Biology

end of topic test revision

What are the organs of the digestive system and their functions?

• Mouth: mechanical digestion, amylase

• Oesophagus: carries food

• Stomach: churns food, protease

• Small intestine: digestion and absorption

• Large intestine: absorbs water

• Liver: produces bile

• Gall bladder: stores bile

• Pancreas: produces digestive enzymes

Food tests required practical

• Benedict's + heat → Sugar → Blue to brick red

• Iodine → Starch → Orange-brown to blue-black

• Biuret → Protein → Blue to purple

What do digestive enzymes do?

Digest large insoluble molecules into small soluble molecules that can be absorbed into the blood.

How do temperature and pH affect enzymes?

• Enzymes have an optimum temperature and pH.

• Too high temperature denatures enzyme.

• Active site's shape changes.

• Substrate no longer fits.

Rate of reaction calculations

Rate = Amount produced ÷ Time

Example: 50 cm³ oxygen in 10s

Rate = 50 ÷ 10 = 5 cm³/s

Explain lock and key theory

• Active site has specific shape.

• Only correct substrate fits.

• Enzyme-substrate complex forms.

• Products released.

• Enzyme unchanged and reused

Production sites and functions of amylase, protease and lipase

Amylase

• Salivary glands

• Pancreas

• Small intestine

• Starch → Sugars

Protease

• Stomach

• Pancreas

• Small intestine

• Protein → Amino acids

Lipase

• Pancreas

• Small intestine

• Lipids → Fatty acids + glycero

Products of digestion

Food	Product
Starch	Sugars
Protein	Amino acids
Lipids	Fatty acids + glycerol

Required practical: effect of pH on amylase

1. Add starch + amylase.

2. Add buffer solution.

3. Place in water bath.

4. Test with iodine every 10s.

5. Record time until starch disappears.

6. Repeat for different pH values.

Variables:

• IV: pH

• DV: reaction rate/time

• Controls: temperature, volume, concentration

What are the products of digestion used for?

• Glucose → respiration

• Amino acids → growth and repair

• Fatty acids & glycerol → energy storage and cell membranes

Where is bile produced and stored?

• Produced in liver

• Stored in gall bladde

What is the function of bile?

• Neutralises stomach acid

• Creates alkaline conditions

• Emulsifies fats

• Increases surface area for lipase