Practicals Flashcards
How is bacteria (+ other microorganisms) grown?
In a “culture medium”
What does a culture medium contain?
Which contains carbohydrates, minerals, proteins and vitamins they need to grow
Give 2 examples of a culture medium
- Nutrient broth solution
2. Solid agar jelly
What will bacteria that’s grown on agar ‘plates’ do? (name 2 things)
Either:
- Form colonies on surface of jelly
- Spread out to give an even covering of bacteria
Where aren’t cultures of microorganisms kept above 25°C in lab at school?
Because harmful pathogens are more likely to grow above this temperature
Describe how you can make an agar plate (2 ways)
- Hot agar jelly is poured into Petri dishes
- When jelly’s cooled and set, inoculating loops can be used to transfer microorganisms to culture medium (zigzag streaks across agar surface)
- Alternatively, sterile dropping pipette and spreader can be used to give even coating of bacteria
In industrial conditions, why are cultures are incubated at higher temperatures?
So they can grow faster
Why do you need uncontaminated cultures? (name 2 reasons)
- Contamination by unwanted microorganism will affect your results
- Could also potentially result in growth of pathogens
Contamination can be where microorganisms from:
- Your experiment get into surroundings = cause potential health hazard
- The surroundings get into your experiment and spoil your results
Name 4 ways to avoid contamination (of your culture)
- Sterilise petri dishes and culture medium before use
- Inoculating loop = sterilised by passing it through a hot flame
- After transferring bacteria, lid of Petri dish should be lightly tapped on
- Petri dish should be stored upside down
After transferring bacteria, why should the lid of Petri dish be lightly tapped on?
To stop microorganisms from the air getting in
Why should the petri dish should be stored upside down
To stop drops of condensation falling onto agar surface
Before and after growing microorganisms, what should you do to your hands and work space?
Thoroughly clean them
After bacteria is added to culture medium, what should you do and why?
Immediately close lid to avoid contamination
Describe how you can investigate the effect of antiseptics on bacterial growth
- Mark underneath of nutrient agar plate (not the lid) into 3 equal sections and label each antiseptic
- Put different antiseptics onto three filter paper discs by either (via spreading or soaking them)
- Carefully, lift lid of agar plate and use forceps to put each disc into each section
- Secure lid of agar plate in place using two small pieces of tape
- Incubate plate at 25 °C for 48 hours
Why shouldn’t you seal lid of the agar plate all the way around?
So oxygen can get in, preventing harmful anaerobic bacteria from growing
While incubating the agar plate, what should happen?
- Antiseptic should diffuse into agar jelly
2. Bacteria around the discs should die, leaving a clear zone
How can you measure the clear zone?
- Measure diameter of clear zone around each disc by placing ruler across centre of disc
- Measure again at 90° to the first measurement so = mean diameter can be calculated
Larger the clear zone…
the more effective the antiseptic
Describe how you could investigate the effect of sugar solutions on plant tissues?
- Cut up potato into identical cylinders (using cork borer and trimming) + get some beakers with different sugar solutions in them
- Measure mass of cylinders + then leave one cylinder in
each beaker for 24 hours or so - Then take them out, dry them with paper towel and measure masses again
- Calculate the % change in mass and plot a few graphs etc
If the potato cylinders have increased in mass, what does this mean?
Means water has been drawn in by osmosis (hypotonic solution)
If the potato cylinders have decrease in mass, what does this mean?
Water has been drawn out by osmosis (hypertonic solution)
When observing the effect of sugar solutions on plant tissues, what is the dependent variable?
Potato chip mass
When observing the effect of sugar solutions on plant tissues, what is the independent variable?
Concentration of sugar solution
When observing the effect of sugar solutions on plant tissues, give 4 examples of variables that you’d have to keep the same
- Time
- Volume of solution
- Temperature
- Type of sugar used
When observing the effect of sugar solutions on plant tissues, what are 2 errors that could occur and what would their effect be?
e. g. if water evaporated from beakers = concentrations of sugar solutions would change
e. g. if some potato cylinders are not fully dry = excess water = give higher mass
When observing the effect of sugar solutions on plant tissues, how can you reduce errors (their effects)?
