TOPIC 5: ECOLOGY and
EVOLUTION

5.1.1
• Species: a group of organism that 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

• Community: a group of populations living and interacting with each other

• Ecology: the study of relationships between living organisms and between organisms and their environment

• Ecosystem: a community and its abiotic (nonliving; temperature, humidity, wind, rainfall etc.) environment

5.1.2: Autotroph/heterotroph
Autotroph: an organism that synthesizes its organic molecules from simple inorganic substances
Heterotroph: an organism that obtains organic molecules from other organisms

Consumers: an organism that ingests other organic matter that is living or recently killed.
Detritivore: an organism that ingests non-living organic matter.
Saprotrophs: an organism that lives on or in non-living organic matter, secreting digestive enzymes into it and absorbing the products of digestion, examples; bacteria and fungi

M09/4/BIOLO/SP2/ENG/TZ2/XX
Define the terms species, population and
community.
Species: Population:. Community: [3]
N08/4/BIOLO/SP2/ENG/TZ0/XX+
Define the term ecosystem.
[1]

5.1.4: Food Chain

Producer
→
Primary consumer
→
Secondary consumer
→
Tertiary consumer
Oak tree
Quercus
→
Caterpillar
Archips
→
Spotted towhee
Pipilo
→
Cooper’s Hawk
Accipitor
Sea lettuce
Ulva
→
Finger limpet
Collisella
→
Saguaro cactus
Carnegiea
→
Jackrabbit
Lepus
→
Rock crab
Cancer
Rattlesnake
Crotalus
→
Giant Octopus
Octopus
→
Red-tailed
Hawk
Beauteo

Describe what is meant by a food chain using an example with four named organisms. [4]
M11/4/BIOLO/SP2/ENG/TZ2/XX food chains describe the feeding relationships between species; arrows show (one) path of energy flow in an ecosystem / energy flow described; food chain with arrows pointing in the correct direction; producer first step in chain; three other named organisms making a realistic food chain; [4 max]
Accept explicit common names exact enough to identify the food source e.g. Oak not tree, sparrow not bird, rye grass not just grass, etc.

N08/4/BIOLO/SP2/ENG/TZ0/XX/M+
Examples must be based on a realistic ecosystem. Award [1] for each of the following clearly
drawn and correctly labelled. a chain (not in a web or pyramid) which includes the names of four organisms and three linkages in a logical feeding order/sequence; each linkage symbolized by an arrow ( ) showing the direction of energy flow; autotroph/producer and consumer labels correctly associated with organism; all three additional consumer labels correctly associated: primary, secondary and tertiary; [4 max]

5.1.5: Food web

Describe what is meant by a food chain and a food web. [6] N10/4/BIOLO/HP2/ENG/TZ0/XX
Accept examples of the points below, provided that the terms underlined are clearly identified. Accept only named examples (latin or common names) from natural ecosystems only. Do not award marks for general names such as “fish” or “tree”.
food chain shows transfer of nutrients/energy in an ecosystem / arrows from one trophic level to the next in examples; between different trophic levels / shown in a correct chain or web; starting with a producer; followed by at least two levels of consumers / shown in a correct chain or web; food web is the (branched) interaction of multiple food chains / cross arrows in examples; using (multiple) producers as a source; transferring nutrients/energy to consumers from different food chains; same consumer could be at different trophic levels in a food web; [6 max]

M07/4/BIOLO/SP2/ENG/TZ2/XX The diagram below shows a simplified food web for a lake.
State the initial energy source for the above food web. [1]
Define the term trophic level. [1]
Deduce the trophic level of the immature game fish.[1]
In the food web shown, identify one heterotroph and one autotroph.
heterotroph:

5.1.6: Trophic level
5 th trophic level
4 th trophic level
3 rd trophic level
2 nd trophic level
1 st trophic level

Explain, using an example of a food chain, how trophic levels can be deduced. [4]
M11/4/BIOLO/SP2/ENG/TZ1/XX diagram of food chain showing at least three organisms and two linkages with arrows showing direction of energy flow; trophic level is a step/position in the movement/flow of energy through an ecosystem;
(in a field situation) observe which organisms eat each other; producer/name from example (first trophic level) does not eat other organisms/captures energy through photosynthesis; primary consumer/name from example (second trophic level) feeds on producers; secondary consumer/name from example (third trophic level) feeds on primary consumers; [4 max]
Since the command term is explain, the answer must be explicit to gain marking points d–f. Named examples for producer and consumers in diagram or explained example must represent a coherent food chain. Reject chains using general names such as fish or tree or grass. But, accept sardine or oak.

(a) light penetration is required for photosynthesis; plants/phytoplankton/photosynthetic organisms are the base of many aquatic food chains; allows interacting organisms to find one another (e.g. predator-prey relationship, courtship); allows interaction with the physical environment (e.g. finding shelter); [2 max]
(b) (i) light / sunlight [1]
(ii) the feeding level/position an organism occupies in a food chain [1]
(iii) secondary consumer [1]
(iv) heterotroph: immature game fish / trout / pike / shad / zooplankton;
autotroph: phytoplankton; [1 max]
Two correct answers needed for [1].

5.1.9: Light energy
• State that light is the initial energy source for almost all communities.

5.1.10: Energy Flow

5.1.11: Energy transformations

5.1.12: Pyramid of Energy

STATE: Energy transformations are never 100% efficient

N06/4/BIOLO/SP2/ENG/TZ0/XX The diagram below represents an energy pyramid and four trophic levels.
Identify the trophic level of the organisms indicated below.
I:
IV
[2]
(ii) Calculate the approximate amount of energy in kilojoules transferred in m–2 yr–1 from trophic level I to trophic level II.
______________________kJ

M08/4/BIOLO/SP2/ENG/TZ1/XX+ Explain the reason for the shape of a pyramid of energy.
[3]
(the shape of pyramid) shows energy lost from base to top of pyramid/at each trophic level;
(because) energy is used/released through cell respiration/heat/movement (at each trophic level); not all tissues are eaten i.e. bone/hair/cellulose/excretion/undigested/die; less energy available at each trophic level / only 10- 20% passed on so each level is (80-90%) smaller than the preceding / a diagram must show the approximate changes in levels; [3 max]

5.1.13: Energy and nutrients

5.1.14: Decomposers
STATE: Saprotrophic bacteria and fungi (decomposers) recycle nutrients

N08/4/BIOLO/SP2/ENG/TZ0/XX+
Outline the role of decomposers in recycling nutrients.
[2] break down/digest dead organic matter; (do
not accept “feed”) unlock/produce inorganic nutrients/soluble compounds/ions; (inorganic nutrients) assimilated by living organisms / an example of this; bacteria/fungi/saprotrophs; [2 max]

State the names of the processes that
(i) convert carbon dioxide into organic compounds in pond weeds and algae.[1] convert organic compounds in pond weeds, algae and primary consumers into carbon dioxide. [1]
Draw arrows on the diagram above to show how the saprotrophs obtain carbon.
(ii) Explain the role of saprotrophs in recycling carbon.[1]
[2]
(c) Draw a box on the diagram in an appropriate position, labelled organic compounds in secondary consumers. Draw arrows to show the links between secondary consumers and other parts of the carbon cycle.