Tissues and Organs

Science Revision

Organs in Animals

  • Organs are made of tissues. A particular organ may contain several different tissues. For example, the stomach is an organ that contains:
  1. Muscular tissue - to churn the food and other contents of the stomach
  2. Glandular tissue - to produce digestive juices including acid and enzymes
  3. 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)

Organ systems are groups of organs that carry out a particular function. The human body has several organ systems, including:

  1. The nervous system
  2. The respiratory system
  3. The reproductive system
  4. The digestive system

The digestive system is an example of an organ system in which humans and other mammals exchange substances with the environment.

Tissues in Animals

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.

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.

Tissues in Plants

Plants are multicellular organisms, just like animals. They also usually contain differentiated cells, tissues and organs.


The table shows some examples of plant tissues and their functions.

Epidermal tissue- Covers the plant

Mesophyll- Carries out photosynthesis

Xylem and phloem- Transport of substances around the plant

Organs in Plants


Examples of plant organs include:

  1. Roots
  2. Stems
  3. Leaves

Leaves are adapted to absorbing sunlight for photosynthesis.

Chlorophyll- To absorb sunlight

Large surface area- To absorb more light

Stomata- To let carbon dioxide diffuse into the leaf

Thin Short distance for carbon dioxide to diffuse into leaf cells

Network of veins- To support the leaf and transport water and carbohydrates

Tissues and Organs

Animal cells and plant cells can form tissues, like muscle tissue. A living tissue is made from a group of cells with a similar structure and function, which all work together to do a particular job. Here are some examples of tissues:

  1. Muscle
  2. The lining of the intestine
  3. The lining of the lungs
  4. Phloem (tubes that carry dissolved sugar around a plant)
  5. Root hair tissue (for plants to take up water and minerals from the soil)

An organ is made from a group of different tissues, which all work together to do a particular job. Here are some examples of organs:

  • Heart
  • Lung
  • Stomach
  • Brain
  • Leaf
  • Root

Organ systems

An organ system is made from a group of different organs, which all work together to do a particular job. Here are some examples of organ systems:

  • Circulatory system
  • Respiratory system
  • Digestive system
  • Nervous system
  • Reproductive system
  • Leaf canopy