A Science teacher by trade, I've also been known to be found teaching Maths and PE! However, strange as it may seem, my real love is designing resources that can be used by other teachers to maximise the experience of the students. I am constantly thinking of new ways to engage a student with a topic and try to implement that in the design of the lessons.
A Science teacher by trade, I've also been known to be found teaching Maths and PE! However, strange as it may seem, my real love is designing resources that can be used by other teachers to maximise the experience of the students. I am constantly thinking of new ways to engage a student with a topic and try to implement that in the design of the lessons.
This lesson bundle contains 5 lesson PowerPoints and together with their accompanying worksheets, they will engage and motivate the students whilst covering the following specification points in module 3.1.1 (Exchange surfaces) of the OCR A-level Biology A specification:
The need for specialised exchange surfaces
The features of an efficient exchange surface
The structures and functions of the components of the mammalian gaseous exchange system
The mechanism of ventilation in mammals
The mechanisms of ventilation and gas exchange in bony fish and insects
Found interspersed within the detailed A-level Biology content in the slides are current understanding and prior knowledge checks and these are followed by displayed mark schemes to allow students to assess their progress. There are also differentiated tasks, guided discussion periods and quiz competitions that introduce key values and terms in a fun and memorable way
If you would like to see the quality of lessons included in this bundle, then download the mammalian gaseous exchange system and ventilation and gas exchange in insects lessons as these have been uploaded for free
This lesson describes the mechanisms of ventilation and gas exchange in insects. The PowerPoint and accompanying worksheets are the part of the second lesson in a series of 2 lessons which have been designed to cover the details that are set out in point 3.1.1 (f) of the OCR A-level Biology A specification. The first lesson in this series describes ventilation and gas exchange in bony fish
In the previous lesson, the students were introduced to the different circulatory systems of mammals and bony fish and this knowledge is checked upon at the start of this lesson. This is relevant because the open circulatory system of an insect explains how oxygen is not transported in the blood but instead is absorbed from the body fluid that bathes the tissues. The next part of the lesson describes the structure of the spiracles, tracheae and tracheoles in the tracheal system and explains how this system is responsible for the delivery of oxygen to the open end of the tracheole for gas exchange with this fluid. As the tracheae are supported by chitin, which is similar in structure and function to cellulose and keratin respectively, a series of exam-style questions are used to challenge the students on their knowledge of those polymers from module 2.1.2 (biological molecules). As always, the mark scheme is embedded in the powerpoint so students can assess their understanding and progress. The final part of the lesson describes how squeezing of the tracheoles by the flight muscles and the changes in the volume of the thorax as a result of the movement of the wings are similar to mechanisms observed in mammals.
This lesson describes how the surfaces in insects, fish and mammals are adapted for gas exchange. The PowerPoint and accompanying worksheets have been designed to cover the detail of point 4.3 (i) of the Edexcel A-level Biology B specification.
The lesson has been intricately planned to challenge the students on their understanding of the surface area to volume ratio (as covered in topic 4.1) and to make direct links to upcoming lessons on the transport systems in humans. The lesson begins by explaining that single-celled organisms are able to diffuse oxygen and carbon dioxide across their body surface but that as organisms increase in size and their SA/V ratio decreases, they need adaptations at their gas exchange surfaces to be able to obtain the oxygen to meet their metabolic demands. This leads into the next part of the lesson which describes the roles of the following structures in insects and bony fish:
spiracles, tracheae, tracheoles and tracheole fluid
operculum, gill arch, gill filaments and lamellae
The next task challenges the students to use their knowledge of topics 1, 2 and 3 to come up with the letters that form the key term, countercurrent flow. This is a key element of the lesson and tends to be a principle that is poorly understood, so extra time is taken to explain the importance of this mechanism. Students are shown two diagrams, where one contains a countercurrent system and the other has the two fluids flowing in the same direction, and this is designed to support them in recognising that this type of system ensures that the concentration of oxygen is always higher in the oxygenated water than in the blood in the lamellae.
