hello everyone and welcome to this year's last minute grass review for AP biology in this video we're going to cover some general tips and pointers for taking the AP biology test some commonly questioned content and some important skill review for things that you may need to know on the day of the test remember this is meant as a fast review it's a cram session it's definitely not meant as introductory content but if you need to go back and review any of these Concepts check out some of the resources on my channel and remember AP biology is a trademark registered by the College Board which is not affiliated with and does not endorse this video if you want to skip the general format and overview section and go straight into the content jump to about 4 minutes in this video and that'll get you started straight away with the biology knowledge lastly I do talk fast so this is a warning that if you're watching this video you may want to slow down the time or if you're pressed for time and you're watching on two time speed just be aware that some of this will seem really fast as I go over the content all right let's dive into the format the test is 3 hours long it is in two parts part one and part two they are both 90 minutes part one is multiple choice questions there are 60 of them part two is six questions those are the free response questions both sections are weighted equally so 50% of your grade comes from part one and 50% of your grade comes from part two remember there are two long and four short biology F frqs each testing different sets of science practices and skills and the multiple choice questions can come individually or as sets with a stimulus on the day of the exam you should bring two pens blue or black ink two number two pencils and a calculator college board has a list of the approved ones it's pretty much any calculator as long as it doesn't connect to the internet you will be provided with a formula sheet from the college board and then some extra paper if you need it to continue writing your free responses if you don't go to the school where you're taking the exam make sure you bring a school ID or a government ID like a driver's license so people can identify you on the day of the test do not bring cell phones or SmartWatches or tablets or cameras they will either be confiscated or you will be removed from the testing area on the free response questions be prepared for two long questions and four short ones the two long ones are more points but all of them are important to try to answer I'll go through some other tips throughout this video but one of the most important ones a lot of teachers say is ATP for answer the prompt so make sure you answer what the question is asking no less no more as far as the topics that are going to show up on the AP biology exam here they are and their percentage breakdowns they're all treated with about similar weights on the exam but natural selection does show a little bit more than some of the other units so make sure that you review topics related to Natural Selection Evolution as much as you can some general tips for the multiple choice questions is to answer all the questions if you're not sure and you're out of time just go ahead and put a random guest you're not going to get penalized for the wrong answer you just won't get points for the correct one a good strategy is to skim the questions first then to read the stem or the stimulus that's the little Reading part above the question some questions have longer paragraphs than others and there are some questions with an experimental description or a diagram and then a set of questions that follow so it's a good idea to skim what you're going to be asked then to do the reading and look carefully for the answers that the questions are asking you about next give yourself about 1 minute per question some of these you may answer much faster but that's okay that's time in the bank remember this is a 90minut question period so if you do 60 Questions one per minute that leaves you about 30 minutes at the end to review your answers or to go back over tricky questions that you might have been stuck on earlier but keep moving forward and try to answer all the questions if not all then as many as you can for the F frqs or free response questions some general tips are to write incomplete sentences avoid bullet points lists outlines and drawings unless they ask you to draw in a specific P space on the test or to make a graph do not obsess over having perfect grammar or spelling points are not counted off for spelling errors or poor sentence structure you do need to be coherent you do need to write legibly but it doesn't have to be a perfect English essay the long F frqs do count for more points so you want to make sure you spend extra time on those and you can avoid lengthy explanations words like thus other words you can avoid are things like love prove and any absolute saying things like always or never lastly if you are asked to round on any of your calculations be sure you know what the place values are so if you're asked to round to the 10th Place know that that's one number after the decimal okay let's dive into some hot topics and content review these are things or themes that come up frequently and we're going to do these in no particular order so hopefully these are all things that you've covered so far in your class this year let's get started let's start with the basic unit of life itself cells all cells are surrounded by a cell membrane a phospholipid bilayer they all contain genetic information mostly DNA and they all contain cytoplasm all living things have a genome and a genome is the entire set of genetic material or all the biological instructions for one organism remember that different units that code for different proteins in DNA are called genes remember that genes code for specific proteins which give cells and organisms their traits but different parts of the genetic instructions are used in different types of cells so not every cell in a multicellular organism