bio and chem practical skills

and data analysis - mix of topics

what is a positive control? how does this differ from a negative control?

• +ve control: control in which we test against a factor which is known to work (e.g. known antibiotic)

• -ve control: control which shows what occurs w/ no treatment (e.g. no antibiotic)

what is the significance of using a positive control?

increases validity

(in an experiment to determine the effect of 2 anaesthetics,) each person was given the same volume of anaesthetic per kg of body mass - suggest why (1)

different body masses but need to have comparable effects

why may the SD be a more suitable calculation to take than the range?

SD not affected by outliners and shows spread of data across mean

the scientists used units of μg g^-1 for the conc of ammonia in soil.

suggest why, in this investigation, the scientists used these units (2)

• (μg because) very little ammonia (in soil)

• (μg because) avoids use of (lots of) d.p. (in their results)/avoids use of powers of 10/avoids use of standard form

• (g^-1) to allow comparisons (between samples)

the scientists set up their cultures in sterile glass bottles.

suggest one suitable method for sterilising the bottles and explain why it was necessary to sterilise them (2)

• boiling water/steam/autoclave/wash in disinfectant/wash in alcohol

• to remove/kill other bacteria/organisms that might break down ammonia

• (not flaming the neck - we want to sterilise the whole bottle)

scientists investigated the effect of a mycorrhizal fungus on the growth of pea plants w/ a nitrate or ammonium fertiliser. the fertilisers were identical, except for nitrate or ammonium.

the scientists took pea seas and sterilised their surfaces. they planted the seeds in soil that had been heated to 85^oC for 2 days before use. the soil was sand that contained no mineral ions useful to the plants.

explain why the scientists sterilised the surfaces of the seeds and grew them in soil that had been heated to 85^o C for 2 days (2)

• to kill any fungus/bacteria on surface of seeds or in soil

• so only the added fungus has any effect on growth

biofuels are fuels which can be produced from plants. scientists have developed a standard method called net life-cycle CO₂ production (NLP) to find the overall effect of producing and using particular biofuels on CO₂ production.

petroleum is used as a comparison when evaluating NLPs of biofuels - suggest 2 reasons why (2)

• widely/commonly used

• provides a standard/baseline

a student concluded from these data that the mean growth rate of the pigs was fastest at 20^oC - do you agree with this conclusion? explain your answer (2)

• (no) - temp may be between 10-30^oC

• intervals are 10^oC/should be smaller

the student used a sharp scalpel to cut the celery. describe how she should ensure she handled the scalpel safely during this procedure (2)

• cut away from body

• against hard surface

when would the median be a suitable measure?

• in the presence of outliers

• in a small sample size

Treatment D is a control - explain how the measurement obtained from this control is used by the scientist (2)

• used to compare effect of other treatments/as a baseline

• shows effect of substance X

using the diagram and the table above, what can you conclude from treatments D and E about root growth? (3)

• D shows substance X is not required for root growth

• substance X moves through plant

• E shows substance X causes increase in root growth

explain how 2 features of the design of this investigation helped to ensure the validity of any conclusions obtained - do not include calculating the mean or SD in your answer (2)

• large sample size so representative

• 12 months so can assess growth

• control (present) for comparison

a simplified diagram of a colorimeter is shown - suggest why it is important that the container for each sample has the same dimensions (1)

absorption depends on distance travelled through soln

a simplified diagram of a colorimeter is shown - suggest why the coloured filter is used (!)

to select the colour/wavelength that is (most strongly) absorbed by the sample

suggest one reason why a colorimetric method might be chosen in preference to titration (1)

quicker to analyse extracted samples than by titration

what is the difference between absorption and absorbance?

• absorption = physical process of light transfer into a medium

• absorbance = quantitative measurement of light transfer into a medium

a student read the report of the researchers’ investigation. she thought that the investigation was unethical but that a conclusion could still be made - suggest why she thought the investigation was unethical (1)

(removing diaphragm means) animals/hamsters are killed

a student concluded that age had a significant effect on the eman number of capillaries per fibre - evaluate this conclusion (4)

• sig diff between young and adult

• not sig diff between adult and old

• for slow and fast fibres

• sig diff between young and old for fast/not sig diff between young and old for slow

• sig where means ±SD do not overlap (vice versa)

• stats test required to establish whether sig of not

what is the uncertainty of a ruler? why?

