BIOL 1011

Lecture 1

Plants and the Colonization of Land

Agriculture

(incented 10,000 years ago)

Consequences:

-permanent villages, towns, cities

-larger family → larger population

-diverse economy

-less cooperation

-socioeconomic classes

-separation of humans from rest of nature

-large scale war

Plants create many things:

rubber → rubber tree

cotton

Drugs: plant Secondary Compounds

-not necessary for metabolism, growth of development

-e.x. quinine

-plant: bark of cinchona tree

-natural range: south america, now introduced worldwide

-treat: malaria (from 1650s in europe) / anemia/ muscle spasms/ cancer/ tonic water

e.x caffeine (coffee tree)

aspirin (willow species) contains acetylsalicylic acid

THC tetrahydrocannabinol (hashish, marijuana - cannabis sativa)

Nicotine (tabacco)

opium, heroine, morphine, codine (opium poppy, papaver)

Taxol (from yew: taxus) → chemotherapy

Importance of Plants:

1. energy: food (agriculture)
2. energy: fossil fuels
3. clothes
4. drugs, medicines
5. ecosystems functioning
6. biodiversity

What is a Plant

Photosynthetic Eukaryotes

Plants and red algae

→ from primary endosymbiosis: prokaryote + eukaryote = eukaryote

non photosynthetic eukaryote engulfed a photosynthetic cyanobacterium (now a plastid)

Other Eukaryotes

→ from secondary endosymbiosis: eukaryote + eukaryote = eukaryote; non photosynthetic eukaryote engulfed a photosynthetic eukaryote (green or red alga)

Plants in History of Life:

-Plants split from red algae -1500 mya

-both single cell and multicellular forms

-only marine

-moist environments near oceans

500mys: colonization of drier environments

adaptations:

-cuticle

-vascular tissue: roots and shoots

-relationship with fungi

-seeds and pollen

since colonizing land: 290,000 species

important: 4550/3500/1st plastid/500

Features of ALL Plants:

1. starch as main energy-storage molecule
   1. polysaccharide (carbohydrate) of glucose residues

→sugar as an energy storage:

-not very reactive

-easily metabolized

-absorbs and holds water - scratch is solution

1. Chlorophyll b
   1. chl a: all photosynthetic eukaryotes
   2. chl b: accessory pigment; passes energy to chl a
   3. chl b: absorbs slightly different wavelengths
2. Cellulose is major component of cell wall
   1. polysaccharide: unbranched glucose residues (different bonds from starch)
   2. most common organic polymer on earth
   3. cotton 90%
3. Thylakoids in stacks (grana)
   1. rather than as simple bands
   2. thylakoids are membranes inside chloroplasts - contain chlorophyll

Ancestors of Land Plants

-charophytes are the closest relatives of land plants

evidence: 1. both nuclear and chloroplasts genes 2. structure

-type of ‘green alga’

-land plants are not descendants from modern charophytes but share a common ancestor with modern charophytes

Features of Charophytes and Land Plants

1. cell plate and phragmoplast (short microtubules)
2. plasmodesmata → extensions of cell membrane through pores in cell wall
3. sperm structure
4. peroxisome enzymes
5. rose-shaped cellulose synthesizing complexes
6. sporopollenin: durable polymer

Sporopollenin:

-durable polymer

-found in walls of plant spores and pollen

-chemically inert

-stable

-persists in environment

-protects from desiccation, decay, etc

Advantages: The Move to Land

-air filters less sunlight than water → there is more light for photosynthesis

-air has more CO2 than water → there is more fuel for photosynthesis

-early terrestrial habitats lacked pathogens or predators/herbivores

-terrestrial soil is richer in nutrients than aquatic

Challenges/Adaptations: Move to Land

Features of LAND Plants:

• cuticle-waxy covering
• multicellular, jacketed (set of sterile cells around them) sex organs = ‘gametangia’

male sex organ: antheridium → produces sperm (haploid)

female sex organ: archegonium → produces egg (haploid)

• embryophyte condition → zygote retained in maternal tissue

zygote: land plants are also called embryophytes

• alternation of generations

both haploid and diploid phase are multicellular

2 Generations: Sporophyte & Gametophyte

-Arose independently in evolution several times

Alternation generations are: →does not occur in charophytes

1. gametophyte (haploid; 1n) → makes gametes by mitosis
2. Sporophyte (diploid; 2n) → makes spores by meiosis

