Exchange And Mass Transport

Question 1

What is the Relationship between the size of organism and its SA:V

Answer 1

Smaller organisms tend to have a higher SA:V than larger organisms
- E.g. hippo vs. mouse

Question 2

Relationship between SA:V (and thus the size of an organism) and metabolic rate

Answer 2

Rate of heat loss / heat lost per unit body mass increases as SA:V increases
- i.e. more heat lost per unit body mass in smaller animals with a high SA:V
- So they need a higher metabolic rate / faster respiration
- To generate enough heat to maintain a constant body temperature i.e. replace lost heat

Question 3

Adaptations to facilitate exchange as this ratio reduces in larger organisms include
changes to body shape and the development of systems

Answer 3

• Larger organisms need a specialised surface / organ for gaseous exchange e.g. lungs
• Because they have a smaller SA:V and a long diffusion pathway (and skin is waterproof / gas
  tight)
• As well as having a high demand for oxygen and to remove carbon dioxide

Question 4

Adaptations of gas exchange surfaces shown by gas exchange…
Across the body surface of a single-celled organism

Answer 4

• Thin, flat shape
• Large SA(:V)
• Short diffusion pathway/distance (all parts of cell are a small distance away from
  exchange surfaces)
• For rapid diffusion e.g. oxygen / carbon dioxide
• movement on internal and external medium

Question 5

Adaptations of gas exchange surfaces shown by gas exchange…
In the tracheal system of an insect

Answer 5

1. Air moves through spiracles (pores) on the surface of the insect
2. Air moves through tracheae
3. Gas exchange at tracheoles directly to/from cells
   - Oxygen diffuses down conc. gradient to respiring cell
   - Carbon dioxide diffuses down conc. gradient from respiring cells
   - Adaptations: lots of thin, branching tracheoles → short diffusion pathway and SA(:V) → rapid
   diffusion
   - Note: rhythmic abdominal movements increase the efficiency of gas exchange by increasing the
   amount of air/oxygen entering → maintains greater concentration gradient for diffusion

Question 6

Adaptations of gas exchange surfaces shown by gas exchange…
Across the gills of fish

Answer 6

Counter current flow
- Blood flows through lamellae and water flows over lamellae in opposite directions
- Always a higher concentration of oxygen in water than the blood it is near
- Hence, a concentration gradient of oxygen between the water and blood is maintained
along the whole length of lamellae (/gill plate) → equilibrium not met
- Maximising diffusion of oxygen

Question 7

Other adaptations of gas exchange surfaces in fish

Answer 7

Each gill is made of lots of gill filaments (thin plates) which are covered in many lamellae → gill
filaments provide a large surface area, lamellae increase surface area even more
- Vast network of capillaries on lamellae → remove oxygen to maintain a concentration gradient
- Thin/flattened epithelium → shorter diffusion pathway between water and blood

Question 8

Adaptations of gas exchange surfaces shown by gas exchange…
By the leaves of dicotyledonous plants

Answer 8

• Process of gas exchange in leaves
• Carbon dioxide / oxygen diffuse through the stomata
• Stomata opened by guard cells
• Carbon dioxide / oxygen diffuse into mesophyll layer into air spaces
• Carbon dioxide / oxygen diffuse down concentration gradient
• Adaptations
• Lots of stomata (small pores) that are close together
• Large surface area for gas exchange / unimpaired movement of gases / gases do
  not have to pass through cells to reach mesophyll
• Interconnecting air space in mesophyll layers (exchange surface)
• Gases come into contact with mesophyll cells
• Mesophyll cells have a large surface area
• Rapid diffusion of gases
• Thin
• Short diffusion pathways

Question 9

Structural and functional compromises between the opposing needs for efficient gas
exchange and the limitation of water loss shown by:
Xerophytic plants

Answer 9

Thick waxy cuticle
- Increases diffusion distance → less evaporation
- Stomata in pits/grooves
- ‘Trap’ water vapour → water potential gradient decreased → less evaporation
- Rolled leaves
- ‘Trap’ water vapour → water potential gradient decreased → less evaporation
- Spindles/needles
- Reduces surface area to volume ratio
- Hairs
- ‘Trap’ water vapour → water potential gradient decreased → less evaporation

