Module 3 all topics

Question 1

outline the features of a (closed) double circulatory system. (humans)

Answer 1

blood travels twice through the heart for each circuit; pulmonary and systemic, oxygenated and deoxygenated blood don’t mix

Question 2

outline the features of a (closed) single circulatory system (fish)

Answer 2

blood passes through the heart once, 2 sets of capillaries

Question 3

outline the features of an open circulatory system

Answer 3

no blood vessels
haemolymph is pumped directly into haemocoel (body cavity)
blood flow can’t be regulated through vasodilation or vasoconstriction
no transport of carbon dioxide or water

Question 4

state the order of layers that forms blood vessels (6)

Answer 4

lumen, endothelium, elastic layer, muscle layer, collagen

Question 5

outline the composition of arteries, relating to their function

Answer 5

0.4-2.5cm
- mostly elastin: stretch to sustain high pressures of blood
- some smooth muscle
- some collagen

Question 6

outline the composition of arterioles

Answer 6

30 micrometres
- mostly smooth muscle
- elastin
- collagen

Question 7

outline the composition of veins, relating to their function.

Answer 7

• largest proportion is collagen
• contains smooth muscle: for vasodilation and vasoconstriction
• contains small proportion of elastin

Question 8

outline the composition of venules

Answer 8

no elastin
no smooth muscle
only collagen

Question 9

explain what can be observed from an ECG showing tachycardia, and explain what somebody suffering from tachycardia is experiencing

Answer 9

shorter distances between the high points
still evenly spaced out no irregularities

fast heart beat, over 100bpm

Question 10

explain what can be observed from an ECG showing bradycardia, and explain what somebody suffering from bradycardia is experiencing

Answer 10

lowered resting heart rate

larger distances between peaks, still evenly spaced out, no irregularities

Question 11

explain what can be observed from an ECG showing atrial fibrillation, and explain what somebody suffering from atrial fibrillation is experiencing

Answer 11

abnormal atria rhythm, ventricles lose regular rhythm
lots of little peaks, big peaks aren’t evenly spaced out

atria are contracting very fast, but don’t contract properly, impulses are passed onto atria which contract much less often- ineffective pumping of blood through the heart.

Question 12

explain what can be observed from an ECG showing an ectopic heart beat, and explain what somebody suffering from this is experiencing

Answer 12

• mostly appears normal, however one beat is followed instantly by another beat, and then an irregular gap. (extra heart beat)

Question 13

referring to its structure, explain how haemoglobin combines with oxygen

Answer 13

Hb has 4 polypeptide chains; each chain is bound to a haem prosthetic group containing iron (Fe2+)
- each Fe group combines with one oxygen molecule (reversible)
Hb + 4O2 -> Hb(O2)4

Question 14

explain the sigmoid curve produced in an oxygen dissociation curve.

Answer 14

as the partial pressure of oxygen increases, saturation of Hb increases.
at low po2, affinity for oxygen is low
- at higher po2, oxygen mol binds to Hb molecule, changing its quaternary structure, making it more easily bind to another oxygen molecule

Question 15

explain why the 4th oxygen molecule binds to Hb at only a slightly higher po2.

Answer 15

when Hb is 75% saturated, the chances of a collision are lowered due to being almost fully saturated. therefore, increasing the pressure doesn’t have much impact

Question 15

explain what happens when red blood cells reach tissue and are presented with high concentrations of carbon dioxide.

Answer 15

high pco2 decreases the affinity of Hb for oxygen
causes one oxygen mol to unload from Hb mol
this unloading changes the shape of Hb facilitating the unloading of more oxygen molecules.

Question 16

outline how xylem are adapted to their function (4)

Answer 16

• long hollow columns of cells, facilitating capillary action/movement of water up xylem
• parenchyma packs around xylem vessel; stores food and contains tannin deposits (plant defences against herbivory)
• lignin in rings/spirals: allows xylem to maintain structure under high pressures of water.
• unlignified areas: pits where water leaves xylem

Question 17

outline the general movement of water during transpiration

Answer 17

1. water moves into root
2. water moves across root
3. water moves into xylem
4. water moves into transpiration stream

Question 18

outline the process by which water enters the root, and how root hair cells are adapted to their function of absorbing water.

Answer 18

water enters by osmosis (high wp to low wp)
root hair cells:
- hairs have large surface area: maximises water uptake
- thin surface layer: short diffusion distance
- cytoplasm has high concentration of solutes (low wp) which maintains the water potential gradient for the movement of water

Question 19

outline the 2 main pathways that water can take across the root to reach the xylem

Answer 19

1. symplast: through cytoplasm of cells, adjacent cells are connected by plasmodesmata
2. apoplast: water moves through cell walls and intercellular spaces

Question 20

explain what the casparian strip is, and what it does.

Answer 20

strip of suberin, which blocks the movement of water through the apoplast pathway, and so pushes it into the symplast pathway.

Question 21

explain how water moves into the xylem from the endodermal cells.

Answer 21

• endodermal cells actively transport mineral ions into the xylem from the cytoplasm.
• this lowers the xylem water potential and raises the water potential of the endodermal cells.
• causes water to enter the xylem by osmosis

Question 22

explain what the transpiration stream is.

Answer 22

the movement of water from the root, up the plant and out through the leaves

Question 23

explain how the properties of water enable capillary action up the xylem vessel in the transpiration stream

Answer 23

water is cohesive:
- the positive regions of one water molecule interacts with the negative regions of another, forming hydrogen bonds
- cohesion allows water to move in a continuous column, which creates tension

Question 24

outline the role of adhesion in the transpiration stream

Answer 24

water molecules form hydrogen bonds with carbohydrates in the xylem vessel walls