 Enormous variety in the size and shape of different cells  Smallest cells belong to group of organisms  Mycoplasma  Only about 0.2 µm in diameter  So small that often beyond the limit of resolution of light microscopes

 Large cells (giant amoeba)  Chaos chaos  About 1000 µm in diameter

 Larger cells  yolks of bird eggs  Single cells containing stored food for the developing bird  for the most part, cells are between 5 & 50 µm in diameter

 certain structures are common to most cells  plants, animals, and related organisms have 3 basic structures:  cell membrane-outer boundary  nucleus-control center  cytoplasm-material between the cell membrane and nucleus

 all cells are separated from their surroundings by a cell membrane  regulates what enters and leaves the cell  aids in the protection and support of the cell  similar to cell walls that surround a house

 it must communicate with other cells, take in food, and water and eliminate wastes  composed of several kinds of molecules  lipids, proteins, cho’s

double layer of lipid molecules, known as a ‘bilayer’ forms the basic unit from which cell membranes are constructed

 some proteins stick to the surface of the lipid bilayer, others are free to move around within the bilayer  some act as channels through which molecules can pass  others act like small pumps, actively pushing molecules from one side of the membrane to the other

 cho’s are attached to proteins or lipids at the membrane surface  many act like chemical id cards, allowing cells to recognize and interact with each other

 in organism such as plants, algae, and some bacteria, the cell membrane is surrounded by a cell wall  helps to protect and support the cell  very porous  water, oxygen, carbon dioxide, and other substances can pass through easily  made up of two or more layers  layers form in a series of steps

 1 st layer to form develops where two plant cells meet  Contains a gluey substance called pectin, that helps hold the cells together  Each of these cells then forms a primary cell wall on its side of this gluey layer  Made up of cellulose (a fibrous material)  Make the cell wall elastic  stretch as it grows

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 Plants that have woody stems, another layer  secondary cell wall, develops  Composed of cellulose and lignin  Lignin makes cellulose more rigid  Wood consists mainly of secondary cell walls

 Nucleus-info center of the cell  Seen in many cells as a large dark structure  1 st described by Robert Brown  Not all cells have nuclei  Small unicellular organism  bacteria and several other kinds of organisms, do not have nuclei

 The absence or presence of a nucleus can be used to divide organisms into two categories:  Prokaryotes-lack nuclei  Eukaryotes-contain nuclei  Karyon=nucleus  Pro=before  Eu=true

 Prokaryotic organism  Bacteria and their relatives  Usually small and unicellular

 Eukaryotic organisms  Both unicellular and multicellular

 Nucleus is the information center of the cell  Contains DNA=instructions for making thousands of different molecules  Directs all the activities that occur in a living cell

 Nuclear envelope  Composed of two membranes that form boundary around nucleus  Inside  dozens of nuclear pores  Molecules move in and out of nucleus through nuclear pores

 Nucleolus  Most nuclei contain a small region called nucleolus  Made up of RNA and proteins  Where ribosomes are made

 Chromosomes  The DNA in the nucleus of eukaryotic cells is attached to special proteins and forms large structures called chromosomes  Contain genetic information that must be passed to each new generation of cells

 Cytoplasm  Area between the nucleus and the cell membrane  Contains important structures

 We will discuss the organelles found within the cytoplasm!!!!!!!!!!!!