A-level Biology Chapter 7

Which statements correctly describe transport pathways in dicotyledonous plants?

• In the apoplast pathway, water does not move through plasmodesmata.

• In the symplast pathway, water does not move through intercellular spaces.

• The apoplast pathway may be blocked by the Casparian strip.

Which properties of water molecules are important in the upward flow of water through xylem?

• Water molecules are attracted to each other by hydrogen bonding.

• Water molecules are attracted to cellulose by adhesion.

• Water molecules have high cohesion in water columns.

• N/A

What is correct for a phloem sieve tube element that is unloading to a sink?

• A

• B

• C

• D

Which statement concerning transpiration is correct?

• On a humid day, the water potential gradient between the intercellular air space and the

  external atmosphere increases to stimulate water loss by evaporation.

• Water arriving at the spongy mesophyll cells via the symplast pathway must move by

  osmosis through the cell surface membrane before evaporation from the surface of the cells.

• Water diffuses down the water potential gradient from the saturated air space through the

  guard cells before evaporating from the surface of the cells into the atmosphere.

• Water moves up the xylem in the apoplast pathway and can continue on this pathway by

  osmosis to reach the spongy mesophyll cells before evaporating into the intercellular air

  space.

The photomicrograph shows tissues in a stained transverse section of a plant stem.

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What is a function of the hairs (trichomes) on xerophytic leaves?

• adding a waterproof layer

• protecting the stomata

• reducing the surface area

• trapping a layer of moist air

Which features of companion cells are essential to their function?

• They are connected by plasmadesmata to the sieve tube elements.

• They have a thinner cell wall than a sieve tube element.

• They contain a nucleus and mitochondria.

What will increase the rate of transpiration?

• increasing the humidity

• increasing the light intensity

• decreasing the temperature

• decreasing the wind speed

Which properties of water are important for transport in xylem?

• cohesion

• adhesion

• high energy requirement for evaporation

• good solvent properties

Transpiration is the consequence of which feature of plants?

• the presence of symplast and apoplast pathways

• the requirement for a transport system in plants

• the requirement for leaves to exchange gases

• the thin waxy cuticle on the lower epidermis of leaves