Presentation Unit 8 June 2012

7/30/2019 Presentation Unit 8 June 2012

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June 2012 6BIO8

Prepared by:

Nadrah Abdul Rahim

Munirah Mansor

Izzati Nadhirah

Nurul Azuwa Mat Riah

Question 1

a) 1. The independent variable is thenew selective weedkiller and the

dependant variable is the percentage

cover of weeds. (1) (5)

2. Choose a 100m x 100m field of

cereal crops. (6)


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3. Carry out random sampling

technique by placing the ten gridedquadrats (1m x 1m) randomly in the

chosen area. (3)

4. Count the number of small squares

out of 25 in a quadrat containing the

cereal plants and broad leaved. (4) (9)

5. The new selective weedkiller of the

same volume of 1 litre and with the

same concentration is sprayed to each

quadrat once a week for a month. (6)

6. After a month, count the number of

small squares out of 25 in a quadrat


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containing cereal crops and broad

leaved weeds. (8)7. Calculate the change of the

percentage cover of weeds and cereal

crops before and after the treatment

with new selective weedkiller. (2)

8. Find another area of 100m x 100m

field of same type of cereal crops and

no weedkiller is sprayed. (7)

9. Repeat another two trials of the

same experiment.

10. The rationale of using the random

sampling technique is to avoid bias and


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it is easier technique since the plant

communities are stationary.

Examiners report: -need to use the

term quadrat correctly by describing

the way on collecting the valid data

using a gridded quadrat. (Candidate 1

point 2)

-The candidate has described the use

of a quadrat but did not describe how

to place quadrat at random locations.

Simply stating, use of random sampling


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technique is not sufficient. (Candidate

2 point 2)

b) 1. Soil (type/pH/organiccontent/minerals)

2. Water content of soil (humidity)

3. Temperature

4. Wind speed5. Light intensity

Examiners report: -The use of the

term nutrients here is far too vague

and was ignored. Sunlight was not

accepted since the candidate should


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refer to relevant property of light, e.g.,

light intensity. (Candidate 1)-Better to use mineral ion

concentration in the soil. (Candidate

1)

b) ii) Variable : pH of the soil

How : Measure the pH of the

soil using pH meter to ensure that the pHin each quardrat is the same

Effect : Different pH of the soil

will provide an additional effect on the

weeds and the cereal crops other than

present of weedkiller.

Examiners report: -


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The description as to how the variable can

be controlled was not accepted as it wasjudged that the proposed method would

not work. An acceptable answer would

have been to suggest that mineral ion

concentration cannot be controlled but

that specified mineral ions could be

measured and areas of the field with

similar concentration used in the

investigation. (Candidate no 1)

The candidate did not describe how pH

affects the results and did not gain a mark.


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At this level, candidates can expected to

recognise that there will be an optimumpH and that changes either side of the

optimum would result in less growth.

Alternatively, the candidate could have

suggested that the cereals and the weeds

grow beat at different optimum pH values

and therefore different soil pH values

would favour growth of one over the

other.

(Candidate no 2)


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c) 1. Selective weedkiller containingthe plant growth regulator such asauxins benefits in promoting the cell

elongation and thus stimulate the

excessive growth of broad-leaved

plants. (1) (2)

2. In the broad-leaved plants, auxins

accumulate in cells causing rapid

growth that kills the plant but the

cereal crops are unaffected. (salters)

3. Hence, this will interferes with the

plant metabolism and their

photosynthesis. (3)


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4. This is due to the function of auxins

as an inhibitor to the protein channeland enzyme activity of the broad-

leaved weeds. (4)

5. Besides, the synthetic auxins are

toxic and affecting the plant mineral

uptake. (5)

(Can refer salters A2 page 216)

Examiners tips: Make sure you

understand and are able to apply the

biological knowledge relevant to the core

practicals.


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-Avoid using vague terms such asdisrupting growth. Instead, state howgrowth might be disrupted.

