paper 2: Energy and Ecosystems

Question 1

define an ecosystem

Answer 1

the community and the abiotic components of its environement

Question 2

how does energy enter an ecosystem?

Answer 2

during photosynthesis, plants synthesise organic compounds e.g. glucose from carbon dioxide, using light energy.

Question 3

give the names of the different biological molecules formed from the sugars produced in photosynthesis and their uses

Answer 3

• amino acid: protein synthesis
• lipids: phospholipid bilayer
• starch (alpha glucose): storage
• beta glucose: form cell wall
  DNA/ RNA: replication

Question 4

what is biomass

Answer 4

mass of organic molecules

Question 5

what 2 ways can biomass be represented as

Answer 5

• dry biomass
• mass of carbon

Question 6

units of biomass

Answer 6

kgm^-1year^-1

Question 7

how would you measure the dry biomass of some grass

Answer 7

• heat grass in oven to evaporate the water
• measure mass of grass
• reheat and find mass again
• repeat until contant mass is rached

Question 8

describe the process of calorimetry

Answer 8

• the sample of living tissue is burned in a combustion chamber
• the heat energy released is transfered to a known volume of water surrounding the tissue
• the increase temperature of the water is measured and used to calculate chemical energy in the biomass

Question 9

give the equation for calculating the energy released from a sample when when it is burnt during calorimetry

Answer 9

energy released (J) = volume of water (cm^3) X temp increase (C) X specific heat capicity (4.2J)

Question 10

why does simple calorimety apparatus cause an inaccurate measurement for the energy content of the combusted biomass

Answer 10

• heat energy can escape to the surroundings and does not enter the water
• heat energy can escape from the water due to the calorimeter not being insulated

Question 11

explain why the features of the enclosed calorimeter which allow it to accurately measure the total heat energy released fromthe combusted biomass

Answer 11

• container is insulated preventing loss of heat by conduction
• the stirer ensures heat is evenly distributed
• water has a high specific heat capacity

Question 12

what is GPP

Answer 12

the chemical energy store in plant biomass in a given area or volume in a given time

Question 13

how does GPP diectly relate to rate of photsynthesis

Answer 13

the greater the rate of photosynthesis the greater the GPP as more organic molecules formed

Question 14

what are the units for GPP

Answer 14

KJ m^-2 year^-1

Question 15

only about 2% of the light energy is converted to bioass in photosynthesis. why so low?

Answer 15

• some light missed by chlorophyll
• some light reflected from leaf
• some light is wrong wavelength for photosynthesis

Question 16

what is NPP

Answer 16

the chemical energy store in plant biomass after respiratory losses to the environment

Question 17

give the equation for calculating NPP

Answer 17

NPP = GPP - R
r= respiratory losses

Question 18

in what ways is energy lost between trophic levels

Answer 18

• energy lost as heat dur to repiration of rganic molecules
• some organic molecules are not absorbed and are lost in faeces
• some organic molecules are excreted in urine
• not all the organism is eaten e.g. bones

Question 19

why is there less energy transferred between producer and primary consumer than primary and secondary consumer

Answer 19

• producers contain lots of cellulose which is difficult to digest so less is absorbed and more energy is lost in egestion/ faeces

Question 20

what is N

Answer 20

the chemical energy stored as biomass in a consumer which is available to the next trophic level

Question 21

give the equation for calculating N

Answer 21

N = I - (F + R)

I = energy ingested from food
F = energy lost in faeces/ urine
R = energy lost in repspiration

Question 22

give the eqaution for calculating the % efficiency of energy transfer between trophic levels in a food chain

Answer 22

% energy transfer = net production fo trophic level

__________________________________

net production of previous trophic level

X100

Question 23

explain how farmers can increase productivity in livestock

Answer 23

• movement can be restricted so less respiration occurs for muscle contraction
• animals can be kept indoors or in heated rooms so less respiration to maintain body temp
• animals fed high calorie controlled diet designed for maximum absorption and minimum faeces production

Question 24

describe methods farmers can use to simplify food webs to increase productivity and explain how this increases energy transfer to humans

Answer 24

• use chemical control ( insecticide to kill pests directly or herbicide to kill weeds which removes interspecific competition)
• use biological control e.g. adding a predator of pests to ecosystem