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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)