As the alveoli as a structure of gas exchange was introduced at GCSE, this final part of the lesson has been written to challenge the recall of that knowledge and to build on it.
The main focus is the type of epithelium found lining the alveoli and students will discover that a single layer of flattened cells known as simple, squamous epithelium acts to reduce the diffusion distance. Again, students will have met this in a lesson in topic 2 on specialised cells (and tissues) so a number of prior knowledge checks are used alongside current understanding checks.
The following features of the alveolar epithelium are also covered:
Surface area
Moist lining
Production of surfactant
The maintenance of a steep concentration gradient
As a constant ventilation supply is critical for the maintenance of the steep concentration gradient, the final task considers the mechanism of ventilation
This bundle contains 4 lessons which cover the following content that’s set out in topic 3.2 (Gas exchange) of the AQA A-level Biology specification:
Adaptations of gas exchange surfaces as shown by the gas exchange in single-celled organisms, insects, bony fish and the leaves of dicotyledonous plants
The gross structure of the human gas exchange system
The essential features of the alveolar epithelium as a surface over which gas exchange takes place
The mechanism of breathing
All of the lessons are detailed and have been intricately planned to contain a wide range of tasks that will challenge the students on their understanding of the current topic as well as their recall of knowledge from previously-covered topics. In this way, the students are encouraged to make links between biological processes in different topics so they are prepared for assessment questions which do just that.
Lessons covering topics 3.1, 3.3 and 3.4 are also uploaded
This lesson describes the adaptations of gas exchange surfaces in single-celled organisms, insects, bony fish and dicotyledonous plants. The PowerPoint and accompanying worksheets are part of the first lesson in a series of 6 lessons that have been designed to cover the detail of point 3.2 (Gas exchange) of the AQA A-level Biology specification.
The lesson has been intricately planned to challenge the students on their understanding of the surface area to volume ratio (as covered in the previous lesson) and to make direct links to upcoming lessons on gas exchange and transport systems in humans. The lesson begins by explaining that single-celled organisms are able to diffuse oxygen and carbon dioxide across their body surface but that as organisms increase in size and their SA/V ratio decreases, they need adaptations at their gas exchange surfaces to be able to obtain the oxygen to meet their metabolic demands. This leads into the next part of the lesson which describes the roles of the following structures in insects and bony fish:
spiracles, tracheae, tracheoles and tracheole fluid
operculum, gill arch, gill filaments and lamellae
The next task challenges the students to use their knowledge of topics 1 and 2 to come up with the letters that form the key term, countercurrent flow. This is a key element of the lesson and tends to be a principle that is poorly understood, so extra time is taken to explain the importance of this mechanism. Students are shown two diagrams, where one contains a countercurrent system and the other has the two fluids flowing in the same direction, and this is designed to support them in recognising that this type of system ensures that the concentration of oxygen is always higher in the oxygenated water than in the blood in the lamellae.
The final part of the lesson describes the role of the stomata and the mesophyll cells in the gas exchange of a dicotyledonous plant. Students will learn that guard cells contain chloroplasts which generate ATP and then they are challenged to order a series of statements to form a description of the events that result in the opening of the stomata. The differing structures of the spongy mesophyll and palisade mesophyll cells are then considered before the students are challenged to explain how carbon dioxide moves through the leaf after entering via the stomata and then how water vapour and oxygen leave. Clear links are made to the loss of water vapour by transpiration so students are prepared for the lessons covering this biological process later in topic 3.
This lesson describes the roles of the buccal cavity, operculum, gill lamellae and countercurrent flow in ventilation and gas exchange in bony fish. The detailed PowerPoint and accompanying resources are part of the first lesson in a series of 2 that have been designed to cover the details of point 3.1.1 (f) of the OCR A-level Biology A specification. The second lesson in this series covers the mechanisms of ventilation and gas exchange in insects.
