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The Human Gastrointestinal (GI) Tract

The Strategy

Humans (and most animals) digest all their food extracellularly; that is, outside of cells.

  • Digestive enzymes are secreted from cells lining the inner surfaces of various exocrine glands.
  • The


A typical plant cell (e.g., in the palisade layer of a leaf) might contain as many as 50 chloroplasts.

The chloroplast is made up of 3 types of membrane:

  1. A smooth outer membrane which is freely permeable to molecules.
  2. A smooth inner membrane which contains many transporters: integral membrane proteins that regulate the passage in an out of the chloroplast of
    • small molecules like sugars
    • proteins synthesized in the cytoplasm of the cell but used within the

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Plant Tissues

A mature vascular plant (any plant other than mosses and liverworts), contains several types of differentiated cells. These are grouped together in tissues. Some tissues contain only one type of cell. Some consist of several.


The main function of meristematic tissue is mitosis. The cells are small, thin-walled, with no central vacuole and no