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All questions of Photosynthesis & Respiration for Grade 12 Exam

The net gain of ATP in glycolysis is__________.
  • a)
    4
  • b)
    8
  • c)
    2
  • d)
    6
Correct answer is option 'B'. Can you explain this answer?

Lalit Yadav answered
Glycolysis is the first stage of the breakdown of glucose in the cell. 
During glycolysis 2 ATP molecules are used up and four ATP molecules are generated. In the entire process of glycolysis, two NADH₂ molecules are also generated. When these molecules undergo ETS they will form 3 ATP per NADH₂  which means 6 ATP.
Therefore the total ATP that are forming are 10 and as 2 ATP is used up the net gain will be 8.
So, the correct option is '8'
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Respiration is
a)Amphibolic process
b)Catabolic process
c)Anabolic process
d)Both anabolic and catabolic
Correct answer is option 'A'. Can you explain this answer?

Geetika Shah answered
Because the respiratory pathway is involved in both anabolism and catabolism, it would hence be better to consider the respiratory pathway as an amphibolic pathway rather than as a catabolic one.

In plants, the gaseous exchange take place in
a) Stomata
b) Roots
c) Stems
d) Lenticles
  • a)
    a and b
  • b)
    a and d
  • c)
    b and d
  • d)
    b and c
Correct answer is option 'B'. Can you explain this answer?

Geetika Shah answered
Plants unlike animals have no special systems for breathing or gaseous exchange. Stomata and lenticels allow gaseous exchange by diffusion.

Which of the following is not correct about the Krebs cycle?
  • a)
    It starts with a six-carbon compound.
  • b)
    It occurs in mitochondria.
  • c)
    It is also called the citric acid cycle.
  • d)
    The intermediate compound which links glycolysis with the Krebs cycle is malic acid.
Correct answer is option 'D'. Can you explain this answer?

Om Desai answered
  1. Krebs cycle is also known as the citric acid cycle because this reaction starts with the six-carbon compound which is citric acid. It occurs in the mitochondrial matrix.
  2. Krebs cycle is a closed-loop cycle. And each loop of the cycle generates a molecule of ATP. This cycle consists of eight steps which include redox, dehydration, hydration, and decarboxylation reactions. It is an aerobic pathway because NADH is produced and the electrons released are used up in the next cycle which uses oxygen.
  3. The process of the cycle starts with the condensation of acetyl- CoA with oxaloacetate.
  4. This reaction is controlled by the amount of ATP present.
  5. If the ATP level increases then the rate of the reaction decreases and vice versa. After glycolysis, the pyruvate is then converted into acetyl CoA which enters the citric acid cycle.
  6. The Krebs cycle is the pathway that all organisms use to generate energy. The intermediate compound that links pyruvate to the Krebs cycle is Acetyl CoA.
  7. So, the answer is option (B) ‘the intermediate compound which links glycolysis with the Krebs cycle is malic acid’.

The site of glycolysis is
  • a)
    Chloroplast
  • b)
    Cytoplasm
  • c)
    Mitochondrial inner membrane
  • d)
    Mitochondrial matrix
Correct answer is option 'B'. Can you explain this answer?

Geetika Shah answered
Glycolysis takes place in the cytoplasm of a cell as the first step in cellular respiration of the Kreb’s cycle. When glycolysis occurs, it breaks down glucose into pyruvic acids in the cytoplasm.

Fermentation is
  • a)
    Excretory process
  • b)
    Aerobic respiration
  • c)
    Incomplete oxidation
  • d)
    Anaerobic respiration
Correct answer is option 'D'. Can you explain this answer?

Vijay Bansal answered
Fermentation normally occurs in an anaerobic environment. In the presence of O2, NADH and pyruvate are used to generate ATP in respiration. Some fermentation processes involve obligate anaerobes, which cannot tolerate oxygen.

