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MCAS Classification

MCAS Classification questions

MCAS 2010 Biology exam

32. The table below shows the classifications of three different sea lions.

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a. Identify which two of the sea lions are most closely related.
b. Justify your answer to part (a).
c. Describe and explain two types of evidence scientists would have used to determine the proper classifications of these three sea lions.


February 2018

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5. A scientist concludes that two organisms belong to the same species within the
class Mammalia. Which of the following observations most likely led the scientist
to conclude that the organisms are the same species?

A. The organisms move in the same way.
B. The organisms live in the same habitat.
C. The organisms are nocturnal and carnivorous.
D. The organisms mate and produce fertile offspring.


24. The brush mouse and the northwestern deermouse are both classified in the
genus Peromyscus. Which of the following conclusions can be made from this information?
A. The two types of mice live in the same habitat.
B. The two types of mice have the same fur color.
C. The two types of mice are closely related to each other.
D. The two types of mice can successfully interbreed with each other.



32. The table below gives the common names, scientific names, and known geographic locations of several wild cats.

Screen Shot 2019-10-23 at 10.21.36 AM

a. Using their common names, identify all the wild cats listed in the table that belong to the same genus.

b. Identify and explain one type of evidence scientists could have used to classify these wild cats.

The three kinds of tigers listed in the table are all classified as one species.

c. Based on the information in the table, identify which kind of tiger has the greatest chance of becoming a separate species. Explain your answer.

d. Describe how scientists could determine if one of the kinds of tigers becomes a separate species.



33. The table below shows taxonomic information for the gray wolf and four other species.

Screen Shot 2019-10-23 at 10.25.25 AM

Based on this information, which of the following lists the species in order from most closely related to least closely related to the gray wolf ?

A. 1, 2, 3, 4
B. 1, 2, 4, 3
C. 2, 1, 3, 4
D. 2, 1, 4, 3


31. All organisms classified in kingdom Animalia must also be classified as
which of the following?
A. Archaea
B. Eubacteria
C. Eukaryota
D. Protista


45. A student researching bears found the chart below in a textbook. The chart shows the
classifications of several types of bears.

Screen Shot 2019-10-23 at 10.27.06 AM

Which of the following conclusions is best supported by the data given in this chart?

A. Modern bears evolved from species that are now extinct.
B. The short-faced bear was the ancestor of the Asiatic black bear.
C. Present day bear species are more closely related than their ancestors were.
D. Natural selection favored the brown bear over the American black bear. .


MCAS Plants

MCAS Plant questions from the Biology MCAS

February 2018

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31. A plant species growing along a coast produces seeds with fluffy hair-like
fibers on one end. A seed from one of the plants is shown below:

Seed fluffy fiber

Some of these seeds were dispersed by the wind to islands off the coast, where new plants grew. Within 10 years, the seeds of the island plants were different
from the seeds of the mainland plants. Compared to the mainland seeds, the
island seeds were heavier and had shorter hair-like fibers. Which of the following statements best explains why heavier seeds with shorter fibers were favored in the island environment?

A. These seeds carried more genes than the mainland seeds did.
B. These seeds were less likely to be blown off the island by wind.
C. The island plants needed to prevent animals from eating the seeds.
D. The island plants used more energy to produce heavy seeds than to grow.


33. Students investigated the effect of acid rain on photosynthesis. Several plants
were given water with a pH of 4 each day for two months. The results showed
that the plants had a reduced rate of photosynthesis.

How did the acidic water most likely reduce the plants’ rate of photosynthesis?

A. by storing excess oxygen produced by the plants
B. by changing the effectiveness of enzymes in the plants
C. by causing root hairs to grow on the roots of the plants
D. by increasing the amount of carbon dioxide taken in by the plants


34. Waxes form a waterproof coating over the stems and leaves of many terrestrial plants. The waxes are composed of fatty acids linked to long-chain alcohols. Based on this information, waxes are which type of organic molecule?

