Bio Tool #29 · SOL Review · Biology Unit 7 · SOL BIO.7a–d
How Populations Change: Evolution for the Biology SOL
Expect about six evolution questions on the Biology SOL, and most of them ask you to reason from something new: a table of DNA differences, a column of rock layers, a population before and after a change. Five ideas carry nearly all of them.
Three questions, cold
Answer these before anything else and keep your score. You will try the same three again at the end.
Every population is full of small inherited differences. A mutation, a change in the DNA base sequence, is the only way a brand-new allele appears. Sexual reproduction shuffles the alleles a population already has into new combinations, and gene flow carries alleles in from another population. A mutation matters to evolution only if it is in an egg or sperm cell, so it can be inherited.
On the test
A question asks where a new trait or allele came from. If the answer choice describes something an animal did or gained in its lifetime, cross it out.
Draw it
Draw a short DNA strand, change one base, and label it “mutation → new allele.” Beside it, draw two parents and a baby with the alleles reshuffled, labeled “sexual reproduction → new combination.”
Natural selection needs four things: individuals differ, the difference is inherited, more young are born than can survive, and one version of the trait helps individuals survive and reproduce. Those individuals leave more offspring, so the helpful allele becomes more common each generation. The population changes; no single organism does.
On the test
Look for a graph or table that changes over generations. The right answer names a mechanism: one version survived and reproduced more and passed the trait on. Answers built on need, wanting or trying are wrong every time.
Draw it
Draw a strip of five boxes, one per generation. Start with mostly light beetles and a few dark ones on dark ground, and draw a bird in box 2. By box 5 most beetles are dark. Under the strip write the four conditions.
Evolution can be fast, and a population without variation is in danger
Bacteria divide so often that natural selection shows up in a few years. An antibiotic kills the bacteria it can, and the few that happen to carry resistance, from random mutations, multiply. The same logic explains extinction: when a new disease or a sudden change arrives, a population with many different alleles is more likely to hold a few survivors. A population with almost none may not.
On the test
Questions about resistance try to get you to say the drug caused it. It did not; resistance comes from random mutations some cells happen to carry, and the drug removed their competition.
Draw it
Draw a dish of bacteria with three resistant cells shaded. Draw an arrow labeled “antibiotic” to a second dish with only the shaded cells left, then a third dish full of shaded cells.
Evidence from rocks, bones, embryos and DNA all points the same way
In undisturbed rock, deeper layers are older, so fossils give an order of events; radioactive dating adds ages in years. Transitional fossils, such as a 375-million-year-old fish with a neck and wrist bones, sit between groups. Homologous structures (same bones, different jobs) and shared embryo stages show common ancestry. DNA is the strongest test: the fewer the differences, the more recently two species shared an ancestor.
On the test
You will be handed data and asked who is most closely related or which fossil is oldest. Pick the pair with the fewest DNA differences, and the fossil lowest in the rock. Analogous structures (same job, different build, like an octopus eye and a human eye) do not show close relatives.
Draw it
Draw a column of four rock layers and label the bottom “oldest.” Next to it, copy the DNA table from your sheet and circle the two smallest numbers, then draw the tree they make.
New species form when separated groups can no longer interbreed
A barrier such as a river, a mountain or a stretch of dry land splits a population and stops gene flow. Each group gathers its own mutations and faces its own selection. Speciation is complete when the groups can no longer interbreed and produce fertile offspring. The fossil record shows two speeds: gradualism, steady change layer by layer, and punctuated equilibrium, long periods of no change broken by short bursts.
On the test
Color, size and food choice can all differ inside one species. The test of a new species is breeding: no fertile offspring. For speed, match the picture: a steady ramp is gradualism, a staircase is punctuated equilibrium.
Draw it
Draw one population, a river through it, and two groups drifting apart over three steps. Then draw two small graphs of “change” against “time”: a ramp labeled gradualism and a staircase labeled punctuated equilibrium.
Read the last line first. It tells you what kind of answer you are hunting for: a cause, a conclusion, an order, a relationship.
Mark the evidence. Circle the numbers in the table or the change in the graph. The right answer always agrees with them.
Cross out the traps. In this unit they sound like: need, want, try, decide, during its lifetime, in order to.
Pick the answer that names a mechanism and say it in one sentence before you tap it.
In the beetle question, the last line asks which explanation fits the data. The data show dark beetles rising from 10% to 80% over 15 generations. One choice says ash coated the beetles and they passed on the color: a lifetime change, crossed out. Another says the fire caused mutations aimed at survival: mutations are random, crossed out. The answer left names the mechanism, dark beetles survived and reproduced more. Try that one.
Practice with every answer explained
Each question tells you why the right answer is right, why the one you picked is not, and where the idea lives in the standards. Nothing is submitted, and your answers stay on your device.
The Biology SOL has 45 scored questions spread across ten units. After this one, these are the best uses of your time, in order.
Classification and biodiversity
It runs on the same evidence: shared structures, DNA and family trees. Expect about six questions, and a photosynthetic single cell with a nucleus (a protist) trips up most students.
