Organisms exchange substances with their environment Flashcards
1
Q
Explain the Adaptations of Red Blood Cells
A
-no nucleus increases surface area for diffusion of oxygen
-bioconcave shape increases surface area for diffusion of oxygen
-flat and thin which creates a short diffusion pathway for oxygen to reach all the haemoglobin inside
2
Q
Describe the simple structure of haemoglobin
A
Haemoglobin is a large protein with a quaternary structure, made of four polypeptide chains, and each chain has a heam group which contains an iron ion. Each molecule can bind too four oxygen molecules as oxygen binds to the heam group.
3
Q
what is formed when haemoglobin and oxygen associate / binds?
A
oxyhaemoglobin
4
Q
what is the name for oxyhaemoglobin releasing its oxygen to respiring cells?
A
dissociation
5
Q
what is partial pressure?
A
the pressure exerted by oxygen within a mixture of gases
6
Q
what conditions are dependent on haemoglobins affinity for oxygen
A
-partial pressure of oxygen
-haemoglobin saturation
-partial pressure of carbon dioxide
7
Q
what affect does partial pressure of oxygen have on haemoglobin affinity for oxygen?
A
as the partial pressure of oxygen increases so does the affinity for oxygen
-as the partial pressure of oxygen decreases so does the affinity for oxygen
8
Q
What is the cooperative nature of oxygen binding?
A
when the first molecule of oxygen binds too the haemoglobin and changes its tertiary structure this uncovers more haem binding sites so it is easier for additional molecules of oxygen to bind.
9
Q
Areas of high oxygen partial pressure:
A
-haemoglobin has a higher affinity for oxygen
- so oxygen associated with haemoglobin
-so the percentage saturation of oxygen is high
10
Q
areas of low oxygen partial pressure:
A
-haemoglobin has a lower affinity for oxygen
-so oxygen disassociates from haemoglobin
-so the percentage saturation of oxygen is low
11
Q
As partial pressure of carbon dioxide increases what happens to the oxygen affinity of haemoglobin?
A
oxygen affinity drcreases as it is harder for oxygen to bind to the haem group of the haemoglobin
12
Q
what does the Bohr Effect suggest
A
the effect of carbon dioxide partial pressure on the disassociation curve- right shift
13
Q
how does the partial pressure of haemoglobin affect the affinity of haemoglobin for oxygen
A
when the partial pressure for carbon dioxide is high oxygen dissociated from haemoglobin more easily allowing more oxygen to be unloaded. This occurs as there is an increased production of carbon dioxide during respiration leading to a decrease in blood pH as it reacts with water to form carbonic acid, and low pH causes the tertiary structure of haemoglobin to alter
14
Q
Binding of one molecule of oxygen to haemoglobin makes it easier for a second oxygen molecule to bind
A
the first oxygen binds causing a change in the tertiary structure of the haemoglobin which expose more oxygen binding sites
15
Q
explain why foetus in the womb have a higher affinity of oxygen compared to an adult human.
(left shift)
A
-foetal haemoglobin binds more easily and is also more reluctant to dissociate, which is important as foetal haemoglobin needs to steel oxygen away from the mother’s haemoglobin when passing in the placenta.
16
Q
explain why animals living in low oxygen environment have a higher affinity for oxygen compared to adult humans
(left shift)
A
there is a lower atmospheric pressure so there will be a low partial pressure of oxygen, so less oxygen avaliable therefore the haemoglobin has to be able to load more oxygen at a lower partial pressure for oxygen to make sure enough oxygen is absorbed
17
Q
Explain why small organisms with high SA:V or organisms with high metabolic rate have a lower affinity of oxygen compared to adult humans.
(right shift)
A
Smaller mammals will lose heat more quickly so will have a higher metabolic rate to maintain there temp, so more respiration is needed therefore there is a greater oxygen demand so the haemoglobin needs to easily unload oxygen to meet their oxygen demand for a faster rate of respiration.
18
Q
Why can’t multi cellular organisms rely on diffusion to transport substances around the body?
A
They have a low surface area to volume ratio and cannot rely on diffusion as the diffusion pathway is too long
19
Q
what is the structure and function of blood vessels?
A
arteries branch into arterioles which can contract to restrict blood flow and relax to increase blood flow.These branch into capillaries then deoxygenated blood flows into the venules which join veins and blood is transported back to the heart.