A. lipids .  B. nucleotides .  C. polysaccharides .  D. proteins


37. Maltose is a carbohydrate molecule that provides energy to plants early in their
life cycle. Which elements are most common in a molecule of maltose?

A. carbon and hydrogen
B. copper and nitrogen
C. iron and phosphorus
D. magnesium and sulfur


Algae, and the scientific method

The rate of photosynthesis in organisms depends in part on the wavelength of visible light. In the late 1800s, Thomas Engelmann demonstrated the relationship between the wavelength of light and the rate of photosynthesis. His experiment is described below.

• Engelmann used a prism to produce a visible light spectrum of violet, blue, green, yellow, orange, and red light.
• He shined the light spectrum onto cells of the algae Spirogyra.
• Once the light was shining on the Spirogyra cells, Engelmann added aerobic bacteria to the system. Aerobic bacteria need oxygen to live and grow.
• After adding the bacteria, Engelmann observed the regions of the light spectrum where the bacteria concentrated around the Spirogyra cells.

The setup and results of Engelmann’s experiment are represented by the diagram below:

Engelmann’s experiment Spirogyra algae spectrum prism

Mark your answers to multiple-choice questions 8 through 11 in the spaces provided in your Student Answer Booklet. Do not write your answers in this test booklet, but you may work out solutions to multiple-choice questions in the test booklet.

8. Why are the greatest numbers of aerobic bacteria found at the 400–500 nm and 600–700 nm wavelengths of light?

A. Photosynthesis rates are highest there, producing large amounts of water.
B. Photosynthesis rates are highest there, producing large amounts of oxygen.
C. Photosynthesis rates are lowest there, producing small amounts of glucose.
D. Photosynthesis rates are lowest there, producing small amounts of carbon dioxide.

9. What is the role of visible light when Spirogyra cells perform photosynthesis?
A. It provides the energy for the photosynthesis reaction.
B. It concentrates the photosynthesis products for export.
C. It activates the DNA that directs the photosynthesis reaction.
D. It transports photosynthesis reactants across the cell membrane.

10. What is exchanged between the Spirogyra and the bacteria in
Engelmann’s experiment?

A. DNA and RNA
B. starch granules and spores
C. chlorophyll and cytoplasm
D. oxygen and carbon dioxide

11. A scientist used Engelmann’s data to predict how the concentrations of different substances in and around Spirogyra cells will change when the cells are exposed to different wavelengths of light. A graph for one substance is shown below.

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What is represented on the y-axis?

A. chlorophyll concentration .        B. hydrogen concentration
C. oxygen concentration .        D. water concentration


Spring 2018 MCAS

3. All corn plants contain the ZmLA1 gene. Some corn plants contain a certain mutation in the ZmLA1 gene. The graph below shows the amount of ZmLA1 RNA produced in plants with the normal gene and in plants with the mutated gene.

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Based on the graph, what most likely happens in corn plant cells as a direct result of the mutated gene?

A. DNA replication increases.
B. Lipid production decreases.
C. Glucose synthesis increases.
D. Protein production decreases.


4. The growth of plants in many ecosystems is limited by the supply of
nitrogen. Which of the following groups of organisms plays the largest role in
moving nitrogen between the atmosphere and plants?

A. bacteria .      B. earthworms .      C. insects .    D. protists


7. Lithops are multicellular organisms found in sandy soil in deserts. They
have large, central vacuoles in their cells that store water. Which of the following best classifies lithops?
A. They are bacteria because they store water.
B. They are animals because they are multicellular.
C. They are fungi because they are found in sandy soil.
D. They are plants because they have large, central vacuoles.


14. There are many fungus species that live inside plant tissues. What determines
whether the relationship between a fungus and a plant is commensalism,
mutualism, or parasitism?

