6.5 Ecosystems

Question 1

Define ecosystem

Answer 1

a community of animals. plants and bacteria interrelated with the physical and chemical environment,involving abiotic and biotic factors

Question 2

Define habitat

Answer 2

place where an organism lives

Question 3

Define population

Answer 3

all organisms of one species who live in the same place at the same time

Question 4

Define community

Answer 4

all populations of diff species who interact with eachother and live at the same place at the same time

Question 5

Define niche

Answer 5

role of a species in an ecosystem

impossible for 2 species to occupy exactly the same niche in the same ecosystem

Question 6

What are the main types of organisms found in a food web?

Answer 6

• producers: plants and some photosynthetic organisms supply chemical energy to all others
• primary consumer = herbivores, eaten by carnivorous secondary consumers
• decomposers : feed on dead animals and wastes

Question 7

What are some abiotic factors? What can they be influenced by?

What are some examples of factors lethal at both extremes vs one extreme?

Answer 7

• pH, humidity, temperature, pollutant conc
• can be influenced by biotic components e.g. in a rainforest the forest canopy influences temp and humidity

BOTH: pH
ONE: pollutant levels

Question 8

Why are ecosystems dynamic? What 3 types of changes can occur?

Answer 8

• non living elements change and the living elements grow and die
• CYCLIC: repeat themselves in a rhythm e.g movement of tide or predator + prey fluctuation
• DIRECTIONAL: one direction, tend to last longer than lifetime of the organisms in that ecosystem. e.g. coast erosion
• ERRATIC: no rhythm or constant direction. e.g. lightning and hurricanes

Question 9

What does biomass consist of? What is recycled, what isnt?

Answer 9

organic components e.g glucose, and inorganic components e.g. ions, but NOT water

materials recycled, energy isn’t

Question 10

What is each level of a food chain called? What is transferred between these?

Answer 10

trophic level

biomass is transferred

Question 11

How is biomass lost at each level?

Answer 11

used up in metabolic processes such as respiration, so some is also transferred as heat and materials are lost as carbon dioxide and water

biomass lost as dead organisms and waste products that only become available to decomposers such as fungi and bacteria

many parts are not digestible/consumed for growth e.g. bones, hair, feathers

Question 12

what is a pyramid of numbers vs a pyramid of biomass?

Answer 12

NUMBERS: used when organisms in a food chain are roughly the same size, and so the area is proportional to the no. of individuals at that level, as an approx for total biomass

BIOMASS: better approach. where area is proportional to DRY MASS of all organisms at that trophic level

Question 13

What is the method for collecting dry mass? Why is this an issue?

Answer 13

put organisms in oven, periodically find mass. when mass stops reducing, take them out

destructive though, especially bad for endangered species, so ecologists often measure wet mass and calculate dry mass based on previously published data

Question 14

How do you calculate ecological efficiency?

Answer 14

biomass at higher level / biomass at lower level
x 100

Question 15

Define nitrogen fixation. What two types of bacteria do this?

Answer 15

Conversion of atmospheric nitrogen into nitrogen containing compounds

Rhizobium in leguminous plants e.g. root nodules = mutualistic
Azotobacter = free living in soil

Question 16

Define nitrification - which 2 bacteria do this? What does it require?
What type of bacteria are they?

Answer 16

Conversion of ammonia/ammonium ions into nitrite/nitrate ions

NH4+ -> NO2- = done by Nitrosomonas in soil

NO2- -> NO3- = Nitrobacter in soil

Chemoautotrophic

Requires oxygen so only occurs in well aerated soil

Question 17

What is denitrification? Where does it occur?

Answer 17

Conversion of nitrates into atmospheric nitrogen
Occurs in waterlogged soils where bacteria use nitrates in respiration

Question 18

What is ammonification?

Answer 18

Decomposition to convert nitrogen containing matter (e.g. nitrogen in soil, or in urea or wastes) into ammonium ions
Bacteria involved in putrefaction of proteins in dead/waste matter

Question 19

Bacteria and fungi involved in decomposition feed in a different way from animals. What is this called and what are the 3 steps?

