Biology · Unit 11

Digestion and Nutrition

The gut, enzymes and nutrients

Digestion is the problem of turning food, which is other organisms, into molecules small enough to cross a cell membrane. Most of the unit is about how the body breaks things down and where each stage happens.

Enzymes do the actual work, and each has a place, a pH it likes and a substrate it acts on. The unit also covers absorption in the small intestine and the roles of the liver and pancreas, which do far more than their share and get far less attention than the stomach.

This unit breaks down into 20 short steps and 120 questions, starting at difficulty 1 and building to 3. Below you can see exactly what it covers, how the path is structured, and worked examples with explanations.

Steps: 20
Questions: 120
Difficulty: 1-3

What this unit covers

The Digestive Tract
Digestive Enzymes
Absorption
Nutrients and Diet
Liver, Pancreas and Gut

Where this fits

Follows Human Body Systems. The enzyme content connects directly to Molecular Biology.

Where people slip

Very little absorption happens in the stomach. It is a mixing and acid-treatment stage; the small intestine is where nutrients actually enter the body, which is why its surface is folded so aggressively.

How the unit is structured

Digestion and Nutrition runs as 20 short steps that unlock in order. 15 are practice rounds and 5 are challenge rounds that pull together everything before them. Questions start at difficulty 1 and climb to 3 as you progress.

Step 1 · easierStep 20 · harder

Challenge rounds

Example questions

30 real questions from this unit, with the answer and the reason behind it, grouped by what they practise. There are 120 in the unit altogether.

Absorption

Fact or fibLevel 1
1. The large intestine absorbs water from the undigested food.
Answer: True
The large intestine absorbs most of the remaining water, leaving semi-solid faeces behind.
Multiple choiceLevel 1
2. In which organ are most digested nutrients absorbed into the blood?
- Small intestinecorrect
- Stomach
- Large intestine
- Oesophagus
Most digested nutrients are absorbed into the bloodstream through the wall of the small intestine.
Build the sentenceLevel 2
3. Build the sentence describing the small intestine.
Answer: The small intestine is very long
The small intestine is very long, around five metres, which gives a huge surface area for absorbing nutrients.
Fill the blankLevel 2
4. The tiny finger-like villi ____ the surface area of the small intestine for absorption.
- increasecorrect
- decrease
- block
- colour
Villi greatly increase the surface area of the small intestine, so nutrients can be absorbed faster.
Choose all that applyLevel 3
5. Which features of a villus make it efficient at absorbing food? Select all that apply.
- A wall only one cell thick, giving a short diffusion path
- A dense network of blood capillariescorrect
- A central lacteal for absorbing fatscorrect
- A thick layer of cartilage
A short diffusion path, a rich blood supply and a lacteal all speed absorption; a thick cartilage layer would only slow it.
Put in orderLevel 3
6. Put the steps of fat digestion and absorption in the correct order.
Answer: Bile salts emulsify fat into tiny droplets -> Lipase breaks triglycerides into fatty acids and monoglycerides -> Micelles carry the products to the epithelial cell membrane -> Triglycerides are reassembled and packed into chylomicrons -> Chylomicrons pass into the lacteal
Fats are emulsified, hydrolysed by lipase, ferried by micelles, reassembled into triglycerides, packed into chylomicrons and absorbed into the lacteal.

Digestive Enzymes

Multiple choiceLevel 1
7. Which enzyme breaks down starch?
- Amylasecorrect
- Protease
- Lipase
- Pepsin
Amylase is a carbohydrase that breaks starch down into smaller sugars such as maltose.
Spell itLevel 1
8. What is the general name for a protein that speeds up the breakdown of food? Spell it.
Answer: enzyme
Enzymes are biological catalysts that speed up digestion without being used up.
Guess the numberLevel 2
9. At about what temperature do human digestive enzymes work best?
Answer: 37 degrees C
Human enzymes have an optimum temperature of about 37 degrees C, which is normal body temperature.
Match the pairsLevel 2
10. Match each digestive enzyme to the food group it breaks down.
Answer: Amylase = Starch; Protease = Proteins; Lipase = Fats; Carbohydrase = Carbohydrates
Each enzyme digests a specific food: amylase acts on starch, protease on proteins, lipase on fats and carbohydrases on carbohydrates.
Fill the blankLevel 3
11. The ____ cells of the stomach lining secrete the hydrochloric acid that makes conditions right for pepsin.
- parietalcorrect
- chief
- goblet
- islet
Parietal (oxyntic) cells pump out hydrochloric acid, lowering stomach pH to around 2 for pepsin activity.
Sort into groupsLevel 3
12. Sort each enzyme by the pH conditions in which it works best.
Answer: Pepsin = Acidic; Salivary amylase = Neutral; Pancreatic trypsin = Alkaline; Pancreatic amylase = Alkaline
Pepsin needs the acidic stomach, salivary amylase works near neutral, and pancreatic enzymes work in the alkaline duodenum.

