Take a Look at the Questions Submitted From Around the Country!
Astronomy
Scientist of the Month: Dr. Philip Blanco, Project Astro, Grossmont College
Q: Can you please tell me how the term "asteroid belt" came about?
A: Thank you for a great question! I was unable to find the first use of the term "asteroid belt" but I'm guessing it would be around 1890-1900, as some history will show. The first four asteroids were found between 1800 and 1810 as part of a search for a possible "missing" planet between the orbits of Mars and Jupiter. They were (and still are) known as "minor planets", since they were discovered by their apparent motion from night-to-night against the background stars, which made it obvious that they are in orbit around the Sun.
The term "asteroid" was coined by famous British astronomer Sir William Herschel, and means "star-like body" since this is how they appear in most telescopes.
The fifth asteroid was not discovered until 1845, but by 1890 about 300 of them were known. When their positions are plotted together on a map of the solar system, most of them lie within a wide circle or "belt" around the Sun between Mars and Jupiter, with orbits in the same direction and plane as the major planets. (In fact, "asteroid doughnut" might be a better description of the space occupied by them). Nowadays we know of thousands of these objects, ranging from about 100km in size down to the sizes of about 100m. (Below this size we call such objects meteoroids, which are almost certainly fragments from collisions of asteroids). More asteroids are discovered every year as astronomers search for dangerous Near-Earth Objects (NEOs) which could possibly hit the Earth. In fact we believe that such a cosmic impact wiped out the dinosaurs 65 million years ago.
The image (download image) shows a solar system plot of those asteroids we have discovered so far. Please note that the "dots" on these plots are MUCH bigger than the objects themseleves, so despite what you see in the movies, asteroids are usually very widely spaced. In fact it takes a lot of math to navigate a spacecraft to visit an asteroid (as a few have done on their way out past Mars), and when they arrive there, the next-closest asteroid is too far away to be visible.
Asteroids are fascinating objects left over from the formation of the solar system. Although there are thousands of them, together they make up less than the mass of our Moon. Apart from the small but real danger of an asteroid collision, studying them provides us with a view of our solar system's history. In the future, asteroids rich in iron or nickel might be mined as a resource for building ships or stations in space, or they could become favorite places for extreme sports enthusiasts who could perform some great tricks in their tiny gravitational fields!
Q: Does the Moon circle the Earth in a elliptical pattern?
A: Yes, but not "very" elliptical. Orbits are classified by their "orbital
eccentricity" which is a number between zero (for circular orbits) and 1
(for an object falling directly towards the Earth's center). The Moon's
orbit has an eccentricity of only 0.055, which is barely distinguishable
from a circle. The eccentricity also tells us by how much the Earth-Moon distance varies
over an orbit. For the Moon's orbital value of e=0.055, its distance
varies by a factor of (1+e)/(1-e) or about 11%. This also means that as
seen from Earth, the size of the Moon's disk varies by 11% over the course
of a lunar month - not enough for us to notice with the naked eye, but
easy to measure. This means that if one takes careful measurements of the Moon's apparent
size, over the lunar month the Moon's disk appear to get bigger and
smaller over a range of 10%. A nice time-lapse movie showing the Moon's appearance from Earth over the course of a month can be found at:
http://antwrp.gsfc.nasa.gov/apod/ap991108.html
Q: What would be a good hands on activity to illustrate constellations?
A: That's something I hope to have an answer for at the upcoming
workshop! This is a simple concept which may yet take some
work to demonstrate effectively. Constellations are a 2-D view of a very 3-dimensional local part of our galaxy. That is, stars that appear to be close on the sky may in fact be
very far away. One option is to build 3D models of stars' locations and
have students view them from an "Earth" viewpoint, then from another
viewpoint. Another is to use planetarium software to "fly" towards the
local constellations. Finally, using flashlights and some patience, you
can recreate constellations' appearance in a darkened classroom by having
students position them in 3D.
Q: What is an easy way to explain Black Holes to my students?
