Unit 3, phloem and translocation Flashcards
What is translocation?
Mass transport of organic substances in plants
What is the function of the leaves?
- photosynthesis takes place here
- produce glucose
What does the phloem tissue include?
Sieve tube elements
Companion cell
What do the sieve tube elements have?
- living cells
- hollow, to reduce resistance for flowing organic substances , this is due to few organelles
- no nucleus
- thin walls allow water to pass through
What does the companion cell do?
- provide ATP which is required for active transport
-has many mitochondria to supply atp
What does the source cell do?
- it is the photosynthesising cell
- it produces glucose/sucrose which is water soluble
- due to being water soluble it lowers the water potential, causing water to enter source cell by osmosis, this increases the hydrostatic pressure
What does the sink cell do?
- the respiring cell which is using up the glucose/sucrose
- by using up the glucose/ sucrose this increases the water potential in the sink cell, causing water to leave sink by osmosis, which causes a decrease in the hydrostatic pressure
Why is the solution forced towards the sink cell?
Due to the source cell having a higher hydrostatic pressure than the sink cell, the solution is forced towards the sink cell
What is the process of translocation?
1) - photosynthesis occurs in the source cell, in the leaf and chloroplasts, creating organic substance, glucose/ sucrose
- organic substance is actively transported out of the the source cell, into the sieve tube, using the atp in the companion cell
2) due to the increasing of organic substance in the sieve tube, this lowers the water potential, causing water from the xylem to enter sieve tube by osmosis, this increases the hydrostatic pressure, forcing liquid to sink cell
3)
- the sucrose from sieve is actively transported into the sink cell, using the atp in the companion cell,
- at the sink cell the organic substance is used in respiration or stored as insoluble starch
-these sink cells now have low sucrose content so sucrose is actively transported into the sink cells from the sieve tubes, decreasing the water potential so water enters the respiring cells by osmosis and some water returns to the xylem
-this causes lower water potential at the sieve tube by the sink cell, decreasing the hydrostatic pressure
How can a tracer be used to investigate translocation?
- a plant is isolated and only given acces to carbon dioxide 14 that is radioactively labelled.
- this radioactive carbon dioxide is used in photosynthesis, creating glucose/sucrose that contains radioactively labelled carbon
- thin slices from the stem are cut out then place on X-ray film
- if the xray film goes black then it has detected radioactively labelled carbon, showing that that is the phloem
How can the ringing experiment be carried out to investigate translocation?
- ring of bark and phloem Is peeled off the tree trunk
- removing the phloem causes a liquid swelling above the ring of removed section, this swelling contains glucose/sucrose
- proving the phloem transports sugars
What is the photosynthesis equation ?
Carbon + water = glucose + oxygen
How is there a mass flow of sucrose solution down the hydrostatic gradient in the sieve tubes?
Due to the water entering the sieve tubes elements at the source and leaving at the sink, there is high hydrostatic pressure at the source and low hydrostatic pressure at the sink.
How is the organic substance actively transported over companion cell?
- by the proton pump
- Hydrogen ions are actively transported out of the sieve tube element
- via co transport the hydrogen ions go down the concentration gradient and carry the organic substances against their concentration gradient
- this creates electro chemical gradient
What does appopastic and symploplastic mean?
- move around
- move through
