One of the distinguishing features of the Archaea is that they are capable of inhabiting extreme environments such as extreme temperatures or anoxic conditions. Outline other extreme environments inhabited by the Archaea.

Describe how methane can be made from biomass.

a. high salinity (halophiles);
b. example of high salinity (eg Dead Sea, Great Salt Lake Utah);
c. extreme pH (acidophiles/alkalinophiles);
d. high pressure (barophiles) / deep oceans;

a. anaerobic fermentation of biomass/manure/suitable biomass material;
b. bacteria convert biomass into organic acids and alcohol;
c. bacteria produce CO₂ and H2;
d. methanogenic bacteria produce methane;
e. by reducing/reacting CO₂ with hydrogen gas/
f. or directly from organic acids/acetate/
Accept suitable word or chemical equations for the last two marking points.

This was the least popular of the HL options but it was encouraging to note some schools studying it with some good standards seen. 

Most candidates were able to get a mark for mentioning the high salinity that halophiles can withstand. Although the question clearly said to outline other extreme environments inhabited by Archaea, many candidates still listed the anaerobic conditions of methanogens, which was in the stem, and thus did not get a mark.  

This was the least popular of the HL options but it was encouraging to note some schools studying it with some good standards seen. 

The description of methane production from biomass was done well by the better candidates who were able to give the products the various bacteria produced, often with correct equations. The weaker candidates only knew that methanogenic bacteria produced methane.