Cell Walls
Cell walls are:– Structural
– Provide defense against invading pathogens
– Provide signaling pathways for cells
Cell Wall Chemistry• Cell walls contain cellulose, pectin
and lignin
• Cellulose is the major component – Most abundant polymer in the world
~40-60% of dry weight of plants– Form strong strands of parallel chains
called Cellulose Microfibrils– Cellulose strands are cemented together
by pectins
TEM photograph
Pectin and Lignin• Pectins are polymers of -galacturonic
acid– Flexible, long molecules that link Microfibrils
together…like ‘glue’
• Lignin is very hard, tough, rigid– Chemistry is not fully elucidated– Polymer of complex, amino-acid derived
monomers– Creates strong cell walls
And don’t forget the 5 colors !
Plant Tissues• Tissues are groups of cells that form
a structural and functional unit
• Vascular plants have three tissue systems:
– Dermal tissueOuter covering for the plant body
– Ground tissuePhotosynthesis, storage and support
– Vascular tissueWater and nutrient conduction system
Functions for Plant Epidermis
1) Prevent water loss in shoot (waxy surface and bark)
2) Controlling exchange of gases in shoot
(stomates)
3) Absorption by roots (root hairs)
4) Produce hairs, called trichomes, that shade
the leaf or protect from herbivores (physically or chemically)
AGymnosperm
BDicot
CMonocot
Yam
DMonocot
EMonocot
Do Animals have epidermis?
What is animal epidermis called?
What does this have to do with Safe Sex?
Cheek cells
Jicama -- Pachyrhizus erosus (L.)
Jicama -- Pachyrhizus erosus (L.)
Eaten in celebration ofDay of the Dead
November 1st Mexico
Plant Tissues• Tissues are groups of cells that form
a structural and functional unit
• Vascular plants have three tissue systems:
– Dermal tissueOuter covering for the plant body
– Ground tissuePhotosynthesis, storage and support
– Vascular tissueWater and nutrient conduction system
Vascular Tissues - Xylem• Xylem conducts water and nutrients from
roots to the rest of the plant• Two types
– Tracheids• Dead at maturity • Main water-conducting cells of fern and gymnosperms• Relatively few plasmodesmata in end of cell in pit fields,
thin areas w/only primary cell wall
– Vessel elements• Dead at maturity – stacked on top of each other• Broader than tracheids, large holes in ends of cell• Much more efficient at water transport
Cell wall
Lumen
(a) (b)
Pits
End wall withperforations
Xylem carrieswater &
soil nutrients
Vessels Tracheids
Xylem Vessel Xylem Tracheid
Vascular Tissues - Phloem
• Transports food materials• Provides structural support• Two types:
- Sieve tube cells• Alive at maturity• Extensive holes via sieve plate at cell ends, with shared
cytoplasm between cells• Reduced cellular organelle volume – some lose nucleus
– Companion cells• Nucleated, support cells for sieve tubes• Connected by many plasmodesmata to sieve tube cell• Involved in sugar transport to sieve tube cell
Fig. 31.05cd
Companion cell
(c) (d)
Plasmodesma
Lateral sievearea
Phloemparenchyma
cells
Sieve tubemember
Sieve plate
Sieve Tube Cell
Companion Cell
Xylem and Phloem Cells
Fiber Cells
Xylem & Phloem: (in Squash)
Xylem
PhloemXylemFibers
Vascular Cambium
Epidermis
Phloem
VascularCambium
Xylem
Notice that the vascular cambium circles all the way around
Dicotstem
Fibers
Jute for burlap
Sisal = fiber from monocot stem
Hemp
Examples of plant fibers from stem vascular bundles
Monocot Stem
VascularBundles
(scattered)
Epidermis
Xylem (big cells &smaller ones in circle
Phloem (all cells within box
Monocot Stem
Air Space
Secondary Growth
Secondary Growth……Why?
* Plant is getting bigger so needs more materials* Old vascular tissue gets “clogged up”
1, 2, 3 yearsOf age
Pith
Rays in wood
Tree Borer For assessing tree rings
How old are these trees?
