Orientation Responses In Plants

Question 1

What is the difference between positive and negative tropisms?

Answer 1

Positive tropisms grow towards a stimulus and negative tropisms grow away from a stimulus

Question 2

What are some names of tropisms and why are they named that way?

Answer 2

Chemotropism - when the stimulus is a chemical
Geotropism or gravitropism - when the stimulus is gravity
Hydrotropism - when the stimulus is water
Thermotropism - when the stimulus is temperature
Thigmotropism - when the stimulus is touch
Phototropism - when the stimulus is light

Question 3

Explain the importance of tropisms

Answer 3

Tropisms are important because they keep plants alive. Plants need light and water for photosynthesis so they usually have a positive phototropism and hydrotropism.

However, plants might want to grow away from dangerous chemicals or substances so they will have a negative chemotropism. Some plants will grow towards a touch, while others will grow away - positive or negative thigmotropism.

Question 4

Explain the difference between a nastic response and a tropism response

Answer 4

With tropisms direction is important and can label a tropism as positive or negative. However, direction is not important with nastic responses as they aren’t always growth movements.

Question 5

What are the stimuli that can cause tropism or nastic responses?

Answer 5

• Chemicals
• Gravity
• Water
• Temperature
• Touch
• Light

Question 6

What is auxin?

Answer 6

A hormone contained in the plant that is produced in the tip of the plant shoots and causes cells to grow longer than normal

Question 7

Explain what auxin does when there is a directional light source

Answer 7

When the plant shoot is exposed to light, auxin diffuses down the dark side of the plant. As a result, the cells on the dark side elongate while the cells on the light side remain the same. Therefore the plant shoot bends towards the light.

Question 8

Explain the role of auxin in roots

Answer 8

Auxin has the opposite effect in roots than it has in plant shoots, as it prevents the roots from elongating. With geotropism the plant roots grow downwards. The auxin moves to the lowest side of the roots due to gravity, and the loss of auxin on the higher side causes cells to elongate while the cells on the lower side stay the same. As a result, the roots start to bend and grow downwards.