Water and sugar transport in plants
Chapter 37: Water and sugar transport in plants
Water moves from areas of high water potential to areas of low water potential. Water’s potential energy in plants is a combination of (1) it’s tendency to move in response to differences in solute concentration and (2) the pressure exerted on it
Plants do not expend energy to replace water that is lost to transpiration when stomata are open and photosynthesis is occurring. Instead, water moves from soil and roots to leaves long a water potential gradient. The gradient exists because water at the air0water surface in leaves in under negative pressure (tension)
The phloem, sugars are transported from “sources”- tissues that release sugars for use elsewhere – to “sinks”- tissues in which sugars are being used or stoned. Movement occurs because cells expend energy to load sucrose actively into phloem cells near source tissues. Water follows by osmosis, creating a pressure gradient that favours the movement of water and sucrose sinks
Stomata are open during the day so that gas exchange can occur between the atmosphere and the cells inside the leaf.
Water loss is a side effect of photosynthesis
The evaporation can actually be beneficial under some conditions because it cools the plant
Water potential and water movement (37.1)
Loss of water via evaporation from the aerial parts of a plant is called transpiration
Transpiration occurs whenever two conditions are met: 1) stomata are open; 2) the air surrounding leaves in drier than the air inside leaves
The second condition is met whenever atmospheric humidity is less than 100%
Water moves from roots to leaves passively – with no expenditure of ATP
The movement occurs because of differences in potential energy of water
The term Water Potential indicated the potential energy of pure water at room temperature and atmospheric pressure – water has a potential during this conditions
Water potential is denoted by ψ
Water always flows from areas of high
Water moves from areas of high water potential to areas of low water potential. Water’s potential energy in plants is a combination of (1) it’s tendency to move in response to differences in solute concentration and (2) the pressure exerted on it
Plants do not expend energy to replace water that is lost to transpiration when stomata are open and photosynthesis is occurring. Instead, water moves from soil and roots to leaves long a water potential gradient. The gradient exists because water at the air0water surface in leaves in under negative pressure (tension)
The phloem, sugars are transported from “sources”- tissues that release sugars for use elsewhere – to “sinks”- tissues in which sugars are being used or stoned. Movement occurs because cells expend energy to load sucrose actively into phloem cells near source tissues. Water follows by osmosis, creating a pressure gradient that favours the movement of water and sucrose sinks
Stomata are open during the day so that gas exchange can occur between the atmosphere and the cells inside the leaf.
Water loss is a side effect of photosynthesis
The evaporation can actually be beneficial under some conditions because it cools the plant
Water potential and water movement (37.1)
Loss of water via evaporation from the aerial parts of a plant is called transpiration
Transpiration occurs whenever two conditions are met: 1) stomata are open; 2) the air surrounding leaves in drier than the air inside leaves
The second condition is met whenever atmospheric humidity is less than 100%
Water moves from roots to leaves passively – with no expenditure of ATP
The movement occurs because of differences in potential energy of water
The term Water Potential indicated the potential energy of pure water at room temperature and atmospheric pressure – water has a potential during this conditions
Water potential is denoted by ψ
Water always flows from areas of high