someone help me understand how do they come up with the surface area/volume ratio? (Biology-Cell)

Biology Today and Tomorrow without Physiology (MindTap Course List)
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Chapter3: Cell Structure
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Screenshot for context. Can someone help me understand how do they come up with the surface area/volume ratio? (Biology-Cell)

Evolutionary Adaptations Circumvent
Cell Size Limits
There is an upper limit to cell size due to the change in the
surface area-to-volume ratio of an object as its size increases
(Figure 4.5). For example, doubling the diameter of a cell
increases its volume by eight times but increases its surface
area by only four times. The significance of this relationship is
that the volume of a cell determines the amount of chemical
activity that can take place within it, whereas the surface area
determines the amount of substances that can be exchanged
between the inside of the cell and the outside environment.
Nutrients must enter cells constantly, and wastes must leave
constantly. However, past a certain point, increasing the
diameter of a cell gives a surface area that is insufficient to
maintain an adequate nutrient-waste exchange for its entire
volume. At that point cell growth must stop or the cell must
divide to begin anew with a functional surface area-to-volume
ratio.
Some cells have adaptations that allow them to circumvent
the surface area limitation just described. For instance, eggs of
some species, such as birds and frogs, are much larger than
FIGURE 4.3 Units of measure and the ranges in which they are
used in the study of molecules and cells. The vertical scale in each box
is logarithmic.
ⒸCengage Leaming 2017
Transcribed Image Text:Evolutionary Adaptations Circumvent Cell Size Limits There is an upper limit to cell size due to the change in the surface area-to-volume ratio of an object as its size increases (Figure 4.5). For example, doubling the diameter of a cell increases its volume by eight times but increases its surface area by only four times. The significance of this relationship is that the volume of a cell determines the amount of chemical activity that can take place within it, whereas the surface area determines the amount of substances that can be exchanged between the inside of the cell and the outside environment. Nutrients must enter cells constantly, and wastes must leave constantly. However, past a certain point, increasing the diameter of a cell gives a surface area that is insufficient to maintain an adequate nutrient-waste exchange for its entire volume. At that point cell growth must stop or the cell must divide to begin anew with a functional surface area-to-volume ratio. Some cells have adaptations that allow them to circumvent the surface area limitation just described. For instance, eggs of some species, such as birds and frogs, are much larger than FIGURE 4.3 Units of measure and the ranges in which they are used in the study of molecules and cells. The vertical scale in each box is logarithmic. ⒸCengage Leaming 2017
Total surface
area
Total
volume
Surface area/
volume ratio
6x²
x³
6:1
6(2x)²-24x²
(2x)³-8x³
3:1
6(3x)² - 54x²
(3x)³ = 27x³
2:1
6(4x)²-96x²
contains the organelles, the cytosol, and the cyto-
skeleton. The organelles ("little organs") are small,
organized structures important for cell function.
The cytosol is an aqueous (water) solution con-
taining ions and various organic molecules. The
cytoskeleton is a protein-based framework of fila-
mentous structures that, among other things, helps
maintain proper cell shape and plays key roles in
cell division and chromosome segregation from cell
generation to cell generation. The cytoskeleton was
once thought to be specific to eukaryotes, but
research has shown that all major eukaryotic cyto-
skeletal proteins have functional equivalents in
prokaryotes.
Many of the cell's vital activities occur in the
cytoplasm, including the synthesis and assembly of
most of the molecules required for growth and
reproduction (except those made in the central
region) and the conversion of chemical and light.
energy into forms that can be used by cells. The
cytoplasm also conducts stimulatory signals from the outside
into the cell interior and carries out chemical reactions that
respond to these signals.
(4x)³ = 64x³
1.5:1
FIGURE 4.5 Relationship between surface area and volume. The surface area of
an object increases as a square of the linear dimension, whereas the volume increases as
a cube of that dimension.
ⒸCengage Leaming 2017
typical cells, meaning that they have a low surface area-to-
volume ratio. In this case the eggs contain a large store of nutri-
ents so no nutrients need to be brought into the cells. In
addition, once fertilized, the eggs divide rapidly to produce a
multicelled embryo with each cell of typical cell size (see Chap-
ter 50). Another adaptation to circumvent the surface area lim-
itation is for cells to be long and thin, or skinny and flat, both
of which increase surface area. Examples are nerve cells (neu-
rons; see Chapter 39) and muscle cells (see Chapter 43). Yet
another adaptation is seen in human intestinal cells, which
have closely packed, fingerlike extensions that increase their
surface area (see Chapter 47).
-Hydrophilic
head
-Hydrophobic
tail
Phospholipid
molecule
ATT
Transcribed Image Text:Total surface area Total volume Surface area/ volume ratio 6x² x³ 6:1 6(2x)²-24x² (2x)³-8x³ 3:1 6(3x)² - 54x² (3x)³ = 27x³ 2:1 6(4x)²-96x² contains the organelles, the cytosol, and the cyto- skeleton. The organelles ("little organs") are small, organized structures important for cell function. The cytosol is an aqueous (water) solution con- taining ions and various organic molecules. The cytoskeleton is a protein-based framework of fila- mentous structures that, among other things, helps maintain proper cell shape and plays key roles in cell division and chromosome segregation from cell generation to cell generation. The cytoskeleton was once thought to be specific to eukaryotes, but research has shown that all major eukaryotic cyto- skeletal proteins have functional equivalents in prokaryotes. Many of the cell's vital activities occur in the cytoplasm, including the synthesis and assembly of most of the molecules required for growth and reproduction (except those made in the central region) and the conversion of chemical and light. energy into forms that can be used by cells. The cytoplasm also conducts stimulatory signals from the outside into the cell interior and carries out chemical reactions that respond to these signals. (4x)³ = 64x³ 1.5:1 FIGURE 4.5 Relationship between surface area and volume. The surface area of an object increases as a square of the linear dimension, whereas the volume increases as a cube of that dimension. ⒸCengage Leaming 2017 typical cells, meaning that they have a low surface area-to- volume ratio. In this case the eggs contain a large store of nutri- ents so no nutrients need to be brought into the cells. In addition, once fertilized, the eggs divide rapidly to produce a multicelled embryo with each cell of typical cell size (see Chap- ter 50). Another adaptation to circumvent the surface area lim- itation is for cells to be long and thin, or skinny and flat, both of which increase surface area. Examples are nerve cells (neu- rons; see Chapter 39) and muscle cells (see Chapter 43). Yet another adaptation is seen in human intestinal cells, which have closely packed, fingerlike extensions that increase their surface area (see Chapter 47). -Hydrophilic head -Hydrophobic tail Phospholipid molecule ATT
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