Cell biology — Eduqas GCSE Combined Science

Cell biology is the study of the structure and function of cells, the basic units of life. In WJEC GCSE Combined Science, you will explore the differences between animal and plant cells, the roles of key organelles, and how cells work together to form tissues and organs. Understanding cell biology is essential because it forms the foundation for topics like genetics, respiration, and photosynthesis, which you will encounter later in the course.

This topic covers the principles of microscopy, including how to calculate magnification and the differences between light and electron microscopes. You will also learn about cell division (mitosis) and the importance of stem cells in medicine. Cell biology is not just about memorising diagrams; it's about understanding how cells carry out life processes such as diffusion, osmosis, and active transport to move substances in and out of cells.

Mastering cell biology will help you explain how organisms grow, repair damaged tissues, and maintain internal balance. It also links to practical skills, such as preparing microscope slides and interpreting biological drawings. By the end of this topic, you should be able to compare different cell types, describe how substances move across membranes, and explain the role of cell division in growth and development.

• →Animal and plant cells: Know the structure and function of the nucleus, cytoplasm, cell membrane, mitochondria, ribosomes, and (for plant cells) cell wall, chloroplasts, and permanent vacuole.
• →Microscopy: Understand how to use a light microscope, calculate magnification (magnification = image size ÷ actual size), and convert between units (mm, μm, nm).
• →Cell division: Describe the stages of mitosis (prophase, metaphase, anaphase, telophase) and its role in growth, repair, and asexual reproduction.
• →Diffusion, osmosis, and active transport: Explain how substances move across cell membranes, including factors that affect rate (e.g., concentration gradient, temperature, surface area).
• →Stem cells: Define stem cells as undifferentiated cells that can divide to produce specialised cells, and give examples of their use in medicine (e.g., treating leukaemia).

• Differences between prokaryotic and eukaryotic cells
• Function of sub-cellular structures (nucleus, mitochondria, chloroplasts, etc.)
• The cell cycle and stages of mitosis
• Role of stem cells in differentiation and medicine
• Lock and key hypothesis for enzyme action
• Factors affecting enzyme activity (pH, temperature, denaturation)
• Word equations for aerobic and anaerobic respiration
• Comparison of aerobic and anaerobic respiration efficiency

• 💡Always use the term 'denatured' when describing the effect of high temperature on enzymes
• 💡Ensure word equations are written correctly without chemical symbols unless specified
• 💡When drawing cells, ensure labels are clear and lines touch the structure being identified
• 💡Practice calculating rates of reaction from graphs by finding the gradient
• 💡Be prepared to discuss the ethical implications of stem cell research
• 💡When drawing cells, always use a sharp pencil and label with straight lines. Include a title and magnification. Examiners look for clear, accurate diagrams.
• 💡For calculation questions, always show your working and include units. A common mistake is forgetting to convert units (e.g., mm to μm). Remember: 1 mm = 1000 μm.
• 💡When explaining diffusion or osmosis, mention the concentration gradient and whether energy is required. Active transport requires energy (ATP), but diffusion and osmosis do not.

• Confusing the function of mitochondria with chloroplasts
• Failing to mention that boiling denatures enzymes by changing their shape
• Incorrectly stating that anaerobic respiration in humans produces ethanol
• Confusing mitosis with meiosis in terms of chromosome number
• Misunderstanding the lock and key hypothesis as a physical lock rather than a specific active site shape
• Misconception: All cells have a cell wall. Correction: Only plant cells, algal cells, and bacterial cells have cell walls; animal cells do not.
• Misconception: Osmosis is the movement of any substance across a membrane. Correction: Osmosis is specifically the movement of water molecules from a dilute to a concentrated solution through a partially permeable membrane.
• Misconception: Mitosis produces genetically different cells. Correction: Mitosis produces two genetically identical daughter cells; meiosis produces genetically different cells for sexual reproduction.