Topic 5.1 Communities and Ecosystems

Question 1

5.1.1 Define species, habitat, population, community, ecosystem and ecology.

Answer 1

Species: a group of organisms with similar characteristics, that can interbreed and produce fertile offspring.

Habitat: the place where an organism lives and reproduces in the environment.

Population: all the organisms in a specific area belonging to the same species.

Community: all the various populations interacting in the area.

Ecosystem: communities of populations and abiotic factors.

Ecology: the study of interactions of organisms with each other and the physical environment.

Question 2

5.1.2 Distinguish between autotroph and heterotroph.

Answer 2

Autotroph: primary producers; can produce their own food by synthesizing their organic molecules from simple inorganic substances (photosynthesis)

Heterotrophs: consumers, detritivores, saprotrophs; cannot produce their own food and must obtain organic molecules from other organisms.

Question 3

5.1.3 Distinguish between consumers, detritivores and saprotrophs.

Answer 3

Consumers: e.g. primary, secondary, tertiary; ingest live or recently killed organic matter.

e.g. locusts, sheep, lions

Detritivores: decomposers; ingest dead organic matter.

e.g. dung beetles, earthworms

Saprotrophs: decomposers; live on or in dead organic matter, obtaining organic molecules from the products of digestion be secreting enzymes into organism.

e.g. bread mould, mushrooms

Question 4

5.1.4 Describe what is meant by a food chain, giving three examples, each with at least three linkages (four organisms).

Answer 4

A food chain shows energy flow and feeding relationships between species in communities. The arrow represents the direction of energy flow as organisms consume each other.

Example 1: dead leaves → insects → robin → fox

Example 2: passionflower → heliconius butterfly → tegu lizard → jaguar

Example 3: carrot plant → carrot fly → flycatcher → sparrowhawk → goshawk

Question 5

5.1.5 Describe what is meant by a food web.

Answer 5

A foodweb shows the direction of energy flow with arrows (similar to a food chain), except it’s a more complex connection diagram between multiple feeding relationships.

Question 6

5.1.6 Define trophic level.

Answer 6

Trophic level: an organism’s position in the food chain

e.g. trophic level 1 = producers

2 = primary consumers

3 = secondary consumers

4 = tertiary consumers

etc.

Question 7

5.1.7 Deduce the trophic level of organisms in a food chain and a food web.

Answer 7

The trophic level of an organism can be determined by counting the number of feeding relationships preceding it and adding one (producer always first)

Trophic Level = # of arrows (in sequence) before organism + 1

In food webs, a single organism may occupy multiple trophic levels

Question 8

5.1.8 Construct a food web containing up to 10 organisms, using appropriate information.

Answer 8

• phytoplankton
• starfish
• sardines
• shrimp
• crab
• seal
• tuna
• seagull
• shark
• dolphin
• killer whale

Question 9

5.1.9 State that light is the initial ______ ______ for almost all communities.

Answer 9

Light is the initial energy source for almost all communities.

Question 10

5.1.10 Explain the energy flow in a food chain.

Answer 10

• Autotrophs convert light energy to chemical energy through photosynthesis
• Organisms at higher trophic levels will consume organisms at lower trophic levels (energy flow)
• Only about 10% of energy will transfer from one organism to the next. The rest of the energy is lost.
• mass, in addition to energy, is lost too ∴ energy content/g of tissue of each successive trophic level is not lower
• energy flow reduces at higher trophic levels, thus number of trophic levels = limited

Question 11

5.1.11 State that energy transformations are _____ 100% efficient.

Answer 11

Energy transformations are never 100% efficient. (More like 10-20% efficient in cell respiration)

Question 12

5.1.12 Explain reasons for the shape of pyramids of energy.

Answer 12

• Each level of pyramid should be 1/10 size of lower level b/c energy transformations are about 10% efficient
• levels of pyramid express units of energy in kJ m^-2 year^-1
• rectangles instead of triangle b/c:
  • significant portion of energy is lost from one trophic level to the next
    
    • some organisms die before others can eat them
    • energy stored in some parts of organisms (bone, hair) aren’t eaten
    • indigestible parts of organisms pass out as feces
    • energy absorbed by an organism is released in cell respiration often as heat. In ATP form, is used in processes like muscle contraction or active transport
    • emigration of animals, thus in particular food chain energy cannot be consumed and is lost

Question 13

5.1.13 Explain that energy enters and leaves ecosystems, but nutrients must be recycled.

Answer 13

• The movement of energy and nutrients through ecosystems both occur by the transfer of substances through feeding relationships
• However, energy cannot be recycled and an ecosystem must be powered by a continuous influx of new energy from an external source (e.g the sun)
• Nutrients refer to material required by an organism, and are constantly being recycled within an ecosystem as food (either living or dead)
• The autotrophic activities of the producers (e.g. plants) produce organic materials from inorganic sources, which are then fed on by the consumers
• When heterotrophic organisms die, these inorganic nutrients are returned to the soil to be reused by the plants (as fertiliser)
• Thus energy flows through ecosystems, while nutrients are recycle within them

Question 14

5.1.14 State that saprotrophic bacteria and fungi (decomposers) _______ nutrients.

Answer 14

Saprotrophic bacteria and fungi (decomposers) recycle nutrients.

(Release enzymes that allow nutrients to be released from organic matter and reused in the environment)