8. Transport in Plants Flashcards
State the functions of xylem and phloem
- Xylem: transport of water and mineral ions, and support
- Phloem – transport of sucrose and amino acids
Relate the structure of xylem vessels to their function
- No cross walls: Form a long continuous tube
- Cell are dead without cell contents: Allows free passage of water
- Outer walls are thickened with lignin: Strengthens the tubes which helps support the plant
State the function of root hair cells
Absorb water and mineral ions such as nitrate and magnesium ions from the soil
State what the large surface of root hairs increases
The large surface area of root hairs increases the uptake of water and mineral ions
Outline the pathway taken by water through the root, stem and leaf
root hair cell → root cortex cells → xylem → leaf mesophyll cells
Investigate, using a suitable stain, the pathway of water through the above-ground parts of a plant
- Put plant like celery in beakers containing different color of food dyes
- After a few hours, the leaves changes to the same color as the dye proving its uptake of the water
- Cut/cross section of the celery stalk will show stains from the food dye, showing that water is being carried by the xylem vessels
Describe transpiration fully
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
Describe the effects of variation of temperature and wind speed on transpiration rate
- Temperature ↑, Rate of Transpiration ↑
- Wind Speed ↑, Rate of Transpiration ↑
Explain water vapour loss
Evaporation (water vapour loss) takes place from the surface of spongy mesophyll cells. The large surface area is created by the many interconnecting spaces between these cells and stomata. Hence water vapour loss happens rapidly when the stomata is open (+ ↑ size and ↑ number)
Explain the mechanism by which water moves upwards in the xylem in terms of a transpiration pull
In terms of transpiration, water moves upwards in the xylem:
1. In a transpiration stream from roots to leaves, producing a ‘pulling’ tension on the water in the xylem by the leaves
2.Water molecules are attracted by cohesive forces, allowing water to be pulled up the plant in a continuous column
Explain the effects on the rate of transpiration of varying the following factors: temperature, wind speed and humidity
- Wind speed ↑, ROT ↑: Higher airflow removes water vapour from the air surrounding the leaf. Setting up a concentration gradient between the leaf and the air; as water goes to an area of lower concentration (air).
- Humidity ↑, ROT ↓: Humidity is a -measure of moisture (water vapour) in the air. When the air is saturated with moisture the concentration gradient is weaker; as the air. has a higher concentration than inside the leaf
- Temperature ↑, ROT ↑: Particles have an increase in kinetic energy. Water molecules evaporate from mesophyll cells and diffuse away at a faster rate.
Explain how and why wilting occurs
- Wilting occurs when more water evaporates from the leaves of a plant than that is available in the soil, to move into the root by osmosis
- Causing all the cells of the plant unable to support the plant with its cell walls as they aren’t full of water (resulting in flaccid leaves and collapse)
Describe translocation
The movement of sucrose and amino acids in phloem from sources to sinks
Describe sources and sinks
- Sources: Parts of plants that release sucrose or amino acids
- Sinks: Parts of plants that use or store sucrose or amino acids
Explain why some parts of a plant may act as a source and a sink at different times
Translocation depends on the stage of development or the time of the year/weather
