Transport in plants

Question 1

what are the three reasons to why plants need transport systems?

Answer 1

• metabolic demands: oxygen and glucose need to be transported for photosynthesis. Mineral ions, hormones and cell waste products need to be transported
• size: effective transport systems need to be built to transport substances all around the plant
• surface area to volume ratio: although leaves have a large sa: v, roots and stems don’t therefore they require gases through transport

Question 2

what are dicotyledonous plants?

Answer 2

plants that make seeds that contain two cotyledons

Question 3

what are cotyledons?

Answer 3

organs that are food stores for developing plant embryos and forms the first leaves when the seeds germinate.

Question 4

what is the vascular bundle(transport system in dicotyledonous plants) made of?

Answer 4

phloem and xylem

Question 5

Describe herbaceous dicots?

Answer 5

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

Question 6

describe woody (arborescent) dicots

Answer 6

dicots which have hard lignified tissues and a long life cycle.

Question 7

what is a vascular system?

Answer 7

a series of transport vessels running through the stem, roots and leaves which are in dicotyledonous plants.

Question 8

Describe the xylem

Answer 8

• transports water and mineral ions
• provides support
• minerals flow from the roots to the shoots and leaves
• most cells in the xylem are dead
• long and hollow
• made of cells fusing together end to end

Question 9

what other tissue is associated with the xylem in herbaceous dicots?

Answer 9

-thick-walled xylem parenchyma packs around the xylem vessels, storing food and containing tannin deposits

Question 10

what is tannin?

Answer 10

bitter tasting chemical that protects plant tissues from attack by herbivores

Question 11

How does spirals of lignin around the lumen of the xylem help the plant?

Answer 11

helps to reinforce the xylem vessels so that they do not collapse under the transpiration pull

Question 12

how is extra mechanical strength provided in the xylem?

Answer 12

xylem fibres are long cells with lignified secondary walls

Question 13

Describe vascular bundles in the stem of a dicot

Answer 13

vascular bundles in the stem are around the edge to give strength and support

Question 14

Describe vascular bundles in the roots of a dicot

Answer 14

in the roots, vascular bundles are in the middle to help the plant withstand the tugging strains that result as the stems and the leaves are blown in the wind.

Question 15

Describe vascular bundles in the leaf of a dicot

Answer 15

In the leaves, the midrib is the main vein carrying the vascular tissue through the organ. It supports the leaf and many small, branching veins spread through the leaf functioning both in transport and support.

Question 16

what are the small undignified areas called in a xylem?

Answer 16

bordered pits. This is where water leaves the xylem and moves into other cells

Question 17

Describe the phloem

Answer 17

a living tissue that transports assimilates and sugars from the leaves where they are made by photosynthesis, needed for respiration. Flow of materials can go up or down.

Question 18

Describe the structure of the phloem

Answer 18

• composed of sieve tube element cells which connect to form a tube
• long and hollow
• not lignified
• sieve tube cells share a perforated sieve plate which cause organelles to breakdown. Mature phloem cells have no nucleus. Less organelles causes sap to flow
• companion cells

Question 19

how are the sieve tube element cells in the phloem closely linked with companion cells?

Answer 19

They are linked by plasmodesmata, linking the cytoplasms. The companion cells act as a life support system as the sieve tube cells have lost most normal cell functions

Question 20

How is the phloem supported?

Answer 20

by supporting tissues including fibres, sclereids and cells with extremely thick cell walls.

Question 21

Provide evidence that shows water is key for structure and metabolism in plants

Answer 21

• turgor pressure from osmosis provides support to stems and leaves
• evaporation keeps plants cool
• mineral ions are transported in aqueous solutions
• water is needed for photosynthesis

Question 22

Where is the exchange surface in plants?

Answer 22

root hair cells which have a long, thin extension and a specialised epidermal cell is found near the growing root tip.

Question 23

What adaptations do root hair cells have for exchange?

Answer 23

• their microscopic size means they can easily penetrate between soil particles
• large surface area to volume ratio
• thin walls
• high concentration of solutes in root hair cells maintains steep water potential gradient

Question 24

describe the concentration of soil

Answer 24

low concentration on minerals but high water potential.

Question 25

once water moves into the root hair cell, it moves across the root to the xylem in what two ways?

Answer 25

symplast pathway and apoplast pathway

Question 26

Describe the symplast pathway

Answer 26

water moves through the symplast- the continuous cytoplasm of plant cells through plasmodesmata by osmosis. The root hair cell has a higher water potential than surrounding plant cells so water moves to neighbouring cells through osmosis. This process occurs until the xylem is reached. It is a largely passive process.

Question 27

How does the water potential of the root hair cell remain lower than the soil?

Answer 27

water leaves the root hair cell by osmosis to neighbouring cells, this maintains a steep water potential gradient

Question 28

Describe the apoplast pathway

Answer 28

movement of water through the apoplast- the cell walls and intercellular spaces. Water fills spaces of the loose network of fibres in the cellulose cell wall.

Question 29

How is there a continuous flow of water through the open structure of the cellulose wall in the apoplast cell wall?

Answer 29

as water molecules move into the xylem, more water molecules are pulled behind due to water cohesive forces which creates tension and little resistance.

Question 30

what is the endodermis?

Answer 30

the layer of cells surrounding the vascular tissue (xylem and phloem) of the roots.

Question 31

what is the casparian strip?

Answer 31

a band of waxy material called Suberin that runs around each of the endodermal cells forming a waterproof layer.

Question 32

How does the casparian strip affect the apoplast pathway?

Answer 32

the casparian strip prevents water in the apoplast pathway to go further causing it to be forced into the cytoplasm of the cell joining the symplast pathway.

Question 33

why is the diversion from the apoplast pathway to the symplast pathway due to the casparian strip significant?

Answer 33

because the water must move through the selectively permeable cell membrane which excludes any potentially toxic solutes from the soil to reach the tissues

Question 34

How is the rate of water moving into the xylem through the symplast pathway increased?

Answer 34

endodermal cells move mineral ions into the xylem by active transport causing water potential in xylem cells to be lower which increases the rate of osmosis into the xylem through the symplast pathway.

Question 35

what is the plant cuticle

Answer 35

It is the outermost layer in plants which is waxy

Question 36

what is root pressure?

Answer 36

the active pumping of mineral into the xylem to produce movement o f water by osmosis causing water to drive upwards

Question 37

what evidence is there that supports the role of active transport in root pressure?

Answer 37

• cyanide prevents production of ATP in the mitochondria. When cyanide is applied to root cells, root pressure disappears.
• root pressure increases with a rise in temperature and falls when temperature decreases, suggesting chemical reactions are involved.
• if levels of oxygen or respiratory substrates fall, root pressure falls

Question 38

what is guttation?

Answer 38

when xylem sap if forced out from pores in the ends of leaves in some conditions e.g at night when transpiration is low

Question 39

adaptations of the xylem?

Answer 39

• lignin (water proof)
• dead cells with no organelles/cytoplasm and cell wall at the ends so water can flow
• narrow enough to ensure water travels upwards in an unbroken column.

Question 40

what kills the xylem cells?

Answer 40

process of lignification

Question 41

what are bordered pits?

Answer 41

holes in the xylem with no lignification. Allows water to move between vessels

Question 42

how does water travel in the xylem and how do assimilates travel in the phloem?

Answer 42

water is transported upwards from roots and assimilates are transported up and down

Question 43

where is xylem and phloem found in a vascular bundle?

Answer 43

inside vessels are xylem, outside vessels are phloem