20
Q
Describe the structure and functions of arteries
A
-narrow lumen to help maintain high pressure
-thick muscular walls and elastic layer allows stretching and recoiling with ventricular contractions maintaining high blood pressure
-folded endothelium with allows stretching to help maintain high pressure
21
Q
describe the structure and functions of veins
A
-wide lumen than arteries as blood is at low pressure
-thinner layers of muscle and elastic tissue
-valves to ensure that blood does not flow backwards
-when veins are compressed this increases pressure and pushes blood along
22
Q
describe the structure and functions of capillaries
A
-site of substance exchange with cells
-walls are one cell thick for short diffusion pathway
-fenestrations between endothelial cells allow substances to diffuse out
-large numbers of capillaries increase the surface area for gas exchange
23
Q
why does blood pressure decrease as you move from arteries to veins?
A
blood flows from high pressure to low pressure due to pressure along the vessels from the aorta due to it branching into many vessels.
24
Q
how do arteries even out blood pressure?
A
the walls of the arteries stretch when blood moves through high pressure then recoils as blood pressure drops which evens out the blood pressure
25
What does the blood transport
Gases, products of digestion, metabolic waste, and hormones
26
Describe the formation of tissue fluid
-at the arteriole end of the capillary bed there is a high hydrostatic pressure inside the capillary compared to out of the capillary
-forcing water and dissolved substances out into the surrounding tissue
-some of the tissue fluid is eventually reabsorbed and waste products are returned to the capillaries with the tissue fluid because the hydrostatic pressure reduces while the water potential in the capillary lowers, water enter down a water potential gradient
-excess is drained into vessels of the lymphatic system know as lymph
27
what happens to the hydrostatic pressure when fluid leaves the capillaries at the arteriole end
Hydrostatic pressure lowers meaning the blood pressure at the venous end of the capillaries is much lower
28
What is the lyphatic system?
A system of tubes that returns excess tissue fluid to the blood system
29
The hydrostatic pressure of the blood at the arteriole end of the capilary helps to form tissue fluid. Explain how.
The high pressure forces water and dissolved substances out of the cappilaries into the surrounding tissue
30
In childeren, some ay result in a low concentration of protein in plasma, causing the accumulation of tissue fluid. Explain the link between a low concentration of protein in plasma and the accumulation of tissue fluid.
Due to incifficient protein in plasma the water potential in the capilaries remains higher as no water is absorbed, therefore more tissue fluid is formed
31
Why does high blood pressure lead to an accumulation of tissue fluid. Explain how.
The blood pressure would be too high for tissue fluid to be re-absorbed into the capilaries, therefore leading to an accumulation of tissue fluid
32
What is atrial systole?
The artia contacts so the volume of the atria reduces and so increases the pressure of blood, when pressure exceeds that’s of the ventricles the atrioventricular valves open forcing blood into the ventricles.
33
what is ventricular systole?
ventricles contract decreasing the volume in the ventricles and so increases the pressure forcing the atrioventricular valves to close as pressure in the ventricles exceeds that of the atria and semi lunar valves are forced open and blood is pumped out through the arteries
34
What is diastole
both atria and ventricles relax so their volume increases and pressure decreases, the pressure in the arteries is greater than the ventricles so the semi lumar valves shut and blood enters the atria from the veins increasing pressure of the atria, eventually exceeding ventricle pressure and AV valves open and blood begins to passively flow into the ventricles
35
what is the calculation for calculating cardiac output?
cardiac output = stroke volume × heart rate
36
Explain how the highest blood pressure is produced in the left venricle?
The thick muscle creates an increased contraction therefore that increases the blood pressure
37
Some babys are born with a hle between the right and left ventricles, these babys are unable to get enough oxygen to there tissues, suggest why?
The hole will decrease the blood presure so the semi-lunar valves will not open so there is a lower volume of oxygenated blood, which is also mixed with deoxygenated blood, leaving to ventricles to the aorta to be pumped around the body, so less oxyenated blood is reaching their tissues.
38
Explain how the heart muscle and the heart valves maintain a one-way flow of blood from the left atrium to the aorta.
