CHAPTER 7

A View of the Cell

CELL THEORY

Before microscopes, people thought

diseases were caused by curses and

supernatural spirits

They had no idea microorganisms, such

as bacteria and viruses existed

When the microscope was invented,

scientists discovered cells exist

Cells are the basic units of living

organisms

CELL THEORY

Anton van Leeuwenhoek (Dutch)

used the first simple light

microscope in the 1600s

It had one lens

Gradually, lenses got better

Compound light microscopes use

a series of lenses to magnify

objects in steps

Can magnify up to 1500 times

The microscopes we use in the lab

CELL THEORY

Robert Hooke (1600s, English) used a light

microscope to study cork, the dead cells of oak

bark

He saw small, geometric shapes that reminded him

of the small rooms monks lived in called cells

Cells are the basic units of all living things

CELL THEORY

Matthias Schleiden (1830s, German) discovered

that all plants are made of cells

Theodor Schwann (German) discovered that all

animals are made of cells

Rudolf Virchow discovered that all cells come

from existing cells

All these scientists (plus others) contributed

ideas that are now summed up in what we call

the cell theory

CELL THEORY

1. All organisms are composed of one or more cells.

2. The cell is the basic unit of structure and

organization of organisms.

3. All cells come from preexisting cells.

ELECTRON

MICROSCOPES

Electron Microscopeslet us see a much greater magnification than light microscopes

They use beams of electrons to produce images

Scanning Electron Microscope

Used for scanning 3-D surfaces

ELECTRON MICROSCOPES

Transmission Electron Microscope

Used for scanning interior structures of cell

The best TEM can produce an image 0.000000005 meters big (that’s half as big as a hydrogen atom)

TYPES OF CELLS

Organelles are small, specialized

structures within cells

Many, but not all are surrounded

by membranes

Prokaryotes are organisms that do

not have membrane-bound

organelles (biology.arizona.edu)

Kingdom Monera ( now split into

Eubacteria & Archaebacteria)

Eukaryotes are organisms that do

have membrane-bound organelles

Kingdoms Animalae, Plantae, Fungi,

Protista

TYPES OF CELLS

Robert Brown (Scottish) observed that

eukaryotic cells have a prominent structure, the

nucleus

the nucleus manages cellular functions

Rudolf Virchow concluded that this prominent

structure was responsible for cell division

SECTION 1 REVIEW

1. How has the history of microscopes

influenced the study of cells?

2. What are the three parts of the cell theory?

3. What is the difference between a light

microscope and an electron microscope?

4. What is the difference between a prokaryote

and a eukaryote?

THE PLASMA MEMBRANE

Cells must maintain proper conditions within itself to function

The plasma membrane is a flexible boundary between the cell and its environment

It allows a steady supply of nutrients into and out of the cell at the appropriate levels

The “bouncer”

The plasma membrane is selectively permeable

This means that it allows some molecules to pass through while keeping others out.

Like a screen in a window

THE PLASMA MEMBRANE

Phospholipids

The “head” is polar, or slightly charged It is hydrophilic (likes water)

The “tail” is nonpolar, or not charged It is hydrophobic (repels water)

The phospholipids arrange themselves form a bi-layer with the fatty acid tails forming the interior and the heads facing both the watery external environments and inside the cell

PLASMA MEMBRANE

The plasma membrane is called a phospholipid bilayer

Arranged in this manner, a barrier is created that is water-soluble at its outer surfaces and water-insoluble in the middle

Keeps out both water soluble and water insoluble molecules

PLASMA MEMBRANE

The current model of the plasma membrane is

called the fluid mosaic model.

The phospholipids actually move around like a

fluid.

The other components of the membrane

(proteins, carbohydrates, cholesterol, etc.)

move around as well

PLASMA MEMBRANE

Cholesterol helps to stabilize the phospholipids by preventing their fatty acid tails from sticking together

Transport proteins move span the membrane and move needed substances or waste materials through the plasma membrane

Other proteins and carbohydrates that stick out help cells to identify surface signals and other cells

These proteins play an important part in protecting cells from infection

SECTION 2 REVIEW

1. What is a phospholipid?

2. Why is the cell membrane a bilayer?

3. What does polar and nonpolar mean?

4. What are the specialized parts of the cell

membrane?

5. Why is the cell membrane referred to as fluid

mosaic?

CELL WALL

Fairly rigid structure located outside the plasma membrane of some cells that provides additional support and protection

Plants, fungus, most bacteria

The cell wall is very porous, made of a tough mesh of fibers

Like framing of a house

NUCLEUS

Membrane-bound (called nuclear

envelope) organelle that

contains the directions to make

proteins

“Boss”

Nuclear pores allow passage

through the nuclear envelope

Chromatin - uncondensed

strands of DNA

When cell is dividing, DNA

condenses into chromosomes

Nucleolus - organelle within the

nucleus that make ribosomes

“Small machine factory”

ORGANELLES

Ribosomes are the sites where the

cell produces proteins according to

the directions of DNA

One organelle without a

membrane

“small machines on assembly

line”

Cytoplasm/Cytosol is the clear,

gelatinous fluid inside the cell

Acts as a medium for things to

move around in the cell

“Organelles can’t fly”

ORGANELLES

The endoplasmic reticulum (ER) is arranged in a series of highly folded membranes suspended in the cytoplasm

In general, ER is involved in the movement of materials throughout the cell

“The factory floor”

Rough ER has ribosomes, which is where protein synthesis takes place

Smooth ER has no ribosomes and is involved in numberous biochemical activities, including the production and storage of lipids

ORGANELLES

The Golgi apparatus is a

flattened stack of tubular

membranes that modifies

the proteins

The Golgi sorts proteins

into packages and packs

them into membrane-

bound structures called

vescicles for later

transport

“Shipping Department”

ORGANELLES

Vacuoles are

membrane-bound

compartments for

temporary storage of

materials

Store food, enzymes,

water, waste

Plant cells have one

very large vacuole

“storage”

ORGANELLES

Lysosomes are organelles

that contain digestive

enzymes

Digest old organelles, food,

viruses, bacteria, etc.

