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

Types of diffusion

Extracts from this document...


Types of Diffusion and Their uses Diffusion is the phenomenon of random motion causing a system to decay towards uniform conditions. Diffusion causes particles to disperse throughout the area it is released in, it can be the diffusion of heat, momentum or concentration. Diffusion usually takes place when there are two mediums of different concentations, in which case diffusion will occur and the two mediums will become isotonic - reaching a state of equilibrium. Osmosis is the movement of water across a partially permeable membrane up a concentration gradient which separates the two solutions at different concentrations. In two volumes of water at different concentrations the solutions will each attempt to pass through the semi-permeable membrane but the solution with a lower concentration will only allow water to pass through as the solute molecules are to big to get through. Osmosis will continue to happen until the 2 solutions reach equilibrium and the flow of water molecules from one side equals the flow of water molecules from the other side through the partially permeable membrane, this is also called isotonic. ...read more.


Carbon dioxide from the bloodstream can also pass back through so it can be breathed out. Due to differences in partial pressures across the alveolar-capillary membrane, oxygen diffuses into the blooad and carbon dioxide diffuses out. Plants use diffusion in the uptake of nutrients and water from the soil. Xylem cells move water and nutrient solutions upwards towards other plant organs from the roots and fine root hairs. Living root cells actively absorb water in the absence of transpiration pull via osmosis creating root pressure (Which allows the plant to transport the nutrients). There are times when plants do not have transpiration pull, usually due to lack of light or other environmental elements. Water in the plant tissues may move to the roots to assist in passive absorption. Different Types of Diffusion * Atomic diffusion * Light diffusion * Brownian motion, for example of a single particle in a solvent * Collective diffusion, the diffusion of a large number of (possibly interacting) ...read more.


The final rationale has to do with the measurement of osmotic pressure by determining how much hydrostatic pressure on the solution is required to prevent the transport of water from a pure source across a semi-permeable membrane into the soluton. A positive pressure must be exerted on the solution to prevent osmotic transport, again congruent with the concept that the osmotic pressure of the pure solvent is relatively "high". * Nevertheless, the dialog continues on Fick's law is used in steady stae diffusion, i.e when the concentration within the diffusion volume does not change with respect to time In one spatial dimension, this is Where: J is the diffusion flux in dimensions of [(amount of substance) length-2 time-1] D is the diffusion coefficient of diffusivity in dimensions of [length2 time-1] is the concentration in dimensions of [(amount of substance) length-3 ?? ?? ?? ?? Antony Rickhuss ...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 Exchange, Transport & Reproduction section.

Found what you're looking for?

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

Here's what a star student thought of this essay

3 star(s)

Response to the question

Overall okay as a means of explaining some of the aspects and uses of diffusion, but not brilliant. The introduction is quite complicated in the wording, so could be worded slightly simpler with more flow to be a little be ...

Read full review

Response to the question

Overall okay as a means of explaining some of the aspects and uses of diffusion, but not brilliant. The introduction is quite complicated in the wording, so could be worded slightly simpler with more flow to be a little be clearer to the reader. Explanation of osmosis is good, but the candidate could have expanded on the meanings of hypertonic and hypotonic and explored these. Sometimes the explanations are not the clearest as the wording can be slightly awkward in places. Main body of the text is okay in most places, but I would like to see the science explained more and the different factors set out clearer. No conclusion. Some sections of text randomly attached with no explanation to their meaning or relevance.

Level of analysis

Level of analysis is good for this level, but could define the different factors affecting diffusion more clearly, for example the diffusion distance, and the concept of moving from a high to low concentration gradient. Misses out active transport and secondary active transport which is another vital method of diffusion. Could also explain the concept of uptake by osmosis in the roots of plants a bit clearer. Uses of diffusion attempts some good examples, but the concept of exchange of CO2 and O2 in the alveoli again could be explained a bit clearer. The different types of diffusion listed are obviously copied and pasted from somewhere with non relevance to biology or the different types of diffusion and their uses explained. No adequate conclusion and random use of Fick's law.

Quality of writing

Spelling okay most of the time, alveoli and blood spelt wrong. Punctuation good. Grammar is okay most of the time, but in some parts the wording order or the use of words makes the meaning overcomplicated or unclear.

Did you find this review helpful? Join our team of reviewers and help other students learn

Reviewed by skatealexia 06/03/2012

Read less
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 Exchange, Transport & Reproduction essays

  1. Marked by a teacher

    Investigate the water potential of celeriac.

    5 star(s)

    It also showed that the celeriac had the least amount of reducing sugar present, so I decided to perform the test for non-reducing sugar on the celeriac. Result from non-reducing sugar test Colour before experiment Colour after experiment Celeriac Copper II Sulphate blue Faint green solution When the solution was

  2. Marked by a teacher

    Describe the molecular structure of starch (amylase), glycogen and cellulose, and relate these structures ...

    4 star(s)

    Amylose is made by many condensations between ?-glucose molecules. In this way a long, unbranching chain of several thousand 1,4 linked glucose molecules is built up. The chains are curved and coil up into helical structures like springs, making the final molecule more compact.

  1. Marked by a teacher

    Human Reproductive System

    4 star(s)

    Pubic symphysis The pubic symphysis is a cartilaginous joint that joins the superior rami of the left and right pubic bones at the front of the pelvis. It is located at the back of the urinary bladder and above the external genitalia.

  2. Marked by a teacher

    The Effect Of Temperature On The Permeability Of The Cell Membrane

    3 star(s)

    I also could have left the boiling tubes in the water baths longer/shorter than the intended time. This means that it is not a fair test as the boiling tube is not left for enough time. So the pigment that should have been released was in plentiful amounts or not

  1. Marked by a teacher

    What is Type 1 diabetes

    3 star(s)

    But learning about how the body functions, giving insulin injections, controlling diet and measuring the blood glucose levels, will help to restore family life and the child's life, back to normal. The healthcare teams at the children's wards can teach you about these areas.

  2. Investigating Water Potential Of Potatoes.

    FAIR TEST In order to make this test fair, there are many things that will need to be constantly checked. Some of the key variables that can be changed are: * Temperature * Surface area of potato * Volume of Solution * Weight of potato * Concentration.

  1. The Skeletal and Muscular System

    This causes the bone to lack in calcium, can causes the bone to soften and thereby cause rickets. b. Osteoporosis. It is a condition affecting mostly older people in which the bones become less dense that makes them weak and more prone to breaks and fractures.

  2. The Endocrine System

    Hormones act by regulating cell metabolism. By accelerating, slowing, or maintaining enzyme activity in receptor cells, hormones control growth and development, metabolic rate, sexual rhythms, and reproduction. Hormones are naturally occurring substances secreted by specialised cells that affect the metabolism or behaviour of other cells possessing functional receptors for the hormone.

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