Topic 9

Question 1

Which stimuli affects plants?

Answer 1

Variety, most which are external factors that have a direct impact on the well being of the plant.
Very sensitive to light, and respond to the direction of light and the length of daily expose to it, also affects how much they grow and when the reproduce. Also sensitive to gravity, water and temperature.
Also affected by chemical signals

Question 2

What are the plant responses?

Answer 2

Chemicals produced in repossessed to specific stimuli. Many act as growth regulator.
Plant hormones, produced in one area of the plant and are transported around the body of the plant and have their effects on cells elsewhere.
In some cases, growth is stimulated or inhibited.

Question 3

What are tropisms?

Answer 3

The directional growth responses to specific environmental cues.

Question 4

How do plants grow?

Answer 4

Permanent increase in size of an organisms. Cell division, new material within the cells. Mains areas of division in plants are the meristems and this occurs just at the tip of a root or shoot. Cell elongation and cell division are sensitive to plant growth substance

Question 5

How do the growth hormones make the plant grow?

Answer 5

Can make it easier for the cellulose walls to be stretched and hence easier for the cell to expand and grow.

Question 6

What are auxins?

Answer 6

Powerful growth stimulants that are effective in LOW concentrations.
Are produced in young shoots and always move DOWN the plant for, shoot to roots.
Involves active transport and calcium ions,

Question 7

Why is auxin involved with apical dominance?

Answer 7

Where they suppress the growth of lateral shoots so that one main stem can grow fastest

Question 8

The more auxin is transported down the stem…

Answer 8

… the more root growth occurs

Question 9

What happens if the tip of the stems in plants are removed

Answer 9

Removes the source of auxin, the stimulation of root growth is removed and root growth slows and stops completely.

Question 10

What are auxins involved with other than growth?

Answer 10

Tropic response of plant shoots in unilateral light. The response of the plant to auxins often depends on both th concentration of th hormone and the region of the plant.

Question 11

How do auxins work in a plant ?

Answer 11

Seem to affect the ability of the plant cell walls to molecules bind to specific receptor sites on the cell surface membrane, activating the active pumping of hydrogen ions into the cell wall spaces. Changes hydrogen ion conc, providing optimum pH of 5 for enzymes that break bones between adjacent cellulose microfibrils.
Cells absorb water by osmosis and turgor pressure is caused , walls stench to allow cells to elongate,

Question 12

Why does the bonds of microfibrils in a cell wall have an impact on growth?

Answer 12

Allows microfibrils to slide past each other very easily, keeping walls flexible.

Question 13

How is IAA destroyed?

Answer 13

By enzymes, as the cells mature. The pH of the cell wall rises and the enzyme is inhibited and bonds form between the cellulose microfibrils. As a result, the cell wall becomes more rigid and cell can’t expand,

Question 14

How does light have an affect of auxins?

Answer 14

side of a shoot exposed to light contains less auxin than the side which isn’t illuminated.
Light seems to cause auxin to move laterally across shoot, greater concentration on the illuminated side. Movement means shoot tip acts as a photoreceptor.

Question 15

How does cell elongation come about with auxins and light?

Answer 15

More hormone diffuses don the region of cell elongation on the dark side, which simulated cell elongation and therefore growth on the dark side. Once shoot is growing directly towards the light, the unilateral stimulus is removed,

Question 16

What is gibberellins?

Answer 16

Growth regulators. Affect the internodes of stem and stimulate elongation of the growing cells,
Also promote the growth of fruit.

Question 17

How do giberellins work?

Answer 17

Involve breaking down dormancy In seeds and in germination. Stimulate the formation of enzymes in seeds. Eg, stimulate amylose which breaks down starch storages. Makes glucose available for the embryo as it developed as the seed germinated.
Also used for bolting, a period of sudden rapid growth and flowering

Question 18

What are cytokinins

Answer 18

Growth regulators that promote cell division in the apical meristems and the cambium through interactions with auxins.

Question 19

How to cytokinins work

Answer 19

Promote lateral bud development, which can overcome, apical dominance if the leading shoots in removed or damaged.
Works synergistically with ethene in the abscission of leaves, flowers and fruits

Question 20

What is synergy and antagonism?

Answer 20

When plant hormones work in interaction with other substances, means that very fine control over the responses of the plant can be achieved.
If they work together, they complement each other, called synergy, like auxin and gibberellins
If they have opposing effects, they balance will determine the response of the plant.

Question 21

What is apical dominance

Answer 21

The balance between auxin and cytokinins is very important in overall development of the plant. Maintenance of apical dominance is main importance
One leading shoot grows bigger and faster than the other, and growth of all other lateral buds is inhibited, as a result of high auxin, first shoot emerges. The auxin acts antaginositcally with cytokinins which stimulates the development in lateral buds.
First shoot grows away and inhibition of auxin is reduced and ctuokinin becomes dominant.

