Source: https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-5-the-kidneys [Revision notes](https://senecalearning.com/en-gb/revision-notes.md) › [IGCSE](https://senecalearning.com/en-gb/revision-notes/igcse.md) › [Biology](https://senecalearning.com/en-gb/revision-notes/igcse/biology.md) › [Cambridge International](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international.md) › [Higher](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher.md) › The Kidneys # The Kidneys Biology: Cambridge International GCSE Supplement, topic 13.1.5 ## Kidneys The kidneys control the water and ion levels in the blood. The main function of the kidney is to remove unwanted substances, such as urea, along with excess water from the body. This is achieved through the following steps: ### Filtering the blood ![Filtering the blood](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/5.3.2-%20Control%20of%20water%20balance/filter.jpg) ### Producing urine ![Producing urine](https://image-v2.cdn.app.senecalearning.com/courseImages/biology/5.3.2-%20Control%20of%20water%20balance/urine.jpg) ## Test yourself on The Kidneys - What do the kidneys control? - What is the main function of the kidney? [Practise this topic for free](https://app.senecalearning.com/classroom/course/43a4d4e0-16f3-11e8-bb3b-679c0a39551b/section/e4bdd8f0-211f-11e8-95c9-1fc2cea67b92/session) - Previous topic: [13.1.4 Water in Urine](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-4-water-in-urine.md) - Next topic: [13.1.6 Urine Production](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-6-urine-production.md) ## Biology: Cambridge International GCSE Supplement contents ### 1 Classification of Living Organisms - 1.1 Characteristics of Living Organisms - [1.1.1 MRS GREN](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-1-1-mrs-gren.md) - [1.1.2 M.R.S.](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-1-2-mrs.md) - [1.1.3 G.R.E.N.](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-1-3-gren.md) - 1.2 Concept and Uses of Classification Systems - [1.2.1 Classification](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-2-1-classification.md) - [1.2.2 Linnaean Classification](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-2-2-linnaean-classification.md) - [1.2.3 Ancestors & DNA](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-2-3-ancestors-and-dna.md) - [1.2.4 Dichotomous Keys](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-2-4-dichotomous-keys.md) - 1.3 Features of Organisms - [1.3.1 Kingdoms - Animals & Plants](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-1-kingdoms-animals-and-plants.md) - [1.3.2 Kingdoms - Fungi, Prokaryotes, Protoctista](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-2-kingdoms-fungi-prokaryotes-protoctista.md) - [1.3.3 Vertebrates](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-3-vertebrates.md) - [1.3.4 Anthropods](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-4-anthropods.md) - [1.3.5 Plant Classification](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-5-plant-classification.md) - [1.3.6 Cellular Structures - Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-6-cellular-structures-cells.md) - [1.3.7 Cellular Structures - Viruses](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/1-3-7-cellular-structures-viruses.md) ### 2 Organisation of the Organism - 2.1 Cell Structure - [2.1.1 Animal Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-1-animal-cells.md) - [2.1.2 Plant Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-2-plant-cells.md) - [2.1.3 Properties of Prokaryotes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-3-properties-of-prokaryotes.md) - [2.1.4 Cells & Tissues](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-4-cells-and-tissues.md) - [2.1.5 Organs](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-5-organs.md) - [2.1.6 Organ Systems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-6-organ-systems.md) - [2.1.7 Organisms](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-7-organisms.md) - [2.1.8 Ciliated Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-8-ciliated-cells.md) - [2.1.9 Root Hair Cells & Palisade Mesophyll Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-9-root-hair-cells-and-palisade-mesophyll-cells.md) - [2.1.10 Neurones](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-10-neurones.md) - [2.1.11 Red Blood Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-11-red-blood-cells.md) - [2.1.12 Sperm & Egg Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-1-12-sperm-and-egg-cells.md) - 2.2 Size of Specimens - [2.2.1 Magnification](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-1-magnification.md) - [2.2.2 Microscopy](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-2-microscopy.md) - [2.2.3 Orders of Magnitude](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-3-orders-of-magnitude.md) - [2.2.4 Microscopy - Calculations](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-4-microscopy-calculations.md) - [2.2.5 Converting Measurements](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-5-converting-measurements.md) - [2.2.6 End of Topic Test - Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-6-end-of-topic-test-cells.md) - [2.2.7 Exam-Style Questions - Cell Structure & Microscopy](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/2-2-7-exam-style-questions-cell-structure-and-microscopy.md) ### 3 Movement Into & Out of Cells - 3.1 Diffusion - [3.1.1 Diffusion](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-1-1-diffusion.md) - [3.1.2 Factors Affecting Diffusion](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-1-2-factors-affecting-diffusion.md) - [3.1.3 Surface Area : Volume](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-1-3-surface-area-volume.md) - 3.2 Osmosis - [3.2.1 Water](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-2-1-water.md) - [3.2.2 Osmosis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-2-2-osmosis.md) - [3.2.3 Osmosis Experiment](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-2-3-osmosis-experiment.md) - [3.2.4 Osmosis in Plants](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-2-4-osmosis-in-plants.md) - [3.2.5 Osmotic Balance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-2-5-osmotic-balance.md) - [3.2.6 Required Practical - Osmosis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-2-6-required-practical-osmosis.md) - 3.3 Active Transport - [3.3.1 Active Transport](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-3-1-active-transport.md) - [3.3.2 Transport in Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-3-2-transport-in-cells.md) - [3.3.3 Carrier Proteins](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-3-3-carrier-proteins.md) - [3.3.4 Grade 9 - Cell Transport](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-3-4-grade-9-cell-transport.md) - [3.3.5 End of Topic Test - Cell Transport](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-3-5-end-of-topic-test-cell-transport.md) - [3.3.6 Exam-Style Questions - Substance Exchange](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/3-3-6-exam-style-questions-substance-exchange.md) ### 4 Biological Molecules - 4.1 Biological Molecules - [4.1.1 Chemical Elements](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/4-1-1-chemical-elements.md) - [4.1.2 Larger Molecules](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/4-1-2-larger-molecules.md) - [4.1.3 Testing for Biological Molecules](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/4-1-3-testing-for-biological-molecules.md) - [4.1.4 DNA](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/4-1-4-dna.md) - [4.1.5 DNA Pairings](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/4-1-5-dna-pairings.md) ### 5 Enzymes - 5.1 Enzymes - [5.1.1 Enzymes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/5-1-1-enzymes.md) - [5.1.2 Rate of Enzyme Action](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/5-1-2-rate-of-enzyme-action.md) - [5.1.3 Investigating Rate](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/5-1-3-investigating-rate.md) - [5.1.4 End of Topic Test - Enzymes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/5-1-4-end-of-topic-test-enzymes.md) - [5.1.5 Grade 9 - Enzymes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/5-1-5-grade-9-enzymes.md) ### 6 Plant Nutrition - 6.1 Photosynthesis - [6.1.1 Photosynthesis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-1-photosynthesis.md) - [6.1.2 Photosynthesis - Plant Gas Exchange](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-2-photosynthesis-plant-gas-exchange.md) - [6.1.3 Uses of Glucose](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-3-uses-of-glucose.md) - [6.1.4 Ion Deficiency Conditions](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-4-ion-deficiency-conditions.md) - [6.1.5 Rate of Photosynthesis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-5-rate-of-photosynthesis.md) - [6.1.6 Photosynthesis Experiments](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-6-photosynthesis-experiments.md) - [6.1.7 Photosynthesis Equation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-7-photosynthesis-equation.md) - [6.1.8 Photosynthesis - Calculations](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-8-photosynthesis-calculations.md) - [6.1.9 Limiting Factors](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-9-limiting-factors.md) - [6.1.10 Limiting Factors 2](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-10-limiting-factors-2.md) - [6.1.11 Grade 9 - Photosynthesis Experiment](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-11-grade-9-photosynthesis-experiment.md) - [6.1.12 Exam-Style Questions - Photosynthesis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-1-12-exam-style-questions-photosynthesis.md) - 6.2 Leaf Structure - [6.2.1 Leaf