The lesson has been specifically planned to prepare students for the content of module 3.1.2 (Transport in animals) and therefore begins with an introduction and a brief description of the single circulatory system of a fish as this has an impact on the delivery of deoxygenated blood to the lamellae. A quick quiz competition is used to introduce the operculum and then the flow of blood along the gill arch and into the primary lamellae and then into the capillaries in the secondary lamellae is described. The next task challenges the students to use their knowledge of module 2 to come up with the letters that form the key term, countercurrent flow. This is a key element of the lesson and tends to be a feature that is poorly understood, so extra time is taken to explain the importance of this mechanism. Students are shown two diagrams, where one contains a countercurrent system and the other has the two fluids flowing in the same direction, and this is designed to support them in recognising that this type of system ensures that the concentration of oxygen is always higher in the oxygenated water than in the blood in the lamellae. The remainder of the lesson focuses on the coordinated movements of the buccal-opercular pump to ensure that the water continues to flow over the gills.
Current understanding and prior knowledge checks are included throughout the lesson and students can assess their progress against the mark schemes which are embedded into the PowerPoint
All 5 lessons in this lesson bundle are highly detailed to cover the specification points shown below that are found in AS unit 2, topic 1 of the WJEC A-level Biology specification:
The classification of organisms into groups based on their evolutionary relationships
The need for classification
The three-domain classification system
The characteristic features of the five kingdoms of living organisms
The use of physical features and biochemical methods to assess the relatedness of organisms
The concept of species
The use of the binomial naming system
Biodiversity as the variety of organisms found within a specified geographic region
Biodiversity can be assessed in a habitat using Simpson’s index of diversity
Biodiversity can be assessed within a species at a genetic level
Biodiversity can be assessed at a molecular level using DNA fingerprinting
Biodiversity has been generated through natural selection
Anatomical, physiological and behavioural adaptations
As well as the A-level Biology content within the slides, current understanding and prior knowledge checks in the form of exam-style questions, differentiated tasks and quiz competitions are included throughout to allow the students to assess their progress
If you would like to sample the quality of the lessons included in this bundle, then download the classification, species and the binomial naming system lesson as this has been shared for free
This lesson explains the meaning of biodiversity and describes how it can be assessed in a habitat, in a species level at a genetic level and at a molecular level. The engaging PowerPoint and accompanying resources have been designed to cover points (h-l) in AS unit 2, topic 1 of the WJEC A-level Biology specification but as a lot of genetic content is covered when considering diversity within a species, this lesson can be used as an introduction to the upcoming topics of inheritance
A quiz competition called BIOLOGICAL TERMINOLOGY SNAP runs over the course of the lesson and this will engage the students whilst challenging them to recognise key terms from their definitions. This quiz introduces biodiversity, loci, allele and recessive and each of these terms is put into context once introduced. Once biodiversity has been revealed, the students will learn that they are expected to be able to assess the biodiversity within a habitat and within a species and at a molecular level.
The variety of alleles in the gene pool of a population increases the genetic diversity so a number of examples are used to demonstrate how the number of phenotypes increases with the number of alleles at a locus. The CFTR gene is used to demonstrate how 2 alleles results in 2 different phenotypes and therefore genetic diversity. Moving forwards, students will discover that more than 2 alleles can be found at a locus and they are challenged to work out genotypes and phenotypes for a loci with 3 alleles (shell colour in snails) and 4 alleles (coat colour in rabbits).
Moving forwards, a step by step guide to complete a worked example to calculate a value of D using Simpson’s index of diversity. Students are challenged with a range of exam-style questions where they have to apply their knowledge and all mark schemes are displayed and clearly explained within the PowerPoint to allow students to assess their understanding and address any misconceptions if they arise.
The final part of the lesson considers how DNA fingerprinting can be used to assess biodiversity at a molecular level and again a series of exam-style questions are used to challenge the students to apply their newly-acquired knowledge to an unfamiliar situation.
