Topic 3b (Chapter 7 of Text Book) – Common Exam Questions and Model Answers

Heart and Circulation
Describe what causes the maximum pressure in the ventricles to be higher than the atria (OR describe what causes the maximum pressure in the left ventricle to be higher than the right ventricle). / ·  (Left) Ventricle has thick wall/more muscular
·  So contractions are stronger/harder
Describe, in terms of pressure, what causes the semi-lunar valves to shut / ·  Blood pressure in the arteries increases higher than the pressure in the ventricles.
Describe in terms of pressure, what causes the AV valves to shut / ·  Pressure in the ventricles greater than the pressure in the atria
Describe how tissue fluid is formed and how it is returned to the circulatory system. / Formation
1. High blood / hydrostatic pressure
2. Forces water;
3. Large proteins remain in capillary;
Return
4. Low water potential in capillary / blood;
5. Due to (plasma) proteins;
6. Water enters capillary / blood;
7. (By) osmosis;
8. Correct reference to lymph;
Explain why a lack of protein in the blood causes a build-up of tissue fluid. / 1.  Water potential in capillary is higher/less negative
2.  Less water removed into capillary;
3.  By osmosis
4.  More water remains as tissue fluid
5.  By osmosis
Haemoglobin
Explain the advantage of the animal having an oxygen dissociation curve shifted to the left
LEFT = LOW OXYGEN / ·  Hb has greater affinity for O2;
·  becomes saturated at low(er) ppO2 / more saturated at same ppO2 / unsaturated at very low ppO2;
·  able to supply enough O2 to its tissues;
Explain the advantage of the animal having an oxygen dissociation curve shifted to the right
RIGHT = RESPIRATION / ·  organism has a greater rate of respiration so has high oxygen demand (accept more O2 needed for respiration);
·  Hb dissociates more readily;
·  more O2 supplied.
Explain how oxygen is loaded, transported and unloaded in the blood / 1. Haemoglobin carries oxygen / has a high affinity for oxygen
2. In red blood cells;
3. Loading/uptake/association in lungs;
4. at high p.O2;
5. Unloads/ dissociates / releases to respiring cells/tissues;
6. at low p.O2;
7. Unloading linked to higher carbon dioxide (concentration);
Blood Vessels
An arteriole contains muscle fibres. Explain how these muscle fibres reduce blood flow to capillaries. / 1. (Muscle) contracts;
2. (Arteriole) narrows/constricts/reduces size of lumen/vessel / vasoconstriction;
Explain the difference in thickness between the artery and the vein. / High pressure / smoothes out blood flow / artery wall contains more collagen / muscle / elastic (fibres) / connective tissue;
The thickness of the aorta wall changes all the time during each cardiac cycle / 1. Aorta wall stretches;
2. Because ventricle contracts
3. Aorta wall recoils;
4. Because ventricle relaxes
5. Maintain smooth flow / pressure;
How is the structure of arteries and arterioles related to function / Elastic tissue
1 Elastic tissue stretches under pressure/when heart beats;
2 Recoils/springs back;
3 Evens out pressure/flow
Muscle
4 Muscle contracts;
5 Reduces diameter of lumen/vasoconstriction/constricts vessel;
6 Changes flow/pressure;
Epithelium
7 Epithelium smooth;
8 Reduces friction/blood clots/less resistance;
Xylem and Water Transport
Explain how water enters xylem from the endodermis in the root and is then transported to the leaves. / (In the root)
1. Casparian strip blocks apoplast pathway;
2. Active transport by endodermis;
3. (Of) ions/salts into xylem;
4. Lower water potential in xylem / water enters xylem by
(Xylem to leaf)
5. Evaporation / transpiration (from leaves);
6. cohesion / H-bonding between water molecules
7. Adhesion / water molecules bind to xylem;
8. Creates continuous water column;

Graph questions very common
Use your knowledge of transpiration to explain the changes in the rate of flow in the xylem shown in the graph. / 1.Stomata open;
2. Transpiration highest around midday;
3. Middle of day warmer / lighter;
4. (Increased) tension / water potential gradient;
5. More water pulled up
6. Cohesion (between water molecules);
7 Sticking/adhesion (between water and) cells/walls/xylem;
8. Pulls xylem in;
Describe what causes root pressure. / 1. Active transport by endodermis;
2. ions/salts into xylem;
3. Lowers water potential (in xylem);
4. Water enters by osmosis;
Why does wind increase transpiration rate? / 1. Removes water vapour;
2. Increases water potential gradient/more diffusion/more evaporation;
Why does increased temperature increase the rate of transpiration? / 1. Increases kinetic energy;
2. Water molecules move faster;
3. Increases diffusion/evaporation;
How is xylem tissue adapted to its function? / long cells / tubes with no end walls;
continuous water columns;
no cytoplasm / no organelles/named organelle;
to impede/obstruct flow / allows easier water flow;
thickening/lignin;
support / withstand tension / waterproof / keeps water in cells;
pits in walls;
allow lateral movement / get round blocked vessels;
Potometer questions are very common. Potometers measure water uptake rather than rate of transpiration because (1) the plant uses some water for photosynthesis (2) there may be leaks in the system. The tap can be open or shut to move the bubble.
Phloem and Sugar Transport
Why does phloem need ATP / ATP supplies energy
for active transport
to move sucrose from phloem tissue
Describe how carbohydrate produced in the leaves is transported to the roots by mass
flow. / 1 sucrose
2 loaded into phloem/sieve tubes;
3 by companion cells
4 sucrose enters by active transport;
5 lowers water potential of sieve tubes/phloem;
6 water diffuses into phloem / enters by osmosis;
7 increases hydrostatic pressure;
8 pressure forces fluid down to roots