organisms exchange substances with their environment Flashcards
1
Q
state 4 examples of things that organisms need to exchange with their environment (exchange)
A
- respiration gases (oxygen, carbon dioxide)
- glucose/nutrients
- heat
- waste (e.g. urea)
2
Q
how do the surface area to volume ratios of small & large organisms affect them? (exchange)
A
- small organisms have a large surface area to volume ratio, therefore can rely only on diffusion for substance exchange
- large organisms have a small surface area to volume ratio, therefore must rely on mass transport systems & other processes (diffusion, osmosis, active transport) for substance exchange
3
Q
what have organisms evolved to have relative to their SA:V ratio? (exchange)
A
- a flattened shape so that no cell is ever far from the surface (e.g. leaf)
- specialised a change surfaces with large areas to increase the SA:V ratio (e.g. lungs in mammals)
4
Q
state 5 features of specialised exchange surfaces (exchange)
A
- a large surface area relative to the volume of the organism, which increases the rate of exchange
- very thin so that the diffusion distance is short & therefore materials cross the exchange surface rapidly
- selectively permeable to allow selected materials to cross
- movement of the environmental medium (e.g. air) to maintain a diffusion gradient
- a transport system to ensure the movement of the internal medium (e.g. blood) to maintain a diffusion gradient
5
Q
what is diffusion proportional to? (exchange)
A
- diffusion ∝ (surface area X difference in concentration) ÷ length of diffusion path
6
Q
what makes up the respiratory ventilation centre & where are they located? (exchange)
A
- made up of an inspiratory centre & expiratory centre
- found in the medulla
7
Q
outline the process of inspiration/inhalation (exchange)
A
- external intercostal muscles contract & internal intercostal muscles relax (ribs move up & out)
- diaphragm contracts & moves down (forms a flattened disc)
- thorax volume increases, which causes pressure in the thorax to decrease
- air is drawn up into the lungs as atmospheric pressure in grater than pulmonary pressure
8
Q
outline the process of expiration/exhalation (exchange)
A
- internal intercostal muscles contract & external intercostal muscles relax (ribs move in)
- diaphragm relaxes & moves upwards (bends back into a disc)
- thorax volume decreases, so pressure in the thorax increases
- air is forced out of the lungs as pulmonary pressure is greater than that of the atmosphere
9
Q
are inspiration & expiration active or passive processes? (exchange)
A
- inspiration (breathing in) is an active process, therefore requires energy
- exhalation (breathing out) is a mostly passive process, so doesn’t require much energy
10
Q
why are mammalian lungs located inside the body? (2) (exchange)
A
- air is not dense enough to support & protect them as they are delicate
- the body as a whole would otherwise lose large amounts of water & dry out
11
Q
why is the volume of oxygen absorbed & carbon dioxide expelled large in mammals? (exchange)
A
- they are large organisms with a large volume of living cells
- they maintain a higher body temperature, which is related to them having high metabolic & respiratory rates
12
Q
outline 8 components of the respiratory system (exchange)
A
- trachea
- bronchi
- bronchiole
- alveoli
- diaphragm
- ribcage
- intercostal muscle
- lung
13
Q
where is the site of gas exchange in mammals? (exchange)
A
- the epithelium of the alveoli
14
Q
what must there be to n sure a constant supply of oxygen to the body? (exchange)
A
- a diffusion gradient must be maintained at the alveolar surface
15
Q
why do organisms with internal exchange surfaces have a means of moving the external medium over the surface? (exchange)
A
- because diffusion alone is not fast enough to maintain adequate transfer of oxygen & carbon dioxide over the trachea, bronchi & bronchioles
16
Q
what lines/surrounds each alveolus? (exchange)
A
- lined with epithelial cells (0.05µm - 0.3µm thick)
- surrounded by a network of pulmonary capillaries (7µm - 10µm thick)
- these capillaries have walls that are only a single layer of cells thick (0.04µm - 0.2 μm)
17
Q
why is diffusion of gases between the alveoli & the blood very quick? (6) (exchange)
A
- red blood cells are slowed as they pass through pulmonary capillaries, which allows more time for diffusion
- the distance between the alveolar air & RBCs is reduced as they pass through RBCs are flattened against the capillary walls
- the walls of both alveoli & capillaries are very thin & therefore the distance over which diffusion takes place is very short
- alveoli & pulmonary capillaries have a very large total surface area
- breathing movements constantly ventilate the lungs, & action around the heart constantly circulates blood around the alveoli. Together they ensure that a step concentration gradient of the gases to be exchanged is maintained
- blood flow through the pulmonary capillaries maintains a concentration gradient of
18
Q
outline the descriptions & symptoms of the following lung diseases & explain their effect on lung function: tuberculosis, fibrosis, asthma, emphysema (exchange)
A
tuberculosis:
- caused by bacteria
- causes an immune response building a wall around the lungs. Hard lumps are formed
- SYMPTOMS = persistent cough, fatigue
- affects lung function as it decreases tidal volume, can lead to fibrosis which also decreases tidal volume
fibrosis:
- scar tissue in the lungs due to infection/chemical exposure
- SYMPTOMS = shortness of breath, dry cough
- affects lung function as they become thick & less elastic so can’t explanations as much. This decreases forced vital capacity & tidal volume
asthma:
- airways become inflames (can be allergy due to dust/pollen)
- SYMPTOMS = wheezing, tight chest
- affects lung function as muscle in the bronchioles contracts & lots of mucus is produced. This constricts the airways & causes decreased air flow & there decreased FEV1
emphysema:
- caused by smoking/pollution(long term)
- SYMPTOMS: inflammation for the alveoli by foreign particles (attracts phagocytes)
- affects lung function as phagocytes break down elastin which means the alveoli can’t stretch & recoil as well. This damages the alveoli walls, which decreases surface area, which decreased the rate of exchange. This decreases FEV1
19
Q
outline the structure of fish gills & how they work (exchange)
A
- located behind the fish head
- are made up of gill filaments that are stacked up in a pile
- gill lamellae are at right angles to the gill filaments. They increase the surface area of the gills
- lots of capillaries maintains a concentration gradient
- water is taken in through the mouth & is forced over the gills & out through an opening on each side of the body
- the flow of blood & water occur in the opposite direction
20
Q
why is the countercurrent flow system important? (exchange)
A
- for ensuring that the maximum possible gas exchange is achieved
- if the water & blood flowed in the same direction far less gas exchange would be achieved
21
Q
what is the countercurrent system?
