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KS3 · Biology

K2 Nutrition and Digestion

AQA N/A - KS3 National Curriculum, styled on AQA KS3 Syllabus conventions · Calculator allowed · about 65 minutes

Name: _______________________________ Date: ____ / ____ / ______

Answer ALL questions. Show all your working.

Which nutrient is the body's main, quickly-used source of energy?

A) Protein
B) Carbohydrate
C) Vitamin
D) Mineral

State the main function in the human body of each of these nutrients.

(a)Protein(1)

(b)Fat (lipid)(1)

(c)Fibre(1)

(d)Vitamin C(1)

Identify the digestive system organ described in each part.

(a)The organ where mechanical digestion begins and saliva (containing amylase) is mixed with food.(1)

(b)The muscular tube that carries food from the throat to the stomach by peristalsis.(1)

(c)The J-shaped organ that churns food and begins protein digestion using acid and protease.(1)

(d)The long tube where most digested food molecules are absorbed into the blood.(1)

Food is pushed along the oesophagus and gut by peristalsis. Describe how peristalsis moves food along the gut.

(3)

Enzymes are described as being specific to one substrate. Using the lock and key model, explain what this means.

(3)

Required practical: chemical tests can be used to identify the food groups present in an unknown food sample. For each test, state the reagent(s) used and the positive result observed.

(a)Test for starch.(2)

(b)Test for reducing sugar.(2)

(c)Test for protein.(2)

(d)Test for fat (lipid).(2)

Complete the missing substrate and product for each digestive enzyme.

(a)Amylase: substrate and product.(2)

(b)Protease: substrate and product.(2)

(c)Lipase: substrate and product.(2)

A packet of oat biscuits shows an energy value of 850 kJ per 100 g. A pupil eats a 35 g portion.

(a)Calculate the energy, in kJ, in the 35 g portion. Give your answer to 3 significant figures.(2)

(b)1 kcal is approximately equal to 4.2 kJ. Calculate the energy of the portion in kcal, to the nearest whole number.(2)

A student wants to test an unknown food sample for the presence of protein using the Biuret test.

(a)Describe the method used, including the reagents added.(2)

(b)The sample turns purple/lilac. What does this indicate?(1)

Bile is produced by the liver and stored in the gall bladder before being released into the small intestine. Explain why bile is important in digestion, even though it is not an enzyme.

(3)

The wall of the small intestine is covered in villi. State three ways the villi are adapted to increase the rate of absorption of digested food.

(3)

The table shows the rate of reaction of amylase breaking down starch at different temperatures.
Temperature (deg C): 10, 20, 30, 40, 50, 60
Rate (arbitrary units): 2, 5, 9, 14, 4, 0

(a)State the optimum temperature for this enzyme, as shown by the data.(1)

(b)Explain, in terms of the enzyme's structure, why the rate of reaction decreases sharply above the optimum temperature.(3)

A pupil's estimated daily energy intake from food is 8700 kJ. Their estimated daily energy use is made up of: basal metabolic rate (BMR) 6000 kJ, physical activity 1900 kJ, and energy used to digest food 400 kJ.

(a)Calculate the pupil's total daily energy use.(1)

(b)Calculate the pupil's daily energy balance (intake minus use), stating whether it is a surplus or a deficit.(2)

(c)State and explain the likely effect on the pupil's body mass over many weeks if this pattern continues.(2)

Priya's meals for one day are shown below.
Breakfast: sugary cereal with whole milk
Lunch: white bread cheese sandwich, packet of crisps, chocolate bar
Dinner: sausages, chips, baked beans
Evaluate whether Priya's diet for the day is balanced. In your answer, identify what is missing or in excess, and suggest one improvement.

(4)

A pasta label states that 100 g of dry pasta contains 12 g of protein. A 13-year-old's recommended daily protein intake is 34 g.

(a)Calculate the mass of dry pasta, in g, that would need to be eaten to provide exactly 34 g of protein. Give your answer to 3 significant figures.(2)

(b)A pupil eats a 75 g portion of the dry pasta. Calculate the percentage of their daily recommended protein intake that this portion provides. Give your answer to 1 decimal place.(2)

A meal of pasta with cheese sauce and mixed vegetables contains carbohydrate, protein, fat, fibre, vitamins and minerals. Explain how this meal is digested and how the useful nutrients are absorbed into the pupil's blood, so that they can be used by cells in the body. In your answer, refer to specific organs, enzymes and the process of absorption.

