Organisation: Digestion (AQA GCSE Combined Science: Trilogy: Biology): Flashcards
Exam code: 8464
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Tissue
A group of cells with a similar structure and function working together.
Organ
An aggregation of tissues that performs a specific function.
Organ system
A group of organs that work together to perform a particular function. Organ systems work together to form the whole organism.
are the basic building blocks of all living organisms.
Cells are the basic building blocks of all living organisms.
List the levels of organisation in a multicellular organism, from smallest to largest.
Cells → tissues → organs → organ systems → organism
Name two organ systems that supply dissolved materials to be transported around the body.
The digestive system (provides nutrients) and the respiratory system (provides oxygen and removes carbon dioxide).
These materials are carried around the body in the blood by the circulatory system.
Digestion
The breakdown of large, insoluble molecules into smaller, soluble molecules that can be absorbed into the bloodstream.
Why is the digestive system described as an organ system?
Several organs work together to digest and absorb food.
During digestion, large molecules are broken down into smaller, soluble molecules that can be absorbed into the bloodstream.
During digestion, large insoluble molecules are broken down into smaller, soluble molecules that can be absorbed into the bloodstream.
Where does the digestion of starch begin, and which enzyme is responsible?
In the mouth, where amylase in saliva (produced by the salivary glands) begins to break starch down into maltose.
What are the two main roles of the stomach in digestion?
Protease enzymes begin the digestion of proteins.
Hydrochloric acid provides a suitable (acidic) pH for these enzymes and destroys pathogens in food.
State the main functions of the small intestine and the large intestine.
Small intestine: enzymes complete digestion and the digested food and water are absorbed into the blood.
Large intestine: remaining water is absorbed, leaving faeces.
Give one role of the bacteria found in the large intestine.
They aid digestion by breaking down substances we cannot digest, supplying essential nutrients, and competing with harmful bacteria to restrict their growth.
Enzyme
A biological catalyst made of protein that speeds up the rate of a chemical reaction without being used up.
Metabolism
The sum of all the chemical reactions in a cell or the body, in which molecules are made (synthesised) or broken down.
Enzymes are not used up during a reaction, so at the end they are and can catalyse further reactions.
Enzymes are not used up during a reaction, so at the end they are unchanged and can catalyse further reactions.
Active site
The region of an enzyme where the substrate binds. Its shape is complementary to the substrate.
Describe the "lock and key" model of enzyme action.
The substrate (key) is complementary in shape to the enzyme's active site (lock).
When they collide the substrate fits into the active site, forming an enzyme-substrate complex, and the reaction occurs.
The product is released and the enzyme is left unchanged.
Why does each enzyme only catalyse one specific reaction?
The shape of the enzyme's active site is complementary to only one substrate, so only that substrate can bind.
Explain the effect of increasing temperature up to the optimum on enzyme activity.
Molecules gain more kinetic energy and move faster, so there are more frequent collisions between enzyme and substrate.
This increases the rate of reaction up to the optimum temperature (about 37°C in humans).
Denatured (enzyme)
When an enzyme's active site changes shape so the substrate can no longer fit, and the enzyme stops working.
Caused by temperatures above the optimum or an extreme pH, and is largely irreversible.
What happens to an enzyme if the pH moves too far from its optimum?
The bonds holding the enzyme's shape are affected, changing the shape of the active site so the substrate no longer fits, reducing activity.
A large change causes the enzyme to denature.
What is the aim of the amylase required practical?
To investigate the effect of pH on the rate of reaction of the enzyme amylase (which breaks down starch).
How is the presence of starch tested for in this practical?
A drop of the reaction mixture is added to iodine solution.
Starch present → iodine turns blue-black.
Starch absent (digested) → iodine stays orange-brown.
What is the continuous sampling technique used in this practical?
At regular time intervals (e.g. every 30 seconds), a drop of the reaction mixture is placed onto iodine solution to test whether starch is still present.
Identify the independent, dependent and control variables in the amylase practical.
Independent: pH (set using buffer solutions).
Dependent: time taken for the starch to be fully digested.
Control: temperature (water bath), plus the volume and concentration of amylase and starch.
The starch has been completely digested when the iodine solution remains .
The starch has been completely digested when the iodine solution remains orange-brown.
How do the results show at which pH amylase works best?
The shorter the time taken for the iodine to stay orange-brown, the faster the starch was digested — so amylase works best at that pH.
Why must temperature be kept constant during this investigation?
Temperature also affects enzyme activity, so it is controlled (using a water bath) to make it a fair test, ensuring only pH affects the rate.
Carbohydrase
An enzyme that breaks down carbohydrates into simple sugars.
Amylase is a carbohydrase that breaks down starch into maltose.
Protease
An enzyme that breaks down proteins into amino acids.
Lipase
An enzyme that breaks down lipids (fats) into glycerol and fatty acids.
State the sites of production of amylase, protease and lipase.
Amylase: salivary glands, pancreas and small intestine.
Protease: stomach, pancreas and small intestine.
Lipase: pancreas and small intestine.
The enzyme amylase breaks down starch into the sugar .
The enzyme amylase breaks down starch into the sugar maltose.
Where is bile made and where is it stored?
Bile is made in the liver and stored in the gall bladder.
State the two main functions of bile.
It is alkaline, so it neutralises the hydrochloric acid from the stomach.
It emulsifies fats, breaking large fat droplets into smaller ones.
How does bile increase the rate of fat breakdown by lipase?
Emulsification breaks fat into small droplets, increasing the surface area for lipase to work on.
The alkaline conditions also provide the optimum pH for lipase, so fat is broken down faster.
What are the products of digestion used for in the body?
To build new carbohydrates, lipids and proteins.
Some glucose is used in respiration to release energy.
How do you test for starch, and what is a positive result?
Add iodine solution.
Positive result: the colour changes from orange-brown to blue-black.
How do you test for sugars (e.g. glucose), and what is a positive result?
Add Benedict's solution and heat in a water bath.
Positive result: the colour changes from blue to green, yellow, orange or brick-red, depending on how much sugar is present.
How do you test for protein, and what is a positive result?
Add Biuret reagent.
Positive result: the colour changes from blue to purple/lilac.
How do you test for lipids, and what is a positive result?
Use the emulsion test: mix the sample with ethanol, then add water.
Positive result: a cloudy white emulsion forms.
How is a solid food sample prepared before carrying out food tests?
Grind the food with a pestle and mortar, add distilled water and stir, then filter to obtain a solution to test.
A positive Benedict's test for a high concentration of sugar changes the solution from blue to .
A positive Benedict's test for a high concentration of sugar changes the solution from blue to brick-red.
Give two safety precautions needed during the food tests.
Wear goggles — Biuret solution (copper sulfate and sodium hydroxide) and iodine are irritants/corrosive.
Keep ethanol away from flames, as it is highly flammable.
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