Blood enters the left atrium and the pressure in the atria is higher than that of the ventricles so the atrioventricular valves open and blood is forced into the ventricles. The semi-lunar valves remain shut as the pulmonary arteries exeed the pressure in the ventricles
39
what is atheroma
They are fibrous plaques made of fatty material which narrow the lumen of arteries
40
when does atheroma formations occur?
occurs when the lining of the artery is damaged usually by high blood pressure, so when white blood cells and platelets try repair the damage they clump together with lipids from the blood to form fatty streaks under the lining. over time this builds up forming atheroma.
41
what is Aneurysm?
A build up of blood behind a blockage causing the artery wall to bulge and weaken increasing the chance of the wall splitting causing internal bleeding which is often fatal
42
what is Thrombosis?
a formation of a blood clot due to an atheroma bursting through the endothelium causing a rough surface, so platets accumulate at the site of damage causing a clot which can completely block the arteries or veins
43
what is Angina
a build up of plaque in the coronary arteries which reduces blood flow to areas of the heart so there is a sufficient amount of blood reaching the heart causing anaerobic respiration, which leads to pain in chest and arms and also makes people breathless
44
what is a Stroke
they are caused by ab interruption to the blood supply to the brain, like a damaged vessel, or a blockage cutting the blood supply, if occurs in main vessels could lead to a serious stroke, and in smaller arterioles the effects are less server
45
what is a Myocardial Infraction
heart attacks can be caused by atherosclerosis, the wall around the plaque are stiffened making them prone to cracks so platelets detect the damage triggering a clotting mechanism which can block the the whole blood vessel, if this occurs in a coronary artery it can cause a heart attack as the heart is starved of oxygen and nutrients stopping contracting
46
what is hypertension (high bp) and how can it be controlled?
-due to increased pressure this damages the artery walls as there is an increased friction therfore increasing the risk of atheroma formation.
-risk factors include: being over weight, excessive alcohol consumption and not exercising enough
-to reduce the risk you can maintain a healthy weight, eat a diet with low saturated fats, do regular exercise
47
what is a risk high blood cholesterol and how can it be controlled?
-increased cholesterol increases risk of atheromas as it is a main constituent which causes the fatty deposits
-risk factors include a diet high in saturated fats
- to reduce high cholesterol eat a diet with low saturated fats and salt, exercise and maintain a healthy weight
48
what are the risks of smoking and how can it be controlled?
-increases risk of cardiovascular disease and myocardial infraction, the CO combines with the haemoglobin which reduces the amount of oxygen that can be transported in the blood, smoking also decreases rhe amount of antioxidants in the blood
-reduce the risk by not smoking
49
what are other factors of cardiovascular disease which cannot be controlled?
-genetics
-age
-gender
-ethnicity
-other illnesses
50
What is myocardial infraction?
A blockage of corronary arteries (aka a heart attack)
51
Describe the structure of the leaf and the functions of the tissues in the leaf
At the top of the leaf the waxy cuticle enables the leaf to be waterproof, the palaside mesophyll which contains many chloroplast so photosynthesis occurs, a spongy mesophyll which is a layer of cells with air spaces between them therefore gas exchange can occur, xylem which transports water and miner ions, phloem which transports dissolved sugars
52
what is the function of the stomata?
The stomata can control how much water leaves.
53
what is transpiration?
Is the loss of water from the plant via evaporation
54
when do guard cells become turgid?
when plants have enough water they are turgid which keep the pores open
55
when does guard cells become flaccid?
When plants are dehydrated they become flaccid causing the hole to close.
56
Describe the structure of Xyem vessels
-elongated tubes formed from dead cells joined together in bundles, and contain no cytoplasm and nucleus
-no end walls between cells forming a long continuous tubes
-thick walls made of lignin which provides support and withstands tension
-gaps called pits in the cell wall to allow lateral movement of water
57
Movement of water can be explained by what?
Cohesion-Tension Theory
58
what is cohesion tension theory?
Water evaporates from the mesophyll due to heat from the sun via transpiration creating a negative water potential, causing water to diffue in through osmosis
This increase in water tension pulls more water into the leaf through transpiration pull
Water molecules are cohesive due to they form hydrogen bonds, so when some water molecules are pulled into the leaf others follow, pulling a whole colum of water in the xylem up from the roots to mesophyll tissue in the leaves
Water enters the stem through the roots.
59
What is the evidence to support cohesion-tension?
