Responses in flowering plants: tropisms

Question 1

Define a tropism

Answer 1

A tropism is a change in the growth of a plant in response to an external stimulus.

Question 2

Define a negative tropism

Answer 2

A negative tropism occurs when the growth is away from the stimulus.

Question 3

Define a positive tropism

Answer 3

A positive tropism occurs when the growth is towards the stimulus.

Question 4

What is the main advantage of tropisms? Give an example

Answer 4

The main advantage of tropisms is that they allow plants to obtain more favourable growing conditions. For example:

Stems grow towards light so they can produce more food by photosynthesis

Question 5

Give 2 examples of tropisms allowing more favourable conditions for plants to grow in

Answer 5

Stems grow towards light so they can produce more food by photosynthesis

Roots grow towards gravity so they can penetrate deeper into the soil for better anchorage and absorption.

Question 6

Define phototropism

Answer 6

Phototropism is the change in growth of a plant in response to light, usually from one direction (.e. unidirectional light)

Question 7

Are stems positively or negatively phototropic?

Answer 7

Stems are positively phototropic (.e. they grow towards light).

Question 8

As stems are positively phototropic, what does this allow for them to do?

Answer 8

This allows the stem (and the leaves) to get more light. In this way they can carry out more photosynthesis and produce more food.

Question 9

Are most roots positively or negatively phototropic?

Answer 9

Many roots are negatively phototropic.

Question 10

Where is the negatively phototropic root clearly seen? (examples)

Answer 10

This is clearly seen in the roots of climbing plants such as ivy, where the roots grow away from light and towards the wall or surface to which they are attached.

Question 11

Define geotropism

Answer 11

Geotropism (or gravitropism) is the change in growth of a plant in response to gravity.

Question 12

In what direction do roots and stems grow as a result of gravity?

Answer 12

Roots usually grow towards gravity (positively geotropic) and stems grow away from gravity (negatively geotropic).

Question 13

If roots grow towards gravity, what are the benefits of this for the plant? (2)

Answer 13

If the roots grow towards gravity they can anchor the plant more efficiently in the soil.
In addition they can absorb more water and minerals.

Question 14

why does the fact that roots grow toward gravity and stems do not increase the yield of food produced by the plant?

Answer 14

By growing away from gravity, stems grow towards the light. This allows plants to produce more food.

Question 15

Define thigmotropism

Answer 15

Thigmotropism is a change in growth of a plant in response to touch.

Question 16

What do climbing plants produce allowing them to wrap around supporting structures?

Answer 16

Climbing plants (e.g. ivy, vines, peas, tomatoes) produce specialised parts, called tendrils, which wrap around supporting structures.

Question 17

What do the specialised parts produced by climbing plants do?

Answer 17

specialised parts, called tendrils, wrap around supporting structures.

Question 18

What are tendrils?

Answer 18

specialised parts, called tendrils, which wrap around supporting structures.

Question 19

Do tendrils exhibit positive or negative thigmotropism? why?

Answer 19

Tendrils exhibit positive thigmotropism, i.e. they grow around any object they touch.

Question 20

Define hydrotropism

Answer 20

Hydrotropism is a change in growth of a plant in response to water

Question 21

In what direction do roots and pollen tubes grow as a result of hydrotropism?

Answer 21

Roots and pollen tubes grow towards water.

Question 22

Define chemotropism

Answer 22

Chemotropism is a change in growth of a plant in response to chemicals.

Question 23

Do roots grow away or towards minerals in the soil(Ca, Mg, fertilizers like phosphorous or potassium)?

Answer 23

Roots grow towards minerals (e.g. calcium and magnesium and fertilisers such as nitrogen, phosphorous and potassium) in the soil.

Question 24

Do pollen tubes grow towards or away from chemicals released by the ovule?

Answer 24

Pollen tubes grow towards chemicals released by the ovule.

Question 25

Give some examples of chemotropism

Answer 25

Roots grow towards minerals (e.g. calcium and magnesium and fertilisers such as nitrogen, phosphorous and potassium) in the soil.

Pollen tubes grow towards chemicals released by the ovule.

Question 26

Are most roots positively or negatively chemotropic to acids or heavy metals (e.g lead or zinc) in the soil?

Answer 26

most roots are negatively chemotropic to acids or heavy metals (e.g. lead and zinc) in the soil.