• Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

Transport across plasma membranes.

Extracts from this document...

Introduction

Transport across plasma membranes The cell surface membrane is approximately 7.5mm thick and is a bi-molecular phospholipid bilayer with inwardly directed hydrophobic (substances which repel water molecules) tails. It is also a fluid structure. A partially permeable membrane is one which allows some substances through but not others. There are a number of different ways in which substances are transported across plasma membranes. The first being diffusion, which occurs across the cell surface membrane. This is a passive process (requires no energy) by which substances move from a region of high concentration to a region of low concentration, of the same substance. The rate of diffusion depends on a number of factors: * The concentration gradient * The distance between the areas * The size of the molecules that are diffusing Particles of gas or solute can also diffuse through a membrane, as long as the membrane has pores that are larger than the particles. Every substance diffuses down its own concentration gradient. ...read more.

Middle

Hypotonic solutions have a higher concentration of water molecules compared to the inside of a cell so there is a net movement of water molecules into the cell. This causes the cell to swell; a cell that is full of water but has not burst is said to be turgid. An example of osmosis taking place is in the vacuole of a plant cell. Facilitated diffusion is a passive process, as it does not need energy. (There is no requirement for ATP as there is no energy consumption.) It uses a carrier protein to transfer a molecule across a membrane along its electrochemical gradient. There are different transport proteins for different molecules or ions. Transport proteins have a highly specific tertiary structure, which gives the molecule a distinctive shape. Facilitated diffusion makes diffusion easier because it is a more rapid exchange due to the channels produced by the carrier proteins. The carrier proteins bind with the molecules causing it to change shape allowing the molecules to be released on the other side of the membrane. ...read more.

Conclusion

A lysosome with lytic enzymes fuses with the phagocytic vessel, and then the lysosome releases enzymes which break down nutrient particles/bacterium. The soluble products are absorbed into the cytoplasm and the insoluble material is removed as the vesicle regains. Macromolecules and larger particles, such as bacteria, are taken into cells by endocytosis. Large molecules, such as proteins, are transported out of cells by exocytosis. Endocytosis includes phagocytosis and pinocytosis. Phagocytosis is when cells obtain particles that are too large to be absorbed by diffusion or active transport. Pinocytosis is similar to phagocytosis, but pinocytosis takes in small droplets of the external solution, forming vesicles. There are different processes for transporting any substance between cells, some which require energy and some which don't. Cells are complex factories and they need constantly to import raw materials and get rid of waste. Molecules and ions with different sizes and electrical charges enter and leave all the time. Some of the exchange of materials occurs as a result of passive processes such as diffusion and osmosis, and some occur as a result of processes which require energy such as facilitated diffusion and active transport. Rebecca Stuckey 12 GBB 27th September 2002 ...read more.

The above preview is unformatted text

This student written piece of work is one of many that can be found in our AS and A Level Molecules & Cells section.

Found what you're looking for?

  • Start learning 29% faster today
  • 150,000+ documents available
  • Just £6.99 a month

Not the one? Search for your essay title...
  • Join over 1.2 million students every month
  • Accelerate your learning by 29%
  • Unlimited access from just £6.99 per month

See related essaysSee related essays

Related AS and A Level Molecules & Cells essays

  1. Peer reviewed

    Transport across membranes How do substances cross into and out of cells.

    3 star(s)

    from a region of (their) higher concentration to a region of (their) lower concentration, so in essence where the stink bomb is broken represents the region of high concentration, the far side of the room will represent the region of lower concentration.

  2. Transport across Plasma Membranes

    Final the thickness of the surface that the gases have to diffuse across. These three factors that affect the rate of diffusion are linked together by Fick's law and this equation, The rate of diffusion through the exchange surface is proportional to: Surface area difference in concentration Thickness of surface

  1. The Movement of Substances Across Cell Membranes

    research it turns out that the cell membrane is very complex and important in a wide range of cells activities and functions. Under an electronic microscope two separate layers can be seen known as the bilipid layer. This is made up of lipid and protein molecules, which form a patchwork

  2. Write about the Transport across Plasma membranes

    also phosphorlated, which keeps the concentration of free glucose low, maintaining that 'diffusion gradient' Facilitated diffusion is a passive process.

  1. The Transport of Substances across the Plasma Membrane

    This is where a large molecule is allowed to mover through a protein- lined pore; the movement of these substances requires two proteins: a channel protein and a carrier protein. The channel proteins line a water-filled pore in the membrane so water-soluble molecules can easily pass through.

  2. The Plasma Membrane

    The main functions of cholesterol are that they immobilize the first few hydrocarbon groups of the phospholipid molecules, making the phospholipid bilayer less deformable and decreases permeability. Therefore with cholesterol a cell would need a cell wall. Another main function of cholesterol is that it prevents crystallization of hydrocarbons and phase shifts in the membrane.

  1. Investigating Osmosis.

    The water is not moving. If you were to poke a hole in the bottom of the bucket, water would leak out. This system would not be at equilibrium because there is action taking place - water is leaking out - and the water level in the bucket would drop.

  2. Transport across Plasma Membranes

    > The size of the molecules or ions. Large molecules require more energy to get them moving than small ones do, so substances with large molecules tend to diffuse more slowly than ones with small molecules. Water molecules can diffuse rapidly across the phospholipid bilayer because they are small enough.

  • Over 160,000 pieces
    of student written work
  • Annotated by
    experienced teachers
  • Ideas and feedback to
    improve your own work