A: 1. Einstein showed that nothing can travel faster than light.
2. Einstein also predicted that light beams "feel" gravity, and can be
bent around massive stars.
This was observed in 1919 using the Sun.
On Earth, if you throw a ball upwards it will come back down. Throw it
faster and the ball travels further upwards. At a critical "escape" speed
though (11 km/s), the ball has enough speed to completely escape Earth's
gravity. But if we do the same experiment on a very massive, compact,
collapsed star, we find that the escape speed is much higher. In 1798, French mathematician Laplace asked: "What if there were a star so massive and compact that even moving at light speed would not allow objects to escape?" And so he perfectly described a black hole
- a collapsed object whose gravity is so strong that even light beams
cannot escape. And therefore from Einstein's "speed limit", nothing can
escape! So although you could in principle travel to a black hole, you
could never report back your findings. All that your colleagues would see
would be an image of you just before you disappeared into the "event
horizon" which is the boundary of the back hole's secret world within.
While it might seem hard to prove the existence of black holes,
astronomers have plenty of indirect evidence that the exist, from the
effects they have on their companion stars, infalling matter, and more
recently, the bending of light around them. Some of these observations
have only been possible in the past 10 years, so it's still an exciting
time to be studying astronomy!
Q: What is the importance to us of the Mars Explorer Missions?
I would like to explain this to my class.
A: The Mars Rovers were sent to the red planet in part to address questions
which we have been pondering for centuries, ever since we realized that
Mars was another "world". We just happen to be very fortunate to live at a
time when technology allows us to come up with answers!
- Was Mars once able to sustain primitive life?
- If Mars' early history was similar to Earth's, what caused it to change
into today's sterile, frozen desert?
- Could Mars sustain life today, human or otherwise, if we chose to
develop i
Your students can probably come up with their own questions, too. Also, by
using rovers to explore the planet, we can cheaply (and safely) pave the
way for future human exploration. In so doing, NASA and JPL have developed
amazing technologies which have applications here on Earth. For instance,
due to the ~ 30min signal delay over such a large distance, the rovers
have to be "semi-autonomous" (i.e. "smart") when it comes to avoiding
obstacles and managing their limited power. Watch for "spinoff"
applications in mine-clearing and search+rescue robots, devices for
assisting the disabled, and yes even toys based on this technology!
The R. H. Fleet Science Center has a photo gallery of NASA "spinoff"
technology called "Origins in Space". See http://www.rhfleet.org/site/exhibition/origins_of_space for details.
To get so much return from $800 million (which would buy about 100 miles
of interstate freeway) is a bargain!
Earth Science
Scientist of the Month: Dr. Dogan Seber, Discover Our Earth, San Diego Supercomputer Center
Q: What are the cause and effects of beach erosion?
Scientist of the Month: Memorie Yasuda, Earthguide, University of California, San Diego
Q: Why is the air cooler at higher altitudes?
A This vertical temperature trend is a consequence of 1) lower atmospheric pressure at higher altitude and 2) heating that takes place at the bottom of the troposphere rather than at the top. The rate of change of temperature with height, is called the lapse rate by meteorologists. In the troposphere, the lowest layer of the Earth’s atmosphere, temperature decreases with altitude. This trend does not continue into the layer above.
Q: How would I explain to my class how and why it snows?
A: It snows when pieces of ice that form in the atmosphere fall to the ground. Ice forms when there is enough water in the air to form snowflakes and it becomes cold enough for ice to form. Solid snowflakes form directly from water vapor in gas form. It may not be cold enough for snowflakes to make the journey to the ground.
Q: Can you please describe rain/precipitation and all of its functions in terms that a fourth grader would understand?
A: What is rain or precipitation? It’s water (H2O) that falls from the sky as drops of water or pieces of ice. When the National Weather Service uses the terms rain and precipitation, they mean very specific things. Rain or drizzle refers to drops of liquid water, depending on the size of the drops. The term precipitation includes all the forms of water that fall to the ground – rain, drizzle, snow, sleet, hail, etc.
