Where is bile made, stored and released?
Made in the liver, stored in the gall bladder and released into the small intestine.
AQA GCSE Combined Science: Trilogy (8464) — Biology — Higher · 4.2.2.1
Revise AQA GCSE Combined Science: Trilogy (8464) — Biology — Higher specification point 4.2.2.1, The human digestive system, with free active-recall flashcards. Flip through the set or review every question and answer below.
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Where is bile made, stored and released?
Made in the liver, stored in the gall bladder and released into the small intestine.
How does bile provide conditions that increase lipase activity?
Alkaline bile neutralises hydrochloric acid from the stomach, providing alkaline conditions.
What does it mean for bile to emulsify fat?
It breaks fat into small droplets.
Why does emulsification increase the rate of fat breakdown?
It increases the surface area available to lipase.
Is bile an enzyme?
No, bile is not an enzyme.
What happens to food molecules during chemical digestion?
Large, insoluble food molecules are broken down into small, soluble molecules.
Why is chemical digestion necessary for absorption?
It produces molecules that can be absorbed from the digestive system.
What is the word equation for lipid digestion by lipase?
Lipid → glycerol + fatty acids
Which two organs produce lipase?
The pancreas and small intestine.
Where does lipase act during digestion?
In the small intestine.
Why can the products of lipid digestion be absorbed?
They are small molecules.
What does amylase break down, and what does it produce?
It breaks down starch into simple reducing sugars.
Where do the salivary glands secrete amylase?
Into the mouth, where it acts on starch in food.
Where does the pancreas secrete amylase?
Into the small intestine, where it continues starch digestion.
What do proteases break proteins down into during digestion?
Amino acids.
Where are the proteases that act in the stomach secreted?
In the stomach.
Which two organs secrete proteases that act in the small intestine?
The pancreas and the small intestine.
What is an enzyme?
A biological catalyst, usually a protein, that speeds up chemical reactions without being used up.
What happens when a substrate binds to an enzyme?
It binds to the active site and is converted into product or products. The products leave, and the enzyme can be used again.
How does the lock and key model explain enzyme specificity?
A substrate fits an enzyme’s active site because their shapes are complementary. This helps explain why an enzyme catalyses a specific reaction.
What is metabolism?
The sum of the chemical reactions in an organism.
What types of metabolic reactions do enzymes catalyse?
Reactions that build up and break down molecules.
Why does enzyme reaction rate generally increase as temperature rises up to the optimum?
Enzyme and substrate molecules gain kinetic energy and collide more frequently.
Why does enzyme reaction rate fall above the optimum temperature?
Heat denatures the enzyme, changing its active site's shape so the substrate no longer fits effectively.
What effect do low temperatures have on enzyme activity and enzyme structure?
They slow enzyme activity but do not normally denature the enzyme.
What is an enzyme’s optimum pH?
The pH at which its activity is greatest.
Why does an enzyme’s activity decrease as pH moves away from its optimum?
Changes in acidity or alkalinity disrupt interactions that maintain the enzyme’s shape. Its active site may change shape, so the substrate binds less effectively.
What can extreme pH do to an enzyme?
It can denature the enzyme.
Do all enzymes have the same optimum pH?
No. Different enzymes can have different optimum pH values.
What does the rate of a chemical reaction measure?
How quickly reactants are used up or products are formed.
How is the mean reaction rate calculated over a time interval?
How is the amount of reactant used or product formed over a time interval found?
From the difference between the measurements at the beginning and end of the interval.
What determines the units of a reaction rate?
The quantity measured and the time unit, for example grams per second.
What does a word equation represent, and what does it use to represent it?
A chemical reaction, using the names of substances.
How do the positions and arrow in a word equation show the relationship between reactants and products?
Reactants are on the left and products on the right. The arrow shows that reactants are converted into products.
What does a plus sign mean in a word equation?
It separates two or more substances on the same side of the equation.
What substances are formed when lipid is broken down?
Glycerol and fatty acids.
Is an enzyme that catalyses a reaction a reactant used up in that reaction?
No. The enzyme is not a reactant used up in the reaction.