Lecture notes
IB NOTES U4
- Module
- IB Biology HL U4
- Institution
- Cambridge University (CAM)
KEY OBJECT TO ACHIEVE 7 IN IB BIOLOGY HL
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4.1 Species, communities and ecosystems: The continued survival of living organisms including humans depends on
sustainable communities.
Nature of science: Looking for patterns, trends and discrepancies—plants and algae
are mostly autotrophic but some are not.
The majority of plants and algae are autotrophic, meaning they produce their
own food through photosynthesis; however, a small percentage of plants and
animals obtain these carbon compounds from other organisms, either by
growing on them and stealing the nutrients from the plant they are growing on
or by consuming dead organic material. Since they obtain these carbon
compounds from other species and cause them harm, they are considered
parasitic.
Only approximately 1% of all plants and algae are considered parasitic
***Do the data-based question on 204***
∑- Understandings:
∑ - Species are groups of organisms that can potentially interbreed to produce fertile
offspring.
Species: a group of organisms that share a common ancestry, can interbreed and
produce fertile offspring and is reproductively isolated from other such groups.
∑ - Members of a species may be reproductively isolated in separate populations.
A population is a group of organisms of the same species who live in the same
area at the same time
Two populations of the same species can live in two different areas and are
unlikely to interbreed; however, they are still part of the same species if they
could potentially interbreed
∑ - Species have either an autotrophic or heterotrophic method of nutrition (a few
species have both methods).
Autotroph:
An organism that synthesizes its own organic molecules (makes their own food)
from simple inorganic substances.
Usually, autotrophs convert light energy to chemical energy through
photosynthesis.
Chemoautotrophs obtain their energy through the oxidation of inorganic
molecules in their environments.
,Heterotroph:
An organism that obtains organic molecules from other living organisms or
their dead remains.
Heterotrophs consume other organisms because they cannot make their own food.
Mixotrophic - Some unicellular organisms use both methods of nutrition such
as Euglena gracilis which have chloroplasts to carry out photosynthesis when there is
enough sunlight; however, they can also feed on detritus (dead or decaying material)
or other smaller organisms.
∑ - Consumers are heterotrophs that feed on living organisms by ingestion.
A consumer is an organism that ingests other organic material that is living or
has been recently killed.
Consumers feed by ingesting their food, then digesting it and absorbing these
products of digestion
Primary consumers feed off autotrophs (example: Eastern Grey Squirrel feeds of
mostly nuts/acorns)
Secondary consumers feed on primary consumers (example: Red Fox feeds on
Eastern Grey Squirrels)
Tertiary consumers would feed on secondary consumers (example: Black Bear can
feed on a Red Fox)
∑ - Detritivores are heterotrophs that obtain organic nutrients from detritus by
internal digestion.
Detritivore: an organism that obtains food by ingesting non-living organic
matter i.e. Vultures and earthworms.
∑ - Saprotrophs are heterotrophs that obtain organic nutrients from dead organisms
by external digestion.
Saprotroph: an organism that lives on or within nonliving organic matter,
secreting digestive enzymes into it and absorbing the nutrients produced by
digestion. Saprotrophs help with the decaying or break down of dead organic
materials.
β - Skill: Classifying species as autotrophs, consumers, detritivores or
saprotrophs from a knowledge of their mode of nutrition.
***Classify organisms using the dichotomous key on page 206***
, ∑ - A community is formed by populations of different species living together and
interacting with each other.
Community: a group of populations living and interacting with each other in a
particular area. Basically, it means all living things in a habitat
All the coral, fish and living organisms on this coral reef in Australia make up a
community
∑ - A community forms an ecosystem by its interactions with the abiotic
environment.
Ecosystem: a community which consists of all the biotic factors such as plants
and animals in an area, functioning together with all of the physical or abiotic
factors of the environment.
So the above example of the coral reef with all the abiotic factors including
water temperature, currents, available nutrients, etc. is an ecosystem
Applications and skills:
β - Skill: Testing for association between two species using the chi-squared test with
data obtained by quadrat sampling. To obtain data for the chi-squared test, an
ecosystem should be chosen in which one or more factors affecting the distribution of
the chosen species varies. Sampling should be based on random numbers. In each
quadrat, the presence or absence of the chosen species should be recorded. The
collection of raw data through quadrat sampling will be done in the North Forest
Example of Quadrat Sampling
Plot-based (quadrat) methods are often used to study populations of different species
within a certain area.
Quadrats are generally square sample areas marked out using a framed structure.
Quadrats are placed in a marked out habitat according to random numbers obtained
using a random number table or a random number generator on a calculator
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