Topic 3 of 8 · Form 5
Transport in plants and mammals; gas exchange
Xylem and phloem structure; water movement through roots (apoplast and symplast pathways, Casparian strip); transpiration and cohesion–tension; xerophytic adaptations; translocation of sucrose by mass flow from source to sink (active loading by companion cells).
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Transport in plants
Xylem and phloem structure; water movement through roots (apoplast and symplast pathways, Casparian strip); transpiration and cohesion–tension; xerophytic adaptations; translocation of sucrose by mass flow from source to sink (active loading by companion cells).
Transport in mammals
Blood vessels; blood cells; tissue fluid formation; haemoglobin and the oxygen dissociation curve (Bohr shift); carbon dioxide transport (carbonic anhydrase, hydrogencarbonate, chloride shift); the cardiac cycle and control (SAN, AVN, Purkyne tissue).
Worked example: Stroke volume is 70 cm³ and heart rate 72 beats per minute. Find the cardiac output.
70 × 72 = 5 040 cm³ min⁻¹ ≈ 5.0 dm³ min⁻¹
Gas exchange
Structure of the trachea, bronchi, bronchioles and alveoli (cartilage, smooth muscle, ciliated epithelium, goblet cells, elastic fibres); efficient gas exchange.
Check yourself
- What is the role of the Casparian strip?
- Explain the Bohr shift.
- Why does the AVN delay the impulse?
Show answers
- It blocks the apoplast pathway, forcing water through cell membranes (selective uptake).
- Higher CO₂ concentration lowers haemoglobin's affinity for oxygen, so more oxygen is released in respiring tissues.
- To allow the atria to finish contracting before the ventricles contract.
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