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MCAS Open response
Sarah and her biological sister Danielle have some physical characteristics that are the same and some that are different, as shown in the table below.
a. Identify the molecule that stores the hereditary information for these characteristics in the chromosomes of every body cell.
b. Identify the total number of chromosomes that should be in one of Sarah’s body cells and the number of chromosomes that should have been contributed by each biological parent.
c. Explain the roles of meiosis and fertilization in achieving the chromosome numbers you identified in part (b).
d. Explain why Sarah and Danielle have some physical characteristics that are different from each other, even though they have the same biological parents.
See
Cortical homunculus
The cortical homunculus is the part of the brain responsible for processing and integration of motor information (muscles, motion) and tactile information (touch, senses)
The reason for the distorted appearance is that the amount of cortex is proportional to how richly innervated that region is, not to its size.
The resulting image appears as a disfigured human with disproportionately huge hands, lips, and face in comparison to the rest of the body.
Sensory
Cortical
from Wikipedia
Herd immunity
What is herd immunity?
It is a form of indirect protection from infectious disease
It occurs when a sufficient percentage of a population becomes immune to an infection, whether through vaccination or previous infections.
Immune individuals are unlikely to contribute to disease transmission. This slows or stops the spread of disease.
The greater the proportion of immune individuals in a community, the smaller the probability that other people will come into contact with an infectious individual.
Let’s see how this works, with a graphic from the National Institute of Allergy and Infectious Disease (NIAID.)
Top box
Shows an outbreak in a community in which a few people are infected (shown in red) and the rest are healthy but unimmunized (shown in blue); the illness spreads freely through the population.
Middle box
Shows a population where a small number have been immunized (shown in yellow); those not immunized become infected while those immunized do not.
Bottom box
A large proportion of the population have been immunized; this prevents the illness from spreading significantly, including to unimmunized people.
In the first example, most healthy unimmunized people become infected, whereas in the bottom example only one fourth of the healthy unimmunized people become infected.
The National Institute of Allergy and Infectious Disease (NIAID)
Herd immunity is not all or nothing
On her blog, Your Local Epidemiologist, Katelyn Jetelina brings up important points:
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Is there some known, specific number we have to reach, in order to claim herd immunity?
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Is mass vaccination useless in stopping the spread of a disease unless we reach this specific percent?
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Does this specific number stay the same, or does it change over time?
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How does our behavior affect herd immunity?
In her home city, health officials stated that their county had reached herd immunity against COVID-19. 80% of people in the county had either previously contracted COVID19 and/or had received at least one vaccination.
In response, Katelyn Jetelina writes
This is exciting. Maybe this means there’s light at the end of the long, pandemic tunnel… However, we cannot come to erroneous conclusions once we reach a magical number in our head or on a county dashboard.
***Herd immunity 101***
I think we all know by now that not 100% of our population has to be immune for COVID19 to wither away. We can get to a point where so few people have COVID19 that even those who can’t be protected (like the immunocompromised ) will never have the chance to get sick. An immunity wall will keep any outbreak or transmission from happening.
On a global stage, we’ve only hit herd immunity once. In 1980, the World Health Assembly declared that smallpox was eradicated thanks to a very successful global vaccination campaign. No cases of naturally occurring smallpox have happened since.
In 2000, the CDC also declared that measles was eradicated in the United States as we reached herd immunity. This was a huge achievement given that the measles is incredibly contagious; we needed ~95% herd immunity threshold. Unfortunately, this is not still the case. Because of the antivaxx movement, we continue to dip below the threshold of protection and outbreaks happen all the time. The 2019 measles outbreak at Disneyland is just one example.
***Herd immunity threshold is really complex to measure.***
We don’t even know what the magic number is for COVID19. In the beginning, scientists estimated a 69.6% threshold was needed to reach herd immunity in the United States. This was based on a lot of mathematical models and educated guesses. Importantly, this guess relied heavily on R(0).
