Period 4

Congratulation, Period 4, on earning 50 Points in the Top Ten Challenge! That means you have followed all of our Classroom Rules on 50 separate occassions. That's quite an accomplishment! Be proud of yourselves, and I hope you enjoyed your King Cake, popcorn, and Capri Suns. Now, let's get to work on reaching 100! Do you think you can earn another 50 points before the iLEAP? I challenge you.

As for classwork...

1. We completed a True/False Catalyst today, correcting some misunderstandings about natural selection.


2. Next, we checked Homework. The homework due today was the fossil record of our trilobite-like organisms. If you were one of the people who did not complete your fossil record, you may turn it in on Monday for a late-grade. You can find the instructions below.


3. We read about structural (physical) and behavioral adaptations in plants, and practiced active reading strategies.

HOMEWORK: (Due Monday, 02/09/09) Complete the chart on the back of the Plant Adaptations packet. You must read the description of each adaptation, and determine whether it is structural or behavioral.


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FOSSIL RECORD HOMEWORK (Due Thursday, 02/05/09)

Step 1) You were given 5 sheets of colored paper. You are going to create a chart with 3 columns and at least 9 rows. Every row must be tall enough to hold 3 of your fossils, and at least one of the columns must be wide enough to contain 2 fossils side-by-side.

I demonstrated in class my preferred way of constructing this chart. However, you may design it any way you like so long as the final chart contains all of the necessary information described in the following steps. What follows is the method I demonstrated in class to construct this large chart:

Fold each sheet once long-ways (hotdog fold) and once short-ways (hamburger fold). Then, take one of the shorter ends and fold it in to the half-way mark. You are left with a piece of paper with 6 squares total, 4 of them half the size of the other two. (See Diagram 1 below. Dotted lines = folds.)

After folding all 5 like this, tape them together in one long chain.
(See Diagram 2, showing 3 sheets taped together.)

After taping the sheets to construct your chart, next you need to beging filling in the information.
Step 2) The first small column of your chart should contain the names of the fictional Geologic Eras that our fossils lived in. These historical epochs were named after states in the United States. For example, the first (and oldest) time-period is called "Wyomington." The next is Ohioian, named after Ohio. Then Nevadian for Nevada, Texian for Texas, and so on. Next to each era's name is written how many years ago the era was supposed to have begun. So for example...

Wyomington occurred 995,000 years ago, according to our chart. Texian was 445,000 years ago.

I asked everyone to copy all this information off the board and on to their charts before beginning any work with the fossils. However, many students failed to do this, in spite of numerous reminders. So for those wishing to make-up this assignment for a late-grade, here again is the list.

TIME PERIOD BEGAN (YEARS AGO)
Wyomington (oldest) 995,000
Ohioian 745,000
Nevadian 545,000
Texian 445,000
Oregonian 395,000
Coloradian 320,000
Montanian 170,000
Californian 80,000
Idahoan (the present) 30,000

Jan. 26 - Jan 30

We have now completed Chapters 5 and 6 in the Green "Cheetah" Life Science Textbook (Holt) covering Genetics and Heredity. Since the Midterm Exam contained some questions relating to Genetics and Heredity, we will not have a separate Unit Test for these chapters. Instead, the next Unit Test (over Evolution and Natural Selection) will contain a small section related to Genetics and Heredity. Here you can download the vocabulary list for these Chapters from our Word Wall.

We are currently on Chapter 7 (pgs. 148-171), "The Evolution of Living Things." The primary topic of concern is the principles behind Natural Selection. In a nutshell...

• We already know that DNA is passed down from parent to offspring, and that offspring resemble their parents because they share the same genetic information.
  
  
• But we also know that random mutations (insertion, deletion, and substitution are the ones we've discussed) are constantly occurring whenever DNA replicates itself or combines with the DNA of another individual during sexual reproduction. The result is Genetic Variation, slight differences between the members of a population.
  
