Case Study Questions Class 11 Biology Chapter 13 Photosynthesis in Higher Plants
CBSE Class 11 Case Study Questions Biology Photosynthesis in Higher Plants. Important Case Study Questions for Class 11 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Photosynthesis in Higher Plants.
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CBSE Case Study Questions Class 11 Biology Photosynthesis in Higher Plants
CASE 1
Light reactions or the ‘Photochemical’ phase include light absorption, water splitting, oxygen release, and the formation of high-energy chemical intermediates, ATP and NADPH. Several protein complexes are involved in the process. The pigments are organised into two discrete photochemical light harvesting complexes (LHC) within the Photosystem I (PS I) and Photosystem II (PS II). These are named in the sequence of their discovery, and not in the sequence in which they function during the light reaction. The LHC are made up of hundreds of pigment molecules bound to proteins. Each photosystem has all the pigments (except one molecule of chlorophyll a) forming a light harvesting system also called antennae. These pigments help to make photosynthesis more efficient by absorbing different wavelengths of light. The single chlorophyll a molecule forms the reaction centre. The reaction centre is different in both the photosystems. In PS I the reaction centre chlorophyll a has an absorption peak at 700 nm, hence is called P700, while in PS II it has absorption maxima at 680 nm, and is called P680.
1.) Identify the actions, which are not includes in light phase of photosynthesis
a.) Splitting of water molecule
b) Combustion of oxygen
c) ATP formation
d) Oxygen release
2.) Photosynthesis is _________________
a) Destructive process
b) Energy releasing process
c) Energy trapping process
d) None of the above
3.) Name the pigment which is referred as reaction centre?
4.) Give reason – Why photosystem 1 is named as P700?
5.) Give reason – Why photosystem 2 is named as P680?
6.) Explain how photosynthetic pigments are arranged?
Answer key
1) b
2) c
3.) Chlorophyll – a pigment is referred as reaction centre.
4.) In PS I the reaction centre chlorophyll a has an absorption peak at 700 nm, hence it is named as P700.
5.) In PS II the reaction centre chlorophyll a has an absorption maxima at 680 nm, hence it is named as P680.
6.) The pigments are organised into two discrete photochemical light harvesting complexes (LHC) within the Photosystem I (PS I) and Photosystem II (PS II). The LHC are made up of hundreds of pigment molecules bound to proteins. Each photosystem has all the pigments (except one molecule of chlorophyll a) forming a light harvesting system also called antennae.
CASE 2
The splitting of water is associated with the PS II; water is split into 2H+, [O] and electrons. This creates oxygen, one of the net products of photosynthesis. The electrons needed to replace those removed from photosystem I are provided by photosystem II. Water splitting complex is associated with the PS II, which itself is physically located on the inner side of the membrane of the thylakoid.
Cyclic and Non-cyclic Photo-phosphorylation
Living organisms have the capability of extracting energy from oxidisable substances and store this in the form of bond energy. Special substances like ATP, carry this energy in their chemical bonds. The process through which ATP is synthesised by cells (in mitochondria and chloroplasts) is named phosphorylation. Photo-phosphorylation is the synthesis of ATP from ADP and inorganic phosphate in the presence of light. When the two photosystems work in a series, first PS II and then the PS I, a process called non-cyclic photo-phosphorylation occurs. The two photosystems are connected through an electron transport chain. Both ATP and NADPH + H+ are synthesised by this kind of electron flow.
When only PS I is functional, the electron is circulated within the photosystem and the phosphorylation occurs due to cyclic flow of electrons. A possible location where this could be happening is in the stroma lamellae. While the membrane or lamellae of the grana have both PS I and PS II the stroma lamellae membranes lack PS II as well as NADP reductase enzyme. The excited electron does not pass on to NADP+ but is cycled back to the PS I complex through the electron transport chain. The cyclic flow hence, results only in the synthesis of ATP, but not of NADPH + H+ . Cyclic photophosphorylation also occurs when only light of wavelengths beyond 680 nm are available for excitation.
1.) Photolysis of water or splitting of water molecule takes place in _____________
a) Photosystem PS I
b) Photosystem PS II
c) Photosystem PS III
d) Both PS I and PS II
2.) Water molecule splits into_________________ in presence of light.
a) Hydrogen, Nitrogen and Electrons
b) Hydrogen, Oxygen and Protons
c) Hydrogen, Oxygen and Neutrons
d) Hydrogen, Oxygen and Electrons
3.) By which mechanism two photosystem can be connected and work in series?
4.) Define phosphorylation and Photo-phosphorylation.
5.) Name the cell organelles in which the process of phosphorylation is carried out.
