Lecture 23: Plant Anatomy/Nutrient Transport

& Photosynthesis

Covers Chapters 7 & 43

Vascular seed plants

• Gymnosperms: non-flowering plants

• Seeds develop on surface of leaves or in a cone– Pine, eucalyptus trees

• Angiosperms: flowering plants

• 2 types, depending on number of cotyledons: a structure in the plant embryo that becomes the first leaf/leaves

– Monocots: ONE COTYLEDON

» some flowers, palm trees, grasses, wheat, rice, corn, oats

– Dicots: TWO COTELYDONS

» trees, other vegetables, some flowers

Gymnosperm

Monocot vs Dicot

Angiosperms

Angiosperms

Let’s stick to angiosperms only!

• Since 80% of all living plant species are angiosperms, we will focus our anatomy lecture and reproductive lecture on angiosperms only!

• There are a number of different types of cells in plants, but let’s just say that just like in humans, cells combine to form tissues.

Cells form Tissues

• Plant cells, as they divide and differentiate, can form different tissues (one or more type of specialized cell that perform a specific function):– Dermal Tissue*– Ground Tissue*– Vascular Tissue*

3 types of plant tissues*– In general, go from outside of plant to inside– Dermal Tissue System: covers outer surface of plant body

• Primary purpose: reduce evaporation of water– Waxy cuticle (waterproof covering on leaves)– Periderm (waterproof covering on stems & roots)

– Ground Tissue System: aka cortex• Primary purpose: photosynthesis, storage and support• Fruit and flowers arise from ground tissue

– Parenchyma: photosynthesis, secretion of hormones, food storage

– Collenchyma & Sclerenchyma: support and strengthen plant (take out?)

– Vascular Tissue System: aka vascular bundle• Primary purpose: transports fluids and dissolved substances throughout plant

body– Xylem: transports water and dissolved minerals (K, Ca, phosphate, Cl)

FROM ROOTS TO TOP OF PLANT– Phloem: transports a solution of sugars, amino acids and hormones from

structures that made it IN ALL DIRECTIONS (up and down plant, to or from leaves)

Plant Tissue

Xylem/Phloem

Tissues combine to form systems*

• Two systems:– Root System: consists of all of the roots– Shoot System: all structures above ground

Root System

• *Roots: branched portions of plant body, usually embedded in soil.• Have either

– taproot system: central root with many branches (dicots)– fibrous system: many roots of equal size (monocots)

• *Contain all three types of tissue– Dermal Tissue: periderm

– Ground Tissue• *Store surplus food (carbs) manufactured in the shoot during

photosynthesis• *Anchor the plant • *Produce some hormones Absorb water and minerals (vascular

tissue)– Vascular Tissue: vascular bundle (X&P)

• *Absorb water and minerals• *Transport water, minerals, sugars and hormones to and from the

shoot

How do roots acquire water/nutrients?

• Plants acquire:

– Carbon from CO2 in the air

– Oxygen from the air or from O2 dissolved in water

– Hydrogen from H20

– Minerals and water from the soil (water by osmosis, minerals by active transport)

root hairepidermis

cortex

endodermisof cortex

pericycle

xylem

phloem

apicalmeristem

vascularcylinder

rootcap

Roots

Fig. 43-13

Shoot System*

• Two basic parts: – Buds:

• Give rise to– Leaves: principle site of photosynthesis– Flowers & Fruit: contain plant reproductive

organs & gametes– Stems:

• elevate, support and separate leaves, flowers and fruit above the ground

Leaves• *Major photosynthetic structure of most plants

• *Contain all three types of tissue

– *Dermal Tissue: waxy cuticle and STOMATA

– *Ground Tissue: Mesophyll cells (photosynthesis here!)

– *Vascular Tissue: vascular bundle (X&P), called VEIN

• Sugars made in mesophyll cells travel in vein to other areas of the plant

• Many plants have evolved specialized leaves depending on climate/location/predators, etc

Stomata*

• Stomata: adjustable pores that can open/close and let CO2 and water in, let O2 out

– Leaves cannot entirely close stomata, because then CO2 cannot get in….therefore, transpiration happens: loss of water through stomata (plant lose 90% of water taken in by roots this way!)

– The water being lost from stomata creates tension that pulls water up from roots (this is how water can get to the top of a 350-foot tall tree!)

– Guard cells line the stomata and can change shape, size and volume, causing stomata to open/close

– Like humans and oxygen, plants need CONTINUOUS CO2!

upper epidermis

petiole

blade

mesophyll

palisadelayer

spongylayer

lowerepidermis stoma guard cell chloroplasts

xylem phloem

vascular bundle

cuticle

cuticle bundle-sheathcell

A Typical Leaf

Fig. 43-6

Stomata

Fig. 43-22

2

1

3

water molecules

Waterevaporatesthrough thestomata of leaves

Water entersthe vascularcylinder of theroot

Cohesion ofwater moleculesto one another byhydrogen bondscreates a “waterchain”

flo

w o

f w

ate

r

Water Flow from Root to Leaf in Xylem

Fig. 43-21

Specialized Leaves

Fig. 43-7

Stems*• Elevate, support and separate leaves • Transport water and dissolved minerals from roots to

leaves• Transport sugars produced in photosynthetic parts of shoot

to roots and other parts of shoot (buds, flowers, fruit)• Contain all three types of tissue

– Dermal Tissue: periderm– Ground Tissue: Cortex & Pith – Vascular Tissue: Vascular bundle (X&P) plus cambium

• Cambium differentiates into secondary X&P: this is the WOOD in the tree.

