3.3 and 3.4

Question 1

Explain what happens in digestion:

Answer 1

Large (insoluble) molecules hydrolysed to smaller (soluble) molecules that are small enough to be absorbed across cell membranes into blood

Question 2

Describe the digestion of starch in mammals:

Answer 2

Amylase produced by salivary glands hydrolyses starch to maltose
Membrane bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose
Hydrolysis of glycosidic bond

Question 3

Describe the digestion of disaccharides:

Answer 3

Membrane bound disaccharidases hydrolyse disaccharides to 2 monosaccharides
Hydrolysis of glycosidic bond

Question 4

Describe the digestion of lipids in mammals, including action of bile salts

Answer 4

Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets
This increases surface area of lipids for increased/faster lipase activity
Lipase (made in pancreas) hydrolyses lipids to monoglycerides and fatty acids
Hydrolysis of ester bond

Question 5

Describe the digestion of proteins by a mammal:

Answer 5

Endopeptidases- hydrolyse internal bonds within a polypeptide- smaller peptides
Exopeptidases- hydrolyse terminal peptide bonds at ends of polypeptide- single amino acids
Membrane-bound dipeptidases- 2 amino acids
Hydrolysis of peptide bond

Question 6

Why are membrane bound enzymes important in digestion?

Answer 6

Membrane bound enzymes are located on cell membranes of epithelial cells lining ileum
By hydrolysing molecules at the site of absorbtion they maintain conc. gradients for absorption

Question 7

Describe the pathway for absorption of products of digestion in mammals:

Answer 7

Lumen of ileum
Cells lining ileum
Blood

Question 8

Describe the absorption of glucose/amino acids in mammals:

Answer 8

Na+ actively transported from epithelial cells lining ileum to blood by Na+/K+ pump
Establishes conc. gradient of Na+
Na+ enters epithelial cells down its conc. gradient with glucose/amino acid against its conc. gradient
Via a co-transporter protein
Glucose/amino acid moves down conc. gradient into blood via facilitated diffusion

Question 9

Describe the absorption of lipids by a mammal including the role of micelles:

Answer 9

Micelles contain bile salts, monoglycerides and fatty acids
-Make monoglycerides and fatty acids more soluble in water
-Carry release fatty acids and monoglycerides to cell/lining of ileum
-Maintain high conc of fatty acids to cell/lining
Monoglycerides/fatty acids absorbed into epithelial cell by diffusion
Triglycerides reformed in epithelial cells and aggregate into globules
Globules coated with proteins forming chylomicrons which are then packaged into vesicles
Vesicles move to cell membrane and leave via exocytosis
Enter lymphatic vessels and eventually return to blood circulation

Question 10

Describe the role of red blood cells and haemoglobin

Answer 10

RBC contain lots of Hb, and have no nucleus, biconcave shape, high SA:V and short diffusion pathways
Hb associates with O2 at gas exchange surfaces where pO2 is high
This forms oxyhaemoglobin which transports O2
Hb dissociates from/unloads O2 near cells/tissues where pO2 is low

Question 11

Describe the stucture of Hb

Answer 11

Protein with quarternary structure
Made of 4 polypeptide chains
Each chain contains a haem group containing an iron ion

Question 12

Describe the loading, transport and unloading of oxygen in relation to the oxyhaemoglobin dissociation curve

Answer 12

Areas with low pO2:
Hb has low affinity for O2
So O2 readily dissociates with Hb
So % saturation is low

Areas with high pO2:
Hb has a high affinity for O2
So O2 readily loads/associates with Hb
So % saturation is high

Question 13

Explain how the cooperative nature of O2 binding results in an s-shaped curve:

Answer 13

Binding of first oxygen changes tertiary/quarternary structure of haemoglobin
This uncover haem group binding sites making further binding of O2 easier

Question 14

Describe evidence for the cooperative nature of oxygen binding:

Answer 14

At low pO2 as oxygen increases there is little/slow increase in % saturation of Hb with oxygen
At higher pO2 as oxygen increases there is a big/rapid increase in % saturation of Hb with oxygen

Question 15

What is the Bohr effect?