But the pandemic is not a fixed. It continuously evolves. Which means this threshold continues to move. The more transmissible the variant (like Delta) the higher the threshold we need.
Our behaviors also impact the threshold. Not wearing masks, not social distancing, etc. will also move our threshold higher. Population density, genetics, environment, and a whole lot of other things can also impact this number.
Thus, herd immunity in the United States can be very different than what is needed in Canada. Because of this, it’s really difficult (in fact I would argue impossible) to forecast an accurate number.
***Even if we knew the number, it’s not a light switch.***
It’s not a finish line. Not a binary decision. Not a static goal post that, once we reach, this nightmare will end and everyone’s risk for COVID19 will be zero.
My friend and colleague, Dr. Malia Jones, explained what it might look like instead:
“(A) receding tide. As more and more people are vaccinated, those who are at highest risk for ending up in the ICU will be protected. We’ll all have growing protection from outbreaks as people who are high transmitters get vaccinated. (Looking right at you, young adults.) Cases will start to ebb overall, but we can expect some ups and downs. There will be more variants, and there will be more surges. We’ll have low enough transmission that we will be able to resume most normal activities.”
***And herd immunity is not a city, county, or even state level metric.***
The 80% threshold that Dallas reached is a pooled estimate. There are still significant pockets within Dallas that remain extremely vulnerable. Even though Dallas reached “herd immunity”, cases continue to rise in Dallas.
But even if there weren’t pockets within, viruses don’t see city lines. We live in a very transient and fluid society. We move between counties, states, and countries.
And it’s dangerous to think that viruses see lines. There’s a very real possibility that people will think they’re protected if we reach a magic number. They may wrongly think this is over, that vaccines aren’t important anymore, and that we can put our guard down. This is a dangerous game to play.
***We may not reach herd immunity. But it isn’t all for nothing.***
We don’t need to reach herd immunity for a pandemic to end; for us to reach some sort of pre-pandemic normality. Herd immunity is not a number we need for cases to all of a sudden plummet. Instead it’s a number we need in order to keep cases down AFTER they are already down. Like Dr. Jones says, it’s a policy goal.
During a Stanford panel, a number of experts agreed that the next phase will be an endemic: “a plateau in infection, with a decrease in prominence over time but continued circulation.” This will be a mild state in which we don’t have exponential swings but, instead, people will get sick on occasion.
***Bottom Line***
There is not going to be a “herd immunity day” where life immediately goes back to normal. We need to start thinking of it as a receding tide rather than a light switch. Yes, we should celebrate vaccine progression. And yes, some are still hopeful that we will eventually reach herd immunity. But it will be slow. It will be quiet. And we will only know we reached it until it’s passed.
About the author: Katelyn Jetelina has a Masters in Public Health and PhD in Epidemiology and Biostatistics. She is an Assistant Professor at a School of Public Health where her research lab resides.
Related articles
Vaccines
The History of Vaccines: Interactive animations
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Action potentials
Andy Maldonado, on Quora, writes
An action potential is the way by which neurons communicate.
Neurons are negatively charged on the inside and positively charged on the outside.
This is due to the different concentrations of Na+, K+, Cl-, Ca2+, and charged proteins distributed both in and outside the neuron.
An action potential begins when a disruption of this distribution causes Na+ to flow into the neuron, through Na+ channels, causing the inside to become more positive.
The more positively charged inside of the neuron triggers adjacent voltage-gated Na+ channels to open and allow more ions to flow through.
The increase in charge inside the neuron triggers K+ channels to open – allowing for ions to flow outside of the cell, and thus lowering the inside charge back to its original state.
This increase and decrease in charge causes a wave-like motion of ions that propagates down the axon of a neuron – and ultimately causes the release of neurotransmitters from the dendrites – which stimulate the next neuron to either initiate or inhibit an action potential.
