AP Biology

Chapter 25.Transport and

Nutrition in Plants

Nutritional needsAutotrophic does not mean autonomous

plants need…sun as an energy sourceinorganic compounds

as raw materials

MacronutrientsPlants require these nutrients in relatively large amounts

C, O, H, N, P, K, Ca, Mg, S

Nutrient deficiencies

Lack of essential nutrients exhibit specific symptomsdependent on function of nutrientdependent on solubility of nutrient

Hydroponics

Transport and Nutrition• H2O & minerals

• Sugars• Gas exchange

Transport in plants• H2O & minerals

– transport in xylem – transpiration

• evaporation, adhesion & cohesion

• negative pressure

• Sugars• Gas exchange

Transport in plants• H2O & minerals

– transport in xylem – transpiration

• evaporation, adhesion & cohesion

• negative pressure

• Sugars– transport in phloem– bulk flow

• Calvin cycle in leaves loads sucrose into phloem

• positive pressure

• Gas exchange

Transport in plants• H2O & minerals

– transport in xylem – transpiration

• Sugars– transport in phloem– bulk flow

• Gas exchange– photosynthesis

• CO2 in; O2 out

• stomates

– respiration• O2 in; CO2 out

• roots exchange gases within air spaces in soilWhy does over-watering kill a

plant?

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Transport in PlantsTransport in Plants

• Water TransportWater Transport– Active transport and Active transport and

root pressureroot pressure• Cause water to move Cause water to move

from soil to rootsfrom soil to roots

– Capillary actionCapillary action• Combined with active Combined with active

transport and root transport and root pressure, moves pressure, moves materials throughout materials throughout the plantthe plant

Ascent of xylem “sap”: is it pushed up or pulled up? BOTH!

Pushing (positive pressure…..increases water potential): Due to Root Pressurenight = low transpirationconstant intake of ions/mineralsroot pressure at night causes guttation

Pulling (negative pressure…lowers water potential): Due to transpiration

PUSHY ROOTS!

Root Pressure

- low transpiration at night-Root cells still pumping ions in-Increase ions decreases water potential-By osmosis, water follows ions-Creates high pressure in roots-Naturally xylem sap moves up-Over the night, this continues, causing guttation

Cellular transport

• Active transport– solutes are moved

into plant cells via active transport

– central role of proton pumps• chemiosmosis – the

definition is…. the topic you thought you wouldn’t see again until the AP exam

STOP PULLING!

Transpiration-Main cause of water movement up a plant-Leaves = Water evaporates through stomata causing a pulling (tension) to replace the lost water-Stem = cohesion and adhesion properties of water (capillary action)-Roots = osmosis from ground to roots, then roots to xylem

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Transport in PlantsTransport in Plants

• Capillary action Capillary action (cohesion and adhesion)(cohesion and adhesion)

– Capillary transport results Capillary transport results from both cohesive and from both cohesive and adhesive forcesadhesive forces

– Water molecules Water molecules attracted to one anotherattracted to one another

– Water is also attracted to Water is also attracted to the xylem tubes in the the xylem tubes in the plantplant

– Causes water to move Causes water to move from roots to the stem from roots to the stem and upwardand upward

Regulation of stomates– light trigger

– temperatures

– depletion of CO2

– K ion concentration

– Natural circadian rhythm

Long distance transport• Bulk flow

– movement driven by pressure• flow in xylem tracheids &

vessels– negative pressure– transpiration creates negative

pressure pulling (mainly) xylem sap upwards from roots

• flow in phloem sieve tubes– positive pressure– loading of sugar from

photosynthetic leaf cells generates high positive pressure pushing phloem sap through tube

Pressure flow in sieve tubes

• Water potential gradient– “source to sink” flow

• direction of transport in phloem is variable

– sucrose flows into phloem sieve tube decreasing H2O potential

– water flows in from xylem vessels• increase in pressure due to

increase in H2O causes flow

What plant structures are sources & sinks?

can flow 1m/hr

2020

• Nutrient Nutrient TransportTransport

– Most nutrients Most nutrients are are pushedpushed through plantthrough plant

– Nutrient Nutrient movement movement takes place in takes place in phloemphloem

• Source to SinkSource to Sink– Source – any Source – any

cell that cell that produces produces sugarssugars

– Sink – any cell Sink – any cell where sugars where sugars are usedare used

– Pressure-flow Pressure-flow HypothesisHypothesis