Q: How much do clouds influence the current predictions of global warming?
A: A lot. So much that it causes significant uncertainty in the specifics of predictions of future climate although there is no doubt that the Earth is warming. While this offers the possibility that clouds counteract global warming to some degree, it raises awareness that the true extent of global warming due to greenhouse gases has been underestimated.
Scientist of the Month: Drs Topper and Schultz, Argonne National Laboratory
Q: Why is mercury a liquid? It is surrounded by solids.
A: Mercury is a sort of special case. Its valence shell is 5d10 6s2, which means that the two outermost electrons are in a spherically symmetric, energetically stable quantum state. So are the elements in the same column of the periodic table (Zn, Cd). However, for reasons that are not completely understood (at least by me), 6s electrons are particularly inert, i.e., unavailable to form chemical bonds. This is also true for the 6s electrons in thallium, lead, and bismuth, but they have additional 6p electrons which can form chemical bonds (note that these are very soft metals though!). Since Hg does not "like" to share its outer electrons, each atom only interacts weakly with the other atoms, and therefore it tends to be liquid at room temperature. This is also the reason that mercury is so volatile (vaporizes easily) and has a low electrical conductivity (can you guess why?). Zn, Cd and Hg are very different from their "neighbors" in the periodic table (copper, silver, gold), not just in the states they exist in at room temperature, but also in just about every thermodynamic property you can think of. This is because they have the electrons in their d orbitals are apparently excited into s states by only a tiny bit of additional energy (like heat energy), and these form metallic bonds.
Q: Why would KNO2 reduce the number of H+ ions in a solution of HNO2?
A: HNO2 is a weak acid. Therefore NO2- is a strong conjugate base. Weak acids do not
dissociate completely in solution (the reason for their "weakness"). So if
you have free NO2- ions floating around, they are oing to grab the H+ ions and
form the more stable HNO2 acid. NO2-ions come from the very soluble KNO2.
The K+ ions left will just hang around and do nothing in the solution (called
a "spectator ion").
Q: How can arsenic be considered to have 5 valence electrons?
A: Valence electrons are the outermost electrons, i.e., those which are farthest from the
nucleus and available (sometimes) to form chemical bonds. For example, the valence electrons of the transition metals can involve d orbitals. However, I
believe that Arsenic has a valence configuration of 2 4s electrons and 3 4p electrons, or 4s^2 4p^3 (total of 5 valence electrons). Maybe you are confused because nitrogen (in the same column) has only 3 valence electrons (2p^3). That is because atomic orbitals become more closely spaced in energy as a function of n (n=2 for a 2p orbital, etc). Thus, although 2s and 2p are widely separated in energy, 4s and 4p are very close in energy. So, if 4P
electrons are available for bonding, it can be possible for 4s electrons to be available also. This is a complex phenomenon, and you have asked an excellent question about it. As an exercise, find out what the valence electrons are of some of the transition metals in the lanthanide series and see if you can rationalize the patterns.
Q: Does exothermic truly mean the reaction releases heat? Could it also be light or is it always heat, then converted into light?.
A: There are several ways to think of this, but I think of "exothermic" or "endothermic" as a
classification of whether a reaction loses energy to its surroundings (exo) or absorbs it from its surroundings endo). Then, one can imagine different mechanisms by which a reaction could absorb or emit energy, on a macroscopic scale. One might be by atomic/molecular collisions, which we associate with heat transfer. Another might be by emitting/absorbing photons, which could happen if, instead of doing the reaction in a beaker, we put it into a
supersonic jet and fire a laser beam into the jet stream (believe it or not, this particular experiment is very common in physical chemistry). In other words, whether an exothermic reaction gives off light or heat depends on several factors, including (1) the reaction conditions and (2) the types of molecules involved.
Biological and Physical Sciences
Scientist of the Month: Dr. Lou Harnisch, Argonne National Laboratory
Q: What causes people to age?
