Orientation responses in plants

Question 1

What is the difference between tropism and nastic responses?

Answer 1

Tropisms are directional responses to a directional external stimuli.
Nastic responses are non-directional responses to the intensity of a stimuli.

Question 2

What is the difference between a positive and negative tropism?

Answer 2

If tropisms grow towards the stimuli it’s positive, if it grows away its negative.

Question 3

What are the possible stimuli that plants respond to?

Answer 3

Light stimuli - Phototropism
Chemical stimuli - Chemotropism
Gravity stimuli - Gravitotropism
Water stimuli - Hydrotropism
Temperature stimuli - Thermotropism
Touch stimuli - Thigmotropism

Question 4

What is the definition of a hormone?

Answer 4

Hormones are molecules that are often produced in one location and do things in another.

Question 5

What is auxin?

Answer 5

Auxin is a plant hormone which is produced in the tip of plant shoots and causes cells to grow larger than normal.

Question 6

What is the role of auxin in phototropisms?

Answer 6

The auxin hormone causes the plant to bend and grow towards light stimuli. When the plant is exposed to light the auxin spreads to the darker side which therefore elongates the plant towards the light.

Question 7

What is the role of auxin in gravitropisms?

Answer 7

The auxin moves to the lower sides of the roots due to gravity, the loss of this auxin at the higher end of the plant causes the roots to grow downwards.

Question 8

What is Abscisic Acid?

Answer 8

A plant hormone. It functions in many plant development processes, particularly bud dormancy.

Question 9

What is Abscission?

Answer 9

The process whereby a plant sheds parts, particularly leaves, fruit and seeds/pods when their loss is beneficial to the plant.

Question 10

What is Autotroph?

Answer 10

An organism that is able to produce complex organic molecules from simpler molecules found in its environment, using an external energy source

Question 11

What is cytokinin?

Answer 11

A group of hormones that promote cell division in plant roots and shoots and the growth of buds.

Question 12

What is ethylene?

Answer 12

A plant hormone that promotes the ripening of fruit.

Question 13

What are Gibberellins?

Answer 13

Plant hormones that regulate growth and influence various developmental processes, including germination, dormancy and flowering.

Question 14

What is a Nyctinasty?

Answer 14

A circadian rhythmic movement of plants in response to the onset of darkness (Eg the closing of the petals of a flower at dusk)

Question 15

What is the photoperiod?

Answer 15

The period of time each day in which an organism receives sunlight.

Question 16

What is Photoperiodism?

Answer 16

The response of an organism to seasonal changes in the photoperiod.

Question 17

What is Photosynthesis?

Answer 17

The process by which plants and some bacteria use the energy from sunlight to produce glucose from carbon dioxide and water.

Question 18

What is the phytohormone

Answer 18

Any of a range of chemicals that regulate plant growth.

Question 19

What are the 2 primary ways in which plants can respond to stimuli?

Answer 19

Growth movements (Tropisms = long term slow) and Turgor movements (Nastic responses = reversible more rapid)

Question 20

Define the phrase “Primary plant growth”

Answer 20

Growth by cell division and elongation and the early stages of differentiation before tissues become woody (Lignified)

Question 21

What are the cells in the tips of shoots and roots of the plant called?

Answer 21

Apical Meristematic cells.

Question 22

How do the Apical Meristematic cells differ from other types of plant cells?

Answer 22

These cells are undifferentiated - They have no specific function, they are still generalised cells that can develop into one of many cell types

Question 23

What happens in the zone of cell division?

Answer 23

Cells multiply by the process of mitosis.

Question 24

What happens in the zone of cell elongation?

Answer 24

Cells grow in both width and length as water fills the vacuole and the elastic cell stretches.

Question 25

What happens in the zone of differentiation?

Answer 25

Elongated cells become specialised. At the upper meristem, they may become leaves etc At the roots they may become root hairs.

Question 26

How do the Apical Meristematic cells differ from other types of plant cells?

Answer 26

These cells are undifferentiated - They have no specific function, they are still generalised cells that can develop into one of many cell types

Question 27

What happens in the zone of cell division?

Answer 27

Cells multiply by the process of mitosis.

Question 28

What happens in the zone of cell elongation?

Answer 28

Cells grow in both width and length as water fills the vacuole and the elastic cell stretches.

Question 29

What happens in the zone of differentiation?

Answer 29

Elongated cells become specialised.

Question 30

What is dormancy?

Answer 30

A period of suspended growth during winter periods. Energy supplies are limited and resources are conserved.

Question 31

What is Vernalisation?

Answer 31

It is what ensures a plant has reproductive development and seed production in spring and summer rather than in autumn.

Question 32

What are the 5 plant hormones used to control most aspects of a plants life cycle?

Answer 32

Abscisic acid (ABA), Gibberellin (GA), Ethylene, Cytokinins, and Auxins (AA).

Question 33

What is a Coleoptile?

Answer 33

The pointed protective sheath covering the emerging shoot in monocotyledons.

Question 34

How do you measure the photoperiod?

Answer 34

By looking at the levels of phytochromes Pr and Pfr

Question 35

Where is auxin produced?

Answer 35

In the apical meristem cells (The tips of shoots and roots)

Question 36

That is thigmotropism?

Answer 36

A movement in which a plant moves or grows in response to touch or contact stimuli.

Question 37

What are nastic responses?

Answer 37

Rapid are reversible responses to stimuli as they usually involve changes in the cell turgor pressure. The direction of these responses are independent of the direction of the stimuli and the rate of the response is always proportional to the intensity of the stimuli.

Question 38

WHow do you measure the photoperiod?

Answer 38

By looking at the levels of Pr and Pfr

Question 39

How do phytochromes trigger/regulate plant growth, seed germination, flowering ect. ?

Answer 39

By using two pigments Pr and Pfr. The levels of these different pigments trigger different responses.

Question 40

How do the pigments Pr & Pfr work?

Answer 40

When Pf absorbs light it is converted into Pfr