transport in the phloem Flashcards
(28 cards)
What is the process that occurs on the phloem?
Translocation
What are carbohydrates transported in the form of?
Sucrose
What are lipids transported in the form of?
Fatty acids and glycerol
What are proteins transported in the form of?
Amino acids
Where are all these organic molecules produced?
Leaves
What is the leaf that produced organic molecules known as?
The source
Where are the products of photosynthesis transported to?
The sinks
What are examples of sinks?
Growing areas (young leaves and shoots), the roots, developing fruits or storage areas
What does the phloem consist of?
Sieve plates and companion cells
What are sieve elements?
They are joined end to end to form sieve tubes
What are the end walls of sieve elements called?
Sieve plates
Why is this?
They possess pores
What do mature sieve elements not possess?
A nucleus
What does the cytoplasm contain in mature sieve elements?
Few organelles
What is next to each sieve element?
Companion cells
What do companion cells contain?
Dense cytoplasm and many mitochondria
What is the main hypothesis for the method of translocation known as?
Mass flow hypothesis
What is mass flow of organic substances thought to occur down?
Hydrostatic or turgor pressure gradient
What is the first part to translocation?
In a source the rate of photosynthesis is greater than the rate of respiration
What is the second step of translocation?
Sucrose is actively transported into sieve tubes by companion cells
What does this do to the water potential?
Lowers it
What is the next step of translocation?
Water enters the sieve tubes from the xylem by osmosis
What is the next step of translocation?
A high hydrostatic pressure is created in the sieve tubes
What is the next step of translocation?
In a sink, sugars are being used in respiration for growth and storage
