•

24 Dec 2025

•

3 pages

Comprehensive Biological Molecules A-Level Biology Revision Sheets

Niamh Cooke

@niamhcooke_yelp

Biological molecules are the building blocks of all living things,... Show more

1 / 3

# OCR Biology Revision Notes

# BIOLOGICAL MOLECULES

## Water

Water is a polar molecule due to an uneven
distribution of charge within the

Water and Inorganic Ions

Ever wondered why you need to drink water to survive? Water is a polar molecule with an unequal charge distribution - hydrogen atoms are slightly positive whilst oxygen is slightly negative. This simple property makes water absolutely essential for life.

Water acts as the perfect solvent for metabolic reactions and has a high specific heat capacity, which means it takes loads of energy to heat up. This is brilliant for your body because it prevents dangerous temperature swings. When you sweat, water's large latent heat creates a cooling effect as it evaporates.

The strong cohesion between water molecules enables plants to transport water up through their stems - imagine tiny water molecules holding hands in an unbreakable chain! Ice floats because it's less dense than liquid water, creating an insulating layer that protects aquatic life in winter.

Inorganic ions like hydrogen (controls blood pH), iron (found in haemoglobin), sodium (helps transport glucose), and phosphates (essential for DNA and ATP) occur throughout your body in varying concentrations. You can test for different biological molecules using simple food tests - Benedict's for sugars, Biuret for proteins, emulsion test for lipids, and iodine for starch.

Quick Tip: Remember food test colours - Benedict's turns red for positive, Biuret goes lilac, emulsion test becomes cloudy, and iodine turns blue-black with starch!

Proteins: The Body's Workhorses

Proteins literally build and run your body - from the enzymes digesting your food to the haemoglobin carrying oxygen in your blood. Amino acids are protein monomers containing an amine group, carboxylic acid group, and a variable 'R' group that makes each of the 20 amino acids unique.

Primary structure refers to the specific order of amino acids in the chain. This sequence determines everything else about the protein's function. Secondary structure describes how the chain folds into either alpha helixes or beta pleated sheets, held together by hydrogen bonds.

The tertiary structure is the final 3D shape - either globular (compact and rounded like enzymes) or fibrous (long and thin like keratin in your hair). This shape determines the protein's job completely.

Collagen demonstrates fibrous proteins perfectly - its incredible strength comes from hydrogen and covalent bonds, with molecules wrapping around each other to form tough fibrils in your tendons and skin. Haemoglobin shows globular proteins in action - its four polypeptide chains each contain a haem group that grabs oxygen molecules and releases them where needed.

Memory Hack: Think of protein structure like building a house - primary is choosing the bricks (amino acid order), secondary is making walls $helixes/sheets$ , and tertiary is the final building shape!

Carbohydrates and Lipids: Energy and Structure

Carbohydrates are your body's preferred fuel source, made entirely of carbon, hydrogen, and oxygen atoms. They range from simple monosaccharides like glucose to complex polysaccharides that store massive amounts of energy.

Glucose exists as alpha or beta forms - this tiny difference matters hugely! Glycogen (your body's energy store) uses alpha glucose with 1,4 and 1,6 glycosidic bonds creating loads of branches for quick energy release. Starch stores plant energy through amylose (unbranched, coiled) and amylopectin (branched). Meanwhile, cellulose uses beta glucose to create incredibly strong plant cell walls.

Lipids are only soluble in organic solvents like alcohol, not water. Saturated fats have no carbon-carbon double bonds and stay solid at room temperature, whilst unsaturated fats contain double bonds that create kinks, keeping them liquid.

Triglycerides store energy efficiently - one glycerol molecule plus three fatty acid chains joined by ester bonds. Phospholipids replace one fatty acid with a hydrophilic phosphate group, creating molecules that love and hate water simultaneously. This dual nature makes them perfect for cell membranes, forming protective barriers with hydrophilic heads facing outward and hydrophobic tails tucked inside.

Key Insight: The shape of molecules determines their function - branched glycogen releases energy quickly, whilst unbranched cellulose creates structural strength!

We thought you’d never ask...

What is the Knowunity AI companion?

Our AI Companion is a student-focused AI tool that offers more than just answers. Built on millions of Knowunity resources, it provides relevant information, personalised study plans, quizzes, and content directly in the chat, adapting to your individual learning journey.

Where can I download the Knowunity app?

You can download the app from Google Play Store and Apple App Store.

Is Knowunity really free of charge?

That's right! Enjoy free access to study content, connect with fellow students, and get instant help – all at your fingertips.

