2.1 Cell Theory 2.1 Cell Theory

IB Biology HL 1IB Biology HL 1

Mrs. PetersMrs. Peters

Fall 2013Fall 2013

What is a Cell?What is a Cell? CellCell: the basic structural : the basic structural

and functional unit of all and functional unit of all organismsorganisms

Discovered by Robert Discovered by Robert Hooke in the late 1600’sHooke in the late 1600’s Examined a piece of cork Examined a piece of cork

with a home-made with a home-made microscopemicroscope

Saw numerous box-shaped Saw numerous box-shaped structuresstructures

Named them “cells” after the Named them “cells” after the rooms or cells that Monks rooms or cells that Monks lived inlived in

Cell TheoryCell Theory

The Cell TheoryThe Cell Theory: : When Schleiden and When Schleiden and Schwann proposed the cell theory in 1838, Schwann proposed the cell theory in 1838, cell biology research was forever changed. cell biology research was forever changed. Schleiden was a botanist (studied plants)Schleiden was a botanist (studied plants) Schwann was a zoologist (studied animals)Schwann was a zoologist (studied animals) Shared notes and came up with the theory Shared notes and came up with the theory

together.together. The cell theory also provides us with an The cell theory also provides us with an

operational definition of "life."operational definition of "life."

Cell TheoryCell Theory

The cell theory states that: The cell theory states that: All life forms are made from one or more All life forms are made from one or more

cells. cells. Cells only arise from pre-existing cells. Cells only arise from pre-existing cells. The cell is the smallest form of life.The cell is the smallest form of life.

Living ThingsLiving Things Living organisms can be Living organisms can be multicellularmulticellular (many (many

cells) or cells) or unicellularunicellular (one cell) (one cell)

All living things need the following to survive:All living things need the following to survive: Metabolism, growth, response to environment, Metabolism, growth, response to environment,

homeostasis, nutrition, and reproductionhomeostasis, nutrition, and reproduction

Which of the following do you think is Which of the following do you think is considered non-living based on cell theory considered non-living based on cell theory and the needs of living things? Why?and the needs of living things? Why?

A. bacteriaA. bacteria B. plantsB. plants C. virusesC. viruses

Living ThingsLiving Things

Answer:Answer: Viruses because they are not made up of Viruses because they are not made up of

cellscells They reproduce by inserting their DNA into They reproduce by inserting their DNA into

the DNA of another organism.the DNA of another organism. Cells become little virus producing factories.Cells become little virus producing factories.

Aids Viruswww.healthoma.com

Influenza Viruswww.dreamstime.com

Needs of Living ThingsNeeds of Living Things

Metabolism: Metabolism: the break down of organic the break down of organic material to make chemicals needed to material to make chemicals needed to sustain lifesustain life

Growth: Growth: ability to grow and develop in ability to grow and develop in different stages (ex: infant to child to adult)different stages (ex: infant to child to adult)

Response to environment: Response to environment: ability to ability to detect change in surroundings and detect change in surroundings and respond accordingly to surviverespond accordingly to survive

Needs of Living ThingsNeeds of Living Things

Homeostasis: Homeostasis: the ability to control its the ability to control its internal environment (this is why you internal environment (this is why you sweat or shiver)sweat or shiver)

Nutrition: Nutrition: must be able to obtain food must be able to obtain food either by producing its own or consuming either by producing its own or consuming other thingsother things

Reproduction: Reproduction: survival depends on survival depends on creating offspring either sexually or creating offspring either sexually or asexuallyasexually

Evidence for Cell TheoryEvidence for Cell Theory

All life forms are made from one or All life forms are made from one or more cells.more cells.

Evidence:Evidence: since Robert Hooke, tissue since Robert Hooke, tissue samples for many different organisms samples for many different organisms have been examined using microscopes have been examined using microscopes and have been found to consist of cells.and have been found to consist of cells.

Evidence for Cell TheoryEvidence for Cell TheoryCells only arise from pre-existing cells.Cells only arise from pre-existing cells.

Evidence:Evidence: experiments can be done using experiments can be done using material that is suitable for sustaining growth material that is suitable for sustaining growth of living cells: If all cells are killed and no new of living cells: If all cells are killed and no new cells are allowed to enter, no cells develop cells are allowed to enter, no cells develop from the non-living material. In growing tissues from the non-living material. In growing tissues where new cells are being produced, division where new cells are being produced, division of the pre-existing cells can be observed of the pre-existing cells can be observed (mitosis), rather than the construction of new (mitosis), rather than the construction of new cells from non-living substances.cells from non-living substances.

Evidence for Cell TheoryEvidence for Cell Theory

The cell is the smallest form of life.The cell is the smallest form of life.

Evidence: Evidence: experiments can be done in experiments can be done in which cells are burst open and the which cells are burst open and the subunits (organelles) are separated subunits (organelles) are separated using a centrifuge, the subunits of cells using a centrifuge, the subunits of cells do not survive long by themselves.do not survive long by themselves.

