B3.2 Transport

Question 1

B3.2.1—Adaptations of capillaries for exchange of materials between blood and the internal or external
environment

Answer 1

Adaptations should include a large surface area due to branching and narrow diameters, thin walls, and
fenestrations in some capillaries where exchange needs to be particularly rapid.

Question 2

B3.2.2—Structure of arteries and veins
Application of skills:

Answer 2

Students should be able to distinguish arteries and veins in micrographs from the
structure of a vessel wall and its thickness relative to the diameter of the lumen.

Question 3

B3.2.3—Adaptations of arteries for the transport of blood away from the heart

Answer 3

Students should understand how the layers of muscle and elastic tissue in the walls of arteries help them
to withstand and maintain high blood pressures.

Question 4

B3.2.4—Measurement of pulse rates

Answer 4

Application of skills: Students should be able to determine heart rate by feeling the carotid or radial
pulse with fingertips. Traditional methods could be compared with digital ones.

Question 5

B3.2.5—Adaptations of veins for the return of blood to the heart

Answer 5

Include valves to prevent backflow and the flexibility of the wall to allow it to be compressed by muscle
action.

Question 6

B3.2.6—Causes and consequences of occlusion of the coronary arteries

Answer 6

Application of skills: Students should be able to evaluate epidemiological data relating to the incidence
of coronary heart disease.
NOS: Students should understand that correlation coefficients quantify correlations between variables
and allow the strength of the relationship to be assessed. Low correlation coefficients or lack of any
correlation could provide evidence against a hypothesis, but even strong correlations such as that
between saturated fat intake and coronary heart disease do not prove a causal link

Question 7

B3.2.7—Transport of water from roots to leaves during transpiration

Answer 7

Students should understand that loss of water by transpiration from cell walls in leaf cells causes water to
be drawn out of xylem vessels and through cell walls by capillary action, generating tension (negative
pressure potentials). It is this tension that draws water up in the xylem. Cohesion ensures a continuous
column of water.

Question 8

B3.2.8—Adaptations of xylem vessels for transport of water

Answer 8

Include the lack of cell contents and incomplete or absent end walls for unimpeded flow, lignified walls to
withstand tensions, and pits for entry and exit of water.

Question 9

B3.2.9—Distribution of tissues in a transverse section of the stem of a dicotyledonous plant

Answer 9

Application of skills: Students should be able to draw plan diagrams from micrographs to identify the
relative positions of vascular bundles, xylem, phloem, cortex and epidermis. Students should annotate the
diagram with the main functions of these structures.

Question 10

B3.2.10—Distribution of tissues in a transverse section of the root of a dicotyledonous plant

Answer 10

Application of skills: Students should be able to draw diagrams from micrographs to identify vascular
bundles, xylem and phloem, cortex and epidermis.

Question 11

B3.2.11—Release and reuptake of tissue fluid in capillaries

Answer 11

Tissue fluid is formed by pressure filtration of plasma in capillaries. This is promoted by the higher pressure
of blood from arterioles. Lower pressure in venules allows tissue fluid to drain back into capillaries.

Question 12

B3.2.12—Exchange of substances between tissue fluid and cells in tissues

Answer 12

Discuss the composition of plasma and tissue fluid.

Question 13

B3.2.13—Drainage of excess tissue fluid into lymph ducts

Answer 13

Limit to the presence of valves and thin walls with gaps in lymph ducts and return of lymph to the blood
circulation

Question 14

B3.2.14—Differences between the single circulation of bony fish and the double circulation of mammals

Answer 14

Simple circuit diagrams are sufficient to show the sequence of organs through which blood passes.

Question 15

B3.2.15—Adaptations of the mammalian heart for delivering pressurized blood to the arteries

Answer 15

Include form–function adaptations of these structures: cardiac muscle, pacemaker, atria, ventricles,
atrioventricular and semilunar valves, septum and coronary vessels.

Students should be able to identify
these features on a diagram of the heart in the frontal plane and trace the unidirectional flow of blood
from named veins to arteries.

Question 16

B3.2.16—Stages in the cardiac cycle
Application of skills:

Answer 16

Students should understand the sequence of events in the left side of the heart that
follow the initiation of the heartbeat by the sinoatrial node (the “pacemaker”). Students should be able to
interpret systolic and diastolic blood pressure measurements from data and graphs.

Question 17

B3.2.17—Generation of root pressure in xylem vessels by active transport of mineral ions

Answer 17

Root pressure is positive pressure potential, generated to cause water movement in roots and stems when
transport in xylem due to transpiration is insufficient, for example when high humidity prevents
transpiration or in spring, before leaves on deciduous plants have opened.

Question 18

B3.2.18—Adaptations of phloem sieve tubes and companion cells for translocation of sap

Answer 18

Include sieve plates, reduced cytoplasm and organelles, no nucleus for sieve tube elements and presence
of many mitochondria for companion cells and plasmodesmata between them. Students should
appreciate how these adaptations ease the flow of sap and enhance loading of carbon compounds into
phloem sieve tubes at sources and unloading of them at sinks.