Difference Between Photosystem 1 And Photosystem 2: Explanation, Types, Steps And FAQs
Photosynthesis needs two light systems: Photosystem 1 (P700) and Photosystem 2 (P680). These are two pigment-protein complexes in chloroplasts. Students often ask about the difference between photosystem 1 and photosystem 2 class 11 because it is a key exam topic. PS 2 splits water to release oxygen and form ATP. PS 1 forms NADPH. Together, they power the Calvin cycle for glucose synthesis. This is why the difference between photosystem 1 and photosystem 2 class 11 is important in biology.
This Story also Contains
- Difference Between Photosystem 1 and Photosystem 2 Class 11
- What are Photosystems?
- Structure of Photosystems in Class 11 Biology
- Photosystem I (PSI) – Structure and Function
- Photosystem II (PSII) – Structure and Function
- Z‑Scheme Mechanism of Photosystem Function
- Photosystem Variations in C3, C4, and CAM Plants
- Photosystem 1 vs Photosystem 2 NEET MCQs (With Answers & Explanations)
Understanding the difference between photosystem 1 and photosystem 2 class 11 is a core topic in Photosynthesis in higher plants. It explains how plants convert solar energy into chemical energy. PS 1 is located in the stroma lamellae, and PS 2 is found in the grana thylakoids. From the difference between photosystem 1 and photosystem 2 class 11, PS 1 supports cyclic and non‑cyclic photophosphorylation. PS 2 supports non‑cyclic photophosphorylation only. These points highlight the structural and functional differences between photosystem 1 and photosystem 2 class 11, making photosynthesis easier to study and apply in exams.
Difference Between Photosystem 1 and Photosystem 2 Class 11
The difference between photosystem 1 and photosystem 2 class 11 is a key concept in photosynthesis. Both photosystems capture light energy but perform different roles. Photosystem 1 (PSI) works with pigment P700 and makes NADPH. Photosystem 2 (PSII) works with pigment P680. It splits water and makes ATP plus oxygen.
Table - Difference Between Photosystem 1 and Photosystem 2:
Feature | Photosystem 1 (PSI) | Photosystem 2 (PSII) |
|---|---|---|
Reaction Centre Chlorophyll | P700 | P680 |
Primary Function | NADPH production | Water splitting and ATP production |
Location | Stroma lamellae | Grana thylakoids |
Oxygen Evolution | No | Yes |
Electron Donor | Plastocyanin | Water |
Electron Acceptor | Ferredoxin | Plastoquinone |
Light Absorption Peaks | 700 nm | 680 nm |
Types of Light Reaction | Later in the Z-scheme | First in the Z-scheme |
Involved in Photophosphorylation | Cyclic and Non-cyclic | Non-cyclic only |
What are Photosystems?
Photosystems are the pigment-protein complexes located in the thylakoid membranes of chloroplasts. They play a critical role in capturing the energy from light to drive electron transport, which results in the formation of ATP and NADPH. These are products essential for the Calvin cycle and glucose synthesis in plants. There are two types of photosystems: Photosystem 1 and Photosystem 2, which differ in their function and composition.
Photosystems are a very basic concept both in plant physiology and bioenergetics. The significance of photosystems is not only associated with their role in the mechanism of photosynthesis, but has far-reaching applications in bioengineering or biological engineering projects like artificial photosynthesis in research, photovoltaic systems development for renewable energy, etc.
Structure of Photosystems in Class 11 Biology
The structure of photosystems is complex and highly specialised. They include the capture and conversion of light energy to the extreme. Each photosystem is the optimal structure for carrying out the light-dependent reactions as well as absorbing the light it needs during its particular range of wavelengths. This structure of photosystems explains how PSI and PSII work differently.
A photosystem consists of the following components:
Component | Functions |
Reaction centre chlorophyll | Absorbs light energy and initiates electron transfer. |
Antenna complex | Captures light energy from pigments and funnels it to the reaction centre. |
Primary electron complex | Receives excited electrons from the reaction centre. |
Protein complexes | Anchors the pigments in the membrane. |
Photosystem I (PSI) – Structure and Function
The key features of photosystem I are:
Reaction centre pigment: P700 (absorbs at 700 nm, far-red region).
Core complex: 6 to 25 chlorophyll molecules and several proteins called the core antenna complex.
Primary electron acceptor: An iron-sulfur protein (ferredoxin).
Location: Found in the stroma lamellae.
Reaction: NADP+ + H+ + 2e− → NADPH
Photosystem II (PSII) – Structure and Function
The key features of photosystem II are:
Reaction centre pigment: P680 (absorbs at 680 nm, red region).
Core complex: There is significant variation in the chlorophyll and carotenoid pigments.