“janitor”

Can fuse with a vacuole to

dump waste or give

enzymes

Lysosomes digest a

tadpole’s tail

ORGANELLES

Plastids are a group of

organelles used for storage

Named for the color or pigment

they contain

Chloroplasts are organelles that

capture light energy and convert

it to chemical energy

(photosynthesis occurs here)

Plastid containing chlorophyll,

which actually traps the light and

gives plants green color

“solar panels”

ORGANELLES

Mitochondria are

membrane-bound

organelles in plant and

animal cells that transform

stored chemical energy into

a usable form for the cell

(ATP)

“power generator”

Has an outer and inner

highly folded membrane

ATP produced on inner folds

ORGANELLES

The cytoskeleton forms a framework for the cell

A network of tiny rods and filaments

“beams or columns holding factory up”

Cytoskeleton is constantly changing its shape

Microtubules are thin, hollow cylinders made of

protein

Microfilaments are smaller, solid protein fibers

Give support for cell

Provide “highway system” for organelles to move

throughout cell

ORGANELLES

Centrioles are organelles made up of microtubules that play a part in cell division

In animals and most protists

Cilia are short, numberous projections that look like hairs

Made of microtubules and help organelles move and feed

Flagella are longer projections that move in a whip-like motion

Made of microtublules - help with movement

Cells usually only have 1 or 2

ANIMAL CELL

PLANT CELL

SECTION 3 REVIEW1. How are highly-folded membranes an advantage for the

functions of cellular parts?

2. Name an organelle that has highly-folded membranes.

3. If a cell synthesizes large quantities of protein molecules, which organelles might be numerous in that cell?

4. A cell’s digestive enzymes are enclosed in a membrane-bound organelle. Why?

5. Compare and contrast the functions of a cell wall to the functions of a plasma membrane.

6. What are the functions of the cytoskeleton?

7. Why are mitochondria and chloroplasts referred to as energy transporters?

OSMOSIS

What is diffusion? (review)

Osmosis is the diffusion of water across a

selectively permeable membrane

This maintains homeostasis in the cell

CELLS IN AN ISOTONIC SOLUTION

Isotonic solution - the concentration of

dissolved substances in the solution is the

same as the concentration of dissolved

substances inside the cell

Water does go in and out of the cell, but

there is no net change in concentration

CELLS IN A HYPOTONIC ENVIRONMENT

Hypotonic solution - the concentration of

dissolved substances is lower in the

solution outside the cell than the

concentration inside the cell

Therefore, water moves through the

plasma membrane into the cell

Pressure increases inside against the cell

membrane and

Animal cells may burst

Plant cells become more “firm” as they

expand against the cell wall. (grocery stores)

HYPOTONIC

CELLS IN A HYPERTONIC SOLUTION

Hypertonic solution - the concentration of

dissolved substances outside the cell is

higher than the concentration inside the

cell

Water moves out of the cell

In animals, cells shrivel

In plants, membrane shrink away from cell

wall

OSMOSIS LAB

PASSIVE TRANSPORT

The movement of molecules across a

membrane by diffusion (no energy

required)

Facilitated Diffusion is passive transport

across the cell membrane using proteins

Transport proteins form a channel to allow

specific molecules to flow across

Carrier proteins change shape to allow a

substance to pass through the plasma

membrane

FACILITATED DIFFUSION

ACTIVE TRANSPORT

The movement of materials through a

membrane against a concentration gradient

Requires energy

Carrier proteins have a specific shape to allow

them to bind with specific molecules

Then then change shape (with energy) so

molecule can be transported across

Carrier protein resumes original shape

ACTIVE TRANSPORT

TRANSPORT OF LARGE MOLECULES

Endocytosis - process by which a cell

surrounds and takes in material from its

environment

Membrane forms around material and

engulfs it

Exocytosis - the expulsion of materials

from a cell (wastes, hormones)

Membrane surrounds material and takes it to

membrane, opens up.

ENDOCYTOSIS

Exocytosis

SECTION REVIEW

1. What factors affect osmosis?

2. How do animal and plant cells react

differently in a hypotonic solution?

3. How are facilitated diffusion and active

transport similar? How different?

4. How do carrier molecules facilitate transport

of molecules across a membrane?

5. A paramecium expels water when in

freshwater. What kind of internal

environment does it have?

DIVERSITY OF CELLS

Unicellular Organisms

Single –celled organisms

Fulfill all characteristics of life in one

cell

More than half of all life

Multicellular Organisms

Individual cells cannot live by

themselves

Through cell specialization, cells each

perform specialized functions (eg –

muscle cells, neural cells, red blood

cells, etc.)

Protozoa

LEVELS OF ORGANIZATION IN LIFE

Cells – the smallest unit of

life

E.g. – cardiac muscle cell

Tissue – a group of similar

cells that perform a particular

function

E.g. – cardiac muscle tissue

Organs – groups of tissue

working together to perform a

function

E.g. - muscle

LEVELS OF ORGANIZATION IN LIFE

Organ System – a group of

organs working together to

perform a specific function

E.g. – cardiovascular system

Organism – an entire living

thing

E.g. – you (probably)

REVIEW

1. What is the difference between a unicellular

organism cell and a cell in a multicellular

organism?

2. What is cell specialization?

3. List the 5 levels of organization in life.

4. Give an example of each of the 5 levels of

organization in life.