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