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Chapter 7 Notes Section 1

Cells Cells remained out of sight during most of human history until the invention of the first microscopes. It was not until the mid 1600s that scientists began to use microscopes to observe living things.

The History of the Cell  1.) In 1665 Robert Hooke used an early compound microscope to look at a thin slice of cork (plant material)

 It was composed of tiny empty chambers that he called “cells”. (Figure 7-1, pg 169)  We now know that cells are not empty but contain living matter.

The History of the Cell  2.) In 1674 Anton van Leeuwenhoek used a single-lens microscope to observe pond water and other things.

 3.) In 1838 Matthias Schleiden concluded that all plant are made up of cells.  4.) The following year Theodor Schwann stated that all animals were make of cells.

The History of the Cell

 5.) In 1855 Rudolf Virchow concluded that new cells could be produced only from the division of existing cells.  These numerous observations made it clear that cells are the basic units of life.

Cell Theory All living things are composed of cells.

Cells are the basic units of structure and function in living things. New cells are produced from existing cells.

Exploring the Cell  Today‟s researchers use microscopes and techniques more powerful than the pioneers of biology could have imagined.  When using a light microscope the light limits the detail of images that can be made.  Electron microscopes are capable of revealing details as much as 1000 times smaller than those visible with light microscopes.

 Transmission electron microscopes (TEMs) make it possible to explore cell structures and large protein molecules.  Cells and tissues must be cut first into thin slices before they can be examined.

 Scanning electron microscopes (SEMs) use a pencil like beam of electrons to scan over the surface of a specimen.  Specimens do not have to be cut.  A stunning three-dimensional image is produced

 Only nonliving preserved cells and tissue can be visualized when using electron microscopes.  In the 1990s researchers perfected a new class of microscopes that produce images by tracing the surfaces of samples with a fine probe. (Figure 7-3, page 172)

Types of Cells  A typical cell ranges from 5 to 50 micrometers in diameter.  Cells have two characteristics in common  1. surrounded by a barrier called a cell membrane.  2. at some point in their lives they contain the molecule that carries biological information (DNA).

 Cells fall into two broad categories, depending if they contain a nucleus:  1. Prokaryotes-Cells that do not contain nuclei  2. Eukaryotes-Cells that do contain nuclei

Cell membrane

Cytoplasm

Cell membrane

Cytoplasm Nucleus

Organelles

Prokaryotes  Smaller and simpler than eukaryotic cells.  Have genetic material that is not contained in a nucleus.

 Some contain internal membranes.  Grow, reproduce, and respond to the environment.  Ex. Bacteria

Eukaryotes  Cells are generally larger and more complex than prokaryotic cells.  Generally contain dozens of structures and internal membranes.  Contain a nucleus in which their genetic material is separated from the rest of the cell.  Ex. plants, animal, fungi, and protists.

Chapter 7 Notes Section 2

Eukaryotic Cells

Eukaryotic cells are divided into two parts Nucleus Cytoplasm Portion outside the nucleus where organelles reside

Nucleus  Contains most of the cell‟s DNA  DNA is the code for making proteins

 Surrounded by a double membrane called the nuclear envelope  Contains chromatin, which consists of DNA bound to protein  Condenses during cell division to form chromosomes

 Nucleolus – small dense region in nucleus where the assembly of ribosomes begins

Ribosomes  Small particles of RNA and protein  Are spread throughout the cell  Are also attached to the rough endoplasmic reticulum

 Ribosomes are the site of protein synthesis

Endoplasmic Reticulum  An internal membrane system  Lipids, some proteins, and other materials are assembled here  Rough ER has ribosomes attached to allow for protein synthesis  Smooth ER has no ribosomes to allow for lipid synthesis

Golgi Apparatus

 Appears as a stack of membranes  Acts like a postman  It changes, sorts, and packages proteins and other materials  Also delivers these “packages” to their final destination

Lysosomes  Small organelles filled with enzymes  Act as a cleaning crew  They break down lipids, carbohydrates, and proteins so the cell can use them  Also break down “old” organelles  Also break down unneeded junk in cell such as bacteria

Vacuoles

Saclike structures used for cell storage Stores water, salts, proteins, and carbohydrates

Mitochondria  “Powerhouse of the cell”  Converts chemical energy stored in food into a form that cells can use

 Has a double membrane  One on the outside of organelle  One folded up inside the organelle

 Contains its own DNA

Chloroplasts

 “Powerhouse for a plant cell”

 Converts energy from sun into chemical energy during process of photosynthesis  Contains its own DNA

Cytoskeleton  A network of protein filaments  Helps cell retain its shape

 Also helps in cell movement  Two of the filaments are microfilaments and microtubules  Microtubules are very important in cell division  As well as centrioles which help organize cell division

Chapter 7 Notes Section 3

Cell Boundries  Cell Membrane All cells are surrounded by this thin, flexible barrier.

