aqa B3 revision

Fuels can be made from natural products by fermentation

But all oxygen must be excluded so anaerobic fermentation can occur

Biogas, mainly methane, can be produced in this way using a wide range of organic or waste materials containing carbohydrates

Anaerobic respiration can be used to produce ethanol based fuels from sugar cane juices or glucose derived from maize starch by the action of carbohydrase

people used to believe living organisms could arise by themselves from non-living things. This is spontaneous generation

Living organisms can be produced by other living organisms in biogenesis

Redi - supported biogenesis

Needham - supported spontaneous generation

Spallanzani - supported biogenesis

Pasteur - proved Needham wrong, supported biogenesis

Yeast in baking

Yeast and sugar and flour

Mixture left in warm place

CO2 makes dough rise (aerobic respiration of yeast)

Bubbles of gas in dough expand as the bread is baked, making the bread light

As the bread is baked, any alcohol produced evaporates off

Yeast in brewing

starch in barley broken down by enzymes in the yeast to a sugary solution

yeast is added and anaerobic fermentation takes place

CO2 is bubbled off, alcohol

Bacteria in yogurt

starter culture of bacteria is added to warm milk in a fermenting vessel

Bacteria ferment the milk sugar, lactose, producing lactic acid which gives a sour taste

lactic acid causes the milk to clot and solidify with yogurt