Solved Exercise, Bio-11, Ch-11




(1) Absorption spectrum of chlorophyll a has two peaks, showing maximum absorption of light at 430 nm and 662 nm in violet-blue and red regions, respectively.

(2) The absorption peak of chlorophyll ‘a’ is higher in red region than that of chlorophyll ‘b’, so chlorophyll ‘a’ is more effective in red part of the spectrum.


(1) Absorption spectrum of chlorophyll ‘b’ has two peaks, showing maximum absorption of light at 453 nm and 642 nm in blue and orange-red regions respectively.

(2) The absorption peak of chlorophyll ‘b’ is higher in blue region than that of chlorophyll ‘a’, so chlorophyll ‘b’ is more effective in blue part of the spectrum.

The carotenoids are present in leaves but are not obvious because they are masked by the green colour of chlorophylls. In autumn, the leaves stop food making, the chlorophyll molecules break down, and the carotenoids of yellow to orange-red colour become obvious and visible. So, the leaves appear brown before fall.

Carrots are rich in beta carotene which is converted into vitamin A by our body on eating.


Consult the textbook at page 216 — 217.

The total ATP yield from the complete oxidation of one molecule of glucose through cellular respiration is approximately 30-32 ATP molecules. Here’s a brief breakdown:

(1) Glycolysis: Generates 2 ATP molecules (net gain).

(2) Formation of Acetyl CoA: Produces 0 ATP directly.

(3) Citric Acid Cycle: Yields 2 ATP molecules (per glucose molecule; it completes two cycles).

(4) Electron Transport Chain and Oxidative Phosphorylation: Produces approximately 26-28 ATP molecules, depending on the specifics of the cell and conditions.

So, the sum is around 30-32 ATP molecules per glucose molecule through the entire process of cellular respiration.

Aerobic Respiration (Presence of Oxygen):

The hydrogen atoms carried by NADH generated in glycolysis are transported to the mitochondria.

In the mitochondria, these hydrogen atoms (electrons) enter the electron transport chain (ETC).

During the ETC, electrons move through a series of protein complexes, and their energy is used to pump protons across the inner mitochondrial membrane.

The final electron acceptor is oxygen, which combines with protons to form water.

The electron transport chain’s activity establishes a proton gradient, and ATP is synthesized through oxidative phosphorylation.

In contrast, when the available oxygen is insufficient to support aerobic respiration (anaerobic conditions), the fate of hydrogen atoms shifts:

Anaerobic Respiration (Insufficient Oxygen):

Since the electron transport chain cannot function effectively without oxygen, an alternative pathway takes place.

In muscle cells, this often leads to lactic acid fermentation.

NADH produced during glycolysis donates its electrons to pyruvate, converting it into lactic acid (lactate).

This regenerates NAD+ so that glycolysis can continue to produce ATP, but without the higher efficiency of oxidative phosphorylation.

In short, under aerobic conditions, hydrogen atoms are efficiently used in the electron transport chain to produce ATP through oxidative phosphorylation. In anaerobic conditions, such as during intense exercise, the cell resorts to fermentation (e.g., lactic acid fermentation), producing ATP without the involvement of the electron transport chain and oxygen. This process is less efficient in terms of ATP yield per glucose molecule.

The Krebs Cycle, also known as the citric acid cycle, is a series of chemical reactions that occur in the mitochondria during cellular respiration. It plays a crucial role in extracting energy from molecules derived from carbohydrates, fats, and proteins. Figure

Here’s a summary of the energy-yielding steps of the Krebs Cycle:

(1) Acetyl CoA Formation:

Acetyl CoA, derived from the breakdown of glucose, fatty acids, or amino acids, enters the cycle.

A two-carbon acetyl group combines with a four-carbon oxaloacetate to form citrate.

(2) Decarboxylation and Redox Reactions:

¨ Citrate undergoes a series of decarboxylation and redox reactions.

¨ Carbon dioxide is released, and NAD+ is reduced to NADH in multiple steps.

(3) ATP Synthesis:

GTP (guanosine triphosphate), a molecule similar to ATP, is produced through substrate-level phosphorylation.

GTP later transfers its phosphate group to ADP, forming ATP.

(4) More Redox Reactions:

FAD (flavin adenine dinucleotide) is reduced to FADH2.

More NAD+ is reduced to NADH.

(5) Regeneration of Oxaloacetate:

The remaining carbon compounds go through additional reactions, ultimately regenerating oxaloacetate to keep the cycle going.

The net result for one turn of the Krebs Cycle (which processes two acetyl-CoA molecules) includes the production of 3NADH molecules, 1 FADH2 molecule, 1 GTP (or ATP), and 2 carbon dioxide molecules. Since each glucose molecule results in two acetyl-CoA molecules entering the cycle, these numbers are doubled for the entire glucose molecule. The NADH and FADH2 molecules produced in the Krebs Cycle carry high-energy electrons to the electron transport chain for further ATP production during oxidative phosphorylation.Top of Form

Consult the textbook at page 224 — 226.

Consult the textbook at page 228 — 229.


(1) Photosynthesis is the process in which energy-poor inorganic oxidized compounds of carbon (CO2) and hydrogen (from H2O) are reduced to energy-rich carbohydrate (glucose), using light energy, absorbed by chlorophyll and some other photosynthetic pigments.

(2) In photosynthesis, carbon dioxide, water and light are the reactants, while glucose and oxygen are the products.

6CO2+6H2O+Light energy ⟶ C6H12O6 + 6O2

(3) Photosynthesis occurs only during day time.         


(1) Respiration is the process by which organisms break down complex compounds containing carbon in a way that allows the cells to harvest a maximum of usable energy.

(2) In respiration, glucose and oxygen are the reactants while carbon dioxide, water and energy are the products.

C6H12O6 +6O2 ⟶ 6CO2+6H2O+Energy

(3) Respiration goes on during day and night.

Consult the textbook at page 216 — 218.

Consult the textbook at page 219 — 221.

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