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HSC Practice Questions Part 3: Skin A • EDTA us used as a preservative in some soaps as in row W so A is the answer. • Glycerin is another name for glycerol or glycerine – it is a byproduct of soap manufacture and is an alcohol, not an enzyme. Commercial soap makers remove the glycerol for other more profitable purposes, while cottage industry soap makers leave the glycerol in soap because there is no simple way to remove it on a small scale and it acts as a skin moisturiser so B is incorrect. • Sodium stearate is the chemical name for soap and it is not an acidifying agent so C is incorrect. • An emulsifying agent helps to stabalise an emulsion of an oil and water. Water is not an emulsifying agent, nor does it inhibit the growth of micro-organisms so D is incorrect. B The skin contains many sweat glands that release sweat as a means of temperature control so B is the answer. The human skin is lightly acidic at around pH 5.5 but it is not the rolde of the skin to react with soaps, which are usually alkaline not acidic so A is wrong. The skin burns in the sun. This is not a role of the skin, but rather an abuse of the skin by overexposure to the sun so C is wrong. Sometimes injury may allow a pathogen to enter through a break in the skin, but the role is to act as a barrier to the entry of pathogens so D is wrong. B They should have added equal volumes of water to each identical samples to ensure their tests were fair so B is correct. They were testing a variety of products so it was size of samples tested that had to be the same not the size or type of package they were sold in that mattered so A is wrong. Ideally they should have used identically sized test tubes so that the product being tested was the only variable but this would not affect the result so C is incorrect. The used by date would be determined differently by different manufacturers, and so is not a valid criteria for a fair test so D is wrong. B • The face wash has “neutral pH” which theoretically is exactly pH=7, so B, with a range so close to 7.0 is the answer. • A,C,D are incorrect because pH<7 as in A, the solution is acidic, and if pH>7 as in C and D, the solution is alkaline. D The diagram shows skin tissue with two hair follicles , an upper epidermis and lower dermis and one sweat gland. D The natural microflora on the skin maintain a slightly acidic pH that inhibits the growth of many pathogenic microorganisms, so D is the answer. The natural microflora react with chemicals in sweat to produce unpleasant rather than pleasant odours so A is incorrect. They have no role in keeping the skin soft and flexible so B is incorrect. They do not engulf bacteria, so C is incorrect. The skin of our bodies has a natural pH. This pH is influenced by factors such as natural oil produced by glands in the skin, microflora on the skin and perspiration. • a) Describe how these THREE factors contribute to the pH of the skin. (3 marks) • b) Explain the relationship between the pH of skin products and the pH of a person’s skin. (2 marks) Sample Answer a) Natural oils are slightly acidic. Microflora produce fatty acids which increase the acidity of the skin’s surface. Perspiration can be slightly acidic and it helps to spread the acidity across the skin’s surface. b) The skin has pH 5-7, so skin products should have a similar pH that is compatible with the pH of the skin in order to avoid irritation or skin damage. Identify TWO roles of the skin. 2 marks Sample Answer • Separates the body from the external environment. • Assists in body temperature control.. Explain ways in which the natural pH of the skin is maintained. 3 marks Sample Answer • Microflora produce acidic secretions which helps maintain the skin’s slightly acidic pH. • Perspiration provides water which is necessary for the production of an acidic environment. Universal indicator solution can be used to determine different pH levels. The pH is determined by comparing the colour of the solution to the universal indicator chart. Why is it a problem to use universal indicator solution to measure the pH of some shampoos? 2 Marks Sample Answer Some shampoos are coloured. Thus, it can be difficult to see any colour change in the universal indicator solution. How do microflora inhibit the growth of disease-causing organisms? 4 Marks Sample Answer Microflora help maintain the normal pH of the skin by digesting dead epidermal cells and excreting slightly acidic chemicals. Some aerobic bacteria produce fatty acids from sebum that inhibit the growth of many pathogenic organisms. The normal colonies of microflora on the skin provide competition for pathogenic microbes and usually outcompete them. The manufacturer of a skin cream claims that it will treat acne. A student wishes to test this claim. • (i) Identify a risk associated with trialling skin creams on humans. (1 mark) • (ii) Describe the consequences associated with changing the natural pH of the skin. (3 marks) Sample Answer i) An ingredient in the skin cream may irritate or damage the skin, or cause an allergic reaction. ii) A change in pH can cause an imbalance in the normal microflora present on the skin. This may allow an increase in the growth of bacteria and yeasts which can cause disease eg. thrush • A) Identify the manufacturer’s claim about gel Brand X that was under investigation. (1 mark) • B) Outline ONE safety issue relating to this investigation. (1 mark) • C) Discuss whether these results support the manufacturer’s claims. (3 marks) Sample Answer a) That the handwash gel, Brand X, removes potentially harmful bacteria. b) The group that did not wash their hands were exposed to potentially harmful bacteria. c) The results support he claim that Brand X removes potentially harmful bacteria as group 1 had significantly less bacteria appear on the agar plates than group 2. However, there is no evidence at all from this investigation to support or refute the manufacturer’s claim that Brand X leaves hands soft and smooth. 7 Marks Sample Answer Microflora are microscopic organisms. Various populations of microflora inhabit human skin and these organisms are usually kept in balance by the dryness of the skin, the slightly acidic pH of skin and the chemicals secreted in sweat. These microflora are necessary to help maintain the correct pH of the skin, digest dead epidermal cells and help prevent harmful bacteria and yeasts from colonising the skin’s surface. Frequent washing of the hands as in these two studies would remove both the normal microflora as well as any harmful organisms that are present on the surface of the skin, but those remaining in hair follicles and sweat glands will soon reestablish normal populations. Therefore washing is not a problem, and is actually beneficial as shown in study 1. The findings of study 1 are what you would expect, especially as organisms causing respiratory diseases are frequently transmitted via the hands and would be removed when the hands are washed. The results of syudy 2 do not appear to be correct because if hands are washed properly, it is unlikely that the normal microflora left behind on the skin would be a problem when handling food and so are not likely to contaminate the food. The manufacturer of Bubbles Liquid Soap claims its product is slightly acidic. (a) Propose a method to test this claim (4 marks) (b) The result of a valid experiment determined that this soap had a pH of 7. 2 Explain whether the manufacturer is making a valid claim. (2 marks)