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Cells. Chapter 3. Outline. History of Cell Theory Modern Microscopes Eukaryotic and Prokaryotic Cells Cell Structure and Communication Cell Components Cellular Reproduction Higher Plant Cells Versus Animal Cells. History of Cell Theory . 1665 - Cells discovered by Robert Hooke.

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Chapter 3


  • History of Cell Theory

  • Modern Microscopes

  • Eukaryotic and Prokaryotic Cells

  • Cell Structure and Communication

  • Cell Components

  • Cellular Reproduction

  • Higher Plant Cells Versus Animal Cells

History of cell theory
History of Cell Theory

  • 1665 - Cells discovered by Robert Hooke.

  • Cell Theory - all living organisms are composed of cells and cells form a unifying structural basis of organization.

  • 1831 - Robert Brown discovered nucleus.

  • 1858 - Rudolf Virchow argued no spontaneous generation of cells.

    • Louis Pasteur experimentally disproved in 1862.

Modern microscopes
Modern Microscopes

  • Light Microscopes - increase magnification as light passes through series of transparent lenses made of glass or calcium fluoride crystals

  • Two main types:

    • Dissecting (Stereomicroscopes)

    • Compound Microscopes

Modern microscopes1
Modern Microscopes

Dissecting Microscopes (Stereomicroscopes)

  • Allow three-dimensional viewing of opaque objects

  • Can magnify up to 30x

Modern microscopes2
Modern Microscopes

Compound Microscopes

  • Light passes through thinly sliced material

  • Can distinguish organelles 2 micrometers or larger in diameter

  • Can magnify up to 1500x

Modern microscopes3
Modern Microscopes

  • Electron Microscopes –use beam of electrons produced when high-voltage electricity is passed through wire

  • Two main types:

    • Transmission Electron Microscopes (TEMs)

    • Scanning Electron Microscopes (SEMs)

Modern microscopes4
Modern Microscopes

Transmission Electron Microscopes

  • Up to 200,000x magnification, but material must be sliced extremely thin

Modern microscopes5
Modern Microscopes

Scanning Electron Microscopes

  • Up to 10,000x magnification

  • Surface detail can be observed on thick objects.

Modern microscopes6
Modern Microscopes

Scanning Tunneling Microscope

  • Uses probe that tunnels electrons upon sample

  • Produces map of sample surface

  • Even atoms can become discernible

  • First picture of DNA segment showing helical structure

Eukaryotic versus prokaryotic cells
Eukaryotic Versus Prokaryotic Cells

  • Prokaryotic - cells lack a nucleus

    • Bacteria and archaea

  • Eukaryotic - cells contain a nucleus

    • Plants, animals, fungi and protists

    • Cell walls - Rigid boundary of cells

    • Organelles - Membrane-bound bodies found within eukaryotic cells

Cell structure and communication
Cell Structure and Communication

  • Cell wall surrounds protoplasm.

  • Protoplasm consists of all living cell components.

    • Bound by plasma membrane

Cell structure and communication1
Cell Structure and Communication

  • Cytoplasm - all cellular components between plasma membrane and nucleus

    • Cytosol - fluid within cytoplasm containing organelles

    • Organelles - persistent structures of various shapes and sizes with specialized functions

      • Most, but not all, bound by membranes

Cell structure and communication cell size
Cell Structure and CommunicationCell Size

  • Cells of higher plants vary in length between 10 and 100 micrometers

    • Smaller cells have relatively large surface to volume ratios enabling faster and more efficient cellular communication

Cell structure and communication cell wall
Cell Structure and CommunicationCell Wall

  • Main structural component of cell walls is cellulose(long chains of glucose monomers)

    • Also contain matrix of:

      • Hemicellulose - holds cellulose fibrils together

      • Pectin - gives stiffness (like in fruit jellies)

      • Glycoproteins - proteins with associated sugars

Cell structure and communication cell wall1
Cell Structure and CommunicationCell Wall

  • Middle lamella-produced when new cell walls are formed

    • Shared by two adjacent cells

    • Flexible primary walls laid down on either side of middle lamella

Cell structure and communication cell wall2
Cell Structure and CommunicationCell Wall

  • Secondary walls produced inside primary walls

    • Derived from primary walls by thickening and inclusion of lignin

    • Cellulose microfibrils embedded in lignin for strength.

