Human Diet & Digestion

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Diet & Deficiencies

A balanced diet includes carbohydrates, proteins, lipids, vitamins, minerals, dietary fibre and water in correct proportions.
Scurvy is a severe vitamin C deficiency causing anaemia, bleeding, gum ulcerations and tooth loss.
Rickets is caused by vitamin D deficiency, leading to soft, weak bones and poor bone growth in children.
Vitamin D is needed for calcium absorption; sources include sunlight, fish, eggs and butter.

Digestive System Overview

The digestive system includes the alimentary canal (mouth, oesophagus, stomach, small intestine, large intestine) and accessory organs (salivary glands, pancreas, liver, gall bladder).
Ingestion – taking food into the mouth.
Mechanical digestion – breaking food into smaller pieces without chemical change (teeth, stomach churning, bile emulsification).
Chemical digestion – enzymes break large insoluble molecules into small soluble ones.
Absorption – digested molecules move into blood/lymph in the small intestine.
Egestion – undigested food passes out as faeces via the anus.

Organs of the human digestive system

Physical Digestion & Teeth

Physical digestion increases surface area for enzyme action.
Teeth types: incisors (biting/cutting), canines (tearing), premolars/molars (grinding).
Tooth structure: enamel (hard outer layer), dentine (protects nerves), pulp (contains nerves & blood vessels), cement (anchors root).
Stomach churning mixes food with gastric juices mechanically.

Types of human teeth

The Stomach & Hydrochloric Acid

Stomach produces gastric juice containing hydrochloric acid and pepsin.
HCl kills bacteria and provides acidic pH (≈2) for pepsin to work.
Pepsin digests proteins into peptides in acidic conditions.
Stomach has muscular, epithelial and glandular tissues.

Tissues of the stomach

Chemical Digestion & Enzymes

Amylase (mouth & pancreas) digests starch → maltose; maltase on small intestine epithelium digests maltose → glucose.
Proteases (pepsin in stomach, trypsin from pancreas) digest proteins → amino acids.
Lipase (pancreas) digests lipids → fatty acids + glycerol.
Enzymes are specific; each catalyses one type of reaction.

The digestion of starch

Bile & Emulsification

Bile is produced by the liver, stored in the gall bladder, and released into the duodenum.
Bile is alkaline – neutralises stomach acid for enzymes in small intestine.
Bile emulsifies fats (physical digestion) into smaller droplets, increasing surface area for lipase.
Emulsification is mechanical, not chemical – no bonds are broken.

Bile production and secretion

Absorption & the Small Intestine

Absorption of glucose, amino acids, vitamins, minerals and water occurs mainly in the small intestine (ileum).
Fatty acids and glycerol are absorbed into lymph via lacteals.
Most water (≈80%) is absorbed in the small intestine; the rest in the colon.
Assimilation – absorbed nutrients are taken up by body cells for growth, repair and energy.

Adaptations of the Small Intestine (Extended)

The ileum is long and has a folded surface with millions of villi (finger-like projections).
Microvilli on villi further increase surface area.
Villus wall is one cell thick – short diffusion distance.
Rich blood capillary network transports glucose and amino acids; lacteal transports fatty acids and glycerol.

Adaptations of the small intestine

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1.Which of the following is a correct function of bile?
Medium
- ATo emulsify proteins
- BTo neutralise the alkaline conditions of food entering the duodenum
- CTo provide enzymes for the digestion of lipids
- DTo increase the surface area of lipids for digestion
2.In which part of the alimentary canal does most of the absorption of water take place?
Easy
- AColon
- BOesophagus
- CSmall intestine
- DStomach
3.Which of the following best describes the function of vitamin D in a human?
Medium
- AVitamin D forms an essential part of collagen protein which is the main component of skin, hair and nails.
- BVitamin D is needed for strong ligaments and a deficiency may cause ligament tears.
- CVitamin D assists with the absorption of calcium and is therefore needed to build strong bones and teeth.
- DVitamin D is an important component of haemoglobin which is needed for the transport of oxygen to the cells.
4.Which disease can be caused by a lack of vitamin C?
Easy
- AAIDS
- BCoronary heart disease
- CRickets
- DScurvy
5.What are the products when proteins are broken down?
Easy
- AAmino acids
- BFatty acids
- CGlycerol
- DSimple sugars
6.What is the dietary importance of fibre in humans?
Easy
- AFor growth and repair of cells
- BTo help food move through the alimentary canal
- CTo maintain strong bones and teeth
- DTo provide energy
7.Which of the following is a correct cause and effect?
Medium
- AIron deficiency causes brittle bones (rickets)
- BIron deficiency causes anaemia
- CVitamin D deficiency causes anaemia
- DVitamin D deficiency caused by lack of red meat causes brittle bones
8.Which row correctly matches the enzyme to what it breaks down?
Medium
- AAmylase breaks down fats
- BMaltase breaks down starch
- CPepsin breaks down starch
- DTrypsin breaks down protein

