IB BIOLOGY UNIT 4: ECOLOGY
4.1.1 ECOLOGY TERMS
● A species is a group of organisms that can potentially interbreed to produce fertile,
viable offspring.
● Members of the same species have a common gene pool.
● A species is made up of organisms that:
● have similar physiological and morphological characteristics — such as same type and
number of chromosomes — that can be observed and measured,
● have the ability to interbreed to produce fertile offspring,
● are genetically distinct from other species,
● have a common family tree.
● Members of a single species are unable to produce fertile, viable offspring with members
from a different species.
● 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 are reproductively isolated and unlikely to
interbreed, however are classified as the same species if interbreeding is functionally
possible.
● A community is a group of populations living together and interacting with each other
within a given area.
● In ecology, the term interacting can mean one population feeding on another, or being eaten. It
can mean that one species provides vital substances for another. It can also mean that one
species gets protection from another or one species acts as the habitat of the other.
● A habitat is the environment in which a species normally lives.
● An ecosystem is a community and its abiotic environment.
● The term abiotic refers to components of the environment that are non-living such as water
and is mostly includes measurements of temperature and humidity.
● Although these factors are not living entities, they are often of great interest for scientific
studies because of the interactions that living things have with them.
● To find out to what extent a particular abiotic factor such as temperature or pH influences a
species' distribution, many measurement of both the abiotic and biotic aspects of the
environment must be taken.
, 4.1.2 HYBRIDS
● Sometimes, members of separate but similar species such as a donkey and a horse can mate
and succeed in producing a hybrid offspring. However, this offspring would be infertile as many
of the genetic identities, one of the main ones being the chromosome number, for the mating
species are not the same.
● This new offspring is not considered to be a new species as it cannot reproduce to create a
population of itself. Instead, it is called an interspecific hybrid.
● Hybrids face several challenges to continue as a population.
4.1.3 ISOLATION OF SPECIES
● If a group from a species is separated from the rest of the species, it might find itself evolving
in a different way compared with the rest of the population.
● The new population in a place away from the parent mainland is said to be reproductively
isolated from the original population of mice.
● Compared with the original population on the mainland, this new population may end up with
different frequencies of certain alleles for specific traits.
4.1.4 MODES OF NUTRITION
● Chemical energy refers to the fact that organic compounds are rich in energy, thanks to the
chemical bonds that exist between the carbon atoms and other atoms.
● Living organisms obtain chemical energy in one of two ways:
● Autotrophs synthesize their own organic molecules from simple inorganic substances
to obtain chemical energy.
● Energy for this process is derived from sunlight (photosynthesis) or via the oxidation of
inorganic molecules (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.
● Because autotrophs synthesise their own organic molecules they are commonly referred to as
producers.
● Examples of autotrophs include cyanobacteria, grass, and algae.
● Heterotrophs obtain organic molecules from other organisms via one of three methods:
● Consumers ingest organic molecules from living or recently killed organisms.
● Herbivores such as cows are consumers that feed principally on plant matter.
, ● Carnivores such as crocodiles are consumers that feed principally on animal
matter.
● Omnivores such as humans are consumers that have a principle diet composed
of both plant and animal matter.
● Scavengers such as crows are opportunistic consumers that principally feed on
dead and decaying carcasses rather than hunting live prey.
● Scavengers should not be confused with decomposers: while scavengers
break down large organic matter into smaller subunits as well,
decomposers break down these smaller subunits at the molecular level.
● Detritivores such as earthworms ingest organic molecules found in the non-living
remnants of organisms such as dead leaves or faeces internally.
● Saprotrophs such as fungi live on or in non-living organic matter to release
digestive enzymes and then absorb the external energy-rich carbon 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.
● As for humans, the only component in our diet that we can synthesize, by exposure to
sunlight, is vitamin D. There are precursors in human skin that absorb UV light waves and
produce vitamin D.
● Certain unicellular organisms, referred to as mixotrophs, may on occasion use both
forms of nutrition, depending on resource availability.
● Euglena gracilis, for example, possess chlorophyll for photosynthesis (autotrophic) but
may also feed on detritus (heterotrophic).
4.1.5 NUTRIENT CYCLING
● 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.
● Normally, once the minerals and organic compounds are absorbed by the organisms, they are
'locked up' and are unavailable to others. However, an effective way to unlock the precious
nutrients stored in the cells of plants and animals is through decay.
● Decomposers — saprotrophs and detritivores — break down the body parts of dead
organisms and convert the organic matter into a more usable form for themselves and
for other organisms.
● For example, proteins are broken down into ammonia which can then be converted into
useful nitrates (NO3-) by bacteria.
● Decomposers play a major role in the formation of soil, without which plant growth would be
greatly impaired.
● The rick black layer of soil called humus is made up of organic debris and nutrients
released by decomposers.
● Thanks to the recycling of nutrients of which the steps are listed below, ecosystems can
continue to be productive and successful for long periods of time.
1. Autotrophs obtain inorganic nutrients from the air, water and soil and convert them into
organic compounds.
● These organic compounds can then be used to produce more complex organic
molecules such as lipids and proteins or can be converted into more complex
carbohydrates such as cellulose which play an important role in the structure and
function of living organisms.
2. Heterotrophs ingest these organic compounds and use them for growth and respiration,
releasing inorganic byproducts.
3. When organisms die, saprotrophs decompose the remains and free inorganic materials
into the soil.
4. The return of inorganic nutrients to the soil ensures the continual supply of raw
materials for the autotrophs.
