Plants Flashcards
Explain how the action of guard cells allows the plant to balance CO2 uptake with control over water loss
- Guard cells are contain vacuoles which contain water and potassium ions.
- K+ ions move out of the vacuoles and out of the guard cells. Water follows K+ ions, moving out of the vacuoles. Guard cells shrink in size, become flaccid, and so the stoma closes.
- K+ ions move into the vacuoles. Water follows ions into vacuoles. This causes the guard cells to swell and the stoma to open.
Define transpiration. How do plants replace water lost from transpiration?
- Transpiration is the loss of water from the leaves and stems of plants.
- More water is absorbed by the roots in order to replace water lost from transpiration.
What allows transport of water?
The cohesive property of water and the structure of the xylem vessels allow transport of water under tension.
How do lignified cell walls keep the xylem vessel from collapsing?
Lignin strengthens the walls so that they can withstand very low pressures without collapse.
How does water’s polar nature keep the xylem vessel from collapsing?
Cohesion of water due to its polarity and the adhesion of water to the cell walls allows H2O to be pulled up from the xylem in a continuous stream.
How are mineral ions absorbed in the roots?
Mineral ions are absorbed by active transport. This is because, the ions are required to go against the concentration gradient in order to be absorbed and so passive transport isn’t possible.
Outline the movement of water from root hairs to the leaves.
- Water is absorbed by osmosis into the root hairs
- Water travels to the xylem through cell walls and the cytoplasm
- Water climbs the stem trough the pull of transpiration and the adhesive and cohesive properties of water
- Water leaves through stomata by transpiration and is replaced by water from the xylem
What are the effects of temperature, light, wind, and humidity on the rate of transpiration?
- Increased temperature speeds up transpiration as it warms the leaf and thus causes more water to escape.
- Increased light speeds up transpiration as it stimulates opening of the stomata.
- Increased wind increases the rate of transpiration as it removes moist layer of air protecting the lead
- Increased humidity reduces the rate of transpiration as it encourages the closing of the stomata
Define xerophyte
Plant adapted to growing and deserts and other dry habitats
Describe three physical adaptations of xerophytes to minimize water loss
- rapid uptake of H2O
- Reducing water lost from transpiration
- storing H2O in leaves
Describe two life-cycle adaptations of xerophytes
- short life-cycles
- remain dormant as embryos
Describe how CAM plant metabolism is an adaptation to preventing water loss in xerophytes.
Open stomata at night. CO2 released at night.
Where is phloem tissue found?
Throughout plants, including stems, roots, and leaves
Describe the structure of sieve tubes
They make up phloem.
- composed of columns of specialized cells called sieve tube cells
- sieve tube cells separated by perforated walls called sieve plates
- closely associated with companion cells
What are companion cells?
- Perform many of the genetic and metabolic functions of the sieve tube cell. Done because the sieve tube needs to be as empty as possible to transport materials.
- Facilitate transport of solute from source to sieve tube and vice versa.
How does the structure of the sieve tubes relate the the function of the phloem?
- Function of phloem is to load, transport and unload carbohydrates long distances (source to sink).
- Living sieve cells depend on the organic membrane maintaining the sucrose and organic molecule concentration that has been established by active transport
- Union with companion cells.
Define translocation.
The transportation of organic solutes in the plant. Can occur in more than one direction.
