Topic 3 AQA A Level

Name the blood vessels that carry blood to the heart muscle

Coronary arteries;

Explain the advantages of lipid droplet and micelle formation/3

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;

Explain the role of the heart in the formation of tissue fluid./2

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

Explain how changes in the shape of haemoglobin result in the S-shaped (sigmoid) oxyhaemoglobin dissociation curve for HbA./2

First oxygen binds (to Hb) causing change in shape; (Shape change of Hb) allows more O2 to bind (easily) / greater saturation with O2 OR Cooperative binding;

Haemoglobin is a protein with a quaternary structure. Explain the meaning of quaternary structure /1.

(Molecule contains) more than one polypeptide (chain).

In tissue fluid formation the hydrostatic pressure falls from the arteriole end of the capillary to the venule end of the capillary. Explain why/1

Loss of water / loss of fluid / friction (against capillary lining).

High blood pressure leads to an accumulation of tissue fluid. Explain how/3

"1. High blood pressure = high hydrostatic pressure; 2. Increases outward pressure from (arterial) end of capillary / reduces inward pressure at (venule) end of capillary; 3. (So) more tissue fluid formed / less tissue fluid is reabsorbed.

The water potential of the blood plasma is more negative at the venule end of the capillary than at the arteriole end of the capillary. Explain why/3

"1. Water has left the capillary; 2. Proteins (in blood) too large to leave capillary; 3. Increasing / giving higher concentration of blood proteins (and thus wp)."

In a healthy person, blood moves in one direction as it passes through the heart. Give two ways in which this is achieved./2

Pressure gradient / moves from high to low pressure; Valves stop backflow

Endopeptidases and exopeptidases are involved in the hydrolysis of proteins. Name the other type of enzyme required for the complete hydrolysis of proteins to amino acids./1

Dipeptidase

Suggest and explain why the combined actions of endopeptidases and exopeptidases are more efficient than exopeptidases on their own/2

"1. Endopeptidases hydrolyse internal (peptide bonds) OR Exopeptidases remove amino acids/hydrolyse (bonds) at end(s); 2. More ends or increase in surface area (for exopeptidases);"

Tubifex worms are small, thin animals that live in water. They have no specialised gas exchange system. Explain how two features of the body of the tubifex worm allow efficient gas exchange./2

1.Thin/small so short diffusion pathway; 2.Flat/long/small/thin so large surface area to volume ratio/surface area : volume;

Some people produce a much higher ventricular blood pressure than normal. This can cause tissue fluid to build up outside the blood capillaries of these people. Explain why./2

"1. More fluid forced/filtered out of capillary/blood (due to high pressure); 2. Less return of fluid (into capillary/blood) due to pressure OR Lymph(atic) (system) cannot drain away all excess fluid;"

Some drugs used to reduce high ventricular blood pressure cause widening of blood vessels.Suggest how widening of blood vessels can reduce ventricular blood pressure./2

1.Larger lumen/volume (of blood vessels); 2.Reduces (blood) pressure (in blood vessels);3.Less friction/resistance (in blood vessels);

Explain how the highest blood pressure is produced in the left ventricle./1

Strongest/stronger contractions;

Describe the role of haemoglobin in supplying oxygen to the tissues of the body./2

1, Oxyhaemoglobin formed/ haemoglobin is loaded/ uptakes/associates/binds with oxygen in area of higher ppO2 / in gas exchange surface/lungs/gills; (oxygen) unloaded/dissociates from/released (in area of lower ppO2 / in capillaries/to cells/tissues);

Name the structure through which gases enter and leave the body of an insect/1

Spiracle

Name the small tubes that carry gases directly to and from the cells of an insect./1

Tracheole/trachea;

Explain the movement of oxygen into the gas exchange system of an insect when it is at rest./3

1. Oxygen used in (aerobic) respiration; 2. (so) oxygen (concentration) gradient (established);3 (so) oxygen diffuses in;

What is the function of the coronary arteries?/2

Carry oxygen/glucose; to heart muscle/tissue/cells/myocytes

The rise and fall in blood pressure in the aorta is greater than in the small arteries.Suggest why./3

1. close / directly linked to the heart / ventricle / pressure is higher / is very high; aorta has elastic tissue; has stretch and recoil

The oxygen dissociation curve for haemoglobin shifts to the right during vigorous exercise. Explain the advantage of this shift./3

1. Lower affinity for oxygen / releases more oxygen / oxygen is released quicker / oxygen dissociates / unloads more readily; 2 to muscles/tissues/cells 3. For high/rapid respiration

Explain how the body shape of a seal is an adaptation to living in a cold environment./2

1. Small SA:VO; 2. So reduces heat loss/ more heat retained

Explain how downward movement of the diaphragm leads to air entering the lungs./2

