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

1. root phloem	2. stem xylem
3. root endodermis	4. leaf mesophyll

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

Which of the following does not enter the plant through roots?
1. carbon dioxide
2. nitrogen
3. potassium
4. water

Wilting of leaves causes decline in photosynthesis because:
1. chloroplasts in wilted leaves cannot photosynthesize.
2. ${\mathrm{CO}}_2$ accumulation in the leaves inhibits Calvin cycle enzymes.
3. of lack of water for photolysis.
4. closure of stomata prevents entry of ${\mathrm{CO}}_2$ entry into the leaf.

Substances travelling via the symplast move from cell-to-cell through:
1. membrane proteins.
2. phospholipid channels.
3. tonoplast.
4. plasmodesmata.