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Key concepts in biology 2 - Coggle Diagram
Key concepts in biology 2
Microscopy
Light microscopes
Use visible part of the EM sepctrum (light) and a convex lense to form an image of a specimen and magnify it
Let us see individual cells and large subcellular structures like nuclei and chloroplasts
Used to study living cells
Electron microscopes
Use electrons instead of light to form an image
Much higher magnification than light microscopes
Much higher resolution (ability to distinguish between two points)
Scanning - created 3D images
Cannot view living cells
Let us see ribosomes and plasmids and small viruses and bacteria
This has given us a greater understanding of how cells work
Transmission - created 2D images
Using a light microscope
Preparing a slide
1) Cut up an onion and seperate it out into layers. Use tweezers to peel off some epidermal tissue from the onion
2) Using tweezers, place the epidermal tissue into the water on the slide
3) Add a drop of iodine solution, iodine is a stain and used to add colour to objects in a cell, making them easier to see ( methylene blue can be used to stain DNA)
4) Place a cover slip on the slide, making sure to avoid air bubbles and squashing the cells
Observing the specimen
1) Turn on the Microscope
2) Place the slide on the stage, clipping it in place
3) Select the lowest power objective lense
4) Use the coase knob to move the stage just below the lense
5) Look through the eyepiece lense, use the coarse adjustement knob to move the stage downwards until the image is roughly in focus
6) Adjust the focus with the fine adjustment knob, until you get a cear image
7) If you need to use a greater magnification, swap to a higher powered objective lense and refocus
Magnification
total magnification = eyepiece lense magnification X objective lense magnification
Magnification = image size / real size
Transport in cells
Osmosis
Isotomic - When water potential is the same inside/ outside the cell
Turgid - High water potential inside the cell (Hypertonic - Low outsdie the cell)
Flaccid - Low water potential inside the cell (Hypotonic - High water potential outside the cell)
The net movement of watermolecules across particallly permeable membrane from a high water potential to a low water potential
Type of diffusion
If a cell is short of water, water will move into the cell by osmosis
If a cell has lots of water, water will be drawn out of the cell
Diffusion
Random movement of particles from an area of high concentration to an area of low concentration
Very small molecules can diffuse through cell membranes
Big molecules can't fit through the partially permeable membrane
Passive process, doesn't need energy to make it work
Active transport
The movement of particles against a concentration gradient
Process requires energy
Allows cells to absorb substances from very dilute solution
Allows nutrients to be taken into the blood
Investigating Osmosis
Variables
Independant - Concentration of sucrose solution, 5 different concentrations
Dependant (measure) - Percentage change in mass of pepper samples
Control - Temperature, volume of solutions, time
Method
1) Measure the sample of pepper before starting
2) Select concentration of sodium chloride 0,5,10,15,20% in 10cm3
3) Place the pepper sample in the test tube with sodium chloride
4) After 20 minutes remove the pepper, and dry it
5) Measure the mass
6) Calculate the percentage change in mass
Repeat 3 times to imrpove accuracy
Hypothesis
As higher concentrations of sodium chloride, more mass is lost
At higher concentrations, there is less water, low water potential, this will lead to a greater rate of osmosis outside the cell
For lower concentrations, there is a high water potential inside the cell, so water will move inside the cell, and mass will increase
Calorimetry
Food can be burnt to see how much energy it contains, energy is released as heat
Process
Weigh a small amount of dry food and then skewer it on a mounted needle
Add a set volume fo water to a boiling tube held with a clamp
Measure the temperature of the water with a thermometer, then set fire to the food using a bunsen burner flame
Immediately hold the burning food under the boiling tube until it goes out, then relight the food and hold it under the tube, keep repeating undtil the food won't catch fire again
Measure the temperature of the water and calculate the change in temperature
Calculating the amount of energy
Work out the total energy in the food = mass X temp change X 4.2
Divide the energy my the mass of the food to find the energy per gram