1. TOPIC 5 – Ecology and evolution
Topic 5.1 - Communities and Ecosystems
5.1.1. Define species, habitat, population, community, ecosystem and ecology.
• Species - a group of organisms which can interbreed and produce fertile offspring
• Habitat - the environment in which a species normally lives or the location of a living organism
• Population - a group of organisms of the same species who live in the same area at the same time
• Community - a group of populations living and interacting with each other in an area
• Ecosystem - a community and its abiotic environment
• Ecology - the study of relationships between living organisms and between organisms and their
environment.
5.1.2. Distinguish between autotroph and heterotroph.
• Autotroph – an organism that synthesizes its organic molecules from simple organic substances
• Heterotroph – an organism that obtains organic molecules from other organisms
5.1.3. Distinguish between consumers, detritivores and saprotrophs.
• Consumer – an organism that ingests other organic matter that is living or recently killed
• Detritovore – an organism that ingests non-living organic matter.
• Saprotroph – an organism that lives on or in non-living organic matter, secreting digestive
enzymes into it and absorbing the products of digestion. Examples are bacteria and fungi.
5.1.4. Describe what is meant by a food chain, giving three examples, each with at least three
linkages (four organisms).
• A food chain is a linear and simple feeding relation, where one organism has one type of food and
is eaten by one type of organism.
5.1.5. Describe what is meant by a food web.
• A food web is more complex than a food chain and it includes a larger variety of organisms. Each
of which feed on a variety of other organisms and they are in turn fed on by more organisms.
Therefore, if one species becomes extinct the ecosystem will still be able to exist. A drawing will
be inserted at a later date of a food web.
5.1.6. Define trophic level.
• Trophic level - the division of species in an ecosystem on the basis of their main nutritional
source. The trophic level that ultimately supports all others consists of autotrophs, or primary
producers.
5.1.7. Deduce the trophic level of organisms in a food chain and a food web.
Students should be able to place an organism at the level of producer, primary consumer, secondary
consumer, and so on, as the terms herbivore and carnivore are not always applicable.
5.1.8. Construct a food web containing up to 10 organisms, given appropriate information.
5.1.9. State that light is the initial energy source for almost all communities.

2. 5.1.10. Explain energy flow in a food chain.
• Energy losses between trophic levels include material not consumed or material not assimilated
and heat loss through cell respiration.
5.1.11. State that energy transformations are never 100% efficient.
• When energy transformations take place, including those in living organisms, the process is never
100% efficient, commonly between 10-20%.
5.1.12. Explain reasons for the shape of a pyramid of energy.
• A pyramid of energy shows the flow of energy from one trophic level to the next in a community.
The units of pyramids of energy are therefore energy per unit area per unit time.
5.1.13. Explain that energy enters and leaves ecosystems, but nutrients must be recycled.
• Sun light is the main source of energy on this planet. It is absorbed by photosynthesizing
organisms, which convert light to chemical energy. Nutrients must be recycled by obtaining them
from other organisms or products of organisms.
5.1.14. State that saprotrophic bacteria and fungi (decomposers) recycle nutrients.
• These organisms feed on dead organisms and products of living organisms. They secrete enzymes
on these materials that cause decomposition, and then they absorb digested products. Examples
include many species of bacteria and fungi. These are essential organisms to an ecosystem, since
they cause recycling of materials between biotic and abiotic parts of the ecosystem.
Topic 5.2 – The greenhouse effect
5.2.1. Draw and label a diagram of the carbon cycle to show the processes involved.

3. 5.2.2. Analyse the change in concentration of atmospheric carbon dioxide using historical records.
5.2.3. Explain the relationship between rises in concentrations of atmospheric carbon dioxide,
methane and oxides of nitrogen and the enhanced greenhouse effect.
The greenhouse effect is a natural phenomenon – human activities are causing an enhanced greenhouse
effect.

