Which do guard cells control?

a. movement through xylem

b. movement through phloem

c. the size of the stomata

d. the rate of food production?

Answer : The correct answer is -

c. the size of the stomata.

Guard cells are the specialized cells, which are present around stomata (tiny holes/openings on the leaves) in plants.

These cells regulate the opening and closing of stomata, which help in the exchange of gases and loss of water in the atmosphere that is transpiration.

Thus, it can be concluded that guard cells help in controlling the size of stomata.

answer: - few nutrients

high pressure

low temperatures

explanation: 1. few nutrients:   open-ocean zone is located way far from the land, which is the main source of the essential nutrients.2. high pressure: pressure increases by 1 atmosphere for every 10 meters increase in depth.3. ample sunlight: a large fraction of the sunlight is reflected back to the atmosphere from the sea surface. 4. varying salinity: below the thermocline, the water is isolated from the atmosphere so the salinity remains stable over the year.5. low temperatures:   the temperature of open-ocean zone ranges from a low of -2°c to an average of 17°c