Answer 15

Effect of CO2 conc. on dissociation of oxyhaemoglobin- curve shifts to the right

Question 16

Explain the effect of CO2 concentration on the dissociation of oxyhaemoglobin:

Answer 16

Increasing blood CO2 (e.g due to increased rate of respiration
Lowers blood pH (more acidic)
Reducing Hbs affinity for oxygen as shape/tertiary/quarternary structure changes slightly
So more/faster unloading of oxygen to respiring cells at a given pO2

Question 17

Explain the advantage of the Bohr effect:

Answer 17

More dissociation of oxygen so faster aerobic respiration/less anaerobic respiration so more ATP produced

Question 18

Explain why different types of haemoglobin can have different oxygen transport properties

Answer 18

Different types of Hb are made of polypeptide chains with slightly different amino acid sequences
Results in different tertiary/quarternary structures/shape so different affinities for oxygen

Question 19

Explain how organisms can be adapted to their environment by having different types of haemoglobin with different oxygen transport properties:

Answer 19

Curve shifts left so Hb has higher affinity for O2:
-More O2 associates with Hb more readily
-At gas exchange surfaces where pO2 is lower
-E.g organisms in low O2 environments (high altitudes/underground/foetuses)

Curve shifts right so Hb has lowere affinity for O2:
-More O2 dissociates more readily
-At respiring tissues where O2 is more needed
-E.g organisms with high rates of respiration/metabolic rate (may be small or active)

Question 20

Define closed double circulatory system:

Answer 20

Blood passes through heart twice for every circuit around the body

Question 21

Describe the general pattern of blood circulation in a mammal:

Answer 21

Deoxygenated blood in right side of heart pumped to lungs, oxygenated returns to left side
Oxygenated blood in left side of heart pumped to rest of body, deoxygenated returns to right

Question 22

Suggest the importance of a double circulatory system:

Answer 22

Prevents mixing of oxygenated/deoxygenated blood so blood pumped to body is fully saturated for aerobic respiration
Blood can be pumped to body at a higher pressure so substances taken to/removed from body cells quicker/more efficiently

Question 23

Name the blood vessels entering and leaving the heart and lungs:

Answer 23

Vena cava- transports deoxygenated blood from respiring body tissues to heart
Pulmonary artery- transports deoxygenated blood from heart to lungs
Pulmonary vein- transports oxygenated blood from lungs to heart
Aorta- transports oxygenated blood from heart to respiring body tissues

Question 24

Name the blood vessels entering and leaving the kidneys

Answer 24

Renal arteries- oxygenated blood to kidneys
Renal veins- deoxygenated blood from kidneys to vena cava

Question 25

Name the blood vessels that carry oxygenated blood to the heart muscle

Answer 25

Coronary arteries- located on surface of heart branching from aorta

Question 26

Suggest why the wall of the left ventricle is thicker than that of the right:

Answer 26

Thicker muscle to contract with greater force To generate higher pressure to pump blood around entire body

Question 27

Explain the pressure and volume changes and associated valve movements during the cardiac cycle that maintain a unidirectional blood flow

Answer 27

Atrial systole: Atria contract- volume decreases, pressure increases Atrioventricular valves open when pressure in atria exceeds pressure in ventricles Semilunar valves remain shut as pressure in arteries exceeds pressure in ventricles So blood pushed into ventricles Ventricular systole: Ventricles contract- volume decreases, pressure increases Atrioventricular valves shut when pressure in ventricles exceeds pressure in atria Semilunar valves open when pressure in ventricles exceeds pressure in arteries So blood pushed out of heart through arteries Diastole: Atria and ventricles relax- volume increases, pressure decreases Semilunar valves shut when pressure in arteries exceeds pressure in ventricles Atrioventricular valves open when pressure in atria exceeds pressure in ventricles So blood fills atria via veins and flows passively to ventricles

Question 28

What is the equation for cardiac output?

Answer 28

Cardiac output = stroke volume x heart rate

Question 29

How can heart rate be calculated from cardiac cycle data?

Answer 29

Heart rate= = 60 ÷ length of one cardiac cycle

Question 30

Explain how the structure of arteries relates to their function:

Answer 30

Thick smooth elastic tissue- can contract and control/maintain blood flow/pressure Thick elastic tissue- can stretch as ventricles contract and recoil as ventricles relax to reduce pressure surges/even out blood pressure/maintain high pressure Thick wall- withstand high pressure/ stop bursting Smooth/folded endothelium- reduces friction/can stretch Narrow lumen- increases/ maintains high pressure

Question 31

What is the function of arterioles?

Answer 31

Direct blood flow to different capillaries/tissue

Question 32

Explain how the structure of arterioles relates to their function:

Answer 32

Thicker smooth muscle layer than arteries: Contracts to narrow lumen (vasoconstriction) and reduce blood flow to capillaries Relaxes to woden lumen (vasodilation) and increases blood flow to capillaries Thinner elastic layer- pressure surges are lower (as further from heart)

Question 33

Explain how the structure of veins relates to their function:

Answer 33

Wider lumen than arteries- less resistance to blood flow Very little elastic and muscle tissue- blood pressure lower Valves- prevent backflow of blood

Question 34

What is the function of capillaries?

