Topic 7: Transport in Plant

Question 1

Adhesion

Answer 1

The attraction between unlike molecules. Molecules of water adhere to the walls of the narrow xylem vessels and to the tiny pores and channels within the cell wall. This adhesion can support the entire column of water in the xylem.

Question 2

Apoplast Pathway

Answer 2

The non-living system of interconnected cell walls extending throughout a plant, used as a transport pathway for the movement of water and mineral ions.
The movement of water between cells through the cellulose cell walls.

Question 3

Angiosperms

Answer 3

Flowering Plants: There are two kinds - Monocotyledons and dicotyledons.
Monocotyledons include grasses and are characterized by long, narrow leaves.
Dicotyledons are characterized by having leaves with blades and stalks called petioles. The mechanism of transport through both type of plant are the same, but there are differences in the distribution of xylem and phloem in their roots, stem and leaves.

Question 4

Cambium

Answer 4

A layer of unspecialized cells within the vascular bundle which give rise to specialized cells that form xylem and phloem.

Question 5

Casparian Strip

Answer 5

Band of cells with impermeable walls, found in the endodermis of plant roots

Question 6

Cohesion- Tension Theory

Answer 6

A theory used to explain the movement of water through the xylem vessels of a plant. As water is lost from the leaves by transpiration, the column of water in the xylem vessels is under tension. This is because transpiration is pulling the water upwards and gravity is pulling it downwards. Water enters the roots by osmosis. The water molecules are held together by cohesion (forces of attraction between the water molecules) and the column is under tension. Water molecules are also attracted to the walls of the xylem vessels (adhesion) and this helps to pull the water upwards.

Question 7

Companion Cell

Answer 7

This is a cell with an unthickened cellulose wall and dense cytoplasm that is found in close association with a phloem vessel element to which it is directly linked via plasmodesmata. The companion cell and the sieve tube element forms a functional unit.

Question 8

Cotyledon

Answer 8

A cotyledon or ‘seed leaf’ is a significant part of the embryo within the seed of a plant. Upon germination, the cotyledon becomes the embryonic first leaves of a
seeding.

Question 9

Cortex

Answer 9

The cortex is the outermost layer of the stem or root of a plant, bounded on the outside by the epidermis and on the inside by the endodermis. In plants, it is composed of large thin-walled parenchyma cells.

Question 10

Endodermis

Answer 10

The cells in the endodermis have a thick, waterproof, wax band of suberin in their cell walls. This band called the Casparain Strip forms an impenetrable barrier to water in the walls of the endodermis cells. The endodermis blocks the apoplast pathway. The only way for water to cross the endodermis is through the cytoplasm of the endodermal cells. As the endodermal cells get older, the suberin deposits become mare extensive, except in certain cells called passage cells, through which water continue to pass freely. It is hypothesized that this arrangement gives a plant control over what inorganic ions may pass into its xylem vessels as everything must cross a cell surface membrane.

Question 11

Fibres

Answer 11

These are elongated cells with lignified walls that help to support the plant. They are dead cells with no living contents.

Question 12

Lignin

Answer 12

A hard substance found in some cell walls which is impermeable to water. Wood is made from xylem and gets its strength from lignin. As lignin builds up around a cell, the contents of the cell die, leaving a completely empty space or lumen inside.

Question 13

Parenchyma Cells

Answer 13

A basic plant tissue typically used as packing tissue between more specialized structures; it is metabolically active and may have a variety of functions such as food storage, support and transport via symplast and apoplast pathways
These are plant cells which have unthickened cellulose cell walls and contain all of the organelles that a plant cell has. However, parenchyma cells in xylem vessels do not usually have chloroplasts, because they are not exposed to light. Parenchyma cells can be a variety of shapes, but are often more or less the same size in all directions.

Question 14

Pericycle

Answer 14

A layer of parenchyma cells that lie just inside the endodermis. It protects and strengthens the vascular bundles.

Question 15

Petiole

Answer 15

This is a leaf stalk.

Question 16

Phloem

Answer 16

Tissue containing sieve tubes and other types of cell, responsible for the translocation of assimilates such as sucrose through a plant
Tissue that transport food in plant stems from leaves.

Question 17

Plasmoesmata

Answer 17

These are pore like structures found in plant cell walls. Plasmodesmata of neighbouring plant cells line up to form tube-like pores through the cell walls, allowing the controlled passage of materials from one cell to another; the pores contain ER and are lined with cell surface membrane.

Question 18

Sieve Element

Answer 18

This is a cell found in phloem tissue with non-thickened cellulose cell walls, very little cytoplasm, no nucleus and end walls with tiny holes to form sieve plates, through which sap containing sucrose is transported.

Question 19

Suberin

Answer 19

This is a waxy, waterproof substance found in some plant cell walls, e.g. the plant cells in bark.

Question 20

Symplast Pathway

Answer 20

The living system of interconnected protoplasts extending throughout a plant, used as a transport pathway for the movement of water and solutes; individual protoplasts are connected via plasmodesmata.
The movement of water through the plasmodesmata and the cytoplasm of plants.

Question 21

Tensile Strength

Answer 21

How much pulling force is required to break a material.

Question 22

Translocation

Answer 22

The transport of assimilates such as sucrose through a plant, in phloem tissue; translocation requires the input of metabolic energy; the term is somtimes used more generally to include transport in xylem.
The transport of substances around the plant.

Question 23

Transpration

Answer 23

The loss of water vapour from a plant to its environment, by diffusion down a water potential gradient; most transpiration takes place through the stomata in the leaves.
Loss of water vapour from the aeriel parts of the plant.

Question 24

Vacuolar Pathway

Answer 24

The movement of water between cells in the root system by osmosis through the vacuoles.

Question 25

Xerophytes

Answer 25

These are plants that live in places where water is in short supply. They often have adaptations to reduce the rate of transpirations.

Question 26

Xylem

Answer 26

Tissue containing xylem vessel elements and otherr types of cells, responsible for support and the transport of water through a plant
Water conducting vessel of plants.

Question 27

Xylem Vessel

Answer 27

A dead, empty tube with lignified walls though which water is transported in plants; it is formed by xylem vessel elements lined up end to end.

Question 28

Xylem Vessel Element

Answer 28

A dead lignified cell found in xylem specialized for transporting water and support; the ends of the cells break down and join with neighbouring elements to form long tubes called xylem vessels