6.3.1 Ecosystems

Question 1

what is ecology

Answer 1

the study of relationships between organisms and their environment

Question 2

what is an ecosystem

Answer 2

the living organisms that interact with each other in a defines area, and also the physical factors present in that region

Question 3

what is it meant by ecosystems being dynamic

Answer 3

they are constantly changing

Question 4

what are the 2 factors that affect an ecosystem

Answer 4

biotic and abiotic factors

Question 5

what are biotic factors

Answer 5

the living factors of an ecosystem

Question 6

what are abiotic factors

Answer 6

the non-living factors of an ecosystem

Question 7

examples of biotic factors

Answer 7

• often refer to interactions between organisms that are living/once lives
• often involve competition for:
• food
• space
• breeding partners

Question 8

examples of abiotic factors

Answer 8

• LIGHT INTENSITY: plants need this to photosynthesise, greater the availability, generally the greater the success of the species, and can adapt to different light intensities
• TEMPERATURE: greatly impacts enzyme controlled metabolic reactions, and plants and endothermic animals (those who control their own internal temperature rather than being effected externally) will develop more rapidly in warmer temps. Changes in temp can trigger migration, hibernation, dormancy and flowering.
  WATER AVAILABILITY: lack of water leads to stress, which can lead to death, and in plants specifically, leaves will wilt (water needed to be turgid) and photosynthesis
  OXYGEN AVAILABILITY: in aquatic ecosystems, cold fast-flowing high O2 water is beneficial, and loss of O2 can lead to suffocation. For plants, water logged soil can reduce availability of O2 for plants
  EDAPHIC (SOIL) FACTORS: different soil types have different particle sizes, which can affect organisms being able to survive in them, e.g. clay (fine and easily waterlogged), loam (different sizes, not waterlogged but retains water) and sandy (coarse, doesn’t retain water and easily eroded)

Question 9

what do all organisms in an ecosystem require, and where does this originate from for almost all ecosystems

Answer 9

• energy to function and survive
• light energy from the sun converted to chemical energy in plants and photosynthetic organisms

Question 10

what is the difference between food chains and food webs

Answer 10

both show the transfer of biomass (mass of living material) and therefore energy through organisms in an ecosystem
- food web is a system of interlinked food chains

Question 11

what is each stage of a food chain called

Answer 11

trophic level

Question 12

what is the first trophic level always

Answer 12

a producer:
- organism that converts light energy into chemical energy via photosynthesis

Question 13

what are all trophic levels except for the first one

Answer 13

consumers:
- organisms that obtain their energy from feeding on other organisms

Question 14

what is the second trophic level always

Answer 14

a primary consumer:
- an animal that eats a producer

Question 15

how are other trophic levels labelled

Answer 15

secondary, tertiary and quaternary consumer
(organisms that eat primary, secondary… consumers)
- usually no further than this, as there is not sufficient biomass or stored energy to support any further organisms

Question 16

how can u represent food webs as a pyramid of numbers

Answer 16

each level shows the number of organisms at that trophic level, with producers at the bottom

Question 17

what is biomass and why do we measure it

Answer 17

the mass of living material present in a particular place or in a particular organism

Question 18

how can you measure biomass

Answer 18

multiply the biomass present in each organism by the total number of organisms in that trophic level

Question 19

what information does a pyramid of biomass show

Answer 19

the biomass present in that moment of time, does not account for seasonal changes

Question 20

what is the easiest way to measure biomass, but why is it not used

Answer 20

• measure the mass of fresh material present
  BUT
• water content must be discounted
• makes the technique unreliable, as there are varying amounts of water in different organisms, so would need a very large sample

Question 21

which technique is usually used to calculate biomass, but why is it problematic

Answer 21

• measuring the “dry mass” of organisms
  BUT
• means organisms have to be killed to be dried (places in oven until all water has been evaporated)
  SO
• to minimise the destruction of organisms and animals, a small sample is usually only taken
• but this might not be representative

Question 22

what is biomass measured in

Answer 22

g m-2 for land
g m-3 for water

Question 23

what happens to biomass through the trophic levels

Answer 23

is is nearly always less than the one below

Question 24

why does biomass decrease as you increase the trophic level

Answer 24

• biomass consists of all cells and tissue of organisms present, including the carbon compounds they contain.
• as carbon is a store of energy, it can be equated to energy content
• when animals eat, only small proportion of the food they eat is converted into new raw tissue
• only this part of biomass is available for next level to eat

Question 25

what is the energy available at each trophic level measured in

Answer 25

kJ m-2 yr-1 (kilojoules per metre squares per year)

Question 26

why is biomass energy measured as per year

Answer 26

to allow for changes in photosynthetic production and consumer feeding patterns throughout the year to be accounted for

Question 27

what is ecological efficiency

Answer 27

the efficiency with which biomass or energy is transferred from one trophic level to the next
- can be presented by a pyramid of energy

Question 28

how much energy do producers convert that they receive

Answer 28

• only convert 1-3% of sunlight that they receive into chemical energy and biomass

Question 29

why do producers convert such little energy into biomass

Answer 29

• not all of solar energy is used for photosynthesis (about 90% is reflected, some transmitted through and some is an unusable wavelength)
• other factors might limit rate of photosynthesis, like water availability
• proportion of the energy is lost, as it is used for photosynthetic reactions

