Studied by 1 person
Used to replace faulty cells in sick people - insulin-producing cells for diabetes and nerve cells for paralysed spinal injuries
Used to replace faulty blood cells
Large surface area - lots of substances can diffuse at once
Lots of blood vessels - to get stuff into and out of the blood quickly
Thin membrane - short distance for substances to diffuse
Often ventilated - air moves in & out
A single layer of surface cells
A very good blood supply to assist quick absorption
The exchange surface in a leaf is covered in stomata which the carbon dioxide diffuses through
The leaf has a flattened shape which increases the area of its exchange surface, therefore it's more effective
The walls of the cells inside the leaf act as another exchange surface
The air spaces inside the leaf increase the area of the exchange surface which increases the chance for carbon dioxide to enter the cells
-an enormous surface area -a moist lining for dissolving gases -very thin walls -a good blood supply
Add a drop of water to the middle of a clean slide
Cut up an onion & separate it out into layers. Use tweezers to peel off some epidermal tissue from the bottom of one of the layers
Using the tweezers, place the epidermal tissue into the water on the slide
Add a drop of iodine solution - a stain used to highlight objects in a cell by adding colour to them
Place a cover slip on top - stand the cover slip upright on the slide, next to the water droplet. Then, carefully tilt & lower it so it covers the specimen. Try not to get any air bubbles under there - there'll obstruct your view
Clip the slide you've prepared onto the stage
Select the lowest-powered objective lens
Use the coarse adjustment knob to move the stage up to just below the objective lens
Look down the eyepiece. Use the coarse adjustment knob to move the stage downwards until the image is roughly in focus
Adjust the focus with the fine adjustment knob, until you get a clear image of what's on the slide
Draw what you see under the microscope using a pencil with a sharp point
Make sure your drawing takes up at least half of the space available & that it is drawn with clear, unbroken lines
Your drawing should not include any colouring or shading
If you are drawing cells, the subcellular structures should be drawn in proportion
Include a title & write down the magnification that it was observed under
Label the important features of your drawing using straight, uncrossed lines
The circular DNA & plasmid(s) replicate
The cell gets bigger & the circular DNA strands move to opposite poles of the cell
The cytoplasm begins to divide & new cell walls begin to form
The cytoplasm divides & two daughter cells are produced. Each daughter cell has one copy of the circular DNA, but can have a variable number of copies of the plasmid(s)
Warm environment
Lots of nutrients
Place paper discs soaked in different types of antibiotics on an agar plate that has an even covering of bacteria. Leave some space between the discs
The antibiotic should diffuse into the agar jelly. Antibiotic-resistant bacteria that aren't affected by the antibiotic will continue to grow on the agar around the paper discs, but non-resistant strains will die. A clear area will be left where the bacteria have died - an inhibition zone
Make sure you use a control - a paper disc that has not been soaked in an antibiotic. Instead, soak it in sterile water so you can be sure that any difference between the growth of bacteria around the control disc & around one of the antibiotic discs is due to the effect of the antibiotic alone
Leave the plate for 48 hours at 25°C
The more effective the antibiotic is, the large the inhibition zone will be
The Petri dishes & culture medium must be sterilised before use (heating to a high temperature), to kill any unwanted microorganisms
If an inoculating loop is used to transfer the bacteria to the culture medium, it should be sterilised first by passing it through a hot flame
After transferring the bacteria, the lid of the Petri dish should be lightly taped on - stops any microorganisms from the air getting it
The Petri dish should be stored upside down - stops drops of condensation falling onto the agar surface
Cut up a potato into identical cylinders, and get some beakers with different sugar solutions in them: one should be pure water & another should be a very concentrated sugar solution
Measure the mass of the cylinders, then leave one cylinder in each beaker for 24 hours
Take them out, dry them with a paper towel & measure their masses again
If the cylinders have drawn in water by osmosis, they'll have increased in mass. If water has been drawn out, they'll have decreased in mass
The dependent variable is the chip mass & the independent variable is the concentration of the sugar solution. All other variables must be kept the same
Some potato cylinders were not fully dried
Water evaporated from the beakers
The potato chips weren't identical sizes
The volumes of water weren't identical
Stem cells grown in the lab may become contaminated with a virus - this will be passed onto the patient & make them sicker
Some people think that human embryos shouldn't be used for experiments - each one is a potential human life
Scientists should focus more on finding & developing other sources of stem cells
Curing existing patients who are suffering is more important than the rights of embryos
Embryos used in the research are usually unwanted ones from fertility clinics - they'd be destroyed otherwise
Used to produce clones of whole plants quickly & cheaply
Used to grow more plants of rare species - prevents them being wiped out
Used to grow crops of identical plants that have desired features for farmers e.g. disease resistance
