Transport in Plants

Which of the following describes the function of the endodermis?

• It controls the movement of water and ions to the xylem using a Casparian strip

• It releases root pressure as water moves into the xylem by osmosis

• It allows water molecules to cling to the surface by cohesion so that a continuous column is created

• It forms a system of inter-connected plasmodesmata through which water and ions can move

The diagram shows some of the cells involved in loss of water from part of a plant. Which of the following correctly identifies the regions labelled P and Q?

• P - Xylem ; Q - Mesophyll cells

• P - Xylem ; Q - Root cortex

• P - Phloem ; Q - Palisade

• P - Phloem ; Q - Stem cortex

The function of the companion cell in mature phloem tissue is that it

• provides structural support for the sieve tubes

• actively moves sucrose out of neighbouring photosynthesizing cells to sieve tubes

• moves sucrose against a concentration gradient into the xylem

• contains a nucleus needed for cell division of the sieve tube elements

Which of the following statements presents the BEST evidence to support the mass flow theory of phloem transport?

• Phloem tissue carries manufactured food to destinations simultaneously, rather than to the greatest 'sink'

• Sieve plates are a barrier and have been reduced in the course of evolution

• Contents of sieve tubes are under pressure and sugar solution exudes of phloem are cut

• Appropriate gradients between 'source' and 'sink' tissues do not exist

Which of the following choices is correct in relation to the translocation of organic material?

• Sugars are always translocated downwards or towards the base of the plant

• The source is a site where sugars are produced, while sinks are sites where sugars are utilized

• The sugar which is transported in all plants is sucrose

• Sucrose travels in the phloem against a concentration gradient

I. Water leaves through the stomata by diffusion into the atmosphere

II. Water evaporates from the surface of the mesophyll cells

III. Water travels from cell to cell down a water potential gradient in the mesophyll

IV. Water passes from the stem xylem into the mesophyll cells.

Which of the following describes the correct sequence by which water is lost by transpiration?

• I - II - III - IV

• I - II - IV - III

• II - I - IV - III

• IV - III - II - I

X is a darkly staining material which is often found as the inner layer of structure Y. What is X?

• Starch

• Lignin

• Callose

• Cellulose

In an experiment, the water potential of the water in a soil, is found to be -40kPa, while that of pure water is 0kPa. This difference is due to the

• presence of mineral ions in the soil water

• greater kinetic energy of the soil water molecules

• small size of the mineral ions in the soil water

• water potential of soil water being positive

In a study of water movement in plants, the cut end of a leafy shoot is placed in a dilute solution of a dye. After a few hours, deposits of the dye accumulated in the leaves. The rate of movement of the dye up the stem is NOT increased by

• humidity

• wind speed

• temperature

• availability of water

Which of the following statements is true according to the mass (pressure) flow hypothesis?

• Sucrose moves in the phloem against a concentration gradient

• The loading of sugars into the phloem in the leaf is achieved by osmosis

• A source is a site where sugars are produced, while a sink is a site where sugars are utilized

• Water is actively transported from the intercellular spaces into the cell sap at the root end of the system