Transcript Plants Review

Introduction to Plants
Kingdom: Plantae
Plants:
 Cell wall
 Autotroph (photosynthesis)
 Multi-cellular
12 Divisions (Phyla)
 Anthophyta = Angiosperms (flowering plants)
 Largest # of species (~250,000 - 90% plants)
 Seed plants: product seed w/in a fruit
 Key adaptations: flowers & fruits
 Sporophytes are trees, shrubs, herbs that flower
 2 main groups: Monocots & Dicots
Monocots vs. Dicots
Monocot
Dicot
• One cotyledon (seed leaf)
•Two cotyledon
• Parallel veins in leaves
•Netted veins in leaves
• Fibrous root system
•Taproot
• Floral parts in multiples of 3
•Floral parts in multiple layers of 4
or 5
• Complex vascular arrangement
•Ring vascular arrangement
• Eg. grass, corn, palm, onion, tulip,
bamboo
•Eg. bean, pea, rose, sunflower
Concept 35.1 The plant body has a heirarchy of
organs, tissues, and cells
Basic Organs
• Roots
• Stems
• Leaves
Types of Tissue
• Dermal
• Vascular
• Ground
Cell Types
•
•
•
•
•
Parenchyma
Collenchyma
Sclerenchyma
Xylem
Phloem
Shoot
system
•Above ground
•Stems, leaves
Root
system
•Underground (usually)
•Roots
A. Roots
 Anchors plant, absorbs H2O & minerals, stores
sugars/starches
 Root hairs – tiny extensions of epidermal cells,
increase surface area for H2O and mineral
absorption
 Mycorrhizae: symbiosis with fungi
Root hairs
Fibrous Roots
Taproots
•Mat of thin roots spread just
below surface
•One thick, vertical root
•Shallow
•Many lateral (branch) roots
•Increased surface area
•Firmly anchors
•Monocots
•Stores food in root
•Dicots
Fibrous Root
(scallion)
Taproot
(carrot)
Roots
B. Stems
Alternating system of nodes (leaf
attachment) and internodes
 Function: display leaves
 Terminal bud – growth concentrated at
apex (tip)
 Apical dominance: terminal bud
prevents growth of axillary buds;
growth directed upward, toward light
 Axillary buds – located in V between leaf
and stem; forms branches (lateral
shoots)
 Pinching/pruning – removing terminal
bud

Stems
Modified stems
Runner or stolin
◦ Aspen, strawberries, grass
◦ Grow on surface
◦ For asexual reproduction
 Rhizome
◦ Iris, ginger, potato, onion
◦ Grow underground
◦ Store food & DNA for new plant
◦ Tuber: end of rhizome
 Bulb – underground shoot
◦ Onion
◦ storage leaves

C. Leaves
◦
◦
◦
◦
epidermis of underside interrupted by stomata (pores)
Mesophyll: ground tissue between upper/lower epidermis
Parenchyma: sites of photosynthesis
Cuticle: waxy layer
Three Tissue
Systems
A. Dermal Tissue
Single layer, closely packed cells that cover
entire plant
 Protect against water loss & invasion by
pathogens
 Cuticle: waxy layer
 Epidermis, periderm

B. Vascular Tissue
Continuous throughout plant
 Transports materials between roots &
shoots

stele
1. Xylem: transport H2O and minerals up from
root
2. Phloem: transports food from leaves to
other parts of plant
C. Ground Tissue
Anything that isn’t dermal or vascular
 Function: storage, photosynthesis, support
 Pith: inside vascular tissue
 Cortex: outside vascular tissue

III. Cell Types
Parenchyma: most abundant
 Perform metabolism, synthesizes & stores
organic products
B. Collenchyma: grouped in cylinders, support
growing parts of plant
C. Sclerenchyma: rigid support cell
D. Xylem: water conduction
 Tracheids, vessel elements – dead, tubular,
elongated cells
E. Phloem: sugar, organic cmpd. conduction
 Sieve tubes, plates, companion cells – alive cells
which aid movement of sugar
A.
WATER-CONDUCTING CELLS OF THE XYLEM
PARENCHYMA CELLS
Vessel
Parenchyma cells in Elodea
leaf, with chloroplasts (LM)
Tracheids
100 µm
60 µm
Pits
COLLENCHYMA CELLS
80 µm
Cortical parenchyma cells
Tracheids and vessels
(colorized SEM)
Vessel
element
Vessel elements with
perforated end walls
Tracheids
SUGAR-CONDUCTING CELLS OF THE PHLOEM
Collenchyma cells (in cortex of Sambucus,
elderberry; cell walls stained red) (LM)
Sieve-tube members:
longitudinal view
(LM)
SCLERENCHYMA CELLS
5 µm
Companion
cell
Sclereid cells in pear (LM)
Sieve-tube
member
Plasmodesma
25 µm
Sieve
plate
Cell wall
Nucleus
Cytoplasm
Companion
cell
30 µm
15 µm
Fiber cells (transverse section from ash tree) (LM)
Sieve-tube members:
longitudinal view
Sieve plate with pores (LM)
Primary and Secondary Growth
(apical vs. lateral meristems)
Concept 35.3 Primary growth lengthens roots and
shoots
Root Hairs
Zone of Maturation: growth & differentiation complete;
fully mature cells
Zone of Elongation: cells elongate; push root tip ahead
Zone of Cell Division: apical meristem; new cells produced
Root cap: protects meristem as it pushes through soil; also
secretes polysaccharide lubricant
Concept 35.4 Secondary growth adds girth to
stems and roots in woody plants
Involves lateral meristems
◦ Vascular cambium: produces secondary xylem
(wood)
◦ Cork cambium: produces tough covering that
replaces epidermis
 Bark = all tissues outside vascular cambium

