Important Questions Class 11 Biology Chapter 13

Class 11 Biology Chapter 13 Important Questions – Photosynthesis in Higher Plants

Biology helps us explain the various phenomena occurring both within and around us. Students must know their Biology oriented concepts early on to have a strong hold on complex concepts in higher classes. Students must develop a good understanding of the ongoing topics to enhance their learning experience at the time of preparation for the examination with Chapter 13 Class 11 Biology important questions. 

Chapter 13 is about photosynthesis in higher plants. Photosynthesis is a crucial chapter in Class 11 Biology that explains the photosynthetic cycle in plants. Questions from this chapter are frequently asked in competitive exams like NEET, MH-CET, and board examinations. By solving exercise questions given in the NCERT books and exemplars, students can prepare themselves well for their examinations.

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Important Questions Class 11 Biology Chapter 13 With Solutions

Class 11 Biology Chapter 13 important questions have been provided after compiling questions from various sources. The chapter covers different topics like the early experiments of scientists such as Joseph Priestley, Julius Von Sachs, and Cornelius Van Neil, the various pigments involved in photosynthesis, light reaction, the electron transport system, cyclic and non-cyclic photophosphorylation, Chemiosmotic Hypothesis of ATP formation, Calvin Cycle (Reductive Pentose Sugar Phosphate Pathway), C4 pathway (Hatch Slack Pathway), Photorespiration and Blackman’s Law. The solutions provided in Important Questions Class 11 Biology Chapter 13 contain explanations for all these essential concepts.

This set of questions will give students an insight into the various topics covered in the chapter. The given solutions follow the latest CBSE syllabus. Hence, students can entirely rely on it. After going through Important Questions Class 11 Biology Chapter 13, students can develop a good core foundation and achieve excellent grades. Given below is one of the question sets for Important Questions Class 11 Biology Chapter 13 along with their solutions:

Question 1. Why is the colour of a leaf kept in the dark frequently yellow, or pale green? Which pigment do you think is more stable?

Answer 1. It is essential to have light to carry out photosynthesis in leaves. When a dark leaf is given more exposure to sunlight, the colour of the leaf changes into a lighter shade through a gradual process. This is due to a green pigment called chlorophyll present in the leaf. The production of chlorophyll pigment is directly proportional to the amount of sunlight available. When light is absent, the amount of chlorophyll and its production stops; as a result, they degenerate. Due to this, the colour of the leaf changes from bright green to a lighter shade of green. 

While this process occurs, the xanthophyll and carotenoid pigments become predominant, which causes the leaf to become yellow. The xanthophyll and carotenoid pigments are more stable and remain unaffected in the absence of light.

Question 2. RuBisCO is an enzyme that acts both as a carboxylase and oxygenase. Why do you think RuBisCO carries out more carboxylation in C4 plants?

Answer 2. The full form of RuBisCO is ribulose-1,5-bisphosphate carboxylase/oxygenase. RuBisCO is formed from Ribulose bisphosphate (RuBP), a five-carbon ketose sugar. RuBisCO is termed the most abundant enzyme on earth. It has a unique feature where it has two active sites and can bind with CO2 and O2. The relative concentration of CO2 and O2 determines which of the two will bind to this enzyme. This enzyme is present in bundle-sheath cells that are around the vascular bundles. However, they are absent in mesophyll cells of C4 plants. The Calvin cycle occurs in the bundle sheath of C4 plants. 

Phosphoenolpyruvate is a three-carbon compound that is a primary CO2 acceptor in these mesophyll cells. Phosphoenolpyruvate is converted into a four-carbon compound called oxaloacetic acid (OAA), which is converted into malic acid. Bundle-sheath cells receive the malic acid where further steps of the Calvin cycle are completed. The malic acid undergoes decarboxylation and CO2 fixation. 

During the C4 pathway, the malic acid from mesophyll cells gets broken down in the bundle sheath. In this process, Co2 gas is released, and the intracellular concentration of CO2 increases. This prevents RuBisCO from acting as an oxygenase and functions like carboxylase. While functioning as carboxylase, it binds with the plants and carries out carboxylation in them.

Question 3. Which property of the pigment is responsible for its ability to initiate the process of photosynthesis? Why is the rate of photosynthesis higher in the red and blue regions of the spectrum of light?

Answer 3: Substances that absorb light at specific wavelengths are called pigments. This implies that different pigments absorb light of different colours. Pigments have the property of excitability. Pigments get excited by absorbing light and providing energy. They send electrons in an excited state. This light can be utilised for the next steps of photosynthesis. 

The most abundant pigment in plants is chlorophyll A. It shows optimum efficiency between red and blue wavelengths. This property is also shown by other pigments but is primarily shown by chlorophyll A. By exhibiting the property of maximum absorption and excitation during the emission of red and blue wavelengths; chlorophyll A initiates the process of photosynthesis.

Question 4. What is the basis of designating C3 and C4 pathways in photosynthesis?

Answer 4. In C3 pathways, carbon is fixed into a 3-carbon compound. It can also be given as 3-PGA. However, in C4 pathways, carbon is fixed as a four-carbon compound. 

In the C4 cycle, the carbon gets fixed into oxaloacetic acid. Hence, the number of carbon atoms in the end product will differ for different pathways. Due to the availability of different forms of carbon, the photosynthesis process is designated in C3 and C4 pathways. 

Students are suggested to read more about this on Chapter 13 Class 11 Biology important questions available on the Extramarks website.

Question 5. In which cells of the leaf, is pyruvate converted to PEP in the C4 pathway?

