Biology Lesson 7: Surface and Volume of a Cell

Is a baby’s red blood cell smaller then that of yours? Most cells in a baby are the same size as that of an adult. Nerve cells my be longer in an adult.

Average cell sizes (for fun) • Ostrich ovum 100 mm • Human ovum 0.100 mm • Red blood cell 0.007 mm • Virus (not a cell) 0.000080 mm

Ostrich ovum

Human ovum

Is bigger better? Big or Small all cells: - perform cellular functions - need to communicate from the nucleus to all parts of the cell Which cell large or small will be better at controlling its internal functions?

Because the distance from the nucleus to the organelles is longer in a larger cell, smaller cells are better at controlling their internal functions.

• A greater number of small cells is more efficient than fewer large cells because they have a larger surface area to volume ratio • Cells must get everything they need from the surrounding fluids, thus more contact with the surrounding environment is better!! • Example: Notice that the cells occupy the same amount of space (volume) but because they are split the smaller cells have more surface area.

Some large cells can have more than one nucleus. Such as some heart cells, liver cells and some stomach cells.

Liver Cells

Look at the next four different cells. 1. Identify the a. heart cell b. nerve cell c. bacteria (compibacter) d. red blood cell 2. What do you notice about the volume and the surface area of each?

• A large surface area is needed in living things where absorption is critical. • Example: Air sacs in lungs/ villi in small intestine. • Surface area may be increased without sacrificing volume by: • - elongation (eg. root hairs) • - folding surfaces (eg. gills, intestinal villi) • - using projections on surfaces • (i.e. microvilli on cells)

Calculating surface area to volume Ratio 1. determine the surface AREA of an object Example. A cube has 6 faces of equal length and height. The area of one face is length X height (or S X S). Since there are six faces we multiply the area of one side by six. This can be written as 6 S2 SA = 6 S2 2 cm

2 cm

2 cm

= 6 (2 cm)2 = 6 (4 cm2) = 24cm2

1cm 2cm 3cm

Calculating the S.A for a rectangle: SA = 2lw + 2lh + 2wh SA = 2(3cm  1cm) + 2(3cm  2cm) + 2(1cm  2cm) SA = 2(3cm2) + 2(6cm2) + 2(2cm2) SA = 6cm2 + 12cm2 + 4cm2 SA = 22cm2

Now try to calculate the Surface area of 1. A cube with 3.0cm sides 2. A Rectangle where l = 10cm, w= 2.0 cm, h= 1.0cm

Cube: SA = 6S2 = 6(3cm)2 = 6(9cm2) = 54cm2 Rectangle: SA = 2lw + 2lh = 2wh SA = 2(10cm2cm) + 2(10cm1cm) + 2(1cm2cm) SA = 2(20cm2) + 2(10cm2) + 2(2cm2) SA = 40cm2 + 20cm2 + 4cm2 SA = 64cm2

2. Determine the VOLUME of an object: Volume = l x w x h Using the above examples: Cube: v =lwh = 3cm x 3cm x 3cm = 27cm3 Rectangle: v=lwh = 10cm x 2cm x 1cm = 20cm3 3. Calculate the Surface Area to Volume Ratio: Ratio = Surface Area Volume Using the above examples: R (cube) = SA = 54 = 2 V 27 R (rectangle) = SA = 64 = 3.2 V 20

• The larger the ratio: -the more surface area for a given volume -the better the cell’s ability to exchange materials with its environment • This explains why the size of single-celled organisms is limited, whereas multicellular organisms can become quite large.

Assignment: read pg 289 to 293, pg 293: questions 1 to 7 Surface Area Volume Workbook pgs 38, 39