Lesson 7 Surface Area to Volume
Completion requirements
Cell Size and Shape
What happens to a cell that cannot get enough nutrients or cannot get rid of waste fast enough?
A7.7 Small surface are to volume ratios kill cells.
If a cell cannot get enough nutrients or remove waste fast enough, the cell will not survive. Cells have to be able to collect enough materials to perform their life functions or those processes will stop happening and the cell will die. At the
same time, if the cell cannot get rid of its wastes fast enough, it will actually poison itself and die. For a cell, and therefore an organism, the ability to quickly transport materials into and out of the cell is the difference between life
and death.
Cells have adapted to this by coming in a variety of shapes. Some cells are long and flat, creating a larger surface area to volume ratio. In this case, there is a smaller volume since the cell is flat.
Cells have adapted to this by coming in a variety of shapes. Some cells are long and flat, creating a larger surface area to volume ratio. In this case, there is a smaller volume since the cell is flat.
Other cells create a folded membrane or little finger-like projections from the surface of the cell. This creates more cell membrane with a very small added volume.
In multicellular organisms such as humans, cells often have specialized functions. In these cases, the cell size and shape is determined by those functions. Nerve cells are often very long and thin in order to cover a large distance quickly. Since the cell is thin, there is a small amount of volume when compared to the surface area.
In multicellular organisms such as humans, cells often have specialized functions. In these cases, the cell size and shape is determined by those functions. Nerve cells are often very long and thin in order to cover a large distance quickly. Since the cell is thin, there is a small amount of volume when compared to the surface area.
© Mariana Ruiz LadyofHats, via Wikimedia Commons
A7.8 Different cell shapes
A7.8 Different cell shapes
A7.10 Human circulatory system
Cells also must think about how fast materials can be transported around inside the cell. If the volume of the cell is too large, the materials cannot be transported around within the cell as easily. This will cause the processes occurring in the
cell to take longer as they have to wait for the materials that are needed. Even if a cell has a shape that makes its membrane as large as possible, it still needs to have a volume small enough for transportation to occur inside the cell.
In multicellular organisms, a transportation system is often developed with specialized cells. This transportation system allows for materials to be transported throughout the body of the organism to help manage the amount of volume. These organisms have also evolved so that no cell is too far away from the vessels of this transportation system. This way all cells get the materials they need as quickly as possible. We will study an example of these transportation systems in Section 3 of this unit.
In multicellular organisms, a transportation system is often developed with specialized cells. This transportation system allows for materials to be transported throughout the body of the organism to help manage the amount of volume. These organisms have also evolved so that no cell is too far away from the vessels of this transportation system. This way all cells get the materials they need as quickly as possible. We will study an example of these transportation systems in Section 3 of this unit.
Did You Know?
A7.9 Red blood cell shape
The shape of a red blood cell, whose job it is to transport oxygen around the body, is biconcave. This means the cell dips in similar to a doughnut but without the hole in the centre. The red blood cell has evolved to have this shape as it increases the surface area to volume ratio, allowing more surface area to absorb oxygen.
Digging Deeper
A7.11 A dragonfly
Millions of years ago, Earth’s atmosphere had a lot more oxygen in it. This allowed multicellular organisms to grow much larger. In fact, insects at that time grew huge. There are fossils of dragon flies the size of birds! Go to the following link for more information. https://quick.adlc.ca/dragonfly
Learn More
Read This
Please read pages 292 and 293 in your Science 10 textbook. Make sure you take notes on your readings to study from later. You should focus on how the surface area to volume ratio affects the size and shape of organisms. Remember, if you have any questions
or you do not understand something, ask your teacher!
Practice Questions
Complete the following practice questions to check your understanding of the concept you just learned. Make sure you write complete answers to the practice questions in your notes. After you have checked your answers, make corrections to your responses (where necessary) to study from.- Is a bigger cell better? Why or why not?
A bigger cell is often not better; in fact, usually a smaller cell is better. This is because cells must have a large surface area to volume ratio to ensure transportation across the cell membrane and within the cell can be done quickly. There
are exceptions to this as some cells have adaptations or functions that allow them to grow bigger
- Give an example from your readings of how a cell or an organism has adapted to increase the surface area to volume ratio.
Your answer should be a variation of the following: Cells have adapted to increase surface area through the following examples:
- by increasing the size of the cell membrane through cell shape. For example, long, flat cells
- through the creation of transportation systems to help reduce reliance on the surface area to volume ratio
- by increasing surface area and decreasing volume by creating small structures (such as villi) to increase the surface area to volume ratio