SNAB T2 Teaching scheme
Topic 2 Genes and health
This teaching scheme is divided into three parts.
- Introduction.
- Road map: a suggested route through Topic 2.
- Guidance notes for teachers and lecturers. These include a commentary that runs parallel with the student book with hints and tips on teaching and references to the associated activities.
There are more detailed notes about individual activities in the teacher/lecturer sheets accompanying most activities.
Introduction
The Road map starting on page 2 is a suggested route through Topic 2.
The learning outcomes are numbered as in the specification.
Here are notes a route through the topic if two teachers/lecturers are sharing a group for Topic 2. The first teacher starts introduces the topic context, making it clear that the problem is a faulty protein in the membrane. The first teacher looks at the effects of this on the lungs, while the second teacher is considering the effect on the digestive and reproductive system. The first teacher would complete sessions 2 / 3 / 6 / 7 / 8 / 9 / 17 / 18 /19 / 20 / 21. The second teacher would complete sessions 4 / 5 / 10 / 11 / 12 / 13 / 14 / 15 / 16 This covers protein structure before enzymes. The first teacher has more sessions, so if they have done the introduction the second teacher may need to complete genetic screening (sessions 20 and 21) at the end of their sequence.
Note that learning outcome 17 Explain how the expression of a gene mutation in people with cystic fibrosis impairs the functioning of the gaseous exchange, digestive and reproductive systemappears in several places throughout the table that starts on page 2.
There is an AS summary chart map at the end of the guidance notes. This shows where concepts are introduced and revisited in later topics. (Some students will have studied cystic fibrosis and its effects, and the associated ethical dilemmas, at GCSE.)
It is assumed that each session is approximately an hour in length. There are more activities than can be done in the time available in most centres, so select a balanced collection according to your and your students’ interests, and the time and resources available. Some activities are labelled ‘Core’. Core activities contain experimental techniques included in the specification, and may appear in questions on the unit exam for this topic. These learning outcomes are in bold in the specification, and in the Read map below. They are underlined in the Guidance notes below. In the Road map, activities are in italics if there is an additional activity covering the same material more directly. Choose which activities students complete, and substitute activities when appropriate.
The Core practicals, and any other practicals completed by students, can be used to assess practical biological skills as part of the Unit 3 coursework assessment.
There are various activities – particularly the interactive tutorials associated with some of the activities – which could be completed by students outside of class time. These activities are shown in the lower half of each ‘Possible activities’ box.
Road map: a route through Topic 2 Genes and health
Session / Areas to be covered / Possible activities1 / Introductory presentation (Interactive tutorial)
Activity 2.1 After the funeral (A2.01L)
Activity 2.2 Personal CF stories (A2.02L)
GCSE review test (Interactive)
2 / Diffusion and surface area to volume ratio
6 Describe the properties of gas exchange surfaces in living organisms (large surface area to volume ratio, thickness of surface, difference in concentration) and explain how the structure of the mammalian lung is adapted for rapid gaseous exchange.
17 Explain how the expression of a gene mutation in people with cystic fibrosis impairs the functioning of the gaseous exchange, digestive and reproductive systems. / Activity 2.3 The effect of size on uptake by diffusion (A2.03L) (Practical)
Q2.1–Q2.13
3 / Structure of alveoli and SA:V ratio; properties of gas exchange surfaces
6 Describe the properties of gas exchange surfaces in living organisms (large surface area to volume ratio, thickness of surface, difference in concentration) and explain how the structure of the mammalian lung is adapted for rapid gaseous exchange. / Activity 2.4 The structure of alveoli (A2.04L) (Practical)
Activity 2.5 Alveoli and lung surface area (A2.05L) (Interactive)
Checkpoint question 2.1
4/5 / Protein structure and function
7 Describe the basic structure of an amino acid (structures of specific amino acids are not required) and the formation of polypeptides and proteins (as amino acid monomers linked by peptide bonds in condensation reactions) and explain the significance of a protein’s primary structure in determining its three-dimensional structure and properties (globular and fibrous proteins and types of bonds involved in three dimensional
structure). / Activity 2.6 Proteins (A2.06L) (Interactive)
Checkpoint question 2.2
6 / Membrane structure
2 Explain how models such as the fluid mosaic model of cell membranes are interpretations of data used to develop scientific explanations of the structure and properties of cell membranes. / Activity 2.7 The fluid mosaic model (A2.07L)
Build models of membranes
7 / Membrane structure
5 Describe how membrane structure can be investigated practically, eg by the effect of alcohol concentration or temperature on membrane permeability. / Activity 2.8 Why does the colour leak out of cooked beetroot? (Core) (A2.08L)
8 / Transport across membranes
3 Explain what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane (consideration of water potential is not required).
