Homeostasis - hormones
Hormones and homeostasis are somewhat abstract concepts. Students have direct experience of a lot of the actions. For example, they know if they drink a lot of water, they will go to the toilet more often to get rid of the excess water. However, the underlying mechanisms of homeostasis are less clear. The challenge comes in helping students to link the internal biology that is taking place with the experiences they have of their own body.
Feedback loops are an important feature and time should be taken to help students to understand the concept. Without a good grounding in this idea, it is difficult to see how various interactions can maintain a regular state.
It is useful to stress why homeostasis is important and explain why we need to keep a constant body temperature, rather than just studying the process in isolation.
Whilst this list provides a source of information and ideas for experimental work, it is important to note that recommendations can date very quickly. Do NOT follow suggestions which conflict with current advice from CLEAPSS, SSERC or recent safety guides. eLibrary users are responsible for ensuring that any activity, including practical work, which they carry out is consistent with current regulations related to Health and Safety and that they carry an appropriate risk assessment. Further information is provided in our Health and Safety guidance.
Controlling Change
This resource contains a lot of relevant material.
An activity that begins on page 63 looks at control systems and feedback loops. This is a vitally important concept for students to grasp if they are to fully understand homeostasis and how hormones work. Look at the activity to see which examples are relevant to your students. The initial examples look at the control of a steam iron’s temperature. Another typical example is the thermostat of a central heating system.
Whichever example is used, it is worthwhile stressing the point that the detector causes a response that returns the system back to normal. Constant monitoring and changing of response is called a feedback loop.
To relate this to homeostasis in the body, the cards on page 84 can be used. These show the process of osmoregulation. Note that the number order is not the correct order of events. In groups, have students go through the process. If they have not yet covered kidney function, a set of cards that show a sequence of events in the regulation of body temperature could be produced.
As a further extension of the idea, students can be challenged to produce their own cards and do the same for the control of blood sugar levels.
Section 4 in the book (starting on page 70) contains a range of activities relating directly to hormonal control systems. A simple experiment on phototropism (page 74) can be used to show students that hormones are involved in the control of plant growth. It helps to remains students that plants are complex organisms.
Keeping Things Steady *suitable for home teaching*
This article, from Catalyst magazine, looks in the broader sense at homeostasis. It discusses examples including the regulation of:
• blood pH
• carbon dioxide and oxygen
• blood sugar levels
• water balance
The good thing about the article is that it describes the effects of imbalances on the cells of the body. This is often an area that is failed to be emphasised. It is assumed that students will know why it is a good idea to maintain a constant body temperature. Reinforcing the link to enzyme optimum temperatures is often omitted.
Students can read the article and then be give time to consider a more open-ended question. “Why is it important to regulate.....” You can choose one of the factors that the students are familiar with and ask them to make the connections with as many body systems (or plant systems) as possible. Students could work individually or in groups. Outputs could include a piece of extended writing, concept map or group discussion.
Blood sugar level graphs
This animation contains a series of graphs that show blood sugar regulation and how it can go wrong in type I and type II diabetes. They are fairly complex and may need to be reviewed several times to make sure students have understood them.
A good sequence would be to first show the graph of a normal response. It can be paused to point out when sugar from a meal enters the blood and how this is represented in the graph. The normal response as a peak in insulin release, followed by lowering of blood sugar level to normal, can be pointed out. You can ask students where this sugar goes to check that they have understood it is being stored, and not just that it is being used up in respiration.
The second and third graphs show responses in type I and type II diabetes.
With type I diabetes, it is useful to show how if untreated blood sugar levels remain damagingly high. How would this normally be detected? Ask students what problems does this cause if left untreated for long periods of time?
Go on to show the response to injected insulin in type I diabetes.
In type II diabetes, ask the students how the graph shows that the body does not respond to the insulin it produces.
Screen captures of the graphs can be used to develop questions to see how well students can interpret the graphs and understand the difference between a normal response and type I and type II diabetes.