Plant Response: Investigating Tropism Flashcards
What is geotropism?
A directional growth response to gravity.
What is phototropism?
A directional growth response to light.
Where in plants does growth occur ad why?
The cell wall of a plant cell limits it’s ability to divide and expand. Growth only happens in particular places in the plant where there are groups of immature cells that are still capable of dividing, called meristems.
Where are apical meristems found and what do they do?
At the tips or the apices (singular: apex) of roots and shoots, and are responsible for the roots and shoots getting longer.
Where are lateral bud meristems found and what do they do?
Lateral bud meristems are found in the buds. These can give rise to side shoots.
Where are lateral meristems found and what are they responsible for doing?
Lateral meristems form a cylinder near the outside of roots and shoots and are responsible for the roots and shoots getting wider.
Where are the intercalary meristems located and what do they do?
They are located between the nodes, where the leaves and buds branch of the stem. Growth between the nodes is responsible for the shoot getting longer.
How can you test phototropism?
By placing an experiment plant and a test plant in different settings. The control plant will be placed in an environment where light is shone on all sides. The experiment plant has light shone on it from only one direction.
Why does a plant bend towards the light?
Because the shady side has elongated more than the illuminated side.
How do you investigate responses to geotropism?
Using a machine called a klinostat a plant is spun constantly at a low speed so that gravity has no effect, this is the control plant. With the experimental plant the klinostat is turned off so that gravity is applied to only one side. In this plant the root bends downwards because the upper side of the root has elongated more than the underside.
What needs to happen for phototropism to occur? How was this tested?
Water and/or solutes need to be able to travel backwards from shoot tip. A permeable gelatine block was inserted behind the shoot tip, the shoot still showed positive tropism. An impermeable mica block was inserted behind the shoot and phototropism was unable to happen.
What was the experiment to confirm the role of the shoot tip in producing a chemical messenger that controls phototrophic responses?
The shoot tip is placed on an agar block. A chemical, later identified as auxin, diffuses from the shoot tip into the agar. Agar block containing auxin stimulates growth. Offset blocks containing auxin stimulate curved growth. Blocks containing no auxin had no effect.
Where are auxins produced?
At the apex of the shoot.
Where do the auxins travel to cause elongation?
To the cells in the zone of elongation.
Why does the plant shoot grow towards the light?
The auxins in the plant move to the shady side of the plant. This causes elongation of the shaded area.
