Cells: The Building Blocks of Life

The cell is the smallest unit of life!

The Cell Theory1. All living things are composed of one or more cells.2. Cells are organisms’ basic units of structure &

function.3. Cells come only from existing cells.

Scientist who developed The Cell TheoryMatthias Schleiden- concluded that plants were composed

of cells.Theodor Schwann- concluded that animals were

composed of cells.Rudolph Virchow- determined that cells only came from

other cells.

ProtocellsOne theory of the origins of cells states that the first life

on earth consisted of several types of tiny protocells, cell-like organisms. These organisms were able to survive and reproduce in a very limited environment because of their simplicity. Over time, some of these protocells came together and shared their specialization in a symbiotic relationship. These colonies of protocells eventually became the cells we know today.

Discovery of Cells

Robert Hooke – discovered the first cells, cells he observed were dead, in 1665 while looking at cork.

Anton van Leeuwenhoek – first person to observe living cells in 1675.

Types of Cells

Prokaryotes - cells with no nucleus or organelles with membranes. Bacteria and blue-green bacteria are prokaryotic cells.

Eukaryotes - cells that contain a nucleus and organelles surrounded by a membrane. The cells of protozoa, algae, fungi, plants, and animals are eukaryotic cells.

Types of OrganismsUnicellular = living organism that consist of only 1

cell.Multicellular = living organism consisting of more

than 1 cell.

Cell Organelles

(Plant & Animal Cell Organelles)Cell membrane

A complex barrier of lipid molecules separating the cell from its external environment.

These molecules can move apart to allow larger particles to move in or out of the cell.

The "selectively permeable" cell membrane regulates what passes into & out of the cell. Some substances, like H2O, move freely through the cell membrane by a process known as osmosis. In osmosis, particles move easily from an area of high concentration to an area of low concentration by molecular motion only. Cells can push particles in the opposite direction, from low concentration to high, but it takes energy from the cell.

Cytoplasm A thick, aqueous solution of salts surrounding the

organelles inside the cell membrane.Nutrients and minerals spread through the cytoplasm to

all parts of the cell.The constant motion of this gel-like substance is called

cytoplasmic streaming.

Nucleus The structure inside the cell that directs cell activities. Contains the DNA of a cell.

RibosomeThe sites of protein synthesis in a cell.These small, spherical structures are the most numerous

organelles in almost all cells.Some ribosomes produce protein to be used within the

cell and some produce protein that is "exported" to other parts of an organism.

Endoplasmic ReticulumA membrane system of folded sacs and tunnels in the

cytoplasm.Rough "ER" is covered with ribosomes. It is common in

cells that export proteins and directs the proteins flow.Smooth "ER" as few or no ribosomes. It functions as a

pathway for molecules to follow.

Golgi Apparatus A stack of membranes or sacs that acts to prepare

substances for export from the cell.Once the Golgi apparatus has enclosed the final product

in a vesicle, or pouch, the product is sent through the cell membrane.

MitochondriaRespiration centers of a cell.Large organelles scattered through most cells, they are

most numerous in cells that use a lot of energy like liver and muscle cells.

Microtubules/MicrofilamentsLong, slender protein tubes are called microtubules; the fine

protein threads are called microfilaments.These form the inner framework of a cell called the

cytoskeleton.

(Animal Cell Organelles)LysosomeDigestive centers of a cell.They produce many different types of enzymes and digest

things from food particles to a cell's own worn out parts.“garbage disposals of the cell”

CentriolesPair of rod-shaped bodies composed of microtubules.Distribute chromosomes during cell division.

Cilia/FlagellaStructures that extend from the surface of cell and aid in

movement.Cilia are short, hair like extensions that occur in large #’s

on the surface of some cells.Flagella are whip like, longer than cilia, that occur

singulary or in pairs.

(Plant Cell Organelles)

Cell wallOn the outside of some cells, bacteria and plants, this

structure functions for support and protection.There are pores in the cell wall allowing substances to

come in contact with the cell membrane.

Types of cell walls:

Primary cell wall - formed during cell growth, it is composed of parallel layers of cellulose and pectin. This structure allows the cell to expand as it grows. While it does provide support, it is not nearly as strong as the secondary cell wall.

Secondary cell wall - formed after cell growth stops, it is composed of interwoven cellulose and lignin fibers. This structure is very strong, but does not give. It gives plants their "woody" characteristic.

Vacuole

Most common in plant cells, they are storage sites within a cell. Some animal cells may have these but they are very small compared to the large vacuole in plant cells

Plastids

Pigment producing organelle in cells.Chloroplast – Contain green pigment called chlorophyll

that absorbs sunlight.Chromoplast – Synthesize and store pigments such as

orange carotenes, yellow xanthophylls, & various red pigments, some of which trap sunlight for energy.

Leucoplast – Store food such as starches, proteins, & lipids.

The End