image from gridgit.com Show In the Cell Membrane unit we will learn that the cell membrane is one of the great multi-taskers of biology. It provides structure for the cell, protects cytosolic contents from the environment, and allows cells to act as specialized units. We will also learn that the membrane is the cell’s interface with the rest of the world - it’s gatekeeper. This phospholipid bilayer determines what molecules can move into or out of the cell, and so is in large part responsible for maintaining the delicate homeostasis of each cell. The unit is planned to take 3 school days Essential Ideas:
Nature of Science
Understandings 1.4.U.1 Particles move across membranes by simple diffusion, facilitated diffusion, osmosis and active transport. (Oxford Biology Course Companion page 35).
Cellular membranes possess two key qualities:
Movement of materials across a biological membrane may occur either actively or passively Diffusion is the passive movement (does not require energy) of particles from a region of high concentration to a region of low concentration.
Osmosis - the passive movement of water molecules, across a semi-permeable membrane, from a region of lower solute concentration to a region of higher solute concentration. Simple diffusion- passive movement of particles from an area of high concentration to an area of low concentration (follows its concentration gradient). Simple diffusion across membranes occurs when substances other than water move across the phospholipid bilayer (between the phospholipids) or through protein channels.
Facilitated Diffusion - specific ions and other particles that cannot move through the phospholipid bilayer sometimes move across protein channels
Active transport - movement of substances across membranes using energy from ATP.
image from www.tes.com 1.4.U 2 The fluidity of membranes allows materials to be taken into cells by endocytosis or released by exocytosis. (Oxford Biology Course Companion page 34/35).
The membrane is principally held together by weak hydrophobic associations between the fatty acid tails of phospholipids. This weak association allows for membrane fluidity and flexibility, as the phospholipids can move around to some extent. This allows for the spontaneous breaking and reforming of the bilayer, allowing larger materials to enter or leave the cell without having to cross the membrane (this is an active process and requires ATP hydrolysis)
Exocytosis
1.4.U3: Vesicles move materials within cells (Oxford Biology Course Companion page 34).
After proteins have been synthesized by ribosomes they are transported to the rough endoplasmic reticulum where they can be modified. Vesicles carrying the protein then bud off the rough endoplasmic reticulum and are transported to the Golgi apparatus to be further modified. After this the vesicles carrying the protein bud off the Golgi apparatus and carry the protein to the plasma membrane. Here the vesicles fuse with the membrane expelling their content (the modified proteins) outside the cell. The membrane then goes back to its original state. This is a process called exocytosis. Endocytosis is a similar process which involves the pulling of the plasma membrane inwards so that the pinching off of a vesicle from the plasma membrane occurs and then this vesicle can carry its content anywhere in the cell.
Application 1.4.A.1 Structure and function of sodium–potassium pumps for active transport and potassium channels for facilitated diffusion in axons.
The axons in nerve cells transmit electrical impulses by translocating ions to create a voltage difference across the membrane. In the resting phase, the sodium-potassium pump releases sodium ions from the nerve cell, while potassium ions are accumulated in. When the neuron fires, these ions swap locations through facilitated diffusion using the sodium and potassium channels Sodium-Potassium Pump An integral protein that exchanges 3 sodium ions out of cell with two potassium ions into the cell. The process of ion exchange against the gradient is energy-dependent and involves a number of key steps: Three sodium ions bind to intracellular sites on the sodium-potassium pump
image from https://online.science.psu.edu/sites/default/files/biol011/Fig-3-7-Sodium-Potassium-Pump.jpg 1.4.A.2 Tissues or organs to be used in medical procedures must be bathed in a solution with the same osmolarity as the cytoplasm to prevent osmosis (Oxford Biology Course Companion page 44).
Hypertonic solution – Is a solution with a higher osmolarity (higher solute concentration) then the other solution. If cells are placed into a hypertonic solution, water will leave the cell causing the cytoplasm’s volume to shrink and thereby forming indentations in the cell membrane. Hypotonic solution – Is a solution with a lower osmolarity (lower solute concentration) then the other solution. If cells are placed in a hypotonic solution, the
water will rush into the cell causing them to swell and possibly burst. Isotonic solution: A solution that has the same salt concentration as cells and blood. Organs placed in hypotonic solution or hypertonic solution would damage cells, therefore isotonic solutions are used (same osmolarity as inside the cell)
Skill 1.4.S.1 Estimation of osmolarity in tissues by bathing samples in hypotonic and hypertonic solutions. (Oxford Biology Course Companion page 41).
