Chapter 38 & 39 - Transpiration, Transport, and Nutrition in Plants

Root Hairs

greatly increase a root’s absorptive surface

Xylem Vessels

pull water up from the roots

Transpiration Tension

water molecules cling to the cells by adhesion and stick to each other by cohesion

Flow of Water

flows upwards from roots

Transpiration

water evaporates from stomata in leaves, pulling more water upward

Water in Photosynthesis

reactant in light reactions, producing electrons, protons, and O2

Water’s Role in Cell Integrity

maintains turgor pressure, keeping cells firm and plants upright

Turgor Pressure

force exerted by water inside a plant cell against the cell wall

Water in Transport

acts as a solvent for nutrients in xylem and phloem

Water in the Stomata

is lost via evaporation

Apoplast Pathway

water goes through cell walls and intercellular spaces (doesn’t cross membranes) to reach xylem

Symplast Pathway

water goes through cytoplasm connected by plasmodesmata to reach xylem

Transmembrane Pathway

water moves across cell membranes and vacuoles to reach xylem

Endodermis with Casparian Strip

blocks passive flow through apoplast

Symplast

minerals enter through here, allowing plant to control what enters the xylem

Palisade Mesophyll

dense, columnar cells packed with chloroplasts

Palisade Mesophyll

maximizes light absorption

Spongy Mesophyll

looser cells with air spaces

Spongy Mesophyll

facilitates CO2 diffusion to photosynthetic cells and O2 release

Cohesion

water molecules stick to each other

Cohesion

forms continuous water column in xylem

Adhesion

water sticks to xylem walls

Adhesion

prevents collapse and helps capillary rise

Water Cohesion & Adhesion

allow transpiration pull to move water from roots to leaves

Low CO2 Concentration

triggers guard cell activity, opening stomata

Sunlight

signals guard cells to accumulate K+ and opens stomates

Biological Clock

internal timing mechanism in guard cells that helps them continue their daily rhythm of opening and closing

Source

region that produces or releases sugars (photosynthates)

ex: leaves performing photosynthesis

Sink

region that uses or stores sugars

ex: roots or fruits

Photosynthates

products of photosynthesis, mainly sucrose or other carb, transported through the phloem to fuel growth or storage

Sieve-Tube Elements

conduct sugars; living but lack nucleus and organelles

Companion Cells

have nuclei + organelles; support sieve tubes

can be attached to multiple sieve-tube elements

Companion Cells

load & unload sugars into sieve tube using active transport, maintain metabolic support, + help regulate pressure flow in phloe

Phloem Photosynthate Transportation

can move sugars up or down plant from sources to sinks depending on where energy or growth is needed

Phloem Sap

transports inorganic ions, amino acids, hormones, sugars

Sugar in Phloem

increases solute concentration, water enters from nearby xylem by osmosis, & increases turgor pressure

Osmosis

movement of water across a semi-permeable membrane from an area of lower solute concentration to high solute concentration

Sugar Source

sugar loaded into phloem tube, raising solute concentration, and drawing water into tube by osmosis 

Sugar Sink

sugars are unloaded into sink cells, decreasing solute concentration; water leaves phloem and moves back into xylem

lowers pressure

Xylem Direction of Transport

one-way, upwards, moving water + minerals from roots to leaves

Phloem Direction of Transport

two-way, bidirectional, moves sugars from sources to sinks

Xylem-Phloem Connection

xylem provides water for phloem’s pressure flow

Phloem-Xylem Connection

phloem delivers sugars to roots and other organs that support xylem growth

Macronutrients (9)

nutrients needed in large amounts for growth and metabolism; 98% of a plant’s dry weight

Micronutrients (8)

nutrients needed in small amounts, mainly as enzyme cofactors; 0.3% of dry weight

PCM: Potassium (K+), Calcium (Ca+2), Magnesium (Mg+2)

1.7% of a plant’s dry weight

Carbon (C)

macronutrient

Hydrogen (H)

macronutrient

Oxygen (O)

macronutrient

Nitrogen (N)

macronutrient

Sulfur (S)

macronutrient

Phosphorus (P)

macronutrient

Chlorine (Cl-)

micronutrient

Iron (Fe2+)

micronutrient

Manganese (Mn+2)

micronutrient

Boron (B)

micronutrient

Zinc (Zn+2)

micronutrient

Copper (Cu+2)

micronutrient

Nickel (Ni+2)

micronutrient

Molybdenum (Mo)

micronutrient

Nutrient Deficiencies

causes visible symptoms shown in shape and color

Nitrogen Deficiency

causes yellowing of older leaves

Phosphorus Deficiency

causes purplish stems or slow growth

Potassium Deficiency

leaf edges turn brown (scorching)

Nitrogen Plants Absorb

Nitrate (NO3-) and ammonium (NH4+) ions through soil

Nitrogen Fixation

nitrogen-fixing bacteria convert atmospheric N2 to ammonia NH3

Ammonifying Bacteria

add to supply of ammonium NH4+ by decomposing organic matter

Nitrifying Bacteria

Convert ammonium to nitrates NO3- (form most often taken up by plants)

Root Nodules

swellings on legume roots that house nitrogen fixing bacteria; creates low-oxygen environment for nitrogenase

Nitrogenase

enzyme that fixes nitrogen (converts N2 —> NH3)

Plant Symbiosis w/ Nitrogen Fixing Bacteria

legumes (peas, beans, alfafa, etc) form root nodules to house nitrogen-fixing symbionts in genus Rhizobium

Mycorrhizae

symbiotic associations between plant roots & fungi that enhance nutrient and water uptake; has evolved with plants

Mycorrhizae Function

act like extensions of plant roots, increasing area for absorption of water and minerals from soi

Mycorrhizae Formation

fungal hyphae grow around or into root cells

Ectomycorrhizae

fungi surround root surface and spaces between cells

Endomycorrhizae (arbuscular)

fungal hyphae penetrate root cells, forming arbuscules for nutrient exchange

Plant Mycorrhizae Benefits

better absorption of phosphorous, nitrogen, and water

Fungus Mycorrhizae Benefits

receives carbohydrates (sugars) from plant photosynthesis