Vascular Transport

Question 1

what are the advantages to life on land

Answer 1

An advantage because:

• less light limitation
• more plentiful oxygen and CO2

Question 2

what are challenges to life on land

Answer 2

A challenge because:

• Gravity has to be overcome, early plants only had cellulose not lignin
• Water is less plentiful: must maintain moisture
• Water/nutrients are at different locations than gases
• Dispersal of gametes and offspring
• Different Stressors like UV light, temperature fluctuations

Question 3

how are plants adapted to maintain moisture

Answer 3

1. Maintain Moisture:
   
   1. Water transport systems: transport from soil to leaves
   2. Cuticle/stomata: avoid / regulate water loss
   3. Pollen grains/seeds: resistant to dessication

Question 4

how have plants adapted to reproduction and dispersal on land

Answer 4

2. Reproduction and dispersal:
   
   1. Animal pollination / fruits
   2. More targeted pollen / seeds dispersal

Question 5

how have plants adapted to Obtain resources from two locations on land

Answer 5

3. Obtain resources from two locations
   
   1. Larger leaves to increase photosynthesis
   2. Larger plants
      
      1. Shoot and root systems
      2. transport systems: Xylem and Phloem

Question 6

how have plants adapted to Support their plant body against gravity on land

Answer 6

4. Support plant body against gravity
   
   1. Support of plant body: thicker cell walls and lignin

Question 7

how have plants adapted to Protect against abiotic and biotic stresses on land

Answer 7

5. Protect against abiotic and biotic stresses
   
   1. Secondary metabolites

Question 8

which came first, increased photosynthetic surfaces, or increased water transport infrastructure

Answer 8

Increase photosynthetic surfaces?

or Increased water transport infrastructure?

It seems that increased water transport infrastructure did. This is based on small plants from the devonian (400mya) that had no true leaf structures, but had xylem and a simple type of. It was found in New Brunswick.

Question 9

what was Psilophyton

Answer 9

Psilophyton: extinct vascular plant (420-360mya) had no leaves, grew to 0.5m tall. Had lignified xylem tissue, upwards growth not to increase photosynthetic area.

For the first 100 million years, no organisms could decompose lignin, lead to carboniferous coal.

Question 10

what do Xylem and Phloem do

Answer 10

Xylem transport: uptake of water and minerals by root, transported upward through xylem driven by respiration.

Phloem transport: Photosynthetic produces sugars which are transported downwards so roots can perform respiration. Gas exchange occurs all over.

Question 11

why aren’t mosses tall

Answer 11

Mosses lack vascular tissue and lignin and so can’t grow as tall as trees.

Question 12

what happens to gases in a plant body

Answer 12

Gas exchange occurs all over the surface of a plant, and doesn’t get transported far.

Question 13

where does secondary growth occur

Answer 13

Secondary growth begins with the formation of a ring/tube shaped lateral meristem called a cambium. It is between the primary phloem and xylem.

Question 14

what happens to meristomaic cells in secondary growth from lateral meristem

Answer 14

The meristomatic cells divide throughout the life of the plant and either push cells inwards (which become xylem type cells , secondary xylem) or push outwards (which become secondary phloem).

Question 15

what is wood

Answer 15

A vascular cambium cell adds xylem more often than phloem in secondary growth. Secondary Xylem = wood

Question 16

How does secondary growth account for added perimeter

Answer 16

Since the cells on the perimeter of the stem can’t divide it would begin to split open as the radius increases. But another lateral meristem forms called the cork cambium which makes more dermal cells to account for the increasing perimeter, make up the outer layer of a stem or root (cork cells).

Question 16

what is Periderm, Phelloderm, and bark

Answer 16

Cork Cambium: secondary dermal tissue (cork) add cork cels to outside and phelloderm inside. Cork cells = Periderm, Periderm + Phelloderm = Bark

Question 17

how is everything organized in the stem of edicts

Answer 17

Vascular bundles in eudicots are organized in a ring. Primary Phloem outside, Primary Xylem inside, with the vascular cambium in between.

Question 18

why do tree rings happen

Answer 18

When there is seasonal changes in secondary xylem production, tree rings form for every year of growth.

At the end of the fall the tree goes dormant, stopping growth. More vascular bundles early in year, less later.

Question 19

what is dendrochronology

Answer 19

Dendrochronology = Looking at tree rings from different years. Looking at thickness, or other factors to correlated to climate, atmosphere, etc.

