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Cell Theory
Scientific theory stating that cells are the smallest units of life, all organisms consist of one or more cells, and all cells come from pre-exisitng ones.
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Cytoplasm
The contents of a cell between the outer plasma membrane and the nucleus.
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Eukaryotic Cell
A cell that has a nucleus containing its DNA.
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Organelle
Any of the compartments and sacs in a cell.
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Plasma Membrane
Covering that encloses a cell's internal parts.
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Prokaryotic Cell
A cell in which the DNA is not contained inside a nucleus.
Bacteria are prokaryotic cells.
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Comparison of Eukaryotic and Projaryotic Cells
- Eukaryotic Prokaryotic
- Plasma Membrane yes yes
- DNA-containing Region yes yes
- Cytoplasmyes yes yes
- Nucleus Inside Membrane yes no
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Lipid Bylayer
The structure of the plasma membrane, in which two parallel layers of phospholipids form with their heads facing outward and their tails facing inward.
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Surface-to-Volume Ratio
The physical relationship by which the volume of a growing three-dimensional object increases faster than its surface area does.
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Micrograph
The photograph of an image formed by a microscope.
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Microscopy
The use of a microscope to view objects, including cells, that are not visible to the unaided eye.
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Selective Permeability
A property of the cell plasma membrane, in which the membrane allows only certain substances to cross it.
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Chromatin
A cell's DNA molecules and proteins attached to them.
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Chromosome
An individual DNA molecule and attached proteins.
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Nuclear Envelope
A double membrane that separates the inside of the nucleus from the cytoplasm. It has many pores.
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Nucleus
Organelle that encloses a eukaryotic cell's DNA.
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Nucleolus
A cluster of the RNA and proteins used to assemble ribosomes from their subunits.
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Endomembrane System
System of membrane-bound cell organelles that mainly modify new proteins, build lipids, and package the completed moelcules (as in vesicles).
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Endoplasmic Reticulum
Channel-like organelle, Lipids are assembled in smooth ER. In rough ER, side chains are added to newly formed polypeptides.
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Gogli Body
Series of flattened saclike organelles in which new lipids and polypeptide chains are processed into their final form.
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Ribosome
Organelle where protein polypeptide chains are built.
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Vesicle
A small, membrane-bound sac in cells. Some vesicles transport substances others contain digestive enzymes.
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Lysosome
Vesicle in which enzymes disgest (break down) unwanted molecules.
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Peroxisome
Vesicle in which enzymes break down fatty acids and amino acids.
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Mitochondrion
Organelle that produces ATP, the main cell fuel.
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Centrioles
Cell structures that give rise to microtubules.
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Cilia
Short, bendable structures built of microtubules.
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Cytoskeleton
The cell's internal structural framework.
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Flagella
Whiplike structures built of microtubules.
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Intermediate Filaments
Cytoskeleton filaments that anchore proteins (actin and myosin) in the cytosol and add strength to it.
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Microtubules
The largest elements of the cytoskeleton.
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Microfilaments
Filaments in the cytoskeleton that reinforce or anchor cell parts.
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Concentration Gradient
A difference in the number of molecules or ions of a substance in two neighboring regions.
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Diffusion
The movement of molecules or ions from a region of higher concentration to a region of lower concentration.
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Hypertonic
Said of a fluid containing more of a given solute than a fluid on the other side of a selectively permeable membrane.
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Hypotonic
Said of a fluid having less of a given solute than the fluid on the other side of a selectively permeable membrane.
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Isotonic
Said of fluids separated by a selectively permeable membrane and that contain equal amounts of a given solute.
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Osmosis
The diffusion (passive transport) of water across a selectively permeable membrane.
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Passive Transport
The diffusion of a substance across a cell membrane; does not require ATP energy.
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Active Transport
Movement of substances across a cell membrane against a concentration gradient, using energy from ATP.
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Endocytosis
Process by which a cell takes in a large molecule or particle by forming a vesicle that encloses it and moves it into the cell cytoplasm.
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Exocytosis
Process in which a vesicle enclosed and moves a large molecule or particle to the cell surface and expels it.
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Phagocytosis
Endocytosis of a cell or other organic matter.
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Active Site
Area on the surface of an enzyme where the enzyme and its substrate can interact.
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Anabolism
Metabolic activity that builds large molecules from smaller ones.
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ATP/ADP Cycle
A cycle in which a phosphate attaches to ADP, forming ATP, then ATP transfers a phosphate elsewhere, becoming ADP again.
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Catabolism
Metabolic activity that breaks down large molecules into smaller ones.
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Metabolism
The chemical reactions in cells.
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Substrate
The particular kind of molecule that interacts with a given enzyme.
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Cellular Respiration
The ovrall aerobic (oxygen-using) process by which cells break down organic molecules to make ATP.
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Electron Transport System
The chain of reactions in mitochondria that uses energy from electrons to generate many ATP molecules.
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Gycolysis
Process that breaks apart glucose molecules, forming pyruvate, in the first stage of cellular respiration.
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Krebs Cycle
Process that produces energy-rich compounds (NADH and FADH2) that deliver elentrons to electron transport systems in mitochondria. The cycle also produces a small amount of ATP.
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Phosphorylation
The transfer of a phosphate group to a molecule.
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