Question 1

We will shortly examine the structure of a generic cell, but the generalizations we draw shouldn’t blind you to the diversity of cellular form and function in humans.

Accepted Answer

There are about 200 kinds of cells in the human body, with a variety of shapes, sizes, and functions.

Question 2

Descriptions of organ and tissue structure often refer to the shapes of cells by the following terms

Accepted Answer

Squamous, Cuboidal, Columnar, Polygonal, Stellate, Spheroidal to ovoid, Discoidal, Fusiform, Fibrous

Question 3

Squamous

Accepted Answer

--------, Cuboidal, Columnar, Polygonal, Stellate, Spheroidal to ovoid, Discoidal, Fusiform, Fibrous

Question 4

Cuboidal

Accepted Answer

Squamous, ------, Columnar, Polygonal, Stellate, Spheroidal to ovoid, Discoidal, Fusiform, Fibrous

Question 5

Columnar

Accepted Answer

Squamous, Cuboidal, -----, Polygonal, Stellate, Spheroidal to ovoid, Discoidal, Fusiform, Fibrous

Question 6

Polygonal

Accepted Answer

Squamous, Cuboidal, Columnar, -----, Stellate, Spheroidal to ovoid, Discoidal, Fusiform, Fibrous

Question 7

Stellate

Accepted Answer

Squamous, Cuboidal, Columnar, Polygonal, Stellate, ------, Discoidal, Fusiform, Fibrous

Question 8

Spheroidal to ovoid

Accepted Answer

Squamous, Cuboidal, Columnar, Polygonal, Stellate, ------, Discoidal, Fusiform, Fibrous

Question 9

Discoidal

Accepted Answer

Squamous, Cuboidal, Columnar, Polygonal, Stellate, Spheroidal to ovoid, -----, Fusiform, Fibrous

Question 10

Fusiform

Accepted Answer

Squamous, Cuboidal, Columnar, Polygonal, Stellate, Spheroidal to ovoid, Discoidal, ------, Fibrous

Question 11

Fibrous

Accepted Answer

Squamous, Cuboidal, Columnar, Polygonal, Stellate, Spheroidal to ovoid, Discoidal, Fusiform, -----

Question 12

Squamous (SKWAY-mus)—

Accepted Answer

a thin, flat, scaly shape, often with a bulge where the nucleus is, much like the shape of a fried egg “sunny side up.” Squamous cells line the esophagus and air sacs (alveoli) of the lungs, and form the surface layer (epidermis) of the skin.

Question 13

Cuboidal (cue-BOY-dul)—

Accepted Answer

squarish-looking in frontal sections and about equal in height and width; liver cells are a good example.

Question 14

Columnar—

Accepted Answer

distinctly taller than wide, such as the inner lining cells of the stomach and intestines.

Question 15

Polygonal—

Accepted Answer

having irregularly angular shapes with four, five, or more sides, like the wax cells of a honeycomb. The densely packed cells of many glands are polygonal.

Question 16

Stellate—

Accepted Answer

having multiple pointed processes projecting from the body of a cell, giving it a somewhat starlike shape. The cell bodies of many nerve cells are stellae.

Question 17

Spheroidal to ovoid—

Accepted Answer

round to oval, as in egg cells and white blood cells.

Question 18

Discoidal—

Accepted Answer

disc-shaped, as in red blood cells.

Question 19

Fusiform (FEW-zih-form)—

Accepted Answer

spindle-shaped; elongated, with a thick middle and tapered ends, as in smooth muscle cells.

Question 20

Fibrous—

Accepted Answer

long, slender, and threadlike, as in skeletal muscle cells and the axons (nerve fibers) of nerve cells.

Question 21

Some of these shapes refer to the way a cell looks in typical tissue sections

Accepted Answer

not to the complete three-dimensional shape of the cell.

Question 22

A cell that looks squamous, cuboidal, or columnar in a tissue section, for example

Accepted Answer

usually looks polygonal if viewed from its upper surface.

Question 23

The most useful unit of measure for designating cell sizes is the -----, formerly called the micron—one-millionth (10⁻⁶) of a meter, one-thousandth (10⁻³) of a millimeter.

Accepted Answer

micrometer (µm)

Question 24

The smallest objects most people can see with the naked eye are about 100 µm, which is about one-quarter the size of the period at the end of a typical sentence of print.

Accepted Answer

A few human cells fall within this range, such as the egg cell and some fat cells, but most human cells are about 10 to 15 µm wide.

Question 25

The longest ------ (sometimes over a meter long) and muscle cells (up to 30 cm long), but both are usually too slender to be seen with the naked eye.

Accepted Answer

human cells are nerve cells

Question 26

There are several factors that limit the size of cells. If a cell swelled to excessive size, it could rupture like an overfilled water balloon.

Accepted Answer

In addition, cell size is limited by the relationship between its volume and surface area.

Question 27

The surface area of a cell is proportional to the square of its diameter, while volume is proportional to the cube of its diameter.

Accepted Answer

Thus, for a given increase in diameter, volume increases much more than surface area.

Question 28

Picture a cuboidal cell 10 µm on each side (fig. 3.2). It would have a surface area of 600 µm² (10 µm × 10 µm × 6 sides) and a volume of 1,000 µm³ (10 × 10 × 10 µm).

Accepted Answer

Now, suppose it grew by another 10 µm on each side. Its new surface area would be 2,400 µm² (20 µm × 20 µm × 6) and its volume would be 8,000 µm³ (20 × 20 × 20 µm).

Question 29

The 20 µm cell has eight times as much cytoplasm needing nourishment and waste removal, but only four times as much membrane surface through which wastes and nutrients can be exchanged.

Accepted Answer

A cell that is too big cannot support itself.

Question 30

Small cell

Diameter: 10 µm

Surface area = 10 µm × 10 µm × 6 = 600 µm²

Volume: 10 µm × 10 µm × 10 µm = 1,000 µm³

Accepted Answer

Large cell

Diameter: 20 µm

Surface area = 20 µm × 20 µm × 6 = 2,400 µm²

Volume: 20 µm × 20 µm × 20 µm = 8,000 µm³

Question 31

Effect of cell growth:

Accepted Answer

Diameter (D) increased by a factor of 2

Surface area increased by a factor of 4 (D²)

Volume increased by a factor of 8 (D³)

Question 32

The Relationship Between Cell Surface Area and Volume

Accepted Answer

As a cell doubles in diameter, its volume increases eightfold, but its surface area increases only fourfold. A cell that is too large may have too little plasma membrane to serve the metabolic needs of the increased volume of cytoplasm.

Question 33

Further, if a cell were too large, molecules couldn't diffuse from place to place fast enough to support its metabolism.

Accepted Answer

The time required for diffusion is proportional to the square of distance, so if a cell diameter doubled, the travel time for molecules within the cell would increase fourfold.

Question 34

The time required for diffusion is proportional to the square of distance, so if a cell diameter doubled, the travel time for molecules within the cell would increase fourfold.

Accepted Answer

if it took 10 seconds for a molecule to diffuse from the surface to the center of a cell with a 10 μm radius, then if we increased the cell radius to 1 mm, it would take 278 hours to reach the center—far too slow to support the cell's life activities.

Question 35

Having organs composed of many small cells instead of fewer large ones has another advantage.

Accepted Answer

The death of one or a few cells has less effect on the structure and function of the whole organ.

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