Nutrition and Photosynthesis — REET Notes
Photosynthesis and nutrition are among the most basic and regularly asked topics in REET Level 2 Science. This page explains the equation, process, and factors of photosynthesis, along with the types of autotrophic and heterotrophic nutrition, with examples in plain language.
- 0 questions in REET 2024
- Class 7-10 level content
- 7 min read
How this topic is asked in REET
To be upfront: no direct question on this topic came up in the REET 2024 paper — it saw zero (0) questions in 2024. This page is built entirely on the language of the official REET Level 2 (Maths-Science) syllabus. Since the syllabus has 'Nutrition' and 'Life Processes' sections, there's a real chance of a direct one-line MCQ on the chemical equation of photosynthesis, where it happens (chlorophyll), and the distinction between autotrophic and heterotrophic nutrition.
Types of nutrition — autotrophic and heterotrophic
Nutrition is the process by which an organism obtains food for its body's growth, energy, and repair. Based on this, living things are divided into two main groups. Autotrophic organisms — such as green plants and some bacteria — make their own food from simple inorganic substances (CO₂ and water) through photosynthesis.
Heterotrophic organisms — such as all animals and humans — cannot make their own food and depend on other organisms for it. Heterotrophic nutrition itself mainly has three modes, explained in detail further below. In other words, autotrophic organisms are able to build their own food from simple raw materials such as carbon dioxide and water using sunlight, while heterotrophic organisms have no such ability and must instead take in food that has already been made by another living being.
The process of photosynthesis
Photosynthesis is the process by which green plants use sunlight, carbon dioxide (CO₂), and water (H₂O), in the presence of chlorophyll, to make glucose (food) and oxygen. Its simple chemical equation is: 6CO₂ + 6H₂O → (in the presence of sunlight and chlorophyll) → C₆H₁₂O₆ + 6O₂. In this equation, carbon dioxide and water are the raw materials (reactants) that go in, while glucose and oxygen are what come out (products), with sunlight supplying the energy and chlorophyll making the reaction possible in the first place.
This process mainly happens in the chloroplasts inside leaf cells. The plant takes in CO₂ from the atmosphere through pores on the leaf surface called stomata, and draws water up from the soil through the roots to the leaves. The oxygen released also exits through the stomata into the atmosphere — this is evidence from the splitting (photolysis) of water that the oxygen released comes from water, not from carbon dioxide.
The two stages of photosynthesis
| Stage | Location | Main event |
|---|---|---|
| Light reaction | Thylakoid/grana (part of the chloroplast) | Photolysis of water, formation of ATP and NADPH, release of oxygen |
| Dark reaction (Calvin cycle) | Stroma (part of the chloroplast) | Using ATP and NADPH to build glucose from CO₂ |
Both stages happen inside the chloroplast, just in different parts of it.
Modes of heterotrophic nutrition
In holozoic nutrition, an organism takes solid food into its body and digests it internally — like humans and most animals. In saprophytic (saprotrophic) nutrition, an organism gets nutrition from dead and decaying organic matter — like fungi (moulds) and many bacteria, which are called decomposers. In parasitic nutrition, an organism lives on or inside another living organism (the host) and steals nutrition from it, harming the host in the process — like Cuscuta (dodder, a parasitic plant that has no chlorophyll) and the leech (an aquatic parasitic animal).
Factors affecting the rate of photosynthesis
- Light intensity
- Rate increases with more light up to a point, then levels off
- Carbon dioxide concentration
- Rate of photosynthesis rises as CO₂ rises (up to a limit)
- Temperature
- Very low or very high temperatures reduce the rate; rate is highest at the optimum temperature
- Availability of water
- Water shortage closes the stomata, which cuts down CO₂ uptake
- Presence of chlorophyll
- Without chlorophyll, converting sunlight's energy into chemical energy isn't possible
The ecological importance of photosynthesis
Photosynthesis isn't limited to plants making their own food — it's the foundation of life for almost every organism on Earth. Green plants sit at the first level of the food chain, meaning all herbivores and carnivores ultimately depend on the food plants make. Beyond that, the oxygen released during photosynthesis is what's available for the respiration of every living organism.
At the same time, plants take in carbon dioxide from the atmosphere during photosynthesis, which keeps the carbon cycle balanced and helps control, to some extent, the environmental imbalance caused by excess CO₂. This is exactly why protecting forests and green cover is considered essential for maintaining environmental balance. So the same process that makes food for a single plant also keeps the wider food chain running and keeps the air breathable for animals and humans alike, which is why this section connects the chemistry of photosynthesis to its much larger role in nature.
How to teach this to students
Classroom activity
Keep a potted plant in the dark for a few days to de-starch it, then cover part of a leaf with black paper and place it in sunlight; a few days later, test the leaf with iodine solution to show that the blue-black colour (starch) forms only in the part that received light.
Teaching aids
A chart of the chloroplast and a cross-section of a leaf, along with bringing an actual potted plant into class to show the stomata and leaf structure, works very well at Class 7-8 level.
Common misconception
Students often think plants absorb 'food' directly from the soil, when soil only supplies water and mineral salts — the plant makes its own food (glucose) through photosynthesis; this needs to be made clear. This distinction between simply absorbing water and minerals through the roots and actually making food through photosynthesis in the leaves is exactly what separates autotrophic nutrition from the way an animal obtains its food.
Assessment idea
Have students write out the photosynthesis equation and identify each component (reactant/product), and give them a worksheet to classify examples of autotrophic and heterotrophic nutrition.