Question 10

Structural and functional compromises between the opposing needs for efficient gas
exchange and the limitation of water loss shown by:
Terrestrial insects

Answer 10

• Thick waxy cuticle
• Increases diffusion distance → less evaporation
• Spiracles can open and close
• Open to allow oxygen in, close when water loss too much

Question 11

The gross structure of the human gas exchange system limited to the alveoli, bronchioles, bronchi, trachea and lungs

Answer 11

bronchi, trachea and lungs
- Trachea
- Splits into two bronchi
- Each bronchus branches into smaller tubes called bronchioles
- Bronchioles end in air sacs called alveoli

Question 12

Ventilation and exchange of gases in lungs

Answer 12

How does gas exchange occur in the alveoli?
- Oxygen diffuses from alveoli
- Down its concentration gradient
- Across the alveolar epithelium
- Across the capillary endothelium
- Into the blood (in haemoglobin)
- Carbon dioxide diffuses from capillary
- Down its concentration gradient
- Across the capillary endothelium
- Across the alveolar epithelium
- Into the alveoli
- Why is ventilation needed?
- Maintains an oxygen concentration gradient
- Brings in air containing higher concentration of oxygen
- Removes air with lower concentration of oxygen

Question 13

The essential features of the alveolar epithelium as a surface over which gas exchange
takes place

Answer 13

• Squamous epithelium = thin/one cell thick
• Short diffusion pathway → fast diffusion
• Large surface area to volume ratio
• Fast diffusion
• Permeable
• Good blood supply from network of capillaries
• Maintains concentration gradient
• Elastic tissue allows it to recoil after expansion
• Surfactant

Question 14

How are the lungs adapted for efficient/rapid gas exchange?

Answer 14

• Many alveoli/capillaries
• Large surface area → fast diffusion
• Alveoli/capillary walls are thin / short distance between alveoli and blood
• Short diffusion distance → fast diffusion
• Ventilation/circulation
• Maintains concentration gradient → fast diffusion

Question 15

Mechanism of breathing including: role of the diaphragm antagonistic interaction
between external and internal intercostal muscles, in bringing about pressure changes
in thoracic cavity

Answer 15

Breathing in (inspiration)
- External intercostal muscles contract, internal intercostal muscles relax (antagonistic)
- Moving ribcage up and out
- Diaphragm muscles contract → flatten/move down diaphragm
- Increasing volume in thoracic cavity / chest
- Decreasing pressure in thoracic cavity
- Atmospheric pressure higher than pressure in lungs
- Air moves down pressure gradient into lungs
- (Active process)
- Breathing out (expiration)
- Internal intercostal muscles contract, external intercostal muscles relax (antagonistic)
- Moving ribcage down and in
- Diaphragm relaxes, moves upwards
- Decreasing volume in thoracic cavity
- Increasing pressure in thoracic cavity
- Atmospheric pressure lower than pressure in lungs
- Air moves down pressure gradient out of lungs
- (Passive process)

Question 16

Why is food digested

Answer 16

• Large biological molecules in food e.g. starch / proteins too big to be absorbed across cell
  membranes
• Digestion breaks them into smaller molecules e.g. glucose / amino acids → absorbed from the
  gut to the blood

Question 17

Digestion of starch (polysaccharide)

Answer 17

• Amylase hydrolyses starch to maltose (polysaccharide to disaccharide)
• Amylase produced by salivary glands, released into mouth
• Amylase produced by pancreas, released into small intestine
• Membrane bound maltase (attached to epithelial cells lining the ileum of the small intestine) →
  hydrolyse maltose to glucose (disaccharide to monosaccharide)
• Hydrolysis of glycosidic bond