(6)

Required practical: in an investigation into enzyme action, a student mixed amylase solution with starch solution at 30 deg C. Every 20 seconds, a drop of the mixture was removed and added to a fresh spot of iodine solution on a spotting tile. The iodine stopped turning blue-black after 100 seconds, showing that all the starch had been broken down.

(a)Calculate the rate of this reaction, using rate = 1000 / time taken (in seconds). Give your answer to 3 significant figures.(2)

(b)Explain why the student tested a fresh drop of the mixture with iodine every 20 seconds, rather than continuously monitoring one drop.(2)

(c)Suggest one way the student could improve the reliability of this result.(1)

BMI (body mass index) can be calculated using the equation: BMI = mass (kg) / [height (m)]^2. A man has a mass of 68 kg and a height of 1.60 m.
BMI categories: Underweight, BMI < 18.5; Healthy weight, BMI 18.5 to 24.9; Overweight, BMI 25.0 to 29.9; Obese, BMI ≥ 30.

(a)Calculate the man's BMI. Give your answer to 3 significant figures.(2)

(b)State which BMI category the man is in.(1)

(c)Evaluate the use of BMI as a measure of whether a person is a healthy weight.(2)

Required practical: a student compared the amount of reducing sugar in three different fruit juices using Benedict's test. For each juice, they added Benedict's solution to a test tube and heated it in a water bath at 80 deg C for 5 minutes.

(a)Explain why the student heated the test tubes in a water bath rather than directly over a Bunsen flame.(2)

(b)State two variables, other than temperature, that the student should control to make this a fair test when comparing the three juices.(2)

A person maintains an average daily energy deficit (energy used minus energy eaten) of 500 kJ for one week. Body fat stores approximately 37 kJ of energy per gram.

(a)Calculate the total energy deficit over the 7 days.(1)

(b)Estimate the mass of body fat, in g, that this deficit could account for, assuming the energy deficit is met entirely from fat stores. Give your answer to 3 significant figures.(2)

A professional marathon runner and an office worker with a sedentary (inactive) lifestyle are the same age, height and mass. Suggest why the marathon runner needs a different diet from the office worker, referring to energy and macronutrient (carbohydrate, protein and fat) requirements.

(4)

Mark scheme · K2 Nutrition and Digestion

Question 1

B1 Correct answer selected: B (Carbohydrate)
Answer: B - Carbohydrate

Question 2

(a) B1 growth and repair of cells/tissues (oe)
(a) Answer: Growth and repair of body cells and tissues.
(b) B1 energy store / thermal insulation / protects organs (any one, oe)
(b) Answer: An energy store (also insulates the body and protects organs).
(c) B1 helps food/waste move through the gut, preventing constipation (oe)
(c) Answer: Helps food and waste move through the digestive system, preventing constipation.
(d) B1 keeps skin and gums healthy / prevents scurvy (oe)
(d) Answer: Keeps skin and gums healthy (a lack of it causes scurvy).

Question 3

(a) B1 mouth (cao)
(a) Answer: Mouth
(b) B1 oesophagus (cao)
(b) Answer: Oesophagus
(c) B1 stomach (cao)
(c) Answer: Stomach
(d) B1 small intestine (cao)
(d) Answer: Small intestine

Question 4

B1 circular muscles in the gut wall contract behind the food (bolus), squeezing the gut narrower
B1 muscles in front of the food relax, widening the gut ahead of it
B1 this coordinated wave of contraction and relaxation pushes the food along the gut
Answer: Circular muscles contract behind the food while muscles ahead of it relax, producing a wave of muscle contraction that pushes the food along the gut.

Question 5

B1 an enzyme has an active site with a specific shape
B1 only a substrate with a complementary (matching) shape can bind to the active site, like a key fitting a lock
B1 this forms an enzyme-substrate complex, allowing the reaction to take place; a substrate with a different shape will not fit or react
Answer: The enzyme's active site has a specific shape that only fits a substrate with a matching (complementary) shape, like a key fitting a lock, so each enzyme only works on one type of substrate.

Question 6

(a) B1 add iodine solution (in potassium iodide) directly to the sample
(a) B1 positive result: colour changes from browny-orange to blue-black
(a) Answer: Add iodine solution: a colour change from browny-orange to blue-black shows starch is present.
(b) B1 add Benedict's solution and heat in a gently boiling water bath
(b) B1 positive result: colour changes from blue to orange/brick-red (precipitate)
(b) Answer: Add Benedict's solution and heat in a water bath: a colour change from blue to brick-red shows a reducing sugar is present.
(c) B1 add sodium hydroxide solution, then a few drops of dilute copper sulfate solution (Biuret test), do not heat
(c) B1 positive result: colour changes from blue to purple/lilac
(c) Answer: Add sodium hydroxide then dilute copper sulfate solution: a colour change from blue to purple/lilac shows protein is present.
(d) B1 add ethanol to the sample, shake, then pour the mixture into water
(d) B1 positive result: a cloudy white emulsion forms
(d) Answer: Add ethanol, shake, then pour into water: a cloudy white emulsion shows fat is present.

