1. How many bacteria can fit in a cm? Can you see cells?
A bacterial cell is 10µm. How much bigger is a human cheek cell that is 100µm?
How many bacteria can fit in a cm?
Can you see cells? 1”
10”

2. Cell City Analogy Answers. What do the cell parts do inside the cell?
1. MITOCHONDRIA
HYDRAULIC DAM
2. RIBOSOMES
SMALL SHOPS
3. NUCLEUS
TOWN HALL
4. ENDOPLASMIC RETICULUM
SPECIAL CARTS
5. GOLGI APPARATUS
POST OFFICE
6. PROTEIN
WIDGETS
7. CELL MEMBRANE
FENCE
8. LYSOSOMES
SCRAP YARD
9. NUCLEOLUS
CARPENTER'S UNION

3. Looking at Cells Cells can vary greatly in their size and shape.
But they are all still very small.
Just how big are cells?
Cell size is limited for a reason.

4. OBJECTIVE
Hypothesize, explore, and understand why cells are SO small, yet can perform life functions.
Compare cells and determine their relative sizes and shapes.
Make connections between cell form (it’s shape) and the functions it performs.

5. Finger width = 16mm Bacteria 200µm = 0.2mm
This is the business end of a needle.
This one’s infested with E. coli.
Finger width
= 16mm
Bacteria
Figure 4.2
Rod-shaped bacterial cells on the tip of a household pin, shown at increasingly higher magnifications (enlargements). The “μm” is an abbreviation for micrometers, or 10–6 meters.
Figure It Out: About how big are these bacteria?
Answer: About 1 μm wide, and 5 μm long
200µm = 0.2mm
Fig. 4-2a, p. 54

6. Figure 4.2
Rod-shaped bacterial cells on the tip of a household pin, shown at increasingly higher magnifications (enlargements). The “μm” is an abbreviation for micrometers, or 10–6 meters.
Figure It Out: About how big are these bacteria?
Answer: About 1 μm wide, and 5 μm long
40µm = 0.04mm
Fig. 4-2b, p. 54

7. Figure 4.2
Rod-shaped bacterial cells on the tip of a household pin, shown at increasingly higher magnifications (enlargements). The “μm” is an abbreviation for micrometers, or 10–6 meters.
Figure It Out: About how big are these bacteria?
Answer: About 1 μm wide, and 5 μm long
1µm = mm
Fig. 4-2c, p. 54

8. Why Are cells so small?

9. WHY ARE THEY SO SMALL??? Why Are Cells So Small?
Fact: Cells stay small because they are more efficient at taking in the stuff they need and removing the stuff they don’t if they’re small.
WHY ARE THEY
SO SMALL???

10. Think of a Cell as a Protein Factory
PROTEINS
Amino acids, sugars, lipids
WASTE

11. Looking at Cells Cells are spectacular machines.
They are both individual power factories and collective cogs, working together to perform magnificent functions.
In order to work properly, they must have fuel, such as sugar, and other materials and must be able to remove waste.
The entrance of needed materials and removal of unwanted waste must be & is regulated.
The efficiency of this regulation is helped out by the cell being so small.

12. Looking at Cells
All substances that enter or leave a cell must cross the surface of the cell.
When a substance is in the cell, the work done on it happens in the volume of the cell’s interior.
So there is a relationship between the amount of surface area of the cell and the amount of volume it has.
This is called surface-area-to-volume ratio.
Cells with higher surface area-to-volume ratios can exchange substances more efficiently and effectively meaning that they perform their jobs better.

13. Looking at Cells
When comparing cells of the same shape, small cells have greater surface area-to-volume ratios than large cells.
So, why are cells so small?
Small cells function more efficiently than large cells.
Think of it like this:
For every unit of surface area, one door exists = one thing can move in or out.
For every unit of volume, one machine exists = one protein or waste can be created.
When a cell gets too large, it quickly becomes too crowded with stuff on the inside and doesn’t have enough surface area to move the stuff out.
The factory gets backed up without enough doors!

14. Relationship between Surface Area and Volume
Cell Surface Area to Volume Animation

22. The Point Is…
Point is:
THE SMALLER THE CELL SIZE THE LARGER THE SA:V RATION IS!
Cells shouldn’t grow larger than having a SA:V larger than 1.
SA:V = 3
SA:V = 1
SA:V = 0.5

23. Relationship between Surface Area and Volume
How does the door to machine ratio compare.
What’s the problem as the cell becomes larger?
Cell Surface Area to Volume Animation

24. How Do You Calculate Surface Area-to-volume Ratio?
Divide surface area by the volume.
You will get a number.
Write this number
Add a colon
Write the number one.
What this means is that for every one volume (machine) there is ‘x’ amount of surface area (doors)

25. Concept check: What type of cell is depicted in the picture
Concept check: What type of cell is depicted in the picture? Determine the cell type and give a minimum of 3 facts of justification. Label at least two features/organelle of each. A C B D

26. Comparing Cell Sizes In groups: Complete the packet.
Check in at the end if complete.
For homework: Complete the packet & “Extension Questions” you picked up.
Quiz Wednesday/Thursday:
Study. Notes, packets, etc.
Cell organelle and their functions.
Parts of the cell theory.
Review how eukaryotic and Prokaryotic cells compare.
Review how plant, animal, and bacterial cells compare. (Use the little sheet you picked up today)
How to calculate SA:V ratio:
Divide surface area by the volume.
You will get a number.
Write this number
Add a colon
Write the number one.
What this means is that for every one volume (machine) there is ‘x’ amount of surface area (doors)

27. Take away: As a cell gets bigger, the SA:V decreases, making cells less effective, BUT the function the cell participates in influences the cell’s reliance on this fact. For example, skin cells, whose job is to form a barrier is less impacted by SA:V hence the reason why skin cells can be round. However, nerve cells, who need to transmit information will need to maximizes SA:V which is why they are branched, similar to the cylinders.
Structure determine function, meaning a cell cannot do what it wasn’t built for. Evolution has promoted cell shape, much like it has determined the best organisms for the roles they serve in ecosystems. Using the SA:V ratio and the function the cell performs would lead us to conclude these would be the best geometric shapes of your cells.

28. Extension Questions What is this graph saying? What does this mean?
That as the size of the cell increase, the rate od transport decreases.
What does this mean?
The SA:V ratio (aka door to machine ratio) is more favorable when the cell is small.
The dot in green is what we could predict if the cell was 20µm big.
About 3µm/sec
The answer to #3, however, (between 8 and 16µm) would be c. 5µm/sec. (red dot)

29. Take out Science Skills WS & Check
Eukaryotic: plant
Cell wall
Central vacuole
Chloroplasts
Prokaryotic: Bacteria
Cell membrane
Cell wall
Chromosome/DNA
Eukaryotic: animal
Smooth ER
Mitochondria
Rough ER