Stem

Fig. 43-8

terminal bud

apicalmeristem

leaf primordia

node lateral bud

internode

vascularbundle

pith

branch(sproutedlateral bud)

petiole

bladeleaf

epidermis

epidermis cortex

cortex

cortex

pith

primary phloem

vascularcambium

vascularcambium

dividingvascularcambium

primary xylem

secondary phloem

cork

newsecondaryxylem

primaryxylem

newsecondaryphloem

primaryxylem

primaryphloem

primaryphloem

pith

pith

cork cambium cork

(a) Primary and secondary growth in a dicot stem (b) Stem cross-sections (c) Vascular bundles

vascularbundle

cork cambium

secondary xylem

sec

on

da

ry g

row

thp

rim

ary

gro

wth

Photosynthesis

• Solar energy is trapped and stored as chemical energy in the bonds of organic molecules as sugars.*

• Occurs in plants, photosynthetic protists, and certain bacteria (we focus on plants)

• Takes place in leaf cells (mesophyll) in chloroplasts: organelles like mitochondria (double-walled organelles in plant cytoplasm)*

Anatomy of a chloroplast*

• Outer membrane• Intermembrane space• Inner membrane• Stroma: area inside inner membrane• Thylakoid: disc-shaped interconnected

membranous sacs in stroma• Chlorophyll: photosynthetic pigment in thylakoid• Thylakoid space: space inside thylakoids

Chloroplast

Closeup of thylakoid

2 stages of photosynthesis*

• Light reactions: (IN THYLAKOID)– Chlorophyll captures sunlight energy and

transfers it to ADP & NADP+ (energy carrier molecules..result is ATP & NADPH). Water is split and O2 gas is byproduct

• Calvin cycle (aka dark reaction): IN STROMA) – CO2 from atmosphere is made into a 3-carbon

sugar (that can be changed into glucose), using chemical energy from the light reaction

An Overview of the Relationship Between the Light Reactions and the Calvin Cycle

Fig. 7-3

A little bit about light

• Light is composed of individual units called photons

• Energy of a photon corresponds to its wavelength: short-wave photons are very energetic, long-wave photons less energetic

• Light hits leaf: could bounce back, pass through, or be captured

• Any light that bounces back reaches our eyes

• Chloroplasts contain pigment molecules that absorb (capture) different wavelengths– Chlorophyll reflects green, making plants look green!

– Carotenoid pigment molecules reflect orange and yellow (leaves in fall have lost chlorophyll, appear red, yellow, orange!)

Light reaction*• Like cell respiration, electrons carry energy from one place to another.

• Takes place within/across thylakoid membrane

• Light hits chlorophyll molecule in thylakoid membrane

• Light energy is transferred to electrons, which travel through two electron transport chains and then transfer the electrons (and a hydrogen ion) to NADP+, which converts it to NADPH.

• H20 is split and this creates a high H+ concentration inside thylakoid space (and low H+ in stroma)

• O2 is created and released from plant to atmosphere

• This concentration gradient is utilized: as H+ moves down its gradient from thylakoid space to stroma, it powers the synthesis of ATP from ADP

Events of the Light Reactions Occur In and Near the Thylakoid Membrane

H+ are pumped into the thylakoid space

ATPsynthase

photosystem I

photosystem II

thylakoidmembrane

lightenergy

+P

ATP

NADP+

ADP

NADPH

Calvincycle

CO2

C6H12O6

sugar

e–

e–

e–

e–

e–e–

1/2

2

H2O

chloroplast

electron transport chain IIelectrontransportchain I

(stroma)

(thylakoid space)

thylakoid

O2

A high H+ concentration iscreated in the thylakoid space

The flow of H+ down their concentration gradientpowers ATP synthesis

H+

H+ H+

H+

H+

H+

H+

H+

H+

H+

H+

1

23

Fig. 7-7

Dark reaction aka Calvin Cycle*• ATP and NADPH from light reaction are now positioned in the stroma

• Calvin cycle is really THREE reactions:

– Carbon fixation: CO2 (plant takes in from atmosphere) is incorporated into a larger molecule.

• Each molecule of CO2 combines with a molecule of RUBP (a 5-carbon sugar) to form TWO molecules of PGA (a 3-carbon sugar), catalyzed by the enzyme RUBISCO

– Synthesis of G3P: energy from ATP & NADPH is used to convert 6 PGA molecules to 6 molecules of G3P (also a 3-carbon sugar)

– Regeneration of RUBP: 5 of the 6 molecules of G3P are used to regenerate RUBP, and 1 molecule of G3P combines with another to form glucose!

• Glucose is then used by cell or stored.

Calvin Cycle