-If a trunk or stem is damaged and a xylem cell is broken water does not leak out which it would if the vessels were under pressure, and when air enters the tree can no longer draw up water because the continuous colom of water is broken
-trucks of trees reduce in diameter during the daytime when transpiration is at its greatest because adhesion of water molecules to the wall of xylem results in a tension which pulls the xylem walls in, and at night there is less tension so diameter increases
60
How does increasing light intensity affect transpiration?
It increases transpiration because increased photosynthesis requires mor carbon dioxide via the stomata, so it needs to be open and more stomata open so more water is evaporated
61
how does increase in temperature affect transpiration?
It increases it as there is an increased evaporation because there is more kinetic energy in molecules creating a water potential gradient
62
how does increased wind intensity affect transpiration?
It increases transpiration as water molecules move away from the stomata quicker incresing the water potential gradient
63
how does increased humidity affect transpiration?
It decreases it as there is a lower water potential gradient so less water is evaporated
64
How is small leaf surface area an adaptation in Xerophytes?
It reduces the surface area for evapotation, and small surface area means fewer stomata.
65
How is sunken stomata an adaptation of xerophytes?
Able to maintain humid air around the stomata to reduce the water potential gradient.
66
How are stomatal hairs an adaptation of Xerophytes?
Able to maintain the humid air around the stomata to reduce the water potential gradient, reducing evapouration.
67
How are rolled leaves an adaptation of xerophytes?
They reduce the affect of wind to reduce the water potential gradient, reducing evapouration.
68
How are extensive root systems an adaptation of xerophytes
They maximise water uptake, therefore increaseing the chances of contact with water as they build a wide area to absorb rain fall. They also often have swollen stems to store the collected water
69
How is having a reduced number of stomata an adaptation of xerophytes?
Reduce the mount of places water can evaporate from.
70
How is having a thicker and waxy cuticle an adaptation o xerophytes?
Waterproof leaves and stems reduce evaporation.
71
What is translocation?
The movement of solutes such as sucrose from the source to the sink.
72
what is the structure of the phloem?
-have a tube formed from elongated living cells called seive tubes
-have a thin layer of cytoplasm around te edge of the cell maximising space for mass flow
-seive tubes are supported by companion cell, contains mitochondria and a nucleus to produce ATP helping to carry out functions
-there are end walls between cells which contain holes to let solutes pass through (seive plates)
73
Why is translocation an active process?
Its is bidirectional meaning sinks can be above the source and some can be below, therefore requiring energy as solutes are pushed around under high pressure
74
Describe the active loading of sucrose into companion cells at the source.
H+ ions are actively pumped out of the companion cell using ATP, into the cells of the source tissue. This creates a hydrogen concentration gradient across the companion cell membrane. H+ ions can diffuse back down the conc. grad. through transport proteins requiring a sucrose molecule to be co-transported. Increaseing the conc. of sucrose in the compannion cell, which can diffuse into the seive tube.
75
What is mass flow?
1).At the source sucrose is actively transported into the seive tubes by companion cells
2).This lowers the water potential in the seive tube, so water enters via osmosis from the xylem
3).This increases hydrostatic pressure in the seive tube creating a hydrostatic pressure gradient
4).So mass flow occurs
5).Sucrose is removed by active transport to be used by respiring cells
76
What is the evidence to support mass flow hypothesis?
-Sucrose concentration is higher in the leaves than the roots
-When a seive tube is cut sap is released, the sap is under high positive pressure within the phloem
77
What is the evidence that goes against mass flow hypothesis?
-The end plates of the seive tube would create a barrier to mass flow, or slow it down so why are the present?
78
Describe the relationship between the size and structure of an organism and
its surface area to volume ratio (SA:V)
As size increases, SA:V tends to decrease
● More thin / flat / folded / elongated structures increase
SA:V
79
How is SA:V calculated?
