Cohesion of water molecules is due to:
1. a high latent heat of vaporization of water
2. higher density of liquid water than solid water
3. hydrogen bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule
4. covalent bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

Which of the following is not required for transpiration?
1. adhesion of water molecules to cellulose.
2. cohesion between water molecules.
3. evaporation of water molecules.
4. active transport through xylem cells.

Identify the incorrect statement regarding transport in plants:

1. Hydrogen bonding causes high cohesion between water molecules that helps in the rise of water in tall trees.

2. Root pressure in some angiosperm may be considerable yet not enough to raise water to the tops of tall trees.

3. Transpiration pull along with cohesion between water molecules is sufficient to raise the water in the xylem in even the tallest trees.

4. Gymnosperms can sometimes develop especially high root pressure, which may account for the rise of water in tall pine trees without transpiration pull.

The normal functioning of which of the following would be least dependent on active transport:

Identify the incorrect statement regarding xylem:
1. Xylem tracheids and vessels perform their vital function only after their death.
2. Tracheids have a strong cell wall deposited with cellulose fibrils forming thickened rings or spirals.
3. Water molecules are transpired from the cells of the leaves, and replaced by water molecules in the xylem pulled up from the roots due to the cohesion of water molecules.
4. Mass flow translocation between the source and the sink occurs due to a turgor pressure gradient.

Xylem transports air by:
1. the proton pump
2. active transport
3. chemiosmosis
4. air is not transported by xylem normally

Advantages of tracheids over vessels for long-distance transport to great heights include:
I. Adhesive forces are proportionally greater in narrower cylinders than in wider cylinders.
II. The smaller the diameter of the xylem, the more likely cavitation will occur.
III. Cohesive forces are greater in narrow tubes than in wide tubes of the same height.
1. Only I and II
2. Only I and III
3. Only II and III
4. I, II and III

All the following regarding the cohesion-tension model are true except:
1. Water movement is driven by transpiration.
2. The water potential of atmospheric air is more positive than that for xylem.
3. Cohesion represents the tendency for water molecules to stick together by hydrogen bonds.
4. The physical forces in the capillary-sized xylem cells make it easier to overcome gravity.

A poison that blocks proton pumps would not directly affect:
1. photosynthesis.
2. phloem loading.
3. xylem transport.
4. cellular respiration.

Guard cells:
1. have endoplasmic reticulum that store potassium ions.
2. accumulate ${\mathrm{K}}^{+}$ and close the stomata.
3. prevent mineral loss through stomata.
4. help balance the photosynthesis-transpiration compromise