Transport systems move substances around large organisms. In humans: the circulatory system (heart, blood, blood vessels). In plants: xylem (water and minerals) and phloem (sugars).
Double circulation: blood passes through the heart twice per circuit. Right side → pulmonary circulation (lungs: deoxygenated → oxygenated). Left side → systemic circulation (body). Heart has 4 chambers: right atrium, right ventricle, left atrium, left ventricle. Valves prevent backflow. Left ventricle wall thicker (pumps to whole body). Arteries: thick muscular walls, carry blood away from heart, high pressure. Veins: thinner walls, valves, carry blood to heart, lower pressure. Capillaries: one cell thick walls, exchange of substances.
Red blood cells: carry oxygen (haemoglobin + O₂ → oxyhaemoglobin). White blood cells: fight infection — phagocytes engulf pathogens, lymphocytes produce antibodies. Platelets: cell fragments, help blood clot at wounds. Plasma: liquid, carries dissolved substances (glucose, CO₂, urea, hormones, antibodies).
Xylem: transports water and dissolved minerals from roots to leaves. Dead hollow tubes, lignified walls. Transpiration: evaporation of water from leaf surfaces (through stomata) → creates transpiration pull → draws water up xylem. Factors: temperature, humidity, wind speed, light (opening of stomata). Phloem: transports sucrose and amino acids (translocation) from source (leaves) to sink (roots, fruits). Living tissue, sieve tubes and companion cells.
A double circulatory system means blood passes through the heart twice per complete circuit — once to the lungs and once to the body. This is important because: (1) blood pressure drops as blood passes through capillaries in the lungs, and (2) the body\'s cells need blood at high pressure to deliver oxygen and nutrients efficiently. By returning to the heart from the lungs, the blood pressure is boosted by the left ventricle before being sent to the body. This ensures efficient delivery to all organs. Fish have a single circulation, which is less efficient — blood pressure is low after passing through the gills.
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