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9.In which vessel would the concentration of fatty acids be highest after a meal?
Hard
- AHepatic portal vein
- BLacteal in a villus
- CCapillary in a villus
- DAorta
10.Which of the following describe prevention methods for rickets?
Medium
- AVitamin D supplementation, adequate intake of protein, adequate intake of iron.
- BVitamin D supplementation, adequate intake of calcium, avoid exposure to sunlight.
- CVitamin D supplementation, adequate intake of calcium, exposure to sunlight.
- DFoods high in vitamin D, vitamin A supplementation, adequate intake of fibre.
11.A person has a condition that reduces the number of villi in the small intestine. What is the likely effect and explanation?
Hard
- AWeight gain because of reduced absorption of digested food molecules.
- BWeight gain because of reduced digestion of maltose to glucose.
- CWeight loss because of reduced lipid digestion and absorption.
- DWeight loss because of reduced absorption of digested food molecules.
12.Which of the following is not an example of physical digestion?
Medium
- ABreaking food into smaller pieces by chewing
- BStarch being broken down into glucose molecules
- CFood churned by stomach muscles
- DBile breaking large fat droplets into smaller ones
13.Where is bile produced?
Easy
- AGall bladder
- BLiver
- CPancreas
- DSmall intestine
14.Which enzyme breaks down starch?
Easy
- AAmylase
- BLipase
- CPepsin
- DTrypsin
15.What is the role of hydrochloric acid in the stomach?
Easy
- ATo emulsify fats
- BTo kill bacteria and provide acidic pH for enzymes
- CTo digest starch
- DTo absorb nutrients
16.A student tests a food sample with Benedict's solution and gets a brick-red precipitate. What does this indicate?
Easy
- APresence of starch
- BPresence of reducing sugar
- CPresence of protein
- DPresence of lipid
17.Which of the following correctly describes assimilation?
Medium
- AMovement of digested food into the blood
- BBreakdown of large molecules into small ones
- CTaking up of digested food molecules by cells for use
- DPassing out of undigested food as faeces
18.The graph shows the change in concentration of pathogens as food passes through the stomach. Which of the following is the main factor that explains the shape of the curve?
Medium
- AAcidic conditions
- BAlkaline conditions
- CProtease enzymes
- DChurning activity
19.A smoothie contains soya protein, iron, fibre, low-fat milk, and water. Which ingredients are missing for it to be a balanced diet?
Medium
- ACarbohydrates, vitamins (C and D), fats and oils
- BCalcium, carbohydrates, vitamins (C and D), fats and oils
- CVitamins (C and D) and mineral ions
- DVitamins (C and D) and calcium
20.A food sample gives a blue-black colour with iodine solution. Which food group is present?
Easy
- AStarch
- BProtein
- CLipid
- DReducing sugar
21.A sample of food is tested with Benedict's solution and gives a blue colour. The same food is then boiled with dilute hydrochloric acid, neutralised, and tested again with Benedict's solution, giving a brick-red precipitate. What does this indicate?
Medium
- AThe food contains starch but not reducing sugars.
- BThe food contains non-reducing sugars that are hydrolysed to reducing sugars.
- CThe food contains reducing sugars that are destroyed by boiling acid.
- DThe food contains protein that reacts with Benedict's solution after acid treatment.
22.In an experiment, a student placed equal volumes of starch solution and amylase solution in a beaker at 37°C. Every minute, a drop of the mixture was removed and tested with iodine solution. The blue-black colour disappeared after 5 minutes. If the experiment is repeated with amylase that was boiled for 10 minutes before adding, what result would be expected?
Medium
- AThe blue-black colour disappears after 5 minutes as before.
- BThe blue-black colour disappears after 10 minutes.
- CThe blue-black colour never disappears.
- DThe iodine solution turns brick-red.