Structure](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-2-1-leaf-structure.md) - [6.2.2 Stomata](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-2-2-stomata.md) - [6.2.3 Plant Tissues](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-2-3-plant-tissues.md) - [6.2.4 Leaf Adaptations](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-2-4-leaf-adaptations.md) - [6.2.5 End of Topic Test - Photosynthesis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/6-2-5-end-of-topic-test-photosynthesis.md) ### 7 Human Nutrition - 7.1 Diet - [7.1.1 Diet](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-1-1-diet.md) - [7.1.2 Vitamins & Minerals](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-1-2-vitamins-and-minerals.md) - [7.1.3 Scurvy & Rickets](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-1-3-scurvy-and-rickets.md) - 7.2 Digestive System - [7.2.1 Digestive System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-2-1-digestive-system.md) - [7.2.2 Functions of the Digestive System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-2-2-functions-of-the-digestive-system.md) - [7.2.3 Steps of Digestion](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-2-3-steps-of-digestion.md) - 7.3 Physical Digestion - [7.3.1 Physical Digestion - Human Tooth](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-3-1-physical-digestion-human-tooth.md) - [7.3.2 Teeth Types](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-3-2-teeth-types.md) - [7.3.3 Tooth Diseases](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-3-3-tooth-diseases.md) - 7.4 Chemical Digestion - [7.4.1 Digestive Enzymes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-1-digestive-enzymes.md) - [7.4.2 Examples of Digestive Enzymes - Amylases](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-2-examples-of-digestive-enzymes-amylases.md) - [7.4.3 Examples of Digestive Enzymes - Proteases](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-3-examples-of-digestive-enzymes-proteases.md) - [7.4.4 Examples of Digestive Enzymes - Lipases](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-4-examples-of-digestive-enzymes-lipases.md) - [7.4.5 Chemical Digestion - Stomach](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-5-chemical-digestion-stomach.md) - [7.4.6 Exam-Style Questions - Digestive Enzymes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-6-exam-style-questions-digestive-enzymes.md) - [7.4.7 Pepsin & Trypsin](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-4-7-pepsin-and-trypsin.md) - 7.5 Absorption - [7.5.1 Small Intestine](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-5-1-small-intestine.md) - [7.5.2 Villi](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/7-5-2-villi.md) ### 8 Transport in Plants - 8.1 Xylem & Phloem - [8.1.1 Plant Vessels](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-1-1-plant-vessels.md) - [8.1.2 Specialised Plant Cells - Xylem](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-1-2-specialised-plant-cells-xylem.md) - 8.2 Water Uptake - [8.2.1 Water Uptake](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-2-1-water-uptake.md) - [8.2.2 Specialised Plant Cells - Root Hair](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-2-2-specialised-plant-cells-root-hair.md) - [8.2.3 Exam-Style Questions - Transport in Plants](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-2-3-exam-style-questions-transport-in-plants.md) - 8.3 Transpiration - [8.3.1 Transpiration](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-3-1-transpiration.md) - [8.3.2 Transpiration Tissues - Xylem](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-3-2-transpiration-tissues-xylem.md) - [8.3.3 States of Stomata](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-3-3-states-of-stomata.md) - [8.3.4 Rate of Transpiration](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-3-4-rate-of-transpiration.md) - [8.3.5 Measuring Transpiration](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-3-5-measuring-transpiration.md) - 8.4 Translocation - [8.4.1 Translocation Tissues - Phloem](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-4-1-translocation-tissues-phloem.md) - [8.4.2 Translocation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-4-2-translocation.md) - [8.4.3 End of Topic Test - Plant Transport](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/8-4-3-end-of-topic-test-plant-transport.md) ### 9 Transport in Animals - 9.1 Circulatory Systems - [9.1.1 Circulatory Systems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-1-1-circulatory-systems.md) - [9.1.2 Double Circulatory Systems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-1-2-double-circulatory-systems.md) - 9.2 Heart - [9.2.1 Mammal Heart Function](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-2-1-mammal-heart-function.md) - [9.2.2 Mammal Heart Structure](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-2-2-mammal-heart-structure.md) - [9.2.3 