Edaphic factor refers to: (a) Water (b) Soil (c) Relative humidity (d) Altitude

NCERT Exemplar · Q15

Q. Edaphic factor refers to:

(a) Water

(b) Soil

(d) Altitude

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Concept understanding — Ecological Pyramid

Picture a real pyramid -- wide at the base, narrowing all the way up to a single point at the top. Ecologists borrow exactly this shape to describe something that has nothing to do with stone: how numbers, weight (biomass), or energy are distributed across the feeding levels of a food chain. This visual model is called an ecological pyramid.

Every ecological pyramid works the same way. In your NCERT textbook (Class 12 Biology, Chapter 12, Ecosystem, section 12.5), the base always represents the producers -- the first trophic level -- and each successive tier above it represents the next trophic level up (herbivores, then primary carnivores, then secondary or top carnivores), with the apex representing the top-level consumer. Three distinct types are studied, because the same food-chain relationship can be measured in three different ways:

Pyramid of numbers -- plots the count of individual organisms at each trophic level. NCERT's own grassland example is dramatic: nearly 6 million producer plants are needed to support just three top-carnivores at the apex.
Pyramid of biomass -- plots the standing crop (usually expressed as dry weight, which is more accurate than fresh weight) of organisms at each level, rather than headcount.
Pyramid of energy -- plots the amount of energy present at each trophic level, measured per unit area, usually annually.

Important

In most ecosystems, all three pyramids come out upright -- producers are more numerous and have more biomass than herbivores, and herbivores more than carnivores -- because energy shrinks at every step up the food chain (the same 10 per cent law behind energy flow: only about 10 per cent of the energy at one trophic level is transferred to the next).

When a pyramid turns upside down -- numbers and biomass pyramids don't always come out upright, and NCERT points to genuine exceptions you're expected to reason through, not just memorise:

A single large tree can support so many feeding insects that a pyramid of numbers built around it is inverted right at the base -- one producer, many primary consumers.
The pyramid of biomass in the sea is commonly inverted: at any given moment the standing crop of tiny, fast-reproducing phytoplankton is small, yet it is turning over fast enough to support a much larger standing crop of the zooplankton feeding on it.

Note

The pyramid of energy is the one type that is never inverted -- it is always upright, in every ecosystem, without exception. Energy is lost as heat at every transfer between trophic levels (unlike nutrients, it is never recycled back), so the level below always has to hold more usable energy than the level feeding on it. …

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Edaphic factors are environmental influences that relate specifically to the physical and chemical properties of soil.

In the study of ecology, organisms interact with their environment, which comprises both living (biotic) and non-living (abiotic) components. Abiotic factors are the non-biological physical and chemical elements that affect an organism's ability to survive and reproduce. These include temperature, light, water, and crucially, the soil.

Among the various abiotic factors, those specifically pertaining to the soil are termed edaphic factors. The word "edaphic" itself is derived from the Greek word "edaphos," meaning ground or soil. These factors are fundamental because soil provides the physical substrate for most terrestrial plants, supplying them with water, nutrients, and anchorage.

Important

Edaphic factors encompass all characteristics of the soil that influence the life within it and above it, particularly plant growth.

Key edaphic factors include:

Soil texture: The proportion of sand, silt, and clay particles, which affects water retention and aeration.
Soil structure: The arrangement of soil particles into aggregates, influencing porosity and root penetration.
Soil pH: The acidity or alkalinity of the soil, which dictates nutrient availability to plants.
Mineral composition: The types and amounts of essential nutrients (like nitrogen, phosphorus, potassium) present in the soil.
Organic matter content: The decomposed plant and animal material that improves soil fertility, structure, and water-holding capacity.
Soil water content: The amount of moisture available in the soil, crucial for plant uptake.
Soil aeration: The presence of air spaces in the soil, necessary for root respiration. …

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Q.Edaphic factor refers to:

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