Bio Tool #29 · SOL Review · Biology Unit 9 · SOL BIO.4a–e
Living Cell or Hijacker? Bacteria and Viruses for the Biology SOL
About five questions on the Biology SOL come from bacteria and viruses. Nearly every one turns on a single difference: a bacterium is a living cell that runs itself, and a virus is a packet of genes that can do nothing until it gets inside a cell.
Three questions, cold
Answer these before anything else and keep your score. You will try the same three again at the end.
The five ideas behind most bacteria & viruses questions
Idea 1BIO.4a · BIO.4c
A bacterium is a cell; a virus is genes in a protein coat
A bacterium is a single prokaryotic cell: membrane, cell wall, ribosomes, a loop of DNA, no nucleus. It eats, grows and divides on its own. A virus has only genetic material (DNA or RNA) inside a protein coat called a capsid, sometimes wrapped in an envelope. It has no ribosomes and no metabolism, so it is usually called nonliving. Outside a cell it does nothing at all.
On the test
If something grows in plain nutrients, it is alive, likely a bacterium. If it increases only when living cells are present, it is a virus.
Draw it
Draw a bacterium and a virus side by side and label every part. Make the virus far smaller: a typical bacterium is about ten times wider than a typical virus.
A virus copies itself by taking over a host cell, fast or slow
A virus attaches only to cells whose surface fits its attachment proteins, which is why a dog virus cannot infect its owner. Its genes get inside, and the cell's own ribosomes and enzymes build new viral parts. In the lytic cycle the new viruses assemble and burst out, usually killing the cell. In the lysogenic cycle the viral DNA joins the host's DNA and is copied every time the cell divides, until a trigger switches it to the lytic cycle.
On the test
Order questions follow attach → genes enter → host builds parts → assemble → release. A delay before any new viruses appear means lysogenic.
Draw it
Draw a circle for the lytic cycle with five steps around it. Off step 2, draw a side loop where the viral DNA joins the chromosome and the cell divides twice, then an arrow back into the circle.
Bacteria double by binary fission and get energy three ways
Most bacteria reproduce asexually by binary fission: copy the DNA, split in two. Each division doubles the population, so one cell dividing every 20 minutes becomes 64 in two hours. Bacteria also differ in how they get energy: some make food from light (photoautotrophs), some from chemicals (chemoautotrophs), and many take in organic matter (heterotrophs).
On the test
Growth questions are doubling questions: count the divisions, then double that many times. Don't add.
Draw it
Draw one cell at the top of a tree, then 2, 4, 8, 16. Mark each row “+20 min.”
A few bacteria and many viruses cause disease, but most bacteria are helpful or harmless. Bacteria decompose dead matter and return nutrients to the soil, fix nitrogen from the air for plants, help digest food in your gut, and turn milk into yogurt and cheese. Viruses that infect bacteria, called bacteriophages, keep bacterial populations in check and are being used to treat infections antibiotics cannot.
On the test
Choices that say all bacteria are harmful, or that every disease comes from bacteria, are wrong. Experiments with a sterilized control are asking you what the living microbes did.
Draw it
Draw a leaf on the soil with bacteria around it, a bean root with nodules, and a gut. Label each with the job the bacteria do there.
Germ theory explains infection, and each tool has one job
Germ theory says many diseases are caused by microorganisms. Evidence such as the drop in deaths when doctors began washing their hands led to sanitation, safe food and water, and sterile technique. A vaccine prepares the immune system ahead of time, so memory cells respond fast if the real pathogen arrives. An antibiotic kills bacteria that are already causing an infection and does nothing to a virus. Stopping an antibiotic early, against the doctor's directions, leaves survivors that are more likely to be resistant.
On the test
Vaccine = prevent, before exposure. Antibiotic = cure a bacterial infection. Antibiotics for the flu or a cold is always a wrong answer.
Draw it
Draw a graph of immune response against time with two bumps: a small, slow one after the vaccine and a tall, fast one at the second exposure. Label the second bump “memory.”
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: all bacteria, antibiotics for a virus, a vaccine cures, viruses are cells.
Pick the answer that names a mechanism and say it in one sentence before you tap it.
In the two-sample question, the last line asks which conclusion fits. The table shows X grew in broth alone and Y grew only when living cells were added. Only a living cell can grow on nutrients alone, and only a virus needs a host, so X is the bacterium and Y is the virus. The other choices fail on one row of the table each. 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.
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; students keep their own score.