A. where the fungus is located in the plant
B. how long the fungus survives in the plant
C. whether the fungus reproduces in the plant with spores, seeds, or runners
D. whether the effect of the fungus on the plant is neutral, positive, or negative


37. Plants in floodplains often get covered by water during floods. Some
plants survive the floods because they can continue photosynthesis
underwater. However, the plants’ rates of photosynthesis are much lower
underwater than above water.

Which of the following helps to explain why the rates of photosynthesis are
lower underwater than above water?

A. There is too much oxygen in the water.
B. There is no carbon dioxide in the water.
C. The chloroplasts do not function underwater.
D. The available light is less intense underwater.


February 2017

17. Carbon fixation is an important part of the carbon cycle. Carbon fixation is the conversion of carbon dioxide into organic compounds such as glucose. Which of the following organisms cannot fix carbon?

A. grass
B. green algae
C. mushrooms
D. oak trees


3. A botanist studied two groups of rice plants to determine how they are related. Both groups of plants have similar shapes, but one group has longer stalks. When the botanist cross-pollinated plants from one group with plants from the other group, the seeds produced did not sprout or grow.

Which of the following conclusions is best supported by this information?

A. The two groups are the same species because the plants have similar shapes.
B. The two groups are different species because they have differently sized stalks.
C. The two groups are different species because the seeds produced cannot sprout or grow.
D. The two groups are the same species because the plants were cross-pollinated and produced seeds


20. A partial food web is shown below. Which organisms in the food web are both primary and secondary consumers?

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A. bluegills
B. cattails
C. coyotes
D. snakes


28. A student looks at a cell under a microscope. Which of the following
observations would indicate that the cell is from a plant rather than an animal?

A. a nucleus located inside of the cell
B. numerous cilia on the outside of the cell
C. chloroplasts in the cytoplasm of the cell
D. a thin membrane around the edge of the cell


30. Prolonged periods of drought in an area cause decreases in plant population
sizes. Which of the following statements describes how the decreases in plant
population sizes then affect other populations in the area?

A. Omnivore population sizes increase, and herbivore population sizes increase.
B. Omnivore population sizes decrease, and carnivore population sizes increase.
C. Herbivore population sizes increase, and carnivore population sizes decrease.
D. Herbivore population sizes decrease, and carnivore population sizes decrease.

Could there be a shadow biosphere?

Could there be a shadow biosphere here on Earth?


I. Life on Earth, but not as we know it?

Excerpted from Life on Earth… but not as we know it, Robin McKie, The Guardian (UK), 4/13/2013

These researchers believe life may exist in more than one form on Earth: standard life – like ours – and “weird life”, as they term the conjectured inhabitants of the shadow biosphere.

All the micro-organisms that we have detected on Earth to date have had a biology like our own: proteins made up of a maximum of 20 amino acids and a DNA genetic code made out of only four chemical bases: adenine, cytosine, guanine and thymine,” says Cleland.

“Yet there are up to 100 amino acids in nature and at least a dozen bases. These could easily have combined in the remote past to create lifeforms with a very different biochemistry to our own. More to the point, some may still exist in corners of the planet.”

Science’s failure to date to spot this weird life may seem puzzling. The natural history of our planet has been scrupulously studied and analysed by scientists, so how could a whole new type of life, albeit a microbial one, have been missed?

Cleland has an answer. The methods we use to detect micro-organisms today are based entirely on our own biochemistry and are therefore incapable of spotting shadow microbes, she argues. A sample of weird microbial life would simply not trigger responses to biochemists’ probes and would end up being thrown out with the rubbish.

That is why unexplained phenomena like desert varnish are important, she says, because they might provide us with clues about the shadow biosphere. We may have failed to detect the source of desert varnish for the simple reason that it is the handiwork of weird microbes which generate energy by oxidising minerals, leaving deposits behind them.

The idea of the shadow biosphere is also controversial and is challenged by several other scientists.

