IB Biology · Theme B: Form and function · SL and HL
B3.2 Transport
A one-page summary of B3.2 Transport, the key terms to know, and sample exam questions with answers. For the full lesson, open the illustrated revision slides or practise in the app.
Guiding questions
What adaptations facilitate transport of fluids in animals and plants?
What are the differences and similarities between transport in animals and plants?
What B3.2 covers
Blood vessels, and water in plants
- B3.2.1Capillaries: built for exchange
- B3.2.2 · SkillArteries and veins in a micrograph
- B3.2.3Arteries: walls for high pressure
- B3.2.4 · SkillFeeling the radial pulse
- B3.2.4 · SkillThe carotid pulse, traditional or digital
- B3.2.5Veins: returning blood to the heart
- B3.2.6When a coronary artery is blocked
- B3.2.6 · NOSCorrelation is not causation
- B3.2.7Water moves from roots to leaves
- B3.2.7Cohesion and tension
- B3.2.8Xylem vessels: pipes under tension
- B3.2.9 · SkillA dicot stem in section
- B3.2.9 · SkillPlan diagram of a stem
- B3.2.10 · SkillA dicot root in section
- B3.2.10 · SkillDrawing a root section
Tissue fluid, the heart and phloem
- B3.2.11 · HLTissue fluid: out and back in
- B3.2.12 · HLExchange with the cells
- B3.2.13 · HLExcess fluid drains into lymph ducts
- B3.2.14 · HLA fish: single circulation
- B3.2.14 · HLA mammal: double circulation
- B3.2.15 · HLThe heart in the frontal plane
- B3.2.15 · HLTracing the flow of blood
- B3.2.15 · HLThe heart's own blood supply
- B3.2.15 · HLValves: flow in one direction
- B3.2.16 · HL · SkillReading blood pressure
- B3.2.17 · HLRoot pressure
- B3.2.18 · HLSieve tubes and companion cells
B3.2 Transport: summary
Blood vessels
- Capillaries: branched, narrow, thin walls, some fenestrated.
- Arteries: muscle + elastic tissue. Veins: thin, flexible walls, valves.
Pulse and coronary arteries
- Pulse: radial or carotid; count and calculate beats per minute.
- Plaque + clot → occlusion → heart attack. Correlation ≠ cause.
Xylem
- Transpiration → tension; cohesion keeps the column continuous.
- No contents, no end walls, lignified walls, pits.
Stem and root
- Stem: ring of bundles, xylem inside, phloem outside.
- Root: central star of xylem, phloem between the arms.
HL · Tissue fluid and circulation
- Out at high pressure, back at lower pressure; excess drains into lymph.
- Fish: single circulation. Mammal: double, repressurized.
HL · Heart, root pressure, phloem
- SA node → atrial systole → ventricular systole → diastole; 120/80.
- Root pressure: ions pumped, water follows. Phloem: source to sink.
Key terms
- Capillary
- a narrow vessel with a wall one cell thick, where exchange happens.
- Fenestration
- a pore in a capillary wall for rapid exchange.
- Pulse
- the surge of pressure in the arteries at each heartbeat.
- Occlusion
- complete blockage of an artery, for example by a clot.
- Correlation coefficient
- r, a number from −1 to +1 for the strength of a correlation.
- Tension
- negative pressure in the xylem created by transpiration.
- Cohesion
- hydrogen bonding that holds water molecules together.
- Lignin
- the polymer that makes xylem walls rigid.
- Plan diagram
- a drawing of tissue outlines, without individual cells.
- Tissue fluid
- fluid formed from plasma that bathes the cells.
- Pressure filtration
- plasma forced out of capillaries by blood pressure.
- Lymph
- excess tissue fluid in lymph ducts.
- Double circulation
- blood passes through the heart twice per circuit.
- Sinoatrial node
- the pacemaker that starts each heartbeat.
- Systole / diastole
- contraction / relaxation of the heart chambers.
- Root pressure
- positive pressure in xylem from active uptake of ions.
- Companion cell
- the cell that loads carbon compounds into a sieve tube.
Sample exam questions
Three of the 66 multiple-choice questions for B3.2. Try each one before opening the answer.
Question 1. Mammals have a double circulation. What does this mean?
- Blood passes through two hearts
- Blood passes the heart twice per circuit
- Arteries and veins carry the same blood
- Blood flows through two lungs at once
Show the answer
Answer: B. Blood goes heart → lungs → heart → body → heart.
Question 2. The wall of the left ventricle is thicker than that of the right ventricle. Why?
- It receives blood from the lungs.
- It contains the pacemaker of the heart.
- It pumps blood at a lower pressure.
- It pumps blood around the whole body.
Show the answer
Answer: D. The left ventricle generates the high pressure needed to pump blood around the body.
Question 3. What is the role of the sinoatrial node?
- It initiates each heartbeat.
- It closes the semilunar valves.
- It supplies blood to the heart.
- It separates left and right sides.
Show the answer
Answer: A. The SA node, in the wall of the right atrium, is the pacemaker.
Linking questions
Questions that connect B3.2 to other parts of the course, the kind that come up in Paper 2.
- How do pressure differences contribute to the movement of materials in an organism? (see B3.1, D2.3)
- The cohesion of water molecules is essential for xylem transport. How do the hydrogen-bonding properties of water (A1.1) enable the transmission of tension from the leaf to the root? (see A1.1)
- Phloem transports sucrose to developing fruits, which are strong sinks. How does the respiration of sucrose in the fruit (C1.2) maintain the fruit's status as a sink and sustain the pressure gradient driving phloem flow? (see C1.2)
- Water moves from xylem into phloem sieve tubes by osmosis. How does the concept of water potential (D2.3) explain this movement, and what role do solute concentrations in source and sink tissues play? (see D2.3)
Practise B3.2
Study notes, every question and full markschemes for B3.2 are in the app with Pro. Two lessons are completely free to try: A1.1 Water and B1.1 Carbohydrates and lipids.