Biofuels

Question 1

Recognise examples of fuels from biomass

Answer 1

• alcohol
• biogas
• wood

Question 2

Explain how plants produce biomass

Answer 2

Biogas is mainly methane and it is produced from animal and plant waste in digesters

Question 3

Understand why biogas (mainly methane) is an
important energy resource in certain remote parts of
the world lacking a mains electricity supply or mains
sewage system

Answer 3

They can produce biogas from human sewage, which solves the problem of safe sewage disposal in remote places

Question 4

where does the rotting of organic material such as

dead plants and animal waste occur?

Answer 4

in marshes, septic tanks and animal digestive systems

Question 5

what does the rotting of organic material such as

dead plants and animal waste produce?

Answer 5

a mixture of gases including methane

Question 6

how is the rotting of organic material such as

dead plants and animal waste caused?

Answer 6

by the action of bacteria

Question 7

how can biogas be produced?

Answer 7

on a large scale using a digester

Question 8

Explain why methane being released from landfill

sites is dangerous

Answer 8

it can burn or explode preventing use of the site for many years

Question 9

how is alcohol made?

Answer 9

from yeast

Question 10

what can alcohol be used as?

Answer 10

a biofuel by mixing with petrol

Question 11

what is a mixture of petrol and alcohol called?

Answer 11

gasohol

Question 12

what is gasohol used as?

Answer 12

for cars in countries such as Brazil

Question 13

Describe the advantages of using biofuels

Answer 13

• alternative sources to fossil fuels
  • no increase in greenhouse gas levels
  • no particulates produced

Question 14

what does biogas contain?

Answer 14

• mainly methane
  • some carbon dioxide
  • traces of hydrogen, nitrogen and hydrogen
  sulfide

Question 15

Describe the uses of biogas

Answer 15

• burning to generate electricity
• burning to produce hot water and steam for
heating systems
• used as a fuel for vehicles

Question 16

Describe different methods of transferring energy

from biomass

Answer 16

• burning fast growing trees

* fermenting biomass using bacteria or yeast

Question 17

Describe how methane can be produced on a large
scale using a continuous flow method of providing
organic waste and removing the gas and remaining
solids

Answer 17

it can be made on a large scale using a continuous-flow method in a digester. Organic material is added daily and the biogas is siphoned off and stored. The remaining solid sludge can be used as fertiliser for crops.

Question 18

Explain why the burning of biofuels does not cause a

net increase in greenhouse gas levels

Answer 18

• if they are burnt at the same rate as the biomass is
being produced
• if areas of land are not cleared of other vegetation
in order to grow crops for biofuels

Question 19

what does the use of large areas of land result in?

Answer 19

habitat loss, extinction of species and the loss of previous food-growing fields

Question 20

what does it mean if biogas containing more than 50%

methane is burnt? But what happens when it contains 10%?

Answer 20

incan be burnt in a controlled way but a lower percentage of about 10% is explosive

Question 21

what is biogas in comparison to other fuels?

Answer 21

is a ‘cleaner’ fuel than diesel and petrol but does not contain as much energy as natural gas

Question 22

Understand why gasohol is more economically viable
in countries that have ample sugar cane and small oil
reserves

Answer 22

it is used more in countries that have large sugar cane reserves, but low crude oil reserves. In these circumstances the production of gasohol is financially attractive.

Question 23

Explain why biogas production is affected by

temperature

Answer 23

• low temperatures = decomposer bacteria reproduce and respire slowly so very little biogas is released
• above 45 degrees C = enzymes in bacteria are denatured and the bacteria are killed

Question 24

Describe why biogas production is affected by

temperature

Answer 24

• low temperatures = little biogas released

- above 45 degrees C no biogas is released