Answer key
1.) b
2.) d
3.) The two photosystems are connected through an electron transport chain, which makes them work in series.
4.) Phosphorylation is the process through ATP molecules are synthesised by cells.
5.) Photo-phosphorylation is the synthesis of ATP from ADP and inorganic phosphate in the presence of light.
6.) Mitochondria and chloroplasts are the cell organelles in which the process of phosphorylation is carried out.
CASE 3
The path of carbon fixation in dark reaction through intermediate compounds leading to the formation of sugar and starch was worked out by Calvin, Benson and their co -workers. For this, Calvin was awarded Nobel Prize in 1961.
The various steps in the dark reactions (Calvin cycle / C-3 pathway) are as follows: carboxylation, reduction and regeneration.
Carboxylation– Carboxylation is the fixation of CO2 into a stable organic intermediate. Carboxylation is the most crucial step of the Calvin cycle where CO2 is utilised for the carboxylation of RuBP. This reaction is catalysed by the enzyme RuBP carboxylase which results in the formation of two molecules of 3-PGA(3-Phosphoglyceraldehyde). Since this enzyme also has an oxygenation activity it would be more correct to call it RuBP carboxylase-oxygenase or RuBisCO.
Reduction – These are a series of reactions that lead to the formation of glucose. The steps involve utilisation of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO2 molecule fixed. The fixation of six molecules of CO2 and 6 turns of the cycle are required for the formation of one molecule of glucose from the pathway. 3.
Regeneration – Regeneration of the CO2 acceptor molecule RuBP is crucial if the cycle is to continue uninterrupted. The regeneration steps require one ATP for phosphorylation to form RuBP.
Hence for every CO2 molecule entering the Calvin cycle, 3 molecules of ATP and 2 of NADPH are required. It is probably to meet this difference in number of ATP and NADPH used in the dark reaction that the cyclic phosphorylation takes place. To make one molecule of glucose 6 turns of the cycle are required.
Plants form a variety of organic compounds required for its structure and function through these complex reactions. Thus, for every 6 molecules of CO2 and Ribulose-1, 5-biphosphate used, 12 molecules of 3-phosphoglyceraldehyde are produced. Out of these 12 molecules, only two are utilized for the formation of a molecule of glucose; the other 10 molecules are converted into ribulose-1, 5-biphosphate which combines with fresh CO2. Thus, the Calvin cycle regenerates ADP and NADP required for the light reaction.
1.) In Calvin cycle, Carboxylation facilitate _________________
a) Regeneration of the CO2 acceptor molecule
b) Fixation of CO2 into a stable organic intermediate.
c) Release of CO2 into a stable organic intermediate.
d) Regeneration of the O2 acceptor molecule.
2.) In Calvin cycle or C3 pathway, _______________ involves utilisation of 2 molecules of ATP for phosphorylation and two of NADPH for reduction per CO2 molecule fixed.
a) Carboxylation
b) Reduction
c) Regeneration
d) Synthesis of glucose
3.) Give reason – Why Calvin cycle is called as C-3 cycle?
4.) Enlist the steps involved in C-3 cycle in correct order.
5.) Name the enzyme which is involved in to the formation of two molecules of 3-PGA from the RuBP.
Answer key
1.) b
2) b
3.) Calvin cycle is called as C-3 cycle because the first major stable intermediate compound is the 3-carbon molecule compound. i.e. 3-PGA
4.) The various steps in the C-3 pathway are as follows:
Carboxylation
Reduction
Regeneration
5.) The formation of two molecules of 3-PGA from the RuBP, This reaction is catalysed by the enzyme named as RuBP carboxylase or RuBisCO.
CASE 4
Plants that are adapted to dry tropical regions have the C4 pathway mentioned earlier. Though these plants have the C4 oxaloacetic acid as the first CO2 fixation product they use the C3 pathway or the Calvin cycle as the main biosynthetic pathway.
C4 plants are special: They have a special type of leaf anatomy, they tolerate higher temperatures, they show a response to high light intensities, and they lack a process called photorespiration and have greater productivity of biomass. The leaves shows different anatomyi.e. ‘Kranz’ anatomy. ‘Kranz’ means ‘wreath’ and is a reflection of the arrangement of cells. The bundle sheath cells may form several layers around the vascular bundles; they are characterised by having a large number of chloroplasts, thick walls impervious to gaseous exchange and no intercellular spaces. Maize or sorghum.
