Digestion Flashcards
All 39 cards in this deck
What is a tissue?
A group of cells with a similar structure and function.
What is an organ?
An aggregation of tissues performing a specific function.
e.g. the stomachWhat is an organ system?
A group of organs that work together to perform a function; organ systems work together to form organisms.
List the levels of organisation in a multicellular organism, from smallest to largest.
Cells → tissues → organs → organ systems → organism.
True or false? The stomach is a tissue.
False. The stomach is an organ, made up of several tissues such as muscular and glandular tissue.
To which level of organisation does the digestive system belong?
An organ system — several organs work together to digest and absorb food.
Which organ makes bile and which organ stores it?
Bile is made in the liver and stored in the gall bladder.
What is the role of the pancreas in digestion?
It produces amylase, protease and lipase, which are released into the small intestine.
What happens to food in the mouth?
It is chewed, and the salivary glands release amylase, which starts the digestion of starch.
What is the function of the small intestine in digestion?
Digestion of food is completed there and the small soluble products of digestion are absorbed into the bloodstream.
What are the products of digestion used for in the body?
To build new carbohydrates, lipids and proteins; some glucose is used in respiration.
True or false? Digestive enzymes break food down into small soluble molecules.
True. Only small soluble molecules can be absorbed into the bloodstream.
Which enzyme is produced by the stomach, and what does it break down?
Protease; it breaks proteins down into amino acids.
Why does the stomach produce hydrochloric acid?
To give the acidic pH (about pH 2) at which stomach protease works best; it also kills bacteria in food.
What does the muscular wall of the stomach do?
It churns the food, mixing it with the acid and enzymes.
True or false? Starch is digested by amylase in the stomach.
False. The stomach is too acidic, so amylase is denatured there; starch is digested in the mouth and small intestine.
What is an enzyme?
A biological catalyst — a protein that speeds up a reaction without being used up.
What is the active site of an enzyme?
The part of the enzyme where the substrate binds; its shape is complementary to the substrate.
What does the 'lock and key theory' say about how an enzyme works?
The substrate binds to the active site because the shapes of the substrate and active site are complementary, so each enzyme catalyses only one specific reaction.
How does temperature affect the rate of an enzyme-controlled reaction?
The rate increases up to the optimum temperature, then falls sharply as the enzyme denatures.
What does it mean if an enzyme has been denatured?
The shape of its active site has changed, so the substrate no longer fits and the reaction stops.
True or false? All enzymes work best at pH 7.
False. Each enzyme has its own optimum pH — e.g. stomach protease works best at about pH 2.
What are the steps to investigate the effect of pH on the rate of reaction of amylase?
e.g. testing amylase at pH 5- Mix amylase, starch and pH 5 buffer in a tube in a water bath at a set temperature.
- Every 30 seconds, put one drop of the mixture into iodine on a spotting tile.
- Record the time when the iodine stays orange-brown — the time to digest all the starch at pH 5.
In the amylase practical, how do you know all the starch has been digested?
The iodine stays orange-brown instead of turning blue-black.
Why is a water bath used when investigating the effect of pH on amylase?
To keep the temperature constant, because temperature also affects enzyme activity — only pH should change.
How is the optimum pH of amylase identified from the results of the practical?
It is the pH with the shortest time to digest the starch — the peak on a graph of rate against pH.
How do you calculate the rate of an enzyme reaction from the time taken?
e.g. starch is completely digested in 50 seconds- Rate
- per second.
True or false? In the amylase practical, iodine solution is added to the test tube containing the amylase and starch.
False. A drop of the mixture is removed every 30 seconds and added to iodine on a spotting tile (continuous sampling).
Name the three parts of the human digestive system that produce amylase.
Salivary glands, pancreas and small intestine.
What is the word equation for the digestion of starch?
starch → sugars (maltose/glucose), catalysed by amylase.
Where are proteases produced in the digestive system?
Stomach, pancreas and small intestine.
What is the word equation for the digestion of protein?
protein → amino acids, catalysed by protease.
What is the word equation for the digestion of a lipid?
lipid → glycerol + fatty acids, catalysed by lipase.
Lipase is produced in the pancreas and small intestine.How does bile increase the rate of fat breakdown by lipase?
It is alkaline, so it neutralises hydrochloric acid from the stomach, and it emulsifies fat into small droplets, increasing the surface area for lipase.
What are the steps in Benedict's test for sugars?
e.g. testing a sample of apple juice- Add Benedict's solution to the food sample.
- Heat in a water bath at about 75 °C for 5 minutes.
- Blue = no sugar; green/yellow/orange/brick-red = sugar present (apple juice turns brick-red).
What are the steps in the iodine test for starch?
e.g. testing a potato sample- Add a few drops of iodine solution to the food sample.
- Orange-brown = no starch; blue-black = starch present (potato turns blue-black).
What are the steps in the Biuret test for protein?
e.g. testing egg white- Add Biuret reagent to the food sample.
- Blue = no protein; purple/lilac = protein present (egg white turns purple).
True or false? A blue colour after Benedict's test shows that sugar is present.
False. Blue is a negative result; green, yellow, orange or brick-red shows sugar is present.
How should a solid food sample be prepared before carrying out food tests?
Grind or mash it with distilled water to make a solution, then filter it.