Compared to C3 plants, C4 plants _____.

This is the answer to the biology question: Compared to C3 plants, C4 plants _____. We collected it at an MCAT practice test in the biology part.

Compared to C3 plants, C4 plants _.

The correct answer & explanation are below.

In the post In C3 plants the conservation of water promotes _____. We talked about the differences between C3 plants and C4 plants. Here are the more detailed differences between C3 plants and C4 plants.

Difference between C3 plants and C4 plants

C4 plants can use the ATP produced under strong sunlight to promote the combination of PEP and CO2 to increase the photosynthetic rate under strong light and high temperatures. In drought, the stomatal aperture can be partially constricted to reduce transpiration water loss, and the photosynthetic rate can be reduced to a relatively small extent. Thus, the water utilization in C4 plants is improved. These characteristics have obvious selective advantages in dry and hot regions. 　　

An important difference between C4 plants and C3 plants is that C4 plants have a low CO2 compensation point. In contrast, C3 plants have a high compensation point, so C4 plants have a higher survival rate at low CO2 levels. 　　

C4 plants are mainly those that live in arid tropical regions. In this environment, plants that open their stomata for a long time to absorb CO2 will result in too rapid loss of water through transpiration.

Therefore, plants can only open their stomata for short periods of time and the intake of CO2 is necessarily low. Plants must use this small amount of carbon dioxide for photosynthesis to synthesize the substances needed for their own growth. 　　

The vascular bundles of C4 plant leaves are surrounded by vascular sheaths, which contain chloroplasts in the cells of the vascular sheaths but have no or poorly developed basidia inside. Here, the Calvin cycle is mainly carried out.

The advantage of this type is that the CO2 fixation efficiency is much higher than that of C3, which facilitates plant growth in drought conditions, and the starch obtained by photosynthesis in C3 plants is stored in the chloroplasts. This is because this is the site of the Calvin cycle, whereas vascular sheath cells do not contain chloroplasts.

In contrast, starch from C4 plants will be stored in the vascular sheath cells because this is where the Calvin cycle occurs in C4 plants. 　　

The C4 plants are: monocotyledons Gramineae and Salicaceae, dicotyledons Asteraceae, Euphorbiaceae, Quinoa and Amaranthaceae.

C4 plants are less photorespiratory than C3 plants.

Photorespiration involves the interplay of three organelles: chloroplasts, peroxisomes and mitochondria. The whole process can be seen as starting with the aerobic decomposition of RuBP into 2-phosphoglycolic acid and 3-phosphoglycolic acid, which undergoes a series of reactions to produce 3-phosphoglycolic acid from the two-carbon compound phosphoglycolic acid. The latter enters the Calvin cycle and can be produced again as RuBP.

In contrast, the chloroplast carries out the reactions at the beginning and end of photorespiration, and the peroxidase body carries out the conversion of toxic substances. Mitochondria, on the other hand, synthesize two molecules of glycine into one molecule of serine and release one molecule of carbon dioxide and ammonia.

The ammonia produced during photorespiration is rapidly fixed and efficiently recycled by the cell through the glutamine-glutamate cycle, a process that consumes one molecule of ATP and NADPH.

In terrestrial C3 plants, more ammonia is produced during photorespiration than can be absorbed by the plant roots, making it an important part of the plant’s own nitrogen metabolism.

Moreover, the ammonia fixation efficiency of photorespiration is 5 to 10 times higher compared to the fixation pathway in which roots get ammonia through nitrate uptake or directly from the rhizosphere.

C3 plants have more peroxisomes in the chloroplasts, whereas C4 plants have most of them in the thin-walled cells of the vascular sheath cells. The peroxisomes were closer to the chloroplasts. In other words, the C4 ones are farther away and photorespiration is relatively weaker.

Correct Answer

From the above, we can learn that Compared to C3 plants, C4 plants _.

• In C3 plants the conservation of water promotes _____.