Divide surface area (size length x side width x number of sides) by volume (length x width x depth)
80
Suggest an advantage of calculating SA:mass for organisms instead of SA:V
Easier / quicker to find / more accurate because irregular shapes
81
What is metabolic rate? Suggest how it can be measured
● Metabolic rate = amount of energy used up by an organism within a given period of time
● Often measured by oxygen uptake → as used in aerobic respiration to make ATP for energy release
82
Explain the relationship between SA:V and metabolic rate
As SA:V increases (smaller organisms), metabolic rate increases because:
● Rate of heat loss per unit body mass increases
● So organisms need a higher rate of respiration
● To release enough heat to maintain a constant body temperature ie. replace lost heat
83
Explain the adaptations that facilitate exchange as SA:V reduces in larger
organisms
1. Changes to body shape (eg. long / thin)
● Increases SA:V and overcomes (reduces) long diffusion distance / pathway
2. Development of systems, such as a specialised surface / organ for gaseous exchange e.g. lungs:
● Increases (internal) SA:V and overcomes (reduces) long diffusion distance / pathway
● Maintain a concentration gradient for diffusion eg. by ventilation / good blood supply
84
Explain how the body surface of a single-celled organism is adapted for gas
exchange
● Thin, flat shape and large surface area to volume ratio
● Short diffusion distance to all parts of cell → rapid diffusion eg. of O2 / CO
85
Describe the tracheal system of an insect
1. Spiracles = pores on surface that can open / close to allow diffusion
2. Tracheae = large tubes full of air that allow diffusion
3. Tracheoles = smaller branches from tracheae, permeable to allow gas exchange with cells
86
Explain how an insect’s tracheal system is adapted for gas exchange
● Tracheoles have thin walls
○ So short diffusion distance to cells
● High numbers of highly branched tracheoles
○ So short diffusion distance to cells
○ So large surface area
● Tracheae provide tubes full of air
○ So fast diffusion
● Contraction of abdominal muscles (abdominal
pumping) changes pressure in body, causing air to
move in / out
○ Maintains concentration gradient for diffusion
● Fluid in end of tracheoles drawn into tissues by
osmosis during exercise (lactate produced in
anaerobic respiration lowers ψ of cells)
○ Diffusion is faster through air (rather than
fluid) to gas exchange surface
87
Explain structural and functional compromises in terrestrial insects that
allow efficient gas exchange while limiting water loss
● Thick waxy cuticle / exoskeleton → Increases diffusion distance so less water loss (evaporation)
● Spiracles can open to allow gas exchange AND close to reduce water loss (evaporation)
● Hairs around spiracles → trap moist air, reducing ψ gradient so less water loss (evaporation)
88
Explain how the gills of fish are adapted for gas exchange
● Gills made of many filaments covered with many lamellae
○ Increase surface area for diffusion
● Thin lamellae wall / epithelium
○ So short diffusion distance between water / blood
● Lamellae have a large number of capillaries
○ Remove O2 and bring CO2 quickly so maintains
concentration gradient
89
What is countercurrent flow?
1. Blood and water flow in opposite directions through/over lamellae
2. So oxygen concentration always higher in water (than blood near)
3. So maintains a concentration gradient of O2 between water and blood
4. For diffusion along whole length of lamellae
90
Explain how the leaves of dicotyledonous plants are adapted for gas
exchange
● Many stomata (high density) → large surface area for gas exchange (when opened by guard cells)
● Spongy mesophyll contains air spaces → large surface area for gases to diffuse through
● Thin → short diffusion distance
91
Explain structural and functional compromises in xerophytic plants that
allow efficient gas exchange while limiting water loss
Xerophyte = plant adapted to live in very dry conditions eg. Cacti and marram grass
● Thicker waxy cuticle
○ Increases diffusion distance so less evaporation
● Sunken stomata in pits / rolled leaves / hairs
○ ‘Trap’ water vapour / protect stomata from wind
○ So reduced water potential gradient between leaf / air
○ So less evaporation
● Spines / needles
○ Reduces surface area to volume ratio
92
Explain the essential features of the alveolar epithelium that make it
adapted as a surface for gas exchange
● Flattened cells / 1 cell thick → short diffusion distance
● Folded → large surface area
● Permeable → allows diffusion of O2 / CO2
● Moist → gases can dissolve for diffusion
● Good blood supply from large network of capillaries →
maintains concentration gradient
93
Describe how gas exchange occurs in the lungs
● Oxygen diffuses from alveolar air space into blood down its concentration gradient
● Across alveolar epithelium then across capillary endothelium
94
Explain the importance of ventilation
● Brings in air containing higher conc. of oxygen & removes air with lower conc. of oxygen
● Maintaining concentration gradients
95
What is inspiration?