Most popular content in Biology

aqa higher tier combined science - biology b1 : cell biology, paper 1

b1: cell biology - paper 1

Biology

Biology Paper 1 Overview

Comprehensive study notes covering key concepts in cellular biology, human digestion, respiration, photosynthesis, and the circulatory system. This resource includes detailed explanations of cell structures, enzyme functions, nutrient absorption, and the impact of environmental factors on biological processes. Ideal for students preparing for Biology Paper 1 exams.

Biology

A-Level Biology Year 1 Overview

Comprehensive summary of AQA A-Level Biology Year 1, covering key topics such as cellular structure, protein synthesis, immune response, gas exchange, and more. Ideal for exam preparation and understanding biological concepts. Includes detailed insights into cellular processes, biological classification, and the circulatory system.

Biology

GCSE Biology Paper 1 Overview

Comprehensive summary of key concepts in GCSE AQA Biology Paper 1, covering topics such as cell structure, photosynthesis, respiration, disease biology, antibiotic resistance, and transport systems. Ideal for exam preparation and revision.

Biology

Biology paper 1 Summary

Notes for Biology paper 1 contains the full course for AQA higher combined!

Biology

Circulatory System Overview

Explore the structure and function of the heart and blood vessels in the circulatory system. This summary covers the roles of arteries, veins, and capillaries, detailing how blood is transported throughout the body. Ideal for AQA GCSE Biology students preparing for exams.

Biology

A-Level Biology Year 2 Overview

Comprehensive study notes covering key concepts in AQA A-Level Biology Year 2, including neuronal communication, genetic modification, nutrient cycles, and hormonal control. This resource is designed to aid understanding of complex topics such as action potentials, photosynthesis, and speciation. Ideal for exam preparation and revision.

Biology

Cell Biology Essentials

Explore key concepts in Cell Biology, including cell structure, transport mechanisms, the heart's anatomy, and digestive processes. This summary covers essential topics for AQA GCSE Biology Paper 1, providing a clear overview of eukaryotic and prokaryotic cells, enzyme functions, and plant systems. Ideal for quick revision and exam preparation.

Biology

Menstrual Cycle Hormones

Explore the key hormones involved in the menstrual cycle, including FSH, LH, estrogen, and progesterone. Understand their roles in egg maturation, ovulation, and the maintenance of the uterine lining. This summary provides a clear overview of hormonal coordination in human reproduction, ideal for GCSE Biology students.

Biology

Most popular content

An Inspector Calls: Character Insights

Explore in-depth analysis and key quotes for characters in J.B. Priestley's 'An Inspector Calls'. This resource covers Gerald Croft, Inspector Goole, Sheila Birling, Mrs. Birling, Eric Birling, and Eva Smith, focusing on themes of class, gender roles, and social responsibility. Ideal for students aiming for Grade 8 and above.

English Literature

aqa higher tier combined science - biology b1 : cell biology, paper 1

b1: cell biology - paper 1

Biology

Sociology of Families: Comprehensive Revision

Dive into an extensive overview of family dynamics, perspectives, and patterns in sociology. This resource covers key concepts such as family diversity, gender roles, marriage, and the impact of social policies on family structures. Perfect for A-Level Sociology students preparing for Paper 2.

Sociology

Comprehensive Crime & Deviance Overview

Explore an extensive revision of crime and deviance topics, including theories, types of crime, and the impact of media. This resource covers key concepts such as Marxism, functionalism, gender and crime, and the influence of globalization on criminal behavior. Ideal for students seeking a thorough understanding of criminology and its various theories. Type: Full Topic Revision.

Sociology

Sociology of Education Overview

Explore comprehensive A-Level Sociology notes on the education system, covering key theories, policies, and sociological perspectives. This resource includes insights on marketisation, gender roles, cultural deprivation, and educational inequalities, providing a thorough understanding of how education shapes social stratification and individual achievement. Ideal for exam preparation and in-depth study.

Sociology

Criminal Justice Evidence Rules

Explore the essential rules governing the use of evidence in criminal cases, including reliability, admissibility, and relevance. This summary covers key concepts such as the roles of personnel in investigations, the impact of witness testimonies, and the implications of plea bargaining. Ideal for Year 13 criminology students preparing for assessments.

Criminology

Biology Paper 1 Overview

Biology

Macbeth: Guilt and Ambition

Explore the complex themes of guilt and ambition in Shakespeare's 'Macbeth'. This analysis covers key characters, including Macbeth and Lady Macbeth, their moral dilemmas, and the tragic consequences of their ambition. Ideal for students studying character motivations, thematic elements, and the psychological impact of power. Includes insights on the natural order, manipulation, and the descent into madness.

