Name of practical AS level 1. Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction 2. Preparation of stained squashes of cells from plant root tips; setup and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index 3. Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue 4. Investigation into the effect of a named variable on the permeability of cell-surface membranes 5. Dissection of animal or plant gas exchange or mass transport system or of organ within such a system 6. Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth A level 7. Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g. leaves from shade-tolerant and shade intolerant plants or leaves of different colours 8. Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts 9. Investigation into the effect of a named variable on the rate of respiration of cultures of single-celled organisms 10. Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze 11. Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample 12. Investigation into the effect of a named environmental factor on the distribution of a given species A Level Required Practicals
Transcript
Name of practicalAS
leve
l1. Investigation into the effect of a named variable on the rate of an enzyme-controlled reaction
2. Preparation of stained squashes of cells from plant root tips; setup and use of an optical microscope to identify the stages of mitosis in these stained squashes and calculation of a mitotic index
3. Production of a dilution series of a solute to produce a calibration curve with which to identify the water potential of plant tissue
4. Investigation into the effect of a named variable on the permeability of cell-surface membranes
5. Dissection of animal or plant gas exchange or mass transport system or of organ within such a system
6. Use of aseptic techniques to investigate the effect of antimicrobial substances on microbial growth
A le
vel
7. Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g. leaves from shade-tolerant and shade intolerant plants or leaves of different colours
8. Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts
9. Investigation into the effect of a named variable on the rate of respiration of cultures of single-celled organisms
10. Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or a maze
11. Production of a dilution series of a glucose solution and use of colorimetric techniques to produce a calibration curve with which to identify the concentration of glucose in an unknown ‘urine’ sample
12. Investigation into the effect of a named environmental factor on the distribution of a given species
A Level Required PracticalsThe following practicals must be carried out by all students. Written papers will assess knowledge and understanding of these and the skills exemplified within each practical
7. Use of chromatography to investigate the pigments isolated from leaves of different plants, e.g. leaves from shade-tolerant and shade intolerant plants or leaves of different coloursOur experiment:
Thin Layer Chromatography for Plant Pigments WARNING: The solvents used in this investigation are flammable.
In this practical you are going to investigate the pigments isolated from leaves of different plants, for example shade-tolerant and shade-intolerant leaves; or leaves of different colours.You will set up a TLC plate for each type of leaf. Below is the procedure on how to set up a TLC plate.
1. Cut a TLC plate into small strips e.g.1.25 x 6.7 cm, so that they fit your tubes. Do not touch the surface of the plates.2. Place 2 - 3 wheat or grass leaves on a slide. Use a second slide to scrape the juice out.3. Add 6 drops of propanone to the green mush and mix. Transfer the dark green liquid to a small watch glass.
4. Repeat steps 2 and 3 until you have about 20 drops of extract. Use a hair dryer to remove all the water from the extract.5. When the extract is completely dry, add 3 - 4 drops of propanone and mix the extract with a fine paint brush.6. Use the brush to transfer tiny drops of extract to the TLC strip. Keep the spot diameter to less than 2 mm. Dry the spot thoroughly between each addition. Repeat until the spot is a very dark green.
7. Slot the TLC strip into a slit in the cork and put it into an empty tube. Mark the tube below the level of the spot. Remove the TLC strip.8. Add running solvent to the mark. Put the TLC strip back in the tube. Make sure that it does not touch the sides of the tube. Watch the chromatogram develop.9. After about 4 minutes remove the strip and immediately use a pencil to mark the solvent front.
10. Measure the distance run by the solvent front and by each of the pigments. All measurements should be made from the centre of the original spot to the front of each pigment spot.11. Calculate how far the pigment has gone relative to the solvent front. This is the Rf value. (Rf = the distance run by the pigment divided by the distance run by the solvent.)12. Draw a suitable results table. For each pigment record: the distance run, its colour, Rf value and possible identity.
(b) The red seaweed lives under water at a depth of 2 metres. Suggest an advantage to the red seaweed of having other pigments in addition to chlorophyll a.
