Transport in flowering plants flashcards

Topic 7: Transport in flowering plants

Transpiration

The loss of water vapour from leaves.

Translocation

The movement of sucrose and amino acids in the phloem from sources to sinks.

How root hair cells take up water and mineral ions

A long, thin extension gives a large surface area. Water enters by osmosis; mineral ions enter by active transport, using energy from respiration (many mitochondria).

Pathway of water through a plant

Root hair cells → root cortex cells → xylem → mesophyll cells. Water then evaporates into the air spaces and diffuses out through the stomata.

Effects of humidity and light intensity on transpiration

Higher humidity: slower, because there is a smaller water vapour concentration gradient. Higher light intensity: faster, because stomata open wider.

Effects of wind speed and temperature on transpiration

Both increase the rate. Wind removes water vapour near the leaf, keeping the gradient steep. Higher temperature gives more kinetic energy, so faster evaporation and diffusion.

How does transpiration pull move water up the xylem?

Water vapour lost from the leaves is replaced from the xylem, creating a pull on the water column. Forces of attraction between water molecules hold the column together, so it is drawn up from the roots.

Wilting

Drooping of leaves and soft stems when water loss exceeds water uptake: cells lose water, become flaccid and lose turgor pressure.

What does a potometer actually measure?

Water uptake (distance an air bubble moves in a set time), used as an estimate of water loss by transpiration.

Source and sink (translocation)

Source: a part that produces or releases sucrose and amino acids, e.g. a photosynthesising leaf. Sink: a part that uses or stores them, e.g. roots, growing tips, fruits, seeds.

Position of xylem and phloem in a non-woody dicot root and stem

Root: xylem in the centre in a star shape, phloem between its arms. Stem: bundles in a ring; xylem on the inner side, phloem on the outer side of each bundle.

Features of xylem vessels and their functions

Thick lignified walls: strength and support. No cell contents: unobstructed water flow. Joined end to end with no cross walls: a continuous tube. Functions: transport of water and mineral ions, and support.