II. Dark matter in biology

This section and image from ‘Dark Matter’ in Biology, Ian Dunn, Biopolyverse, 3/21/2011

… All current examples of ‘biological dark matter’ cited in the literature are, in essence, uncharacterized manifestations of known types of entities. Consider the issue of ‘dark’ products of complex genomes, in the form of numerous transcribed RNAs with unknown functions. However exotic the biological roles of certain non-coding RNAs, the general chemical nature of any RNA molecule is very familiar

A strict analogical extension of cosmic to biological dark matter would then be the discovery of a biological effect that cannot be accounted for by ‘ordinary’ biological mediators or processes. And just as dark matter in the universe is a recent finding, such a hypothetical biological effect might itself be long unrecognized, rendering the agency involved truly obscured.

… there are levels and levels of ‘darkness’ in any area of investigation, not least of which is biology. In other words, a hierarchy of novelty / unfamiliarity / strangeness can be readily constructed when we consider new biological discoveries, and speculate upon their ‘outer limits’...

Some discoveries may provide interesting precedents for processes or structures hitherto unreported, but without causing too many eyebrows to be raised.

MS spectra Mass Spectrometry Dark Matter ID

This image from Illuminating the dark matter in metabolomics, Ricardo da Silva, PNAS. http://www.pnas.org/content/112/41/12549

Still other findings may indeed cause considerable supra-ocular hair elevation, yet fall short of seriously challenging key biological principles. With these considerations in mind, it is not difficult to categorize the experimental input of new biological information as a spectrum of sorts

III. Hypothetical Dark life from Dark matter

This section from Could Dark Matter Spawn ‘Shadow Life’? Ian O’Neill, 2/7/2018, HowStuffWorks

The vast majority of mass in our universe is invisible, and for a while, physicists have been trying really hard to understand what this elusive “stuff” is. Assumed to be some kind of particle, there are hopes that the Large Hadron Collider might produce a dark matter particle or that a space telescope might detect the obvious gamma-ray telltale signature of dark matter particles colliding. But so far, hints have been few and far between; a problem that’s forcing theoretical physicists to think up new ideas.

In a mind-bending 2017 op-ed for Nautilus, famed theoretical physicist Lisa Randall delved into one of the more extreme possibilities for dark matter. Rather than thinking of dark matter as one type of particle, might dark matter be composed of an entire family of particles that create dark stars, dark galaxies, dark planets and, perhaps, dark life? This dark universe’s chemistry might be as rich and varied as our “ordinary chemistry.”

…Astrophysicists have hypothesized in the past that “dark stars” — stars made of dark matter — may have existed in our primordial universe and may persist to this day. If this is the case, Randall argues, perhaps “dark planets” may have formed, too. She then takes this idea a step further: If there’s a family of dark matter particles, governed by forces only accessible in the dark sector, might this realm also have complex chemistry? If so, might there be life? If there is “shadow life” living out its days parallel to our universe, you can forget any hopes of detecting it, however.

IV. Does Dark Matter Harbor Life?

Excerpted from Does Dark Matter Harbor Life? An invisible civilization could be living right under your nose. By Lisa Randall

… The Standard Model contains six types of quarks, three types of charged leptons (including the electron), three species of neutrinos, all the particles responsible for forces, as well as the newly discovered Higgs boson. What if the world of dark matter—if not equally rich—is reasonably wealthy too?…

If we were creatures made of dark matter, we would be very wrong to assume that the particles in our ordinary matter sector were all of the same type. Perhaps we ordinary matter people are making a similar mistake. Given the complexity of the Standard Model of particle physics, which describes the most basic components of matter we know of, it seems very odd to assume that all of dark matter is composed of only one type of particle. Why not suppose instead that some fraction of the dark matter experiences its own forces?

In that case, just as ordinary matter consists of different types of particles and these fundamental building blocks interact through different combinations of charges, dark matter would also have different building blocks—and at least one of those distinct new particle types would experience nongravitational interactions….

Ordinary matter’s many components have different interactions and contribute to the world in different ways. So too might dark matter have different particles with different behaviors that might influence the universe’s structure in a measurable fashion.

