Biological Hierarchy
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For multicellular organisms to function effectively and live successfully in order to reproduce, there needs to be a high level of organisation in the arrangement of their specialised cells.
\scriptsize \text{atoms} \rightarrow \text{molecules} \rightarrow \text{organelles} \rightarrow \text{cells} \rightarrow \text{tissues} \rightarrow \text{organ systems} \rightarrow \text{organisms}| Level of Organisation | Explanation | Example |
|---|---|---|
| Atomic Level | Atoms are the smallest unit of an element that still maintains the property of that element | Carbon, Hydrogen, Oxygen |
| Molecular Level | Atoms form to combine into molecules which can have entirely different properties than the atoms they contain | Water, DNA, Carbohydrates |
| Cellular Level | Cells are the smallest unit of life; they are enclosed by membrane or cell wall and often perform specific functions | Muscle cell, Skin cell, Neuron |
| Tissue Level | Groups of cells with similar functions | Muscle, Connective |
| Organ Level | Organs are 2 types of tissue that work together to complete a task | Heart, Liver, Stomach |
| Organ System Level | Group of organs that carry out a more generalised set of functions | Digestive system, Circulatory system |
| Organismal Level | Several organ systems which function together | Human |
Human Body Systems
| Body System | Main Structural Features | Function |
|---|---|---|
| Integumentary System | – Hair – Skin – Nails | – Act as a barrier – Retains body fluid – Regulates body temp |
| Skeletal System | – Bones – Tendons – Ligaments – Cartilage | – Movement – Calcium storage – Support – Organ protection |
| Lymphatic System | – Lymph nodes – Spleen – Thymus | – Removal of excess fluids – Absorption of fatty acids – Protection of immune cells |
| Respiratory System | – Airways – Lungs – Oesophagus | – Allows the intake and expel of oxygen and carbon dioxide |
| Muscular System | – Muscle – Muscle fibre – Blood vessels nerves | – Generation of force for movement – Speech – Eating |
| Nervous System | – Spinal cord – Brain – Nerves | – Allows bodily communication |
| Digestive System | – Stomach – Liver – Gallbladder – Large intestine – Small intestine | – Processes food for use in the body – Removes waste from undigested food |
| Urinary System | – Kidneys – Urinary bladder | – Controls water balance in the body – Removes waste from the blood and excretes them |
| Endocrine System | – Pituitary gland – Thyroid gland – Pancreas – Adrenaline gland – Testes → male – Ovaries → female | – Secretes hormones – Regulates body temp |
| Circulatory System | – Heart – Blood vessels | – Delivers oxygen and nutrients to tissues – Equalises body temp |
| Male Reproductive System | – Prostate – Epididymis – Testes | – Produces sex hormones – Delivers gametes to the female |
| Female Reproductive System | – Mammary glands – Ovaries – Uterus | – Produces sex hormones and gametes – Supports embryo and gametes until birth |