Topic 2 – Cells and control — Edexcel GCSE Biology

Topic 2 – Cells and control in Edexcel GCSE Biology explores how cells divide, grow, and specialise, and how the body controls these processes. You'll learn about the cell cycle, mitosis, and the importance of stem cells in growth and repair. This topic also covers the nervous system, including the brain and the eye, and how hormones control key functions like the menstrual cycle and blood glucose levels. Understanding these mechanisms is essential for grasping how organisms develop, maintain themselves, and respond to their environment.

This topic builds on your knowledge of cell structure from Topic 1 and connects to later topics like genetics and health. For example, mistakes in cell division can lead to cancer, and understanding the nervous system helps explain reflexes and drug actions. Mastery of this topic is crucial for exam success, as it appears in both Paper 1 and Paper 2, and forms the basis for many applied questions about medical treatments and diseases.

By the end of this topic, you should be able to describe the stages of mitosis, explain how stem cells can be used in medicine, and outline the roles of the brain, eye, and hormones in coordination. You'll also need to interpret diagrams of the cell cycle and nervous pathways, and evaluate the ethical issues surrounding stem cell research. This topic is not just about memorising facts—it's about understanding how living systems are controlled and regulated.

• →Cell cycle and mitosis: The cell cycle consists of interphase (growth and DNA replication) and mitosis (division of the nucleus). Mitosis produces two genetically identical daughter cells for growth and repair.
• →Stem cells: Undifferentiated cells that can divide to produce more stem cells or differentiate into specialised cells. Embryonic stem cells are pluripotent (can become any cell type), while adult stem cells are multipotent (limited to certain types).
• →The nervous system: Includes the central nervous system (brain and spinal cord) and peripheral nerves. Neurones transmit electrical impulses; synapses use neurotransmitters to pass signals between neurones.
• →The brain and eye: The brain controls voluntary and involuntary actions; key areas include the cerebrum, cerebellum, and medulla. The eye focuses light onto the retina; accommodation and pupil reflex are key control mechanisms.
• →Hormonal control: Hormones are chemical messengers transported in the blood. Key examples include insulin and glucagon (blood glucose regulation), and FSH, LH, oestrogen, and progesterone (menstrual cycle).

• Definition of health as physical, mental and social well-being
• Distinction between communicable and non-communicable diseases
• Pathogens include viruses, bacteria, fungi and protists
• Mechanisms of pathogen spread and prevention
• Physical and chemical human body defences
• Specific immune system response (antigens, antibodies, memory lymphocytes)
• Antibiotics only treat bacterial infections
• Stages of medicine development (discovery, development, testing)
• Production and use of monoclonal antibodies
• Lifestyle factors affecting non-communicable diseases (BMI, alcohol, smoking)

• 💡Ensure you can distinguish between the lytic and lysogenic pathways of viruses
• 💡Be prepared to calculate cross-sectional areas of bacterial cultures using pi*r^2
• 💡Understand the ethical and practical implications of using monoclonal antibodies
• 💡Know the specific physical and chemical barriers of the human body
• 💡Be able to evaluate treatments for cardiovascular disease
• 💡When describing mitosis, use the correct order: prophase, metaphase, anaphase, telophase (PMAT). Mention that chromosomes condense, align at the equator, separate, and then the cell divides (cytokinesis).
• 💡For questions on the eye, always use the terms 'ciliary muscles' and 'suspensory ligaments' when explaining accommodation. Remember: for near objects, ciliary muscles contract, suspensory ligaments slacken, lens becomes more curved.
• 💡In hormonal control questions, be precise about which gland releases each hormone and the target organ. For example, the pituitary gland releases FSH and LH, which act on the ovaries.

• Confusing communicable and non-communicable diseases
• Assuming antibiotics can kill viruses
• Misunderstanding the role of memory lymphocytes in secondary immune response
• Incorrectly calculating BMI or waist:hip ratios
• Failing to describe aseptic techniques correctly in microbial culture investigations
• Misconception: Mitosis and the cell cycle are the same thing. Correction: The cell cycle includes interphase (where DNA replicates) and mitosis (where the nucleus divides). Mitosis is just one part of the cycle.
• Misconception: Stem cells can only be obtained from embryos. Correction: Adult stem cells are found in bone marrow, skin, and other tissues. They are multipotent and can differentiate into several cell types, but not all.
• Misconception: The pupil reflex is a voluntary action. Correction: The pupil reflex is an involuntary, automatic response controlled by the autonomic nervous system to regulate light entering the eye.