When first studying partially interacting dark matter, I was astonished to find that practically no one had considered the potential fallacy—and hubris—of assuming that only ordinary matter exhibits a diversity of particle types and interactions….

… Perhaps nuclear-type forces act on dark particles in addition to the electromagnetic-type one. In this even richer scenario, dark stars could form that undergo nuclear burning to create structures that behave even more similarly to ordinary matter than the dark matter I have so far described. In that case, the dark disk could be populated by dark stars surrounded by dark planets made up of dark atoms. Double-disk dark matter might then have all of the same complexity of ordinary matter.

  • Lisa Randall is the Frank B. Baird, Jr., Professor of Science at Harvard University, where she studies theoretical particle physics and cosmology. @lirarandall


#shadowbiosphere #shadowlife #darklife #exobiology

Further reading

Hypothetical types of biochemistry, Wikipedia

Purple Earth Hypothesis, Wikipedia

‘Dark Matter’ in Biology

Paradigms and Biological ‘Dark Matter’

‘Dark Matter’ in Biology: Great Expectations and Biological Limits

A Dark Shadow Biosphere with Unorthodox Orthogonality?

A Dark Shadow Biosphere with Unorthodox Orthogonality?
Does ‘Dark’ Biology Have Its CHARMs?

Learning Standards

Next Generation Science Standards: Science & Engineering Practices
● Ask questions that arise from careful observation of phenomena, or unexpected results, to clarify and/or seek additional information.
● Ask questions that arise from examining models or a theory, to clarify and/or seek additional information and relationships.
● Ask questions to determine relationships, including quantitative relationships, between independent and dependent variables.
● Ask questions to clarify and refine a model, an explanation, or an engineering problem.
● Evaluate a question to determine if it is testable and relevant.
● Ask questions that can be investigated within the scope of the school laboratory, research facilities, or field (e.g., outdoor environment) with available resources and, when appropriate, frame a hypothesis based on a model or theory.
● Ask and/or evaluate questions that challenge the premise(s) of an argument, the interpretation of a data set, or the suitability of the design

MA 2016 Science and technology

Appendix I Science and Engineering Practices Progression Matrix

Science and engineering practices include the skills necessary to engage in scientific inquiry and engineering design. It is necessary to teach these so students develop an understanding and facility with the practices in appropriate contexts. The Framework for K-12 Science Education (NRC, 2012) identifies eight essential science and engineering practices:

1. Asking questions (for science) and defining problems (for engineering).
2. Developing and using models.
3. Planning and carrying out investigations.
4. Analyzing and interpreting data.
5. Using mathematics and computational thinking.
6. Constructing explanations (for science) and designing solutions (for engineering).
7. Engaging in argument from evidence.
8. Obtaining, evaluating, and communicating information.

Scientific inquiry and engineering design are dynamic and complex processes. Each requires engaging in a range of science and engineering practices to analyze and understand the natural and designed world. They are not defined by a linear, step-by-step approach. While students may learn and engage in distinct practices through their education, they should have periodic opportunities at each grade level to experience the holistic and dynamic processes represented below and described in the subsequent two pages… http://www.doe.mass.edu/frameworks/scitech/2016-04.pdf



Biological differences between men and women impact perception of pain and choice of medication

From Wired Magazine – Women’s Pain Is Different From Men’s—the Drugs Could Be Too

male female gender pain brains neurons

Men and Women can’t feel each other’s pain. Literally. We have different biological pathways for chronic pain, which means pain-relieving drugs that work for one sex might fail in the other half of the population.

So why don’t we have pain medicines designed just for men or women? The reason is simple: Because no one has looked for them. Drug development begins with studies on rats and mice, and until three years ago, almost all that research used only male animals. As a result, women in particular may be left with unnecessary pain—but men might be too.

Now a study in the journal Brain reveals differences in the sensory nerves that enter the spinal cords of men and women with neuropathic pain, which is persistent shooting or burning pain. The first such study in humans, it provides the most compelling evidence yet that we need different drugs for men and women.

