Transport in plants Flashcards
What is the function of xylem?
transport of water and mineral ions, and support (transports up from roots to leaves)
What is the function of phloem?
transport of sucrose and amino acids (transports in all directions)
What is the function of phloem?
transport of sucrose and amino acids (transports in all directions)
Where is xylem and phloem in vascular bundle?
cells on top or the bigger cells are xylem and cells on bottom or smaller cells are phloem
What are the adaptations of xylem vessels?
- Cells joined end to end withno cross wallsto form a long continuous tube
- Cells have no cell contents
- Thick cell walls that are strengthened by lignin
What are root hair cells and what are their function?
- Root hair cells are the ones that have finger-like projections coming out of them
- They grow between soil particles and absorb water and minerals from the soil
- Water enters the root hair cells byosmosis
- The large surface area of root hairs increases the uptake of water and mineral ions because it increases the rate of osmosis/diffusion
What is the path of water in a plant?
Water moves through a root hair by osmosis. It then travels by osmosis through the cortex, from cell to cell, until eventually it reaches the xylem vessels in the middle of the root. These transport it all the way up through stem and into the mesophyll layer of leaves and evaporates out through stomata into the atmosphere
How can you experiment transport in plants?
- The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well)
- After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery
- If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water, showing that the water is being carried in specific vessels through the stem - these are thexylem vessels
What is transpiration?
the loss of water vapour from leaves
Why does transpiration happen?
Transpiration happens because water evaporates from the surfaces of the mesophyll cells into the air spaces and then diffuses out of the leaves through the stomata as water vapour
How does the large surface area in the spongey mesophyll layer increase transpiration?
The many interconnecting air spaces between the mesophyll cells and the stomata creates a large internal surface area. This increases the rate of transpiration as it allows water vapour to move freely and easily meaning evaporation can happen rapidly when stomata are open. The size and number of stomata on a leaf’s surface also affect this process. A larger number of stomata or larger stomata can potentially increase the rate of water vapour loss due to increased opportunities for diffusion.
Experiment to test effects on transpiration
To measure the transpiration rate, you’ll need a potometer. A potometer consists of:
- A container of water
- A capillary tube
- A scale
- Rubber tubing (The rubber tubing connects the capillary tube and the plant)
The scale is used to measure how far the bubble travels in the capillary tube – due to transpiration the transpiration pull created by the plant, as the water column is sucked up, the bubble moves up.
There are two measures of transpiration rate you can calculate using this method:
- Distance travelled by bubble per unit time (your unit will be m/s or m/min or cm/min, depending on the units of distance and time that you use.)
- The volume of water transpired per minute (your unit will be ml/min or l/min (litres/minute)). This is a more accurate measure of the transpiration rate than the first one.
To calculate 1, simply measure the distance travelled by the bubble in a known length of time. Then divide the distance travelled by the time taken.
To calculate 2, measure the distance travelled by the bubble in a known length of time. Measure the diameter of the capillary tube, and then divide it in half to calculate the radius. Calculate the cross-sectional area of the capillary tube using , where is the radius. Multiply the cross-sectional area into the distance travelled by the bubble to get the volume transpired. Divide volume transpired by the time taken, to get the rate of transpiration. Note: some potometers come with a volume scale, so you don’t need to go through all of the described steps to calculate the volume of water transpired.
Temperature and transpiration correlation
- To investigate the effect of varying temperature on transpiration, conduct the experiment under different temperature conditions (cold room and warm room, or next to a heater and far away from the heater).
- The higher the temperature, the greater the transpiration rate because water vapour molecules will have more kinetic energy and hence move out of the leaf faster. This happens until the plant is transpiring at its maximum rate. Then the transpiration rate remains at its maximum. Hypothetically, if you increased the temperature high enough that you damaged the plant, the transpiration rate would fall back down to zero.
Wind speed and transpiration correlation
- To investigate the effect of varying wind speeds on transpiration, conduct the experiment using an electric fan to mimic different wind speeds
- The faster the wind speed, the higher the rate of transpiration because good airflow removes water vapour from the air surrounding the leaf which sets up a concentration gradient between the leaf and the air, increasing water loss.
Humidity and transpiration correlation
- To investigate the effect of varying humidity on transpiration, conduct the experiment in: A room with a dehumidifier, a normal room and spray water in a plastic bag and wrap the bag around the plant.
- The higher the humidity of the air outside the leaf relative to the air inside the leaf, the lower the transpiration rate. This is because water usually diffuses down a concentration gradient. However, if the air outside is already saturated with water, the concentration gradient is weaker so less water is lost.
