14 Ass 7 pt 2 Plant transport Flashcards
As the young leaf matures, the quantity of sugar taken up by the leaf decreases to zero, but the need for water increases.
Suggest and explain why the quantity of sugar taken up by the developing leaf decreases to zero over time, but the need for water increases. 4
The sugar uptake decreases because as the leaf matures from sink to source,
it produces sugar which is transported out of the leaf to the rest of the plant through photosynthesis
the need for water increases due to increased transpiration
and the need to maintain turgidity
What types of sugars are transported as part of phloem sap?
Monosaccharides and disaccharides
Define the term disaccharide
A sugar made of 2 monosaccharides joined together
Define the term polysaccharide and give 3 examples 4
A polymer made of more than 2 sugar monomers and is not a sugar.
starch
glycogen
cellulose
Q22 b read context & draw diagram
See memo
What causes the mass flow of phloem sap from source to sink?
A pressure gradient in sieve tubes
What happens to cause the pressure gradient in plants that causes mass flow?
A decrease in water potential & increase in hydrostatic pressure in phloem sap
What causes a decrease in water potential of phloem sap during mass flow?
High sucrose concentration from loading of assimilates into sieve tube elements
What causes an increase in hydrostatic pressure of phloem sap during mass flow?
large volume of water moving in and out of phloem tubes by osmosis
Define the term transpiration. 3
When water is absorbed through roots
before traveling up the plant
and being released as water vapor through the stomata in the leaves
Q 23 b) use table 5.1 to calculate the mean rate of movement of the bubble
(12.5+12+11.5)/3 = 36/3 =12
It’s in 10 minutes and we’re calculating how fast it moves per minute, so 12/10=1.2
1.2 mm min^-1
Explain why air movement increases the rate of transpiration
The water potential gradient is steeper from there being less water in the air around the plant
Explain how water moves up through a xylem vessel in the stem of the plant 5
Water moving out of the leaf creates tension in the xylem vessel
this allows water to move up, down the water potential gradient
Water molecules are attracted to each other, through hydrogen bonding, forming cohesion
Adhesion is created from water being attracted to polar molecules in cellulose and lignin
This creates a continuous column of water
Define adhesion
Water molecules sticking to cellulose molecules in lining of the xylem vessel
Q24 b read context and see fig. The general pattern of results in Fig. 4.1 is the same for the three Barlinka
grapevines. Explain why the general pattern of results is the same. 3
During the day, the stomata are open
so the rate of transpiration is higher
The daytime is also warmer