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AS Biology > Practicals > Flashcards

Practicals Flashcards

1
Q

TOPIC 1A - (1) What does Catalase catalyse?

A

It catalyses the breakdown of hydrogen peroxide into water and oxygen

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2
Q

TOPIC 1A - (1) How do you measure the oxygen released in the experiment?

A

The oxygen displaces water from the measuring cylinder so you measure the empty part of the cylinder

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3
Q

Topic (1) What could you use to hold the cylinder upside down?

A

A stand and a clamp

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4
Q

TOPIC 1A - (1/2) What are the two ways of measuring the rate of an enzyme controlled reaction?

A

1 - You can measure how fast the product of the reaction is made (1)

2 - You can measure how fast the substrate is broken down (2)

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5
Q

TOPIC 1A - (2) What does amylase catalyse?

A

The breakdown of starch to maltose

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6
Q

TOPIC 1A - (general question) MAKE SURE YOU CAN INTERPRET GRAPHS OF ENZYME CONTROLLED REACTIONS. LOOK AT QUESTIONS ON THEM

A

EXAM MATERIAL

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7
Q

TOPIC 1A - (general question) How can you use a tangent to calculate the rate of a reaction?

A
  1. Draw a tangent at the point you want to find out the rate at
    • Work out the gradient at that point (change in y/change in x)
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8
Q

Topic 2A -(1) Describe how you can observe mitosis using root tips (Step 1-5)

A

1- Cut 1cm from tip of growing root (growth occurs here so mitosis also happens here). If you’re using ethano-orcein to stain the cells, the tips will also need to be fixed in ethanoic acid

  1. Prepare a boiling tube containing 1M HCL and put in water bath at 60 degrees.
  2. Transfer root tip into boiling tube and incubate for 5 mins
  3. Use pipette to rinse the root tip well with cold water and then leave the tip to dry on a paper towel
  4. Place the root tip on a microscope slide and cut 2mm from the very tip of it. Get rid of the rest`
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9
Q

Topic 2A - (1) Describe how you can observe mitosis using root tips (Step 6-9)

(DIAGRAM)

A

6- Use a mounted needle to break the tip open and spread the cells out thinly

  1. Add few drops of stain and leave for few mins. The stain will make chromosomes more visible under microscope. Stains include toluidine Blue O, ethano-orcein, feulgen stain (if using feulgen, you’ll need an extra rinse)
  2. Place cover slip over cells and push down firmly to squash tissue. This will make tissue thinner and allow light to pass through it. DONT smear cover slip sideways or you’ll damage the chromosomes)
  3. Now look at all stages of mitosis under microscope
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10
Q

TOPIC 2A - Describe how to observe cells using an optical microscope

A

1- Clip the slide you’ve prepared onto the stage
2- Select the lowest-powered objective lens (one with lowest mag)
3- Use course adjustment knob to bring stage up to just below objective lens
4- Look down eyepiece (which contains ocular lens). Use course adjustment knob to move the stage downwards, away from objective lens, until the image is roughly in focus
5- Adjust focus with fine adjustment knob, until you get a clear image of what’s on the slide.
6- If you need to see the slide with a greater mag, swap to a higher-powered objective lens and refocus

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11
Q

Topic 2A - what is the mitotic index?

A

The proportion of cells undergoing mitosis

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12
Q

Topic 2A - How do you calculate mitotic index?

A

Mitotic index = number of cells with visible chromosomes/total number of cells observed

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13
Q

Topic 2A - What does mitotic index tell us?

A
  • It lets you work out how quickly tissue is growing and if there’s anything weird going on
  • A plant root tip is constantly growing so you’d expect a high mitotic index
  • In other tissue samples, a high mitotic index could mean that tissue repair is taking place or that there is cancerous growth in the tissue
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14
Q

Topic 2A - What should you include in a microscope drawing?

A
  1. The mag that the specimen was viewed under

2. Label the drawing

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15
Q

Topic 2A - (2) What could you use to calculate the size of cells

A

A Graticule and a micrometer

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16
Q

Topic 2A - (2) What is an eyepiece graticule and where is it fitted?

A

It’s like a transparent ruler with numbers, but no units and it is fitted onto the eyepiece

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17
Q

Topic 2A - (2) What is a stage micrometer, where is it placed and what is it used for?