Cell structure and communication communication between cells
Cell Structure and CommunicationCommunication Between Cells

  • Fluids and dissolved substances pass through primary walls of adjacent cells via plasmodesmata

    • Plasmodesmata - cytoplasmic strands that extend between cells through minute openings

Two adjacent cells connected by plasmodesmata

Cell components plasma membrane
Cell ComponentsPlasma Membrane

  • Plasma Membrane - semipermeableouter boundary of living part of cell

    • Regulates movement of substances into and out of cell

Model of plasma membrane

Cell components nucleus
Cell ComponentsNucleus

  • Nucleus-control center of cell and contains DNA

    • Sends coded messages from DNA to be used in other parts of cell

    • Bound by two membranes constituting nuclear envelope

    • Structurally complex pores occupy up to one-third of total surface area

      • Permit only certain kinds of molecules to pass between nucleus and cytoplasm

Cell components nucleus1
Cell ComponentsNucleus

  • Contains fluid nucleoplasm in which are:

    • Nucleoli - composed primarily of RNA

    • Chromatin strands

      • Composed of DNA and proteins

      • Coil and become chromosomes

Cell components endoplasmic reticulum
Cell ComponentsEndoplasmic Reticulum

  • Endoplasmic reticulum - enclosed space consisting of network of flattened sacs and tubes forming channels throughout cytoplasm

    • Facilitates cellular communication and channeling of materials

    • Synthesizes membranes for other organelles and modifies proteins

Cell components endoplasmic reticulum1
Cell ComponentsEndoplasmic Reticulum

  • Rough ER -ribosomesdistributed on outer surface of ER

    • Associated with protein synthesis and storage

  • Smooth ER -devoid of ribosomes and associated with lipid secretion

Endoplasmic reticulum and ribosomes

Cell components ribosomes
Cell ComponentsRibosomes

  • Ribosomes - consist of two subunits composed of RNA and proteins

    • Link amino acids to construct complex proteins

    • Subunits assembled in nucleolus

    • May occur on outside of rough ER, or in cytoplasm, chloroplasts or other organelles

    • No bounding membranes

Cell components dictyosomes
Cell ComponentsDictyosomes

  • Dictyosomes -(Golgi bodies in animals) - stacks of flattened discs or vesicles


Cell components dictyosomes1
Cell ComponentsDictyosomes

  • Dictyosomes function:

    • To modify carbohydrates attached to proteins synthesized and packaged in ER

    • To assemble polysaccharides and collect them in small vesicles

      • Vesicles pinched off from margins of dictyosomes

      • Vesicles migrate to plasma membrane, fuse with it, and secrete contents to outside of cell

        • Contents may include cell wall polysaccharides, floral nectars, and essential oils in herbs

Cell components plastids
Cell ComponentsPlastids

  • Chloroplasts - most conspicuous plastids

    • Bound by double membrane and contain:

      • Granamade up ofthylakoids

        • Thylakoid membranes contain chlorophyll

        • First steps of photosynthesis occur in thylakoidmembranes

      • Stroma -matrix of enzymes involved in photosynthesis

      • Small circular DNA molecule

        • Encodes for production of certain proteins for photosynthesis

Cell components plastids1
Cell ComponentsPlastids

TEM and drawing of chloroplast structure

Cell components plastids2
Cell ComponentsPlastids

  • Other types of plastids include:

    • Chromoplasts

      • Synthesize and accumulate carotenoids (yellow, orange, red)

    • Leucoplasts

      • Colorless

      • May synthesize starches (amyloplasts)

      • Or oils (elaioplasts)

Chromoplasts in red pepper cells

Cell components mitochondria
Cell ComponentsMitochondria

  • Mitochondria - release energy produced from cellular respiration

    • Bound by two membranes

    • Inward membrane forms numerous folds = cristae

    • Increase surface area available to enzymes in matrix

    • Matrix also includes DNA and RNA

Cell components microbodies
Cell ComponentsMicrobodies

  • Microbodies- small, spherical bodies distributed throughout cytoplasm containing specialized enzymes