Heart Monitoring](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-2-3-heart-monitoring.md) - [9.2.4 Exercise Recovery](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-2-4-exercise-recovery.md) - [9.2.5 Heart Disease](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-2-5-heart-disease.md) - [9.2.6 Treatment of Heart Disease](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-2-6-treatment-of-heart-disease.md) - 9.3 Blood Vessels - [9.3.1 Types of Vessels - Arteries](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-3-1-types-of-vessels-arteries.md) - [9.3.2 Types of Vessels - Veins](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-3-2-types-of-vessels-veins.md) - [9.3.3 Types of Vessels - Capillaries](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-3-3-types-of-vessels-capillaries.md) - [9.3.4 Important Vessels](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-3-4-important-vessels.md) - [9.3.5 End of Topic Test - Circulatory System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-3-5-end-of-topic-test-circulatory-system.md) - [9.3.6 Exam-Style Questions - Circulatory System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-3-6-exam-style-questions-circulatory-system.md) - 9.4 Blood - [9.4.1 Blood Components](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-4-1-blood-components.md) - [9.4.2 Red Blood Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-4-2-red-blood-cells.md) - [9.4.3 White Blood Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-4-3-white-blood-cells.md) - [9.4.4 Platelets](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-4-4-platelets.md) - [9.4.5 Blood Clotting](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/9-4-5-blood-clotting.md) ### 10 Diseases & Immunity - 10.1 Diseases & Immunity - [10.1.1 Health Issues](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-1-health-issues.md) - [10.1.2 Causing Diseases](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-2-causing-diseases.md) - [10.1.3 Preventing Infection](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-3-preventing-infection.md) - [10.1.4 Human Defence Systems - Non-Specific Defences](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-4-human-defence-systems-non-specific-defences.md) - [10.1.5 Human Defence Systems - Immune Systems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-5-human-defence-systems-immune-systems.md) - [10.1.6 Cholera](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-6-cholera.md) - [10.1.7 Antibodies](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-7-antibodies.md) - [10.1.8 Vaccination & Immunity](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-8-vaccination-and-immunity.md) - [10.1.9 Passive Immunity](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-9-passive-immunity.md) - [10.1.10 Viruses](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-10-viruses.md) - [10.1.11 End of Topic Test - Health & Disease](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/10-1-11-end-of-topic-test-health-and-disease.md) ### 11 Gas Exchange in Humans - 11.1 Gas Exchange in Humans - [11.1.1 Exchange Surface](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-1-exchange-surface.md) - [11.1.2 Lung Gas Exchange](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-2-lung-gas-exchange.md) - [11.1.3 Alveoli](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-3-alveoli.md) - [11.1.4 Breathing Process](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-4-breathing-process.md) - [11.1.5 Breathing Composition](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-5-breathing-composition.md) - [11.1.6 Breathing & Exercise](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-6-breathing-and-exercise.md) - [11.1.7 Thorax](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/11-1-7-thorax.md) ### 12 Respiration - 12.1 Respiration - [12.1.1 Respiration Uses](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-1-1-respiration-uses.md) - [12.1.2 Investigating Respiration](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-1-2-investigating-respiration.md) - [12.1.3 End of Topic Test - Respiration](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-1-3-end-of-topic-test-respiration.md) - [12.1.4 Exam-Style Questions - Respiration During Exercise](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-1-4-exam-style-questions-respiration-during-exercise.md) - 12.2 Aerobic & Anaerobic Respiration - [12.2.1 Respiration Reactions](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-2-1-respiration-reactions.md) - [12.2.2 Oxygen Use & Debt](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-2-2-oxygen-use-and-debt.md) - [12.2.3 Aerobic and Anaerobic Respiration](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/12-2-3-aerobic-and-anaerobic-respiration.md) ### 13 Excretion in Humans - 13.1 Excretion in Humans - [13.1.1 Excretion in