hi everyone welcome to IGCSE study buddy where you can revise biology topics from the Cambridge IGCSE syllabus this video summarizes topic 1 characteristics and classification of living organisms biology is the study of living things which are often called organisms there are seven characteristics that an organism must have in order to be recognized as a living thing Mrs Green is going to help us with this Mrs Gren is a mnemonic that may help us remember the seven characteristics of living things m stands for movement R stands for respiration s stands for sensitivity G stands for growth R stands for reproduction e stands for excretion and n stands for nutrition movement is an action by an organism or part of an organism causing a change of position or place respiration is the chemical reactions in cells that break down nutrient molecules and release energy for metabolism sensitivity is the ability to detect and respond to changes in the internal or external environment growth is a permanent increase in size and dry Mass reproduction are the processes that make more of the same kind of organism excretion is the removal of the waste products of metabolism and substances in excess of requirements and nutrition is the taking in of materials for energy growth and development let's move on to the concept and users of classification systems there are millions of species of organisms on Earth what is a species a species is described as a group of organisms that can reproduce to produce fertile offspring these species can be classified into groups by the features that they share for example generally all mammals have hair offer are warm-blooded and give birth to life Young next we must know what a binomial system is the binomial system of naming species is an internationally agreed system in which the scientific name of an organism is made up of two parts showing the genus and the species A genus is a group of related species this system allows the subdivision of living organisms into smaller groups the species in these groups have more and more features in common the most subdivided they get in this system the scientific name of an organism is made up of two parts starting with the genus which always starts with a capital letter and followed by the species starting with a simple letter when typed binomial names are always in italics which indicates they are Latin example homo sapien let's learn about dichotomous Keys dichotomous keys are used to identify organisms based on a series of questions about their features dichotomous means branching into two and it helps you identify the name of an organism by giving two descriptions at a time and asking you to choose each choice leads you onto another two descriptions until you end up with the name of the organisms let's look at an example of how we can use dichotomous keys this is a simple question from a past paper where we must choose the correct answer by navigating through the dichotomous Keys there's a picture of an animal given and we may first read through the descriptions in one to choose where to go next the two descriptions are body covered with scales and body covered with hair by looking at the picture we can see that this organism's body is covered with hair so we must go to three the descriptions in number three are has webbed feet or does not have webbed feet you may notice that the organism has webbed feet therefore the answer is C now let's understand what classification means classification basically means putting things into groups the main reason for classifying living things is to make it easier to study them classification systems aim to reflect evolutionary relationships between species traditionally organisms were classified based on the features that they shared so it was understood that the more features they shared the more closely related they were however this method of using similar physical features of species to categorize them has its difficulties and is not enough with the advancement of Technology scientists were able to study DNA sequences of different species and this helped to classify organisms using a more scientific approach this method showed that the more similar the base sequences in the DNA of two species the more closely related those two species are and the more recent they are common ancestor is the first step to classify living things is to put them into one of five kingdoms they are animals plants fungi productists and prokaryotes let's take a look at animals first the main features of all animals are they are multicellular or made of many cells their cells contain a nucleus but no cell walls or chloroplasts and they get their nutrition by eating other living things here's a picture of an animal cell as you can see they have a nucleus cell membrane mitochondria ribosomes and cytoplasm the next Kingdom is plants main features of all plants are they are multicellular their cells contain a nucleus chloroplasts and cell walls made from cellulose and they get their nutrition by making their own food through a process called photosynthesis this is a picture of a plant cell you might notice that in addition to what an animal cell has a plant cell has a cell wall and chloroplasts next let's take a look at the main features that help to place organisms into the kingdom of fungi a mushroom is an example of a fungus fungi are usually multicellular cells have nuclei and cell walls are not made from cellulose they feed by saprophytic nutrition that is Undead or decaying material or parasitic nutrition that is on live material here's an illustration of a fungal cell they have a cell wall but it's not made of cellulose like in the plant cell the main features of organisms in the productist kingdom are most are unicellular but some are multicellular