A
- blood & water flow over the gills lamellae in opposite directions
22
Q
what does the arrangement of the countercurrent flow system mean for blood? (exchange)
A
- blood that is already well loaded with oxygen meets water, which has its maximum concentration of oxygen
- therefore diffusion of oxygen from the water to the blood takes place
- blood with little oxygen in it meets water that has had most (but not all of) its oxygen removed
- this means that diffusion of oxygen from the water to the blood takes place
23
Q
what does the countercurrent flow system mean for oxygen uptake? (exchange)
A
- a diffusion gradient for oxygen uptake is maintained across the entire width of the gill lamellae
- this means that 80% of the oxygen available in the water is absorbed into the blood of the fish
24
Q
outline & explain the process of gas exchange in single celled organisms (4)(exchange)
A
- are small & therefore have a large SA:V ratio
- oxygen is absorbed by diffusion across their body surface (this is covered by only a cell-surface membrane
- carbon dioxide from respiration diffuses across their body surface in the same way
- when a living cell is surrounded by a cell wall, there is no additional barrier to the diffusion of gases
25
what are the characteristics of an insect? (4) (exchange)
- 3 body segments (head, thorax, abdomen)
- 3 pairs of jointed legs
- normally have antennae
- wings (1 or 2 pairs)
26
what have insects evolved to have to aid gas exchange? (2) (exchange)
- tracheae (internal network of tubes) that are supported by strengthened rings to stop them from collapsing
- these are further divided into smaller dead-end tubes (trachaeoles) that extend throughout the body tissues of the insect
27
outline the route taken by oxygen into an insect (exchange)
- spiracles —> trachea —> trachaeoles —> oxygen diffuses directly into relieving cells (no oxygen is transported around the body)
28
explain 3 ways in which respiratory gases can move in & out of the tracheal system (exchange)
along a diffusion gradient:
- when cells are respiring, O2 is used up so its concentration towards the end off the trachaeoles falls
- this creates a diffusion gradient that causes O2 to diffuse from the atmosphere along the tracheae & trachaeoles
- CO2 produced during respiration creates a diffusion gradient in the opposite direction they causes CO2 to diffuse along the trachaeoles & trachea to the atmosphere
mass transport:
- the contraction of muscles in insects can squeeze the trachea, enabling mass movements of air in & out
- this further speeds up the exchange of respiratory gases
the ends of trachaeoles are filled with water:
- during periods of major activity, the muscle cells around the trachaeoles respire & carrot out some anaerobic respiration
- this produces lactate, which is soluble & lowers the water potential of the muscle cells, therefore water moves into the cells via osmosis
- the water in the end of the trachaeoles decreases in volume & in doing so draws air further into them
- this means the final diffusion pathway is in a gas rather than liquid phase & therefore diffusion is more rapid
- this increases the rate at which air is moved in the trachaeoles, but leads to greater water evaporation
29
explain what spiracles are & how they work (4) (exchange)
- holes on the body surface that gases enter & leave the tracheae from
- when they are open water vapour can evaporate from the insect
- most of the time they are closed to prevent water loss
- they are periodically opened to allow for gas exchange
30
why must insects be small? (exchange)
- to maintain a short diffusion distance
31
what is abdominal pumping in insects & why is it effective? (4) (exchange)
- occurs during vigorous exercise
- insects flex their abdomen repeatedly
- this increases abdominal pressure & ‘squeezes’ the tracheae/trachaeoles
- the creation of a pressure gradient helps to force out CO2
32
what happens to oxygen & carbon dioxide when photosynthesis is taking/not taking place? (4) (exchange)
taking place:
- although some carbon dioxide comes from respiration of cells, most if it is obtained from the external air
- in the same way, come oxygen from photosynthesis is used in respiration but most of it diffuses out of the plant
not taking place:
- oxygen diffuses into the leaf because it is constantly being used by cells during respiration
- in the same way, carbon dioxide produced during respiration diffuses out of
33
how is gas exchange in plants similar to that of insects? (2) (exchange)
- no living cell is far from the external air, & therefore a source of oxygen & carbon dioxide
- diffusion takes place in the gas phase (air), which makes it more rapid than if it were in water
34
what is the diffusion pathway like in plants & why? (3) (exchange)
- short & fast
- no living cell is far from a source of oxygen/carbon dioxide
- diffusion takes place in air, which if faster than if it were in water
35
where does most of the gas exchange in plants occur? (exchange)
- the leaves
36
outline 3 leaf adaptations that allow for rapid diffusion (exchange)
- lots of stomata (small pores) so no cell is far from one, & therefore the diffusion pathway is short
- numerous interconnecting air-spaces that occur throughout the mesophyll so that bases can readily come in contact with the mesophyll cells
- large surface area of mesophyll calls for rapid diffusion
37
where are stomata mostly found? (exchange)
- the underside of leaves
38
what surrounds each stoma & why are the important? (2) (exchange)
- each stoma is surrounded by a pair of guard cells that c open & close the stomata pore, so that they can control the rate of gas exchange
- this is important because terrestrial organisms lose water by evaporation
39
how do plants control the rate of water lost? (2) (exchange)
- by closing the stomata at times where water loss would be excessive
- this balances the conflicting needs of gas exchange & the control of water loss
40
how do insects limit water loss (3) (exchange)
- they have a small SA:V ratio to minimise the area over which water is lost
- they have waterproof coverings over their body surfaces. Insects have a rigid outer skeleton of chitin that is covered with a waterproof cuticle
- spiracles are the openings of the tracheae at the body surfaces that can be closed to reduce water loss. This conflicts with he need for exogenous & so occurs largely when the insect is at rest
41
why can’t plants have a small SA:V ratio? (2) (exchange)
- because they photosynthesise
- this requires a large leaf surface area for the capture of light & for the exchange of gases