This lesson introduces the three-domain system and describes some of the biochemical methods used in classification to overcome the problems of morphological convergence. The PowerPoint and accompanying resources have been designed to cover points [c] and [e] in AS unit 2, topic 1 of the WJEC A-level Biology specification
The lesson begins with an introduction of Carl Woese and goes on to describe how he is most famous for his definition of the Archaea as a new domain of life. Students were introduced to domains and the other classification taxa in a previous lesson, so their recall of this knowledge is continually tested and built upon as details are added. Students will discover the key differences between Archaea and Bacteria that led to the splitting of the prokaryotae kingdom and the addition of this higher classification rank. Moving forwards, the rest of the lesson considers other molecules that can be compared between species for classification purposes and the primary structure of cytochrome is described and discussed. At this point in the lesson, the students are also tested on their knowledge of the nature of the genetic code and have to explain how mutations to DNA can also be used for comparative purposes. The use of DNA genetic fingerprinting is briefly introduced and this is described in greater detail in a future lesson about assessing biodiversity at a molecular level
This lesson describes how biodiversity is generated through natural selection and leads to behavioural, anatomical and physiological adaptations. The PowerPoint and accompanying resources have been designed to cover specification points (m) & (n) in AS unit 2, topic 1 of the WJEC A-level Biology specification
President Trump’s error ridden speech about antibiotics is used at the beginning of the lesson to remind students that this is a treatment for bacterial infections and not viruses as he stated. Moving forwards, 2 quick quiz competitions are used to introduce MRSA and then to get the students to recognise that they can use this abbreviation to remind them to use mutation, reproduce, selection (and survive) and allele in their descriptions of evolution through natural selection. The main task of the lesson challenges the students to form a description that explains how this strain of bacteria developed resistance to methicillin to enable them to see the principles of natural selection. This can then be used when describing how the anatomy of the modern-day giraffe has evolved over time. The concept of convergent evolution is introduced and links are made to the need for modern classification techniques as covered earlier in topic 1. Moving forwards, students will understand how natural selection leads to adaptations and a quick quiz competition introduces the different types of adaptation and a series of tasks are used to ensure that the students can distinguish between anatomical, behavioural and physiological adaptations. The Marram grass is used to test their understanding further, before a step by step guide describes how the lignified cells prevent a loss of turgidity. Moving forwards, the students are challenged to explain how the other adaptations of this grass help it to survive in its environment. A series of exam-style questions on the Mangrove family will challenge them to make links to other topics such as osmosis and the mark schemes are displayed to allow them to assess their understanding. The final part of the lesson focuses on the adaptations of the anteater but this time links back to the topic of taxonomy and students have to answer questions about species and classification hierarchy.
Due to the extensiveness of this lesson and the detail contained within the resources, it is estimated that it will take in excess of 2 hours of allocated A-level teaching time to deliver this lesson.
This lesson describes the characteristic features of the Animalia, Plantae, Fungi, Protoctista and Prokaryotae kingdoms. The engaging PowerPoint and accompanying resources have been designed to cover point (d) in AS unit 2, topic 1 of the WJEC A-level Biology specification
This lesson begins with a knowledge recall as students have to recognise that prior to 1990, kingdom was the highest taxa in the classification hierarchy. Moving forwards, they will recall the names of the five kingdoms and immediately be challenged to split them so that the prokaryotae kingdom is left on its own. An opportunity is taken at this point to check on their prior knowledge of the structure of a bacterial cell as covered in unit 1, topic 2. These prior knowledge checks are found throughout the lesson (along with current understanding checks) as students are also tested on their knowledge of the structure and function of cellulose. This is found in the section of the lesson where the main constituent of the wall can be used to distinguish between plantae, fungi and prokaryotae. Quick quiz competitions, such as YOU DO THE MATH and SAY WHAT YOU SEE are used to introduce key values and words in a fun and memorable way. The final part of the lesson looks at the protoctista kingdom and students will come to understand how these organisms tend to share a lot of animal or plant-like features.
Both of the accompanying resources have been differentiated to allow students of differing abilities to access the work and this lesson has been written to tie in with the previously uploaded lesson on classification and the binomial naming system
This lesson describes the classification system, focusing on the biological classification of a species and the 7 taxa found above this lowest taxon. The engaging PowerPoint and accompanying resource have been designed to cover points (a), (b), (f) & (g) in AS unit 2, topic 1 of the WJEC A-level Biology specification and also describes the binomial naming system which uses the genus and species. The lesson also contains links to upcoming lessons where the three-domain classification system and the characteristics of the five kingdoms are covered.
