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Cambridge IGCSE0610

Diet

Biology 0610 Chapter Notes

What this chapter covers

DietDigestive systemPhysical digestionChemical digestionAbsorption
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In this chapter

  1. 1A balanced diet
  2. 2Carbohydrates, fats and oils, and proteins
  3. 3Vitamin C and scurvy
  4. 4Vitamin D and rickets
  5. 5Mineral ions: calcium and iron
  6. 6Fibre (roughage) and water
  7. 7The alimentary canal
  8. 8The associated organs
  9. 9Ingestion and digestion
  10. 10Absorption and assimilation
  11. 11Egestion
  12. 12What physical digestion does
  13. 13Types of teeth and their jobs
  14. 14Structure of a tooth
  15. 15The stomach
  16. 16Bile and emulsification
  17. 17What chemical digestion does
  18. 18Amylase, protease and lipase
  19. 19Where the enzymes are made and act
  20. 20Hydrochloric acid in gastric juice
  21. 21Starch digestion in two stages
  22. 22Bile and the right pH
  23. 23Pepsin and trypsin
  24. 24Where nutrients are absorbed
  25. 25Absorption of water
  26. 26Villi and microvilli
  27. 27Structure of a villus
  28. 28Capillaries and lacteals

1. A balanced diet

A balanced diet contains all the nutrients in the correct proportions. The components are carbohydrates, fats and oils, proteins, vitamins, mineral ions, fibre and water.

Correct does not mean equal. A balanced diet is about nutrients, not lifestyle.

Examiner insight

“The idea of the correct proportions was infrequently given, or incorrectly stated as equal proportions.” “A few candidates confused a balanced diet with a healthy lifestyle and so commented on eating enough vegetables, going to bed early and having enough exercise.”

Worked example 12 marks

Vitamins, mineral ions and proteins are part of a balanced diet. State two other components of a balanced diet.

  1. 1

    carbohydrates (or fats / oils / lipids) [1]

  2. 2

    fibre / roughage (or water): any two of the four score [1]

2. Carbohydrates, fats and oils, and proteins

Carbohydrates are needed for energy. Proteins are needed for growth and repair of cells. Fats and oils are a component of a balanced diet.

Milk contains all three, in different amounts. Write that energy is released, never that it is produced.

Examiner insight

“Some candidates mentioned producing (instead of releasing) energy for either protein or carbohydrate.”

Worked example 11 mark

The table shows the composition of milk R and milk S. What is a comparison between milk R and milk S?

A Milk R contains 50% more fat than milk S. · B Milk R contains 400% more protein than milk S. · C Milk S provides more amino acids for growth. · D Milk S provides more energy for growth.

type of milkcarbohydrate / g per 100 g of milkfat / g per 100 g of milkprotein / g per 100 g of milk
R57.017.016.5
S4.68.53.3
  1. 1

    fat: 17.0 - 8.5 = 8.5, and 8.5/8.5 × 100 = 100% more, so A is wrong

  2. 2

    protein: 16.5 - 3.3 = 13.2, and 13.2/3.3 × 100 = 400% more, so B is right

  3. 3

    B: milk R contains 400% more protein than milk S. C and D are wrong: milk S has less of all three. [1]

3. Vitamin C and scurvy

Scurvy is caused by a diet that is low in vitamin C.

A good source is citrus fruits, or another fruit or vegetable. A diet of only meat, oily fish, cheese and bread, with only water to drink, is low in vitamin C.

Wholemeal bread is not credited as a source of vitamin C.

Examiner insight

“The cause of scurvy was not well known.” “Some candidates incorrectly stated wholemeal bread.”

Worked example 12 marks

Scurvy and rickets are two diseases caused by a diet that is low in some nutrients. Draw one line from each disease to the nutrient that is low in the diet.

Nutrients: calcium · iron · protein · vitamin C

  1. 1

    rickets to calcium [1]

  2. 2

    scurvy to vitamin C [1]

4. Vitamin D and rickets

Rickets is caused by a diet that is low in vitamin D. A diet that is low in calcium is also a cause of rickets.

Vitamin D is needed for the development of strong bones and teeth. A deficiency gives weak bones or teeth. A lack of sunlight is a cause of vitamin D deficiency.

