Exchange and Transport Systems

Question 1

What features increase the rate of movement of molecules across surfaces?

Answer 1

-large SA:V ratio
-very thin
-selectively permeable
-molecules can be moved away to keep the concentration gradient steep

Question 2

Calculating SA:V

Answer 2

(surface area/volume):1

Question 3

Describe and explain the relationship between an organism’s size and SA:V ratio.

Answer 3

The larger the organism the smaller the surface area to volume ratio, so the more heat they lose, the the higher the metabolic rate

Question 4

Explain gas exchange in single-celled organisms

Answer 4

-Relatively large surface area, a thing surface and short diffusion distance (oxygen can take part in reactions as soon as it diffuses into the cell)- no need for specialised gas exchange system

Question 5

Explain gas exchange in fish
(conc of oxygen in air<conc of oxygen in water)

Answer 5

-gills made of lots of thin plates called gill filaments giving a large SA for gas exchange therefore increased rate of diffusion
-gill filaments covered in lamellae (tiny structures) increasing the SA even more
-lamellae have lots of blood capillaries and a thin surface layer of cells to speed up diffusion between the water and the blood

counter-current system:
-blood flows through lamellae in one direction and water flows over them in the opposite direction
-means that water with a high oxygen concentration always flows next to blood with a lower oxygen concentration
-steep conc gradient maintained
-as much oxygen as possible diffuses from water into blood
-diffusion along length of lamellae

Question 6

Explain gas exchange in dicotyledonous plants.

Answer 6

-mesophyll cells (in leaf) have a large SA
-gases move in and out through stomata
-guard cells control opening and closing of stomata and therefore water loss

Question 7

Explain how the structure of plants helps them to limit water loss.

Answer 7

-hairs on epidermis trap water vapour round the stomata reducing the water potential gradient
-thick waxy cuticle reduces evaporation
-curled leaves protect stomata from wind that would otherwise increase the rate of diffusion and evaporation
-stomata in pits to trap water vapour reduce the water potential gradient
-reduced number of stomata- fewer places for water to escape

Question 8

Explain gas exchange in insects.

Answer 8

-terrestrial insects have trachea (microscopic air-filled pipes) that branch off into smaller tracheoles which have thin permeable walls and go into individual cells
-air moves into trachea through pores on the surface called spiracles- oxygen diffuses directly into respiring cells
-air moves in and out of spiracles using rhythmic abdominal movements

Question 9

How are insects adapted for efficient gas exchange?

Answer 9

-tracheoles have thin walls-short diffusion distance
-highly branched-short diffusion distance therefore large exchange surface area
-trachea provide tubes full of air- fast diffusion
-fluid in end of tracheoles that moves out during exercise- faster diffusion through air to gas exchange surface
-body can be moved by muscles to move air-maintains diffusion gradient for oxygen

Question 10

What are the different ways respiratory gases can move in and out of the tracheal system in insects?

Answer 10

-along diffusion gradient- oxygen in, carbon dioxide out
-mass transport-muscle contraction squeezes trachea
-end of tracheoles filled with water- allow water and thus air to be drawn in due to a lowered water potential from lactate (product of anaerobic respiration)

Question 11

Explain the advantage for larger animals having a specialised system that facilitates oxygen uptake.

Answer 11

-larger organisms have a smaller surface area to volume ratio
- specialised system overcomes long diffusion pathway
-faster diffusion

Question 12

Describe the gross (not microscopic) structure of the human gas exchange system.

Answer 12

-the trachea have cartilage rings that strengthen it and prevent it from collapsing
-trachea divided into bronchi, bronchioles then alveoli

Question 13

Describe what happens during inspiration.
ACTIVE

Answer 13

-The volume of our thoracic cavity increases and pressure decreases as the external intercostal muscles and diaphragm contract whilst the internal intercostal muscles relax

Question 14

Describe what happens during expiration.
PASSIVE

Answer 14

-The volume of the thoracic cavity decreases and pressure increases as the internal intercostal muscles contract whilst the external intercostal muscles and diaphragm relax

Question 15

Describe and explain how the lungs are adapted to allow rapid exchange of oxygen between air in the alveoli and blood in the capillaries around them.

