Unit 3: Energy Budgets Flashcards
What are the 4 main types of energy demands that organisms allocate their energy based on?
Maintenance (cellular processes), growth, reproduction, and thermoregulation. This is called an energy budget, and the divisions will vary based on the animal and their needs.
Larger body mass means more ______ required ______. However small body mass means:
Larger body mass means more energy is required total to support the larger amount of substance present. However, for smaller body masses more energy is required PER GRAM of substance. Therefore, if you normalize the graphs of energy required, the smaller animal will require more energy per gram per year.
As you increase size, how does the surface area and volume change?
Increasing size increases the surface area but increases the volume to a much larger extent. Therefore at a certain size, the volume will be too large that the surface area is not great enough to support the exchange of nutrients required for the thing to live. As well, if it is too large, diffusion will not occur quick enough, which is why prokaryotic cells rely on the surface area to volume ratio.
How have larger animal adapted to counteract the issues that the small surface area to volume ratio create? What are the three main disadvantages that these larger animals have?
What are the 2 advantages?
Many have evolved intestines as a way of providing a LOT of surface area to contact with the environment and therefore get a lot more nutrients from food.
The three disadvantages are:
1) Reduced efficiently because there is so much biomass that needs to be serviced by things from the outside and there is relatively little surface area (in comparison) to do it. So energy has to be put in to move those nutrients around the body rather then just allowing simple diffusion to take place.
2) Diffusion distance is increased, and so stuff needs to flow a long way to get to where it needs to be. Even with other mechanisms it still takes longer then simple diffusion in smaller organisms. This is also why prokaryotic cells are limited based on size but eukaryotic with membrane systems are not.
3) Specialized systems are required inside big organisms to keep them alive, such as the respiratory, digestive and circulatory systems — all transfer needed items throughout the body to ensure the body is getting everything it needs efficiently. Can think of these as similar to the endomembrane system in eukaryotic cells, as they allow organisms to be bigger with a smaller SA:V ratio since it helps to counteract the issues things would otherwise face due to diffusion.
-this is why the intestines were created, to increase the efficiency of nutrients getting transported throughout the body.
Advantages:
1) Because there is less surface area contacting the surface, heat retention is greater, allowing internal temperature to be better regulated in cold places.
2) This decreased surface area also allows for water conservation — less places for the water to evaporate from — and structural strength, because more dense and support on bones.
What is allometry? What is the formula that describes this?
Allometry describes disproportionate changes in size or function that occur in different parts of an organism as its body size increases. So essentially, it many traits that occur as a response to body size do not change linearly, leading to a curved graph with the responding variable changing at a different rate then the manipulated (mass/body size).
Y=aX^b
If b < 1, then the graph will be concave down, because the responding variable is changing at a slower rate then the manipulated, and so as body size increases the other variable increases at a slower rate.
b>1, it will be concave up because as the mass increases, the other variable increases at an even larger rate.
Why would allometry be used? (Cat vs elephant)
Well when you scale the skeleton of a cat to the size of an elephant skeleton, the elephant skeleton will still have thicker and larger bones, as this is needed to adequately support its much larger weight. So even when masses are the same, the energy devoted tot eh production of bones will not be the same in each organism and therefore will change at differing rates depending on the organism being talked about.
Another example that can use allometry is explaining why a 7kg paediatric patient doesn’t receive one tenth of the dose of drug as a 70kg adult. Again, this is because as mass changes the other factor does not change at a proportional rate, creating a non-linear relationship.
To actually analyze allometry data, what do we have to do to that data?
What does the slope mean?
To analyze it, we have to log both sides of the graph, as this will produce a linear relationship. This allows the actual accurate values to be pinpointed and relationships to be seen more clearly.
Y=ax^b for original graph
Log y = log(ax^b)
Log y = log a + log(x^b)
Log y = log a + blogx, and this is the new relationship not he straightened graph.
The slope of this new relationship is then the SCALING FACTOR between the two variables, or how those variables relate. Essentially it shows how if the mass increases by 1, how does the other variable increase?
If the slope is >1, then rise/run >1 and therefore the other variable increases to a larger degree then the mass. This would be a concave up relationship without logs.
If the slope is <1, then rise/run <1 and therefore the rise (other variable) increases to a lesser degree then the mass. This would create a concave down relationship without logos.
So if the responding variable is growing at a slower rate then the manipulated, it will concave downwards. when you take the log of this, this exponent value because the slope of the graph, and so the slope will be less then one in this case as the responding (y) variable will be increasing at a rate less then 1, (if the manipulated is considered to be 1).
