Summary
IB Biology: Ecology Summary
Ecology (unit 4) Summary
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4.1 SPECIES AND ECOSYSTEMSA species is a group of organisms that can potentially interbreed to produce fertile,
viable offspring. Members of a single species are unable to produce fertile, viable
offspring with members from a different species. When two different species do
produce offspring by cross-breeding, these hybrids are reproductively sterile (e.g.
liger, mule).
A population is a group of organisms of the same species that are living in the same
area at the same time . Organisms that live in different regions (i.e. different
populations) are reproductively isolated and unlikely to interbreed, however are
classified as the same species if interbreeding is functionally possible.
Species: A group of organisms that can potentially interbreed to produce fertile,
viable offspring
Population: A group of organisms of the same species, living in the same area at
the same time
Community: A group of populations living together and interacting with each other
within a given area
Habitat: The environment in which a species normally lives, or the location of a living
organism
Ecosystem: A community and its abiotic environment (i.e. habitat)
Ecology: The study of the relationship between living organisms, or between living
organisms and their environment#
Autotrophs
Synthesises its
own organic
molecules from
simple inorganic
substances (e.g.
CO2, nitrates).
Energy for this
process is derived
from sunlight
(photosynthesis) or
via the oxidation of
inorganic
molecules (chemosynthesis). Because autotrophs synthesise their own organic
molecules they are commonly referred to as producers.
, Heterotrophs obtain organic molecules from other organisms (either living or recently
killed or their nonliving remains and detritus). Because heterotrophs cannot produce
their own organic molecules and obtain it from other sources, they are called
consumers
Mixotrophs are unicellular organisms that may on occasion use both forms of
nutrition, depending on resource availability. Euglena gracilis possess chlorophyll for
photosynthesis (autotrophic) but may also feed on detritus (heterotrophic).
Autotrophs synthesise organic molecules from simple inorganic substances. Most
autotrophs derive the energy for this process from sunlight (via photosynthesis).
Some may derive the needed energy from the oxidation of inorganic chemicals
(chemosynthesis).
Autotrophs obtain the simple inorganic substances required for this process from the
abiotic environment. These nutrients – including carbon, nitrogen, hydrogen, oxygen
and phosphorus – are obtained from the air, water and soil.
Heterotrophs also may obtain some simple inorganic substances from the
environment, but principally obtain their carbon and nitrogen from the organic
molecules produced by autotrophs. Heterotrophs obtain organic molecules from
other organisms via different feeding mechanisms and different food sources.
Consequently, heterotrophs can be differentially classified according to their feeding
pattern.
Saprotrophs live on (or in) non-living organic matter, secrete digestive enzymes into
it and absorbing the products of digestion. Unlike other types of heterotrophs,
saprotrophs do not ingest food but use enzymatic secretion to facilitate external
digestion. Because saprotrophs facilitate the breakdown of dead organic material,
they are commonly referred to as decomposers. Examples of saprotrophs include
bacteria and fungi.
Nutrients refer to the material required by an organism, and include elements such
as carbon, nitrogen and phosphorus. The supply of inorganic nutrients on Earth is
finite – new elements cannot simply be created and so are in limited supply .
Hence chemical elements are constantly recycled after they are used:
★ Autotrophs obtain inorganic nutrients from the air, water and soil and convert
them into organic compounds
★ Heterotrophs ingest these organic compounds and use them for growth and
respiration, releasing inorganic byproducts
★ When organisms die, saprotrophs decompose the remains and free inorganic
materials into the soil
★ The return of inorganic nutrients to the soil ensures the continual supply of
raw materials for the autotrophs
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