8. Investigation into the effect of a named factor on the rate of dehydrogenase activity in extracts of chloroplasts
Our experiment:
IntroductionIn this investigation you will use a chloroplast suspension to investigate the role of chloroplasts in the light-dependent reaction of photosynthesis. Chlorophyll molecules release electrons in the presence of light. A blue dye, DCPIP, accepts these electrons and becomes colourless. This is shown in the diagram.
You will investigate whether the time taken for DCPIP to become colourless is affected by ammonium hydroxide. Ammonium hydroxide is a substance that affects the light-dependent reaction in a similar way to many weed killers. You will collect data when ammonium hydroxide is not present. Then you will carry out one experiment to show the effect of ammonium hydroxide. For Stage 2 you will be supplied with more data showing the effect of ammonium hydroxide.MaterialsYou are provided with
spinach leaves access to a blender measuring cylinder muslin (or material for filtering) filter funnel beaker to use as beaker 1 large beaker to use as beaker 2 small beaker to use as beaker 3 ice isolation medium (cold) DCPIP solution (cold) distilled water (cold) ammonium hydroxide solution (cold) test tubes test tube rack syringes (1 cm3 and 5 cm3) piece of aluminium foil lamp marker pen timer
You may ask for any other apparatus you require.
Outline method
Read these instructions carefully before you start your investigation.1. Put about 50 cm3 of isolation medium into a beaker (beaker 1).2. Tear all 8 spinach leaves into small pieces and put the pieces into the isolation
medium in the beaker. Do not put pieces of the midrib (the thickened central region of the leaf) or the leaf stalk into beaker 1.
3. Half fill the large beaker (beaker 2) with ice and place the small beaker (beaker 3) on top of the ice.
4. Put three layers of muslin over the top of the filter funnel and wet it with isolation medium. Rest the filter funnel in beaker 3.
5. Pour the contents of beaker 1 into the blender and blend for about 15 seconds. Pour the blended mixture back into beaker 1.
You can carry out step 7 and part of step 10 while you are waiting to use the blender.6. Pour a little of your blended mixture from beaker 1 through the muslin into
beaker 3. Carefully fold and squeeze the muslin to assist the filtering process. Repeat until most of the blended mixture has been filtered. Label this filtrate, which is now in beaker 3, as your chloroplast suspension.
7. Label five test tubes A, B, C, X and Y. Stand these five tubes in the ice in beaker 2. Position the lamp about 10 cm from the beaker so that all tubes are illuminated. Turn on the lamp.
8. Set up tubes A and B as follows.Tube APut 5 cm3 DCPIP solution + 1 cm3 water + 1 cm3 chloroplast suspension in the tube.Immediately wrap the tube completely in aluminium foil.Tube BPut 5 cm3 DCPIP solution + 1 cm3 water + 1 cm3 isolation medium in the tube.Tubes A and B are control experiments. Leave both tubes until the end of your investigation.
9. Set up tube C as follows.Put 6 cm3 water + 1 cm3 chloroplast suspension in the tube.Tube C is for you to use as a standard to help you to determine when any colour change is complete.
10. Set up tube X as follows.Put 5 cm3 DCPIP solution + 1 cm3 water in the tube.Add 1 cm3 chloroplast suspension to tube X, quickly mix the contents and start the timer. Record in seconds how long it takes for the contents of tube X to change colour from blue-green to green. This is when all signs of blue have disappeared. Use tube C to help you determine when the colour change is complete.
11. Repeat step 10 four more times. You may assume that this will give you sufficient data for statistical analysis in this investigation.
12. Set up tube Y as follows
Put 5 cm3 DCPIP solution + 1 cm3 ammonium hydroxide solution in the tube. Add 1 cm3 chloroplast suspension to tube Y, quickly mix the contents and start the timer. Record in seconds how long it takes for the contents of tube Y to change colour from blue-green to green. Use tube C to help you determine when the colour change is complete. However, if this has not taken place within 300 seconds (5 minutes), record the colour at this point. Record your results in Table 1 on page 4.
You are not required to repeat step 12. Data will be supplied in the next lesson for your statistical analysis.