Question 18

Digestion of disaccharides

Answer 18

• Membrane bound disaccharidases, e.g. maltase, sucrose, lactase (attached to epithelial cells
  lining the ileum of the small intestine) → hydrolyse disaccharide to x2 named monosaccharides
• E.g. maltase – maltose → glucose + glucose
• E.g. sucrase – sucrose → fructose + glucose
• E.g. lactase – lactose → galactase + glucose
• Hydrolysis of glycosidic bond

Question 19

Digestion in mammals of lipids by lipase, including the action of bile salts

Answer 19

• Bile salts produced by the liver
• Bile salts emulsify lipid to smaller lipid droplets
• Increasing surface area (to volume ratio) of lipids speeds up action of lipases
• Lipase made in the pancreas, released to small intestine
• Lipase hydrolyses lipids → monoglycerides + fatty acids
• Breaking ester bond
• Monoglycerides, fatty acids and bile salts stick together to form micelles

Question 20

Digestion in mammals of proteins by endopeptidases, exopeptidases and membrane-
bound dipeptidases

Answer 20

• Endopeptidases
• Hydrolyse peptide bonds within a protein / between amino acids in the central region
• Breaking protein into two or more smaller peptides
• Exopeptidases
• Hydrolyse peptide bonds at the ends of protein molecules
• Removing a single amino acid
• Dipeptidases (type of exopeptidase)
• Often membrane bound in ileum
• Hydrolyse peptide bond between a dipeptide
• = 2 amino acid

Question 21

Mechanisms for the absorption of the products of digestion by cells lining the ileum of
mammals, to include co-transport mechanisms for the absorption of amino acids and of
monosaccharides

Answer 21

1. Sodium ions actively transported out of epithelial cells lining the ileum, into the blood, by the
   sodium-potassium pump. Creating a concentration gradient of sodium (higher conc. of sodium
   in lumen than epithelial cell)
2. Sodium ions and glucose move by facilitated diffusion into the epithelial cell from the lumen, via
   a co-transporter protein
3. Creating a concentration gradient of glucose – higher conc. of glucose in epithelial cell than
   blood
4. Glucose moves out of cell into blood by facilitated diffusion through a protein channel

Question 22

Mechanisms for the absorption of the products of digestion by cells lining the ileum of
mammals, to include the role of micelles in the absorption of lipids

Answer 22

• Monoglycerides and fatty acids diffuse out of micelles (in lumen) into epithelial cell
• Because lipid soluble
• Monoglycerides and triglycerides recombine to triglycerides which aggregate into globules
• Globules coated with proteins to form chylomicrons
• Leave via exocytosis and enter lymphatic vessels
• Return to blood circulation

Question 23

Describe circulatory system

Answer 23

Closed double circulatory system – two circuits
- Blood passes through heart twice for each complete circulation of body
- Pulmonary circulation
- Deoxygenated blood in right side of heart pumped to lungs → oxygenated blood
returns to left side of heart
- Systemic circulation
- Oxygenated blood in left side of heart pumped to tissues / organs of body →
deoxygenated blood returns to right side

Question 24

Closed double circ system - Important for mammals because…

Answer 24

• Prevents mixing of oxygenated and deoxygenated blood → so blood pumped to
  body is fully saturated with oxygen → efficient delivery of oxygen and glucose for
  respiration
• Blood can be pumped at a higher pressure (after being lower from lings) →
  substances taken to and removed from body cells quicker and more efficiently

Question 25

Coronary arteries function

Answer 25

Deliver oxygenated blood to cardiac muscle

Question 26

Blood vessels entering and leaving heart

Answer 26

• Aorta – takes oxygenated blood from heart → respiring tissues
• Vena cava – takes deoxygenated blood from respiring tissues → heart
• Pulmonary artery and pulmonary vein

Question 27

Blood vessels entering and leaving lungs

Answer 27

• Pulmonary artery – takes deoxygenated blood from the heart → lungs
• Pulmonary vein – takes oxygenated blood from the lungs →heart

Question 28

Blood vessels entering and leaving kidneys

Answer 28

• Renal arteries – take deoxygenated blood → kidneys
• Renal veins – take deoxygenated blood to the vena cava from the kidneys

