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A Tour of the Cell

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“cell”• In 1665, an English scientist

named Robert Hooke coined the term "cell" after viewing slices of cork through a microscope.

• The term came from the Latin word cella which means "storeroom" or "small container".

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The Cell Theory

1. All living things are composed of cells.

2. Cells are the basic unit of structure and

function in living things.

3. All cells come from pre-existing cells.

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Microscope

• Instrument for observing small objects

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Types of Microscopes

Light Microscopes:• Use visible light• Magnify about 1000 times• Not powerful enough to view

internal cell structures

Electron Microscopes:• Electron beams used for

magnification• Magnify up to a million

times

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Stage

Focus Adjustment

Base

Objective lens

Source of light

Different parts of a microscope

Eyepiece

Arm

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Basic types of cells:

Animal Cell Plant Cell Bacterial Cell

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Number of Cells

Organisms may be:• Unicellular – composed of one cell• Multicellular- composed of many cells

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Cells May be Prokaryotic

– Prokaryotes lack a nucleus and organelles

– Nucleoid region contains the DNA

– Cell membrane & cell wall– First organisms to appear

in fossil record

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Cells May be Eukaryotic

Plant Cell Animal Cell

Have a nucleus and organelles

Two main types:

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Organelles

• Very small in size• Can only be observed under a microscope• Have specific functions • Found throughout cytoplasm

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Golgi Apparatus

• Stacks of flattened sacs• Modifies, stores, and

repackages cell products in vesicles

• Routes repackaged vesicles with chemical products to their destinations

Transport

vesicle

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Lysosome

• Contain digestive enzymes

• Break down food and worn out cell parts for cells

• Programmed for cell death (release enzymes to break down & recycle cell parts)

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Smooth & Rough Endoplasmic Reticulum

• Smooth ER lacks ribosomes & makes proteins USED In the cell

• Rough ER has ribosomes on its surface & makes proteins to EXPORT

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Ribosomes

• Site of protein synthesis• It could be found free in

cytoplasm or on outer surface of ER

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Mitochondria

• Cell Powerhouse• It provides the energy a cel

l needs to move, divide & etc . . .

• It is the site of Cellular respiration

• Burns sugar to produce ATP (energy)

• Active cells like muscles have more mitochondria

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• Surrounds the cell• Made of protein and

phospholipids• Selectively permeable• Controls the movement of

materials into and out of the cell

Cell Membrane

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• Jelly-like substance enclosed by cell membrane

• Provides a medium for chemical reactions to take place

Cytoplasm

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• Controls the normal activities of the cell

• Contains chromosomes; DNA

• Each cell has a fixed number of chromosomes that carry genes

• humans 46

Nucleus

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Nucleolus

• Inside the nucleus• Makes ribosomes that

make proteins

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• Contain the green pigment chlorophyll

• Traps sunlight to make glucose (sugar) through a process called photosynthesis

Plant Cell Organelle:Chloroplast

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• Dead layer: Strong and rigid• Made of cellulose• Freely permeable• Protects and supports the

enclosed substances• Gives shape to the cell

Plant Cell Organelle:Cell Wall

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• Have a large central vacuole• It plays roles in intracellular

digestion and the release of cellular waste products

Plant Cell Organelle:Vacuole

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Different kinds of animal cells

white blood cell

red blood cell

cheek cells

sperm

nerve cell

muscle cell

Amoeba

Paramecium

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Similarities between plant cells and animal cells

Both have a cell membrane surrounding the cytoplasm

Both have a nucleus

Both contain mitochondria

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Animal cells Plant cells

Vacuole small or absent

Glycogen as food storage

Nucleus at the center

Large central vacuole

Starch as food storage

Nucleus near cell wall

Differences between Plant Cells and Animal Cells

Relatively smaller in size

No cell wall

Relatively larger in size

Cell wall present

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Cell Membrane

The cell membrane is made of proteins and 2 layers of phospholipids called the phospholipid bilayer.

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Phospholipids:

• Contains 2 fatty acid chains that are nonpolar and a head that is polar.

• Polar heads are hydrophilic “water loving”

• Nonpolar tails are hydrophobic “water fearing”

• Makes membrane “Selective” in what crosses

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Passive Transport:

Types of Transport across Cell Membranes

Diffusion

• Doesn’t require energy• Moves high to low

concentration• Example: Oxygen diffusing

into a cell

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Passive Transport:

Types of Transport across Cell Membranes

Facilitated diffusion

• Doesn’t require energy• Uses transport proteins to move

high to low concentration• Example: Glucose or amino acids

moving from blood into a cell.

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Osmosis

• The passive transport of water across a selectively permeable membrane.

• Moves from HIGH water potential (low solute) to LOW water potential (high solute)

Diffusion across a membrane

Semipermeable

membrane

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Diffusion of H2O Across A Membrane

High H2O potentialLow solute concentration

Low H2O potentialHigh solute concentration

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Types of osmotic solutions

• Hypertonic Solution: a solution whose solute concentration is higher than the solute concentration inside the cell

• Animal cells will lose water and shrivel when placed in a hypertonic solution

• Water moves out of the cell

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Cell in Hypertonic Solution

CELLCELL

15% NaCL85% H2O

5% NaCL95% H2O

What is the direction of water movement?

ENVIRONMENTENVIRONMENT

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Types of osmotic solutions

• Hypotonic Solution: a solution whose solute concentration is lower than the solute concentration inside the cell

• Animal cells will swell and possibly burst when placed in a hypotonic solution

• Water moves into the cell

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Cell in Hypotonic Solution

CELLCELL

10% NaCL90% H2O

20% NaCL

80% H2O

What is the direction of water movement?

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Types of osmotic solutions

• Isotonic Solution: a solution whose solute concentration is equal to the solute concentration inside the cell

• Animal cells retain their normal shape when

placed in isotonic solutions• No net gain or loss of water inside the cell

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Cell in Isotonic Solution

CELLCELL

10% NaCL90% H2O

10% NaCL

90% H2O

What is the direction of water movement?

The cell is at _______________.equilibrium

ENVIRONMENTENVIRONMENT

NO NET MOVEMENT

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Osmosis in Red Blood Cells

Isotonic Hypotonic Hypertonic

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Active Transport

Types of Transport Across Cell Membranes

• Requires energy or ATP• Moves materials from LOW to

HIGH concentration• AGAINST concentration

gradient• A specific transport protein

pumps a solute across a membrane.

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EX: Sodium-Potassium Pump

3 Na+ pumped in for every 2 K+ pumped out

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Too large Must be packaged in membrane sacs called vesicles

• It requires energy

• Exocytosis - moving materials out

• Endocytosis: Moving materials in

Moving the “Big Stuff”

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Endocytosis

• Phagocytosis: cell membrane takes in particle of solid material; “cell eating”

• Pinocytosis: cell membrane takes in small droplet of liquid; “cell drinking”

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That’s it!