DCPIP is a blue dye that can be converted to colourless reduced DCPIP by gaining electrons. This is summarised below.
D C P IP(b lu e )
re d u ced D C P IP(c o lo u rle ss)
e le c tro n s
A chloroplast suspension was made by grinding fresh leaves in buffer solution and centrifuging the mixture. Tubes were prepared and treated in different ways. The colour of the tube contents was recorded at the start and after 15 minutes. This
information is summarised in the table.
Tu b e C o n ten ts Trea tm en t
A 2 cm ch lo ro p las t su sp en s io n6 cm D C P IP
tu b e k ep t inb rig h t lig h t
b lu e / g ree n g ree n
b lu e / g ree n b lu e / g reen
b lu e b lu etu b e k ep t inb rig h t lig h t
tu b e k ep t ind ark
2 cm ch lo ro p las t su sp en s io n6 cm D C P IP
2 cm b u ffe r so lu tio n6 cm D C P IP
B
C
3
3
3
3
3
3
a t sta r t a fte r 15m in u tes
C o lo u r
(f) (i) Tube C was included as a control. Explain why this control was necessary
(g) (i) The chloroplast suspension produced by centrifugation may also contain mitochondria. Explain the evidence from tube B that mitochondria are not responsible for reducing the DCPIR.
15. A student investigated the rate of anaerobic respiration in yeast. She put 5 g of yeast into a glucose solution and placed this mixture in the apparatus shown in the figure below.She then recorded the total volume of gas collected every 10 minutes for 1 hour.
(a) Explain why a layer of oil is required in this investigation.
(iii) Yeast can also respire aerobically. The student repeated the investigation with a fresh sample of yeast in glucose solution, but without the oil. All other conditions remained the same.Explain what would happen to the volume of gas in the syringe if the yeast were only respiring aerobically.
(c) Some students investigated the effect of temperature on the rate of anaerobic respiration in yeast. The apparatus they used is shown in the diagram. The yeast suspension was mixed with glucose solution and the volume of gas collected in five minutes was recorded.
(i) Each student repeated the experiment and the results were pooled. Explain the advantages of collecting a large number of results.
(ii) At 30 °C, one student obtained the following results.
Volume of gas collected in 5 minutes / cm3
Result 1 Result 2 Result 3
38.3 27.6 29.4
Calculate the mean rate of gas production. Give your answer in cm3 s–1.
Answer ............................... cm3 s–1
(2)
(iii) If aerobic respiration had been investigated rather than anaerobic respiration, how would you expect the volumes of gas collected at 30°C to differ from these results?
How should the maggots have been kept prior to the experiment?
How could you calculate the rate of movement of the maggots?
What type of behaviour was observed in the maggots?
17. In an investigation by a student into the responses of maggots, the bottom of a large box was marked with six coloured segments, as shown in the diagram.
30 maggots were placed on each segment in the box. A transparent cover was put on the box and light bulbs were positioned so that the segments were evenly illuminated. The positions of the maggots were recorded after one hour. The intensity of the light reflected by each segment was measured.
The experiment was repeated three more times. The total number of maggots in each segment from the four experiments is shown in the table.
Colour of segment
Intensity of reflected light / arbitrary units
Total number of maggots
Black 4 154
Red 25 229
Blue 10 178
White 44 47
Green 25 48
Yellow 40 64
(a) Give one conclusion about the responses of maggots which is supported by these results.
(b) The chi-squared test was used to analyse the data. For the results obtained, suggest one null hypothesis which might be analysed by a chi-squared test.
(c) It was suggested that the movement of the maggots might have been influenced by the Earth’s magnetic field. Suggest one simple way of repeating the investigation which would avoid this possibility.
18. The human body-louse is an insect which lives and feeds on the surface of the skin. A louse was placed in a chamber, half of which was kept at 35 °C and half at 30 °C. The diagram shows the pattern of movement of the louse.
(a) Name the type of behavioural response shown by the body-louse in this investigation.
19. Termites are insects. Some species live in colonies in the soil. Although most termites are wingless, winged termites are sometimes produced. The winged termites fly from the soil, mate and start new colonies.
