Chapter 7 A View of the Cell

7.1 The Discovery of Cells Section Objectives  Relate advances in microscope technology to discoveries about cells and cell structure.  Compare the operation of a microscope with that of an electron microscope.  Identify the main ideas of the cell theory.

The History of the Cell Theory  Cells are the basic units of living organisms  Cells could not be discovered until microscopes had been invented because cells are microscopic

Microscopes  Two types of microscopes  Light Microscope – uses light to view the specimen  Compound light microscope – has multiple lenses  Electron Microscope – uses beams of electrons to view the specimen  Very detailed images

Light Microscope Image Electron Microscope

History of the Cell Theory (1800’s)  Robert Hooke, an English scientist, was the first person to view a cell under a microscope  Looked at cork (dead cells of oak bark)  Gave the boxed shaped structures the term cells  Matthias Schleiden observed a variety of plants and concluded that all plants are composed of cells  Theodor Schwann made observations of animal cells

The Cell Theory  The cell theory is made up of three main ideas: 1.All organisms are composed of one or more cells 2.The cell is the basic unit of structure and organization of organisms 3.All cells come from preexisting cells

Two Basic Cell Types  All cells contain small structures called organelles  Each organelle has a different function  All cells can be classified as either a prokaryote or eukaryote

Prokaryotes Prokaryotes – simple cells Do not contain organelles with membranes (such as a nucleus)Do not contain organelles with membranes (such as a nucleus) Example – Bacteria onlyExample – Bacteria only

Eukaryotes Eukaryotes – more complex cells Contain a nucleus and other organelles with membranesContain a nucleus and other organelles with membranes Example – everything besides bacteriaExample – everything besides bacteria

7.1 Section Review 1.Name the first scientist to view cells. 2.What are the two main types of microscopes? 3.List the 3 parts of the cell theory. 4.Name and describe the two types of cells. Give an example of each. 5.What is an organelle?

7.3 Organelles Golgi apparatus Nucleus Nucleolus Endoplasmic reticulum RibosomesCilia Plasma Membrane Cytoplasm Mitochondria Vacuole

Plasma Membrane Structure – lipid bilayer Function – maintain homeostasis by controlling what enters and leaves the cell Cell Wall Structure – rigid layer on outside of plant cells only Function – gives support to cell

Nucleus Structure – membrane bound organelle in center of cell Function – control cell’s activities Endoplasmic reticulum Structure – layers of membranes, may be covered with ribosomes Functions – directs materials throughout the cell Ribosomes - The site of protein synthesis

Golgi apparatus Structrue – layers of membranes closest to plasma membrane Fuction – packages and distributes materials to outside of cell Vaculoes Used for storage

Chloroplast Structure – stacks of membranes inside a fluid-filled organelle Function – site of photosynthesis Mitochondria Structure – folded inner membrane inside an outer membrane Function – break down food and release energy

Cilia Short, hair-like projections used for movement Flagella Long, whip-like projection used for movement

Other Organelles  Lysosomes – small, membrane-bound organelles that contain enzymes to digest old cell parts  Cytoskeleton – protein fibers which provide shape and support for organelles  Consist of several types of fibers such as microtubles

7.2 Plasma Membrane  All living things must maintain homeostatsis (a balanced internal environment)  The plasma membrane is the barrier between a cell and its surroundings  The plasma membrane is selectively permeable, it allows some things to pass through while keeps other things out

 A concentration gradient influences what moves in and out of the cell  Larger or non-polar molecules can not simply diffuse through the membrane

Plasma Membrane  Phospholipids build the plasma membrane  Each has a polar head and a non-polar tail  They form a double layer, called lipid bilayer, because polar water inside/outside cell repeals the non-polar tails Polar Head Non-polar Tail

Plasma Membrane The plasma membrane is called a “fluid mosaic” because the phospholipids can slide around each other as long as the heads and tails stay pointed the correct way

Plasma Membrane Protein Channel Protein channels (or transport proteins) allow the passage of polar molecules into and out of the cell