The lesson begins by looking at the meaning of a population in Biology so that the term species can be introduced. A hinny, which is the hybrid offspring of a horse and a donkey, is used to explain how these two organisms must be members of different species because they are unable to produce fertile offspring. Moving forwards, students will learn that classification is a means of organising the variety of life based on relationships between organisms using differences and similarities in phenotypes and in genotypes and is built around the species concept and that in the modern-day classification hierarchy, species is the lowest taxon. A quiz runs throughout the lesson and this particular round will engage the students whilst they learn (or recall) the names of the other 7 taxa and the horse and the donkey from the earlier example are used to complete the hierarchy. Students will understand that the binomial naming system was introduced by Carl Linnaeus to provide a universal name for each species and they will be challenged to apply their knowledge by completing a hierarchy for a modern-day human, by spotting the correct name for an unfamiliar organism and finally by suggesting advantages of this system.
This bundle contains 18 detailed and engaging lessons which cover the following specification points in module 3 (Exchange and transport) of the OCR A-level Biology A specification:
3.1.1: Exchange surfaces
The need for specialised exchange surfaces
The features of an efficient exchange surface
The structures and functions of the components of the mammalian gaseous exchange system
The mechanism of ventilation in mammals
The mechanisms of ventilation and gas exchange in bony fish and insects
3.1.2: Transport in animals
The double, closed circulatory system in mammals
The structure and functions of arteries, arterioles, capillaries, venules and veins
The formation of tissue fluid from plasma
The external and internal structure of the heart
The cardiac cycle
How heart action is initiated and coordinated
The use and interpretation of ECG traces
The role of haemoglobin in transporting oxygen and carbon dioxide
The oxygen dissociation curve for foetal and adult haemoglobin
3.1.3: Transport in plants
The structure and function of the vascular systems in the roots, stems and leaves
The transport of water into the plant, through the plant and to the air surrounding the leaves
The mechanism of translocation
As well as the detailed A-level Biology content of the PowerPoint slides, the resources contain a wide range of tasks including guided discussion points, exam-style questions and quiz competitions which will engage and motivate the students
This bundle contains 7 lessons which are highly detailed and cover the following points in the surface area to volume ratio, gas exchange and digestion and absorption topics of the AQA A-level Biology specification:
The relationship between the size of an organism or structure and its surface area to volume ratio
The development of systems in larger organisms as adaptations that facilitate exchange as this ratio reduces
Adaptations of gas exchange surfaces in single-celled organisms, insects, bony fish and in the leaf of a dicotyledonous plant
The gross structure of the human gas exchange system
The essential features of the alveolar epithelium over which gas exchange takes place
Ventilation and the exchange of gases in the lungs
Digestion in mammals of carbohydrates, proteins and lipids
Mechanisms for the absorption of the products of digestion by cells lining the ileum
If you would like to sample the quality of lessons in this bundle, then download the alveolar epithelium and absorption in the ileum lessons as these have been uploaded for free
This lesson describes the structures and functions of the components of the mammalian gaseous exchange system. The PowerPoint and accompanying resources have been designed to cover point 3.1.1 [c] of the OCR A-level Biology A specification and contains links to future topics such as transport in animals as well as prior knowledge checks of their recall of the content of previously covered modules.
