Nutrition in Plants and Photosynthesis
Nutrition in Plants and Photosynthesis
Photosynthesis is the single most examined process in the biology block and gives 2 questions. The equation, the conditions and the modes of nutrition are the three areas asked, and the direction of the gas exchange is where candidates most often slip.
Modes of Nutrition
| Mode | Meaning | Examples |
|---|---|---|
| Autotrophic | Makes its own food | Green plants |
| Heterotrophic | Depends on others | Animals, fungi |
| Parasitic | Lives on a host and harms it | Cuscuta (amarbel) |
| Insectivorous | Traps and digests insects | Pitcher plant, Venus flytrap |
| Saprophytic | Feeds on dead and decaying matter | Fungi, mushroom, bread mould |
| Symbiotic | Two organisms benefit each other | Lichen, Rhizobium in roots |
The pitcher plant is green and photosynthesises, but its soil lacks nitrogen, so it traps insects to obtain it. That reason is what questions ask for, not merely the name.
Lichen is the standard symbiosis example: an alga makes food and a fungus provides shelter and water. Rhizobium lives in the root nodules of leguminous plants and fixes atmospheric nitrogen, which is why pulses restore soil fertility.
Photosynthesis
Carbon dioxide + Water —(sunlight, chlorophyll)→ Glucose + Oxygen
- Four things are needed: carbon dioxide, water, sunlight and chlorophyll.
- It occurs in the chloroplast, mainly in the leaves.
- Carbon dioxide enters through the stomata; water comes up from the roots.
- Glucose is stored as starch, which is why the iodine test turns a leaf blue-black.
- Oxygen is released as a by-product.
✗ Plants take in oxygen and give out carbon dioxide during photosynthesis | ✓ Photosynthesis takes in carbon dioxide and releases oxygen; respiration does the reverse
The iodine test is the classroom experiment behind this topic, and a question may describe the experiment rather than name it — a destarched leaf, partly covered, exposed to light, then tested with iodine to show that light is necessary.
Photosynthesis and Respiration Together
| Point | Photosynthesis | Respiration |
|---|---|---|
| Gas taken in | Carbon dioxide | Oxygen |
| Gas released | Oxygen | Carbon dioxide |
| Energy | Stored | Released |
| When | Only in light | Day and night |
| Where | Chloroplast | Mitochondria |
Both processes go on in a plant during the day; only respiration continues at night. Saying that plants respire only at night is the classic misconception, and correcting it is exactly what a class 7 teacher is expected to do.
Why It Matters Beyond the Plant
Photosynthesis is the origin of almost all food and all atmospheric oxygen, which makes green plants the producers at the base of every food chain. Without it there would be no consumers. That link ties this topic to the environment chapter and is often the framing of a longer statement-based question.
प्रकाश संश्लेषण CO₂ लेता है और O₂ छोड़ता है — श्वसन इसका उलटा करता है।
TRE pointer: The gas-direction question is asked in some form every year, and the day-night respiration myth is the reasoning question behind it. Learn the pitcher plant's nitrogen reason and the Rhizobium nitrogen fixation link, because both connect biology to the crop-production topic in the next chapter. Since the iodine starch test is a classroom demonstration, a question may describe it without naming it. With −1/3 negative marking, read whether the question says photosynthesis or respiration.
60-Second Recap
- Autotrophs make their own food; Cuscuta is parasitic, mushroom saprophytic, lichen symbiotic.
- The pitcher plant traps insects for nitrogen, not for energy.
- Rhizobium in root nodules of legumes fixes atmospheric nitrogen.
- Photosynthesis needs carbon dioxide, water, sunlight and chlorophyll.
- It takes in carbon dioxide and releases oxygen; food is stored as starch.
- Respiration continues day and night; photosynthesis needs light.
Frequently Asked Questions
Why does a pitcher plant trap insects if it is green?
Because it grows in soil that is poor in nitrogen. It photosynthesises normally for its energy but cannot obtain enough nitrogen from the soil, so it digests insects to get it. The reason, not simply the fact of trapping, is what questions ask for.
Do plants take in oxygen or carbon dioxide?
Both, but through different processes. Photosynthesis takes in carbon dioxide and releases oxygen, and happens only in light. Respiration takes in oxygen and releases carbon dioxide, and continues day and night. During the day photosynthesis dominates, so plants appear to release oxygen overall.
What is the role of Rhizobium?
Rhizobium bacteria live in the root nodules of leguminous plants such as gram and pea, and convert atmospheric nitrogen into a form the plant can use. In return the plant provides them with food and shelter, which makes it a symbiotic relationship.
How does the iodine test show that light is necessary for photosynthesis?
A destarched leaf is partly covered and exposed to light. When tested with iodine, only the uncovered part turns blue-black, showing that starch formed only where light reached. The covered part stays brown, proving light is essential for the process.