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SB1a - How do you calculate Actual Size?

Image Size / Magnification    


SB1a - How do you calculate total magnification in a light microscope?

Objective Lens x Eyepiece Lens


SB1a - List 3 differences between Light and Electron Microscopes

Electron microscopes produce a much higher resolution image due to the shorter wavelength of electrons Light Microscopes can show a true colour whereas electron microscopes will show a black and white image since electrons don't have a colour spectrum Light microscopes can use a live specimen whereas electron microscopes have to use dead specimens due to electrons having to pass through a vacuum  


SB1a - Draw SI Units Table 


SB1a - What 2 things determine how good a microscope is at showing small details?

* Magnification: How much it can zoom in * Resolution: The smallest distance between two distinctly different points


SB1a - What has the development of the electron microscope allowed us to do?

It has allowed us to see sub-cellular structures as they have a much more powerful resolution and magnifcation


SB1b - How are animal cells different to plant cells?

* Animal cells, do not have cell walls, chloroplasts or vacuoles like plants do. * They only have nuclei, ribosomes, mitochondria, cytoplasm and a cell surface membrane.


SB1b - What do the sub-cellular structures in eukaryotic cells do?

* Cell membrane: controls what enters and leaves the cell * Nucleus: contains DNA that controls cell activities * Cytoplasm: fills the cell and where reactions occur * Mitochondria: Where respiration takes place * Ribosomes: Where protein synthesis takes place Plant only: * Cell wall: Protects the cell * Chlorplasts: Contain chlorophyll used in photosynthesis * Vacuole: Stores cell sap


SB1b CP - How do you use use a microscope?

* Put a thin sample of tissue (e.g. onion epidermis) onto a microscope slide * Add a few drops of a suitable stain/dye (e.g. iodine), so that the sample can be seen * Place a coverslip on top of the tissue and place the slide onto the microscope stage. * Use the objective lens with the lowest magnification, and focus on the sample. * Increase the magnification and refocus to see different features of the cell. * If you record the image you see, note down the magnification it was taken at  Option 2: You microhope you're doing it right 


SB1c - What are the adaptations of the following cells: * Egg cell * Sperm cell * Cilliated epithelial cell * Cells lining the small intestine

Egg cell: Has a haploid nucleus, with a special cell membrane to allow only one sperm cell in and many nutrients in its cytoplasm Sperm cell: Has an acrosome with enzymes to penetrate the egg cell with lots of mitochondria and a tail to swim Ciliated epithelial cell: Lined with cilia and packed with mitochondria this allows the cell to have a 'wavy' movement to move an egg along Microvilli: The cells lining the small intestine have small folds called microvilli which increase its surface area making absroption easier


SB1c - What is the function of a gamete?

* Gametes are sex cells used in reproduction. * Examples are sperm and egg cells.


SB1d - What are the differences between eukaryotic and prokaryotic cells?

 A prokaryotic cell will not contain a nucleus, mitochondria or chloroplasts Eukaryotic cells can be up to x1000 times larger than a Prokaryotic Cell   


SB1d - What are the functions of structures in bacteria?

* Single loop of DNA: Contains chromosomes and genes * Plasmids: Contain additional genes * Flagellum: Used to propel the bacteria * Flexible cell wall: for support * Cytoplasm: Containing prokaryotic ribosomes


SB1e - What are enzymes and what are they made up of made up of?

* Enzymes are biological catalysts that speed up reactions. * They break down proteins/substances called substrates. * Enzymes are made up of amino acids and they are proteins. * They are needed to speed up reactions we cannot live without


SB1e - What are the three main nutrient based enzymes? Where are they found and what do they do?

* Amylase: Found in saliva. breaks down starch into Sugar * Protease: Found in the stomach, breaks down proteins into amino acids * Lipase: Found in the stomach and pancreas, breaks down lipids into fatty acids and glycerol


SB1e - What is a polymer?

