IP Combined Science Notes (Lower Sec, Year 1-2): 06) Transport Systems in Humans & Plants
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Transport systems move substances efficiently over distances too large for diffusion alone. Understand structure-function relationships to explain oxygen delivery, sugar transport, and water movement.
Learning targets
- Describe the structure of the human circulatory system and pathway of blood flow.
- Use cardiac output formulas to solve numerical problems and compare fitness levels.
- Explain the roles of xylem and phloem, including adaptations for their functions.
- Analyse factors affecting transpiration rate and interpret potometer data.
1. Human circulatory system
Key components: heart (four chambers), blood vessels (arteries, veins, capillaries), and blood.
| Vessel | Structure | Function |
| Artery | Thick muscular walls, small lumen. | Carry blood away from heart under high pressure. |
| Vein | Thinner walls, large lumen, valves present. | Return blood to heart at low pressure. |
| Capillary | One-cell-thick walls. | Exchange gases, nutrients, and wastes with tissues. |
Blood pathway (systemic circuit)
\[ \text{Left ventricle} \rightarrow \text{Aorta} \rightarrow \text{Body} \rightarrow \text{Vena cava} \rightarrow \text{Right atrium}. \]
Pulmonary circuit mirrors this with lungs as the gas-exchange site.
Cardiac output calculation
\[ \text{Cardiac output} = \text{Stroke volume} \times \text{Heart rate}. \]
Worked example
An athlete has stroke volume \( \pu{75 mL} \) at rest and heart rate \( \pu{58 beats.min-1} \).
\[ \text{CO} = 75 \times 58 = 4350 \space \pu{mL.min-1} = 4.35 \space \pu{L.min-1}. \]
During exercise, heart rate rises to \( \pu{150 beats.min-1} \) with stroke volume \( \pu{120 mL} \):
\[ \text{CO} = 120 \times 150 = 18000 \space \pu{mL.min-1} = 18.0 \space \pu{L.min-1}. \]
2. Blood components
- Red blood cells: transport \( \ce{O2} \) via haemoglobin.
- White blood cells: immune defence (phagocytosis, antibody production).
- Platelets: clot formation.
- Plasma: transports nutrients, hormones, \( \ce{CO2} \), and waste products.
3. Plant transport
| Tissue | Structure | Function |
| Xylem | Dead, hollow vessels; lignified walls. | Transport water and minerals from roots to leaves; provide support. |
| Phloem | Living sieve tube elements with companion cells. | Translocate sucrose/amino acids between sources and sinks. |
Transpiration factors
| Factor | Effect on rate |
| Light intensity | Increases (stomata open for photosynthesis). |
| Temperature | Increases (higher kinetic energy and evaporation). |
| Humidity | Decreases (reduced concentration gradient). |
| Wind speed | Increases (removes saturated air). |
Potometer question
Water level in a capillary tube drops \( \pu{12 mm} \) in \( \pu{5 min} \). Tube radius \( \pu{0.50 mm} \).
- Volume change:
\[ V = \pi r^2 h = \pi (0.50)^2 \times 12 = 9.42 \space \pu{mm3} = 9.42 \times 10^{-3} \space \pu{cm3}. \]
- Rate:
\[ \text{Transpiration rate} = \frac{9.42 \times 10^{-3}}{5} = 1.88 \times 10^{-3} \space \pu{cm3.min-1}. \]
Discuss how ensuring airtight seals and cutting the stem underwater improves accuracy.
Try it yourself
- Compare artery and vein structures in terms of elasticity, muscle thickness, and presence of valves.
- Describe how guard cells regulate stomatal opening in response to light and water status.
- A student records that a plant loses \( \pu{0.75 g} \) of mass overnight due to transpiration. Assuming density of water \( \pu{= 1 g.cm-3} \), calculate the average volume of water lost per hour and suggest two methods to reduce further loss.
Shift to forces and motion at https://eclatinstitute.sg/blog/ip-combined-sciences-lower-sec-notes/IP-Combined-Science-Lower-Sec-07-Forces-Motion-and-Simple-Machines.
