Introduction to Cells

What Are Cells? The smallest biological unit that can perform all life processes Allows living things to obtain and use energy, respond to environment, and to reproduce.

Your Turn Draw and describe what you think a typical cell looks like.

Scientists and cells… Robert Hooke (1665) looked at a slice of cork (dead plant cells) under the microscope. He saw “little boxes” which he named cells. His microscope only magnified 30x

Scientists and cells… Anton van Leeuwenhoek (1675) Discovered living single-celled organisms in pond water Observed bacteri`a His microscope magnified 270x

Scientists and cells… Matthias Schleiden (1838) Concluded that cells make up every part of a plant

Scientists and cells… Theodor Schwann (1839) Discovered that animals are also made up of cells

Scientists and cells… Rudolph Virchow (1858) Proposed that cells come only from the division of existing cells

Your Turn How can you remember what each scientist discovered?

The Cell Theory There are three parts to the cell theory: All living things are composed of one or more cells. Cells are the basic units of structure and function in an organism. Cells come only from the reproduction of existing cells.

Cell Diversity Not all cells are alike…in our own body we have over 200 different cell types. They differ by… size shape internal organization

Size: Cell size is limited by a cell’s surface area-to-volume ratio All substances that enter or leave a cell must pass through the surface of the cell

Your Turn Why do you think cells are so small? Why do you think cells have different shapes?

Shape: A cell’s shape reflects its function Larger cells often have shapes that increase the surface area These differences (size and shape) enable different cells to perform highly specific functions in the body Examples: Skin cells are broad and flat to cover the body. Nerve cells have long extensions (can be 10,000x longer than they are thick) that allow it send and receive nerve impulses.

Shape:

Internal Organization Cell Structures That All Cells Have In Common… Cell Membrane Cell’s outer boundary that acts as a barrier between the outside environment and inside of the cell Cytoplasm Includes the fluid (cytosol) and almost all of the structures that are suspended in it inside the cell

Internal Organization Cell Structures That All Cells Have In Common… Ribosome Structure on which proteins are made DNA The genetic material containing instructions for making proteins, regulates cellular activities, and enables cells to reproduce

Your Turn List the 4 things that all cells have in common

Types of Cells : Prokaryotes Unicellular (made of only 1 cell) Simple structure No nucleus No membrane bound organelles Example: bacteria

Types of Cells: Eukaryotes Can be unicellular or multicelled Able to carry out more specialized functions than prokaryotic cells DNA is stored in a nucleus Have membrane-bound organelles Example = plant and animal cells

Your Turn Compare and contrast prokaryotic and eukaryotic cells

Types of Cells : Prokaryotes Organism that is a single prokaryotic cell UNICELLULAR Genetic material is a single loop of DNA Ribosomes, enzymes, & DNA are free floating in the cytoplasm No nucleus or other membrane bound organelles Surrounded by a cell wall (outside of cell membrane) that provides structure and support 1st appeared about 3.5 billion years ago Very simple and small Example = bacteria

Types of Cells: Eukaryotes Organism that is made up of one or more eukaryotic cells Some are single cells, others are multicellular Able to carry out more specialized functions than prokaryotic cells DNA is stored in a nucleus Have a membrane, cytoplasm, ribosome, a nucleus, AND membrane-bound organelles 1st appeared 1.5 billion years ago More complex and relatively large Example = plant and animal cells