A scientist studied the behaviour of winged termites. He divided these termites into three groups.
• Group A had their eyes covered.
• Group B had their antennae removed.
• Group C was the control group.
He put individual winged termites on a sloping board that was illuminated from one side. The diagram shows the direction of movement of a typical termite from each of the three groups.
(a) (i) What type of behaviour was shown by the termite from group B?
20. A flatworm is a simple soft-bodied animal. The diagram shows the movements of an aquatic flatworm in light and in shade. The path followed by the flatworm over a period of three minutes was traced on the side of a tank.
(i) Name the type of behaviour shown. Give a reason for your answer.
Type of behaviour .........................................................................................
1. How did you create the dilutions required? ___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
2. Why can the reducing sugar test be classed as semi-quantitative?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
3. Why use a red filter?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
4. What is the purpose of the blank?___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
5. Health professionals can use Clinistix. Compare with the method you used.___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
6. Explain how you identified the concentration of the unknown samples using the calibration curve.___________________________________________________________________________________________________________________________________________________________________________________________________________________________________________________
Exam questions:21
22
12. Investigation into the effect of a named environmental factor on the distribution of a given species
Our experiment:
Equipment Thermometer Light meter Quadrat frame Measuring tape Notebook and pencil
Method1 Select a suitable site which will enable you to investigate the changes from
inside the woodland, where the light intensity is low, to open ground with a high light intensity. Alternatively, the investigation can compare the organisms in a shaded area beneath a large tree with those in open ground.
2 With the measuring tape, mark out a line extending from the most shaded area to open ground (a transect line). Decide how many samples you are going to take: this could depend on the nature of the vegetation and the total distance involved.
3 At each sampling site, place a 50 cm 50 cm subdivided quadrat on the ground and use it to estimate percentage frequency or percentage cover of the plant species, as described earlier. If you are only interested in finding out how the distribution of one species is affected by the abiotic factors, then you need only record the abundance of that species.
4 At each sampling site, you need to record the light intensity and the temperature.
5 To measure light intensity, use a light meter. As light meters can vary, follow the instructions given for the model you are using. When taking your measurement, decide the height above the ground at which you position the light meter and remember to keep this the same for all your readings. Record your reading for each sampling site.
6 Use the thermometer to measure and record the air temperature just above the ground level at each sampling site. Try to standardise your readings by taking them at the same height above the ground each time. Ideally, you should take both the light and temperature readings at the same height above the ground. It is also important to take the light intensity and temperature readings at the same time.
How could you amend this method to study the species density of a field?
How do you avoid bias in your investigation?
How do you ensure a reliable sample?
What is the difference between percentage frequency and percentage cover and when would you use each method of measuring abundance?
Exam questions:
23. Mayflies are insects which lay their eggs in streams and rivers. The nymphs which hatch from the eggs live in the water for several years.
Mayfly nymphs were collected by disturbing the gravel of a stream bed. A net placed immediately downstream caught any animals which were washed out of the gravel. Eight samples were collected from shallow, fast-flowing parts of the stream and eight from deeper, slow-flowing parts. Nymphs from two different families of mayfly were found. The results are given in the table.
(a) Describe how you would have collected the samples in order to ensure they were representative of the habitats being investigated and could be compared with each other.
Climatic factors, such as temperature and rainfall, vary greatly over short distances across mountain ranges. In an investigation, populations of the plant, Achillea lanulosa, were sampled from several sites on a transect across a mountain range. At each sampling site, seeds were collected at random. Each batch of seeds was germinated and grown to maturity under the same experimental conditions.
The diagram shows• a profile indicating the position and altitude of the sampling sites• the mean height of mature plants grown from each sample of seeds• the standard deviation of heights of the mature plants grown from
each sample of seeds.
(a) (i) Give one limitation of using a line transect to collect these data.
(iii) There was a significant difference between the mean heights of the plants grown from seeds taken from sites A and D. Describe the evidence from the information given which shows that this is likely to be due to genetic differences between the two populations.