Primary Electron Acceptor: Plastoquinone.
Special feature: Contains Oxygen Evolving Complex (OEC), which is responsible for water-splitting and the evolution of oxygen.
Location: Found in the thylakoid membrane, across the stack of grana.
Reaction: 2H2O → 4H+ + 4e− + O2
Z‑Scheme Mechanism of Photosystem Function
The electron transport chain of photosystems is a cascade of redox steps that process light energy, eventually converting it into the chemical energy in the coenzymes ATP and NADPH.
PS II absorbs light energy of wavelength 680 nm and transfers electrons to plastoquinone (PQ).
Water molecules split to replace lost electrons and release oxygen.
Electrons are donated to plastocyanin (PC) and the cytochrome b6f complex.
PS I absorb light by P700, electrons get excited and are transported to the primary electron acceptor, ferredoxin.
Catalysis of the formation of NADPH by the enzyme ferredoxin-NADP+ reductase.
ATP is synthesised via ATP synthase due to the proton gradient.
Photosystem Variations in C3, C4, and CAM Plants
Photosystems may have slight variations from one type of plant to another, making some more efficient or compatible with certain environments than others.
Plant Type | Description of PSI and PSII | Adaptation |
C3 Plants | Normal structure and functioning of PSI and PSII. | Moderate temperature efficiency |
C4 Plants | Enhanced light capture and ATP production. | High temperature environments |
Temporal separation of the activity of PSI and PSII | Minimises water loss |
Photosystem 1 vs Photosystem 2 NEET MCQs (With Answers & Explanations)
Important topics for NEET are:
Types of Photosystems (PSI & PSII)
Mechanism of Photosystem
Difference between photosystem 1 and photosystem 2
Practice Questions for NEET
Q1. In photosynthesis, oxygen is produced by
Photosystem I from carbon dioxide.
Photosystem II from carbon dioxide.
Photosystem I from water.
Photosystem II from water.
Correct answer: 4) Photosystem II from water.
Explanation:
The splitting of water is associated with PS II. The water splits into H+, [O], and electrons. This produces oxygen, one of the net products of photosynthesis. The water splitting complex is associated with PS II, which itself is physically located on the inner side of the membrane of the thylakoid. The electrons required to replace the removed electrons from photosystem I are provided by photosystem II.
2H2O ------ 4H+ + O2 + 4e-
Hence, the correct answer is option 4) photosystem II from water.
Q2. PS- I comprised of
a) p - 680, chlorophyll a - 695, p -700, chlorophyll b and carotenoids
b) Chlorophyll a - 670, chlorophyll a - 690, chlorophyll b and phycobilin
Both a and b are correct
Both a and b are incorrect
a is correct
b is correct
Correct answer: 3) a is correct
Explanation:
Light wavelengths have the pigments affected by them divided into two: PS-I and PS-II. PS- I comprise p - 680, chlorophyll a - 695, p -700, chlorophyll b and carotenoids. PS-II consists of chlorophyll a - 670, chlorophyll a - 690, chlorophyll b and phycobilin
Hence, the correct answer is option 3) a is correct.
Q3. ____________is a light-harvesting complex made up of proteins and numerous chlorophyll a, chlorophyll b, and carotenoid molecules embedded in the thylakoid membrane of plants.
Antenna Complex
Reaction Centers
Energy-fixing reaction
Chemiosmosis
Correct answer: 1) Antenna Complex
Explanation:
Antenna Complex is a light-harvesting complex made up of proteins and numerous chlorophyll a, chlorophyll b, and carotenoid molecules embedded in the thylakoid membrane of plants.
The photosystem's reaction centre is where energy from absorbed light is directed to excite the molecules of chlorophyll.
Moving ions across a semipermeable membrane to produce ATP is known as chemiosmosis. Chemiosmosis is the process by which hydrogen ions move from the thylakoid space into the stroma via ATP synthase during photosynthesis.
Hence, the correct answer is option 1) Antenna complex is a light-harvesting complex made up of proteins and numerous chlorophyll a, chlorophyll b, and carotenoid molecules embedded in the thylakoid membrane of plants.
Frequently Asked Questions (FAQs)
Photosystem 1 produces mainly NADPH, while photosystem 2 facilitates the splitting of water and the formation of ATP.
PSII has the oxygen-evolving complex. It splits water and produces oxygen, which PSI cannot do.
PSI absorbs light at 700 nm (P700). PSII absorbs light at 680 nm (P680). PSI makes NADPH, and PSII makes ATP and oxygen.
PSII initiates the chain that produces ATP and PSI yields electrons to NADP+ to generate NADPH.
PSI best absorbs light at 700 nm, while PSII best absorbs light at 680 nm.