1. Diaphragm muscles contract → flattens
2. External intercostal muscles contract, internal
intercostal muscles relax (antagonistic) →
ribcage pulled up / out
3. Increasing volume and decreasing pressure
(below atmospheric) in thoracic cavity
4. Air moves into lungs down pressure gradient
96
What is expiration?
1. Diaphragm relaxes → moves upwards
2. External intercostal muscles relax, internal
intercostal muscles may contract → ribcage
moves down / in
3. Decreasing volume and increasing pressure
(above atmospheric) in thoracic cavity
4. Air moves out of lungs down pressure gradient
97
Suggest why expiration is normally passive at rest
● Internal intercostal muscles do not normally need to contract
● Expiration aided by elastic recoil in alveoli
98
Suggest how different lung diseases reduce the rate of gas exchange
● Thickened alveolar tissue (eg. fibrosis) → increases diffusion distance
● Alveolar wall breakdown → reduces surface area
● Reduce lung elasticity → lungs expand / recoil less → reduces concentration gradients of O2 / CO2
99
Suggest how different lung diseases affect ventilation
● Reduce lung elasticity (eg. fibrosis - build-up of scar tissue) → lungs expand / recoil less
○ Reducing volume of air in each breath (tidal volume)
○ Reducing maximum volume of air breathed out in one breath (forced vital capacity)
● Narrow airways / reduce airflow in & out of lungs (eg. asthma - inflamed bronchi)
○ Reducing maximum volume of air breathed out in 1 second (forced expiratory volume)
● Reduced rate of gas exchange → increased ventilation rate to compensate for reduced oxygen in blood
100
Suggest why people with lung disease experience fatigue
Cells receive less oxygen → rate of aerobic respiration reduced → less ATP made
101
Suggest how you can analyse and interpret data to the effects of pollution,
smoking and other risk factors on the incidence of lung disease
● Describe overall trend → eg. positive / negative correlation between risk factor and incidence of disease
● Manipulate data → eg. calculate percentage change
● Interpret standard deviations → overlap suggests differences in means are likely to be due to chance
● Use statistical tests → identify whether difference / correlation is significant or due to chance
○ Correlation coefficient → examining an association between 2 sets of data
○ Student’s t test → comparing means of 2 sets of data
○ Chi-squared test → for categorical data
102
suggest how you can evaluate the way in which experimental data led to
statutory restrictions on the sources of risk factors
● Analyse and interpret data as above and identify what does and doesn’t support statement
● Evaluate method of collecting data
○ Sample size → large enough to be representative of population?
○ Participant diversity eg. age, sex, ethnicity and health status → representative of population?
○ Control groups → used to enable comparison?
○ Control variables eg. health, previous medications → valid?
○ Duration of study → long enough to show long-term effects?
● Evaluate context → has a broad generalisation been made from a specific set of data?
● Other risk factors that could have affected results?
103
Explain the difference between correlations and causal relationships
● Correlation = change in one variable reflected by a change in another - identified on a scatter diagram
● Causation = change in one variable causes a change in another variable
● Correlation does not mean causation → may be other factors involved
104
Explain what happens in digestion
● Large (insoluble) biological molecules hydrolysed to smaller (soluble) molecules
● That are small enough be absorbed across cell membranes into blood
105
Describe the digestion of starch in mammals
● Amylase (produced by salivary glands / pancreas) hydrolyses starch to maltose
● Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
● Hydrolysis of glycosidic bond
106
Describe the digestion of disaccharides in mammals
● Membrane-bound disaccharidases hydrolyse disaccharides to 2 monosaccharides:
○ Maltase - maltose → glucose + glucose
○ Sucrase - sucrose → fructose + glucose
○ Lactase - lactose → galactose + glucose
● Hydrolysis of glycosidic bond
107
Describe the digestion of lipids in mammals, including action of bile salts
● Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
● This increases surface area of lipids for increased / faster lipase activity
● Lipase (made in pancreas) hydrolyses lipids (eg. triglycerides) → monoglycerides + fatty acids
● Hydrolysis of ester bond
108
Describe the digestion of proteins by a mammal
● Endopeptidases - hydrolyse internal (peptide) bonds
within a polypeptide → smaller peptides
○ So more ends / surface area for exopeptidases
● Exopeptidases - hydrolyse terminal (peptide) bonds at
ends of polypeptide → single amino acids
