Cell structure and organisation — Eduqas A-Level Biology

Cell structure and organisation is a foundational topic in A-Level Biology, focusing on the detailed anatomy of eukaryotic and prokaryotic cells. You will explore the functions of organelles such as the nucleus, mitochondria, ribosomes, and chloroplasts, and understand how these structures work together to maintain life. This topic also introduces the concept of cell specialisation, where cells differentiate to perform specific roles, and the organisation of cells into tissues, organs, and systems. Mastery of this topic is essential for understanding more complex processes like respiration, photosynthesis, and protein synthesis.

In the WJEC A-Level specification, this topic is assessed through both multiple-choice questions and longer essay-style answers. You will need to recall specific details, such as the double membrane structure of mitochondria and the role of the nucleolus in ribosome production. Practical skills are also tested, including the use of microscopes to identify cell structures and the interpretation of electron micrographs. Understanding cell structure is not just about memorisation; it requires you to link structure to function, a key skill for higher-level biology.

This topic connects to many other areas of biology, including genetics (DNA in the nucleus), cell division (role of centrioles), and disease (how pathogens exploit host cells). By mastering cell structure, you build a mental map of the cell that will help you visualise biochemical pathways and physiological processes. It is also directly relevant to modern medicine, such as understanding how antibiotics target bacterial cell walls or how cancer cells differ from normal cells.

• →Eukaryotic cells have membrane-bound organelles (e.g., nucleus, mitochondria, ER) while prokaryotic cells lack a nucleus and have smaller ribosomes (70S).
• →The endomembrane system (rough ER, smooth ER, Golgi apparatus) works together to modify, package, and transport proteins and lipids.
• →Mitochondria and chloroplasts are semi-autonomous organelles with their own DNA and double membranes; they are sites of aerobic respiration and photosynthesis respectively.
• →Cell specialisation leads to differentiated cells (e.g., red blood cells, neurones) with unique adaptations for their functions.
• →Tissues are groups of similar cells performing a common function; organs are made of multiple tissues; organ systems coordinate to carry out complex processes.

• Structure and function of organelles: mitochondria, ER (rough/smooth), ribosomes, Golgi, lysosomes, centrioles, chloroplasts, vacuoles, nucleus, chromatin, nuclear envelope, nucleolus, plasmodesmata
• Structural differences between eukaryotic cells (animal/plant), prokaryotic cells, and viruses
• Levels of organisation: cells to tissues, tissues to organs, organs to organ systems
• Identification of epithelia, muscle, and connective tissue from prepared slides
• Interpretation of electron micrographs of prokaryotic and eukaryotic cells

• 💡Practice interpreting electron micrographs to identify organelles based on their specific ultrastructural features
• 💡Ensure you can clearly state the differences between prokaryotic and eukaryotic cell structures
• 💡Be prepared to link the structure of an organelle to its specific function within the cell
• 💡Use appropriate terminology when describing levels of organisation
• 💡When describing organelles, always link structure to function. For example, 'The inner mitochondrial membrane is folded into cristae to increase surface area for ATP production.' This shows deeper understanding.
• 💡In exam questions about cell specialisation, use specific examples (e.g., 'Red blood cells lack a nucleus to maximise space for haemoglobin, allowing efficient oxygen transport'). Avoid vague statements like 'cells are adapted for their job'.
• 💡For electron micrograph identification, learn key visual features: mitochondria have a double membrane with cristae, chloroplasts have thylakoid stacks (grana), and the nucleus has a double membrane with nuclear pores. Practice labelling diagrams.

• Confusing the functions of rough and smooth endoplasmic reticulum
• Failing to distinguish between the structure of prokaryotic and eukaryotic cells
• Inaccurate labelling of organelles in electron micrographs
• Misunderstanding the hierarchical relationship between tissues, organs, and systems
• Misconception: All cells have a cell wall. Correction: Only plant cells, bacteria, and fungi have cell walls; animal cells do not. Plant cell walls are made of cellulose, while bacterial cell walls contain peptidoglycan.
• Misconception: The nucleus is the only location of DNA. Correction: Mitochondria and chloroplasts also contain their own circular DNA, which is inherited maternally in animals.
• Misconception: Ribosomes are only found free in the cytoplasm. Correction: Ribosomes can also be bound to the rough endoplasmic reticulum (RER), where they synthesise proteins for secretion or membrane insertion.