Dietary sources of vitamin D include oily fish, egg yolk, red meat, liver and fortified milk.

Examiner insight

“Some candidates gave an effect of vitamin D deficiency rather than a cause.” “‘Weak’ or ‘weakness’ without further qualification was insufficient. Brittle bones are not an effect of vitamin D deficiency.”

Worked example 11 mark

A lack of which component of the diet causes rickets?

A iron · B protein · C vitamin C · D vitamin D

  1. 1

    D: vitamin D. [1]

5. Mineral ions: calcium and iron

Calcium is needed for strong bones and teeth.

Iron is needed to make haemoglobin in red blood cells, which is involved in the transport of oxygen. A lack of iron causes anaemia.

Do not swap the two. Building bones, rickets and scurvy are not answers about iron. Write haemoglobin, not just blood.

A diet of meat, oily fish, cheese and bread is not low in calcium or iron.

Examiner insight

“However, the role of iron in the diet and the effects of an iron deficiency were often confused with the importance of calcium and vitamin D.” “Often candidates did not make it clear that iron is needed for making the haemoglobin in red blood cells. Many simply stated that iron was needed for making blood.”

Worked example 12 marks

State the importance of calcium and of iron in the diet.

  1. 1

    calcium: for strong bones and teeth [1]

  2. 2

    iron: to make haemoglobin for the transport of oxygen [1]

6. Fibre (roughage) and water

Fibre, also called roughage, is needed to prevent constipation. It helps food to move through the alimentary canal.

Plant material is a source of dietary fibre. Meat is not the main source, and white fish has no fibre.

Water is a component of a balanced diet.

Examiner insight

“Some candidates incorrectly believed that dietary fibre is used for growth and repair of cells.”

Worked example 11 mark

State one reason why fibre is needed in the diet.

  1. 1

    to prevent constipation (or: to help food move through the alimentary canal) [1]

Recap

  • A balanced diet contains all the nutrients in the correct proportions.
  • Carbohydrates are for energy. Proteins are for growth and repair of cells.
  • Lack of vitamin C causes scurvy. Citrus fruits are a source.
  • Lack of vitamin D causes rickets. Oily fish and egg yolk are sources.
  • Calcium is for strong bones and teeth. Iron is for haemoglobin and oxygen transport.
  • Fibre (roughage) prevents constipation.

7. The alimentary canal

The alimentary canal runs through the body in this order: mouth, oesophagus, stomach, small intestine, large intestine.

The small intestine has two parts: the duodenum and the ileum. The large intestine has three parts: the colon, rectum and anus.

The ileum has a large surface area for the absorption of digested food. Most water absorption in the alimentary canal takes place in the small intestine. The colon absorbs some water too, but it does not absorb the most.

Examiner insight

“A significant number of candidates did not appreciate the distinction between the small and large intestines and incorrectly stated the ileum and duodenum.” “It was a common misconception that the colon absorbs the most water.”

Worked example 13 marks

Name the two parts of the small intestine. State which part has a large surface area for the absorption of digested food.

  1. 1

    duodenum [1]

  2. 2

    ileum [1]

  3. 3

    the ileum has the large surface area for absorption of digested food [1]

8. The associated organs

The associated organs are the salivary glands, pancreas, liver and gall bladder. The stomach is part of the alimentary canal, so it is not an associated organ.

The salivary glands and the pancreas make the enzyme amylase. Bile is stored in the gall bladder. Bile neutralises stomach acid. The liver is responsible for storage and assimilation.

Examiner insight

“Many candidates thought that the liver or gall bladder produced amylase rather than the pancreas.” “Some candidates incorrectly believed that bile is produced in the gall bladder rather than stored there.”

Worked example 12 marks

The pancreas and the gall bladder are associated organs of the digestive system. State one function of each organ.

  1. 1

    pancreas: makes enzymes, e.g. amylase [1]

  2. 2

    gall bladder: stores bile [1]

9. Ingestion and digestion

Ingestion is the taking of substances, e.g. food and drink, into the body. Ingestion takes place in the mouth.

Digestion is the breakdown of food. Amylase is made by the salivary glands and the pancreas. Protease is made by the stomach lining. Mechanical digestion takes place in the mouth or the stomach.