Action potentials trigger neuronal pathways which can stimulate or inhibit certain functions in our body. For example, action potentials in the motor region of the brain may stimulate a neural pathway with leads to the muscles in your arms resulting in flexion. Action potentials also facilitate communication between neuronal networks in the brain which allow us to have conscious thoughts, emotions, and memories.
Animation
By Laurentaylorj, on Wikimedia
As a nerve impulse travels down the axon, there is a change in polarity across the membrane.
The Na+ and K+ gated ion channels open and close in response to a signal from another neuron. At the beginning of action potential, the Na+ gates open and Na+ moves into the axon. This is depolarization. Repolarization occurs when the K+ gates open and K+ moves outside the axon. This creates a change in polarity between the outside of the cell and the inside. The impulse continuously travels down the axon in one direction only, through the axon terminal and to other neurons.
External links
http://blog.eyewire.org/the-nervous-system-action-potential-crash-course-2/
Learning Standards
2016 Massachusetts Science and Technology/Engineering Curriculum Framework
HS-LS1-2. Develop and use a model to illustrate the key functions of animal body systems: Emphasis is on the primary function of the following body systems… nervous (neurons, brain, spinal cord).
College Board Science Standards
LSH-PE.5.5.4 Construct a simple representation of a feedback mechanism that maintains the internal conditions of a living system within certain limits as the external conditions change.
LSH-PE.5.5.5 Construct a representation of the interaction of the endocrine and nervous systems (e.g., hormones and electrochemical impulses) as they interact with other body systems to respond to a change in the environment (e.g., touching a hot stove). Explain how the representation is like and unlike the phenomenon it is representing.
Lack of exercise is a major cause of chronic diseases
Lack of exercise is a major cause of chronic diseases
U.S. Air Force photo by Staff Sgt. Christopher Hubenthal
Chronic diseases are major killers in the modern era. Physical inactivity is a primary cause of most chronic diseases.
The initial third of the article considers: activity and prevention definitions; historical evidence showing physical inactivity is detrimental to health and normal organ functional capacities; cause vs. treatment; physical activity and inactivity mechanisms differ; gene-environment interaction [including aerobic training adaptations, personalized medicine, and co-twin physical activity]; and specificity of adaptations to type of training.
Next, physical activity/exercise is examined as primary prevention against 35 chronic conditions
[Accelerated biological aging/premature death, low cardiorespiratory fitness (VO2 max), sarcopenia, metabolic syndrome, obesity, insulin resistance, prediabetes, type 2 diabetes, non-alcoholic fatty liver disease, coronary heart disease, peripheral artery disease, hypertension, stroke, congestive heart failure, endothelial dysfunction, arterial dyslipidemia, hemostasis,
deep vein thrombosis, cognitive dysfunction, depression and anxiety, osteoporosis, osteoarthritis, balance, bone fracture/falls, rheumatoid arthritis, colon cancer, breast cancer, endometrial cancer, gestational diabetes, preeclampsia, polycystic ovary syndrome, erectile dysfunction, pain, diverticulitis, constipation, and gallbladder diseases].
The article ends with consideration of deterioration of risk factors in longer-term sedentary groups; clinical consequences of inactive childhood/adolescence; and public policy. In summary, the body rapidly maladapts to insufficient physical activity, and if continued, results in substantial decreases in both total and quality years of life. Taken together, conclusive evidence exists that physical inactivity is one important cause of most chronic diseases. In addition, physical activity primarily prevents, or delays, chronic diseases, implying that chronic disease need not be an inevitable outcome during life.
Source
Lack of exercise is a major cause of chronic diseases
Frank W. Booth, Ph.D., Christian K. Roberts, Ph.D., and Matthew J. Laye, Ph.D.
PMC 2014 Nov 23, and Comprehensive Physiology 2012 Apr; 2(2): 1143–1211.5
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC4241367/
https://onlinelibrary.wiley.com/doi/abs/10.1002/cphy.c110025
Detecting genetic disorders with 3d face scans
It is possible to detect numerous types pf genetic disorders with 3d face scans
How do we make measurements of the face?