1. Increases volume in lungs/thorax; lowers pressure in lungs/thorax; air pushed in by higher outside pressure/down pressure gradient

An arteriole is described as an organ. Explain why./2

Made of different tissues/more than one tissue

An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries/2

1. Muscle conracts. 2. Arteriole narroes/constricts/reduces size of lumen/ vessel/ vasoconstriction

A capillary has a thin wall. This leads to rapid exchange of substances between the blood and tissue fluid. Explain why./1

Short diffusion distance / pathway;

Blood flow in capillaries is slow. Give the advantage of this./1

More time for exchange/diffusion of substances

Kwashiorkor is a disease caused by a lack of protein in the blood. This leads to a swollen abdomen due to a build up of tissue fluid. Explain why a lack of protein in the blood causes a build up of tissue fluid./3

1. Water potential (in capillary) not as low / is higher / less negative / water potential gradient is reduced2. Less / no water removed (into capillary); 3. By osmosis (into capillary);

Describe how oxygen in air in the alveoli enters the blood in capillaries./2

1. Diffusion. 2. Across alveoli epithelium/ capillary endothelium

A leaf is an organ. What is an organ?/1

A group of tissues

Describe how carbon dioxide in the air outside a leaf reaches mesophyll cells inside the leaf/3.

1. (Carbon dioxide enters) via stomata; 2 (Stomata opened by) guard cells; 3. Diffuses through air spaces; Allow concentration gradient. Reject along gradient unless direction made clear 4. Down diffusion gradient;

Explain, in terms of pressure, why the semilunar valves open in the heart during contraction./1

Pressure is greater below valve / in ventricle than (artery);

The haemoglobin in one organism may have a different chemical structure from the haemoglobin in another organism. Describe how./1

Different primary structure / amino acids / different number of polypeptide chains;

Explain the importance of elastic fibres in the wall of the aorta/2

"Stretches / 'expands' under high pressure / when ventricle contracts / systole and recoils / 'springs back' under low pressure / when ventricle relaxes / diastole;2. Smooths blood flow / maintains blood pressure / reduces pressure surges;"

Explain the importance of muscle fibres in the wall of an arteriole./2

"1. (Muscle) contracts;2. (Arteriole) constricts / narrows / alters size of lumen / reduces / regulates blood flow (to capillaries);"

Describe the path by which oxygen goes from an alveolus to the blood./2

1. Through alveolar epithelium. 2Through capillary epithelium / endothelium;

Miner's lung means dust causes the alveolar epithelium to become thicker. Explain why people with miner's lung have a lower concentration of oxygen in their blood/1

Longer diffusion pathway

Describe how ventilation helps to maintain this difference in oxygen concentration between alveoli and lung capillaries/2

Brings in air containing a high(er) oxygen concentration; Removes air with a low(er) oxygen

Explain how mitochondria help the cell to absorb the products of digestion./2

(Site of aerobic) respiration / ATP production / energy release; Active transport/ transport against the concentration gradient

An increase in respiration in the tissues of a mammal affects the oxygen dissociation curve of haemoglobin. Describe and explain how./2

Increase in / more carbon dioxide; curve moves to right/depressed

People living at high altitude (with less oxygen) have more red blood cells than people living at sea level. Explain the advantage of this to people living at high altitude./2

More haemoglobin; so can load/pick up more oxygen

Explain the advantage to people living at high altitude of having the oxygen dissociation curve shifted to the right/2

(Haemoglobin) has lower affinity for oxygen / more oxygen released; In / to the cells / tissues;

Explain when calculating stomatal density Explain why it was important that the piece of the epidermis that the student removed was thin./2

Single layer of cells / few layers of cells; So that light that can pass through / cells absorb light;

Suggest how a student can used a slide with lower epidermis on it to find the number of stomata per cm2 / 3

Method of determining area of field of view / area seen using microscope; Count number of stomata in field of view; Repeats and calculation of mean;

The stomata on the leaves of pine trees are found in pits below the leaf surface. Explain how this helps to reduce water loss/2

Water vapour accumulates / increased humidity / reduced air movement (around stomata); Water potential / diffusion gradient reduced;

Give one way in which blood plasma is different from tissue fluid / 1

More / larger proteins / less urea / carbon dioxide / more glucose / amino acids / fatty acids / oxygen / high(hydrostatic) pressure;

The blood pressure is high at the start of the capillary. Explain how the left ventricle causes the blood to be at high pressure/1

Contracts

The blood pressure decreases along the length of the capillary. What causes this decrease in pressure/1

Loss of fluid/volume; friction/resistance of capillary wall

In children, some diets result in a low concentration of protein in blood plasma. This can lead to the accumulation of tissue fluid. Explain why/3

