IGCSE Biology Notes for 2026 Exams

Hosni Showike • 1 November 2024

Diffusion, Osmosis and Active Transport

1. Understanding Diffusion

Diffusion is the net movement of particles from a region of higher concentration to a region of lower concentration. This process occurs due to the kinetic energy of particles, causing them to move randomly. Four factors affect the diffusion rate: surface area, distance, concentration gradient, and temperature.

2. Factors Affecting Diffusion

Surface Area: Structures like alveoli and villi have large surface areas to facilitate faster diffusion.

Short Distance: Thin structures, such as alveolar walls, speed up diffusion.

Concentration Gradient: A steeper gradient increases diffusion speed.

Temperature: Higher temperatures enhance particle movement, accelerating diffusion.


3. Exploring Osmosis

Osmosis is the movement of water molecules through a semipermeable membrane from higher to lower water potential. Unlike diffusion, osmosis specifically involves water and requires a semipermeable membrane.

4. Osmosis in Action

Water potential influences osmosis, with water moving from areas of high to low potential. The cell membrane's selective permeability allows only small particles like water to pass through, while larger molecules like glucose cannot.

5. Osmosis in Plant vs. Animal Cells

Plant cells have a rigid cell wall and large vacuole, affecting osmosis differently than in animal cells. The cell wall prevents dramatic shape changes, while the vacuole's membrane facilitates osmosis.

6. Effects of Osmosis on Cells

In dilute solutions, animal cells may burst due to excess water intake, while plant cells become turgid. In concentrated solutions, animal cells shrink (crenation), and plant cells lose turgor pressure, becoming flaccid.

7. The Role of Turgor Pressure

Turgor pressure, exerted by the vacuole on the cell wall, is crucial for plant rigidity. It helps plants remain upright and prevents wilting. Loss of turgor pressure leads to wilting and plasmolysis in plant cells.

8. Active Transport Explained

Active transport moves particles from lower to higher concentration areas using energy from respiration. Carrier proteins in the cell membrane facilitate this process by changing shape to transport particles.

9. Carrier Proteins and Energy

Carrier proteins are essential for active transport, using energy to move particles across membranes. They return to their original shape after transporting molecules, highlighting the dynamic nature of cellular processes.


