Chapter 3 Notes, part 1 “Looking at Cells” Cells were discovered in the 17 th century, when microscopes were invented….
Mar 27, 2015
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
Typical prokaryote:
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!!!