My notes and thoughts from Biology 111, for Monday, August 25, 2008. The entire series can be found here.
We began Monday’s lecture where we left off on Friday (which is always a good place to start). Doc put the tree of life back up on the white board, and we did a quick review of what we went over on Friday regarding inheritance and emergence.
We then began to work a bit on Natural Selection, using Salmon as an example.
*Individuals with certain traits produce more offspring than those with other traits.
Doc stressed that Natural Selection works at the Population level, and not at the individual level. It’s important to stress this, as it’s the beginning of the explanation of why dogs don’t give birth to cats, that tired old moronic Creationist standby.
(Continued Below the Fold)
We talked about the life cycle of the salmon. Salmon breed and spawn up river, in fresh-water lakes. The young remain in the lake until they are ready, then swim downstream to the ocean. Once out on the ocean, they mature. When they are ready to breed, they return up the same river in which they were born, spawning in the same waters as their parents did.
There is a natural variation in the body size of adult salmon. Remember We’re talking about adult salmon size, not babies. That becomes important in a moment.
This is a gill net. It is the tool used by commercial fishermen to catch salmon. Of course, the fishermen want to catch the largest fish, to maximize the price they get per fish. To accomplish this, the net is sized with large holes between the strands, so that smaller fish get through.
The way a gill net works is that as the fish swim through, the large ones get partially through, then can go no further. In an attempt to escape, the salmon back up. At that point, their gills get caught in the net.
So what happens is that in a river fished with commercial gill nets, the smaller fish have a selective advantage, and live to breed another season. This imparts a genetic tendency toward smaller size salmon, as smaller salmon tend to have smaller offspring.
In a river not fished with commercial gill nets, the larger fish have a selective advantage, as they outsize a certain proportion of their natural predators. The predators pick off the smaller fish, and that population of salmon will tend to have larger offspring. The larger fish have a smaller pool of predators large enough to eat them, so the larger salmon have an advantage here, and tend to live longer – long enough to breed. It’s good to be bigger than the guy who wants to eat you.
Looking back at the tree of life chart, one population can be said to acquire trait Q, a smaller size, and the other population trait X, a larger size. As other changes take place due to other selective pressures that differ in the two populations of salmon, there may come a speciation event.
Again, speciation does not occur at the individual organism level, but at the population level. Descent with Modification is an emergent property at the population level.
Chapter Two – The Chemical Context of Life
This was pretty basic chemistry stuff.
There are 92 naturally occurring elements —> about a dozen are important to biology
An atom is the smallest unit of an element.
|e–||Electron||–||≤ 1/1800 Dalton*|
The number of p+ in an atom = the atomic number: each element has a unique atomic number.
|Naturally Occurring Elements in the Human Body
(From the chart on page 32 of the textbook)
|Elements making up about 96% of human body weight|
|Elements making up about 4% of human body weight|
Atoms normally are electrically neutral.
Number of p+= number of e-
*The unit of mass for subatomic particles is the Dalton (also sometimes known as the Atomic Mass Unit or AMU), named for John Dalton, the modern developer of Atomic Theory. Click here to return to the chart
Electrical attraction stablizes orbits, as the protons and electrons attract one another due to opposite electrical charges, but protons will repel each other and electrons will repel each other due to same electrical charges. Bear in mind that sketch is not to scale.
Note the protons and neutrons clustered in the nucleus, which gives the nucleus a positive charge.
Lab notes will have to wait, as I have Spanish and Precalc homework that needs attention. (Preview hint: we got to play with live termites!)
From whence came the art:
The first image is of our textbook, Biology, Eighth Edition, by Campbell & Reese et al.