Answer 15

-constant blood supply maintains concentration gradient so oxygen can rapidly diffuse into blood
-thin walls of blood capillaries create short diffusion distance
-flattened epithelium so short diffusion distance so fast diffusion
-ventilation maintains concentration gradient so fast diffusion
-many alveoli-large SA

Question 16

Define digestion.

Answer 16

The hydrolysis of large insoluble molecules into smaller soluble molecules.

Question 17

Describe starch digestion.

Answer 17

-amylase
-hydrolyses
-glycosidic bonds
-starch broken down into maltose
-maltase
-hydrolyses
-maltose to glucose

Question 18

Explain how digestion of starch in the small intestine leads to an increase in the concentration of glucose in the blood.

Answer 18

-starch hydrolysed by amylase, then maltase
-produces glucose
-facilitated diffusion of glucose across the epithelium into the blood

Question 19

Describe the processes involved in the absorption of the products of starch digestion.

Answer 19

-sodium ions removed from epithelial cell by active transport/sodium-potassium pump
-into blood
-maintaining low concentration of sodium ions in epithelial cell
-glucose moves in with sodium ions into epithelial cell
-via facilitated diffusion through a co-transport protein
-glucose moves into blood
-by (facilitated) diffusion

Question 20

Describe protein digestion.

Answer 20

-endopeptidases hydrolyse the peptide bonds between the amino acids in the centre of the polypeptide
-increasing the SA, creating more ends for exopeptidases
-exopeptidases hydrolyse the peptide bonds between the terminal amino acids of the polypeptides
-this creates dipeptides and single amino acids
-membrane-bound dipeptidases hydrolyse the peptide bonds between the amino acids in these dipeptides

Question 21

Describe lipid digestion.

Answer 21

-large fat droplets containing triglycerides
-triglycerides are emulsified by bile salts into small fat droplets making them more soluble
-small fat droplets
-lipase hydrolyses the ester bonds in triglycerides
-forming micelles (droplets of monoglycerides and fatty acids)

Question 22

Describe lipid absorption.

Answer 22

-micelles are absorbed into the epithelial cell (diffuse in as they are NON-POLAR)
-they are transported to the smooth ER where they are reformed into triglycerides
-triglycerides transported in vesicles to Golgi apparatus which modifies and processes them
-triglycerides associate with cholesterol and lipoproteins to form structures called chylomicrons
-chylomicrons are packaged into Golgi vesicles for release from the cell via exocytosis
-then absorbed into lacteals in the villi

Question 23

A student s concluded that the fish gas exchange
system is more efficient than the human gas exchange system.
Justify this conclusion

Answer 23

In fish, blood leaving has more oxygen than water leaving
(But) in humans, blood leaving has less oxygen than air leaving

Question 24

Describe and explain the mechanism that causes lungs to fill with air

Answer 24

Diaphragm contracts and external intercostal muscles
contract
Causes volume increase and pressure decrease
Air moves down a pressure gradient

Question 25

Describe the structure of haemoglobin

Answer 25

-quaternary structure made of 2- alpha and 2-beta polypeptide chains -each chain is attached to a haem group so there are 4 haem groups -each haem group has an iron ion and each iron ion combines with oxygen to form oxyhaemoglobin - so 4 oxygen molecules can be carried by a single haemoglobin molecules in humans

Question 26

Explain why the binding of one molecule of oxygen makes it easier for a second oxygen molecule to bind

Answer 26

-binding of first oxygen changes the tertiary structure and therefore quaternary structure of haemoglobin -uncovering another binding site -positive cooperativity

Question 27

Describe the association and dissociation of oxygen

Answer 27

Association Hb + oxygen -> oxyhaemoglobin takes place in the lungs Hb has a high affinity for oxygen so takes up more oxygen easily but releases less easily Dissociation Oxyhaemoglobin -> Hb + oxygen takes place at respiring tissues oxyhaemoglobin has a low affinity for oxygen so takes up oxygen less easily but releases more easily

Question 28

What must haemoglobin do to transport oxygen?

