B7: DECAY

Question 1

What organisms are responsible for decomposition (+ examples)?

Answer 1

-microorganisms (eg: bacteria)
-fungi
-detritus feeders (eg: woodlice, worms)

Question 2

How do decomposers decompose dead/ waste material?

Answer 2

-secrete digestive enzymes to break down dead/waste material into small soluble molecules that can be absorbed by the organism and released nutrients (eg: mineral ions) into the environment

Question 3

What 4 factors affect rate of decay?

Answer 3

-temp
-O2 availability
-water availability
-no. of decaying organisms

Question 4

How would increasing temp affect rate of decay?

Answer 4

-up to optimum temp, rate of decay would increase due to more frequent and successful collisions
-after optimum temp, rate of decay would decrease because the enzymes would denature

Question 5

How would increasing O2 availability affect rate of decay?

Answer 5

-more O2 available for respiration
-respiration releases energy in the organisms
-energy used to make enzymes to digest/decay
-rate of decay increases

Question 6

How would increasing water availability affect rate of decay?

Answer 6

-rate of decay increases because more water is available for biological processes (eg: digestion)

Question 7

How would increasing no. of decaying organisms affect rate of decay?

Answer 7

-increases rate of decay due to increase in rate of enzyme activity

Question 8

How does a compost bin provide optimum conditions for decomposition?

Answer 8

-open for aeration
-open to allow water in
-open to allow decomposers in
-more decomposers meaning more enzyme activity with means that rate of respiration increases and so energy is released at thermal energy

Question 9

What is biogas?

Answer 9

-fuel
(-mainly methane)

Question 10

How is biogas produced?

Answer 10

-produced by microorganisms anaerobically decaying organic material and waste

Question 11

What are the 2 types of generator used to produce biogas?

Answer 11

-batch generators (small batches of biogas produced, manually loaded)
-continuous generators (make biogas at steady rate continuously on a larger scale)

Question 12

RP - investigate the effect of temp on the rate of decay of fresh milk by measuring change in pH: method

Answer 12

-label a boiling tube ‘lipase’ and add 5cm^3 of the lipase solution
-label another boiling tube ‘milk’ and add 5 drops of phenolphthalein
-use a calibrated dropping pipette to add 5cm^3 of milk to the ‘milk’ boiling tube
-use another pipette to 7cm^3 of sodium carbonate solution to the ‘milk’ boiling tube to make the milk alkaline (solution should be pink)
-put a thermometer into the ‘milk’ boiling tube
-set up a water bath to the first chosen temp
-put both boiling tubes into water bath and wait until contents reach same temp as water bath
-use another dropping pipette to transfer 1cm^3 of lipase from the ‘lipase’ tube to the ‘milk’ tube and immediately start a stop clock
-stir contents of ‘milk’ boiling tube until solution turns white (phenolphthalein becomes colourless when pH falls below 8.2)
-record time taken for colour to change to white in seconds
-repeat with different temps

Question 13

RP - investigate the effect of temp on the rate of decay of fresh milk by measuring change in pH: variables

Answer 13

IV - temp
DV - time taken for colour change from pink to colourless(/white) (rate of decay)
CVs - volume of milk, source of milk, conc of lipase, volume of lipase, conc of sodium carbonate solution, volume of sodium carbonate solution