Video Transcript
If we measure the rate of photosynthesis in a wheat seedling that was grown under
minimal light exposure, what will be true about the obtained measurements? (A) The photosynthesis rate will be higher than usual. (B) The photosynthesis rate will be at the optimum level. (C) The photosynthesis rate will be lower than usual. Or (D) the photosynthesis rate will be zero.
When wheat germinates, it uses up the energy stored in the seed. So, when it becomes a seedling, it will start to produce structures involved in
photosynthesis, like chloroplasts, thylakoid membranes, and chlorophyll. This is so it can start to harvest light energy to produce its own food, glucose.
Building and maintaining structures that are involved in photosynthesis needs energy
as well. For this reason, it is unsurprising that environmental factors like carbon dioxide
concentration and light intensity, which are both factors that affect
photosynthesis, have an influence on how many photosynthetic structures are
built. For example, if light exposure is low, only a small amount of glucose can be produced
by photosynthesis.
So investing a lot of energy into building and maintaining photosynthetic structures
could mean that more energy is used than can be gained through photosynthesis. It has been shown that a low light intensity reduces the expression of genes which
code for structures that are involved in photosynthesis. A reduced gene expression means that fewer photosynthetic structures are
produced. Fewer photosynthetic structures means that less photosynthesis can be performed.
With this in mind, if we look at our question and answer options, we can exclude (A)
and (B). Furthermore, we can exclude answer choice (D). The rate of photosynthesis would not be zero, as there is a minimal light exposure
and the seedling would die if it could not photosynthesize. The correct answer is therefore (C). The obtained measurements would show the photosynthesis rate to be lower than
usual.
