Biology

As you know, altering light intensity will affect the rate of photosynthesis. The compensation point is the light intensity where the rate of photosynthesis is equal to the rate of cellular respiration. While the rate of respiration is relatively constant, the rate of photosynthesis will vary throughout the day due to increasing/decreasing sunlight intensity. It will start off low during sunrise, followed by an increase to a peak at the most intense light period, followed by a decrease to low levels again during sunset (a "bell-curve" shape). If you imagine these rates plotted on the same graph against time, the (relatively) linear respiration rate would intersect the bell-curve photosynthesis rate twice; which is usually at dusk and dawn. These are the compensation points.

What you'll most likely be shown is a graph of net CO2 uptake (on the y-axis) against light intensity (on the x-axis). Since the rate of both processes is equal, and both reactions consume/produce equal amounts of CO2, the compensation point would be where the graph intersects the X-axis (i.e when the net gain of CO2 is 0).