Investigating transport in Plants Flashcards
What is the structure of a woody stem in relation to the phloem and xylem?
Woody stems have an outer protective layer of bark, inside of which is a layer of phloem that extends around the stem. The xylem is located inside the phloem
What is a ringing experiment?
A ringing experiment involves removing a section of the outer layers (protective layers and phloem) around the complete circumference of a woody stem while it remains attached to the plant
What happens to the stem above the removed ring in a ringing experiment?
The region above the ring swells due to the accumulation of sugars and other dissolved organic substances in the phloem
What conclusion is drawn from ringing experiments regarding sugar transport in plants?
The phloem is responsible for translocating sugars, as their accumulation above the ring and the death of tissues below indicate an interruption in sugar flow
What happens to the tissues below the removed ring in a ringing experiment?
Non - photosynthetic tissues below the ring wither and die due to the lack of sugars for respiration and growth
Why does the ringing experiment show that xylem is not responsible for translocation of sugars?
The xylem remains intact in the experiment, meaning if it were responsible for sugar transport, sugars would still reach tissues below the ring, but they do not
How is carbon - 14 introduced into a plant in tracer experiments?
As radioactive carbon dioxide, which the plant uses in photosynthesis to produce radioactive sugars
What are radioactive isotopes used for in plant experiments?
They are used to trace the movement of substances, such as sugars, within a plant
Which radioactive isotopes is commonly used to trace sugar movement in plants?
Carbon - 14, which is incorporated into sugars during photosynthesis
What technique is used to track the movement of radioactive sugars in plants?
Autoradiography - placing thin cross - sections of the plant stem on X - ray film
How does autoradiography show where sugars have been transported?
The X - ray film blackens in areas where it has been exposed to radiation from carbon - 14 labelled sugars
What does autoradiography reveal about sugar transport in plants?
The blackened areas correspond to the phloem, showing that phloem is responsible for translocating sugars
Why does the experiment support the conclusion that phloem transports sugars?
Other tissues do not cause blackening on the X - ray film, indicating they do not transport sugars
What happens when the phloem is cut, and what does this indicate?
A solution of organic molecules flows out, showing that phloem transports organic substances like sugars
How does radioactive carbon dioxide provide evidence for translocation in the phloem?
Plants exposed to carbon - 14 dioxide show radioactive carbon in the phloem after a short time, proving that sugars are made in photosynthesis are transported through the phloem