The lesson is filled with a range of activities such as guided discussion periods, exam-style questions (with markschemes) and quiz competitions and these run alongside the slides containing the detailed A-level Biology content to cover the following features:
The incomplete rings of cartilage, ciliated pseudostratified columnar epithelium and goblet cells in the trachea
The narrowing airways of the primary, secondary and tertiary bronchi
The elastic fibres and smooth muscle in the terminal and respiratory bronchioles and the change from simple columnar epithelium to simple cuboidal epithelium
The large surface area to volume ratio and the simple squamous epithelium of the alveoli
The pleural cavity and fluid of the lungs
When describing the production of mucus by the goblet cells in the trachea, time is taken to consider cystic fibrosis and the inheritance of this autosomal recessive disorder. Students will be supported in working out genotypes from a pedigree tree to prepare them for module 6.1.2 (Patterns of inheritance)
This lesson describes the gross structure of the human gas exchange system and the functions of the structural components like goblet cells. The PowerPoint and accompanying resources have been designed to cover points 9.1 (a & c) of the CIE A-level Biology specification and has been specifically planned to prepare students for an upcoming lesson where the gas exchange between the alveoli and the blood is described.
The lesson is filled with a range of activities such as guided discussion periods, exam-style questions (with markschemes) and quiz competitions and these run alongside the slides containing the detailed A-level Biology content to cover the following features:
The incomplete rings of cartilage, ciliated pseudostratified columnar epithelium and goblet cells in the trachea
The narrowing airways of the primary, secondary and tertiary bronchi
The elastic fibres and smooth muscle in the terminal and respiratory bronchioles
The pleural cavity and fluid of the lungs
When describing the production of mucus by the goblet cells in the trachea, time is taken to consider cystic fibrosis and the inheritance of this autosomal recessive disorder. Students will be supported in working out genotypes from a pedigree tree to prepare them for topic 16 (Inherited change)
This lesson describes the gross structure of the human gas exchange system, including the trachea, bronchi, bronchioles and lungs. The PowerPoint and accompanying resources are part of the third lesson in a series of 6 which have been designed to cover the detail of topic 3.2 in the AQA A-level Biology specification which is titled gas exchange and this lesson has been specifically planned to prepare students for the next lesson where the essential features of the alveoli are described.
The lesson is filled with a range of activities such as guided discussion periods, exam-style questions (with markschemes) and quiz competitions and these run alongside the slides containing the detailed A-level Biology content to cover the following features:
The incomplete rings of cartilage, ciliated pseudostratified columnar epithelium and goblet cells in the trachea
The narrowing airways of the primary, secondary and tertiary bronchi
The elastic fibres and smooth muscle in the terminal and respiratory bronchioles
The pleural cavity and fluid of the lungs
When describing the production of mucus by the goblet cells in the trachea, time is taken to consider cystic fibrosis and the inheritance of this autosomal recessive disorder. Students will be supported in working out genotypes from a pedigree tree to prepare them for the topic of inheritance (7.1)
This lesson explains why large organisms with a low surface area to volume ratio need specialised gas exchange surfaces and a mass transport system. The PowerPoint and accompanying worksheets have been designed to cover points 4.1 (i & ii) of the Edexcel A-level Biology B specification and have been specifically planned to prepare students for the upcoming lessons on gas exchange (4.3) and circulation (4.4)
The students are likely to have been introduced to the surface area to volume ratio at GCSE, but understanding of its relevance tends to be mixed. Therefore, real life examples are included throughout the lesson that emphasise the importance of this ratio in order to increase this relevance. A lot of students worry about the maths calculations that are associated with this topic so a step by step guide is included at the start of the lesson that walks them through the calculation of the surface area, the volume and then the ratio. Through worked examples and understanding checks, SA/V ratios are calculated for cubes of increasing side length and living organisms of different size. These comparative values will enable the students to conclude that the larger the organism or structure, the lower the surface area to volume ratio. A differentiated task is then used to challenge the students to explain the relationship between the ratio and the metabolic demands of a single-celled and multicellular organisms and this leads into the next part of the lesson, where the adaptations of large organisms to increase this ratio at the exchange surfaces are covered. The students will calculate the SA/V ratio of a human alveolus (using the surface area and volume formulae for a sphere) and will see the significant increase that results from the folding of the membranes. In addition to the ratio, time is taken to discuss and describe how the maintenance of a steep concentration gradient and a thin membrane are important for the rate of diffusion and again biological examples are used in humans and other organisms to increase the understanding. Fick’s law of diffusion is also introduced as a mechanism to help the students to recall that surface area, concentration difference and thickness of membrane govern the rate of simple diffusion.
