5.1.1 Plant Responses

Question 1

What are some plant responses?

Answer 1

• Tropisms
• Responses to touch
• Responses to herbivory
• Abiotic Stress

Question 2

What is a tropism?

Answer 2

Growth movement of a part of a plant in response to a directional stimulus

Question 3

What is a positive and negative tropism?

Answer 3

A positive tropism is one TOWARDS the stimulus
A negative tropism is one AWAY from stimulus

Question 4

What is phototropism?

Answer 4

Response to light, which is an abiotic stimulus. Maximises photosynthesis by making sure plant has as much light as possible

Question 5

What is a geotropism?

Answer 5

Response to abiotic factor GRAVITY, where shoots exhibit negative tropism and grow away from the pull of gravity, and the roots show positive geotropism, growing towards gravity, so into the soil. All of this ensures the shoots and roots grow in the right directions regardless of orientation of seed.

Question 6

What is hydrotropism?

Answer 6

Response to abiotic factor MOISTURE. Root tip grows towards damp areas of soil which increases the plants access to water.

Question 7

What is thigmotropism?

Answer 7

Plant response to abiotic or biotic factor TOUCH. It is important for climbing plants which are adapted to climb high so they can access as much light as possible in rainforests.

Question 8

What is chemotropism?

Answer 8

Response to abiotic or biotic factor of CHEMICALS. Pollen tubes grow down flower’s stigma towards ovules due to chemotropism.

Question 9

What is mimosa pudica and whats special about it

Answer 9

• Sensitive plant
• Thigmotropism
• Leaflets fold in rapidly when touched
• Bioelectrical signals initiated
• Caused by rapid water uptake and increase in volume of cells at base of leaflet, and rapid loss of water at site of touch, so the adjacent leaves collapse
• Nastic Movement

Question 10

Responses to herbivory notes

Answer 10

• Repellent chemicals which can be poisonous
• In response to damage or stress

Example chemicals
- Tannins
- Alkaloids
- Pheromones

Question 11

What are tannins?

Answer 11

• Water soluble carbon compounds
• Stored in vacuoles
• Can be fatal to herbivorous insects, (when broken down in gut of herbivore, toxic chemicals are released)
• Bitter taste can put off herbivores

Question 12

What are alkaloids?

Answer 12

• Nitrogenous compounds
• Bitter tasting and toxic to herbivores and insects

Question 13

What are pheromones?

Answer 13

• Chemicals released affecting behavior of other organisms
• Toxic to herbivores