Mass transport

Question 1

Describe the structure of haemoglobin

Answer 1

-primary = order of a.a joined by polypeptide bonds
-secondary =alpha helix/beta pleated sheets, held by H bonds
-tertiary = specific 3D structure held by H bonds, disulphide bridges and ionic bonds
-quaternary = 4 polypeptide chains and prosthetic haem group

Question 2

haemoglobin

Answer 2

-red pigment inside erythrocyte which transports oxygen
-2 alpha and 2 beta polypeptide chains. Each chain is attached to a haem group that can combine with oxygen
-protein made of 4 polypeptide chains

Question 3

Describe the functions of haemoglobin

Answer 3

-readily associate with oxygen at the surface where gas exchange takes place
-readily disassociate from oxygen at those tissues requiring it

Question 4

Explain the differences between haemoglobin in different organisms and the reasons for these differences

Answer 4

-affinity (chem attraction) for o2 = how readiy haemoglobin binds to o2. This is controlled by the shape of haemoglobin molecule
-different haemoglobins have different affinities for o2 - different organisms have haemoglobin with different amino acid sequences therefore different tertiary and quaternary structures which affects the affinity for o2

Question 5

what’s partial pressure

Answer 5

measure of its conc in kPa

Question 6

Explain what’s meant by loading and uploading of oxygen

Answer 6

-Loading/association of oxygen: the process by which haemoglobin binds with oxygen
-Unloading/dissociation of oxygen: the process by which haemoglobin releases oxygen

Question 7

associating

Answer 7

o2 and haem bind together

Question 8

disassociation

Answer 8

haem releases o2

Question 9

affinity

Answer 9

-high affinity for o2 = take up more o2 easily but releases it less easily
-low affinity for o2 = take up o2 less easily but releases it more easily

Question 10

Haem

Answer 10

-in each haem group there’s one Fe2+ ion
-each iron can combine with single oxygen molecule
-a single haemoglobin molecule therefore can carry 4 oxygen molecules

Question 11

Describe and explain the shape of oxyhaemoglobin disassociation curve

Answer 11

-in low pp haemoglobin has a low affinity for o2 (disassociates o2 more easily), the curve is shallow
-curve becomes steeper as the affinity for oxygen increases
-curve levels off at nearly 100% saturation at high pp of oxygen - haemoglobin has high affinity for o2 (disassociates less easily)

Question 12

Explain how the binding of oxygen affects the shape of haemoglobin

Answer 12

-hard for o2 to bind as haem group are in the middle of the haemoglobin molecule
-first o2 causes a conformational change in the haemoglobin (change in shape) making it easier for the second and third molecule to bind
-harder to reach final binding site so fourth oxygen binds less easily

Question 13

Explain how the properties of the haemoglobin in different organisms relate to their environment and way of life of the organism concerned

Answer 13

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Question 14

Comment on the saturation of haemoglobin with oxygen at high partial pressures

Answer 14

Hb is highly saturated

Question 15

Comment on the saturation of haemoglobin at low partial pressures

Answer 15

Hb has low saturation

Question 16

Describe and explain the Bohr effect

Answer 16

-Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide.
-This means it loads oxygen less readily and unloads more easily. This is called the Bohr effect.
-Dissolved carbon dioxide is acidic and this causes haemoglobin to change shape.
-At gas exchange surfaces there is little carbon dioxide, affinity for oxygen in high, oxygen loads readily.
-At respiring tissues carbon dioxide concentration is high, affinity for oxygen is low, oxygen is readily unloaded.

Question 17

Explain how, with reference to haemoglobin, animals are adapted to their environment

Answer 17

-An animal that lives in an environment with low partial pressure of oxygen will have haemoglobin with a high affinity for oxygen, the curve is to the left - this allows fully saturated haemoglobin at low partial pressures of oxygen

Question 18

Describe and explain the shape of the oxyhemoglobin disassociation curve

Answer 18

-low affinity for oxygen (dissociates oxygen more easily),
-the curve is shallow Curve becomes steeper as the affinity for oxygen increases
-Curve levels off at nearly 100% saturation at high partial pressures of oxygen - haemoglobin has a high affinity for oxygen (dissociates less easily)

Question 19

Explain the effect of carbon dioxide concentration on the curve and the reason why

Answer 19

-Hard for first oxygen to bind as haem groups are in the middle of the haemoglobin molecule
-First oxygen causes a conformational change in the haemoglobin (change in shape) making it easier for the second and third molecules to bind
-Harder to reach final binding site so fourth oxygen binds less easily

Question 20

Describe and explain the Bohr effect

Answer 20

-Haemoglobin has a reduced affinity for oxygen in the presence of carbon dioxide. This means it loads oxygen less readily and unloads more easily. This is called the Bohr effect. -Dissolved carbon dioxide is acidic and this causes haemoglobin to change shape.
-At gas exchange surfaces there is little carbon dioxide, affinity for oxygen in high, oxygen loads readily.
-At respiring tissues carbon dioxide concentration is high, affinity for oxygen is low, oxygen is readily unloaded.