The splitting of water molecules is associated with
  • a)
    PS II
  • b)
    PS I
  • c)
    Cyclic phosphorylation
  • d)
    Non-cyclic phosphorylation
Correct answer is option 'A'. Can you explain this answer?

Swara Sarkar answered
This is achieved by electrons available due to splitting of water. The splitting of water is associated with the PS II; water is split into H+, [O] and electrons.

The colour of light not utilized during photosynthesis is :–
  • a)
    Violet
  • b)
    Green
  • c)
    Red
  • d)
    Blue
Correct answer is option 'B'. Can you explain this answer?

Jeeshan Ahmed answered
The only color in the visible spectrum not used at all by green plants would be green because that is the light that is getting reflected off of the plant.

The dark reaction in photosynthesis is called so because
  • a)
    It does not depend on light energy.
  • b)
    It can occur in dark also.
  • c)
    It cannot occur during day light.
  • d)
    It occurs more rapidly at night.
Correct answer is option 'A'. Can you explain this answer?

Anshika Shah answered
Photosynthesis is a process by which green plants and some other organisms convert light energy into chemical energy stored in the bonds of glucose or other organic compounds. Photosynthesis occurs in two stages: the light-dependent reactions and the light-independent reactions. The light-dependent reactions occur in the thylakoid membranes of chloroplasts and produce ATP and NADPH, which are used in the light-independent reactions. The light-independent reactions occur in the stroma of the chloroplasts and use the ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into glucose.

The light-independent reactions are also known as the Calvin cycle or the dark reactions because they do not require light energy to occur. The dark reactions can occur at any time, day or night, as long as the necessary enzymes and substrates are present.

Why is the dark reaction in photosynthesis called so?

The dark reaction in photosynthesis is called so because it does not depend on light energy. The term "dark" in this context does not mean that the reactions only occur in the dark. Instead, it refers to the fact that the reactions can occur in the absence of light. The dark reactions can occur during the day or night, as long as the necessary enzymes and substrates are present. The dark reactions use the ATP and NADPH produced in the light-dependent reactions to fix carbon dioxide into glucose.

Conclusion

The dark reaction in photosynthesis is an important process that occurs in the stroma of chloroplasts in green plants and some other organisms. The term "dark" in this context refers to the fact that the reactions do not require light energy to occur, and can occur at any time, day or night, as long as the necessary enzymes and substrates are present.

During anaerobic respiration less energy is produced than aerobic respiration because
  • a)
    Incomplete oxidation of glucose takes place
  • b)
    It takes place is micrograms
  • c)
    It takes place in inert medium
  • d)
    Glucose is not available
Correct answer is option 'A'. Can you explain this answer?

Kuldeep Kuldeep answered
Option a is correct. Because, in Anaerobic Respiration, respiration takes place on the absence of oxygen. Iteans, the oxidation of pyruvate takes place in the absence of oxygen to release CO2, Ethanol along with the release of Energy. Here, in Anaerobic Respiration, Water is not yet released due to the absence of oxygen. So, there will be incomplete oxidation of glucose takes place.

The TCA cycle is named after
  • a)
    Robert Emerson
  • b)
    Melvin Calvin
  • c)
    Embden
  • d)
    Hans Krebs
Correct answer is option 'D'. Can you explain this answer?

Hitakshi Tamta answered
*Tricarboxylic acid (TCA) cycle is a series of enzyme-catalyzed chemical reactions used by all aerobic organisms to release the stored energy........ *It is a part of cellular respiration........ *It is also called as citric acid cycle or Krebs cycles which is named after it's discoverer Hans Krebs..... Thus, the correct answer is option 'D'.

In the half-leaf experiment of photosynthesis, KOH solution is used because​
  • a)
    It provides O2 to the leaf.
  • b)
    It provides moisture to the leaf.
  • c)
    It helps in CO2 fixation.
  • d)
    It absorbs CO2.
Correct answer is option 'D'. Can you explain this answer?