The drawings show two dogwhelks taken from two different populations. Dogwhelk A came from a sheltered shore and dogwhelk B from a shore exposed to heavy wave action. The dogwhelks attach themselves to rocks with a muscular foot which comes out through the aperture. The shell length : aperture length ratios (L/A) were calculated. The mean and standard deviation for each population are shown under the drawings.
mean L/A ratio = 1.91 mean L/A ratio = 1.78standard deviation = 0.19 standard deviation = 0.10
(a) Describe how you would collect a random sample of each population.
M10. (a) (i) pigment reflects / does not absorb green or yellow or orange;pigment absorbs blue or violet;pigment absorbs red;
(accept correct wavelengths instead of colours)(any 2 for 1 mark)
1
(ii) light (energy) absorbed by chlorophyll;raises energy level of electrons / electrons are excited / emitted;ATP formed;
3
(b) more wavelengths / colours absorbed;more (efficient) photosynthesis can occur at these depths / low light intensitiesormore (efficient) photosynthesis can occur when some wavelengths are notpresent;
2[6]
11
12
14. (a) 1 and 3;
(b) Some energy lost as heat; 1
(c) (i) Arrow indicates between Glucose to Triose phosphate;
(ii) Arrow indicates between Triose phosphate to Pyruvate; 2[Note: Extra arrow cancels][Reject: Ambiguous labels /arrows]
(d) 4; 1
(e) (i) Grana/ thylakolds/ internal membranes; 1
(ii) Reduces/ reducing power/ source of hydrogen/ electrons;Glycerate-3-phosphate to Triose phosphate/ GP to TP; 2[Ignore: Reference to molecules]
(f) (i) To show chloroplasts responsible for change;
(ii) Photolysis/ light splits water molecule/ excitation of chlorophyll:Electrons released;Electrons reduce DCPIP/ DCPIP becomes colourless;So can only see (green) colour of chloroplasts/ chlorophyll; max 3
(g) (i) Mitochondria are sites of (aerobic) respiration/ active in dark;Reactions also release hydrogen ions/ electrons;(Tube B) would also become green/ reduce DCPIP (if responsible);[Reject: Colourless] [Reject.- Converse argument]
OR Tube B shows light is necessary for colour change;Mitochondria do not have pigment to absorb light/ chlorophyll; max 2
(ii) Only one set of results/ not repeated; 1[Reject: Need more results]
[15]
15.(a) Prevents oxygen being taken up / entering / being absorbed;Accept: any idea of no contact with oxygen.
13
Neutral: for anaerobic respiration / anaerobic conditions.Neutral: prevents entry of air.Reject: prevents entry of oxygen and another named gas.
1
(b) (i) 0.0155 / 0.016 = 2 marks;;
0.0775 / 0.077 / 0.078 / 0.08 = 1 mark
/ 0.62 = 1 mark2
(ii) Glucose decreases / is a limiting factor / increase in ethanol / yeast / cells die / toxins build up;
Accept: glucose is used up.1
(iii) 1. (Stays the) same / level / (relatively) constant;
2. Same volume / amount of oxygen uptake and carbon dioxide release;Note: if m.p.1 is awarded m.p 2 can be obtained without referring to ‘same volume / amount’.
