Structure and Function of Cells:Structure and Function of Cells:Teeny, Tiny CellsTeeny, Tiny Cells

All About YouScience Teacher Education Course

Summer 2013

Teeny, Tiny CellsKey Take-Away

• We will write it at the end of the lesson

Objectives• Visualize how the scale of a cell affects its metabolism• Calculate surface area to volume ratios to determine

efficient cell size

Warm UpPlace the following items in order from largest to smallest in your science journals

coffee bean

E. coli

egg cell

flu virus

glucose

red blood cell

grain of rice grain of salt

water molecule

skin cell

sesame seed

NOTE: items are not to scale

Warm UpPlace the following items in order from largest to smallest in your science journals

coffee bean

E. coli

egg cell

flu virus glucosered blood cell

grain of rice

grain of salt

water molecule

skin cell

sesame seed

Teeny, Tiny CellsThink about a typical cell and compare it to the size

of your bodyWhy do our cells have to be so small?

Teeny, Tiny Cells All cells have organelles, each of which has a specific job to fulfill to ensure

that the cell is properly functioning One of the jobs of organelles is to undergo cellular transport - the constant

flow of materials into and out of cells through the cell membrane.

Substances go in and out of cells. What would happen if they didn’t?

BA C

Why are cells small? Cells undergo metabolism in order to sustain life Many of the substances that are necessary for metabolism are

microscopic - so small that they cannot be seen with the unaided eye

That’s 8 millionths of a

meterThat’s 275

trillionths of a meter

Teeny, Tiny CellsOur cells need to be microscopic - specifically the

need to have a large surface area compared to its volume (how much it holds)

Surface Area: the number of units that cover the outside of an object. On a cell, the area of its cell membrane or wall.

Volume: the amount of three-dimensional space enclosed by a boundary. In a cell, the volume is the space within the cell membrane or wall

Teeny, Tiny CellsLet’s explore surface area:Your task is to dry off quickly. Which would you rather use: a towel or a bed sheet? Why?

Let’s explore volume:Your task is to drain water quickly. Which would you rather drain: a bath tub or a sink? Why?

versus

versus

Calculating Surface AreaSurface Area: the number of units that cover the outside of an object.

Calculating surface area of a cube

Surface area = height x width x number of sides

4”

4”

6 sides

Calculating VolumeVolume: the amount of three-dimensional space enclosed by a boundary.

Calculating volume of a cube

Volume = height x width x length

4”

4”

4”

Teeny, Tiny CellsPart 1: Surface Area to Volume Ratios of

Individual Cubes

1” 2” 3”

Teeny, Tiny CellsPart 2: Surface Area to Volume Ratios of an

Individual Cube Compared to a Group of Cubes

3”

3”

3”6 sides

1”

1”1”

Teeny, Tiny Cells If our cells were too big compared to these necessary substances, it would

take a long time, and possibly use more energy, for the cells and organelles to undergo metabolism

Thus our cells need to be small—microscopic—in order to be an efficient system for metabolism

Teeny, Tiny CellsWhat is the lesson’s key take-away?

How does this lesson specifically relate to:

• The Characteristics of Life

• Homeostasis

• Form Fits Function