Biology Definitions

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Cellulose A straight chain polymer of glucose molecules secreted by plants and Used as structural supporting material.

Cell wall A relatively rigid structure composed of cellulose that encloses the Cells of plants. The cell wall gives these cells their shape and limits their Expansion in hypotonic media.

Chloroplasts A group of structures that has the general name plastid. Plastids Are membrane-bound organelles found only in plant cells. Usually plastids are Spherical bodies that float freely in the cytoplasm, holding pigment molecules or starch. Chloroplasts contain the green pigment chlorophyll, a substance that gives plants the green color. Chlorophyll is a special molecule that has the ability to trap light and to convert it to a form of energy that plants can use in carrying out the chemical steps of the food-making process known as Photosynthesis. A double membrane surrounds each chloroplast. Inside the Chloroplast is numerous flattened membranous sacs called thylakoids (formerly called grana).

The thylakoids are the structures that contain the chlorophyll and it is within these sacs that photosynthesis takes place.

Endoplasmic reticulum Spreading throughout the cytoplasm, extending from the Cell membrane to the membranes of the nucleus is a network of membranes that Form channels, tubes, and flattened sacs; this network is named the endoplasmic reticulum. One function of the endoplasmic reticulum is the movement of materials throughout the cytoplasm and to the plasma membrane. The endoplasmic reticulum has other important functions related to the synthesis of materials and their packaging and distribution to sites needed.

Metabolism An inclusive term concerning all of the biochemical activities carried on by cells, tissues, organs, and systems necessary for the sustaining of life. Metabolic activities in which large molecules are built from smaller ones or in which nutrients are changed into protoplasm are called anabolic activities, or anabolism.



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