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HL Biology (Option G): What is the definition of a hormone, what different types are there (with an example of each) and how do these differ in their modes of action? A Hormone is defined as a chemical messenger secreted by endocrine glands into the blood and transported to specific target cells. You need to memorise all the parts of this definition off by heart! Types of hormone include: 1. Steroid hormones such as Oestrogen and Testosterone 2. Peptide hormones such as Insulin, Glucagon and Anti-Diuretic Hormone (also known as Vasopressin) 3. Tyrosine derivative hormones such as Thyroxine (T4), Adrenaline and Noradrenaline (Obviously there are other examples!) Steroid hormones work by passing through the lipid bilayer of the cell membrane and travelling directly to the nucleus of the cell. Here they have a direct effect on genes by altering the pattern of gene expression (specifically, transcription). You don't need to know this, but it might help you to remember how steroid hormones work if you know that steroids (synthetic versions which are given as a treatment for some diseases) often take a few days to have an effect. This is because they're altering gene expression directly and it takes a little while for the genes to be up-regulated or down-regulated in order to see the effects. Peptide hormones do not enter the cell! Instead they work by binding to receptors on the outside of cells. Receptors are themselves glycoproteins. The hormones attach to the receptor which in turn activates a series of intracellular messengers. These messengers set off cascades of reactions which overall change the actions of the cell. Again you don't need to know this, but I think it helps to remember the difference between steroid and peptide hormones - if you think that things like insulin, glucagon and ADH all need to have very rapid effects in order to maintain important things like blood sugar and blood volume, then you can't afford to spend a few days waiting for the patterns of gene transcription to change (as with steroid hormones). You need a much more instant reaction mediated by secondary messengers setting off cascades within the cell. You only need to be able to distinguish between the actions of steroid and peptide hormones, so don't worry about the tyrosine derivative hormones (although for the record, they basically act just like the peptide hormones do). Revision tip!The best way I found to remember which hormones are of what type and their mode of action is as I described above. Think of steroid hormones as these slow acting things due to the fact they're altering gene transcription and the results take a while to see. Hormones which we don't need quickly and which have effects in lots of different places such as Oestrogen and Testosterone will belong to this group. Peptide hormones are the speed machines with rapid secondary messengers that help us keep a very fine-tuned level of control over things like blood sugar with Insulin and Glucagon both rapidly released. As for the Tyrosine-derivatives, perhaps just that Thyroxine and Tyrosine both start (almost) with Ty! As ever, please ask any questions on this thread or in the Biology forum

IBS has a system set up which allows you to enter in various bits of code and have them appear as mathematical symbols called Tex tags. For instance, rather than writing x^3, you can write . This is a quick guide explaining how to make this work for some of the more common Maths symbols you need for the IB. It may also come in handy as a way to copy/paste in as graphics for IAs, where relevant. For a more comprehensive overview, please take a look at this site: http://en.wikibooks.org/wiki/LaTeX/Mathematics Additional Links (kindly suggested by Chrypton) Detexify - This site contains a white drawing area where you can draw a math symbol that you don't know the LaTeX code for. Very helpful. AoPS LaTeX Guide - A comprehensive guide to using LaTeX. It also shows you how to create good-looking LaTeX documents. Also thanks to Ezeh for suggesting some of the symbols on this list. Skip to: 1 Activating the Code 2 Indices 3 Fractions 4 Binomials and Vectors 5 Square Root 6 Integration & Differentiation 7 Matrices 8 Greek Symbols 9 Trigonometry (sin, cos etc.) 10 Sums & Limits 11 Miscellaneous Symbols 1 Activating the Code To do this, you need to enter whatever piece of Maths you're doing in using Tex tags. You can either type these in directly - [ tex ] content [ /tex ] (without the spaces) OR you can select it from the list shown in the top left of your reply box. Where it says "Other Styles", click and scroll down until you find Tex. 2 Indices Achieved by: x^7 Achieved by: x^{-7} (To include the negative sign in negative indices please enclose it in squiggly brackets { and }) 3 Fractions Achieved by: {n \over k(n-k)} 4 Binomials & Vectors Achieved by: {n \choose k} 5 Square Root Achieved by: \sqrt{\frac{a}{b}} OR Achieved by: \sqrt[n]{1+x+x^2+x^3+\ldots} 6 Integration & Differentiation Achieved by: \int\limits_a^b Achieved by: \frac{du}{dt} Achieved by: \int_0^\infty e^{-x}\,\mathrm{d}x 7 Matrices Achieved by: A_{m,n} = \begin{pmatrix} a_{1,1} & a_{1,2} & \cdots & a_{1,n} \\ a_{2,1} & a_{2,2} & \cdots & a_{2,n} \\ \vdots & \vdots & \ddots & \vdots \\ a_{m,1} & a_{m,2} & \cdots & a_{m,n} \end{pmatrix} Just to sum this one up, basically you start a matrix using the code \begin{pmatrix} You then enter in the terms horizontally, so along the line, using & to indicate the next term e.g. {1,1} & {1,2} & {1,3} Please note that if you wish to enter anything into the matrix which is more than just a letter (e.g. a, b, c) or number (e.g. 1, 5, 10 etc.) such as coordinates which have a comma in the middle (i.e. 1,2 2,2, 3,2 etc.) then you need to enclose those inside these squiggly brackets { and } in order for them to come out properly. So {1,2}, {2,2}, {3,2} as in the example above. This is also true for negative numbers. Basically you can think of it as the squiggly brackets indicating to your browser that all symbols within a term belong together. To indicate that you require a new line in the matrix, use a double backwards slash - \\ Use \end{pmatrix} to close the matrix. To put all this together, say I wanted a 3 x 3 Matrix with a, b, c // d, e, f // g, h, i... I would put in: \begin{pmatrix} a & b & c \\ d & e & f \\ g & h & i \end{pmatrix} 8Greek Symbols Achieved by: \theta \epsilon \alpha \beta \kappa \lambda \delta \mu \pi \sigma \tau \omega Literally a backwards slash followed by the name of the symbol you desire. Note that if you spell the symbol with a capital letter (e.g. \Beta) you will get the capital version B as opposed to spelling it with lowercase (\beta) in which case you get , the lower case version. 9 Trigonometry Achieved by: \cos (2\theta) = \cos^2 \theta - \sin^2 \theta In other words, and can be achieved using \cos \sin \tan 10 Sums & Limits Achieved by: \sum_{i=1}^{10} t_i Where i is the number at the bottom and the top number is the 10. Achieved by: \lim_{x \to +\infty} 11 Miscellaneous Symbols Achieved by: ^{\circ} (This is the degrees sign!) Achieved by: \mathrm{C} (This is to get non-italic text - for instance as in ) This post is still being added to! Please reply with any requests for things to be added to this basic list or clarifications. For anything not on this list, please refer to the site linked to at the top. Thank-you!