Science: SA:V Ratio and Plasma Membrane

Diffusion

- a process by which the cell moves materials, is fast over short but extremely slow over long distance. Ex. perfume - the rate of diffusion of substances is proportional to the surface area of the plasma membrane, but the rate of using substances is proportional to cell volume. Therefore, cells can only survive if the surface area to volume ratio is large enough.

How are surface area and volume different?

Surface area and volume are different because surface area it the outside of an object, whereas the volume is the inside of an object. Also, surface area is measured in square centimeters, whereas volume is measured in centimeters cubed.

Define surface area in your own words.

Surface area is the measurement of the surface on the outside of the item. It's how much space there is to cover on the outside of an object (the crust on a loaf of bread). It is measured in square centimeters.

In your own words, define surface area.

Surface area is the measurement of the surface on the outside of the item. It's how much space there is to cover on the outside of an object (the crust on a loaf of bread). It is measured in square centimeters.

How does surface area-to-volume ratio limit cell size? Explain by comparing an organism that is a single large cell with a multicellular organism made up of many small cells.

Surface area to volume ratio limits cell size because at one point the surface area to volume ratio becomes so small that its surface area gets too small to supply the volume its basic nutrients which stops the cell from getting larger. For example, bacteria are single celled organisms that are very small, whereas humans are multicellular organisms that can grow to be much larger than bacteria.

Which of the three cubes had the greatest volume?

The 3 cm cube had the greatest volume. It's volume is 27 cm3, while the 2 cm cube has a volume of 8 cm3, and the 1 cm cube has a volume of 1 cm3.

Why are cells small?

to maximize their surface area to volume ratio which makes transport of materials more efficient.

What are large molecules like carbohydrates use?

transport proteins to move across cell membranes.

What trends do you observe when comparing the volume, surface area, and surface area-to-volume ratios of a small, medium, and large cube as the cubes get larger? (Ex: As cube size increases, the volume...)

As cube size increases, the volume increases. As cube size increases, the surface area increases. As cube size increases, the surface area to volume ratio decreases.

Cholesterol

Cholesterol is a lipid in the cell membrane that makes the membrane more fluid and adds to its flexibility.

simple diffusion

Ex. phospholipids can allow water and other non polar molecules to pass thru into or out of the cell. something that does not require energy and the water or molecules are moving with the concentration gradient.

Glycolipids

Glycolipids are carbohydrate chains that are attached to lipids, and they also help with cell recognition.

Glycoproteins

Glycoproteins are carbohydrate chains attached to membrane proteins that help with cell recognition.

If you have something large and you divide it into small pieces, what increases: surface area or volume? Give an example in biology of an increased surface area-to-volume ratio and explain how this is beneficial to the organism using what you know about surface area-to-volume ratios.

If you have something large and you divide it into small pieces, the surface area increases because it still takes up the same amount of space, but the outside area of it increases. Plant roots are an example of increased surface area-to-volume ratio. It is beneficial to plants because it helps the plant absorbs more water and nutrients more efficiently.

Describe the fluid mosaic model of the plasma membrane.

On the outside of the plasma membrane are the hydrophilic heads of the phospholipids. The top layer also has glycoprotein and glycolipids branching off its top. Mixed into the layer from the top and bottom is cholesterol which helps the membrane maintain fluidity. Cutting through the membrane from top to bottom is the integral proteins. The peripheral proteins are only on one side of the membrane on top or bottom of the integral proteins. SEE DIAGRAM!!

Peripheral proteins

Peripheral proteins are only found on one side of the membrane and are only temporary. They help with reactions inside the cell.

Which of the three cubes had the greatest surface area to volume ratio?

The cube with the greatest surface area to volume ratio is the smallest cube, the 1 cm cube, with a surface area to volume ratio of 6:1.

Why is a greater surface area to volume ratio important in cells, especially in cell transport?

The greater surface area to volume ratio is important in cells, especially in cell transport because it makes it more efficient for cells to take in and get rid of nutrients from their surroundings if they have a greater surface area to volume ratio. So, it is important for cells to be very small so they can have the greatest surface area to volume ratio possible.

Phospholipid head

The phospholipid head is the hydrophilic layer on the outside of the phospholipid bilayer.

Phospholipid tail

The phospholipid tail is the hydrophobic layer on the inside of the phospholipid bilayer.

Explain the importance of the plasma membrane in maintaining homeostasis in an organism.

The plasma membrane is important because it helps to maintain homeostasis by keeping the cell's internal and external environments seperate. This helps the cell maintain a stable inner environment regardless of what's happening in its outer environment.

In the image to the right there are three cubes made to represent cells of different volumes, each soaked in the same amount of a substance that represents nutrients. Using this image, explain what is meant by the phrase "as you get bigger, your outside is unable to keep up with the needs of the inside".

This phrase is represented in the image above because as the cube size increases the surface area to volume ratio decreases, it harder for the nutrients to get distributed to all parts of the cell, making it harder for each cube to meet the needs of its inside.

Transport proteins

Transport proteins are proteins that go all the way through the bilayer and are also called integral proteins. They help transport certain materials across the cell membrane.

Define volume in your own words.

Volume is how much space an item takes up, or how much can fit inside an object. Volume is measured in cubic centimeters.

In your own words, define volume.

Volume is how much space an item takes up, or how much can fit inside an object. Volume is measured in cubic centimeters.

When the bread was cut into more pieces, which increased: surface area or volume? Explain your answer.

When the bread was cut into more pieces, its surface area increased, but its volume did not. This is because when the bread is cut, it still takes up the same amount of space, yet, it has now two new surfaces or sides that contribute to its surface area, making its surface area larger. This shows that by making something smaller, you can increase its volume to surface area ratio.

Examples to high surface area to volume ratios in nature

anemones tree and plant roots lunggs intestines inner mitochondrial membrane elephant ears

Phospholipid structure

head = glycerol and phosphate group tail = chains of fatty acid.

cell membrane is also called...

plasma membrane - made of phospholipid bilayer.

What is embedded in the phospholipid bilayer?

proteins that aid in diffusion and cell recognition.