Transport Systems — Edexcel Linear - OL Revision Notes & Topical Questions

To function, organisms must exchange substances such as food molecules and waste with their environment.

The movement of sucrose through the phloem is called translocation; sucrose moves from sources (leaves) to sinks (growing regions, roots and storage organs).

Root hair cells are tiny, single-celled extensions of epidermis cells in the root.

Transpiration is the evaporation of water vapour from the surface of a plant, mainly from the leaves through open stomata. It creates a pull that draws water up through the xylem (the transpiration stream), which brings minerals, supplies water for photosynthesis, keeps cells turgid and cools the leaf.

As an organism increases in size, its volume grows faster than its surface area, so the surface area to volume ratio falls.

We can investigate the effect of environmental conditions (temperature, humidity, light intensity, air movement) on transpiration with a potometer, which measures water uptake by a cut shoot. Two types are used: a simple potometer with a capillary tube and an air bubble, and a reservoir potometer that allows the bubble to be reset.

Example resultlamp at 10 cm, bubble moved 32 mm in 30 min, so rate = 32 ÷ 30 = 1.07 mm/min.

Blood consists of red blood cells, white blood cells, platelets and plasma. Over half the volume is plasma; most of the remainder is red blood cells.

Plasma transports digested food and mineral ions from the small intestine to cells; carbon dioxide from the tissues to the lungs; urea to the kidneys; hormones from endocrine glands to target organs; and heat from respiration to cooler parts or the skin where it can be lost.

White blood cells are part of the immune system and defend against pathogenic microorganisms. There are two main types: phagocytes, which engulf and digest pathogens (phagocytosis), and lymphocytes, which produce antibodies and, in some cases, antitoxins. The number of white blood cells rises during an infection.

In an exam you may be given a table of bubble distances for different lamp distances or temperatures.

Also note that the volume of the blood in an adult is about five litres, of which a little over half is plasma. The numbers of cells per cubic millimetre are about five million red cells and about seven thousand white cells, showing that white cells are far fewer than red cells.

An antigen is a marker on the surface of a cell or pathogen that the body sees as foreign and that triggers an immune response.

Vaccines help the body develop immunity to infectious diseases and have drastically reduced, or even eradicated, some diseases.

Platelets are cell fragments involved in clotting and forming scabs. When the skin is broken, platelets arrive to stop the bleeding. They release chemicals causing soluble fibrinogen to convert into insoluble fibrin fibres, which form a mesh that traps blood cells and forms a clot, later a scab. This prevents blood loss and the entry of pathogens.

The heart is a double pump. Oxygenated blood from the lungs enters the left side and is pumped to the body (systemic circuit); deoxygenated blood from the body enters the right side and is pumped to the lungs (pulmonary circuit). The left ventricle has a thicker wall because it pumps blood at high pressure around the whole body.

Heart rate is the number of heart beats per minute (bpm).

The coronary arteries supply the cardiac muscle with oxygen and glucose. In coronary heart disease (CHD), layers of fatty material (plaque, mainly cholesterol) build up inside the arteries, narrowing the lumen. Partial blockage restricts blood flow and causes severe chest pain called angina. Complete blockage prevents cells in that area from respiring aerobically, leading to a heart attack.

Arterioles branch from arteries; venules lead into veins.

The circulatory system is a closed network of vessels connected to the heart, with blood flowing in one direction. It is a double circulation. Arteries carry blood away from the heart and usually oxygenated blood; the pulmonary artery is the exception.