Cells and Cell Theory
What advantages does small size give to a cell?
Many cellular processes occur by diffusion, which is efficient over short distances, but less efficient over long distances. Since all materials going in and out of a cell must pass through the plasma membrane, the greater the surface area of this membrane, the faster a given quantity of molecules can pass through. Smaller cells have a much greater surface-to-volume ratio than larger cells and therefore can "feed" all areas of the cell in less time.
What is "surface-to-volume ratio," and how does it affect cell size?
The surface-to-volume ratio is a mathematical relationship between the volume of an object and the amount of surface area it has. This ratio often plays an important role in biological structures. Think of a cell as a sphere:
The surface area of a sphere can be calculated by
4ð r2 where r is the radius of the sphere.
Volume of a sphere can be calculated by
4/3 ð r3.
An increase in r will increase the surface area by a power of two, but increase the volume by a power of three. This means that the volume will increase much faster than the surface area. This puts an upper limit on the size of a cell, because if the cell volume gets too big, there won't be enough membrane to transport the amount of food in and wastes out to support that large cell size.
What is the difference between prokaryotic and eukaryotic cells?
Prokaryotic cells are more simple: they are usually much smaller and don't have a nucleus or any other membrane-bound organelles. Bacteria are prokaryotes. Eukaryotic cells are much more complex, are usually larger, and have a nucleus and several other membrane-bound organelles that allow them to compartmentalize their functions. All multicellular plants and animals are eukaryotes. A helpful trick to remember is that "you" are a "eu"karyote.
Are there any single-celled eukaryotes?
Yes--yeast, for example. Yeast are single-celled organisms, but they do contain a membrane-bound nucleus, mitochondria, and other organelles.
What are the advantages and disadvantages of prokaryotic compared to eukaryotic cells?
Although prokaryotes may seem more primitive than eukaryotes, they are among the most successful species on our plant and comprise a very large percentage of the total mass of all living things on earth. Simple, small, and single-celled organisms can reproduce quickly and evolve quickly. Prokaryotes can generate millions of progeny in a short period of time.
There are many different cells that do many different things. But all of these cells fall into two categories: prokaryotic and eukaryotic cells. Eukaryotic cells contain a nucleus and are larger in size than prokaryotic cells. Prokaryotic cells do not contain a nucleus, are smaller and simpler than eukaryotic cells. Two of their similarities are they both have DNA as their genetic material and are covered by a cell membrane.
to construct and or maintain the cell membrane. In a microscopic view of the cell membrane we can
This cell membrane plays an important part in Diffusion. Cell membrane and Diffusion Diffusion is the movement of the molecules of gas or liquids from a higher concentrated region to a lower concentration through the partially permeable cell membrane along a concentraion gradient. This explanation is in the diagram shown below: [IMAGE] Turgor When a plant cell is placed in a dilute solution or a less concentrated solution then the water particles pass through the partially permeable membrane and fill the cell up with water. The cell then becomes Turgor or hard. An example of this is a strong well-watered plant.
The side of the membrane that has the higher concentration is said to have the concentration gradient. It drives diffusion because substances always move down their concentration gradient. The pressure gradient also plays a role in diffusion. Where this is a pressure gradient there is motion of molecules. The pressure gradient is a difference in pressure between two different points.
Eukaryotic cells, whether from animals, plants, protists, or fungi, are the most structurally advanced of the major cell types. Eukaryote are single-celled or multicellular organism whose cells contain nucleus and any other structures (organelles) enclosed within the membrane that perform specific functions. The surface of the cell is covered with a thin film or plasma membrane, which is the boundary that separates the living cell from its nonliving surroundings. Plasma membranes are composed mostly of proteins and lipids (Simon, 02/2012, p. 59-60).
Prokaryotic cell: have no membrane covered organelles, they also have circular DNA and bacteria, Eukaryotic cell: have membrane covered organelles, they also have linear DNA and all other cells. Also the cell cycle is short in prokaryotic cells, roughly taking about 20-26 minutes to complete. And in eukaryotic cells, the cell cycle is long, it usually takes about 12-24 hours to complete. Below is a table of some of the differences between the cells:
The Importance of Diffusion to Living Organisms Diffusion is basically the movement of chemical species (ions or molecules) under the influence of concentration difference. The species will move from the high concentration area to the low concentration area till the concentration is consistent in the whole system. Diffusion mostly occurs in gases and liquids as these can move freely. The main features of an efficient diffusion system would be that it has a large surface area, thin membrane and a continuous supply of substances. A large surface area is needed so that high amount of substances can be exchanged at a time while the thin membrane means that the diffusion pathway would be short so that it is more efficient.
On a cellular level, Mrs. Jones’ cells are dehydrated due to osmotic pressure changes related to her high blood glucose. Cells dehydrate when poor cellular diffusion of glucose causes increased concentrations of glucose outside of the cell and lesser concentrations inside of the cell. Diffusion refers to the movement of particles from one gradient to another. In simple diffusion there is a stabilization of unequal of particles on either side of a permeable membrane through which the particles move freely to equalize the particles on both sides. The more complex facilitated diffusion is a passive transport of large particles from a high concentration of particles to a lower concentration of particles with the aid of a transport protein (Porth, 2011). The cellular membranes in our bodies are semipermeable allowing for smaller molecules to flow freely from the intracellular to extracellular space. The glucose molecule, however; is too large to diffuse through the cellul...
However, tumours can spread into some tissues more easily than others. For example, large blood vessels that have very strong walls and dense tissues such as cartilage are hard for tumours to grow into.
π is equal to the osmotic pressure, V is equal to the cell volume and B is the intracellular solids (Hall). Ponder’s R value is the ratio of intracellular solvent volume to the water in its environment; R=(Vi -b)/W. These two equations are related because Ponder’s R value is a measure of how much of an osmometer a cell is while the van’t Hoff relation shows what the osmotic pressure is, both inside and outside the cell. Overall cell membrane permeability can be measured by Ponder’s R value while the osmotic pressure differentials between the external environment and the internal environment are seen with the van’t Hoff relation (Hall). Cells evolved to become great osmometers, but not perfect osmometers, in order to provide a way for solutes to move along permeable membranes. The van’t Hoff relation permits organisms to live in environments of varying osmolarity because regulating solute concentration within a cell can increase or decrease the cell’s affinity for osmosis (Darnell et al). Ponder’s R value, on the other hand, shows how a cell can never become a perfect osmometer. If a cell could become a perfect osmometer, it could cause cell lysis or shrinkage of the cell (Hall). The avoidance of perfect osmometry can be seen within the human erythrocyte as a small portion of cell water will not take part in an osmotic exchange due to tonicity within its
So how big are cells? Most human cells are about ten microns in diameter. This is about o...
The Cell, the fundamental structural unit of all living organisms. Some cells are complete organisms, such as the unicellular bacteria and protozoa, others, such as nerve, liver, and muscle cells, are specialized components of multicellular organisms. In another words, without cells we wouldn’t be able to live or function correctly. There are Animal Cells and Plant Cells. In Biology class the other day we studied the Animal Cell. We were split into groups of our own and we each picked a different animal cell slide to observe. My group chose the slide,'; Smeared Frog Blood ';.
- Suface Area: if you are to change the surface area it is going to