42
what are xerophytes? (exchange)
- plants that are adapted for life in warm, dry or windy habitats
- they are all adapted to prevent water loss
- e.g. cacti & marram grass
43
outline 5 plant adaptations of xerophytes that prevent water loss (exchange)
- a thick cuticle —> although the waxy cuticle of leaves forms a waterproof barrier, up to 10% of water loss can still occur by this route. The thicker the cuticle, the less water can escape by this means (e.g. holly)
- rolling up of leaves —> most leaves have their stomata largely (or entirely) confined to the lower epidermis. The rolling f the leaves in a way that protects the lower epidermis from the outside helps to trap a region of still air within the rolled leaf. This region becomes saturated with water vapour & so has a very high water potential. There is no water potential gradient between the inside & outside of the leaf & therefore no water loss (e.g. marram grass)
- hairy leaves —> a thick layer of hairs on laves (especially on the lower epidermis) traps still, moist air next to the leaf surface. The water potential gradient between the inside & the outside of the leaves is reduced & therefore less water is lost by evaporation (e.g. heather plants)
- stomata in pits or grooves —> trap still, moist air next to the leaf & reduce the water potential gradient (e.g. pine trees)
- a reduced SA:V ratio of the leaves —> by having leaves that are small & roughly circular in cross section (e.g. like in pine needles) rather than leaves that are broad & flat, the rate of water loss can be reduced. This reduction in SA is balanced against the need for a sufficient area for photosynthesis to meet the requirements of the plant
44
what should adaptations of xerophytes always be related to? (exchange)
- reducing water potential gradient & therefore slower diffusion, less water loss from air spaces & hence reduced evaporation of water
45
what is digestion? (exchange)
- the process in which large molecules are hydrolysed by enzymes into small molecules, which can be absorbed & assimilated
46
outline the 7 main components of the digestive system (exchange)
- oesophagus
- stomach
- ileum
- large intestine
- rectum
- salivary glands
- pancreas
47
what is the role of the oesophagus in the digestive system? (exchange)
- carries food from the mouth to the stomach
48
what is the role of the stomach in the digestive system? (3) (exchange)
- is a muscular sac with an inner layer that produces enzymes
- it stores & digests food (especially proteins)
- it has glands that produce enzymes that digest protein
49
what is the role of the ileum in the digestive system? How is it adapted for this? (4) (exchange)
- food is further digested in the ileum by enzymes that are produced by its walls & glands that pour their secretions into it
- the inner walls are folded into villi, which gives them a large SA
- the SA of the villi is further increased by microvilli (millions of tiny projections) on the epithelial cells of each villus
- this adapts the ileum for its purpose of absorbing the products of digestion into the bloodstream
50
what is the role of the large intestine in the digestive system? (2) (exchange)
- absorbs water
- most of the water absorbed is water from the secretions of the digestive glands
51
what is the role of the rectum in the digestive system? (2) (exchange)
- final section of the intestines
- faeces are stored here before being periodically removed from the anus in egestion
52
what is the role of the salivary glands in the digestive system? (3) (exchange)
- located near the mouth
- they pass their secretions via a duct into the mouth
- these secretions contain amylase, which hydrolyses starch into maltose
53
what is the role of the pancreas in the digestive system? (exchange)
- found below the stomach that produces pancreatic juice
- this secretion contains proteases to hydrolyse proteins, lipase to hydrolyse lipids & amylase to hydrolyse starch
54
what are the 2 stages of digestions? (exchange)
- physical breakdown
- chemical breakdown
55
outline & explain the process of physical breakdown during digestion (3) (exchange)
- if food is large it is broken down into smaller pieces by the teeth
- this makes it possible to digest the food & also provides a large surface area for chemical digestion
- food is churned by the muscles in the stomach wall (also physically breaks it up)
56
outline & explain the process of chemical breakdown in digestion (3) (exchange)
- process hydrolyse large insoluble molecules into smaller soluble ones
- all digestive enzymes function by hydrolysis
- enzymes are specific so more than 1 is usually needed to hydrolyse a large enzyme
57
what is the role for the following digestive enzymes?: carbohydrates, lipases & peptidases/proteases (3) (exchange)
- carbohydrates hydrolyse carbohydrates to monosaccharides
- lipases hydrolyse lipids into glycerol/monoglycerides & fatty acids
- proteases hydrolyse proteins into amino acids
58
outline the process of carbohydrate digestion (exchange)
- amylase is produced in the mouth & pancreas
- it hydrolyses the alternate glycosidic bonds of a starch molecule to produce maltose
- this is then hydrolysed into alpha glucose by maltose (second enzyme), which is produced in the lining of the ileum
59
what is a membrane bound disaccharidase? (exchange)
- enzymes in the cell surface membranes of the epithelial cells in the ileum
- e.g. maltase that breaks down maltose
60
outline the process of lipid digestion (4) (exchange)
- lipids are hydrolysed by lipases
- lipases are produced in the pancreas & hydrolyse the ester bonds in triglycerides into fatty acids & minoglycerides
- lipids split up into tiny droplets called micelles by bile salts produced in the liver
- this process is emulsification & increases SA of lipids so that the action of lipases is sped up
61
outline the process of protein digestion & state/explain the 3 types (4)
- proteins are hydrolysed by peptidases
- endopeptidases hydrolyse the peptide bonds between AAs in the central region of a protein molecules forming a series of peptide molecules
- exopeptidases hydrolyse the peptide bonds on the terminal AAs of the peptide molecules formed by endopeptidases. In this way they progressively release dipeptides & single AAs
- dipeptidases hydrolyse the bond between the two amino acids of a dipeptide. They are membrane bound as they are part of the CSM of the epithelial cells lining the ileum
62
how are villi adapted to increase the efficiency of absorption? (5) (exchange)
- they increase the SA of the ileum for diffusion & therefore tehe rate of absorption
