Viruses compared with cells, and how viruses spread

Grade 9 Science Worksheet

Circle the best answer.

1. 1.

   Esme fills in step 3 of the copying cycle of a virus. What happens at the blank step?

   • The virus's own ribosomes read its genetic material and build its proteins
   • The host cell's machinery copies the genetic material and makes proteins
   • The finished virus particles pass out of the host cell into the surroundings
   • The virus divides in two, and each half goes on to build its own proteins

2. Read this first

   Use the table

   Phage Q attaches only where its tail fibers fit receptor R (model data)

   cell	type	receptor R on surface
   X	bacterium	yes
   Y	bacterium	no
   Z	plant cell	no

3. 2.

   Jun reads a table of cells. Phage Q attaches only where its tail fibers fit receptor R. Which cell or cells can phage Q infect?

   • Cells X and Y, because both are bacteria and both have a plasma membrane
   • Cells X, Y and Z, because each cell has a plasma membrane
   • Cell Z, because a plant cell is larger than a bacterium
   • Cell X, because it has receptor R for the tail fibers to fit

4. Model drawing, not to scale

   a bacteriophage attached to the cell wall of a bacterium at step 2 of the copying cycle. Phage: genetic material (DNA or RNA) inside a protein coat (capsid), with a tail touching the cell wall. Bacterium: cell wall, plasma membrane, ribosome, nucleoid.

5. 3.

   Luz reads about a phage attached to a bacterium. What happens next, when the phage's genetic material enters?

   • The phage's ribosomes go in with its genetic material to build proteins
   • The whole phage goes in, and its protein coat breaks down inside the cell
   • The phage's genetic material stays outside and copies itself there
   • The phage's genetic material goes in, and the protein coat stays outside

6. Phage card T (model data)

   stage	what the card records
   after entry	the phage DNA is copied many times inside the bacterium
   later	new phage particles are made inside the bacterium
   at the end	the bacterium bursts and the new particles are released

7. 4.

   Noah reads a model card for phage T. Which cycle does the card show?

   • Lysogenic cycle, because the phage DNA joins the host cell's DNA
   • Neither cycle, because a phage cannot copy itself in a bacterium
   • Lytic cycle, because new particles are made and the cell bursts
   • Lysogenic cycle, because the bacterium keeps on dividing normally

8. Prophage card (model data)

   time	what the card records
   before the stress	the phage DNA sits in the bacterium's own DNA as a prophage and is passed on at each division
   after the stress	some prophage DNA leaves the host DNA and new phage particles are made

9. 5.

   Tala reads a card about a prophage in bacteria after a change in conditions. Which cycle do the stressed bacteria begin?

   • Lysogenic cycle, because the phage DNA stays in the host DNA
   • Lytic cycle, because the prophage leaves the host DNA
   • Lysogenic cycle, because new particles are made
   • No new cycle, because a prophage cannot leave the host DNA

10. Model data

    particle	width
    model virion	100 nm
    model bacterium	2 µm

    1 µm = 1,000 nm.

11. 6.

    Zee compares a model bacterium with a model virion. How many times as wide as the virion is the bacterium?

    • 0.05
    • 2,000
    • 200
    • 20
12. 7.

    Ari imagines virions of this width lined up across one eukaryotic cell. How many virions fit across the cell?

    • 12,500
    • 5
    • 20
    • 200
13. 8.

    Bo uses the rule that a bacterium is about 100 times as wide as a virion. How wide is the model bacterium in µm?

    • 4,000
    • 4
    • 0.04
    • 0.4

14. Use this

    Route card (model). A flu virus lands on a door handle. Later, a different person touches the handle and then touches their own nose.

15. 9.

    Milo reads a second model route card. Which statement about this route fits what CDC says?

    • It is a droplet route, which happens less often than a surface route
    • It is a surface route, and it is the main way flu viruses spread
    • It is a surface route, less common than spread by droplets
    • It is a droplet route, the main way flu viruses spread

16. Use this

    Route card (model). A plant virus is carried by an insect. The insect pierces a leaf and makes a small tear in the leaf surface. Virus particles pass through the tear into leaf cells. A plant cell has a cell wall, and a plant virus has no way of its own to cross it.

17. 10.

    Ren reads about how a plant virus gets into a leaf cell. According to the card, why does the insect matter?

    • The insect makes the virus copy itself, since viruses need an animal host
    • A plant cell has no wall, so the virus enters as an animal virus does
    • The tear lets the virus past the cell wall, which it cannot cross by itself
    • The insect's saliva gives the virus a tail like a phage, so it crosses the wall