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The Life of a Cell In 1665, Robert Hooke examined the

bark of an oak tree under an early

microscope. He thought he was looking

at something similar to the small rooms

of dormitories and prisons; hence the

name: cells.

Now, we know that Robert Hooke was

not looking at living cells, but the

remains of dead cell walls.

Some history… Life is Based on the Existence of Cells

The Cell Theory:

Living things are made of cells.

Cells are the basic unit of life.

Cells come from preexisting cells.

The study of cells is

called cytology.

Cells are diverse

• Even though cells are tiny,

they are very complex! • They vary in several ways:

– Size – Shape – Function (job)

Cell Shape

Shape relates to a cell’s function.

• A flat shape of dead skin cells is well suited for

covering the body surface.

• The long, thin, threadlike shape of nerve cells is

well suited for transmitting messages throughout

the body.

Why is there so much variety in cell shape? Cell Size: Why are cells so small?

1. Volume increases faster than surface area.

2. Surface area is too small for cell to receive materials fast enough.

3. As a result, the cell divides

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Surface Area = 96 mm2

Volume = 64 mm3

Ratio = 1.5 : 1

Surface Area = 192 mm2

Volume = 64 mm3

Ratio = 3: 1

4 m

m

4 m

m

4 mm 4 mm

Organisms are divided into TWO groups based on cell type:

1. Prokaryotic cells

2. Eukaryotic cells

Prokaryotic Cells

Lack a nucleus and membrane-bound organelles.

Unicellular.

Fossils date to 3.5 billion years ago.

Small, simple cells.

All prokaryotes are bacteria.

Eukaryotic Cells

Have a nucleus and membrane-bound organelles.

Some are unicellular, most are multicellular.

Fossils date to 1.7 billion years ago.

Large, highly organized cells.

Plants, animals, protists and fungi are eukaryotes.

Prokaryotes

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What are prokaryotic cells? Unicellular organisms that lack a nucleus.

PROKARYOTES

Archaebacteria “ancient” or extreme

Eubacteria “true” or common

Example of Prokaryotic Cells: Bacteria

In the space provided in your notes, write what you already know about bacteria.

What do bacteria look like?

• Bacillus: rod-shaped.

• Coccus: sphere-shaped.

• Spirilus: spiral- or helical-shaped.

Arrangement of Bacteria Where do bacteria live?

Can be found on most materials and surfaces

– Billions on and in your body right now

E. Coli O157:H7

can make you

very sick.

Streptococcus

can cause strep

throat.

This E. coli helps

you digest food.

Organization of a Bacterial Cell

Nucleoid (DNA)

Cell Wall

ribosomes

Plasmid (DNA)

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Some bacteria contain

• Flagella: used for movement

• Pilli: hair-like structures that anchor bacteria to a surface

• Capsule: outside layer that protect the bacteria from white blood cells.

Some bacteria contain

Endospore:

• Thick wall that encloses DNA

• Protects against harsh conditions (drought, harsh temperatures)

Bacteria Reproduce

1) Asexually Binary fission

Bacteria Reproduce

2) Sexually Conjugation

Bacteria exchange

plasmid DNA.

How can bacteria be helpful? • Bacteria play a large role in modern medicine,

agriculture, and ecology.

• Decomposers break down organic material.

• Fermentation (bread, dairy, beer).

• Genetic engineering (GMOs and antibiotics).

• Take nitrogen in atmosphere and turn it into something organisms can use

How can bacteria be harmful?

• Pathogens: Disease causing agents

Bacteria cause disease by destroying living cells or by releasing chemicals that harm the body.

• Examples of sicknesses caused by bacteria:

– Strep throat

– Ear infections

– Lyme disease

– Tetanus

– Tuberculosis

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Eukaryotes

Why do cells have organelles? Division of labor into separate compartments

(organelles) makes cell activities more ORGANIZED and EFFICIENT.

This is made possible by the presence of LIPID membranes that form boundaries around each organelle (membrane-bound organelles).

Nucleus

Control center because it contains DNA

Surrounded by the nuclear membrane

Nuclear membrane has pores to allow things to enter/leave nucleus

nucleus

DNA Exists in Two Different Forms

CHROMATIN

Loose, uncoiled DNA.

Stretched out so the cell can “read” the DNA.

Present during the normal, everyday life of the cell.

CHROMOSOMES

DNA is tightly wound and organized

Only during cell division

Plasma (Cell) Membrane Boundary of cell (mostly lipids)

Controls movement of materials in and out; maintains HOMEOSTASIS

outside of cell

inside of cell

Cell Wall

Rigid outer layer of plant cells

Made of cellulose

Gives plant cells strength and support.

Only in PLANT Cells

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Cytoplasm

Jelly-like material that fills cell

cytoplasm

Chloroplast (a type of plastid) Present in LEAF cells

Photosynthesis: Process of making food (glucose)

Contain chlorophyll (green pigment)

chloroplasts

Plastids (only in PLANT cells)

Store food or pigment molecules.

chromoplasts in red pepper cells Leucoplasts in potato cells

store starch

Mitochondria

The Powerhouse

Breaks down food

molecules (glucose) to release usable energy (ATP)

Vacuole

Fluid-filled storage area:

– Water

– Salts

– Enzymes

– Carbohydrates

PLANT cells have one large

vacuole; ANIMAL cells have

several small ones.

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Ribosomes

Small, round organelles that produce proteins

Can be scattered throughout the cytoplasm or bound to the Rough ER

ribosomes

Nucleolus

Circular structure inside the nucleus

Makes ribosomes

Nucleus

Nucleolus

Endoplasmic Reticulum (ER)

System of tubes and channels

Rough ER has ribosomes for protein production

Smooth ER produces lipids and also breaks down toxins

smooth ER

rough ER

Golgi Apparatus Packaging factory for newly made lipids, proteins, and

other molecules

Vesicles - Small, circular packages that ship materials

vesicles

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Lysosome

Contains DIGESTIVE ENZYMES to breakdown:

a) food

b) old cell parts

c) waste

d) invading viruses and bacteria

e) the cell itself

lysosomes

Cytoskeleton

Network of protein fibers that provide structure and support to the cell.

Anchors the organelles in the cytoplasm.

cytoskeleton

Centrioles

Pair of cylindrical structures that assist in cell reproduction (division)

Only in ANIMAL cells

Cilia and Flagella Cilia short hair-like

extensions on the surface of some cells.

Help move substances across the cell’s surface.

Flagella are longer than cilia and less numerous.

Whip-like motion moves a cell from place to place.

Plant vs. Animal Cell Plant Animal

Cell wall and cell membrane

1 large vacuole

No centrioles

Plastids

Chloroplasts

Square shape

Cell membrane only

Several vacuoles

Centrioles

No plastids

Variety of shapes (due to the flexible cell membrane)

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