Question 22

What are the sensory systems in plants?

Answer 22

Seeds grown if exposed to light, but only red light. If exposed o far red light, won’t germinate. It’s the last light it’s exposed to that determines if it grows or not. This is called phytochrome.

Question 23

What are phytochromes?

Answer 23

Plants make number of phytochromes, but all respond to light in same way.
When one form of the pigment absorbed light, it is converted reversibly into the other form. As a seed breaks through soil and exposed to red light, it makes far red light.
The length of time it takes to convert depends on the light intensity.

Question 24

What is the most stable light for plants?

Answer 24

Red light is the more stable pigment

Question 25

How is the balance of the two pigments affected in phytochromes

Answer 25

Affected by varying periods of light and dark.
Normal sunlight, contains more red light, therefore more far red light in the plant.
When night, it converts all the far red into red light. Used to explain the germination not lettuce seeds.

Question 26

What do phytochromes enable the plant to respond?

Answer 26

Respond to environmental cues such as change in day length

Question 27

Hat are short day long day and natural day plants.

Answer 27

Short day- days are short and nights are long
Long day - days are long and nights are short
Day neutral- unaffected by length of day. Usually in tropical regions

Question 28

How are signals received in a plant?

Answer 28

All research on photoperiodism points towards involvement of phytochromes in the sensitivity of flowing pattern of plants to the photoperiod.
Caused by disturbing the dark epriods.
Red light inhibits flowing of short day plants, but if red light is followed by far red, inhibition is lifted.

Question 29

What happens to short day plants when lack of light?

Answer 29

Active molecules far red lighter inhibits flowing and lack of it allows flowering. Long epriods of darkness, levels of far red fall as it converted to red knight. Allows flowering

Question 30

What happens to long day plants with light?

Answer 30

High levels of far red light stimulates flowers, the nights are short so little far red is converted, therefore stimulates flowering.

Question 31

What happens to day neutral plants with light

Answer 31

Levels of far red and red light are similar all year around, so even in temperate regions, Rhea don’t reasons to change in day length.

Question 32

What is photomorphogenesis?

Answer 32

Process by which the form of develop,end of a plant is controlled by the levels of and type of light

Question 33

What is Florigen?

Answer 33

Hypothetical plant hormone which is involved in the photoperiodic response.

Question 34

What happens to plants when the grow in the shade or dark?

Answer 34

They become etiolated. They grow rapidly, using up their food reserves in attempt to reach the light,
As a result, the plants are thin, tall with fragile stems, long internodes and small yellowish leaves

Question 35

What are the characteristics of etiolation?

Answer 35

Rapid stem lengthening but little thickening
Relatively little root growth
No leaf growth
No chlorophyll

Question 36

What changes when a new shoot breaks though the surface of the soil into the light during etiolation?

Answer 36

The elongation of the stem slows down
The stem straightens
The cotyledons open
The chlorophyll forms and seedlings begin to germinate

Question 37

How is the changes of photomorphogenesis Controlled?

Answer 37

By phytochrome interconversion.
In the seed there is plenty of red light, but no far red light, without far red, the internodes grow but the leaves don’t and the chlorophyll doesn’t form. Move plant is exposed to levels of red light, it is rapidly converted into far red light and so stops growth in the internodes. Stimulates lead development.

Question 38

How does the seed grow before out of the soil?

Answer 38

These changes happen before seed breaks through soil, as little light penetrates surface.

Question 39

How can phytochrome be used as a transcription factor?

Answer 39

Far red light acts as a transcription factor, involved in switching genes on and off in the nuclei of the plant cells.

Question 40

What is green fluorescent protein?

Answer 40

The recombinant DNA linking the genes for production of phytochrome to a gene for the production of green fluorescent protein GFP. By inserting these hybrid genes into plant cells, scientists produce plants with Fluorescent phytochrome.

Question 41

What happens to fluorescent seedlings if kept in the dark?

Answer 41

Fluorescence linked to the inactive red light was spread evenly through cytoplasm. When seedlings exposed to red light, ther Fred converting into to far red, scientists observed the fluorescence moved into the nucleus.

Question 42

Why does the fluorescence move into the nucleus?

Answer 42

When red light is converted to far red in the reserve of light, it moves into the nucleus though pores in the nuclear membrane. It binds to a nuclear portion known as phytochrome-interacting factor 3, which is a transcription factor. It only bonds to far red and not red light, therefore only activates gene transcription and the formation of mRNA when bound to far red