Humans](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-1-excretion-in-humans.md) - [13.1.2 Urea](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-2-urea.md) - [13.1.3 Water Balance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-3-water-balance.md) - [13.1.4 Water in Urine](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-4-water-in-urine.md) - [13.1.5 The Kidneys](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-5-the-kidneys.md) - [13.1.6 Urine Production](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-6-urine-production.md) - [13.1.7 Urinary System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-7-urinary-system.md) - [13.1.8 Kidney Transplants](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-8-kidney-transplants.md) - [13.1.9 Kidney Transplants - Pros & Cons](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/13-1-9-kidney-transplants-pros-and-cons.md) ### 14 Coordination & Response - 14.1 Coordination & Response - [14.1.1 The Nervous System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-1-1-the-nervous-system.md) - [14.1.2 Reflex Actions](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-1-2-reflex-actions.md) - [14.1.3 Reflex Arc](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-1-3-reflex-arc.md) - [14.1.4 Synapses](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-1-4-synapses.md) - [14.1.5 End of Topic Test - Nervous Control](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-1-5-end-of-topic-test-nervous-control.md) - [14.1.6 Exam-Style Questions - Nervous System](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-1-6-exam-style-questions-nervous-system.md) - 14.2 Sense Organs - [14.2.1 Sense Organs](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-2-1-sense-organs.md) - [14.2.2 Eye Anatomy](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-2-2-eye-anatomy.md) - [14.2.3 Eye Function - Light](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-2-3-eye-function-light.md) - [14.2.4 Eye Function - Focus](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-2-4-eye-function-focus.md) - [14.2.5 Eye Function - Detecting Colour](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-2-5-eye-function-detecting-colour.md) - 14.3 Hormones - [14.3.1 Hormones in Humans](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-3-1-hormones-in-humans.md) - [14.3.2 Endocrine Glands](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-3-2-endocrine-glands.md) - [14.3.3 Nervous vs Endocrine](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-3-3-nervous-vs-endocrine.md) - [14.3.4 Adrenaline](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-3-4-adrenaline.md) - 14.4 Homeostasis - [14.4.1 Homeostasis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-1-homeostasis.md) - [14.4.2 Regulating Internal Conditions](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-2-regulating-internal-conditions.md) - [14.4.3 Control Systems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-3-control-systems.md) - [14.4.4 Negative Feedback](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-4-negative-feedback.md) - [14.4.5 Thermoregulation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-5-thermoregulation.md) - [14.4.6 Thermoregulation - Hot and Cold](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-6-thermoregulation-hot-and-cold.md) - [14.4.7 Thermoregulation - Skin](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-7-thermoregulation-skin.md) - [14.4.8 Thermoregulation - Sweating & Shivering](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-8-thermoregulation-sweating-and-shivering.md) - [14.4.9 Thermoregulation - Hairs](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-9-thermoregulation-hairs.md) - [14.4.10 Thermoregulation - Blood Vessels](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-10-thermoregulation-blood-vessels.md) - [14.4.11 Blood Glucose](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-11-blood-glucose.md) - [14.4.12 Detecting Glucose](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-12-detecting-glucose.md) - [14.4.13 Type 1 Diabetes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-13-type-1-diabetes.md) - [14.4.14 End of Topic Test - Homeostasis & Hormones](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-14-end-of-topic-test-homeostasis-and-hormones.md) - [14.4.15 Grade 9 - Hormonal Coordination](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-4-15-grade-9-hormonal-coordination.md) - 14.5 Tropic Responses - [14.5.1 Types of Tropisms](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-5-1-types-of-tropisms.md) - [14.5.2 Auxins and Tropisms](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-5-2-auxins-and-tropisms.md) - [14.5.3 Required Practical - Plant Hormones](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/14-5-3-required-practical-plant-hormones.md) ### 15 Drugs - 15.1 Drugs - [15.1.1 