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Biology

Key Terms

BiologyKey Terms
A horizon
consists of a mixture of organic material with inorganic products of weathering
B horizon
soil layer that is an accumulation of mostly fine material that has moved downward
bedrock
solid rock that lies beneath the soil
C horizon
layer of soil that contains the parent material, and the organic and inorganic material that is broken down to form soil; also known as the soil base
clay
soil particles that are less than 0.002 mm in diameter
epiphyte
plant that grows on other plants but is not dependent upon other plants for nutrition
horizon
soil layer with distinct physical and chemical properties, which differs from other layers depending on how and when it was formed
humus
organic material of soil; made up of microorganisms, dead animals and plants in varying stages of decay
inorganic compound
chemical compound that does not contain carbon; it is not part of or produced by a living organism
insectivorous plant
plant that has specialized leaves to attract and digest insects
loam
soil that has no dominant particle size
macronutrient
nutrient that is required in large amounts for plant growth; carbon, hydrogen, oxygen, nitrogen, phosphorus, potassium, calcium, magnesium, and sulfur
micronutrient
nutrient required in small amounts; also called trace element
mineral soil
type of soil that is formed from the weathering of rocks and inorganic material; composed primarily of sand, silt, and clay
nitrogenase
enzyme that is responsible for the reduction of atmospheric nitrogen to ammonia
nodules
specialized structures that contain Rhizobia bacteria where nitrogen fixation takes place
O horizon
layer of soil with humus at the surface and decomposed vegetation at the base
organic compound
chemical compound that contains carbon
organic soil
type of soil that is formed from sedimentation; composed primarily of organic material
parasitic plant
plant that is dependent on its host for survival
parent material
organic and inorganic material in which soils form
rhizobia
soil bacteria that symbiotically interact with legume roots to form nodules and fix nitrogen
rhizosphere
area of soil affected by root secretions and microorganisms
sand
soil particles between 0.1–2 mm in diameter
saprophyte
plant that does not have chlorophyll and gets its food from dead matter
silt
soil particles between 0.002 and 0.1 mm in diameter
soil
outer loose layer that covers the surface of Earth
soil profile
vertical section of a soil
symbiont
plant in a symbiotic relationship with bacteria or fungi
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