active loading

• where does translocation occur?

  The phloem
• What is translocation?

  Translocation is the movement of assimilates throughout the plant.
• what are assimilates?

  Assimilates are substances made by the plant, using substances absorbed from the environment. These include sugars and amino acids.
• What is the part of the plant that loads assimilates in the phloem sieve called?

  The source
• What is the part of the plant that removes assimilates from the phloem sieve tubes called?

  The sink
• Sucrose is loaded into the sieve tube by an active process. It is active because it involves the use of energy in the companion cells. The energy is used to actively transport Hydrogen ions out of the companion cells.
• What does the active transport of hydrogen ions do to the concentration outside of the sieve tube element cells, and the companion cells- what does this result in?

  The active transport of hydrogen ions increases the concentration outside of the sieve tube element cells, and decreases the concentration inside of the companion cells. This creates a concentration gradient.
• How do hydrogen ions diffuse back into companion cells?

  Hydrogen ions travel through co transporter proteins in the membranes. These proteins will only allow the movement of hydrogen ions back into the cell if they are accompanied by sucrose molecules.
• Why is the process of how hydrogen ions move back into the companion cell called secondary active transport?

  It is also called secondary active transport because it results from the active transport of hydrogen ions out of the cell, and moves the sucrose against its concentration gradient. As the concentration In the companion cell increases, it can diffuse through the plasmodesmata into the sieve tube.