Cell Structure and Function

Chapter 3

CELL THEORY 3.1

Key Concept

• Cells are the Basic unit of life

Cell Theory

• Due to the invention and improvement of the microscope

• Many scientists contributed

Cell Theory

• A unifying concept of biology

Three Principles of C.T.

1. All organisms are made of cells.

Three Principles of C.T.

2. All cells are produced by other existing cells.

Three Principles of C.T.

3. The cell is the most basic unit of life.

All Cells

• Share certain characteristics: – cells tend to be microscopic

– all cells are enclosed by a membrane

– all cells are filled with cytoplasm

cell membrane

cytoplasm

Cell Types

• Two basic types of cells: – prokaryotic cells - eukaryotic cells

Prokaryotic Cells

• Examples: – bacteria

– blue-green algae

• Lack a nucleus

• No membrane-bound organelles

Eukaryotic Cells

• Examples: – plant cells

– animal cells

• Have a nucleus

• Have membrane-bound organelles

CELL ORGANELLES 3.2

Key Concept

• Eukaryotic cells share many similarities.

Cells Have an Internal Structure

• The cytoskeleton – supports and shapes the cell

– helps position and transport organelles

– provides strength

– assists in cell division

– aids in cell movement

Nucleus

• Stores genetic information

Endoplasmic Reticulum

• Make proteins and membranes

• Two types: – Rough ER

• contain ribosomes

– Smooth ER • no ribosomes

Golgi Apparatus

• Packages proteins for secretion outside of the cell

Ribosomes

• Link amino acids to form proteins

Vesicles

• Membrane-bound sacs that hold materials

Mitochondria

• Supply energy to the cell

Vacuole

• Fluid-filled sacs that hold materials

Lysosomes

• Contain enzymes to digest materials

Centrioles

• Tubes found in the centromeres – help divide DNA

– form cilia and flagella

Plant Cells

• Have cell walls – provides rigid

support

Plant Cells

• Have chloroplasts – convert solar energy to chemical energy

CELL MEMBRANE 3.3

Key Concept

• The cell membrane is a barrier that separates a cell from the external environment.

Cell Membranes

• Composed of two layers • Two major functions:

– forms a boundary between the inside and outside of the cell

– controls passage of materials

cell membrane outside cell

inside cell

Structure of C.M.

• Phospholipid bilayer • Other molecules are embedded in the

membrane • Called the fluid mosaic model

Selectively Permeable

• Allows only certain substances in or out

Some molecules

can cross the

membrane while

others cannot.

DIFFUSION AND OSMOSIS 3.4

Key Concept

• Materials move across membranes because of concentration differences.

Passive Transport

• Does not require energy input from a cell – allows molecules to move across a cell

membrane • Two types:

– diffusion – osmosis

Diffusion

• No energy required

• Moves from high to low concentration

Osmosis

• Diffusion of water molecules across a semi-permeable membrane

Types of Solutions

• Isotonic

• Hypertonic

• Hypotonic

Isotonic

• Equal concentration of dissolved particles

Hypertonic

• Higher concentration of dissolved particles outside the cell

Hypotonic

• Higher concentration of dissolved particles inside the cell

Transport Proteins

• Allow some molecules to pass through the phospholipid bilayer

• Called facilitated diffusion

HIGH

LOW

ACTIVE TRANSPORT, ENDOCYTOSIS, AND EXOCYTOSIS

3.5

Key Concept

• Cells use energy to transport materials that cannot diffuse across a membrane.

Active Transport

• Requires energy input from a cell – ATP

• Substances go from low to high concentration

• Occurs through transport protein pumps

• Used to maintain homeostasis

Active Transport

• Many models & mechanisms

ATP ATP

Endocytosis

• Transport of materials inside the cell – can be large material – or large quantities of materials

• Phagocytosis – cell eating

• Pinocytosis – cell drinking

Exocytosis

• Transport of materials outside the cell