Examiner insight

“Egestion was sometimes confused with digestion.”

Worked example 13 marks

State the term for the breakdown of food. Name two organs that make the enzyme amylase.

  1. 1

    digestion [1]

  2. 2

    salivary glands [1]

  3. 3

    pancreas [1]

10. Absorption and assimilation

Absorption is the movement of nutrients from the intestines into the blood.

Assimilation is the uptake and use of nutrients by cells.

Assimilation happens after absorption. In assimilation, food molecules become part of a body cell. Neither one is digestion.

Examiner insight

“A common error was to join absorption to movement into cells instead of into the blood.” “The definition of absorption was not well known. Many candidates described digestion or assimilation instead.”

Worked example 12 marks

Distinguish between absorption and assimilation.

  1. 1

    absorption is the movement of nutrients from the intestines into the blood [1]

  2. 2

    assimilation is the uptake and use of nutrients by cells [1]

11. Egestion

Egestion is the removal of undigested food from the body as faeces. Egestion occurs at the anus.

Egestion is not excretion. Excretion is the removal of the waste products of metabolism and substances in excess of requirements.

Examiner insight

“A significant number of candidates incorrectly believed that undigested food is removed by excretion.” “Knowledge of egestion was vague, with most candidates identifying it with any part the colon, and not where defecation occurs.”

Worked example 12 marks

A student says that faeces are removed from the body by excretion. Explain why this is incorrect.

  1. 1

    faeces contain undigested food, which is removed by egestion [1]

  2. 2

    excretion is the removal of the waste products of metabolism and substances in excess of requirements [1]

Recap

  • Small intestine: duodenum and ileum. Large intestine: colon, rectum and anus.
  • Associated organs: salivary glands, pancreas, liver and gall bladder.
  • Ingestion = the taking of substances, e.g. food and drink, into the body.
  • Digestion = the breakdown of food.
  • Absorption = the movement of nutrients from the intestines into the blood.
  • Assimilation = the uptake and use of nutrients by cells.
  • Egestion = the removal of undigested food from the body as faeces. It is not excretion.

12. What physical digestion does

Physical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules.

It increases the surface area of food for the action of enzymes in chemical digestion. Teeth, the stomach and bile all do this job.

Examiner insight

“Only a minority of candidates identified the correct statement about physical digestion, that is, it increases the surface area of food.” “Vague references to chewing did not gain credit unless qualified by breaking large pieces of food into smaller pieces.”

Worked example 11 mark

State the name of the type of digestion involving teeth.

  1. 1

    physical (digestion) [1]

13. Types of teeth and their jobs

There are four types of human teeth: incisors, canines, premolars and molars.

Incisors are used for biting and cutting food. Premolars and molars are used for chewing, grinding and crushing food. Grinding is not the job of incisors or canines.

Examiner insight

“Many candidates correctly identified the teeth which are used for grinding food, that is the premolars (tooth 1) and the molars (tooth 2).” “The commonest incorrect function given was ‘grinding’ for both the canines and incisors.”

Worked example 12 marks

A student bites a piece from an apple and then chews it. Name the type of tooth used to bite and cut the apple. State the function of a molar.

  1. 1

    incisor [1]

  2. 2

    molars chew / grind / crush food [1]

14. Structure of a tooth

The white outer layer of a tooth is the enamel. Under the enamel is the dentine. The pulp holds the nerves and blood vessels.

Cement is also part of a tooth. Teeth are embedded in bone and the gums.

Examiner insight

“Common errors were to confuse enamel (A) and dentine (B) and give cement for gum (D). The term crown was not accepted for enamel.” “Most candidates were able to identify the gum and the nerves, but few could identify the cement.”

Worked example 11 mark

State the name of the white outer layer of a tooth.

  1. 1

    enamel [1]

15. The stomach

Physical digestion does not only take place in the mouth. The stomach has a churning action on the food.

Churning breaks the food into smaller pieces. This increases the surface area for enzymes.

Examiner insight

“Many candidates saw chemical digestion in the question and that prompted them to write about the action of enzymes in the stomach. This meant that the churning action of the stomach and emulsification were not included in their answers.”

Worked example 12 marks

State the function of the stomach in physical digestion.