4 Explain what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP), endocytosis and exocytosis and describe the involvement of carrier and channel proteins in membrane transport. / Activity 2.9 Methods of transport within and between cells (A2.09L) (Practical)
9 / Membrane transport in epithelial cells
3 Explain what is meant by osmosis in terms of the movement of free water molecules through a partially permeable membrane (consideration of water potential is not required).
4 Explain what is meant by passive transport (diffusion, facilitated diffusion), active transport (including the role of ATP), endocytosis and exocytosis and describe the involvement of carrier and channel proteins in membrane transport. / Activity 2.10 CFTR protein and membrane transport (A2.10L) (Interactive)
10 / Enzyme structure and function
8 Explain the mechanism of action and specificity of enzymes in terms of their three-dimensional structure and explain that enzymes are biological catalysts that reduce activation energy, catalysing a wide range of intracellular and extracellular reactions
17 Explain how the expression of a gene mutation in people with cystic fibrosis impairs the functioning of the gaseous exchange, digestive and reproductive systems. / Checkpoint questions 2.3 and 2.4
11/12 / Enzyme concentration and digestion
9 Describe how enzyme concentrations can affect the rates of reactions and how this can be investigated practically by measuring the initial rate of reaction.
17 Explain how the expression of a gene mutation in people with cystic fibrosis impairs the functioning of the gaseous exchange, digestive and reproductive systems. / Activity 2.11 Enzyme concentrations and enzyme activity (Core) (A2.11L) (Practical)
Checkpoint question 2.5
13 / DNA structure
10 Describe the basic structure of mononucleotides (as a deoxyribose or ribose linked to a phosphate and a base, ie thymine, uracil, cytosine, adenine or guanine) and the structures of DNA and RNA (as polynucleotides composed of mononucleotides linked through condensation reactions) and describe how complementary base pairing and the hydrogen bonding between two complementary strands are involved in the formation of the DNA double helix. / Activity 2.13 Extraction of DNA (A2.13L) (Practical)
Activity 2.12 DNA model (A2.12L)
14/15 / Protein synthesis
14 Outline the process of protein synthesis, including the role of transcription, translation, messenger RNA, transfer RNA and the template (antisense) DNA strand (details of the mechanism of protein synthesis on ribosomes are not required at AS).
12 Explain the nature of the genetic code (triplet code only; non-overlapping and degenerate not required at AS). / Activity 2.14 Nucleic acids and protein synthesis (A2.14L) (Interactive)
16 / DNA replication
11 Describe DNA replication (including the role of DNA polymerase), and explain how Meselson and Stahl’s classic experiment provided new data that supported the accepted theory of replication of DNA and refuted competing theories.