5–30 min · The five ideas, about five minutes each: draw the bacterium and the virus together first, then the cycles, the doubling tree, the jobs bacteria do, and the immune-memory graph.
30–40 min · Students work the practice set on iPads at their own pace; every answer explains itself.
40–45 min · Retry the warm-up and choose the next unit to practice. With a full hour, add 15 minutes of mixed review from the units students named, using the Challenge questions.
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.
Bacteria & Viruses: SOL Review
Name ______________________________ Date __________ Warm-up score: before ____ / 3 after ____ / 3
Five ideas · draw each one as we go
1. A bacterium is a cell; a virus is genes in a protein coat
Draw a bacterium and a virus side by side and label every part. Make the virus far smaller: a typical bacterium is about ten times wider than a typical virus.
2. A virus copies itself by taking over a host cell, fast or slow
Draw a circle for the lytic cycle with five steps around it. Off step 2, draw a side loop where the viral DNA joins the chromosome and the cell divides twice, then an arrow back into the circle.
3. Bacteria double by binary fission and get energy three ways
Draw one cell at the top of a tree, then 2, 4, 8, 16. Mark each row “+20 min.”
4. Most bacteria help, and some viruses do too
Draw a leaf on the soil with bacteria around it, a bean root with nodules, and a gut. Label each with the job the bacteria do there.
5. Germ theory explains infection, and each tool has one job
Draw a graph of immune response against time with two bumps: a small, slow one after the vaccine and a tall, fast one at the second exposure. Label the second bump “memory.”
Practice · circle your answer, then check online
1. Biologists usually describe viruses as nonliving, even though viruses cause many diseases. Which reason best supports that description?
Viruses are too small to see with a light microscope
Viruses contain no genetic material of any kind
Viruses are not made of cells and cannot carry out metabolism or copy themselves without a host cell
Viruses only infect bacteria, never larger organisms
2. A virus infects a dish of growing bacteria. For many generations the bacteria look healthy and divide normally. Weeks later, after the dish is exposed to ultraviolet light, many cells burst and release new viruses. What best explains the delay?
The viruses were sleeping outside the cells until the light woke them
The bacteria were immune at first and then lost their immunity
The viral DNA was destroyed and then rebuilt itself
The viral DNA joined the bacterial chromosome and was copied each time a cell divided, then later switched to making new viruses
3. One bacterium lands in warm milk. Under these conditions each cell divides by binary fission every 20 minutes. If none die, how many bacteria will there be after 2 hours?
6
12
64
120
4. A class puts equal dry masses of oak leaves into two loosely covered jars of damp soil. Jar 1's soil was heat-sterilized first; Jar 2's was not. After 8 weeks the leaves are dried and weighed.
Jar 1 (sterilized soil)
Jar 2 (untreated soil)
Dry leaf mass at start (g)
20
20
Dry leaf mass after 8 weeks (g)
19
7
Which conclusion is best supported?
Heat sterilization made the leaves in Jar 1 heavier
The leaves in Jar 2 were eaten by insects that hatched from the leaves
Damp soil alone breaks down leaves, whether or not anything lives in it
Living microbes in Jar 2, such as bacteria, broke down the leaves and released their materials into the soil
5. In 1847 a doctor at a large hospital in Vienna noticed that mothers on one maternity ward died of fever far more often than on a second ward. Doctors on the first ward came straight from examining bodies in the autopsy room. In May he required them to wash their hands in a chlorine solution before seeing patients.
Month in 1847 (first ward)
Deaths per 100 mothers
April
18.3
May (handwashing begins partway through the month)
12.2
June
2.2
Which conclusion do these data best support?
Fever is caused by bad air, which chlorine cleared from the ward
Something carried on the doctors' hands from the autopsy room caused the fevers, and washing removed it
Mothers became stronger as the weather warmed in summer
Handwashing makes no difference, because deaths had already started to fall in May
6. A student receives a vaccine against a virus. A year later the student is exposed to that virus and does not become sick. What best explains this?
The vaccine stayed in the blood for a year and killed the virus on contact
The vaccine was an antibiotic that kept working
The immune system had already learned to recognize the virus and responded quickly enough to stop it
The vaccine changed the student's cells so the virus could not enter them
My plan
☐ Check these six online: scan the code, then tap “All 17 practice questions.” Write the ones I missed: __________
☐ The idea I will say out loud tonight in one sentence: ________________________________________________
☐ Next unit I will practice: Evolution ☐ Cell structure ☐ Classification ☐ Ecology ☐ ______________