  1. 1

    the stomach churns the food [1]

  2. 2

    into smaller pieces, increasing the surface area for enzymes [1]

16. Bile and emulsification

Bile emulsifies fats and oils. It breaks large droplets of fat into smaller droplets.

This increases the surface area for chemical digestion. The fat molecules are not changed.

Examiner insight

“The most common error was the mention of emulsification being the breakdown of fats into smaller molecules. This statement implies that bile is responsible for chemical digestion.”

Worked example 13 marks

Outline the role of bile in the digestion of fats and oils.

  1. 1

    bile emulsifies fats [1]

  2. 2

    breaks large droplets into smaller droplets [1]

  3. 3

    increases the surface area for chemical digestion [1]

Recap

  • Physical digestion = breakdown of food into smaller pieces without chemical change to the food molecules.
  • It increases the surface area of food for the action of enzymes in chemical digestion.
  • Types of teeth: incisors, canines, premolars, molars. Incisors bite and cut; premolars and molars grind and crush.
  • Tooth: enamel, dentine, pulp (nerves, blood vessels), cement. Teeth are embedded in bone and the gums.
  • The stomach churns food into smaller pieces.
  • Extended: bile emulsifies fats and oils into smaller droplets, increasing the surface area for chemical digestion.

17. What chemical digestion does

Chemical digestion is the breakdown of large insoluble molecules into small soluble molecules.

Its role is to produce small soluble molecules that can be absorbed. Large insoluble molecules cannot be absorbed.

The word soluble carries a mark. "Smaller molecules" alone is not enough.

Examiner insight

“Many candidates stated that smaller molecules were formed without the additional detail of soluble products being formed.” “Many candidates understood the role of chemical digestion in producing small soluble molecules from large insoluble molecules but fewer went on to state that the purpose of this is to enable the absorption of the small molecules.”

Worked example 12 marks

Explain why starch must go through chemical digestion before it can be absorbed.

  1. 1

    starch is a large insoluble molecule, so it cannot be absorbed [1]

  2. 2

    chemical digestion breaks it down into small soluble molecules that can be absorbed [1]

18. Amylase, protease and lipase

Amylase breaks down starch to simple reducing sugars.

Proteases break down protein to amino acids.

Lipase breaks down fats and oils to fatty acids and glycerol. Each product carries its own mark, so give both.

Examiner insight

“The majority of candidates gave carbohydrate rather than starch as the substrate for amylase.” “Very few gained two marks for the products of the breakdown of fat; most stated fatty acids only.”

Worked example 15 marks

Test-tube 1 contained a mixture of starch suspension and amylase solution. Test-tube 2 contained a mixture of starch suspension and pepsin solution. After 10 minutes, Benedict's solution was added to both test-tubes and they were heated. Predict and explain the expected results for test-tube 1 and test-tube 2.

  1. 1

    test-tube 1 turns red and test-tube 2 stays blue [1]

  2. 2

    test-tube 1: amylase breaks down starch into a reducing sugar [1]

  3. 3

    test-tube 1: the shape of the active site of amylase is complementary to starch [1]

  4. 4

    test-tube 2: pepsin does not break down starch, it breaks down proteins [1]

  5. 5

    test-tube 2: no enzyme-substrate complexes are formed [1]

19. Where the enzymes are made and act

Amylase is secreted by the salivary glands and the pancreas. It acts in the mouth and the small intestine. It does not act in the stomach.

Proteases are secreted by the stomach lining and the pancreas. They act in the stomach and the small intestine.

Lipase is secreted by the pancreas and acts in the small intestine.

Examiner insight

“Many candidates thought that the liver or gall bladder produced amylase rather than the pancreas.” “Many candidates did not know where amylase acts with many choosing the stomach or the pancreas.”

Worked example 11 mark

Some parts of the alimentary canal are listed: 1 duodenum, 2 ileum, 3 mouth, 4 stomach. In which parts of the alimentary canal is starch digested?

A 1 and 3 · B 1 and 4 · C 2 and 3 · D 2 and 4

  1. 1

    amylase acts in the mouth and the small intestine, not the stomach, so B and D are wrong

  2. 2

    A: the duodenum, which is part of the small intestine, and the mouth. [1]

20. Hydrochloric acid in gastric juice

Hydrochloric acid in gastric juice has two functions. It kills harmful microorganisms in food. It provides an acidic pH for optimum enzyme activity.