2
(c) 1. Oxygen is final / terminal (electron) acceptor / oxygen combines with electrons and protons;
2. Oxidative phosphorylation / electron transport chain provides (most) ATP / only glycolysis occurs without oxygen / no Krebs / no link reaction;
2[8]
16. (a) (i) glycolysis;1
(ii) oxygen removed from pyruvate / reduced NAD is oxidised / donates hydrogen / donates electrons;
1
(iii) allows NAD to be recycled / re-formed;so that glycolysis / described / candidates answer to (i) can proceed / so that (more) glucose can be converted to pyruvate / so that process X can continue;
2
(b) (i) ATP formed / used;pyruvate formed / reduced;NAD / reduced NAD;glycolysis involved / two stage process;
2 max
(ii) ethanol / alcohol formed by yeast, lactate (allow lactic acid)by muscle cell; CO2 released by yeast but not by muscle cell;
(note: need both parts of the comparison for the mark)2
(c) (i) allows anomalies to be identified / increases reliability (of means / averages / results);allows use of statistical test;
(iii) Volume(s) less / no gas evolved;So (volume) CO2 evolved = (volume of) O2 taken in;
3[15]
17 (a) one mark for conclusion:maggots move to / respond to / prefer / like / red rather than green;
(reject ‘most prefer red’)
maggots move to / prefer / like areas of lower light intensity (except green);maggots respond more to colour than light intensity / do not respond todifferences in light intensity;
(reject conclusion relating to single result)
one mark for:evidence matching conclusion:more in red than green, but light intensity the same;more in segments with lower light intensity;more differences in different colours, little difference in light intensity;large difference in number of maggots on segments with 25 a.u.light intensity;
2 max
(b) valid statement expressed as null hypothesis, i.e. in negativeform, e.g. no difference in response to different colours / light intensities;
(must relate to a possible hypothesis)1
(c) rotate box (so segments in different direction) / change order of colouredsegments;place magnets around box / create alternative magnetic field;
random movements = 1 mark, eg/ degree of turning / number of turns depends on strength of stimulus / on temperature / allow specific ref. to more turning at 35° than at 30° / non-directional stimulus / response;
ignore ‘speed’2
(b) stays longer in warmer area / at 35° / tends to leave cooler area / to leave 30° / stays in favourable conditions ;
remains near food source / on host;2
[4]
19 (a) (i) Taxis;Ignore references to positive and negative, and prefixes such as photo-Accept taxes / tacticAllow phonetic spelling
1
(ii) Moves towards stimulus / towards light;Direction must be correct.
1
(b) Gravity;
Antennae involved;
Doesn’t show light is involved / doesn’t respond to light as they areunable to see / as eyes are covered;
Accept geotaxis
3
(c) Helps them to leave the soil / ground / reach the surface;
Disperse / produce new colonies;
Avoid competition;2 max
[7]
20 (i) kinesis;movement is random / rate of turning changes / does not move towards / away from light;
2
(ii) advantage related to light / shade;e.g. remains in shade so avoids predators
1[3]
21 D
23 (a) Samples collected at random;Method for choosing random sites – randomcoordinates / position from tables / calculator / other suitablemeans;
Other named factor constant e.g.:
22
Same size of net / same width of opening of net / use of onequadrat / Quadrats of same size / of stated size / same areadisturbed / collect each Sample for same time;
3
(b) Caenidae in deep water – because highest standarddeviation / ‘S.D.= 7.92’
1
(c) (i) An organism’s role / in the ecosystem / community;[ALLOW refs. To trophic levels / named]
(IGNORE refs. To habitat)1
(ii) Caenidae found mainly in deep water AND Baetidae inshallow water / one family mainly in deep water AND theother in shallow water;
1
(iii) Reduces competition for named factor – e.g. food / shelter / O2 ;To ensure both types survive / otherwise better adapted type displaces other type;ORRef. to ‘Competitive exclusion principle’ = 2 marks
max 2[8]
24.
(a) (i) transect line may not go through representative areas / may avoid certain areas;1
(ii) large sample;how random coordinates are generated / how random placeschosen;
2
(b) (i) spread of values around the mean height of the plant;1
(ii) smaller plants at higher altitude;greater the altitude the lower the standard deviation ;reference to figures to make a comparison;
2 max
(iii) the plants measured were grown under uniform conditions;1
[7]25.
(a) generation of random co-ordinates;use of 10 or more quadrats;collection of all dog whelks in quadrat;
3
(b) greater variation for sheltered population / population A;range / spread around the mean;
(or converse)2
(c) (i) smaller ratio means relatively larger foot / population B hasrelatively large foot;
better able to grip;larger / longer shells have greater area exposed / are subjectto greater force;
(ii) wave action limits the max. L / A ratio / extremes;valid point about age, e.g. greater age range on shelteredshore / live longer on sheltered shore;
(allow shell size marking point in either (c)(i)or (c)(ii) but only credit once)
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