“There’s a huge amount of suffering that’s happening that we could solve,” says Ted Price, professor of neuroscience at the University of Texas, Dallas, and an author of the Brain article. “As a field, it would be awesome to start having some success stories.”

Modern-day pain control is notoriously dismal. Our go-to medicines—opioids and anti-inflammatories—are just new versions of opium and willow bark, substances we’ve used for thousands of years. Although they are remarkably effective in relieving the sudden pain of a broken bone or pulled tooth, they don’t work as well for people with persistent pain that lasts three months or longer.

Some 50 million people struggle with pain most days or every day, and chronic pain is the leading cause of long-term disability in the United States. Women are more likely than men to have a chronic pain condition, such as arthritis, fibromyalgia, or migraines.

Meanwhile, pain medications are killing us. About 17,000 people die each year from prescribed opioids as clinicians write almost 200 million opioid prescriptions, or more than one for every two American adults.

The failure to include sex differences in the search for better pain relief stems in part from flawed but deep-seated beliefs. “[Medical researchers] made the assumption that men and women were absolutely identical in every respect, except their reproductive biology,” says Marianne Legato, a cardiologist who began sounding an alarm in the 1980s about differences in heart attack symptoms among women. She went on to pioneer a new field of gender-specific medicine.

The physiology of pain is just one of many ways that men and women differ, she says. But she isn’t surprised that no sex-specific medicines have emerged. The medical community—including pharmaceutical companies—didn’t appreciate the variation between men and women, including in their metabolisms, immune systems, and gene expression.

“If there were differences in how their drugs worked between men and women, they didn’t want to hear about it,” she says.

… Tailoring new medicines to men or women would be revolutionary, particularly considering that it took many years for women (and female animals) to get included in pain research at all.

Fearful of potential birth defects, in 1977 the FDA cautioned against including women of childbearing age in clinical trials, which meant women used drugs solely designed for men. By 1993, the thinking had changed, and Congress passed a law requiring the inclusion of women in clinical trials funded by the National Institutes of Health. Although clinical trials now include both men and women, they often don’t report results by sex.


Related articles

Why the sexes don’t feel pain the same way –  After decades of assuming that pain processing is equivalent in all sexes, scientists are finding that different biological pathways can produce an ‘ouch!’. Amber Dance, Nature, 3/27/2019

Sex differences in pain responses, Current Opinion in Physiology, Volume 6, December 2018, Pages 75-81, by Robert E Sorge, Larissa J Strath

Sex differences have been reported in the experience of pain and in the prevalence of chronic pain conditions. However, recently work has uncovered biological differences in the utilization of immune cells and basic function of afferents that shed light on the underpinnings of these sex-dependent findings. In addition, work in healthy controls and chronic pain patients have highlighted biases in attribution of pain and assessment of pain intensity that further reinforce sex differences. Together, the combination of biological differences, distinct psychological coping strategies and outside bias result in the maintenance of disparities in the experience of pain based on sex. Recognition of sex differences and the underlying mechanisms can only improve treatment and patient outcomes.

Does Gender Influence Pain Sensitivity? Biology may play a role in nociception and analgesia, and researchers are examining the potential effects of social and psychologic factors. Neurology Reviews. 2017 May;25(5):16-19

All Pain Is Not the Same: Psychologist Discusses Gender Differences in Chronic Pain, Translating Research in Women’s Health and Mental Health to Practice.

Women suffer needless pain because almost everything is designed for men. Why women are 50 percent more likely to be misdiagnosed after a heart attack and 17 percent more likely to die in a car crash. By Sigal Samuel, Apr 17, 2019, Vox

Berkley KJ. Sex differences in pain. Behav Brain Sci. 1997;20(3):371-380; discussion 435-513.

Mogil JS. Sex differences in pain and pain inhibition: multiple explanations of a controversial phenomenon. Nat Rev Neurosci. 2012;13(12):859-866.

