8.2 Human Digestive System (Cambridge (CIE) O Level Biology): Flashcards
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What is the main purpose of the digestive system?
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Cards in this collection (90)
What is the main purpose of the digestive system?
To break large, insoluble food molecules into small, soluble molecules that can be absorbed into the blood.
Define ingestion.
Ingestion is the taking of substances, such as food and drink, into the body through the mouth.
Define egestion.
Egestion is the passing out of undigested food as faeces through the anus.
What are the two roles of the mouth in digestion?
mechanical digestion: teeth chew food to increase its surface area
chemical digestion: amylase in saliva begins digesting starch
What is the function of the stomach in digestion?
It churns food (mechanical digestion), while protease begins protein digestion and hydrochloric acid kills bacteria and provides a low pH.
What does the pancreas produce?
All three types of digestive enzyme — amylase, protease and lipase — secreted into the duodenum.
What is the function of the large intestine?
It absorbs water from the undigested material in the colon to form faeces, which are stored in the rectum.
What is the only material that passes out in faeces?
Large, indigestible molecules such as cellulose (dietary fibre) and some water.
The is the muscular tube that connects the mouth to the stomach.
The oesophagus is the muscular tube that connects the mouth to the stomach.
Bile is produced by the liver and stored in the .
Bile is produced by the liver and stored in the gall bladder.
True or False?
The liver produces bile.
True.
The liver produces bile, which is then stored in the gall bladder before being released into the duodenum.
True or False?
Most digested food is absorbed in the stomach.
False.
Most absorption of digested food takes place in the small intestine (ileum), not the stomach.
Define physical digestion.
Physical digestion is the breakdown of food into smaller pieces without any chemical change to the food molecules.
Why is physical digestion important for chemical digestion?
It increases the surface area of food so that enzymes can act on it more quickly.
Which three processes carry out physical digestion?
chewing by the teeth
churning by the stomach
emulsification of fats by bile
What is another name for physical digestion?
Mechanical digestion.
Which organ churns food as a form of physical digestion?
The stomach.
Where does the emulsification of fats take place?
In the duodenum of the small intestine, where bile breaks large fat droplets into smaller ones.
Define emulsification.
Emulsification is the breakdown of large fat droplets into smaller droplets by bile.
Physical digestion increases the of food for enzymes to act on.
Physical digestion increases the surface area of food for enzymes to act on.
The action of the stomach is a form of physical digestion.
The churning action of the stomach is a form of physical digestion.
True or False?
Chewing food with the teeth is an example of physical digestion.
True.
Chewing breaks food into smaller pieces without changing its chemical structure, so it is physical digestion.
True or False?
Physical digestion changes the chemical structure of food molecules.
False.
Physical digestion only breaks food into smaller pieces; it does not change the chemical structure of the molecules.
What is the role of the teeth in mechanical digestion?
They chew food to break it into smaller pieces, increasing its surface area so digestive juices can act more quickly.
Define incisors.
Incisors are chisel-shaped teeth used for biting and cutting food.
Define canines.
Canines are pointed teeth used for tearing, holding and biting food.
What is the function of the premolars and molars?
They have large, flat surfaces with ridges for chewing and grinding food.
Why does chewing food help digestion?
It increases the food's surface area, so saliva and other digestive juices can break it down more quickly.
Define enamel.
Enamel is the hard outer layer that covers and protects the tooth.
What does the pulp cavity of a tooth contain?
Nerves and blood vessels.
are chisel-shaped teeth used for biting and cutting food.
Incisors are chisel-shaped teeth used for biting and cutting food.
Incisors are chisel-shaped teeth used for and cutting food.
Incisors are chisel-shaped teeth used for biting and cutting food.
True or False?
Molars are used for grinding and chewing food.
True.
Molars have large, flat, ridged surfaces suited to grinding and chewing food.
True or False?
Chewing food chemically changes the food molecules.
False.
Chewing is mechanical digestion; it increases surface area but does not change the food molecules chemically.
Define chemical digestion.
Chemical digestion is the breakdown of large, insoluble molecules into small, soluble molecules.
What is the role of chemical digestion?
To produce small, soluble molecules that can be absorbed through the wall of the intestine.
Where in the gut does chemical digestion take place?
It starts in the mouth and continues in the stomach and the small intestine.
Define absorption.
Absorption is the movement of small food molecules and ions through the wall of the intestine into the blood.
Define assimilation.
Assimilation is the movement of digested food molecules into the cells of the body, where they become part of the cells.
Define egestion.
Egestion is the passing out of food that has not been digested or absorbed, as faeces, through the anus.
What are the six stages food goes through in the alimentary canal?
ingestion
mechanical digestion
chemical digestion
absorption
assimilation
egestion
Chemical digestion breaks large, molecules into small, soluble molecules.
Chemical digestion breaks large, insoluble molecules into small, soluble molecules.
Chemical digestion begins in the and continues in the stomach and small intestine.
Chemical digestion begins in the mouth and continues in the stomach and small intestine.
True or False?
Chemical digestion breaks large, insoluble molecules into small, soluble molecules.
True.
This is the definition of chemical digestion, producing soluble molecules that can be absorbed.
True or False?
