Ch 36: Resource Acquisition and Transport in Vascular Plants

What resources do plants acquire?

• Co₂

• H₂O

• Light

• Sugar

Are there any trade-offs in resource acquisition?

What are the two major transport continuums in plants?

Apoplast and symplast

How are resources transported over short distances within the plant?

How are resources transported over long distances within the plant?

What are the main ways plants acquire resources?

Through leaves (above ground) and roots(below ground_

What is acquired through the shoots?

Sunlight and CO2

very rarely water through stomata

What is acquired through the roots?

water and dissolved minerals

Why is sunlight and CO2 needed?

• for photosynthesis

• Co2 + H2O + Sunlight → Sugar (Chemical Energy) + O2

What are the common minerals absorbed by the roots?

• Nitrogen

• Phosphorous

• Potassium

Why are N, K, and P needed for plants?

• for many cell functions like photosynthesis

• They are important components of organic compound

  • proteins (made of nitrogen) and nucleic acids (made of nitrogen and phosphorous)

What is LAI?

• stands for Leaf area index

• represents the ratio of the total leaf area to the ground area beneath the plants

• indicates how much leaf surface is available for photosynthesis and other processes.

What are the different stem length patterns?

• Short stems

• Long stems - to grow above others and avoid shading

What are the different branching patterns?

• lots of branching - improves sunlight interception and increases LAI

• small amnt of branching

What is the tradeoff for different stem and branching patterns?

• plants have to choose between growing tall or having more branches

What different ways shoots can vary for resource acquisition?

• stem length and branching pattern

• Leaf size, arrangement, and orientation

• Opening/closing of stomata

What are the different types of leaf size for resource acquisition?

• large leaves - wet envrionments

• Small leaves - dry environments

What is the tradeoff for larger leaves?

• larger leaves require more water and lose more water than smaller leaves because of their greater surface area

What are the different ways leaves can be arranged on a stem?

• Opposite or alternate

• On one plane or more planes

Describe opposite vs alternate leaf arrangement?

• Opposite: Two leaves per node, positioned directly across from each other.

• Alternate: One leaf per node, positioned alternately along the stem.

What are the different ways leaves can oriented?

• vertical

• horizontal

Describe leaf arrangement on one plane vs many?

• One Plane: All leaves are in the same plane, either around a central point or along a straight line (common in rosettes or some opposite/alternate arrangements).

• Many Planes: Leaves grow at different angles and positions, forming a spiral or helical pattern, creating a 3D arrangement that allows better light interception (common in pine trees, cacti, and ivy)

  • many = higher LAI

What are the benefits of vertical leaf orientation?

• less exposed to the intense midday sun to reduce heat stress and water loss

• where sunlight is limited, such as shaded or crowded areas, vertical leaves may help the plant maximize light capture by avoiding shading from other leaves.

• less likely to catch wind to avoid damages

• Prevents water from collecting on leaf which reduces fungal or mold growth

What are the benefits of horizontal leaf arrangement?

• large surface area to capture sunlight

• improved CO₂ absorption

• maximized water collection

• provide protection for lower leaves

• improved heat dissipation

• adapted for crowded environments to capture light through gaps

In what ways can stomata’s be used for resource acquisition?

• opening the stomata to take in more CO₂

• closing the stomata to stop loss of water

How much water is lost through the stomata?

• 95%

What is a tradeoff of water loss through the stomata?

• Closed stomata means less water loss but also means less CO₂ intake = lower photosynthesis levels

What parts of plants help to keep water in?

Leaves and stems that have waxy cuticles

How can stomatal density be affected by genetics and environments?

• Plants adapt genetically to dry/wet environments by have less/more stomata

• Low levels of CO₂ during leaf development will increase stomata

How are stomata’s able to open and close?

• guard cells

• if swollen with water, they are turgid and bow out to open the stomata (accumulation of K+ in vacuoles)

• K+ leaves guard cells, water follows, stomatas are shrunken and closed

What are the 3 primary cues for a stomata to open?

1. Light at dawn

2. Co2 Depletion in air spaces

3. internal circadian clock

Why would the stomata want to be open during the day?

• to get more CO2 to come into the plant while the sun is out so photosynthesis can take place

When might the stomata close?

• When too much water is being lost

• Under water stress like a drought

• closed stomata conserves water

In what ways can roots change to for optimized resource acquisition?

• Root length/depth

• branching pattern

• hair density

When might root length/depth change?

• to access deeper nutrients or water

• if water levels lower, roots can grow to reach it

What are the benefits of different root branching patterns?

• accessing water at varying depths

• Branching into pockets with more nutrients

What are the benefits of different root hair density?

• high density increases water and nutrient uptake

• Low density = less uptake

In what ways are roots genetically controlled to be different?

• monocots have fibrous roots that are more spread out horizontally to access water closer to the surface

• eudicots have tap roots that grow deeper to access deeper water

What plants are known to have vertical leaf arrangment?

cacti and some grasses

What plants are known to have horizontal leaf arrangement?

• sunflowers

• cabbage

• many grasses

What is apoplast?

• a major transport continuum including everything external to living cell plasma membranes

• includes cell wall, extracellular spaces, interiors of dead cells like tracheids and vessel elements (water collecting cells of xylem).

• crosses through many cell membranes

What is symplast?

• a major transport continuum

• includes everything internal to cell plasma membranes like cell membrane and protoplasm

• crosses one cell membrane and more to other cells through plasmoedsma

What is protoplasm?

a term used for the cell membrane and its contents

What is plasmodesma?

• “doors/tunnels” that connect different cells

What is the transmembrane route?

• it goes through both apoplast and symplast transport continuums

At what level does short distance transport occur?

