Transport in Plants

Question 1

The need for transport system in multicellular plants

Answer 1

• larger plants have a smaller surface area to volume ratio so less surface are for absorbotion of nutriebts and gases and secretion of waste
• large diffusion distance.
• -rate of diffusion into plant tissue is too slow
• high metabolic rate

Question 2

Vascular system

Answer 2

-made up of xylem and phloem

Question 3

What do phloem tissue transport ?

Answer 3

assumilates from the source to the sink up and down the plant

Question 4

Where is the xylem and phloem located in root?

Answer 4

• the centre. The centre core is the xylem often found in the shape of an X
• the pholem is found between the arms of the x- shaped xylem tissue

Question 5

Where is the xylem and phloem located in the stem ?

Answer 5

• xylem is found towards the inside amd the phloem towards the outside.
• there are layers of cambium in between the xylem and phloem which is a layer of meristem cells that divide to produce new xylem and phloem .

Question 6

Where is the xylem and phloem located on the leaves ?

Answer 6

-xylem in the inside and phloem on the outside

Question 7

Structure and function of the xylem vessels

Answer 7

• lignified cell walls - adds strength to withstand the hydrostatic pressure so the vessels do not collapse. Impermeable to water
• no end plates, cytoplasm or organelles that would slow the flow of water
• bordered pits which allows water to make lateral movements to adjacent vessels
• narrow tubes to ensure that water travels upwards in an unbroken column effective capillary action.
• ligin is deposited in different pattern’s allowing flexibility and prevent the stem from breaking.
• ## hollow tubes allowing the continuos flow of water

Question 8

Transpiration

Answer 8

the evaporation of water from the stomata

Question 9

How does temperature affect transpiration rate

Answer 9

• increase temperature. Increases transpration rate as water molecules have more kinetic energy to diffuse through the stomata

Question 10

Affect of air movement on transpiration

Answer 10

• increase air movement increases rate of transpiration as water vapour that have been diffused out of the leaf is carrier away by the air maintaining a high water vapour concentration gradient

Question 11

Affect of humidity on transpiration

Answer 11

-high humidity= lower rate of transpiration as there is a less steep diffusion gradient therefore less water leaves the leaf via evaporation

Question 12

Affect of light intensity on transpiration

Answer 12

• increase light intensity. Increases rate of transpiration as more stomata opens to allow gaseous exchange for photosynthesis so more H20 diffuses out of the cell

Question 13

Structure and function of phloem vessels

Answer 13

• phloem transports sugars and other assimates both upwards and downwards.

consists of two types of cells:

• sieve tube elements lined up end to end
• little cytoplasm and no nucleus to maximise space for mass flow of sap. Are alive
• at the ends of the tube are ‘sieve plates’ which have lots of holes in them to allow solutes to pass through

Companion cells

• in between sieve tubes.
• lots of mitrochondria to produce ATP needed for active processes. Carrys out metabolic processes needed to load assimilates actively into the sieve tubes.
• parenchyma( packing cells) in beteeen the sieve tubes and companion cells

Question 14

Apoplast pathway

Answer 14

Water moves through spaces in the cell walls and between the cells by tension. Known as mass flow as it does not past through a partially mermeable barrier( plasma membrane)

Question 15

Symplast pathway

Answer 15

• water moves through the cytoplasm by diffusion and through the plasmodesmata from one cell to the next by osmosis

Question 16

Plasmodesmata

Answer 16

• gaps in the cell wall containing cytoplasm that connects two cells

Question 17

Water movement across the root

Answer 17

• water travels through the apoplast pathway as far as the endodermis. But must enter the symplast pathway as the apoplaat pathway is blocked by a caparian strip. This is so toxins can be filtered out by passing a partially permeable membrane and filtered out.
• the mineral ions in the water are transported into the xylem by active transport using ATP making the water potential of the xylem more negative therefore water enters the xylem from the endodermis by osmosis.