Antibiotics](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/15-1-1-antibiotics.md) - [15.1.2 Antibiotic Resistance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/15-1-2-antibiotic-resistance.md) - [15.1.3 Resistant Bacteria](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/15-1-3-resistant-bacteria.md) ### 16 Reproduction - 16.1 Asexual Reproduction - [16.1.1 Asexual Reproduction](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-1-1-asexual-reproduction.md) - [16.1.2 Advantages of Asexual Reproduction](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-1-2-advantages-of-asexual-reproduction.md) - 16.2 Sexual Reproduction - [16.2.1 Sexual Reproduction](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-2-1-sexual-reproduction.md) - [16.2.2 Gametes vs. Zygotes](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-2-2-gametes-vs-zygotes.md) - [16.2.3 Advantages of Sexual Reproduction](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-2-3-advantages-of-sexual-reproduction.md) - 16.3 Sexual Reproduction in Plants - [16.3.1 Flower Anatomy](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-3-1-flower-anatomy.md) - [16.3.2 Pollination Methods](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-3-2-pollination-methods.md) - [16.3.3 Self-pollination & Cross-polination](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-3-3-self-pollination-and-cross-polination.md) - [16.3.4 Germination](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-3-4-germination.md) - 16.4 Sexual Reproduction in Humans - [16.4.1 Human Reproductive Systems - Male](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-1-human-reproductive-systems-male.md) - [16.4.2 Human Reproductive Systems - Female](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-2-human-reproductive-systems-female.md) - [16.4.3 Human Gametes - Sperm Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-3-human-gametes-sperm-cells.md) - [16.4.4 Human Gametes - Egg Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-4-human-gametes-egg-cells.md) - [16.4.5 Human Gametes - Egg vs. Sperm](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-5-human-gametes-egg-vs-sperm.md) - [16.4.6 Pregnancy](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-6-pregnancy.md) - [16.4.7 Pregnancy Health](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-7-pregnancy-health.md) - [16.4.8 Birth - Labour](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-8-birth-labour.md) - [16.4.9 Birth - Breast-feeding](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-4-9-birth-breast-feeding.md) - 16.5 Sex Hormones in Humans - [16.5.1 Puberty](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-1-puberty.md) - [16.5.2 Menstruation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-2-menstruation.md) - [16.5.3 Menstrual Cycle](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-3-menstrual-cycle.md) - [16.5.4 Menstrual Hormones](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-4-menstrual-hormones.md) - [16.5.5 Baby Planning](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-5-baby-planning.md) - [16.5.6 Infertility](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-6-infertility.md) - [16.5.7 Fertility Treatments Pros & Cons](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-7-fertility-treatments-pros-and-cons.md) - [16.5.8 End of Topic Test - Reproductive Hormones](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-8-end-of-topic-test-reproductive-hormones.md) - [16.5.9 Exam-Style Questions - Hormones & Contraception](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-5-9-exam-style-questions-hormones-and-contraception.md) - 16.6 Sexually Transmitted Infections - [16.6.1 HIV](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/16-6-1-hiv.md) ### 17 Inheritance - 17.1 Chromosomes, Genes & Proteins - [17.1.1 Genome](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-1-1-genome.md) - [17.1.2 Genome Diagram](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-1-2-genome-diagram.md) - [17.1.3 Gene Expression](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-1-3-gene-expression.md) - [17.1.4 DNA Pairings](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-1-4-dna-pairings.md) - [17.1.5 Protein Synthesis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-1-5-protein-synthesis.md) - [17.1.6 Synthesis Process](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-1-6-synthesis-process.md) - 17.2 Mitosis & Meiosis - [17.2.1 Cell Division](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-2-1-cell-division.md) - [17.2.2 Stem Cells](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-2-2-stem-cells.md) - [17.2.3 Meiosis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-2-3-meiosis.md) - 17.3 Monohybrid Inheritance - [17.3.1 Alleles](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-1-alleles.md) - [17.3.2 Phenotype](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-2-phenotype.md) - [17.3.3 Sex