Question 7

(a) B1 substrate: starch
(a) B1 product: sugars (maltose / glucose), oe
(a) Answer: Substrate: starch. Product: sugars (maltose/glucose).
(b) B1 substrate: protein
(b) B1 product: amino acids
(b) Answer: Substrate: protein. Product: amino acids.
(c) B1 substrate: fat (lipid)
(c) B1 product: fatty acids and glycerol
(c) Answer: Substrate: fat (lipid). Product: fatty acids and glycerol.

Question 8

(a) M1 850 x 35/100 (or equivalent correct method shown)
(a) A1 298 kJ (awrt 298, accept 297.5)
(a) Answer: 298 kJ (3 sf)
(b) M1 their (a) value (or 297.5) divided by 4.2
(b) A1 71 kcal (ft from (a), awrt 71)
(b) Answer: 71 kcal

Question 9

(a) M1 add a few drops (or equal volume) of sodium hydroxide solution to the sample
(a) A1 then add a few drops of dilute copper sulfate solution; do not heat
(a) Answer: Add sodium hydroxide solution to the sample, then add a few drops of dilute copper sulfate solution, without heating.
(b) B1 protein is present (cao)
(b) Answer: Protein is present in the sample.

Question 10

B1 bile emulsifies fats, breaking large fat droplets into many smaller droplets
B1 this increases the surface area of the fat exposed to lipase
B1 bile is alkaline and neutralises stomach acid, giving the correct (alkaline) pH for intestinal enzymes to work
Answer: Bile emulsifies fat into smaller droplets, increasing the surface area for lipase to act on, and it neutralises stomach acid so intestinal enzymes work at their optimum (alkaline) pH.

Question 11

B1 large surface area (many villi and microvilli)
B1 thin wall (one cell thick), giving a short diffusion distance
B1 good blood supply (many capillaries) maintaining a steep concentration gradient (accept lacteals for fat absorption)
Answer: Villi have a large surface area, a thin (one-cell-thick) wall, and a good blood supply, all of which speed up diffusion of digested food into the blood.

Question 12

(a) B1 40 deg C (cao)
(a) Answer: 40 degrees C
(b) B1 above the optimum temperature the enzyme (protein) structure, including the active site, changes shape (denatures)
(b) B1 the substrate (starch) can no longer fit/bind to the active site
(b) B1 so enzyme-substrate complexes cannot form and the rate of reaction decreases, eventually to zero
(b) Answer: Above the optimum temperature, the enzyme denatures (its active site changes shape), so the substrate no longer fits and the reaction rate falls, eventually to zero.

Question 13

(a) M1 6000 + 1900 + 400 = 8300 kJ (cao)
(a) Answer: 8300 kJ
(b) M1 8700 - their (a) value
(b) A1 400 kJ surplus (ft from (a), cao label)
(b) Answer: 400 kJ surplus
(c) B1 body mass will increase (ft from (b))
(c) B1 because the surplus energy that is not used is stored (mainly as fat)
(c) Answer: The pupil's body mass will increase, because the daily energy surplus is stored in the body as fat.

Question 14

B1 identifies the diet is not balanced, with a supporting reason
B1 identifies a food group/nutrient that is lacking, e.g. little or no fruit/vegetables, so low in fibre and vitamin C
B1 identifies an excess, e.g. high in fat and/or sugar and/or salt from crisps, chocolate and sausages
B1 gives a valid, specific improvement, e.g. swap the crisps or chocolate bar for a piece of fruit, or add a portion of vegetables at dinner
Answer: The diet is not balanced: it lacks fruit and vegetables (so is low in fibre and vitamin C) and has too much fat, sugar and salt; Priya could improve it by swapping the crisps or chocolate bar for a piece of fruit.

