Topics to revise
Organisation - Plants P2
Earth's resources P2
Required practical - Plant hormones
You made it! Finish these last two topics. In the rest of your time between exams, you are ready to practice exam papers.
It is still great practice to do more targeted questions. The only benefit to whole papers is to practice timing.
Checklist - Earth's Resources
Mind map
Tropisms
Investigate phototropism or gravitropism in newly germinated seedlings; record lengths and labelled biological drawings
Check your understanding with these quick common questions. Use the drop down boxes to see the correct answers.
Tropisms
Key rules to remember
Positive tropisms - plants grow towards a stimulus, e.g towards light, towards the PULL of gravity.
Roots and shoots respond differently to auxins. Auxins make shoot cells elongate and grow quicker. In roots they make cells grow slower.
Independent: Direction/intensity of light (full light vs partial vs dark, or side-lit).
Dependent: Growth response (Measure the angle from the surface, measure total height).
Control: Seed species/age, number of seeds per dish, water volume, temperature, growth medium (cotton wool/agar), time allowed to grow.
Petri dishes,
cotton wool/agar,
ruler
mustard (or cress/Brassica) seeds,
access to light source & dark cupboard/foil covers.
Improve accuracy by using a protractor to measure the angle the seedlings are growing at
Control validity by ensuring other variables are the same - temperature of the room, volume of water added.
Use a large number of seedlings as each will show lots of variability. Use at least 10-100, 3 is too low.
Seedlings will grow towards the light. If no light is provided, seedlings will grow taller as they try to find light using up their storage reserves. Plants exposed to light do not grow as tall but grow more leaves.
Line Petri dishes with damp cotton wool; place an equal number of seeds per dish. (e.g 20)
Set conditions: full light, partial light, dark (or set orientations for gravitropism) or shine light from different angles .
Leave to germinate and grow for several days, keeping moisture constant.
Each day, measure shoot/root lengths; make labelled drawings showing direction/curvature.
Compare means between conditions and conclude.