Biology Foundation: Living Organisms, Classification & Cells

The Nature and Variety of Living Organisms

Comprehensive Overview for IGCSE Biology Curriculum

---

Photo by National Cancer Institute on Unsplash

• Characteristics of Living Organisms
• Biological Classification & Diversity
• Cell Structure & Organization
• Levels of Organization
• Viruses and Non-living Entities

---

Photo by National Institute of Allergy and Infectious Diseases on Unsplash

• Movement: Ability to move position or internal parts.
• Respiration: Chemical reactions to release energy from nutrients.
• Sensitivity: Ability to sense and respond to stimuli.
• Growth: Permanent increase in size/cell number.
• Reproduction: Ability to produce offspring.
• Excretion: Removal of toxic/waste metabolic materials.
• Nutrition: Requirement for materials for energy and growth.

---

Photo by National Institute of Allergy and Infectious Diseases on Unsplash

1

Classification & Diversity

The Linnaean Hierarchy and Modern Systematics

• Linnaean taxonomy classifies organisms into ranked groups based on shared characteristics.
• Principal ranks: Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species.
• Binomial nomenclature: Modern naming system (genus species).
• Evolutionary classification: Reflects relationships between living and extinct species.
• Domains: Bacteria, Archaea, Eukarya (includes Animalia, Plantae, Fungi, Protista).

---

Photo by Sangharsh Lohakare on Unsplash

2

Cell Structure & Organization

Fundamental units of life: prokaryotes vs. eukaryotes

---

Photo by Tayfun Dikmen on Unsplash

Prokaryotes

• Lack nucleus and membrane-bound organelles.
• Small size.
• Example: Bacteria.
• DNA is free in cytoplasm.

Eukaryotes

• Have nucleus and specialized organelles.
• Generally larger and more complex.
• Examples: Animal cells, Plant cells, Fungi.
• DNA contained within a nucleus.

---

Photo by National Cancer Institute on Unsplash

• Hierarchy: Organelles -> Cells -> Tissues -> Organs -> Organ Systems -> Organisms.
• Complexity increases with multicellularity.
• Viruses: Not classified as living organisms (cannot reproduce independently, require host cells).
• Homeostasis: Internal environment maintained despite external changes.

---

Photo by Tayfun Dikmen on Unsplash

Conclusion: The Study of Life

Living organisms are defined by specific biological processes and systematic classification. Understanding the unity and diversity of life is the foundation for further study in all biological sciences.

---

Photo by Marita Kavelashvili on Unsplash