Biotechnology (Cambridge O Level Biology)

Biofuels

• Yeast is a single-celled fungus that uses sugar as its food source
• When it respires, ethanol and carbon dioxide are produced (and energy is released)

 Fermentation of Glucose

The alcohol produced by fermentation of glucose can be used as biofuel

• The ethanol produced in this reaction is increasingly being used as a biofuel (a fuel made from living organisms rather than a fossil fuel like oil, coal or gas)
• In countries such as Brazil, biofuel is partly replacing petrol as the fuel for cars and other vehicles
• Plant material is used as the substrate for producing ethanol (as a source of glucose) - it is chopped up into small pieces and mixed with yeast which respires anaerobically and produces ethanol
• The liquid is separated from the remaining solids and any water is removed, leaving a concentrated solution of ethanol
• Sometimes the waste parts of crop plants, such as the stalks or outer leaves, are used, but in other places, crops are grown specifically to be harvested for making ethanol
• In some places, this is causing concern that there is less land available for local people to grow food crops needed for survival

Bread

• Yeast will respire anaerobically if it has access to plenty of sugar, even if oxygen is available
• This is taken advantage of in bread making, where the yeast is mixed with flour and water and respires anaerobically, producing carbon dioxide:

Yeast and Making Bread 

The carbon dioxide produced by fermentation (anaerobic respiration) of glucose is what makes bread dough rise

• The carbon dioxide produced by the yeast during respiration is caught in the dough, causing the bread to rise

Fruit Juice Production

• Fruit juice is produced by squeezing the fruits to remove the juice
• Chopping the fruit up before squeezing helps to release a lot more juice, but this does not break open all the cells so a lot of juice is lost
• By adding an enzyme called pectinase to the chopped up fruit, more juice is released
• Pectinase works by breaking down a chemical called pectin that is found inside plant cell walls
• Once pectin is broken down, the cell walls break more easily and more juice can be squeezed out of the fruit
• Adding pectinase to fruits also helps to produce a clearer juice as larger polysaccharides like pectin can make the juice seem cloudy - once they are broken down into smaller molecules, the juice becomes clearer

Biological Washing Powders

• Many stains on clothes are organic molecules – oil from skin, protein from blood, fat and protein from food
• Detergents that only contain soap can remove some of these stains when mixed with hot water, but it can take a lot of time and effort and very high temperatures to remove the stains entirely
• Biological washing powders contain enzymes similar to the digestive enzymes produced in the alimentary canal that help to break down large food molecules
• Using biological washing powders has several advantages, including:
  • Quickly breaking down large, insoluble molecules such as fats and proteins into smaller, soluble ones that will dissolve in washing water
  • They are effective at lower temperatures, meaning less energy (and money) has to be used in order to wash clothes to get them clean as washing water does not need to be heated to higher temperatures
  • They can be used to clean delicate fabrics that would not be suitable for washing at high temperatures

Lactose-free milk

• Lactose is the sugar found in milk
• Human babies are born with the ability to produce lactase, the enzyme that breaks down lactose
• In certain areas of the world, many people lose the ability to produce lactase as they get older
• This means that they can become lactose intolerant and react badly to the lactose in milk and products made from milk (cheese, yoghurt etc)
• Symptoms of lactose intolerance include nausea, flatulence and diarrhoea as their digestive system is upset by the lactose
• Milk can be made lactose free by adding the enzyme lactase to it and leaving it to stand for a while to allow the enzyme to break down the lactose

Using Lactase to Produce Lactose-free Milk

Lactose-free milk is a product made by adding the enzyme lactase to dairy milk to break down the sugars in it.