oxygen then diffuse down a concentration gradient.

Question 17

how do stomata open?

Answer 17

1) guard cells absorb water by osmosis and becomes turgid
2) causes stomata to open during the day to allow diffusion of CO2

Question 18

how do stomata close?

Answer 18

1) guard cells lose water by osmosis and becomes flaccid
2) causes stomata to close at night as no photosynthesis is happening

Question 19

why is there a net CO2 uptake during the day? (3)

Answer 19

1) photosynthesis rate is higher than respiration rate
2) more CO2 is used for photosynthesis than is made by respiration
3) CO2 diffuses in through open stomata

Question 20

in plants why is there a net uptake of O2 at night? (3)

Answer 20

1) respiration rate is higher than photosynthesis rate/ photosynthesis is not occurring
2) more O2 is being used for respiration than is being made by photosynthesis
3) O2 diffuses in through closed stomata

Question 21

what is the ‘compensation point’ in photosynthesis? (2)

Answer 21

1) photosynthesis and respiration rates are equal
2) all CO2 made by respiration is used for photosynthesis

Question 22

why are the stomata usually open in the daytime and closed at night? (3)

Answer 22

1) allow CO2 to diffuse in for photosynthesis
2) closed at night to prevent loss of water through evaporation/transpiration
3) no photosynthesis occurs at night

Question 23

why would a herbicide that closes the plant’s stomata cause the death of that plant? (3)

Answer 23

1) CO2 cannot diffuse in through stomata
2) less photosynthesis will happen
3) no glucose/sugars produce so plant will die

Question 24

describe the similarities and differences between plant leaves and insect tracheal system as gas exchange systems (5)

Answer 24

1) both have a large surface area (air spaces in the spongy mesophyll layer and lots of branched tracheoles)
2) both have a short diffusion pathway as insects are small and thin tracheole walls and leaves are thin and flat.
3) both have pores to allow gas exchange (stomata and spiracles) which can be closed to reduce water loss through evaporation
4) insects have the ability to ventilate trachea by contracting muscles whereas leaves cannot
5) they differ in which gases diffuse in and out. During the day, CO2 diffuses into the leaves and O2 diffuses out. Whereas in insects, O2 diffuses in and CO2 diffuses out.

Question 25

explain how young fish get enough oxygen to their cells without having gills (2)

Answer 25

1) diffusion across body surface/skin 2) short diffusion pathway/ large SA:V ratio

Question 26

what is an organ?

Answer 26

a group of tissues which which work together to perform a specific function

Question 27

what is the advantage of having a one-way flow of water over gills? (2)

Answer 27

1) less energy needed 2) continuous flow of water/ O2

Question 28

outline the gross structure of the human gas exchange system and describe how air moves when we inhale (6)

Answer 28

1) trachea- lined with C-shaped cartilage to keep to open 2) bronchi- 2 branches which extend from trachea 3) bronchioles- highly branched narrow tubes which extend from bronchi 4) alveoli-tiny air sacs found on the ends of bronchioles which give a large surface area 5) lungs- act as a specialised exchange surface which humans need as we have a small SA:V ratio and fast metabolic rate. 6) when breathing air travels from the mouth, down the trachea, bronchi and bronchioles down a pressure gradient, before arriving in the alveoli which is the site of gas exchange

Question 29

describe the mechanism of breathing when humans inhale (6)

Answer 29

1) external intercostal muscles contract to lift the ribcage upwards and outwards 2) internal intercostal muscles relax due to the antagonistic interaction between external and internal intercostal muscles 3) diaphragm muscle contracts and becomes and flatter 4) this increases the volume of the lungs and thorax 5) so decreases pressure in the lungs 6) air moves into the lungs from a higher pressure to a lower pressure down a concentration gradient

Question 30

describe the mechanism of breathing when humans exhale (6)

Answer 30

1) external intercostal muscles relax allowing the ribcage to fall due to gravity 2) diaphragm relaxes and returns to its dome shape 3) this decreases the volume of the lungs and thorax 4) so increases pressure in the lungs 5) air moves out of the lungs from a higher to lower pressure 6) this mechanism is helped by the elastic recoil of the alveoli which raises the alveolar pressure to push air out