Answer 28

-readily bind (associate) with oxygen at the lungs -readily release (dissociate) with oxygen at the respiring tissues

Question 29

How can haemoglobin associate and dissociate with oxygen?

Answer 29

-it can change its affinity for oxygen in different conditions -by changing its shape in the presence of some substances e.g. carbon dioxide

Question 30

Describe partial pressure

Answer 30

-the pressure of a gas compared to the total pressure of a mixture of gases -measured in kilopascals

Question 31

What does the oxygen dissociation curve show?

Answer 31

-the relationship between saturation of haemoglobin with oxygen and partial pressure of oxygen

Question 32

Explain the shape of the oxygen dissociation curve at the start. (low pO2 in respiring tissues)

Answer 32

-the gradient of the curve is shallow -the first oxygen does not bind easily with the Hb due to closed united polypeptide chains -therefore little oxygen binds to Hb

Question 33

Explain the shape of the oxygen dissociation curve in the middle. (medium pO2)

Answer 33

-the gradient is very steep -binding of the first oxygen changes the tertiary and quaternary structure of haemoglobin, making it easier for the 2nd and 3rd oxygen to bind to the haem group- positive cooperativity -a small increase in partial pressure of oxygen causes a big increase in oxygen saturation

Question 34

Explain the shape of the oxygen dissociation curve at the end. (high pO2 in the lungs)

Answer 34

-the curve plateaus -after binding of 3rd oxygen, the majority of binding sites are occupied and the Hb is saturated -therefore is it less likely that an oxygen will find a binding site- probability

Question 35

Explain how changes in the shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin dissociation curve for HbA.

Answer 35

-1st oxygen binds to Hb causing change in shape -allowing more oxygen to bind easily

Question 36

Explain the advantage to foetuses of oxygen dissociation curve being to left of that for its mother

Answer 36

-higher affinity for oxygen -at low partial pressure for oxygen -oxygen moves from mother to foetus

Question 37

Why are there many different oxygen dissociation curves?

Answer 37

-shape of haemoglobin can change under different conditions -changing its affinity for oxygen

Question 38

Why does haemoglobin vary?

Answer 38

-different oxygen levels in habitat -different metabolic rates- linked with SA:V

Question 39

Where is the oxygen dissociation curve of small mammals in relation to that of humans and why?

Answer 39

-to the right -affinity for oxygen is lower even at higher pO2 -oxygen more easily dissociated from Hb to tissues -tissues can respire more and produce more heat

Question 40

Where is the oxygen dissociation curve of large mammals in relation to that of humans and why?

Answer 40

-to the left -higher affinity for oxygen even at lower pO2 -smaller SA:V ratio so less heat loss per unit body mass but greater rate of respiration due to total number of cells

Question 41

How does carbon dioxide affect the transport of oxygen by haemoglobin? ( the Bohr effect)

Answer 41

-the more active a tissue is, the more oxygen is unloaded -higher rate of respiration-more carbon dioxide tissues produce-the lower the pH-the greater the haemoglobin shape change-the more readily oxygen is dissociated-the more oxygen is available for respiration -Hb will only release 1 oxygen to resting tissues but ~3 to very active tissues

Question 42

What is the double circulatory system?