- they have very thin walls, therefore reducing the diffusion distance
- they contain muscle & so are able to move. This helps maintain diffusion gradients as their movement mixes the contents of the ileum. This ensures that new material rich in digestion products replaces absorbed material
- they are well supplied with blood vessels so that blood can carry away absorbed molecules & therefore maintain a diffusion gradient
- epithelial cells lining the villi have mircovilli that further increase the area for absorption
63
what 2 processes are used during the absorption of amino acids & monosaccharides? (exchange)
- diffusion
- co-transport
64
outline the process of absorption of triglycerides (7) (exchange)
- monoglycerides (MGs) & fatty acids stay with the bile salts that initially emulsified them to form micelles
- micelles come into contact with epithelial cells lining the ileum through movement of material in its lumen, where they break down to form MGs & fatty acids
- they can easily diffuse into the epithelial cells as they are non-polar
- when inside they are transported to the ER & are recombined to form triglycerides
- in the ER & Golgi apparatus they associate with cholesterol & lipoproteins to from chylomicrons (particles adapted for the transport of lipids)
- chylomicrons move out of epithelial cells by exocytosis & enter lacteals (lymphatic vessels) that are found at the centre of each villus
- the chylomicrons pass into the blood system & the triglycerides in them are hydrolysed by an enzyme found in the endothelial cells of blood capillaries, where they diffuse into cells
65
what are the haemoglobins? (exchange)
- a group of chemically similar molecules that are found in a wide variety of organisms
- they are protein molecules with a quaternary structure that has evolved to make it efficient as loading & unloading oxygen under different sets of conditions
66
outline the primary, secondary tertiary & quaternary structure of haemoglobin (exchange)
- primary structure —> sequence of amino acids in the 4 polypeptide chains
- secondary structure —> each of the polypeptide chains is coiled into a helix
- tertiary structure —> each polypeptide chains is coiled is folded into a precise shape (an important factor in its ability to carry oxygen)
- quaternary structure —> all 4 polypeptides are linked together. Each polypeptide is associated with a haem group that has a Fe2+ (ferrous) ion. Each Fe2+ ion can combine with one O2 molecules (so 4 O2 molecules can be carried by a single haemoglobin molecule in humans)
67
name the process in which haemoglobin binds with oxygen & where this takes place (exchange)
- loading/associating
- occurs in the lungs
68
name the process by which haemoglobin releases its oxygen & where this occurs (exchange)
- unloading/dissociating
- occur is in the tissues
69
how easily does haemoglobin with a high/low affinity for oxygen bind to & release it? (
- high affinity for oxygen = take it up more easily but releases it less easily
- low affinity = takes it up less easily but releases it more readily
70
what is the role of haemoglobin? (exchange)
- to transport oxygen around the body
71
what must haemoglobin do to be efficient as transporting oxygen? (2) (exchange)
- readily associate with oxygen at the surface where gas exchange takes place
- readily dissociate from oxygen at tissues requiring it
72
what can haemoglobin change under different conditions? (exchange)
- its affinity for oxygen
73
how can haemoglobin change its affinity for oxygen under different conditions?
- its shape changes in the presence of certain substances (e.g. in the presence of CO2 the new shape binds more loosely to oxygen so it releases its oxygen
74
why do different haemoglobins have different affinities for oxygen? (4) (exchange)
- depends in the shape of the molecule
- each species produces a haemoglobin with a slightly different amino acid sequence
- the haemoglobin of each species therefore has a slightly different tertiary & quaternary structure, so has different oxygen binding abilities
- depending in its structure, haemoglobin molecules can either have a high or low affinity for oxygen
75
what creates the oxygen dissociation curve? (exchange)
- when haemoglobin is exposed to different partial pressures of oxygen it doesn’t bind to the oxygen evenly
76
explain the shape of the oxygen dissociation curve & state the axis labels (exchange)
- x = partial pressure of O2 (kPa)
- y = saturation of haemoglobin with O2 (%)
- gradient is shallow as little haemoglobin binds to oxygen at low oxygen concentrations
- the gradient of the curve steepens due to positive cooperativity (it is easier for the 2nd oxygen to bind than the 1st (as 1st changes the quaternary structure making it easier to bind to O2) so it takes a smaller increase in the partial pressure of O2 to bind the second oxygen molecule)
- gradient of the curve reduced & the graph flattens as it becomes harder for O2 to bind to haemoglobin (becomes harder after the binding of the 3rd oxygen as it is not probable that a single O2 molecule will find an empty site to bind to)
77
why are there multiple types of oxygen dissociation curve? (exchange)
- different species have different types of haemoglobin (with different affinities for oxygen) & the shape of any type of haemoglobin can change under different conditions
78
what is does it mean the further to the left & right the oxygen dissociation curve is? (2) (exchange)
- the further to the left the curve, the greater the affinity of haemoglobin for oxygen (loads O2 readily but unloads it less easily)
- the further to the right the curve, the lower the affinity of haemoglobin for oxygen (does not load O2 readily but in loads it easily)
79
what does the presence of CO2 mean for the affinity of haemoglobin for O2? (exchange)
- has a reduced affinity for O2 in the presence of CO2
80
what is the Bohr effect & what does it explain? (2) (exchange)
- the greater the CO2 the more readily the haemoglobin releases its O2
- explains why the behaviour of haemoglobin changes in different regions of the body
81
what happens to the concentration of CO2 at the gas exchange surface & how does this affect haemoglobin & the oxygen dissociation curve? (3) (exchange)
- concentration of CO2 is low because it diffuses across the exchange surface & is excreted from the organism
- the affinity of haemoglobin for oxygen is increased, which means oxygen is readily loaded by haemoglobin
- the reduced CO2 concentration shifts the oxygen dissociation curve to the left
82
