Plant Nutrition Quiz 3

At 1 and 2, increasing light intensity increases the rate of photosynthesis. Hence, light intensity is the limiting factor. At 3 and 4, increasing light intensity no longer increases the rate of photosynthesis. Hence, carbon dioxide is now the limiting factor.

A limiting factor is any factor that directly affects the rate of a process when its quantity is changed. Although light intensity continues to increase after point X the rate of photosynthesis increases very slowly and reaches a constant-light saturation point is reached, i.e. when the graph reached a plateau.

Increasing the temperature up to an optimum temperature of 40°C increases the rate of photosynthesis. Further, an increase in temperature caused photosynthesis to slow down and eventually stop because the enzymes that catalyze the dark stage of photosynthesis have become denatured.

During photosynthesis, carbon dioxide molecules combine with water molecules to form sugars, liberating oxygen in the process.

The water plant absorbs carbon dioxide during photosynthesis to manufacture carbohydrates. It is one of the limiting factor affecting photosynthesis. The higher the carbon dioxide concentration, the higher the rate of photosynthesis. Oxygen is released as the by-product of photosynthesis.

In test tube A, both pondweed and pond snail carry out only respiration in the dark resulting in a faster rate of removal of oxygen from the water and a faster rate of increase in carbon dioxide produced. In test tube B, the rate of increase in carbon dioxide is slower because only the pond respires. In tube C, both photosynthesis and respiration occur. The carbon dioxide produced by the pond snail is absorbed by pondweed for photosynthesis and oxygen formed during photosynthesis replaces the oxygen used by the snail for respiration. In tube D, only respiration occurs.

Cell D is a transverse section of a guard cell (cell P)

Region Q has no chlorophyll and region S lacks Carbon dioxide.

Increasing light intensity increases the rate of photosynthesis; therefore, the rate of oxygen gas formation is the highest at midday, i.e. point A and decreases to a minimum at night, i.e. point C.

Light energy is essential for photosynthesis. The rate of photosynthesis decreases with decreasing light intensity.