Liver, Pancreas and Gut

Multiple choiceLevel 2
13. What does bile do to large drops of fat in the small intestine?
- Breaks them into tiny droplets (emulsifies them)correct
- Turns them into protein
- Absorbs them straight into the blood
- Freezes them solid
Bile emulsifies fats, breaking large fat drops into tiny droplets so lipase can digest them faster.
Odd one outLevel 2
14. Three of these are jobs of the liver. Which one is NOT a liver function?
- Secreting insulin into the bloodcorrect
- Deaminating excess amino acids
- Storing glucose as glycogen
- Producing bile
Secreting insulin is a job of the pancreas (its islets of Langerhans); deamination, glycogen storage and bile production are all liver roles.
Choose all that applyLevel 3
15. The liver acts as a store for the body. Select the substances the liver stores.
- Glycogencorrect
- Ironcorrect
- Vitamin Acorrect
- Dietary fibre
The liver stores glycogen, iron and fat-soluble vitamins like A and D, but fibre is never absorbed or stored.
Fill the blankLevel 3
16. The liver converts the toxic ammonia made during deamination into ____, which the kidneys then excrete.
- ureacorrect
- uric acid
- ammonia
- glucose
The ornithine (urea) cycle in the liver turns ammonia into much less toxic urea for removal by the kidneys.
Match the pairsLevel 3
17. Match each secretory cell to the substance it releases.
Answer: Beta cells = Insulin; Alpha cells = Glucagon; Acinar cells = Digestive enzymes; G cells = Gastrin
Different cells specialise: beta cells make insulin, alpha cells glucagon, acinar cells enzymes, and G cells the hormone gastrin.
Sort into groupsLevel 3
18. Sort each job by whether it is done by the liver or the pancreas.
Answer: Deamination of amino acids = Liver; Producing bile = Liver; Secreting insulin = Pancreas; Secreting digestive enzymes = Pancreas
The liver deaminates amino acids and makes bile; the pancreas secretes insulin and digestive enzymes.

Nutrients and Diet

Choose all that applyLevel 1
19. Select the items that are among the seven main nutrient groups the body needs.
- Vitaminscorrect
- Mineralscorrect
- Enzymes
- Sunlight
The seven nutrient groups are carbohydrates, proteins, fats, vitamins, minerals, fibre and water; enzymes and sunlight are not food groups.
Multiple choiceLevel 1
20. Why is fibre an important part of a healthy diet?
- It keeps food moving through the gut and prevents constipationcorrect
- It is the body's main energy source
- It builds strong muscles
- It is digested into amino acids
Fibre is not digested, but it adds bulk that helps the gut push food along and prevents constipation.
Build the sentenceLevel 2
21. Build the phrase that defines basal metabolic rate.
Answer: energy used by the body at complete rest
Basal metabolic rate is the energy the body uses at complete rest, just to stay alive.
Fact or fibLevel 2
22. People with lactose intolerance cannot fully digest the sugar in milk because they lack enough of the enzyme lactase.
Answer: True
Without enough lactase, undigested lactose passes to the large intestine where bacteria ferment it, causing gas, bloating and diarrhoea.
Fill the blankLevel 2
23. A lack of vitamin A in the diet often causes ____ blindness, making it hard to see in dim light.
- nightcorrect
- colour
- snow
- sudden
Vitamin A is needed to make the eye pigment used in dim light, so a shortage causes night blindness.
Match the pairsLevel 3
24. Match each nutrient to the deficiency disease it prevents.
Answer: Vitamin D = Rickets; Vitamin B1 = Beri-beri; Iron = Anaemia; Iodine = Goitre
Each disease comes from lacking one nutrient: vitamin D-rickets, B1-beri-beri, iron-anaemia and iodine-goitre.

The Digestive Tract

Multiple choiceLevel 1
25. Which tube carries food from the mouth down to the stomach?
- Oesophaguscorrect
- Trachea
- Small intestine
- Bile duct
The oesophagus is the muscular tube that carries swallowed food from the mouth to the stomach.
Put in orderLevel 1
26. Put these parts of the digestive system in the order food travels through them, starting at the mouth.
Answer: Mouth -> Oesophagus -> Stomach -> Small intestine -> Large intestine -> Rectum
Food travels mouth to oesophagus to stomach to small intestine to large intestine to rectum before waste leaves the body.
Fill the blankLevel 2
27. The waves of muscle contraction that squeeze food along the gut are called ____.
- peristalsiscorrect
- digestion
- absorption
- respiration
Peristalsis is the wave-like muscle contractions that push food along the digestive tract.
Guess the numberLevel 2
28. How many teeth does a typical adult human have?
Answer: 32 teeth
A full adult set has 32 teeth, including incisors, canines, premolars and molars.
Choose all that applyLevel 3
29. Select the flavours that count as one of the five basic tastes the tongue detects.
- Sweetcorrect
- Bittercorrect
- Umami (savoury)correct
- Spicy hot
The five basic tastes are sweet, sour, salty, bitter and umami; spicy heat is a pain sensation, not a taste.
Fact or fibLevel 3
30. Rabbits eat some of their own soft droppings so their food is digested twice.
Answer: True
Rabbits pass food through the gut twice by eating special soft droppings, getting more nutrients from grass.

Where these questions come from. Each unit starts as a plan of the concepts it should cover and the difficulty it should span. Questions are written against that plan with AI assistance, then checked by a validator that rejects anything without a single defensible answer, an explanation, or plausible wrong options. How we write questions sets out the whole process, and corrections are fixed in the bank and reach the site and the app the same day.

How you practise

This unit mixes 17 different question formats, so you are recalling and applying rather than recognising the same layout every time.

Build the sentence
Choose all that apply
Fact or fib
Fill the blank
Guess the number
Listen and choose
Match the pairs
Multiple choice
Odd one out
Picture question
Put in order
Sequence recall
Sort into groups
Spell it
Tap the pairs
True or false
Type the answer

Practise Digestion and Nutrition

120 questions across 20 steps. Start with step one and crawl at your own pace.

Play this unit

Read about Digestion and Nutrition

Explainers from our blog on what this unit covers. Each one ends with real questions from the bank.

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