How do animals and plants move substances around their bodies through transport systems?
The human circulatory system (heart, blood vessels and blood), the double circulation, the structure of arteries, veins and capillaries, the components and roles of blood, and transport in plants by xylem and phloem with transpiration and translocation.
A focused answer to the OCR Gateway GCSE Combined Science A topic B2 on transport systems, covering the heart and double circulation, arteries, veins and capillaries, the components of blood, and transport in plants by xylem (transpiration) and phloem (translocation).
Reviewed by: AI editorial process; not yet individually human-reviewed
Have a quick question? Jump to the Q&A page
Jump to a section
What this topic is asking
OCR wants you to describe the human circulatory system and double circulation, explain how arteries, veins and capillaries are adapted, state the components of blood and their roles, and describe transport in plants through xylem and phloem.
The heart and double circulation
The heart is a muscular pump with four chambers: the two atria receive blood, and the two ventricles pump it out. Deoxygenated blood from the body enters the right atrium, passes to the right ventricle, and is pumped to the lungs, where it picks up oxygen and loses carbon dioxide. Oxygenated blood returns to the left atrium, passes to the left ventricle, and is pumped at high pressure all around the body. The left ventricle has a thicker, more muscular wall than the right because it must pump blood much further (round the whole body) than the right (just to the lungs). Valves keep blood flowing in one direction, and the resting heart rate is set by a group of cells in the right atrium that act as a natural pacemaker.
Blood vessels and blood
There are three types of blood vessel, each adapted to its job:
- Arteries carry blood away from the heart at high pressure, so they have thick, muscular and elastic walls and a narrow lumen.
- Veins carry blood back to the heart at low pressure, so they have thinner walls, a wider lumen, and valves to stop blood flowing backwards.
- Capillaries are tiny vessels with walls just one cell thick, so substances such as oxygen, glucose and carbon dioxide diffuse quickly between the blood and the surrounding cells.
Transport in plants
Plants have two transport tissues. Xylem vessels are dead, hollow tubes strengthened with lignin that carry water and dissolved mineral ions upwards from the roots to the leaves. Water is lost from the leaves by evaporation and diffusion through the stomata, a process called transpiration, and this loss pulls more water up through the xylem in the transpiration stream. The rate of transpiration increases with higher temperature, more air movement, lower humidity and higher light intensity (which opens the stomata). Phloem tissue carries dissolved sugars (made in the leaves by photosynthesis) up and down the plant to where they are needed or stored, a process called translocation. Guard cells open and close the stomata to balance gas exchange against water loss.
Exam-style practice questions
Practice questions written in the style of OCR exam questions on this dot point, with worked answer explainers. The year tag is the paper they imitate, not the source.
OCR 20194 marksExplain how the structure of an artery is adapted to its function, and state one way a capillary differs from an artery.Show worked answer →
A Biology Paper 1 structured question on blood vessels. Reward: an artery carries blood away from the heart at high pressure, so it has a thick, muscular and elastic wall that can withstand and smooth out the high pressure, and a relatively narrow lumen. The elastic wall stretches and recoils as the heart pumps. One difference for a capillary: a capillary has a wall just one cell thick (so substances such as oxygen and glucose can diffuse quickly into the surrounding cells) and a very narrow lumen, unlike the thick-walled artery. Markers credit linking the thick muscular wall to high pressure and naming the one-cell-thick capillary wall.
OCR 20216 marksDescribe how water travels from the roots to the leaves of a plant, and explain three factors that increase the rate of transpiration.Show worked answer →
A B2 six-mark extended response, marked on levels. Reward: water is absorbed by root hair cells by osmosis, travels up the stem through xylem vessels (dead, hollow tubes strengthened with lignin), and reaches the leaves where it evaporates from the cells and diffuses out through the stomata as water vapour. This loss is transpiration, and it pulls more water up in the transpiration stream. Three factors that increase the rate: higher temperature (faster evaporation and diffusion), increased air movement or wind (removes water vapour and keeps the gradient steep), and lower humidity (a steeper concentration gradient out of the leaf). Increased light intensity also opens the stomata. Top answers name xylem, link evaporation to the pull of water, and explain each factor in terms of evaporation or the diffusion gradient.
Related dot points
- Eukaryotic and prokaryotic cells, the function of sub-cellular structures (nucleus, mitochondria, ribosomes, chloroplasts, cell wall, vacuole, plasmids), light and electron microscopy, the magnification equation, and the use of standard form and SI units for cell sizes.
A focused answer to the OCR Gateway GCSE Combined Science A topic B1 on cell level systems, covering eukaryotic and prokaryotic cells, sub-cellular structures, light and electron microscopy, the magnification equation, and using standard form for cell sizes.
- Diffusion, osmosis and active transport as ways substances move across membranes, the factors affecting the rate of diffusion, surface area to volume ratio, and the adaptations of exchange surfaces such as alveoli, villi and root hair cells.
A focused answer to the OCR Gateway GCSE Combined Science A topic B2 on transport across membranes, covering diffusion, osmosis and active transport, the factors affecting diffusion rate, surface area to volume ratio, and adaptations of exchange surfaces.
- Aerobic and anaerobic respiration and their word equations, photosynthesis as an endothermic reaction, the limiting factors of light intensity, carbon dioxide concentration and temperature, and the inverse square law relating light intensity to distance.
A focused answer to the OCR Gateway GCSE Combined Science A topic B1 on respiration and photosynthesis, covering aerobic and anaerobic respiration, photosynthesis as an endothermic reaction, limiting factors, and the inverse square relationship between light intensity and distance.
- The structure of the nervous system, the reflex arc and the role of synapses, receptors and effectors, the principle of homeostasis, and the control of body temperature, blood glucose and water as examples of negative feedback.
A focused answer to the OCR Gateway GCSE Combined Science A topic B3 on the nervous system and homeostasis, covering the central and peripheral nervous systems, the reflex arc and synapses, receptors and effectors, and homeostasis as negative feedback controlling temperature, glucose and water.
- Enzymes as biological catalysts, the lock and key model and the active site, the effect of temperature, pH and substrate concentration on enzyme activity, denaturing, and the breakdown of carbohydrates, proteins and lipids by digestive enzymes.
A focused answer to the OCR Gateway GCSE Combined Science A topic B1 work on enzymes, covering enzymes as biological catalysts, the lock and key model, the effects of temperature, pH and concentration, denaturing, and the digestive enzymes amylase, protease and lipase.