Question 21

Explain how, with reference to haemoglobin, animals are adapted to their environment

Answer 21

-An animal that lives in an environment with low partial pressure of oxygen will have haemoglobin with a high affinity for oxygen, the curve is to the left - this allows fully saturated haemoglobin at low partial pressure

Question 22

Explain why large animals have a transport system

Answer 22

Large animals have a small SA:volume and therefore have specialed exchange surfaces. Transport system is required to take substances from the exchange surfaces to all of the cells in the body

Question 23

Describe the features of the transport systems of large organisms

Answer 23

-A medium to carry materials (eg blood).
-A form of mass transport to move the medium in bulk.
-A closed system of vessels to tranport the medium to all areas of the body.
-A mechanism to move the medium in vessels

Question 24

Describe the circulatory systems of mammals

Answer 24

Closed, double circulatory system. Deoxygenated blood is pumped to the lungs from the heart, oxygenated blood flows back to the heart and then is pumped around the body.

Question 25

Describe the stages of the cardiac system - Diastole

Answer 25

-atria is relaxed - begin to fill with blood
-atrioventricular valves open
-ventricles relaxed -lower pressure, blood enters from atria
-arterial pressure high
-semilunar valves close to prevent back flow of blood

Question 26

Describe the stages of the cardiac system - atrial systole

Answer 26

-atria contracts = higher pressure
-ventricles relaxed = lower pressure
-atrioventricular valves opens
-blood flows from atria to ventricles

Question 27

Describe the stages of the cardiac system - ventricular systole

Answer 27

-ventricles contract = higher pressure
-atria relaxed = lower pressure
-atrioventricular valves close to prevent back flow of blood
-semilunar valves open
-blood flows from ventricles to arteries

Question 28

Explain how valves control the flow of blood through the heart

Answer 28

-Valves prevent back flow of blood.
- They open when the pressure in front of the valve exceeds the pressure behind the valve and close when pressure behind the valve exceeds pressure in front of the valve

Question 29

Explain the volume and pressure changes which take place in the heart during the cardiac cycle

Answer 29

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Question 30

Describe the general structure of arterioles, arteries and veins

Answer 30

-Lumen - space that blood flows through
-Endothelium - one cell thick and smooth
-Elastic layer - stretches and recoils
-muscle layer - can contract to control blood flow
-Tough fibrous outer layer - resists pressure changes

Question 31

Describe how the structure of arteries related to its function

Answer 31

-arteries transport blood rapidly under high pressure from heart to tissues
-THICK MUSCULAR LAYER - smaller arteries can be constricted + dilate to control volume of blood passing through
-THICK ELASTIC LAYER - stretching and recoiling to allow pressure to be maintained and smooth
-THICK WALL - withstand high pressure and prevent vessel from bursting

Question 32

Describe how the structure of arterioles relates to its function

Answer 32

-arterioles carry blood to tissues at relatively high pressure (lower than arteries) from arteries to capillaries and control blood flow between the two
-THICK MUSCLE LAYER - allows constriction of the lumen to control blood flow to tissues
-THIN ELASTIC LAYER - blood pressure is lower

Question 33

Describe how the structure of veins relate to its function

Answer 33

-veins transport blood slowly, under low pressure from capillaries in tissues to heart
-THIN MUSCLE LAYER - no need to control blood flow to capillaries
-THIN ELASTIC LAYER - low pressure of blood within veins, pressure too low to cause recoil
-THIN WALL - low pressure , can also be easily flattened aiding blood flow
-valves - prevent blood flow

