Mass transport：练习题

In the mammalian cardiac cycle, a student is analyzing the pressure changes in the left side of the heart. At which point during the cycle does the left atrioventricular (mitral) valve close?

In mass transport in plants, according to the mass flow hypothesis, what is the primary cause of the movement of the sap from the source to the sink in the phloem?

At the arterial end of a capillary bed, the hydrostatic pressure is \( 5.1\text{ kPa} \) and the water potential (osmotic) pressure exerted by plasma proteins is \( -3.3\text{ kPa} \). At the venous end, the hydrostatic pressure is \( 1.6\text{ kPa} \) and the water potential pressure is \( -3.3\text{ kPa} \). Calculate the net pressure at both ends and identify the direction of fluid movement.

Which of the following describes a correct structural adaptation of the mammalian heart for maintaining unidirectional blood flow during the cardiac cycle?

In the mammalian heart, the pressure in the left ventricle must exceed the pressure in the aorta for blood to be ejected. Which of the following events marks the end of this ejection phase during the cardiac cycle?

The cohesion-tension theory describes the mass transport of water in plants.

a) Explain how the dipolar nature of water molecules leads to the property of cohesion and how this allows water to move as a continuous column. (3 points)
b) Describe the role of transpiration from the leaves in creating the tension required for water movement. (2 points)
c) In the mass flow hypothesis of phloem transport, explain how the active loading of sucrose at the source leads to a high hydrostatic pressure. (3 points)

The diagram represents the pressure changes in the left side of the heart during one cardiac cycle. The graph shows three lines representing the pressure in the aorta, the left ventricle, and the left atrium over time (s).

a) Identify the time at which the semi-lunar valves open and explain why this occurs based on the pressure data. (2 points)
b) If the total time for one cardiac cycle is \( 0.8 \text{ s} \), calculate the heart rate in beats per minute. (2 points)
c) Explain the role of the atrioventricular valves in maintaining a unidirectional flow of blood when the ventricle contracts. (2 points)