NDA Biology · Teaching notes
Ecology and Environment — NDA Biology
Ecology and Environment is a small but reliable NDA Biology chapter — 12 PYQs across 2018–2024, mostly EASY with a few MODERATE multi-statement items. Almost every question is recall plus reasoning: identify a food chain, name an organism's trophic level, recognise a symbiotic relationship, classify a biome, or spot the one statement that is wrong about greenhouse gases, biogas or biodiversity. The chapter teaches in two movements, building the ecosystem machinery first and then the environmental-issue facts that sit on top of it: (1) Ecosystems, biomes and ecological interactions — what an ecosystem is, how energy flows through trophic levels and food chains, the nutrition modes of organisms (autotroph vs heterotroph), the three kinds of symbiosis (mutualism, commensalism, parasitism), and the world's land and aquatic biomes; (2) Environment and biodiversity — greenhouse gases and global warming, biogas and biomass as renewable energy, biodiversity and its conservation (hotspots, sacred groves), and groundwater depletion. Nine concepts, every PYQ tagged. Most concepts are reference tables: memorise the table, win the marks.
Subtopic notes
Ecosystems, Biomes and Ecological Interactions
6 PYQsAn ecosystem is a community of living organisms (biotic) interacting with their non-living surroundings (abiotic); energy flows one way through trophic levels while organisms feed on one another and live in named biomes around the world.
Open note
Environment and Biodiversity
6 PYQsThe environmental-issues half of the chapter: greenhouse gases and global warming, biogas and biomass as renewable energy, the variety of life (biodiversity) and how it is conserved, and the depletion of groundwater.
Open note
PYQ weightage by concept
9 concepts · 12 PYQs — where the marks actually sit, so you know what to drill first
PYQ weightage by concept
9 concepts · 12 PYQs — where the marks actually sit, so you know what to drill first
| Concept | PYQs | Share |
|---|---|---|
| Trophic levels, food chains and the 10% law | 2 | 17% |
| Biomes — land and aquatic ecosystems | 2 | 17% |
| Nutrition modes — autotrophs, heterotrophs, decomposers | 1 | 8% |
| Ecological interactions — mutualism, commensalism, parasitism | 1 | 8% |
| What an ecosystem is — biotic and abiotic componentsfoundation | — | — |
| Concept | PYQs | Share |
|---|---|---|
| Biogas and biomass — renewable energy from waste | 2 | 17% |
| Biodiversity, hotspots and conservation | 2 | 17% |
| Greenhouse gases and global warming | 1 | 8% |
| Groundwater depletion and conservation | 1 | 8% |
Formula & revision sheet
1 formulas · 6 reference tables · 13 gotchas across all subtopics — the exam-eve cheat-sheet
Formula & revision sheet
1 formulas · 6 reference tables · 13 gotchas across all subtopics — the exam-eve cheat-sheet
Reference tables (3)
Nutrition modes — autotrophs, heterotrophs, decomposers4 rows
| Mode | Carbon source | Examples |
|---|---|---|
| Autotroph | Carbon dioxide (CO₂), fixed via photosynthesis or chemosynthesis | Green plants, algae, cyanobacteria NDA 2023 — organisms using CO₂ as their principal carbon source are AUTOTROPHS. |
| Heterotroph | Organic matter from other organisms | All animals, fungi, most bacteria |
| Decomposer | Dead organic matter (detritus) | Bacteria, fungi, earthworms |
| Parasite | Living host's body | Tapeworm, Plasmodium, Cuscuta |
Ecological interactions — mutualism, commensalism, parasitism5 rows
| Interaction | Effect (species 1 / 2) | Example |
|---|---|---|
| Mutualism | Benefit / Benefit (+ / +) | Bee and flower (nectar for pollination); lichen NDA 2023 — the flower-and-honeybee relationship helps the flower with POLLINATION (a mutualism). |
| Commensalism | Benefit / No effect (+ / 0) | Orchid on a tree; remora on a shark |
