Which one of the following is the process involved in photosynthesis?
Contents12
- APotential energy is released to form free energy.
- BFree energy is converted into potential energy and stored.
- CFood is oxidized to release carbon dioxide and water.
- DOxygen is taken, and carbon dioxide and water vapour are given out.
Show answer
Answer: (B) Free energy is converted into potential energy and stored.
Photosynthesis is the process where plants CAPTURE light energy (free energy from sunlight) and CONVERT it into chemical potential energy stored in glucose (food).
The equation:
6CO2 + 6H2O + Light energy → C6H12O6 + 6O2.
So energy goes FROM free/light energy → TO stored potential energy.
Why other options are wrong:
(a) Releasing potential energy = respiration (the reverse process).
(c) Oxidising food to release CO2 and water = respiration, not photosynthesis.
(d) Taking in O2 and releasing CO2 = also respiration.
Trick: Photosynthesis STORES energy. Respiration RELEASES energy. They are opposite processes.
Photosynthesis converts free energy from sunlight into chemical potential energy stored as glucose, making it the fundamental energy storage process for all life on Earth.
UPSC is testing whether students can distinguish photosynthesis (energy storage) from respiration (energy release) - these are opposite processes that students frequently confuse.
Photosynthesis Process & Mechanism
Environment photosynthesis free energy potential energy
Photosynthesis: Energy Conversion & Chemical Equation
Photosynthesis converts free energy (sunlight) into potential energy (glucose)
Chemical equation: 6CO2 + 6H2O + Light → C6H12O6 + 6O2
Occurs in chloroplasts using chlorophyll pigment
Two stages: Light reactions (capture energy) + Calvin cycle (fix carbon)
What Is Photosynthesis
Photosynthesis is the process where plants capture light energy from the sun and convert it into chemical energy stored as glucose. This is energy conversion from free energy (available light) to potential energy (stored in chemical bonds).
Two Stages of Photosynthesis
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Light Reactions (Thylakoids)**
**Chlorophyll** absorbs light energy → splits **H2O** → releases **O2** → produces **ATP** and **NADPH**`"]
s2["`**Calvin Cycle (Stroma)**
Uses **ATP** and **NADPH** → fixes **CO2** → produces **glucose** (C6H12O6)`"]
s1 --> s2Question Connection
The question tests energy conversion direction. Option B correctly identifies that photosynthesis converts free energy (sunlight) into potential energy (glucose). Options A, C, and D describe cellular respiration - the opposite process.
Trap: Confusing photosynthesis with cellular respiration - they are opposite processes
Remember: Photosynthesis stores energy, respiration releases energy
Gas exchange trick: Photosynthesis takes in CO2, gives out O2. Respiration does the reverse
Energy direction: Free energy → Potential energy (photosynthesis). Potential → Free energy (respiration)
Cellular Respiration
Environment oxidized carbon dioxide oxygen
Cellular Respiration: Energy Release from Food
Cellular respiration releases stored energy from glucose to produce ATP
Equation: C6H12O6 + 6O2 → 6CO2 + 6H2O + ATP
Takes in oxygen, releases carbon dioxide and water
Opposite process to photosynthesis
Energy Release Process
Cellular respiration is how organisms break down glucose (food) to release stored potential energy as ATP. This involves oxidizing food molecules in the presence of oxygen.
Photosynthesis vs Cellular Respiration
Process | Energy Direction | Takes In | Releases | Location |
|---|---|---|---|---|
Photosynthesis | Stores energy | CO2 + H2O + Light | O2 + Glucose | Chloroplasts |
Cellular Respiration | Releases energy | O2 + Glucose | CO2 + H2O + ATP | Mitochondria |
Stages of Cellular Respiration
%%{init: {"flowchart": {"wrappingWidth": 460}}}%%
flowchart TD
s1["`**Glycolysis (Cytoplasm)**
**Glucose** broken into **pyruvate** → small ATP production`"]
s2["`**Krebs Cycle (Mitochondria)**
**Pyruvate** oxidized → produces **CO2** + electron carriers`"]
s3["`**Electron Transport Chain**
**O2** used as final acceptor → major **ATP** production + **H2O**`"]
s1 --> s2
s2 --> s3Wrong options C & D in the question describe respiration, not photosynthesis
Gas confusion: Plants do both processes - photosynthesis (day) and respiration (24/7)
Energy trap: Don't confuse energy storage (photosynthesis) with energy release (respiration)
Energy Types in Biology
Science And Technology free energy potential energy
Free Energy vs Potential Energy in Biological Systems
Free energy = available energy that can do work (like sunlight)
Potential energy = stored energy in chemical bonds (like glucose)
Photosynthesis converts free → potential energy
Respiration converts potential → free energy (as ATP)
Energy Definitions
Free energy is readily available energy that can immediately do work - like light from the sun or heat. Potential energy is stored energy held in chemical bonds, positions, or structures that can be released later.
Energy Types in Living Systems
Energy Type | Form | Examples | Biological Role |
|---|---|---|---|
Free Energy | Available/Active | Sunlight, Heat, ATP | Powers immediate biological work |
Potential Energy | Stored/Inactive | Glucose, Starch, Fats | Energy storage for future use |
Kinetic Energy | Movement | Molecular motion | Heat generation, transport processes |
Energy Conversions in Plants
# Plant Energy Transformations
## Input Sources
- **Sunlight** (free energy)
- **CO2** from air
- **H2O** from roots
## Conversion Process
- **Photosynthesis**
- **Chloroplast reactions**
- **Enzyme catalysis**
## Storage Forms
- **Glucose** (immediate)
- **Starch** (short-term)
- **Cellulose** (structural)
## Energy Release
- **Cellular respiration**
- **ATP production**
- **Metabolic work**UPSC loves energy direction: Remember photosynthesis captures and stores, respiration releases and uses
Free vs Potential confusion: Free = available now, Potential = stored for later
Don't mix up: Light energy is free energy, not potential energy