B3.2 Transport - OCR First Exams 2025 PDF

First Exams 2025 B3.2 Transport Theme: Form and Function Level of Organisation: Organisms SL and HL Content Capillaries Capillaries are small blood vessels which connect arteries to veins. The function of capillaries is to exchange materials...

First Exams 2025 B3.2 Transport Theme: Form and Function Level of Organisation: Organisms SL and HL Content Capillaries Capillaries are small blood vessels which connect arteries to veins. The function of capillaries is to exchange materials between the blood and cells. SL and HL Content Adaptations of Capillaries Adaptations of capillaries include: Large surface area, as capillaries are highly branched with narrow diameters. Narrow lumen, which is wide enough for one red blood cell to pass through at a time. Thin walls allow rapid exchange of materials by diffusion. Capillaries Capillaries are typically one cell thick. SL and HL Content Micrograph of Arteries and Veins Arteries have a relatively thick wall and a narrow lumen. Veins have a relatively thin wall and wide lumen. A ❓ Determine, with reason, whether blood vessel A is an artery or a vein. B Micrograph of blood vessels SL and HL Content Micrograph of Arteries and Veins Blood vessel A is an artery. It has a thicker wall, and a relatively narrow lumen. A Artery Blood vessel B is a vein. It has a much thinner wall, and a relatively wider lumen. B Vein Micrograph of blood vessels SL and HL Content Arteries Arteries transport blood away from the heart. ❓ Explain how arteries are adapted to withstand and maintain high blood pressure. SL and HL Content Arteries Arteries are adapted to withstand and maintain high blood pressure in the following ways: Arteries have a thick wall allowing them to withstand high blood pressure. Collagen in the outer wall of the artery strengthens the artery to withstand high blood pressure. Smooth muscle in the artery can contract to maintain blood pressure Structure of an Artery between heart beats. SL and HL Content Arteries Elastic fibres in the artery wall allow the arteries to stretch and recoil as pressure increases and decreases due to heart beats. The recoil helps keep the blood moving in the artery. A narrow lumen helps maintain high blood pressure. The lumen is lined with smooth endothelial cells, which reduces Structure of an Artery friction as blood flows. SL and HL Content Measuring Pulse Rate The pulse is caused by the beating of the heart. The pulse can be felt, using fingertips, at the radial artery in the wrist, or the carotid artery in the neck. SL and HL Content Measuring Pulse Rate The pulse rate can be determined by counting the number of beats Pulse Rate per unit time. Alternatively, technologies such as smart watches and oximeters can be used to determine pulse rate. We compare the results determining for pulse rate using their fingers on the wrist against using technology such as oximeters Oximeters include Pulse Rate SL and HL Content From B3.2.5: Adaptations of veins for the return the IB of blood to the heart Include valves to prevent backflow and the flexibility of the wall to allow it to be compressed by muscle action. SL and HL Content Veins Veins return blood to the heart. Blood returning to the heart is moving slowly, and is not under high pressure. ❓ Explain how veins are adapted to return blood to the heart. SL and HL Content Veins Veins are adapted to return blood to the heart in the following ways: Thin wall, which allows the vein to be compressed by skeletal muscles. The compression moves blood Structure of a Vein back to the heart. Wide lumen, which allows Valves in veins prevent the the vein to carry a large backflow of blood. volume of blood. SL and HL Content Arteries and Veins ❓ Compare and contrast the structure of arteries and veins. Structure of Blood Vessels SL and HL Content Arteries and Veins Both arteries and veins have three layers of tissue in their walls. Feature Arteries Veins Lumen Narrow, maintaining Wide high pressure Relative thickness of wall Thick Thin Direction of blood flow Away from the heart Back to the heart Valves Valves prevent None backflow of blood SL and HL Content Atherosclerosis Atherosclerosis is the hardening and narrowing of the arteries due to the build of cholesterol, triglycerides and other substances on artery walls. Read the linked article. SL and HL Content Occlusion of Coronary Arteries Coronary arteries branch off of the main artery, the aorta, and supply the heart with oxygen and nutrients. The coronary arteries can be occluded (blocked) due to atherosclerosis. Occlusion of the coronary arteries can lead to the death of heart tissue, and heart attacks. Normal and Occluded Artery SL and HL Content Causes of Atherosclerosis The inner lining of an artery is damaged, due to high blood pressure. The response to the damaged artery includes: Macrophages (a type of white blood cell) are attracted to sites of damage within the arteries, and the macrophages release growth factors which stimulate the development of fibrous tissue. The macrophages consume cholesterol, and begin to form a plaque. Over time plaque continues to grow and may occlude (block) the artery. The plaque can break away from the artery and cause a blood clot. SL and HL Content Risk Factors for Atherosclerosis ❓ List risk factors associated with atherosclerosis. Genetics - several genes are associated with increased risk of atherosclerosis. Age, as the arteries of older people are more likely to be damaged. Gender - males are more likely to develop atherosclerosis. These factors are outside of our control. Atherosclerosis SL and HL Content Causes of Atherosclerosis The following risk factors are under our control: Obesity, which increases blood pressure and damages artery walls. Physical inactivity, which can lead to obesity. Smoking, which increases blood pressure. A diet high in fats and cholesterol. Atherosclerosis