How can we automate such measurements and make them accurate?
(Facial recognition technology will change the way we live, The Economist)
Detecting genetic disorders with 3d face scans
Johan at the Phineas Gage Fan Club writes:
Following on from last week’s post on smile measuring software, The Scotsman (via Gizmodo) reports on the work by Hammond and colleagues at UCL, who are developing 3d face scans as a quick, inexpensive alternative to genetic testing.
This is not as crazy as it sounds at first since it is known that in a number of congenital conditions, the hallmark behavioural, physiological or cognitive deficits are also (conveniently) accompanied by characteristic appearances.
The classic example of this is Down syndrome, which you need no software to recognise. More examples appear in the figure above, where you can compare the characteristic appearances of various conditions to the unaffected face in the middle.
Hammond’s software can be used to identify 30 congenital conditions, ranging from Williams syndrome (a sure topic of a future post) to Autism,
Detecting genetic disorders with 3d face scans
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Diagnostically relevant facial gestalt information from ordinary photos
Rare genetic disorders affect around 8% of people, many of whom live with symptoms that greatly reduce their quality of life. Genetic diagnoses can provide doctors with information that cannot be obtained by assessing clinical symptoms, and this allows them to select more suitable treatments for patients. However, only a minority of patients currently receive a genetic diagnosis.
Alterations in the face and skull are present in 30–40% of genetic disorders, and these alterations can help doctors to identify certain disorders, such as Down’s syndrome or Fragile X.
Extending this approach, Ferry et al. trained a computer-based model to identify the patterns of facial abnormalities associated with different genetic disorders. The model compares data extracted from a photograph of the patient’s face with data on the facial characteristics of 91 disorders, and then provides a list of the most likely diagnoses for that individual. The model used 36 points to describe the space, including 7 for the jaw, 6 for the mouth, 7 for the nose, 8 for the eyes and 8 for the brow.
This approach of Ferry et al. has three advantages. First, it provides clinicians with information that can aid their diagnosis of a rare genetic disorder. Second, it can narrow down the range of possible disorders for patients who have the same ultra-rare disorder, even if that disorder is currently unknown. Third, it can identify groups of patients who can have their genomes sequenced in order to identify the genetic variants that are associated with specific disorders.
from Quentin Ferry et al, eLife 2014;3:e02020
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This App Uses Facial Recognition Software to Help Identify Genetic Conditions
A geneticist uploads a photo of a patient’s face, and Face2Gene gathers data and generates a list of possible syndromes
… Face2Gene, the tool Abdul-Rahman used, was created by the Boston startup, FDNA. The company uses facial recognition software to aid clinical diagnoses of thousands of genetic conditions, such as Sotos syndrome (cerebral gigantism), Kabuki syndrome (a complicated disorder that features developmental delay, intellectual disability and more) and Down syndrome.
This App Uses Facial Recognition Software to Help Identify Genetic Conditions, Smithsonian Magazine
Related resources
How phenotypes lead to genotypes (infographic?)
Scientific journal articles
Detecting Genetic Association of Common Human Facial Morphological Variation Using High Density 3D Image Registration, Shouneng Peng et al, PLoS Comput Biol. 2013 Dec; 9(12)
Digesting nutrients
This next section comes from BBC KS3 Bitzesize Science, http://www.bbc.co.uk, Organisms, behaviour and health
Enzymes
Special proteins that can break large molecules into small molecules.
Different types of enzymes can break down different nutrients:
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carbohydrase or amylase ⇒ break down starch into sugar
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protease ⇒ break down proteins into amino acids
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lipase ⇒ break down fats into fatty acids and glycerol
Carbohydrates
Saliva in your mouth contains amylase, which is a starch digesting enzyme.
Proteins
Proteins are digested in the stomach and small intestine.
Protease enzymes break down proteins into amino acids.