Bristlecone Pine
Oldest one is
4,800 years old
The oldest living trees on earth.
http://www.curlyredwoodlodge.com/rooms.htm
The Curly Redwood Lodge is one of northern California’s most unique lodges. It was built from one curly redwood tree that produced 57,000 board feet of lumber. The tree (cut down in 1952) was 18 feet wide at the trunk. Curly redwood is unique because of the curly grain
of the wood, unlike typical straight grained redwood.
1952
Jewelry meant for Queen Nerfititi (Egypt) was found on a sunken wooden ship that was built in 1316 B.C.
King Midas (Turkey) was buried in a funeral mound built with logs that were cut in 718 B.C.
Lost Colony of Roanoke, Virginia
Can also study when major forest fires occurred in the past.
A researcher in Tennessee noticed that hurricanes cause heavy-oxygen to accumulate in “late wood” (because
hurricanes usually occur in late fall).
She has been accurate back to 100 years ago….wants to go back 500 years.
• Two small, old-mining towns that are currently military posts (Arizona and Nevada)
• Unusually high levels of childhood leukemia cases• High levels of tungsten in the urine of townspeople• Is there a cause:effect relationship between tungsten (a heavy metal, like lead or mercury) exposure and leukemia? …still being investigated
• But tree-ring specialists have discovered that the levels of tungsten in the environment have increased dramatically in the last 20 years….each annual ring captured whatever chemicals that might have occurred in the environment that year!!!
September, 2002
Heartwood
Sapwood
Sycamores
Cork
Xylem
Fibers
Phloem
Girdling can kill plants
Carpenters talk about two kinds of wood:
Softwood and Hardwood
Softwood = light, easy to put nails/screws into…so are best for construction. Gymnosperms generally make softwoods. Since Pines grow so fast they are the most popular. Paper is made from pine mostly.
Hardwood = from Dicot trees mostly; more of a mixture of xylem cells (including fibers); that makes them more dense. Used for furniture and art/crafts.
Gymnosperms like pines, junipers, spruce, fir, and redwood.
Most of the xylem cells are one kind...called Tracheids.
Also, little or no Fibers.
Dicots like oak, maple,ash, hickory, walnut.
Contain both tracheids and vessels and fibers. The fibers make the wood harder to cut and nail into, But will also be sturdier forMaking furniture, flooring, art, etc.
Not all Hardwoods are actually “harder” than Softwoods, and not all Softwoods have wood that is “softer” than Hardwoods.
Hickory
(Hardwood)
Mostly tracheids& fibers withA very large
vesselsinterspersed.
Very slowgrowing.
Some non-vascular cellsare gelatinous
•Wright Brothers plane•Pioneer wagon wheels•Baseball bats• Skis•Axes, hammer handles, etc.• Golf clubs• wooden floors
of Wheat
Embryo
Scutellum = Cotyledon
Starchy food supply(Endosperm)
Dietary Fiber
Primates typically live in Tropical Rainforests (using hands & feet to climb trees)….
…they eat leaves, fruits, seeds & insects.
It is believed that the early hominids were eventually forced to live in a biome that was different than the Tropical Rainforest.
This might have been due to: 1) global-climate change, or 2) rising competition for resources due to population pressures, or 3) a combination of these two factors.
Which biome do you think they would have ended up in (according to this
scenario)?
Primates typically live in Tropical Rainforests (used hands & feet to climb trees)…. …eats leaves, fruits, seeds & insects.
< Living in the Savanna??
Australopithecus (3 million years ago)...eating more roots, grains & meat
Chimpanzee (5 million years ago)…eats leaves, fruit, seeds, resin, bugs
Tropical Rainforest
Savanna
Roots, tubers, bulbs, rhizomes
Primates typically live in Tropical Rainforests (used hands & feet to climb trees); eat leaves, fruits, and insects.
< Climate-change…more Savanna-like
More difficult life…more challenges: • Bipedalism (to move further & to see predators & prey better & get less sun & use hands to carry things • Develop use of tools• More social organization (language?)• Larger brains• Larger teeth to eat roots & grains & meat
Cassava Parsnips
Taro root
Carrots