expresses the exact same DNA so for example we have neurons and skin cells and red blood cells and they're all going to look a little bit different from each other because they have expressed different sections of the DNA signal transduction Pathways now this was a topic that was really heavily missed on last year's exam so you want to make sure you know that a signal transduction pathway involves a signal transduction and a response these pathways are highly specific and regulated one signal molecule can cause a Cascade effect releasing thousands of molecules in a Cell so that amplification can happen when one single molecule then sets off potentially 10 others and these Pathways could have evolved from a common ancestor millions of years ago remember the result of a signal transaction pathway could be something like gene expression the production of a hormone suppression of a genetic activity or even apoptosis programed cell death so this take a look at this diagram right here this is a simple depiction of a signal transduction pathway we have a hormone or a liend binding to our receptor to start the signal transaction pathway in Signal reception and then we have the Cascade that is going to amplify the signal from the membrane to other affectors within the cell and then finally within the nucleus we see that the final part of this pathway is where our Target genes are reached and we have our response something maybe is turned on a gene is stimulated or something is repressed maybe a gene is turned off hopefully you remember a little bit about protein synthesis where the enzyme RNA prelas is going to synthesize mRNA molecules in the 5 to 3 Prime Direction by reading the template DNA strand in the 3 to 5 Prime Direction so we have our RNA polymerase synthesizing that molecule the MRNA leaving the nucleus and then undergoing certain modifications which we'll get into a little bit later and then in the cytool at the ribosome we have our TRNA bringing around our amino acids and it recognizes each codon with an anti-codon on the TRNA and that amino acid chain is built from the MRNA transcript in procaryotic organisms this happens all at once transcription is coupled to translation but in UK carotic organisms we have this occurring in our different locations once we have our amino acid sequence we can undergo even more protein modifications to get the final functional protein now again there's lots of regulation of genes and transcription and translation some types of gene regulation in procaryotic organisms include operons let's start with inducible operons and it's ual State we do not have transcription happening that's mostly because we have a repressor here that's bound to a section called the operator in this operon now the purpose of these genes Lac Z lack Y and Lac a is to provide instructions for the cell to build parts of proteins to digest lactose if there's no lactose in the cell these genes don't need to be turned on because we don't need any enzyme to digest lactose but when lactose does show up a version of it Alo lactose can bind to the repressor removing it from the operator this allows RNA polymerase to move down the operon and transcription can occur once transcription occurs we have the lack mRNA which can then later be transcribed into a protein that can digest the lactose once that lactose is all gone it no longer binds through oppressor which means it's back on the operator and we cannot have transcription any longer now there are many levels of gene expression and regulation in eukariotic organisms and there's many points at which the transcripts can be changed or modified along the way to becoming active protein there's even pre-transcriptional regulation that can occur a big one to know is part of RNA processing where we have introns and exons our non-coding sequences are introns and then those are later removed so that we only have exons in our final mRNA transcript with alternative splicing we can get multiple versions of mRNA from the same original Gene be sure you know the basics of what PCR is gel electropheresis is DNA sequencing and then bacterial transformation you won't have to detail step by step how these occur or the laboratory procedures for these but you should know the purpose for example PCR is the amplification of DNA to make lots and lots of copies from a small bit gel electropheresis is the separation of our DNA molecules based on size so that we can see any patterns after they're cut with restriction enzymes this is useful for evolutionary analysis as a step in genetic transformation or for forensics and crime scene analysis bacterial transformation or genetic transformation involves the removal of a gene of interest from a particular organism in erting it into a plasma so that our Gene of interest can then be taken up by our organism that will later go and express that Gene as a protein make sure you know the four main categories of biological macromolecules nucleic acids proteins carbohydrates and lipids know their monomers the structure of their monomers so nucleic acids are made of nucleotides proteins are made of amino acids carbohydrates are made of monosaccharides and lipids are made of fatty acids and glycerols focusing really quickly on proteins here we know that proteins are chains of amino acids they're drawn very simply here in the pink but then we can also see the 3D molecular models proteins can have thousands of amino acids and be very complicated with their different folding patterns including active sites that may interact with different molecules now remember the changing shape of a protein may cause it to become inactive so for example if we have a phosphate group that is added to the protein that charge phosphate group could change the structure and shape of the protein which would then change its ability to interact with other molecules and maybe change its function or make it active one of my favorite ways to remember all the steps of cellular respiration is going crazy can offer purpose and that stands for