Digestion of proteins in the stomach is helped by stomach acid, which is strong hydrochloric acid. This also kills harmful micro-organisms that may be in the food.
Fats
Lipase enzymes break down fat into fatty acids and glycerol. Digestion of fat in the small intestine is helped by bile, made in the liver. Bile breaks the fat into small droplets that are easier for the lipase enzymes to work on.
Things that are not digested
Minerals, vitamins and water are already small enough to be absorbed by the body without being broken down
Fiber – these are carbohydrates that our body can’t digest
Breaking proteins and fats down into smaller parts
How does the digestive system break larger molecules down into smaller molecules?
Hydrolysis – adding an H2O molecule can break bonds apart.
Here we see hydrolysis breaking a tiny protein down into two separate amino acids.
(And then, the animation shows how the opposite can occur when needed: How two separate amino acids can be condensed together by removing an OH from one of them, and and H from the other, creating a new H2O molecule left over.)
Similarly, here we see hydrolysis breaking a fat (triglyceride) down into smaller pieces (glycerol and 3 fatty acids.)
(And then, the animation shows how the opposite can occur when needed: How they all can be condensed together by removing an OH from one of them, and and H from the other, creating a new H2O molecule left over.)
How does does starch enter the bloodstream
Absorption and egestion
http://www.bbc.co.uk/bitesize/ks3/science/organisms_behaviour_health/diet_drugs/revision/6/
These are the processes that happen in the digestive system:
ingestion (eating) → digestion (breaking down) → absorption → egestion
Digested food molecules are absorbed in the small intestine. This means that they pass through the wall of the small intestine and into ourbloodstream.
Once in the bloodstream, the digested food molecules are carried around the body to where they are needed.
Only small, soluble substances can pass across the wall of the small intestine.
Large insoluble substances cannot pass through.
The inside wall of the small intestine needs to be thin, with a really big surface area.
This allows absorption to happen quickly and efficiently. If the small intestine had a thick wall and a small surface area, a lot of digested food might pass out of the body before it had a chance to be absorbed.
To get a big surface area, the inside wall of the small intestine is lined with tiny villi (one of them is called a villus).
These stick out and give a big surface area. They also contain blood capillaries to carry away the absorbed food molecules.
Pancreas
Pancreas has two major jobs: Digestion, and hormonal control of blood sugar levels
I. Releases pancreatic juice
• released into the duodenum (first part of the small intestine)
• is alkaline (the opposite of acid).
This neutralizes the acid that had been created by your stomach.
• contains lipases – enzymes which break down fats
• contains proteases – enzymes which break down proteins
• contains amylases – enzymes which break down carbohydrates
II. Pancreas’s endocrine cells release hormones
Hormones regulate your blood sugar levels.
When [blood sugar] too high -> pancreas releases insulin
causes muscle and fat cells to take in more sugar, so this decreases [blood sugar]
promotes glycolysis – conversion of sugar into ATP, also decreases [blood sugar]
makes liver store glucose as glycogen
When [blood sugar] too low -> pancreas releases glucagon
tells liver to break down glycogen into glucose, so this increases [blood sugar]
stops cells taking in more sugar, so this increases [blood sugar]
STOPS glycolysis, so sugar isn’t turned into ATP, so this increases [blood sugar]
from dynamicscience.com.au, feedbackloops
…
Mollusk family tree
Cladograms and Evolution
Molluscs are invertebrate animals with a three part body plan that includes
(a) mantle = large body mass, with internal organs. Mantle is usually wholly or partly enclosed in a calcium carbonate shell.
(b) radula = fleshy structure used for feeding, sometimes compared to a tongue. Covered in very tiny denticles (miniature teeth.) Only found in molluscs. In all molluscs (except the bivalves.)
(c) a nervous system (almost all animals have a nervous system)
Several categories
Gastropods- “stomach foot”. Includes snails, slugs, limpets, and sea cucumbers.