4. • Increased industry and burning of fossil fuels have caused the release of excessive amounts of
carbon dioxide into the atmosphere
• Nitrous oxides are also released when fossil fuels such as petrol are burnt
• Methane is a greenhouse gas being released from paddy fields and increasing numbers of cows
• The planet is now enveloped by a layer of greenhouse gases thicker than would be there naturally,
which allows the sun radiation to enter our atmosphere, but prevents it from going out.
• Shorter wave radiation enters Earth’s atmosphere, but re-radiated radiation is trapped by this layer
of gases
• This causes the trapping of heat into our atmosphere, and the consequent gradual increase in
temperature around the world, hence global warming.
• This effect is called the greenhouse effect, since the layer of carbon dioxide around our planet has
similar effects to the glass walls of a greenhouse in causing increased temperature inside.
• Its effects have included an increase in global temperature by several degrees over the past
decade, a melting of glacial deposits across the globe, and the recent thinning of Artic and
Antarctic pack ices; all of the effects reported as the much-publicized global warming.
• Many scientists predict more drastic changes in temperature and environment in the future if
current warming patterns continue.
5.2.4. Outline the precautionary principle.

5. The precautionary principle holds that, if the effects of a human induced change would be very large,
perhaps catastrophic, those responsible for the change must prove that it will not do harm before
proceeding. This is the reverse of the normal situation, where those who are concerned about the change
would have to prove that it will do harm in order to prevent such changes going ahead.
5.2.4. Evaluate the precautionary principle as a justification for strong action in response to the
threats posed by the enhanced greenhouse effect.
5.2.5. Outline the consequences of a global temperature rise on arctic ecosystems.
• Increased rates of decomposition of detritus previously trapped in permafrost
• Expansion of the range of habitats available to temperate species
• Loss of ice habitat
• Changes in distribution of prey species affecting higher trophic levels
• Increased success of pest species including pathogens
Topic 5.3 - Populations

6. 5.3.1. Outline how population size can be affected by natality, immigration, mortality and
emigration
• Population size can be affected by natality (birth) because as birth rate increases, the population
increases. The increase in a population is exponential, as the population increases so does the birth
rate.
• Immigration is the arrival to the population from another area. This adds to the numbers in the
total population.
• Mortality is death, and the mortality rate, like the birth rate, increases as the population increases.
This, along with emigration (migration of population to another area) can help to stabilize
population growth.
• In order for a population to be stable in size, Natality + immigration = mortality + emigration.
5.3.2. Draw and label a graph showing the sigmoid (S-shaped) population growth curve.
5.3.3 Explain reasons for the exponential growth phase, the plateau phase, and the transitional
phase between these two phases.
• The exponential growth phase exists because that is when the population has already begun to
grow, but not a lot yet, and it rises quickly because there are no limiting factors yet and the

7. resources are in unlimited amounts. The plateau phase begins when the organism hits its carrying
capacity, which is the maximum number of organisms in a population that can be supported by the
environment at a certain time, in a certain ecosystem. The transitional phase in between these two
phases occurs because this is when the limiting factors in the environment start to limit the
increase, slowing the population increase.
5.3.4. List three factors which set limits to population increase.
Three factors that set limits to population increase are
• Availability of nutrients
• Number of predators
• Accumulation of waste materials.
Topic 5.4 - Evolution
5.4.1. Define evolution.
• Evolution is the cumulative change in the heritable characteristics of a population.