• the cellular level = moving substances into or out of the cell

How is short distance transport controlled?

• through membrane permeability (passive or active)

What is passive transport?

• no energy input from cell

• substance moves along its concentration gradient

• includes diffusion and osmosis

What is active transport?

• needs energy(atp) from the cell

• substance moves against its concentration gradient

• includes pumps and transport proteins

What is diffusion?

net movement of particles from area of greater concentration to area of lesser concentration

What is osmosis?

the diffusion of “free” water molecules

What is water potential?

• Symbol = Ψ (like trident)

• It is the gradient for water movement in osmosis

How does water move along the water potential?

• It moves from high to low potential to reach equillibirum

What is the formula for water potential?

Ψ= Ψ_S+ Ψ_P

What are the two components of water potential?

• solute potential (Ψ_S)

• pressure potential (Ψ_P)

What is the unit for water potential?

Mega Pascal (MPa)

What is the water potential of pure water?

0 MPa

What is a solute potential?

• Ψ_S

• component of water potential based on solute concentration

• highest value it can be = 0

• Adding solutes decreases Ψ_S and water will follow

What is pressure potential?

• Ψ_P

• component of water potential based on physical pressure exerted on water within a system

• Can be a positive or negative value

  • positive = turgid cells, water moving water from the pressure

  • negative = tension cells, water moving towards the pressue

What does it mean for a plant cell to be turgid?

• The cell is filled with water

• lower solute potential inside the cell compared to surroundings

• pressure potential is postive

What does it mean for a plant cell to be flaccid?

• Water is leaving the cell

• the surroundings have lower solute potential

• pressure potential is negative

If isolated plant cells with a water potential averaging​-0.5 MPa are placed into a solution with a water potential of​-0.3 MPa which of the following would be the most likely​ outcome and why?

A. The pressure potential of the cells would increase

B. The cell walls would rupture, killing the cells

C. Water would move out of the cells

D. Solutes would move out of the cells

• Because water moves from high water potential to low water potential, water would move into the cell because it has a more negative value than the solution

• SO the pressure potential of the cells would increase and water potential would increase

If isolated plant cells with a water potential averaging​-0.5 MPa are placed into a solution with a water potential of​-0.3 MPa What would the water potential of the cell be at equilibrium?

• Outside it would stay -0.3 MPa and the inside would also be -0.3 MPa to be equal

• Outside = Inside

How do plants use proton pumps?

• uses energy to pump H+ protons out of the cell to establish a membrane potential and proton gradient

• Protons are now able to diffuse back into the cell, with solutes(moving against their gradient), through cotransporters

What type of pumps does plants use?

• proton pumps

• (unlike animals which use sodium-potassium pumps)

What are cotransporters?

• A type of protein that H+ protons will use to get back into cell after a membrane potential and proton gradient are established

What is bulk flow?

• type of active transport

• The movement of a fluid driven by a pressure gradient

  • the fluid is pushed or pulled in a uniform direction

How are resources transported over long distances?

• through active transport like proton pumps

Why can diffusion and osmosis not be used for long distance transport?

• Because those pathways are too slow

What moves though cells of xylem and pholem?

• water and solutes together

What do branching veins ensue in regards to cells?

• ensure all cells are within a few cells of vascular tissue so they can receive water and nutrients

What routes are used to move water from soil to xylem?

• apoplastic

• symplastic

• transmembrane

What is the process of moving water form soil to xylem? (5 steps)

1. Apoplastic route

2. symplastic route

3. transmembrane route

4. to endodermis

5. transport in the xylem

What is endodermis?

What drives bulk flow in xylem?

Pulls water and minerals up using negative pressure through Transpiration

What is transpiration?

It is the evaporation of water from a plant’s surface (through the stomata)

What allows water to be pulled in xylem?

• Because of cohesion of the water molecules sticking together

• AND because of adhesion of water molecules to xylem wall

What is the maximum height a plant can be and still have transpiration and cohesion pulling water up?

• 116 meters

• Taller than statue of liberty and big ben

As water is pulled up through roots what is happening in regards to pressure vs. water evaporating through the leaves?

• Pressure is increasing in the roots then decreases as water exits through leaves

• water is moving from high pressure to low pressure

What is the world’s tallest tree?

• Hyperion (red wood tree)

• In California

• about 116 meters tall

Is the movement of resources in the phloem more pushing or pulling?

• Pushing which is a positive pressure

What is phloem sap?

• a solution of water and sugar

• can include others like amino acids, hormones, and minerals

What is translocation?

• the movement of sugars from source (like leaves) to sinks (like roots)

• preformed by phloem

How does sugar move from mesophyll leaf cells to phloem cells?

• through apoplastic or symplastic routes

What is needed to transport sugar into phloem cells?

• ATP to move the sugar against its concentration gradient

As sugar moves from source to phloem what happens in regards to pressure?

• Pressure potential is increasing, and water follows and solute potential is decreasing

• As sugar moves down plants to sinks, pressure potential decreases, water leaves, and solute potential is increasing.

In storage roots, where is the sink vs. source?

• Sink = leaves

• Source = roots

• Sugar is moving from roots to leaves

Q4: Which of the following is a correct statement about a difference between xylem and phloem transport?

A. Active transport moves xylem sap but not phloem sap

B. Xylem sap moves from sugar source to sink, but phloem sap does not

C. Transpiration moves phloem sap but not xylem sap

D. Xylem sap moves up; phloem sap moves up or down

D. Xylem sap moves up; phloem sap moves up or down

Is phloem sap movement only one way?

• No, it can go up or down depending on the type of plant.

Is xylem movement only one way?

• yes, it is only roots to shoots