Your backyard (or front or side yard) is already probably full of all sorts of living things you may never have noticed.  The  big categories of living things most likely to appear in your yard are:
Plants:
      Trees :  Woody perennial plants usually over 10 feet in height, usually with a single main stem or trunk
      Shrubs: Woody perennial plants, usually less than 10 feet in height, often with multiple stems
     Grasses:  Non-woody, usually low growing plants with narrow leaves, jointed stems and seed-like fruits
     Herbs and forbs:  Low growing flowering plants other than grass
     Ferns: Non-flowering green plants, with feathery or leafy fronds, usually found in clumps in damp areas.
     Mosses : Rootless, non-flowering  green plants that grow in rounded cushions or carpets in damp places
Animals:
     Birds, butterflies, bees, bugs, worms, furry creatures (mammals), fish, snakes, frogs, toads, lizards and lots more depending on the climate.
Fungi:
     Mushrooms, toadstools, bracket fungi and other slightly woody decomposers.
Microscopic organisms:
     TIny organisms that are alive, that help to break down dead plants and animals to make new soil. 
We will use the ones that you are most likely to encounter in books, at garden shops and in magazines. 
For a more  scientific overview of plants watch this PowerPoint:  
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