Question 31

describe the mechanism of breathing when humans undergo forced expiration (5)

Answer 31

1) same process a regular expiration 2) internal intercostal muscles contract to actively pull ribs downwards 3) decreases the volume of the thorax and lungs more quickly 4) pressure in the lungs rises more quickly so there is a greater pressure gradient 5) air moves out of the lungs more quickly

Question 32

describe the diffusion of oxygen through the alveolar epithelium

Answer 32

during gas exchange oxygen diffuses from the alveolus cavity across the alveolar epithelium and capillary endothelium into the blood, travelling down a diffusion gradient, whilst carbon dioxide diffuses in the opposite direction

Question 33

what are the essential features of the alveolar epithelium as a surface over which gas exchange takes place (5)

Answer 33

1) alveolar epithelium is thin/one cell thick and thin capillary endothelial cells create a short diffusion pathway 2) millions of tiny create a large surface area for gas exchange 3) each alveolus is surrounded by a network of capillaries to remove exchanged gases and therefore maintains a large concentration gradient 4) this is achieved by ventilating the lungs to maintain air with a high oxygen concentration in the alveoli and exhaling poor air. Blood flow through capillaries also ensures that deoxygenated blood is brought to the capillaries around the alveoli 5) blood flow through capillaries is also slow, to allow time for more oxygen to diffuse

Question 34

how do you calculate breathing rate from a graph?

Answer 34

60 sec/ time for 1 breath (work this out using the graph)

Question 35

what is tidal volume?

Answer 35

volume breathed in during 1 breath

Question 36

how do you calculate pulmonary ventilation rate?

Answer 36

tidal volume x breathing rate

Question 37

during exercise, what 2 factors could cause the pulmonary ventilation rate to increase? why is this necessary? (3)

Answer 37

1) increase tidal volume 2) increase breathing rate 3) to diffuse more oxygen for respiration

Question 38

how can you work out inspiration is occurring from a graph? (2)

Answer 38

1) lung volume increases 2) lung pressure is below 0/ below atmospheric pressure

Question 39

how can you work out expiration is occurring from a graph? (2)

Answer 39

1) lung volume decreases 2) lung pressure is above 0/ above atmospheric pressure

Question 40

pulmonary fibrosis causes thickening of the alveoli epithelial issue and the loss of recoil of the alveoli, explain how this causes a lack of oxygen in an infected person's blood (3)

Answer 40

1) slower diffusion of oxygen into the person's blood 2) thicker epithelial cells means there's a longer diffusion pathway 3) lack of elastic recoil makes expiration of deoxygenated air less effective, reducing the concentration gradient of oxygen.

Question 41

what happens during digestion?

Answer 41

large biological molecules are hydrolysed to smaller molecules that can be absorbed across cell membranes.

Question 42

outline the digestion of carbohydrates by amylases and membrane-bound disaccharidases (5)

Answer 42

1) carbohydrates are hydrolysed by carbohydrases into monosaccharides 2) starch digestion begins in the mouth where salivary amylase hydrolyses the glycosidic bonds in the starch to form the disaccharide maltose 3) salivary amylase is denatured by the low pH of stomach acid 4) pancreatic amylase continues this hydrolysis in the small intestine 5) the glycosidic bond in maltose is then hydrolysed by maltase, a membrane bound disaccharidase, to form a-glucose

Question 43

where is maltase found?

Answer 43

part of the cell-surface membranes of the epithelial cells that line the small intestine

Question 44

outline the digestion of lipids by lipase, including the action of bile salts (4)

Answer 44

1) lipids are hydrolysed by lipases to form glycerol and fatty acids 2) before this happens, emulsification of the lipids occurs 3) emulsification describes when lipids are firstly split up into tiny droplets called micelles by bile salts which are produced by the liver 4) this is important as it increases the surface area of the lipids so lipase digestion is speeded up

Question 45

outline the digestion of proteins by endopeptidases, exopeptidases and membrane-bound dipeptidases (5)

Answer 45

1) proteins are hydrolysed by proteases into amino acids 2) in stage 1, endopeptidases only hydrolyse the 'internal' peptide bonds in the polypeptides due to the shape of its active site, forming di and tri peptides 3) this increases substrate concentration for exo/ dipeptidases 4) in stage 2, the di & tri peptides are hydrolysed into amino acids by exopeptidases and dipeptidases. 5) these only hydrolyse the 'terminal' peptide bond

