Question

QUESTION 8 Which order of events for the Calvin cycle is correct? I. Reduction II. Regeneration of the CO2 acceptor (RuBP) III. Carbon fixation I, II, III III, II, I III, I, II II, I, III I, III, II QUESTION 11 The process of harnessing light energy to build carbohydrates in autotrophs is glycolysis. photosynthesis. cell fermentation. cell respiration. anaerobic metabolism. QUESTION 12 Where does glycolysis takes place? mitochondrial membrane cytosol mitochondrial inner membrane mitochondrial matrix mitochondrial intermembrane space

QUESTION 15

Stroma close all day and open all night.

True

False

Answer 1

Q. 8:

The process by which plants fix carbon dioxide in the atmosphere to organic molecules like glucose is known as Calvin cycle. It is the second phase in the process of photosynthesis. There are many other terms in use to refer to Calvin cycle, like Calvin-Benson cycle and dark reactions. The term dark reaction is now outdated and is replaced by the name light independent reactions, since these reactions do not use light directly but the energy rich molecules like ATP and NADPH formed during light reactions. Carbon dioxide (CO2) enters the leaves through stomata, where it diffuses over short distances through intercellular spaces until it reaches the mesophyll cells. Once in the mesophyll cells, CO2 diffuses into the stroma of the chloroplast, the site of light-independent reactions of photosynthesis. There are 3 major steps in Calvin cycle which sequentially, namely:

· CO2 Fixation: here one molecule of Carbon is fixed or attached to a 5-Carbon molecule – RuBP (Ribulose1,5 Bisphosphate) to form two 3-Carbon molecules – 3PGA (3-Phospho Glyceric Acid). This reaction is catalyzed by the enzyme RUBISCO.

· Reduction: in this second step of Calvin cycle ATP and NADPH, formed during light reaction, are used to convert the 3-PGA molecules into glyceraldehyde-3-phosphate (G3P). This step is named as ‘Reduction’ because NADPH donates electrons to (in other words, reduces) a three-carbon intermediate to form G3P.

· Regeneration: The starting molecule of Calvin cycle – RuBP needs to be regenerated. Fixation of 3 CO2 molecules leads to the formation of 6 molecules of G3P. One of these G3P exits Calvin cycle and forms Glucose whereas the rest are used in the regeneration of RuBP.

The description above elucidates the sequence of reactions during Calvin cycle. The order of events in Calvin cycle is: III. Carbon Fixation, I. Reduction and III. Regeneration. Therefore the answer is option 3 : III   I    II

Q.11:                  

The process of harnessing light energy to build carbohydrates in autotrophs is known as photosynthesis. The other options given are:

· Glycolysis: the process in which one glucose molecule is broken down to form two molecules of pyruvic acid. It is a multi-step metabolic pathway that occurs in the cytoplasm of plant cells.

· Fermentation: the process by which pyruvate is converted into carbon dioxide and ethanol in plant and yeast cells is called fermentation. It takes place in the absence of Oxygen and yields only two molecules of ATP per glucose molecule broken down.

· Respiration: is the process by which the glucose molecules are broken down to yield ATP molecules, using Oxygen.

· Anaerobic metabolism: it is a type of respiration that takes place without oxygen. In plants, the glucose is anaerobically converted to ethyl alcohol, ATP and carbon dioxide.

Q.12:

As already mentioned in Q.11, Glycolysis the process in which one glucose molecule is broken down to form two molecules of pyruvic acid. It is a multi-step metabolic pathway that occurs in the cytoplasm of plant cells.

Q. 15:

The opening and closing of stomata differs in mesophytic and xerophytic plants. In xerophytes, stomata close during daytime and opens at night as an adaptation to conserve water, whereas in mesophytes, stomata remains open during daytime and closes during night. So the given statement is true in case of xerophytes and false in case of mesophytes. Since the plant type is not mentioned in the question, let us consider mesophytes (the intention of the question might be to test the understanding of stoma behavior in general) and therefore the answer is ‘ False’.