Study Hack Lab

RP 8Biology

Plant responses

Write-up template

Name
Date
Course: GCSE Biology
Board and specification: AQA GCSE Biology (8461), 4.5.4.1Apparatus and techniques: AT 1, AT 3, AT 4, AT 7
Class and teacher

Aim

Investigate the effect of the direction of light on the growth of mustard seedlings, and the effect of gravity on the growth of bean roots, recording lengths and labelled drawings.

Plan and risk assessment
Apparatus
Method
Results
Graph
Analysis
Conclusion and evaluation
Make safe and clear up

A blank write-up for use in a real lesson. The headings follow the AQA required practical; the readings are yours to take. Layout v1, practical v2. Original material; not affiliated with AQA, which has not reviewed it.

1 Plan and risk assessment

Plants respond to light and gravity by growing unevenly. Auxin, a plant hormone made in the tips of shoots and roots, is spread unevenly when light comes from one side or the plant lies on its side. In a shoot, more auxin on the shaded side makes those cells elongate more, so the shoot bends towards the light. In a root lying on its side, more auxin collects on the lower side and the upper side grows faster, so the root bends down.

Shoots grow towards light (positive phototropism); roots grow towards gravity (positive gravitropism).

Variables

Independent (you change)
Dependent (you measure)
Control (you keep the same)

Prediction

Dish A gets light only through a slit on one side. How will its shoots grow?

How will the seedlings grown in the dark (dish B) compare with those in light from all round (dish C)?

Bean A lies on its side in the dark, its root growing sideways. What will the root do?

Risk assessment

Hazard	Harm it could cause	Control

2 Apparatus

Three Petri dishes with cotton wool The seeds germinate and grow on the damp cotton wool.
White mustard seeds (untreated), one packet The same species and age of seed in every dish.
10 cm³ syringe and a beaker of water (resolution 0.5 cm³) The same volume of water for every dish.
Marker pen Labels the dishes and marks the thread.
Forceps Thin each dish to the same number of seedlings.
Light-proof box with a slit in one side Light reaches dish A from one direction only.
Light-proof box with its slit taped over Keeps dish B in the dark.
Two LED lamps One shines at the slit; one lights dish C from above.
30 cm ruler (resolution 1 mm) Measures shoots and roots.
Cotton thread Laid along a curved shoot or root, then measured against the ruler.
Two germinated broad bean seedlings Their roots show the effect of gravity.
Pins, and two dishes of damp cotton wool Hold each bean in place, kept damp all round.
Waterproof ink and a fine brush Marks each root every 2 mm, to show where it grows.
Clinostat Turns bean B slowly so gravity acts equally on all sides of its root.
Dark cupboard Keeps light from the beans.

3 Method

Write numbered steps someone else could follow. Say what you measure, with which instrument, and how you keep it a fair test.

4 Results

The table is drawn before you measure. Record each reading to the resolution of the instrument, then work out the mean of your repeats, leaving out any anomaly.

Seeds that germinated · 10 white mustard seeds were sown in each dish and left 3 days on the bench.

Dish	Seeds sown	Seeds that germinated
A
B
C

Height of each seedling · Five seedlings in each dish, measured at the start and after 4 days. Curved shoots measured along their length.

Dish	Seedling	Height at the start in mm	Height after 4 days in mm	Increase in height in mm
A
A
A
A
A
B
B
B
B
B
C
C
C
C
C

Mean increase in height · Any seedling you left out as anomalous is not in its dish’s mean.

Dish	Light	Mean increase in height in mm
A
B
C

Bean roots (2 days in the dark)

Bean	How it was kept	Root length at the start in mm	Root length after 2 days in mm	Increase in root length in mm	What the root did
A
B

Observations

What you looked at	What you saw
Dish A (light from one side) after 2 days
Ink marks on root A after 2 days
Dish B (dark) beside dish C after 4 days

Anomalies

Ring any anomalous result. Say what probably went wrong and whether you repeated it.

5 Graph

Bar chart of the three dishes · Draw a bar chart. Light goes along the bottom.

6 Analysis

Mean increase in height, dish A
mean = sum of the increases ÷ number of seedlings
Answer
How much more did the dark seedlings grow?
percentage difference = (mean in the dark − mean in light from all round) ÷ mean in light from all round × 100
Answer
Labelled drawing of a seedling
Answer

7 Conclusion and evaluation

Conclusion

Conclusion: what do your results show? Use your own numbers.

Sources of error

For each, say whether it is systematic or random, and how it affected your results.

Measuring bent shoots with a ruler held upright

One dish drying out (water added by eye)

A warm lamp over dish C

Light leaking into the dark box

Different numbers of seedlings in each dish

Differences between seedlings

Only five seedlings in each dish

Reading a small, curved shoot to the nearest millimetre

Beans left in the light

Improvement

How could you improve the method? Say why it would help.

8 Make safe and clear up

Switch off the lamps and the clinostat
Put the seedlings, beans and cotton wool in the bin (seal any mouldy dish in a bag first)
Count the pins back into their box
Wash the Petri dishes, put the ruler, thread and boxes back, and wash your hands