Communication and homestasis (5.1.1)
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|Content (from A-level)
The content from the specification that is covered by this delivery guide is:
|5.1.1 Communication and homeostasis|
|(a)||the need for communication systems in multicellular organisms||To include the need for animals and plants to respond to changes in the internal and external environment and to coordinate the activities of different organs.|
|(b)||the communication between cells by cell signalling||To include signalling between adjacent cells and signalling between distant cells.|
|(c)||the principles of homeostasis||To include the differences between receptors and effectors, and the differences between negative feedback and positive feedback.
|(d)||the physiological,and behavioural responses involved in temperature control in ectotherms and endotherms.||To include:
A general introduction to this topic could be shown by growing mustard seed.
When the shoots are about 1cm in length, students move the light source and then note how the seeds grow towards the light. This could be connected with measurements or merely observational. This would incorporate PAG11. If time is limited there are many time lapse videos available. For one example, see Time lapse video resource.
Both approaches allow for an open discussion on why plants/animals need to respond to changes in their environment (5.1.1a). This would link in with 5.1.5 plant and animal responses.
Cell signalling for 5.1.1b can be a daunting topic for students as they often feel they need to know all the permutations that occur. There are many signalling pathways that can be downloaded in poster form. See Pathway posters resource.
It should be stressed that this level of involvement is not required and merely used to ‘wet their appetite’ for further study beyond A level.
A good, general video clip on receptor mediated cell signalling can be found within the Receptor mediated cell signalling resource. This can be combined with the synapse video (see resource), which does not have commentary. This is a good introduction to 5.1.3 neuronal communication and connects it with this topic.
To differentiate between receptors and effectors (5.1.1c) examples should be given which would be familiar to the students. This could easily be combined with 5.1.1d for thermoregulation as this is a very straightforward example to illustrate these keywords. The activity ‘Accentuate the positive’ is a fun way of illustrating the general principles behind the feedback mechanisms.
The sequence of events that occur for endotherms can be introduced in an experimental fashion with the ‘One snowy night’ activity.
There are many variations of this form of role play to illustrate negative & positive feedback. Students take on various roles (outlined below) that they can have imposed on them (good differentiation) or they choose.
Norm characters; represent the normal values for homeostasis and having 2 throwing a ball to each other in a straight line helps students to visualise the norm line when they draw feedback loops.
Detector character, Stimulus character, Processor character, Effector character.
Two students can represent ‘the norm’ and throw a ball to each other at a regular tempo, music can be added to keep the activity moving. The stimulus character throws more balls at one of the ‘norms’, the detector character counts the extra balls and passes them to the processor character, during which the norm characters are having to increase their pace to cope with the extra balls. The brain/processor character passes the balls one by one to the effector character who throws them away (or something to remove them) and when all the extra balls are removed, the norm characters can go back to throwing one ball to each other at a regular pace.
Positive feedback can follow on from this where the effector character does not throw the balls away but gives them, one by one, to the norm characters who have to increase their pace for throwing the balls and adds in more balls! This could be shown with the norm characters not throwing any balls at first to illustrate that, in non pathological circumstances, positive feedback occurs only when a stimulus initiates a ‘norm’ not exacerbates an existing one.
The events that would occur on a snowy night can be imitated by students sitting next to a fan and timing how long it takes for goosebumps or hairs to rise on their arms. This can be utilised quantitatively or merely a starting point for discussing the stages involved in thermoregulation. As before, this links with PAG11 and students could choose additional variables to investigate e.g. distance from fan, speed of fan.
This topic should be taught from an animal behaviour/physiological perspective and examples of animal/humans provided at every opportunity. The ‘One snowy night’ activity (in Curriculum content activities) illustrates the humans response to a decrease in temperature and the timing aspect of the activity helps to illustrate the ‘delay’ that occurs for a response due to the need for detection and processing. Students easily follow the effectors path for thermoregulation but often fail to follow the detection events as thoroughly.
The behavioural activity of ectotherms and the physiological activity of endotherms in terms of evaporation/convection etc is not easily understood by students who may feel it is too physics based for their comfort. ‘Blowing hot and cold’ activity is an interesting way of illustrating observations on thermoregulation with sufficient explanation for this level.
Ectotherm behaviour can be observed in amusing video clips, see Video clip 1 resource, which shows the ‘dancing’ activity of the shovel lizard.
The behavioural aspects of endotherms is illustrated well with penguin huddling and this can be observed within the time lapse video, (see Video clip 2 resource).
‘Why do penguins huddle’ activity follows through with this observation and also allows further discussion of convection and conduction in terms of this huddling activity and shows students that this is not limited to ectotherm behaviour.
Cards are given to students who have to match the correct observation with the explanation. This can be linked with 4.2.2g for adaptations. For example:
- Dogs pant on hot days
- Birds look ‘fatter’ on a cold day
- Walruses have thick blubber
- Humans feel cooler on hot dry day compared to hot humid days.
- Allows cooling by evaporation
- Traps layer of air so reduces temperature gradient from air to skin
- Fat is an insulator and reduces heat loss
- Dry days have large concentration gradient between moisture on skin and moisture in the air so evaporation can occur, having a cooling effect.
This is a popular key stage 3 activity which can be used to illustrate the behavioural activity of endotherms. The general activity can be found on the tes.com website (see resource).
The math behind The Huddle resource is a short article which explains why penguins huddle.
This is a good introductory topic to more detailed homeostatic responses that follow on from this topic (5.1.2/3/4).
There are many video clips to illustrate behavioural activities towards thermoregulation and good websites showing thermal images of various animals. E.g. Images from the BBC website.
Introducing key concepts and words for homeostasis can be done as a role play e.g with the activity ‘Accentuate the positive’ (Curriculum content activity).
Experiments can be performed very easily for a general introduction to the topic or for endotherm thermoregulation. This can become as simple or detailed as time allows and would fulfill PAG11. Even fun experiments can be introduced e.g. with the activity ‘Why do penguins huddle?’ (Thinking conceptually activity.)
Graphical analysis can also be introduced as outlined in the activity ‘Whose temperature is rising?’ (see below) and would encompass M3.2.
Students are given data for internal temperature as external temperature increases. They have to plot the data and match with pictures of the animals involved. This allows for good use of M3.2 with the added interest of picture matching.
Data for this can be found within the Data resource.
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