Consider (y=2x^3) and (y=2x^5).
If we log both sides for each:
Logy = log2x^3
= 3logx + log2
AND
Logy = log2x^5
= 5logx + log 2
Clearly here log 2= the constant, so it is the b value (exponent or constant multiplier in the original) that determines the relationship between the two. The one with the larger exponent (grows faster over time) will have the larger slope, indicating that the responding variable grows faster then the manipulated compared to the ratio for the smaller b value. So as one dimension increases, another increases much faster — is all we have to know.
Why does this work? Well logs are the inverse of the exponents, and so when you apply logarithms to exponents, they essentially cancel out and just equal to x. SO because the relationship we are given is exponential, going back to y is not just going back to what we started with. It’s actually going back to a linear relationship that we could not have seen before. It simply allows use to compare how one factor grows with respect to another one.
If b<1 (concave down), then slope <1.
b>1, slope >1.
b=1 (reference point) then it is a directly proportional relationship.
What are the three types for allometry patterns that are seen? What is an example of each one? What are the slopes of the log graphs and what do the normal graphs look like?
- Isometry: This is where the value b=1 (about), and so the relationship will be linear already, and when you take the log of both manipulated and responding variables, the slope will be equal to 1 (as one increases, another increases at a directly proportional rate).
Ex: Heart mass scales at the same rate as body mass in marsupials as we do not want to put too much energy into powering a larger organ then we need, but we also need a big enough organ to survive based on our mass. - Positive allometry: This is where the original graph is exponentially increasing (concave up), because the exponent (b) is greater then 1. This means that as the manipulated variable increases, the responding variable increases at an increasing rate. So as mass increases, some other factor increases at an even larger rate then it did before. By taking the log of each side, we can then see that as the mass increases, that other factor increases in a larger proportion, leading to a slope which is greater than 1.
So in general, as one dimension, another increases at a faster rate (and with each step up it increases by a larger increment as well).
Ex: For crabs, those with bigger claws will have more mating, and more mating will in turn lead to bigger claws. So the claw size based on this sexual selection will increase at a faster rate than the rest of the body, due to this positive feedback loop. - Negative allometry: This is where as the mass increases, another dimension will increase at a slower rate (and with each constant increase in mass, the other factor will increase by a smaller and smaller amount). This will show as a graph that increases quickly at first and then flattens out, due to a smaller rate. This means that the b value is less then 1, and so the slope on the logged graph is less than 1. Therefore, as the mass increases, the other variable will increase at a smaller rate.
Ex: As mass increases over time, the mass of the brain specifically will increase at a smaller rate, because it grows very quickly when young and then only slightly grows after that until it begins to decay.
What are energy budgets? What equation must be true based on the first law of thermodynamics? What is energy in made of? What is energy assimilation? What is energy in made of?
Energy budgets are the specific amounts of energy that organisms have dedicated to various processes, and the amount that is dedicated will depend on the organism and their lifestyle.
To keep the first law of thermodynamics true, all energy that an organism takes in must be equal to what comes out, because energy is only transferred, it’s not simply absorbed and disappears. It doesn’t mean that all energy just comes out as waste, it means that some of the energy goes into other processes which use that energy and hence make it leave the body, whilst the rest is excreted as waste.
Energy assimilation = the amount of energy that is taken in and used for bodily processes, rather then excreted. So essentially, how much of that energy is converted to usable cellular energy through cell respiration in the mitochondria? This then provides the body with energy for maintenance (resting metabolic rate), energy of activity (actually carrying out certain actions) and energy of production (reproduction or producing something that other animals rely on).
Energy assimilation = energy in - energy excreted (in waste)
Energy excreted is how much energy passes through the body and is not absorbed by the body, and therefore leaves the body in waste. Although there is active transport in the intestines, things have to keep moving and so not all the energy present in food will be able to be absorbed. But the longer digestion takes, the more energy that CAN be absorbed. As well, this can be thought of as essentially the energy that DOESN’T enter the mitochondria, and isn’t converted to usable energy through cell respiration.
Energy in is then made of every thing that comes into the body. This includes energy used for all the above processes, AND the energy that is simply excreted (it must have come in if it’s going to come out).