  
• These differences can either be helpful to the organism's survival, or else may hurt their chances of surviving (or more commonly, have no measurable effect). If the trait helps the organism survive in some way, we say that is has an evolutionary advantage over the other members of its species. It will survive better, and in the long run produce more offspring that carry that same trait in their genes.
  

(Examples: An organism that can blend into its background (camouflage) may be hard to spot, allowing it to hunt prey and hide from predators more easily. On average, fewer individuals with camouflage are going to be caught and eaten, or else go hungry and starve, than individuals who stand out from the environment -- think of a black bear born among polar bears. It would probably not be able to catch much because it's prey would have an easy time seeing it coming!

Likewise, a dark-colored rabbit living among all-white arctic hares would be the first one picked off, because it would be very easy to see and track.

Another example: The red-eyed gulls in the Gallapagos islands have developed better night-vision than other seagulls that allows them to search for food at night. Uncoincidentally, they frequently feed on a type of sea life that is phosphorescent, meaning it glows at night! If the gulls couldn't see at night, they wouldn't be able to hunt and eat the phosphorescent fish. They would have a much harder time of surviving.)

• Anything trait that develops in a species over time that helps that species survive and reproduce is called an adaptation. We say that the organisms is "well-adapted" to its environment. If an organism was not well-adapted to its environment, chances are that it would die quicker, or more frequently, than those that are. Consequently, it would reproduce less often, produce less offspring, and fewer and fewer with each passing generation would have those same poorly-adapted genes. The genes of more successful, well-adapted individuals would be passed on and would be growing more and more common in the gene pool.
  
  
• This is known as competition. Your book calls it the "struggle to survive." There's simply not enough food and water and land, etc., for a limitless number of organisms to survive on. Only the ones best-suited for survival will live long enough to pass on their genes. ("Only the strongest survive.") The "weakest" often get eaten by predators, or can't get enough to eat, themselves, when they're competing with their "stronger," more well-adapted family members. When it's time reproduce, only the "strongest" will attract mates and make lots of babies, if the "weak" ones are even still alive anymore.
  
  
• This is the known as differential reproduction, which you can remember simply as successful reproduction. Successful reproduction is the key to natural selection. Remember, genes can only get passed down through reproduction. If you want your genes in future generations, then you had better be successful at reproducing. But if you are poorly-adapted, and can't get enough food, or just don't look terribly attractive to members of the opposite sex, then chance are you're not going to reproduce, or at least not as much as well-adapted members. So you'll have fewer offspring. And so fewer members of the next generation will carry your genes. And then fewer in the next generation. And then fewer. And then fewer. And then next thing you know, the "bad," or unhelpful (disadvantageous) genes have been weeded out.

Here are the Basic Ideas behind Natural
Selection in 4 Easy Steps! (see pg. 162)

1) Overproduction. Every species gives birth to too many babies than can possibly survive. Some are going to die off. :-(

2) Genetic Variation. Each baby is just a little bit different. Some of are good-different. Some are bad-different. Whether your differences are good or bad depends on whether or not they help you survive.

3) Struggle to Survive. All the members in a population of organisms are competing against each other for food, water, territory, mates, etc. and only the best-suited, best-adapted ones are going to be successful.

4) Successful Reproduction. The ones that are best-suited to survival survive, and those that are ill-suited die off. The ones that are best-suited have more babies. The ones that are poorly-suited have fewer. So through each generation, more and more babies have the helpful, well-adapted genes, and fewer and fewer babies are born with the unhelpful, poorly-adapted genes.

Over time, almost all the member of a population take on the helpful trait, now called an adaptation. We looked at a video of the ancient ancestors of modern-day elephants. The evolved long trunks to help them hold things and collect more food. The short-nose elephant ancestors weren't as successful as those with long noses, and so over many, many thousands of years, the short-nosed ones eventually died off, and more and more elephants were being born from parents with long-noses.