Sorge RE, Mapplebeck JC, Rosen S, et al. Different immune cells mediate mechanical pain hypersensitivity in male and female mice. Nat Neurosci. 2015;18(8):1081-1083.

#science #gender

Backup The Particle Physics of You

This is a class backup of the article, The particle physics of you, 11/03/15 By Ali Sundermier. Symmetry Magazine.

Not only are we made of fundamental particles, we also produce them and are constantly bombarded by them throughout the day.


Fourteen billion years ago, when the hot, dense speck that was our universe quickly expanded, all of the matter and antimatter that existed should have annihilated and left us nothing but energy. And yet, a small amount of matter survived.

We ended up with a world filled with particles. And not just any particles—particles whose masses and charges were just precise enough to allow human life. Here are a few facts about the particle physics of you that will get your electrons jumping.

Particle Physics of You Body to atoms to gluons quarks

The particles we’re made of

About 99 percent of your body is made up of atoms of hydrogen, carbon, nitrogen and oxygen. You also contain much smaller amounts of the other elements that are essential for life.

While most of the cells in your body regenerate every seven to 15 years, many of the particles that make up those cells have actually existed for millions of millennia. The hydrogen atoms in you were produced in the big bang, and the carbon, nitrogen and oxygen atoms were made in burning stars. The very heavy elements in you were made in exploding stars.

The size of an atom is governed by the average location of its electrons. Nuclei are around 100,000 times smaller than the atoms they’re housed in. If the nucleus were the size of a peanut, the atom would be about the size of a baseball stadium. If we lost all the dead space inside our atoms, we would each be able to fit into a particle of lead dust, and the entire human race would fit into the volume of a sugar cube.

As you might guess, these spaced-out particles make up only a tiny portion of your mass. The protons and neutrons inside of an atom’s nucleus are each made up of three quarks. The mass of the quarks, which comes from their interaction with the Higgs field, accounts for just a few percent of the mass of a proton or neutron. Gluons, carriers of the strong nuclear force that holds these quarks together, are completely massless.

If your mass doesn’t come from the masses of these particles, where does it come from? Energy. Scientists believe that almost all of your body’s mass comes from the kinetic energy of the quarks and the binding energy of the gluons.

Particle Physics of You Gamma rays radioactive atoms Carbon Potassium

The particles we make

Your body is a small-scale mine of radioactive particles. You receive an annual 40-millirem dose from the natural radioactivity originating inside of you. That’s the same amount of radiation you’d be exposed to from having four chest X-rays.

Your radiation dose level can go up by one or two millirem for every eight hours you spend sleeping next to your similarly radioactive loved one.

You emit radiation because many of the foods you eat, the beverages you drink and even the air you breathe contain radionuclides such as Potassium-40 and Carbon-14. They are incorporated into your molecules and eventually decay and produce radiation in your body.

When Potassium-40 decays, it releases a positron, the electron’s antimatter twin, so you also contain a small amount of antimatter.

The average human produces more than 4000 positrons per day, about 180 per hour. But it’s not long before these positrons bump into your electrons and annihilate into radiation in the form of gamma rays.

Particle Physics of You Cosmic Rays Solar Neutrinos Geoneutrinos Pions cascade

The particles we meet

The radioactivity born inside your body is only a fraction of the radiation you naturally (and harmlessly) come in contact with on an everyday basis. The average American receives a radiation dose of about 620 millirem every year. The food you eat, the house you live in and the rocks and soil you walk on all expose you to low levels of radioactivity. Just eating a Brazil nut or going to the dentist can up your radiation dose level by a few millirem. Smoking cigarettes can increase it up to 16,000 millirem.

Cosmic rays, high-energy radiation from outer space, constantly smack into our atmosphere. There, they collide with other nuclei and produce mesons, many of which decay into particles such as muons and neutrinos. All of these shower down on the surface of the Earth and pass through you at a rate of about 10 per second. They add about 27 millirem to your yearly dose of radiation. These cosmic particles can sometimes disrupt our genetics, causing subtle mutations, and may be a contributing factor in evolution.

