Biology Chapter I: Living Organisms and Cells

Chapter I: The Living Organism and the Cell

• This chapter covers living organisms and the fundamental unit of life, the cell.
• Living organisms possess the ability to acquire energy from organic matter (e.g., glucose, galactose). Energy production occurs via fermentation (anaerobic) or respiration (aerobic).
• Living organisms reproduce, grow and differentiate.
• They possess genetic material encoding enzymatic and non-enzymatic elements crucial for vital functions.
• The fundamental unit of life is the cell. Cells can be single-celled (unicellular) or multi-celled (multicellular).
• Living organisms perform catabolism (degradation of biomolecules) and anabolism (synthesis of biomolecules).

Kingdoms of the Living Things

• Organisms are classified into five kingdoms: Monera, Protista, Plantae, Fungi, and Animalia.
• Monera are prokaryotic and unicellular.
• Protista are eukaryotic and unicellular or multicellular. They can have cell walls.
• Plantae are eukaryotic and multicellular, with cell walls.
• Fungi are eukaryotic and multicellular, with cell walls.
• Animalia are eukaryotic and multicellular, without cell walls.

I: Prokaryotic Cell

• Prokaryotes are the most primitive life forms, simple, single-celled organisms.
• Prokaryotes include bacteria and archaeabacteria.
• They can be free-living, photosynthetic, parasitic (living inside other organisms) or saprophytic (feeding on dead/decaying matter).
• Prokaryotes exist in various environments - land, water bodies, atmosphere, hydrothermal vents and even inside living organisms.

Prokaryotic Cell Structure

• Essential elements:

  • Cell wall: External covering, protecting the bacterial cell and giving it shape. Gram-positive bacteria have thick peptidoglycan, Gram-negative have thin peptidoglycan.
  • Plasma membrane: Encloses the cytoplasm, regulates substance flow.
  • Cytoplasm: Gel-like substance containing water, enzymes, salts, cell components and organic molecules.
  • Nucleoid/nuclear area: Region holding the prokaryote's single DNA molecule.
  • Ribosomes: Structures responsible for protein production.

• Optional elements:

  • Plasmid: Small, circular DNA fragment.
  • Bacterial capsule: Protective shield.
  • Flagellum: Motility organelle.
  • Pili: Hair-like projections.
  • Chromatophores: Membrane systems (photosynthetic bacteria).
  • Gas vacuoles: Help provide buoyancy (aquatic bacteria).

Prokaryotic Reproduction

• Prokaryotes reproduce asexually mainly by binary fission.

II: Eukaryotic Cell

• Eukaryotes have a true nucleus and membrane-bound organelles.
• Eukaryotes include single and multi-celled organisms (plants, animals, fungi, protists)
• Eukaryotic cells are generally larger (10-100 µm) than prokaryotic cells.
• Possess well developed endomembrane system compared to prokaryotic cells.
• Contains organelles that perform specialized physiological functions for diverse metabolic reactions.

Eukaryotic Cell Structure

• Nucleus: Contains genetic material, bounded by a double membrane called the nuclear envelope
• Plasma membrane: Similar structure to in prokaryotes.
• Cytoplasm: Contents within the plasma membrane excluding the nucleus.
• Endoplasmic reticulum (ER): A membrane network. Rough ER has ribosomes, smooth ER lacks them.
• Golgi apparatus: Stacked membrane sacs, involved in modifying and packaging substances.
• Mitochondria: Sites for cellular respiration (ATP production).
• Cytoskeleton: Network of protein filaments, supporting structure and aiding movement.
• Peroxisomes: Contain enzymes that break down hydrogen peroxide.
• Lysosomes: Contain hydrolase enzymes for breaking down waste.

III: Animal Eukaryotic Cell

• Centrosoma: A organelle near the nucleus, where microtubules are formed/made.

IIII: Plant Eukaryotic Cell

• Cell wall: Surrounds the plasma membrane; composed of cellulose, hemicellulose, pectin, lignin.
• Vacuole: Membrane-bound compartment storing water and various molecules.
• Plastids: Organelles like chloroplasts (photosynthesis), found in plants and algae.
• Plasmodesmata: Cytoplasmic bridges connecting plant cells, enabling cell communication.

III: Acaryotes (Viruses)

• Viruses are small, infectious agents that need a host cell to replicate.
• Viruses have either DNA or RNA as genetic material.
• Viruses have three main components:
  • Nucleic acid: DNA or RNA.
  • Capsid: Protein coat protecting the nucleic acid.
  • Envelope (optional): Lipid layer acquired from the host cell. Some viruses have envelopes, some don't.