4.1.1 ECOLOGY TERMS
● A species is a group of organisms that can potentially interbreed to produce fertile,
viable offspring.
● Members of the same species have a common gene pool.
● A species is made up of organisms that:
● have similar physiological and morphological characteristics — such as same type and
number of chromosomes — that can be observed and measured,
● have the ability to interbreed to produce fertile offspring,
● are genetically distinct from other species,
● have a common family tree.
● Members of a single species are unable to produce fertile, viable offspring with members
from a different species.
● 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 are reproductively isolated and unlikely to
interbreed, however are classified as the same species if interbreeding is functionally
possible.
● A community is a group of populations living together and interacting with each other
within a given area.
● In ecology, the term interacting can mean one population feeding on another, or being eaten. It
can mean that one species provides vital substances for another. It can also mean that one
species gets protection from another or one species acts as the habitat of the other.
● A habitat is the environment in which a species normally lives.
● An ecosystem is a community and its abiotic environment.
● The term abiotic refers to components of the environment that are non-living such as water
and is mostly includes measurements of temperature and humidity.
● Although these factors are not living entities, they are often of great interest for scientific
studies because of the interactions that living things have with them.
● To find out to what extent a particular abiotic factor such as temperature or pH influences a
species' distribution, many measurement of both the abiotic and biotic aspects of the
environment must be taken.
, 4.1.2 HYBRIDS
● Sometimes, members of separate but similar species such as a donkey and a horse can mate
and succeed in producing a hybrid offspring. However, this offspring would be infertile as many
of the genetic identities, one of the main ones being the chromosome number, for the mating
species are not the same.
● This new offspring is not considered to be a new species as it cannot reproduce to create a
population of itself. Instead, it is called an interspecific hybrid.
● Hybrids face several challenges to continue as a population.
4.1.3 ISOLATION OF SPECIES
● If a group from a species is separated from the rest of the species, it might find itself evolving
in a different way compared with the rest of the population.
● The new population in a place away from the parent mainland is said to be reproductively
isolated from the original population of mice.
● Compared with the original population on the mainland, this new population may end up with
different frequencies of certain alleles for specific traits.
4.1.4 MODES OF NUTRITION
● Chemical energy refers to the fact that organic compounds are rich in energy, thanks to the
chemical bonds that exist between the carbon atoms and other atoms.
● Living organisms obtain chemical energy in one of two ways:
● Autotrophs synthesize their own organic molecules from simple inorganic substances
to obtain chemical energy.
● Energy for this process is derived from sunlight (photosynthesis) or via the oxidation of
inorganic molecules (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.
● Because autotrophs synthesise their own organic molecules they are commonly referred to as
producers.
● Examples of autotrophs include cyanobacteria, grass, and algae.
● Heterotrophs obtain organic molecules from other organisms via one of three methods:
● Consumers ingest organic molecules from living or recently killed organisms.
● Herbivores such as cows are consumers that feed principally on plant matter.
, ● Carnivores such as crocodiles are consumers that feed principally on animal
matter.
● Omnivores such as humans are consumers that have a principle diet composed
of both plant and animal matter.
● Scavengers such as crows are opportunistic consumers that principally feed on
dead and decaying carcasses rather than hunting live prey.
● Scavengers should not be confused with decomposers: while scavengers
break down large organic matter into smaller subunits as well,
decomposers break down these smaller subunits at the molecular level.
● Detritivores such as earthworms ingest organic molecules found in the non-living
remnants of organisms such as dead leaves or faeces internally.
● Saprotrophs such as fungi live on or in non-living organic matter to release
digestive enzymes and then absorb the external energy-rich carbon 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.
● As for humans, the only component in our diet that we can synthesize, by exposure to
sunlight, is vitamin D. There are precursors in human skin that absorb UV light waves and
produce vitamin D.
● Certain unicellular organisms, referred to as mixotrophs, may on occasion use both
forms of nutrition, depending on resource availability.
● Euglena gracilis, for example, possess chlorophyll for photosynthesis (autotrophic) but
may also feed on detritus (heterotrophic).
4.1.5 NUTRIENT CYCLING
● 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.
● Normally, once the minerals and organic compounds are absorbed by the organisms, they are
'locked up' and are unavailable to others. However, an effective way to unlock the precious
nutrients stored in the cells of plants and animals is through decay.
● Decomposers — saprotrophs and detritivores — break down the body parts of dead
organisms and convert the organic matter into a more usable form for themselves and
for other organisms.
● For example, proteins are broken down into ammonia which can then be converted into
useful nitrates (NO3-) by bacteria.
● Decomposers play a major role in the formation of soil, without which plant growth would be
greatly impaired.
● The rick black layer of soil called humus is made up of organic debris and nutrients
released by decomposers.
● Thanks to the recycling of nutrients of which the steps are listed below, ecosystems can
continue to be productive and successful for long periods of time.
1. Autotrophs obtain inorganic nutrients from the air, water and soil and convert them into
organic compounds.
● These organic compounds can then be used to produce more complex organic
molecules such as lipids and proteins or can be converted into more complex
carbohydrates such as cellulose which play an important role in the structure and
function of living organisms.
2. Heterotrophs ingest these organic compounds and use them for growth and respiration,
releasing inorganic byproducts.
3. When organisms die, saprotrophs decompose the remains and free inorganic materials
into the soil.
4. The return of inorganic nutrients to the soil ensures the continual supply of raw
materials for the autotrophs.