Question 29

How the structure of the heart relates to its function (valves and walls of ventricles)

Answer 29

• Atrioventricular valves
• Prevent backflow of blood from ventricles to atria
• Semi lunar valves
• Prevent backflow of blood from arteries to ventricles
• Left has a thicker muscular wall
• Generates higher blood pressure
• For oxygenated blood has to travel greater distance around the body
• Right has thinner muscular wall
• Generates lower blood pressure
• For deoxygenated blood to travel a small distance to the lungs where high
  pressure would damage alveoli

Question 30

The structure of arteries in relation to their function

Answer 30

Arteries – carry blood from heart to rest of body at high pressure
- Thick smooth muscle layer
- Contract pushing blood along
- Control/maintain blood flow/pressure
- Elastic tissue layer
- Stretch as ventricle contracts (when under high pressure) and recoil as ventricle
relaxes (when under low pressure)
- Reduces pressure surges / even out blood pressure and maintain high pressure
- Thick wall
- Withstands high pressure and prevents artery bursting
- Smooth (and thin) endothelium
- Reduces friction
- Narrow lumen
- Increases and maintains high blood pressure

Question 31

The structure of aterioles in relation to their function

Answer 31

Arterioles – division of arteries to smaller vessels which can direct blood to different capillaries /
areas
- Note: their structure in relation to their function is similar to that of arteries, but…
- Thicker muscle layer than arteries
- Constricts (contracts) to reduce blood flow by narrowing lumen
- Dilates (relaxes) to increase blood flow by enlarging lumen
- Thinner elastic later as lower pressure surges

Question 32

How structure of veins relates to its function

Answer 32

carry blood back to heart under lower pressure
- Wider lumen than arteries
- Very little elastic and muscle tissue
- Valves
- Prevent backflow of blood

Question 33

Structure of capillaries and the importance of capillary beds as exchange surfaces

Answer 33

• Capillaries allow the efficient exchange of gases and nutrients between blood and tissue fluid
• Capillary wall is a thin layer (one cell thick) of squamous endothelial cells
• Short diffusion pathway → rapid diffusion
• Capillary bed is made of a large network of (branched) capillaries (which are all thin)
• Increase surface area (to volume ratio) → rapid diffusion
• Narrow lumen
• Reduces flow rate so more time for diffusion / exchange

Question 34

What is tissue fluid

Answer 34

the fluid surrounding cells / tissues
- Provides respiring cells with e.g. water / oxygen / glucose / amino acids
- Enables (waste) substances to move back into the blood e.g. urea, lactic acid, carbon
dioxide

Question 35

The formation of tissue fluid

Answer 35

at / nearest arteriole end of capillaries (start)…
- Higher blood / hydrostatic pressure inside capillaries (due to contraction of left ventricle)
than tissue fluid (net outward pressure/force)
- Forces fluid / water out of capillaries (into spaces around cells)
- Large plasma proteins remain in capillary (too large to leave capillaries)

Question 36

Return of tissue fluid to circulatory system

Answer 36

towards venule end of capillaries (end) …
- Hydrostatic pressure reduces as fluid leaves capillary (also due to friction)
- (Due to water loss,) an increasing concentration of plasma proteins (too large to leave
capillaries) lowers the water potential in the capillary below the water potential of the
tissue fluid
- Water (re-)enters the capillaries from the tissue fluid by osmosis down a water potential
gradient
- Excess water taken up by lymph system (lymph capillaries) and is returned to the
circulatory system (through veins in the neck

Question 37

2 causes of accumulation of tissue fluid

Answer 37

• Low concentration of protein in blood plasma can lead to an accumulation of tissue fluid
• Water potential in capillary not as low so water potential gradient is reduced
• More tissue fluid formed at arteriole end
• Less / no water absorbed into blood capillary by osmosis
• High blood pressure can lead to an accumulation of tissue fluid
• High blood pressure = high hydrostatic pressure
• Increases outward pressure from arterial end of capillary / reduces inward
  pressure at venule end of capillary
• So more tissue fluid formed / less tissue fluid is reabsorbed
• And the lymph system is not able to drain tissues fast enough