Question 15

(a) M1 (34 / 12) x 100
(a) A1 283 g (awrt 283)
(a) Answer: 283 g
(b) M1 protein in 75 g = 75 x 12/100 (= 9 g); then 9/34 x 100
(b) A1 26.5% (awrt 26.5)
(b) Answer: 26.5%

Question 16

Level 1 (1-2): Basic statements about digestion, e.g. food is broken down in the gut and some nutrients are absorbed. Little or no correct use of scientific vocabulary; points are not linked.
Level 2 (3-4): Describes mechanical and/or chemical digestion occurring in more than one named organ, correctly naming at least one enzyme with its substrate or product; some reference to absorption, though the account may be incomplete or only partly linked.
Level 3 (5-6): Clear, logically linked account describing digestion through the gut (mouth, stomach, small intestine), correctly naming relevant enzymes (amylase, protease, lipase) with their substrates and products, and explaining absorption of the digested (soluble) nutrients into the blood through the villi, with reference to surface area and/or diffusion; notes that undigested material passes on to the large intestine.
Indicative content:
- Mechanical digestion (chewing in the mouth, churning in the stomach) breaks food into smaller pieces, increasing surface area for enzymes.
- Amylase (from saliva and the pancreas) breaks down starch (carbohydrate) into sugars/maltose.
- Protease (in the stomach and from the pancreas) breaks down protein into amino acids.
- Lipase (from the pancreas) breaks down fat into fatty acids and glycerol.
- Bile (from the liver) emulsifies fat, increasing its surface area for lipase to act on.
- Digestion of starch, protein and fat is completed in the small intestine.
- Digested (soluble) food molecules, such as glucose, amino acids, fatty acids, glycerol, vitamins and minerals, are absorbed into the blood through the villi lining the small intestine.
- Villi have a large surface area, thin walls and a good blood supply, which speeds up absorption by diffusion.
- Fibre and other undigested material pass into the large intestine, where water is absorbed, before egestion.

Question 17

(a) M1 1000 / 100
(a) A1 10.0 (arbitrary rate units per second), cao
(a) Answer: 10.0 units per second
(b) B1 sampling at fixed, regular time intervals allows the point at which starch has disappeared to be identified accurately
(b) B1 using a fresh drop each time avoids adding iodine (which would affect the reaction) to the main starch-amylase mixture
(b) Answer: Testing a fresh drop every 20 seconds lets the student find the exact time starch disappears without contaminating the main reaction mixture with iodine.
(c) B1 repeat the experiment (at each temperature) and calculate a mean time/rate
(c) Answer: Repeat the experiment and calculate a mean time (or mean rate).

Question 18

(a) M1 68 / 1.60²
(a) A1 26.6 (awrt 26.6)
(a) Answer: 26.6
(b) B1 overweight (ft from (a))
(b) Answer: Overweight
(c) B1 BMI does not distinguish between mass due to muscle and mass due to fat, so very muscular/athletic people may be wrongly classed as overweight or obese
(c) B1 BMI does not show where fat is distributed on the body (e.g. around the waist/organs), which also affects health risk
(c) Answer: BMI is a limited measure because it cannot tell muscle mass from fat mass, and it does not show where on the body any fat is stored, both of which affect actual health risk.

Question 19

(a) B1 a water bath heats the sample more gently and evenly, at a controlled, known temperature
(a) B1 direct flame heating could make the mixture boil too quickly, spit, or boil over, and is less safe
(a) Answer: A water bath gives gentle, even heating at a controlled temperature, whereas a direct flame could overheat the mixture unevenly and cause it to boil over or spit, which is less safe.
(b) B1 same volume of juice used for each sample
(b) B1 same volume (and concentration) of Benedict's solution used for each sample (accept: same heating time)
(b) Answer: Same volume of juice, and same volume/concentration of Benedict's solution, used each time (also accept: same heating time).

Question 20

(a) M1 500 x 7 = 3500 kJ (cao)
(a) Answer: 3500 kJ
(b) M1 their (a) value / 37
(b) A1 94.6 g (ft from (a), awrt 94.6)
(b) Answer: 94.6 g

Question 21

B1 the runner has a much higher energy requirement/expenditure due to intense, regular exercise, so needs a higher energy (kJ/kcal) intake than the office worker
B1 the runner needs a higher proportion/amount of carbohydrate, to replenish glycogen stores in muscles/liver used during exercise
B1 the runner needs more protein than the office worker, for growth and repair of muscle tissue damaged during training
B1 if the office worker ate the same high-energy diet as the runner without matching the exercise, the excess energy would be stored as fat, leading to weight gain/obesity risk
Answer: The runner needs more energy overall (to fuel exercise), more carbohydrate (to replenish muscle/liver glycogen) and more protein (to repair exercised muscle) than the office worker; if the office worker ate the runner's diet without the matching activity, the surplus energy would be stored as fat.

Nutrition and Digestion - Worksheets, Questions and Revision