Answer 34

Allows efficient exchange of substances between blood and tissue fluid

Question 35

Explain how the structure of capillaries relates to their function:

Answer 35

Wall is a thin layer of endothelial cells to reduce diffusion distance Capillary bed is a large network of branched capillaries to increase SA for diffusion Small diameter/narrow lumen- reduces blood flow rate so more time for diffusion Pores in walls between cells- alllow larger substances through

Question 36

Explain the formation of tissue fluid:

Answer 36

At arteriole end of capillaries: Higher blood/hydrostatic pressure inside capillaries (due to contraction of ventricles) than tissue fluid Forces water (and dissolved substances out of capillaries Large plasma proteins remain in capillary

Question 37

Explain the return of tissue fluid to the circulatory system

Answer 37

At venule end of capillaries Hydrostatic pressure reduces as fluid leaves capillary Increasing conc. of plasma proteins lowers water potential of capillary below that of tissue fluid Water enters capillaries from tissue fluid by osmosis down a water potential gradient Excess water taken up by lymph capillaries and returned to circulatory system through veins

Question 38

Suggest and explain causes of excess tissue fluid accumulation:

Answer 38

Low conc. of protein in blood plasma: Water potential in capillary not as low so water potential gradient reduced So more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis High BP- high hydrostatic pressure: Increased outward pressure from arterial end, and reduced inward pressure at venule end So more tissue fluid formed at arteriole end/less water absorbed at venule end by osmosis Lymph system may not be able to drain excess fast enough

Question 39

What is a risk factor?

Answer 39

An aspect of a person's lifestyle or substance in a person's body/environment That have been shown to be linked to an increased rate of disease

Question 40

Describe the function of xylem tissue

Answer 40

Transports water (and mineral ions) through the stem, up the plant to leaves of plants

Question 41

Suggest how xylem tissue is adapted for its function:

Answer 41

Cells joined with no end walls to form a long continuous tube- water flows down as a continuous column Cells contain no cytoplasm/nucleus so easier water flow/no obstructions Thick cells walls with lignin- provides support/withstand tension/prevents water loss Pits in walls- allow lateral water movement

Question 42

Explain the cohesion tension theory:

Answer 42

Water lost from leaf by transpiration- water evaporates from mesophyll cells into air spaces and water vapour diffuses through open stomata Reducing water potential of mesophyll cells So water drawn out of xylem down a water potential gradient Creating tension in xylem Hydrogen bonds result in cohesion between water molecules so water pulled up as one continuous column Water also adheres to walls of xylem Water enters roots by osmosis

Question 43

How does light intensity affect transpiration rate?

Answer 43

Increases rate of transpiration Stomata open in light to let in CO2 for photosynthesis allowing water to evaporate faster Stomata close when its dark so there is a low transpiration rate

Question 44

How does temperature affect transpiration rate?

Answer 44

Water molecules gain kinetic energy as temperature increases so water evaporates faster

Question 45

How does wind intensity affect transpiration rate?

Answer 45

Wind blows away water molecules from around stomata, decreasing water potential of air around stomata Increases water potential gradient so water evaporates faster

Question 46

How does humidity affect transpiration rate?

Answer 46

More water in air so it has a higher water potential Decreases water potential gradient from leaf to air so water evaporates slower

Question 47

Describe the function of the phloem tissue

Answer 47

Transports organic substances in plants

Question 48

Suggest how the phloem tissue is adapted for its function

Answer 48

Sieve tube elements -no nucleus/few organelles to maximise space for/easier flow of organic substances -End walls between cells perforated Companion cells -many mitochondria so high rate of respiration to make ATP for active transport of solutes

Question 49

What is translocation?

Answer 49

Movement of assimilates/solutes such as sucrose From source cells to sink cells by mass flow

Question 50

Explain the mass flow hypothesis for translocation in plants:

Answer 50

At source end, sucrose is actively transported into phloem sieve tubes/cells by companion cells This lowers water potential in sieve tubes so water enters by osmosis This increases hydrostatic pressure in sieve tubes/ creates a hydrostatic pressure gradient So mass flow occurs- movement of source to sink At sink, sucrose is removed by active transport to be used by respiring cells or stored in storage organs

Question 51

Describe the use of tracer experiments to investigate transport in plants:

Answer 51

Leaf supplied with radioactive tracer e.g CO2 containing radioactive isotope 14C Radioactive carbon incorporated into organic substances during photosynthesis These move around plant by translocation Movement tracked using autoradiography or a Geiger counter

Question 52

Describe the use of ringing experiment to investigate transport in plants:

Answer 52

Remove/kill phloem e.g remove a ring of bark Bulge forms on source side of ring Fluid from bulge has higher conc. of sugars than below- shows sugar is transported in phloem Tissues below ring die as cannot get organic substances