GCSE Biology Revision - Heart & Circulation

During exercise, the demand for energy in the muscles increases. This energy is produced through cellular respiration, which requires oxygen. Therefore, more oxygen is needed by muscle cells to support the increased energy production during exercise. This is why more blood is delivered to the leg muscles during exercise, as the blood carries oxygen from the lungs to the muscles.

The left ventricle has the thickest muscle compared to the other heart chambers. This is because it is responsible for pumping oxygenated blood to the rest of the body, requiring more forceful contractions. The left ventricle receives oxygen-rich blood from the left atrium and then pumps it out through the aorta to supply oxygen to the body's tissues. Its thick muscular walls allow it to generate sufficient pressure to propel blood throughout the systemic circulation.

Arteries have the highest proportion of elastic tissue in their blood vessel walls. This elastic tissue allows the arteries to stretch and recoil, helping to maintain blood pressure and ensuring continuous blood flow throughout the body. The elastic properties of arteries also help to dampen the pulsatile nature of blood flow generated by the heart's contractions, resulting in a smoother flow of blood. This is why arteries are able to withstand the high pressure generated by the heart and efficiently transport oxygenated blood from the heart to the rest of the body.

Valves are present in veins. Valves in veins help to prevent the backflow of blood and ensure that blood flows in one direction towards the heart. This is important because veins carry deoxygenated blood back to the heart from various parts of the body. The presence of valves in veins helps to maintain the flow of blood and prevent pooling or stagnation of blood in the veins.

Blood pressure is highest in the arteries and gradually decreases as blood flows through the circulatory system. Arteries carry oxygenated blood away from the heart, and their thick, muscular walls help maintain high pressure to propel blood to the tissues. Capillaries are tiny vessels with thin walls where the exchange of nutrients and waste products occurs. Blood pressure drops significantly in the capillaries to allow for efficient exchange. Venules collect blood from the capillaries and merge into larger veins, which return deoxygenated blood to the heart. Veins have thinner walls and lower pressure compared to arteries.

Oxygen leaves the blood as it passes through capillaries in organs like the liver or pancreas. This is because oxygen is transported by red blood cells and released into the tissues where it is needed for cellular respiration. In the liver and pancreas, oxygen is used by the cells for various metabolic processes. Carbon dioxide, on the other hand, is produced as a waste product in these organs and is removed from the tissues and transported back to the lungs to be exhaled. Starch and urea are not directly involved in the gas exchange process in capillaries.

In distance running, the best description of the type of respiration occurring is mostly aerobic. Aerobic respiration is the process by which the body produces energy in the presence of oxygen. During distance running, the body requires a sustained and continuous supply of energy, which is efficiently provided through aerobic respiration. This process allows the body to break down carbohydrates and fats to produce ATP, the main energy source for muscles. While some anaerobic respiration may occur during intense bursts of speed or when oxygen supply is limited, the majority of energy production during distance running is aerobic.

During anaerobic respiration in humans, when there is a lack of oxygen, glucose is broken down to produce energy. This process, known as fermentation, occurs in the absence of oxygen and results in the production of lactic acid. Lactic acid is produced in muscles when they are working strenuously and cannot receive enough oxygen to meet their energy demands. This buildup of lactic acid causes muscle fatigue and soreness. Therefore, the correct answer is lactic acid.

The volume of blood leaving the left ventricle per beat is 50 cm^3. The heart rate is 70 beats per minute, so the volume of blood leaving the left ventricle per minute is 50 cm^3/beat * 70 beats/minute = 3500 cm^3/minute. In 10 minutes, the volume of blood leaving the left ventricle would be 3500 cm^3/minute * 10 minutes = 35,000 cm^3.

The liver is the organ mainly responsible for removing lactic acid following vigorous exercise. Lactic acid is produced during intense physical activity when the body cannot supply enough oxygen to the muscles. The liver plays a crucial role in converting lactic acid into glucose through a process called gluconeogenesis. This glucose can then be used as an energy source by the body or stored for later use. The liver's ability to remove lactic acid helps to prevent muscle fatigue and allows the body to recover more quickly from exercise.

Heart sounds are produced when the heart valves close. When the heart contracts, the valves between the chambers close to prevent the backflow of blood. The closure of these valves creates vibrations that can be heard as heart sounds. These sounds, known as the "lub-dub" sound, are the first and second heart sounds. The first sound, "lub," is produced when the mitral and tricuspid valves close at the beginning of systole. The second sound, "dub," is produced when the aortic and pulmonary valves close at the beginning of diastole. Therefore, the correct answer is heart valves close.

Glycogen is not transported in blood plasma because it is a stored form of glucose in the liver and muscles. When energy is needed, glycogen is broken down into glucose and released into the bloodstream. Glucose, on the other hand, is transported in blood plasma to provide energy to cells. Urea is a waste product of protein metabolism and is transported in blood plasma to be excreted by the kidneys. Oxygen is transported in blood plasma bound to hemoglobin in red blood cells. Therefore, glycogen is the only substance in the given options that is not directly transported in blood plasma.

Regular exercise strengthens the heart muscles, allowing them to contract more forcefully during rest. This increased contractility results in a more efficient pumping of blood throughout the body, leading to a lower resting heart rate.

Oxyhemoglobin is the correct answer because the pulmonary vein carries oxygenated blood from the lungs to the heart. Oxyhemoglobin is formed when oxygen binds to hemoglobin in red blood cells, allowing it to be transported to the body tissues. Therefore, it is expected to be in the highest concentration in the pulmonary vein as it is carrying oxygen-rich blood.

Deoxygenated blood enters the right atrium through the vena cava, then moves to the right ventricle and enters the pulmonary artery, transporting it to the lungs. Oxygenated blood returns through the pulmonary veins to the left atrium, flows into the left ventricle, and is pumped into the aorta, distributing it to the body's tissues.

The advantage of humans having a double circulatory system is that it keeps blood pressure high in body capillaries. This is important because high blood pressure ensures that oxygen and nutrients are delivered efficiently to the body's tissues and organs. It also helps to maintain proper circulation and prevents the buildup of waste products in the capillaries. By maintaining high blood pressure in body capillaries, the double circulatory system supports overall cardiovascular health and optimal functioning of the body.