What does a
plant need?
Solute transport
across plant cell
plasma membranes
Osmosis



**Water potential (ψ): H2O moves from high ψ  low
ψ potential, solute conc. & pressure
◦ Pure water: ψ = 0 MPa
◦ Plant cells: ψ = 1 MPa
Water potential equation: ψ = ψS + ψP
◦ Solute potential (ψS) – osmotic potential
◦ Pressure potential (ψP) – physical pressure on
solution; turgor pressure
Bulk flow: move H2O in plant from regions of high 
low pressure
** Review AP Lab 1
Flaccid: limp (wilting)
 Plasmolyze: shrink, pull away from cell wall (kills
most plant cells) due to H2O loss
 Turgid: firm (healthy plant)

Turgid Plant Cell
Plasmolysis
Vascular Tissues: conduct molecules
Xylem
Phloem
Nonliving functional
Living functional
Xylem sap = H2O &
minerals
Phloem sap = sucrose,
minerals, amino acids,
hormones
Source to sink
(sugar made) to (sugar
consumed/stored)
Apoplast = continuum of cell walls/extracellular spaces
Symplast = continuum of cytosol
Absorption of H2O and minerals
Root hairs: increase surface area of absorption
at root tips
 Mycorrhizae: symbiotic relationship between
fungus + roots
◦ Increase H2O/mineral absorption

The white mycelium of the fungus
ensheathes these roots of a pine tree.
Transport of H2O and minerals from
root hairs xylem
Guttation: exudation of water droplets seen in
morning (not dew), caused by root pressure
Stomata regulate rate of transpiration


Stomata – pores in epidermis of leaves/stems, allow gas
exchange and transpiration
Guard cells – open/close stoma by changing shape
◦ Take up K+  lower ψ  take up H2O  pore opens
◦ Lose K+  lose H2O  cells less bowed  pore closes
Cells stimulated open by: light, loss of CO2 in
leaf, circadian rhythms
 Stomata closure: drought, high temperature,
wind

Sugar Transport
Translocation: transport of
sugars to phloem by pressure
flow
 Source  Sink
◦ Source = produce sugar
(photosynthesis)
◦ Sink = consume/store sugar
 Via sieve-tube elements
 Active transport of sucrose

Nutritional Requirements
Essential element: required for plant to
complete life cycle and produce another
generation
 Macronutrients (large amounts): CHNOPS +
K, Ca, Mg
◦ Nitrogen = most important!
 Micronutrients (small amounts): Fe, Mn, Zn,
Cu, etc.
Mutualistic Relationships:
Rhizobium bacteria supply nitrogen at roots
(fix atmospheric N2 to usable N)
• Plant supplies sugar & amino acids
2. Mycorrhizae (plant + fungus)
1.
Unusual nutritional adaptations:
epiphytes, parasitic plants, canivorous
plants
Epiphyte: grow on another plant, absorb H2O
from rain through leaves
Parasitic Plants: not photosynthetic; absorb
sugar and minerals from living hosts
Carnivorous Plants: photosynthetic, but obtain
some nitrogen and minerals by digesting small
animals
Angiosperms have 3 unique Features:
1.
2.
3.
Flowers
Fruits
double Fertilization
Alternation of Generations:
Sporophyte (2n)  (meiosis)  Spores 
(mitosis)  gametophytes  (mitosis)
gametes (n)  (fertilization)
Male Gametophyte
Female Gametophyte
= Pollen Sac
= Embryo Sac
Produced in anther
Produced in ovule (in ovary)
Has 2 haploid nuclei:
1.Tube nucleus (forms pollen tube)
2.Generative nucleus (divides to
form 2 sperm cells)
Has 3 important haploid nuclei:
1.Egg (fuses with sperm)
2.2 polar nuclei (fuses with 2nd
sperm to make 3n endosperm)
Pollination: transfer pollen from anther to
stigma
 Pollen tube grows down into ovary

Double Fertilization
Union of 2 sperm cells with different cells of
embryo sac
1. One sperm + egg  zygote (2n)
2. One sperm + 2 polar bodies  endosperm
(triploid 3n)

