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Surface Area To Volume Ratio

The document explains the importance of the surface area to volume (SA:V) ratio in cells, highlighting that smaller cells are more efficient at diffusion due to their higher SA:V ratio. As cell size increases, the SA:V ratio decreases, leading to less efficient diffusion and necessitating cell division. It also discusses how unicellular organisms maintain efficiency through their small size, while multicellular organisms have adapted features to enhance material exchange despite larger cell sizes.

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128 views1 page

Surface Area To Volume Ratio

The document explains the importance of the surface area to volume (SA:V) ratio in cells, highlighting that smaller cells are more efficient at diffusion due to their higher SA:V ratio. As cell size increases, the SA:V ratio decreases, leading to less efficient diffusion and necessitating cell division. It also discusses how unicellular organisms maintain efficiency through their small size, while multicellular organisms have adapted features to enhance material exchange despite larger cell sizes.

Uploaded by

aaaz
Copyright
© © All Rights Reserved
We take content rights seriously. If you suspect this is your content, claim it here.
Available Formats
Download as PDF, TXT or read online on Scribd
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No Brain Too Small BIOLOGY

Surface area to volume ratio.


efficiency

Surface area refers to the outside area of an object, e.g. it is the area around the Why is SA:V ratio important:
outside of a cell. Unit = cm2. Cells need to be small because they rely on diffusion for getting substances into
Volume refers to the amount of space inside of the object, e.g. it is the space and out of their cells. When a cell grows, there is comparatively less membrane
multicellular

inside the cell. Unit = cm3. for the substances to diffuse through resulting in the centre of the cell not
receiving the substances that it needs. Diffusion is less efficient, cell processes
slow down and the cell stops growing. The cell then needs to divide into two
smaller cells, which each have a larger SA: V ratio and can diffuse materials more
efficiently again.
unicellular organism

Small cells are more efficient at diffusion as


they have a HIGH SA:V ratio.
Cube size Surface area Volume SA:V ratio
2 cm cube 2 x 2 x 6 = 24cm2 2 x 2 x 2 = 8cm3 24 to 8 = 3:1 In class you may have done an experiment where you placed special agar into a
4 cm cube 4 x 4 x 6 = 96cm2 4 x 4 x 4 = 64cm3 96 to 64 = 1.5:1 solution of NaOH. All three cubes soaked in the solution for the same amount of
6 cm cube 6 x 6 x 6 = 216cm2 6 x 6 x 6 = 216cm3 216 to 216 = 1:1 time but the bigger cubes did not change colour on the inside as the NaOH hadn’t
8 cm cube 8 x 8 x 6 = 384cm2 8 x 8 x 8 = 512cm3 384 to 512 = 0.75:1 diffused in yet. This shows that large cell takes long/is less efficient at diffusing
materials into the centre of the cell.
diffusion

As the cube size increases or the cell gets bigger , then the surface area to volume Cubes cut in
ratio - SA:V ratio decreases. half to
measure how
When an object/cell is very small, it has a large surface area to volume ratio, while far the NaOH
has diffused.
a large object/ cell has a small surface area to volume ratio.
SA:V ratio

When a cell grows, its volume increases at a greater rate than its surface area,
therefore it’s SA: V ratio decreases.
SA:V ratio in unicellular organisms. Their small size means that they have a large
Cells may increase their SA:V ratio by having: SA:V ratio and it is adequate for the many materials to move into and out of the
volume

Long thin shape / elongated shape. e.g. nerve cells cell by diffusion and active transport. But it does limit the organism’s size. Once
Folding the surface of the object/ cell they get too big, they must divide.
membrane. e.g. villi of the lining in the small
intestines SA:V ratio in multicellular organisms. By being multicellular, plants and animals
surface area

Plant cells are much larger than animal cells and have overcome the problems of small cell sizes. Each cell has a large SA:V ratio
they have a large vacuole which pushes the but they have evolved features such as gas exchange organs (lungs) and
organelles to the edge of the cell where they get circulatory system (blood) to speed up and aid the movement of materials into
regular access to resources. and out of the organism.

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