Determination](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-3-sex-determination.md) - [17.3.4 Monohybrid Inheritance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-4-monohybrid-inheritance.md) - [17.3.5 Punnett Square](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-5-punnett-square.md) - [17.3.6 Blood Groups](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-6-blood-groups.md) - [17.3.7 Sex-linked Disorders](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-7-sex-linked-disorders.md) - [17.3.8 Cystic Fibrosis](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-8-cystic-fibrosis.md) - [17.3.9 Cystic Fibrosis - Punnett Square](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-9-cystic-fibrosis-punnett-square.md) - [17.3.10 Cystic Fibrosis - Pedigree Diagram](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-10-cystic-fibrosis-pedigree-diagram.md) - [17.3.11 Test Crosses](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-11-test-crosses.md) - [17.3.12 End of Topic Test - Genes & Inheritance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/17-3-12-end-of-topic-test-genes-and-inheritance.md) ### 18 Variation & Selection - 18.1 Variation - [18.1.1 Variation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-1-1-variation.md) - [18.1.2 Continuous & Discontinuous Variation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-1-2-continuous-and-discontinuous-variation.md) - [18.1.3 Mutations](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-1-3-mutations.md) - [18.1.4 Sickle Cell Symptoms](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-1-4-sickle-cell-symptoms.md) - [18.1.5 Sickle Cell & Malaria](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-1-5-sickle-cell-and-malaria.md) - [18.1.6 Sickle Cell Inheritance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-1-6-sickle-cell-inheritance.md) - 18.2 Adaptive Features - [18.2.1 Adaptive Features](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-2-1-adaptive-features.md) - [18.2.2 Plant Adaptations](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-2-2-plant-adaptations.md) - 18.3 Selection - [18.3.1 Natural Selection](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-1-natural-selection.md) - [18.3.2 Evolution](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-2-evolution.md) - [18.3.3 Antibiotic Resistance](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-3-antibiotic-resistance.md) - [18.3.4 Selective Breeding](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-4-selective-breeding.md) - [18.3.5 Selective Breeding Process](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-5-selective-breeding-process.md) - [18.3.6 Uses of Selective Breeding](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-6-uses-of-selective-breeding.md) - [18.3.7 Grade 9 - Evolution](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-7-grade-9-evolution.md) - [18.3.8 End of Topic Test - Variation & Evolution](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/18-3-8-end-of-topic-test-variation-and-evolution.md) ### 19 Organisms & Their Environment - 19.1 Energy Flow - [19.1.1 Energy Flow](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-1-1-energy-flow.md) - 19.2 Food Chains & Food Webs - [19.2.1 Food Chains & Webs](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-1-food-chains-and-webs.md) - [19.2.2 Decomposers](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-2-decomposers.md) - [19.2.3 Trophic Levels](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-3-trophic-levels.md) - [19.2.4 Pyramids of Biomass](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-4-pyramids-of-biomass.md) - [19.2.5 Editing Food Chains](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-5-editing-food-chains.md) - [19.2.6 Reasons for Energy Wastage](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-6-reasons-for-energy-wastage.md) - [19.2.7 Transfer Efficiency](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-7-transfer-efficiency.md) - [19.2.8 Exam-Style Questions - Biomass](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-8-exam-style-questions-biomass.md) - [19.2.9 End of Topic Test - Food and Trophic Levels](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-2-9-end-of-topic-test-food-and-trophic-levels.md) - 19.3 Nutrient Cycles - [19.3.1 Importance of Cycling](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-3-1-importance-of-cycling.md) - [19.3.2 Carbon Cycle](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-3-2-carbon-cycle.md) - [19.3.3 Peat Bog](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-3-3-peat-bog.md) - [19.3.4 Water Cycle](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-3-4-water-cycle.md) - [19.3.5 Nitrogen Cycle](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-3-5-nitrogen-cycle.md) - [19.3.6 Nitrogen Cycle & Microorganisms](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-3-6-nitrogen-cycle-and-microorganisms.md) - 