| Parasitism | Benefit / Harm (+ / −) | Tapeworm, Plasmodium, Cuscuta on host |
| Predation | Benefit / Harm (+ / −) | Lion eats deer |
| Competition | Harm / Harm (− / −) | Two plants competing for light/water |
Biomes — land and aquatic ecosystems6 rows
| Biome | Climate | Signature life |
|---|---|---|
| Tropical rainforest | Hot, high rainfall all year | Dense evergreen trees; greatest biodiversity |
| Temperate forest | High rainfall, cold-to-mild seasons | Deciduous trees (maple, oak, hickory); raccoons, squirrels NDA 2024 — deciduous maple/oak/hickory + raccoons + cold-to-mild + high rainfall = TEMPERATE forest. |
| Taiga / Boreal | Cold | Coniferous evergreens (pine, spruce) |
| Desert | Very low rainfall | Cacti, xerophytes, reptiles |
| Tundra | Coldest, frozen | No trees; mosses, lichens |
| Ocean (aquatic) | Saltwater | Phytoplankton = main producers NDA 2018 — phytoplankton produce most of the ocean's organic carbon (true); algae are NOT limited to the cold-water biome (false). |
Watch out for (7)
- A food chain must START with a producer→ Trophic levels, food chains and the 10% law
- Primary consumer = herbivore, not 'the first animal you see'→ Trophic levels, food chains and the 10% law
- Decomposers are heterotrophs, not autotrophs→ Nutrition modes — autotrophs, heterotrophs, decomposers
- Bee + flower benefits the flower with POLLINATION, not 'germination' or 'size'→ Ecological interactions — mutualism, commensalism, parasitism
- Don't confuse commensalism with mutualism→ Ecological interactions — mutualism, commensalism, parasitism
- Deciduous + cold-to-mild = temperate, not tropical or boreal→ Biomes — land and aquatic ecosystems
- Phytoplankton are everywhere in the ocean, not just cold water→ Biomes — land and aquatic ecosystems
Reference tables (3)
Greenhouse gases and global warming5 rows
| Gas | Greenhouse gas? | Note |
|---|---|---|
| Water vapour (H₂O) | Yes | Most abundant GHG |
| Carbon dioxide (CO₂) | Yes | Main man-made driver |
| Methane (CH₄) | Yes | Strong; from cattle, paddy, biogas |
| Oxygen (O₂) | No | A main gas of air, but does NOT trap heat NDA 2023 — Oxygen is NOT a main greenhouse gas (the odd one out). |
| Nitrogen (N₂) | No | 78% of air, but not a GHG |
Biodiversity, hotspots and conservation5 rows
| Fact | Detail |
|---|---|
| Term 'biodiversity' coined by | Walter G. Rosen (1986) |
| Term 'biodiversity hotspot' coined by | Norman Myers (1988) |
| Number of hotspots worldwide | About 36 (NOT more than 100) NDA 2021 — 'More than 100 hotspots are identified' is the INCORRECT statement. |
| Causes of loss | Deforestation, over-exploitation, encroachment, hunting |
| Sacred groves | Conserve biodiversity (do NOT reduce it) NDA 2020 — maintaining sacred groves is NOT a cause of biodiversity decrease. |
Groundwater depletion and conservation4 rows
| Activity | Effect on groundwater |
|---|---|
| Excessive pumping | Depletes — over-extraction lowers the water table |
| Loss of forests | Depletes — bare soil means more runoff, less seepage |
| Large-scale concrete buildings | Depletes — paving stops rain soaking in |
| Afforestation (planting trees) | Conserves / recharges — roots and litter aid seepage NDA 2020 — afforestation is NOT a cause of groundwater depletion (it recharges it). |
Watch out for (6)
- Oxygen and nitrogen are NOT greenhouse gases→ Greenhouse gases and global warming
- Biogas heating value is HIGH, not low→ Biogas and biomass — renewable energy from waste
- Biogas is the largest component methane — not carbon dioxide→ Biogas and biomass — renewable energy from waste
- Sacred groves CONSERVE biodiversity→ Biodiversity, hotspots and conservation
- There are about 36 hotspots, not 'more than 100'→ Biodiversity, hotspots and conservation
- Afforestation RECHARGES groundwater — it is the odd one out→ Groundwater depletion and conservation