Question 18

Water movement across the stem

Answer 18

• the action of the endodermis moving water and mineral ions into the xylem creates root pressure pushing water up the xylem
• (Cohesion- tension theory)water molecules are attracted to eachother by cohesion between the hydrogen bonds creating a column. Water molecules are lost from the top of the column, the whole column is pulled up as one chain. Creating tension.
• ahesion attracts water molecules to the sides of the xylem vessel. Because xylem vessels are narroe the force’s of attraction pull the water up the sides of the vessels

Question 19

Describe how to use a potomer to measure the rate of transpiration

Answer 19

• a sample of a plant must be cut underwater, this is to prevent any air from entering the xylem and breaking the water column
• the potometer is filled with water and the air bubbles are removed
• the cut leafy plant is then attached to the potometer using seals and petroleum jelly to make the equipment air tight
• one air bubble is introduced and the distance the air bubble moves towards the plant is recorded

Question 20

How to calulate transpiration rate from a potometer?

Answer 20

surface area of a circle x length the buble has moved/time

Question 21

What variables would be controlled of you were to perform the potometer test of two different species

Answer 21

• the surface area of leaves

Question 22

.How transpirations causes water movement across the cells

Answer 22

• water leave through the leaves by transpiration
• water potential in that cell lowers
• water potential in neighbouring cell is higher so eater diffuses into that cell with the lower water potential
• when this cell loses water the water potential is lowered and the same thing occurs throughout the cells

Question 23

Name one other part of a leaf from which water may be lost

Answer 23

• the cuticle

Question 24

What do xylem vessels transport?

Answer 24

• water and minerals ions

- these move up the plant from the roots to the leaves

Question 25

how does the number of stomata affect the rate of transpiration

Answer 25

-more stomata= increase transpration rate as more stomata can open for water to evaporate from

Question 26

how does the presence of a waxy cuticle affect the rate of transpiration

Answer 26

-thicker the waxy cuticle the lowr the rate of transpiration as waxy cuticle reduces water loss from the plant

Question 27

why does the potometer not accurately meaasure the rate of water uptake

Answer 27

-water is used in turgor pressure of the plant and some ater is used up in photosynthesis

Question 28

Cohesion adhesion theory

Answer 28

There is a high hydrostatic pressure in the roots
-There is a low hydrostatic pressure in the leaves;
As water evaporates through the stomata;
This creates tension in the xylem;
Water moves up the xylem along the hydrostatic pressure gradient;
by cohesion; adhesion;
capillary action;
By mass flow;

Question 29

Dissection of plant stem cells

Answer 29

• use a scalpel to cut a thin cross-section of the stem( transverse or longitudinal)
  -transfer section to a dish containing stain
  -examine

Question 30

Adaptations of xerophytics ( cacti and marram grass)

Answer 30

• rolled leaves to reduce surface area for evaporation
  -Trap a layer of water vapour;
  creating a higher water vapour potential outside the stomata;
  reducing the water vapour potential gradient;
• Also hairy leaves for that reason
  -sunken stomata = less water taken away by wind to reduce rate of transpiration
  -cacti have spines to reduce the surface area
  -Thicker waxy cuticle; which is waterproof and prevents water leaving though evaporation;
  -Less stomata; which will be closed in the day; most will be found on the lower surface of the leaves to reduce evaporation;

Question 31

Hydrophytes

Answer 31

-air spaces in which allows buoyancy so plant can float on the surface increasing the amount of light they receive
-Large surface area for leaves; to increase the rate of photosynthesis as water is not a limiting factor

Question 32

source

Answer 32

-where sugars are made
-e.g. leaf or roots

Question 33

sink

Answer 33

-whwre the sugars are used in respiration which is any where in the plant or convereted for storage such as starch in the roots

Question 34

describe active loading in translocation

Answer 34

-hydrogen ions in the companian cells are actively transported out into surrounding tissue
-hydrogen ions move back into the companion cell with sucroe using a cotransporter protein therefore the process is faccililated diffusion
-sucrose diffuses through the plasmodesmata into the seive tube elements
-this lowers the water potentional therefore water diffuses inside the seive tube element
-this causes an increase in the hydrostatic pressure inside theseive tube element

Question 35

describe the removal of sucrose at the sink of the phloem

Answer 35

sucrose leaves the seive tube elements by diffusion increasing the water potential of the seive tube element
-water leaves the seive tube elemts via osmosis
-decreaseing the hydrostatic pressure in the seive tube elements
-therefore assimulates move from source where there is a high hydrostatic pressuret to the sink down the hydrostatic pressure gradient by mass flow

Question 36

translocation

Answer 36

-energy requiring process which transports assumilates such as suroce from the source to the sink of the phloem