The structure of plants and animals follows a hierarchy of organs namely tissues and cells. Tissue is a group of cells with a common function, structure or both. An organ consists of several types of tissues that together carry out particular functions. Tissue is a collection of interconnected cells that perform a similar function within an organism. The function of tissues in plants include protective covering, transport of materials and nutrients, storage, photosynthesis and support. While tissues in animals provide protection, connectivity, movement and communication.

There are four basic types of tissues in the body of all animals including the human body namely epithelium, connective tissue, muscle tisue and nervous tissue. Epithelium is composed of layers of cells that cover organ surfaces such as surface of the skin and inner lining of digestive tract: the tissues that serve for protection, secretion, and absorption. Bone and blood are examples of connective tissues, which hold everything together.

Muscle tissues are separated into three distinct categories: visceral muscle which is found in the inner linings of organs; skeletal muscle which is found attached to bone in order for mobility to take place; and cardiac muscle, which is found in the heart. Nervous tissues are found in brain, spinal cord and peripheral nervous system.

Tissues in plants include vascular tissues with xylem and phloem that transport fluid and nutrients internally. The xylem is mainly responsible for the transportation of water and mineral nutrients throughout the plant. Xylem sap consists mainly of water and inorganic ions, although it can contain a number of organic chemicals as well.

hloem is the living tissue composed of still–living cells that transport sap to carry organic nutrients particularly sucrose, a sugar, to all parts of the plant where needed. The sap is a water–based solution, but rich in sugars made by the photosynthetic areas. These sugars are transported to non–photosynthetic parts of the plant, such as the roots or into storage structures, such as tubers. Ground tissue in plants manufactures nutrients by photosynthesis and stores reserve nutrients.