Cephalopods- “head foot”. Includes octopi, squid, cuttlefish, and nautilus.
Bivalves- foot projects from shell. Includes clams, oysters, scallops, mussels
(there are a few other smaller categories)
Image from Phylogenomics reveals deep molluscan relationships, by Kocot et al.
Nature volume 477, pages 452–456 (22 September 2011) doi:10.1038/nature10382
Learning Standards
Massachusetts Science and Technology/Engineering Curriculum FrameworkLife
Science (Biology), Grades 6–8.
Classify organisms into the currently recognized kingdoms according to characteristics that they share. Be familiar with organisms from each kingdom.
Biology, High School
5.2 Describe species as reproductively distinct groups of organisms. Recognize that species are further classified into a hierarchical taxonomic system (kingdom, phylum, class, order, family, genus, species) based on morphological, behavioral, and molecular similarities.
Benchmarks for Science Literacy, American Association for the Advancement of Science
Students should begin to extend their attention from external anatomy to internal structures and functions. Patterns of development may be brought in to further illustrate similarities and differences among organisms. Also, they should move from their invented classification systems to those used in modern biology… A classification system is a framework created by scientists for describing the vast diversity of organisms, indicating the degree of relatedness between organisms, and framing research questions.
Evolution and diversity: Origin of life, evidence of evolution, patterns of evolution, natural selection, speciation, classification and diversity of organisms.
Teaching About Evolution and the Nature of Science, National Academy Press (1998)
Biological classifications are based on how organisms are related. Organisms are classified into a hierarchy of groups and subgroups based on similarities which reflect their evolutionary relationships. Species is the most fundamental unit of classification.
MCAS Evolution
MCAS Evolution
Feb 2016 MCAS. Scientists often compare fossils of extinct organisms with living organisms to help determine evolutionary relationships. What is the primary information that scientists use when comparing fossils with living organisms?
A. the types of minerals that formed the fossils
B. the size of the rocks that contained the fossils
C. the cause of death for the fossilized organisms
D. the physical characteristics of the fossilized organisms
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Feb 2016 MCAS .
The pictures below show the shells of some species of land snails found on a Pacific island. Each species was found on a different hill on the island. Based on the snails’ shell shapes, scientists made hypotheses about the evolutionary relationships among the snails. Which of the following would be the best characteristic to compare in order to test these hypotheses?
A. the size of the snails
B. the diet of the snails
C. the DNA of the snails
D. the average age of the snails
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Scientists hypothesized that several species of frogs called tiger frogs evolved from a recent common ancestor. The hypothesis was based on fossil evidence and on physical similarities among living species.
Which of the following provides the best additional support for the scientists’ hypothesis?
A. Tiger frogs have longer life spans than other frog species.
B. Tiger frogs have the same diet and all use enzymes to digest food.
C. Tiger frogs live near each other and are all preyed upon by the same predator species.
D. Tiger frogs have similarities in their mitochondrial DNA that are not shared by other frog species.
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Spring 2017
Some populations of Atlantic tomcod fish have an allele that makes the fish resistant to toxic pollutants called PCBs. Tomcod populations in several rivers were analyzed for the presence of this allele. Each river had varying levels of PCB pollution. Which of the following results would best support the conclusion that natural selection is influencing the presence of this allele in the tomcod populations?
A. All of the tomcod in each of the rivers have this allele.
B. The percentage of tomcod with this allele remains the same from year to year in each river.
C. The rivers with high PCB levels have larger percentages of tomcod with this allele than the rivers without PCBs.
D. Eggs from tomcod without this allele can hatch in rivers with or without PCBs, and eggs from tomcod with this allele can only hatch in rivers without PCBs.
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Spring 2017.
A researcher observed army ants, which form colonies with one queen ant and many worker ants. The researcher observed worker ants moving from place to place to hunt and collect a variety of food for the colony. The queen ant was observed mating with a male ant from another ant colony. The queen produced many eggs after this mating. Which of the following could help increase the genetic diversity in the colony of army ants?
