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Chapter 4
Cell Structure
19
Science
7th Grade
09/22/2008

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Term
Cell membrane page 50
Definition
a thin covering that forms the outer boundary of the cell.
They sense and repsond to changes in the surrounding environments.
Term
selectively permeable page 50
Definition
certain molecules go through them and other molecules do not.
Term
passive transport page 51
Definition
the movement of substances through a membrane without the use of the cell's own energy.
There are two main forms of passive transport: diffusion and osmosis
Term
diffusion page 51
Definition
the movement of molecules from a place where there are many of them (high concentration) to a place where there are few of them. (low concentration)
Term
osmosis page 51
Definition
the diffusion of water through a selectively permeable membrane.
Term
active transport page 54
Definition
a way that substances move through a membrane which requires the cell to use its own energy to move substances through the membrane.
Term
cell wall page 55
Definition
a bouncry around the cell. The cell wall supports and protects the cell.
Term
organelle page 57
Definition
The parts of the cell that perform many of the functions that keep the cell alive. Organelles make up cytoplasm
Term
mitochondria page 58
Definition
The cell's powerhouses. They are usually long oval structures made of two layers of membranes. The inner membrane stores the energy in small units until it is ready to be used.
Term
endoplasmic reticulum (ER) page 58
Definition
the maze of passageways formed by a golded membrane passing throughout the cytoplasm. It is the cell's delivery system.
Term
ribosomes page 58
Definition
tiny organelles that direct the assembling (building) of proteins.
Term
Golgi Apparatus page 58
Definition
This collects chemicals from the cytoplasm.
Term
Vacuoles page 58
Definition
organelles that look like bubbles and serve as containers inside the sytoplasm of some cells.
Term
Lysosomes page 58
Definition
Tiny enzyme-filled capsules that circulate in the cytoplasm and use their enzymes as a demolition crew.
Term
Chloroplasts page 59
Definition
organelles made of an outer membrane and stacks of inner membranes that contain the green pigment chlorophyll.
Chlorophyll captures energy from the sun and then uses it to make sugar in photosynthesis.
Term
Cilia page 59
Definition
tiny hairlike structures on the outside of the cell that are extensions of the cell membrane. Cilia are short and there are many of them. They move back and forth to move the cell.
Term
flagella page 59
Definition
structures on the outside of the cell that are extensions of the cell membrane. They are longer than cilia and there is only a few of them. They whip back and forth to move the cell.
Term
nucleus page 59
Definition
a compact, roundish structure that functions as the control center for the cell. It is surrounded by a nuclear membrane, which is made up of a double layer of membranes.
Term
chromosome page 61
Definition
structures inside the nucleus which are made of DNA and other molecules. DNA contains the coded information needed for making various parts and controlling the activities of the cell.
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