23.How does physical digestion help chemical digestion?
Easy
- AIt changes large insoluble molecules into small soluble molecules.
- BIt increases the surface area of food.
- CIt provides the acidic conditions needed.
- DIt absorbs digested nutrients directly into the blood.
24.The table shows the energy content of four foods. Which food provides the most energy per gram? | Food | Energy (kJ) per 100 g | |---|---| | A | 800 | | B | 1200 | | C | 1500 | | D | 2000 |
Easy
- AA
- BB
- CC
- DD
25.In an experiment, a student placed equal volumes of starch solution and amylase solution in a beaker at 37°C. Every minute, a drop of the mixture was removed and tested with iodine solution. After 5 minutes, the iodine remained orange-brown. What does this indicate?
Medium
- AAmylase has denatured.
- BAll starch has been digested.
- CThe temperature is too low for amylase to work.
- DThe pH is too low for amylase to work.
26.Which structure in a villus contains lymph and transports fatty acids and glycerol away from the small intestine?
Medium
- ABlood capillary
- BLacteal
- CEpithelium
- DMicrovilli
27.Which part of a tooth is the hard, outer layer that protects the tooth?
Easy
- AEnamel
- BDentine
- CPulp cavity
- DCement
28.A student set up an experiment to investigate the effect of pH on the digestion of protein by pepsin. Four test tubes containing equal amounts of protein and pepsin were adjusted to different pH values and kept at 37°C. After 30 minutes, the amount of amino acid produced was measured. The results are shown in the table. | pH | Amino acid produced (mg) | |---|---| | 2 | 15 | | 4 | 10 | | 6 | 4 | | 8 | 1 | What is the optimum pH for pepsin?
Easy
- A2
- B4
- C6
- D8
29.Which of the following is a symptom of scurvy?
Easy
- ABone pain
- BSpontaneous bleeding
- CSoft, weak bones
- DLack of bone growth
30.Bile is produced in the gall bladder.
Easy
True or false?
31.Which of the following is an example of physical digestion?
Easy
- AAmylase breaking down starch into maltose
- BPepsin breaking down protein into amino acids
- CBile emulsifying fats into smaller droplets
- DLipase breaking down lipids into fatty acids and glycerol
32.Match each tooth type to its function:
Easy
- Incisors
- Canines
- Premolars and molars
- Biting and cutting
- Tearing, holding and biting
- Chewing and grinding
33.Which of the following are adaptations of the small intestine for absorption? (Select all that apply)
Medium
- ALong length
- BThick wall
- CMany villi
- DFew blood capillaries
- EOne-cell-thick wall
34.Vitamin D is required for the absorption of calcium into the body.
Easy
True or false?
35.Arrange the following processes in the order they occur during digestion of a meal:
Medium
- Chemical digestion of starch by amylase in the mouth
- Absorption of glucose into the blood in the ileum
- Emulsification of fats by bile in the duodenum
- Churning of food in the stomach
36.Which of the following is NOT a function of hydrochloric acid in the stomach?
Medium
- AKilling bacteria in food
- BProviding an acidic pH for pepsin
- CEmulsifying fats
- DDenaturing enzymes in pathogens
37.Arrange the following processes in the order they occur during digestion of a meal: ingestion, chemical digestion, egestion, absorption, mechanical digestion.
Medium
- ingestion
- mechanical digestion
- chemical digestion
- absorption
- egestion
38.Complete the sentence:
Easy
The enzyme that breaks down starch into maltose in the mouth is ____.
39.Name the organ where bile is stored.
Easy
40.What is the optimum pH for the enzyme pepsin in the stomach?
Easy
41.Complete the sentence: The enzyme that digests starch into maltose in the mouth is ___.
Easy
The enzyme that digests starch into maltose in the mouth is ____.
42.Explain how the structure of a villus helps the small intestine absorb digested food efficiently.
Hard
43.What is the optimum pH for the enzyme pepsin in the stomach?
Easy
- A2
- B1
- C4
- D3

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