Biology 250

Chapter 4

Robert Hooke

Microscopes opened a whole new world

• Looked at cork under a microscope

• Gave cells their name

These remind me of the rooms monks sleep in which are

called cells…. I shall call these little boxes

cells!

And this guy….

• 1st to look at living cells

• Took scrapings of tartar from his teeth Anton van

LeeuwenhoekI saw “many small animalcules, the

movement of which was

pleasing to see!”

The Cell Theory

• All living things are composed of one or more cells.

• The cell is the basic unit of structure and function in all living things.

• All cells come from the reproduction of existing cells.

Proposed by Schleiden, Schwann

and Virchow

So… why are cells so small?

Surface Area to Volume Ratio: As a cell increases in size, the surface area increases with the square of the diameter but the

volume increases with the cube.

Everything a cell needs to live has to comein through its surface.

All wastes must leave through its surface.

Eventually, the volume of the cell gets so largeThe cell cannot get nutrients to the center

Or wastes to the surface fast enough.The cell dies.

Two Main Types of Cells

Prokaryotic – Do NOT have a nucleus or organelles surrounded by membranes.

These are BACTERIA.

Eukaryotic – DO have a nucleus and organelles surrounded by membranes.

Everything BUT bacteria!

Animal Cell Plant Cell

Organelle – A cell part which performs

a function for the cell.

There are two main types of eukaryotic cells:Animal Cells and Plant Cells.

Both contain many of the same organelles.

Aaaaaaand yes, you have to be able to name and

describe all of them.

Organelles of the animal cell

Cell Membrane:• Surrounds all cells.• Controls what enters and

leaves the cell• Selectively Permeable –

Only allows certain substances to enter/exit the cell.

• Composed of a lipid (fat) bilayer (2 layers of a special kind of fat called a phospholipid)

This is a model of the cell membrane.

Contains 2 layers of phospholipids. The type of fat that makes up the

membrane.Also contains 2 types of proteins:1. Peripheral Proteins – Located on the inner surface or

outer surface of the membrane.2. Integral Proteins: Located inside of the membrane.

Fluid Mosaic Model:The cell membrane behaves as a fluid. Phosolipids and both types of proteins can move around freely.

Organelles of the animal cell

Cytoplasm:The clear, jelly-like substance

which makes up the bulk of the cell.

Mitochondrion• Makes ATP (energy) for the

cell.• Nicknamed: The Powerhouse

of the cell.• Has two membranes, an inner membrane and an outer membrane.

Organelles of the animal cell

Endoplasmic Reticulum• Acts as an intracellular

highway.• Two Types

• Rough ER – Studded with ribosomes. Makes proteins for export.

• Smooth ER – Breaks down toxic substances.

Ribosomes – Located free floating in the cytoplasm OR embedded in the rough endoplasmic reticulum. FUNCTION: make proteins

Organelles of the animal cell

Golgi Apparatus:Processes and

packages proteins for export.

They say it looks like a stack of flattened pancakes!

Lysosomes: Contain digestive enzymes. Break down old & worn out organelles, cellular debris and wastes.

Organelles of the animal cell

CytoskeletonThe cytoskeleton is a network of fibers called microtubules and

microfilaments. It provides structure and support to the cell.

Some cells also have the ability to move. Those cells have one of the following:

Flagellum: Long, and whiplike. Enables movement.

Cilia: Short, hairlike, very numerous. Enable movement.

Organelles of the animal cell

Let’s look at the nucleus: The nucleus controls the activities

of the cell.

Nuclear Envelope: The double membrane that surrounds the nucleus. Contains pores to allow material to enter/exit.

Nucleolus: Round ball inside the nucleus which makes ribosomes.

Chromatin: The DNA of the cell in it’s unwound form.. When it’s wound up, it becomes chromosomes.

Organelles of the animal cell

1. Cell Membrane2. Cytoplasm3. Mitochondrion

(mitochondria)4. Endoplasmic Reticulum

1. Smooth ER2. Rough ER

5. Ribosomes6. Golgi Apparatus7. Lysosomes8. Cytoskeleon9. Flagellum (flagella)10.Cilia (cillium)11.Nucleus12.Nuclear Envelope13.Nucleolus14.Chromatin

Break Time

Review Time!Can you give the function of these organelles?

Cytoplasm

Cytoskeleton

Nucleus

Nuclear Envelope

Flagellum

Ribosomes

Endoplasmic Reticulum

CiliaNucleolus

Smooth ER

Mitochondrion

Rough ER

Chromatin

Lysosome

Cell Membrane

Golgi Apparatus

Plants have most of the organelles that animals do (except

the ones for movement) plus 3

more!

Vacuole: Takes up a lot of space! Filled with fluids and wastes.

Cell Wall: Rigid structure made of cellulose. Supports plant. Enables plants to stand upright.

Chloroplasts: Contain the green pigment chlorophyll and make food for the plant through photosynthesis.

Levels of Multicellular Organization

• Some organisms are made from more than one cell and their cells are organized.

• Tissue – A group of similar cells working together to perform a common task.

• Organ – A group of tissues working together to perform a common task.

• Organ System – A group of organs working together to perform a common task.

• Organism – All the organ systems working together

Questions?