Transport systems — Eduqas GCSE Combined Science

Transport systems in biology refer to the mechanisms by which essential substances like oxygen, nutrients, and waste products are moved around an organism. In humans, this involves the circulatory system, which includes the heart, blood vessels, and blood. The heart pumps blood through a double circulatory system: one loop carries deoxygenated blood to the lungs for oxygenation (pulmonary circulation), and the other delivers oxygenated blood to the rest of the body (systemic circulation). This system is vital for maintaining cellular respiration, removing waste, and regulating body temperature.

In plants, transport systems consist of xylem and phloem tissues. Xylem transports water and dissolved minerals from the roots to the leaves, driven by transpiration pull. Phloem transports sugars (produced during photosynthesis) from the leaves to other parts of the plant, a process called translocation. Understanding these systems is crucial for grasping how organisms maintain homeostasis and support life processes. For WJEC GCSE Combined Science, you need to know the structure and function of these transport systems, including adaptations like valves in veins and the role of stomata in transpiration.

This topic connects to other areas of biology such as respiration, photosynthesis, and gas exchange. For example, the circulatory system delivers oxygen for aerobic respiration, while the plant transport system supplies water for photosynthesis. Mastery of transport systems also underpins understanding of health issues like heart disease and plant wilting. By studying these systems, you'll appreciate how organisms are efficiently designed to meet their metabolic demands.

• →Double circulatory system: Humans have two circuits – pulmonary (heart to lungs) and systemic (heart to body). This ensures efficient separation of oxygenated and deoxygenated blood.
• →Heart structure: Know the four chambers (right atrium, right ventricle, left atrium, left ventricle) and the roles of valves (tricuspid, bicuspid, semilunar) to prevent backflow.
• →Blood vessels: Arteries carry blood away from the heart (thick walls, high pressure), veins carry blood towards the heart (valves, low pressure), and capillaries allow exchange of substances (thin walls, large surface area).
• →Xylem and phloem: Xylem vessels are dead, hollow tubes with lignin for support; they transport water and minerals upwards. Phloem sieve tubes are living cells with sieve plates; they transport sugars in both directions.
• →Transpiration: The loss of water vapour from leaves through stomata creates a transpiration pull that draws water up the xylem. Factors like light, temperature, and humidity affect transpiration rate.

• Diffusion is a passive process moving substances down a concentration gradient.
• Osmosis is the diffusion of water through a selectively permeable membrane from high water concentration to low water concentration.
• Active transport moves substances against a concentration gradient and requires energy.
• The human circulatory system is a double circulatory system.
• Arteries carry blood away from the heart; veins carry blood to the heart.
• Capillaries have thin walls for efficient exchange of substances.
• Xylem transports water and minerals from roots upwards; phloem transports sugars (translocation).
• Stomata and guard cells regulate transpiration.
• Surface area to volume ratio explains the need for transport systems in multicellular organisms.

• 💡Use the term 'selectively permeable membrane' when describing osmosis.
• 💡Always link the structure of blood vessels or plant tissues to their specific function.
• 💡Remember that active transport is the only process listed that requires energy.
• 💡Be prepared to interpret data from potometer experiments regarding transpiration rates.
• 💡Ensure you can label the heart and leaf structures accurately.
• 💡When describing the heart, always refer to the direction of blood flow: deoxygenated blood enters the right atrium from the vena cava, then to right ventricle, then to lungs via pulmonary artery. Oxygenated blood returns to left atrium via pulmonary vein, then to left ventricle, then to body via aorta. Use this sequence to avoid losing marks.
• 💡For plant transport, remember that transpiration is not a 'force' but a pull caused by evaporation. Explain how water molecules cohere (stick together) and adhere to xylem walls. Mention that transpiration rate increases with light intensity and temperature, and decreases with high humidity.
• 💡In exam questions, always use correct terminology: 'translocation' for sugar transport in phloem, 'transpiration' for water loss. Don't say 'food' for phloem – use 'sucrose' or 'sugars'. Also, note that phloem transport requires energy (active transport) while xylem transport is passive.

• Confusing the direction of movement in osmosis (water vs solute concentration).
• Failing to mention that active transport requires energy.
• Confusing the functions of xylem and phloem.
• Incorrectly describing the double circulatory system.
• Misunderstanding the role of guard cells in transpiration.
• Misconception: Arteries always carry oxygenated blood. Correction: The pulmonary artery carries deoxygenated blood from the heart to the lungs. Only arteries in the systemic circuit carry oxygenated blood.
• Misconception: Veins have no pulse because blood flows slowly. Correction: Veins have no pulse because blood pressure is low after passing through capillaries, but they rely on skeletal muscle contractions and valves to move blood.
• Misconception: Xylem transports food. Correction: Xylem transports water and minerals; phloem transports sugars (food). Confusing these two is a common error in exams.