Unit 9.5 Human biology (12 hours)
Outline of unit:
This unit starts with learners considering excretion in the context of the human renal system. Learners then study reproduction (another characteristic of living organisms) in the human context; they focus on gametes and fertilisation while exploring the role of DNA, genes and chromosomes. The inheritance of biological sex is studied in terms of XX and XY chromosomes. Finally, learners discuss how fetal development is influenced by maternal health including her diet and whether she drinks alcohol, smokes or uses drugs (legal or illegal).
During this unit, learners have opportunities for describing the strengths and limitations of models as well as understanding that models reflect current scientific evidence and they can change when new evidence is discovered. Learners also have opportunities to use symbols to represent scientific ideas when using information about XX and XY chromosomes and to interpret data about fetal development in relation to maternal health.
Recommended prior knowledge or previous learning required for the unit:
Learners will benefit from previous experience of:
● knowing the seven characteristics of living organisms including excretion
● explaining how the structure of some specialised cells are related to their functions
● describing the functions of the cell nucleus
● knowing that animals, including humans, produce offspring that have a combination of features from their parents
● describing how human growth, development and health can be affected by lifestyle, including diet and smoking
● knowing that blood contains blood cells and dissolved substances.
Suggested examples for teaching Science in Context:
9SIC.03 Evaluate issues which involve and/or require scientific understanding.
Learners can discuss the need for two kidneys and some of the ethics involved in donating kidneys to those who have no functioning kidneys. They can consider if the ethics change depending on if the donor is living or deceased. This could be approached by giving learners a ‘for’ or ‘against’ position and the opportunity to use secondary information sources to carry out some research and discuss their ideas. This could be followed with a class debate on the pros and cons of donating a kidney and, more generally, organ donation.
9SIC.02 Describe how science is applied across societies and industries, and in research.
Knowledge about the effects of maternal smoking, diet and drugs on fetal development has greatly advanced in recent years and advice resulting from research into these areas is now much more readily available. Learners can discuss the different ways in which advice can be given so that it reaches as many parents and prospective parents as possible.
Learning objective Key vocabulary Possible models and representations Possible misconceptions 9Bs.02 Describe the
structure of the human excretory (renal) system and its function (limited to kidneys filtering blood to remove urea, which is excreted in urine).
Excretory system (renal system), excretion, kidney, filtration, urea, urine
Learners could use a combination of the following models:
● physical models illustrating the anatomy of the kidneys and associated renal system
● coloured diagrams illustrating the human excretory system
● animations showing the process of filtration of blood by the kidneys and the formation of urine
● physical filtration models to represent a kidney (e.g. simple sieves; filter funnels and filter paper) can be used to show that dissolved substances (e.g. urea) will pass through a filter while insoluble substances and large components (e.g. blood cells) will not pass through.
Some learners may need guidance on what the term ‘excretion’ means in terms of the human renal system; ‘excretion’ can sometimes be confused with ‘egestion’. Explain that excretion always means getting rid of products made in the body whereas egestion means is the process of voiding undigested food.
Some learners may have the idea that urine and faeces are analogous. Explain that urine is produced from urea that has been absorbed into the blood and then is excreted. Faeces are largely made of waste materials that have not been absorbed into the blood and are egested.
The idea that ‘dirty’ blood is filtered to make the blood ‘clean’ may be held by some learners. Ensure that correct terminology is used and emphasise the idea that filtering removes a waste product (urea) from the blood but the blood itself if not ‘dirty’.
Any confusion between ‘urea’ and ‘urine’ can be overcome by showing learners how urea dissolves to form a solution of urine. If urea is not available, solid sugar can be dyed with a little yellow food colouring and then dissolved.
9Bs.03 Know that chromosomes contain genes, made of DNA, and that genes contribute to the determination of an organism's
characteristics.
DNA, genes, chromosomes,
organisms, characteristics
Learners can use coloured diagrams or animations to show the relationships between DNA, genes and chromosomes.
Some learners may be confused by the relative sizes of DNA, genes and chromosomes. Explain that genes are smaller than chromosomes; the extremely long DNA molecules (often said to be about 3m per cell) are packaged into
chromosomes. Making DNA models will help learners understand the relationships between DNA, genes and chromosomes.
Learners might have a simplistic view of the relationship between genes and characteristics, thinking either that genes decide everything or
genes are irrelevant. Discuss with learners there is a range of different ways genes contribute to characteristics and some genes do not have a direct impact on an organisms characteristics while others are vital to an organism’s survival. Examples of genes and their role in human biology can highlight the variation.
9Bp.01 Describe the fusion of gametes to produce a fertilised egg with a new combination of DNA.
Fusion, gametes,
fertilisation, egg, DNA Physical models of male gametes, female gametes and fertilised eggs will help learners appreciate the relative size and structures of these cells.
Coloured diagrams, showing some simple chromosome structures of gametes and the fertilised egg, will help learners appreciate that fertilised eggs have a new combination of DNA.
Animations can help learners understand the processes of fusion and fertilisation, as well as the formation of a new combination of DNA within a fertilised egg.
The idea of fusion is different from just ‘meeting’
and it is helpful to make this clear to learners, so that they fully understand how the fertilised egg has a new combination of DNA. Ensure that the term
‘fusion’ is used wherever appropriate and that learners understand this term. Also ensure learners understand gametes contain DNA from the parents.
9Bp.02 Describe the inheritance of sex in humans in terms of XX and XY chromosomes.
Inheritance, sex, chromosomes, XX chromosomes, XY chromosomes, male, female, parent, offspring
Learners can use sets of cards, individually marked with an X or a Y, to model chromosomes and to work out the chances of a fertilised egg forming a baby boy or girl.
Pedigree diagrams and Punnet squares can be used to show the inheritance of X and Y chromosomes.
XX and XY and their role in humans can be confused (especially if learners find out about sex determination in other species such as birds).
Provide plenty of opportunities for learners to link the pairs of chromosomes to the correct sex.
Biological sex and gender are not the same thing in terms of scientific language. Clarify the difference and try to use the terms correctly to encourage learners to do the same.
9Bp.08 Discuss how fetal development is affected by the health of the mother, including the effect of diet, smoking and drugs.
Fetus, fetal development, health, diet, smoking, medicine, drugs
Videos that discuss how the health of a mother affects fetal development are useful in portraying real life examples that learners may relate to, but such videos should be previewed to make sure that they are appropriate for learners.
Learners may have misconceptions about diet including that there are ‘unhealthy’ foods and
‘healthy’ foods. When discussing diet, make sure that learners appreciate that a diet being
considered ‘unhealthy’ is about the quality and/or quantity of each item. For example, some foods considered healthy may be unhealthy if eaten in excess. This is important when addressing the misconception pregnant women require more food due to being pregnant when no extra calories are required in the first 6 months and only an extra 10%
are required in the last 3 months.
Some learners may not understand how a pregnant woman smoking may affect her fetus. This can be addressed by showing data about the effects of maternal smoking on fetal health. Learners could also be given diagrams that show how substances in a mother’s blood can cross the placenta and enter fetal blood.
Some learners may think that only illegal drugs may harm a fetus. Explain that there are common, legally available drugs, including alcohol and medicines, that can affect the health of a fetus if taken by the mother.