Question 30

what is gross production

Answer 30

the total solar energy that plants convert to organic matter

• even this is reduced, as 20-50% is used for respiration
• remaining energy is converted to biomass, called net production which is available for the next trophic level

Question 31

which formula is used for calculating the net production of biomass

Answer 31

net production = gross production - respiratory losses

• what is available to next trophic level

Question 32

how much energy do consumers convert into biomass

Answer 32

at most 10% goes to their own organic tissue

Question 33

why do consumers convert such little biomass

Answer 33

• not all of the biomass of the organisms is eaten, e.g. roots and bones
• some energy is transferred to the environment as metabolic heat ( due to movement and respiration)
• some parts are eaten but indigestible, and so are egested as faeces
• some energy is lost in excretory materials such as urine

Question 34

how much energy does a tertiary consumer have compared to sunlight first present

Answer 34

about 0.001%

Question 35

what is the equation for calculating ecological efficiency between each trophic level

Answer 35

energy/biomass after transfer DIVIDED BY energy/biomass before transfer x 100

Question 36

how do humans use agriculture to manipulate the environment

Answer 36

• plants we want are provided with abiotic conditions needed to thrive, e.g. water, warmth)
• competition is removed and so is predators

Question 37

how does agriculture create efficient biomass transfer

Answer 37

• for animals, only 3 trophic levels, of animal feed, livestock and humans
• for plants, only 2 trophic levels, of crops and humans
• fewer trophic levels that present naturally means minimum energy is lost, so as much biomass can be eaten by humans

Question 38

what is decomposition

Answer 38

a chemical process in which a compound is broken down into smaller molecules, or its constituent elements

Question 39

what is a decomposer

Answer 39

an organisms that feeds on and breaks down dead plant or animal matter, thus turning organic compounds into inorganic ones available to photosynthetic producers in the ecosystem

Question 40

give examples of common decomposers

Answer 40

microscopic fungi and bacteria, but also larger bacteria such as toadstools and bracket fungi

Question 41

why can decomposers be called saprotrophs

Answer 41

they obtain their energy from dead or waste organic material, called saprotrophic nutrition

Question 42

how do decomposers digest their food

Answer 42

• digest their food externally
• secrete enzymes onto dead organisms or organic waste matter
• enzymes break down complex organic molecules into simpler soluble molecules
• decomposers can absorb these molecules
• through this process, they can also released stored inorganic compounds and elements back into the environment

Question 43

what are detritivores

Answer 43

• another class of organisms involved in decomposition

Question 44

how do detritivores help with decomposition

Answer 44

• speed up decay by feeding on on detritus (dead and decaying material)
• they break it down into smaller pieces of organic material
• this increases the surface area for decomposers to work on
• e.g. woodlice breaking down wood and earthworms breaking down dead leaves

Question 45

what type of digestion do detritivores perform

Answer 45

internal digestion

Question 46

what is nitrogen needed for and how is it obtained

Answer 46

essential element in amino acids, proteins, and nucleic acids

• animals can obtain for food, but plants need it from their environment

Question 47

how is nitrogen most abundant, and why is this a problem

Answer 47

• 78% of the air is nitrogen gas
• this form however CANNOT be taken up by plants
• must be combined with other elements like O and H
• bacteria plays a very big role in converting nitrogen into usable sources for plants

Question 48

what are the bacteria involved in nitrogen fixation

Answer 48

Azotobacter and Rhizobium

• both contain enzyme nitrogenase

Question 49

where does azotobacter and

Question 50

explain process of nitrogen fixation

Answer 50

nitrogenase combines with atmospheric N2 and H2 to produce ammonia NH3
- this is a form of nitrogen that can be absorbed and used by plants

Question 51

what is azotobacter

Answer 51

free-living bacterium

Question 52

where do most of the nitrogen-fixing bacteria live, and give an example

Answer 52

• inside root nodules
• these are growths on the roots of leguminous plants (peas, beans and clover)

Question 53

explain the symbiotic relationship between bacteria and nitrogen fixation

Answer 53

• plant gains amino acids from the Rhizobium, which are produced by fixing nitrogen in the air into ammonium in the bacteria
• bacteria gains carbohydrates produced by the plant during photosynthesis, which is used as an energy source

Question 54

what is nitrification

Answer 54

the process by which ammonium compounds in the soil are converted into nitrogen-containing molecules that can be used by plants

Question 55

what type of bacteria takes part in nitrification

Answer 55

free-living bacteria in the soil called nitrifying bacteria

Question 56

what type of reaction is nitrification, and what does this mean

Answer 56

• oxidation reaction
• needs to take place in well-aerated soil

Question 57

what are the 2 steps of nitrification

Answer 57

1) nitrifying bacteria (such as Nitrosomonas) oxidise ammonium compounds into nitrites NO2-

2) other nitrifying bacteria (Nitrobacter) oxidise nitrites into nitrates NO3-

• NO3- ions are highly soluble, so this is the form that most nitrogen enters a plant

Question 58

what is denitrification

Answer 58

• in absence of oxygen,