Practical Report: 1 full experimental report

Structure & Function of Cells

• All cells contain:
• Nucleus:
• - controls cell activities
• - passes on information to next generation
• Cytoplasm:
• site of biochemical reactions
• Cell Membrane:
• - controls substances moving in & out of cells

Structure & Function of Cells

• Structures only in plant cells:
• Chloroplast:
• - Contains chlorophyll
• - absorbs light to help photosynthesis
• Cell Wall:
• - made of cellulose,
• - keeps cell shape semi-rigid
• Vacuole:
• - regulates water & solute content

Yeast

• - single celled fungus
• - doesn’t photosynthesise (no chlorophyll)
• - reproduces by budding
• - can feed using oxygen
• - this is aerobic respiration
• - or without oxygen
• - this is anaerobic respiration
• - respiration is the release of energy from food

Uses of yeast

• During anaerobic respiration
• - Sugar Alcohol + CO2 + energy
• This is known as alcoholic fermentation
• In baking
• - sugar in dough is fermented to alcohol & CO2
• - bubbles of CO2 makes dough rise
• - alcohol is boiled off by the oven

Brewing/Wine making

• Beer making uses maltose
• Maltose produced by germinating barley grains
• Wine making uses sugar from crushed grapes
• Alcohol production stops when yeast get poisoned by the alcohol content
• Dead yeast must be filtered out

Alternative Fuels

• Gasohol
• - fuel produced from plant fermentation
• - mixture of alcohol and petrol
• Biogas
• - anaerobic bacteria feed on organic waste
• - waste converted to methane (‘biogas’)
• - methane is a useful fuel

Antibiotics

• A natural chemical produced by micro-organisms
• These chemicals can kill or stop the growth of other micro-organisms
• If growth is stopped – micro-organism is sensitive to the antibiotic
• If it isn’t stopped – it is resistant

Effect of antibiotics on sensitive bacteria

• Antibiotics damage bacteria in different ways:
• - damage cell membrane
• - damage or affect chromosomes
• - stop synthesis of cell wall
• - stop chemical reactions in cytoplasm
• However, many bacteria develop resistance to the antibiotics
• Some can develop multiple resistance – e.g. MRSA

Need for a wide range of antibiotics

• No one antibiotic is effective against all bacteria
• Some people are allergic to certain antibiotics
• New resistant strains appear to a particular antibiotic, so others may be needed instead
• - in this example 2 antibiotics have no effect

Lactic Acid

• Milk is rich in sugar, protein & fat
• When milk sours, bacteria feed on the milk
• They convert lactose into lactic acid
• Lactic acid makes milk proteins clump together (coagulate)
• This forms a semi-solid food – yoghurt
• The acid conditions (low pH) acts as a preservative

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