Introduction
This final chapter covers Plant Biology and Ecology/Environment — photosynthesis, plant classification,
and core ecosystem concepts that complete the Railway General Science syllabus.
Photosynthesis
📌 Core Equation: 6CO₂ + 6H₂O + Sunlight → C₆H₁₂O₆ (glucose) + 6O₂ — plants convert carbon dioxide and water into glucose and oxygen using sunlight, captured by the green pigment chlorophyll.
| Requirement | Role |
|---|
| Sunlight | Energy source for the reaction |
| Chlorophyll | Green pigment in chloroplasts that captures light energy |
| Carbon Dioxide | Absorbed from the air through stomata |
| Water | Absorbed from soil through roots |
Plant Classification
| Category | Description | Example |
|---|
| Herbs | Small, soft-stemmed plants | Wheat, tomato |
| Shrubs | Medium-sized, woody, multiple stems from the base | Rose, hibiscus |
| Trees | Tall, single woody stem (trunk) | Mango, banyan |
| Climbers | Weak-stemmed, use support to grow upward | Grapevine, money plant |
| Category | Description | Example |
|---|
| Flowering Plants (Angiosperms) | Produce seeds enclosed within a fruit | Most familiar plants |
| Non-Flowering Plants (Gymnosperms) | Produce seeds not enclosed in a fruit | Pine, conifers |
Plant Tissues — Xylem and Phloem
| Tissue | Function |
|---|
| Xylem | Transports water and minerals from roots to leaves (one-way, upward) |
| Phloem | Transports food (glucose) made in leaves to the rest of the plant (both directions) |
Ecosystem — Basic Concepts
| Term | Definition |
|---|
| Ecosystem | A community of living organisms interacting with their physical environment |
| Producers | Organisms that produce their own food (plants, via photosynthesis) |
| Consumers | Organisms that depend on other organisms for food |
| Decomposers | Break down dead organic matter, recycling nutrients (bacteria, fungi) |
| Consumer Type | Diet | Example |
|---|
| Herbivore (Primary Consumer) | Plants only | Deer, cow |
| Carnivore (Secondary/Tertiary Consumer) | Other animals | Lion, tiger |
| Omnivore | Both plants and animals | Humans, bears |
Food Chain and Food Web
📌 Key Distinction: A Food Chain is a single, linear sequence of who-eats-whom (e.g., grass → deer → lion). A Food Web is a more realistic network of multiple interconnected food chains within an ecosystem.
Environmental Issues — Key Terms
| Term | Description |
|---|
| Global Warming | Long-term rise in Earth's average surface temperature, largely due to greenhouse gas emissions |
| Greenhouse Effect | Trapping of heat in the atmosphere by gases like CO₂, methane, and water vapour |
| Ozone Layer Depletion | Thinning of the protective ozone layer, largely caused by CFCs (chlorofluorocarbons) |
| Biodiversity | The variety of life forms within a given ecosystem or on Earth as a whole |
| Deforestation | Large-scale removal of forests, contributing to habitat loss and climate change |
Major International Environmental Agreements
| Agreement | Focus |
|---|
| Kyoto Protocol | Binding emission reduction targets for developed countries |
| Paris Agreement | Global effort to limit temperature rise, with nationally determined contributions |
| Montreal Protocol | Phasing out substances that deplete the ozone layer |
Q. In a food chain: Grass → Grasshopper → Frog → Snake, which organism is the primary consumer?
Grass is the producer; the organism that eats the producer directly is the primary consumer
Answer: Grasshopper (herbivore, eats grass directly)
✅ Exam Focus: Photosynthesis equation and requirements · Plant classification (herbs/shrubs/trees, angiosperms/gymnosperms) · Xylem (water, upward) vs Phloem (food, both directions) · Producer-consumer-decomposer roles · Food chain vs food web distinction · Key environmental terms and agreements.