Plant Orientation Responses

Question 1

What are all the abiotic and biotic factors that might affect the growth of a plant?

Answer 1

Environmental Factors

Question 2

What is the prefix for light?

Answer 2

Photo

Question 3

What is the prefix for chemicals?

Answer 3

Chemo

Question 4

What is the prefix for gravity?

Answer 4

Geo or Gravi

Question 5

What is the prefix for touch?

Answer 5

Thigmo

Question 6

What is the prefix for water?

Answer 6

Hydro

Question 7

What is the prefix for temperature?

Answer 7

Thermo

Question 8

What is the prefix for current?

Answer 8

Rheo

Question 9

Define a tropism

Answer 9

A plant growth response towards or away from an environmental factor coming from one direction only

Question 10

The name of the type of tropism in which a plant grows towards the direction of an environmental stimulus

Answer 10

Positive

Question 11

Name this tropism - A pea plant tendrils grow around a climbing frame

Answer 11

Positive thigmotropism or heliotropism

Question 12

Name this tropism - A seed germinates underground and grows upwards

Answer 12

Negative geotropism

Question 13

Name this tropism - A pollen tube grows towards the ovule in response to the chemical it secretes

Answer 13

Positive chemotropism

Question 14

The name of the hormone that controls many plant tropic responses

Answer 14

Auxin

Question 15

What does auxin promote or inhibit in cells?

Answer 15

Cell elongation

Question 16

Explain how auxin encourages cell elongation

Answer 16

It releases the tension of the cellulose in the cell wall of plant cells

Question 17

Does a high concentration of auxin in root cells promote or inhibit cell elongation?

Answer 17

Inhibits cell elongation

Question 18

Does a high concentration of auxin in shoot/stem cells promote or inhibit cell elongation?

Answer 18

Promotes cell elongation

Question 19

What is the name of the root that emerges from a seed?

Answer 19

Radicle

Question 20

Why do radicles bend downwards once they germinate?

Answer 20

Auxin accumulates on the lower side on the radicle due to the pull of gravity. A high concentration of auxin on the lower side inhibits cell elongation in root cells. A low concentration of auxin on the upper side promotes cell elongation causing the root to bend downwards.

Question 21

Name three reasons why roots bend downwards linked to biological processes.

Answer 21

Towards a greater source of water for photosynthesis.
Towards nutrients that are used in cell division, respiration and photosynthesis
To increase the stability of the plant in the ground

Question 22

What is the name of the shoot that emerges from a seed?

Answer 22

Plumule

Question 23

Why do plumules bend upwards once they germinate?

Answer 23

Auxin accumulates on the lower side on the plumule due to the pull of gravity. A high concentration of auxin on the lower side promotes cell elongation in shoot cells. A low concentration of auxin on the upper side inhibits cell elongation causing the shoot to bend downwards.

Question 24

Name two reasons why shoots bend upwards linked to biological processes.

Answer 24

To emerge quickly from the soil so they can produce flowers, get pollinated and reproduce.
To emerge and capture sunlight for a faster rate of photosynthesis.

Question 25

Name the response of a plant that grows towards the sun.

Answer 25

Positive phototropsim

Question 26

Explain the mechanism behind why positive phototropism occurs

Answer 26

The photoreceptor at the tip of the shoot detects the direction of the sunlight. Auxin is produced and moves across and down the 'dark side' of the shoot (opposite side to where light is coming from). A high concentration of auxin on the dark side promotes cell elongation in shoot cells. A low concentration of auxin on the 'light side' inhibits cell elongation causing the shoot to grow towards the sun.

Question 27

Why do plants grow towards the sun?

Answer 27

To receive a higher light intensity for a faster rate of photosynthesis.

Question 28

What is the mechanism behind positive thigmotropism/ heliotropism?

Answer 28

The touch inhibits auxin and causes it to move to the non-touch side. A low concentration of auxin on the touch side inhibits cell elongation. The opposite side of the touch has a high concentration of auxin promoting cell elongation. This causes the plant to grow around the touching object.

Question 29

Why would a growing plant grow around a climbing frame?

Answer 29

To provide support for a plant so it can dedicate cell division to grow upwards quicker rather than outwards. This means it can outcompete other plants for light for photosynthesis.

Question 30

Define a nastic response.

Answer 30

A plant growth response to a change in the intensity of an environmental stimulus, not its direction

Question 31

Name this response - Mimosa folds its leaflets inwards when touched.

Answer 31

A thigmonastic response

Question 32

Why would Mimosa fold its leaflets in response to touch?

Answer 32

To reduce the chances of its leaves being grazed

Question 33

What is the mechanism that causes Mimosa leaves to fold inwards?

Answer 33

Turgor pressure - the leaves pump ions out of the leaf in response to touch by active transport (energy cost). This causes water to leave the vacuoles inside the cells and the leaves go limp and fold inwards.

Question 34

Name this response - Leaves droop at night and rise up and open during the day.

Answer 34

A photonastic response/nictonasty

Question 35

Why do leaves show a photonastic/nictonastic response during the day?

Answer 35

Lifting up and opening out during the day increases the surface area exposed to the sun so it can capture more light energy for photosynthesis.

Question 36

Why do leaves show a photonastic/nictonastic response during the night? Give two reasons

Answer 36

Drooping leaves are less likely to be grazed. | Hanging reduces surface area exposed to the cold night and frost damage.