Transport in plants

Question 1

Structure of xylem vessel elements

Answer 1

Mature xylem consists of elongated dead cells, arranged end to end to form continuous vessels (tubes). Mature xylem vessels: contain no cytoplasm. The xylem tracheary elements consist of cells known as tracheids and vessel members, both of which are typically narrow, hollow, and elongated. Tracheids are less specialized than the vessel members and are the only type of water-conducting cells in most gymnosperms and seedless vascular plants.

Question 2

Structure of phloem sieve tube elements

Answer 2

Sieve tubes consist of sieve elements which are elongated cells, connected to each other via sieve plates to form a continous tube system that spreads out through the entire plant. Mature sieve elements contain structural phloem specific proteins (P-proteins), mitochondria, ER, and sieve elements plastids.

Question 3

Phloem sieve tube elements

Answer 3

Phloem is composed of various specialized cells called sieve tubes, companion cells, phloem fibres, and phloem parenchyma cells.

Question 4

Sieve tube

Answer 4

A tube consisting of an end-to-end series of thin-walled living plant cells held to function in translocation of organic solutes.

Question 5

Companion cells

Answer 5

Cells that appear to regulate the activity of the adjacent sieve element and to take part in loading and unloading sugar into the sieve element.

Question 6

Phloem fibres

Answer 6

A fibre that provides great tensile strength and pliability and that differs from the xylem fiber in that its pits are usually small and simple.

Question 7

Phloem parenchyma cells

Answer 7

They are located near the finest branches and terminations of sieve tubes in leaf veinlets, where they also function in the transport of foods.

Question 8

Sieve tube plate

Answer 8

The connection sites between sieve elements. Sieve plates allow the food to pass through the phloem tubes. The tiny pores present on these tubes helps in the transport and absorption of food particles. Thes have long and elongated structures that connect the roots and al other parts of plants.

Question 9

Movement of water between plant cells

Answer 9

Osmosis plays a central role in the movement of water between cells and various compartments within plants. In the absence of transpiration, osmotic forces dominate the movement of water into roots.

Question 10

Movement of water between a plant cell and its environment

Answer 10

Osmosis, active transport and diffusion are responsible for this.

Question 11

How is hydrogen bonding involved with the movement of water between plant cells

Answer 11

Hydrogen bonds make water molecules stick together, a process known as cohesion. It describes the way water moves through the xylem using cohesion (the water molecules stick to each other) and tension (because transpiration is drawing water out of the leaves). The hydrogen bonds have tension between them, so water molecules stick together and move together.

Question 12

Pathways and mechanisms by which water and minerals are transported from soil to xylem and from roots to leaves

Answer 12

Water and minerals are presented into the soil. This transportation is initiated by root cap. They travel into the root by diffusion. They the particles reach the vascular system of the root. The xylem then transports the water and the phloem transports the minerals. This transport is taken to other parts of the plant by creating pressure in root cells which pump up the water and minerals.

Question 13

Transpiration

Answer 13

The process of water movement through a plant and its evaporation from aerial parts, such as leaves, stems and flowers. It is also an inevitable consequence of gas exchange in plants.

Question 14

Factors that affect transpiration rate

Answer 14

Temperature, humidity, wind speed and light intensity.

Question 15

Temperature

Answer 15

Plants transpire more rapidly at higher temperatures because water evaporates more rapidly as the temperature rises.

Question 16

Humidity

Answer 16

As the relative humidity of the air surrounding the plant rises the transpiration rate falls. It is easier for water to evaporate into dryer air than into more saturated air.

Question 17

Wind speed

Answer 17

Increased movement of the air around a plant will result in a higher transpiration rate. Wind will move the air around, with the result that the more saturated air close to the leaf is replaced by drier air.

Question 18

Light intensity

Answer 18

The transpiration rate is increased due to the increase in light intensity. During daytime in the sunlight, the rate of transpiration is faster. This is because the stomata remains open to allow the inward diffusion of carbon dioxide for photosynthesis.

Question 19

Movement of sucrose and amino acids

Answer 19

Sucrose is transported over long distance in solution in the phloem sap. This flow of sap occurs in a specialised network of cells, called the sieve elements. They move between sources.

Question 20

How is sucrose loaded into phloem sieve tubes

Answer 20

Sucrose is loaded into the phloem at a source, usually a photosynthesizing leaf. The sucrose can then diffuse down the concentration gradient into the sieve tube element via the plasmodesmata that connects the companion cell with the sieve tube element.

Question 21

Mass flow in phloem sap

Answer 21

The pressure flow hypothesis, also known as the mass flow hypothesis, is the best-supported theory to explain the movement of sap through the phloem. This creates turgor pressure, also known as hydrostatic pressure, in the phloem. Movement of phloem sap occurs by bulk flow (mass flow) from sugar sources to sugar sinks.