Additional Biology (Unit 2)-Cell Organisation

Specialised cells carry out particular functions.

The process at which cells become specialised for a particular job is called differentiation.

Differentiation occurs during the development of multicellular organism.

These specialised cells form tissues, which form organs, which form orgarn systems.

Large multicellular organisms(e.g. squirrels) have different systems inside them for exchanging and transporting materials.

A tissue is a group of similar cells that work together to carry out a particular function.It can include more than one type of cell.

In humans/mammals examples of tissues include:

• Muscular tissue- contracts(shortens) to move whatever it's attached to.
• Glandular tissue- which makes and secretes chemicals like enzymes and hormones.
• Epithelial tissue- which covers some parts of  the body e.g. the inside of the gut.

An organ is a group of different tissues that work together to perform a certain function.

For example the stomach is made of these tissues:

• Muscular tissue- moves the stomach to churn up the food.
• Glandular tissue- makes digestive juices to digest the food.
• Epithelial tissue- covers the outside and inside of the stomach.

An organ system is a group of organs working together to perform a particular function.

An example could be the digestive system which breaks down food and is made up of organs:

• Glands (e.g. the pancreas and salivary glands) which produce digestive juices.
• The stomach and small intestine, which digest food.
• The liver, which produces bile.
• The small intestine, which absorbs soluble food molecules.
• The large intestine, which absorbs water from undigested food, leaving faeces.

The digestive system exchanges materials with the environment by taking in nutrients and releasing substances such as bile.