(Candidate no 2)

Question 2 (a)

There will be no significant correlation in

the time it takes for the snail to re-

emerge/ start moving and the number of

taps received.Question 2 (b)

Tap

time /

min

Time taken to re-emerge ( and

start moving ) / seconds

A B C mean0 90 108 80 93

2 40 60 48 49

4 30 40 80 50

6 10 15 20 15

8 0 5 0 2


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10 0 0 0 0

12 2 0 0 1

Question 2 (c)

0

10

20

30

40

50

60

70

80

90

100

0 1 2 3 4 5 6 7 8

meantim

etakentore-emerge/seconds

number of taps


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Question 2 (d)

Anomalous result

1) Snail C at 4 minutes / third tap / 802) Snail A at 12 minute / seventh tap /

2

3) Mean result at 4 minutes / third tap/ 50

4) Mean result at 2 min / twelve tap /1

Reason

1) Time respond increase from secondto third tap

2) It is expected that all at 12 minutesto be zero


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3) Wider width of the range barindicating that there is anomalous in

the result.

Question 2 (e)

1) The critical value is 0.79 becausethe number of means in theexperiment is 7.

2) At 95% confidence level, thecalculated value = 0.93 is greater than

the critical value = 0.79.3) Therefore, there is a significant

negative correlation between the

number of taps received by the snail

and the time it takes the snail to re-emerge.

4) Repeated stimulation results in lossof response.


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5) The snails ignore the stimulibecause of lack of reinforcement /

reward / punishment.

6) Ca2+ channels become lessresponsive so less Ca2+ crosses the

presynaptic membrane.

7) There is less depolarization of thepostsynaptic membrane so no action

potential is triggered in the motor

neurone.


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Question 3 (a)

1. Alcohol is flammable. Keep nakedflame away from it/

Alcohol is irritant. Do wear glove when

handling it (1)

2. Growth of harmful bacteria need tobe prevented (2) Thus, do not incubatethe petri dishes at 37

oC as it is the

optimum temperature for the growth

of harmful bacteria.

3. Use aseptic technique/Use strain of bacteria that is not

harmful/


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Secure lid on plate but not air tight to

prevent anaerobic condition/

Use antiseptic/Need safe disposal of plates (3)

3 (b)

1. Select suitable timescale formeasuring growth of bacteria. For

example 24 hours after incubation (3)

2. Check the method to measure theeffect of ethanol on the growth of

bacteria. Observe and measure the

diameter of zone inhibition by using

ruler. (4)

3. Consider what other variable needto be controlled. Temperature of the


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incubator should be fixed at less than

37oC. (5)

4. Check the most suitable method ofadding alcohol to the plate. Immerse

the sterile paper discs in ethanol and

place them on the surface of the agar

gel. (6)

5. Determine the suitable range ofethanol to be used in the experiment.

The ranges should not be too high andirritate the skin but at the same time

still effective against bacteria. (60%,

65%, 70%, 75%, 80%) (7)

6. Determine which strain of bacteriato use. Staphylococcus aureus is

selected. It exists on the skin so

suitable for this experiment. (8)


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7. These proposed method above arepracticed to see if it will work. (1)

6. A bacteria strain, StaphylococcusAureus is used and the bacterial culture

is prepared by lawn spreading

technique. (7) (13)


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7. Other variables that need to be

controlled in this experiment are

diameter of paper disc by measuring itsdiameter, d=0.5cm using meter ruler

and secondly concentration of agar

have to be at same concentration of

0.1%. (8)(9)(10)(11)

8. The experiment is repeated twice

at each of these concentration of

alcohol (60, 65, 70, 75, & 80%) to

obtain the mean value. (12)

3 (d) i) tabulated data

Concentratio

n of alcohol

(%)

Diameter of inhibition

zone (including

diameter of paperdisc)/ (cm)

Tria

l 1

Tria

l 2

Tria

l 3

Mea

n

60

65


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70

75

80

ii) Graph

Diameter of inhibition zone (cm)


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conc. Of alcohol (%)

60 65 70 75 80

iii) Data analysis

A Spearmans correlation test at 5%

significant level is used.

3(e)

1.

Difficulty to control all variablesaffecting bacterial growth as bacteria

may be contaminated.

2. The bacteria may not be equallydistributed in agar plate at the start.

3. Another variable may be acting aslimiting factor for bacterial growth

such as temperature, as the agar is

too hot it may interfere with the

bacterial growth and division.


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4. There is a need to test theeffectiveness of difference

concentration of alcohol on more

than one type of bacteria such as

E.coli.

Documents

Presentation Unit 8 June 2012