A: A deep and far-reaching question! Aging is indeed programmed (a
part of normal development). It is moderated by a complex interaction of
hormones to a large extent. Yet, diet (fats), metabolism (production of free
radicals), and being over-weight all seem to contribute to aging. I
personally doubt we will be able to stop aging, but we might be able to slow
its progress, particularly at certain stages, if we can find more pieces.
Perhaps there are some future researchers who are reading this answer who will
add greatly to our understanding and find a kind of "fountain of youth" for
future generations.
Q: When does mitosis of a cell really end? Is it when the nuclear
membranes form around the nuclei or when the cell membrane forms around the
two new cells?
A: It is an on-going cycle, so any beginnings and endings are
arbitrary. Generally, if you go from interphase to interphase, the formation
of the nuclear membrane in each of the daughter cells would conclude the
cycle. Chromatin needs to uncoil and key genes become active again via
transcription of mRNA.
Q: I have a student who would like some information about vitamin C.
What are the key words associated with this topic?
A: Key words: Ascorbic Acid, water soluble, collagen formation
(hydroxylation of amino acids proline and lysine), removal of ammonia,
cholesterol metabolism, enhanced absorption or protection of folacin.
Deficiency leads to scurvy (takes several months on a " C free diet"). All
animals need it, but only primates (humans includes), guinea pigs, fruit bats,
and an Indian bird cannot make it so it is required in the diet. Any good
nutrition or biochemistry college text will have plenty of informatio
Q: What would be the evolutionary purpose for allergies?
A: First, the frequency of individuals having a negative trait is
often maintained in the population (this relates to population genetics). If
the condition is only slightly harmful those frequencies may even increase.
Also, there is or was a silver lining behind many negative traits (sickle cell
anemia, cystic fibrosis, etc). Many had some advantage which kept the gene
frequencies up despite their obvious drawbacks. Lastly, it is the interaction
or total impact of all the genes in an individual that determines fitness.
Genes for mildly negative traits may tag along with little negative selection
pressure. It is only the severe autoimmune disease or immunodeficiency
disorders that will prove lethal and have little opportunity for being kept.
Allergies are quite mild by comparison. How allergies develop in an
individual is still a very important part of this puzzle. If man-made
compounds in any way enhance this process, it would further explain any
increases in their frequency. Of course medication helps us cope and minimize
the negative effects as well.
Physics
Scientist of the Month: Jeff Sale, San Diego Supercomputer Center
Q: What is the Uncertainty Principle?
A: Those are big questions that are difficult to answer, but very important to at least try to get your brain around. Wikipedia ( http://en.wikipedia.org/ ) has a wonderful reference for those who are already familiar with the concept, such as those of you who have taken a high school or college course or the equivalent. I think wikipedia's definition is a bit difficult to understand if you have not taken a class in quantum physics, and this explanation is for those who have not. As always, be more thorough in your explorations than simply searching the web. There are many excellent books to be found with minimal effort, and most libraries have several good ones to choose from. The link in 'Further References' below for the Stanford Encyclopedia of Philosophy has a fine bibliography for those interested in learning more from the developers of the principle themselves, including Werner Heisenberg, Neils Bohr, and Wolfgang Pauli..
A relatively simple way to understand the uncertainty principle is to consider the difficulty in trying to exactly measure the position and the direction of something very small with something else very small and of comparable size (the concept of size is an elusive one at this scale, but we will still use it for simplicity), such as trying to measure the position and the direction of an electron using a photon (once again, please refer to wikipedia for details on electrons and photons). An electron is a 'subatomic' particle, which means it is very small, about 0.0000000000000000000000000000002 pounds. When we try to measure the position of an electron and the direction in which it moves, one way is to hit it with a photon (in a sense by shining a light on it so we can see it), but when we hit it with a photon we change the direction it is moving, making it impossible to precisely measure its position AND location at the same time with infinite precision. There will always be some uncertainty in one or the other measurement. We can kow exactly where it is located but not exactly what direction it is travelling at the same time. At large spatial scales, this uncertainty doesn't matter nearly as much, and our measurements of things are often 'good enough' to accomplish many amazing and wonderful things. For example, radar technology can locate the position and direction of an airplane with enough precision to guide it to a safe landing or shoot it out of the sky. Hitting it with photons does not change the direction sufficiently to cause a problem.