what happens to the concentration of CO2 in respiring tissues & how does this affect haemoglobin & the oxygen dissociation curve? (3) (exchange)
- concentration of CO2 is high
- the affinity of haemoglobin for oxygen is reduced so oxygen is readily unloaded from the haemoglobin into the muscle cells
- the increased CO2 concentration shifts the oxygen dissociation curve to the right
83
why does haemoglobin release O2 more readily in garter CO2 concentrations? (exchange)
- dissolved CO2 is acidic & the low pH causes haemoglobin to change shape
84
outline the how pH is changed at the gas exchange surface due to CO2 (2) (exchange)
- CO2 is constantly being removed at the gas exchange surface
- the pH is slightly raised due to the low concentration of CO2
85
what a raised pH do to haemoglobin? (2) (exchange)
- higher pH changes shape of haemoglobin into one that enables it to load O2 readily
- shape also increases the affinity of haemoglobin for O2 so it isn’t released while being transported in the blood to the tissues (where CO2 is produced by respiring cells)
86
outline how CO2 in solution changes the pH of blood in tissues (3) (exchange)
- CO2 is acidic in solution so the pH of the blood within the tissues is lowered
- the lower pH changes the shape of haemoglobin into one with lower affinity for oxygen
- haemoglobin releases its O2 into the respiring tissues
87
outline the process of release of O2 in active tissues (6) (exchange)
- the higher the rate of respiration —> the more CO2 produced by the tissues —> the lower the pH —> the greater the haemoglobin shape change —> the more readily O2 is unloaded —> the more O2 is available for respiration
88
what happens to the saturation of haemoglobin as it reaches tissues with low respiratory rates? (
- in most cases haemoglobin is not fully saturated in humans (97% overall)
- when this reaches a tissue with a low respiratory rate only one molecule is usually released
- therefore blood returning to the lungs is still 75% saturated
89
how can different species live in different conditions, in terms of haemoglobin? (
- different types of haemoglobin (from different species) have evolved to adapt to different environments & conditions
- e.g. species that love in lower partial pressure of O2 have evolved haemoglobin that has a higher affinity for O2 than the haemoglobin of animals that live where the partial pressure of O2 is higher
90
what does the need for a specialised transport medium & if it is circulated by a pump depend on? (2) (exchange)
- the SA:V ratio
- how active the organism is
91
outline & explain 7 features of transport systems? (exchange)
- a suitable medium to carry materials (e.g. blood). This is normally a liquid based on water as water readily dissolves substances & can be moved easily, but can be a gas breathed in & out of the lungs
- a form of mass transport in which the transport medium is moved around in bulk over large distances (more rapid than diffusion)
- a closed system of tubular vessels that contains the transport medium & forms a branching network to distribute it to all parts of the organism
- a mechanism for moving the transport medium within vessels. This requires a pressure difference between one part of the system & another (animals use muscular contraction either side & player rely on natural passive processes like evaporation of water)
- a mechanism to maintain the mass flow movement in one direction (e.g. valves)
- a means of controlling the flow of transport medium to suit the changing needs of different parts of the organism
- a mechanism for the mass flow of water or gases (e.g. the intercostal muscles & diaphragm during breathing in mammals)
92
what type of circulatory system do mammals have? (exchange)
- closed & double circulatory system where blood is confined to vessels & passes through the heart twice for each complete circuit of the body
93
outline the first & second circuit of a heart beat (exchange)
- first circuit pumps deoxygenated blood to the lungs to take in O2 & remove CO2. Blood then returns to the heart
- second circuit pumps oxygenated blood around the body. Blood gives up its O2 at body cells & the deoxygenated blood (full of CO2) returns to the heart to be pumped to the lungs again
94
why is deoxygenated blood returned to the heart to be pumped to the lungs again? (4) (exchange)
- because blood’s pressure is reduced when it passes through the lungs
- if it were to pass immediately to the body it’s low pressure would make circulation very slow
- therefore it it’s returned to the heart to boost pressure before being circulated to the rest of the body
- this means that substances are delivered to the rest of the body quickly (important for mammals as they have a high body temperature so a high metabolic rate)
95
why is the final exchange from blood vessels into cells rapid? (exchange)
- it occurs over a large SA & short distances & there is a steep concentration gradient
96
what do the left & right side of the heart deal with in terms of blood? (3) (exchange)
- left pump deals with oxygenated blood from the lungs
- right pump deals with deoxygenated blood from the body
- it is important the oxygenated & deoxygenated blood is kept separate
97
what are the atria & ventricles? (exchange)
- the atria are thin walled & elastic that stretches as it collects blood. They receive blood from the veins
- the ventricles have a thicker muscular wall as they have to contract strongly to pump blood some distance (either to the lungs or the rest of the body). They pump blood away from the heart into the arteries
98
what are the 2 main valves in the heart? (exchange)
- the left atrioventricular/bicuspid valve
- the right atrioventricular/tricuspid valve
99
what are pulmonary vessels? (exchange)
- vessels that connect the heart to the lungs
100
explain the roles of the 4 main blood vessels in the heart (exchange)
- the aorta (artery) is connected to the left ventricle & carried oxygenated blood to all parts of the body, except the lungs
- the vena cava (vein) is connected to the right atrium & brings deoxygenated blood from the tissues of the body (except the lungs). It is divided into the superior & inferior vena cavas
- the pulmonary artery is connected to the right ventricle & carries deoxygenated blood to the lungs, where its oxygen is replenished & its CO2 is removed ( unusually for an artery, it carries deoxygenated blood)
- the pulmonary vein is connected to the left atrium & brings oxygenated blood back from the lungs (unusually for a vein, it carried oxygenated blood)
101
how is the heart muscle supplied with oxygen?
