SL Content Statements

• B3.2.1

  Adaptations of capillaries for exchange of materials between blood and the internal or external environment

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  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.
  

• B3.2.2

  Structure of arteries and veins

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  AOS: 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.
  

• B3.2.3

  Adaptations of arteries for the transport of blood away from the heart

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  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.
  

• B3.2.4

  Measurement of pulse rates

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  AOS: 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.

• B3.2.5

  Adaptations of veins for the return of blood to the heart

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

• B3.2.6

  Causes and consequences of occlusion of the coronary arteries

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  AOS: 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.
  

• B3.2.7

  Transport of water from roots to leaves during transpiration
  

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  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.
  

• B3.2.8

  Adaptations of xylem vessels for transport of water

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  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.
  

• B3.2.9

  Distribution of tissues in a transverse section of the stem of a dicotyledonous plant

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  AOS: 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.
  

• B3.2.10

  Distribution of tissues in a transverse section of the root of a dicotyledonous plant

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

AHL Content Statements

• B3.2.11

  Release and reuptake of tissue fluid in capillaries
  

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  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.
  

• B3.2.12

  Exchange of substances between tissue fluid and cells in tissues

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  Discuss the composition of plasma and tissue fluid.
  

• B3.2.13

  Drainage of excess tissue fluid into lymph ducts

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

• B3.2.14

  Differences between the single circulation of bony fish and the double circulation of mammals

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

• B3.2.15

  Adaptations of the mammalian heart for delivering pressurized blood to the arteries

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  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.
  

• B3.2.16

  Stages in the cardiac cycle

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  AOS: 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.
  

• B3.2.17

  Generation of root pressure in xylem vessels by active transport of mineral ions
  

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  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.
  

• B3.2.18

  Adaptations of phloem sieve tubes and companion cells for translocation of sap

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  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.