A
  • It is a microscope slide with an accurate scale (with units) and it is placed on the stage
  • It is used to work out the value of the divisions on the eyepiece graticule at a particular magnification
  • This means that when you take the stage micrometer away and replace it with the slide containing your tissue sample, you’ll be able to measure the size of the cells
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18
Q

Topic 2A - (2) Give an example of how the graticule and micrometer could be used

A

1- Line up the eyepiece graticule and the stage micrometer
2- Each division on micrometer is 0.1mm
3- At said mag , 1 division on stage micrometer is the same as 4.5 divisions on graticule (example)
4- So 1 division on graticule is 0.1/4.5 = 0.22mm
5- So if you look at the microscope at that mag and its 4 eyepiece divisions long, you’ll know it measures 4*0.22 = 0.88mm

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19
Q

Topic 2A - (1) What are artefacts?

A

Artefacts are things that you can see down the microscope that aren’t part of the cell or specimen that you’re observing (including dust, air bubbles, fingerprints etc
- They are usually made during the prep of your slides so you must prepare your root tip cells carefully to avoid them

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20
Q

Topic 2A - Why are artefacts especially common in electron micrographs

A
  • Because specimen need a lot of prep before you can view them under an electron microscope
  • The first scientists to use these microscopes could only distinguish between artefacts and organelles by repeatedly preparing specimens in different ways. If an object could be seen with one prep technique but not another, it was more likely to be an artefact than an organelle
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21
Q

Topic 2B - (1) Describe the practical method to investigate how temperature affects beetroot membrane permeability

A

1) Use a scalpel to carefully cut 5 pieces of beetroot (on a cutting board). Rinse the pieces to remove any pigment released during cutting
2) Add the 5 pieces to 5 diifferent test tubes, each containing 5cm^3 of water (use pipette or measuring cylinder to measure water)
3) Place each etst tube in a water bath at a different temperature e.g. 10, 20, 30, 40, 50 degrees for the same length of time. (measure time with stopwatch)
4) Remove the pieces of beetroot from the tubes, leaving just the coloured liquid
5) Use a colorimeter. The higher the absorbance, the more pigment releaser, so the higher the permeability of the membrane
6) You can connect colorimeter to a computer and use software to collect the data and draw a graph of results

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22
Q

Topic 2B - (1) What is a colorimeter and what should you remember to do before using it to test your samples?

A

It is a machine that passes light through a liquid and measures how much of the light is absorbed

  • You should give it 5 minutes to stabilise before using it and you should calibrate it at zero by taking an initial measurement through pure water
23
Q

Topic 2B - (1) What happens to membrane permeability at temperatures below 0? (DIAGRAM)

A

BELOW 0:

  • The phospholipids dont have much energy so they can’t move very much.
  • They’re packed closely together and the membrane is rigid but channel and carrier proteins deform, increasing the permeability of the membrane.
  • Ice crystals may form and pierce the membrane, making it highly permeable when it thaws
24
Q

Topic 2B - (1) What happens to membrane permeability at temperatures between 0 and 45 degrees? (DIAGRAM)

A

BETWEEN 0 AND 45 DEGREES:

  • The phospholipids can move around and aren’t packed as tightly together - the membrane is partially permeable.
  • As the temp increases the phospholipids move more because they have more energy - this increases the permeability of the membrane
25
Q

Topic 2B - (1) What happens to membrane permeability at temperatures above 45? (DIAGRAM)

A

ABOVE 45:-

  • The phospholipid bilayer starts to break down and the membrane becomes more permeable
  • Water inside the cell expands, putting pressure on the membrane. Channel proteins and carrier proteins deform so they can’t control what enters or leaves the cell - this increases the permeability of the membrane
26
Q

Topic 2B - (1) What results show you expect if you tried the permeability practical by investigating the effects of solvents

A

Surrounding cells in an increasing concentration of a solvent (such as alcohol or acetone) increases membrane permeability because the solvent dissolves the lipids in the cell membrane, causing it to lose its structure

27
Q

Topic 2B - (2) - Describe how you can investigate water potential using serial dilution (may use diagram)

