Introduction to Biology and Laboratory Rules, practice questions

B, The responding variable is what is measured as a result of the change made; here, the rate of oxygen production is measured in response to the concentration that the experimenter deliberately changes.

B, A hypothesis must state the direction of the relationship between the manipulated and responding variables, not simply that one 'affects' the other.

C, Biological drawings represent structure using outline alone; shading, colouring or artistic texture is not part of the convention and costs marks.

B, A burette has fine graduations and a tap for controlled delivery, making it the most accurate apparatus among these options for measuring a variable volume of liquid, as used in a titration.

B, Placing the unit once in the column heading, such as 'Volume / cm³', keeps every value in the column as a plain number, which is the convention markers expect.

B, Blood group is discrete, categorical data with no continuous numerical order between categories, so a bar chart, not a line graph, is the appropriate choice.

B, The readings are consistent with each other (precise) because the same 2 °C offset appears every time, but they are not accurate, since they do not match the true value.

C, A safety precaution should name the specific hazard and the specific protective action; option C links the goggles to the exact hazard (corrosive acid splashes), unlike the vague statements in the other options.

B, Randomising the coordinates prevents the researcher from unconsciously choosing quadrat positions that support a particular expected result, which would introduce bias into the sample.

B, Microbiology is the study of microorganisms such as bacteria and fungi, and its application to food safety leads directly to a career such as a food microbiologist.

• Aim: to investigate the effect of light intensity on the rate of photosynthesis in Hydrilla.
• Hypothesis: as light intensity increases, the rate of photosynthesis increases up to a certain point, after which it levels off.
• Manipulated variable: light intensity (e.g. varied by changing the distance of a lamp from the plant).
• Responding variable: rate of photosynthesis (e.g. number of oxygen bubbles released per minute, or volume of gas collected).
• Fixed variable: e.g. temperature of the water, concentration of sodium hydrogencarbonate solution, or the length of the Hydrilla shoot used (any one, with a reason).
• Apparatus for the responding variable: a bubble counter or a gas syringe/inverted measuring cylinder to collect and measure the gas produced, and a stopwatch to time each count.

• Safety precaution 1: point the mouth of the test tube away from yourself and others while heating, since a suddenly boiling liquid can spurt out (bumping).
• Safety precaution 2: use a test tube holder rather than fingers to hold the hot test tube, and use the yellow (safety) flame of the Bunsen burner whenever it is not actively being used to heat.
• Apparatus to hold the test tube: a test tube holder and a test tube rack (for use before and after heating).
• Apparatus to measure the volume: a measuring cylinder (or burette for a smaller, more precise volume).

• Not appropriate, because time is continuous numerical data, and a bar chart implies the values are separate, unrelated categories rather than points along a continuous scale.
• A line graph should be used instead, with the points joined by a single best-fit line or smooth curve.
• A likely further error: axes may be unlabelled with units, or the scale chosen does not use at least half of the available graph paper, either omission would also cost marks under standard graphing convention.

Biology branches into areas such as medicine, genetics, microbiology and ecology, each leading to specific careers.

Correct handling of apparatus, chemicals and specimens, plus fire and glassware rules, prevents accidents.

A fair test changes one manipulated variable, measures the responding variable, and keeps all other (fixed) variables constant.

A testable statement predicting how the responding variable depends on the manipulated variable.

The ordered steps of aim, hypothesis, variables, apparatus, procedure, results and conclusion.

Clear line drawings with a title, magnification and labels using straight, non-crossing label lines.

Findings are recorded as labelled diagrams, data tables with units placed in the column heading, and graphs with a sensible scale; each format has its own conventions, and an answer loses marks if a label, a unit or an axis title is missing.

Standard units such as cm, g, s and °C are used throughout biology so that measurements can be compared and repeated by anyone. Readings within one table are recorded to the same number of decimal places so precision is not overstated.

A metre rule or measuring cylinder measures length or volume, a stopwatch measures time, a thermometer measures temperature, and a beam balance measures mass. Matching the apparatus to the quantity being measured is itself an examinable skill.

Besides changing the manipulated variable and measuring the responding variable, every other factor that could affect the result is kept fixed. Without this control, a change in the responding variable cannot be attributed to the manipulated variable alone.

A report may be a full write-up from aim to conclusion, or a structured Paper 3 answer with headed sub-sections; SPM usually expects the structured form, where each part is clearly labelled rather than written as continuous prose.

Accuracy is how close a reading is to the true value, while precision is how consistent repeated readings are with each other; a set of readings can be precise, meaning close together, without being accurate if the apparatus itself is faulty.

Specimens used in practical work, such as small organisms in an ecology study, are handled gently and returned to their original habitat where possible, since unnecessary harm to living things is avoided in any investigation.

Outdoor investigations, such as a simple quadrat survey, still need a stated aim, a way of sampling that avoids bias, and a table of results, even though fewer variables can be tightly controlled than in a laboratory setting.