- doesn’t use oxygenated from the oxygenated blood in its left side
- supplied by its own blood vessels (coronary arteries) which branch off the aorta after it leaves the heart
102
what does a blockage of the coronary arteries lead to? (2) (exchange)
- leads to myocardial infarction/heart attach
- this is because an area of the heart muscle is deprived of blood & therefore oxygen. The muscle cells in this region are unable to respire aerobically & therefore die
103
outline the key structures of the human heart (exchange)
- see physical flashcards
104
name the 2 stages of the heart beating (exchange)
- systole (contraction of heart muscle)
- diastole (relaxation of heart muscle)
105
106
what is a heart beat describes as occurring in 2 stages? (exchange)
- contraction occurs in the ventricles & atria so is describes in 2 stages
107
outline the process of diastole (relaxation of the heart) (7) (exchange)
- blood returns to the atria through the pulmonary vein (from lungs) & the vena cava (from body)
- as the atria fill, the pressure in them rises
- when this pressure in greater than that in the ventricles, the atrioventricular valves open - allowing blood to flow into the ventricles
- the passage of blood is aided by gravity
- the muscular wall on both sides of the atria & ventricle are relaxed at this stage
- the relaxation of the ventricle walls causes them to recoil & reduces the pressure within the ventricle
- this causes the pressure to be lower than that in the aorta & pulmonary artery, & so the semi-lunar valves in the aorta & pulmonary artery close
108
outline the process of atrial systole (contraction of the atria) (2) (exchange)
- the contraction of the atrial walls, along with the recoil of the relaxed ventricle walls, forced the remaining blood into the ventricles from the atria
- throughout this stage, the ,suckle of the ventricle walls remains relaxed
109
outline the process of ventricular systole (contraction for the ventricles) (7) (exchange)
- after a short delay (to allow the ventricles to fill with blood), their walls contract simultaneously
- this increases the blood pressure within them, forcing shut the atrioventricular valves & preventing back flow of blood into the atria
- when they are closed, the pressure in the ventricles keeps rising
- once it exceeds that in the aorta & pulmonary artery, blood is forced from the ventricle into them
- the ventricles contract forcefully as they have thick muscular walls
- this creates the high pressure needed to pump blood around the body
- the thick wall of the left ventricle has to pump blood to the extremities of the body, while the thinner wall of the right ventricle has to pump blood to the lungs
110
which regions of pressure does blood flow from/to? (exchange)
- always moves from a region of high pressure to one of low pressure
111
what is the role of valves in the control of blood flow? (
- they are designed so that they open when the difference in blood pressure either side of it favours the movement of blood into he needed direction
- they close when the pressure differences are reversed (when blood would flow in the opposite direction to what is necessary)
112
what are the roles of the atrioventricular valves in the heart? (3) (exchange)
- located between in the atrium & ventricle
- prevent the back flow of blood when contraction of the ventricles means that ventricular pressure exceeds atrial pressure
- closure of them ensures that when the ventricles contract forcefully contracts, blood within them moved to the aorta & pulmonary artery rather than back to the atria
113
what is the role of semi-lunar valves in the heart? (3) (exchange)
- located in the aorta & pulmonary artery rather than
- prevent back flow of blood into the ventricles when the pressure in the vessels exceeds that in the ventricles
- this arises when the elastic walls of the vessels recoil, increasing the pressure within them & when the ventricle walls relax, reducing the pressure within them
114
what is the role of pocket valves in veins? (2) (exchange)
- located in veins in the venous system
- they ensure that when the veins are squeezed (e.g. when skeletal muscles contract), blood flows back towards the heart rather than away from it
115
what type of circulatory system do mammals have? (exchange)
- they have a closed circulatory system where blood is confined to vessels, which allows the pressure within them to be maintained & regulated
116
define cardiac output & state what it is dependent on (2) (exchange)
- the volume of blood pumped by one ventricle of the heart in 1 minute
- depends of heart rate (rate at which the heart beats) & the stroke volume (volume of blood pumped out at each beat)
117
state the equation & units for cardiac output (exchange)
- cardiac output = heart beat X stroke volume
- usually measured in dm3 min-1
118
what is an ECG? Outline what one looks like during a heart attach & fibrilation (4) (exchange)
- electrocardiography
- patterns of large peaks & small troughs that repeat identically at regular intervals
- heart attack = shows less pronounced peaks & larger troughs that are repeated in a similar but not identical way
- fibrilation = heart muscle contracts in a disorganised what that leads to an irregular ECG reading
119
what are the roles of arteries, arterioles, capillaries & veins? (exchange)
- arteries carry blood away from the heart & into arterioles
- arterioles are smaller arteries that control blood flow from arteries to capillaries
- capillaries are tiny vessels that link arterioles to veins
- veins carry blood from capillaries back to the heart
120
outline & explain the 5 basic structures in blood vessels (exchange)
- tough fibrous outer layer that resists pressure changes from both within & outside
- muscle layer that can contract & so control the flow of blood
- elastic layer that helps to maintain blood pressure by stretching & springing back (recoiling)
- thin inner lining (endothelium) that is smooth to reduce friction & thin to allow diffusion
- lumen that is the central cavity of the blood vessel, which blood flow through the
121
what is the function of arteries? (exchange)
- transports blood rapidly under high pressure from the heart to tissues
122
outline & explain 4 ways artery structure is adapted to its function (exchange)
- muscle layer is thick compared to veins. This means that smaller arteries can be constricted & dilated in order to control the volume of blood passing though them
- elastic layer is thicker than veins because it is import at that blood pressure in the arteries is kept high for blood to reach the extremities. Elastic wall is stretched at each systole & springs back during diastole, which helps to maintain high pressure & smooth pressure surges created by the heart beating
- overall thickness of wall is great, which also resists the vessel bursting under pressure
- no valves (except in arteries leaving the heart) because blood is under constant high pressure sue to the heart pumping blood into the arteries. This means it doesn’t tend to flow backwards
123
what is the function of arterioles? (2) (exchange)
- carry blood (under lower pressure than arteries) from arteries to capillaries
- also control the b flow of blood between them
124
outline explain 2 ways in which arteriole structure is relation to its function (exchange)
- muscle layer is thicker than in arteries. The contraction of this muscle allows contraction of the arteriole lumen. This restricts blood flow & so controls movement into the capillaries that supply the tissues with blood
- elastic layer is thinner than in arteries because blood pressure is lower
125
what is the function of veins? (exchange)
- transport blood slowly & under low pressure from the capillaries in tissues to the heart
126
outline & explain 4 ways in which vein structure is related to its function (exchange)
