Cells and organisms

One living organism can have one cell or many

An organism is an individual living thing. Cells are its living units, not inert building blocks. Some organisms consist of one cell; others contain many cells

One-celled

In a unicellular organism, one cell is the complete organism. It is not an unfinished many-celled organism

Many-celled

In a multicellular organism, many cells belong to one organism. A plant is one example. A plant is living even though it does not move from place to place

Cells come from cells

New cells arise from existing cells. Changing a picture or viewing window does not make a cell divide; the mechanism of division comes later

Distinguish one cell from many

A sample is not necessarily a whole organism

A sample is material selected for study. Ask whether each visible cell is a complete organism or a cell from part of a larger organism. Use a reliable source record, not its outline alone

Three separate organisms

A sample contains three separate one-celled organisms. Each organism is one complete cell. Sharing a sample does not join them into one organism

A patch from one plant

A patch from the inner surface of one onion bulb layer contains nine adjoining cells. The plant contains many more cells. This patch is not a whole plant, and each cell is not a separate plant

Follow the source

If a supplied record says three sampled cells all came from one plant, they represent one source organism. Their visible count does not tell you the plant's total cell count

An enlarged image is not a larger cell

Most individual cells need magnification to study them. Magnification makes the image larger, not the actual cell. The next drawing keeps the specimen fixed and changes the region shown in a same-size viewing window

Wide and Close

Close makes each cell's image larger and shows a smaller region. Wide shows a larger region with smaller cell images. Cells outside the window still belong to the specimen

Read the dashed edge

The dashed rectangle marks the viewing region. Solid lines show cell boundaries. A boundary cut by the dashed edge belongs to a partial view of a cell, not a newly smaller cell

Know what the drawing omits

These are explanatory drawings, not microscope photographs. Internal structures are omitted, not absent. The controls do not simulate focusing, optical resolution, growth or division. Enlargement alone does not add new resolved detail

Predict what will happen to the central cell's image and the visible region when you change Wide to Close, then test it. Switch to Onion patch and repeat. Compare the dashed region in the small overview with the enlarged view, including cells cut by its edge

What stays the same when you change Wide to Close for one specimen?

Read the source relationship

Changing back reverses the image change

Changing from Close back to Wide makes each cell's image smaller and shows a larger region of the same specimen. More cells may enter the view without any new cells being made

Keep three quantities separate

The cell's actual size stays fixed. Its image size changes. The region visible in the window changes in the opposite direction to image size

No biological change is shown

The drawing does not show cells growing, dividing or dying. A cropped cell boundary does not indicate damage to the cell

Compare the wider view

One cell in view does not settle the whole-organism question

A view contains one complete cell. Without its source record, that cell could be a whole one-celled organism or a cell taken from a many-celled organism. The picture alone does not settle the question

Several cells can also be inconclusive

Several visible cells could be separate one-celled organisms or cells belonging to a many-celled organism. You need evidence of their relationship, not just a count

Use information when it is supplied

A reliable record confirming that one cell is a complete organism establishes one-celled organisation. A record confirming that it came from an organism with many cells establishes a many-celled source

Unknown is not absent

Not recorded means the evidence is missing. It does not mean there are no other cells or that the specimen is non-living

Two close views each show one complete cell. Record A confirms its cell is a complete organism. Record B says nothing about its cell's source. Which conclusion is justified?

Use a known source

Identify missing source evidence

Use a reliable whole-organism record

Use the reliable supplied record

Which conclusion about the source organism or organisms is justified?

The separate reliable record establishes that this one cell is the entire organism. The conclusion uses that record, not just the count in the view

One-celled (unicellular). Use sufficient source information; do not answer that information is missing when the record supplies it

Separate the cell, the view and the whole organism

An organism can contain one cell or many. A sample can contain several organisms or cells from part of one organism. Use its reliable source information before drawing a whole-organism conclusion

Explain the viewing change

A larger cell image fits a smaller specimen region into the same window. The actual cells stay unchanged. A cell outside the view has not disappeared from the specimen

Make your own explanation

Explain why seeing one cell does not always establish a one-celled organism. Give the extra source information that would settle the question in each direction

Observe with a teacher

Use an approved prepared slide or reputable micrograph with a teacher. Record visible features, make your own scientific drawing, and distinguish what is observed from what a source says about the whole organism

Beyond this activity

Do not collect cultures, use stains or prepare biological samples without appropriate supervision