    • Bound by a single membrane

    • Peroxisomes -serve in photorespiration

    • Glyoxisomes -aid in conversion of fat to carbohydrates

Cell components vacuoles
Cell ComponentsVacuoles

  • In mature cells, 90% of volume may be taken up by central vacuoles

    • Bounded by vacuolar membranes, tonoplasts

    • Filled with cell sap - helps maintain pressure within cell

      • Contains dissolved substances i.e., salts, sugars, organic acids, and small proteins

      • Frequently contains water-soluble pigments called anthocyanins (red, blue, purple)

Cell components cytoskeleton
Cell ComponentsCytoskeleton

  • Cytoskeleton -involved in movement within cell and in cell’s architecture

    • Network of microtubules and microfilaments

    • Microtubules:

      • Control addition of cellulose to cell wall

      • Involved in movement of flagella and cilia

      • Found in fibers of spindles and phragmoplasts in dividing cells

      • Are thin, hollow, tubelike and composed of tubulins (proteins)

    • Microfilaments -role in cytoplasmic streaming

Cellular reproduction cell cycle
Cellular ReproductionCell Cycle

  • Cell cycle -orderly series of events when cells divide

    • Divided into interphase and mitosis

  • Interphase

    • Occupies up to 90% of cell cycle

    • Period when cells are not dividing

      • G1 -cell increases in size

      • S - DNA replication takes place

      • G2 -mitochondria and other organelles divide, and microtubules produced

Cellular reproduction mitosis
Cellular ReproductionMitosis

  • Mitosis- process of cellular division

    • Produces two daughter cells with equal amounts of DNA and other substances duplicated during interphase

    • Each daughter cell exact copy of parent cell

    • Occurs in meristems

    • Although a continuous process, divided into 4 phases: prophase, metaphase, anaphase and telophase

Cellular reproduction mitosis1
Cellular ReproductionMitosis

  • Prophase

    • Chromosomes condense by coiling and tightening to become shorter and thicker.

      • Chromosomes made of two identical chromatids held together by centromeres

        • Kinetochore (protein complex) located on outer surface of each centromere

        • Spindle fibers (microtubules) attach to kinetochoreand anchored to two poles of cell

  • Nuclear envelope fragments and nucleolus disintegrates

Cellular reproduction mitosis2
Cellular ReproductionMitosis


  • Metaphase

    • Chromosomes align between poles around circumference of spindle at cell’s equator

      • Spindle fibers collectively referred to asspindle

      • At end of metaphase, centromeres holding each sister chromatid separate lengthwise.


Cellular reproduction mitosis3
Cellular ReproductionMitosis

  • Anaphase

    • Sister chromatids separate and pulled to opposite poles, with centromeres leading the way

      • Spindle fibers shorten as material is continuously removed from polar ends

      • Chromatids after separation are called daughter chromosomes


Cellular reproduction mitosis4
Cellular ReproductionMitosis

  • Telophase

    • Each group of daughter chromosomes become surrounded by nuclear envelope

    • Daughter chromosomes become longer and thinner and eventually, indistinguishable

    • Nucleoli reappear

    • Spindle fibers disintegrate

    • Phragmoplast and cell plate form at equator


Cellular reproduction mitosis5
Cellular ReproductionMitosis

  • Cell Plate Formation:

    • Phragmoplast develops between daughter cell nuclei

      • Phragmoplast - complex of microtubules and ER

    • Microtubules trap dictyosome-derived vesicles

    • Vesicles fuse to form cell plate

      • Cell plate grows outward toward mother cell walls

Cell plate formation

  • Portions of ER trapped between vesicles, forming plasmodesmata

Higher plant cells versus animal cells
Higher Plant Cells Versus Animal Cells

  • Plants:

    • Cell walls

    • Cell plate and plasmodesmata

    • Plastids and vacuoles

  • Animals:

    • Internal or external skeletons; no cell walls

    • Plasma membrane called cell membrane

    • Divide by pinching in two; no cell plate nor plasmodesmata

    • Centrioles present during cell division

    • No plastids nor vacuoles


  • History of Cell Theory

  • Modern Microscopes

  • Eukaryotic and Prokaryotic Cells

  • Cell Structure and Communication

  • Cell Components

  • Cellular Reproduction

  • Higher Plant Cells Versus Animal Cells