Viruses and bacteria are both made of cells.

A student compares a bacterial cell with a human cheek cell under a microscope. Which structure is present in the cheek cell but absent from the bacterium?

Some bacteria in a culture carry a small extra ring of DNA that sits apart from the main chromosome, and only cells carrying it survive when an antibiotic is added. What is that small ring of DNA?

Penicillin blocks the enzymes that build peptidoglycan. Growing bacteria burst and die, but the human cells around them are unharmed. Why are the human cells unaffected?

A drop of sugar solution is placed at one edge of a slide of pond water, and bacteria swim toward it. Which structure moves them?

A single bacterial cell that divides by binary fission produces two cells carrying the same genetic information as the parent cell.

A flask is inoculated with 500 bacterial cells. Under ideal conditions the cells divide by binary fission every 15 minutes. How many cells are in the flask after 2 hours?

A culture that started with 400 cells contains 25,600 cells after 3 hours of ideal growth. How long does one round of binary fission take in this culture?

Raw ground beef leaves the refrigerator carrying 100 bacterial cells per gram and is left on a warm counter, where the cells divide every 30 minutes. How many cells per gram are present after 5 hours?

A sealed flask of broth is counted every hour. The count doubles on schedule for several hours, then levels off and finally falls, even though the flask is kept warm the whole time. What best explains the change?

No sunlight reaches a deep-sea hydrothermal vent, yet dense communities of tube worms and crabs live around it. What supports these communities?

A farmer spreads nitrate fertilizer on a field. After a week of heavy rain leaves the soil waterlogged and low in oxygen, much of the nitrate is gone and nitrogen gas bubbles out of the wet soil. Which bacteria are responsible?

A cow eats grass but makes no enzyme that digests cellulose. Bacteria living in its rumen break the cellulose down, and the cow absorbs the products. How is this relationship best described?

A student put 100 g of dried leaves on each of two trays of forest soil. Tray A had been heated in an oven to kill soil organisms; tray B was untreated. After six months tray A held 92 g of leaves and tray B held 31 g. What do the results show?

A farmer grows soybeans in a field one year and corn in the same field the next year, and the corn crop needs far less nitrogen fertilizer than usual. Which bacterial activity explains the saving?

Shredded cabbage packed in salty brine turns sour over two weeks and then keeps for months without refrigeration. What are the bacteria in the jar doing?

A patient stops taking an antibiotic as soon as the symptoms fade, and the infection returns worse and no longer responds to that drug. What happened in the bacterial population?

A student with a heavy cold asks for antibiotics and the doctor refuses. What is the biological reason?

Human insulin for treating diabetes is made by inserting the human insulin gene into the bacterium E. coli and growing the bacteria in large tanks. Why are bacteria used rather than cultured human cells?

At a sewage treatment plant, air is bubbled continuously through large tanks of wastewater before the water is released. What does the bubbling achieve?