B7 - practicals Flashcards
What do you need to do to make sure your working safely in a lab?
Wear lab coat to protect skin and clothing
Wear safety googles
Wear gloves if the chemical is an irritant
Keep anything flammable away from Bunsen burner if used
Do not touch hot equipment directly
Handle glassware carefully so it doesn’t break.
What are the ethical issues when organisms are involved.
Animals need to be treated humanely - handled carefully and returned to original habitat
If involving humans they should not be forced to participate against their will or feel pressured
A student wants to test the distribution of an organism in an area. She takes sample of one part of an area. What could she do better.
Random sampling to give a more accurate representation of the whole area.
Divide the field into a grid .
Label the grid with numbers.
Use a random number generator to select coordinates
Take your samples with a quadratic at these coordinates.
How to measure length?
Small - ruler
large - metre stick or tape measure
The smaller unite have a higher degree of accuracy
How to measure area?
Measure length and width
Area of a rectangle = length * width
area of circle - pie r^2
Area of triangle - 1/2 b*h
How to measure mass
To weigh a solid,
Start by putting the container you are weighing your substance into on a balance
Set the balance to 0
Then weigh out the correct amount of substance.
How to measure time
Use a stopwatch - measures to the nearest 0.1s so it is more accurate.
Same person should do the timing so results are more precise.
How to measure temperature?
Use a thermometer to measure the temperature
Read scale on thermometer at eye level
How to measure volume of a liquid
Pipette - dropping pipette is used to transfer drops of liquid
Graduate pipette is used to transfer accurate volumes
Always read volume from bottom of meniscus
Measuring cylinder
A student counts the number of bubbles produced by the pondweed. How can she make this practical better and why is this not the best method.
It is not the best method because it is less accurate and does not tell you the total volume produced.
A better way is to measure volume of gas using gas syringe.
Or use a upside down measuring cylinder filled with water, the gas will displace the water so you can read the volume off the scale.
A students is investigating amount of gas produced however there is a gap in her experiment. What could this do to her results ?
Gas can escape so it will not be accurate
How to measure pH
Indicators change colour depending if it is an acid or an alkali.
A student wants to measure pH but doesn’t want the entire solution to turn a different colour. What should she do ?
Use indicator paper, the paper touches the solution and it will change colour .
Or use a pH meter to digitally display an accurate value.
How to measure heart rate?
Find your pulse on the wrist . Count the number of beats in 15 seconds and multiply by 4 to get the number per minute.
How to use a Bunsen burner safely?
Use a heat proof mat
Always put on clear visible flame, safety flame, if not using
Use the top of the blue flame to heat
If heating something over flame, e.g. beaker of water, use a tripod and gauze
A student would like to heat a beaker of water at a constant temperature what should she do?
Use a water bath , which can be turned to a specific temperature.
Use a thermometer to check it is the correct temperature
A student would like to take continuous samples, but redoing practicals again and again doesn’t seem practical. What is a good method for this.
Data loggers. - decide what you are measuring. Connect the external sensor to the data logger. Decide how often you want the data logger to take readings.
Computer will view the data and to process it draw graphs.
It is more accurate and you can take larger sample size.
One scientist thinks that the results of 105 bubbles at 12.5cm away may be an error.
Describe how she can be more certain that 105 Is the true value
Repeat the reading for 12.5cm
If the number of bubbles is close to 105 then she can be more certain it is the true value.
How could similar apparatus be used to allow the scientists to investigate the effect of temperature on the rate of photosynthesis.
Use a water bath to vary the temperature and count the number of bubbles given off at each temperature
A student is carrying out a field investigation to determine the population of woodlice in the schools wildlife garden.
Describe a method the student could use to determine the population size of woodlice.
Mark the individuals
Release the individuals
Collect a second sample and count the number of marked individuals
Use equation
Number 1st sample * Number 2nd Sample / Number 2nd marked
Woodlice are often found under logs and bark where it is damp.
Suggest why woodlice prefer damp places.
Loses less water
Water is required for decomposition by microorganisms of food source.
Nina wants to investigate how changing the light intensity affects the rate of water uptake by a leafy shoot. Describe the experimental procedure Nina should follow and how she should process her results.
Use the lamp to change the light intensity.
Place lamp at different distances from the leafy shoot
Use metre ruler to measure distance of lamp from leafy shoot
Use at least 4 different distances and use a stopwatch,
Control variables are the same time, control amount of ambient light and control air movement by closing windows.
Describe how you can test for the presence of glucose
Use Benedicts solution
Look for a red brown precipitate
What breaks down starch
Amylase breaks down starch. Starch is broken down into sugar.