It acts in the stomach. It does not digest food itself.

Name it in full. Stomach acid and gastric acid are not accepted.

Examiner insight

“Few candidates were able to state that hydrochloric acid provides a suitable pH for enzymes. Many incorrectly referred to the acid digesting or breaking down food.” “Some candidates seemed unaware that hydrochloric acid kills bacteria.”

Worked example 13 marks

(i) State where hydrochloric acid acts in the digestive system.(ii) Describe two functions of hydrochloric acid in the digestive system.

  1. 1

    (i) the stomach [1]

  2. 2

    (ii) killing (harmful) microorganisms / bacteria in food [1]

  3. 3

    (ii) provides an acidic / suitable pH for enzymes [1]

21. Starch digestion in two stages

Amylase breaks down starch to maltose. This stage happens in the mouth.

Maltase breaks down maltose to glucose. It acts on the membranes of the epithelium lining the small intestine.

Examiner insight

“A significant number of candidates stated that glucose was the product. Glucose is produced through the action of maltase.” “Many described named parts of the small intestine or in the villi instead of the epithelial cells.”

Worked example 11 mark

Starch in food is digested in two stages. In which parts of the alimentary canal do the two stages occur?

starch into maltosemaltose into glucose
Aduodenumstomach
Blining of small intestinemouth
Cmouthlining of small intestine
Dstomachduodenum
  1. 1

    amylase acts in the mouth; maltase acts on the lining of the small intestine

  2. 2

    C: mouth, then lining of small intestine. [1]

22. Bile and the right pH

Bile is an alkaline mixture. It neutralises the acidic mixture of food and gastric juices entering the duodenum from the stomach.

This provides a suitable pH for enzyme action in the small intestine.

Bile is made by the liver and stored in the gall bladder. It contains no enzymes. It also emulsifies fat.

Examiner insight

“Some candidates stated that the pancreas was the organ responsible for the production of bile.” “Some candidates incorrectly believed that bile is produced in the gall bladder rather than stored there.”

Worked example 12 marks

In the small intestine, bile provides a suitable pH for type Q lipase.(i) State one other function of bile.(ii) State the name of the organ that produces bile.

  1. 1

    (i) emulsifies fats / lipids / oils [1]

  2. 2

    (ii) the liver [1]

23. Pepsin and trypsin

Pepsin breaks down protein in the acidic conditions of the stomach.

Trypsin breaks down protein in the alkaline conditions of the small intestine.

Both are proteases. Trypsin digests protein, not fats.

Examiner insight

“The function of trypsin was less well-known with a number of candidates suggesting its function as the digestion of fats into fatty acids and glycerol.” “A number of candidates confused pepsin and trypsin, pepsin being secreted in the stomach and not the pancreas.”

Worked example 11 mark

Where in the alimentary canal do the enzymes pepsin, trypsin and maltase act?

pepsintrypsinmaltase
Asmall intestinestomachsmall intestine
Bsmall intestinestomachmouth
Cstomachsmall intestinesmall intestine
Dstomachsmall intestinemouth
  1. 1

    pepsin acts in the stomach, trypsin in the small intestine, maltase in the small intestine

  2. 2

    C [1]

Recap

  • Chemical digestion: large insoluble molecules to small soluble molecules, so they can be absorbed.
  • Amylase: starch to simple reducing sugars. Protease: protein to amino acids. Lipase: fats and oils to fatty acids and glycerol.
  • Amylase is made in the salivary glands and pancreas and acts in the mouth and small intestine.
  • Hydrochloric acid kills harmful microorganisms and gives an acidic pH for enzymes.
  • Extended: amylase gives maltose. Maltase gives glucose on the epithelium membranes of the small intestine.
  • Extended: bile is alkaline and neutralises the acidic mixture entering the duodenum.
  • Extended: pepsin works in the acid stomach. Trypsin works in the alkaline small intestine.

24. Where nutrients are absorbed

Digested food molecules are absorbed in the small intestine. They pass into the blood.

The colon is part of the large intestine. It is not where nutrients are absorbed.

