*APPLICATION/PRACTICALS*

Question 1

an environmental scientist investigated a possible relationship between air pollution and the size of seeds produced by one species of tree. he was provided with a very large number of seeds collected from a population of trees in the centre of a city and also a very large number of seeds collected from a population of trees in the countryside.

describe how he should collect and process data from these seeds to investigate whether there is a difference in seed size between these two populations of trees (5)

Answer 1

1. use random sample of seeds from each population
2. use large enough sample to be representative of whole population
3. indication of what size wads measured eg. mass
4. calculate a mean and standard deviation for each population
5. use student’s t-test
6. analyse whether there is a significant difference between the means of the populations

Question 2

suggest two ways to improve a scientific drawing (2)

Answer 2

1. add scale bar
2. don’t use shading
3. add annotations
4. don’t cross label lines
5. only use single lines

Question 3

a student did not have access to a colorimeter. describe a method this student could use to prepare colour standards and use them to give data (3)

Answer 3

1. use known concentration of extract
2. prepare dilution series/serial dilution
3. compare results with these colour standards to give a value

Question 4

describe and explain three ways in which the scientists would ensure he used aseptic technique (3)

Answer 4

1. wash hands to kill microbes
2. bunsen burner close by to create upward current of air
3. disinfect bench to prevent contamination
4. flame equipment to sterilise
5. lift lid slightly to prevent entry of microbes

Question 5

explain the purpose of 1. boiling the agar and 2. transferring the same volume of liquid culture onto each agar plate (2)

Answer 5

1. so no contamination
2. so same number of bacteria transferred to allow comparison

Question 6

describe two precautions the student should take when clearing away after the dissection (2)

Answer 6

1. carry sharp instruments (scalpel) by holding the handle/pointing away from body
2. disinfect surfaces/instruments
3. disinfect hands/wash hands with soap and water
4. put organ in a separate bag to dispose

Question 7

give two safety precautions that should be followed when dissecting a heart (1)

Answer 7

1. use a sharp scalpel/scissors
2. wash hands/wear gloves
3. disinfect bench/equipment
4. cover any cuts
5. cut away from others
6. safe disposal

Question 8

suggest what the student should have done when she saw that block 2 was damaged. (1)

Answer 8

repeat/replace with an undamaged block

Question 9

a student prepared a plant root to observe cells undergoing mitosis. he put the root in a small bottle of hydrochloric acid in a 40C water bath.

why did he put the plant root in acid? (1)

Answer 9

to stop mitosis

Question 10

state two precautions when working with hydrochloric acid (2)

Answer 10

1. eye protection
2. gloves
3. add water to spills immediately
4. do not pour away down a sink

Question 11

a student compares the mitotic index in the roots of two different species. give two considerations within her method to ensure this comparison is valid (2)

Answer 11

1. same growing condition
2. same distance from root tip
3. same time in acid/same temp of acid
4. same concentration of acid
5. several field views
6. same time of day

Question 12

the student produced the sucrose solution with different concentrations from a concentrated sucrose solution.

name the method that she would have used to produce these sucrose solutions. (1)

Answer 12

serial dilution OR dilution series

Question 13

a student determined the size of a cell structure from a photograph obtained using a microscope.

he used a ruler and a calculator and gave the answer in um.

describe how he determined the size of the structure (2)

Answer 13

ANY PAIR:

1. measure length of structure and divide by magnification
2. correct conversion from measured length to um, x1000 from mm

OR

1. measure length of structure and divide by image length of scale bar
2. multiply by actual length of scale bar

Question 14

give one way in which the sampling procedure could be standardised (1)

Answer 14

1. same size of area samples
2. same size net/mesh
3. same sampling time
4. samples taken at same time of day/on same day

Question 15

suggest one way how the scientist measured the rate of water flow in the river (1)

Answer 15

1. movement of floating object over known distance and given time
2. time to fill container of known volume
3. use of data logging device

Question 17

a student investigated the use of cinnamon oil as an antimicrobial substance. she investigated the effect of cinnamon oil on the growth of five different bacterial cultures grown on agar plates.

the student added 100 mm3 of each bacterial culture from its glass bottle onto a separate agar plate. she spread each bacterial culture evenly over the agar using a spreader.

describe the aseptic techniques she should use (3)

Answer 17

1. wash hands with soap OR disinfect surfaces
2. use sterile pipette/syringe to transfer bacteria
3. remove bottle lid and flange neck of bottle
4. lift lid of agar plate at an angle
5. use a sterile spreader
6. place pipette/spreader into disinfectant

Question 18

in chromatography, explain why the student marked the origin using a pencil rather than using ink (1)

Answer 18

with pencil the origin will be visible, if ink was used the ink and pigments would mix