Transport

• Unicellular organisms like amoeba have very large surface areas in comparison to their volumes, meaning that the distance between the surface of the organism to its centre is very small.
• Unicellular organisms do not need to have specialist exchange surfaces or transport systems as diusion, osmosis and active transport through the cell membrane occur at a sufficient rate to meet their needs.
• Multicellular organisms like humans have relatively small surface areas in comparison to their volumes, meaning that the distance between the surface of the organism to its centre is relatively long.
• Large multicellular organisms usually have exchange surfaces and transport systems as diusion, osmosis and active transport cannot occur at a sufficient rate to meet their needs.
• Exchange surfaces in animals include the lungs and alveoli for gas exchange and the small intestines and villi for absorption of digested food.
• Transport systems in animals include the blood and circulatory system which carries the necessary substances around the body.
• Exchange surfaces in plants include roots and root hairs where mineral ions and water are absorbed and the leaves for gas exchange.
• Transport systems in plants include the xylem which moves water and mineral ions from roots to shoots and the phloem which moves sugars and amino acids to where they are needed in the plant.
• Mass potometer measures a change in mass of a plant as a measure of the amount of water that has evaporated from the leaves and stem.
• The method for investigating the effect of light intensity on transpiration using a bubble potometer involves cutting a shoot underwater to prevent air entering the xylem and placing it in a tube, setting up a lamp 10cm from the leaf, allowing the plant to adapt to the new environment for 5 minutes, recording the starting location of the air bubble, leaving for 30 minutes, recording the end location of the air bubble, changing the light intensity, resetting the bubble by opening the tap below the reservoir, and repeating the experiment.
• There are two different types of potometer that could be used to investigate the effect of environmental conditions on transpiration.
• There are two types of potometer: mass potometer and bubble potometer.
• Investigating the effect of light intensity on transpiration using a bubble potometer involves setting up the apparatus as shown in the diagram, making it airtight using Vaseline to seal any gaps, and then drying the leaves of the shoot.
• Potometer is an apparatus used to investigate the effect of different environmental conditions on the rate of transpiration.
• The rate of transpiration can be calculated by dividing the distance the bubble travelled by the time period.
• The further the bubble travels in the same time period, the greater the rate of transpiration.
• Bubble potometer measures the uptake of water by a stem as a measure of the amount of water that is being lost by evaporation, consequently pulling water up through the stem to replace it.
• The many interconnecting air spaces between the mesophyll cells and the stomata create a large surface area, allowing evaporation to happen rapidly when the stomata are open.
• After a few hours, the leaves of the celery will turn the same colour as the dyed water, indicating that water is being taken up by the celery.
• Transpiration is defined as the loss of water vapour from the parts of the plant that are above ground (leaves, stem, flowers).
• Due to cohesion, the water in the xylem creates a continuous unbroken column, each individual molecule ‘pulls’ on the one below it.
• Transpiration produces tension or ‘pulls’ on the water in the xylem vessels.
• If a cross-section of the celery is cut, only certain areas of the stalk are stained the colour of the water, showing that the water is being carried in specific vessels through the stem - these are the xylem vessels.
• Transpiration has several functions in plants: transporting mineral ions, providing water to keep cells turgid in order to support the structure of the plant, providing water to leaf cells for photosynthesis, and keeping the leaves cool.
• The rate of transpiration increases when these factors are high, and decreases when they are low.
• The use of heat to convert water into water vapour helps to cool the plant down.
• The pathway of water into and across a root can be investigated by placing a plant like celery into a beaker of water that has had a stain added to it.
• Loss of water occurs through evaporation of water at the surfaces of the spongy mesophyll cells followed by diffusion of water vapour through the stomata.
• Water moves through the xylem vessels in a continuous transpiration stream from the roots to the leaves via the stem to replace the water that has been lost due to transpiration.
• There are several environmental conditions which have an impact on the rate of transpiration: air movement, humidity, temperature, and light intensity.
• There are three main types of blood vessels: arteries, veins, and capillaries.
• The effect of a narrowed lumen in a coronary artery is reduced blood flow to the heart.
• Arteries carry blood at high pressure away from the heart, carry oxygenated blood (except the pulmonary artery), have thick muscular walls containing elastic fibers, and have a narrow lumen.
• Complete blockage of the coronary arteries means cells in that area of the heart will not be able to respire aerobically, leading to a heart attack.
• Risk factors for coronary heart disease include obesity, increased weight, high blood pressure, high cholesterol, smoking, and carbon monoxide poisoning.
• Each vessel has a particular function and is specifically adapted to carry out that function efficiently.
• Capillaries carry blood at low pressure within tissues, carry both oxygenated and deoxygenated blood, and have a small lumen.
• Smaller vessels that branch off from arteries are called arterioles (small arteries) and those that branch into veins are called venules (small veins).
• Coronary heart disease (CHD) occurs when a coronary artery becomes partially or completely blocked by fatty deposits, reducing the blood flow to the heart muscle.
• Treatment of CHD involves either increasing the width of the lumen of the coronary arteries using a stent, or prescribing statins to lower blood cholesterol.