[Green alga without alternation of generations]

most of life: single cell/haploid

origin of alternation of generation:

Zygote delays meiosis and divides and grows = multicellular diploid

Lecture 2

Major Groups of Land and their Reproduction

In Land Plants:

Meiosis produces Spores

Spore:

Single cell that can divide to produce a multicellular organism (often with protective coat)

Gamete:

Single cell that can unite with another gamete to produce a diploid zygote

→ There are 10 divisions (phyla) of land plants (the embryophytes)

→ 4 major divisions of land plants:

1. mosses
2. ferns
3. conifers
4. angiosperms

Moss:

-15,000 species

-Low growing

-confined to damp areas

→ swimming sperm

→no true vascular tissue (rudimentary vascular system)

-no true leaves

-Gametophyte dominant

→ Major step in evolution: Vascular Tissue

Pterophyta: Ferns (horsetails, etc.)

-20,000 species

-mainly tropical

-appeared 400 mya

-Vascular tissue

-Xylem and phloem

-support and supply

-swimming sperm

-sporophyte dominant

(fern sporangia)→ 2 kinds of leaves:

1. cinnamon fern
2. group of sporangia

Fern spore release:

cinnamon fern:

Spore Size:

1. Homoespory
   1. 1 size of spore from meiosis
   2. mosses and most ferns
2. Heterospory
   1. 2 sizes of spore from meiosis
   2. some ferns and all seed plants

Seed Plants:

5 divisions (phyla) of seed plants

1. cycadophyta
2. ginkgophyta
3. coniferophyta
4. gnetophyta
5. anthophyta

→ have both seeds and pollen

Seed:

-embryo + nutrition + seed coat

-develops from ovule

-novel structure appearing in seed plants

-site of (female) meiosis

-contains female gametophyte, female sex organs, egg and embryo

Ovule (conifer) at early stage (BEFORE meiosis in megasporangium)

Ovule (conifer) at early stage (AFTER meiosis in megasporangium)

Ovule becomes seed

→Both seeds and pollen cont.

Pollen:

-Mature male gametophyte

-Few cells in size

Coniferophyta - the conifers

-550 species

-reproductive organs in cones

-sporophyte dominant

-Heterosporous

-Microgametophyte = pollen

-Megagametophyte

→ within ovule

→ makes egg and then nourishes

e.x. white pine / larch,tamarack /Bald cypress

→ in conifers:

seed:

-embryo + megagametophyte + seed coat

(rest is the same)

Conifer Gametophytes:

Mega Gametophyte

-makes egg in archegonium

-nourishes embryo

Micro Gametophyte

-pollen grain (makes sperm)

Life Cycles:

1. Heterosporous 2. Seed-Plant

Phylum Coniferophyta - summary

-seeds and pollen

-cones: separate male and female

-naked seeds: “gymnosperms”

-seed: embryo nourished by megagametophyte

-slow reproduction

E.X. slow reproduction: Jack Pine

Male cones:

-development started 1yr ago

-this year they will pollinate female cones (started 1 year ago)

Female cone:

-initiated 2 yrs ago

-pollinated 1 year ago (female meiosis after pollination)

-will mature into woody cone this year with mature seeds

Summer Year 1:

-initiate male and female cones

Summer year 2:

-male meiosis: pollen

-pollination

-female meiosis after pollination

Summer Year 3:

-Fertilization (summer)

-Mature seeds (late summer/fall)

Lecture 3

Flowering Plants and Structure of Growth of Land Plants

→Anthophyta appeared around 150 mya then exploded into many species

Angiosperm Terrestrial Revolution

Fact: The diversification of the angiosperm coincided with a dramatic diversification of other organisms

Hypothesis: “Many of the most diverse organisms today, including angiosperms, spiders, insects and vertebrates showed their major diversifications fueled by the angiosperm terrestrial revolution”

• the origins of modern biodiversity

-today 85% of plant, animal, and fungal species live on land rather than in the sea

→ half live in tropical rainforests

-an explosive boost to terrestrial diversity occurred from c. 100-50 million years ago