Mathematically, the uncertainty principle can be explained with a very simple equation using basic math (algebra):
P x D > C
or
Position x Direction > Planck's Constant
Direction is typically included in terms of 'Momentum' which is equal to the product of mass and velocity, where velocity is defined as the speed of an object in a particular direction. Simply stated, the equation above says that the product of the position and direction of a particle must exceed or equal a certain minimum value, Planck's Constant. This product cannot be equal to zero which would be the case if we could achieve infinitely precise measurements at all scales.
Q: What does it mean to say ‘the observer plays a role in what is being observed?'
A: The statement 'the observer plays a role in what is being observed' ought to have a very limited meaning at this early stage in our understanding of the ramifications of the Uncertainty Principle. It is tempting to use it to suggest that there are mysterious events in our daily life that can occur unpredictably with no explanation. True, there are many things that science still cannot explain well, or even at all. However, these things may have nothing whatseover to do with the Uncertainty Principle. The definition of the Uncertainty Principle is so rigorously well-defined there should little confusion for those truly interested in understanding its ramifications, which are predominantly an issue only at the molecular, atomic, and subatomic scales.
At the atomic scale this uncertainty can present challenging problems for scientists and engineers in a variety of disciplines. For example, computer and electrical engineers are confronted by it when they deal with electricity manipulated in devices called transistors. Transistors are found in just about every technological device built these days, such as the computer you are using to read this web page.
A: A blue sky depends on the light from our sun, the reflectivity of different colors in the visible spectrum, and our eye's ability to detect different colors with varying sensitivity. Essentially, blue light has more energy than all other colors of the visible spectrum except violet, and so it has just the right amount of energy to be scattered by the oxygen and nitrogen molecules in our atmosphere. Light from the sun of lower energy, including red, orange, yellow, and green, have longer wavelengths than blue and can go right through our atmosphere so that we only see them mainly right around the sun, meaning we need to look directly at the sun to see them (not recommended). The only time these lower-energy longer-wavelength colors really can be seen is during sunset when there is more atmosphere for the sun's light to shine through and reddish colors have a higher chance of being scattered.
Q: What color reflects the most light? I'm specifically interested in the light spectrum that includes household lighting (incandescent)?
A: Typically, white is the color with the optimal reflective properties for visible light. Any object with a white color means that it does not absorb much visible light but instead reflects visible light across the entire visible spectrum. A white surface will also be cooler than a black surface when in direct sunlight because it absorbs less infrared (heat) energy. However, a mirror or some sort of silver reflective material could have even greater reflective properties depending on a variety of conditions. Often one will observe that the inside of some sleeping bags are lined with a silvery material because it is most effective at reflecting our own body heat and keeping us warm. However, sometimes a mirror or silver reflective material is not as practical to use for simple household purposes. For more information, please see http://www.newton.dep.anl.gov/askasci/phy00/phy00399.htm
or http://www.exploratorium.edu/snacks/give_and_take.html.
Environmental Science
Scientist of the Month: Jeff Sale, San Diego Supercomputer Center
Q: Is global warming really caused by humans? Should we be worried?
A: Human activities (especially the burning of fossil fuels and the destruction of large forested areas) are proven contributors to the buildup of greenhouse gasses. The ultimate consequences of greenhouse gas buildup are being studied by many different kinds of scientists to understand how the many global changes we now see might ultimately influence one another and what consequences are most likely. Scientists do see clear evidence of global warming. The evidence (data) is not disputed. Many scientists believe that the changes they observe are happening faster than normal. Other scientists argue that climate change cycles have happened throughout the history of Earth, and what is currently happening is a perfectly normal climate fluctuation..
