📌Definition Table

Term	Definition
Eukaryote	A cell containing a true nucleus and membrane-bound organelles.
Organelle	A specialised structure within a cell with a specific function.
Cytoskeleton	A network of protein filaments providing structural support and movement.
Endoplasmic Reticulum (ER)	Network of membranes for protein and lipid synthesis (rough ER) or lipid metabolism (smooth ER).
Golgi Apparatus	Organelle that modifies, packages, and distributes proteins and lipids.
Mitochondrion	Site of aerobic respiration, producing ATP.

📌Introduction

Eukaryotic cells are larger and more complex than prokaryotic cells, found in animals, plants, fungi, and protists. They contain membrane-bound organelles that compartmentalise cellular functions, allowing greater efficiency and specialisation. Their internal complexity enables them to perform more advanced metabolic processes and support multicellular life.

📌 General Characteristics of Eukaryotes

• Possess a nucleus containing DNA wrapped around histones.
• Contain 80S ribosomes in the cytoplasm and 70S ribosomes in mitochondria and chloroplasts.
• Exhibit compartmentalisation — separation of functions into organelles.
• Larger cell size (10–100 μm) compared to prokaryotes.
• Have a complex cytoskeleton for movement, shape, and intracellular transport.
• Reproduce through mitosis (asexual) and meiosis (sexual).

🧠 Examiner Tip: Always include the presence of membrane-bound organelles when defining eukaryotic cells — many students miss this and lose marks.

📌 Nucleus and Genetic Control

• Enclosed by a double membrane (nuclear envelope) with pores for molecule exchange.
• Contains chromatin (DNA + proteins) and the nucleolus, where ribosomes are assembled.
• DNA is linear and associated with histones.
• Controls gene expression and coordinates cell activities.
• Nuclear pores allow mRNA and ribosomal subunits to exit to the cytoplasm.
• Replication and transcription occur inside the nucleus.

🌍 Real-World Connection: Knowledge of plant cell structure supports crop improvement strategies in agriculture.

📌 Endomembrane System

• Rough ER has ribosomes and synthesises proteins for secretion or membranes.
• Smooth ER synthesises lipids, detoxifies drugs, and stores calcium.
• Golgi apparatus modifies, sorts, and packages proteins and lipids into vesicles.
• Lysosomes contain hydrolytic enzymes for digesting macromolecules and old organelles.
• Secretory vesicles transport molecules to the plasma membrane for exocytosis.
• Endocytosis brings materials into the cell via vesicles.

🔍 TOK Perspective: The endosymbiotic theory shows how indirect molecular evidence can strongly support historical biological events.

📌 Specialisation: Plant vs Animal Cells

• Plant cells have a rigid cell wall, chloroplasts, and a large central vacuole.
• Animal cells have centrioles and more lysosomes.
• Plant vacuole maintains turgor pressure and stores materials.
• Cell wall provides structure and protection.
• Some plant cells have plasmodesmata for cell-to-cell communication.
• Animal cells often have specialised shapes for specific functions.

📝 Paper 2: Data Response Tip: When comparing plant and animal cells, use a table format for clarity and always include at least three similarities and three differences.