Examiner insight

“A common misconception was that absorption of food molecules occurs in the large intestine.” “This posed no problem for most candidates, but a few selected the colon as the site of absorption.”

Worked example 12 marks

A student says that digested food molecules are absorbed in the colon. State the region of the alimentary canal where nutrients are absorbed and say whether the student is correct.

  1. 1

    the small intestine [1]

  2. 2

    the student is not correct: the colon is not the site where food molecules are absorbed [1]

25. Absorption of water

Most water is absorbed from the small intestine.

Some water is also absorbed from the colon, which makes the faeces semi-solid.

Examiner insight

“The colon absorbs some water to produce semi-solid faeces, whereas the small intestine is constantly secreting and absorbing water.” “Most water absorption takes place in the small intestine.”

Worked example 11 mark

Which part of the alimentary canal is where most water is absorbed into the blood?

A oesophagus · B colon · C stomach · D small intestine

  1. 1

    D: small intestine. [1]

26. Villi and microvilli

Villi and microvilli increase the internal surface area of the small intestine. Microvilli are on the epithelial cells that line the villi.

A larger surface area means nutrients are absorbed at a faster rate, by diffusion across the cell membrane.

Microvilli are not cilia. They do not move food along.

Examiner insight

“Some said that the increased surface area is for more absorption rather than for faster absorption.” “A common misconception was that microvilli help to move food along the intestines.”

Worked example 13 marks

Explain the significance of villi and microvilli in the small intestine.

  1. 1

    villi and microvilli increase the internal surface area of the small intestine [1]

  2. 2

    for the absorption of nutrients, by diffusion across the cell membrane [1]

  3. 3

    so nutrients are absorbed at a faster rate [1]

27. Structure of a villus

A villus is lined with epithelial cells, which have microvilli.

Inside the villus are blood capillaries and a lacteal. These adapt the villus for absorption, not for gas exchange.

Examiner insight

“Some gave responses linking the villus to gas exchange rather than to absorption.” “Many did not describe the structure of the villus or its role in sufficient depth for credit.”

Worked example 13 marks

Name three structures that adapt the villi of the small intestine for absorption.

  1. 1

    microvilli [1]

  2. 2

    lacteal [1]

  3. 3

    blood capillaries [1]

28. Capillaries and lacteals

Blood capillaries carry absorbed nutrients away in the blood.

The lacteal absorbs fat (fatty acids and glycerol) and transports it into the lymphatic system.

Examiner insight

“Few candidates gave the absorption of fat (or fatty acids and glycerol) and the transport of fat into the lymphatic system.” “Many thought that the lacteal transports its contents directly to the liver.”

Worked example 12 marks

Describe the role of the lacteal in a villus.

  1. 1

    absorbs fat (fatty acids and glycerol) [1]

  2. 2

    transports it into the lymphatic system [1]

Recap

  • Nutrients are absorbed in the small intestine.
  • Most water is absorbed in the small intestine. Some is absorbed in the colon.
  • Extended: villi and microvilli increase the internal surface area, so absorption is faster.
  • Extended: a villus has epithelial cells with microvilli, blood capillaries and a lacteal.
  • Extended: capillaries carry nutrients in the blood. The lacteal takes fat into the lymphatic system.

End-of-chapter exercise

Test yourself on the whole chapter. Work through these before moving on.

