Transport In Plants

Question 1

What is the vascular system?

Answer 1

Xylem and phloem tissue in plants. Xylem is for carrying water and minerals and phloem is for carrying sugars

Question 2

What is parenchyma?

Answer 2

Packing and supporting tissue

Question 3

What are the functions of xylem?

Answer 3

Transport of water and mineral ions up a plant

Structural support for the plant

Question 4

What is xylem?

Answer 4

Dead cells fused to form hollow vessels, strengthened by lignin

Question 5

Why are there pits in the xylem wall?

Answer 5

To allow water to move out into adjacent xylem vessels or other cells

Question 6

What is the purpose of xylem parenchyma cells?

Answer 6

To store food

Question 7

What is the function of phloem vessels?

Answer 7

To transport solutes (e.g. sugars and amino acids) up and down a plant

Question 8

What are phloem vessels?

Answer 8

Siege tube elements (living cells) joined end to end forming a tube with internal pores (sieve plates)

Question 9

What are companion cells?

Answer 9

Cells that carry out all the metabolic functions of the phloem tissue (as tubes lack nuclei). Materials pass into sieve tubes via plasmodesmata

Question 10

What are 3 roles played by water in plants?

Answer 10

Maintaining turgor, transport medium for mineral ions and sugars, raw material in photosynthesis

Question 11

How are root hair cells adapted for water uptake?

Answer 11

Long and narrow so have large SA:V ratio, able to penetrate between soil particles to reach water, active transport of mineral ions into vacuole gives it a low water potential, creating a gradient and water diffuses in by osmosis

Question 12

What is the symplast pathway?

Answer 12

Movement of water through the cytoplasm

Question 13

What is the apoplast pathway

Answer 13

Movement of water through the cell walls

Question 14

What does the casparian strip do and why?

Answer 14

Forces water in the apoplast pathway into the symplast pathway to prevent toxic solutes from continuing to move up the plant and stops water from returning to the root cortex from xylem vessels

Question 15

What is root pressure?

Answer 15

Initial flow of water into vascular tissue helps to force water up stem (although transpiration pull is a more significant factor)

Question 16

How does water first enter the xylem?

Answer 16

Endodermal cells pump mineral ions into the xylem by active transport, water diffuses into xylem by osmosis due to a lower water potential in the xylem

Question 17

What is transpiration?

Answer 17

The evaporation of water from a plants leaves (from cells in the leaves, diffusing out through stomata)

Question 18

What is the transpiration pull?

Answer 18

Water is pulled up xylem vessels to replace the water lost through transpiration

Question 19

What is the transpiration stream?

Answer 19

An unbroken chain of water molecules hydrogen bonding together that is pulled up the xylem vessels (exhibiting cohesion)

Question 20

How does capillary action aid transpiration?

Answer 20

Water molecules adhere to the sides of xylem vessels, aiding the movement of the transpiration stream up the narrow vessels

Question 21

What evidence is there for the cohesion-tension theory?

Answer 21

Trees become narrower when they transpire (due to tension in xylem during transpiration)
Air sucked up (rather than water leaking out) when a stem is cut
Water no longer moves up a broken stem as the air breaks the transpiration stream

Question 22

Which cells control the opening and closing of stomata?

Answer 22

Guard cells

Question 23

What instrument is used to measure transpiration rates?

Answer 23

Potometer

Question 24

What is translocation?

Answer 24

Movement of organic solutes through phloem sieve tubes

Occurs from sources to sinks

Question 25

What is glucose converted into to be transported around a plant and why?

Answer 25

Sucrose, because it is much less reactive than glucose, preventing unwanted and potentially dangerous reactions from occurring in a plant during translocation

Question 26

What are some examples of sources in plants?

Answer 26

Green leaves and stems, storage sites (e.g. tubers)

Question 27

What are some examples of sinks in plants?

Answer 27

Developing seeds and fruits (which are laying down food stores), growing roots

Question 28

How is sucrose loaded into phloem cells?

Answer 28

H+ ions are pumped out of companion cells by active transport, creating a proton gradient. Protons and sucrose are co-transported into the companion cells by facilitated diffusion (H+ ions move down concentration gradient). The sucrose can then move into the phloem through plasmodesmata.

Question 29

What are some adaptations of xerophytes?

Answer 29

Sunken stomata, fewer stomata, lower leaf SA, Thick waxy cuticle, curled leaves, increased water storage (e.g. cacti), Long roots

Question 30

What are some adaptations of hydrophytes?

Answer 30

No waxy cuticle (or very thin), Open stomata on upper surface of floating leaves, less internal structural support, air sacs and floating leaves, small roots

Question 31

Why are results from potometer experiments not entirely representative of the transpiration rates of a plant in its natural habitat

Answer 31

Conditions in a lab may be different to in the wild
Cutting the plant may damage it
Isolated shoot is smaller than the entire plant and may not be representative