key concept cells are the basic unit of life

3.1 Cell Theory

KEY CONCEPT Cells are the Basic unit of life.

3.1 Cell Theory

The cell theory grew out of the work of many scientists

and improvements in the microscope.

• Many scientists contributed to the cell theory.

3.1 Cell Theory

Early studies led to the development of the cell theory.

• The Cell theory has three principles.

–All organisms are made of cells.

3.1 Cell Theory

Early studies led to the development of the cell theory.

• The Cell theory has three principles.

–All organisms are made of cells.

–All existing cells are produced by other living cells.

3.1 Cell Theory

Early studies led to the development of the cell theory.

• The Cell theory has three principles.

–All organisms are made of cells.

–All existing cells are produced by other living cells.

– The cell is the most basic unit of life.

3.1 Cell Theory

Prokaryotic cells lack a nucleus and most internal

structures of eukaryotic cells.

• All cells share certain characteristics.

–Cells tend to be microscopic.

–All cells are enclosed

by a membrane.

–All cells are filled with

cytoplasm.

Bacterium

(colored SEM; magnification 8800x)

cell membrane

cytoplasm

3.1 Cell Theory

There are two cell types: eukaryotic cells and prokaryotic

cells.

• Eukaryotic cells have a

nucleus.

• Prokaryotic cells do

not have membrane-

bound organelles.

nucleus

cell membrane

organelles

3.1 Cell Theory

There are two cell types: eukaryotic cells and prokaryotic

cells.

• Prokaryotic cells do not

have a nucleus.

• Prokaryotic cells do not

have membrane-bound

organelles.

nucleus

cell membrane

organelles

cytoplasm

3.2 Cell Organelles

KEY CONCEPT Eukaryotic cells share many similarities.

3.2 Cell Organelles

Cells have an internal structure.

• The cytoskeleton has many functions.

– supports and shapes cell

– helps position and transport organelles

– provides strength

– assists in cell division

– aids in cell movement

3.2 Cell Organelles

Several organelles are involved in making and

processing proteins.

• The nucleus stores genetic information.

3.2 Cell Organelles

Several organelles are involved in making and

processing proteins.

• The nucleus stores genetic information.

• Many processes occur in the endoplasmic reticulum.

• There are two types of endoplasmic reticulum.

– rough endoplasmic

reticulum

– smooth endoplasmic

reticulum

3.2 Cell Organelles

Several organelles are involved in making and

processing proteins. (continued)

• Ribosomes link amino acids to form proteins.

3.2 Cell Organelles

Several organelles are involved in making and

processing proteins. (continued)

• Ribosomes link amino acids to form proteins.

• Vesicles are membrane-bound sacs that hold materials.

3.2 Cell Organelles

Other organelles have various functions.

• Mitochondria supply energy to the cell.

3.2 Cell Organelles

Other organelles have various functions.

• Mitochondria supply energy to the cell.

• Vacuoles are fluid-filled sacs that hold materials.

3.2 Cell Organelles

Other organelles have various functions.

• Mitochondria supply energy to the cell.

• Vacuoles are fluid-filled sacs that hold materials.

• Lysosomes contain enzymes to digest material.

3.2 Cell Organelles

Other organelles have various functions.

• Mitochondria supply energy to the cell.

• Vacuoles are fluid-filled sacs that hold materials.

• Lysosomes contain enzymes to digest material.

• Centrioles are tubes found in the centrosomes.

–Centrioles help divide

DNA.

–Centrioles form cilia and

flagella.

3.2 Cell Organelles

Plant cells have cell walls and chloroplasts.

• A cell wall provides rigid support.

3.2 Cell Organelles

Plant cells have cell walls and chloroplasts.

• A cell wall provides rigid support.

• Chloroplasts convert solar energy to chemical energy.

3.3 Cell Membrane

KEY CONCEPT The cell membrane is a barrier that

separates a cell from the external environment.

3.3 Cell Membrane

cell membrane

Cell membranes are composed of two phospholipid

layers.

• The cell membrane is made of a phospholipid bilayer.

• There are other molecules embedded in the membrane.

• The fluid mosaic model describes the membrane.

protein

cholesterol

proteincarbohydrate

chain

protein channel

3.3 Cell Membrane

Cell membranes are composed of two phospholipid

layers.

• The cell membrane is selectively permeable.

Some molecules can cross the membrane

while others cannot.

3.3 Cell Membrane

Chemical signals are transmitted across the cell

membrane.

• Receptors bind with ligands and change shape.

• There are two types of receptors.

– intracellular receptor

–membrane receptor

KEY CONCEPT Materials move across membranes

because of concentration differences.

3.4 Diffusion and Osmosis

Passive transport does not require energy input from a

cell.

• Molecules can move across the cell membrane

through passive transport.

• There are two types of

passive transport.

• osmosis

• diffusion

3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive

transport.

• Molecules diffuse down a

concentration gradient.

3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive

transport.

• Osmosis is the diffusion of water molecules across a

semipermeable membrane.

3.4 Diffusion and Osmosis

Diffusion and osmosis are types of passive transport.

• There are three types of solutions.

• isotonic

3.4 Diffusion and Osmosis

• hypotonic

• hypertonic

Some molecules can only diffuse through transport

proteins.

• Some molecules cannot easily diffuse across the cell

membrane.

• Facilitated diffusion is

diffusion through transport

proteins.

3.4 Diffusion and Osmosis

KEY CONCEPT Cells use energy to transport materials

that cannot diffuse across a membrane.

3.5 Active Transport, Endocytosis, and Exocytosis

Active transport requires energy input from a cell

and enables a cell to move a substance against its

concentration gradient.

• Passive transport requires no energy from the cell.

• Active transport is

powered by chemical

energy (ATP).

3.5 Active Transport, Endocytosis, and Exocytosis

• Cells use active transport

to maintain homeostasis.

• Active transport occurs

through transport protein

pumps.

A cell can import and export large materials or large

amounts of material in vesicles during the

processes of endocytosis and exocytosis.

• Cells use energy to transport material in vesicles.

• Endocytosis is the process of

taking material into the cell.

3.5 Active Transport, Endocytosis, and Exocytosis

• Phagocytosis is a type of

endocytosis.

A cell can import and export large materials or large

amounts of material in vesicles during the

processes of endocytosis and exocytosis.

• Cells use energy to transport material in vesicles.

• Exocytosis is the process of

expelling material from the

cell.

3.5 Active Transport, Endocytosis, and Exocytosis