Edexcel IAL Biology Notes for 2025 - 2026 Exams

Hosni Showike • 19 September 2024

Topic 1: Biological Molecules

ial biology notes biological molecules

1.1 Dipole Nature

The water molecule has unique properties, making it play essential roles in all organisms.

The shared electrons in the water molecule are quite closer to the oxygen atom than the two hydrogen atoms. As a result, the oxygen becomes slightly (partially) negative, while the two hydrogens become slightly positive. These opposite partial charges on each side of the water molecule turn the water molecule into a dipole. Dipole: refers to the separation of opposite charges within the water molecule.

1.2 Hydrogen Bonds

Water molecules are attracted to each other due to their dipolar nature. The partially negative (δ-) oxygen atom in one water molecule is attracted to a partially positive (δ+) hydrogen atom in a neighbouring water molecule. These attractions are known as hydrogen bonds. Hydrogen bonds are weak attraction forces; however, they do affect the properties of different molecules. Other than water molecules, hydrogen bonds do also exist in DNA, proteins, starch and many other molecules. Hydrogen bonds must include hydrogen atoms (δ+) attracted to either oxygen or nitrogen atoms in another molecule. The reason why hydrogen bonds only exist between these specific atoms is that both nitrogen and oxygen atoms tend to be slightly negative (δ-), and they get attracted very well to the slightly positive hydrogen atoms.

1.3 Importance Of Water In Transport

The dipolar nature of water and its ability to form hydrogen bonds explain all the unique properties of water:

a. Water is the transport medium in all organisms (such as blood), and this can be attributed to these properties:

  1. Water is a good solvent for charged (like salts) and polar molecules (like glucose).
  2. Water is a liquid over a large temperature range which can be explained by two characteristics:
  • i. Water has a high latent heat of evaporation: a large amount of heat energy is needed for water molecules to turn from the liquid state to the gas state.
  • ii. Water has a high specific heat capacity: lots of heat energy is needed to raise the temperature of the water. This means that the temperature in water remains relatively stable despite the significant changes in the temperature of the surrounding environment.

Water assists the mass flow of fluids: mass flow is the movement of fluids in one direction down a pressure gradient (from high to low pressure). The circulation of blood is a good example of mass flow. Two essential properties of water help mass flow happen:

  • i. Water is cohesive: water molecules stick to each other due to hydrogen bonds.
  • ii. Water is adhesive: hydrogen bonds allow water to get attracted to the vessels where it is flowing through.

1.4 Solubility In Water

Polar molecules can be either fully charged like ionic compounds (salts) or partially charged like sugars.

Polar molecules dissolve well in water because water surrounds these molecules and forms bonds with them. Non-polar molecules are usually hydrocarbons (made up of carbon and hydrogen only). They are described as being hydrophobic. Hydrocarbons do not dissolve in water because they cannot form bonds with it.

Size also plays an essential role in solubility; smaller molecules are more likely to dissolve than larger ones.

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