what does a cell membrane do?

Question

im doing a science project and need to know

Answer 1

The plasma membrane is a dynamic structure. It is composed of 2 layers of lipid material with protein molecules interspersed through out. The phospholipids have 2 definite ends , a hydrophilic ( focusing to the outside and inside of the membrane) and a hydrophobic one ( forming the center of the membrane). The proteins are of two types Integral ( passing through the width of the membrane ( act as transport channels) and peripheral ( act as recognition sites ). These peripheral proteins contain carbohydrates to help in cell to cell recognition. These carbohydrates are called oligosaccharides. I f they bind to proteins they become glycoproteins, if they bind to lipids , they become glycolipids. Cholesterol molecules are found in animal membranes to help add support to its structure. The majority of the phospholipids contain unsaturated fatty acids to keep it fluid. Looking at the over all picture of the membrane the term fluid mosaic should become evident.

Traffic of molecules across the membrane:
1. Hydrophobic molecules (Hydrocarbons and Oxygen) can cross with ease because they can dissolve in the lipid bilayer.
2. Small polar (uncharged) molecules will pass ( water and carbon dioxide).
3. Large polar (uncharged) molecules will not pass ( sugar).
4. Ions will not readily pass ( H+, Na+, Cl-).

Transport Proteins:

1. Uniport - one molecule moves in only one direction.

2. Symport - Two different molecules moving in only one direction.

3. Antiport - Two molecules moving in opposite directions.

These transport proteins work in the following ways: provide a tunnel to allow material to flow through, bind to the substance and physically move it, and they are specific for the substance they move.

Answer 2

1/ Cell membrances are semi-permeable meaning they select what will enter or leave the cell.
2/ They form a type of separation from the extracellular environment and the cell content. For example if the pH of the extracellular fluid is 4 and the cell content needs a pH of 11 the membrance don't allow for mixing of pH vallues.
3/ They separate contents of organelles from each other for example Nuclear Membrane (which by the was is a double membrane) is separates the nucleus from the cytoplasm and other organelles such as chloroplast, etc.

Answer 3

It is a lipid bi-layer found on the outside of the cell. It contains protein-receptors sensitive to hormones and transport channels, along with cholesterol for additional stability. It controls what goes in to and out of a cell, through the channels/pores, etc. It maintains the internal environment of the cell. It also maintains a kind of shape to the cell.. But it offers very little protection & support as it is ~very~ thin and soft. In plant cells they also have a cell wall around the outside of a cell made of cellulose, this gives the cell extra support and a strong rigid structure. As animal cells contain no cell wall they are far weaker (smaller too).

Answer 4

A cell membrane is the outermost part of a cell which provides the shape and size of the cell. It is also a protective layer which allows the entry of protiens, minerals etc. and the exit of water energy etc. it also protects the nucleus and its constituents too. but the features of some organisms may change with the thickness, density and layering of the cytoplasm

Answer 5

The cell membrane:
1) Protects the cell
2) Separates the cell from its environment
3) Controls what is allowed to enter the cell
4) Controls what is allowed to leave the cell
5) Allows osmosis and diffusion to occur

Answer 6

cell walls keep the plant cells rigid. The cell membrane functions as a barrier between the environment within the cell and outside the cell.

Answer 7

Holds everything inside the cell. Permits certain things to pass in and out.

Answer 8

It acts like skin for a cell. It holds everything in.

Answer 9

it protects the cell and decides what goes into and comes out of the cell

Answer 10

it holds the nucleus and other parts together as a unit. i guess it's kinda like the surface tension of water or on a larger scale, probably like your skin holds your insides.. well, inside. I hope my perspective helps you.