Generalizations about energy needs for larger animals:
Because they have a larger stomach, intestines and lungs, they can take in more food at once. As well, they also need to eat more to service the larger amount of mass they are made of, and these larger organs allow them to do that. As well, they can take in more air at once (in one breath) and therefore can produce more CO2 at once. As well, they have a proportionally larger heart, allowing them to pump more blood with each heartbeat (which is required to service all parts of the body adequately).
How does energy required per unit mass compare between large and small animals? How does this result in the amount of food required per unit body weight? Why?
Large animals require less energy per unit body weight, and therefore although they eat more overall, they eat less in proportion to their larger body weight.
This is because as an animal’s volume increases, its surface area increases more slowly, and so the surface area to volume ratio decreases. Therefore, larger animals lose heat more slowly than smaller animals, so they don’t need to use as much energy to maintain their body temperature. It is more easily regulated.
As well, larger animals have a higher proportion of non-metabolically active tissues, like bones and muscles (since they have to be stronger and require more force to propel their larger mass forwards) relative to their body mass. Smaller animals have a higher proportion of metabolically active organs relative to their size, and therefore require more energy per unit body weight to support this. This is because they have a weaker skeleton and hence do not need as much fat and muscles to support that skeleton. As well, they don’t have as long muscles since they don’t need to generate as much force per unit body weight, and so they don’t need as much energy to service those muscles.
Kitty has a mass of 20kg, and Kitty ate 20% of its body mass. If its kibble provides 200J per gram, then how much energy did Kitty take in (assuming this is the only energy source).
Later, Kitty excretes 50g of urea (10J/g) and 200g of feces (250J/g). What was Kitty’s energy excretion and energy assimilation assuming this is the only food that is consumed?
Energy in = 0.2 x 20kg x 1000g/kg x 200J/g = 800000J or 800kJ
Energy excreted = (50g x 10J/g) + (200g x 250J/g) = 50500J or 50.5kJ.
Energy assimilation = energy in - energy excreted (how much energy passed through the body and was actually integrated and used by the body to carry out bodily processes? So we subtract waste from this value because it wasn’t actually used, it just passed through the body.
800kJ - 50.5kJ = 749.5kJ or 749500J assimilated (actually used by the body).
Waste still has energy in it!
Animals want to MAXIMIZE Energy ____________ and minimize Energy _______________ from the energy they take in. What are strategies that can help to minimize that value?
Animals want to MAXIMIZE energy assimilated (actually used) and minimize energy excreted (waste energy) from the energy they take in. To do this, several strategies can be used:
-Chew for longer to digest more immediately from the enzymes in saliva
-because if you chew more slowly, more saliva is produced and more food is broken down and hence can more easily be digested in the gut.
-Select more palatable foods (so that they digest easier and hence most of the energy can be assimilated from them)
-Have a longer gut (to absorb more nutrients as the food goes along). This is why humans have a small and large intestine, to focus on taking out certain nutrients, and therefore we can maximize the amount of nutrients we get from that food.
-Increase food retention time (amount of time the food is in you. The longer this is, the more time that can be spend on taking energy out of the waste, and missing less).
Ex. A python swallows prey whole and then keeps it in its stomach for a LONG time to digest it using strong stomach acids.
How does gut retention time relate to body size? What about gut length?
Gut length increases at a an increasing rate as body mass increases, and so this is a hyperallometric relationship. Since body size is larger and therefore the surface area to volume ratio is decreased, there must be more surface area inside to help to digest the large amount of food that large animals can take in. This allows increased surface area to counteract that decrease surface area to volume ratio on the outside, and therefore keep larger animals alive.
However, gut retention time increases at a smaller rate as body mass increases, meaning that larger animas keep their food inside them for a shorter time in comparison to smaller animals. This is likely because larger animals can take in more food at once, and so overall they can get more nutrients without assimilating as much energy from that food. But smaller organisms can’t take in as much food at once, and so they must keep that food in them for longer to get all the energy out of it that they can. This means that larger animals would be excreting more waste per gram taken in, since larger particles require more time to digest and they have a shorter gut retention time. This may be okay though, since larger animals require less energy per gram of body mass.
Food type and quality effects retention time example:
For starlings, in the fall and winter starling migrate and get more their food from plants, which are made of cellulose and hence require more time and energy to digest. This means that they can increase their gut length and size as a type of plasticity. This allows them to get the most out of their tightly compacted food.
In the spring and summer, they are feeding on insects, which take less time to digest and have more readily available energy. Therefore, they can decrease their gut length and size to not waste excess energy on maintaining that gut, and still get as much energy out of the gut as possible.