Question 38

Atrial systole

Answer 38

Atria contract → decreasing volume and increasing pressure inside atria
- Atrioventricular valves forced open
- When pressure inside atria > pressure inside ventricles, atrioventricular valves
open
- Blood pushed into ventricles
- (note: semilunar valves are shut)

Question 39

Ventricular systole

Answer 39

• Ventricles contract from the bottom up → decreasing volume and increasing pressure
  inside ventricles
• Semilunar valves forced open
• When pressure inside ventricles > pressure inside arteries
• Atrioventricular valves shut
• When pressure inside ventricles > pressure inside atria
• Blood pushed out of heart through arteries

Question 40

Diastole

Answer 40

Atria and ventricles relax → increasing volume and decreasing pressure inside chambers
- Blood from veins fills atria (increasing pressure inside atria slightly) and flows passively to
ventricles
- Atrioventricular valves open
- When pressure inside atria > pressure inside ventricles blood flows passively to
ventricles

Question 41

Purpose of valves being shut

Answer 41

the purpose of valves shutting is to prevent back flow into (named chamber / vein) to
maintain unidirectional flow of blood through the heart

Question 42

Cardiac output =

Answer 42

Stroke volume x heart rate

Question 43

Define …
Cardiac output
Heart rate
Stroke volume

Answer 43

Cardiac output = amount of blood pumped out of the heart per minute
- Stroke volume = volume of blood pumped by the ventricles in each heart beat
- Heart rate = number of beats per minute

Question 44

Semi lunar valve is closed when …

Answer 44

When pressure in aorta / pulmonary artery is higher than in ventricle → prevents
backflow of blood from arteries to ventricles

Question 45

Semi lunar valve open when …

Answer 45

When pressure in ventricle is higher than in aorta / pulmonary artery → blood
flows from ventricle to aorta

Question 46

Atrioventricular valve closed when …

Answer 46

When pressure in atrium is higher than in ventricle → prevents backflow of blood
from ventricle to atrium

Question 47

Atrioventricular valve open when …

Answer 47

When pressure higher in ventricle than atrium → blood flows from ventricle to
atrium

Question 48

Haemoglobin structure

Answer 48

Quaternary structured protein – made of 4 polypeptide chains
- Each polypeptide chain contains a Haem group containing an iron ion (Fe2+) which
combines with oxygen

Question 49

How oxygen is loaded, transported and unloaded in the blood

Answer 49

Haemoglobin in red blood cells carries/transports oxygen (as oxyhaemoglobin)
- Haemoglobin can carry 4 oxygen molecules – one at each Haem group
- In the lungs, at a high pO2, haemoglobin has a high affinity for oxygen → oxygen readily loads /
associates with haemoglobin
- At respiring tissues, at a low pO2, oxygen readily unloads / dissociates from haemoglobin
- Also, concentration of CO2 is high, increasing the rate of unloading (Bohr effect – see
further on)

Question 50

At High po2 haemoglobin is

Answer 50

Saturated w o2

Question 51

At low po2 haemoglobin

Answer 51

Less saturated with o2

Question 52

Cooperative binding

Answer 52

Haemoglobin has a low affinity for oxygen as the 1st oxygen molecule binds
After the 1st oxygen molecule binds, the shape of haemoglobin changes in a way that
makes it easier for the 2nd and 3rd oxygen molecules to bind too i.e. haemoglobin has a
higher affinity for oxygen
After the 3rd molecule binds, and haemoglobin starts to become saturated, the shape of
haemoglobin changes in a way that makes it harder for other molecules to bind too
- At a high pO2, the rate increase in % saturation decreases

Question 53

The effects of carbon dioxide concentration on the dissociation of oxyhaemoglobin –
the Bohr effect