  1. State what is meant by a balanced diet.2 marks
  2. Name the disease caused by a diet low in vitamin C and the disease caused by a diet low in vitamin D.2 marks
  3. State two dietary sources of vitamin D.2 marks
  4. State one type of food that is a good source of fibre and one reason why fibre is needed.2 marks
  5. On a long voyage, a sailor eats no fruit or vegetables. Name the nutrient that is low in his diet and the disease this causes.2 marks
  6. State two causes of rickets.2 marks
  7. The table gives the protein and fat in food P and food Q. (a) Calculate the percentage more protein in food P than in food Q. (b) State the importance of protein in the diet. | food | protein / g per 100 g of food | fat / g per 100 g of food | | --- | --- | --- | | P | 20.0 | 4.0 | | Q | 5.0 | 12.0 |3 marks
  8. A student writes: ‘Scurvy is caused by a lack of iron. Iron is needed for strong bones. Fibre is needed for growth and repair of cells.’ Correct the mistakes in the student's statements.4 marks
  9. A person eats one serving of cereal X each morning. They change to one serving of cereal Y. The table gives the label values and the serving eaten. (a) Calculate the mass of fibre in one serving of cereal X. (b) Calculate the percentage change in the mass of fibre eaten each morning after the change to cereal Y. Give your answer to two significant figures. (c) State one benefit of this change for the person. | cereal | fibre / g per 100 g of cereal | mass of one serving / g | | --- | --- | --- | | X | 2.8 | 45 | | Y | 7.0 | 30 |5 marks
  10. Four scientists spend three months at a polar research station with no sunlight. They eat only dried meat, tinned oily fish, cheese and bread, and drink only water. (a) One scientist says the diet is balanced because it contains carbohydrate, fat, protein, mineral ions and water. Explain why the diet is not balanced. (b) Another scientist suggests taking iron tablets to prevent scurvy. Explain why this is wrong, and state what iron is needed for. (c) Name the vitamin that a lack of sunlight puts at risk, and one food in this diet that is a source of it.6 marks
  11. Name the process by which food and drink are taken into the body.1 mark
  12. Name the three parts of the large intestine.3 marks
  13. Name the associated organ that stores bile.1 mark
  14. A student writes that the liver makes amylase. Name two organs that do make amylase.2 marks
  15. Define absorption.1 mark
  16. Define assimilation.1 mark
  17. Nutrients from a meal pass from the ileum into the blood. Later a muscle cell takes up some of them and uses them. Name the term for each of these two events.2 marks
  18. Name the process that each event in the table describes. | Event | Process | | --- | --- | | A drink enters the mouth | | | Nutrients move from the small intestine into the blood | | | Undigested food leaves the body as faeces | |3 marks
  19. In one day, 9.0 dm³ of water passes into a woman's small intestine. The table gives the volume of water absorbed by two parts of her alimentary canal. The rest of the water leaves her body in the faeces. (a) Calculate the volume of water that leaves her body in the faeces. (b) Calculate the percentage of the absorbed water that is absorbed by the small intestine. Give your answer to 3 significant figures. (c) A student says that the colon absorbs most of the water. Use the table to state whether the student is correct. (d) Name the process by which faeces leave the body. Name the part of the alimentary canal where it occurs. | Part of the alimentary canal | Volume of water absorbed / dm³ | | --- | --- | | small intestine | 8.3 | | colon | 0.6 |6 marks
  20. A student writes this account of what happens to a meal of rice. ‘The rice is ingested at the mouth. Amylase made by the liver breaks down the starch in the rice. Bile, which is made in the gall bladder, neutralises the stomach acid. The nutrients are then assimilated into the blood through the wall of the colon. Finally, the undigested food is excreted at the rectum.’ The account contains six mistakes. Identify each mistake and correct it.6 marks
  21. State what is meant by physical digestion.2 marks
  22. State why physical digestion helps the action of enzymes.1 mark
  23. A child bites a piece off a carrot. Name the type of tooth she uses to bite. A student says that this type of tooth also grinds food. State whether the student is correct and give a reason.2 marks
  24. Name the two types of teeth that grind food.2 marks
  25. Name the white outer layer of a tooth. State two things that a tooth is embedded in.3 marks
  26. A dentist looks at a tooth. Name the layer directly beneath the enamel and the part that holds the nerves.2 marks
  27. State the type of digestion that takes place when the stomach churns food. Give the effect on the food.2 marks
  28. A student writes: ‘Molars break starch into smaller molecules.’ Use the term physical digestion to correct the statement.3 marks
