cell theory and structure biology corsicana high school
TRANSCRIPT
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Cell Theory and Structure
BiologyCorsicana High School
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Development of the Cell Theory
• Robert Hooke (1665)---first to observe cells. Looked at thin slices of cork. Saw “little boxes.” Named them cells.
• Anton von Leeuenhoek (1675)---first to observe living cells: “wee beasties” in drop of pond water
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Definitions
• cell---the smallest unit that can carry on all the processes of life
• unicellular---a complete living thing that consists of only one cell
• multicellular---a living thing consisting of more than one cell
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Development of the Cell Theory (continued)
• Matthias Schleiden (1838)---concluded that all plants are composed of cells
• Theodor Schwann (1839)---concluded that all animals are composed of cells
• Rudolph Virchow (1855)---determined that cells come only from other cells
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The Cell Theory• All living things are composed
of one or more cells.• Cells are organisms’ basic units
of structure and function.• Cells come only from existing
cells.
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Two Main Types of Cells
• eukaryotes---contain a definite nucleus and membrane-bound organelles– examples: animal cells, plant cells– “eu” = true; “karyo” = nucleus
• prokaryotes---cells that do not have a definite nucleus or organelles– example: bacteria– “pro” = before
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Parts of the Cell
• organelles---cell components that perform specific functions in the cell (“little organs”)
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Three Main Components of Cells
• cell membrane---forms the outer boundary of the cell
• cytoplasm---inside the membrane. Contains water, salts, organelles
• nucleus---contains DNA and directs the activities of the cell
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Cytoplasmic Organelles
• ribosome---tiny granules, site of protein synthesis
• endoplasmic reticulum---system of membranes throughout the cytoplasm. Acts as a transportation system– smooth ER---does not have ribosomes
attached to it– rough ER---has ribosomes attached
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Cytoplasmic Organelles
• Golgi apparatus---stack of fluid-filled membranes or sacs near the nucleus. The cell’s processing, packaging and secreting organelle
• mitochondrion---respiration centers of the cell– release energy from molecules– produce ATP– have their own DNA
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Cytoplasmic Organelles
• lysosomes---organelles that contain digestive enzymes– only in animal cells– “suicide sacs”
• microtubules---long, slender protein tubes which shape and support the cells– spindle fibers---specialized microtubules
that aid in movement of chromosomes during cell division
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Cytoplasmic Organelles
• microfilaments---fine protein threads which contract to move cellular materials– cytoskeleton---microfilaments and
microtubules collectively forming the framework of the cell
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Organelles for Movement• cilia---large numbers of short, hairlike
extensions out from the surface of the cell; for movement
• flagellum---long, whiplike structure for movement. Occur singly or in pairs
• “9 + 2” construction of cilia and flagella---composed of 9 pairs of microtubules around the circumference and 2 in the center
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Plant Cell Organelles• cell wall---surrounds the cell
membrane. Supports and protects the plant cell– structure is long chains of cellulose
embedded in pectin and lignin
• vacuole---large, fluid-filled cavity which stores enzymes, wastes, etc. In a mature plant cell, the vacuole may take up 90% of the volume of the cell.
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Plastids
• make and/or store food or pigments• chloroplast---contains chlorophyll;
the site of photosynthesis• chromoplast---synthesizes and
stores other pigments• leucoplast---stores food such as
starches, proteins, lipids
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Nucleus
• contains DNA and directs the activities of the cell
• nuclear membrane (nuclear envelope)---double membrane that surrounds the nucleus. Has pores for substances to enter and leave
• nucleolus---spherical body in nucleus; stains dark; synthesizes ribosomes
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Nucleus (continued)
• chromatin---fine strands in nucleus made of DNA and protein– chromosome----when the cell gets ready
to divide, the chromatin coils and condenses and can be seen with a microscope as these rod-shaped bodies in the nucleus
• nucleoplasm---dense, protein-rich substance inside the nuclear membrane
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Cell Membrane
• selectively permeable---allows some molecules to pass through, but not others
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Composition of Cell Membrane
• 2 layers of lipid molecules– carboxyl group (hydrophilic) is turned
to outside of membrane– hydrocarbon end (hydrophobic) is
turned to inside of membrane
• protein molecules embedded in the lipid layer
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Outside the cell
Inside the cell
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Fluid Mosaic Model
• the lipid molecules in the membrane can move around (flow---->fluid)
• proteins also move• the pattern (“mosaic”) of proteins
and lipids is constantly changing
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Cell Types
• size ranges from 2 meters long (nerve cell in giraffe’s leg) down to 0.2 micrometers (bacteria)– usually 10--50 micrometers– size is limited by ratio of surface area to
volume
• shape is mostly cube- or sphere-shaped. The shape of a cell depends on its functions
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Differences Between Plant Cells and Animal Cells
• lysosomes found only in animal cells• vacuoles are large, central
structures in plant cells. If present in animal cells, they are small and scattered
• cell wall found only in plant cells• plastids (chloroplasts, chromoplasts,
leucoplasts) found only in plant cells
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Multicellular Organization• In true multicellular organisms:
– cell specialization---each cell does only one particular job for the organisms
– division of labor---each cell depends on other cells to perform one or more functions to keep the entire organism alive
• colonial organism---a group of more or less similar cells that live together in closely-connected groups, but in which there is no cell specialization
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Levels of Structure
• cell---the basic unit of life• tissue---a group of similar cells that
carry out a common function• organ---several types of tissues that
interact to perform a specific function• organ system---a group of organs
that work together to perform a set of related tasks