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Looking at Cells Microscopes: A basic biology tool that allowed for the discovery of cells and cell parts. Scientists of Cells Robert Hooke was the English scientist (1665) who discovered and named the cell while viewing a thin slice of cork. Anton van Leeuwenhoek—Dutch microscope maker and textile manufacturer (1675) who was the first to view living cells using a microscope. Matthias Schleiden—German botanist (1838) discovered that all plants were made of cells. Theodore Schwann—German zoologist (1839) discovered that all animals were made of cells. Rudolf Virchow—German physician (1855) discovered that cells can only come from preexisting cells after observing mitosis. Cell Theory 1. 2. 3. These scientists’ work helped to form the Cell Theory: All organisms are composed of one or more cells. The cell is the basic unit of organization of organisms. All cells come from preexisting cells. Basic Cell Parts All cells are surrounded by a membrane, and contain DNA and cytoplasm. Most contain ribosomes. The fluid matrix within the cell is the cytoplasm. It is a gelatinous fluid with water as its main component. It helps hold organelles in place and is the site of many chemical reactions. Structures within cells that perform specialized functions are calls organelles. Ex—ribosome, mitochondrion, and lysosome. Prokaryotic cells are cells that do not contain a nucleus or membrane-bound organelles. All bacterial cells are prokaryotic or prokaryotes. Prokaryotic organisms are all unicellular. They do not have need for different types of cells. Prokaryotes are the oldest living organisms. Believed to be the first type of cells on earth. Evolved before the need for a nucleus. (Pro- before; karyonucleus) Eukaryotic cells do contain a nucleus or membrane-bound organelles. All cells other than bacterial cells are eukaryotic cells or eukaryotes Eukaryotic organisms can be unicellular (protists) or multicellular (plants, animals, fungi). Cell differentiation in multicellular, eukaryotic organisms allows for different types of cells. The shape of a cell usually reflects its function. Specialized Animal Cells Muscle cells Red blood cells Cheek cells copyright cmassengale 13 Specialized Plant cells Guard Cells Pollen Xylem cells copyright cmassengale 14 Cell Membrane The cell membrane is the outer boundary of the cell which regulates which materials enter and exit the cell. Cell membranes are described as selectively permeable or semipermeable. The cell membrane is made of a phospholipid bilayer with embedded proteins. The lipids are non-polar so that makes the membrane a good barrier to separate a cell from its environment. The nucleus controls all cell activities, especially growth and reproduction. The nucleolus is a small dense area inside the nucleus which makes rRNA which is the main component of ribosomes. Nucleoplasm is the fluid matrix inside of the nucleus. It is the “cytoplasm” of the nucleus. There are different forms of DNA. Chromosomes are the compact versions of DNA that forms when the cell is about to divide. Chromatin is the threadlike genetic material found in the nucleus of a nondividing cell. The nuclear envelope or nuclear membrane is a porous doublemembrane that separates the nucleus from the cytoplasm. Ribosomes The ribosomes are the site of protein synthesis. They can be found floating freely within the cytoplasm or on the rough ER. E. R. The endoplasmic reticulum (also called ER) is a set of tubular passageways involved in the transport of materials throughout the cell. It connects the nucleus to the cell membrane. There are two types of ER. Rough ER is involved in the transport of proteins and has many ribosomes attached to its surface. Smooth ER is involved in the manufacture and transporting of lipids. Cytoskeleton The cytoskeleton is a network of protein filaments that helps the cell to maintain its shape and function. It is made of microfilaments and microtubules. Golgi Apparatus The Golgi Apparatus is responsible for sorting and packaging compounds so they can be sent to the appropriate destination. Mitochondria The mitochondria are organelles that release energy from the stored food molecules in the form of ATP. It is also called the “powerhouse of the cell”. Vacuoles Vacuoles are storage sacs that store food, water, wastes, salts, and other material. They are larger in plant cells than they are in animal cells. Centrioles (Animals) The centrioles are found only in animal cells and are tubular structures that are involved in cell division. Lysosomes (Animals) Lysosomes contain powerful enzymes that break down substances to be used by the cell as well as toxic substances. Poisons and wastes are detoxified within the lysosomes. Cell Wall & Chloroplast All plant cells are surrounded by a nonliving layer called a cell wall which provides protection and support for the cell and helps give the cell its shape. Chloroplasts are found in plant cells and are the site of photosynthesis. Cilia & Flagella Some cells use whip-like structures called flagella for movement. This is used as a paddle to move a cell through liquid. Ex- Sperm. Cilia are hair-like projections that are also used for movement. Many bacteria have these. Cell Movement with Cilia & Flagella copyright cmassengale 34