Radioactive tracer experiments

• What radioactive carbon isotope is often used in experiments?

  ^14C
• How do plants absorb radioactive carbon during photosynthesis?

  Through radioactive CO₂ exposure
• What happens to radioactive carbon after it is absorbed by plants?

  It is incorporated into glucose and sugars
• Where do labeled sucrose and organic compounds move in the plant?

  Through the phloem
• What is the process of collecting samples from the plant after labeling?

  • Allow time for labeled substances to move
  • Collect thin slices of plant tissue (e.g., stems, leaves)
  • Place tissues on X-ray film or photographic paper
  • Detect radioactivity in the tissue
• What is the purpose of placing tissue slices on X-ray film?

  To detect radioactivity in the tissue
• What occurs during autoradiography with the tissue slices?

  • Tissue slices are placed on X-ray film
  • Film is developed to show darkened areas
  • Dark spots indicate presence of radioactive substances
• What do the position and intensity of dark spots in autoradiography indicate?

  Where radioactive sugars have accumulated
• What does the radioactive label demonstrate about sugar movement in plants?

  It supports pressure-driven mass flow in phloem
• How can researchers compare sugar movement in plants?

  • Compare samples from source (leaves)
  • Compare samples from sink areas (roots, fruits)
  • Show active loading of sugars into phloem
• What creates high pressure in the phloem during sugar transport?

  Active loading of sugars at the source
• What do autoradiographs allow researchers to observe?

  • Movement of radioactive substances
  • Accumulation of sugars in the phloem
  • Confirmation of mass flow hypothesis
• What are the key findings from radioactive autoradiography supporting mass flow?

  • Movement of labeled sugars from source to sink
  • Higher concentration of sugars at the source
  • Unidirectional flow from source to sink
• What supports the idea of pressure differences in sugar transport?

  Higher sugar concentration at the source
• How does autoradiography demonstrate the direction of flow in phloem?

  By showing flow from source to sink
• What concept does the flow of substances in the phloem support?

  The concept of unidirectional flow