Answer 42

-blood passes through the heart twice -PULMONARY CIRCUIT- between the heart and lungs -SYSTEMATIC CIRCUIT-between the heart and other organs

Question 43

Describe the circulation of blood through the heart (starting with blood entering left side of heart)

Answer 43

-oxygenated blood from lungs enters the left atrium of the heart through the pulmonary vein -the atrium contracts and the blood flows through the open atrio ventricular valve into the left ventricle -blood leaves the left side of the heart by a huge contraction of the left ventricle forcing blood at high pressure through the semi-lunar valve and into the aorta to be pumped around the body -in the body oxygen is used by tissues for respiration (Hb dissociates from oxygen) -deoxygenated blood enters the right atrium of the heart through the vena cava -when the right atrium is full contraction occurs forcing the blood through the atrio ventricular valve into the right ventricle, the valve closes -when the right ventricle is full contraction occurs forcing the blood up through the semi-lunar valve and into the pulmonary artery to be pumped to the lungs -in the lungs blood is oxygenated (Hb associates with oxygen) and carbon dioxide is removed

Question 44

What direction does blood flow in and how does this affect valve movement?

Answer 44

-Blood flows from high pressure to low pressure -valves are always closed when pressure pf next chamber is greater than current one e.g Atrioventricular valves close when blood is in ventricles because pressure in ventricles>pressure in atrium -contractions increase pressure

Question 45

Describe the valves (3)

Answer 45

-atrioventricular valves between atria and ventricles, prevent back flow of blood into the atria -semi-lunar valves in pulmonary artery and aorta, prevent back flow of blood in the ventricles -pocket valves in the venal system preventing back flow of blood when veins are squeezed by muscles

Question 46

What is the vein and artery connecting 1. kidney to vena cava and 2. aorta to kidney

Answer 46

1.renal vein 2.renal artery

Question 47

What is the lymphatic system?

Answer 47

-drainage system -drains fluid from tissues and deposits it in the vena cava

Question 48

What is tissue fluid?

Answer 48

-fluid that bathes tissue -contains water, glucose, amino acids, oxygen -allows exchange of materials into and out of cells

Question 49

Explain tissue fluid formation

Answer 49

-high hydrostatic pressure in arterioles due to contractions -small molecules (glucose, oxygen, water) leave the capillaries, larger molecules remain --called ultrafiltration -hydrostatic pressure decreases in capillaries and water potential decreases as water has been filtered out

Question 50

Explain how tissue fluid returns

Answer 50

-water re-enters capillaries from high to low hydrostatic pressure via osmosis from high to low water potential -water brings carbon dioxide and other waste products with it back into capillary some fluid enters lymph vessels to form lymph -vessels form the lymphatic system which connects the blood system nearer the heart at the vena cava via the thoracic duct

Question 51

Describe the general structure of blood vessels.

Answer 51

Tough fibrous outer layer- resists pressure changes from within and outside Muscle layer- contracts to control blood flow by constricting/dilating Elastic layer- maintains blood pressure by stretching and recoiling Endothelium- is smooth to reduce friction and thin to allow diffusion Lumen- central cavity

Question 52

How is the artery structure related to its function?

Answer 52

Muscle layer thick compared to veins- smaller arteries can be constricted and dilated to control vol of blood passing through Thicker elastic layer than veins- keep blood pressure high so blood can reach extremities of body, elastic wall is stretched during systole and recoils during diastole maintaining a high blood pressure Great overall thickness of wall-resists vessel bursting under pressure No valves- blood constantly under high pressure so doesn't flow backwards

Question 53

How is arteriole structure related to function?

Answer 53

Muscle layer thicker than in arteries- contraction of this layer constricts the lumen restricting blood flow and controlling its movement into capillaries Thinner elastic layer than arteries- blood pressure is lower because they have branched off from arteries

Question 54

How is vein structure related to function?

Answer 54

Muscle layer thin compared to arteries- carry blood away from tissues therefore constriction and dilation cannot control blood flow to tissues Thinner elastic layer than arteries- low pressure of blood so no risk of bursting or chance of recoil action Small overall thickness of wall-no need as pressure is to low to burst, allows them to be flattened easily aiding blood flow Pocket valves- ensures blood flows in one direction, as pressure is low, and when muscles contract veins are compressed pressurising the blood so valves ensure this pressure directs the blood back to the heart only

Question 55

How is capillary structure related to function?