→ biosphere expanded to a new level of productivity

→ coincided with innovations in flowering plant biology and evolutionary ecology,

including: flowers and efficiencies in reproduction

coevolution with animals, especially in pollinators and herbivores

photosynthetic capacities

adaptability; ability to modify habitats

→rise of angiosperms triggered a macroecological revolution on land and drove modern biodiversity to new high level, a series process we name the Angiosperm Terrestrial Revolution

Expanding Angiosperm Diversity and Species Number

• insect pollination
• flexibility in seed production and dispersal
• greater genetic and phenotypic flexibility in cell and shoot elongation
• more complex mechanisms for activating and repressing
• the genes
• greater complexity of the flower

Div.Anthophyta - Flowering Plants

• 300,000 (named)
• 400,000 (estimated) species
• reproductive organs in flowers
• sporophyte dominant
• heterosporous
• microgametophyte = pollen
• megagametophyte: 8 nuclei

Flower Structure

→ 4 whorls of modified leaves

Monocots

Grasses:

• maize
• wheat
• rice
• bamboo

Orchids:

• irises
• lilies
• palms

Eudicots

• oaks
• maples
• dandelions
• sunflowers
• legumes
• melons
• potato
• poppies
• roses

Male and Female Sex Organs within a Flower: Hermaphroditic

→ 85% of angiosperm species have cosexual = hermaphroditic flowers

→ Monoecy: separate male and female flowers on the same individual (e.x. paper birch)

→ Dioecy: Male and female sex organs on different individuals (e.x. willow)

Pollination:

→ arrival of pollen on stigma (flowering plant) or on a receptive female cone (conifers)

• occurs only in seed plants
• conifers: wind
• flowering plants: 1. insects 2. birds 3. bats 4. wind

Pollination in Angiosperms:

reward for pollinator:

• nectar (sugar water)
• pollen

Advertisements by plant:

• showy flower
• possibly odor

→ BOTH reward and advertisement are costly

Pollination Syndromes:

-Integrated sets if floral traits (e.g. morphology, colour, odour, size, rewards) associated with particular pollinator groups

e.x. of convergent evolution

• traits have evolved separately many times, can thus occur in unrelated plant species

Pollination by Bees:

syndrome:

• shape: various; can be highly specialized or not
• Colour: various; including yellow, blue, orange (not red)
• Odour: none or highly specialized

Pollination by Bats or Moths:

Syndrome:

• shape: tubular, open at night
• Colour: yellow or white
• Odour: strong and sweet
• Nectar: large quantity

Pollination by Birds:

Syndrome:

• Shape: tubular
• Colour: red most common, also yellow
• Odour: none
• Nectar: large quantity, often weak (20% sugar)

Pollination by Wind:

• Shape: not showy (reduced petals)
• Odour: none
• Nectar: none
• Pollen: very large quantity

Pollination cont.

-there is great variation among plant species

some plants:

1. pollinated by many animal species
2. pollinated by one animal species
3. provide no reward: deceit pollination (e.x. pink lady slipper orchid)

Pollination by Deceit: (in some orchids)

Orchids:

• pollen in 2 packets (pollinia)

Reward:

• nectar
• none: deceit pollination

→ pollination syndromes are not perfect

Angiosperm Life Cycle:

note: double fertilization → 2 sperm nuclei in pollen

- 1 fertilizes egg → embryo (2n, diploid)

-1 fertilizes central cell → endosperm (3n, triploid)

Pollen growth:

1. pollen lands on stigma: pollination
2. pollen tubes grow towards ovules

Angiosperm Ovules and Ovaries:

-ovules become seeds

-ovaries becomes fruit

Dispersal of Seeds and Fruits:

Winds:

• maple
• cottonwood

Water:

• coconut
• water lily

Animals:

• blueberry
• cocklerburr

Nourishing the Embryo

Conifers:

• megagametophyte (1n)

Angiosperms:

• endosperm (3n) (2 haploid from mom 1 haploid from dad)

Endosperm is the principal foodstuff of civilization:

• more than half of (direct) daily calories worldwide
• especially 3 cereal grasses: rice, wheat, corn (maize)
• domesticated around 10,000 years ago

Conquest of the Land:

• cuticle
• sporopollenin
• jacketed sex organs (antheridia, archegonia)
• embryo retention
• stomates (stomata)
• vascular tissue (xylem, phloem)
• seed and pollen
• flower
• fruit

Conifers and Flowering Plants:

3 Variations of Alternation of Generations

Land Plant Structure and Growth

Two Systems in Vascular Plants:

• shoots
• roots

Evolutionary Adaptations of Stems:

1. Iris Rhizome
   1. rhizomes grow underground
   2. vertical shoots emerge from axillary buds at nodes
2. Strawberry Stolon
   1. stolons grow along surface
   2. plantlets from nodes: asexual reproduction
3. Potato Tuber (stolon or rhizome)
   1. storage
   2. ‘eyes’ are axillary buds at nodes

Plant Cell Walls:

→ cellulose microfibrils: adjacent, parallel cellulose molecules

• extracellular: outside of membrane
• composed mostly of cellulose (polysaccharide of glucose units)
• 2 kinds: 1. primary wall (thin, in all cells)

2. Secondary wall: thicker (in some cells) strength

Function of Plant Cell Wall:

1. determines and maintains cell shape
2. provides support and mechanical strength (allows plants to get tall, hold out thin leaves to obtain light)
3. prevents the cell membrane from bursting (i.e. resists water pressure)
4. Controls the rate and direction of cell growth and regulates cell volume
5. responsible for the plant architectural design
6. Physical Barrier to:
   1. pathogens
   2. water in suberized (waxy) cells
      1. note: wall is very porous and allows the free passage of small molecules
7. hh

Plant Cell Wall Composition:

3 kinds of polysaccharides:

1. cellulose
   1. polymer (chain) up to 25,000 glucose molecules
   2. around 36 chains bond to make microfibril
2. cross-linking glycans (hemicellulose) - bond with cellulose
3. Pectin - jellylike glue

Cells Sticking Together:

Middle Lamella

• material between cells
• made of pectin substances

3 Tissue System in Vascular Plants

1. Dermal Tissue
   1. single layer; secrets cuticle (waxy)
2. Vascular Tissue
   1. Xylem and phloem: support and supply
3. Ground Tissue
   1. Bulk of young plant; fills space between dermal and vascular tissues; mostly parenchyma; storage, photosynthesis, support

Plant Cell Types:

Dermal Tissue:

• Epidermis

Ground Tissue:

• Parenchyma
• Collenchyma
• Sclerenchyma

Vascular Tissue:

• Tracheids and vessel elements
• sieve elements

Epidermal Cells:

-Outermost cells

-single layer (single sheet) covering leaves, stems and roots of non woody plants or plant parts

-Functions:

- waterproofing

- protection from pathogens: viruses, bacteria, fungi

- (other specialized roles): hairs (trichomes) / nectary/ guard cells: gas exchange

Cuticle:

→ formed by the epidermal cells outermost part is wax

protection against;

• water loss
• pathogens
• ultraviolet (UV) radiation

→Secretory Trichomes

3 Kinds of Trichomes on 1 leaf

1. Trichomes
2. Secret oils (defense)
3. Hinder crawling insects (defense)

Lecture 4

Cell Types and Primary Growth

Parenchyma Cells

1. Functions

• Many; often specialized
• Most metabolic processes (photosynthesis, storage, secretion, food stroage)

1. Features

• A type of ground tissue (when in stems and roots)
• Lack secondary wall
• Often divide and differentiate at maturity

1. E.X.

• Fruit flesh
• Endosperm
• Pith and cortex of stems and roots
• Chloroplasts-laden cells inside leaves

Collenchyma Cells

1. Functions

• Support (esp. Of young and growing organs)

1. Features

• Type of ground tissue
• Thick, uneven primary wall
• No secondary wall
• ALWAYS occur just below epidermis
• Often occur in strands
• Alive at maturity; can elongate

1. E.X.

• Celery leaf midrib and petiole

Sclerenchyma Cells

1. Function

• Support
• Protection (of tissues no longer elongating)

1. Features

• Type of ground tissue
• Thick secondary cell wall with lignin (rigid polymer)
• Cannot elongate at maturity (may be dead)
• 2 forms: fibers and sclereids

1. E.X.

• Burlap bags (jute fibers)
• Fibers in a bundle (cross section)
• FIBER: Hemp (cannabis sativa)
• SCLEREIDS: Nutshell (pak acorn) →note: thick wall

Water-Conducting Cells of the Xylem:

Tracheids and Vessel Elements

1. Functions

• Support and supply of water and minerals

1. Features

• Dead at maturity
• Secondary wall lignified; often spiral
• 2 kinds: tracheids and vessel elements
• Type of vascular tissue

Lignin

• Class of complex organic polymers (NOT polysaccharide)
• 2nd most abundant natural polymer (after cellulose)
• Deposits in cell walls; fills spaces and bind cellulose, hemicellulose and pectin
• Gives strength to wood and bark
• Can occur in cell walls of non-woody plants (palm trees, bamboo, wheat)
• Human uses:
  • Wood: 20-33% lignin by dry weight
  • Rope, clothing, rugs (sclerenchyma fibers)
  • Paper: lignin removed to leave cellulose
  • Artificial Vanillin (real vanillin is from vanilla orchid)

Sugar-Conducting Cells of the Phloem: Sieve-Tube Elements

1. Functions

• Transports sugars (esp. sucrose), other organic compounds, some minerals

1. Features

• Type of vascular tissue
• Alive at maturity
• With companion cell (parenchyma)

Plants Grow from Meristems

Meristems:

• Ultimate source of all parts of the mature sporophyte
• Undifferentiated
• Retain “forever” the ability to divide

Types of Location of Meristems

1. Apical Meristems (AM)

• Root AM and shoot AM
• Primary growth

1. Lateral Meristems

• Vascular cambium and cork cambium
• Secondary growth

Apical Meristem (AM): Shoot

• Source of primary growth of both root and shoot
• Makes 3 meristems:

1. Protoderm (epidermis) → dermal tissue
2. Procambium → vascular tissue
3. Ground meristem → ground tissue

Shoot Apical Meristem and Differentiation

Youngest tissue at shoot tip

Young Stems (shoots)

Root Apical Meristem and Development Root Primary Growth: 3 Zones

Root Primary Growth: (another view)

Root Hairs Increase Surface Area

4-month old rye plant

• 14 billion root hairs
• Surface area 400 sq. meters
• Placed end to end >10,000km

Young Roots

• Endodermis: innermost layer of cortex
• Stele or Vascular Tissue: all cells inside endodermis; arise from procambium

Lateral Root

• Originates in pericycle (outermost layer of vascular cylinder)
• Grows out through cortex and epidermis

Structure of Primary (non-woody) Roots: SUMMARY

1. Root cap: protects
2. Root Hairs: epidermal cells, increase absorption area
3. Endodermis: innermost layer of cortex; surrounds vascular cylinder
4. Vascular cylinder (stele): center of root; contains vascular tissue (xylem and phloem) and some ground tissue
5. Pericycle: between vascular cylinder and endodermis; origin of lateral roots

Lecture 5

Secondary Growth, Transport

Types and location of Meristems

Apical Meristems

• Root AM and shoot AM
• Primary Growth
• All vascular plants

Lateral Meristems

• Vascular cambium and cork cambium
• Secondary growth
• Only in conifers and woody eudicots
• Make wood and bark

Secondary Growth

Produces: → wood and bark

Occurs in: → conifers and woody eudicots

Secondary Growth in Stems:

Vascular Cambium is a Meristem:

VC Produces:

1. Secondary xylem to inside (wood)
2. Secondary phloem to outside
3. More VC (to increase circumference)
4. Rays - parenchyma for lateral transport

Vascular Cambium:

Fusiform initials make:

• Tracheids and vessel elements (xylem)
• Sieve elements (phloem)

Ray Initials make:

• Rays (in both xylem and phloem)

Wood: Oak

• Secondary xylem
• Lignin (polymer) in secondary walls of tracheids and vessel elements
• Heartwood vs. sapwood

Protection in Woody Plants:

Cord Cambium (Phellogen)

• New lateral meristem
• Arises from cylinder of cortex cells outside the vascular cambium and secondary phloem
• Produces periderm: 3 layers

1. Phelloderm to inside (some woody species)
   1. Thin layer of living parenchymal cells
2. Cork cambium itself
3. Cork to outside
   1. Suberized, dead cells
   2. Protects woody plant (there is no more epidermis)

Anatomy of Tree Trunk:

Tissues of Woody Stem:

Transport:

1st Law of Thermodynamics

→ cannot create or destroy energy, can only change from one form to another

2nd Law of Thermodynamics

→Energy spontaneously tends to flow only from being concentrated in one place to becoming spread out, or for a combined system and surroundings, entropy never decreases