Answer 19

Saprotrophically

1. Saprotrophs secrete enzymes onto dead and waste material
2. Enzymes digest the material into small molecules, which are then absorbed into the saprotrophs body
3. Having been absorbed, the molecules are stored or respired to release energy

Question 20

What are the key processes that add carbon dioxide to the atmosphere and remove it from the atmosphere?

Answer 20

ADD
Respiration in animals and plants
Decomposition of detritus, humus and wastes
Weathering of limestone and chalk adds it to water, which dissolves to form carbonic acid
Combustion of fossil fuels

REMOVE
Terrestrial plants use it in photosynthesis, and aquatic organisms use dissolved carbonates

Question 21

What is productivity?

Answer 21

Rate of energy transfer through each trophic level in a food chain

Question 22

What is GPP vs NPP?

Answer 22

GPP: rate at which plants convert light energy into chemical energy

• only some light energy enters LDR, some of this involved in glucose production, and some of this glucose used for growth

NPP: proportion of energy from the Sun available to enter the food chain - the chemical energy in plant biomass after respiratory losses have been taken into account

Question 23

How do humans increase primary productivity? (7)

Answer 23

• plant crops early to provide a longer growing season, or in light banks
• drought resistant strains bred
• greenhouses provide warmer temps = inc rate of biomass production
• crop rotation stops reduction of inorganic ions in soil
• pest-resistant plants bred, GM, or use of pesticides
• herbicides to kill weeds and dec competition
• fungicides, or breeding or GM -> prevent fungal diseases

Question 24

How do humans increase secondary productivity? (4)

Answer 24

• young animals invest more energy into growth, so harvesting animals before adulthood decreases energy loss
• selective breeding = improved breeds
• antibiotics = avoid energy loss to pathogens
• zero grazing/keeping indoors = stops movement and keeps constant temp

Question 25

Define succession

Answer 25

progressive change in a community of organisms over time

Question 26

whats the diff between primary and secondary succession?

Answer 26

primary = bare, new ground
secondary = an area previously occupied is disturbed and recolonised (starts on existing soil)

Question 27

Outline the first step in primary succession - what adaptations are needed?

Answer 27

1. Algae/lichens begin to live on the bare rock and colonise the land = pioneer species

ability to fix nitrogen from atmosphere, tolerate harsh conditions, can photosynthesise, rapidly germinating seeds

Question 28

Outline steps 2-5 of primary succession

Answer 28

2. Pioneer species die and organic soil is created, allowing larger plants to grow. the humus provided supports new species
3. these larger plants are SECONDARY colonisers. they require nitrates and water within humus to grow and outcompete the pioneer species.
4. secondary species continue to decay and add more humus to soil
5. process continues with INC biodiversity until a stable community is reached with no further succession = CLIMAX community

Question 29

Define deflected succession

Answer 29

• community only remains stable due to human activity preventing succession
• no climax community reached
• reaches phagioclimax
• graving, herbicides, burning etc

Question 30

What two pieces of data can you collect from quadrats?

Answer 30

distribution: presence/absence/spread/location of each species. usually at least 50% of plant has to be in the quadrat to count

abundance:
no. of individuals of each species -> count individuals , or do % cover using a point frame lowered into quadrat or one with a grid.

Question 31

Where do you place the quadrats?

Answer 31

randomly. lay out two tape measures on two edges of site. generate pairs of random numbers as coordinates. lay bottom left hand corner at those coordinates.

OR sample at regular distances across habitat

Question 32

How do you calculate population density?

Answer 32

no of individuals in quadrat(s) or sample / area of sample of quadrat(s)

Question 33

Step 3 of a method: while facing north, place the left-hand corner of a quadrat on the point where the coordinates meet.

identify a limitation with step 3 of the students’ method and explain why this might affect the data collected

Answer 33

placement of quadrat could be biased

coordinates difficult to judge

doesn’t specify top or bottom corner