But what causes the change? The global climate change we observe is certainly correlated with major changes in human behaviors such as the industrial revolution, fossil fuel consumption, and destruction of large areas of vegetation around the globe. However, correlation is not proof of cause, and that is the crux of what scientists continue to debate: a cause-effect link that can be tested and proven. Since Earth is a difficult laboratory and experiments would probably take a very long time, we turn to computer models to simulate Earth processes and test climate change hypotheses. Computer models, based on existing data and what is understood about the physics and chemistry of climate processes, have become critical virtual laboratories for understanding what is likely to occur, and what kinds of actions by humans might affect the outcome. Climate change simulations often use supercomputers, including those at SDSC. Worrying about it won’t solve anything. Instead, you can learn more, make sure that you understand the issues so you won’t be fooled by political rather than meaningful solutions, and do what you can to minimize your own contributions to global warming. The National Oceanic and Atmospheric Administration online global warming FAQ can provide many details regarding your first question. This site can be found at http://lwf.ncdc.noaa.gov/oa/climate/globalwarming.html
Q: How can I learn about threatened or endangered species in my area? What is the definition of an endangered species?
A: The United States Fish and Wildlife Service provides a complete list of all endangered species in the U.S. as well as plenty of additional information about threatened and endangered species completely online at:
http://www.fws.gov/endangered/. What defines an endangered species depends on multiple factors. The process of listing a species as threatened or endangered follows strict legal procedures to determine the degree of threat it faces. Under the Endangered Species Act, the major factors for determining whether or not to list a species as endangered are:
-the present or threatened destruction, modification, or curtailment of the species’ habitat or range;
-overutilization for commercial, recreational, scientific, or educational purposes;
disease or predation;
-the inadequacy of existing regulatory mechanisms; and
-other natural or manmade factors affecting the species’ continued existence
Q: How do I cause water pollution at home or at school? How can I help reduce water pollution? How can I conserve water?
A: The pollution you cause at your home is called ‘domestic sewage’. This includes organic and inorganic waste such as food (animal and vegetable), chemical soaps, acrylic and oil-based paints and solvents. Pay close attention to what you or your family puts down the kitchen sink disposal or pours out into the drain on your street. These run through your community’s sewage system, and depending on where you live, might not even be treated before it enters the local watershed. Learn about your local sewage system by contacting your local government. Pay close attention to how much trash you throw out. Your trash will probably end up in a landfill that can potentially cause leaching of chemicals into the groundwater in heavy rain.
Domestic sewage can often contain disease-causing microbes. In the U.S., most communities have good sewage systems and treatment plants to process domestic sewage in environmentally-sensitive ways. Still, there are many people all over the world living in communities that have poor sewage systems or none at all. Wikipedia is a good place to start to learn more about methods for recycling water and using it more efficiently. Please see
http://en.wikipedia.org/wiki/Water_pollution for more information. The study of pollution falls within the science of hydrology. A Consortium of Universities for the Advancement of Hydrologic Science (CUAHSI, http://www.cuahsi.org/) was recently formed to help better understand hydrologic processes. Pay attention to how often your toilets are flushed? How many showers does your family take? Low-flow toilets and shower heads help reduce the amount of water used. Learn more about water conservation at the Water Conservation Portal, http://www.waterconserve.info/
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Computational Science
Scientist of the Month: Dr. Robert Panoff, The Shodor Education Foundation
Q: What exactly is computational science?
A: Computational science involves the appropriate use of a computational architecture (possibly a computer, calculator, abacus, dice, poker chips, etc.) to apply some algorithm, or method, to solve some scientific application, or problem. This combination of Application, Algorithm, and Architecture results in a model, which can be used as a scientific tool.
Q: How does computational science fit in with traditional descriptions of science?
A: Often the mathematical sciences are described in terms of experimental science, theoretical science, and observational science.
