Nutrition in Animals

11 Grade 10 General Science questions on Nutrition in Animals, with worked marking schemes. 11 questions are available on this topic in full.

1. Question 1

   4 marks

   (a) Distinguish between mechanical digestion and chemical digestion. (2 marks)

   (b) A nutritionist advises learners to chew their food thoroughly before swallowing. Explain how thorough chewing speeds up chemical digestion. (2 marks)

   (4 marks)

   Marking scheme

   (a) 1 mark each (2 marks): - Mechanical digestion is the physical breakdown of large pieces of food into smaller pieces without changing their chemical nature (e.g. chewing by teeth, churning in the stomach) - Chemical digestion is the breakdown of large insoluble food molecules into small soluble molecules by enzymes (b) Any two of the following, 1 mark each (2 marks): - Chewing breaks food into small particles, increasing the surface area - The larger surface area allows enzymes to act on more of the food at the same time - Chewing mixes food thoroughly with saliva, bringing salivary amylase into contact with the starch - Saliva moistens and softens the food so enzymes penetrate it easily

2. Question 2

   4 marks

   (a) Describe how the Biuret test for proteins is carried out on a sample of egg white solution. (2 marks)

   (b) A learner carried out the Biuret test on egg white solution and on glucose solution. Draw a table to show the expected observation and conclusion for each sample. (2 marks)

   (4 marks)

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3. Question 3

   1 mark

   A nurse explains that a patient lying flat on a hospital bed can still swallow porridge and it reaches the stomach. Which of the following explains how the bolus moves along the oesophagus?

   A. Circular muscles ahead of the bolus contract, dragging it forward

   B. Cilia lining the oesophagus beat and sweep the bolus downwards

   C. Circular muscles behind the bolus contract, squeezing it forward

   D. Gravity alone moves the bolus while the muscles stay relaxed

   (1 mark)

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4. Question 4

   1 mark

   The stomach wall is made of living cells, yet it is not damaged by the gastric juice that it secretes. Which feature of the stomach mainly protects its wall?

   A. Hydrochloric acid that kills harmful bacteria

   B. Mucus secreted by cells lining the wall

   C. A rich blood supply carrying away absorbed food

   D. Thick muscles that churn food into chyme

   (1 mark)

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5. Question 5

   4 marks

   A patient has a growth that blocks the pancreatic duct, so pancreatic juice cannot reach the duodenum. Explain why the digestion of starch, proteins and fats in the duodenum would be affected. (4 marks)

   (4 marks)

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6. Question 6

   1 mark

   In a food test, a learner added 2 cm³ of Benedict's solution to 2 cm³ of ripe pawpaw juice and heated the mixture in a boiling water bath. The colour changed from blue through green to orange. What should the learner conclude?

   A. The juice contains starch but no sugar

   B. The juice contains a non-reducing sugar only

   C. The juice contains a reducing sugar

   D. The juice contains a large amount of protein

   (1 mark)

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7. Question 7

   4 marks

   Describe how you would carry out the ethanol emulsion test to find out whether groundnut paste contains lipids. Include the expected result for a positive test and one safety precaution. (4 marks)

   (4 marks)

   Marking scheme

   Procedure: any two of the following, 1 mark each (2 marks): - Place a small amount of groundnut paste in a clean, dry test tube - Add about 2 cm³ of ethanol and shake thoroughly (to dissolve any lipid) - Allow it to settle, then pour the clear ethanol into another test tube containing an equal volume of distilled water (or add water to the ethanol) Expected result (1 mark): - A milky white emulsion forms, showing that lipids are present Safety precaution: any one (1 mark): - Keep ethanol away from naked flames because it is highly flammable / do not heat the ethanol - Wear safety goggles and avoid spilling ethanol on the skin or eyes

8. Question 8

   5 marks

   Wanjiru ate a lunch of githeri (maize and beans). Describe how the proteins in the beans are digested from the time they reach the stomach until the products are absorbed in the ileum. (5 marks)

   (5 marks)

   Marking scheme

   Any five of the following, 1 mark each (5 marks): - In the stomach, hydrochloric acid provides an acidic medium (about pH 2) and activates pepsinogen to pepsin - Pepsin digests/hydrolyses proteins into polypeptides (shorter chains) - Churning of the stomach walls mixes food with gastric juice, exposing more protein to the enzyme - In the duodenum, bile and pancreatic juice provide an alkaline medium suitable for the enzymes there - Trypsin from the pancreas (activated from trypsinogen by enterokinase) digests proteins/polypeptides into peptides - In the ileum, peptidase (erepsin) in intestinal juice digests peptides into amino acids - Amino acids are absorbed through the villi into the blood capillaries

9. Question 9

   1 mark

   Juma, a Grade 10 learner, gets a bloated stomach, gas and diarrhoea a short time after drinking fresh milk, although he digests other foods well. Which of the following best explains his condition?

   A. Lactase in the ileum fails to digest lactose

   B. Villi in the ileum fail to absorb milk proteins

   C. The colon fails to absorb water from the milk

   D. Salivary amylase fails to digest the milk sugar

   (1 mark)

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10. Question 10

    5 marks

    Mr Kamau had his gall bladder removed at Kenyatta National Hospital. The doctor advised him to eat smaller meals containing less fat.

    (a) Name the organ that produces bile. (1 mark)

    (b) State two ways in which bile helps digestion in the duodenum. (2 marks)

    (c) Explain why the doctor advised Mr Kamau to eat meals with less fat. (2 marks)

    (5 marks)

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11. Question 11

    1 mark

    A patient had a large part of the colon removed after a road accident. Which of the following is the patient most likely to experience?

    A. Weaker churning of food in the stomach

    B. Slower breakdown of starch in the mouth

    C. Lower absorption of glucose into the bloodstream

    D. Watery faeces from less water reabsorption

    (1 mark)

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