A

1) Line up 5 test tubes in a rack
2) Add 10cm^3 of the initial 2M sucrose solution to the first test tube and 5cm^3 of distilled water to the other 4 test tubes
3) Then, using a pipette, draw 5cm^3 of the solution from the 1st test tube, add it to the distilled water in the 2nd test tube and mix the solution thoroughly. You now have 10cm^3 of solution thats half as concentrated as the solution in the first test tube
4) Repeat this process 3 more times to create solutions of 0.5M, 0.25M, and 0.125M

28
Q

Topic 2B - (3) Describe how you could make 15cm^3 of 0.4M sucrose solution by finding the scale factor

A
  1. Star with solution of a known conc, e.g. 1 M
  2. Find the scale factor by dividing the conc of the solution by the conc of the solution you want to make. So 1/0.4 = 2.5
    3) Solution you want to make is 2.5 times weaker than current one. To make solution 2.5 times weaker, use 2.5 times less of it, 15cm^3/2.5 = 6cm^3. Transfer this amount to a clean test tube
    4) Top up test tube with distilled water to get the volume you want to make. So to make 15cm^3, add 9 more cm^3 of distilled water
29
Q

Topic 2B - (4) Describe how to use solutions to find the water potential of potato cells

A

1) Use a cork borer to cut potatoes into identically sized chips, about 1cm in diameter
2) Divide the chips into groups of 3, and measure the mass of each group using a mass balance
3) Place 1 group into each of your sucrose solutions
4) Leave the chips in the solutions for at least 20 mins (making sure they all get same amount of time)
5) Remove chips and pat dry gently with a paper towel
6) Weigh each group again and record your results
7) Calculate % change in mass for each group
8) Use results to make a calibration curve, showing % change in mass against sucrose concentration

30
Q

Topic 2B - (4) What should your results be for the potato experiment?

A

The potato chips will gain water (and therefore mass) in solutions with a higher water potential than the chips, and lose water in solutions with a lower water potential

31
Q

Topic 2B - (4) How would you analyse the point at which the curve crosses the x axis, for the potato experiment?

A
  • This point is where the % change in mass is 0 as the water potential of the sucrose solution is the same as the water potential of the potato cells
  • Find the conc at this point, then look up the water potential for that conc of sucrose potential in e.g. a textbook
32
Q

Topic 3A - (1) Why would lungs deflate by themselves when you blow into it with a bicycle pump or a foot?

A

Because of the elasin in the walls of the alveoli

33
Q

Topic 3A - (1) What is the trachea supported by?

A

Tough Cartilage rings

34
Q

Topic 3A - (1) Why would the lung tissue feel spongy?

A

Because of the air trapped in all the alveoli

35
Q

Topic 3A - (1) What health and safety precautions should be taken when carrying out a lung dissection (including trachea)

A
  1. Wear a lab coat/goggles
  2. Use dissecting tools that are clean, sharp, free from dust.
  3. As Cartilage is tough, use a scalpel to cut it lengthways, down the gap in the C-shaped rings. Cut downwards and don’t apply to much pressure.
  4. Place lungs in a clear plastic bag before you start to stop bacteria in lungs from being released in room
  5. Wash your hands and disinfect work surfaces to avoid bacteria that could lead food poisoning
36
Q

Topic 3A - (2) How should you carry out a fish dissection?

A
  1. Place fish on cutting board
  2. Push back operculum (bony flap) and use scissors to remove gill arches
  3. Examine gill arches to see gill filaments
37
Q

Topic 3A - (2) What health and safety shouldbe taken when dissecting a fish

A
  1. Wear a lab coat

2. Use a cutting board/dissection tray

38
Q

Topic 3A - (3) How would you keep an insect in place to dissect it?

A

Use a dissecting board and put dissecting pins through its legs to keep it in place

39
Q

Topic 3A (3) - How would you examine the tracheae of an insect?

A
  1. Carefully cut and remove the exoskeleton (hard outer shell) from along length of insects abdomen
  2. Use syringe to fill abdomen with saline solution to observe tracheae
  3. Use a microscope to observe rings of chitin in tracheae walls
40
Q

Topic 3A (3) - Why do trachea in insects look silvery grey?

