Life on Earth

Question 1

State one role of living organisms other than humans in soil formation (1)

Answer 1

soil formed from the remains of organisms;
decomposers/detritivores;
break down dead organisms/forms humus;
organic sorting/mixing/aeration/improve structure;
release nutrients/ nutrient recycling;
weather/erode/break up bedrock/parent material

Question 2

State one role of living organisms other than humans in soil conservation (1)

Answer 2

vegetation/soil biota reduces the rate of runoff;
vegetation reduces wind erosion;
vegetation reduces impact/damage due to rain;
root binding/slope stabilisation;
humus binds soil together;

Question 3

Describe the main conditions that allow life to survive on earth. (8)

Answer 3

Water:
role of water;;    
solvent for chemical reactions
transport within organisms
mineral uptake
required for photosynthesis
structure of cells/organisms
habitat/medium for organisms/cells
anomalous expansion 
specific heat capacity/temperature regulation
albedo 
transparency allows light penetration (allow only once see similar mp in light)
acts as a carbon sink 

Temperature:
importance of temperature range;;
suitable for stable biological molecules/enzymes
warm enough for chemical/metabolic reactions
liquid water

Ambient gases:
role of gases;;
O2 for (aerobic) respiration 
O2 forms O3 (ozone)
N2 for nitrogen fixation/proteins
CO2 for photosynthesis
greenhouse gases
gaseous water for hydrological cycle 
atmospheric pressure allows liquid water
(allow 1 mark if all of O2,CO2,photosynthesis and respiration mentioned but not clearly linked)

Light/solar radiation:
importance of radiation;;
source of energy for photosynthesis/conversion to chemical energy
ozone layer protection from UV radiation
vision/directional stimulus
photolysis of water
transparency of water allows light penetration (allow only once, see above)

Geology:
importance of geology;; 
mass controls gravity/gravitational pull
retention of atmosphere
source of minerals
magnetic field protects from solar wind

Position in solar system:
importance of position;;
distance from sun controls temperature
larger planets protect from asteroids/comets
moon controls tides/axis of rotation

Question 4

Give two ways in which atmospheric carbon dioxide is important for life on earth. (2)

Answer 4

needed for photosynthesis;
climate/temperature control/heat absorption/acts as greenhouse gas;
raw material for carbonaceous structure;
eg coral reefs, exoskeletons, shells

Question 5

Describe how sunlight is important for the survival of life on earth. (2)

Answer 5

energy for photosynthesis;
photolysis;
(converted) to heat;
vision;
enables sense of time/periodicity;
energy for hydrological cycle/winds/ocean currents;
energy for nitrogen/carbon/biogeochemical cycle;
synthesis of vitamin D;

Question 6

Describe how early photosynthetic organisms changed the composition of the atmosphere. (2)

Answer 6

reduced concentration of/absorbed carbon dioxide/CO2;
increased concentration/released oxygen/O2;
(oxygen enables) formation of ozone/03 layer;

Question 7

State one way in which plants increase atmospheric humidity. (1)

Answer 7

(evapo)transpiration/ evaporation;

Question 8

Explain how research into unexploited species may aid future food production. (3)

Answer 8

new food species;
different range of tolerance/ adapted to different conditions;
source of new genes/new characteristics/GM/hybridisation (to improve existing food species);
biological pest control;
source of natural pesticides;
improve nutrient supply;
eg green manures, legumes, pollination/ seed dispersal;

named examples;