glycolysis the KB cycle and oxidative phosphorilation now it's important to remember the location of all these different steps so glycolysis happens in the cytool outside the mitochondria the citric acid or the KB cycle happens within the mitochondrial Matrix and then finally we have our electron transport chain which is positioned across the inner mitochondrial membrane in order to establish a proton gradient and then this provides energy for oxidative phosphorilation so in this process of cellular respiration and ATP synthesis remember that oxygen is our final electron acceptor at the end of the process and of course cellular respiration and photosynthesis are highly connected especially with the cycling of carbon in the biosphere remember photosynthesis removes carbon dioxide from the atmosphere and fixes that carbon into organic molecules or sugars remember photosynthesis takes place in chloroplast and we think that the very first chloroplast were actually procaryotic organisms that performed photosynthetic like Pathways and that they were engulfed by large single cellular organisms who after a very long time formed a symbiotic relationship together and developed into the chloroplast that we know today this is part of the theory of endosymbiosis and some of the evidence pieces that point to this are the double membrane that surrounds the chloroplast and the fact that the chloroplast itself has its own DNA all right let's get to the good stuff there's two main parts of photosynthesis that we're going to study at the AP biology level we have the light dependent or the light reactions of photosynthesis and we have the dark or carbon fixation reactions now remember all of this is taking place within the chloroplast and the space in the chloroplast is called the stroma but then there's also a third membrane this thid membrane and these membranes are going to be able to provide us with concentration gradients for some really essential parts of the process to happen now the light dependent reactions are dependent on light and so sunlight is going to be absorbed by chlorophyll pigments at first and water one of our main ingredients for photosynthesis is going to enter here now we have complexes of proteins and pigments called photosystems and these photosystems photosystem 2 and photosystem 1 are basically there to split the water and pass electrons down an electron transport change very similar to the electron transport chain that we see in cellular respiration but in this electron transport chain the final electron acceptor is nadp plus which will yield nadph an very important ingredient for the next part of photosynthesis this process also is going to generate a proton gradient and we also have ATP synthes here just like we have in cellular respiration and so at ATP synthes will generate ATP and that ATP will also help with the next part of photosynthesis so again those light reactions take place within the thilo covid or across the membranes of the thilo covid they involve protein complexes called photosystem 2 and photosystem 1 water goes in here water is split here and oxygen comes out of that splitting of the water so all of the oxygen on Earth actually comes from the light reactions of photosynthesis here in AP biology you do not need to memorize all the steps in this electron transport chain or the finer details of it these are the main components you will need to know about this part of the pro process your teacher may go into more detail about the different protein complexes or what's happening with the electrons here but it's really important to know that at the end of the light dependent reactions we have ATP and nadph to power the dark reactions or the carbon fixation reactions that happen outside the thilo covid in the stroma of the chloroplast these reactions are part of a cycle called the Calvin cycle and in the Calvin cycle carbon dioxide enters and eventually with the help of at p and nadph sugars are produced in AP biology you do not need to memorize the steps of the Calvin cycle but you do need to know what goes in and what comes out of it now these sugars are not going to be glucose immediately after the Calvin cycle in fact it takes a couple more turns of the Calvin cycle and a few more steps to get to glucose but you can say sugars or organic compounds are generated here these sugars do contain carbon which comes directly from carbon dioxide that enters the carbon cycle organisms use feedback loops to maintain their internal environments and respond on to internal and external changes feedback loops help organisms regulate homeostasis and the failure to maintain homeostasis can cause disease or death negative feedback loops are very common in organisms these are going to result in the slowing of a process or getting something back to a set point so for example blood pressure blood sugar regulation temperature regulation so that the body can return to the levels at which it needs positive feedback loops are an amplification of a particular output or signal it's going away from homeost basis so for example increased contractions during childbirth the production of milk and mammals or even the ripening of fruit some common topics and themes that show up related to molecules and molecular biology enzymes at high temperatures will unfold or denature or lose their shape and lose then their function so remember an increase in temperature above the optimum range for the enzyme can definitely alter the shape of the active site and reduce a reaction rate water has a lot of very special properties such as high heat of vaporization the fact that it's polar surface tension just to name a few this can relate back to a lot of reactions processes within our bodies and cells including homeostasis for example that high heat of vaporization is involved with sweat because the water and sweat absorbs a large quantity of heat during that liquid to gas phase change which is going to lower body temperature and bring us back to the temperature that our body needs to be you definitely