Here is the answer and explanation of In C3 plants the conservation of water promotes _.
In C3 plants, what the conservation of water promotes?
Q: In C3 plants the conservation of water promotes _.
- A shift to C4 photosynthesis.
- The opening of stomata.
- Photorespiration.
- The light reactions.
- Photosynthesis.
The correct answer and explanation are below.
C3 plants
Plants in which the initial product of CO2 assimilation is the three-carbon compound 3-phosphoglycerate in the photosynthetic carbon cycle are called C3 plants. For example, wheat, soybean, tobacco, and cotton are all C3 plants.
C3 plants have a higher CO2 compensation point than C4 plants, so C3 plants have a lower survival rate at low CO2 levels than C4 plants.
Malvin Calvin of the University of California, Berkeley, and his colleagues were studying an algae called Chlorella to determine how plants fix CO2 during photosynthesis, at a time when C14 tracer technology and two-way paper chromatography were well established. Calvin happened to use both techniques in his experiments.
They placed the cultured algae in a closed container containing unlabeled CO2. Then C14-labeled CO2 was injected into the container. After a fairly short period of incubation, the algae were immersed in hot ethanol to kill the cells and denature the enzymes in the cells and render them inactive.
Then they extracted to the molecules in solution. The extracts were then separated from the various compounds by applying bi-directional paper chromatography. The spots above the radioactivity were then analyzed by radiographic autoradiography and compared with the known chemical composition.
CO2 labeled with C14 is quickly converted to organic matter. Within seconds, radioactive spots appear on the chromatography paper. When compared to the known chemical, the chemical in the spots was glycerol triphosphate, an intermediate of glycolysis.
This first extracted product is a three-carbon molecule. Therefore, this CO2 fixation pathway is called the C3 pathway, and the plants that fix CO2 through this pathway are called C3 plants. Later studies also revealed that the C3 pathway of CO2 fixation is a cyclic process, which people call the C3 cycle. This cycle is also known as the Calvin cycle.
In C3 plants, such as rice and wheat, CO2 enters the leaves through the stomata and then goes directly to the leaf flesh for the Calvin cycle. In contrast, the vascular sheath cells of C3 plants are small and contain no or few chloroplasts, where the Calvin cycle does not occur.
C4 plants
Plants in which the initial product of CO2 assimilation is not the three-carbon compound 3-phosphoglyceric acid from the photosynthetic carbon cycle, but the four-carbon compound malic acid or aspartic acid. Also called C4 plants.
For example, corn, sugarcane, sorghum, and amaranth are C4 plants .
There are about 300 species of economic plants in the family Gramineae that belong to C4 plants. Breeding efforts have been ongoing to breed hybrid rice, for example, by hybridization or cell fusion, to have carbon dioxide uptake similar to that of C4 plants. The breeding of new varieties similar to C4 plants is of great importance for the improvement of the food situation worldwide.
Reaction process
Phosphoenolpyruvate (PEP) in the chloroplast is combined with CO2 by the action of PEP carboxylase to form malate or aspartate.
These tetracarbon bicarboxylic acids are transferred to the sheath cells and release CO2 by the action of decarboxylase. The latter enters the photosynthetic carbon cycle in the chloroplasts of sheath cells by the action of ribulose diphosphate (RuBP) carboxylase.
This metabolic pathway of forming tetracarbon bicarboxylic acid from PEP and then decarboxylating it to release CO2 is called the four-carbon pathway.
Its leaf pulp cells contain a unique enzyme, phosphoenolpyruvate carbon oxidase. This allows CO2 to be first assimilated by a three-carbon compound, phosphoenolpyruvate, to form the four-carbon compound oxaloacetate.
After oxaloacetate is converted to malate and enters the vascular sheath, it is broken down to release carbon dioxide and a molecule of pyruvate. The carbon dioxide enters the Calvin cycle and is followed by the same C3 process. Pyruvate is then re-synthesized into phosphoenolpyruvate, a process that consumes ATP.
c4 plants differ from c3 and cam plants in that c4 plants
C4 plants have many advantages over C3 plants such as strong growth capacity, high CO2 utilization, and low water requirement.
The survival rate of C3 plants at low CO2 content is lower than that of C4 plants.
Carbon dioxide is first fixed in the tetracarbon carboxylic acid in the chloroplast, then transported to the vascular sheath cells for decarboxylation, and the released carbon dioxide is fixed again by the carboxylation reaction catalyzed by Rubisco.
This pathway actually adds a tetracarbon bicarbonate cycle to the carbon dioxide assimilation. This cycle acts as a CO2 pump, resulting in a much higher CO2 concentration in the carboxylation site of Rubisco than in carbon 3 plants, thus reducing photorespiration. As a result, carbon 4 plants have higher photosynthetic efficiency than carbon 3 plants under strong light.
Correct Answer
- C. Photorespiration
In C3 plants the conservation of water promotes Photorespiration.