Water potential in capillary not as low/is higher/less negative/water potential gradient is reduced; more tissue fluid formed (at arteriole end); Less / no water absorbed (into blood capillary) by osmosis; (into blood capillary);

A fish uses its gills to absorb oxygen from water. Explain how the gills of a fish are adapted for efficient gas exchange./6

"1. Large surface area provided by lamellae / filaments increases diffusion / makes diffusion efficient;;Q Candidates are required to refer to lamellae or filaments. Do not penalise for confusion between two 2. Thin epithelium / distance between water and blood; 3. Water and blood flow in opposite directions / countercurrent; 4. maintains concentration gradient (along gill) / equilibrium not reached / as water always next to blood with lower concentration of oxygen; 5. Circulation replaces blood saturated with oxygen; 6. Ventilation replaces water (as oxygen removed);"

The concentration of oxygen is higher in the surface waters than it is in water close to the seabed. Suggest why/2

"Mixing of air and water (at surface); Air has higher concentration of oxygen than water; Diffusion into water; Plants / seaweeds near surface / in light; Produce oxygen by photosynthesis;"

"Describe and explain one way in which the composition of fluid tissue fluid differs from that of fluid plasma/2."

"fluid Y contains little / no protein; molecules too large (to pass through capillary wall); OR fluid Y contains less glucose; some will have entered tissue cells; accept any other biologically correct difference marked in a similar way."

Explain how fluid leaves the capillary at the arterial end./2

"hydrostatic pressure / blood pressure / arterial pressure; greater than osmotic effect which forces molecules / fluid out;"

Describe the part played by arterioles in redistributing blood to different organs./2

The muscle in the wall / sphincter contracts; Reducing blood flow/narrowing/closing arteriole

Describe how the change in blood flow to the muscles of a seal differs from the change in blood flow to human muscles as activity increases./1

Blood flow increased in humans/reduced in seals

The intercostal muscles are between the ribs. In normal breathing, describe the part played by the intercostal muscles during inspiration/3

"contract; ribs move upwards / out; increasing volume / decreasing pressure in chest / thorax / lungs;"

A large number of small alveoli is more efficient in gas exchange than a smaller number of larger alveoli. Explain why/2

(Small alveoli with) large surface area; For diffusion;

Just before a person starts to exhale, the composition of the air in an alveolus differs from the composition of the air in the trachea. Give 2 ways in which the composition would differ /1

Less oxygen / more carbon dioxide / more water vapour;

Through which vessel does blood leave the heart to go to the lungs?/1

Pulmonary artery

Suggest why blood returning to the heart from the lungs contains some carbon dioxide./2

"Concentrations reach equilibrium / become equal; Diffusion occurs when there is a concentration gradient (so some will remain in blood); OR Lung cells / vessel cells respire; Add / produce carbon dioxide;

Describe the part played by the diaphragm in causing air to enter the lungs during breathing./3

"Diaphragm (muscle) contracts; Flattens / Increases volume of chest; Reduced pressure allows air to enter;"

Explain how the shape of a red blood cell allows it to take up a large amount of oxygen in a short time.

" Large surface area to volume ratio; For diffusion; OR Flat / thin; So oxygen can reach all haemoglobin / centre rapidly / short pathway;"

Haemoglobin is a protein with a quaternary structure. What is meant by a quaternary structure?/1

Structure resulting from aggregation of several polypeptide chanins / tertiary structures / eq:

Explain how oxygen in a red blood cell is made available for respiration in active tissues/3

"Low pH / (more)H+ ; due to (increased) CO2 (increased) respiration; (increased) dissociation of haemoglobin; Oxygen diffuses from r.b.c. to tissues

Give an advantage of lactase and other digestive enzymes being located in the plasma membranes of cells lining the small intestine, rather than being secreted into the lumen of the small intestine./1

"Enzymes not lost (with gut contents) / more effective absorption of products formed by these enzymes;"

The absorption of galactose from the small intestine is reduced if the absorbing cells are treated with a respiratory inhibitor, such as cyanide. Suggest an explanation for this./2

No ATP formed / no energy released by respiration; Link ATP to active transport (of galactose) into cells;

The elastin fibres in the wall of the artery help to smooth out the flow of blood. What happens to these fibres as the pressure of the blood in the artery changes?/2

"Stretch as pressure increases; Recoil / spring back as pressure drops;"

Give one way in which the structure of the wall of an artery is similar to the structure of the wall of a capillary./1

Both have an endothelium / epithelium / squamous cells;

Describe how the increase in pressure of the blood in the artery results from the events in the cardiac cycle./2