2nd Law in Life

• Movement of fluid in plants follows the 2nd law of thermodynamics
• The most equitable distribution of energy corresponds to maximum entropy

E.x. -osmosis

-diffusion

-fluid movement because of differences in hydrostatic pressure

Routes of Water Movement within a Plant:

3 cell compartments

Cytoplasm:

• All material inside cell membrane

Cytosol:

• Part of cytoplasm excluding organelles

3 transport Routes

Cellulose:

• Main component of cell walls
• Highly absorbent (hydrophilic)
• Polysaccharide (polymer)
• Most abundant organic compound on earth

Water Potential: Psi

• Water potential energy
• Unit: megapascal (MPa)
  • 1 MPa = about 10 atm (bars)
• Potential refers to water’s capacity to perform work
• Energy and entropy are intimately linked (outside our discussion)
• Determine DIRECTION of movement water
• Water flows from regions of higher to lower water potential
• Combines effects of solute concentration and pressure

Water Potential: 2 Components

1. Solute potential
2. Pressure potential

Water Potential in Plant Cells:

Water and Minerals Travel Upward in Xylem:

• Tracheids (all vascular plants)
• Vessel Elements (flowering plants)

Water Enters Roots: lateral transport H20 and Minerals:

Apoplast:

Non living continuum outside cytosol, including

• Cell walls
• Xylem cells
• Extracellular spaces

Symplast:

Continuum of cytosol connected by plasmodesmata

Endodermis:

• Cylinder 1-cell thick
• Stele: all material inside endodermis
  • Xylem and phloem
  • Pith
  • Pericycle (origin of lateral roots)

- Casparian strip

- Where primary wall and middle lamella were

- Waterproof and impermeable to ions: suberin

- All water and ions entering xylem must pass through endodermal cells; must cross

cell membrane

Mycorrhizae - A Mutualism between Plants and Fungi

• Increase surface area
• Aid absorption of minerals

Pathway of Water and Minerals: (in herbaceous plant)

1. Soil
2. Root and hair mycorrhizae
3. Cortex
4. Endodermis
5. Xylem
6. Atmosphere

How Water and Minerals move up a Plant:

1. Capillary action
2. Pumps
   1. From above
   2. From below
3. Transpiration-cohesion-tension mechanism

Generation of Transpirational Pull:

Negative pressure (tension) at the air-water interface in the leaf is the basis of transpirational pull, which draws water out of xylem

Water Flow in Xylem: Ascent of Sap:

Steps:

1. Water evaporates from moist cells in leafs stomates (transpiration)
2. Water potential is lowered at air-water interface, causing negative pressure (tension) in xylem
3. Hydrogen bonds hold water molecules together (cohesion)
4. Xylem under tension gradient: pressure potential - lowest (most negative) at top
5. Water is pulled up by pressure gradient
6. Water and minerals enter root by osmosis

Facts:

• Total path in xylem from highest (lest neg.) to lowest (most neg.) water potential
• Passive process
• Tracheids and vessel elements are dead cells
• Upward only

Control of Transpiration by Stomates

Cues to open at dawn:

• Light
• CO2 deletion
• Circadian rhythm

Dry conditions:

Abscisic acid: hormone

• Causes k+ to leave guard cells
• Stimulates stomatal closure

Phloem Transport:

What: sugar in solution and other compounds

Where: sieve-tube elements

How: pressure-flow hypothesis

Transport within plants: keys to understanding

• Water spontaneously moves from regions of higher to regions of lower potential energy
• In any regions, water potential energy is the SUM of
  • Solute (osmotic) potential energy (0 to negative)
  • Pressure potential energy (any value)
• 2 Main tissues for transport

Two Vascular Tissues: SUMMARY

Lecture 6

Transport, Photosynthesis and Control System

Photosynthesis

Importance:

• Source of oxygen in atmosphere
  • 50% terrestrial plants
  • 50% marine phytoplankton and macroalgae
• First step in moving energy into the living world; source of all energy in ecosystems

Photosynthesis

Electron Transfer: REDOX

Electron Transfer

• Here, 6 water molecules have been subtracted from each side to give the net reaction to produce 1 molecule glucose
• Water is split, loses electrons (get oxidized), and electrons are transferred along with hydrogen ions from water to carbon dioxide, reducing it to sugar

