‘Eating’:
Introduction:
This is a computer simulation showing the relationship between a person’s hunger, the fullness of their stomach, and when they decide to eat. At the start, the man has no food in his stomach and so is hungry. When he eats a banana, it is converted into food particles that travel to his stomach (orange). When these food particles hit the detectors (green) on the stomach’s wall, they release leptin molecules (purple). These leptin molecules travel to his brain (in particular, a region called the hypothalamus), where their number determines how hungry the man is. Many leptin molecules in the brain makes the man less likely to eat. Only when the amount of leptin drops below a certain level (set by the appetite parameter) will the man eat again. These molecules in the brain decay with time, and so his hunger level falls again. If his hunger level drops below his appetite, he eats again. Food particles in the stomach also break down over time and leave along the small intestine (not shown). The man’s body size is determined by the number of food particles in his stomach.
Please follow the worksheet and try to gain an understanding of how the simulation works so that you will be able to answer the questions in the quiz that will be presented afterwards.
A parameter of a model is any part of the model that you can change. Changing parameters may have a large effect on how often the man eats. Important parameters to explore:
Only change before pressing setup:num-of-detectors / the number of food particle detectors around the stomach’s wall
Change before pressing setup and while the simulation is running:
appetite / if leptin drops below this level, the man will eat
particles-in-banana / how many food particles there are in a banana
You can change the values of these three parameters by clicking on their sliders on the left side of the screen. Set the parameter values, and then press the setup button to restart the simulation, and wait for a few seconds – it may take awhile to set up. Press the go button to start the man being hungry, which leads to him eating. Press go again to stop the simulation. [For the appetite and particles-in-banana parameters, you can change the values during the run, and so do not need to press setup and start the run again after altering their values.] You can use the leptin buttons to add or delete leptin particles within the man’s stomach or brain. First, select whether you want to add or delete leptin, and then click on the place in the stomach or brain where you would like to do this.
The data plot keeps track of certain values during the simulation.The purple line shows the number of leptin molecules in the man’s brain, and the brown line shows his appetite.
Worksheet:
1. Set up the simulation using the initial parameters, and then let it run for a while. Watch what happens on the graph as time passes. Do the plots settle into a repeating pattern? Describe this pattern. Are you able to predict what will happen next?
2. If you increase/decrease the man’s appetite, what effect does this have on how often he wants to eat? Why? If you change how much food each banana represents (particles-in-banana), how does this affect how often he eats? Observe the plots on the graph, along with the box displaying how many time steps since he last ate, as you alter these parameters in order to get a better idea of what is going on.
3. Next, explore what happens when different numbers of food detectors (num-of-detectors) are in the man’s stomach at the start of each run. What effect does this parameter have on how often he eats? Why?
4. Set up the run as normal. Then add lots of leptin in the man’s brain using theadd leptin molecules button. Now click go to start the run. How do the data plot and the man’s eating differ to previous runs when no leptin was in his brain at the start? Do these differences continue, or does the man’s eating become similar to previous runs after a while? Why?
5. Now spend some time exploring the simulation further, until you feel ready to take the quiz (or the experimenter tells you the time is up). In particular, try playing with the leptinbuttons before, and during, a run. Are you able to influence how often the man needs to eat? How? Is it possible to make the man never need to eat? Can you find parameter settings so that the man always eats bananas in twos? In threes? In fours?
Quiz:
1. If you reduce the number of detectors in the man’s stomach -
a) the man eats more often because the leptin has less of an effect on his hunger level
b) the man eatsless often because the leptin has more of an effect on his hunger level
c) the man eats less often because each banana tends to make less leptin and so he is less hungry
d) the man eats more often because each banana tends to make less leptin and so he remains hungry *
2. If the leptin level on the graph falls below the man’s appetite -
a) the man eats bananas until his stomach is full of food particles
b) the man eats bananas until his brain is free of all leptin particles
c) the man eats bananas until his brain has the same number of leptin particles as his appetite *
d) the man eats several bananas because then he won’t be hungry again for a while
3. What happens if you increase the number of particles in each banana the man eats?
a) this will lead to more food particles in his stomach each time he eats one, releasing more leptin and increasing his fullness quicker *
b) this will lead to more food particles in his stomach each time he eats one, although this will not affect how much leptin is produced
c) this will lead to more food particles in his stomach each time he eats one, and so will decrease the man’s appetite level
d) this will lead to more food particles in his stomach each time he eats one, leading to an increase in the man’s appetite over time
4. Which of these methods would lead to the man never being hungry or eating a banana?
a) set the number of food particles in a banana to be very high
b) keep adding leptin particles manually to the stomach or brain *
c) set the number of food particles in a banana to be very low
d)keep deleting leptin particles from the stomach or brain
5. Which cycle best describes the system featured in the simulation (where ‘→’ means ‘leads to’)?
a)leptin level goes above appetite → man eats food → leptin level falls to appetite
b)leptin level falls below appetite → man doesn’t eat food → leptin level increases to appetite
c) leptin level falls below appetite → man eats food → leptin level increases to appetite *
d)leptin level goes above number of particles in banana → man eats food → leptin level falls to number of particles in banana
6. Which of the following situations would cause the man to almost never stop eating?
a)a very high number of particles in each banana and a very low appetite
b)a very high number of particles in each banana and a very high appetite
c)a very low number of particles in each banana and a very low appetite
d) a very low number of particles in each banana and a very high appetite *
7. Which of these methods would have a similar outcome to adding leptin particles to the stomach manually?
a) increasing the man’s appetite
b) increasing the number of particles in a banana *
c) decreasing the number of detectors in the man’s stomach
d) decreasing the number of particles in a banana