Flashcards · 0610 · Topic 8

Transport in plants flashcards

19 cards on Topic 8, subtopics 8.1 to 8.4. Pick a subtopic or study them all.

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Functions of xylem and phloem: Xylem: transports water and mineral ions, and gives support. Phloem: transports sucrose and amino acids.
Position of xylem and phloem in a root: Xylem in the centre in a star or cross shape, with phloem between its arms.
Position of xylem and phloem in a stem: Vascular bundles in a ring near the edge: xylem on the inner side of each bundle, phloem on the outer side.
Structure of xylem vessels linked to functionExtended: Thick walls with lignin: strength and support. No cell contents: unobstructed water flow. Cells joined end to end with no cross walls: a long continuous tube.

Function of root hair cells, and how their shape helps: They take up water and mineral ions. The long extension gives a large surface area, increasing uptake.
Pathway of water from the soil to the leaf: Soil → root hair cells → root cortex cells → xylem → mesophyll cells.
How does water enter a root hair cell?: By osmosis.
Investigating the pathway of water with a stain: Stand a cut celery stalk in water with a dye such as methylene blue for a few hours, then cut a thin transverse section: the dye appears in a ring of spots, showing the xylem.

Transpiration: The loss of water vapour from leaves.
Where does water leave the leaf in transpiration?: Water evaporates from the surfaces of mesophyll cells into the air spaces, then water vapour diffuses out through the stomata.
Effect of temperature and wind speed on transpiration rate: Increasing either increases the rate of transpiration.
What does a potometer measure?: The rate of water uptake (from how far an air bubble moves in a set time), which is close to the rate of water loss.
Transpiration pullExtended: Water vapour lost from the leaves creates a pull that draws a continuous column of water up the xylem. The column holds together because of forces of attraction between water molecules.
Explain why transpiration is slower when humidity is highExtended: There is more water vapour in the air outside the leaf, so the concentration gradient is smaller and water vapour diffuses out through the stomata more slowly.
Why do plants wilt?Extended: Water is lost by transpiration faster than it is taken up. Cells lose water by osmosis, turgor pressure falls, cells become flaccid and no longer support the leaves and stems.

TranslocationExtended: The movement of sucrose and amino acids in the phloem from sources to sinks.
Source and sinkExtended: Source: a part of a plant that releases sucrose or amino acids. Sink: a part of a plant that uses or stores sucrose or amino acids.
Examples of sources and sinksExtended: Source: a mature photosynthesising leaf. Sinks: growing root and shoot tips, developing fruits and seeds, a storage organ being filled.
How can one part of a plant be both a source and a sink?Extended: At different times. A storage organ is a sink while it fills with starch, and a source at the start of new growth, when starch is broken down and sucrose released.