- muscle layer is thinner than arteries as veins carry blood away from tissues & therefore their constriction & dilation can’t control blood flow to tissues
- elastic layer is thinner than arteries because the low pressure of blood within the veins won’t cause them to burst & pressure is too low to create a recoil action
- overall wall thickness is small because pressure is too low to create any risk of bursting. It also allows them to be flattened easily, aiding blood flow in them
- there are valves as intervals throughout to ensure that blood doesn’t backwards (which it may otherwise do due to low pressure). When body muscles contract, veins are compressed, which pressures the blood in them. The valves ensure this pressure directs the blood in 1 direction only (towards the heart)
127
what is the function of capillaries? (2) (exchange)
- exchange metabolic materials (e.g. O2, CO2 & glucose) between the blood & cells of the body
- blood flow is much slower
128
outline & explain 5 ways in which capillary structure is relation to its function (exchange)
- walls consist mostly of a lining layer, so they are extremely thin, meaning the diffusion distance is short. This allows fro rapid idffusion of materials between the blood & other cells
- there are lots of them & they are all highly branched, therefore they provide a large surface area for exchange
- have a narrow diameter & so permeate tissues, meaning that no cell is far from a capillary & there is a short diffusion pathway
- lumen is narrow that red blood cells are squeezed flat against the side of the capillary. This brings them even closer to the cells that they supply oxygen to, reducing diffusion distance
- there are spaces between the lining/endothelial cells that allow white blood cells to escape in order to deal with infections within tissues
129
what is tissue fluid? (3) (exchange)
- contains glucose, amino acids, fatty acids, ions in solution & O2, which it supplies to tissues
- receives CO2 & other waste materials from tissues
- is the means by which materials are exchanges between blood & cells
130
what is tissue fluid made from? (exchange)
- formed from blood plasma, the composition of which is controlled by homeostatic systems
131
outline the process of the formation of tissue fluid (6) (exchange)
- pumping by the heart creates high hydrostatic pressure at the arterial end one of the capillaries
- this hydrostatic pressure causes tissue fluid to move out of the blood plasma
- this outwards pressure is opposed by 2 forces; hydrostatic pressure of the tissue fluid outside the capillaries (which resists out war movement of liquid): the lower water potential of the blood, due to plasma proteins, that causes water to move back into the blood within the capillaries
- the combined effect of these forces creates an overall pressure that pushes tissue fluid out of the capillaries at the arterial end
- this pressure is only enough to force small molecules out the capillaries (leaving cells & proteins in the blood as they are too large to cross the membranes
- this type of filtration under pressure is ultrafiltration
132
where does most of the removed tissue fluid return to? (exchange)
- most return to the blood plasma directly via the capillaries
133
outline the process of the return of tissue fluid to the circulatory system (7) (exchange)
- the loss of tissue fluid from the capillaries reduces the hydrostatic pressure within them
- as a result, by the time the blood has reached the venous end of the capillary networks, its hydrostatic pressure is usually lower that that of the tissue fluid outside of it
- therefore tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside of them
- the plasma has lost water & still contains proteins. It therefore has a lower water potential than the tissue fluid
- as a result, water leaves the tissue by osmosis down a water potential gradient
- the tissue fluid has lost lots of its O2 & nutrients by diffusion into the cells, but has gained CO2 & waste materials in return
134
outline what happens to tissue fluid that doesn’t return to the plasma via the capillaries (3) (exchange)
- the remainder is carried back via the lymphatic system
- the larger vessels in the lymphatic system drain their contents back into the bloodstream via 2 large ducts that join veins close to the heart
- the contents of the lymphatic system are moved by; hydrostatic pressure of the tissue fluid that has left the capillaries: & contraction of body muscles that squeeze the lymph vessels (valves in the lymph vessels unsure that the fluid inside them moves away from the tissues towards the heart)
135
what are oxygen & what adaptations do they have? (4) (exchange)
- long, hollow tubes made up of dead cells with no walls for continuous water columns
- have no cytoplasm or organelles to allow easier water flow (meaning there are no obstructions)
- walls are made up of lignin, which provided support & withstands tension. They are also waterproof
- pits in the walls allow a lateral movement of water
136
what is transpiration in the xylem (2) (exchange)
- transpiration is the evaporation of water from a plant’s surface (mainly leaves)
- water moved down the water potential gradient as there is more water in the leaf than in the air outside
137
is transpiration an active or passive process? (exchange)
- the energy needed is suppled by the sun so the process is passive
138
outline how water moves out through stomata (5) (exchange)
- the humidity of the atmosphere is usual at less than that of the air spaces next to the stomata
- as a result there is a water potential gradient from the air spaces through the stomata to the air
- as long as the stomata are open, water vapour molecules diffuse out of the air spaces into the surrounding air
- water lose by diffusion from the air spaces is replaced by water evaporating from the cell walls of the surrounding mesophyll cells
- plants can control their rate of transpiration by changing the size of the stomata pores
139
outline the process of the movement of water across leaf cells (4) (exchange)
- water is lost from the mesophyll cells by evaporation from their cell walls to the air spaces of the leaf
- this is replaced by water reaching the mesophyll cells from the xylem via cell walls or cytoplasm
- in the cytoplasmic route water movement occurs because; mesophyll cells lose water to the air spaces by evaporation sue to heat from the sun; these cells now have a lower water potential & so water enters by osmosis from neighbouring cells: the loss of water from these neighbouring cells lowers their water potential: they then take in water front heir neighbours by osmosis
- in this way, a water potential gradient is established that pulls water from the xylem, across the leaf mesophyll & out into the atmosphere
140
outline & explain 4 factors affecting the rate of transpiration (exchange)
- light intensity—> higher LI increases transpiration rate as the plant would be photosynthesising & the stomata would be open to let in CO2. This allows water to evaporate conspired to when it is dark & the stomata are closed
- wind —> wind moves air molecules close to stomata so water Vapor is removed faster = increased transpiration rate
- temperature —> plants respire more rapidly at higher temperatures because water evaporated more quickly = high temperature causes increased transpiration rate
- humidity —> high humidity reduces the water potential gradient between inside leaf & outside air = decreased transpiration rate
141
outline the process of the movement of water up the xylem/cohesion tension theory (6) (exchange)
- water evaporated from mesophyll cells due to heat from the sun, leading to transpiration
- water molecules form hydrogen bonds between one another & so stick together (cohesion)
- water forms a continuous in broken columns across the mesophyll cells & down the xylem
