If a rat consumes 90% of its basal metabolic rate, independent of the ratios of fats, carbohydrates and proteins the diet is composed of, then the rat will lose weight.

Question

To test this hypothesis two individuals designed the following experiments.

The first individual used two rats. One rat was feed a diet of 36 calories per day with the sources of the calories being 25% fats, 35% proteins and 40% carbohydrates. The second rat was feed a diet of 36 calories per day with the sources of the calories being 40% fats, 40% protein and 20% carbohydrates. The rats were housed in a large cages in which they were free to move about. At the end of a month the rats were weighed and their weights were compared.

The second individual used a total of 20 rats. The thirty rats were weighed and they were put into two groups such that the average body weight of the two groups were as close to being equal as possible. 10 rats were feed a diet of 30 calories per day with the sources of calories being 20-25% fats, 30-40% proteins and 35-50% carbohydrates. The other group of 10 rats were feed a diet of 35 calories per day with the sources of calories being 5-10% fats, 35-45% proteins and 35-60% carbohydrates. The rats were housed in cages which allowed a minimum of activity and the activity was monitored using a motion sensor. The temperature of the room they were housed in was maintained at 22°C. At the end of each week the rats were weighed and the average weight of each group was computed. The experiment continued for six weeks. The data was then plotted as average weight versus weeks on the diet. 

What are the independent variables, dependent variable, control group. experiment group, and controlled variables?

Answer 1

Hi Ashley! Let's break this down.

So you have an experiment where the scientist wants to know if a rat will lose weight if it consumes no more than 90% of the calories that the rat also burns with its metabolism. Additionally, the scientist hypothesize that this fact will not change depending on the ratios of nutrients that the rat consumes. Now let's take it one experiment at a time.

Sometimes it helps to read through the experiment and summarize (either in your head or take some notes) the experiment so that you understand what is happening. These two experiments being compared are a little different, so i suggest thinking about them separately.

Experiment 1:

this scientist used a total of 2 rats. He gave them both the same environment, fed them, and checked their weight after 1 month. Each rat got the same number of calories but had differering ratios of macronutrients (proteins, carbs, and fats). So basically this guy wants to figure out if the rats will lose the same amount of weight or different amounts of weight based on their different diets.

1. Independent variable = what "I" change in the experiment, or what the scientist makes different between the test subjects. So this would be the ratios right? It's the ONLY thing different between the 2 rats.
2. Dependent variable = what changes in response to the independent variable (because it DEPENDS on it), or what the scientist is MEASURING. So if we know the independent variable was the diet ratio, the dependent variable will be the amount of weight each rat loses.
3. control group = a control group is a group in an experiment where there are no major changes to the independent variable. For example, if you wanted to know what heps a plant grow the most, your control plant would be one that is just sitting on your porch, but your experimental groups might have something added like one with water added, or one with extra sunlight, or one with fertilizer. It is not really reasonable to identify a control group here because both of the rats are being measured with strict diets; there is not technically a "normal/baseline" rat. There are control variables though, or things that are the same between both rats (like how all the plants are on the porch). So things that are the same for the rats are their calorie intake amount and the size of the open cages.
4. Experimental group = In the plant example, The experimental groups are the ones with changes to their baseline. Again, both of these rats are being measured - neither one is a "normal" or control. Both of the rats are technically "experimental." So we can consider the experimental variables or what is different between the rats. Again, this would be the dietary macronutrient ratios.
5. Controlled variables = see answer in number 3, maybe you could ask your teacher about this, but I am pretty sure we can't consider either of these rats a control group, only controlled variables.

I feel like I gave you a lot of information for the first experiment that can then help you with the second one - just do the same thing! I can give check/help you with the answers if you reply to this message or send me a message. Hope this helps!