Mass Transport In-plants

Question 1

What is the cohesion tension theory?

Answer 1

Movement of water up the plant caused by the evaporation of water through the stomata. This lowers the water potential in the mesophyll of the leaf. This causes a transpiration pull. Between the water molecules there are hydrogen bonds causing cohesion allowing for a continuouswater column pulling the walls of the xylem in.

Question 2

What are the features of a xylem?

Answer 2

Long hollow tube allows for a continuous water column, no organelles allow for no chemical reactions to slow water movement no obstructions, covered in lignin which provides structural support and allows it to be waterproof, pits in walls for lateral movement.

Question 3

What sort of oathway goes through the cell wall?

Answer 3

Apoplastic pathway

Question 4

What type of pathway goes through the cytoplasm?

Answer 4

Symplastic pathway

Question 5

What factors can affect transpiration?

Answer 5

Humidity cuases less evaporation through the stomatat as there is a no concentration gradient, light as potassium moves into guard cells stomata open, temparature causes more or less evaporation and kinetic energy, wind carries water molecules away giving it a steeper concentration gradient

Question 6

What are the features of the phloem?

Answer 6

Very few organelles give more space for movement, sieve plates for structural support, companion cells provide nutrients and has lots of mitochondria.

Question 7

What are arguments for mfh?

Answer 7

Companion cells posses mitochondria and ATP, concentration of sucrose is higher in source than in sink, there is a high pressure within sieve tubes shown by sap being released.

Question 8

What are arguments against mfh?

Answer 8

Not all solutes move at same speed, function of sieve plates is unclear as they could hinder mass flow.

Question 9

What is the process of translocation?

Answer 9

At the source eg leaf sugars are moved against the concentration gradient via active transport into the sieve tube element. This decreases water potential as sugars in the phloem make the environment very concentrated so water moves in from xylem via osmosis, that creates high hydrostatic pressure . In the sink sugars move from phloem to companion cell and is stored as starch, this lowers concentration of sugar and increases the water potential