 It regulates what enters and leaves the cell and provides protection and support.  Contains protein molecules that are embedded in the lipid bilayer with carbohydrates attached.

 The Carbohydrates act like „chemical identification cards‟.

Outside of cell

Proteins

Carbohydrate chains

Cell membrane

Inside of cell (cytoplasm)

Protein channel

Lipid bilayer

 Cell Wall Lie outside the cell membrane.

 Porous enough to allow water, oxygen, and carbon dioxide through.  The main function is to provide support and protection for the cell.  Plant cell walls are made mostly of cellulose

Measuring Concentration  The cytoplasm contains a solution of many different substances in water.  The concentration of a solution is the mass of solute in a given volume of solution (mass/volume).  EX: If you had 12 g of salt in 6 L of water, what is the concentration.

Diffusion  The process by which molecules of a substance move from areas of higher concentration to areas of lower concentration.  Particles will move until equilibrium is reached.

 Does not require the cell to use energy.

Glucose molecules

High Concentration

Cell Membrane

Low Concentration

Osmosis  If a substance is able to diffuse across a membrane the membrane is said to be permeable to it.  Most biological membranes are selectively permeable; some substances can pass across and others cannot.  Osmosis is the diffusion of water through a selectively permeable membrane.

Osmosis  When a solution has a higher solute concentration than the cell, it is said to be hypertonic. (“above strength”)  When a solution has a lower solute concentration than the cell, it is said to be hypotonic. (“below strength”)  When the concentration is the same inside and outside the cell, it is said to be isotonic. (“same strength”)

Osmotic Pressure  For organisms to survive, they must have a way to balance the intake and loss of water.  Sometimes the cell takes on too much water and may burst.  Large organisms are not in danger of this.

 Bacteria and plant cells are surrounded by a tough cell wall that tries to prevent this.

Facilitated Diffusion

 Sugar glucose molecules cannot pass through the membrane on their own.  The cell membrane protein channels are said to facilitate (help) the diffusion of glucose across the membranes lipid bilayer.

Active Transport  Materials move against a concentration difference.

 This process requires energy and transport protein “pumps”.  Potassium, calcium and sodium move across this way.

Endocytosis  The process of taking material into the cell by means of infoldings, or pockets, of the cell membrane.  Two types:  Phagocytosis “cell eating”- Extensions of cytoplasm surround a particle and package it within a food vacuole. The cell then engulfs it. (Amoebas)  Pinocytosis-Tiny pockets form along the cell membrane, fill with liquid, and pinch off to form vacuoles within the cell.

Exocytosis

 The membrane of the vacuole surrounding the material fuses with the cell membrane, forcing the contents out of the cell.  EX: The removal of water by a contractile vacuole.

Chapter 7 Notes Section 4

Unicellular Organisms

 Only has one cell  Can carry out all the essential functions of life  Grow, reproduce, respond to the environment, etc.

Multicellular Organisms Made of many cells that do different tasks (cell specialization) Examples  Muscle cells are packed with dense fibers that contract  blood cells have special proteins that bind to oxygen to transport it around the body  nerve cells have the ability to transmit messages throughout the body

Plants also have specialized cells Examples:  Guard Cells – monitor the plants internal conditions

Levels of Organization

Individual Cells  Tissues  Organs  Organ Systems  Organism

Tissues Groups of similar cells that perform a specific function Four main types Muscle Epithelial

Nervous Connective

Organs

 Many groups of tissues working together to perform a specific function

 Example  The stomach is an organ made up of smooth muscle tissue, epithelial tissue and nervous tissue

Organ Systems Many organs working together to perform a specific function Example Digestion – includes the stomach, large and small intestines, esophagus, mouth, and pharynx, liver, and pancreas