hello everyone and welcome to the first in a series of regents biology review videos these are meant to help students review essential content for the regents living environment exam done in new york state but they can be used as a refresher on a lot of basic biology topics or for exam review if you're coming from another state as you follow along i encourage you to use the resources linked in the video description and go ahead and subscribe if you find this kind of material useful for biology science living environment exam review the regents living environment exam is a four-part exam it's a mix of multiple choice and open-ended questions and some of it's going to test you on laboratory skills and scientific inquiry this video is going to focus on specific biology knowledge and content from throughout the year and less so on laboratory skills in this video we're going to go over key ideas one through three which is about half of the knowledge of the biology or living environment content knowledge you'll need for this exam you can see what the regents exams are like by going to the region's website and i'll post the link in the video description below as well this will give you a great idea of the kind of questions that are asked the format of the exam and the level of knowledge that you need to be prepared for this test the first thing you probably want to refresh yourself on are levels of organization in life remember life is organized it's one of our characteristics of life we know that a group of organisms of one species and one location is a population and populations can be categorized by functions that they serve right here we're looking at a food web organisms are characterized in different trophic levels or energy levels depending on where they feed and what they consume producers can generate their own food usually from sunlight energy sometimes chemical energy as well consumers consume the producers and decomposers break down organic material from other organisms a food chain shows one pathway of energy flow a food web like you see here can show the interconnectedness of many food chains within a particular ecosystem important word here is an autotroph also known as a producer but these are organisms that can make their own food or are able to form their own organic molecules for food plants are autotrophic heterotrophs are organisms that must consume other organic compounds for food and that means consuming other organisms heterotrophs are consumers for example humans are able to obtain nutrients by consuming other organisms or the products of other organisms right here we're looking at a trophic pyramid at the bottom we have producers then we have our primary consumers followed by our secondary consumers and our tertiary consumers at each level in a trophic pyramid we know that energy is lost usually as heat but up to 90 percent of energy is lost every time you go up a level in an energy pyramid we know that it's more efficient to consume lower on the pyramid than it is to be a tertiary or quaternary consumer in one ecosystem we have lots of biotic living or abiotic factors and an ecosystem is shaped by the interactions between these non-living and living factors in every single environment there is competition between different organisms and interactions between different populations and often within one ecosystem or environment there are natural checks in place that keep populations and ecosystems relatively stable over hundreds or thousands of years though sometimes we might see certain individuals that have what looks like unlimited or exponential growth most of the time most populations will reach what we call as a carrying capacity within a particular environment because there are limited resources within a particular environment like food availability water space at some point those organisms are going to reach the maximum population that that ecosystem or environment is able to sustain and even though that may fluctuate over time a population may be relatively stable once it hits its carrying capacity if we see a sharp decline like this it's probably because there was an introduction of a disease or a new predator or an invasive species let's bring humans back into this equation humans are pretty complex we're made of molecules and groups of those compose our cells groups of cells compose different tissues in our body and different groups of tissues can make up our organs our organ systems are several different organs working together for example our digestive system our circulatory system our respiratory system our excretory system our immune system cetera all of these systems perform different life functions that are essential to our survival we have different specialized cells for different functions in the body and these cells can work together to perform specialized functions one of our characteristics of life is that all organisms maintain homeostasis or stable internal balance organisms have to maintain homeostasis in order to survive often the result of not maintaining homeostasis is often disease or death as an example humans sweat as our body temperature rises usually our brain is going to send signals to our blood vessels to dilate which is going to help us lose heat in the environment then our sweat glands in different parts of the body are also going to secrete fluid then by evaporative cooling our body will start to cool down all of this is part of homeostasis we also can shiver in order to maintain homeostasis and organisms that aren't able to regulate their temperature internally will often move to a warmer location or a cooler location in order to help maintain that stable internal environment these organisms like lizards are ectotherms remember if there's any disruption in a human body system there might be a disruption in homeostasis when we look closer at our cells we know that these are specialized structures with organelles inside of them and organelles are specialized structures with specific functions within the cell we see the mitochondria here we see these dots as representing ribosomes and of course the nucleus in the center of the