Which Of The Following Is A Major Cause Of The Size Limits For Certain Types Of Cells

What limits cell size ?

Different types of cells reach different sizes. In general the reasons for prison cell size limits are due to the mechanisms needed for cell survival and how cells' requirements are met by the structures that course and are independent within cells. (Click on the diagrams on the right for details about the structures of different types of cells.)

The factors limiting the size of cells include:

Surface expanse to book ratio (surface surface area / volume)
Nucleo-cytoplasmic ratio
Fragility of jail cell membrane
Mechanical structures necessary to concord the cell together (and the contents of the jail cell in place)

The to a higher place limitations impact unlike types of cells to different extents.

Notes well-nigh each of the principal limitations of cell size follow.

1. Surface expanse to volume ratio

When the size of a cell (having a simple *shape) increases:

the prison cell volume increases to the cube of the linear increment, while
the surface area of the cell increases only to the square of the linear increase.

Examples of elementary formulae:

Volume of a Cube:

Surface Area of a Cube:

Volume = r³

Surface Expanse = 6 r²

where r is the length of each side of the cube.

Volume of a Sphere:

Surface Surface area of a Sphere:

where r is the radius of the sphere.

The diameter (d) of the sphere is twice the radius so the above could be re-written in terms of diameter using the relationship d=2r

*.

Using the above formulae, it is easy to express the ratios of surface area to book for these very simple shapes:

Surface Area / Volume
ratio for a Cube:

= ^half-dozen/_r

where r is the length of each side of the cube.

Surface Expanse / Volume
ratio for a Sphere:

= ⁱⁱⁱ/_r= ⁶/_d

where r is the radius of the sphere.

The bore (d) of the sphere is twice the radius so the in a higher place could exist re-written in terms of diameter using the relationship d=2r

And so, in the cases of very elementary shapes such equally cubes and spheres,
the larger the size of the object (r), the smaller it's surface surface area to volume ratio. Expressed to other way,
the smaller the size of the object (east.1000. a cell), the larger its (surface area) / volume ratio.

A large (surface area) / volume ratio is helpful because nutrients needed to sustain the prison cell enter via the surface of the cell (supply) and are needed in quantities related to the cell volume (requirement). Put another way, more than cytoplasm results in higher demands for supplies via the cell membrane.

Surface-area : Volume ratio especially limits the size of bacterial cells, i.e. prokaryotic cells.

This is because, prokaryotic cells are incapable of endocytosis (the process by which minor patches of the cell membrane enclose nutrients in the external environment, breaking-away from the structure of the jail cell membrane itself to form membrane-bound vesicles that carry the enclosed nutrients into the jail cell.) Endocytosis and exocytosis enable eukaryotic cells to have larger surface-expanse : book ratios than prokaryotic cells considering prokaryotic cells rely on elementary diffusion to move materials such every bit nutrients into the cell - and waste products out of the cell.

Note that some animal cells increase their expanse by forming many tiny projections called microvilli.

two. Nucleo-cytoplasmic ratio

Not all cells accept a membrane-bound nucleus. Eukaryotic cells (including plant cells and animal cells) have nuclei and membrane-bound organelles, while prokaryotic cells (i.e. bacteria) do non. Nuclei contain information needed for protein synthesis so command the activities of the whole prison cell.

Each nucleus tin only command a sure book of cytoplasm.

This is i of the limitations of the size of certain biological cells.

Some cells overcome this particular limitation by having more i nucleus, i.e. some special types of cells have multiple nuclei. Cells that contain multiple nuclei are chosen multinucleate cells and are also known as multinucleated cells and every bit polynuclear cells. A multinucleate prison cell is also called a coenocyte. Examples of multinucleate cells include musculus cells in animals and the hyphae (long, branching filamentous structures - often the chief mode of growth) of fungi.

3. Fragility of the cell membrane

All cells have and need a cell membrane (sometimes labelled a "plasma membrane") even if the prison cell also has a jail cell wall. The structure of cell membranes consist of phospholipids, cholesterol and various proteins. It must be flexible in order to enable important functions of cell membranes such as exocytosis (movement of the content of secretory vesicles out of the prison cell), endocytosis (movement of the content of secretory vesicles into of the cell) etc.. However the structure of the plasma membrane that enables it to perform its many functions too results in its fragility to environmental variation e.g. in temperature and h2o potential.

Temperature: Fifty-fifty small increases in temperature can reduce the (hydrophobic) interactions between the hydrocarbon tails of the phospholipids - leading to reduced or complete loss of protein role.
Water potential: Even small reductions in the water potential of the cytoplasm can outcome in too much water inbound the cytoplasm, causing a fragile animal prison cell to burst due the outward pressure level from the fluid within the jail cell membrane.

As the size of cells increase, the hazard of damage to the prison cell membrane also increases.

This limits the maximum size of cells - especially of brute cells because they do non have cell walls.

See below for more about the effects on prison cell size of the structures that hold cells together.

four. Structures that hold the cell together

As indicated on the pages near brute cells, plant cells and bacteria cells, the contents and internal structures of cells vary co-ordinate to the general type of cell and its specific function within the organism. Some cells are circuitous structures that comprise 100s or 1000s of structures (including different types of organelles) within the cell membrane. For example, in a typical animal cell specialized organelles occupy around 50% of the total cell volume. In order for cells to survive they must remain intact so sufficient mechanical structures must hold the cell contents together.

The prison cell membrane (mentioned in a higher place) has many of import functions including enclosing the contents of the cell - but it is non solely responsible for providing enough structure to concur the prison cell together.

Cells need sufficient structural back up, which is provided past:

Support from exterior the cell membrane :
Most cells take some class of "extracellular" support.
Found cells and bacteria cells have jail cell walls - although they are different types of prison cell walls. The structure of plant prison cell walls consists of cellulose microfibrils forming a mesh (imagine a fine internet) around the outer surface of the cell membrane and a matrix of polysaccharides including pectins and hemicelluloses occupying the regions defined by the mesh of microfibrils. The overall effect is formation of a strong composite structure that supports and protects its contents e.yard. confronting damage to the cell membrane due to expansion of the cytoplasm due to endocytosis.
Prison cell walls enable plant cells to exist larger than fauna cells - establish cells are usually bigger than animal cells.
So what class of extracellular support do animal cells have ?
Glycocalyx: External to the prison cell membrane, animal cells take a fine outer-layer of extracellular polymeric fabric (glycoprotein) which is called the glycocalyx. It consists of brusk-concatenation polysaccharides and provides some mechanical support - but much less support than that provided past a cell wall.
Glycocalyx isn't limited to animal cells. It also forms the capsule, or "slime layer" of some bacteria (prokaryotes).

Back up from within the cell membrane :
i.east. "intracellular" support.
The prison cell membrane and the cytoplasm and organelles within it are inter-connected by many protein structures that, together, grade the cytoskeleton of the prison cell. The functions of the cytoskeleton include protecting and supporting the construction of the cell as well as helping to maintain the shape of the cell.

See as well jail cell functions (in general), the functions of the cell membrane
and table to compare establish, animal and bacterial cells.