Emergent PropertiesEmergent Properties

Emergent Properties/Characteristics are Emergent Properties/Characteristics are Properties that arise from the interaction of Properties that arise from the interaction of component partscomponent parts

Different cell types interact with each other Different cell types interact with each other to allow more complex functions to take to allow more complex functions to take placeplace

Ex: nerve cells interact with muscle cells to Ex: nerve cells interact with muscle cells to stimulate movementstimulate movement

Main Types of CellsMain Types of Cells

Two main types of cells determined by Two main types of cells determined by structurestructure Prokaryotes Prokaryotes

• Greek meaning “before the nucleus”Greek meaning “before the nucleus” EukaryotesEukaryotes

• Cells that have a nucleusCells that have a nucleus

ProkaryotesProkaryotes General Characteristics:General Characteristics:

Small in size Small in size UnicellularUnicellular No organellesNo organelles No nucleusNo nucleus

Types:Types: BacteriaBacteria

• Spirals, rods, spheresSpirals, rods, spheres

EukaryotesEukaryotes General Characteristics:General Characteristics:

Larger in sizeLarger in size Unicellular or multicellularUnicellular or multicellular Organelles Organelles True NucleusTrue Nucleus

Types:Types: PlantPlant AnimalAnimal Fungi (don’t need to Fungi (don’t need to

worry about this one!)worry about this one!)

Cell SizeCell Size Most cells are too small to see Most cells are too small to see

with the naked eye; light and with the naked eye; light and electron microscopes are electron microscopes are needed to see themneeded to see them

Virtual Field Trip Time!Virtual Field Trip Time! Write down relative size Write down relative size

comparisons for atoms, comparisons for atoms, molecules, bacteria, organelles, molecules, bacteria, organelles, eukaryotes (must use correct eukaryotes (must use correct units)units)

Membrane thickness is ~7nmMembrane thickness is ~7nm

Relative Size ReviewRelative Size ReviewInvisible: Invisible: • 0.04 nm Atom0.04 nm Atom• 0.05-1 nm small molecules0.05-1 nm small molecules• 1.2-2 nm large molecules1.2-2 nm large molecules

Visible with electron microscope:Visible with electron microscope:• 7nm Cell Membrane Thickness7nm Cell Membrane Thickness• 50-90 nm Viruses50-90 nm Viruses

Visible with light microscope:Visible with light microscope:• 0.5-1 µm Bacteria0.5-1 µm Bacteria• 20 nm-1 µm Organelles20 nm-1 µm Organelles• 20 µm Animal cell20 µm Animal cell• 40 µm Plant cell40 µm Plant cell

Surface Area to Volume RatioSurface Area to Volume Ratio Cells are very small, the size of the Cells are very small, the size of the

organism does not change the size of cellsorganism does not change the size of cells

The The volumevolume of a cell determines the of a cell determines the level level of metabolic activityof metabolic activity that takes place in it that takes place in it

The The surface area surface area of a cell determines the of a cell determines the rate of exchange of materials rate of exchange of materials with the with the outside environmentoutside environment

Surface Area to Volume RatioSurface Area to Volume Ratio As volume increases, As volume increases,

so does surface area, so does surface area, but not proportionatelybut not proportionately

If a cell is cube shaped, If a cell is cube shaped, let’s see what happens let’s see what happens as the cube changes as the cube changes sizesize SA = surface areaSA = surface area Vol = volumeVol = volume

Side (mm)

SA (mm2)

Vol (mm3)

Ratio SA to Vol

1 6 1 6:1

2 24 8 3:1

3 54 27 2:1

Surface Area to Volume RatioSurface Area to Volume Ratio

As a cell grows larger, it has less surface As a cell grows larger, it has less surface area to obtain materials and the rate of area to obtain materials and the rate of exchange becomes limiting; the cell can’t exchange becomes limiting; the cell can’t keep up with its requirementskeep up with its requirements

Cells with thin projections or folds (microvilli) Cells with thin projections or folds (microvilli) on their surface, increase surface area on their surface, increase surface area without increasing volumewithout increasing volume

Larger organisms don’t have larger cells, Larger organisms don’t have larger cells, they have more cellsthey have more cells

Surface Area to Volume RatioSurface Area to Volume Ratio

Cell size is limited by surface area to Cell size is limited by surface area to volume ratiovolume ratio The smaller the cell, the higher the surface The smaller the cell, the higher the surface

area to volume ratioarea to volume ratio High surface area to volume ratio facilitates High surface area to volume ratio facilitates

the exchange of materials between the cell the exchange of materials between the cell and its environment more quicklyand its environment more quickly

Surface Area to Volume RatioSurface Area to Volume Ratio

Time to create!Time to create! Obtain a piece of clay and directionsObtain a piece of clay and directions Make each shape and record the surface area Make each shape and record the surface area

and volume ratiosand volume ratios Compare surface area and volume for each Compare surface area and volume for each

shapeshape

Microscopes Part 2Microscopes Part 2

Draw the following from Prepared Slides:Draw the following from Prepared Slides: Paramecium or EuglenaParamecium or Euglena Three types of bacteriaThree types of bacteria Frog BloodFrog Blood SpirogyraSpirogyra

Start a new paper for this set of drawings, Start a new paper for this set of drawings, remember:remember:• Use pencil or colored pencilsUse pencil or colored pencils• Fill the boxFill the box• Label the box (what and magnification)Label the box (what and magnification)