1 mm (0.5 × 2) - make 2 judgements: measurement at 0 mm and final length

the scientist used data to calculate a correlation coefficient r. the scientist then used a statistical test to determine the probability P associated w/ the value of r.

r = -0.98 (P > 0.05)

what can you conclude from this result? (2)

• strong -ve correlation

• probability of correlation occurring by chance is < 0.05

• reject null hypothesis

using all the information, what can you conclude about aorta diameter and the risk of developing an aneurysm? (3)

• as diameter increases, risk of tears increases and risk of aneurysms increases

• few people have high risk of aneurysms

• diameters > 4.5 at high risk of tears so may have aneurysms

• high tear risk does not mean aneurysm will occur

suggest and explain the effect EE2 pollution in frog habitats will have on frog breeding - use info from Table 6 and 7 in your answer (4)

• less breeding

• fewer advertisement calls so females not attracted

• fewer mating calls as males less sexually active

• more rasping calls as males not sexually active

• less time spent in courtship

from the data in table 1 it is not possible to determine the highest pressure measured - explain why (1)

don’t know range

the scientists used the % change in the mean resting heart rate after the exercise programme to compare the results the results for males and females - explain why they used percentage change in the resting heart rate (2)

• allows comparison

• initial heart rates differ between males/females

the surgeon concluded that there was sufficient evidence for him to continue using this treatment - how does the information above support his conclusion? (3)

the surgeon concluded that there was sufficient evidence for him to continue using this treatment - how does the information not above support his conclusion? (3)

the scientists concluded that heat stress reduces the activity of rubisco in plant leaves by affecting rubisco activase - use all the information to evaluate their conclusion (4)

a teacher studying these data w/ her students told her class that no definite conclusions could be drawn when comparing the mean values in the graph - suggest why the teacher said this (2)

how would you join the points? give a reason for your answer (1)

straight lines point to point as not possible to predict intermediate values/values between points

use the graph to describe the effect of MCP on mean antibody production (2)

• increases then levels/falls

• max antibody production 180 units/at dose of 0.25 g per kg

the does of MCP given to the mice was calculated in g per kg body mass - explain why the does was calculated per unit mass (1)

a newspaper suggested that these data show that taking MCP will give people increased resistance to disease - w/ reference to the data, give two reasons this conclusion may not be valid (2)

any 2 from:

• response only observed in mice

• disease organisms not investigated

• not all disease caused by pathogens/cured by antibodies

give 3 conclusions you can make from the data in the table above about the time taken for rejection (3)

atrial fibrillation (AF) is a condition that causes an irregular heart rate. scientists used a statistical test to investigate the association between different factors and the risk of developing AT.

the table below shows some of the scientists’ results, including the probability values (P) obtained using the statistical test - what can you conclude from the table? (3)

p < 0.05 = sig diff !!! (this is a p < 0.05 that the difference is due to chance)

the doctors used a statistical test to compare the results for AD and LD - they obtained a value for P of 0.047 - what does this result show about the difference between the means for AD and LD? use the words probability and chance in your answer (2)

a student who read this investigation concluded that there was a relationship between the amount of myelin in a person’s brain and whether or not they had dementia - do the data support this conclusion? give reasons for your answer (4)

the scientists suggest that the WHO recommendations for CO concentrations resulting in 2.5% COHb should be reduced - evaluate the scientists’ conclusion (3)

scientists investigated a drug called MiTMAB as a treatment for cancer - MiTMAB inhibits cytokinesis.

use all the information given to explain the results shown in Figure 9 (3)

evaluate the ethics of the production process shown (1)

the scientists recommend that the new test is used for the identification of dengue fever in all countries around the world.

discuss this recommendation - use all the information given (3)

the scientists concluded that treatment w/ hydroxyurea would increase the concentration of oxygen in the blood of babies w/ SCD - suggest how the graph and table above support this conclusion (3)

can you conclude that the insect pest resistant to Bt toxin found in the years 2002 to 2005 was the same insect species? explain your answer (1)

no - graph only shows no. of species, not the name of the species

use Figure 2 to evaluate whether more trehalose in the diet could be a factor in the increased no. of antibiotic-resistant C. difficile infections (3)

if given the frequency, how do we work out the actual no. of indivuals?

actual no. = total x freq

use all the information to evaluate whether a weight-loss programme is an effective treatment for type II diabetes (4)