Practical Skills Notes

Independent Variable (IV): The factor you change in an experiment. Limit to only one IV.
- Example: Light color.
Dependent Variable (DV): The factor that changes because of the independent variable. This change must be measurable.
- Example: Plant height (as a measure of growth).
Controlled Variable (CV): Factors kept constant to improve the validity of the experiment.
- Examples: Species of plant, age of plant, initial height, amount of sunlight, volume of water, etc.
Control: A setup for comparison to demonstrate that the change happens because of the independent variable
- Example: A plant without any light at all

SP LaTuK is an acronym to remember the components of a good graph
S = Scale/Size: The graph should be linear and greater than half a page in size.
P = Points: Accurately plotted data points.
L = Line: Drawn with a ruler, dot-to-dot, and not extending beyond the first or last point.
A = Axes: Independent variable (IV) on the x-axis, dependent variable (DV) on the y-axis.
T = Title: Specific enough to describe experiment, going beyond just axis labels.
U = Units: Indicated in brackets on the axes (or using the word "in").
K = Key: Include a key if necessary.
Notes: A key and/or title may be unnecessary sometimes. Brackets for units can sometimes be replaced with the word "in".

Accuracy: Results are close to the true value; achieved by using good equipment.
- Example: A weighing scale that measures to more decimal places.
- Example: measuring the rate of photosynthesis by using an inverted cylinder to measure the VOLUME of oxygen produced rather than the number of bubbles produced per minute.
Reliability: Consistent results are obtained when repeating an experiment; improved by repeating the experiment at least 3 times and calculating a mean.

Two Options:
- CORMMS
- Variables, control, and repeats.
Technique: Use SCRAP, then write out the experimental design in full sentences.

CORMMS Breakdown:
- C = CHANGE: What is being changed in the investigation (Independent Variable).
- O = ORGANISM: A control related to the organism being used (if relevant).
- R = REPEAT: Repeats must be carried out for reliable results.
- M1 = MEASUREMENT 1: How the dependent variable is measured.
- M2 = MEASUREMENT 2: What time scale is used (dependent variable).
- S1 and S2 = SAME: What is controlled in the investigation (Controlled Variables).
Example Question:
- Investigate the effect of cold water and hot water on a plant.
Answer Template:
1. IV: cold water and hot water / range of temperatures/eq
2. Organism: same species/size/ age of plant
3. Repeats: repeats / average
4. Measurement 1: mass/length / number of leaves / ruler/eq
5. Measurement 2: ref to time;
6. 3x CVs: same light / carbon dioxide/water/mineral conc./pH/eq
Mark Allocation: 6 marks total.

Describe: State what you see and use data if it's a graph or table.
Explain: Give a scientific reason why or how.
Compare: Give both similarities and differences and make direct comparisons (within the same sentence).
Suggest: Use your scientific knowledge and apply it to new situations.
Evaluate: Similar to compare (give both pros and cons) but ALSO include a conclusion.

Scenario: Ripening bananas investigation (Ethene gas).
Outline: Put green bananas into bags – some with a ripe tomato (source of ethene). Record time for the bananas to turn yellow.
Student Response Breakdown (CORMS):
- O: Use bananas from the same bunch (same variety, size, color).
- C: Put bananas into identical transparent polybags. Five bags with one banana, five with one banana and one tomato. Seal the bags.
- R: Observe 5 sets of bags for reliability.
- S: Keep bags in a dark cupboard with the same temperature.
- M: Check bags twice a day, record date, time, and color of each banana. Use a photograph of a ripe banana to check the final yellow color. Record the time, in hours, for each banana to become yellow and compare the results.
Mark Scheme Breakdown:
- (1) C - bananas in container with and without tomato
- (2) O-same variety of banana / same stage of ripeness / same colour at start
- (3) R-repeats with several bananas / several batches bananas/
- (4) M1-measure colour of banana (e. g. match on colour scale)
- (5) M2-time stated to reach this colour
- (6) S1 same container around same number of bananas + tomato
- (7) S2 same temperature/same light / same humidity / same other variable
- Total = 6 Marks

Write down 'CORMS' to start as a checklist.
Planning the method in outline helps before writing in more detail.
Marks are awarded for written text, not necessarily for correct CORMS labels.
C (Change/Comparison/Control): Independent variable; presence (or not) of ethene.
O (Organism): Same species or variety; bananas from the same batch and starting at the same ripeness stage.
R (Replication/Repeats): Several results are obtained.
M1 + M2 (Measurements): Dependent variable
- M1: An "end-point" on the color scale to represent ripeness stage.
- M2: A timescale (how long it takes to reach the chosen color).
S1 + S2 (Same/Controlled Variables): Quantity used (same volume, same mass) or other variables (same temperature, same humidity).

Design an experiment to investigate the effect of smoking on breathing rate during exercise (6 marks).
C
- IV: Smoking Status (Smoker vs. Non-Smoker)
- What will you change in this investigation?
- What is the independent variable?
O
- Which organism will be involved in the investigation and what will you keep the same about it?
R
- How will you make sure the experiment is reliable?
- How often will you repeat the experiment?
- Or how many different organisms will you use so you can do several experiments at the same time?
M1 and M2
- DV: Breathing Rate.
- How will you measure the dependent variable?
- What equipment will you use to measure it?
- How long will you wait before you will take your results?
S M1 and M2
- What about the environment needs to be kept constant?
- What are your environmental control variables
  Minimum 4x CVs:
- Organism (x2)
- Experiment (x2)
- Control (if there is one):
- Repeats + mean