Plant Regulation and Control

Question 1

how do plants compensate for their relative immobility ?

Answer 1

by modifying their growth in response to stimuli from the environment

Question 2

what are Internal factors ?

Answer 2

known as Phytohormones, these are hormones found in plants.

Question 3

what are External factors ?

Answer 3

environmental factors such as light intensity, temperature, day length & gravity.

Question 4

how do hormones affect growth by causing as change in?

Answer 4

• Changes in cell division and elongation.

- Death in some parts of the plant.

Question 5

A hormone’s influence growth is by?

Answer 5

– Changing enzyme activity or permeability of membranes.

– Inhibiting the synthesis of proteins.

Question 6

What is positive tropism?

Answer 6

– Growth towards a stimulus

Question 7

What is negative tropism?

Answer 7

– Growth away from a stimulus

Question 8

Types of Tropisms?

Answer 8

– Phototropism ( towards light)
– Geotropism (roots go down towards gravity)
– Thigmotropism (touch)
– Photoperiodism (flowering)

Question 9

what is Phototropism?

Answer 9

– is when a plant moves in response to light.
– Stem grows towards light – positive phototropism.
– Roots grow away from light – negative phototropism

Question 10

what is geotropism?

Answer 10

– is the growth response of a plant in response to gravity.
– Roots exhibit positive geotropism
– while stems and leaves exhibit negative geotropism.

Question 11

what is Thigmotropism?

Answer 11

is the response of a plant to physical contact (touch).
• Plants that cling to physical structures such as walls exhibit positive thigmotropism.
• Ex. Tendrils of vines wrapping around things, venus fly traps

Question 12

Hormones are Classified into 5 Groups which are?

Answer 12

–	Auxins
–	Cytokinins
–	Gibberellins
–	Abscisic acid
–	Ethylene

Question 13

What is the role of Auxin?

Answer 13

– Controls stretching of plant cells
– Stimulate growth of roots that grow out of a stem
– At high concentrations auxins inhibits root growth.
– Inhibits side branch growth – Apical dominance

Question 14

what happens when there is a Removal of Apical Bud ?

Answer 14

, the lateral buds grow and the plants become thicker.

– If you cut off the tip of a seedling, there will not be any growth or bending of the plant.

Question 15

what is the role of Cytokinins?

Answer 15

– Responsible for increase in cell division
– Breaks dormancy
– Produced in the roots
– Promotes cell division

Question 16

what is the role of gibberellins?

Answer 16

Responsible for cell division and growth in cell size

Question 17

what is ethylene?

Answer 17

is a gas that is released by ripening fruits that encourage the aging processes .

Question 18

what is the role of Abscisic acid ?

Answer 18

– Responsible for dormancy of various types
– Causes the falling of leaves and fruits – ‘Abscission’
– Produced in older leaves, root cap and stem.
– Occurs in Autumn

Question 19

what is Photoperiodism?

Answer 19

– When plants may respond to the length of daylight and dark.
– This can have an effect on the timing of flowering in a plant.

Question 20

what are the 3 types of plants?

Answer 20

• short day
• long day
• day neutral

Question 21

what do short day plants require?

Answer 21

– require an uninterrupted long period of darkness (long, dark nights) in order to flower.
– They typically flower in early spring.
Even just a flash of light during the long dark may be enough to stop the flowering

Question 22

what do long day plants require?

Answer 22

• require short periods of darkness to flower (i.e. shorter nights).
• They usually flower in Summer.

Question 23

what do day neutral plants require?

Answer 23

flowering does not depend on length of day or night

Question 24

Circadian Rhythm?

Answer 24

• is any activity that follows a 24 hour cycle.

* For example, Mimosa pudica leaves are horizontal during the day but fall into a sleeping position at night

Question 25

Nastic Movement?

Answer 25

• a response of plants and flowers to a stimulus which is not connected with the direction from which the stimulus comes, e.g. the closing of flowers at night

Question 26

Trigger Plant?

Answer 26

When an insect lands on the centre of the flower, the tube jumps up to strike the insect, covering it with pollen which it then takes to another flower.
The “trigger” usually reset itself within about 20 minutes.

Question 27

Vernalisation

?

Answer 27

In some plants the young plant cannot flower unless it has been exposed to a period of cold before spring growth.
A ‘cold naps’ or frost is needed to stimulate flowering.
This is why bulbs are often stored in the fridge before they are planted.