Photosynthesis: 2 stages

1. Light reactions
2. Calvin cycle (dark reactions)

Chloroplast structure and Function:

1. Light reactions: thylakoid membrane
2. Calvin Cycle: Stroma

Light Reaction: STEPS

1. Light hits chlorophyll molecule
2. Electrons bounced to higher energy level and OFF chlorophyll molecule
3. Chlorophyll steals electrons from H2O (Oxidized)
4. Causes water molecule to fall apart: photosynthesis → oxygen
   1. H2O → 2H+ + 2e + O
5. Electrons and Hydrogens from H2O transferred to NADP+ (gets reduced)
   1. NADP+ + 2e- + h+ → NADPH (greater reducing power than H2O)
6. ADP + Pi yields ATP (chemical energy): photophosphorylation

OVERVIEW:

• Light energy is converted first to chemical energy of NADPH and ATP
• Oxygen gas O2 is released (comes from water)

Chemical Bonds from Electrons:

NADP+ and NAD+

• Oxidizing agents
• Remove (accept) electrons from other molecules, including H2O (2 e- and 1 proton - nucleus of H atom)
• NADP+ in photosynthesis, NAD+ in respiration

NADPH and NADH

• Reducing agents
• Place electrons on other molecules
• NADPH in photosynthesis, NADH in respiration

Chlorophyll Absorption Spectra

→ why plants are green!

Chlorophyll A:

• Absorbs mostly violet-blue and red
• Reflects or transmits green light
• Accessory pigments broaden absorption

Photosynthesis Action Spectrum

• Matches the combined absorption spectrum of chl a and accessory pigments including chl b carotenoids

→ photosynthesis is driven by visible wavelengths

Dark Reactions (Calvin Cycle)

• Make sugar (precursor)
• Occur in stroma of chloroplast
• Use NADPH and ATP from light reactions
• Supply light reactions with NADP+ and ADP

Photosynthesis: Reaction

Rubisco

• Most abundant protein
• Most important protein
• Dual nature

Rubisco attaches O2 to RuBP Metabolic Pathway that:

• Consumes O2
• Releases CO2
• Makes NO ATP
• Wastes energy
• Decreases photosynthetic output
  • SOLUTION: a new enzyme: PEP carboxylase (PEPC)

C4 Photosynthesis

Mesophyll Cells:

• O2 exits (light reactions)
• CO2 enters
• NO rubisco

Rubisco

• Is only in bundle-sheath cells
• Thus kept away from potentially low [CO2]

C4 vs CAM (Crassulacean acid metabolism)

C4: Spatial separation of steps

CAM: Temporal separation of steps

• 10% of species (e.x. cactus/pineapple/blue agave)

Control Systems

Plants Respond to Herbivores

Physical Defense

• Thorns
• Trichomes

Chemical Defense

• Distasteful compounds
• Toxic compounds

Some plants even recruit predatory animals that help defend against specific herbivores

8 Hormones

1. Abscisic Acid
2. Ethylene
3. Auxins
4. Cytokinins
5. Gibberellins
6. Brassinosteroids
7. Jasmonates
8. Strigolactones

Hormone:

• Organic substance made in one place and transported to another place where it affects growth and other processes

Hormone Action

• A hormone binds to a specific protein receptor, either embedded in the plasma membrane or in the cytoplasm
• Receptor protein’s confirmation thus changes
• Stimulates the production of ‘relay molecules’ in the cytoplasm
• Relay molecules trigger various responses to the original signal

Abscisic Acid: ABA

Stomate Regulation

Dry Conditions:

-ABA stimulates stomatal closure → causes K+ to leave guard cells

Ethylene - A Gas

Where: most plant parts

Functions:

• Leaf abscission (shedding)
• Triple response in seedlings
• Fruit ripening
• Root hair production

Discovered around 1901 by Nelijubov in Russia

1910: Emanations from oranges caused premature ripening of bananas

Now the most commercially produced organic compound in world - many uses

Abscission and Ethylene: Maple Leaf

→ Caused by a change (increase) in ratio of ethylene.auxin

Ethylene and the Triple Response:

Germinating pea seedlings grown in dark

1. Slowing stem elongation
2. Stem thickening
3. Horizontal stem growth

Effect of ethylene on Fruit Ripening

• Promotes fruit ripening and is produced during fruit ripening
• Autocatalytic: promotes its own production
• Increase respiration

