Plant transport

Question 1

Draw a diagram of a root cross section and label it

Answer 1

Should include epidermis, cortex, endodermis and vascular bundle with xylem and phloem

Question 2

Draw a diagram of a stem cross section and label xylem and phloem

Answer 2

Vascular bundle should be in circles around outside. Xylem on inside phloem on outside

Question 3

How are mineral ions like nitrate absorbed into root hair cells?

Answer 3

Active transport (mostly via symplast pathway)

Question 4

Give two adaptations that root hair cells have.

Answer 4

Large surface area, many mitochondria and transport proteins

Question 5

Where does water move into the plant?

Answer 5

Water moves across the cortex of the root to the endodermis by THREE routes- apoplast, symplast, vacuolar

Question 6

What is the apoplast pathway?

Answer 6

Passive movement (cohesion)of water through diffusing through the cellulose cell wall. Stops at casparian strip

Question 7

What is the symplast pathway?

Answer 7

Passive movement of water (osmosis) through the cytoplasm and plasmodesmata

Question 8

What is the vacuolar pathway?

Answer 8

Water can also move between the cytoplasm and the large central vacuole – movement between cells is via the plasmodesmata.

The vacuolar route is the slowest route for transport across the cortex. Each time water has to cross membranes, there is resistance to movement and the speed of transport decreases.

Question 9

Can water move between pathways?

Answer 9

Yes.
Called transmembrane route where water moves between cells through the cell membranes rather than through the plasmodesmata.

Question 10

Which is the fastest pathway for water through the root and why?

Answer 10

Apoplast is fastest because it has least resistance to flow, vacuolar is slowest because it has the greatest resistance due to the number of membranes that need to be crossed

Question 11

Where is the Casparian strip located and what is it made of?

Answer 11

Endodermis cells, suberin (waterproof wax)

Question 12

Why does water move into the xylem?

Answer 12

Cohesion and the transpiration stream, capillary action and root pressure

Question 13

What is root pressure?

Answer 13

Mineral ions are actively transported from the endodermis into the pericycle. This lowers the water potential in the pericycle and water follows by osmosis

Question 14

What is the function of the casparian strip?

Answer 14

To block the apoplast pathway and force water into the symplast pathway, meaning it must pass through a cell membrane

Question 15

What four factors can affect the rate of transpiration?

Answer 15

Humidity, temperature, wind speed, light intensity

Question 16

Why is water uptake in a plant not the same value as water lost by transpiration?

Answer 16

Water is used in photosynthesis and hydrolysis, made in respiration and used to increase turgor of cells

Question 17

What does a potometer measure?

Answer 17

The distance moved by an air bubble in one minute, which can be used to calculate rate of water uptake

Question 18

Describe the structure of the xylem

Answer 18

Dead tissue, divided into tracheids (narrower) and vessels (wider). Surrounded by waterproof lignin. Presence of pits

Question 19

Describe the structure of the phloem

Answer 19

Living tissue. Companion cells packed with organelles, connected to sieve tubes by plasmodesmata. Sieve tubes have very reduced cell contents

Question 20

Comparison of cell walls of phloem and xylem

Answer 20

xylem= thick, ridgid (made out of lignin), impermeable
phloem= thin, flexible (made out of cellulose), permeable

Question 21

Comparison of cytoplasm of phloem and xylem

Answer 21

xylem= none
phloem=cytoplasmic stands

Question 22

Comparison of direction of transport for phloem and xylem

Answer 22

xylem= from root upwards
phloem= To and from sites of photosynthesis/storage (SOURCE) to growing regions and sites of storage (SINK)

Question 23

How do sugars and amino acids move through the phloem?

Answer 23

Translocation, potentially by mass flow

Question 24

List the problems with the mass flow theory

Answer 24

Presence of sieve plates, companion cells, mitochondria. Use of oxygen, stopped by cyanide, 10000x faster than diffusion

Question 25

Give three alternative hypotheses to mass flow

Answer 25

Cytoplasmic streaming, protein filaments, active loading of phloem

Question 26

Give the features of a xerophyte that help to reduce water loss

Answer 26

Rolled leaves, sunken stomata, hairs. All of these trap water vapour and reduce the diffusion gradient.

Question 27

What is the epidermis function (root)

Answer 27

Presence of root hairs for the uptake of water and mineral ions. Epidermal cells protect roots as they grow through the soil.

Question 28

What is the cortex parenchyma function

Answer 28

Can act as a storage organ. Intercellular spaces allow movement of water and ions.

Question 29

What is the endodermis function (root)

Answer 29

Has a waterproof layer that forces water and ions into the cytoplasm of the endodermal cells and controls transport into the xylem.

Question 30

What is the Pericycle function (root)

Answer 30

Has a role in controlling transport into the xylem. Site of lateral root growth.

Question 31

What is the Xylem function

Answer 31

Transports water and ions from the roots to the stem and leaves. Provides support for the plant.

Question 32

What is the phloem function

Answer 32

Transports the products of photosynthesis to the roots from the leaves.

Question 33

What is the cambium function

Answer 33

A meristematic tissue that can undergo mitosis to produce more xylem and phloem.

Question 34

Adaptions to root hair cells to increase absorption

Answer 34

-thin cellulose cell wall on root hair extension so the distance for transport is short -large numbers of root hairs each with a long and thin extension into soil to increase the surface area for absorption -large number of mitochondria to produce ATP for active transport of ions.

Question 35

How can water be absorbed

Answer 35

-it can be absorbed passively into the cell wall which acts as a sponge -it can move into the cell cytoplasm through osmosis.

Question 36

What is the cuticle function (stem)

Answer 36

Reduces water loss through evaporation. Transparent to allow light to pass through for photosynthesis (in green stems).

Question 37

What is the epidermis function (stem)

Answer 37

Protection of the stem. May have hairs to deter insects/animals from eating them.

Question 38

What is the collenchyma function (stem)

Answer 38

Cell walls thickened with cellulose to strengthen the stem while remaining flexible

Question 39

What is pith collenchyma function (stem)

Answer 39

Thin-walled cells that act as packing tissue – often breaks down in older stems.

Question 40

What is Sclerenchyma function (stem)

Answer 40

Lignified cells that provide strength and support to the stem.

Question 41

Types of xylem cell types

Answer 41

-xylem vessels: transport water and minerals from the roots to other parts of a plant; the end walls of xylem vessels break down to form long tubes that extend from the roots to the stem and leaves -tracheids: provide strength to the tissue -xylem parenchyma: thin walled, living cells that act as packing tissue between the xylem vessels.