Pearson Baccalaureate Biology Standard Level 2nd Edition Print and Ebook Bundle for the IB Diploma
Complete summaries and study guides on the chapters of Pearson Baccalaureate's Biology Standard Level IB book. Detailed summaries of up to 10 pages with illustrations. These documents helped me get a good 6 in the IB exams of May 2019 :)
--> This document is on Chapter 4: Ecology
Chapter IV: Ecology
4.1 Species, communities and ecosystems
Terminology
Species A group of organisms that can interbreed and produce fertile offspring. (e.g.
domestic dogs)
Autotrophs Organisms capable of producing their own organic molecules as a source of
food. They synthesize organic molecules from inorganic substances.
Heterotrophs In order to obtain organic molecules, they must use other organisms as a source
of food. They cannot make their own food from inorganic matter.
Consumers Heterotrophs are automatically consumers. They need to eat other organisms.
(Products of autotrophs or other heterotrophs.)
Detritivores Eat non-living organic matter e.g. dead leaves, faeces and carcasses. They digest,
in comparison to saprotrophs, internally though. (e.g. earthworms, dung
beetles.)
Saprotrophs They live on/in non-living organic matter and secrete digestive enzymes and
absorb the products of the external digestion. They play an important role in the
decay of dead organic material. (Saprotroph fungi and bacteria: also
decomposers because they break down waste material.)
Community Group of populations living an interacting with each other in an area. (forest:
plants, animals and fungi)
Population A population is all of the individuals of the same species within an ecological
community.
Hybrid Infertile offspring of two different but similar species. = interspecific hybrid →
genetic barrier between species
Abiotic factors: Sunlight, water, temperature, precipitation, soil.
Biotic factors: Autotrophs, omnivores, herbivores, carnivores, decomposers.
Biomes: Distinct biological communities that have formed in response to a shared physical climate. (e.g.
aquatic, tundra, deserts, forests and grasslands.)
Isolation of populations → speciation, a new species formed from an old one
A group from a species can evolve very differently if its separated from the rest of the species.
→ beneficial mutations are genetically passed on = group can become so distinct from original species
that breading becomes impossible
Ecosystem and nutrient cycle (e.g. Co2 or nitrogen cycle):
Ecosystem: biological community of living organisms (biotic) and non-living organisms (abiotic) in an
area.
Autotrophs are the first step of the food chain in an ecosystem. They produce their own organic
molecules by synthesizing them from inorganic substances = photosynthesis. However, autotrophs still
need minerals to grow, and there aren’t enough minerals in the atmosphere to supply all organisms. →
ecosystems must recycle carbon, nitrogen and other elements in order for life to exist but those
important minerals and natural compounds are locked up in the living organisms which use them
to build their cells. That’s when the decomposers come into play. The nutrients such as minerals and
organic compounds are passed on within the food chain. When an organism dies however, the
decomposers recycle nutrients so they are available for themselves and the whole ecosystem
again. All of it is given back to the soil, the atmosphere and all of the organisms again and the cycle
starts of again. → sustainability
- Nitrogen cycle: Nitrogen is an important element needed in nucleotides and amino acids.
Nitrogen starts cycle as gas in atmosphere. Bacteria fixate nitrogen into useful forms, such as
nitrates, in a process called nitrogen fixation. Nitrate is then absorbed by plant roots and so the
, nitrogen-rich nutrients are passed on to the consumers. The nitrogen is returned to soil through
urine and faeces.
Random sampling:
Randomly place a quadrat (square of a particular dimension made of a rigid material) on an area and
identify and count number of individuals of the chosen species found inside the quadrat. → repeat
process. Later, determine how many individuals there were per square meter and use the surface area
calculation to estimate the total number of individuals on the total area.
Systematic sampling techniques
A transect, a line traced from one environment to another, is made using some kind of tape or rope. A
quadrat is laid down at specific intervals along the transect. → count organisms along and inside the
transect
= see relationship between distribution of organisms and abiotic factors that change along the transect
4.2 Energy flow
All life on earth relies either directly or indirectly on the sunlight. Autotrophs convert light energy from
the sun into chemical energy (food). = importance of photosynthesis Carbohydrates, Lipids and
proteins are high in energy thanks to the chemical bonds that exist between the carbon atoms and
the other atoms.
Food chains: pattern of feeding
Process of passing on chemical energy from one organism to another organism through a food chain
= Flow of energy through a food chain.
Grassland ecosystem: grass = producer → grasshopper = primary consumer → toad
= secondary consumer → snake = tertiary consumer → hawk … 4 – 5 trophic
River ecosystem: grass → mayfly larvae → juvenile trout → kingfisher levels
Marine ecosystem: diatoms → copepods → herring → seals → great white shark
Coastal ecosystem: phytoplankton → krill → penguin → seal
→ food chains are relatively short as with every step, only 10% of the chemical energy is passed on and
90% is “lost”:
- heat (= chemical energy) is lost at each step due to cellular respiration (= not all chemical energy
is used for ATP production).
- not every part of the organism is eaten
- movement and maintenance of body temperature (= maintenance processes)
+ At the end of every food chain, decomposers will break up the dead organic material and the minerals
will enter the food chain again.
Energy cannot be recycled
Unlike with nutrients, when the energy leaves an organism in form of e.g. heat, it cannot be reused by the
ecosystem. Not a problem as sun never stops shining. = provides us with energy all over again.
Pyramid of energy: is used to portray the energy levels at each trophic level.
Biomass: The biomass of a trophic level is an estimate of the mass of all the organisms in an ecosystem
within that level. The amount of sunlight (=energy) influences the amount of biomass and the amount of
steps the food chain can provide. Some molecules aren’t passed on in the biomass chain because they are
“lost” in various forms: water during transpiration, Co2 during cellular respiration and urea during
excretion. So, just as not all energy is passed on from one trophic level to the next, not all biomass is
passed on either. → will biomass run out? Thomas Malthus = we’ve not reached the peak
4.3 Carbon cycling
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