Question 46

outline the human digestive system (6)

Answer 46

1) Glands - the salivary glands and glands in the pancreas produce digestive juices/enzymes 2) oesophagus- muscles squeeze food along 3) The stomach and small intestine - the sites of digestion 4) The liver - produces bile 5) Small intestine - the site of absorption and digestion through hydrolysis 6) Large intestine - site of water reabsorption

Question 47

outline the mechanisms for the absorption of glucose by cells lining the ileum (4)

Answer 47

1) the absorption of monosaccharides such as glucose use the mechanism of co-transport 2) sodium ions and glucose molecules are co-transported into the epithelial cells via facilitated diffusion 3) the glucose molecules diffuse across the epithelial cell and enter the capillary at the other end of the cell by facilitated diffusion using a glucose carrier protein 4) the concentration gradient of sodium ions is maintained by the active transport of sodium ions out of the cell and into the blood via a sodium-potassium pump at the other end of the cell

Question 48

outline the mechanisms for the absorption of amino acids by cells lining the ileum (4)

Answer 48

1) the absorption of amino acids uses the mechanism of co-transport 2) sodium/potassium pump uses ATP to actively transport sodium out of the cell and create a low conc. od sodium in the cell 3) sodium and an amino acid are co transported bringing a sodium down its conc gradient and an amino acid against its conc gradient, from the intestine into the epithelial cell 4) amino acid carrier protein allows facilitated diffusion of the amino acid

Question 49

outline the mechanisms for the absorption of lipids by cells lining the ileum and the role of micelles (8)

Answer 49

1) in the intestines, monoglycerides and fatty acids associate with bile salts to form micelles which are small spheres/droplets 2) monoglycerides and fatty acids are not very soluble so the micelles aid the transport of these molecules to the surface of the epithelial cells 3) micelles break down when they come into contact with the epithelial cells lining the ileum, releasing the monoglycerides and fatty acids 4) fatty acids and monoglycerides are non polar so do simple diffusion across the epithelial cell membrane and are transported to the SER 5) at the SER the fatty acids and monoglcyerides are recombined to form triglycerides 6) triglcyerides combine with lipoproteins and cholesterol to form chylomicrons 7) chylomicrons leave the cell via exocytosis of small vesicles 8) lymph and blood vessels transport chylomicrons to endothelial cells which rehydrolyse the triglycerides into fatty acids and glycerol for storage or respiration

Question 50

why is the left ventricle wall thicker than the right ventricle wall? (2)

Answer 50

1) there is more muscle which is required to contract with more force and generate a higher pressure 2) this allows it to pump blood around the body and to the kidney, which requires high pressure blood for ultrafiltration

Question 51

explain the importance of the atrioventricular valves between the atria and ventricles (2)

Answer 51

1) atrioventricular valves close when ventricle pressure is greater than atrial pressure 2) to stop blood flowing backwards from the ventricles to atria

Question 52

explain the importance of valve/heart tendons (2)

Answer 52

1) heart/valve tendons stop atrioventricular valves from inverting 2) allowing them to work correctly to prevent blood from flowing backwards from ventricles to atria

Question 53

what is stage 1 of the cardiac cycle? (4)

Answer 53

1) atrial systole (typically 0.1 sec) 2) atria contract so their pressure rises 3) this opens the atrioventricular valves as atrial pressure is greater than ventricle pressure 4) so blood flows from the atria to the ventricles

Question 54

what is stage 2 of the cardiac cycle? (5)

Answer 54

1) ventricular systole (typically 0.2 sec) 2) ventricles contract so their pressure rises 3) this opens the semi-lunar valves as ventricle pressure is greater than artery pressure 4) so blood flows from the ventricles into the arteries 5) atrioventricular valves close because ventricle pressure is greater than atrial pressure, so prevents blood from flowing backwards

Question 55

how can you identify ventricular systole from a diagram? (2)

Answer 55

1) semi-lunar valves will be open as ventricle pressure is > than artery pressure 2) atrioventricular valves will be closed as ventricle pressure is > than atrial pressure so prevents blood from flowing backwards