The final part of the lesson considers how a mass transport system is needed alongside the specialised gas exchange surface to allow the oxygen to be delivered to the respiring cells to enable them to continue to carry out aerobic respiration to generate ATP.
This lesson explains the need for specialised exchange surfaces and uses examples to describe the features of an efficient exchange surface. The PowerPoint and accompanying worksheets have been designed to cover points 3.1.1 (a & b) of the OCR A-level Biology A specification and also have been specifically planned to prepare the students for the upcoming lessons in module 3 on gas exchange and mass transport in animals.
The students are likely to have been introduced to the surface area to volume ratio at GCSE, but understanding of its relevance tends to be mixed. Therefore, real life examples are included throughout the lesson that emphasise the importance of this ratio in order to increase this relevance. A lot of students worry about the maths calculations that are associated with this topic so a step by step guide is included at the start of the lesson that walks them through the calculation of the surface area, the volume and then the ratio. Through worked examples and understanding checks, SA/V ratios are calculated for cubes of increasing side length and living organisms of different size. These comparative values will enable the students to conclude that the larger the organism or structure, the lower the surface area to volume ratio. A differentiated task is then used to challenge the students to explain the relationship between the ratio and the metabolic demands of a single-celled and multicellular organisms and this leads into the next part of the lesson, where the adaptations of large organisms to increase this ratio at the exchange surfaces are covered. The students will calculate the SA/V ratio of a human alveolus (using the surface area and volume formulae for a sphere) and will see the significant increase that results from the folding of the membranes. In addition to the ratio, time is taken to discuss and describe how the maintenance of a steep concentration gradient and a thin membrane are important for the rate of diffusion and again biological examples are used in humans and other organisms to increase the understanding. Fick’s law of diffusion is also introduced as a mechanism to help the students to recall that surface area, concentration difference and thickness of membrane govern the rate of simple diffusion.
As well as making links to upcoming topics, prior knowledge checks are used to challenge the students on their knowledge of previously-covered modules which include inorganic ions, organelles, cell membrane transport and tissues.
This lesson describes how Fick’s law of diffusion is governed by the three main properties of gas exchange surfaces in living organisms. The PowerPoint and accompanying worksheets have been designed to cover points 2.1 (i & ii) of the Edexcel International A-level Biology specification and there is a particular focus on the relationship between the size of an organism or structure and its surface to volume ratio.
Adolf Fick is briefly introduced at the start of the lesson and the students will learn that his law of diffusion governs the diffusion of a gas across a membrane and is dependent on three properties. The students are likely to know that surface area is one of these properties but although they may have been introduced to the surface area to volume ratio at iGCSE, their understanding of its relevance tends to be mixed. Therefore, real life examples are included throughout the lesson that emphasise the importance of this ratio in order to increase the relevance. A lot of students worry about the maths calculations that are associated with this topic so a step by step guide is included at the start of the lesson to walk them through the calculation of the surface area, the volume and then the ratio. Through worked examples and understanding checks, SA/V ratios are calculated for cubes of increasing side length and living organisms of different size. These comparative values will enable the students to conclude that the larger the organism or structure, the lower the surface area to volume ratio. A differentiated task is then used to challenge the students to explain the relationship between the ratio and the metabolic demands of an organism and this leads into the next part of the lesson, where the adaptations of a human to increase the ratio at the gas exchange surface is covered. The students will calculate the SA/V ratio of a human alveolus (using the surface area and volume formulae for a sphere) and will see the significant increase that results from the folding of the membranes. The remainder of the lesson introduces concentration difference and thickness of membrane as the other two properties in Fick’s law of diffusion and students are reminded that the maintenance of a steep concentration gradient and a reduction in the diffusion distance are critical for this transport mechanism.
This lesson has been specifically planned to prepare students for the next lesson which describes how the structure of the mammalian lung is adapted for rapid gas exchange (specification point 2.1 [iii])