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

Question 4

Give two adaptations that root hair cells have.

Answer 4

Large surface area, many mitochondria and transport proteins

Question 5

What is the apoplast pathway?

Answer 5

Movement of water through the cellulose cell wall

Question 6

What is the symplast pathway?

Answer 6

Movement of water through the cytoplasm and plasmodesmata

Question 7

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

Answer 7

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 8

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

Answer 8

Endodermis cells, suberin (waterproof wax)

Question 9

Why does water move into the xylem?

Answer 9

Cohesion and the transpiration stream, capillary action and root pressure

Question 10

What is root pressure?

Answer 10

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 11

What is the function of the casparian strip?

Answer 11

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

Question 12

What four factors can affect the rate of transpiration?

Answer 12

Humidity, temperature, wind speed, light intensity

Question 13

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

Answer 13

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

Question 14

What does a potometer measure?

Answer 14

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

Question 15

Describe the structure of the xylem

Answer 15

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

Question 16

Describe the structure of the phloem

Answer 16

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

Question 17

How do sugars and amino acids move through the phloem?

Answer 17

Translocation, potentially by mass flow

Question 18

List the problems with the mass flow theory

Answer 18

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

Question 19

Give three alternative hypotheses to mass flow

Answer 19

Cytoplasmic streaming, protein filaments, active loading of phloem

Question 20

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

Answer 20

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