Only $2.99/month

Biology 1114 Final Exam

Terms in this set (376)

* Gene duplications are an essential source of genetic novelty that can lead to evolutionary innovation. Duplication creates genetic redundancy and if one copy of a gene experiences a mutation that affects its original function, the second copy can serve as a 'spare part' and continue to function correctly. Thus, duplicate genes accumulate mutations faster than a functional single-copy gene, over generations of organisms, and it is possible for one of the two copies to develop a new and different function. This is an examples of neofunctionalization.
* Gene duplication is believed to play a major role in evolution; this stance has been held by members of the scientific community for over 100 years. It has been argued that gene duplication is the most important evolutionary force since the emergence of the universal common ancestor.
* Another possible fate for duplicate genes is that both copies are equally free to accumulate degenerative mutations, so long as any defects are complemented by the other copy. This leads to a neutral "subfunctionalization" model, in which the functionality of the original gene is distributed among the two copies. Neither gene can be lost, as both now perform important non-redundant functions, but ultimately neither is able to achieve novel functionality. Subfunctionalization can occur through neutral processes in which mutations accumulate with no detrimental or beneficial effects. However, in some cases subfunctionalization can occur with clear adaptive benefits. If an ancestral gene is pleiotropic and performs two functions, often times neither one of these two functions can be changed without affecting the other function. In this way, partitioning the ancestral functions into two separate genes can allow for adaptive specialization of subfunctions, thereby providing an adaptive benefit
* The Earth is 4.5 billion years old (give or take 200 million years!) formed from a rotating disk of gas and dust in the young Solar system. The earliest evidence we have for life on Earth comes from rocks 3.75 years old in Greenland. clock
* These sedimentary rocks record the cooling and stablisation of the Earth's crust, and contain a ratio of 12C/13C isotopes which indicate an organic origin for the rock carbon. In other words, life had originated nearly 3.8 billion years ago, about as early as was possible considering the time required for the young Earth to cool.
* The earliest morphological evidence for life is 3.5 billion years old, fossils of stromatolites (colonies of cyanobacteria) and single, undifferentiated cells, or Prokaryotes. For 1.6 billion years these simple cells were the only kind of living organism, until the arrival of Eukaryotes, or single cells with differentiated nuclei and cell organelles. Although representing a large leap in complexity, the Eukaryotes were still only single cells or cell aggregates. It was another 1.4 billion years before complex, multicellular life made an appearance in the form of the Ediacaran faunas (see fossils), followed by all the variety of the true Cambrian animals about 550 million years ago.
* Therefore 80% of the history of life on Earth is exclusively single or undifferentiated multi-cellular. 3 billion years went by before complex multicellular life appeared, but when it did it only took between 5 and 10 million years for all the basic body plans of the organisms we see around us today to be established. This is why the origin of multicellular life, in particular the metazoans or large animals with complex body plans, is termed the Cambrian explosion.
* Often brought up in the origins debate is how evolution does not explain the origin of life. Let's get something abundantly clear: abiogenesis and evolution are two completely different things. The theory of evolution says absolutely nothing about the origin of life. It merely describes the processes which take place once life has started up. There may also be multiple pathways to producing naturally occurring "life". Depending, of course, on the definition of life. This is something that Ben Stein is apparently willfully ignorant of.
* An objection to the distinction is that it is goalpost moving but this would only be true if evolution at some point did try to explain the origin of life and then people moved away from it. This is not the case at all. Evolutionary theory started with the observation of the mutability of species - a property that only exists once life has begun, indeed later definitions of "life" have often used the ability to evolve as a key component. This, of course, has been known for some time as animals and crops have been selectively bred for thousands of years. Later, the idea was refined by Charles Darwin in the form of natural selection, where nature provides the selection criteria to drive evolution. At no point was evolution, nor natural selection, about explaining the origin of life.
* One objection is that explaining the origin of life is a natural extension to what evolution has to explain. In fairness this is true, and theories surrounding abiogenesis often use natural selection as a jumping point for how organised molecules could themselves develop further (thus making such molecule groups "alive" by the definition discussed above). But whether evolution and natural selection can explain this stage in the development of life is absolutely irrelevant to its validity to living creatures post abiogenesis. A common analogy to the fallacy of rejecting evolution due to it not explaining the origin of life is that gravity doesn't explain the origin of life. Another might be that it is akin to confusing a university's admission process with grading, advancement, and graduation once students are admitted.
* Forty or fifty years ago, thanks to antibiotics, scientists thought medicine had all but eradicated infectious agents as a major health threat. Instead, the past two decades have seen an alarming resurgence of infectious diseases and the appearance of new ones.
* Today, the AIDS virus, tuberculosis, malaria, diarrheal diseases and other infectious agents pose far greater hazards to human existence than any other creatures.
* This upsurge of infectious disease is a problem we have unwittingly created for ourselves. The rise of rapid, frequent, and relatively cheap international travel allows diseases to leap from continent to continent. Inadequate sanitation and lack of clean drinking water are another factor. A third is the "antibiotic paradox" -- the overuse of the "miracle drugs" to the point that they lose their potency.
