Week 02 · Thursday: One Cell or Many (Cells and Systems 6-8)

Thursday: Reading a Cell Size Table

Raven lays a table on the Windowsill. It lists sizes and magnifications. "This is from the college biology texts."

Rocket reads the first rows. "Bacteria, 0.1 to 5 micrometers. Plant and animal cells, 10 to 100. What do the other rows mean?"

"Magnification," Raven says. "How many times bigger a microscope makes something look. What do you notice about the numbers?"

"Four hundred times. One thousand times." Rocket whistles. "That is why Hooke could see cork cells."

Nova hovers over the pin from Tuesday. "Now compare the pin head to the cells," she says.

Rocket does the division. "Twenty to two hundred cells across one pin head." Raven grins. "Read the table and prove it."

The table from the biology texts

The sizes below come from the open college textbooks Concepts of Biology and Biology. The prefixes come from the National Institute of Standards and Technology.

A micrometer is one millionth of a meter. A millimeter is one thousandth of a meter, so one millimeter is one thousand micrometers.

Magnification is the degree of enlargement. A microscope at 400 times makes a 10 micrometer cell look 4,000 micrometers, which is 4 millimeters.

Item	Value
Bacterial cell, across	0.1 to 5 micrometers
Plant or animal cell, across	10 to 100 micrometers
Pin head, across	about 2 millimeters, or 2,000 micrometers
Dissecting microscope	magnifies 20 to 80 times
Light microscope in a college lab	magnifies up to about 400 times
Light microscope with an oil lens	magnifies about 1,000 times

USE THE TABLE

Read the question.
Tap your answer.

A plant cell is 100 micrometers across. How many could line up across a 2,000 micrometer pin head?

A bacterial cell is 1 micrometer across. Which microscope could you use to see it clearly?

A 50 micrometer cell is viewed at 400 times. How big does it look?

One millimeter is ____ micrometers.

A light microscope with an oil lens magnifies about ____ times.

Statement	True or false?
A pin head is wider than any single plant cell.	?
Bacterial cells are larger than plant cells.	?
At 400 times, a 10 micrometer cell looks about 4 millimeters across.	?
A dissecting microscope is the best tool for seeing a bacterium.	?

WHY THIS EXERCISEReading sizes in micrometers tells you why a single cell is invisible on your windowsill.

FROM TINY TO VISIBLE

Tap a card.
Then tap its spot.

1Smallest

2Next

3Next

4Largest

Try it

Measure a dried bean with your ruler in millimeters. Convert it to micrometers by multiplying by 1,000.
Divide your answer by 50, a middle-sized plant cell. That is roughly how many cells could line up across the bean.
Check the seed jar and add water if needed. Record the longest root.

Try this

Write three lengths in micrometers: your ruler's smallest gap, a pin head and a bacterium.
Say each one aloud as a fraction of a meter. Which one is one millionth?

Draw a line 2 millimeters long for a pin head. Below it, draw a line 20 millimeters long for the same pin head at 10 times.

Describe in words what the number 1,000 times means for a microscope.Why do you think no one saw a cell before lenses were made? Write two sentences.Record today's seed check: towel dampness, roots and the longest root in millimeters.

Excellent data work. Tomorrow you find one-celled and many-celled living things all over your home, and review the week.