Why do plants need to respond to stimuli? (1)
To increase their chance of survival by responding to changes in their environment, similar to animals
What is tropism? (1)
The response of a plant to a directional stimulus.
What is phototropism, and how do plants respond to light? (3)
Phototropism is the growth of a plant in response to light;
Shoots are positively phototropic (grow toward light);
Roots are negatively phototropic (grow away from light)
What is geotropism, and how do plants respond to gravity? (3)
Geotropism is the growth of a plant in response to gravity;
Shoots are negatively geotropic (grow upward);
Roots are positively geotropic (grow downward)
What is hydrotropism, and how do plants respond to water? (2)
Hydrotropism is the growth of a plant in response to water;
Roots are positively hydrotropic (grow towards water)
What is thermotropism? (1)
The growth of a plant in response to temperature
What is thigmotropism? (1)
The growth of a plant in response to contact with an object
What are alkaloids, and how do they defend plants against herbivory? (2)
Bitter-tasting, nitrogenous compounds that deter or kill herbivores;
Example: Nicotine in tobacco plants is highly poisonous to insects
What are tannins, and how do they defend plants against herbivory? (2)
Taste bitter and bind to proteins in the gut of herbivores;
Making plants hard to digest and deterring herbivores
What are pheromones, and how do plants use them? (3)
Chemicals that affect the behaviour of other organisms;
Alarm pheromones are released when a plant is grazed on, triggering nearby plants to produce defences like tannins;
Corn plants release pheromones to attract parasitic wasps that kill caterpillars eating the plant
How does the Mimosa pudica plant respond to touch? (2)
Folds up quickly when touched;
Possibly to scare off herbivores or knock off insects
How do plants respond to extreme cold? (4)
Produce antifreeze proteins;
That bind to ice crystals and lower the freezing temperature;
Preventing more ice from forming and damaging the plant;
E.g. carrots
How do you set up a practical investigation to study phototropism in plants? (7)
- Take 9 wheat shoots of equal height and plant them in individual pots with the same soil;
- Cover 3 shoots with a foil cap;
- Leave 3 shoots without foil;
- Wrap the base of 3 shoots with foil, leaving only the tip exposed;
- Place the shoots in front of a light source, ensuring each is the same distance from the light source;
- Control variables like temperature and water;
- After 2 days, observe and record the amount and direction of growth
What results should you expect from the phototropism experiment? (3)
Shoots with exposed tips should grow towards the light (positive phototropism);
Shoots with the tip covered by foil will grow straight up (no phototropism);
Shoots with the base covered but the tip exposed will grow towards the light
How do you set up a practical investigation to study geotropism in plants? (7)
- Line 3 petri dishes with moist cotton wool, using the same amount of water and cotton wool in each;
- Place 10 cress seeds in each dish and press them into the cotton wool;
- Tape a lid onto each dish and cover them with foil to block light;
- Leave the dishes in a warm place;
- Prop one dish upright at 90°, another at 45°, and the third horizontally;
- Leave the seeds for 4 days;
- Measure the growth of the shoots and roots, and the angle of growth
What results should you expect from the geotropism experiment? (2)
In all positions, the shoots will grow away from gravity (negative geotropism);
The roots will grow towards gravity (positive geotropism)