Experimental science is what is generally described by many high school textbooks as "scientific method", where a hypothesis is tested by the use of a controlled study. For instance, a medical researcher might take different groups of three pack a day smokers who wish to quit, and apply different "treatments" to each group, and record the success rate for each group.
Theoretical science is the application of mathematical logic to attempt to either predict new scientific laws from known laws, or to deduce simple laws, which describe known phenomena. Some Social scientists refer to this type of research as Philosophical science. An example of theoretical science is Albert Einstein's theory of relativity, which resulted from his applying the known behavior of electromagnetic fields to gravitation, and predicting the results, which would occur.
A third branch of science, which is often lumped in with experimental science, is observational science (sometimes called descriptive science). Often, it is either not feasible, or immoral, to perform a controlled study of scientific phenomena. An astronomer simply cannot travel to the distant stars, but must rely on collecting and interpreting the light from the cosmos. Our medical researcher studying the effects of treatments to help people stop smoking would be thrown in jail for performing an experiment in which he/she required subjects to smoke three packs a day in order to study the effects.
Computational science has elements of theoretical science, in that it relies heavily on mathematical logic. It has elements of experimental science, in that a model, once built, can be varied one parameter at a time to study individual effects. It has elements of observational science in that its ultimate goal is a better description of the world around us.
Computational science differs from theoretical science in that in order to apply theory, one often has to make broad assumptions. The widespread use of problems in which all objects are treated as spheres lead to the phrase "spherical cow model" to be applied to many theoretical solutions. While numerically cumbersome, computational science allows us to trade an exact solution to a very limited case for an approximated solution to a real world case.
Computational science differs from experimental science and observational science in that it is a model of nature, not nature itself. However, if we know how nature behaves, we can use the computer to create models that can be used in place of experiments. The computational scientist can model the inside of the star (given some knowledge of how nuclear reactions occur). The computational scientist can study the effects on the population of widespread use of tobacco, without ever forcing a cigarette to a subject’s lips.
When used in its proper place, computational science can be an effective tool for allowing us to better understand the world around us.
Life Science
Resouce of the Month: California Academic Content Standards for Middle School Life Science (7th Grade)
Q: Where is the genetic information in plant and animal cells found?
A: The nucleus is the repository for the genetic information. Chromosomes containing genes reside in the nucleus. When an interphase cell is observed by using a light microscope, the inside of the nucleus may appear to be homogeneous because the chromosomal DNA is not condensed. In an appropriately fixed and stained section of onion root (obtainable from commercial sources), the DNA will be visible as a disk-shaped area, apparently constrained within a nucleus. This is the best stage in which to visualize DNA in learning the content of the standard. If the root tissue had a high rate of growth at the time it was sectioned and fixed, a fraction of the cells may be in one of the stages of mitosis. In that case the chromosomes will be visibly condensed but will not be limited by a nuclear membrane. This phenomenon must be explained carefully so that students do not develop a misconception about the distribution of DNA in a cell on the sole basis of their observation of mitotic chromosomes.
Q: What happens when cells divide through the process of mitosis?
A: This results in two daughter cells with identical sets of chromosomes. Just as living organisms are said to have a life cycle that relates to their periods of growth and reproduction, cells are said to have a “cell cycle.” Cells reproduce themselves by a process called mitosis. The process takes place after a period of growth during which the DNA in the nucleus is replicated and cytoplasmic organelles, such as mitochondria and chloroplasts, are doubled in number. During mitosis the replicated DNA chromosomes are segregated so that each daughter cell receives exactly the same number of chromosomes of each type (e.g., two of each type in a diploid organism). Students may observe mitotic chromosomes by light microscopy in a stained section of rapidly growing tissue. Time-lapse videos and movies of cell division will also help to illuminate the process of chromosome segregation.
Q: I know that DNA is the genetic material of living organisms but where is it located in each cell?