Question 56

how can you identify atrial systole from a diagram? (2)

Answer 56

1) atrioventricular valves will be open as atrial pressure is greater than ventricle pressure 2) atria are contracting which may be indicated by arrows

Question 57

what is stage 3 of the cardiac cycle? (4)

Answer 57

1) diastole (typically 0.5 sec) 2) heart relaxes and atria fill will blood 3) blood trickles through open atrioventricular valves into the ventricles 4) semi-lunar valves are closed because artery pressure is greater than ventricle pressure, so prevents blood from flowing backwards from the arteries into the ventricles

Question 58

how do you calculate the length of 1 cardiac cycle?

Answer 58

60/ heart rate

Question 59

what is cardiac output?

Answer 59

volume of blood pumped out per minute

Question 60

how do you calculate cardiac output?

Answer 60

heart rate (bpm) x stroke volume (vol pumped in 1 beat)

Question 61

exam Q: a student investigated the effect of changing surface area on the rate of diffusion of a solution into the centre if agar blocks state 5 variables the student controlled in order to obtain valid results (5)

Answer 61

1) temperature 2) conc. of indicator 3) pH of solution 4) type of agar 5) ensure total surface area of the block is in contact with the solution/acid/

Question 62

exam Q: describe how gas exchange occurs in single-celled organisms and explain why this method cannot be used by large, multicellular organisms (3)

Answer 62

1) diffusion across cell surface membrane 2) large organisms have a smaller sa: vol ratio 3) diffusion pathway would be too long/ too slow for large organisms

Question 63

exam Q: describe how the structure of the insect gas exchange system: - provides cells with sufficient oxygen - limits water loss (5)

Answer 63

1) insect gas exchange system consists of spiracles, tracheae and tracheoles 2) spiracles allow diffusion of O2 into the insect 3) tracheoles are highly branched so large surface area for gas exchange 4) tracheole walls are thin so short diffusion pathway 5) tracheole walls are permeable to oxygen 6) spiracles can close so no water loss 7) hairs around spiracles reduce water loss

Question 64

exam Q: describe how humans breathe in and out (5)

Answer 64

breathing in: 1) diaphragm contracts and flattens 2) external intercostal muscles contract and ribcage is pulled up and out 3) volume increases and pressure deceases in the lungs and thorax breathing out: 4) diaphragm relaxes and returns to dome shape 5) external intercostal muscles relax and ribcage moves down and in 6) volume decreases and pressure increase in the lungs and thorax

Question 65

exam Q: explain why death of alveolar epithelium cells reduces gas exchange in human lungs (3)

Answer 65

1) reduced surface area 2) increased distance for diffusion 3) reduced rate of gas exchange

Question 66

exam Q: to observe the fish gills, 2 stains must be used, the first stain binds to DNA, the second stain binds to the red blood cells explain why a second stain would be needed to stain the red blood cells

Answer 66

red blood cells do not have a nucleus/ DNA

Question 67

exam Q: the damage to the gills causes uncontrolled cell division in the cells around the capillaries in the gill filaments. Other than SA:V, describe one way this uncontrolled cell division changes the gills and how this difference would affect gas exchange (3)

Answer 67

1) more cells so wider/thicker gill filament 2) longer diffusion pathway 3) so slower gas exchange/ rate of diffusion

Question 68

exam Q: describe and explain one feature of the alveolar epithelium that makes the epithelium well adapted as a surface for gas exchange. Do not refer to surface area or moisture in your answer. (2)

Answer 68

1) flattened cells/ single layer of cells/ one cell thick 2) reduces diffusion pathway OR 3) permeable 4) allows diffusion of oxygen/ CO2

Question 69

exam Q: tidal volume is the volume of air inhaled and exhaled during a single breath when a person is resting. The tidal volume in a person with emphysema is reduced compared with the tidal volume in a healthy person. Suggest and explain how a reduced tidal volume affects the exchange of carbon dioxide between the blood and alveoli (3)

Answer 69

1) less carbon dioxide exhaled/ moves out of the lung/ more carbon dioxide remains in the lung 2) so reduced diffusion/ concentration gradient between blood and alveoli 3) so less/slower movement of carbon dioxide out of the blood/ more carbon dioxide stays in the blood

