Chapter 3 Notes, part 1 “Looking at Cells” Cells were discovered in the 17th century, when microscopes were invented….
Cells were discovered by….. • Robert Hooke, in 1665 he looked at a thin piece of cork and ‘saw a lot of little boxes’ which reminded him of the small rooms where monks live, so he called them cells • Anton von Leeuwenhoek used a microscope ten years later to view water from a pond, and he called the tiny organisms he saw ‘animalcules’
Measurement • See table 1, p. 50 • Cells are measured in units of micrometers, abbreviated μm. The symbol μ stands for the prefix ‘micro’ • See figure 2, page 51, which shows the sizes of different objects
Know these words….. • Magnification: the amount of times a specimen being viewed is enlarged in order to be seen, varies with power of microscope • Resolution: the ability that the microscope has to distinguish between two different objects, ie. The nucleus vs. the endoplasmic reticulum • Contrast: ability to see detail within the specimen clearly
Types of microscopes • Light microscope • Transmission and scanning electron microscopes • Scanning tunneling microscope
Compound light microscopes • What we work with in class • Light rays pass through specimen and come into focus through two glass lenses. • The eyepiece lens gives a total of 10x magnification. The objective lens varies with microscopes but can be up to 100x magnification. Total magnification is found by multiplying eyepiece lens by objective lens.
Transmission Electron Microscopes • Use electrons to pass through specimens to view detail; image projected onto screen or photographic film
Scanning electron microscopes • The specimen is first coated with a thin layer of metal and an image is produced by the electrons which bounce off of the image
Scanning tunneling microscopes • New video and computer techniques are increasing microscope resolution and magnification • This type of microscope uses a needle-like probe to measure voltages of electrons. It can track the movement of electrons and can see atoms!
Compare the images produced by different microscopes….. • See p. 52 for a light microscope image of sperm • See p. 53 for a T.E.M. image of sperm • See p. 54 for an S.E.M. image of sperm
Section 3.2: Cell Features • The cell theory: was bulit on the ideas of Hooke and Leeuwenhooek by the following: • Schleiden who said that cells make up every part of a plant • Schwann who claimed that animals are also made of cells • Virchow who determined that cells come from other cells.
The cell theory summarized… • All living things are made of one or more cells • Cells are the basic unit of structure and function in organisms • All cells arise from existing cells
Cell size and sufrace area:volume ratio • Small cells function more efficiently than larger cells • If the surface area of a cell is larger than it’s volume, then the cell can gather essential nutrients and water and they can get in fast. • If the surface area to volume ratio is close in number to the volume, it takes too long for materials to reach the interior of the cell • See table 2 p. 55
Common features of cells: • Most cells have… • A cell membrane: encloses cell, separates interior • Cytoplasm: the fluid in which interior cell structures are suspended, also called cytosol • Cytoskeleton: for cellular structure • Ribosomes: make proteins • DNA: all cells have DNA which contains instructions for making proteins, regulating the activities of the cell, and allowing the cell to reproduce. Red blood cells lose their DNA at a certain point in their life.
Prokaryotes • A single-celled organism that lacks a nucleus and other internal compartments • Common prokaryotes which cause infection and spoil food: Bacteria
Characteristics of Prokaryotes: • Have little internal structure • Many have a capsule and flagella • DNA is located near the center of the cell and is not contained in a nucleus • A cell wall surrounds the membrane and provides structure and support • Many have flagella which propel them along
Eukaryotic Cells • Cells with a nucleus and other organelles • An organelle is a structure within a cell that carries out specific activities for that cell • Some eukaryotic cells have cilia which are short hairlike structures that protrude from the surface of the cells
cytoskeleton • Provides the internal framework of an animal cell, much as our skeleton provides the internal framework of our bodies • Three types of cytoskeleton fibers: • Actin fibers: found just inside of the cell membrane; helps cell membrane move • Microtubules: transport information from nucleus to different parts of the cell • Intermediate fibers: keep ribosomes and enzymes in place within cell
The cell membrane • to separate the internal from external environment of the cell • Regulates materials entering and leaving the cell. • Helps the cell, in turn the organism, maintain homeostasis
cell membrane structure • Made up of a phospholipid bilayer • Phospholipid: a molecule with a hydrophilic (water-loving) head and a hydrophobic (water-fearing) tail
Cell membrane proteins • Proteins embedded in the membrane have polar and nonpolar ends just like the membrane; this keeps them embedded inside of the membrane • These proteins have different functions: • Receptor proteins recognize and bind to substances outside the cell • Enzymes assist chemical reactions in the cell • Transport proteins help substances move across the membrane
Upcoming Biology Schedule: • This weekend’s homework: worksheet packet • Monday: chapter 3 lab (read) • Wednesday: go over lab/test review • Friday (Happy Halloween!) TEST!!!