Transport in plants- Xylem Flashcards
What do xylem tissue transport?
-Water and mineral ions in solution
-These solutions move up the plant from the roots to the leaves
What do phloem tissue transport?
-Organic substances like sugars both up and down the plant.
What are xylem vessels and what do they do?
-Transports the water and ions
-Very long, tube-like structures formed from dead cells (vessel elements) joined end to end- no end walls in these cells, making an uninterrupted tube that allows water to pass up through the middle easily
How do water move up a plant-Cohesion-tension theory of water transport?
1)Water evaporates from the leaves at the top of xylem-transpiration
2)This creates tension, which pulls more water into the leaf
3)Water molecules are cohesive so when some are pulled into the leaf others follow- whole column of water in the xylem, from the leaves down to the roots, moves upwards
4)Water enters the stem through the roots
What is transpiration?
-Evaporation of water
-Water evaporates from the moist cell walls and accumulates in the spaces between cells in the leaf
-When stomata open, it moves out of the leaf down the conc gradient
Factors affecting the transpiration rate?
-Light
-Temperature
-humidity
-Wind
How do light affects the transpiration rate?
-Lighter it is the faster the transpiration rate. Stomata open when it gets light to let in CO2 for photosynthesis. When its dark, stomata usually closed
How do temperature affects the transpiration rate?
-Higher the temperature the faster the the transpiration rate. Warmer molecules have more energy so they evaporate from the cells inside the leaf faster-increases the conc gradient between the inside and outside of the leaf, making water to diffuse out of the leaf faster.
How do humidity affects the transpiration rate?
-The lower the humidity the faster the transpiration rate- if the air around the plant is dry, the conc gradient between the air and the leaf is increased, which increases transpiration
How do wind affects the transpiration rate?
-The windier it is the faster the transpiration rate. Lots of air movement blows away the water molecules around the stomata - increases the conc gradient, increases transpiration
Why do we use a potometer?
Measures water uptake by a plant and it is assumed that water uptake by the plant is directly related to water loss by the leaves
How to dissect plants?
1)Use a scalpel to cut a cross-section of the stem- as thinly as possible
2)Use tweezers to gently place the cut sections in water until you come to use them-stop them from drying out
3)Transfer the each section to a dish containing a stain (TBO) and leave for one minute. TBO stains the lignin in the walls of the xylem vessels blue-green-let you see the position of the xylem vessels and examine their structure.
4)Rinse off the sections in water and mount each one onto a slide