"Caused by blood leaving the heart / entering artery; As a result of ventricles contracting / systole;"

Explain how the cuticle of a leaf reduces water loss/1.

impermeable to water / waterproof / stops water passing through;

Explain how the structure of the arteries reduces fluctuations in blood pressure./2

" elastic tissue / fibres / wall; expands / recoils / springs back (to smooth the pressure surges);"

Explain how the structure of capillaries is related to their function./2

"walls / endothelium one cell thick / made of flattened cells; short diffusion pathway OR narrow lumen; reduces rate of flow / more time for diffusion; OR gaps / pores between cells (accept fenestrations between cells); increased rate of diffusion / fluid movement out of vessel;"

Water containing dissolved oxygen flows over the gill in the opposite direction to the blood flow inside. Explain why this arrangement is important for efficient oxygen uptake./2

maintains diffusion / concentration gradient / equilibrium not reached; diffusion occurs across whole length (of lamellae / gill);

Suggest how the atrioventricular valves help to maintain the flow of blood in one direction through the heart./2

"(valves close) due to high blood pressure / when ventricles contract; Y prevent valve from being inverted / restricts / stops valve movement;"

Explain how aerobic respiration in cells leads to a change in the pH of blood plasma./2

"CO2 is produced (in respiration); forms carbonic acid / hydrogen ions released;"

What is the advantage to tissue cells of a reduction in the affinity of haemoglobin for oxygen when the plasma pH decreases?/2

low pH because high rate of respiration; cells need more O2; more O2 released / O2 released faster;

Explain the advantage for mice living at high altitude in having a haemoglobin dissociation curve which is to the left of the curve for mice living at low altitude./2

"high altitudes have a low partial pressure of O2; high saturation / affinity of Hb with O2 (at low partial pressure O2); so sufficient / enough O2 supplied to cells / tissues;"

The producers in one marine ecosystem are seaweeds, which have a large surface area to volume ratio. Give two advantages to seaweeds of having a large surface area to volume ratio./2

"(larger area) to absorb light; (larger surface area) to absorb carbon dioxide; short diffusion pathway for gases / oxygen / CO2; light able to penetrate to all cells;"

Describe the advantage of having elastic tissue in the wall of an artery./2

"elastic tissue allows recoil (reject if wording implies a muscle e.g. contract / relax)(ignore expand); maintains blood pressure / constant / smooth blood flow"

When first hatched, the young of some species of fish are less than 2 mm long. Explain how these young fish get enough oxygen to their cells without having gills./2

"exchange / diffusion across body surface / skin; short diffusion pathway / distance / large SA:V ratio;"

Explain why there is a net loss of water from a capillary at the arterial end./2

(at arterial end) hydrostatic pressure / blood pressure; greater than ressure of water potential gradient / greater than osmotic uptake;

The total volume of fluid that passes from the capillaries to the surrounding tissue fluid is normally greater than the volume that is reabsorbed into them. Describe what happens to this extra fluid/2

removed by lymphatic system / lymph; returned to blood;

Tissue fluid accumulates in the tissues of people who do not eat enough protein. Explain why./2

less protein in blood; water potential gradient is lower

A stem was cut from a transpiring plant. The cut end of the stem was put into a solution of picric acid, which kills plant cells. The transpiration stream continued. Suggest an explanation for this observation./2

water moves in dead cells / xylem is non-living tissue; the process is passive / no energy is needed;

Which type of blood vessel has most elastic tissue in its wall?/1

Artery

How does elastic tissue in arteries help to smooth out the flow of blood in it / 2

stretches / expands to accommodate increase in blood volume / when ventricle contracts / increase in blood pressure;

recoils when blood volume decreases / when ventricle relaxes / blood pressure decreases

Describe and explain the relationship between humidity and transpiration rate./3

increased humidity leads to decreased transpiration;

high humidity means more water in the air / increased saturation / increased water potential;

reduced diffusion gradient / water potential gradient;

slower rate of water loss / less evaporation;

Describe two differences between active transport and facilitated diffusion./2

"Active transport against / facilitated down with concentration gradient; Active transport uses ATP/energy, /facilitated doesn't; Active uses carrier (proteins), / facilitated (often) uses channel (proteins);

Explain why molecules of oxygen and carbon dioxide are able to diffuse across membranes/2

" Lipid/fatty acid part of membrane is non-polar/hydrophobic; Oxygen and carbon dioxide small/non-polar; Oxygen/carbon dioxide can diffuse through/dissolve in/ get between molecules in this layer; Down a concentration gradient;

Explain why ventilation of the lungs increases the efficiency of gas exchange/2

Brings more oxygen/removes carbon dioxide; Maintains diffusion/concentration gradients; Between alveoli and blood/capillaries;