A

Because they’re filled with air

41
Q

Topics 3A (3) - What is the role of the rings of chitin in the tracheae of animals?

A

For support

42
Q

Topics 3A (3) What are the 2 main ethical issues with dissecting animals

A
  1. Some argue it is morally wrong to kill animals for dissections, as its unnecessary killing. Even though, for school dissections, the animals have already been killed for their meat before, some disagree with killing altogether
  2. animals used for dissections are not raised in human way e.g .overcrowding, lack of food, temp extremes, may not be killed humanely
43
Q

Topic 3B (1) What is a potometer used for?

A
  1. To estimate transpiration rate by measuring water uptake of a plant as it is assumed that water uptake is directly related to water loss
  2. To estimate how different factors affect transpiration rate
44
Q

Topic 3B (1) Describe the practical method to investigate transpiration using a potometer

A
  1. Cut shoot underwater to prevent air entering xylem and at a slant to increase surface area for water uptake
  2. Assemble potometer in water and insert shoot underwater, so no air can enter
  3. Remove end of apparatus from water but keep end of capillary tube submerged in beaker of water
  4. Check apparatus is watertight and airtight
  5. Dry leaves, allow time for shoot to acclimatise and then shut tap
  6. Remove end of capillary tube from beaker until 1 air bubble is formed, then put end of tube back into water
  7. Record starting position of air bubble
  8. Start stopwatch and record distance moved by bubble per unit time e.g. per hour. The rate of air bubble movement is an estimate of transpiration rate
  9. Only change 1 variable at a time e.g. temp. All other conditions must be kept constant
45
Q

Topic 3B (1) What is another name for the air bubble in the experiment?

A

The air-water meniscus

46
Q

Topic 3B (1) Why do we need a reservoir of water as part of our potometer apparatus?

A

To return the bubble to start for repeats

47
Q

Topic 3B (2) Explain the method used to observe xylem or phloem in plant tissue

A
  1. Use scalpel (or razor-blade) to cut cross-section of stem and cut sections as thin as possible (makes it easy to see under microscope)
  2. Use tweezers to gently place cut sections in water until you use em. This stops em from drying out
  3. Transfer each section to dish with a stain e.g. toluidine blue O (TBO) and leave for 1 min. TBO stains lignin in walls of xylem vessels blue-green, letting you see position of xylem vessels to examine their structure
  4. Rinse off sections in water & mount each onto slide
48
Q

Topic 4B (1) - describe a method to test the effects of antibiotics on bacterial growth

A
  1. Use wire inoculation loop to transfer bacteria from liquid broth to agar plate - Petri dish containing agar jelly. Spread bacteria over plate using loop
  2. Place paper discs soaked with different antibiotics is various concs, spaced apart on plate. (make sure you add negative control disc soaked only in sterile water) pg 104
  3. Tape lid onto petri dish, invert, and incubate plate at about 25 degrees for 24-48 hrs to allow bacteria to grow
49
Q

Topic 4B (1) - what is the zone of inhibition and what does it tell us?

A

It is the area on the agar plate where bacteria can’t grow and it tells us how well an antibiotic works

50
Q

Topic 4B (1) - why is the use of aseptic techniques important?

A

To prevent contamination of cultures by unwanted microorganisms as:

  1. this can affect growth of microorganism that youre working with
  2. Disease-causing microbes can make you ill
51
Q

Topic 4B (1) - Describe a few aseptic techniques that you must use in this experiment

A
  1. Regularly disinfect work surfaces to minimise contamination
  2. Work near bunsen flame so when hot air rises, microbes are drawn away from culture
  3. Sterilise wire inoculation loop before and after each use by passing it through flame for 5 secs. This will kill any microbes on loop
  4. Briefly flame neck of glass container of broth just after it’s opened and just before it’s closed - this causes air to move out of container, preventing unwanted organisms from falling in
  5. Sterilise all glassware before and after use in autoclave
52
Q

Topic 4B (1) - what is an autoclave?

A

A machine that steams equipment at high pressure

53
Q

What is the difference between a systematic error and a random error?

A
  • A systematic error: An error that continues throughout the length of an experiment due to one thing consistently being a problem
  • A Random error: errors that occurs in some parts of the experiment but not all of them.

AS Biology (12 decks)

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