  29. A student models physical digestion. Block A is a cube of cooked egg white with sides of 2 cm. Block B is an identical cube that is cut into 8 equal cubes with sides of 1 cm. Each is put into the same volume of the same enzyme solution. The pieces of block B are digested in less time. (a) Calculate the total surface area of block A and of the 8 pieces of block B. (b) Explain why the pieces of block B are digested in less time. (c) State two places in the body where food is broken into smaller pieces, and how it is done in each.6 marks
  30. A student mixes oil with different liquids in three tubes. Lipase is an enzyme that digests fats and oils. The table gives the percentage of the oil that is chemically digested after 20 minutes. (a) Describe what bile does to the oil in tubes Y and Z. (b) Calculate how many times more oil is digested in tube Y than in tube X. Explain the difference. (c) A student concludes: ‘Bile digests oil into smaller molecules.’ Use the result for tube Z to explain why this is wrong. | tube | contents | oil digested / % | | --- | --- | --- | | X | oil and lipase | 15 | | Y | oil, lipase and bile | 60 | | Z | oil and bile | 0 |7 marks
  31. Define chemical digestion.2 marks
  32. A student says that digestion is needed because the body cannot use large pieces of food. State the role of chemical digestion in terms of molecules.2 marks
  33. Name the enzyme that breaks down fats and oils. State the two products.3 marks
  34. A student mixes protease solution with starch suspension and leaves it for 10 minutes. Predict whether simple reducing sugars will be present. Explain your answer.2 marks
  35. State where amylase is secreted and where it acts.4 marks
  36. Describe two functions of hydrochloric acid in gastric juice.2 marks
  37. A patient takes a drug that stops the stomach lining from making hydrochloric acid. Suggest two problems this could cause in the stomach.2 marks
  38. A sample taken from the lining of the small intestine contains maltose. Name the enzyme that breaks down maltose and the product. State exactly where in the small intestine the enzyme acts.3 marks
  39. Egg-white protein is insoluble, so it makes a cloudy suspension. A student adds a protease to the suspension and times how long the mixture takes to go clear. She tests two human proteases, X and Y, at three pH values. The table gives her results. (a) Identify X and Y. Give the evidence from the table for each. [2] (b) State where in the alimentary canal each protease acts. [2] (c) Explain, in terms of molecules, why the mixture goes clear. [2] | pH | time to go clear with X / minutes | time to go clear with Y / minutes | | --- | --- | --- | | 2 | 4 | stays cloudy | | 7 | 25 | 12 | | 9 | stays cloudy | 5 |6 marks
  40. A blockage stops bile reaching the duodenum of a patient. The table gives the pH of the contents of the stomach and the duodenum. (a) Explain why the healthy person's duodenum has a higher pH than the stomach. [3] (b) Predict and explain the effect on the action of trypsin in the patient's duodenum. [2] (c) The patient also digests fat slowly. A student says this is because the enzymes in bile are missing. Correct the student's statement. [2] | | pH in stomach | pH in duodenum | | --- | --- | --- | | healthy person | 2 | 8 | | patient | 2 | 3 |7 marks
  41. Name the region of the alimentary canal where nutrients are absorbed.1 mark
  42. Water is absorbed from two regions of the alimentary canal. Name the two regions and state which absorbs most.2 marks
  43. A student writes: ‘Glucose is absorbed when a body cell takes it in and uses it.’ State the region where glucose is absorbed, and what the glucose passes into when it is absorbed.2 marks
  44. In one day, 8000 cm³ of liquid enters the small intestine. 1100 cm³ passes on into the colon. 100 cm³ leaves in the faeces. Assume all the liquid lost in each region is water that is absorbed. Calculate the volume of water absorbed in the small intestine and the volume absorbed in the colon. State which region absorbs most water.3 marks
  45. Describe the role of microvilli in the small intestine.2 marks
  46. Explain how villi and microvilli affect the rate at which nutrients are absorbed in the small intestine.3 marks
  47. After a meal, glucose and fatty acids are both absorbed in a villus. State where each is carried away from the villus.2 marks
  48. Describe the structure of a villus and explain how it is adapted for absorption.5 marks
  49. A scientist measures the small intestines of two species of bat, P and Q. The results are in the table below. (a) Calculate the total number of villi in the small intestine of each bat. (b) A student says: ‘Bat P must absorb nutrients at the faster rate, because it has more villi per cm.’ Use your answers to (a) to comment on this. (c) Name one other feature, not in the table, that also increases the internal surface area of the small intestine. | bat | length of small intestine / cm | villi per cm | | --- | --- | --- | | P | 20 | 90 | | Q | 35 | 60 |5 marks
  50. In one condition, the villi of the small intestine become much shorter and the lacteals inside them are blocked. The epithelial cells still have microvilli and the blood capillaries are not affected. Predict and explain the effect of this condition on the absorption of nutrients in general, of glucose and of fat.6 marks

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