Question 70

how do heart valves/ valve tendons help to maintain the flow of blood in one direction through the heart? (2)

Answer 70

1) stop valves from inverting 2) prevents blood from flowing backward from ventricles to atrium

Question 71

describe the processes involved in the absorption and transport of digested lipid molecules from the ileum into lymph vessels (5)

Answer 71

1) micelles contain bile slats, monoglcyerides and fatty acids 2) they release these fatty acids and monoglycerides into the cells lining the ileum 3) fatty acids/monoglycerides are then absorbed by diffusion into the cell 4) triglycerides reformed in cells 5) vesicles move to cell membrane/ exocytosis

Question 72

describe the role of micelles in the absorption of fats into the cells lining the ileum (3)

Answer 72

1) micelles include bile salts and fatty acids 2) release fatty acids to cells lining the ileum 3) fatty acids absorbed by diffusion

Question 73

describe the role of enzymes in the digestion of proteins in a mammal (4)

Answer 73

1) hydrolysis of peptide bonds 2) endopeptidase act in the middle of polypeptide 3) exopeptidases act at end of protein/polypeptide 4) dipeptidase acts on dipeptide/between two amino acids/ dipeptidase produces single amino acids

Question 74

Explain the advantages of lipid droplet and micelle formation (3)

Answer 74

1) droplets increase surface areas (for lipase action) 2) So faster hydrolysis / digestion (of triglycerides / lipids) 3) Micelles carry fatty acids and glycerol / monoglycerides through membrane / to (intestinal epithelial) cell

Question 75

how is the Golgi apparatus involved in the absorption of lipids (3)

Answer 75

1) modifies/processes triglycerides 2) combines triglycerides with proteins 3) packaged for release/exocytosis so forms vesicles

Question 76

Cells lining the ileum of mammals absorb the monosaccharide glucose by co-transport with sodium ions. Explain how (3)

Answer 76

1) sodium ions actively transported from ileum cell to blood; Golgi (apparatus); 2) maintains / forms diffusion gradient for sodium to enter cells from gut (and with it, glucose); 3) glucose enters by facilitated diffusion with sodium ions;

Question 77

what is the general pattern of blood circulation in a mammal? (Names are required only of the coronary arteries and of the blood vessels entering and leaving the heart, lungs and kidneys). (10)

Answer 77

1) mammals have a double circulatory system 2) blood passes through the heart twice on a complete circuit of the body 3) oxygenated blood leaves the heart through the aorta to the rest of the body 4) oxygen is diffused to respiring tissue 5) deoxygenated blood enters the heart through the vena cava 6) blood leaves to go to the lungs via the pulmonary artery 7) blood becomes oxygenated at the lungs 8) oxygenated blood then enters the heart through the pulmonary vein, ready to be pumped out via the aorta 9) the renal artery takes blood to the kidneys where it leaves by the retail vein 10) the coronary arteries take oxygenated blood to heart cells

Question 78

what is the structure of arterioles related to its function? (3)

Answer 78

1) extra muscle layer that contracts- causes constriction of the arteriole 2) muscle relaxation causes dilation of the arterioles 3) allow blood flow to organs to be reduced/increased according to need

Question 79

what is the structure of arteries related to its function? (4)

Answer 79

1) thick elastic layer that stretches and recoils with each surge of blood to even out the flow 2) thick muscle layer to ensure arteries don't burst under high pressure 3) carry high pressure, usually oxygenated blood, away from the heart 4) no valves needed, except those immediately next to the ventricles, as blood is under high pressure

Question 80

what is the structure of capillaries related to its function? (4)

Answer 80

1) very narrow lumen causing red blood cells to squeeze through- reduced diffusion pathway 2) many, many capillaries increase the surface area for faster diffusion 3) minimal diffusion pathway from blood to tissue fluid 4) vessel wall is a single layer of endothelial cells, with increased permeability

Question 81

what is the structure of veins related to its function? (4)

Answer 81

1) large lumen reduces overall friction to aid blood flow back to the heart 2) thin muscle layer and thin elastic layer as the blood is at low pressure, with little risk of bursting vein 3) valves present to prevent back flow of low pressure blood 4) veins are compressed by major leg muscles to help blood flow against gravity