welcome back to our ib biology video series this is the first video in ib biology topic 1 cell biology where we will be looking at cell theory stem cells functions of life and the microscope the cell theory describes the cells found in all living organisms it has three key principles cells are the smallest unit of life all living organisms are made up of cells and all cells come from pre-existing cells all cells are considered to follow these three rules atypical cells are those which do not follow the general trend of other cells you can consider them like exceptions and there are three you need to be aware of the first is skeletal muscle because they are multi-nucleated the second is a septate fungi because they contain hyphae but no septa the third is acetabularia also known as giant algae because they are very large but single celled in general cells can all be different shapes and sizes however as a cell grows it is limited by its surface area to volume ratio as a cell increases in size the surface area to volume ratio decreases this is important as it reduces the speed at which substances both enter and exit the cell this therefore reduces the rate of both energy and heat transfer limiting the rate of metabolism ultimately this restricts the size of the cell hence why most cells are small some cells can change into different types this is the process known as differentiation differentiation can be defined as the development of cells in different ways to carry out specific functions it involves the expression of certain genes in a cell's genome and enables what are called emergent properties emergent properties are characteristics of an organism not evident on a cellular level created by interactions between cells but why can't all cells undergo differentiation well for a cell to be able to divide to form a new type of cell it must be what is known as a stem cell stem cells can differentiate to form any cell in the body when describing stem cells you may hear the terms pluripotent and multipotent so let's take a minute to define these pluripotent is when a stem cell can differentiate to form any cell in an organism multipotent is when a stem cell can differentiate to form many different cells in an organism but not any cell stem cells in humans can be found in three main situations the first are embryonic stem cells these are contained within the embryo as a result they are pluripotent but they are not fully compatible with the human once grown to adulthood the second are called blood stem cells these are found in the umbilical cord of the child as a result they are only multi-potent but they are fully compatible with the grown adult the third are adult stem cells these are found in the bone marrow of an adult like cold blood stem cells they are multi-potent and fully compatible but why are stem cells so important well other than the fact that they formed all the cells in your body they are recently being used to treat diseases there are two main diseases explored in the ib syllabus in this way the first is stargardt's disease this is a form of blindness in children due to a dysfunction of retinal cells in the eye stem cells are injected into the eye where they can then differentiate to form healthy retinal cells curing the blindness the second disease is leukemia this involves the production of abnormal white blood cells to cure this stem cells are extracted from the bone marrow before chemotherapy to kill their remaining white blood cells the stem cells are then reintroduced to the bone marrow where they differentiate to form new healthy white blood cells as you can probably imagine stem cells are incredibly powerful and will pave the way for a new generation of science all organisms can be said to follow the seven functions of life whether they are unicellular or multicellular these functions of life can be remembered using the mnemonic mr g hearn in this m stands for metabolism the complex web of all enzyme-catalyzed reactions in an organism r stands for reproduction the production of offspring g stands for growth the irreversible increase in mass or volume h stands for homeostasis maintaining a constant internal environment e stands for excretion removal of the waste products of metabolism r stands for response reacting to external stimuli and n stands for nutrition obtaining food for metabolism the ib syllabus expects you to be able to complete two different examples in relation to these functions of life let's look at the examples of paramecium a heterotroph and clammydominus an autotroph both carry out metabolism via enzymatic reactions reproduce by binary fission grow by an increase in size carry out homeostasis to maintain internal conditions and excrete via expulsion of waste however for response paramecium reacts to solids whereas clammy dominus responds to light then for nutrition paramecium obtains nutrients via endocytosis whereas clammydominus obtains nutrients via photosynthesis ensure you can give a description of how each of these two organisms fulfill their functions of life it comes up a lot in the final part of this video we will be looking at the most useful tool in biology the microscope the ib considers it important for you to describe both the structure and functioning of a microscope let's start with the structure a microscope shines a lamp through the condenser lens at the stage on which you will have a sample this passes light through the objective lens and nosepiece into the eyepiece through use of the focusing knob one can move the diaphragm up and down and left and right to position the sample as needed you may have heard the term resolution before in the context of a microscope this is the ability to distinguish two objects that are close together the shorter the wavelength the higher the resolution in a light microscope like this one it is done using light which has a long wavelength so the resolution is low transmission electron microscopy is an alternative approach that uses electron beams instead which have a short wavelength producing a much higher resolution in the exam you need to be confident in calculating the magnification of a provided microscopic image to do this you should use the key formula of magnification equals size of the image divided by size of the specimen in this formula your measurements must be in the same units let's look at a question the pollen grain on microscopic analysis was measured to be 50 micrometers wide what is the magnification of this image in the exam you would start by measuring the size of the pollen grain on your paper using a ruler let's say it was 20 millimeters then using the formula and converting our units magnification equals size of the image divided by size of the specimen which would give us a magnification of 400 simple if you are struggling to convert the units for each measurement you may encounter learn this handy table we hope you enjoyed the first video in our ib biology topic 1 video series check out our notes flash cards and questions on our website to reinforce your understanding from this video