Biology - PPE 2
What are the differences between light and electron microscopes?
Light microscopes use light and lenses to form an image of a specimen and magnify it, allowing us to see individual cells. Whereas electron microscopes use electrons to form a picture, they have a higher magnification and a higher resolution.
What is the equation for magnification?
magnification = image size/real size
What are all of the light microscope parts?
Eyepiece - Thing you look through
Coarse adjustment knob - Bigger circle on side
Fine adjustment knob - Smaller circle on side
Stage - The platform
Light - The bright thing
Lenses - To adjust the focus
What are the steps of looking at an onion under a light microscope?
Add a drop of water onto the slide.
Cut up an onion and separate it into layers.
Pick one of the layers and peel off the epidermal tissue (with tweezers) and place it on top of the water on the slide.
Add a drop of iodine solution (this is used as a stain).
Place a cover slip on top of the iodine, specimen and water.
Name 5 specialised cells.
Sperm cell
Root hair cell
Muscle cell
Phloem cell
Xylem cell
What is differentiation?
It is the process by which a cell changes to become specialised for carrying out its function.
How do prokaryotic cells (bacteria) replicate?
Binary Fission:
The circular DNA and plasmids replicate.
The cell gets bigger, and the circular DNA strands move to opposite ends of the cell.
The cytoplasm begins to divide, and new cell walls begin to form.
The cytoplasm divides, and two daughter cells are produced. Each daughter cell has one copy of the circular DNA.
How do you grow bacteria in a lab?
Hot agar jelly is placed in a petri dish.
When the jelly is cooled, the inoculating loops can be used to transfer microorganisms to the culture medium.
Bacteria grown on the agar will form visible colonies on the surface.
The ideal temperature is 25°C or below because harmful pathogens are more likely to grow above 25°C
The microorganisms multiply.
What is diffusion?
Diffusion is the gradual movement of particles from places where there are lots of them to places where there are fewer of them. (High concentration to Low concentration).
What is osmosis?
Osmosis is the movement of water molecules across a partially permeable membrane from a more dilute solution to a more concentrated solution.
What is active transport?
Active transport is the movement of substances against their concentration gradient.
Where does gas exchange happen in people?
It happens in the bronchioles, and on these bronchioles are alveoli.
How are the alveoli specialised to maximise diffusion?
They have a huge surface area (75m²).
They have a moist lining.
They have very thin walls.
They always have a good blood supply.
What is in the digestive system?
Glands - Pancreas, which produces digestive juices
The stomach and the small intestine, which digest food
The liver, which produces bile
The small intestine, which absorbs soluble food molecules
The large intestine, which absorbs water from undigested food
What happens if the temperature of an enzyme gets too low or high?
If it gets too hot, some of the bonds holding the enzyme break.
If the pH is too high or too low, it damages the bonds in the enzyme.
What is amylase an example of, and what does it do?
Amylase is an example of a carbohydrate. It breaks down starch into maltose.
What does protease do?
It breaks down proteins into amino acids.
What does lipase do?
It breaks down lipids into glycerol and fatty acids.
What does bile do?
Bile neutralises the stomach acid and emulsifies fats.
How do you test for sugars in bread?
Prepare 5cm³ of a sample of bread and place it in a test tube
Prepare a water bath set to 75°C
Add 10 drops of BEDEDICTS solution
Place the test tube in the bath and leave it for 5 minutes
If positive, it'll turn from blue to green, yellow or brick red (depending on how much sugar is present)
How do you test for starch in pasta, rice and potatoes?
Prepare 5cm³ of a sample of pasta and place it in a test tube
Add a few drops of IODINE solution and gently shake the tube
If positive, it'll change from browny-orange to black or blue-black
How do you test for proteins in meat?
Prepare 2cm³ of a sample of meat and place it in a test tube
Add 2cm³ of BIURET reagent to the sample and gently mix
If positive, it'll go from blue to purple
How do you test for lipids in olive oil?
Prepare 5cm³ of a sample of meat and place it in a test tube
Add three drops of SUDAN 3 to the sample and gently mix
If positive, the mixture will separate out into two layers. The top layer will be bright red.