chapter 5: cell structure and function 5-1 the cell theory
TRANSCRIPT
Chapter 5: Cell Structure and Function
5-1 The Cell Theory
The Cell Theory
All living things are made of cells Cells are the basic units of structure and
function in living things Anton van Leeuwenhoek, a Dutch
biologist, was the inventor of the microscope – Enabled him to see things that no one had
ever seen before
The Cell Theory
Van Leeuwenhoek’s work interested other people– Robert Hooke examined slices of cork– Saw that it was composed of thousands of tiny chambers– Called these chambers cells
Over the next 200 years, other scientists began to discover that cells were not only found in plants but in other living things too– Robert Brown—1833—discovered the nucleus– Matthias Schleiden—1838—stated that all plants are made
of cells– Theodore Schwann—1839—all animals are made of cells– Rudolf Virchow—1855—all cells arise from preexisting cells
The Cell Theory
The observations of these scientists are summarized into the cell theory– All living things are composed of cells.– Cells are the basic units of structure
and function in living things.– All cells come from preexisting cells.
Chapter 5: Cell Structure and Function
5-2: Cell Structure
Cell Structure
Enormous variety in the size and shape of cells Despite differences in size and shape, there
are certain structures that are common to most cells
The cells of animals, plants, and related organisms have three basic structures: the cell membrane, or boundary of the cell; the nucleus, or control center; and the cytoplasm, or material between the cell membrane and the nucleus
Cell Membrane
All cells are separated from their surroundings by a cell membrane– Regulates what enters and leaves the cell– Aids in protection and support of the cell
It must communicate with other cells, take in food and water, and eliminate wastes
Composed of several kinds of molecules– Lipids (bilayer)– Proteins– Carbohydrates
Cell Wall
In organisms such as plants, algae, and some bacteria, the cell membrane is surrounded by a cell wall– Helps protect and support the cell– Very porous—allows water, oxygen,
carbon dioxide, and other substances to pass through
– Made of cellulose
Nucleus
In many cells we can see a large, dark structure, called the nucleus– Contains DNA
Prokaryotes are organisms whose cells lack nuclei– Bacteria– Small and unicellular
Eukaryotes are organisms whose cells contain nuclei– Mostly multicellular
Nuclear Envelope
Surrounding the nucleus are two membranes that form the nuclear envelope– Form the boundary around the nucleus
• Contains dozens of nuclear pores allowing substances to flow in and out of the nucleus
Nucleolus
Most nuclei contain a small region called the nucleolus that is made up of RNA and proteins
– The structure in which ribosomes are made
• Aid in the production of proteins within the cell
Chromosomes
The DNA in the nucleus of eukaryotic cells is attached to special proteins and forms large structures called chromosomes– Contain the genetic information that must
be passed to each new generation of cells
Cytoplasm
The cytoplasm is the area between the nucleus and the cell membrane
Contains many important structures
Chapter 5:Cell Structure and Function
5-3: Cytoplasmic Organelles
Cytoplasmic Organelles
The structures inside the cytoplasm are generally called organelles
An organelle is a tiny structure that performs a specialized function in the cell.– Each organelle has a special job
Mitochondria and Chloroplasts: Power Stations All living things require energy The mitochondrion and the
chloroplast are key organelles that change energy from one form to another– Mitochondria change chemical energy in
food into compounds that the cell can use– Chloroplasts trap solar energy and convert
it into chemical energy
Mitochondria and Chloroplasts: Power Stations Mitochondrion
– Contains two special membranes• Outer membrane surrounds the organelle• Inner membrane has many folds that increase the
surface area of the mitochondrion Chloroplast
– Found only in plant cells and algae– Three membranes
• Two envelope-like membranes• Third membrane where the sun’s energy is
changed into chemical energy
Ribosomes: Protein Factories
Ribosomes are the structures in which proteins are made– Made of RNA and protein– Some are attached to membranes; some
are found free in the cytoplasm– Among the smallest organelles
Endoplasmic Reticulum and Golgi Apparatus: Manufacturers and Shippers
Many cells are filled with a complex network of sacs known as the endoplasmic reticulum, or ER
– Transports materials through the inside of the cell
– Two types:
• Smooth—no ribosomes attached
• Rough—ribosomes attached—involved in the synthesis of proteins
Endoplasmic Reticulum and Golgi Apparatus: Manufacturers and Shippers
Proteins are often modified by special enzymes that attach carbs and lipids to them
