unit 2

Multicellular organisms usually contain differentiated cells, adapted for specific functions. Tissues consist of groups of similar cells. Organs contain different tissues, working together to carry out particular functions. Organ systems contain different organs. The different organ systems work together in an organism.

Tissues During the development of a multicellular organism, cells differentiate so that they can carry out different functions. Differentiation is the process by which a cell becomes a specialised type of cell. A tissue is a group of specialised cells that have a similar structure and function. The table shows some examples of tissues and their functions. Types of tissues and their functions Tissue FunctionMuscular tissue                   Contracts, bringing about movementGlandular tissue                   Produces substances such as enzymes and hormonesEpithelial tissue                   Covers some parts of the body  

Organs Organs are made of tissues. A particular organ may contain several different tissues. For example, the stomach is an organ that contains: Muscular tissue - to churn the food and other contents of the stomach Glandular tissue - to produce digestive juices including acid and enzymes Epithelial tissue - to cover the inner and outer surfaces of the stomach The stomach is one of the organs that form the digestive system. The stomach contains various tissues, and each tissue is made of a particular type of cell. In order of increasing size and complexity: cells → tissues → organ (the stomach) → organ system (the digestive system)

The digestive system Organ systems are groups of organs that carry out a particular function. The human body has several organ systems, including: The nervous system The respiratory system The reproductive system The digestive system The digestive system is an example of an organ system in which humans and other mammals exchange substances with the environment. The table shows its main tissues and organs, and their functions: Part(s) FunctionPancreas and salivary glands Produce digestive juicesStomach Digests foodLiver Produces bileSmall intestine Digest and absorb soluble foodLarge intestine Absorbs water from undigested food, producing faeces

Organs in animals intro

Tissues

Organs

The digestive system