Biology 3.2A Cell Features
The Cell Theory In 1838, the German botanist Mattias Schleiden concluded that cells make up not only the stems of plants but every part of a plant. A year later, German zoologist Theodore Schwann determined that cells animals are also made of cells. In 1858, Rudolph Virchow, a German physician, determined that cells came from other cells Cell home movies
Cell Theory The observations of Schleiden, Schwann, and Virchow form the cell theory which has three parts. All living things are made of one or more cells. Cells are the basic units of structure and function in organisms. All cells arise from existing cells.
Cell Size Small cells function more efficiently than large cells. Small cells can exchange substances more readily than larger cells because small objects have a higher surface area-to-volume ratio than larger objects. As a result, substances do not need to travel as far to reach the center of a smaller cell.
Common Cell Features All cells have a cell membrane, an outer boundary that encloses the cell and separates the cell interior, called the cytoplasm, from it’s surroundings.
Cell Features: Cell membrane The cell membrane also regulates what enters and leaves the cell including gases, nutrients, and wastes
Cell Features: Cytoskeleton Within the cytoplasm are many structures, often suspended in a system of microscopic fibers called the cytoskeleton. Cytoskeleton shown in green
Cell Features Most cells have ribosomes as well. Ribosomes are the cellular structures on which proteins are made. Ribosomes shown In a micrograph
Cellular Structure All cells also have DNA which provides instructions for Making proteins Regulates cellular activities Enables cells to reproduce
Features of Cells The smallest and simplest cells are prokaryotes. Prokaryotes are single-celled organisms that lack a nucleus and other internal compartments. Without separate compartments to isolate materials, prokaryotes cells cannot carry out many specialized functions For nearly two billion years, prokaryotes were the only life forms on Earth.
Characteristics of Prokaryotes Prokaryotes can exist in a broad range of environmental conditions. The cytoplasm of a prokaryotes contains everything inside the cell membrane. A prokaryotes enzymes and ribosomes are free to move around in the cytoplasm because there are no internal structures that divide the cell into compartments. There is NO Nucleus!
Prokaryotes In prokaryotes, the genetic material (material that carries hereditary information) is a single circular molecule of DNA. Prokaryotic cells have a cell wall surrounding the cell membrane that provides structure and support. Prokaryotes lack an internal support skeleton so they rely on a strong cell wall to give the cell shape.
Prokaryotes Some prokaryotes cell walls are surrounded by a structure called a capsule. The capsule enables the prokaryotes to cling to almost anything; teeth, skin, food, etc. Many prokaryotes have flagella which are long, threadlike structures that protrude from the cell’s surface and allow movement. Prokaryotic flagella rotate propelling the organism up to 20 cell lengths per second.
Eukaryotic cells: Nucleus The first cells with compartments were primitive eukaryotic cells which evolved about 2.5 billion years ago. A eukaryote is an organism whose cells have a nucleus. The nucleus is an internal compartment that houses the cell’s DNA.
Eukaryotic cells: Organelle Other internal compartments, or organelles, enable eukaryotic cells to function in ways different from prokaryotes. An organelle is a structure that carries out specific activities in the cell.
Eukaryotic cells A complex system of internal membranes connects some organelles within the cytoplasm. These membranes provide channels that guide the distribution of substances within the cell.
Eukaryotic cells: flagella and cilia Many single celled eukaryotes use flagella for movement. Short hair-like structures called cilia protrude from the surface of many eukaryotic cells. Flagella or cilia propel some cells through their environment. In other cells, cilia or flagella move substances across the cell’s surface.
Eukaryotic cells: Cytoskeleton A web of protein fibers makes up the cytoskeleton. The cytoskeleton holds the cell together and keeps cell membranes from collapsing.