Answer 55

Walls consist of mostly lining layer (endothelium)- makes them thin so short diffusion distance therefore rapid diffusion of metabolite materials between blood and cells Numerous and highly branched-providing a large SA for exchange Narrow diameter- permeate tissues so no cell is far from a capillary so short diffusion distance Very narrow lumen- red blood cells squeezed flat against the side of a capillary- brings closer to cells they supply oxygen to so reduced diffusion distance Spaces between endothelial cells- allow white blood cells to escape to fight infections within tissues

Question 56

What is the cardiac cycle?

Answer 56

The sequence of contraction and relaxation of the heart chambers during one heartbeat caused by an electrical impulse in the cardiac muscle

Question 57

Describe what happens during diastole (relaxation)

Answer 57

-blood returns to atria through pulmonary vein and vena cava -as atria fill pressure in them increases until it exceeds that in the ventricles so the AV valves open -muscular walls of atria and ventricles relaxed -relaxation of ventricle walls causes them to recoil, lowering the pressure in the ventricle -this causes pressure in ventricle

Question 58

Describe what happens during atrial systole

Answer 58

-contraction of atrial walls along with recoil of relaxed ventricle walls forces remaining blood into ventricles from atria -throughout this stage muscle of ventricle walls remains relaxed

Question 59

Describe what happens during ventricular systole

Answer 59

(after blood fills the ventricles) -ventricle walls contract simultaneously -this increases blood pressure within them forcing shut the AV valves preventing backflow of blood into atria -this increases pressure even more- once exceeding that in the aorta and pulmonary artery blood is forced into these vessels -wall of left ventricle thick to pump blood to extremities of the body

Question 60

Define the cardiac output and give the equation

Answer 60

The volume of blood pumped by 1 ventricle in 1 minute cardiac output (CO)= heart rate x stroke volume Stroke volume is total vol of blood pumped out in 1 cardiac cycle

Question 61

How can you identify heart rate on ECGs and tables?

Answer 61

ECG- heart rate = distance between the peaks Tables- heart rate= where start and end volume is the same

Question 62

Define risk and health risk

Answer 62

Risk- the probability that and event will happen Health risk- 1 in (population/number died)

Question 63

What are risk factors for CHD?

Answer 63

Smoking High saturated fats diet Inactivity High blood cholesterol High blood pressure Stress

Question 64

How do scientists prove causation?

Answer 64

-suggest a reliable mechanisms to explain how a variable causes the causation -set up a null hypothesis

Question 65

Explain the advantage of giving data as percentages

Answer 65

-easier to compare if sample size is effectively the same -different numbers of people in each group

Question 66

Why does a potometer not truly measure the rate of transpiration?

Answer 66

-water used in photosynthesis -water used for turgidity

Question 67

How could you measure rate of water loss per mm squared of surface area?

Answer 67

-draw round leaf on graph paper -of both sides of leaf -divide rate by surface area

Question 68

Why may the rate of water uptake through a shoot in a potometer not be the same as the rate of water uptake through the shoot of a whole plant?

Answer 68

-plant has roots -xylem cells are very narrow

Question 69

Explain the evaporation of water from a plant.

Answer 69

-stomata open as guard cells are turgid -spongy mesophyll contains water vapour -water vapour evaporates from stomata down water potential gradient

Question 70

How are features in a leaf cross section adapted?

Answer 70

-waxy cuticle is transparent do light reaches palisade mesophyll -palisade mesophyll cells are elongates to can be tightly packed so more light reaches chloroplasts

Question 71

When are guard cells turgid (open) and why?

Answer 71

-in the day photosynthesis produces glucose, lowering the water potential of guard cells so water moves in by osmosis

Question 72

What is transpiration?

Answer 72

The movement of water from roots through xylem vessels in stem to the leaves where is evaporates PASSIVE (energy supplied by sun)

Question 73

Structure of xylem vessels:

Answer 73

-dead so cannot actively move water -no end walls so forms continuous column- cohesion-tension theory -contains lignin- forms rings or spirals around vessel and strengthens it and allows stems to be flexible -contains pits to allow lateral movement of water

Question 74

How does water move through the stomata?

