Chapter 19, Problem 3P

Interpretation Introduction

(a)

Interpretation:

The most suitable matching pair should be selected.

Concept introduction:

Photosynthesis is the process by whichenergy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction.

Answer to Problem 3P

a) Light reactions − generates ATP, NADPH and O₂

Explanation of Solution

Photosynthesis consists of two main stages - light reaction and dark reaction.

In light reaction, two photo systems (PS I and PS II) participate.

PSII absorb680 nmwavelengthof sunlight. After absorbing energy from the sunlight, chlorophyll a molecule in PSII release excited high energy electrons. The electron defect occurred in PSII is fulfilled by hydrolysis of water which produce O₂as by product. Consider this as reaction 1.

${\text{2H}}_{\text{2}}\text{O}\to {\text{4H}}^{\text{+}}{\text{+4e+O}}_{\text{2}}$

Theelectronsfrom reaction I are used to fulfill the electron defect inphotosystem. The high energy electrons go through the series of electron acceptorsto assimilate this energy. ADP takes up the energy of these electrons to form ATP. This is known as photophosphorylation.

${\text{ADP+PO}}^{\text{3-}}{}_{\text{4}}\stackrel{\text{Energy from electrons}}{\to }\text{ATP}$

Similar reaction occurs in PS I. PSI absorb 700 nm wavelength of sunlight, followed by high energy electrons release. Like PSII, the high energy electron goes through a series of electron acceptors. At the end of this series NADP+accepts the electron to form NADPH. Consider this as reaction 2.

${\text{2e+2H}}^{\text{+}}{\text{+2NADP}}^{\text{+}}\to \text{2NADPH}$

$H^{+}$ ions used in this reaction are from reaction 1

Figure 1: A diagrammatic representation of light reaction

Interpretation Introduction

(b)

Interpretation:

The most suitable matching pair should be selected.

Concept introduction:

Photosynthesis is the process by which energy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction.

Answer to Problem 3P

b) Chloroplasts − cellular location of photosynthesis

Explanation of Solution

Chloroplast is the organelle in a plant cell which is responsible for conducting photosynthesis. Chloroplast consists of a double membrane structure known as thylakoid. Thylakoids are the primary site for light reaction which assimilate the light energy to produce the energy moieties, ATP and NADPH. These energy molecules are used in the dark reaction to produce six carbon sugar molecule and oxygen as byproduct. The dark reaction takes place in the stroma of chloroplast.

Interpretation Introduction

(c)

Interpretation:

The most suitable matching pair should be selected.

Concept introduction:

Photosynthesis is the process by which energy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction.

Answer to Problem 3P

c) Reaction Center − site of photoinduced charge separation.

Explanation of Solution

In light reaction, two photosystems called PS I and PS II participate.

In these photosystems, the reaction center is a special chlorophyll a molecule, chlorophyll a. The process happening in these two systems is quite similar.

PSII absorbs light energy of 680 nm wavelength of light while PS I absorb energy of 700 nm wavelength of light, followed by releasing high energy electrons.

When the chlorophyll a molecule releases its electrons, the chlorophyll molecule gets positively charged. It generates the charge separation at the chlorophyll molecules. This charge separation is due to the absorbed light energy. So, it is known as photo induced charge separation.

A photosynthetic reaction center is a complex structural view. It is composed of several proteins, pigments and other co-factors. It is a collection of CF₁− CF₀ complex. This is responsible for executing the primary energy conversion reactions related to photosynthesis. Molecular excitations occur at the reaction center give rise to electron transfer reactions along the path of a series of protein-bound co-factors like chlorophylls.

Interpretation Introduction

(d)

Interpretation:

The most suitable matching pair should be selected.

Concept introduction:

Photosynthesis is the process by which energy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction.

Answer to Problem 3P

d) Light-harvesting complex- Primary photosynthetic pigment

Explanation of Solution

Photosynthesis is the process by which energy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction. In the light reaction, the sunlight is assimilated, and the energy is stored in the biomolecules like ATP and NADPH.

The photosynthetic pigments such as chlorophyll a and b, xanthophyll and carotenoids form the two photosystems (Photosystem I and II) which absorbs different wavelength of light. Chlorophyll a form the reaction center of the photosystems.

Interpretation Introduction

(e)

Interpretation:

The most suitable, matching pair of answers should be selected.

Concept introduction:

A light-harvesting complex is a collection of subunit proteins. These subunit proteins are again a part of largersupercomplex of a photosystem.

