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Methods of Transport across a Plasma Membrane Biology

Paper Type: Free Essay Subject: Biology
Wordcount: 2174 words Published: 23rd Sep 2019

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Methods of Transport across a Plasma Membrane Biology

The plasma membrane is present in both the eukaryotic and prokaryotic cell and is also known as the biological membrane and. It works as a barrier between the inner and outer surface of a cell hence is also called the cell membrane. In plant cells it is present just beneath the cell wall whereas in animal cells the plasma is present in the outer most layer of the cell. It is vital for materials to be able to move through the plasma membrane in order for the cell cytoplasm to communicate with the external environment. There are number of mechanisms through which this movement occurs. The different types of transport methods are:


 There are 2 types of diffusion;

  • The movement of molecules from a higher concentration area to an area with lower concentration to the point where they are equally distributed is known as simple diffusion. This process is a passive one hence does not require any form of energy from respiration to be carried out. Also the greater the concentration gradient is the more increased rate of diffusion is.
  • Facilitated diffusion is the process where ions and polar molecules are transported across membranes by channel proteins and carrier proteins. The difference between the two forms of  proteins i.e. channel proteins and carrier proteins is that the former have a fixed shape whereas the latter change shape as they transfer molecules, e.g., when glucose is moved across the membrane.  This form of diffusion i.e. facilitated diffusion also does not need energy from respiration.

Image 1.1

Adela Waters, (2017), Passive Transport across Membrane [ONLINE]. Available at: www.slideplayer.com/slide/10435337/ [Accessed 2 November 2018].


Osmosis is another method used for moving materials across the plasma membrane. Osmosis is a special case of the diffusion of water. Water moves through a partially permeable membrane from a hypotonic place to a hypertonic place. A hypotonic solution is a solution with less negative water potential and a hypertonic is a solution with more negative water potential. However it is known as isotonic when these solutions are at the same concentration.

Image 1.2

Stella Lutman, (2017), Passive Transport learning Targets [ONLINE]. Available at: www.slideplayer.com/slide/2484013/ [Accessed 2 November 2018].

Active transport

The fourth type of movement across the membrane is active transport and takes place when molecules or ions are transported across a membrane, against a concentration gradient by carrier proteins. This form of transport (i.e. active transport) does require energy from respiration. The energy used is known as ATP. Factors reducing respiration would result in a reduced level of active transport, such factors could be; dropped temperatures, reduced levels of oxygen or respiratory and metabolic inhibitors. As this process requires the transportation of proteins in the membrane the Cells involved in the process of Active Transport have a relatively substantial number of mitochondria which is needed to provide the ATP required for the actual conveyance to occur.

Image 1.3

Maurice Stephens, (2018), starter activity biology [ONLINE]. Available at: www.slideplayer.com/slide/4623357/ [Accessed 2 November 2018].

Bulk transport

Cells need bulk transport mechanisms to be able to take up something big like an entire bacterium. As channel proteins and carrier proteins are only able to transport specific kinds of small molecules across the membrane. The mechanisms used in bulk transport involve engulfing the matter to be moved, in their own small pouches of membrane, which then in turn move the substance across using their ability to bud from or combine with the membrane to do so. The majority of cells in our body do not engulf entire microorganisms however mostly they do some form of bulk transport. The reason for this is that it allows cells to be able to acquire nutrients from the environment; selectively some “grab” certain more desired particles out of the extra cellular fluid, or release gesticulating molecules in order to communicate with neighbours. bulk transport is an energy requiring and a extremely energy intensive process similar to the active transport processes which move ions and small molecules via carrier proteins. There are a few means of bulk transport such as; phagocytosis, pinocytosis, receptor mediated endocytosis, and exocytosis.

Image 1.4

Grace Carson, (2017), AP Biology [ONLINE]. Available at: https://gracemcarson.wordpress.com/category/uncategorized/ [Accessed 2 November 2018].

Endocytosis is a way in which large particles, such as cells or cellular debris, are brought into the cell. A form of endocytosis is phagocytosis which is also known as cell eating. This process involves engulfing and ingesting foreign bodies such as bacteria or other cells by phagocytes or certain protists, such as amoebas.

Image 1.5

Mosby, (2009), Mosby’s Medical Dictionary, 9th Edition [ONLINE]. Available at: https://medical-dictionary.thefreedictionary.com/phagocytosis [Accessed 4 November 2018].

Pinocytosis is a method by which cells consume extracellular fluid and its contents. this process involves creating of invaginations by the cell membrane which  then ingest the fluid  and in turn they close and break off in order to form fluid-filled vacuoles in the cytoplasm. This process is known as cell drinking.

Image 1.6

Miller Keane, (2003), Miller-Keane Encyclopaedia [ONLINE]. Available at: https://medical-dictionary.thefreedictionary.com/pinocytosis [Accessed 4 November 2018].

Receptor-Mediated Endocytosis the process of binding together molecules such as hormones, antibodies and other proteins, and lipids to particular receptors within the plasma membrane. It is then followed by their clustering or concentration at specific membrane sites, which are then internalized or engulfed by the cell and taken away from the site.

Image 1.7

Unknown, (2018), Membrane Transport for Macromolecules [ONLINE]. Available at: www.biologyexams4u.com [Accessed 4 November 2018].

Exocytosis is the process of omitting waste from a cell of particles that are too big to be able to diffuse through the wall. This process mirrors the process of endocytosis as it does the complete opposite. It is also known as the aggregation of migrating Leukocytes in the epidermis as part of the inflammatory response.

Image 1.8

Unknown, (2017), Structural Biochemistry [ONLINE]. Available at: www.slideplayer.com/slide/4623357/ [Accessed 2 November 2018].


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