Question

• Given what you know about photosynthesis, what do you think may occur given a change in the available light to plants on earth, where only the green and red wavelengths of light are available to plants? Include a bit of information about how light is used by plants for photosynthesis.

• Review section 4.1 and 4.4 regarding glycolysis and fermentation, respectively. Compare and contrast the two processes including the components that are involved in each. When you think about the concept of fermentation, what are some benefits of conducting this type of energy production and provide two examples of organisms that use it.

Answer 1

1.Plants absorb maximum light at blue and red wavelengths. Green light plants do not absorb. They emit green light. Of the two color lights, blue and red, blue color is absorbed more than red color by chlorophyll a. So, if a plant is exposed only to red and green lights, the rate of photosynthesis will reduce. This is because the light that can be absorbed for photosynthesis has reduced.

Plants have photosynthetic pigments like chlirophyll a, chlorophyll b, carotenoids for absorbing light.These different photosynthetic pigments are arranged in a specific manner called photosystems. There are two photosystems PS I and PS II. Chlorophyll a is the photo center of the photosystem. The light absorbed by all other pigments is passed on to chorophyll a ultimately. When the light energy reaches chlorophyll a, it emits electrons. The electrons from PS II pass through electron transport chain (ETC) where the energy is used to make ATP. The electrons from ETC reach PS I. The electrons emitted by PS I reach NADP+ to make NADPH. These two ATP and NADPH are important molecules produced when the light is absorbed by photosynthetic pigments.

These two compounds are used in Calvin cycle to produce sugars.

2. Glycolysis is a path way which occurs in cellular respiration. It occurs in the cytoplasm of the cell.In this process one glucose molecule is broken in ot 2 pyruvate molecules producing 2 ATP and 2 NADH molecules. Under normal cellular respiration, pyruvate produced will enter in to Kreb's cycle to produce energy. In the process of Kreb's cycle, the pyruvate is completely broken to liberate CO2, H2O and lot of energy.

In the process of fermentation, glucose is not completely broken in to CO2 and water. It is incompletely broken in to ethyl alcohol and CO2 or in to lactic acid. Here Kreb's cycle does not occur. The process of fermentation involves only glycolysis which occurs in cytoplasm. The pyruvate formed by glycolysis incompletley broken by ethyl alcohol and Co2 or lactic acid. The amount of energy produced is only 2 ATP. The NADH formed during glycolysis is consumed when the pyruvate gets converted in to ethyl alcohol and CO2 or lactic acid. So, the net gain is only 2 ATP molecules.

When there is no sufficient O2 available to organisms , they under go fermentation process. This process produces energy in the absence of O2. Otherwise the organism will suffer from lack of energy in the ansence of O2.

Yeast under goes ethyl alcohol fermentation where CO2 is also produced.

Lacto bacillus is another organism under going anaerobic respiration. Here lactic acid is produced in the absence of O2.

Strenuously working muscles in humans also undergo fermentation to produce lactic acid.