Try a free Class

IGCSE and IAL Guide for 2025 - 2026 Exams

Teenage student solving a chemistry multiple-choice exam at a clean desk with periodic table
by Hosni Showike 27 May 2026
Score 36+ on IGCSE Chemistry Paper 2 with a proven 4-stage past paper method. Includes diagnostic test, error logging, and timed mock strategy from an expert teacher.
A focused student in a dark blue sweater sits at a rustic wooden desk, circling MCQs on paper
by Hosni Showike 22 May 2026
Master IGCSE Biology and Chemistry Paper 2 with 10 proven MCQ techniques. Process of elimination, command lines, extreme words, and the examiner mindset explained.
Edexcel IAL Biology Unit 5 exam prediction thumbnail with exam paper and teacher portrait.
by Hosni Showike 13 May 2026
Claim every free mark on Edexcel IAL Biology Unit 5 WBI15. Your final-week strategy for the scientific article, practicals, and definitions in June 2026.
Editorial-style infographic showing IGCSE Chemistry 2026 grade boundaries with laboratory glassware,
by Hosni Showike 12 May 2026
Six sessions of CIE IGCSE Chemistry grade boundary data analysed for Papers 2, 4 and 6. Understand what score you need for each grade in the June 2026 exam.
Editorial-style infographic showing IGCSE Biology 2026 grade boundaries, exam paper predictions
by Hosni Showike 12 May 2026
Full breakdown of IGCSE Biology grade thresholds for Cambridge 2026. What score gets you an A*, A, or B — and how to use boundary data to target your revision.
IGCSE Biology Paper 6 2026 exam guide cover image with lab equipment, graphs, investigation sheets,
9 May 2026
Ten practical tips to improve your IGCSE Biology Paper 6 score in June 2026. Covers experimental design, data analysis, graph technique, and common mark losses.
Students sitting IGCSE exam in a school hall with invigilators.
by Hosni Showike 2 May 2026
A clear guide for IGCSE and A-Level students on how Cambridge handles exam leaks, protects grade integrity, and what students should do if a paper is compromised.
IAL Chemistry revision with teacher portrait and text β€œThese tips drastically change your grade
by Hosni Showike 17 April 2026
Ten exam-focused IAL Chemistry revision tips for Pearson Units 2 and 3. Covers high-yield topics, past paper strategy, and mark scheme technique for June 2026.
High-yield IGCSE Biology topics study guide cover (CIE 2026)
by Hosni Showike 14 April 2026
Data-driven guide to the highest-yield IGCSE Biology topics for CIE 2026. Based on past paper frequency analysis across multiple exam sessions — revised for June.
Pearson Edexcel enhanced grading vs contingency graphic for 2026 exams
by Hosni Showike 9 April 2026
For students in affected countries such as Kuwait, UAE, Bahrain, and Lebanon, the 2026 exam session includes special arrangements confirmed by Pearson . These changes introduce two official grading routes: Enhanced Grading and International Contingency Grading (ICG) . Understanding these is essential because your final grade — and your revision strategy — depends on which route applies to you. Official Pearson Guidance for Affected Countries According to Pearson , when exams cannot proceed as normal in affected regions: Students may receive grades using existing unit results (Enhanced Grading) Or through school-submitted evidence (Contingency Grading) You can read the official policy here This confirms that grading remains structured, evidence-based, and regulated — not estimated or random. 🟣 Enhanced Grading (No Exam Required) Enhanced grading is the simplest pathway , but only available if you meet specific conditions. No exams required Based entirely on previous unit results Final grade awarded directly by the exam board To qualify: AS students must have already completed Unit 1 A Level students must have already completed Unit 4 If you meet these requirements and choose to cash-in , your grade can be calculated without further exams. πŸ‘‰ In simple terms: If you have already demonstrated your level, Pearson may use that performance to award your final grade. πŸ”΅ International Contingency Grading (ICG) Contingency grading is used when enhanced grading is not possible . Schools submit evidence of student performance This includes mock exams, past papers, and controlled assessments Pearson examiners review this evidence to award final grades This applies when: You are retaking units You haven’t completed required units (Unit 1 or Unit 4) You are entering multiple units together without prior results πŸ‘‰ This is NOT predicted grades — it is evidence-based grading under exam conditions . Key Scenarios You Must Understand AS Students Completed Unit 1 + taking Units 2 & 3 → Enhanced Grading (if cash-in) Retaking Unit 1 → Contingency Grading A Level Students Completed AS (Units 1–3) + Unit 4 + taking Units 5 & 6 → Enhanced Grading (full A Level) Completed AS but not cashing in → Contingency Grading Mixed or Full Entries Taking all 6 units together → Contingency Grading Taking 4–5 units only → Contingency Grading πŸ‘‰ Core rule from Pearson: If suitable previous results exist → Enhanced Grading If not → Contingency Grading IGCSE Modular Students For modular IGCSE pathways: Taking both units in the same session → Contingency Grading Taking Unit 2 after Unit 1 → Final grade may be awarded directly Taking only Unit 1 → Exam postponed to a later session (e.g. October) Private Candidates (Important Clarification) According to the British Council : Private candidates will still sit exams as usual No enhanced or contingency grading applies Standard exam route remains in place πŸ‘‰ Exams are still considered the most reliable assessment method for private candidates. How This Affects Your Revision Strategy This update is not just administrative — it directly impacts how you should study. If you are under Contingency Grading: Your mock exams are critical Every assessment becomes evidence You must treat all school tests like real exams If you qualify for Enhanced Grading: Your past results determine your final grade Focus on securing strong outcomes in completed units Final Advice for Students in Affected Countries The biggest mistake right now is not knowing which pathway applies to you . Before continuing youar revision: Confirm your completed units Check if you meet Enhanced Grading conditions Speak to your school about your assessment route Students who understand this early can adjust their strategy, focus on the right assessments, and maximise their final grade — even under changing exam conditions.
Show More