Mass transport in plants

Question 1

What transports water in plants?

Answer 1

Xylem

Question 2

What is transpiration?

Answer 2

Evaporation of water from the leaves once it has been pulled through the xylem vessels in the stem

Question 3

Why does the xylem have tubes with no end walls?

Answer 3

Water can be pulled up in a continuous column maintaining a transpiration stream

Question 4

Why is it good that the xylem has no cytoplasm?

Answer 4

Nothing to impeede the flow of water

Question 5

What is lignin in the shape of in the xylem and why is it useful?

Answer 5

Spiral shapes to provide support and prevent collapse under tension while also being flexible and allowing it to grow

Question 6

What do the thick walls of the xylem do?

Answer 6

Prevent collapse under negative pressure

Question 7

Why is the xylem waterproof?

Answer 7

To keep water in the cells

Question 8

What do the pits in the walls of the xylem do?

Answer 8

Allow lateral movement so water can get around blocked vessels

Question 9

What does the cohesion tension theory state?

Answer 9

Water is evaporated from the leaf reducing the water potential so water is drawn up the leaf from a high to low water potential which creates tension and negative pressure. There are cohesive forces between the water molecules and adhesive forces between the water and xylem walls which means water can be pulled up in a continuous column

Question 10

What are the 3 pieces of evidence for the cohesion tension theory?

Answer 10

When transpiration is high the diameter of the tree trunk shrinks, if xylem is broken water can no longer be drawn up as not a continuous column, when vessels are broken water won’t leak as it is under tension

Question 11

What happens to the diameter of a tree trunk as light increases?

Answer 11

decreases due to increased rate of transpiration due to greater evaporation from stomata so greater flow due to more pull

Question 12

What happens to the diameter of a tree trunk as temperature increases?

Answer 12

decreases due to increased rate of transpiration water molecules have more kinetic energy so move up the xylem faster

Question 13

Why does the diameter decrease?

Answer 13

More cohesion between molecules so more adhesion between water and the xylem walls which causes tension and negative pressure pulling the walls of the xylem in decreasing the diameter

Question 14

What happens to transpiration rates as humidity increases?

Answer 14

decreases transpiration rate as less steep water potential gradient due to outside air being more moist so less water evaporated

Question 15

What happens to transpiration as wind increases?

Answer 15

Removes moisture increases water potential gradient so increases transpiration

Question 16

How do you use a potometer?

Answer 16

Cut the leafy shoot to reduce air entering and breaking the continuous column then seal the joints with waterproof jelly to prevent water loss and record the distance the air bubble moves and repeat to find mean by opening the resevoir tap

Question 17

How are root hair cells adapted?

Answer 17

thin cell wall, Large SA for absorption, long hair like projections and lots of mitochondria for active transport

Question 18

What does the phloem do?

Answer 18

Transport sugars and minerals around the plant by translocation

Question 19

What is the structure of the xylem?

Answer 19

Long structures with sieve tubes at the ends supported by companion cells

Question 20

Where does the phloem transport sugars from and to

Answer 20

source in the leaves to sinks e.g. roots

Question 21

What is the mass flow hypothesis of translocation?

Answer 21

Sugars are produced in the leaf in photosynthesis and are actively transported into the hollow sieve tubes by companion cells. This lowers the water potential in the sieve tubes so water enters by osmosis increasing pressure causing mass movement towards sink or root

Question 22

What are the sugars mainly used for?

Answer 22

Respiration or storage

Question 23

How are sieve tubes adapted for their function?

Answer 23

Few organelles so substances can flow through easily

Question 24

How are companion cells adapted for their function?

Answer 24

Contain lots of mitochondria which releases ATP for active transport and contains lots of ribosomes to produce proteins needed to act as carrier proteins

Question 25

What does the ringing experiment show?

Answer 25

Above bulge of sugar above dead tissue below shows it is a continuous column

Question 26

What does adding radioactive CO2 in the tracer experiment show?

Answer 26

Will blacken under x ray where phloem tissues are

Question 27

What else can you use to prove it is phloem?

Answer 27

Aphids can suck out sugars