Question 34

Explain the structure of capillaries and how its related to its function

Answer 34

-capillaries exchange metabolite materials between the blood and cells
-THIN ENDOTHELIUM - shorter diffusion path > rapid diffusion
-NUMEROUS AND HIGHLY BRANCHED - Large SA for exchange
-NARROW LUMEN - RBC squeezed flat against side of capillary > brings them even closer to cells to which they supply oxygen > reduces diffusion distance
-SPACES BETWEEN ENDOTHELIAL CELLS - allow WBC to pass through tissues to deal with infections within tissues

Question 35

Describe the composition of tissue fluid

Answer 35

Tissue fluid contains:
-water, glucose, amino acids, fatty acids, ions and oxygen

Question 36

Explain how tissue fluid is formed

Answer 36

-high Ψ and hydrostatic pressure at arterial end
-water, glucose and oxygen move out from capillary to tissues due to pressure gradient
-this lowers Ψ in the capillary (protein and cells remain)
-at the venous end, water, urea and CO2 move down their Ψ gradient into capillary by osmosis
-excess tissue fluid goes into the lymph vessels and returns to the blood via lymphatic system

Question 37

Define what transpiration is

Answer 37

The process where evaporation of water from the leaves pulls a stream of water through the xylem vessels of the stem

Question 38

Explain how water moves through the leaf

Answer 38

-Water evaporates from the cell walls of the mesophyll cells into the air spaces in the leaf.
-This lowers water potential in mesophyll cell and water moves by osmosis from neighbouring cells
-The process is repeated through the cells
-Replaced by water from the xylem

Question 39

Explain how water moves up the xylem

Answer 39

-Cohesion-tension theory
-Water evaporates from mesophyll cells
-Water molecules form hydrogen bonds between each other - cohesion
-Water forms continuous, unbroken column through mesophyll cells and xylem - transpiration pull
-This causes a negative pressure within the xylem
-No energy required other than that from the sun which drives evaporation

Question 40

Explain how water moves through the leaf

Answer 40

-Water evaporates from the cell walls of the mesophyll cells into the air spaces in the leaf.
-This lowers water potential in mesophyll cell and water moves by osmosis from neighbouring cells
-The process is repeated through the cells
-Replaced by water from the xylem

Question 41

Explain how water moves up the xylem

Answer 41

-Cohesion-tension theory
-Water evaporates from mesophyll cells
-Water molecules form hydrogen bonds between each other - cohesion
-Water forms continuous, unbroken column through mesophyll cells and xylem - transpiration pull
-This causes a negative pressure within the xylem
-No energy required other than that from the sun which drives evaporation

Question 42

Evidence for cohesion-tension theory

Answer 42

-change in the diameter of tree trunks according to rate of transpiration > during day , when transpiration is greater there’s more tension (more negative pressure) in xylem > pulls walls of xylem vessels inwards causing trunk shrink in diameter > at night when transpiration is at its lowest there is less tension in xylem and so diameter of tree trunk increases
-if xylem vessel is broken and air enters it, the tree can no longer draw up water > due to continuous column of water breaking broken so water molecules can no longer stick together
-when a xylem vessel is broken, water does not leak out as would be the case if it were under pressure, instead it is drawn in which is consistent wit it being under pressure

Question 43

Describe the mass flow mechanism for the transport of organic substances in the phloem

Answer 43

-Glucose produced in photosynthesising cells converted to sucrose
-Hydrogen ions actively transported out of companion cell
-Hydrogen ions return to companion cell through co-transport protein with sucrose (facilitated diffusion)
-Sucrose moves into sieve tube elements lowering water potential
-Water moves from the higher water potential in xylem to the sieve tube element creating a higher hydrostatic pressure
-Sucrose at the sink is used in respiration or converted to starch
-Sucrose is actively transported from sieve tube element to sink cells lowering water potential
-Water leaves sieve tubes down water potential gradient via osmosis creating a lower hydrostatic pressure
-Sucrose moves by mass flow down the hydrostatic pressure gradient from source to sink

Question 44

Summarise the evidence for and against the mass flow mechanism

Answer 44

FOR:
-Pressure in sieve tubes (sap released when cut)
-Concentration of sucrose higher in leaves than roots
-Downward flow in phloem only occurs in the light
-Increase in sucrose in leaf followed later by similar increase in sucrose in phloem
-Lack of oxygen inhibits translocation of sucrose in phloem
-Companion cells have many mitochondria

AGAINST:
-Function of sieve plates unclear - hinder mass flow
-Not all solutes move at same speed - they would in mass flow
-Sucrose delivered same rate to all regions - not dependent on sucrose concentration of sink as mass flow would suggest