Light & the Rate of Photosynthesis Flashcards

All 7 cards in this deck

What is the relationship between light intensity and the rate of photosynthesis at low light levels?

Directly proportional — as light intensity increases, the rate increases.

Why does a graph of rate of photosynthesis against light intensity level off?

Light intensity is no longer the limiting factor — another factor, e.g. temperature or $CO_2$, is limiting.

How is light intensity related to the distance from a light source?

Inversely proportional to the square of the distance (the inverse square law).

What is the formula for relative light intensity using the inverse square law?

relative light intensity $= \dfrac{1}{d^2}$, where $d$ is the distance from the lamp.

What are the steps to find the relative light intensity at a given distance from a lamp?

e.g. a lamp 2 cm from the plant

1. Note the distance: $d = 2$ cm
2. Square it: $d^2 = 4$
3. Take the reciprocal: $1/4 = 0.25$ (arbitrary units)

True or false? Doubling the distance from a lamp halves the light intensity.

False. It quarters the light intensity, because intensity $\propto 1/d^2$.

True or false? The rate of photosynthesis is directly proportional to the distance from a light source.

False. It is inversely proportional to the distance (an inverse square relationship).