Answer 53

When rate of respiration is high e.g. during exercise → releases CO2
- High pCO2 lowers pH and reduces haemoglobin’s affinity for oxygen as haemoglobin changes
shape
- Increases rate of oxygen unloading
- Advantageous because provides more oxygen for muscles/tissues for aerobic respiration
- Oxygen dissociation curve for haemoglobin shifts to the right

Question 54

When curve shifts to the left

Answer 54

haemoglobin has a higher affinity for oxygen
- More oxygen associates with haemoglobin more readily (in the lungs) at the lower pO2
BUT dissociates less readily
- Advantageous to organisms such as those living in high altitudes, underground, or
foetuses

Question 55

When curve shifts to the right

Answer 55

haemoglobin has a lower affinity for oxygen
- Oxygen dissociates from haemoglobin more readily to respiring cells at a higher pO2 BUT
associates less readily
- Advantageous to organisms such as those with a high rate of respiration (metabolic rate)
e.g. small / active organisms

Question 56

The cohesion-tension theory of water transport in the xylem

Answer 56

• Cohesion tension theory: How water moves up the xylem against gravity via the transpiration
  stream
• Water evaporates from the leaves via the (open) stomata due to transpiration
• Reducing water potential in the cell and increasing water potential gradient
• Water drawn out of xylem
• Creating tension
• Cohesive forces between water molecules pull water up as a column
• Water lost enters the roots via osmosis
• Water is moving up, against gravity
• Water is also cohesive so sticks to the edges of the column

Question 57

The mass flow hypothesis for the mechanism of translocation in plants

Answer 57

• Translocation:
• Movement of solutes/ assimilates from source to sink/ one place to another
• E.g. sugars made from photosynthesis in the leaves are transported to the site of
  respiration
• At the source:
• High concentration of solute
• Active transport loads solutes from companion cells to sieve tubes of the phloem
• Lowering the water potential inside the sieve tubes
• Water enters sieve tubes by osmosis from xylem and companion cells
• Increasing pressure inside sieve tubes at the source end
• At the sink:
• Low concentration of solute
• Solutes removed to be used up e.g. enzymes hydrolyse
• Increasing the water potential inside the sieve tubes
• Water leaves tubes via osmosis
• Lowering pressure inside sieve tubes
• Mass flow:
• Pressure gradient from source to sink
• Pushes solutes from source to sink
• Solutes used or stored at the sink e.g. respiration

Question 58

Adaptations of the phloem

Answer 58

• Sieve tube elements have no nucleus and few organelles
• Companion cell for each sieve tube element to carry out the living functions for the sieve cells
  i.e. ATP for active transport of solutes

Question 59

Use of tracers

Answer 59

• Supply plant with radioactive tracer such as 14C in CO2 to a photosynthesising leaf by
  pumping the radioactive CO2 into a container surrounding the leaf
• 14C is incorporated into the organic substances produced by the leaf e.g. sugars via
  photosynthesis
• Organic substances undergo translocation
• Autoradiography – plant killed and placed in a photographic film, film turns black where
  the radioactive substance is present
• Identifies where radioactive substance has moved to and thus where the organic
  substances have moved to via translocation from source to sink
• Can show this over time by taking autoradiographs at different times

Question 60

Light affects on transpiration

Answer 60

The higher the light intensity, the faster the transpiration rate (positive
correlation)
- Because stomata open in light to let in CO2 for photosynthesis
- Allowing more water to evaporate faster
- Stomata close when it’s dark so there is a low transpiration rate

Question 61

Temp affect on transpiration

Answer 61

The higher the temperature, the faster the transpiration rate (positive
correlation)
- Water molecules gain kinetic energy as temperature increases
- Move faster
- Water evaporates faster

Question 62

Humidity affect on transpiration

Answer 62

The lower the humidity, the faster the transpiration rate (negative correlation)
- Because as humidity increases, more water is in the air so it has a higher water
potential
- Decreasing the water potential gradient from leaf to air
- Water evaporates slower

Question 63

Wind affect on transpiration

Answer 63

The windier, the faster the transpiration rate (positive correlation)
- Wind blows away water molecules from around the stomata
- Decreasing the water potential of the air around the stomata
- Increasing the water potential gradient
- Water evaporates faster