* Whenever antibiotics wage war on microorganisms, a few of the enemy are able to survive the drug. Because microbes are always mutating, some random mutation eventually will protect against the drug. Antibiotics used only when needed and as directed usually overwhelm the bugs. Too much antibiotic use selects for more resistant mutants. When patients cut short the full course of drugs, the resistant strains have a chance to multiply and spread.
* In some countries, such as the United States, patients expect and demand antibiotics from doctors, even in situations where they are inappropriate or ineffective. Our immune systems will cure many minor bacterial infections on their own, if given the chance, and antibiotics have no effect on viral infections at all. Every time antibiotics are used unnecessarily, they add to the selective pressure we are putting on microbes to evolve resistance. Then, when we really need antibiotics, they are less effective.
* While drug companies race to develop new antibiotics that kill resistant microbes, scientists are urging patients and doctors to limit antibiotic use.
* That means not asking for penicillin when all you have is a cold, since colds are caused by viruses that are not affected at all by antibiotics. It means taking all the pills that are prescribed, even if you're feeling better. Physicians have to resist prescribing the strongest and most broadly effective drugs unless the disease absolutely requires it. If society adopts these measures rigorously, the drugs may regain at least some of their lost "miracle" powers.
* Cells are so small so the surface area and volume of them can be proportional to each other. This helps with the efficiency of the cell's absorption and waste expulsion processes. Also by the cell's smallness, communication from the nucleus to other organelles is fast and the cell can be regulated while the conditions for diffusion are still ideal.
* Cells are so small because they must constantly interact with their surrounding environments. This interaction causes cells to replicate themselves by breaking large molecules into smaller ones which allows for the entire surface area of the cell to be in contact with the environment once again. Environmental contact is vital to cells in order for nutrients and other items to pass through the cell membrane for nourishment. Cells are also so small because it is simply easier to replace them without disrupting the functioning of other cells within the normal environment (ex: human body or plant cells).
* The main reason cells are so small is because they need to maintain a surface area to volume ratio that allows them to obtain enough material to carry-on the metabolic processes and get rid of the waste products of said processes. Volume is the determining factor in how much material is needed to be imported and exported from the cell, while surface area determines the rate at which this can be done. Since, mathematically speaking, volume increases at a greater rate than surface area when expanding the size of anything, in cells that get too large the surface area is not able to import and export materials fast enough to support the volume of the cell and the cell dies.
* There are four main ways that plants adapted to life on land and, as a result, became different from algae:
1. In plants, the embryo develops inside of the female plant after fertilization. Algae do not keep the embryo inside of themselves but release it into water. This was the first feature to evolve that separated plants from green algae. This is also the only adaptation shared by all plants.
2. Over time, plants had to evolve from living in water to living on land. In early plants, a waxy layer called a cuticle evolved to help seal water in the plant and prevent water loss. However, the cuticle also prevents gases from entering and leaving the plant easily. Recall that the exchange of gasses—taking in carbon dioxide and releasing oxygen—occurs during photosynthesis.
3. To allow the plant to retain water and exchange gases, small pores (holes) in the leaves called stomata also evolved (Figure below). The stomata can open and close depending on weather conditions. When it's hot and dry, the stomata close to keep water inside of the plant. When the weather cools down, the stomata can open again to let carbon dioxide in and oxygen out.
4. A later adaption for life on land was the evolution of vascular tissue. Vascular tissue is specialized tissue that transports water, nutrients, and food in plants. In algae, vascular tissue is not necessary since the entire body is in contact with the water, and the water simply enters the algae. But on land, water may only be found deep in the ground. Vascular tissues take water and nutrients from the ground up into the plant, while also taking food down from the leaves into the rest of the plant. The two vascular tissues are xylem and phloem. Xylem is responsible for the transport of water and nutrients from the roots to the rest of the plant. Phloem carries the sugars made in the leaves to the parts of the plant where they are needed.
* The term coevolution is used to describe cases where two (or more) species reciprocally affect each other's evolution. So for example, an evolutionary change in the morphology of a plant, might affect the morphology of an herbivore that eats the plant, which in turn might affect the evolution of the plant, which might affect the evolution of the herbivore...and so on.

Coevolution is likely to happen when different species have close ecological interactions with one another. These ecological relationships include:

Predator/prey and parasite/host
Competitive species
Mutualistic species
Bull thorn acacia

Plants and insects represent a classic case of coevolution — one that is often, but not always, mutualistic. Many plants and their pollinators are so reliant on one another and their relationships are so exclusive that biologists have good reason to think that the "match" between the two is the result of a coevolutionary process.

But we can see exclusive "matches" between plants and insects even when pollination is not involved. Some Central American Acacia species have hollow thorns and pores at the bases of their leaves that secrete nectar (see image at right). These hollow thorns are the exclusive nest-site of some species of ant that drink the nectar. But the ants are not just taking advantage of the plant — they also defend their acacia plant against herbivores.

This system is probably the product of coevolution: the plants would not have evolved hollow thorns or nectar pores unless their evolution had been affected by the ants, and the ants would not have evolved herbivore defense behaviors unless their evolution had been affected by the plants.