● Membrane-bound dipeptidases - hydrolyse (peptide)
bond between a dipeptide → 2 amino acids
● Hydrolysis of peptide bond
109
Suggest why membrane-bound enzymes are important in digestion
● Membrane-bound enzymes are located on cell membranes of epithelial cells lining ileum
● (By hydrolysing molecules at the site of absorption they) maintain concentration gradients for absorption
110
Describe the pathway for absorption of products of digestion in mammals
Lumen (inside) of ileum → cells lining ileum (part of small intestine) → blood
111
Describe the absorption of amino acids and monosaccharides in mammals
Co-transport:
1 ● Na
+ actively transported from epithelial cells lining ileum to blood (by Na+/K+ pump)
● Establishing a conc. gradient of Na+ (higher in lumen than epithelial cell)
2 ● Na + enters epithelial cell down its concentration gradient with glucose against its concentration gradient
● Via a co-transporter protein
3 ● Glucose moves down a conc. gradient into blood via facilitated diffusion
112
Describe the absorption of lipids by a mammal, including the role of micelles
● Micelles contain bile salts, monoglycerides and fatty acids
○ Make monoglycerides and fatty acids (more) soluble in water
○ Carry / release fatty acids and monoglycerides to cell / lining of ileum
○ Maintain high concentration of fatty acids to cell / lining
● Monoglycerides / fatty acids absorbed (into epithelial cell) by diffusion (lipid soluble)
● Triglycerides reformed in (epithelial) cells and aggregate into globules
● Globules coated with proteins forming chylomicrons which are then packaged into vesicles
● Vesicles move to cell membrane and leave via exocytosis
○ Enter lymphatic vessels and eventually return to blood circulation
113
Explain how the structure of veins relates to their function
Function – carry blood back to heart at lower pressure
● Wider lumen than arteries → less resistance to blood flow
● Very little elastic and muscle tissue → blood pressure lower
● Valves → prevent backflow of blood
114
Explain how the structure of arterioles relates to their function
Function – (division of arteries to smaller vessels which can) direct blood to different capillaries / tissues
● Thicker smooth muscle layer than arteries
○ Contracts → narrows lumen (vasoconstriction) → reduces blood flow to capillaries
○ Relaxes → widens lumen (vasodilation) → increases blood flow to capillaries
● Thinner elastic layer → pressure surges are lower (as further from heart / ventricles)
115
Explain how the structure of arteries relates to their function
Function – carry blood away from heart at high pressure
● Thick smooth muscle tissue → can contract and control / maintain blood flow / pressure
● Thick elastic tissue → can stretch as ventricles contract and recoil as ventricles relax, to
reduce pressure surges / even out blood pressure / maintain high pressure
● Thick wall → withstand high pressure / stop bursting
● Smooth / folded endothelium → reduces friction / can stretch
● Narrow lumen → increases / maintains high pressure
116
How can heart rate be calculated from cardiac cycle data?
Heart rate (beats per minute) = 60 (seconds) / length of one cardiac cycle (seconds)
117
Describe the equation for cardiac output
Cardiac output (volume of blood pumped out of heart per min) = stroke volume (volume of blood pumped in
each heart beat) x heart rate (number of beats per min)
118
Suggest and explain causes of excess tissue fluid accumulation
● Low concentration of protein in blood plasma OR high salt concentration
○ Water potential in capillary not as low → water potential gradient is reduced
○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
● High blood pressure → high hydrostatic pressure
○ Increases outward pressure from arterial end AND reduces inward pressure at venule end
○ So more tissue fluid formed at arteriole end / less water absorbed at venule end by osmosis
○ Lymph system may not be able to drain excess fast enough
119
How do humans breath in by by inspiration?
1. Diaphragm muscles contract → flattens
2. External intercostal muscles contract, internal intercostal muscles relax (antagonistic) →ribcage pulled up / out
3. Increasing volume and decreasing pressure(below atmospheric) in thoracic cavity
4. Air moves into lungs down pressure gradient
120
How do humans breath out by exhalation?
1. Diaphragm relaxes → moves upwards
2. External intercostal muscles relax, internal intercostal muscles may contract → ribcage moves down / in
3. Decreasing volume and increasing pressure (above atmospheric) in thoracic cavity
4. Air moves out of lungs down pressure gradient
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Suggest why expiration is normally passive at rest
● Internal intercostal muscles do not normally need to contract
● Expiration aided by elastic recoil in alveoli
