Resource Acquisition and Transport in Vascular Plants

Question 1

why didn’t ancestor plants need a vascular system?

Answer 1

• Algal plant ancestors had no need for complex vascular systems: life in ocean provided buoyancy and ample water
• Earliest forms of plants (bryophytes), lacking vascular systems, require intimate contact with water → moist environments

Question 2

What were the affects of vascular tissue forming in plants?

Answer 2

• The evolution of conducting tissues in vascular plants changed everything
  » Allowed true tissue differentiation
  » Roots absorb water and minerals from the soil and distrib- ute them to the rest of the plant via the vascular tissue
  » Shoot system harvests the sun’s energy and atmospheric CO2 for photosynthesis

Question 3

What was the result of an increase in non-vascular plants

Answer 3

• ## As non-vascular plants increased in numbers, competition for light, water and nutrients also increased

Question 4

What adaptions in non-vascular plants where favored due to the competition for resources?

Answer 4

• Favoured taller plants and leaves with larger surface area
  » But larger surface = more evaporation, greater need for water
  » And taller plant require stronger anchorage
• That, in turn, favoured
  » Production of multicellular, branching root
  » Production of more efficient leaves, covering wider surface area
  » More efficient long distance transport system between roots to leaves

Question 5

What is the first step of transport of water and nutrients in plants?

Answer 5

• Roots absorbe water and dissolved minerals from the soil

Question 6

What is the 2nd step of transport of water and nutrients in plants?

Answer 6

• Water and minerals are transported upward from roots to shoots as xylem sap.

Question 7

What is the 3rd step of transport of water and nutrients in plants?

Answer 7

• Transpiration, the loss of water from leaves (mostly through stomata). Creates a force within leaves that pulls xylem sap upwards.

Question 8

What is the 4th step of transport of water and nutrients in plants?

Answer 8

• Through stomata, leaves take in CO2 and expel O2. The CO2 provides carbon for photosynthesis. Some O2 produced by photosynthesis is used in cellular respiration.

Question 9

What is the 5th step of transport of water and nutrients in plants?

Answer 9

• Sugars are produced by photosynthesis in the leaves.

Question 10

What is the 6th step of transport of water and nutrients in plants?

Answer 10

• Sugars are transported as phloem sap to roots and other parts of the plant

Question 11

What is the 7th step of transport of water and nutrients in plants?

Answer 11

• Roots exchange gases with the air spaces of soil taking in O2 and discharging CO2.
• In cellular respiration, O2 supports the breakdown of sugars.

Question 12

Draw a diagram of the overview of transport in non-vascular plants.

Answer 12

Google Doc:

https://docs.google.com/document/d/1BpabtfqIj5MGsWdBTMRokVNMhJZjMkFjHpc7UqK5cCk/edit?usp=sharing

Question 13

What are the two types of transport in plants?

Answer 13

• Short distance: cell–to cell transport at tissue level

- Long distance: transport of sap in xylem and phloem in the vascular system at ‘whole’ plant level

Question 14

In short distance transport, what are the three routes for transporting materials between plant cells

Answer 14

• Apoplastic: external to the cell membrane
• Symplastic: via the cytosol of the cell (requires entry into 1 cell, then can move via plasmodesmata)
• Transmembrane: between cells across the cell membrane (repeated crossing)

Question 15

What is short distance travel of substances controlled by?

Answer 15

• Short-distance movement of substances into and out of cell is controlled by
  » Selective cell membrane permeability
  » Both active and passive transport

Question 16

What powers membrane transport in plants?

Answer 16

• H+ important to power membrane transport (≈ Na+ in animal cell)
  » Membrane potential established through pumping H+ by proton pumps
  » Energy of H+ gradients used to co-transport other solutes by active transport (eg, sucrose)

Question 17

How does short distance transport of water occur and what is it measured in?

Answer 17

• Absorption or loss occurs by osmosis (diffusion of free water across channels in plasma membrane called aquaporins)
• Likelihood of water to move into or out of a cell by osmosis is measured by the water potential (Ψ)
  » Expressed in pressure units of megapascal (MPa)

Question 18

What is water potential?

Answer 18

• Ψ is the sum of the solute potential (ΨS) and the pressure potential (ΨP): Ψ = ΨS + ΨP
  » ΨS is proportional to solute concentration
  • Always a negative number; more concentrated = more negative
  » ΨP is the physical pressure (push/pull) of solution

Question 19

What is Turgor pressure?

Answer 19

• A measure of ΨP in plant cells: turgor pressure and turgidity
• Turgor pressure: pressure put on cell wall by protoplast (living part of the cell, ie, everything within cell membrane) from swelling caused by water

Question 20

What are the measured of Turgidity?

