2.1 describe the levels of organisation within organisms: organelles, cells, tissues, organs and systems.

In order from smallest to largest....

Organelles

• Have a specific function inside the cell
• Made up of small molecules
• Example: mitochondria, ribosomes, etc. 

Cells

• The basis of all living things
• Said to be a functional unit
• Made up of organelles
• Examples: red blood cells, white blood cells, etc.

Tissues

• Made up of many cells
• Cells serve a common function
• Examples: muscle tissue, neural tissue

Organs

• Made up of tissues 
• Form a large functioning unit
• Examples: liver, heart, etc.

Organ systems

• Made up of many organs
• Serve a common or related function in the body
• Many organs working together
• Examples: respiratory system, skeletal system, etc.

Figure 1