Biology 2.4.3 Flashcards
Why does Water Travel up the Xylem from the Roots into the Leaves of the Plant?
To Replace the Water that has been Lost due to Transpiration.
What is ‘Transpiration’?
The Loss of Water Vapour from Plant Leaves by Evaporation of Water at the Surfaces of the Mesophyll Cells followed by Diffusion of Water Vapour through the Stomata.
Explain the Role of Lignin in the Xylem. (3)
-A Substance called Lignin is Deposited in the Cell Walls which Causes the Xylem Cells to Die.
-These Cells then become Hollow, as they lost all their Organelles & Cytoplasm. They join end-to-end to Form a Continuous Tube for Water & Mineral Ions to Travel through from the Roots.
-Lignin Strengthens the Plant to help it Withstand the Pressure of the Water Movement.
Movement in the Xylem only takes place in ___ Direction; from the ___ upwards to the ___.
1, Roots, Leaves.
Explain the Effect of the Condition ‘Air Movement’ on the Rate of Transpiration.
Good Airflow Removes Water Vapour from the Air Surrounding the Leaf, which sets up a Concentration Gradient between the Leaf & the Air, Increasing Water Loss.
Explain the Effect of the Condition ‘Humidity’ on the Rate of Transpiration.
Humidity is a Measure of Moisture (Water Vapour) in the Air; when the Air is Saturated with Water Vapour, the Concentration Gradient is Weaker, so Less Water is Lost.
Explain the Effect of the Condition ‘Light Intensity’ on the Rate of Transpiration.
Guard Cells are Responsive to Light Intensity; when it is High, they are Turgid, & the Stomata Open, allowing Water to be Lost.
Explain the Effect of the Condition ‘Temperature’ on the Rate of Transpiration.
At Higher Temperatures, Particles have more Kinetic Energy, so Transpiration occurs at a Faster Rate, as Water Molecules Evaporate from the Mesophyll & Diffuse away Faster than at Lower Temperatures.
