The student's statement is largely correct. The structure of arteries is indeed better suited to carrying blood than the structure of veins. This is because the functions of arteries and veins are fundamentally different, and their structures reflect these differences.

Arteries carry blood away from the heart under high pressure. The thick, elastic walls of arteries are essential for withstanding this high pressure and ensuring a continuous, forceful flow of blood. The elasticity allows the arteries to stretch and recoil with each heartbeat, maintaining blood pressure and preventing a significant drop in pressure between heartbeats. The structure of the tunica media, with its abundance of elastic fibres, is crucial for this function.

Veins, on the other hand, carry blood back to the heart under low pressure. The veins do not need to withstand high pressure, so their walls are thinner and less elastic. Instead, veins rely on valves to prevent the backflow of blood, especially in the limbs where blood is fighting against gravity. The thinner walls of veins mean that they are more easily compressed, which helps to propel blood back towards the heart. The valves are a key structural adaptation for this function.

Therefore, the structure of arteries, with their thick, elastic walls, is specifically adapted for carrying blood under high pressure, while the structure of veins, with their thinner walls and valves, is adapted for carrying blood under low pressure and preventing backflow. The statement accurately reflects this functional relationship between structure and function.

A four-chambered heart is significantly more efficient than a two-chambered heart. In a two-chambered heart (like that of fish), oxygenated and deoxygenated blood mix. This means that less oxygen is delivered to the tissues, reducing the overall efficiency of oxygen delivery.

In a four-chambered heart, the separation of oxygenated and deoxygenated blood prevents mixing. This ensures that oxygenated blood is delivered directly to the body's tissues, maximizing oxygen uptake. The separation also allows for higher blood pressure in the pulmonary and systemic circuits, leading to faster and more efficient circulation. The complete separation of these circuits prevents the loss of energy that would occur if blood were mixed.

Here's a comparison:

Independent Variable: The independent variable is the factor that the student manipulates or changes. In this case, the independent variable is the level of physical activity. This could be represented as:

• No exercise (Rest)
• Moderate-intensity exercise (e.g., jogging)

Dependent Variable: The dependent variable is the factor that is measured to see if it is affected by the independent variable. In this case, the dependent variable is the pulse rate. This is what the student observes and records to determine the effect of the exercise.