IB 103 Chapter 3: Microscopy, Cell Walls, and Mitosis

• IB 103 is an introduction to plant biology
• Chapter 3 focuses on Cells
• Lecture 5 goes over Microscopy and Cell Walls

Labs This Week

• No pre-lab quiz for this week's lab
• Project proposals should be finalized
• A fast Plant growth experiment is being set up
• Basic stats in Excel are covered this week

Learning Outcomes

• One should remember the structure and organization of a plant cell
• Describe the communication between and within cells accurately
• Understand the structure and function of organelles
• Assess how information flows from the nucleus to other parts of the cell
• Have full knowledge of the cell cycle as well as the four phases of mitosis
• Distinguish the unique structures of plant cells

Outline

• Introduction to Cells
• History of Cells
• Modern Microscopes
• Eukaryotic versus Prokaryotic Cells
• Cell Structure and Communication
• Cell Size
• The Cell Wall
• Communication between Cells
• Cellular Reproduction
• The Cell Cycle
• Interphase
• Mitosis
• Higher Plant Cells Versus Animal Cells

Moodle Question Topics

• What are the major layers and regions of the plant cell?
• Which structural components are most prevalent in each layer of the plant cell wall?

History of Cell Theory

• In 1665, cells were discovered by Robert Hooke.
• Cell Theory states that all living organisms have common features, varying lifespans, and form a structural basis of organization.
• Matthias Schleiden and Theodor Schwann largely developed cell theory around 1838
• In 1831, Robert Brown discovered the nucleus.
• In 1858, Rudolf Virchow argued against spontaneous generation of cells.
• In 1862, Louis Pasteur experimentally disproved spontaneous generation.

Modern Microscopes: Light Microscopes

• Light Microscopes increase magnification by using a series of transparent lenses made of glass or calcium fluoride crystals.
• Two major types: Dissecting Microscopes and Compound Microscopes

Modern Microscopes: Dissecting Microscopes

• Can also be called Stereo microscopes
• Allow three-dimensional viewing of opaque objects
• Magnification up to ~40x

Modern Microscopes: Compound Microscopes

• Has two optical components: The objective lens system and the eye piece system
• Light passes through thinly sliced material being observed
• Can generally distinguish organelles 2 micrometers or larger in diameter
• Magnification up to 1500x

Modern Microscopes: Electron Microscopes

• Utilizes an electron beam to form an image, instead of a beam of light, for extremely high resolution.

Modern Microscopes: Scanning Electron Microscopes

• Uses a focused beam of electrons to scan the surface of an object
• The interaction of electrons with the atoms in the sample produces signals that contain information about the surface topography and sample composition
• Magnification is typically up to10,000x magnification

Microscopes: Transmission Electron Microscopes

• Consists of three essential systems:
  • An electron gun and condenser for producing and projecting electrons
  • An image-producing system that focuses the electrons passing through the specimen to form a real, highly magnified image
  • Image-recording system that converts the electron image into a perceptible form (fluorescent screens and digital camera)
• Magnification is typically up to 200,000x, but material must be sliced extremely thin.

Eukaryotic vs. Prokaryotic Cells

• Prokaryotic: Cells lack a nucleus and organelles; includes Archaea and Bacteria
• Eukaryotic: Cells contain a nucleus and organelles; includes Protists, Fungi, Plants, and Animals
• Organelles: Membrane-bound bodies with specialized structures that perform various functions inside cells; literally means "little organs"

Plant Cell components

• Cell wall
• Protoplast (= plasma membrane + protoplasm)
• Plasma membrane
• Protoplasm (= cytoplasm + nucleus)
• Cytoplasm (= cytosol + organelles)
• Cytosol
• Nucleus – DNA transcription, ribosome biogenesis
• Endoplasmic reticulum – protein and lipid synthesis
• Ribosomes - protein synthesis
• Dictyosomes (Golgi apparatus)
• Plastids (Chloroplast, contain stroma) – photosynthesis
• Mitochondria - respiration
• Microbodies - conversion of stored lipid into sucrose
• Vacuoles (contain cell sap)
• Cytoskeleton

Cell Structure and Communication

• Cell wall surrounds the protoplasm; it is a rigid layer of mostly polysaccharides outside the plasma membrane of eukaryotic cells
• In algae and plants, cellulose is a primary component of cell walls
• Protoplasm consists of all living cell components and is bound by the plasma membrane
• Cytoplasm consists of all cellular components between the plasma membrane and the nucleus
• Cytosol is the fluid within the cytoplasm that contains organelles (which also have their own membranes)

Cell Size

• Cells of higher plants generally vary in length between 10 and 100 micrometers, mostly about 30 micrometers
• Some prokaryotic cells measure less than 0.5 micrometers
• As surface area in a spherical cell increases relative to the square of its diameter, the increase in volume is relative to the cube of its diameter
• Smaller cells have relatively large surface-to-volume ratios; this enables faster and more efficient cellular communication

Cell Wall

• Mostly contains cellulose, along with a matrix of:
  • Hemicelluloses - Polysaccharides which hold cellulose fibrils together
  • Lignins - water-insoluble, long-chain heterogeneous polymers that consist of the cross-linked component of three alcohols; it is the second most abundant polymer after cellulose
  • Pectins - water-soluble structural acidic heteropolysaccharides (e.g., in fruit jellies)
  • Glycoproteins - Proteins with associated sugars

Cell Wall Layers

• Middle lamella: Pectin-rich material; first layer produced when new cell walls are formed, shared by adjacent cells
• Primary cell wall: Cellulose, hemicellulose, and small amounts of pectin and glycoprotein
• Secondary cell wall: Lots of cellulose, lignin, and hemicellulose, very little pectin and glycoprotein
  • Derived from primary walls by thickening and inclusion of lignin, secondary metabolites derived from amino acids
  • Cellulose microfibrils embedded in lignin for strength

Communication Between Cells

• Fluids and dissolved substances can pass through primary walls of adjacent cells via plasmodesmata
• Plasmodesmata are nano-sized (50 - 60 nanometers) membranous channels that cross adjacent plant cell walls, linking plasma membranes, cytoplasm, and endoplasmic reticulum