cell with our dna or our genetic information we see a vacuole for storage here and we see our cell membrane which surrounds the cell and allows for molecules to move in and out our plant cell over here also has a cell wall and a chloroplast as well through diffusion through our cell membranes or through special transport proteins we can get the molecules we need to break down either for energy or other important processes within our bodies generally larger organic molecules need to be broken down before they're taken in by our cells but once they enter the cell our cells can use them as the building blocks for other important molecules within our bodies like i showed you here sometimes the mitochondria might be simplified into an oval with a little squiggle line sometimes it may look a little bit more complex where you can see all of those inner folds or cristae within the mitochondria the chloroplast as well can be a little bit more complex than this drawing here where you can see these stacks of thylakoids where important processes of photosynthesis take place remember our mitochondria within our cells is used for energy production it's the site of aerobic cellular respiration within our bodies a vacuole is used for storage ribosomes are there to make proteins the nucleus is the storage site of dna and eukaryotic organisms and our plasma membrane is a semi-permeable barrier that is made of phospholipids cell wall is there for structure and support and the chloroplast is a location of photosynthesis a few main differences between eukaryotic and prokaryotic cells that eukaryotic cells typically are more complex have membrane-bound organelles are larger and have their dna enclosed within a nucleus prokaryotic cells have very few organelles in fact they just generally have ribosomes and some other internal structures but no membrane-bound internal organelles they'll have a cell membrane they'll have ribosomes and they'll have their dna but it won't be enclosed in a nucleus sometimes they may have cilia or flagellum procratic cells are remember cells like bacteria or archaea they came first in our history of life on earth eukaryotic cells are more complex and they include cells like animals and plant cells cells can also communicate with other cells or other parts of the body through special signaling pathways for example this protein embedded in the cell membrane can receive signals from other parts of the body these are receptor molecules and they play an important role in interactions between different cells for example hormones that are released by different glands in the body will then be sent to different cells within the body for a particular reaction the nervous system will produce signaling molecules like neurotransmitters that will allow us to have different effects within the body as well but if our signaling pathways are disrupted or our receptor molecules are blocked for example our cell communication can be disrupted and the cell or the organism itself and their stability could be affected for example when we consume caffeine caffeine actually blocks the signaling molecule for adenosine which is going to make us sleepway when we don't receive those special signals anymore our body will feel less sleepy and we'll feel less tired single-celled organisms have specialized structures and functions as well that can help them perform tasks similar to that of multicellular organism for example a pseudopod within a particular single cellular organism can help organisms move remember we get a lot of our traits from our genes which are inherited but the expression of our genes can be modified by the environment and we can see this in humans when we see separation of identical twins if identical twin girls are separated at birth and grow up in two different environments in two different households we might see that after 20 years the different girls have different heights and weight this is because each twin was provided a different diet had different physical activities and was exposed to different environmental factors throughout their lives so genes don't determine everything and the environment can have a huge influence on your genes as well most of the traits that we have are actually influenced by multiple different genes at once and in our own nucleus we have thousands of different genes we say genes this is just a section of dna that's going to code for a specific protein dna remember is a nucleic acid it's made of nucleotides and one nucleotide is composed of a phosphate a sugar and then that base and the order of these bases within a dna is going to determine what proteins that dna will code for and those proteins will give us the traits that we have now all of your cells in your body have the same dna however different parts of that dna are turned on and off in different cells so for example your muscle cells will contain the same dna as your skin cells but they won't have all of the dna working all at once it's like a cookbook no one chef is going to cook all of the recipes at once they're going to pull out a few different recipes at a time and cook those for dinner think of the dna like the cookbook of your cells all of your cells have the same cookbook but we're only cooking a few recipes in each different cell we zoom out and we look at multiple nucleotides put together we see that each base either a t g or c is going to connect with a complementary base on the other side dna is a twisted ladder or a double helix and each base will match up with its complement connected by a hydrogen bond our base pairs are adenine and thymine so a always pairs with t and guanine and cytosine g always pairs with c you want to make sure you remember this and try to think of a way that it's easy to stick in your head for example you can think of apple tree good cookie i've also heard all teachers can go whatever sticks in your mind help you remember your base pairing rules this is something that will be important for your biology studies so for example if you need to write the complementary or the matching base pair sequence of this strain of dna you would remember that t pairs with a