About six questions, and one of the hardest items on the state's most recent released test was about pioneer species: only about 3 in 10 Virginia students answered it correctly.
Virginia also posts its released Biology test so students can practice in the same TestNav system the real test uses. Find it on the Virginia Department of Education's SOL practice items page, then come back here to study whatever you miss.
0–5 min · Warm-up: three questions cold on iPads or the paper sheet; students keep their own score.
5–30 min · The five ideas, about five minutes each: say the idea, draw it together on the board while students draw on the sheet, then one check question read aloud with a vote.
30–40 min · Students open the practice set on their iPads and work at their own pace; every answer explains itself. Circulate and ask students to say the mechanism out loud.
40–45 min · Retry the same three warm-up questions, compare scores, and choose the next unit to practice from the list.
The paper version prints on two pages: the five ideas with a box to draw in, six practice questions without answers, and a plan for what to study next, with a QR code back here. Students without a device can do the whole session on paper; the explanations are online for later. Practice questions are original and written from the Virginia 2018 Biology Standards of Learning and the VDOE Instructional Guide; they are not produced or endorsed by the Virginia Department of Education.
Evolution: SOL Review
Name ______________________________ Date __________ Warm-up score: before ____ / 3 after ____ / 3
Five ideas · draw each one as we go
1. New alleles come only from mutation
Draw a short DNA strand, change one base, and label it “mutation → new allele.” Beside it, draw two parents and a baby with the alleles reshuffled, labeled “sexual reproduction → new combination.”
2. Natural selection changes how common an allele is
Draw a strip of five boxes, one per generation. Start with mostly light beetles and a few dark ones on dark ground, and draw a bird in box 2. By box 5 most beetles are dark. Under the strip write the four conditions.
3. Evolution can be fast, and a population without variation is in danger
Draw a dish of bacteria with three resistant cells shaded. Draw an arrow labeled “antibiotic” to a second dish with only the shaded cells left, then a third dish full of shaded cells.
4. Evidence from rocks, bones, embryos and DNA all points the same way
Draw a column of four rock layers and label the bottom “oldest.” Next to it, copy the DNA table from your sheet and circle the two smallest numbers, then draw the tree they make.
5. New species form when separated groups can no longer interbreed
Draw one population, a river through it, and two groups drifting apart over three steps. Then draw two small graphs of “change” against “time”: a ramp labeled gradualism and a staircase labeled punctuated equilibrium.
Practice · circle your answer, then check online
1. A population of deer mice carries two alleles for coat color. A third coat-color allele, one that no member of the species has ever carried, appears in a newborn mouse. What most likely produced it?
A mouse that lived in a darker forest passed on the dark coat it developed there
Crossing over during meiosis mixed the two existing alleles into new combinations
A mouse moved in from a neighboring population and mated with local mice
A mutation changed the DNA sequence of the coat-color gene in a parent's egg or sperm cell
2. In a model study, a meadow is home to a ground beetle that comes in a tan form and a dark form; the color is inherited. A wildfire leaves the ground covered in black ash for years, and birds hunt the beetles by sight.
Generations after the fire
0
5
10
15
Dark beetles (% of population)
10
25
55
80
Which explanation best fits the data?
The dark form became more common because birds found tan beetles more easily, so dark beetles survived to reproduce and passed on the dark color
Ash coated the beetles, and their offspring were born with the darker color their parents had acquired
The heat of the fire caused mutations that turned tan beetles dark
Tan beetles chose to leave the meadow, so dark beetles moved in to fill the space
3. In a model road cut, four undisturbed layers of sedimentary rock are exposed. A geology class records which fossils appear in each layer.
Layer (top to bottom)
Fossils found
Layer 1 (top)
Small mammal teeth
Layer 2
Land plant leaves and seeds
Layer 3
Fish-like animals with jaws
Layer 4 (bottom)
Shelled sea animals only
Which conclusion do these layers support?
The fish-like animals in Layer 3 are older than the leaves and seeds in Layer 2, because deeper layers are older
All four kinds of organisms lived at the same time, because they are in the same road cut
The mammals are the oldest, because the top layer formed first
Nothing about relative age can be said without radioactive dating
4. Scientists sequence the same gene in four crayfish species, J, K, L and M, from Virginia streams and count the base differences between each pair.
Pair
J–K
J–L
J–M
K–L
K–M
L–M
Base differences
4
22
23
21
24
6
Which conclusion is best supported?
J and L are each other's closest relatives
All four species are equally related
J and K share a recent common ancestor, and L and M share a different one
M is most closely related to J
5. Two groups of a salamander have lived on separate Blue Ridge peaks for a very long time, cut off from each other by warm, dry valleys. Which finding would show that they have become two separate species?
The two groups now differ slightly in color
The two groups eat different insects
When brought together, they cannot interbreed and produce fertile offspring
One group is larger than the other
6. Two lines of fossil snails (lineages) are traced through the same 10 million years of rock. Lineage 1 changes a little in every layer, so its shell grows thicker step by step. Lineage 2 stays almost unchanged for millions of years, changes to a new form within a few thousand years, then stays unchanged again. Which pair of labels is correct?