all have a nucleus some may have cell walls and chloroplasts some get their nutrition by making their own food through photosynthesis and some get their nutrition by eating other living things here are some examples of prototist cells as you can see some may have cell walls and chloroplasts and some may not the final kingdom is prokaryote bacteria is an example of prokaryotes the main features of all prokaryotes are they are often unicellular their cells have cell walls that are not made of cellulose and cytoplasm but no nucleus or mitochondria here's an illustration of a typical bacterial cell as you may notice a bacterial cell doesn't have a nucleus instead it has strands of DNA and plasmids okay now that we know something about the five kingdoms let's dive into the animal kingdom and learn how organisms within the animal kingdom can be furthest classified two major groups within the animal kingdom are vertebrates and invertebrates this diagram shows that vertebrates can be further divided into mammals birds reptiles amphibians and fish and invertebrates can be further classified into myriapods insects arachnids and Crustaceans let's learn about vertebrates first vertebrates are animals that have a backbone the five classes of vertebrates are mammals birds reptiles amphibians and fish the first group mammals may be very familiar since we humans also belong to this group some characteristics of mammals are they have fur or hair young feed on milk from mammary glands their heart has four chambers and they have different types of teeth which are in scissors canines primolars and molars cats and elephants are examples of mammals the next group of vertebrates are birds some characteristics of birds are they have feathers they lay eggs with hard shells they have a beak and they have wings instead of four limbs some examples of birds are toucan parrot and Flamingo reptiles are another group of vertebrates they have scaly skin and they lay eggs with rubbery shells snakes crocodiles and turtles are some examples of reptiles amphibians are vertebrates that live on both land and water some characteristics of amphibians are they have moist skin without scales eggs are laid in water lava lives in water so they have gills adults often live on land so they have lungs frogs and toads belong to this group the last group of vertebrates is fish all fish live in water except for one or two types fish have scales on their skin they also have gills and fins so those were the five major groups of vertebrates or animals with a backbone now let's learn about invertebrates you may take a guess invertebrates are animals without a backbone one of the characteristics used to further classify invertebrates is whether they have legs or not arthropods are a group of invertebrates that have jointed legs foreign there are four groups of arthropods and they are myriapods insects arachnids and crustaceans these are the characteristics of the first group of arthropods which is miliapods their bodies have many segments or sections and each segment has at least one pair of jointed legs examples of media pods are centipedes and millipedes insects are the next group of arthropods their bodies are divided into three parts head thorax and abdomen they have three pairs of jointed legs and two pairs of wings Grasshoppers and butterflies are examples of insects the next class of arthropods are arachnids some of their characteristics are that they have four pairs of jointed legs and they breathe through gills called book lungs examples of arachnids are spiders and scorpions the final class of arthropods are crustaceans some of their features are that they have more than four pairs of jointed legs and they breathe through gills they are not millipedes or centipedes crabs and lobsters are types of crustaceans now we will learn how organisms within the plant kingdom can be grouped as we know already at least some parts of any plant are green this is because of the green pigment chlorophyll which absorbs light energy from the Sun for photosynthesis the plant kingdom can be sorted into Ferns and flowering plants flowering plants may be further divided into monocotyledons and dicotyledons let's look at ferns first ferns have leaves called fronds they do not produce flowers but instead reproduce by spores which are present on the underside of fronts flowering plants are the plants that are most familiar to us they reproduce by means of flowers and seeds their seeds are produced inside the ovary of the flower ing plants may be divided into two groups monocotyledons and dicotyledons a cotyledon is a significant part of the embryo within the seed of a plant this table helps to differentiate between monocotyledons and dicotyledons or monocots and dicots for short monocots have a branching root system while dicots have a Taproot system the veins in monocot leaves run parallely and dicot leaves are broader with branching winds monocot flowers have petals in multiples of tree while dicot flowers have petals in multiples of four or five this entire chapter we have been learning about the classification of living organisms so it is important to know that a virus doesn't belong in any classification system viruses are not considered to be living things since they cannot carry out the southern life processes on their own they can only take over another living cell in order to make multiple copies of themselves here's an illustration of a virus a virus is not made of a cell it's simply genetic material surrounded by a protein coat so these are the main things to know from chapter one characteristics and classifications of living organisms hope you found this useful thank you for watching and please don't forget to subscribe to IGCSE study buddy for more biology revision videos bye