A: They are located in the chromosomes. Chromosomes in eukaryotes are complexes of DNA and protein. Chromosomes organize the genetic make-up of a cell into discrete units. Humans, for example, have 23 pairs of chromosomes that vary in size. When looking through a microscope at an appropriately stained section of onion root tip, students may see cells that are engaged in mitosis and that have visible, condensed chromosome structures. The proteins in a chromosome help to support its structure and function, but the genetic information of a cell is uniquely stored in the DNA component of the chromosome.
Physical Science
Resource of the Month: California Academic Content Standards for Middle School Physical Science (7th Grade)
Q: Are changes in velocity due to changes in speed, direction, or both?
A: Since velocity is a vector quantity, the velocity of an object is determined by both the speed and direction in which the object is traveling. Changing the speed of an object changes its velocity; changing the direction in which an object is traveling also changes the velocity. A change in either speed or direction (or both) will, by definition, change the velocity. (Although the term is not included in this standard set, the rate at which velocity changes with time is called acceleration. When a car speeds up or slows down, it undergoes acceleration. When a car rounds a curve maintaining the same speed, it also undergoes acceleration because it changes direction.)The important idea is that a change in the speed of the object, the direction of the moving object, or both is a change in velocity.
Q: How do you interpret graphs of position versus time and graphs of speed versus time for motion in a single direction?
A: In plotting position versus time, you should learn that the vertical axis represents distances away from an origin either in the positive (++) or negative (--) direction. The horizontal axis represents time. Every data point lying on the horizontal axis is “at the origin” because its distance value is zero. Given a graph of position versus time, you should be able to generate a table and calculate average speeds for any time interval (v = d/t). If the graph of position versus time is a straight line, the speed is constant; you should be able to find the slope and know that the slope of the line is numerically equal to the value of the speed in units corresponding to the labels of the axes. A graph of speed versus time consisting of a horizontal line represents an object traveling at a constant speed. Use d = rt to calculate the distance (d ) traveled during a time interval (t). A graph of speed versus time that is not a horizontal line indicates the speed is changing.
Earthquake Science
Scientist of the Month: OMSI Science Online, Portland, Oregon
Q: What is the possibility of a 10.5 earthquake?
A: A 10.5 earthquake could not occur.. The bigger an earthquake is, the more energy is released, and the bigger number we give it. To have more energy, you need a longer fault line, and to have a 10.5 earthquake you'd need a fault line as big as the Earth.
Q: What is the difference between sedimentary, metamorphic and igneous rocks?
A: Super question! A sedimentary rock is a layered rock resulting from the consolidation of sediment. Sandstone, mudstone, and shale are good examples of sedimentary rocks. A metamorphic rock is a rock (sedimentary or igneous) that has undergone intense pressure and temperature so that the rock's mineralogical, chemical and/or structural properties have changed. Examples of metamorphic rocks include schist, quartzite, and gneiss. An igneous rock has a volcanic origin and can include granite, basalt, and pumice.
A: The blue color of the sky is due to Rayleigh scattering. As light moves through the atmosphere, most of the longer wavelengths pass straight through. Little of the red, orange and yellow light is affected by the air. However, much of the shorter wavelength light is absorbed by the gas molecules. The absorbed blue light is then radiated in different directions. It gets scattered all around the sky. Whichever direction you look, some of this scattered blue light reaches you. Since you see the blue light from everywhere overhead, the sky looks blue.
Q: Why are sunsets red?
A: As the sun begins to set, the light must travel farther through the atmosphere before it gets to you. More of the light is reflected and scattered. As less reaches you directly, the sun appears less bright. The color of the sun itself appears to change, first to orange and then to red. This is because even more of the short wavelength blues and greens are now scattered. Only the longer wavelengths are left in the direct beam that reaches your eyes. The sky around the setting sun may take on many colors. The most spectacular shows occur when the air contains many small particles of dust or water. These particles reflect light in all directions. Then, as some of the light heads towards you, different amounts of the shorter wavelength colors are scattered out. You see the longer wavelengths, and the sky appears red, pink or orange.
