Biology: Section 5

Crop plants

Ways of increasing crop yield:

1. Glass houses and polythene tunnels. These can control conditions inside:

- Temperature - to ensure enzymes are at optimum (limiting photosynthesis factor)

- Carbon dioxise - limiting photosynthesis facotr

- Control/optimise watering (including addition of minerals/fertilisers)

- Control lighting conditions (limiting photosynthesis factor)

2. Fertilisers - mixtures of minerals needed by plants to optimise growth --> increased yield. 

eg. NPK fertiliser

Pest control

A pest is an organism that reduces the yield of a crop plant or animal.Therefore pest control is an important way of optimising yield. 

There are 2 types of pest control - chemical pesticide and biological control. 

Chemical control - using a solution or powdered chemicals to kill pests

Advantages - can work effectively 

          - easy to apply 

          - may be specific 

Disadvantages - can kill indiscriminately (eg kill good/beneficial organisms)

      - Can enter a food web/chain in bioaccumulation

      - not natural - crops not organic   

Microorganisms 

Beer production 

1. Harvesting of barley

2. Malting - by inducing germination. Starch is converted to sugar. Protein is converted to amino acids. 

3. Cracking - stop germination by heating (enzymes become denatured). Then the seeds are passed through rollers to open seeds. 

4. Mashing - with hot water to remove sugar and amino acids - remainder forms brewers grain (animal feed)

5. Boiling of the 'wort' - additional sugar may be added. Hops are added to the boiling wort to add flavour and anti-microbial substances.

6. Cooling

7. Fermentation - YEAST is added to convert sugar into ethanol and carbon dioxide, in ANAEROBIC conditions. Glucose -> ethanol + carbon dioxide. This takes 5-7 days at 14-23°C. (CO2 and yeast)

8. Conditioning of the beer - it is stored in casks. Yeast settles -> beer filtered -> standardisation of colour and flavour. 

9. Bottled/sold in barrels - 3.5-8.0% ethanol. 

Yoghurt production 

1. heat milk to 85-95°C for 15-30minutes (kills bacteria)

2. Homogenise the milk (mix to distribute fat)

3. Cool milk to incubation temperature (so bacterial starter is not killed due to high temps)

4. Add the bacterial starter - lactic acid bacteria ferment lactose -> lactic acid. (gives yoghurt its sour flavour)

5. Incubate mixture at 40°C for 4 hours until pH = 4.3

6. Stir and cool to 4°C

7. Add fruit/flavourings if required

8. Pack and dispatch yoghurt - keep refigerated 

Fish farming

Fish can either be catght by fishing or reared in special fish farms for human consumption. A fish farm is a man-made construction that is completely seperate to natural (wild) fish. 

In a fish farm, farmers can:

•  Control water quality - filtering and removing faeces
• Control the diet of the fish
• Use chemicals to prevent disease/kill pests
• Remove predators
• Oxgenate the water - stirring

Disadvantages 

• Disrupt local environment/habitat
• Faeces from fish may pollute waterways - risk of eutrophication 
• Chemicals may pollute the environment
• The fish may attratc predators - affect local fish stocks 

Advantages 

• Avoid depletion of natural fish stocks
• Fish are easier to catch 
• Fish have less diseases
• Fish are larger/healthier due too controlled diet and faeces removal
• Increased yields