- as water evaporates front he mesophyll cells into air spaces beneath the stomata, more molecules of water are drawn up behind it as a result of this cohesion
- a column of water is therefore pulled up the xylem as a result of transpiration (transpiration pull)
- transpiration pull puts the xylem under tension (negative pressure in the xylem)
142
outline 2 pieces of evidence supporting the cohesion tension theory (exchange)
- is a xylem vessel is broken & air enters it, the tree can no longer draw up water. This is because the continuous column of water is broken so the water molecules can no longer stick together
0 when a xylem vessel is broken, water doesn’t leak out (as would be the case if it were under pressure). Instead air is drawn in , which is consistent with it being under tension instead
143
outline the process of using a photometer to measure transpiration (6) (exchange)
- a plant stem is sealed into the photometer using a rubber bung
- fill potometer completely with water so there are no air bubbles
- an air bubbles is introduced into the capillary tube
- the distance the bubble travels (per minute)shows how much water the stem has taken p & gives an indirect measurement of rate. A mean is calculated
- using the mean value the volume of water lost is calculated
- the experiment can be repeated to compare water uptake under different conditions
144
what is translocation? (exchange)
- process by which organic molecules & mineral ions are transported through the plant via the phloem
145
outline the structure of the phloem (3) (exchange)
- made up of sieve tubes arranged from end to end
- their end walls are perforated to form sieve plates
- companion cells are associated with the sieve tube elements
146
outline the theory behind ‘sources’ & ‘sinks’ & how this affects translocation (2) (exchange)
- plants transport sugars produced in photosynthesis dorm the sites of production (sources) to places where it will be used directly or stored for future use (sinks)
- translocation can occur in either direction as sinks can be anywhere in the plant
147
give some examples of organic molecules & inorganic ions transported during translocation (exchange)
- organic molecules = sucrose, amino acids
- inorganic ions = potassium ions, chloride ions, phosphate ions, magnesium ions
148
why can’t translocation be explained by diffusion? (exchange)
- the rate of movement is too fast
149
outline the 3 stages to the mass flow theory (exchange)
- transfer of sucrose into sieve elements from photosynthesising tissue
- mass flow of sucrose though sieve tube elements
- transfer of sucrose from the sieve tube laments into storage or other cells
150
outline the first stage of the mass flow theory (transfer of sucrose into sieve elements from photosynthesising tissue) (5) (exchange)
- sucrose is manufactured from the products of photosynthesis in cells with chloroplasts
- the sucrose diffuses down. Concentration gradient by facilitated diffusion from the photosynthesis cells into companion cells
- hydrogen ions are actively transported from companion cells into he spaces within cell walls using ATP
- these hydrogen ions diffuse down a concentration gradient through carrier proteins into the sieve tube elements
- sucrose molecules are transported along with H+ ions via co-transport via co-transport proteins
151
outline the second stage of mass flow theory (mass flow of sucrose through sieve tube elements) (10) (exchange)
- the sucrose produced by photosynthesis cells (sources) is actively transported into the sieve tubes
- this causes the sieve tubes to have a lower (more negative) water potential
- as the xylem have a higher (less negative) water potential, water moves from the xylem unto the sieve tubes by osmosis, creating a higher hydrostatic pressure within them
-at the respiring cells (sink), sucrose us either used up during respiration or converted to starch for storage
- these cells therefore have a low sucrose content & so sucrose id actively transported unto them from the sieve tubes, lowering their water potential
- due to this lowered water potential, water also moves into these repairing cells (from the sieve tubes) via osmosis
- the hydrostatic pressure of the sieve tubes in this region is therefore lowered
- as a relit of water entering the sieve tube elements at the source & leaving at the sink, there is a higher hydrostatic pressure hydrostatic pressure at the source & a low one at the sink
- there is therefore a mass flow of sucrose solution down this hydrostatic gradient in the sieve tubes
- the process is active as active transport is required for the transport of sugars
152
outline the third stage of mass flow hypothesis (transfer of sucrose from the sieve tube elements into storage or other cells (exchange)
- the sucrose is actively transported by companion cells, out of the sieve tubes & into the sink cells
153
outline 3 pieces of supporting evidence for mass flow theory (exchange)
- companion cells have many mitochondria & readily produce ATP
- the concentration of sucrose is higher in leaves (sources) than in roots (sink)
- downward flow in the phloem occurs in daylight, but stops when leaves are shaded/at night
154
outline 3 pieces of evidence against mass flow theory (exchange)
- not all solutes move at the same speed - they should do so if movement is by mass flow
- sucrose is delivered at more or less the same rate to all regions, rather than going more quickly to the ones with the lowest sucrose solution (which mass flow theory would suggest)
- the function of sieve plates is unclear, as they would seem to hinder mass flow (it has been suggested that they may have a structural function, helping to prevent the tubes from bursting under pressure)
155
outline how a ringing experiment is carried out to investigate transport in plants (4) (exchange)
- a section of the outer layers (protective layer & phloem) is removed around the complete circumference of a woody stem while it is still attached to the rest of the plant
- after a period of time, the region of the stem immediately above the missing ring of tissue starts to swell
- samples of the liquid the acculturates in this swollen region are found to be rich in sugars & other dissolved organic substances
- some non-photosynthesising tissues below the ring are found to wither & die, while those above it continue to grow
156
what do observations from ringing experiments tell us about removing the phloem around the stem? (2) (exchange)
- leads to the sugars of the phloem accumulating above the ring, leading to swelling in this region
- least I the interruption fo slow of sugars to the region below the ring & the death of the tissue is this region
157
what conclusions can be made from ringing experiments? (2) (exchange)
- it is the phloem that are responsible for translocating sugars in plants
- as the ring of tissue removed hadn’t included the xylem, it’s continuity hadn’t been broken
158
outline the process & findings from tracer experiments (7) (exchange)
- radioactive isotope 14C is used to make radioactive 14CO2
- if a plant is grown in n environment with 14CO2, the 14C isotope will be present in the sugars produced during photosynthesis
- these can be attracted as the move within a plant using autoradiograpy
- take thin cross sections of the plant stems & place then on x-ray film
- the film blackens when it has been exposed to the 14C sugars
- the blackened areas correspond to where the phloema re located
- the other tissues don’t blacked so don’t carry the sugars
159
outline 3 other pieces of evidence that translocation occurs in the phloem (exchange)
- when phloem is cut, a solution of organic molecules flow out
- plants provided with radioactive CO2 can be shown to have radioactively labelled carbon in phloem after a short time
- the removal of a ring of phloem around the circumference of a stem leads to the accumulation of sugars above the ring & disappearance from below it