English Literature

Language Paper 1 Strategies

Master the AQA English Language Paper 1 with this comprehensive guide. Explore key strategies for language and structural analysis, critical evaluation, and creative writing. Learn how to effectively analyze texts, utilize literary techniques, and enhance your writing skills to excel in your exams.

English Language

Can't find what you're looking for? Explore other subjects.

Students love us — and so will you.

4.9/5

App Store

4.8/5

Google Play

The app is very easy to use and well designed. I have found everything I was looking for so far and have been able to learn a lot from the presentations! I will definitely use the app for a class assignment! And of course it also helps a lot as an inspiration.

Stefan S

iOS user

This app is really great. There are so many study notes and help [...]. My problem subject is French, for example, and the app has so many options for help. Thanks to this app, I have improved my French. I would recommend it to anyone.

Samantha Klich

Android user

Wow, I am really amazed. I just tried the app because I've seen it advertised many times and was absolutely stunned. This app is THE HELP you want for school and above all, it offers so many things, such as workouts and fact sheets, which have been VERY helpful to me personally.

Anna

iOS user

Best app on earth! no words because it’s too good

Thomas R

iOS user

Just amazing. Let's me revise 10x better, this app is a quick 10/10. I highly recommend it to anyone. I can watch and search for notes. I can save them in the subject folder. I can revise it any time when I come back. If you haven't tried this app, you're really missing out.

Basil

Android user

This app has made me feel so much more confident in my exam prep, not only through boosting my own self confidence through the features that allow you to connect with others and feel less alone, but also through the way the app itself is centred around making you feel better. It is easy to navigate, fun to use, and helpful to anyone struggling in absolutely any way.

David K

iOS user

The app's just great! All I have to do is enter the topic in the search bar and I get the response real fast. I don't have to watch 10 YouTube videos to understand something, so I'm saving my time. Highly recommended!

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

very reliable app to help and grow your ideas of Maths, English and other related topics in your works. please use this app if your struggling in areas, this app is key for that. wish I'd of done a review before. and it's also free so don't worry about that.

Rohan U

Android user

I know a lot of apps use fake accounts to boost their reviews but this app deserves it all. Originally I was getting 4 in my English exams and this time I got a grade 7. I didn’t even know about this app three days until the exam and it has helped A LOT. Please actually trust me and use it as I’m sure you too will see developments.

Xander S

iOS user

THE QUIZES AND FLASHCARDS ARE SO USEFUL AND I LOVE THE SCHOOLGPT. IT ALSO IS LITREALLY LIKE CHATGPT BUT SMARTER!! HELPED ME WITH MY MASCARA PROBLEMS TOO!! AS WELL AS MY REAL SUBJECTS ! DUHHH 😍😁😲🤑💗✨🎀😮

Elisha

iOS user

This apps acc the goat. I find revision so boring but this app makes it so easy to organize it all and then you can ask the freeeee ai to test yourself so good and you can easily upload your own stuff. highly recommend as someone taking mocks now

Paul T

iOS user

Stefan S

iOS user

Samantha Klich

Android user

Anna

iOS user

Best app on earth! no words because it’s too good

Thomas R

iOS user

Basil

Android user

David K

iOS user

Sudenaz Ocak

Android user

In school I was really bad at maths but thanks to the app, I am doing better now. I am so grateful that you made the app.

Greenlight Bonnie

Android user

Rohan U

Android user

Xander S

iOS user

Elisha

iOS user

Paul T

iOS user

Biology

•

1,001

•

24 Dec 2025

•

3 pages

Comprehensive Biological Molecules A-Level Biology Revision Sheets

Niamh Cooke

@niamhcooke_yelp

Biological molecules are the building blocks of all living things, from the water in your cells to the proteins that make your muscles work. Understanding these molecules - water, carbohydrates, lipids, and proteins - helps explain how your body functions... Show more

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Water and Inorganic Ions

Quick Tip: Remember food test colours - Benedict's turns red for positive, Biuret goes lilac, emulsion test becomes cloudy, and iodine turns blue-black with starch!

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Proteins: The Body's Workhorses

Memory Hack: Think of protein structure like building a house - primary is choosing the bricks (amino acid order), secondary is making walls $helixes/sheets$ , and tertiary is the final building shape!

Sign up to see the contentIt's free!

Access to all documents

Improve your grades

Join milions of students

By signing up you accept Terms of Service and Privacy Policy

Carbohydrates and Lipids: Energy and Structure

Key Insight: The shape of molecules determines their function - branched glycogen releases energy quickly, whilst unbranched cellulose creates structural strength!