want to be able to recognize how different molecules are going to be able to cross the membrane for example small non-polar molecules like carbon dioxide and oxygen can freely pass through membranes So speaking of membranes cells have membranes that allow them to establish and maintain internal environments that are going to be different from their external environments and then we have internal membranes that are going to help with different cellular processes and it minimizes different interactions that are going to be competing within the cell and increases our surface areas where our reactions can occur and we can also use this as evidence for the endosymbiosis hypothesis but all of these themes are important when we talk about organel now these are the organel that you really should be able to know recognize and understand how their functions work for AP biology there's a lot of other organel out there and some major ones that are not on this list but not in the exam these are the ones that might show up and you might be tested on out of this list the most important ones you really need to know and recognize are cell membranes mitochondria and chloroplast when we're talking about cell membranes remember these are very complex they go beyond just a phospholipid Bayer they have integral proteins that are embedded in the membrane for transport support cell surface reception cell identification other activities they also have carbohydrates and cholesterols in the membrane so be able to recognize how membranes are going to contribute to cell structure function communication a lot of other themes and processes mitochondria and chloroplast of course are going to show up when we talk about cellular energetics we already talked about mitochondria and chloroplast a little bit with endosymbiosis but make sure you're very familiar with them their role and their structure for both cellular respiration and photosynthesis one thing to remember about mitochondria specifically is that mitochondria have their own DNA this can often throw a loop in some patterns of inheritance we'll talk about those in a minute so remember that unlike nuclear DNA which can come from both parents mitochondrial DNA is only inherited from the mother through maternal inheritance if we look back at our organic compound structure each nucleotide has a phosphate a sugar and a base atg or C and so when we put these together A's and T's we can see always pair together with these are little hydrogen bonds in the middle G's and C's always pair together and the backbone of the DNA molecule is made of phosphate and sugar molecules and to contrast it RNA is single sided it does have structural similarities to DNA it still has a sugar a phosphate group our nitrogenous base but RNA has osell DNA has thyine DNA obviously is double stranded and DNA usually is just stain put in the nucleus and UK carotic organisms whereas RNA is going to leave the nucleus to perform the other steps of protein synthesis another Hot Topic topc is the cell cycle and checkpoints there's a number of internal controls or checkpoints that are going to regulate progression through the cell cycle you don't need to know specific cycle independent kindness pairs or specific growth factors but do know that if something is wrong or if there is an error detected within the cell cycle typically the cell will commit apoptosis again program cell death but errors in that cycle or errors in recognizing those steps could also lead to uncontrolled cell growth disease like cancer or we have uncontrolled cell division or unregulated cell division now speaking of cell division and reproduction mitosis is going to produce two genetically identical daughter cells make sure you review different types of reproduction meiosis is going to produce cells with half the normal amount of genetic material generally going from diploid to haid cells and these are gamt or sex cells there's a lot of different steps that contribute to genetic diversity first of all we have independent assortment where we have a lot of different possibilities of orientations of how the chromosomes could line up there's random fertilization which again happens after but we need to be able to create these haids to be fertilized beforehand and then during crossing over we can have a bunch of different combinations of information familiarize yourself with errors or Consequences if some steps in the process of meiosis go wrong make sure to review cell transport situations while water move by osmosis from areas of high water potential to areas of low water potential this is is probably going to be recognizing where water would move within a certain situation is probably more likely to show up on the exam than an actual water potential problem as far as genetics goes inheritance patterns that might show up include single gene or monohybrid inheritance di Hybrid inheritance is a possibility as well where we're tracking two genes sexlink inheritance where we have a trait generally it's going to be an xlink sexlink trait that we're tracking remember males only need one copy of those in order to display the trait female need to if it's recessive we can talk about genetically linked inheritance these are when two genes are close together on chromosomes so typically they're inherited together and then inheritance of things like traits and mitochondrial DNA remember your mitochondria is going to come from the egg or the ovom and so that is going to be inherited from the mother as far as the ecology and the environment there's a lot of related topics that could show up on the exams a very common one is environmental impacts on molecular functions or environmental impacts on gene expression so recognize how certain genes can be turned on or off or have extra expression due to certain environmental factors environmental pressures can also strongly influence natural selection so make sure you connect those ideas and then of course population interactions like symbiotic relationships predation and lots of community