Required Practical's - Biology Flashcards
What are all 6 biology required practical’s?
- Microscopes
- Culturing Microorganisms
- Effects of osmosis on plant tissue
- Food Tests
- Effect of pH on Amylase
- Photosynthesis
What are the parts of a light microscope and there purposes?
- Stage is where you place the microscope slide
- Clips are what hold the slide in place
- Lamp so light from the lamp passes up through the microscope slide.
- Objective lenses for different levels of magnification
- Eyepiece where you can look through and the eye piece has a magnification of 10x
- Coarse focussing dial to move the objective lens up or down.
- Fine focussing dial so you can focus on the cells.
How do you use a light microscope?
Use the clips to hold the slide in place. Then select the lowest magnification objective lens. Position the lens so it almost touches the microscope slide. Do this by turning the coarse focussing dial. Then turn the coarse focussing dial until the cells come into focus.
How do you calculate total magnification?
Total magnification = Eyepiece magnification x Magnification of Objective lens.
What can you see on animal cell inside a light microscope?
- Mitochondria
- Cell Membrane
- Nucleus
- Cytoplasm
What can you see on plant cell inside a light microscope?
- Cytoplasm
- Nucleus
- Cell wall
- Vacuole
- Chloroplasts
What are the two ways to culture bacteria?
- Agar gel plate
- Nutrient Broth Solution
How are agar gel plates made?
They are made out of nutrient broth solution and then to turn them into gel they use agar and then they pour it into a petri dish.
Why do we use agar plate?
So we can clearly see the bacteria grow and also see there colonies.
How do we make sure our agar gel plates do not get contaminated in making?
- First sterilise all petri dishes, bacterial nutrient broth and agar.
- Bacteria are transferred in by the inoculating loop. To sterilise this loop we let it pass through a Bunsen burner flame.
- Then attach the lid with adhesive tape so the lid does not fall off.
- Then you place the agar plate upside down into the incubator and this stops moisture dripping down onto the bacteria and disrupting the colonies.
What is the correct temperature to incubate agar gel plates?
- In school laboratories, we normally incubate bacteria at 25C
- This reduces the chances that harmful bacteria will grow
How do you do the practical the effects of antibiotics on bacterial growth using an agar gel plate?
- Clean the bench with disinfectant solution. This kills microorganisms that could contaminate our culture
- Sterilise an inoculating loop by passing it through a Bunsen burner flame.
- Open a sterile agar gel plate near a Bunsen burner flame. The flame kills bacteria in the air.
- Now use the loop to spread the chosen bacteria evenly over the plate.
- Place sterile filter paper discs containing antibiotics onto the plate.
- Incubate the plate at 25C and leave for a few days.
What is the zone of inhibition?
Around the antibiotic discs we have a region where the bacteria have not grown on the agar gel plate.
How do you do the practical to see the effects of osmosis on plant tissue?
- First peel the potato since the potato skin can affect osmosis.
- Use a cork borer to produce 3 cylinders so they have the same diameter and mass. Then use a scalpel to trim them down to the same length around 3cm each.
- Measure the length by using a rule and the mass by using a balance.
- Now place each piece of potato into a test tube and add 10cm cubed of 0.5 mol sugar solution in one test tube. Then do the same for the second test tube with 0.25 mol. The last one use distilled water only.
- Leave potato cylinders over night to let osmosis take place.
- Remove potato cylinders and gently role on a towel to remove surface moisture.
- Measure length and mass of potato again.
How do calculate percentage change?
% change = Change in value / original value x 100
What does it show if the change in mass decreases and goes across the concentration of sugar solution (x axis)?
The concentration is the approximate concentration inside the cell.
How do you do the food test practical?
- Take the food sample and grind this with distilled water using a mortar and pestle. We want to make a paste.
- Transfer the paste to a beaker and add more distilled water. Stir so the chemicals in the food dissolve in the water.
- Filter the solution to remove suspended food particles. Then place 2cm cubed of food solution to a test tube.
- To test for starch you will put a few drops of iodine and if it is present it will turn from orange to blue - black.
- Testing for sugar you will add 10 drops on benedict solution and place the test tube in a hot water bath for five minutes. If sugars are present it will go from light blue to green to yellow and then brick red.
- To test for protein you will add 2cm cubed of biuret solution and if proteins present it will turn from light blue to purple or lilac.
- To test for lipids do not filter the solution. Then you add a few drops of distilled water then ethanol. Then gently shake the solution and a cloudy white will be shown.
How do you do the practical for looking at the affects of pH on amylase.
- You will put one drop of iodine in each well of a spotting tile.
- There is 3 test tube. In 1 there will be 2cm cubed starch solution. The second one will be 2cm cubed amylase solution. The third one will be 2cm cubed pH buffer solution.
- Place all test tube in a water bath at 30C for 10 minutes to reach temperature.
- Now combine the 3 solutions into one test tube and mix with a stirring rod, Return to the water bath and start a stopwatch.
- In 30 second intervals place a drop of the solution into a well. When the iodine remains orange this shows starch is no longer present. Record this time.
- Now repeat the experiment 7 times using different pH buffers.
What are the problems with the affects of pH on amylase practical?
- We are only taking samples every 30 seconds and it is not approximate to fix this we can do it every 10.
- We are looking for the time when iodine does not go blue and black and sometimes it is not obvious since it is gradual. One way to address it is to get 7 people to decide when the reaction has completed.
How do you do the light intensity on photosynthesis practical?
- Start by taking a boiling tube and placing it 10cm away from an LED light source.
- Now fill the boiling tube with sodium hydrogen carbonate solution.
- Put a piece of pondweed into the boiling tube with the cut end at the top.
- Leave this for five minutes to acclimatise to the conditions in the boiling tube.
- Bubbles of gas will be produced by the end of the pondweed which is oxygen showing photosynthesis.
- Start a stop watch and count the number of bubbles produce in one minute and do this 2 more times and calculate the mean for a minute.
- Then do the same at 20cm, 30cm, 40cm and 50cm.
What are the problems with the light intensity on photosynthesis practical?
- The number of bubbles can be too fast to count accurately.
- The bubbles are not always the same size. A large bubble would count the same as a small bubble.
- To stop this you will use a funnel to catch the oxygen with a measuring cylinder on top filled with water to find out how much oxygen has been produced.
How to do the reaction time practical?
- 2 people will measure the reaction time of one of them. That person sits on a stool with upright posture with his arm over the edge of the table.
- The person 2 will place the meter stick vertically. The 0cm should be between the thumb and first finger of the arm over the table.
- Then the ruler gets dropped at a random time and the other person catches it
- Then record the result and find the length above the thumb.
- Test is repeated 7 time and a mean is calculated.
- Do the same with the other person.
What is the independent and dependent variable of the reaction time practical?
The person having their reaction time tested is the independent.
The dependent is the reaction time.
What are the control variables to the reaction time practical.
- The starting distance between the thumb and the first finger should be kept constant.
- We should always measure the rule ruler at the top of the thumb.
- Keep the conditions of the room the same.
