5.1 Communities And Ecosystems

Question 1

Define species

Answer 1

A group of organisms that can interbreed and produce fertile, viable offspring

Question 2

Define habitat

Answer 2

The environment in which a species normally lives or the location of a living organism

Question 3

Define population

Answer 3

A group of organisms of the same species who live in the same area at the same time

Question 4

Define community

Answer 4

A group of populations living and interacting with each other in an area

Question 5

Define ecosystem

Answer 5

A community and its abiotic environment

Question 6

Define ecology

Answer 6

The study of relationships between living organisms and between organisms and their environment

Question 7

Define autotroph

Answer 7

• An organism that synthesises its organic molecules from simple inorganic substances (e.g. CO2and nitrates)
  
  • Autotrophs areproducers

Question 8

Define hetrotroph

Answer 8

• An organism that obtains organic molecules from other organisms
  
  • Heterotrophs areconsumers

Question 9

Define consumer

Answer 9

An organism that ingests other organic matter that is living or recently killed

Question 10

Define detritivore

Answer 10

An organism that ingests non-living organic matter

Question 11

Define saprotroph

Answer 11

An organism that dereives nourishment from decaying organic matter. Saprotrophs secrete digestive enzymes and absorbing the products of digestion.

Question 12

Describe what is meant by a food chain

Answer 12

• A food chain shows the linear feeding relationships between species in a community
  
  • The arrows represent the transfer of energy and matter as one organism is eaten by another (arrows point in the direction of energy flow)
  • The first organism in the sequence is the producer, followed by consumers (1°, 2°, 3°, etc.)
  • The position (level) of a species in a food chain (or food web) is called its trophic level

Question 13

Give three examples of food chains

Answer 13

1. Plankton → Krill → Mullet → Shark
2. Oak tree → Caterpillar → Sparrow → Domestic Cat
3. Rosebush → Aphid → Spider → Magpie

Question 14

Describe what is meant by a food web

Answer 14

• A diagram that shows how food chains are linked together into more complex feeding relationships within a community or ecosystem
  
  • Shows flow of energy within an ecosystem
  • There can be more than one producer in a food web, and consumers can occupy multiple trophic levels
  • Organisms rarely feed on only one other organism, usually fed on by more than one organism
    
    • If one species becomes extinct, the ecosystem will adapt

Question 15

Define trophic level

Answer 15

• An organism’s trophic level refers to the position it occupies in a food chain
  
  • Producers always occupy the first trophic level, while saprotrophs would generally occupy the ultimate trophic level of a given food chain or food web

Question 16

State the initial energy source for almost all communities

Answer 16

Light (the sun)

Question 17

Explain how light is the initial energy source for almost all communities

Answer 17

• All green plants, and some bacteria, are photo-autotrophic - they use light as a source of energy for synthesising organic molecules
  
  • This makes light the initial source of energy for almost all communities
  • Some bacteria are chemo-autotrophic and use energy derived from chemical processes (e.g. nitrogen-fixating bacteria)

Question 18

State how energy in a food chain is measured

Answer 18

Units of energy per unit area per unit time

Question 19

Describe how energy transformations are never 100% efficient

Answer 19

• During transfer of energy between trophic levels, process is never 100% efficient
  
  • Only ~10% of energy will be passed on to next level
  • This energy may be lost as heat, be used up during cellular respiration, be excreted in faeces or remain unconsumed as the uneaten part of food

Question 20

Describe energy flow in a food chain

Answer 20

• Light converted into chemical energy by autotrophs
  
  • Energy passed to herbivores when they eat plants
  • Energy passed to carnivores when they eat herbivores

Question 21

Explain how energy is lost in a food chain

Answer 21

• Only ~10% of energy is passed from one trophic level to the next, the rest is lost
○ Not ingested
○ Not digested or assimilated
○ Excreted
○ Lost as heat from respiration
• Because ~90% of energy is lost between trophic levels, the number of trophic levels are limited as energy flow is reduced at higher levels.
• Ultimately, all energy lost as heat

Question 22

Explain the reason for the shape of pyramids of energy

Answer 22

• A pyramid of energy is a graphical representation of the amount of energy of each tropic level in a food chain
  
  • Narrowing shape shows gradual loss of energy as trophic level increases
  • Never appear inverted as some of the energy stored in one source is always lost when transferred to the next source
  • Each level should be approximately one tenth the size of the level preceding it, as energy transformations are ~10% efficient

Question 23

Explain how energy flows and leaves ecosystems

Answer 23

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)

At every trophic level, energy is lost as heat. The narrowing of the energy pyramid shows that all energy is eventually radiated as heat into space.

Question 24

Explain how nutrients cycle within an ecosystem

Answer 24

New matter is not produced, nor is it lost the way energy is.
• Producers (autotrophs) take inorganic molecules and convert them into organic compounds, allowing them to be recycled and reused.
• Consumers take in this organic matter and use it for their own growth.

Carbon, nitrogen and oxygen are cycled this way.

Question 25

Describe how saprotrophic bacteria and fungi (decomposers) recycle nutrients

Answer 25

Unlike energy, nutrients are not lost, but recycled and reused.
• In order for organisms to grow and reproduce, they need a supply of the elements of which they are made
• The saprotrophic activity of decomposers (certain bacteria and fungi), free inorganic materials from the dead bodies and waste products of organisms, ensuring a continual supply of raw materials for the producers (which can then be ingested by consumers)
• Thus saprotrophic bacteria and fungi play a vital role in recycling nutrients within an ecosystem