Transport systems in dicotyledonous plants 9.1

Question 1

what is the pressure in the phloem

Answer 1

It is around 2000 kPa

Question 2

What 3 main reasons are there for why multicellular plants need transport systems

Answer 2

Metabolic demands
size
surface area (SA:V)

Question 3

What about metabolic demands means that plants need transport systems

Answer 3

The cells of the green parts of the plant make their own glucose and oxygen by photosynthesis - but many internal and underground parts of the plant do not.
They need oxygen and glucose transported to them and the waste products of cell metabolism removed.
Hormones made in one part of a plant need transporting to the areas where they have an effect.
Mineral ions absorbed by the roots need to be transported to all cells to make the proteins required for enzymes and the structure of the cell

Question 4

what about the size of the plants means that they need transport systems

Answer 4

some plants are very small but because plants continue to grow throughout their lives, many perennial plants (plants that live a long time and reproduced year after year) are large and some of them are enormous.
This means plants need very effective transport systems to move substances both up and down from the tup of the roots to the topmost leaves and stems

Question 5

What about the surface area : volume ratio of plants means that they need transport systems

Answer 5

Leaves are adapted to have a relatively large SA:V ratio for the exchange of gases with the air.
However, the size and complexity of multicellular plants means that when the stems, trunks and roots are taken into account they still have a relatively small SA:V ratio.
This means they cannot rely on diffusion alone to supply their cells with everything they need

Question 6

what are dicotyledonous plants

Answer 6

Dicotyledonous plants (dicots) make seeds that contain 2 cotyledons, organs that act as food stores for the developing embryo plant and form the first leaves when the seed germinates

Question 7

what are the 2 types of dicotyledonous plants

Answer 7

There are herbaceous dicots & woody dicots

Question 8

what are the characteristics of hebaceous dicots

Answer 8

Herbaceous dicots, with soft tissues and a relatively short life cycle (leaves and stems that die down at the end of the growing season to the soil level)

Question 9

What are the characteristics of woody dicots

Answer 9

woody dicots have hard lignified tissues and a long life cycle (in some cases 100s of years)

Question 10

what part of the plants are known as the vascular system

Answer 10

Dicotyledonous plants have a series of transport vessels running through the stem, roots and leaves. This is known as the vascular system

Question 11

What 2 types of vessels make up the vascular system

Answer 11

The vascular system is made up of the xylem and the phloem

Question 12

How are the xylem and phloem arranged in the vascular system

Answer 12

The transport tissues are arranged together in vascular bundles in the leaves, stems and root of herbaceous dicots

Question 13

How are the vascular bundles arranged in the stems of herbaceous plants

Answer 13

Question 14

How are the vascular bundles arranged in the roots of herbaceous plants

Answer 14

Question 15

How are the vascular bundles arrange in the stems of herbaceous plants

Answer 15

Question 16

what is the function of the xylem

Answer 16

The transport of water and mineral ions, and support.

Question 17

What is the structure and composition of the xylem

Answer 17

They are long, hollow structures made by several columns of cells fusing together end to end.
Lignin in the xylem can for springs, spirals or relatively solid tubes with lots of small unlignified areas called bordered pits.

Question 18

what is the composition of the xylem

Answer 18

• largely non-living tissue.
• made up of several types of cells
  ^most of which are dead when they are functioning in the plant.
• xylem contains
  ^Thick-walled xylem parenchyma
  ^Xylem fibres
• Lignin can be laid down in the walls of the xylem vessels

Question 18

why is there tannin deposits in the xylem tissue

Answer 18

Tannin is a bitter, astringent-tasting chemical that protects plant tissues from attack by herbivores

Question 19

What is the function of xylem parenchyma

Answer 19

it packs around the xylem vessels, storing food and containing tanninin deposits

Question 20

What is the structure and function of xylem fibres

Answer 20

they are long cells with lignified secondary walls that provide extra mechanical strength but do not transport water.

Question 21

What is the function of bordered pits in the lignin with in the xylem

Answer 21

This is where water leaves the xylem and moves into other cells of the plant

Question 22

what is the function of the phloem

Answer 22

Phloem is a living tissue that transports food in the form of organic solutes around the plant from the leaves where they are made by photosynthesis.
The phloem supplies the cells with sugars and amino acids needed for cellular respiration and for the synthesis of all other useful molecules.
The flow of materials in the phloem can go both up and down the plant

Question 23

what is the main transporting vessel in the phloem

Answer 23

The main transporting vessel of the phloem are the sieve tube elements

Question 24

what are the sieve tubes made up of

Answer 24

like the xylem, they are made up of many cells joined end to end to from a long, hollow structure, unlike the xylem they are not lignified

Question 25

what are sieve plates and what is there function

Answer 25

In the areas between the cells, the walls become perforated to from sieve plates, which look like sieves and let the phloem contents low through

Question 26

as phloem cells become perforated to form sieve plates what occurs

Answer 26

• the tonoplast, nucleus and some of the other organelles break down
• phloem becomes a tube filled with phloem sap
• mature phloem cells have no nucleus

Question 27

what are the similarties and differences in the structure of the xylem and mature phloem cells

Answer 27

Neither xylem vessels nor mature sieve tubes have nuclei, but xylem vessels are dead and phloem vessels are living tissue

Question 28

what cells form with the sieve tube elements

Answer 28

companion cells

Question 29

How are the companion cells and sieve tube elements linked

Answer 29

These cells are linked to the sieve tube elements by many plasmodesmata

Question 30

what are plasmodesmata

Answer 30

microscopic channels through the cellulose cell walls linking the cytoplasm of adjacent cells

Question 31

what is the function of companion cells

Answer 31

They maintain their nucleus and all their organelles.
The companion cells are very active cells and it is thought that they function as a ‘life support system’ for the sieve tube cells, which have lost most of their normal cell functions

Question 32

what supporting tissues are also found in the phloem tissue

Answer 32

Phloem tissue also contains supporting tissues including fibres and sclereids, cells with extremely thick cell walls