Question
The micrograph displays xylem vessels in a longitudinal section of a plant stem.
How do the structures labeled X assist in the movement of water upward through the stem?
A. They make xylem walls more permeable to water.
B. They develop cohesive forces with water molecules.
C. They allow xylem vessels to withstand low pressures.
D. They increase adhesion between neighbouring xylem vessels.
▶️Answer/Explanation
Ans. C
Xylem, the structure labeled X in the diagram, helps move water up through a plant’s stem by using root pressure, transpiration pull, and cohesion:
The pressure of water and ions from the soil within the root pushes water up to a certain height.
Transpiration pull
Water is evaporated from the leaves through transpiration, which pulls water molecules up through the xylem.
Cohesion
Water molecules are polar, meaning one end is slightly negatively charged and the other is slightly positively charged. The hydrogen atoms in one water molecule are attracted to the oxygen atom in a neighboring water molecule, forming a hydrogen bond that sticks the water molecules together. This property of water molecules sticking together is called cohesion.
Xylem is a long, non-living tube that runs from the roots to the leaves through the stem. The cells that make up the xylem are called vessels, and they lose their end walls to form a continuous, hollow tube. Lignin, a chemical, strengthens the vessels and provides support to the plant.
Question
The micrograph shows the cross-section of the vascular tissue in a dicotyledonous root. Which letter identifies phloem sieve tubes?
▶️Answer/Explanation
Ans:C
Question
The image shows part of a section through the stem of a non-woody plant. Where does transport of sucrose occur?
▶️Answer/Explanation
Ans:D
Question
An individual was presented with a stimulus resulting in the release of epinephrine. What was the most likely nature of the stimulus?
A. Sunset and the onset of darkness
B. An image of a close friend
C. The intake of glucose
D. A coach shouting to begin physical activity
D
Question
When intense physical activity is anticipated, which factor in the blood will increase the frequency of sinoatrial signals to heart muscle?
A. pH
B. Oxygen level
C. Thyroxin
D. Epinephrine
Ans:D