19.4 Populations - [19.4.1 Ecosystems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-4-1-ecosystems.md) - [19.4.2 Population Growth Factors](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-4-2-population-growth-factors.md) - [19.4.3 Population Growth](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-4-3-population-growth.md) - [19.4.4 Human Population](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-4-4-human-population.md) - [19.4.5 Grade 9 - Ecosystems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-4-5-grade-9-ecosystems.md) - [19.4.6 End of Topic Test - Ecosystems](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/19-4-6-end-of-topic-test-ecosystems.md) ### 20 Human Influence on Ecosystems - 20.1 Food Supply - [20.1.1 Food Supply & Modern Technology](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-1-1-food-supply-and-modern-technology.md) - [20.1.2 Food Supply & Modern Technology Drawbacks](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-1-2-food-supply-and-modern-technology-drawbacks.md) - [20.1.3 Food Supply & Populations](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-1-3-food-supply-and-populations.md) - [20.1.4 Causes of Famine](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-1-4-causes-of-famine.md) - [20.1.5 Declining Fish Stock](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-1-5-declining-fish-stock.md) - 20.2 Habitat Destruction - [20.2.1 Habitat Destruction](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-2-1-habitat-destruction.md) - [20.2.2 Deforestation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-2-2-deforestation.md) - [20.2.3 Exam-Style Questions - Deforestation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-2-3-exam-style-questions-deforestation.md) - 20.3 Pollution - [20.3.1 Humans & Waste](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-1-humans-and-waste.md) - [20.3.2 Nuclear Waste](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-2-nuclear-waste.md) - [20.3.3 Land Pollution](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-3-land-pollution.md) - [20.3.4 Waste Production - Plastics](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-4-waste-production-plastics.md) - [20.3.5 Air Pollution](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-5-air-pollution.md) - [20.3.6 Greenhouse Effect](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-6-greenhouse-effect.md) - [20.3.7 Global Warming](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-7-global-warming.md) - [20.3.8 Eutrophication](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-3-8-eutrophication.md) - 20.4 Conservation - [20.4.1 Conservation](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-1-conservation.md) - [20.4.2 Reasons to Conserve Biodiversity](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-2-reasons-to-conserve-biodiversity.md) - [20.4.3 Renewable Resources](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-3-renewable-resources.md) - [20.4.4 Recycling](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-4-recycling.md) - [20.4.5 Sustainability](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-5-sustainability.md) - [20.4.6 Sewage Treatment](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-6-sewage-treatment.md) - [20.4.7 Sustainable Fishing](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-7-sustainable-fishing.md) - [20.4.8 Sustainable Forest](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-8-sustainable-forest.md) - [20.4.9 Endangered Species](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-9-endangered-species.md) - [20.4.10 Causes of Endangering](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/20-4-10-causes-of-endangering.md) ### 21 Biotechnology & Genetic Modification - 21.1 Biotechnology & Genetic Modification - [21.1.1 Bacteria in Biotechnology](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-1-1-bacteria-in-biotechnology.md) - 21.2 Biotechnology - [21.2.1 Yeast in Biotechnology](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-2-1-yeast-in-biotechnology.md) - [21.2.2 Enzymes in Biotechnology](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-2-2-enzymes-in-biotechnology.md) - [21.2.3 Penicillin](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-2-3-penicillin.md) - 21.3 Genetic Modification - [21.3.1 Genetic Modification](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-3-1-genetic-modification.md) - [21.3.2 Genetic Modification - Process](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-3-2-genetic-modification-process.md) - [21.3.3 Genetic Modification - Controversy](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-3-3-genetic-modification-controversy.md) - [21.3.4 Pros & Cons of Genetic Modification](https://senecalearning.com/en-gb/revision-notes/igcse/biology/cambridge-international/higher/21-3-4-pros-and-cons-of-genetic-modification.md)