Answer to Problem 3P

e) Light − harvesting complex − uses resonance energy transfer to reach the reaction center

Explanation of Solution

A light-harvestingcomplex (also known as photosystem)is a collection of proteins.The light harvest system is used by plants and photosynthetic bacteria to collect energy from sun light. During photosynthesis, the reaction centers absorbs light energy of 680nm and 700 nm sun light. This reaction center is a special chlorophyll a molecule. Light harvesting complex assist on this energy absorbance.

Light-harvesting complexes show a huge variation among the different photosynthetic organisms. The complexes consist of proteins and photosynthetic pigments like chlorophylls and surround by the photosynthetic reaction center. This special structural adaptation is to focus energy, absorbed from the photons toward the reaction center as resonance transfer.

Figure 3: close view of a light harvesting complex

Interpretation Introduction

(f)

Interpretation:

The most suitable matching pair of answers should be selected.

Concept introduction:

Photosynthesis is the process by which energy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction.

For the light reaction two photosystems called PS I and PS II participate.

Answer to Problem 3P

f) Photosystem I − powers the formation of NADPH

Explanation of Solution

Photosystem is a collection of pigment moleculesand is known as light harvest complex. In photosystem I, PS I absorb energy from 700 nm photons of sunlight, followed by releasing high energy electrons. The electron goes through a series of electron acceptors. At the end of this series NADP reacts with electron to form NADPH.

$2e+2H^{+}+2NADP\to 2NADPH$

$H^{+}$ s are from reaction of water oxidation which is happening photosystem two.

Figure 4: Figure 5: Diagrammatic representation of reactions happen in photosystem one

Interpretation Introduction

(g)

Interpretation:

The most suitable, matching pair of answers should be selected.

Concept introduction:

Photosynthesis is the process by which energy of the sunlight is stored as chemical energy. The process takes place in the chloroplast of the plant cells in two main stages - light reaction and dark reaction.

For the light reaction two photosystems called PS I and PS II participate.

Answer to Problem 3P

g) Photosystem II − Transfer electron from H₂O to P₆₈₀.

Explanation of Solution

For the light reaction two photosystems called PS I and PS II participate. PSII absorbs light energy of 680 nm wavelength of sun light After absorbing energy the chlorophyll a molecule in PSII releases excited, high energy electrons. To fulfill the electron defect occurred at PSII water hydrolysistakes place at PSII.

$\begin{array}{l}2H_{2}O\to 4H^{+}+4e+O_2\\ \end{array}$

These released electrons are used to overcome the electron defect in photosystemII.

Figure : Diagrammatic representation of reactions happen in photosystem one

Interpretation Introduction

(h)

Interpretation:

The most suitable, matching pair of answers should be selected.

Concept introduction:

The chloroplast cytochrome bf complex is a collection of multiple numbers of subunit proteins.

Answer to Problem 3P

h) Cytochrome bf complex − pumps protons

Explanation of Solution

The chloroplast cytochrome bf complex is a collection of multiple numbers of subunit proteins. These subunit proteinsconsist of four polypeptides. These four types are

1. Cytochrome f
2. Heme containing cytochrome b 6
3. Rieske iron-sulfur protein
4. 17 kD polypeptide

Most mechanisms suggest that the transfer of a single reducing equivalent which is an electron results in the translocation of two protons across the membrane. So, this complex mainly workes as a proton pump.

Interpretation Introduction

(i)

Interpretation:

The most suitable, matching pair of answers should be selected.

Concept introduction:

Photosynthesis is the process by storing energy of sunlight as chemical energy in glucose. Process happens in the chloroplast of a plant cell. Photosynthesis happens via two main stages as light reaction and dark reaction.

Answer to Problem 3P

i) Water -oxidizing complex- site of oxygen generation.

Explanation of Solution

For the light reaction, two photosystems called PS I and PS II participate. PSII absorbs light energy of 680 nm wavelength of sun light After absorbing energy the chlorophyll a molecule in PSII releases excited, high energy electrons. To fulfill the electron defect occurred at PSII water hydrolysis takes place at PSII.

$\begin{array}{l}2H_{2}O\to 4H^{+}+4e+O_2\\ \end{array}$

The hydrolysis of water is taken care of by water oxidizing complex. Thereleased electrons are used to overcome the electron defect in photosystem II.

Interpretation Introduction

(j)

Interpretation:

The most suitable matching pair should be selected.

Concept introduction:

A photosynthetic reaction center is a complex structural. It is composed of several proteins, pigments and other co-factors. It is a collection of CF₁− CF₀complex.

Answer to Problem 3P

j) ATP synthase − CF₁- CF₀ complex

Explanation of Solution

A photosynthetic reaction center is a complex structural. It is composed of several proteins, pigments and other co-factors.It is a collection of CF₁− CF₀ complex. This is responsible for executing the primary energy conversion. The energy is stored in the form of ATP via this complex.