Osmolarity is a measure of solute concentration, as defined by the number of osmoles of a solute per litre of solution (osmol/L) Solutions may be loosely categorised as hypertonic, hypotonic or isotonic according to their relative osmolarity Solutions with a relatively higher osmolarity are categorised as hypertonic (high solute concentration ⇒ gains water) The osmolarity of a tissue may be interpolated by bathing the sample in solutions with known osmolarities The tissue will lose water when placed in hypertonic solutions and gain water when placed in hypotonic solutions
Key Terms:
PowerPoint presentation Topic 1.4 Cellular Membrane by Chris Paine Correct use of terminology is a key skill in Biology. It is essential to use key terms correctly when communicating your understanding, particularly in assessments. Use the quizlet flashcards or other tools such as learn, scatter, space race, speller and test to help you master the vocabulary. Helpful Links: Optional Online Practice Quizzes3 levels of quizzes (Note- not all questions are related to content we are studying.) , from McGraw Hill Diffusion appletfrom Ohio Biosci Diffusion animation,by John Kyrk How osmosis works,from McGraw Hill Clear osmosis animation,from StOlaf.edu Membrane transport,from Wiley Interactive Concepts in Biochemistry Isotonic Equilibrium: Osmosis Simulation,from Carnegie Mellon Facilitated Diffusion PhET Lab simulation: Membrane Channels(allow Java to run) Membrane transport,from Wiley Interactive Concepts in Biochemistry How facilitated diffusion works, from McGraw Hill Facilitated diffusion,from Northland Passive transport: simple and facilitated diffusionfrom Freeman Lifewire Active Transport & ATP Membrane transport,from Wiley Interactive Concepts in Biochemistry Sodium-potassium pump, from McGraw Hill Sodium-potassium pump, from StOlaf Active transportfrom Northland Active transportfrom Freeman Lifewire Vesicle Transport: Endo- and Exocytosis Vesicle transportfrom Learn.Genetics Exocytosis, from StOlaf Animated plasma membrane, by John Kyrk Phagocytosis (endocytosis), from McGraw Hill Endoplasmic reticulum and Golgi apparatus, from Freeman Lifewire Lysosomes,from McGraw Hill Membrane Fluidity Membrane fluidityfrom Learn.Genetics Animated plasma membrane, by John Kyrk Membrane fluidity, from Carnegie Mellon Membrane fluidityfrom John Gianni News: , from ScienceDaily Membrane fusion discovered in 2002, from Brookhaven National Laboratory Video Clips: Hank Green discusses how molecules come in infinite varieties, so in order to help the complicated chemical world make a little more sense, we classify and categorize them. One of the most important of those classifications is whether a molecule is polar or non-polar, which describes a kind of symmetry - not just of the molecule, but of the charge
Explore the types of passive and active cell transport with the Amoeba Sisters! Transport types covered include simple diffusion, facilitated diffusion, endocytosis, and exocytosis.
Hank describes how cells regulate their contents and communicate with one another via mechanisms within the cell membrane.
Paul Andersen describes how cells move materials across the cell membrane. All movement can be classified as passive or active. Passive transport, like diffusion, requires no energy as particles move along their gradient. Active transport requires additional energy as particles move against their gradient. Specific examples, like GLUT and the Na/K pump are included.
Plasmolysis in Elodea plant
Amoebae are single-celled eukaryotes, which can carry out all the functions of life. The fluidity of their plasma membrane allows them to feed through phagocytosis (endocytosis of solids):
The sodium potassium pump, is responsible for maintaining the electrical charge inside the cell and keep the cells resting potential by pumping out sodium ions and pumping in potassium ions with the help of adenosine triphosphate also known as ATP. Leaky ion channels are also responsible for altering and stabilizing the electrical charge inside the cell and keep the cells resting potentia
What are the 4 methods of transport across a cell membrane?Movement of Substances Across Cell Membrane. Simple diffusion.. Facilitated diffusion.. Osmosis.. What are the 4 types of cell transport?There are four types of transport mechanisms in a cell. These are simple diffusion, facilitated diffusion, primary active transport and secondary active transport.
What are the 4 ways substances move into and out of cells?Four ways by which substances move into cells are diffusion, osmosis, active transport and facilitated transport. All this substances passed in, out though the cell membrane. This cells membrane allows only some substances to pass through not others.
What are the 4 main types of passive transport explain?There are four types of passive transport:. Simple Diffusion.. Facilitated Diffusion.. Filtration.. Osmosis.. |