Transport in Plants and Plant Control Systems

This set of vocabulary flashcards covers the mechanisms of water and sugar transport in plants, specifically focusing on cohesion, adhesion, root pressure, and the pressure-flow theory, as well as plant growth responses like phototropism and gravitropism.

Redwood tree

The tallest tree recorded in California, measuring over $115\,m$ or equal to a 42-storey building.

Polarity of water

The property of water where the hydrogen end is slightly positive and the oxygen end is slightly negative, making it a polar molecule.

Cohesion

The force where water molecules are attracted to each other, allowing one molecule to pull others along as it rises up the xylem tube.

Adhesion

The force that causes water molecules to stick to other substances, such as the walls of the xylem.

Root pressure

The pressure created as water moves into roots following the active transport of minerals, which makes the root cells hypertonic to their surroundings.

Transpirational pull

The pulling of water molecules up the plant created by the vacuum that occurs when water evaporates out of the leaves through transpiration.

Source

The part of the plant where sugar is produced, specifically the leaves.

Sink

The location in a plant where sugar must move to be used or stored.

Pressure-flow theory

The concept describing the movement of materials in and out of the phloem.

Stimuli

A change in the environment that creates a response within an organism.

Phototropism

The tendency of a plant to grow toward the light (photo = light; tropism = response to stimuli).

Positive phototropism

A response seen in plant stems where they grow toward the light.

Negative phototropism

A response seen in plant roots where they grow away from the light.

Darwin’s Experiment

An investigation by Charles and Francis Darwin involving five trials to determine that the tip of the plant is responsible for positive phototropism.

Opaque cap

A non-transparent covering used in Darwin's Trial 3 to test if covering the tip prevented the plant from bending toward light.

Boysen-Jensen’s experiment

A 1913 investigation that hypothesized the communication between the plant tip and seedling occurs through diffusion, as the signal passed through gelatin but not mica.

Area of elongation

The part of the plant stem that bends toward light because the cells on the dark side become longer.

Auxin

A plant hormone isolated by F.W. Went in 1926 that is produced in the plant and causes cells to elongate upon contact.

Gravitropism

The direction of plant growth in response to gravity, often relying on heavy starch particles as indicators.

Negative gravitropism

Growth against gravity, which is exhibited by plant stems.

Positive gravitropism

Growth downward with gravity, which is exhibited by plant roots.

Response to touch

A control system seen in plants like the pea plant, which anchors itself to surfaces, or the Venus fly trap, which closes on insects.

Response to light availability

A control system such as that in Poinsettias, which bloom in response to long periods of darkness.