A. the queen ant mating with the ant from a different colony
B. the worker ants collecting the food for the colony to eat
C. the worker ants moving from place to place
D. the queen ant eating a variety of food
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Scientists discovered a 375-million-year old fossil in Canada. The diagram below shows the top and side views of the fossil.
Which observation would best support the hypothesis that this organism was
a transitional form between amphibians and fish?
A. The fossil has a long body, which both modern amphibians and modern fish have.
B. The fossil is larger than most modern amphibians, but smaller than most ancient fish.
C. The fossil has some body structures that are similar to amphibians and some body structures that are similar to fish.
D. The fossil was discovered near a lake, which shows that the organism
needed water to reproduce, as do amphibians and fish.
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Some plants in an area produce a toxin that protects them from being eaten by a variety of insect species. The toxin decreases reproductive rates in insects. Because of a genetic mutation, some fruit flies can detect the plant toxin and therefore avoid eating the plant.
a. Describe how the number of fruit flies in the population that can detect the toxin will most likely change over the next 25 years.
b. According to the mechanism of natural selection, explain how the change you described in part (a) will occur.
c. Based on the changes in the fruit fly population, describe what will most likely happen to the plants’ production of the toxin. Explain your answer.
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Sperm whales have vestigial hip bones, and a small percentage of sperm whales
also have vestigial hind limbs. Which of the following statements best explains
the presence of these vestigial structures in sperm whales?
A. Sperm whales evolved from ancestors that walked on land.
B. Sperm whales are in the process of evolving into land mammals.
C. These structures are acquired by each individual sperm whale during its lifetime.
D. These structures resulted from sperm whales having a long period of embryonic development.
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2014 MCAS Open response question
An elephant shrew and a shrew are pictured below.
For many years, scientists had classified elephant shrews in the same family as shrews. In the 1990s, however, scientists gathered evidence for the evolutionary tree below and reclassified elephant shrews into a different family from shrews.
a. Describe the most likely reason why scientists originally classified elephant shrews with shrews.
b. Using the evolutionary tree, identify the groups to which elephant shrews are most closely related.
c. Identify and explain the evidence scientists most likely used to build the evolutionary tree and reclassify elephant shrews.
d. Identify one other type of evidence that scientists use to determine evolutionary relationships and build evolutionary trees.
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Scientists measured and recorded the average body size in a bird population over time. One year, a period of cold weather killed many of the birds. A few generations later, the scientists observed that the average body size in the population was larger than it had been before the cold weather. The scientists concluded that the population had evolved through natural selection. Which of the following would provide the best evidence to support the scientists’ conclusion?
A. The size of the bird eggs also increased over time.
B. The birds with the largest body size were the males.
C. The frequency of alleles for body size changed in the bird population.
D. The number of birds in the population had decreased by 50% or more.
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The three-spined stickleback is a species of fish. It lives in the ocean and in streams that flow into the ocean. Some scientists think that the ocean populations and stream populations may be evolving into separate species. Which of the following statements describes how speciation of these fish would most likely occur?
A. Fish from stream populations would start to reach maturity at the same time as fish from ocean populations.
B. Fish from stream populations would sometimes swim into the ocean but fish from ocean populations would stop swimming into streams.
C. Ocean populations and stream populations would each mate fewer times per year and would have decreased birth rates over time.
D. Ocean populations and stream populations would each adapt differently to their environments and would accumulate enough differences over time to prevent interbreeding
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In a certain insect species, body color varies from very light gray to very dark gray. These insects are eaten by birds that find their prey by sight. A brush fire occurs, blackening the ground where one population of this insect species lives. Which of the following is most likely to occur over the next few years?
A. The body color in the population will mutate to black.
B. The percentage of very dark gray individuals will increase.
C. The distribution of body color in the population will not change.
D. The very light gray individuals will learn how to reproduce at a later age.
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KaiserScience 