Krishna Iyer answered
KOH (Potassium Hydroxide) absorbs carbon dioxide. The leaf inside the bottle containing KOH solution does not become blue-black when compared with the leaf which is exposed to atmospheric air. This shows that carbon dioxide is necessary for photosynthesis.

Can you explain the answer of this question below:

Which range of wavelength (in nm) is called photosynthetically active radiation (PAR)?

  • A:

    400-700

  • B:

    760-10,000

  • C:

    100-390

  • D:

    390-430

The answer is a.

Krishna Iyer answered
Photosynthetically active radiation. Photosynthetically active radiation, often abbreviated PAR, designates the spectral range (wave band) of solar radiation from 400 to 700 nanometers that photosynthetic organisms are able to use in the process of photosynthesis.

F0−F1 particles participate in the synthesis of
  • a)
    NADPH
  • b)
    FADH2
  • c)
    ADP
  • d)
    ATP
Correct answer is option 'D'. Can you explain this answer?

Lalit Yadav answered
  • Oxysomes refer to small round structures present within the folds of the cristae of the inner mitochondrial membrane. It is also known as F0-F1 particles.
  • F0 and F1 particles are found in the inner mitochondrial region and are attached to the cristae and help in ATP production and oxidation.

The process common to both aerobic and anaerobic organisms is
  • a)
    TCA cycle
  • b)
    Krebs cycle
  • c)
    Glycolysis
  • d)
    Glyoxylate cycle
Correct answer is option 'C'. Can you explain this answer?

Shreya Gupta answered
Glycolysis ( process of break down of glucose into pyruvic acid ) is the process common to both aerobic and anaerobic respiration. 

 Element which helps in electron transport in the process of photosynthesis is
  • a)
    Zinc
  • b)
    Molybdenum
  • c)
    Boron
  • d)
    Mangnese
Correct answer is option 'D'. Can you explain this answer?

Preeti Iyer answered
During noncyclic electron flow the electron hole in P-680 is filled by electrons obtained by photolysis of water. As a result, there is an evolution of oxygen and the electron move through Mn-protein bound to PS II. In this transport Mn++ is oxidised to Mn+++ and then reduced to Mn++ in a cyclic manner. The manganese thus transfers electrons from water to photosystem II and thus plays an important role in electron transport in the process of photosynthesis.

The by product of photosynthesis is
  • a)
    CO2
  • b)
    Oxygen
  • c)
    Energy
  • d)
    Sugar
Correct answer is option 'B'. Can you explain this answer?

Rajni Kokate answered
6(CO2) + 12(H2O) ----------> C6H12O6 +6(O2) + 6H2O
In photosynthesis phototrophs synthesize glucose and water and evolve O2 as by product

Most of the enzymes of the TCA cycle are present in
  • a)
    Intermembrane space of mitochondria
  • b)
    Mitochondrial matrix
  • c)
    Inner membrane of mitochondria
  • d)
    Cytoplasm
Correct answer is option 'B'. Can you explain this answer?

Anjali Iyer answered
Mitochondrial matrix.
In the mitochondrion, the matrix is the space within the inner membrane. ... The enzymes in the matrix facilitate reactions responsible for the production of ATP, such as the citric acid cycle, oxidative phosphorylation, oxidation of pyruvate and the beta oxidation of fatty acids.

Aerobic respiration is common in
  • a)
    Yeast
  • b)
    Higher organisms
  • c)
    Prokaryotes
  • d)
    Unicellular eukaryotes
Correct answer is option 'B'. Can you explain this answer?

Rajesh Banerjee answered
Aerobic respiration is a process in which organisms break down glucose to produce energy in the presence of oxygen. This process is common in higher organisms, which include animals and plants.

Reasons why aerobic respiration is common in higher organisms:

1. Energy production: Higher organisms require a lot of energy to carry out their daily activities, such as movement, reproduction, and growth. Aerobic respiration provides a large amount of energy in the form of ATP, which is used for these activities.