C4 pathway that has been named the Hatch and Slack Pathway, is again a cyclic process. The primary CO2 acceptor is a 3-carbon molecule phosphoenol pyruvate (PEP) and is present in the mesophyll cells. The enzyme responsible for this fixation is PEP carboxylase or PEPcase. It is important to register that the mesophyll cells lack RuBisCO enzyme. The C4 acid OAA is formed in the mesophyll cells. It then forms other 4-carbon compounds like malic acid or aspartic acid in the mesophyll cells itself, which are transported to the bundle sheath cells. In the bundle sheath cells these C4 acids are broken down to release CO2 and a 3-carbon molecule. The 3-carbon molecule is transported back to the mesophyll where it is converted to PEP again, thus, completing the cycle. The CO2 released in the bundle sheath cells enters the C3 or the Calvin pathway, a pathway common to all plants. The bundle sheath cells are rich in an enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO), but lack PEPcase. Thus, the basic pathway that results in the formation of the sugars, the Calvin pathway, is common to the C3 and C4 plants. In the C4 plants it does not take place in the mesophyll cells but does so only in the bundle sheath cells.
1.) In the C4 plants, Calvin pathway take place in the
a) Bundle sheath cells
b) Mesophyll cells
c) Both a and b
d) None of the above
2.) In C4 pathway, ________________ is the first carbon dioxide acceptor.
a.) Phosphphenol pyruvate
b) Phosphoenol pyruvate
c) Phosphoethanol pyruvate
d) PEP carboxylase
3.) Give the examples of plant which shows Kranz anatomy.
4.) Give reason – Why Hatch Slack pathway is referred as C-4 pathway?
5.) Explain Kranz anatomy in C-4 plants.
6.) Name the catalyst which is responsible for CO2 fixation in C4 pathway.
Answer key
1.) a
2.) b
3.) Maize and sorghum plant shows Kranz anatomy in leaves.
4.) In Hatch Slack pathway, first stable product of CO2 fixation is a 4-carbon compound, oxaloacetic acid. Hence it is referred as C-4 pathway and such plants are called C4 plants.
5.) C4 plants show Kranz anatomy. In the leaves of such plants, there is a bundle sheath around the vascular bundles. The chloroplasts in the bundle – sheath cells are large and almostwithout or less developed grana, where as in the mesophyll cells, the chloroplasts are small but with well-developed grana.
6.) The enzyme responsible for CO2 fixation in C4 pathway is PEP carboxylase or PEP case.
CASE 4
Plants that are adapted to dry tropical regions have the C4 pathway mentioned earlier. Though these plants have the C4 oxaloacetic acid as the first CO2 fixation product they use the C3 pathway or the Calvin cycle as the main biosynthetic pathway.
C4 plants are special: They have a special type of leaf anatomy, they tolerate higher temperatures, they show a response to high light intensities, and they lack a process called photorespiration and have greater productivity of biomass. The leaves shows different anatomyi.e. ‘Kranz’ anatomy. ‘Kranz’ means ‘wreath’ and is a reflection of the arrangement of cells. The bundle sheath cells may form several layers around the vascular bundles; they are characterised by having a large number of chloroplasts, thick walls impervious to gaseous exchange and no intercellular spaces. Maize or sorghum.
C4 pathway that has been named the Hatch and Slack Pathway, is again a cyclic process. The primary CO2 acceptor is a 3-carbon molecule phosphoenol pyruvate (PEP) and is present in the mesophyll cells. The enzyme responsible for this fixation is PEP carboxylase or PEPcase. It is important to register that the mesophyll cells lack RuBisCO enzyme. The C4 acid OAA is formed in the mesophyll cells. It then forms other 4-carbon compounds like malic acid or aspartic acid in the mesophyll cells itself, which are transported to the bundle sheath cells. In the bundle sheath cells these C4 acids are broken down to release CO2 and a 3-carbon molecule. The 3-carbon molecule is transported back to the mesophyll where it is converted to PEP again, thus, completing the cycle. The CO2 released in the bundle sheath cells enters the C3 or the Calvin pathway, a pathway common to all plants. The bundle sheath cells are rich in an enzyme Ribulose bisphosphate carboxylase-oxygenase (RuBisCO), but lack PEPcase. Thus, the basic pathway that results in the formation of the sugars, the Calvin pathway, is common to the C3 and C4 plants. In the C4 plants it does not take place in the mesophyll cells but does so only in the bundle sheath cells.
1.) In the C4 plants, Calvin pathway take place in the
a) Bundle sheath cells
b) Mesophyll cells
c) Both a and b
d) None of the above
2.) In C4 pathway, ________________ is the first carbon dioxide acceptor.
a) Phosphphenol pyruvate
b) Phosphoenol pyruvate
c) Phosphoethanol pyruvate
d) PEP carboxylase
3) Give the examples of plant which shows Kranz anatomy.
