Q: The figure given below represents an experiment to demonstrate a particular aspect of photosynthesis. The alphabet ' A ' represents a certain condition inside the flask.(i) What is the aim of the experiment?(ii) Identify the special condition inside the flask.(iii) Name an alternative chemical that can be used instead of KOH .(iv) In what manner do the leaves 1 and 2 differ at the end of the starch test?

\textbf{Solution:} \textbf{i)} \bullet The aim of the experiment is to show that plants require CO_2 for photosynthesis. \bullet CO_2 and water are raw materials that are used by the plant to convert it into carbohydrates by using sunlight and in the presence of chlorophyll. \textbf{ii)} \bullet The leaf inside the flask does not get atmospheric CO_2 because KOH absorbs all the CO_2 in the flask. \bullet Since KOH absorbs CO_2 , therefore, if the leaf does not produce any starch, this will prove that leaves require carbon dioxide to perform photosynthesis (make food on their own). \textbf{iii)} \bullet KOH is used to absorb all the CO_2 present in the flask. \bullet An alternative chemical that can be used instead of KOH is NaOH. \textbf{iv)} \bullet KOH absorbs all the CO_2 present in the flask and therefore, leaf 1 does not get CO_2 . \bullet The absence of CO_2 inside the flask does not allow leaf 1 to produce starch and the leaf does not turn blue-black when a starch test is done (iodine is added and the yellow colour of iodine remains the same) \bullet Leaf 2, on the other hand, gets atmospheric CO_2 and at the end of the starch test, the yellow colour of iodine turns into a blue-black colour due to the presence of starch in the leaves

Question 1

The figure given below represents an experiment to demonstrate a particular aspect of photosynthesis. The alphabet ' A ' represents a certain condition inside the flask.(i) What is the aim of the experiment?(ii) Identify the special condition inside the flask.(iii) Name an alternative chemical that can be used instead of  KOH .(iv) In what manner do the leaves  1  and  2  differ at the end of the starch test?

Accepted Answer

extbf{Solution:} 	extbf{i)} \bullet  The aim of the experiment is to show that plants require  CO_2  for photosynthesis. \bullet   CO_2  and water are raw materials that are used by the plant to convert it into carbohydrates by using sunlight and in the presence of chlorophyll. 	extbf{ii)} \bullet  The leaf inside the flask does not get atmospheric  CO_2  because KOH absorbs all the  CO_2  in the flask. \bullet  Since KOH absorbs  CO_2 , therefore, if the leaf does not produce any starch, this will prove that leaves require carbon dioxide to perform photosynthesis (make food on their own). 	extbf{iii)} \bullet  KOH is used to absorb all the  CO_2  present in the flask. \bullet  An alternative chemical that can be used instead of KOH is NaOH. 	extbf{iv)} \bullet  KOH absorbs all the  CO_2  present in the flask and therefore, leaf 1 does not get  CO_2 . \bullet  The absence of  CO_2   inside the flask does not allow leaf 1 to produce starch and the leaf does not turn blue-black when a starch test is done (iodine is added and the yellow colour of iodine remains the same) \bullet  Leaf 2, on the other hand, gets atmospheric  CO_2  and at the end of the starch test, the yellow colour of iodine turns into a blue-black colour due to the presence of starch in the leaves

Question 2

Why we should not test for glucose instead of starch in the green leaves?

Accepted Answer

Photosynthesis is the process of formation of organic food from carbon dioxide and water in the presence of sunlight where chlorophyll traps the solar energy in cells. Oxygen is produced as byproduct. Simple carbohydrate or sugar (e.g.glucose) is the main product from which other organic substances are formed. Excess of glucose is stored as starch to function as internal energy reserve to be used as and when required. So, we test starch instead of glucose in leaves. Starch develops a blue-black colour with iodine solution. Therefore, the correct answer is option A.

Question 3

Will a leaf taken from a potted plant kept in a dark room for a few days turn blue-black when tested for starch? Give reasons for your answer.

Accepted Answer

When the leaf was kept in a dark room, it used all the starch that was reserved for various activities of the plant. Further, the leaves were not able to synthesize starch in absence of sunlight. So, the leaf will not turn blue-black when tested for starch.

Question 4

Who proved that plant purify the air and animals make the air impure?

Accepted Answer

A) Stephen Hales is called the father of plant physiology for his extensive research on photosynthesis.B) Joseph Priestley showed that animals exhale carbon dioxide (impure air) and plants give out oxygen (pure air).C) Ingenhousz showed that light is essential for photosynthesis.D) Von Helmont proved that plants require minerals from the soil for photosynthesis.So the correct answer is 'Priestley'.

