2.1 Cell Theory IB Biology HL 1 Mrs. Peters Fall 2013

What is a Cell?  Cell: the basic structural and functional unit of all organisms  Discovered by Robert Hooke in the late 1600’s Examined a piece of cork with a home-made microscope Examined a piece of cork with a home-made microscope Saw numerous box-shaped structures Saw numerous box-shaped structures Named them “cells” after the rooms or cells that Monks lived in Named them “cells” after the rooms or cells that Monks lived in

Cell Theory  The Cell Theory: When Schleiden and Schwann proposed the cell theory in 1838, 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 together. Shared notes and came up with the theory together.  The cell theory also provides us with an operational definition of "life."

Cell Theory  The cell theory states that: All life forms are made from one or more cells. All life forms are made from one or more 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 Things  Living organisms can be multicellular (many cells) or unicellular (one cell)  All living things need the following to survive: Metabolism, growth, response to environment, homeostasis, nutrition, and reproduction Metabolism, growth, response to environment, homeostasis, nutrition, and reproduction  Which of the following do you think is considered non-living based on cell theory and the needs of living things? Why? A. bacteriaB. plantsC. viruses

Living Things  Answer: Viruses because they are not made up of cells Viruses because they are not made up of cells They reproduce by inserting their DNA into the DNA of another organism. They reproduce by inserting their DNA into the DNA of another organism. Cells become little virus producing factories. Cells become little virus producing factories. Aids Virus Influenza Virus

Needs of Living Things  Metabolism: the break down of organic material to make chemicals needed to sustain life  Growth: ability to grow and develop in different stages (ex: infant to child to adult)  Response to environment: ability to detect change in surroundings and respond accordingly to survive

Needs of Living Things  Homeostasis: the ability to control its internal environment (this is why you sweat or shiver)  Nutrition: must be able to obtain food either by producing its own or consuming other things  Reproduction: survival depends on creating offspring either sexually or asexually

Evidence for Cell Theory All life forms are made from one or more cells. Evidence: since Robert Hooke, tissue samples for many different organisms have been examined using microscopes and have been found to consist of cells.

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

Evidence for Cell Theory The cell is the smallest form of life. Evidence: experiments can be done in which cells are burst open and the subunits (organelles) are separated using a centrifuge, the subunits of cells do not survive long by themselves.

Emergent Properties  Emergent Properties/Characteristics are Properties that arise from the interaction of component parts  Different cell types interact with each other to allow more complex functions to take place  Ex: nerve cells interact with muscle cells to stimulate movement

Main Types of Cells  Two main types of cells determined by structure Prokaryotes Prokaryotes Greek meaning “before the nucleus”Greek meaning “before the nucleus” Eukaryotes Eukaryotes Cells that have a nucleusCells that have a nucleus

Prokaryotes  General Characteristics: Small in size Small in size Unicellular Unicellular No organelles No organelles No nucleus No nucleus  Types: Bacteria Bacteria Spirals, rods, spheresSpirals, rods, spheres

Eukaryotes  General Characteristics: Larger in size Larger in size Unicellular or multicellular Unicellular or multicellular Organelles Organelles True Nucleus True Nucleus  Types: Plant Plant Animal Animal Fungi (don’t need to worry about this one!) Fungi (don’t need to worry about this one!)

Cell Size  Most cells are too small to see with the naked eye; light and electron microscopes are needed to see them  Virtual Field Trip Time!  Write down relative size comparisons for atoms, molecules, bacteria, organelles, eukaryotes (must use correct units)  Membrane thickness is ~7nm

Relative Size Review Invisible: 0.04 nm Atom 0.04 nm Atom nm small molecules nm small molecules nm large molecules nm large molecules Visible with electron microscope: 7nm Cell Membrane Thickness 7nm Cell Membrane Thickness nm Viruses nm Viruses Visible with light microscope: µm Bacteria µm Bacteria 20 nm-1 µm Organelles 20 nm-1 µm Organelles 20 µm Animal cell 20 µm Animal cell 40 µm Plant cell 40 µm Plant cell

Surface Area to Volume Ratio  Cells are very small, the size of the organism does not change the size of cells  The volume of a cell determines the level of metabolic activity that takes place in it  The surface area of a cell determines the rate of exchange of materials with the outside environment

Surface Area to Volume Ratio  As volume increases, so does surface area, but not proportionately  If a cell is cube shaped, let’s see what happens as the cube changes size SA = surface area SA = surface area Vol = volume Vol = volume Side (mm) SA (mm 2 ) Vol (mm 3 ) Ratio SA to Vol 1616: : :1

Surface Area to Volume Ratio  As a cell grows larger, it has less surface area to obtain materials and the rate of exchange becomes limiting; the cell can’t keep up with its requirements  Cells with thin projections or folds (microvilli) on their surface, increase surface area without increasing volume  Larger organisms don’t have larger cells, they have more cells

Surface Area to Volume Ratio  Cell size is limited by surface area to volume ratio The smaller the cell, the higher the surface area to volume ratio The smaller the cell, the higher the surface area to volume ratio High surface area to volume ratio facilitates the exchange of materials between the cell and its environment more quickly High surface area to volume ratio facilitates the exchange of materials between the cell and its environment more quickly

Surface Area to Volume Ratio  Time to create! Obtain a piece of clay and directions Obtain a piece of clay and directions Make each shape and record the surface area and volume ratios Make each shape and record the surface area and volume ratios Compare surface area and volume for each shape Compare surface area and volume for each shape

Microscopes Part 2  Draw the following from Prepared Slides: Paramecium or Euglena Paramecium or Euglena Three types of bacteria Three types of bacteria Frog Blood Frog Blood Spirogyra Spirogyra Start a new paper for this set of drawings, remember: Start a new paper for this set of drawings, 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)