ecology topics could show up here and there one last thing to add is that biodiversity or increased biodiversity in an ecosystem will increase resilience of that ecosystem so if there's any disruption like a disease the more likely the area is to recover than a less biodiverse ecosystem we know that organisms have different strategies for regulating body temperature so a type of homeostasis uh two main ones are endotherms and ectotherms where endotherms use their metabolism so thermal energy from their metabolism to generate the warmth that helps them maintain homeostasis to the temperature that they need to be ectotherms though are dependent on the environment so they can regulate their temperatures through behaviors like moving into the Sun or moving into the shade like like lizards here sitting on a rock which can help them regulate their internal body temperatures now when we talk about energy availability typically smaller organisms have higher metabolic rates they have higher energy needs so something like a fly or a small rodent is going to have a higher metabolic rate than a larger organism like a cow for example and in general obviously organisms consume other organisms to gain energy and a net gain of energy is going to result in growth for the organism and storage of energy and overall survival a net loss of energy we get a loss of math mass of the organism and then later death for the organism this is a typical trophic or energy pyramid that you might see in a diagram for AP biology there's different types of pyramids too like pyramids of biomass and pyramids of numbers but here what we're looking at are these different trophic levels or levels that that organisms feed at and we want to keep in mind that at every level we have a significant amount of energy lost so it is inefficient we have about a 90% energy lost every single time we go up a trophic level we often talk about core features that are conserved across all domains of life and currently scientists organize life into three main domains bacteria ARA and ukara you're probably most familiar with the eukariotic organisms which are then further organized into kingdoms now when we establish these groups or relationships between different organisms uh we can organize them in different ways one way to display how organisms are related is through a diagram called a philogenetic tree or a cladogram and these can be drawn in many different ways but it's a model that helps us visualize relationships between organisms and we can see different branching lines and different directions for how groups have evolved or how they're related and so a group is typically at the end of a branch and we can work backwards to see where a common ancestor might have existed between two different organisms or two different organismal groups we also might see hash marks or these lines here representing different traits that have evolved at different times within evolutionary history so anything that comes after a particular trait means it has it so for here with seeds it means that anything that comes after the seeds Mark like pine trees and flower and plants have seeds as a characteristic now we can use other biochemical evidence to help us determine which proteins and DNA are similar in different organisms this helps us construct our tree of life and gathers more evidence for evolution helps us figure out how different organisms are related to each other we can also use embryonic development fossil evidence or morphology or different physical characteristics to to determine which organisms might be related and where they came from we know that Earths present a species developed from earlier distinct species when we get new combinations of existing genes or mutations in genes and these are inherited they can be passed on to offspring and we can see variations in populations over time organisms that are better adapted to their environment are more likely to survive and reproduce and pass on their genes to the Next Generation for example if we have a population of bacteria and some of those bacteria are naturally resistant to antibiotics we treat that population with antibiotics only the ones with the resistance Will Survive then that gives way to give the opportunity to the resistant bacteria to survive and reproduce and pass on the resistant Gene to their offspring and what we've done here is created an antibiotic resistant population the resistant bacteria were more fit and they have survived and reproduced at a greater rate than non-resistant bacteria and anything we talk about with evolution is that there is variation within populations now we can get genetic variation in a population through a variety of ways we've mutation genetic drift and sexual selection as well as artificial selection remember that evolution is the change in the genetic makeup in a population over time not just the changing of one organism individuals don't evolve populations evolve so humans can impact the diversity within a population either making it more diverse less diverse or favoring a certain trait for our benefit the way we do this is by controlling which organisms reproduce certain traits in cows for example milk yield milk production over the years has increased in certain dairy cows because we select the ones that produce the most milk and choose those to go on and breed to produce more for the production of more milk also going to mention convergent evolution which is not always a type of artificial selection in fact it's its own type of evolution this is when we see similar selective pressures that lead to similar phenotypes in very different populations or different organisms one of the most commonly used examples of this is how birds and bats both evolved flight separately and independently what happens is that environmental pressures are going to cause certain traces to be more favorable within a population and then those individuals will survive and reproduce so we could see this in body plans of certain species we could see this in drug