Most cells are too small to see With the naked eye. Scientists became aware of Cells only after microscopes Were invented, in the 1600’s. When the English scientist Robert Hooke used a crude Scope, he saw a bunch of Little boxes he called cells.

Robert Hooke ( )

10 years after Hooke, Anton Van Leeuwenhoek used a Microscope to view pond Water, and saw tons of Tiny animals. Today we know that they are Not animals, but single cell Organisms.

Leeuwenhoek

In a light microscope, light Passes through one or more Lenses to produce an Enlarged image of something. An electron microscope forms An image of a specimen using A beam of electrons instead Of light.

It took scientists more than 150 Years to fully appreciate the Discoveries of Hooke and Leeuwenhoek.

In 1838 the German botanist Mattias Schleiden concluded That cells make up Entire plants.

A year later, the German Physician Theodor Schwann Concluded that all animals Are made up of cells.

Rudolf Virchow stated that All cells come from other cells.

All of these studies combined To form the cell theory, Which has three parts… All living things are composed of one or more cells Cell are the basic units of structure and function All cells come from preexisting cells

All cells have the same Common features… Cell membrane = outer boundary Nucleus = “center” command center Cytoplasm – everything between the cell membrane and nucleus

All cells also have ribosomes Which are where proteins Are made. All of them also have DNA that Provide instructions on how Everything is made and done.

The smallest and simplest cells Are prokaryotes. Prokaryotes are single celled Organisms that lack a nucleus And other internal stuff. Bacteria are prokaryotes.

The DNA of a bacteria is Circular and just floating around In the cytoplasm. All bacteria have a cell wall. Some bacteria are also enclosed In a capsule which allows them To stick to almost anything.

Many bacteria have flagella, Which are long, threadlike Structures that enable them To move around.

The cytoplasm and organelles Of a cell are contained by Its membrane. The membrane is made up of Lipids that stick together. Phospholipids are lipids that are Made up of a phosphate group And 2 fatty acids.

Same in plants, animals and microorganisms Lipid bilayer

electron micrograph of a cell membrane at approx. 240,000x

One way cells maintain homeostasis Is by controlling the movement Of substances across the cell Membrane. Homeostasis is the process Of maintaining the cell’s environment.

The transport of a substance Across the cell membrane against Its concentration gradient is Called active transport.

Many substances that are too Large to be transported by Carrier proteins, such as Protein and polysaccharides, are Moved across the cell membrane By vesicles.

The movement of a substance Into a cell by a vesicle is called Endocytosis.

The movement of a substance by A vesicle to the outside of a cell Is called exocytosis.

Most all of the eukaryotic Cell functions are controlled By the cell’s nucleus. Unlike prokaryotic cells, Eukaryotic cells have a System of internal organelles.

Eukaryotic cells are cells that Have a nucleus. The nucleus is where the DNA is held. These cells have many organelles. An organelle is a structure that Carries out specific activities.

The endoplasmic reticulum, Or ER, is an extensive system Of internal membranes that Move proteins and other Substances through the cell.

The ER is broken into 2 parts, Smooth and Rough. The rough ER has ribosomes Attached to it and the Smooth does not.

The Golgi apparatus is a set Of flattened, membrane Bound sacs that serve as The packaging and Distribution center of the cell.

Lysosomes are small organelles That contain the digestive Enzymes for the cell.

Nearly all eukaryotic cells Have mitochondria. Mitochondria are organelles That harvest energy from Organic compounds to Make ATP.

Mitochondria have their own DNA and ribosomes. It is widely accepted that Mitochondria were once Prokaryotes that got sucked Into eukaryotes and stayed.

Plant cells are eukaryotic Cells that have different parts Than animal cells. They have cell walls, Chloroplasts and central Vacuoles.

A cell wall supports and Protects the cell and allows Plant cells to be stacked On top of each other. The cell wall is made up of Proteins and polysaccharides. We (humans) cannot digest Cell walls. (fiber)

Chloroplasts are organelles That use light energy to Make carbohydrates From carbon dioxide And water.

The central vacuole is a large Membrane bound space that Stores water and many Substances including ions, Nutrients and wastes. When the vacuole is full, it Presses the cytoplasm against The cell wall, making the cell Very rigid.

Many single celled organisms Have cilia that work like Flagella. (they can also Have flagella)