Biology Notes: Systems & Biological Hierarchy

What Is a System?

A system is a group of interacting parts that work together to perform a function.

In biology, systems exist at many levels, from tiny molecules to the entire biosphere.

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Biological Hierarchy

Atom → Molecule → Organelle → Cell → Tissue → Organ → Organ System → Organism → Population → Community → Ecosystem → Biome → Biosphere

 

System From Small to Large

Level | Description | Example

Atom | Basic unit of an element | Carbon Atom

Molecule | Atoms bonded together | Water Molecule

Organelle | Structure inside a cell | Mitochondrion

Cell | Basic unit of life | Muscle cell

Tissue | Similar cells working together | Muscle tissue

Organ | Tissues working together | Heart

Organ System | Organs working together | Circulatory system

Organism | Individual living thing | Human

Population | Same species in an area | Deer

Community | Different populations interacting | Forest organisms

Ecosystem | Community + nonliving environment | Pond

Biome | Large region with similar climate/ecosystems | Desert

Biosphere | All areas of Earth where life exists | Earth

 

Systems Within Systems

Each level is connected to the levels around it.

Cells → Tissues → Organs → Organ Systems → Organisms

For example:

Muscle cells
↓
Muscle tissue
↓
Heart
↓
Circulatory system
↓
Human

 

Emergent Properties

An emergent property is a characteristic that results when parts of a system interact.

The whole system can do things that individual parts cannot do alone.

Example: Individual heart cells cannot circulate blood throughout the body, but the heart and circulatory system can.

 

Systems Are Interconnected

Changes in one part of a biological system can affect other parts.

Example:

Respiratory system
→ brings in oxygen

↓

Circulatory system
→ transports oxygen

↓

Cells
→ use oxygen for cellular respiration

↓

Mitochondria
→ help produce ATP (Energy)

 

Key Ideas to Remember

• Systems = interacting parts working together.

• Biology is organized into a hierarchy.

• Each level contains interacting parts from lower levels.

• Emergent properties result from interactions between parts.

• Biological systems are interconnected.

• A change in one part of a system can affect other parts.

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Easy Way to Remember:

Small parts → interact → create larger systems → produce new functions