Plants, like animals and many microbes, respire and utilize energy to grow and reproduce. Cell walls provide structural support for the plant and also provide fibers and building materials for humans, insects, birds and many other organisms. Plants exhibit diversity in size and shape ranging from single cells to gigantic trees. Plants are a primary source of fiber, medicines and countless other important products in everyday use. Plants, like animals, are subject to injury and death due to infectious diseases caused by microorganisms.
Plants have unique ways to defend themselves against pests and diseases.
Water is the major molecule present in plant cells and organs. In addition to an essential role in plant structure, development and growth, water can be important for the internal circulation of organic molecules and salts. Plant growth and development is under the control of hormones and can be affected by external signals such as light, gravity, touch or environmental stresses. Plants live and adapt to a wide variety of environments. Plants provide a wide variety of environments for birds, beneficial insects and other wildlife in ecosystems.