2. Efficiency: Aerobic respiration is a highly efficient process, producing a large amount of energy from each glucose molecule. This makes it an ideal process for higher organisms, which require a lot of energy to survive.

3. Oxygen availability: Higher organisms have complex respiratory systems that allow them to take in oxygen and distribute it throughout their bodies. This makes it possible for them to carry out aerobic respiration, which requires oxygen.

4. Evolution: Higher organisms have evolved to carry out aerobic respiration as a means of producing energy. This process has been refined over millions of years of evolution, making it an integral part of their biology.

In summary, aerobic respiration is common in higher organisms because it provides a large amount of energy, is highly efficient, requires oxygen, and has evolved as a means of energy production.

Incomplete oxidation of glucose into pyruvic acid with several intermediate steps is known as[1988]
  • a)
    TCA-pathway
  • b)
    glycolysis
  • c)
    HMS-pathway
  • d)
    Krebs cycle
Correct answer is option 'B'. Can you explain this answer?

Maheshwar Saini answered
Glycolysis involves the process of partial oxidation of glucose or similar hexose sugar into two molecules of pyruvic acid through a series of ten enzyme mediated reactions. It occurs in cytoplasm.

The Calvin cycle leads to reduction of​
  • a)
    RUBP
  • b)
    RUMP
  • c)
    O2
  • d)
    CO2
Correct answer is option 'D'. Can you explain this answer?

Rajat Kapoor answered
In fixation, the first stage of the Calvin cycle, light-independent reactions are initiated; CO2 is fixed from an inorganic to an organic molecule. In the second stage, ATP and NADPH are used to reduce 3-PGA into G3P; then ATP and NADPH are converted to ADP and NADP+, respectively.

In higher plants, the shape of the chloroplast is
  • a)
    Reticulate
  • b)
    Girdle-shaped
  • c)
    Discoid
  • d)
    Cup-shaped
Correct answer is option 'C'. Can you explain this answer?

EduRev JEE answered
Chloroplasts are the green plastids which take part in photosynthesis and temporary or  permanent storage of starch. These are discoid (disc-shaped) in higher plants with diameter of 4-6 μm and thickness of 2-4.μm.

Select the incorrectly matched pair with regard to the C4 cycle.​
  • a)
    Primary CO2 fixation product – PGA
  • b)
    C4 plant – Maize
  • c)
    Primary CO2 acceptor – PEP
  • d)
    Site of initial carboxylation – Mesophyll cells
  • e)
    Location of enzyme RuBisCO – Bundle sheath cells
Correct answer is option 'A'. Can you explain this answer?

Vignesh answered
The primary CO
2 
fixation product in C
4 
plants is oxaloacetic acid, which is converted to malic acid or aspartic acid that is transported to the bundle sheath cells where the acid is decarboxylated and the CO
2 
thus released enters the Calvin cycle.

The C4 plants show higher rate of photosynthesis in
  • a)
    Optimum temperature
  • b)
    High temperature 
  • c)
    Absence of temperature
  • d)
    Low temperature
Correct answer is option 'B'. Can you explain this answer?

Shreya Saini answered
C4 planets show higher rate of photosynthesis in higher temperatures because there is no energy loss in photorespiration in these plants, i.e.at high temperature they show full efficiency of production.

Mitochondria are called the powerhouses of the cell. Which of the following observations support this statement?
  • a)
    Mitochondria are found in almost all plant and animal cells.
  • b)
    The enzymes of the Krebs cycle and the cytochromes are found in mitochondria.
  • c)
    Mitochondria synthesise ATP.
  • d)
    Mitochondria have a double membrane.
Correct answer is option 'C'. Can you explain this answer?

Riya Banerjee answered
Mitochondria (singular - Mitochondrion) are known as the powerhouse of the cell because they are responsible for the release of energy from food ,i.e, cellular respiration. This energy is released in the form of ATP (adenosine triphosphate), the energy currency of the cell.
While the cells release 2 ATP, mitochondria releases 34 ATP which adds up to 36 ATP. Since a major portion of the ATP is released by mitochondria, they are called the powerhouse of the cell.

