Biology · Paper 1
Digestion and Enzymes
How the body breaks down food. The levels of organisation and the organs of the digestive system, enzymes and the lock and key model, the effect of temperature and pH, the digestive enzymes and bile, and the required practicals on food tests and on amylase and pH. Matches AQA Biology topic 4.2.1 and 4.2.2.1, and the matching sections of Edexcel and OCR. Every lesson is for both Combined Science and separate Biology, at Foundation and Higher.
Lessons
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1
Levels of Organisation and the Digestive System
A human body is not a big bag of identical cells. This lesson builds up from cells to tissues, organs and organ systems, uses the digestive system as the main…
10 terms -
2
Enzymes
Almost every reaction in your body is sped up by an enzyme. This lesson explains what enzymes are, how the lock and key model explains why each one is…
11 terms -
3
Digestive Enzymes and Bile
Starch, protein and fat each need a different enzyme. This lesson names the digestive enzymes, says where they are made and what they produce, and explains the…
11 terms -
4
Food Tests
How do you find out what is in a food? This lesson covers the required practical on food tests: the reagents for starch, sugar, protein and lipids, what a…
11 terms -
5
Investigating the Effect of pH on Amylase
This lesson covers the required practical on how pH affects the enzyme amylase. It explains the method with continuous sampling, the variables, how to turn the…
11 terms
Key terms in this chapter
All 54, gathered from every lesson.
- Tissue
- A group of similar cells that work together to do a particular job.
- Organ
- A group of different tissues that work together to do a particular job.
- Organ system
- A group of organs that work together to do a particular job.
- Organism
- A whole living thing, made of organ systems working together.
- Muscular tissue
- Tissue that contracts to produce movement, such as the churning of food in the stomach.
- Glandular tissue
- Tissue that makes and releases substances such as digestive juices.
- Epithelial tissue
- Tissue that covers the surfaces of the body and of organs.
- Digestive system
- The organ system that breaks down food and absorbs the products into the blood.
- Gland
- An organ or tissue that makes and releases a substance such as an enzyme or hormone.
- Digestion
- The breakdown of large, insoluble food molecules into small, soluble ones.
- Enzyme
- A biological catalyst, made of protein, that speeds up a reaction in a living thing.
- Catalyst
- A substance that speeds up a chemical reaction and is not used up.
- Substrate
- The substance that an enzyme acts on.
- Product
- A substance that is made in a reaction.
- Active site
- The region of an enzyme, with a particular shape, into which the substrate fits.
- Enzyme-substrate complex
- The enzyme and its substrate joined together while the reaction takes place.
- Lock and key model
- A model in which the substrate fits the active site as a key fits a lock.
- Specific
- Working on one particular substrate only.
- Denatured
- Having lost its normal shape, so that the active site no longer fits the substrate.
- Optimum
- The temperature or pH at which an enzyme works fastest.
- Rate of reaction
- A measure of how fast a reaction goes.
- Carbohydrase
- An enzyme that breaks down carbohydrates into simple sugars.
- Amylase
- A carbohydrase that breaks down starch into simple sugars.
- Protease
- An enzyme that breaks down proteins into amino acids.
- Lipase
- An enzyme that breaks down lipids into glycerol and fatty acids.
- Simple sugars
- The small, soluble molecules that carbohydrates are broken down into, such as glucose.
- Amino acids
- The small molecules that proteins are broken down into.
- Fatty acids and glycerol
- The small molecules that lipids are broken down into.
- Bile
- An alkaline fluid, made in the liver, that neutralises acid and emulsifies fat.
- Emulsify
- To break large drops of fat into many tiny droplets.
- Neutralise
- To remove the acidity of a solution by adding an alkali.
- Surface area
- The total area of the outside of an object. A larger surface area means more space for reactions.
- Reagent
- A chemical used to detect another substance because it changes colour or appearance.
- Qualitative test
- A test that shows whether a substance is present, but does not measure how much.
- Iodine solution
- The reagent that turns blue-black when starch is present.
- Benedict's reagent
- The blue reagent that turns green, yellow, orange or brick red when heated with sugar.
- Biuret reagent
- The blue reagent that turns purple when protein is present.
- Emulsion test
- The test for lipids using ethanol and water, which makes a cloudy white emulsion.
- Starch
- A carbohydrate made of many sugar molecules joined together.
- Positive result
- A result showing that the substance being tested for is present.
- Negative result
- A result showing that the substance being tested for is not present.
- Control
- A test that shows what a result looks like when nothing is present, or when it definitely is.
- Water bath
- A container of warm or hot water used to heat things gently and evenly.
- Continuous sampling
- Taking a small sample at regular intervals during a reaction and testing each one.
- Buffer solution
- A solution that keeps the pH constant at a particular value.
- Spotting tile
- A tile with small wells, used to test many small drops one after the other.
- Independent variable
- The variable that you change in an investigation.
- Dependent variable
- The variable that you measure in an investigation.
- Control variable
- A variable that you keep the same, so that it does not affect the results.
- Water bath
- A container of water at a steady temperature, used to keep the temperature of the tubes constant.
- Optimum pH
- The pH at which an enzyme works fastest.
- Rate of reaction
- A measure of how fast a reaction goes, worked out here as 1000 ÷ time.
- Anomalous result
- A result that does not fit the pattern, and is probably due to an error.
- Reliable
- Giving similar results when the investigation is repeated.