Answer 20

» Turgid: when a cell has taken up the maximum amount of water and the cell wall exerts pressure back on the protoplast
» Flaccid: equilibrium between water uptake and water loss
» Plasmolysed: when a cell has lost so much water its plasma membrane is no longer connected to cell wall

Question 21

What does it mean when a plant is turgid?

Answer 21

• A walled cell with a greater solute concentration than its surroundings (hyperosmostic) is turgid (ie, very firm)
  » In a non-woody tissue push against each other → stiffening of tissues

Question 22

What does it mean when a plant is wilting?

Answer 22

• If the cell becomes iso- or hypo-osmotic in relation to its surroundings, then it becomes flaccid → turgor loss → wilting: leaves and stems droop as a result of cells losing water

Question 23

Where and how does water and nutrients enter the roots?

Answer 23

• Water and dissolved minerals enter root at root hair
  » Apoplastic route: passive diffusion into hydrophilic cell wall
  » Symplastic route: active uptake into cells

Question 24

Before reaching the vascular cylinder, where does the nutrients and water have to pass through and why?

Answer 24

• Before reaching vascular cylinder, the nutrients and water pass through the endoderm
  » The Casparian strip prevents passage via cell wall (apoplastic)
  » This Forces it to pass through cell membrane at least once before reaching the vascular system → keeps many toxic substances out

Question 25

Where does long distance transport occur?

Answer 25

• Occurs by bulk flow
  » In the tracheids (and vessel elements) of xylem for the transport of water and nutrients
  • Xylem is perfect because it is a dead cell with no organelles and no cytoplasm, only the cell wall → “pipes”
  » In sieve-tube elements of phloem for sugars and organic compounds
  • Almost devoid of organelles → “pipes”

Question 26

What does the ascent of Xylem sap (nutrients and water) depend on?

Answer 26

• The ascent of xylem sap depends on transpiration at leaves and physical cohesion of water molecules

Question 27

Explain how “transpiration” and “physical cohesion of water” works?

Answer 27

» Water molecules lost by evaporation at stomata
» Because of high surface tension of water, this water loss induces a negative pressure potential → pulls water from within the leaf to restore surface tension
» This induces a tension within the leaf → pulls water from deeper within the leaf → pulls water from the xylem → from the root → from surrounding soil → from farther away in the surrounding soil etc …
» Nutrients, dissolved in water, move with it
» Xylem sap can flow upwards at > 15 m/h

Question 28

draw diagram of transpiration and Cohesion.

Answer 28

Google Doc:

https://docs.google.com/document/d/1BpabtfqIj5MGsWdBTMRokVNMhJZjMkFjHpc7UqK5cCk/edit?usp=sharing

Question 29

What is the first step of the generation of transpiration pull?

Answer 29

• In transpiration, water vapour diffuses from the moist air spaces of the leaf to the drier air outside via stomata

Question 30

What is the second step of the generation of transpiration pull?

Answer 30

• At first, the water vapour lost by transpiration is replaced by evaporation from the water film that coast mesophyll cells

Question 31

What is the third step of the generation of transpiration pull?

Answer 31

• The evaporation of the water film causes the air-water interface to retreat further into the cell wall and to become more curved. This curvature increases the surface tension and the rate of transpiration

Question 32

What is the fourth step of the generation of transpiration pull?

Answer 32

• The increased surface tension created in step three pulls water from surrounding cells and air spaces

Question 33

What is the fifth step of the generation of transpiration pull?

Answer 33

• Water from the xylem is pulled into the surrounding cells and air spaces to replace the water that was lost.

Question 34

What is transpiration regulated by?

Answer 34

• The rate of transpiration is regulated by stomata
• Generally on leaf underside
• Regulate gas exchange
  » CO2 in, O2 out
• Most often open during the day when carbon dioxide is required for photosynthesis
• Generally close at night to stop loss of water
  » But remember C3/C4/CAM adaptations

Question 35

How does phloem sap move in plants?

Answer 35

• The pressure-flow hypothesis
• In angiosperms, phloem sap flows in sieve-tube elements
  » Contains up to 30% sucrose + amino acids, hormones, and minerals
• Flows from site of sugar production to site of sugar use/storage
  » “Sugar source” → “sugar sink” (growing roots, stems, fruits)
• Moves by active transport +(positive pressure) bulk flow

Question 36

What does Phloem transport?

Answer 36

• Phloem transports:
  » Small organic molecules (sugars, amino acids)
  » Macromolecules (proteins, RNA)
  » Viruses
  » Chemical messengers (hormones)
• Phloem is a systemic transport (throughout the body)
  » Critical to integrate all functions of the plant