resistance in certain pathogens again that's Human Action because we've created those drugs we've seen this in anti-freeze proteins in particular fish both in the Arctic and in the Antarctic two different species two different locations but similar selective environmental pressures are going to produce a similar type of protein for these fish to survive well Hardy Weinberg is actually an equation that we can use to determine the frequency of alals in a population at a given time Hardy Weinberg is used as a model for describing and predicting alic frequencies in nonevolving populations remember it represents ideal populations that aren't changing and since natural populations do change Hardy Weinberg provides us with a baseline to gauge that degree of change now there's two equations you're going to need to know in order to do Hardy wiberg problems so these are provided to you on the formula sheet that you'll get for the AP biology exam so there's no need to memorize that so p is going to equal the frequency of the dominant alal in a population sometimes we represent that with a capital letter like big a next up Q is going to represent the frequency of the recessive Al in a population so for example little a p^ s is the frequency of homozygous dominant genotypes in the population so for example big a big a 2pq is going to be the frequency of the heterozygous genotype in the population so big a little a and then you guessed it q^2 is going to represent the frequency of the homozygous recessive genotype and a populational design make sure you recognize how we measure dependent variables remember these are the things that are measured and how we take our data in the experiment independent variables are the things that are changed tested or manipulated think I the experimenter what am I changing for the independent variable and D what am I measuring for my data for the dependent variable when it's asking you to make a prediction make sure you state something specific don't just say I think this variable will change or I think there will be a different you do want to make sure that you include whether it's an increase a decrease death growth whatever but you don't need to include your justification unless it asks you to justify which it probably will on a particular step of the frq but answer what the question is asking don't do more don't do less now you will have to create some sort of graph on the AP biology exam make sure you choose the most appropriate graph to explain your data I do have a whole video on that if you'd like to check it out line graphs usually show a change over time bar graphs usually display the comparison of different different categories you might have to draw a scatter plot as well it is unlikely you would have to create a pie chart for the AP Bio exam more than likely you'll probably have to create a line or a bar graph just make sure you choose the appropriate one for the exam remember if error bars are not overlapping there is a statistically significant difference between the values which means our experimenters can consider the measured values as not the same but if the a bars are overlapping at any point then we can probably say there is not a statistically significant difference between the values and probably not a statistically significant difference in the data as far as the math there are some equations on your formula sheet that you probably shouldn't waste too much time on because it's not likely they'll show up on the exam and that's standard deviation standard error of the means surface area equations and pH equations they are on the formula sheet but it's not likely you'll see them on the test equations you should be familiar with are things like the Ki Square the Hardy Weinberg equations water potential population growth and caring capacity and maybe Simpsons diversity index I do have a longer video going through examples of each of these so be sure to check that out if you're interested in doing a fast AP biology math review but really quickly I wanted to highlight Ki Square because this is something that a lot of students get stressed out about it is used in science to test if data that you observe from an experiment is the same as the data that you would expect to come or predict from the experiment what's really important in ki square is to know how to do it and how to interpret the results sometimes you'll use this in a genetics problem and if you're using it in a genetics problem you'll probably State a null hypothesis some something like the data are consistent with the predicted method of inheritance you calculate your Ki Square value and then you make sure you know your degrees of freedom which is the number of categories total minus one in this particular case if we're looking at colors we have 1 2 3 4 5 six colors minus one that would be 5 degrees of freedom after we got our Ki Square value we would look at that on our critical value table and we would see if our Ki Square value was greater than the critical value in the chart please go back and check out my Kai Square video or my AP biology math video if you want to see a full example of this here are some examples of null hypotheses which you might need to be able to State again if you're talking about a null hypothesis in genetics you would say something like the data are consistent with the predicted method of inheritance if you reject a null hypothesis that means that there is some difference in the data in the experiment and that the variables did have an effect on the particular outcome of the experiment okay so I have lots of other AP biology resources study plans stats practice even some fq tips on this channel so if you're taking the exam this year and you have some extra time to prep be sure to watch those videos so you're totally prepared for the exam format test content and all the tips and tricks students need to be successful on the AP biology test good luck on your exams thanks so much for watching give this video a like if it's been helpful and I'll see you later