Question 5

Chlorophyll 'a' and 'b' shows maximum absorption in:

Accepted Answer

Chlorophyll 'a' is a specific form of chlorophyll used in oxygenic photosynthesis. It absorbs most energy from wavelengths of violet-blue and orange-red light. Chlorophyll 'b' is a form of chlorophyll. It helps in photosynthesis by absorbing light energy. It is more soluble than chlorophyll in polar solvents because of its carbonyl group. Its color is yellow and primarily absorbs blue light. So, the correct answer is option C.

Question 6

Question 7

6CO _2  + 6H _2 O  \rightarrow  C _6 H _{12} O _6  + 6O _2 The site of this process is:

Accepted Answer

A chloroplast is essentially the centre of photosynthesis in eukaryotes. The light reaction of photosynthesis takes place in the thylakoid membrane whereas the dark reaction takes place in the stroma, both being constituents of the chloroplast.So, the correct answer is option 'In the chloroplast'.

Question 8

During photochemical reaction of photosynthesis:

Accepted Answer

The photochemical reaction of photosynthesis is the light reaction. It occurs in the thylakoid. Oxygen is produced as a product of the process of photolysis of water. ATP and NADPH _2  are also produced which are further used during the dark reaction of the photosynthesis.So, the correct answer is option C.

Question 9

The reaction center for PS- I and PS- II are:

Accepted Answer

Photosystem I has a reaction centre of P {_7} {_0} {_0}  and photosystem II has reaction centre P {_6} {_8} {_0} . Both are involved in non-cyclic photophosphorylation.

Question 10

The immediate electron donor to PS I is:

Accepted Answer

Plastocyanin acts as an electron carrier. It accepts only one electron from the cytochrome b _6 f complex (and is thus reduced), before reducing PSI (and is thus oxidized). In this step, the electron that is passed to PSI replaces that which has been lost by excitation by a photon of light, thus this may be considered the step that directly links the two photosystems. So, plastocyanin is the immediate electron donor for PS I. Plastoquinone is an electron acceptor which accepts two excited electrons from PSII and 2H ^+  from the stroma to become plastoquinol (PQH _2 ). It has the dual functions of transferring excited electrons from PSII to the cytochrome b6f complex (below) as part of the ETC, and of shuttling protons from the stroma to the thylakoid lumen as part of the generation of a proton motive force. This latter function is important for the generation of ATP. Ferredoxin is the final electron carrier in the light-dependent reactions, which accepts an electron from PSI to become reduced ferredoxin, before reducing NADP ^+  in the reaction catalyzed by ferredoxin NADP ^+  reductase (below). Quinones have important roles in carrying electrons between the components of the light reactions. Since they are lipid soluble, they can diffuse through the membrane. They can carry one or two electrons, and, in their reduced form (with added electrons), they carry hydrogen atoms that can be released as hydrogen ions when the added electrons are passed on, for example, to a cytochrome. So, the correct answer is option D.

Question 11

The source of oxygen evolved during photosynthesis is:

Accepted Answer

In the light reaction, the splitting of water occurs. The protons and oxygen formed by splitting of water are released within the lumen of the thylakoid. The oxygen produced is released as one of the net products of photosynthesis.So, the correct option is 'H _2 O'

Question 12

In noncyclic photophosphorylation, PS I is reduced by:

Accepted Answer

In noncyclic photophosphorylation, PS I is reduced by an electron from PS II. When light excites P- {_6} {_8} {_0}  it releases electrons and via intermediate electrons transporters it reaches PS I. So, the correct answer is option B.

Question 13

Who received the Nobel Prize for working out the early carbon pathway of photosynthesis?

Accepted Answer

Melvin Calvin received Nobel Prize for working out the early carbon pathway of photosynthesis. It was shown that the carbon first binds to a molecule of ribulose 1,5-bisphosphate (RuBP), then immediately splits, forming two molecules of phosphoglycerate (PGA). So, the correct answer is 'Calvin'

Question 14

' C_4  plants are special.' Comment upon the statement.

Accepted Answer

C_4  plants are special. They have a special type of leaf anatomy (Kranz anatomy), they tolerate high temperatures, they show a response to high light intensities, they lack a process called photorespiration and have greater productivity of biomass.