◦
Endosperm = nutrition for embryo plant
3. Ovule
develops into seed; ovary develops
into fruit
◦
Seed = embryo + endosperm
Self-incompatibility: prevent reject own
pollen or closely related individual
Stigma
Stigma
Anther
with
pollen
Pin flower
Thrum flower
“Pin” and “thrum” flower types reduce self-fertilization
The development of a eudicot plant embryo
Fruit
Protects enclosed seed(s)
 Aids in dispersal by water, wind, or
animals

Simple
Single ovary of
one flower
Cherry
Aggregate
Multiple
Many ovaries of Many ovaries of
one flower
many flowers
Raspberry
Pineapple
Seeds
Adaptations:
1. Dormancy = “resting”


Low metabolic rate, not growing or developing
Increases chances of germination in most
advantageous time & place
2. Dispersal: variety
of methods
3. Protection: well protected by fruit
Seed
Structure
Germination

Imbibition: uptake of H2O
◦ Seed expands and seed coat ruptures
◦ Trigger metabolic changes to begin growth
◦ Enzymes digest storage materials of
endosperm (cotyledons)
◦ Nutrients transferred to growth regions of
embryo
Germination
Radicle  Root
Shoot tip emerges above ground
1.
2.

Stimulated by light
3.
Foliage leaves expand & turn green 
photosynthesis

Very hazardous for plants due to
vulnerability
◦
Predators, parasites, wind
Dicot and
Monocot
Seed
Germination
Plant Reproduction
Sexual
Asexual
Both ways to reproduce
Flower  seeds
Runners, bulb, root, graft,
vegetative (grass), fragmentation
Genetic diversity
Clone
More complex & hazardous for
plant
Simpler & safer for plant
• Monoculture - cultivate w/ 1
plant
• Reduces competition
• Benefits farmers
Tip of coleoptile senses
light
Cells on darker side
elongate faster than
cells on brighter side
AUXIN = chemical
messenger that
stimulates cell
elongation
Excised tip placed
on agar block
Growth-promoting
chemical diffuses
into agar block
Control
(agar block
lacking
chemical)
has no
effect
Control
Agar block
with chemical
stimulates growth
Offset blocks
cause curvature
Hormones: chemical messengers that coordinate
different parts of a multicellular organism
Important plant hormones:
1. Auxin – stimulate cell elongation; fruit development; apical
dominance; phototropism & gravitropism
2. Cytokinins – stim. cell division & growth; germination;
delay senescence (aging)
3. Gibberellins – promotes seed & bud germ.; stem elong. &
leaf growth; stim. flowering & fruit development
4. Abscisic Acid – inhibit growth; closes stomata during H2O
stress; encourage dormancy
5. Ethylene – promote fruit ripening; inhibit/promote growth
& dev. depending on species
The effects of gibberellin on stem elongation
and fruit growth
Ethylene gas: fruit
ripening
Plant Movement
1.
Tropisms: growth responses  SLOW
 Phototropism – light
 Gravitropism – gravity
 Thigmotropism – touch
2.
Turgor movement: allow plant to make
relatively rapid & reversible responses
 Venus fly trap, mimosa leaves, “sleep”
movement
Plant Responses to Light
Plants can detect direction, intensity, & wavelenth of light
 Phytochromes: light receptors, absorbs mostly red light
◦ Two forms: Pr (red light) and Pfr (far-red light)
◦ Pr  Pfr: switches depending on light in greatest supply
◦ Pfr aids in detection of sunlight
◦ Regulate seed germination, shade avoidance

Photoperiodism: physiological response to
the relative length of night & day (i.e.
flowering)
Short-day plants: flower when nights are
long (mums, poinsettia)
 Long-day plant: flower when nights are
short (spinach, iris, veggies)
 Day-neutral plant: unaffected by
photoperiod (tomatoes, rice, dandelions)

Night length is a critical factor!
How does
interrupting the
dark period with
a brief exposure
to light affect
flowering?
Plant Response to Stress
Causes of stress:
1.
2.
3.
4.
5.
6.
7.
Drought (H2O deficit)
Flooding (O2 deprivation)
Salt excess
Heat
Cold
Herbivores
Pathogens
1.
H2O deficit:
 close stoma
 release abscisic acid to keep stoma closed
 Inhibit growth
 roll leaves  reduce SA & transpiration
 deeper roots
2.
Flooding (O2 deprivation):
 release ethylene  root cell death  air tubes
formed to provide O2 to submerged roots
3.
Salt:
 cell membrane – impede salt uptake
 produce solutes to ↓ψ - retain H2O
4.
Heat:
 evap. cooling via transpiration
 heat shock proteins – prevent denaturation
5.
Cold:
 alter lipid composition of membrane (↑unsat.
fatty acids, ↑fluidity)
 increase cytoplasmic solutes
 antifreeze proteins
6.
Herbivores:
 physical (thorns)
 chemicals (garlic, mint)
 recruit predatory animals (parasitoid wasps)
7.
Pathogens:
 1st line of defense = epidermis
 2nd line = pathogen recognition, host-specific