Memory trick / exam tip
Remember the photosynthesis equation with the number pattern '6-6-1-6': 6CO₂ + 6H₂O → C₆H₁₂O₆ + 6O₂. And remember the word roots: 'auto' means 'self' (autotrophic) and 'hetero' means 'other' (heterotrophic) — with that, you'll never confuse the two again.
Practice questions
Question 1
In which part of a plant cell does the process of photosynthesis occur?
- Aमाइटोकॉन्ड्रिया
- Bहरितलवक (क्लोरोप्लास्ट)
- Cकेंद्रक
- Dराइबोसोम
Explanation
Photosynthesis happens in the chloroplast because that's where the green pigment chlorophyll is found, which absorbs sunlight.
Question 2
The oxygen released during photosynthesis is mainly derived from which of the following?
- Aकार्बन डाइऑक्साइड से
- Bग्लूकोज़ से
- Cजल से
- Dक्लोरोफिल से
Explanation
During the light reaction, water undergoes photolysis, which releases oxygen — this is an experimentally proven fact.
Question 3
Which of the following organisms is an example of saprophytic nutrition?
- Aअमरबेल (Cuscuta)
- Bअमीबा
- Cफफूंद (कवक)
- Dजोंक
Explanation
Fungi (moulds) get nutrition from dead and decaying organic matter, which is why they're called saprophytic, or decomposers.
Question 4
Which mode of nutrition is found in the Cuscuta (dodder) plant?
- Aस्वपोषी
- Bहोलोजोइक
- Cपरजीवी
- Dमृतजीवी
Explanation
Cuscuta has no chlorophyll; it attaches to other plants and sucks their sap, making it an example of parasitic nutrition.
Question 5
The exchange of gases (CO₂ and O₂) in a leaf mainly occurs through which structure?
- Aजड़ रोम
- Bरंध्र (स्टोमेटा)
- Cजाइलम
- Dफ्लोएम
Explanation
The tiny pores on the leaf surface, called stomata, are the main route for gas exchange and transpiration.
Question 6
The dark reaction of photosynthesis occurs in which part of the chloroplast?
- Aथाइलेकॉइड
- Bग्रेना
- Cस्ट्रोमा
- Dबाह्य झिल्ली
Explanation
The dark reaction (Calvin cycle) happens in the stroma, where the ATP and NADPH made in the light reaction are used to build glucose from CO₂.
Question 7
What is the main characteristic of autotrophic nutrition?
- Aजीव दूसरे जीवों को खाकर भोजन प्राप्त करता है
- Bजीव सरल अकार्बनिक पदार्थों से अपना भोजन स्वयं बनाता है
- Cजीव मृत पदार्थों से पोषण लेता है
- Dजीव किसी परपोषी पर निर्भर रहता है
Explanation
Autotrophic organisms make their own food from simple inorganic substances using CO₂, water, and sunlight; they don't need external food.
Question 8
A teacher covers part of a leaf with black paper, keeps it in sunlight for a few days, and then tests it with iodine. What is this experiment meant to demonstrate?
- Aपौधे में जल की मात्रा
- Bप्रकाश की उपस्थिति में ही स्टार्च (भोजन) बनता है
- Cपौधे की जड़ों की लंबाई
- Dपत्ती का रंग परिवर्तन तापमान से होता है
Explanation
The uncovered (light-exposed) part turns blue-black with iodine while the covered (dark) part doesn't form starch, which proves that light is necessary for photosynthesis.
Question 9
Which of the following factors does NOT affect the rate of photosynthesis?
- Aप्रकाश की तीव्रता
- Bकार्बन डाइऑक्साइड की सांद्रता
- Cतापमान
- Dचंद्रमा की स्थिति
Explanation
The rate of photosynthesis is affected by light intensity, CO₂ concentration, temperature, and water availability; the position of the moon has no scientific link to it.
Question 10
Which is the most appropriate example of holozoic nutrition?
- Aमनुष्य ठोस भोजन खाकर उसे शरीर के अंदर पचाता है
- Bफफूंद सड़े फल से पोषण लेती है
- Cअमरबेल दूसरे पौधे का रस चूसती है
- Dहरा पौधा प्रकाश संश्लेषण करता है
Explanation
In holozoic nutrition, an organism takes in solid food and digests it inside its body, as seen in humans and most animals.
Frequently asked questions
What is the chemical equation of photosynthesis?+
6CO₂ + 6H₂O → (in the presence of sunlight and chlorophyll) → C₆H₁₂O₆ + 6O₂ — that's the standard photosynthesis equation.
In which part of the plant does photosynthesis happen?+
It mainly happens in the chloroplasts present in leaf cells, since that's where chlorophyll is found.
What is parasitic nutrition?+
When an organism lives on or inside another organism (the host) and gets nutrition from it while harming the host, it's called parasitic nutrition — like Cuscuta (dodder).
How many REET questions have come from this topic?+
No direct question on photosynthesis and nutrition came up in REET 2024, but being a regular part of the syllabus, it stays important for upcoming exams.
Where does the oxygen released in photosynthesis come from?+
This oxygen comes from the photolysis of water (H₂O), not from carbon dioxide — this happens during the light reaction.
What is holozoic nutrition?+
When an organism takes solid food into its body and digests it internally, it's called holozoic nutrition — humans and most animals get nutrition this way.
Read next
Plant Structure and Function
REET notes: Plant Structure and Function — read this before this topic.
Respiration
REET notes: Respiration — read this after this topic.
REET Syllabus
See the full official REET Level 1 and Level 2 syllabus, subject by subject.
REET 2024 Solved Paper
All REET 2024 questions with solutions and explanations in Hindi.
Official Sources
Change Log
- 17 September 2026 — English page published — mirrors the fact-checked Hindi page, independently bilingual-accuracy checked