NDA Biology · Formula sheet
Ecology and Environment formulas
1 formula, 6 reference tables and 13 common traps for NDA Biology Ecology and Environment, grouped by subtopic.
Ecosystems, Biomes and Ecological Interactions
Learn this subtopic in the notesTrophic levels, food chains and the 10% law
The 10% law of energy transfer
- energy available at trophic level n
- energy passed to the next (higher) level
Nutrition modes — autotrophs, heterotrophs, decomposers
| 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 |
Autotroph = producer (makes food from CO₂); heterotroph = consumer (eats others); decomposer = recycler of dead matter.
Ecological interactions — mutualism, commensalism, parasitism
| 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 |
Read the sign pair: both + is mutualism; + and 0 is commensalism; + and − (host kept alive) is parasitism.
Biomes — land and aquatic ecosystems
| 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). |
Identify a land biome from its trees + climate; remember phytoplankton are the ocean's primary producers.
Common traps
A food chain must START with a producer
'Goat, cow and human' is not a food chain — goat and cow are both herbivores and neither eats the other. A valid chain begins with a producer (grass) and each later organism eats the one before it.
Primary consumer = herbivore, not 'the first animal you see'
The primary consumer is the organism that eats the PRODUCER — a herbivore (caterpillar, goat, grasshopper). A frog or sparrowhawk eats other animals, so they are secondary or higher consumers, not primary.
Decomposers are heterotrophs, not autotrophs
A common distractor calls decomposers a kind of autotroph. They are not — they cannot fix CO₂. They are heterotrophs that feed on DEAD matter (saprotrophs), while autotrophs are the green producers that make food from CO₂.
Bee + flower benefits the flower with POLLINATION, not 'germination' or 'size'
The distractors offer 'quick germination of pollen' or 'increase in size'. The flower's benefit from the bee is pollination — the bee carries pollen between flowers, enabling cross-pollination. This is a mutualism (the bee gets nectar).
Don't confuse commensalism with mutualism
In mutualism BOTH species benefit (+ / +). In commensalism one benefits and the other is unaffected (+ / 0). The bee-flower pair is mutualism because the bee also gains food.
Deciduous + cold-to-mild = temperate, not tropical or boreal
Tropical forests are hot and evergreen; boreal/taiga forests are coniferous evergreens. A forest of deciduous maple/oak/hickory with cold-to-mild seasons and high rainfall is a temperate forest.
Phytoplankton are everywhere in the ocean, not just cold water
Phytoplankton (and algae) produce most of the ocean's organic carbon — true — but they are NOT restricted to cold-water biomes. A statement claiming algae are produced only in cold water is false.
Environment and Biodiversity
Learn this subtopic in the notesGreenhouse gases and global warming
| 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 |
The major GHGs are water vapour, CO₂ and methane. Oxygen and nitrogen are NOT greenhouse gases.
Biodiversity, hotspots and conservation
| 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. |
Rosen coined 'biodiversity' (1986); Myers coined 'hotspot' (1988); ~36 hotspots; sacred groves protect, not harm.
Groundwater depletion and conservation
| 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). |
Pumping, deforestation and concreting deplete groundwater; afforestation and rainwater harvesting recharge it.
Common traps
Oxygen and nitrogen are NOT greenhouse gases
They are the two main gases of the air, which tempts students to mark them as greenhouse gases. They are not — only gases that absorb outgoing heat (water vapour, CO₂, methane, N₂O) qualify.
Biogas heating value is HIGH, not low
Because biogas is mostly methane, it burns well and has a high calorific value. A statement claiming 'heating capacity of biogas is very low' is the INCORRECT one the bank wants you to catch (NDA 2020).
Biogas is the largest component methane — not carbon dioxide
CO₂ is present (the second-largest part), but the LARGEST component is methane (~50–70%). Marking carbon dioxide as the main component is the classic error.
Sacred groves CONSERVE biodiversity
In a 'which is NOT a cause of biodiversity decrease?' question, the answer is the conservation activity — maintaining sacred groves protects forest, so it does not reduce biodiversity (NDA 2020).
There are about 36 hotspots, not 'more than 100'
Rosen (1986) coined 'biodiversity' and Myers (1988) coined 'hotspot' — both true. The false statement is that more than 100 hotspots exist; the recognised figure is about 36 (NDA 2021).
Afforestation RECHARGES groundwater — it is the odd one out
In a 'which is NOT a cause of groundwater depletion?' question, pick the conservation action. Afforestation helps rainwater seep in and recharge the water table, so it does not deplete groundwater (NDA 2020).