Coordination And Control - Flowering Plants

Question 1

Suggest why only certain tissues in a plant will respond to a particular plant growth substance.

Answer 1

Each growth substance has a specific shape that will only bind to a specific receptor with a complementary shape on the surface membrane of particular cells.

Question 2

Which wavelength of light does sunlight contain more of, wavelength 660nm or wavelength 730nm?

What are these wavelengths called?

Answer 2

Sunlight contains more of wavelength 660nm (red light) than 730nm (far-red light)

Question 3

During daylight, what is converted to what? (Light)

Answer 3

P660 is converted to P730, which accumulates.

Question 4

Which form of light is the physiologically active form?

Answer 4

P730 - this either stimulates or inhibits flowering.

Question 5

What is crucial for flowering plants?

Answer 5

The period of continuous darkness

Question 6

How is P730 removed from a plant?

Answer 6

In darkness, P730 SLOWLY converts to P660 and so is removed during a long night (short day).

Question 7

In long-day plants, is P730 stimulatory or inhibitory?

Answer 7

Stimulatory i.e. high level of P730 is required. Short night = sufficient P730 remains to promote flowering.

Question 8

Why is the removal of P730 necessary in short-day plants?

Answer 8

P730 inhibits flowering in short-day plants, therefore a long period of continuous darkness (nighttime) is required to convert P730 back to P660, removing this inhibitory effect.

Question 9

A long-day plant normally flowers when the dark period becomes critically short. Explain what would happen if, before flowering was induced, the light period (day length) was interrupted by a short period of far-red light.

Answer 9

Far-red light would cause the rapid conversion of P730 to P660.
The level of P730 would be reduced and flowering would not occur.