Plant Cell Structure Unit Botany Plant Cell Structure Unit Textbook Reading Requirement Chapter 3 (pp. 27-39) Objectives: To describe the basic structure of typical plant cells. To describe, in detail, cellular structures unique to plant cells.* To observe and draw examples of plant cells using the microscope.

(1655- 1897) Robert Hooke, Marcello Malpighi, Nehemiah Grew, Anton von Leeuwenhoek, Jean Babptist de LaMarck Renee J.H. Durochet, Robert Brown, Matthias Schleiden, Theodor Schwann, Rudolph Virchow, Louis Pasteur, Edward Buchner. Cell Theory -All living things and only living things are composed of cells -Cells are the structural unit of living things. -Cells arise from other living cells.

Prokaryotic Cells- cells lacking membrane bounded organelles (w/o nucleus) Blue green algae: Anabaena

Eukaryotic Cells- cells with membrane bounded organelles w/ nucleus Algae: Chlamymadomonas

PROKARYOTIC CELLS EUKARYOTIC CELLS 1. Lacks a nuclear membrane 2.Has a single long strand of DNA and several plasmids. 3. Have no membrane bounded organelles 4. Asexual reproduction by binary fission 5. Sexual reproduction unknown. EUKARYOTIC CELLS 1. Have a nuclear membrane 2. Have two to hundreds of chromosomes per cell. 3. Have membrane bounded organelles 4. Asexual reproduction by mitosis 5. Sexual reproduction involves the fusion of sex cells.

Cells Size of cells vary: smallest (bacteria) 0.5 micrometers most (higher plants) 10 - 100 micrometers largest (unique!) 2 cm - 20 cm Due to the typical small size of cells, the number of cells in an average higher plant is “astronomical”! 1 mature leaf of a pear tree = 50 million cells (est.) 1 mature pear tree = 15 trillion cells (est.)

“Trees have no bones or similar internal support structures as do animals. yet, they are able to support branches & leaves weighing many tons.” “A single mature redwood exceed the mass and volume of the largest land animals by more than a hundred times.” “The wood from a single redwood could support the combined weight of a thousand elephants.” How? The combined strength of its cell walls!

Robert Hooke’s sketches Cell Wall Basics Cell Wall- nonliving boundary, produced by the living components of the cell that supports and protects. - strong, rigid (with a degree of elasticity) - typically composed of cellulose Robert Hooke’s sketches of cork cells S.E.M. micrograph of cork cells S.E.M.

Hemicellulose. S.E.M. 25,000X Electron micrograph of a plant cell wall showing cellulose microfibrils. Microfibrils are held together by a glue-like substance termed Hemicellulose.

Additional Components of the Cell Wall Most plant cells possess thin, elastic cell walls- Primary Cell Wall Cell walls are separated from one another by the middle lamella. Middle lamella is composed of pectin (thick, gelatinous polysaccharide) (Cellulose & Hemicellulose) (Pectin)

“The thickness of a plant cell wall can occupy from Layers can be added to the primary cell wall providing additional support - Secondary Cell Wall Secondary cell walls are composed of additional layers of cellulose Which may be impregnated with other substances: Lignin - hardening agent (wood, shells of nuts) Suberin and Cutin - waterproofing agents (bark, cork, leaves) “The thickness of a plant cell wall can occupy from 5% to 95% of a cell’s total volume!”

Cell Walls

S.e.m. of wood

LIGNIN

SUBERIN

Movement of materials through cell walls involves Plasmodesmata. Plasmodesmata are small strands of cytoplasm that connects one plant cell to adjacent plant cells

Plastids Plastids- group of plant cell organelles with a variety of functions. Three Types of plastids: (based on color & function) 1) Chloroplast- green plastids / site of photosynthesis. Contains chlorophyll and other pigments T.E.M.

Stroma Granum (Grana) T.E.M. 10,000X Thylakoids

2. Leucoplast- plastids that are involved with food storage Colorless; Primarily store starches and oils. (amyloplasts, elaioplasts) Development of a leucoplast

3. Chromoplasts- type of plastid whose function is the storage of certain pigments. (red, yellow, orange, blue). These plastids give rise to the colors seen in flower petals, fruits and other parts of certain plants. (colorbodies)

Plastids are capable of changing from one type to another. green tomato (chloroplasts) --------> red tomato (chromoplasts) Potato (leucoplasts) ----------------> potato (chloroplasts)

Vacuoles Organelles that act as storage sites for a variety of plant substances (starch, sugars, oil, pigments, water, wastes) as well as maintaining cell pressure (turgor). Young plant cells have small vacuoles that are few in number. As cells mature their vacuoles increase in size and coalesce to form a single, large structure which may occupy 95% of the cell lumen. The name given to the Liquid found in plant cell Vacuoles is cell sap.

Elodea

Starch grains in root tip cells.