15 Explain how errors in DNA replication can give rise to mutations and explain how cystic fibrosis results from one of a number of possible gene mutations / Activity 2.15 Meselson and Stahl’s experiment on DNA replication (A2.15L) (Interactive)
17 / Monohybrid inheritance
16 Explain the terms: gene, allele, genotype, phenotype, recessive, dominant, homozygote and heterozygote; and explain monohybrid inheritance, including the interpretation of genetic pedigree diagrams, in the context of traits such as cystic fibrosis, albinism, thalassaemia, garden pea height and seed morphology / Activity 2.16 Reebops (A2.16L) (Practical)
Checkpoint question 2.6
18 / Monohybrid inheritance
16 Explain the terms: gene, allele, genotype, phenotype, recessive, dominant, homozygote and heterozygote; and explain monohybrid inheritance, including the interpretation of genetic pedigree diagrams, in the context of traits such as cystic fibrosis, albinism, thalassaemia, garden pea height and seed morphology
Activity 2.17 Inheritance problems (A2.17L)
19 / Gene therapy
18 Describe the principles of gene therapy and distinguish between somatic and germ line therapy. / Activity 2.18 Gene therapy – another side to the story (A2.18L)
20 / Genetic screening
19 Explain the uses of genetic screening: identification of carriers, preimplantation genetic diagnosis and prenatal testing (amniocentesis and chorionic villus sampling) and discuss the implications of prenatal genetic screening.
20 Identify and discuss the social and ethical issues related to genetic screening from a range of ethical viewpoints. / Activity 2.19 Genetic screening (A2.19L)
21 / Genetic screening
20 Identify and discuss the social and ethical issues related to genetic screening from a range of ethical viewpoints. / Activity 2.20 Passing it on (A2.20L)
Class discussion
Activity 2.21 Gene mutation – a personal story (A2.21L)
Guidance notes for teachers and lecturers
You could complete these continuing professional development modules before starting Topic 2: CPD1 A road map for SNAB: Building knowledge and principles through the course and CPD2 Contextualised biology teaching through storylines.
Introduction and GCSE review
The topic starts by introducing a couple, Claire and Nathan, and the dilemma they face in deciding whether or not to start a family knowing that Claire’s sister had cystic fibrosis (CF). A wide range of traditional biology concepts is required to understand the causes and consequences of cystic fibrosis. The ethical issues faced by the couple as they try to make the decision are highlighted. Some students will have studied cystic fibrosis and its effects, and the associated ethical dilemmas, at GCSE.
Teachers or lecturers may be presenting this material to groups containing either a student with CF or a student who has a close relative or friend who has or had the disease. A great deal of sensitivity will be needed. It is nearly always best to talk before the session to the student(s) concerned on a one-to-one basis, and see how they would like it to be handled.
Discussing the topic with students in advance may help you to find out if any of them have connections with CF. Encourage the student(s) in question to take a positive role within the group; their experiences can make a valuable contribution to discussions. If it is difficult for a student, you may need to present the material in a more traditional way as a series of biological principles.
The sections in the topic address the questions that Claire and Nathan may have asked in their search for information to help their decision-making. The opening page poses some of these questions.
On the first spread there is a reference to the initial GCSE review and the GCSE review test. These cover the main GCSE ideas that students will be expected to draw on during the topic – lung structure and function, digestion, genetics and enzymes. The test itself is open access, and it is assumed that it will be completed outside of class time.
The interactive introduction provides an overview of the topic.
Activity 2.1 After the funeral (A2.01L)
This provides an overview of the topic. The play, performed or read as a group activity, provides the opportunity for some discussion. The play is set in the past when Claire was younger. Students use the text of the play to produce a mind map summarising the main issues. This acts as a framework for the topic. Additional notes could be added to this map as the topic unfolds.
Activity 2.2 Personal CF stories (A2.02L)
These personal stories give further insights into the effect of CF on affected individuals and their families. This could be used as an alternative to Activity 2.1.
2.1 The effects of CF on the lungs
The basic structure of the lungs and the mechanism of breathing are covered in the GCSE review. The media archive within the electronic resources contains the lung diagram of Figure 2.2 with and without labels. Labelling the diagram could be a starting-point. If students have completed the GCSE review this should be straightforward.
In CF patients there is a build up of sticky mucus in the airways. An X-ray of the lungs of a CF patient shows this clearly. There is a CF patient X-ray and CAT scan in the general weblinks for Topic 2. Photographs of normal and CF-affected lungs and pancreases can also be found via the weblinks.