4) Give reason – Why Hatch Slack pathway is referred as C-4 pathway?
5) Explain Kranz anatomy in C-4 plants.
6) Name the catalyst which is responsible for CO2 fixation in C4 pathway.
Answer key
1) a
2) b
3) Maize and sorghum plant shows Kranz anatomy in leaves.
4) In Hatch Slack pathway, first stable product of CO2 fixation is a 4-carbon compound, oxaloacetic acid. Hence it is referred as C-4 pathway and such plants are called C4 plants.
5) C4 plants show Kranz anatomy. In the leaves of such plants, there is a bundle sheath around the vascular bundles. The chloroplasts in the bundle – sheath cells are large and almostwithout or less developed grana, where as in the mesophyll cells, the chloroplasts are small but with well-developed grana.
6) The enzyme responsible for CO2 fixation in C4 pathway is PEP carboxylase or PEP case.
CASE 5
Photosynthesis is under the influence of several factors, both internal (plant) and external. The plant factors include the number, size, age and orientation of leaves, mesophyll cells and chloroplasts, internal CO2 concentration and the amount of chlorophyll. The plant or internal factors are dependent on the genetic predisposition and the growth of the plant. The external factors would include the availability of sunlight, temperature, CO2 concentration and water. As a plant photosynthesises, all these factors will simultaneously affect its rate.
When several factors affect any biochemical process, Blackman’s (1905) Law of Limiting Factors comes into effect. This states that, “If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed.”
Light quality, light intensity and the duration of exposure to light these light factors affects photosynthesis. There is a linear relationship between incident light and CO2 fixation rates at low light intensities. At higher light intensities, gradually the rate does not show further increase as other factors become limiting. It is interesting to note is that light saturation occurs at 10 per cent of the full sunlight. Hence, except for plants in shade or in dense forests, light is rarely a limiting factor in nature. Increase in incident light beyond a point causes the breakdown of chlorophyll and a decrease in photosynthesis.
Carbon dioxide is the major limiting factor for photosynthesis. The concentration of CO2 is very low in the atmosphere (between 0.03 and 0.04 per cent). Increase in concentration upto 0.05 per cent can cause an increase in CO2 fixation rates; beyond this the levels can become damaging over longer periods. The C3 and C4 plants respond differently to CO2 concentrations. At low light conditions neither group responds to high CO2 conditions. At high light intensities, both C3 and C4 plants show increase in the rates of photosynthesis. The fact that C3 plants respond to higher CO2 concentration by showing increased rates of photosynthesis leading to higher productivity has been used for some greenhouse crops such as tomatoes and bell pepper. They are allowed to grow in carbon dioxide enriched atmosphere that leads to higher yields.
The dark reactions being enzymatic are temperature controlled. Though the light reactions are also temperature sensitive they are affected to a much lesser extent. The C4 plants respond to higher temperatures and show higher rate of photosynthesis while C3 plants have a much lower temperature optimum. The temperature optimum for photosynthesis of different plants also depends on the habitat that they are adapted to. Tropical plants have a higher temperature optimum than the plants adapted to temperate climates.
1.) As per low of limiting factors, If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is ________________.
a) Nearest to its minimal value
b) Nearest to its maximal value
c) Nearest to its optimal value
d) None of the above
2) In photosynthesis, increase in incident light beyond optimum level causes the ___________
a) Breakdown of chlorophyll and increase in photosynthesis.
b) Activation of chlorophyll andincrease in photosynthesis.
c) Breakdown of chlorophyll and decrease in photosynthesis.
d) Breakdown of chlorophyll and decrease in photooxidation.
3.) What concentration of CO2 is present in our atmosphere or surrounding?
4.) Give the Blackman’s (1905) Law of Limiting Factors.
5.) How C3 and C4 plants respond to CO2 concentration?
Answer key
1) a
2) c
3) The concentration of CO2 is very low in the atmosphere between 0.03 and 0.04 per cent.
4) Blackman’s (1905) Law of Limiting Factors comes into effect. This states that, “If a chemical process is affected by more than one factor, then its rate will be determined by the factor which is nearest to its minimal value: it is the factor which directly affects the process if its quantity is changed.”
5) The C3 and C4 plants respond differently to CO2 concentrations. At low light conditions neither group responds to high CO2 conditions. At high light intensities, both C3 and C4 plants show increase in the rates of photosynthesis. The fact that C3 plants respond to higher CO2 concentration by showing increased rates of photosynthesis leading to higher productivity has been used for some greenhouse crops such as tomatoes and bell pepper. They are allowed to grow in carbon dioxide enriched atmosphere that leads to higher yields.