2.4 - Levels of Organisation in Multicellular Organisms

Different tissues combine to form an organ. Organs perform specific functions through the combined action of their tissues. Different organs then work together to carry out a specific function as an organ system. All organ systems are coordinated and work together as one complete organism.

$\text{Cell}\to \text{Tissue}\to \text{Organ}\to \text{System}\to \text{Multicellular organism}$

The Heart as an Organ

• The heart contains epithelial tissue, cardiac muscle tissue, connective tissue and nerve tissue.
• Epithelial tissue fills spaces in the heart.
• Cardiac muscle tissue pumps blood to the rest of the body.
• Connective tissue such as blood connects the systems in the organ.
• Nerve tissue regulates the rhythm of the heartbeat.

Organ Systems in Humans

• Respiratory system
  • Components: Trachea, nose, lungs and diaphragm.
  • Main function: Exchanges oxygen and carbon dioxide between the body and the external environment.
• Digestive system
  • Components: Mouth, oesophagus, stomach, liver, pancreas, small intestine and large intestine.
  • Main function: Digests food into a simpler form for easy absorption.
• Blood circulatory system
  • Components: Heart, artery, vein and blood capillary.
  • Main function: Transports nutrients, respiratory gases and waste products.
• Lymphatic system
  • Components: Spleen, lymph nodes and lymph vessels.
  • Main function: Maintains the balance of bodily fluids and prevents infectious diseases.
• Nervous system
  • Components: Brain, spinal cord and peripheral nerves.
  • Main function: Detects and sends information in the body and coordinates body activities.
• Integumentary system
  • Component: Skin.
  • Main function: Protects the body from physical injury, infection and dehydration.
• Endocrine system
  • Components: Endocrine glands that secrete hormones.
  • Main function: Coordinates body activities with the nervous system.
• Skeletal system
  • Components: Bone, cartilage, ligament and tendon.
  • Main function: Supports the body, protects internal organs and provides a base for muscle adhesion.
• Muscular system
  • Components: Skeletal muscles, smooth muscles and cardiac muscles.
  • Main function: Contracts and relaxes to produce movement in different parts of the body.
• Urinary system
  • Components: Kidney, ureter, urethra and bladder.
  • Main function: Eliminates waste products such as urea and uric acid from the body.
• Male reproductive system
  • Components: Testes, prostate gland and penis.
  • Main function: Produces sperm and male sex hormones.
• Female reproductive system
  • Components: Ovary, uterus, Fallopian tube, vagina and cervix.
  • Main function: Produces ovum and female sex hormones.

Systems in Plants

Shoot System

• Consists of stems, leaves, shoots, flowers and fruits.
• Stems and twigs support leaves vertically to allow maximum absorption of sunlight during photosynthesis.
• Flowers are involved in pollination.

Root System

• Consists of all roots in a plant.
• Absorbs water and mineral salts and provides support for the plant.