There are two major consequences of sticky mucus in the lungs: the first is an increased chance of infection because the mucus cannot be cleared from the lungs, so pathogenic bacteria can take hold; the second is the blockage of airways by the mucus. The infection problem is described in the student book and Q2.1 and Q2.2 are linked to this section. The blockage of the airways occurs to a greater extent in the later stages of the disease.
The main consequence of airway blockage is a reduction in the effective surface area for gas exchange. The student book has a Key biological principle box with questions introducing the importance of a large surface area to volume ratio. This is followed by a section on the features and properties of gas exchange surfaces. These are complemented by Activities 2.3 to 2.5.
It may be helpful if the continuing professional development module CPD3 Developing practical skills is completed by teachers/lecturers before starting practical work with students.
Activity 2.3 The effect of size on uptake by diffusion (A2.03L)
This provides a practical investigation of the effect of surface area on uptake by diffusion. It is supported by student book questions Q2.3 to Q2.13, which guide the student through the ideas.
Activity 2.4 The structure of alveoli (A2.04L)
Students follow the instructions on the activity sheet as they observe slides of lungs. The activity is an opportunity to introduce the use of an eye-piece graticule and stage micrometer for measuring. See the Practical support sheet ’Measuring: Size and scale’ (P0.09S). Precision in measuring can be discussed.
Activity 2.5 Alveoli and lung surface area (A2.05L)
In this interactive web-based tutorial, students determine the increase in surface area due to the presence of alveoli using calculations of volume. Students also examine a photomicrograph showing a section through lung tissue, and identify features that increase the efficiency of gas exchange. The interactive tutorial can support students as they complete the calculations on the activity sheet, it can also be done without the tutorial. This web-based tutorial could be used instead of Activity 2.4, or could be set as a class assignment to confirm the ideas covered in Activity 2.4.
Checkpoint question 2.1 can be used as a summary question at the end of this section or as a revision question later. Answers to Checkpoint questions are given on the snabonline website; these are only accessible to teachers.
2.2 Why is the CF mucus so sticky?
To answer this question, students need to understand what is happening in epithelial cells not affected by the disease. Mucus in the lungs is ‘runny’ because of salt and water transport across the epithelial cells. The mucus is sticky in people with CF; this is due to disruption caused by a faulty transport protein channel in the surface membrane of the epithelial cells. Students therefore need to know about the structure and function of proteins. They also need to know about membrane structure and methods of transport across membranes.
A Key biological principle box in the student book relates protein structure to function. Activity 2.6 is found within this box.
Activity 2.6 Proteins (AS2.06L)
This interactive tutorial describes the basic structure of amino acids and follows the processes involved in the formation of polypeptides. The student worksheet can be completed using the student book without the tutorial.
The interactive tutorial does not differentiate between globular and fibrous proteins – this distinction is made in the student book. Checkpoint question 2.2 requires students to compare and contrast these two types of protein.
Cell membrane structure
The student book goes on to describe the structure of cell membranes, and considers evidence for the fluid mosaic model which explains the structure and properties of cell membranes. These ideas are covered in the interactive tutorial accompanying Activity 2.7. The information is applied in Activity 2.8. Building a model of the cell membrane may help students understand the three-dimensional structure of the membrane; plasticine can be used.
Activity 2.7 The fluid mosaic model (A2.07L)
In this activity students evaluate the evidence for different models explaining the structure and function of cell membranes.
Activity 2.8 Why does the colour leak out of cooked beetroot? (A2.08L) Core practical
In this core practical, students use beetroot to examine the effect of temperature or alcohol on cell membranes and relate this to membrane structure. The activity sheet provides detailed procedures for students to follow. Before starting, students are asked to make a hypothesis and check that the procedure will test their hypothesis. Prompts help them focus on various practical and investigative skills.
How so substances pass through cell membranes?
The student book describes diffusion, osmosis, active transport, exocytosis and endocytosis.
Activity 2.9 Methods of transport within and between cells (A2.09L)
This activity consists of a set of simple experiments or demonstrations for diffusion and osmosis. There is an interactive simulation of the final experiment using blood in the Biochemistry support on the snabonline website. Students will not have to do any calculations using water potentials.