8. • If we accept not only that species can evolve, but also that new species arise by evolution from
pre-existing ones, then the whole of life can be seen as unified by its common origins
• Variation within our species is the result of different selection pressures operating in different
parts of the world, yet this variation is not so vast as to justify a construct such as race having a
biological or scientific basis
5.4.2. Outline the evidence for evolution provided by the fossil record, selective breeding of
domesticated animals and homologous structures
5.4.3. State that populations tend to produce more offspring than the environment can support.
5.4.4. Explain that the consequence of the potential overproduction of offspring is the struggle for
survival.
• Organisms produce many more offspring than can live off of these limited resources.
• Therefore, there is a struggle to survive between offspring.
• This allows for natural selection, because those best suited for their environment survive and pass
on their better-suited genes.
5.4.5. State that the members of a species show variation.
5.4.6. Explain how sexual reproduction promotes variation in a species.
• Sexual reproduction promotes variations because, unlike the cloning that occurs in asexual
reproduction, every offspring is a genetic combination of his of her parents.
• This allows for infinite possibilities, as one can easily see by looking at the people around them.
• During meiosis, many different gametes are created because chromosomes are independently
assorted during meiosis.
• Then, during fertilization, one of the many gametes from the mother joins with one of the many
gametes from the father, creating a new and unique combination of genes.
5.4.7. Explain how natural selection leads to evolution.
• Overproduction leads to a struggle for survival
• We can see that a group of different organisms are all competing to occupy a certain niche (a
place in the ecosystem).
• An organism that is better suited to an environment will be able to reproduce and pass on their
superior genes.
• The ability of better suited organisms to reproduce more than other organisms that are not as
suited for their environment allows for the better suited organisms to produce more organisms
with those same genes.
• These organisms have inherited the superior genes, so the amount of organisms with superior
genes has increased.
5.4.8. Explain two examples of evolution in response to environmental change; one must be
antibiotic resistance in bacteria
Example 1: Two varieties of the moth Biston betularia exist in the forms of different body colour.
One is black, the other is speckled. The black moth is easily seen by predators while the speckled one
is camouflaged. When on a tree covered in lichens, the peppered moth blends in very well. The
number of speckled moths was greater than the number of black moths, because the speckled genes
made the speckled moths more suitable for their environment of lichen-covered trees. Because they
were able to camouflage, they could evade predators more than black moths could, which allowed

9. them to reproduce more moths with the genes for speckled color. Then, the trees began to get covered
in soot due to industrialisation, and the black moth was able to be more camouflaged than the
speckled moths. Because of this, more black moths than speckled moths evaded predators, allowing
them to produce more black moths. So the population of black moths then increased and the speckled
moth population decreased.
Example 2: Resistance to antibiotics in bacteria. If a culture of bacteria is sprayed with antibiotics,
most of the bacteria are killed. A small number that naturally have genes resistant to antibiotics will
remain. It is important to note that these bacteria did not "learn" to resist antibiotics. These bacteria
have mutated genes that somehow allowed them to resist antibiotics. These bacteria will reproduce
and pass on their resistant genes. Natural selection “chose” the antibiotic resistant ones, so those are
the only ones to exist. This can become a problem when trying to kill a bacterial infection in a patient,
because if the bacterium is resistant to the antibiotics given, then it can't be killed. Someone would
have to come up with a new antibiotic that it is not resistant to, which can be difficult.
Topic 5.5- Classification
5.5.1. Outline the binomial system of nomenclature.
• Organisms are given two names in this system (binomial).
• The first name indicates the genus and the second indicates the species.
• The genus is written in a capital letter and the species in small letters, e.g. Homo sapiens
• Also the two names are usually printed in italics or underlined.

10. • Naming organisms in this way facilitates the process of identification and helps in overcoming
language barriers between scientists.
5.5.2. List the seven levels in the hierarchy of taxa - kingdom, phylum, class, order, family, genus
and species - using an example from two different kingdoms for each level.
Long-tailed macaque - Scientific classification
Kingdom: Animalia
Phylum: Chordata
Class: Mammalia
Order: Primates
Family: Cercopithecidae
Genus: Macaca
Species: M. fascicularis
Subspecies: M. f. umbrosa
Bunga Raya - Scientific classification
A hibiscus flower.
Kingdom: Plantae
Division: Magnoliophyta
Class: Magnoliopsida
Order: Malvales
Family: Malvaceae
Genus: Hibiscus
Species: Hibiscus rosa-sinensis
5.5.3. Distinguish between the following phyla of plants, using simple external recognition
features: bryophyta, filicinophyta, coniferophyta and angiospermatiohyta.
• Bryophyta include mosses. They are non-vascular plants - they cannot transport fluids through their
bodies. Instead, they must rely on surrounding moisture to do this job for them. Small in stature,
mosses do not have a sophisticated root system so live in moist environments.
• Filicinophyta (ferns) have a vascular system to transport fluids through their bodies but like the
mosses, they reproduce from spores rather than seeds.