Question 64

adaptations of insect tracheal system

Answer 64

Spiracles, tracheae, tracheoles;
2. Spiracles allow diffusion (of oxygen
. Tracheoles are highly branched so large
surface area (for exchange);
4. Tracheole (walls) thin so short diffusion
distance (to cells)
Tracheole permeable to oxygen/air;
6. Cuticle/chitin/exoskeleton (impermeable) so
reduce water loss;
7. Spiracles (can) close so no/less water loss
Hairs around spiracles reduce water loss;

Question 65

describe how humans breathe in and out

Answer 65

Breathing in
1. Diaphragm (muscles) contract and diaphragm
flattens;
2. External intercostal muscles contract and
ribcage pulled up/out;
3. (Causes) volume increase and pressure
decrease in thoracic cavity (to below
atmospheric pressure);
Breathing out
4. Diaphragm (muscles) relaxes and diaphragm
moves up;
5. External intercostal muscles relax and ribcage
moves down/in;
6. (Causes) volume decrease and pressure
increase in thoracic cavity (to above
atmospheric pressure);

Question 66

how do fatty acids and gylcerol enter intestinal epithelial cell

Answer 66

diffussion

Question 67

explain the advantage of lipid droplet and micelle formation

Answer 67

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

Question 68

golgi app role in absorption of lipids

Answer 68

2. Modifies / processes triglycerides;
3. Combines triglycerides with proteins;
4. Packaged for release / exocytosis
   OR
   Forms vesicles;

Question 69

explain role of the heart in formation of tissue fluid

Answer 69

1. Contraction of ventricle(s) produces high
   blood / hydrostatic pressure;
2. (This) forces water (and some dissolved
   substances) out (of blood capillaries);

Question 70

scientist used a statistical test to see wheher there was sig diff in amino acid conc of wine
name stat test used and reason why
and explain test result

Answer 70

t-test;
Reason for choice: Looking for differences
between two means;
Explanation: Difference is significant / not due to
chance because the P value is 0.04 / is less than
0.05;

Question 71

explain how an arteriole can reduce blood flow into capillaries

Answer 71

1. Muscle contracts;
2. Constricts/narrows arteriole/lumen;

Question 72

describe the processes involved in absorption and transport of digested lipid moleculs from ileum into lymph vessels

Answer 72

1. Micelles contain bile salts and fatty
   acids/monoglycerides;
2. Make fatty acids/monoglycerides (more) soluble
   (in water)
   OR
   Bring/release/carry fatty acids/monoglycerides to
   cell/lining (of the iluem)
   OR
   Maintain high(er) concentration of fatty
   acids/monoglycerides to cell/lining (of the ileum);
3. Fatty acids/monoglycerides absorbed by
   diffusion;
4. Triglycerides (re)formed (in cells);
5. Vesicles move to cell membrane

Question 73

describe and explain mechanism that causes lungs to fill with air

Answer 73

1. Diaphragm (muscle) contracts and external
   intercostal muscles contract;
2. (Causes volume increase and) pressure
   decrease;
3. Air moves down a pressure gradien

Question 74

describe the role of enzymes in the digestion of proteins in a mammal

Answer 74

1. (Reference to) hydrolysis of peptide bonds;
2. Endopeptidase act in the middle of
   protein/polypeptide
   OR
   Endopeptidase produces short(er) polypeptides/
   increase number of ends;
3. Exopeptidases act at end of protein/polypeptide
   OR
   Exopeptidase produces dipeptides/amino acids;
4. Dipeptidase acts on dipeptide/between two
   amino acids
   OR
   Dipeptidase produces (single) amino acids

Question 75

describe and explain effect of increasing carbon dioxide concentration to dissociation of oxyhaemoglobin

Answer 75

1. Increases/more oxygen dissociation/unloading
   OR
   Deceases haemoglobin’s affinity for O2;
2. (By) decreasing (blood) pH/increasing acidity;

Question 76

Define Microvilli

Answer 76

Folded cell membrane