a pairs with t t pairs with a g pairs with c etcetera etcetera until we get our full strand of complementary dna now remember dna is going to hold the instructions for proteins in a cell that dna will be transcribed into mrna which is our special messenger molecule sent out of the nucleus to where a protein will be built in the ribosome the process of making proteins is called protein synthesis more specifically it's the process by which dna is translated and transcribed into proteins so our dna code is transcribed into mrna our mrna is then translated into a chain of amino acids to form a protein protein molecules are pretty long they're made of 20 different types of amino acids and what's crazy is that all organisms on earth share the same universal genetic code remember that the sequence of amino acids within a protein is going to determine the structure and then the function of that protein if we change the order of amino acids we could change the shape of the protein and we could change how it works now we use all of our knowledge of dna within genetic engineering and biotechnology for thousands of years humans have been doing artificial selection and selective breeding where we have new varieties of cultivated plants and domestic animals because of the ones that we select to breed and pass on their traits we can get a little bit more specific manipulating genes and other organisms though through genetic engineering one of the tools for that is gel electrophoresis also known as a dna fingerprint which is used for forensic analysis paternity testing or studying evolutionary relationships transgenic organisms are organisms like plants animals bacteria that are created for agriculture and industry using genes from multiple organisms for example we can produce bt corn which has specialized genes that can fight off different insects we can also modify bacteria to help us clean up oil spills taking a closer look at gel electrophoresis we know that dna is negatively charged so what we can do is take our dna put it into a specialized gel and run an electrical current through it at the top there's going to be a negative charge at the bottom there'll be a positive charge because dna is negatively charged it's going to go towards that positive end of the gel and we'll start to see the bands of the dna separated because of enzymes that have cut up the dna in special places now here we see evidence from a crime scene and we're going to look at it compared to the dna from different suspects we find we look to see where the bands have matched up and then when we see similar bands we can confirm that the suspect and here with suspect 3 is the one that most closely matches the dna found at the crime scene now we can use similar gel electrophoresis techniques or 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 determine which organisms might be related and where they came from we know that earth's present-day 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 for example if there's a random mutation in this dna where this a is changed into a g this could then produce a different amino acid which could then lead to a different function of a protein and give us a different trait mutations can be caused by different mutagens like radiation or chemicals but they can only be passed onto offspring if they occur in sex cells we have mutations occurring in body cells they're only going to be passed to other body cells that arise from the mitosis or the cell growth of current cells in the body 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 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 when there is more variation within a species and a species is more genetically diverse they are more likely to survive when there's changes in the environment we have different types of adaptations these can lead to the survival of different organisms we know that behavioral adaptations structural adaptations and reproductive adaptations have helped different organisms survive through hundreds and thousands and millions of years we know that billions of years ago life first arose billions of years later then came our multicellular organisms that were much more complex one of the main tools that scientists use for comparing evolutionary histories or relatedness among species is called a phylogenetic tree or a cladogram and we can use this diagram to determine when characteristics arose or how different organisms have been related sometimes we'll see different branching patterns and what we want to do to determine how different species are related is how many branches away from each other they are for example the kangaroo and the human are more closely related because they have a much more recent common ancestor than the human and the shark whose most recent common ancestor would be all the way down here where this branch starts in order to read a tree like this we also might see traits sometimes any organism that comes after a particular trait on the tree will have that trait for example on this particular tree kangaroos and humans have mammary glands but bullfrogs and sharks do not because they come before this trait appears remember that there's no one ultimately evolved organism environments are constantly changing and so populations will continue to change also remember that individuals do not evolve populations evolve and evolution is just the change in different frequencies of different alleles over time sometimes we can have extinction of a species when we don't have adaptive characteristics that are sufficient for survival we do see a lot of extinction in the history of life on earth and most of the species that have ever existed on earth are actually now extinct and we can tell this by the fossil record alright so that was a very quick review of the key ideas one through three and standard four of our living environment or biology curriculum in the state of new york if you're reviewing for the test be sure you stay tuned for our next part in this video series i wish you the best of luck in your exam review make sure you give this video a like if it's been helpful thanks so much for watching