Chapter 3:Cells and

cell structure

Cells• A cell is the smallest unit of life.

• Each cell is alive and has all of the characteristics of life.

• Cytology is the study of cells.

• Scientists began learning about cells after the development of the microscope

Robert Hooke - 1665

Hooke was the 1st person to see cells. Hooke coined the word “cell” after viewing cork cells with a microscope

Anton von LeeuwenhoekWas the 1st to observe living cells. He saw unicellular living organisms (“wee beasties”)and other living cells.

Leeuwenhoek’s microscope

Late 1600s

What did Leeuwenhoek see?

Algae

Bacteria

Vorticella, a protist

Schleiden & Schwann

• Mattias Schleiden observed that all plants were made up of cells.

• Theodor Schwann observed that all animals were made up of cells.

The Cell Theory

• All living things are made of one or more cells.

• Cells are the basic building blocks of organisms.

• All cells come from from existing cells by the process of cell reproduction.

Virchow

All cells come from preexisting cells

History of Cells 5 min

Microscopes

Magnification

making an image appear

larger

Resolution

a measure of the clarity of an image

have:

Microscopes

1. Compound Light Microscope

2. Transmission Electron Microscope (TEM)

3. Scanning Electron Microscope (SEM)

Compound Light Microscope

Up to about 1000x

Elodea leaf at 40x Elodea leaf at 400x

Answer this!

A student wants to view cells under the compound microscope at a total magnification of 400X. If the eyepiece is 10X, which objective lens should be used?

Transmission Electron Microscope (TEM)

Highly magnified, 2-dimensional images

Plant cell

Transmission electron micrograph

Liver cell

more Transmission Electron Micrographs

A nucleus in a cell

A mitochondrion

Even more TEMs

Endoplasmic reticulum

Golgi apparatus

Scanning Electron Microscope (SEM)

3-dimensional images

Tsetse fly head

Scanning Electron Micrographs

Human hair in a knot

Human hair with dandruff

More SEMs

Human hair with split ends

Human hair emergingfrom skin

More SEMs

Dog tongue

More SEMs

A daphnia (water flea)

More SEMs

Scotch tape

More SEMs

Paper towel

Why are cells so small?

All substances must pass through the cell membrane. Thus, the surface area of the cell membrane must be sufficient for the volume of a cell.

All Cells Have:1) Cell membrane - the outer boundary. It

separates the inside from the outside & controls what enters & leaves the cell.

2) Cytoplasm – everything inside the cell except for the nucleus.

3) Ribosomes - the place on which proteins are made

4) Genetic material (DNA) - instructions for the cell. In eukaryotes, it is kept in the nucleus. It is often called the “brain” of the cell.

Types of Cells

Pro & Euk 1 min

Prokaryotes vs Eukaryotes• Prokaryotes are single cells that lack a

true nucleus. Prokaryotes are bacteria.

• Eukaryotes are cells that have a true nucleus and membrane-bound internal organelles.

• An organelle is a structure surrounded by a membrane, found only in eukaryotic cells.

Relative Sizes of Prokaryotes and Eukaryotes

Prokaryotes are Bacteria• Bacteria are found in all environments on

earth.

• Bacteria are hypothesized to have been the first life on earth. The first bacteria “ate” organic molecules. Later, bacteria evolved that could do photosynthesis, getting energy from the sun. Oxygen was released into the atmosphere and other cells could develop, and eventually multi-cellular organisms appeared.

Prokaryote Video 2 min

Archaebacteria

Many are Extremophiles,living in extreme environments such as hot springsand acid pools.

Eubacteria, common bacteria

E. coli are found in yourintestines

Bacterial Cell

Structure of a Prokaryote:

• Cell wall – provides structure & protection.

• Pili – helps bacteria stick to surfaces

• Flagella – allows bacteria to move

Yet another bacterial cell

Bacillus: Rod-shaped bacteria

Coccus: Round-shaped Bacteria

Spirilla: Spiral-shaped Bacteria

Many bacteria are beneficial

• Food

• Some antibiotics

• Decomposers (saprobes)

• Nitrogen fixation – converts nitrogen gas in the air to a form that plants can use.

• Photosynthesis (cyanobacteria)

• Environmental cleanup

Cyanobacteria: Photosynthetic bacteria

Bacteria that caused bubonic plague

Y. pestis

Some bacteria are pathogens

Pathogen: a disease-causing agent

Pathogenic Bacteria

Bacteria that are pathogenic secrete a toxin (poison)

Antibiotic – a chemical that kills bacteria

Bacteria that cause anthrax

Bacteria that cause botulism

Some other bacterial diseases

Cholera

Dental cavities

Lyme disease

Tuberculosis

Typhus

Strep throat

Botulism (a type of food poisoning)

A Eukaryote

Eukaryotes

• All cells except bacteria are eukaryotic.

• Early bacteria released oxygen into the air through photosynthesis. Oxygen is necessary for eukaryotic cells to make energy. So, eukaryotic cells could develop. This is called the “oxygen revolution”.

Eukaryotic Animal Cell

Eukaryotic Plant Cell

Cell Membrane: controls what enters & leaves the cell

Plasma (cell) Membrane

Cell Wall

•Found only in plant cells

•Gives plant cells structure

•Makes up the bark of trees

Cell Wall Video 35 sec

Nucleus

Contains DNA, so the nucleus is called the “brain” of the cell. It controls all cell activities.

Nucleus

DNA

Nucleolus & Ribosomes

• Nucleolus is found within the nucleus.

• It makes ribosomes, which will then leave the nucleus and go into the cytoplasm.

• Ribosomes: the place where proteins are made.

Endoplasmic Reticulum

Endoplasmic Reticulum (ER)

•Passageways in the cell for transportation of molecules

•Rough ER has ribosomes

•Smooth ER does not have ribosomes

ER 1 min

Golgi Apparatus

Golgi apparatus

•Repackages proteins and lipids.

•It exports molecules through structures called vesicles.

Lysozomes

Lysosomes

•Digestion of worn-out cell parts

•The lysosomes contain digestive enzymes.

Mitochondria

Mitochondria

• The “mighty mitochondria” provides energy for the cell.

• It is referred to as the “powerhouse” of the cell.

The mitochondria is folded!

• The mitochondrion has an inner membrane and an outer membrane. The inner membrane has many folds. Energy (ATP) is made along these folds.

• The folds allow for high surface area, which means that a lot of energy can be made in a small space.

Chloroplast

• This green structure is found only in plant cells.

• Photosynthesis occurs here.

• Photosynthesis is the process by which plants use carbon dioxide and water to make

glucose (sugar) and oxygen.

Chloroplasts

Cytoskeleton

A series of protein fibers and microtubules that provide structure and movement of organelles inside of the cell.

Cilia and flagella are structures that help a cell to move.

Cilia

Flagella

Cilia & Flagella 40 sec

Plant vs Animal Cells

• All cells (prokaryotic & eukaryotic) have 4 structures in common – remember them?

• Plant and animal cells are both eukaryotic cells.

• Some animal cells have cilia and flagella.

• Plant cells have:

– chloroplasts (for photosynthesis)

– cell wall

– large central vacuole

Organization of Organisms

Organization of Cells in a Multicellular Organism

• Multicellular: made up of many cells

• Multicellular organisms can be large because cells specialize and do different functions.

• Specialized cell: a cell programmed by its DNA to perform one primary job for the organism.

Organization of Cells in a Multicellular Organism

• Cell

• Tissue – a group of cells with similar structure & function.

• Organ – a group of tissues which have formed a specialized structure with a specific function.

• Organ system – group of organs which carry out a major body function

• Organism