In addition to bombarding us with photons that dictate the way we see the world around us, our sun also releases an onslaught of particles called neutrinos. Neutrinos are constant visitors in your body, zipping through at a rate of nearly 100 trillion every second. Aside from the sun, neutrinos stream out from other sources, including nuclear reactions in other stars and on our own planet.

Many neutrinos have been around since the first few seconds of the early universe, outdating even your own atoms. But these particles are so weakly interacting that they pass right through you, leaving no sign of their visit.

You are also likely facing a constant shower of particles of dark matter. Dark matter doesn’t emit, reflect or absorb light, making it quite hard to detect, yet scientists think it makes up about 80 percent of the matter in the universe.

Looking at the density of dark matter throughout the universe, scientists calculate that hundreds of thousands of these particles might be passing through you every second, colliding with your atoms about once a minute. But dark matter doesn’t interact very strongly with the matter you’re made of, so they are unlikely to have any noticeable effects on your body.

The next time you’re wondering how particle physics applies to your life, just take a look inside yourself.

Artwork by Sandbox Studio, Chicago with Ana Kova.

This website is educational. Materials within it are being used in accord with the Fair Use doctrine, as defined by United States law.
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RNA World

Background vocabulary: monomer and polymer

Monomer Polymer Lego analogy

Life today

Living things have genetic information stored in a polymer of DNA.

That info gets copied into polymers of RNA.

That is translated, with the help of mRNA, into polymers of proteins.

And each of these steps needs special enzymes.

Interesting thought

Life in today’s cells, and even viruses, is wicked complicated.

Hard to imagine all it all evolved, all at once. But who says it had to do it all at once?

Maybe one simple kind of reaction developed, then later, other kinds of reactions, and then over a loooong period of time, even other types.

Life in the very beginning

Perhaps once upon a time, RNA was all that life had.

Pieces of RNA were both the genes and the catalyst.

  e.g. RNA could do base pairing with itself, bend, and graph other molecules.


RNA sequences could be copied by other RNAs.

Only later did DNA and proteins evolve.

This is the idea of the RNA world

A hypothetical stage in the history of life on Earth

Idea – RNA developed before DNA and proteins developed.

Alexander Rich first proposed the concept in 1962

Alexander Rich RNA

Growing amounts of evidence for this is strong enough that the hypothesis has gained wide acceptance.

How is RNA like DNA?

Both can store and replicate genetic information;

How is RNA like an enzyme?

Both can catalyze (start) chemical reactions.

Are any enzymes today made of RNA?

the ribosome is composed primarily of RNA.

Ribosomes are part of many important enzymes, such as Acetyl-CoA, NADH, etc.

So why does life depend on DNA replication nowadays?

DNA is more stable than RNA


What does RNA, and DNA, look like?



How would RNA monomers assemble into polymers?

How could copies be made?

first genes may have been RNA nucleotides

So let us look at the possible in steps, in order.

At the far left is long ago… then an RNA based world of life developed… and later a DNA and protein based world of life developed.

RNA World Abiogenesis



“Oil” is a general name for any kind of molecule which is


that just means that its electrons are evenly distributed

PHET Polar molecules app

liquid at room temperature

of course, it could become solid if cooled, or evaporate if heated

Molecule has one end which is hydrophobic and another end which is lipophilic

The hydrophobic end likes to stick to water molecules. But hates sticking to oils.

The lipophilic end likes to stick to oil molecules, but hates sticking to water,

hydrophobic hydrophilic

Made with many C and H atoms

Oils are usually flammable. Here we see oils in an orange skin interacting with a candle.

flammable orange oil

So Petroleum is?

Petroleum is a mix of naturally forming oils, which we drill from the Earth, and use in a variety of ways. See our article on petroleum and producing power.