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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 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