* A polymer is a chain of single substances called monomers. * The formation of a polymer is called synthesis. * Enzymes often break down polymers into monomers


SB1f CP - What tests are used to identify main components in food? * Starch * Proteins * Lipids * Sugars

* Starch: Iodine will go from yellow to blue-black * Proteins: Biruet's solution will go from blue to purple * Lipids: Add ethanol and shake - a white emulsion-fatty layer should form if it is present * Sugars: Benedict's solution while heating which will turn anywhere from green to yellow to red, indicating how much sugar is present This is a semi-quantitative test. It mostly gives non-measurable values


SB1f- How can we use a calorimeter?

* Burn a known mass of the food under a boiling tube filled with a known volume of water. * Calculate the change in temperature of the water.


SB1g - How do enzymes work?

* Each type of enzyme is in a shape that is specific to their substrate. * They can be re-used as long as they don't become denatured * The idea that an enzyme bonds with a specific substrate is the lock-and-key mechanism


SB1g - What is the function of the active site of an enzyme?

The active site is unique to an enzyme so each enzyme can only work on specific substrates and is where the substrate must be for anything to take place


SB1g - What is the lock and key model?

The lock and key model is a model of how enzymes work - it compares enzyme action to a lock and key because of how the substrate and active site fit together When the substrate binds to the active site, it forms the Enzyme-Substrate complex. After the enzyme catalyses the reaction, the products are released because they no longer fits tightly into the active site The enzyme is free to be used again


SB1g- How are enzymes denatured?

* Changes in pH and temperature can affect the shape of an enzymes active site. * When the active site can no longer accept any substrates, it is said to have become denatured.


SB1h - Explain how the rate of enzyme reaction is affected by temperature

At very low temperatures, the particles do not have enough energy to move, so the enzyme is inactive; the rate of reaction is very low As the temperature increases, particles begin to move more as they gain kinetic energy; the rate of reaction will increase Eventually, the enzyme reachs an optimum temperature where it is working at it's fastest However, if the temperature increases too far beyond that, the active site will begin to chagne shape and the rate of reaction will decrease Eventually, if high enough temperatures are reached, the shape of the active site is changed to a point where the substrate is no longer able to bind to it. It becomes denatured. 


SB1h - How is enzyme activity affected by pH?

An enzyme has an optimum pH where it works best. The further away from this, it will get slower till it becomes denatured


SB1h- Explain how the rate of enzyme action is affected by substrate concentration

At first, the more substance you use, the higher the rate of reaction as it causes more collisions to occur However, at high concentrations most enzyme active sites conatin substrate molecules therefore there is no benefit to adding more substrate, the rate of reaction won't increase beyond that point


SB1i - How do cells transport substances against a concentration gradient?

* Using active transport which is carried out by transporter proteins on membranes which require energy to run. * They take in the molecule and then change shape to move it through the membrane. * This works against the concentration gradient.


SB1i - What is the difference between diffusion and osmosis?

* Diffusion is when particles move from a high concentration to a low concentration. * In osmosis this is the same principal except across a semi permeable membrane where a solvent moves from and area of high concentration to an area of low concentration


SB1i CP - Describe the method you would use to investigate osmosis through potatoes

* Cut discs of raw potato, blot them dry, and measure their mass. * Put each disc in a sugar (or salt) solution of different concentrations * After 30 minutes, measure the mass of each disc again. * Subtract the initial mass from the final mass of each disc. * Divide this number by the initial mass and then multiply by 100 to give a percentage change in mass. * The highest change in mass means there was the greatest difference between water concentration as osmosis works with the concentration gradient This can work with any semi-permeable membrane


SB1i CP - Explain why potatoes will gain mass when put into a very dilute solution

The concentration of water in the solution will be higher than the concentration of water in the potatoes, so water will move into the potato by osmosis which increases mass


SB1i CP - Explain why potatoes will lose mass when put into a very concentrated solution

The water concentration of the potatoes will be higher than that of the solution, so water will move into the solution due to osmosis. Therefore, the potatoes will lose mass.