Plants do not use all the waters they absorb ? most of it is lost during transpiration. Why then plants absorb more water than they need
Answers
Answer:
POP-UP - Did you know that an acre of corn can transpire up to 400,000 gallons of water
in one growing season?
POP-UP – Because water molecules stick together so well due to hydrogen bonding,
water can be pulled up trees 100 meters tall (that’s over 300 feet or three times the height
of most shade trees!).
What is transpiration? In actively growing plants, water is continuously evaporating
from the surface of leaf cells exposed to air. This water is replaced by additional
absorption of water from the soil. Liquid water extends through the plant from the soil
water to the leaf cell surfaces where it is converted from a liquid into a gas through the
process of evaporation. The cohesive properties of water (hydrogen bonding between
adjacent water molecules) allow the column of water to be ‘pulled’ up through the plant
as water molecules are evaporating at the leaf surface. This process has been termed the
Cohesion Theory of Sap Ascent in plants.
Why do plants transpire?
Evaporative cooling: As water evaporates or converts from a liquid to a gas at
the leaf cell and atmosphere interface, energy is released. This exothermic
process uses energy to break the strong hydrogen bonds between liquid water
molecules; the energy used to do so is taken from the leaf and given to the water
molecules that have converted to highly energetic gas molecules. These gas
molecules and their associated energy are released into the atmosphere, cooling
the plant.
Accessing nutrients from the soil: The water that enters the root contains
dissolved nutrients vital to plant growth. It is thought that transpiration enhances
nutrient uptake into plants.
Carbon dioxide entry: When a plant is transpiring, its stomata are open,
allowing gas exchange between the atmosphere and the leaf. Open stomata allow
water vapor to leave the leaf but also allow carbon dioxide (CO2) to enter.
Carbon dioxide is needed for photosynthesis to operate. Unfortunately, much
more water leaves the leaf than CO2 enters for three reasons:
1) H2O molecules are smaller than CO2 molecules and so they move to
their destination faster.
2) CO2 is only about 0.036% of the atmosphere (and rising!) so the
gradient for its entry into the plant is much smaller than the gradient for
H2O moving from a hydrated leaf into a dry atmosphere.
3) CO2 has a much longer distance to travel to reach its destination in the
chloroplast from the atmosphere compared to H2O which only has to
move from the leaf cell surface to the atmosphere.
This disproportionate exchange of CO2 and H2O leads to a paradox. The larger
the stomatal opening, the easier it is for carbon dioxide to enter the leaf to drive
photosynthesis; however, this large opening will also allow the leaf to lose large
quantities of water and face the risk of dehydration or water-deficit stress. Plants
Answer:
heya!!
Explanation:
read your question properly!!!
it has the answer!!
it needs more water so that it can loose some in transpiration!!
hope it helps!!