Question 20

what are Annual vs Perennial Plants

Answer 20

Annual plant = Herbaceous plant - mostly composed of a primary body (derived from embryo)

Perennial plants = shrubs and trees - composed of primary and secondary tissues.

Question 21

how do primary and secondary growth help transport

Answer 21

Primary and secondary growth helps to transport water in tall trees.

Leaves evaporate water → helps to pull up xylem sap

Secondary xylem (wood) → stabilizes stem, forms new xylem every year.

Question 22

what are the three transport routes in plants

Answer 22

Water and nutrients in the plant body move via three pathways with different properties

1. Apoplastic
2. Symplastic
3. Transmembrane

Apoplastic route: Inside cell walls - easy

Symplastic rout: in cytosol, through plasmodesmata -easy

Transmembrane: crossing lipid bilayer more than once, in and out of cell - harder

Question 23

What are some examples of transmembrane transport of solutes in plants

Answer 23

Active transport: proton pump creates membrane potential pH gradient

Co-transport of ions/nitrates with protons (e.g. mineral uptake into roots)

Co-transport of neutral solutes with protons (e.g. sucrose in phloem)

Passive transport: ion channels (don’t depend on protons, may be gated)

Question 24

what happens to water in regards to plasma membranes

Answer 24

Plasma membrane is made of fats (lipids) - Although water-repellant, they are not water impermeable - Aquaporins: bidirectional channel proteins that allow only water molecules to pass in a single file at a rate of 3 billion per second (faster than diffusion through membranes) Free water will move into cells with a high solute [] due to osmosis

Question 25

what is water potential

Answer 25

Potential energy of water under given conditions. Compared to pure water under reference conditions. → Direction of water flow is driven by water potential (**Ψ)** - Measured in MPa - Free water moves from regions of higher water potential to regions of lower water potential - **Ψ = Ψs + Ψp**

Question 26

how do solutes and pressure affect water pressure

Answer 26

Solutes have a negative affect on **Ψ by binding water molecules** Positive pressure has a positive effect on **Ψ by pushing water** Negative pressure has a negative effect on **Ψ by pulling water**

Question 27

what is solute potential

Answer 27

The Solute potential **Ψs = osmotic potential of a solution, is directly proportional to its molarity** - **Ψs is always negative. Solutes in plants cells: ions and sugar**

Question 28

what is pressure potential

Answer 28

Pressure potential **Ψp is the physical pressure on a solution** ex: Turgor pressure = positive pressure, xylem sap is under negative pressure

Question 29

what is water pressure in living plant cell, pure water, and 0.1M sugar solution

Answer 29

Definition: pure water **Ψ = 0** Osmotic pressure of 0.1M sugar solution: -0.2MPa Pressure of living plant cell: 0.5-1MPa (70-120 Psi)

Question 30

how much water do trees use

Answer 30

Trees use 500-2,000L of H2O daily if not limited Western red cedar used 800L / day for example

Question 31

how is water taken up in roots

Answer 31

In the endodermis is a ring of cells that act as a barrier. The Casparian strip runs through their cell walls and blocks transport, forcing everything to go through the cells. So water must pass through the symplastic rout. Once in the xylem it is only apoplastic.

Question 32

how much water is lost from evaporation in trees

Answer 32

Water evaporates at the leafs surface. One maize plant losses 60L per season, passes through stoma.

Question 33

how is water pulled up xylem

Answer 33

A different in water potential pulls water up through the plant’s xylem until it leaves via transpiration or is used by the plant. Cohesion by h-bonds keeps water together. Adhesion by h-bonds cause water to stick to cell walls Molecules pull each other along according to the cohesion-adhesion theory.

Question 34

what happens if hydrogen bonds break in xylem

Answer 34

If the hydrogen bonds break - cavitation occurs, air get in the xylem and it stops working. Most transport is in young xylem.

Question 35

how is water loss regulated in plants

Answer 35

Transpiration: Water loss by aerial organs Cuticle prevents water loss at surface → 95% of H2O is lost through stomata, regulated by stomata density and pore opening/closing.

Question 36

how are guard cells opened and closed

Answer 36

K+ ions are pumped into cells, H2O floods in and guard cells ballon to open stomata. Potassium ions are pumped out of cells, H2O floods out and guard cells shrink to close stomata.