CBSE · Class 10 · Biology · Chapter 13

Our Environment — Formula Sheet

Board Formulas

14 formulas

1.Components of an Ecosystem
$Ecosystem = biotic components + abiotic components$
Biotic: plants, animals, microorganisms. Abiotic: temperature, rainfall, wind, soil, minerals. Forests, ponds and lakes are natural ecosystems; gardens and crop-fields are human-made (artificial) ecosystems.
2.Biotic Components by Nutrition
$Producers (autotrophs); Consumers (herbivores, carnivores, omnivores, parasites); Decomposers$
All green plants and certain bacteria (such as blue-green algae) make food by photosynthesis. Decomposers (bacteria and fungi) break down dead remains and wastes into simple substances that return to the soil.
3.A Food Chain
$Grass \to Grasshopper \to Frog \to Snake \to Eagle$
A series of organisms each feeding on the one before it. Arrows point in the direction of energy flow (from food to feeder). Many interconnected food chains form a food web.
4.Trophic Levels
$T_{1} : producers \to T_{2} : herbivores \to T_{3} : small carnivores \to T_{4} : large carnivores$
Each step of a food chain is a trophic level. Herbivores are primary consumers, small carnivores are secondary consumers and large carnivores are tertiary consumers.
5.Energy Captured by Green Plants
$Food energy \approx 1% of sunlight falling on leaves$
In a terrestrial ecosystem, green plants convert only about 1% of the sunlight that falls on their leaves into food energy.
6.Ten Per Cent Law★
$E_{n + 1} = \frac{10}{100} \times E_{n}$
$E_{n}$ : Energy available at trophic level n (J or kJ) · $E_{n + 1}$ : Energy available at the next trophic level (J or kJ)
On average only 10% of the food eaten is turned into the consumer's own body and passed on. The rest is lost as heat, used in digestion and work, or spent on growth and reproduction.
7.Energy at the nth Trophic Level
$E_{n} = E_{1} \times (\frac{1}{10})^{n - 1}$
$E_{1}$ : Energy available at the producer level (J or kJ) · $n$ : Trophic level number (producers are n = 1)
Apply the 10 per cent law once for every step. To go back down the chain, multiply by 10 for each step.
8.Length of Food Chains
$Usual food chain = 3 or 4 trophic levels$
The energy loss at each step is so large that very little usable energy remains after four trophic levels.
9.Number of Organisms at Each Level
$Producers > herbivores > carnivores (number of individuals, generally)$
There are generally more individuals at the lower trophic levels; the greatest number is of the producers.
10.Unidirectional Flow of Energy★
$Sun \to autotrophs \to herbivores \to carnivores$
Energy captured by autotrophs does not go back to the solar input, and energy passed to herbivores does not come back to autotrophs. Energy is not available to previous levels.
11.Biological Magnification★
$Concentration of non-biodegradable chemicals: T_{1} < T_{2} < T_{3} < \dots$
Pesticides and other chemicals wash into soil and water, are absorbed by plants and enter the food chain. Since they are not degradable, they accumulate at each trophic level. Humans at the top get the maximum concentration.
12.Formation of Ozone★
$O_{2} UV O + O; O + O_{2} \to O_{3}$
High-energy UV radiation splits some O₂ molecules into free oxygen atoms, which combine with O₂ to form ozone. The ozone layer shields the Earth from the Sun's UV radiation; at ground level ozone is a deadly poison.
13.Ozone Depletion and CFCs
$CFCs \Rightarrow ozone loss (from the 1980s); UNEP 1987: freeze CFC production at 1986 levels$
Chlorofluorocarbons are synthetic chemicals used as refrigerants and in fire extinguishers. It is now mandatory for manufacturers to make CFC-free refrigerators worldwide.
14.Biodegradable and Non-biodegradable
$Biodegradable: broken down by biological processes; Non-biodegradable: not broken down, persist$
Bacteria and other saprophytes break down biodegradable matter (vegetable peels, paper). Non-biodegradable substances such as plastics may stay in the environment for a long time or harm members of the ecosystem.