Question 15

During dark reaction for fixation of carbon, the three carbon atoms of each molecule of 3-phosphoglyceric acid (PGA) are derived from:

Accepted Answer

During the carboxylation phase of the Calvin cycle, Ribulose -1,5-bisphosphate (RuBP) ( =  Ribulose diphosphate) acts as  CO_{2}  acceptor and 6 molecules of RuBP react with 6 molecules of  CO_{2}  and 6 molecules of water giving rise to 12 molecules of 3-phosphoglyceric acid.

Question 16

Rearrange the following stages of Calvin cycle in correct order.1. Reduction during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH.2. Regeneration, during which the carbon dioxide acceptor ribulose-1,5-biphosphate is formed.3. Carboxylation during which carbon dioxide combines with ribulose-1,5-biphosphate.

Accepted Answer

In Calvin Cycle, carboxylation is during which carbon dioxide combines with ribulose-1,5-bisphosphate. Reduction is the second step during which carbohydrate is formed at the expense of the photochemically made ATP and NADPH. Regeneration is the third step, during which the carbon dioxide acceptor ribulose- 1,5- bisphosphate is formed and regenerated back.

Question 17

In photorespiration, what is the role of peroxisome?

Accepted Answer

Peroxisomes lie between chloroplasts and mitochondria in the plant cell and serve to pass the 2-carbon products of oxygenation on for further metabolism.In the chloroplast, the phosphoglycolate is dephosphorylated. Glycolate is transported to the peroxisome, where molecular oxygen further oxidizes it into glyoxylate. The product is hydrogen peroxide, which is rapidly broken down by catalase to water and oxygen. The glyoxylate is amidated to the amino acid glycine in the peroxisome.So, the correct answer is 'Help in the oxidation of glycolate'.

Question 18

The energy wastage occurs during:

Accepted Answer

Photorespiration is a process in plant metabolism, which attempts to reduce the consequences of a wasteful oxygenation reaction by the enzyme RuBisCO. The desired reaction is the addition of carbon dioxide to RuBP (carboxylation), a key step in the Calvin&#8211;Benson cycle, however approximately 25% of reactions by RuBisCO instead add oxygen to RuBP (oxygenation), producing a product that cannot be used within the Calvin&#8211;Benson cycle. This process reduces the efficiency of photosynthesis, potentially reducing photosynthetic output by 25% in  C_3  plants. Photorespiration involves a complex network of enzyme reactions, that exchange metabolites between chloroplasts, leaf peroxisomes, and mitochondria.So, the correct answer is option D.

Question 19

Photorespiration is a characteristic feature of :

Accepted Answer

Photorespiration occurs when the  CO_2  levels inside a leaf become low.This happens on hot dry days when a plant is forced to close its stomata to prevent excess water loss. If the plant continues to attempt to fix  CO_2 , when its stomata are closed, the  CO_2  will get used up and the  O_2  ratio in the leaf will increase relative to  CO_2  concentrations. Photorespiration is absent in  C_4  plants and CAM plants. Thus they are more efficient than  C_3  plants.So, the correct answer is option B.

Question 20

Photorespiration is favoured by:

Accepted Answer

Correct option: DExplanation:Photorespiration is favoured by High  O_2  and low  CO_2 . It occurs when the  CO_2  levels inside a leaf become low.RuBP instead of being converted to 2 molecules of PGA binds with  O_2  (high concentration) to form one molecule of phosphoglycerate and phosphoglycolate. There is no synthesis of ATP or NADPH or sugars.It is seen in hot and dry weather when stomata are closed to prevent excess water loss.Thus, Option D is correct.

Question 21

Blackman's law of limiting factor is applied to:

Accepted Answer

Blackman proposed the law of limiting factors in 1905. According to this law, when a process depends on a number of factors, its rate is limited by the pace of the slowest factor. Blackman's law of limiting factors determines the rate of photosynthesis.

Question 22

If the  CO_2  content of the atmosphere is as high as 300 parts per million, then:

Accepted Answer

The photosynthetic rate is influenced by many external (light, temperature, carbon dioxide, water, oxygen) and internal (chlorophyll content, protoplasmic condition, accumulation of end products) factors. The concentration of carbon dioxide in the atmosphere is 0.03 percent (300 parts per million). Plants can thrive well in this condition.

Question 23

Are the following statements true or false? Give reason in support of your answer. The outside atmospheric temperature has no effect on the rate of photosynthesis.

Accepted Answer

The given statement is false.With the rise in temperature, the rate of photosynthesis rises. This rise occurs up to the optimum temperature of  35^oC  (maximum suitable temperature when the photosynthesis occurs best) after which falls and stops above  40^oC .

Photosynthesis In Higher Plants