Lecture 7

Introduction to Fungi

Characteristics of Fungi

• Heterotrophs
• Eukaryotic
• Main body is haploid
• Multicellular or unicellular
  • Yeast: unicellular without flagella
• Cell wall made of chitin
  • Polysaccharide
  • Arthropod shells, cephalopod beaks, fish scales
• External digestion of food

2 Kinds of Hyphae

Generalized Life Cycle

Spores in Fungi

• Haploid (1n)
• Most <20 um (rarely >100um)
• Each contains nucleus, dehydrated cytoplasm and protective coat
• Some can remain dormant for long periods
• Produced by:
  • Mitosis: Asexual reproduction
  • Meiosis: Sexual reproduction
• Purpose (functions):
  • Move to new food source
  • Avoid or “wait out” adverse environment
  • New genetic combination (sexual reproduction)

Sexual Fungal life Cycle:

Zygotic Meiosis

Asexual Reproduction: HOW

1. Spores in sporangia
2. Conidia (spores) in conidiophores
3. Budding (e.x. Baker’s yeast)

5 Phyla of fungi

→ phylogeny of fungi is the subject of ongoing research

Phylum of Chytridiomycota

• 1000 species
• Single cells or colonies with hyphae
• Flagellated spore (zoospore)
  • Haploid, asexually produced
  • “Zoo” because swims
• Aquatic soil
• Decomposers, parasites, commensals (digestive)

Spores Release in a Chytrid

→ has converted the entire contents of its flasked-shape body, or thallus, into flagellated asexual zoospores

Phylum Zygomycota

• 1000 species
• Coenocytic (non-septate) hyphae
• Decomposers, parasites, commensals

→ spore infects, fungus grows

Death at dusk

Mind control: summiting, head glued

E.X. Black bread mold = asexual spores

Phylum Glomeromycota

• 160 species
• Non-septate hyphae
• Asexual only
• Obligate symbionts: mycorrhizae

Phylum Basidiomycota

• 30,000 species
• Decomposers & ectomycorrhizal
• Long-lived dikaryotic mycelium
• Multicellular (and some yeats)
• Septate mycelium
• Multicellular sexual reproduction
  • Fruiting body = ‘basidiocarp’

Decomposers

Basidiomycota: sexual reproduction

E.x. puffballs (spores on inside)

Stinkhorns

Amanita

Shiitake

Phylum Ascomycota

• ‘Sac’ fungi
• 65,000 species
• Multicellular or unicellular (yeast)
• Multicellular asexual repro: conidia
• Multicellular sexual reproduction
  • Fruiting body = ‘ascocarp’
  • (cup fungi, morels, truffles)

Penicillium: Source of Penicillin

→ isolation of antibiotic penicillin by alexander Fleming (1928) clinical treatment 1941

Asexual Reproduction in Ascomycota

Unicellular: Yeast_budding

Multicellular: Formation of conidia (spores) on conidiophores

Sexual Reproduction: Asci

→8 spores in each ascus

Ergot Alkaloids (claviceps purpurea)

• Several kinds
• Restrict blood flow: gangrenous ergotism
• St.anthony’s fire
• Salem (massachusetts) witch trials ?
• Others: medical uses
• LSD
  • Lysergic acid diethylamide (ergot alkaloid derivative)
  • Synthesized by Albert hofmann 1938 (LSD-25)

Aspergillus Fumigatus

• Inhabits solids worldwide
• Wide thermal tolerance
• Sonidia exposure constant and unavoidable
• We inhale > 100 conidia daily
• Concentration in the air indoors or outdoors is 1-100 conidia/m3
• Spores small so can reach deep into respiratory pathways
• Normally cleared from respiratory pathways
• Invasive aspergillosis disease in immunocompromised individuals (chemo,organ transplant)
• Difficult to treat

Candida albicans

• Normal part of human gut flora
• Also on skin and in oral cavity, urogentical tract
• Transmitted from mother to child duringn childbirth
• 2 morphological forms: yeast and hyphal

OVERVIEW: fungal phyla

Fungi: the future

Evolution:

• Phylogenetic relationships
• Relations to animals
• Multicellularity: how many times arose?
• Diploidy vs. haploidy
• No sex in glomerom