Mechanical digestion breaks the chemical bonds within food molecules.
False.
Mechanical digestion only breaks food into smaller pieces; it does not break bonds or change the food chemically.
What does amylase digest, and into what?
It digests starch into maltose (a sugar).
Where is amylase produced?
In the mouth (salivary glands) and the pancreas, which secretes it into the duodenum.
What does the enzyme maltase do?
It digests maltose into glucose on the lining of the small intestine.
What do proteases digest, and into what?
They digest proteins into amino acids.
Where does pepsin work, and in what conditions?
In the stomach, in acidic conditions.
Where is trypsin produced and where does it act?
It is produced in the pancreas and acts in the duodenum, in alkaline conditions.
Define lipase.
Lipase is an enzyme that digests lipids into fatty acids and glycerol.
Where is lipase produced?
In the pancreas, from where it is secreted into the duodenum.
Amylase digests starch into .
Amylase digests starch into maltose.
Lipase digests lipids into fatty acids and .
Lipase digests lipids into fatty acids and glycerol.
True or False?
Proteases break down proteins into amino acids.
True.
Proteases such as pepsin and trypsin digest proteins into amino acids.
True or False?
Amylase is produced in the stomach.
False.
Amylase is produced in the mouth and the pancreas, not the stomach.
What are the two main roles of hydrochloric acid in the stomach?
it kills bacteria in food
it provides a low pH for stomach enzymes to work
Define gastric juice.
Gastric juice is the mixture of fluids, including hydrochloric acid, produced by the stomach.
How does hydrochloric acid kill bacteria in food?
The low pH denatures the enzymes in the bacterial cells, so they cannot carry out the reactions needed to stay alive.
Which stomach enzyme works best in acidic conditions?
Pepsin, a protease with an optimum pH of around 2.
What is the optimum pH of pepsin?
Around pH 2.
How are the cells lining the stomach adapted to hydrochloric acid?
They are specially adapted to withstand the acidic conditions.
Hydrochloric acid provides a low so that pepsin can work at its fastest rate.
Hydrochloric acid provides a low pH so that pepsin can work at its fastest rate.
The stomach enzyme has an optimum pH of around 2.
The stomach enzyme pepsin has an optimum pH of around 2.
True or False?
Hydrochloric acid kills bacteria that are ingested with food.
True.
The low pH denatures the enzymes in bacterial cells, killing the bacteria in food.
True or False?
The stomach provides alkaline conditions for pepsin to work.
False.
The stomach is acidic (low pH); pepsin has an optimum pH of around 2.
Why must the stomach maintain a low pH?
To keep conditions within the optimum range for pepsin to work at its fastest rate.
Define emulsification.
Emulsification is the breaking down of large fat droplets into smaller droplets by bile.
Where is bile produced and where is it stored?
It is produced in the liver and stored in the gall bladder.
What are the two main roles of bile?
to neutralise the hydrochloric acid from the stomach (it is alkaline)
to emulsify fats
Why is it important that bile is alkaline?
It neutralises the hydrochloric acid from the stomach, giving the higher pH that small-intestine enzymes need.
Why does emulsification help the digestion of fats?
It increases the surface area of the fat so that lipase can break it down more quickly.
Which enzyme chemically digests fat after it has been emulsified?
Lipase, which breaks it down into fatty acids and glycerol.
Bile is produced by the liver and stored in the .
Bile is produced by the liver and stored in the gall bladder.
Emulsification increases the of fat so that lipase can act faster.
Emulsification increases the surface area of fat so that lipase can act faster.
True or False?
Bile is alkaline and neutralises stomach acid.
True.
Bile is alkaline, so it neutralises the hydrochloric acid arriving from the stomach.
True or False?
Emulsification is an example of chemical digestion.
False.
Emulsification is mechanical digestion — it breaks fat into smaller droplets without breaking any chemical bonds.
Does bile contain any enzymes?
No — bile emulsifies fats physically; it does not contain digestive enzymes.
Define peristalsis.
Peristalsis is the wave of muscle contractions that moves food along the alimentary canal.
Which two types of muscle control peristalsis?
Circular muscles and longitudinal muscles.
What happens when the circular muscles contract during peristalsis?
They reduce the diameter of the lumen of the gut.
What happens when the longitudinal muscles contract during peristalsis?
They reduce the length of that section of the gut.
What is the role of mucus in peristalsis?
It lubricates the food mass and reduces friction as it moves along the gut.
How does dietary fibre help peristalsis?
It provides the roughage for the muscles to push against.
What happens to food in the stomach after it arrives by peristalsis?
It is churned into a less solid form called chyme, which then passes into the small intestine.
Peristalsis is controlled by circular and muscles.
Peristalsis is controlled by circular and longitudinal muscles.
is produced to lubricate the food and reduce friction during peristalsis.
Mucus is produced to lubricate the food and reduce friction during peristalsis.
True or False?
Circular muscles contract to reduce the diameter of the gut lumen.
True.
Contraction of the circular muscles narrows the lumen, helping to squeeze food along.
True or False?
Peristalsis relies on gravity to move food down the oesophagus.
False.
Peristalsis uses waves of muscle contraction, not gravity, so food can move even against gravity.
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