When fats are the respiratory substrate, the value of RQ would be​
  • a)
    Approx. 0.7
  • b)
    Approx. 1.0
  • c)
    More than 1.0
  • d)
    None of the above
Correct answer is option 'A'. Can you explain this answer?

Surbhi Mishra answered
Ans.

The respiratory quotient (or RQ or respiratory coefficient), is a dimensionless number used in calculations of basal metabolic rate (BMR) when estimated from carbon dioxide production. ... If metabolism consists solely of lipids, the Respiratory Quotient is 0.7, for proteins it is 0.8, and for carbohydrates it is 1.0.

Who described the first action spectrum for photosynthesis?
  • a)
    T. W. Engelmann
  • b)
    Cornelius van Niel
  • c)
    Joseph Priestley
  • d)
    Julius von Sachs
Correct answer is option 'A'. Can you explain this answer?

Arun Khanna answered
Engelmann used a prism to split light into its spectral components, and then illuminated a green alga, Cladophora, placed in a suspension of aerobic bacteria. The bacteria were used to detect the sites of oxygen evolution.

He observed that bacteria mainly accumulated in the region of blue and red light of the split spectrum, thus giving the first action spectrum of photosynthesis.

End product of glycolysis is [1990]
  • a)
    acetyl CoA
  • b)
    pyruvic Acid
  • c)
    glucose 1-phosphate
  • d)
    fructose 1-phosphate
Correct answer is option 'B'. Can you explain this answer?

Shivani Tiwari answered
Pyruvic acid is formed as an end product of glycolysis, a process that breaks down glucose (a six-carbon molecule) into two molecules of pyruvate (a three-carbon molecule) and simultaneously yields a small net gain of the universal energy storage molecule adenosine triphosphate (ATP), used to power cellular function.

Anaerobic respiration in muscles gives rise to​________.
  • a)
    C2H5OH
  • b)
    CH3COCOOH
  • c)
    CH3COOH
  • d)
    C3H6O3 
Correct answer is option 'D'. Can you explain this answer?

Janhavi Khanna answered
Anaerobic Respiration in Muscles

- Anaerobic respiration is a type of respiration that occurs in the absence of oxygen.
- It is also called fermentation and is an inefficient process that produces very little ATP (energy) compared to aerobic respiration.
- Anaerobic respiration in muscles occurs when there is not enough oxygen available to meet the energy demands of the muscles.
- As a result, the muscles switch to anaerobic respiration to produce ATP.
- The end product of anaerobic respiration in muscles is lactic acid (C3H6O3).

Lactic Acid

- Lactic acid is a three-carbon molecule that is produced by the anaerobic breakdown of glucose.
- It is a byproduct of anaerobic respiration in muscles and is responsible for muscle fatigue and soreness.
- Lactic acid can accumulate in the muscles during intense exercise and can cause a burning sensation.
- It is eventually transported to the liver where it is converted back into glucose through a process called gluconeogenesis.

Conclusion

- Anaerobic respiration in muscles produces lactic acid as the end product.
- Lactic acid is responsible for muscle fatigue and soreness.
- It is eventually converted back into glucose in the liver.

Energy obtained by a cell from catabolic reaction is stored immediately in the form of
  • a)
    Pyruvic acid
  • b)
    Glucose
  • c)
    ATP
  • d)
    DNA
Correct answer is option 'C'. Can you explain this answer?

Hitakshi Tamta G answered
The energy obtained by a cell from catabolic reactions is stored immediately in the form of ATP, as it is the energy currency of the cell.
Hence, option 'C' is correct.

Chapter doubts & questions for Photosynthesis & Respiration - Biology for Grade 12 2025 is part of Grade 12 exam preparation. The chapters have been prepared according to the Grade 12 exam syllabus. The Chapter doubts & questions, notes, tests & MCQs are made for Grade 12 2025 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests here.

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