In most cases, the proteins are first moved into special compartments known as the Golgi apparatus– Flattened stack of membranes– After modification, the proteins may then be
released from the cell**The Golgi apparatus modifies, collects,
packages, and distributes molecules made at one location of the cell and used at another**
Lysosomes: Cleanup Crews
When a cell encircles a particle, the cell membrane forms a pocket around the foreign material
The foreign material must now be digested,or broken down– Lysosome
• Contain chemicals and enzymes necessary for digestion
• Formed by the Golgi apparatus• Plants cells do not have lysosomes
Vacuoles and Plastids: Storage Tanks Vacuoles store materials such as water,
salts, proteins, and carbohydrates Plastids are plant organelles that may take
many forms, one of which is the chloroplast– Involved in the storage of food and
pigments– Examples:
• Leukoplasts—store starch• Chromoplasts—store pigments
Cytoskeleton: Framework
Most cells are capable of some type of movement
Cytoskeleton – framework of filaments and fibers that support cell structure and drive cell movement– Microfilaments-long, thin fibers that function in
the movement and support of the cell– Microtubules-hollow tubes made out of
proteins• Cilia and flagella
Chapter 5:Cell Structure and Function
5 – 4
Movement of Materials Through the Cell Membrane
Diffusion
The driving force behind the movement of many substances across the cell membrane is called diffusion
Diffusion is the process by which molecules of a substance move from areas of higher concentration of that substance to areas of lower concentration
Several factors determine whether diffusion occurs across a membrane– Equilibrium point is reached– Permeability
• Most membranes are known as selectively permeable
Osmosis
Water molecules pass through most cell membranes very rapidly
The diffusion of water molecules through a selectively permeable membrane is called osmosis
The force exerted by osmosis, or osmotic pressure, tends to move water across membranes from a more dilute solution into a more concentrated solution
If water moves in too freely, the volume of a cell will increase until the cell becomes swollen and bursts like an over inflated balloon
Osmosis
Cells deal with the problem of osmotic pressure in a variety of ways– Cells of many organisms do not come into
contact with fresh water– Plant cells and bacteria have cell walls that
prevent the cells from expanding– Some cells pump out the water with a
contractile vacuole
Facilitated Diffusion
Osmosis and diffusion are forms of passive transport across the cell membrane because energy is not needed
But, many molecules are transported across a membrane in the direction of lowest concentration by a carrier protein
– Facilitated diffusion
• Is fast, specific, and does not require energy…it is still driven by diffusion
• Can only occur if a concentration distance exists cross that membrane
Active Transport Active transport is an energy-requiring process that enables material to
move across a cell membrane against a concentration difference Two types
– Individual molecules are carried through membrane-associated pumps
– Large amounts of materials are transported through movements of the cell membrane
• Endocytosis– Process of taking material into the cell by means of
infoldings, or pockets, of the cell membrane• Phagocytosis
– Process that occurs when large particles are taken in by endocytosis
• Pinocytosis– Process in which cells take in liquid and pinch off to form
vacuoles within the cell• Exocytosis
– Process that occurs when large materials are removed from the cell
Chapter 5:Cell Structure and Function
5 – 5
Cell Specialization
Cell Specialization
Cell specialization is one of the key characteristics of cells in a multicellular organisms
By cell specialization, we mean that cells are often uniquely suited to perform a particular function within the organism– Movement– Make products
Chapter 5:Cell Structure and Function
5 – 6
Levels of Organization
Levels of Organization
The levels of organization in a multicellular organism include cells, tissues, organs, and organ systems that make up the organism
Tissues
In multicellular organisms, cells – the first level of organization – are organized in specialized groups called tissues
– A group of similar cells that perform similar functions
– Most animals, which are multicellular organisms, have four main types of tissues
• Muscle, epithelial, nerve, and connective tissue
Organs
An organ is a group of tissues that work together to perform a specific function
Many types of tissue may be used to form a particular organ
Each tissue performs an essential task to help the organ function successfully
Organ Systems
An organ system, or a group of organs, works together to perform a certain function
There are 10 organ systems in the body including the muscular system, circulatory system, and digestive system