Cell Organization Living things are constructed of cells. Living things may be unicellular or multicellular. Cell structure is diverse but all cells share common characteristics.

The cell theory states: All organisms are composed of one or more cells. Cells are the basic unit of structure and function in organisms. All cells come only from other cells. Cell Theory came about through the work of seventeenth century scientists who had invented fairly primitive microscopes. Antonie van Leeuwenhoek made his own microscopes and observed many types of tiny things. Englishman Robert Hooke was the first to use the term “cell” and confirmed Leeuwenhoek’s findings. During the 1830s, German microscopist Matthias Scheiden found that plants were composed of cells, and Theodore Schwann found that animals were composed of cells. Rudulf Virchow of Germany came to the conclusion that cells come only from preexisting cells. All of these scientists contributed to the Cell Theory. Modern scanning and transmission electron microscopes have allowed scientists to determine the structure of cells at the level of the organelle.

Cells are small so they can exchange materials with their surroundings. Surface area relative to the volume decreases as size of cell increases. - limits the size of cells

Sizes of living things

Eukaryotic and Prokaryotic Cells Eukaryotic cells have a cell membrane, organelles and a nucleus controlling the cell. Prokaryotic cells have a cell wall and genetic material but no nucleus.

The cell membrane regulates what enters and exits the cell. Inside the cell membrane, the nucleus is surrounded by cytoplasm. Plant cells have a cell wall in addition to the plasma membrane. Cytoplasm is a semi-fluid medium. Primary cell walls are made from cellulose. The secondary cell wall, which forms inside the primary wall, is formed from lignin. Its purpose is to give strength to the cell.

Animal and plant cells have organelles. Organelles compartmentalize functions within the cell. The organelles of animal and plant cells are similar to each other except that centrioles are present only in animal cells, and chloroplasts are present only in plant cells.

Animal Cell Anatomy

Plant Cell Anatomy

Ribosomes Protein synthesis occurs at tiny organelles called ribosomes. Ribosomes are composed of a large subunit and a small subunit. Ribosomes can be found alone in the cytoplasm, in groups called polyribosomes, or attached to the endoplasmic reticulum.

Structure of the Nucleus Chromatin: DNA and proteins Nucleolus: Chromatin and ribosomal subunits Nuclear envelope(membrane): Double membrane with pores

The endoplasmic reticulum The endoplasmic reticulum (ER) is a system of membranous channels. Rough ER is studded with ribosomes and is the site of protein synthesis and processing. Smooth ER lacks ribosomes and is the site of synthesis of phospholipids and the packaging of proteins into vesicles, among other functions. Saccules are flattened vesicles.

The Golgi apparatus The Golgi apparatus consists of a stack of curved saccules. The Golgi apparatus receives proteins from the ER, packages, processes, and distributes them within the cell.

Lysosomes and vacuoles Lysosomes are vesicles produced by the Golgi apparatus and aid in digestion. Vacuoles (large) and vesicles (small) are membranous sacs in the cell that store water and other substances. Digestion within the cell disposes of worn-out cell parts and is necessary for cell rejuvenation. Vacuoles and vesicles can store a variety of substances for the cell. Anything from water to plant pigments and toxic substances are stored in these membranous sacs.

Energy-Related Organelles The two energy-related organelles of eukaryotes are chloroplasts and mitochondria. Both organelles house energy.

Mitochondria Mitochondria are found in plant and animal cells. Mitochondria are bounded by a double membrane surrounding fluid-filled matrix.

Centrioles Centrioles are short cylinders with a 9 + 0 pattern of microtubule triplets. Centrioles may be involved in microtubule formation and disassembly during cell division and in the organization of cilia and flagella.