all life consists of cells we can see cells with a normal light microscope and maybe the nucleus but the subcellular structures won't really be visible using an electron microscope however allows us to see far finer details so we can see an image of the organel as such these microscopes have a better resolving power and a higher resolution we say we can calculate the actual size of a cell by knowing the magnification of the microscope magnification is equal to image size divided by object size therefore rearranging this we can measure the size of the image then divide by the magnification and that gives us the actual cell size we put them into two main groups eukariotic cells have a nucleus in which their DNA is found that's your plant and animal cells for example procaryotic cells don't have a nucleus and their DNA is found in a ring called a plasmid both eukaryotic and procaryotic cells contain similar organel or subcellular structures the cell membrane keeps everything inside the cell but they're also semi-permeable which means they allow certain substances to pass through plant cells and most bacteria have an extra cell wall made of cellulose providing a rigid structure for them cytoplasm is the liquid that makes up the cell in which most chemical reactions take place mitochondria is where respiration takes place releasing energy for the cell to function ribosomes are where proteins are assembled or synthesized plant cells also contain chloroplasts which contain chlorophyll where photosynthesis takes place plant cells also contain a permanent vacuo in which sap is stored just for triple bacteria multiply by binary fision so the number doubles every say 10 minutes so if we started with one bacterium after an hour we'd have 2 to the^ of 6 that's 64 after 6 hours that's 36 lots of 10 minutes so in theory we'd have 2 to the^ of 36 that's in standard form 6.87 * 10 10 we can do a practical on this by producing a culture on Ager in a Petra dish using aseptic technique that is making sure nothing else contaminates the culture we lift the lid of the dish towards a flame which causes other microbes in the air to move away and upwards from the dish and it destroys them too using sterilized equipment we can either put a drop of bacteria culture in the middle or spread it all around and put spots of different antibiotics on top instead we put a few bits of taper around the dish to hold the lid on but not all the way around otherwise air will not get in and the bacteria will respire anerobic we then incubate at 25° once the culture has grown we can either calculate the size of the culture from an initial drop or the area in which bacteria did not grow or were killed by an antibiotic to then compare with others in both cases we use p r^ s or pi d^2 over 4 to calculate the area of the circles eukariotic cell nuclei contain DNA which is stored in several chromosomes humans have 23 pairs of these in every nucleus so we call them diploid cells that's not the case for gtes though they have half so just 23 not 23 pairs so therefore we call them haid cells new cells must constantly be made for growth and repair they do this by duplicating by mitosis here's the process the mitosis process the genetic material is duplicated and the number of ribosomes in mitochondria is doubled as well the nucleus breaks down and one set of each chromosome pair is pulled to opposite sides of the cell a new nucleus forms in each of these to house the copied chromosomes and we now have two identical cells by the way AQA just say the nucleus devise which isn't quite right but you will get the Mark if you put it cells specialize depending on the function they need to fulfill for example nerve muscle root xylm flm cells stem cells are those that haven't yet specialized they're found in human and animal embryos and the merry stem of plants that's the top of the shoot stem cells are made in your bone marrow throughout your life as well but these ones can only specialize into blood cells we can use stem cells to combat conditions like diabetes and paralysis in fact right out of the movie the island people are now getting clones of themselves made then harvesting the stem cells as these won't be rejected by the patient personally I think this is a dystopian man-made horror Beyond apprehension you have to weigh up the ethical Arguments for yourself cloning plants can be used to prevent species from becoming extinct or produce crops with specific characteristics diffusion is the movement of molecules or particles from an area of high concentration to an area of low concentration we say they move down the concentration gradient like a ball just rolling down a hill it'll do it by itself this doesn't require any energy input so we say it's passive this will happen across a semi-permeable membrane if the holes are large enough for the molecules to move through for example water can pass through but glucose will not at least not by diffusion anyway osmosis is the name specifically given to the diffusion of water across such a membrane for example if there is a higher concentration of glucose outside a cell the glucose cannot diffuse in to balance the concentration so instead the water moves out of the cell resulting in a decrease in its mass the rate of diffusion on osmosis can be increased by increasing the difference in concentrations increasing the temperature or increasing the surface area this is why the Vil in your small intestin or lumpy as well as alveoli in your lungs and rot hair cells for example too the Practical on osmosis goes as follows cut equal size cylinders from a potato or other vegetable weigh them and place in test tubes with varying concentration of sugar solution after a day or so we remove them dab the excess water off their surface and reway we calculate percentage change in mass by doing final Mass take away initial mass divided by the initial mass time 100 if it's lighter than it was before this must be a negative change in mass we plot these percentages against sugar concentration and we draw a line of best fit where this crosses the xaxis is what concentration should result in no change in mass so no osmosis so this means this must be the same as the concentration inside the pot glucose and other nutrients and minerals can move through a membrane by active transport where carrier proteins use energy to move substances through the membrane as there's energy used this can actually move them against a concent ation gradient for example moving mineral ions into plant root hair cells so I hope you found that helpful leave a like if you did and pop any questions or comments below I'll see you in the next video