Answer 74

-humidity of atmosphere is less than humidity of air spaces next to stomata -so there is a water potential gradient -water diffuses out of air spaces into surrounding air when stomata are open -this water lost is replaced by water evaporating from cell walls of surrounding mesophyll cells to air spaces -changing size of stomatal pores controlling rate of transpiration

Question 75

How does water move across cells of a leaf?

Answer 75

-water lost from mesophyll cells replaced by water from the xylem (moving through cells walls or cytoplasm) -water potential gradient established pulling water from xylem to leaf mesophyll to atmosphere

Question 76

How does water move up stem in the xylem (cohesion-tension theory)?

Answer 76

-water is drawn up the xylem as water evaporates from the mesophyll cells -lowering the water potential of mesophyll cells -it forms a long continuous column -because there are hydrogen bonds between water molecules causing them to stick together (there is cohesion) -adhesion of water molecules to walls of xylem -this causes a transpiration pull forces increasing tension in the xylem

Question 77

Evidence to support cohesion-tension theory:

Answer 77

-change in diameter of tree trunks according to rate of transpiration- in the day shrunken diameter as high rate so more tension in xylem so xylem pulled inwards whereas at night wider diameter -if xylem vessel broken and water enters tree water can no longer draw up water- continuous column with hydrogen bonds

Question 78

How can you measure water uptake using a potometer?

Answer 78

-leafy shoot cut underwater- so not gases from atmosphere get into xylem breaking column of water -potometer filled with water -removed from underwater -air bubble introduced -distance moved by air bubble in a given time measured and a mean is calculated

Question 79

Factors that increase the rate of transpiration:

Answer 79

-increased temp -increased CO2 -increased wind speed -decreased humidity -increased number of stomata -no waxy cuticle

Question 80

What is translocation?

Answer 80

-sucrose and amino acids transported from sources (sites of production) to sinks (sites of respiration or storage) up/down the plant

Question 81

Structure of phloem:

Answer 81

sieve plates with pores replace end walls companion cells contain a nucleus

Question 82

Describe the mass flow theory

Answer 82

-sucrose diffuses down a conc gradient by facilitated diffusion from palisade cells into companion cells -hydrogen ions acitvely transported from companion cells to spaces within cell walls using ATP -then diffuses down conc gradient through carrier proteins into sieve tube elements -sucrose transported with them- co-transport -sucrose entering sieve tubes lowers WP of them so water moves from xylem (high WP) to sieve tubes (low WP) by osmosis -this increases hydrostatic pressure in sieve tubes (sources) -at sinks sucrose is used to cells have a low sucrose content to sucrose actively transported from sieve tubes to respiring cells -water potential of sinks decreases so water moves into them by osmosis so hydrostatic pressure of sieve tubes (sinks) lowered -mass flow of sucrose down this hydrostatic pressure gradient

Question 83

Evidence for mass flow theory:

Answer 83

-a pressure within sieve tubes shown by sap being released when cut -conc of sucrose is higher in leaves (sources) than roots (sinks) -downwards flow in phloem in daylight-ceases at night -companion cells have many mitochondria- ATP

Question 84

Explain ringing experiments

Answer 84

-phloem vessels outside xylem vessels -phloem selectively removed by cutting a ring -swelling above the ring and reduced growth below the ring and leaves unaffected show sugars transported downwards

Question 85

Explain radioactive tracer experiments

Answer 85

-a plant grown in a lab where one leaf is exposed to CO2 containing isotope 14C which is taken up and incorporated into glucose then sucrose -plant frozen in liquid nitrogen to stop movement of sucrose and placed onto photographic film in the dark for days -autoradiograph shows location of compounds containing 14C

Question 86

Evidence against mass flow theory

Answer 86

-function of sieve plates is unclear -not all solutes move at same speed