11. • Coniferophyta conifers add the next level of complexity to plant evolution: they reproduce from
seeds instead of spores. The seeds, however, are "naked" - not covered by an ovary. Usually, the
seed is produced inside a cone-like structure such as a pine cone, hence the name "conifer."
• Angiospermatiohyta (flowering plants) add the final improvement to plant reproduction: they grow
their seeds inside an ovary) which is, itself, embedded in a flower. After it is fertilised, the flower
falls away and the ovary swells to become a fruit.
• Angiosperms in the class Dicotyledoneae grow two seed-leaves (cotyledons). In addition, foliage
leaves typically have a single, branching, main vein originating at the base of the leaf blade, or
three or more main veins that diverge from the base.
5.5.4. Distinguish between the following phyla of animals, using simple external recognition
features: porifera, cnidaria, platyhelminthes, annelida, mollusca and arthropoda.
• Porifera (sponges) are primarily marine; their cells are specialized so that different cells perform
different functions, but similar cells are not organised into tissues and bodies are a sort of loose
aggregation of different kinds of cells. Other characteristics of sponges include a system of pores
(also called ostia) and canals, through which water passes. Water movement is driven by the
beating of flagellae, which are located on specialized cells called choanocytes (collar cells).
Sponges capture food (detritus particles, plankton, bacteria) that is brought close by water currents
created by the choanocytes. Food items are taken into individual cells by phagocytosis, and
digestion occurs within individual cells.
• The Phylum Cnidaria includes such diverse forms as jellyfish, hydra, sea anemones, and corals.
They have achieved the tissue level of organization, in which some similar cells are associated into
groups or aggregations called tissues, but true organs do not occur. Cnidarian bodies have two or
sometimes three layers. A gastrovascular cavity (coelenteron) has a single exterior opening that
serves as both mouth and anus. Often tentacles surround the opening.
• Cnidarians have two basic body forms, medusa and polyp. Medusae, such as adult jellyfish,
are free-swimming or floating. Polyps, in contrast, are usually sessile. They have tubular
bodies; one end is attached to the substrate, and a mouth (usually surrounded by tentacles) is
found at the other end.
• The name Cnidaria comes from the Greek word "cnidos," which means stinging nettle.
Casually touching many cnidarians will make it clear how they got their name when their
nematocysts eject barbed threads tipped with poison.
• Platyhelminthes (flatworms) are unsegmented, bilaterally symmetrical worms that lack a coelom
but that do have three germ layers. Some forms are free living but many are parasitic. Flatworms
have a nervous system that consists of head ganglion, usually attached to longitudinal nerve cords
that are interconnected across the body by transverse branches.
• Annelida (segmented worms) have a segmented body and are bilaterally symmetrical. They have
a body wall with outer circular and inner longitudinal muscle layers and chitinous setae. The
coelum is well-developed. There are three classes of annelids; Class Polychaeta, Class

12. Oligochaeta (e.g. earthworm) and class Hirudinea – Leeches.
• Next to Arthropoda, the phylum Mollusca (Snails, Clams, Squid & Octopus) has the most named
species in the animal kingdom -probably about 50,000 living species. The name Mollusca
indicates one of their distinctive characteristics: a soft body.
• Body bilaterally symmetrical; unsegmented, usually with definite head.
• Ventral body wall specialised as a muscular foot, variously modified but used chiefly for
locomotion.
• Arthropoda (Spiders, Insects, Crabs), the largest invertebrate phylum, show bilateral symmetry,
have an exoskeleton and jointed limbs. The coelom is reduced; most of body cavity consisting of a
hemocoel.
5.5.5 Apply and/or design a key for a group of up to eight organisms.