Answer. A plant that fixes Co2 in a molecule consisting of four carbon atoms before the initiation of the Calvin cycle during the process of photosynthesis is called a C4 plant. 

In plants following the C4 pathway, initial fixation takes place in mesophyll cells. Phosphoenolpyruvate is the primary acceptor of CO2. Co2 gets fixed in the bundle sheath during the Calvin cycle. The pyruvate is sent back where it gets converted to phosphoenolpyruvate by mesophyll cells. Hence in mesophyll cells of the leaf, pyruvate is converted to PEP in the C4 pathway.

Question 6. What are the important events and end products of the light reaction?

Answer 6. The important events occurring in the light reaction and its end products are as follows:

• Absorption of light: 

The process of light absorption is carried out by the light-harvesting complex (LHC). Different photosystems from the light-harvesting system have different pigments except for chlorophyll A. The pigments are also called antennae. These pigments increase the system’s efficiency by absorbing light of different wavelengths. The chlorophyll A molecule works as a reaction centre. By absorbing light, these chlorophyll molecules emit a pair of electrons and utilise their energy to form ATP from ADP + Pi. The process is called photophosphorylation.

• Splitting water: 

Energy absorbed from the sunlight is utilised to split water. The water molecules are converted into hydrogen ions and oxygen. At the same time, the extra electrons released after the splitting process are utilised in the conversion of NADP+ to NADPH.

              The splitting reaction of the water molecule is given as:

                       H2O⟶4H+4e−+O2↑ (b) NADP+2H+⟶NADPH

• Release of oxygen: 

Oxygen is released after the reaction in splitting the water molecule. This oxygen goes out through the stomata.

• Formation of high-energy intermediates like ATP and NADH: 

This is the final step of the light reaction. At the end of this reaction, the two energy-rich products formed are ATP and NADH. These products are utilised for further reactions. 

Question 7. How do photosynthetic bacteria such as cyanobacteria conduct photosynthesis in the absence of chloroplasts?

Answer 7. Photosynthesis occurs in plants and algae in tiny organelles called the chloroplast. These chloroplasts are located inside the cell. Cyanobacteria and photosynthetic bacteria are termed prokaryotes. They lack well-defined organelles with a membrane-bound covering around them. However, they contain photosynthetic pigments in membranous forms which are primitive. 

Being primitive, these pigments can trap solar energy and utilise it for further steps. Oxygenic cyanobacteria is a pigment more primitive in nature and contains light-harvesting pigments. They absorb carbon dioxide and release oxygen. Hence the process of photosynthesis is carried out

Question 8. The rate of photosynthesis decreases at higher temperatures. Why?

Answer 8: The process of photosynthesis is enzyme-specific. Enzymes work efficiently when they are exposed to an optimum range of temperatures. The optimum temperature range of enzymes lies between 25 to 35∘C. When exposed to higher temperatures above optimum value, the enzyme gets denatured. This hampers the photosynthetic process. As a result, under high-temperature conditions, the rate of photosynthesis decreases.

Key Topics Covered in Class 11 Biology Chapter 13

The various key topics that are covered in Class 11 Biology Chapter 13 are:

A general idea of photosynthesis: This topic gives us a general idea of the process of photosynthesis. It talks about how green plants synthesise various organic compounds using light energy. This enzyme-mediated process is anabolic. Chlorophyll, light and Co2 are essential for the process of photosynthesis.

Early experiments: This unit covers the early experiments depicted by different scientists to explain the phenomenon of photosynthesis. The experiments led by John Priestley expressed that air plays an essential role in the growth of green plants. He also discovered the use of oxygen gas. 

Julius Von Sachs explained that starch is an energy source stored in green plants. 

1. W. Engelmann discovered the various effects of different energy wavelengths on photosynthesis. It is also known as the action spectrum. 

Cornelius Van Neil showed how photosynthesis is a light-dependent process in which hydrogen is reduced to sugar.

Pigments involved in photosynthesis: The various pigments involved in photosynthesis are chlorophyll a, chlorophyll b, xanthophyll, carotenoids etc. They absorb light and transmit energy to use it for various other processes.

The electron transport system: The electron transport systems give a brief explanation of cyclic and non-cyclic photophosphorylation. It explains the transfer of electrons in a Z scheme due to its shape.

Calvin cycle: The Calvin cycle or C3 cycle is a cycle of chemical reaction in which carbon is fixed into sugars. This process occurs in the chloroplast of plant cells. The various steps involved in the Calvin cycle are carboxylation, reduction and regeneration.

C4 pathway: This pathway was given by Hatch and Slack and is observed in plants like maise, sugarcane etc. Due to the formation of a four-carbon stable compound, it is named as C4 pathway. The leaves of C4 plants exhibit Kranz’s anatomy. This pathway involves chloroplast, peroxisome and mitochondria.

Blackmans law: When more than one factor affects a chemical process, then the rate of the reaction is determined by the factor with minimal value. If the quantity changes, it directly affects the factor, and its value changes. 

Benefits of Solving Chapter 13 Biology Class 11 Important Questions

Biology focuses more on conceptual learning and understanding. Students should try to understand all concepts and chapters in lower classes to develop an easy understanding for some of the complex topics which will be covered in higher classes. We suggest students register themselves at the Extramarks website and access the study material designed by our expert science faculty. Students can improve their scores by a regular revision of the concepts and question solving, based on various topics.

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• Our experienced Biology teachers have carefully curated sets of various important questions in every chapter after an accurate study of all past years’ exam papers and NCERT books. 
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• With regular practice, students develop a familiarity with the ongoing examination pattern.
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