By repeating experiment and calculating a mean % change at each concentration
Describe how you could investigate the effect of temperature on enzyme activity
- Put iodine solution into every well of spotting tile
- Set up water bath at set temp. (e.g. 20°C)
- Put (set vol.) starch solution into boiling tube
- Put (set vol.) amylase solution into different boiling tube
- Place both boiling tubes in water bath and leave them until their contents have reached temperature (check with thermometer)
- Pour amylase solution into boiling tube with starch solution and mix with glass rod
- Immediately, start clock and use continuous sampling to record how long it takes for amylase to break down all of starch
- Repeat whole experiment with different temperatures
What are the difficulties when investigating the effect of temperature on enzyme activity (name 2 things)
- Hard to control heat loss, when removed from water baths
- Iodine was not changing colour (subjective judging statement)
i. e. Starch would set at bottom of container + starch solution was not concentrated enough
When investigating the effect of temperature on enzyme activity, how can you prevent the starch from sinking?
Use more soluble starch solution
When investigating the effect of temperature on enzyme activity, how can you reduce heat loss?
Keeping the reaction in water baths
When investigating the effect of temperature on enzyme activity, how can you make the iodine less dark?
Use a weaker concentration of iodine
When investigating the effect of temperature on enzyme activity, how can you decide the colour change?
- Ask several people to decide when the reaction was completed
- Use reference card or colorimeter
What can you use to detect starch?
Iodine solution
If starch is present, what colour will the iodine solution be?
Blue-black
If starch isn’t present, what colour will the iodine solution be?
Brown
Describe how you can investigate the effect of pH on enzyme activity (7 steps)
- Put iodine solution into every well of spotting tile
- Add amylase solution + buffer solution (with pH of 5) to boiling tube (using a syringe)
- Add starch solution to boiling tube (using different syringe)
- Place both boiling tubes into water bath and leave them until their contents have reached the temperature
- Add amylase solution + buffer solution to starch solution & immediately, mix contents of boiling tube and start clock
- Use continuous sampling to record how long it takes for amylase to break down all of starch
- Repeat whole experiment with buffer solutions at different pH values
Investigating Enzymes Reactions: Describe how to do continuous sampling
- Use dropping pipette to take fresh sample from boiling tube every 30 seconds and put a drop into a well
- When iodine solution remains browny-orange = starch is no longer present
How can you measure your pulse?
Put 2 fingers on inside of your wrist or neck & count number of pulses in a minute
When investigating the effect of exercise on the body, how can you reduce random errors?
Do it as a group + plot average pulse rate for each exercise
Why is measuring lactic acid hard?
Because it’s subjective
Name 2 ways to study distribution of an organism
- Measure how common an organism in 2 sample areas (e.g. using quadrats) and compare them
- Study how distribution changes across an area (e.g. line transect)
Describe how you would compare how common an organism is in 2 sample areas
- Place quadrat on ground at a random point within 1st sample area
- Count all organisms within quadrat
- Repeat steps 1 and 2 as many times as you can
- Work out mean number of organisms per quadrat within 1st sample area
- Repeat steps 1 to 4 in second sample area
- Finally, compare 2 means
How can you pick a random point (when using a quadrat) on e.g. a field? Name 2 ways
- Divide area into grid and use random number generator to pick coordinates
- Throw quadrat with eyes closed
Describe how you could study the distribution of organisms
Line Transect:
1. Mark out a line in area you want to study using tape measure
2. Then collect data along the line via…
…counting all organisms you’re interested in that touch that line
…or, by using quadrats: can be placed next to each other along the line or at intervals
Describe how you could measure the rate of photosynthesis
- Source of white light placed at a specific distance from pondweed
- Pondweed left (placed in sodium hydrogencarbonate) to photosynthesis for set amount of time
- Number of bubbles produced are counted
- Experiment repeated thrice with light source at same distance = mean no. bubbles calculated
- Whole experiment is repeated with light source at different distances from pondweed
Measuring the Rate of Photosynthesis: How can the experiment be altered measure effect of temperature on photosynthesis
- Test tube of pondweed can be put into water bath (at set temp)
- Experiment can be repeated with different temperatures of water
Measuring the Rate of Photosynthesis: How can the experiment be altered measure effect of carbon dioxide on photosynthesis
- Pondweed can be put into test tube with measured amount of sodium hydrogencarbonate dissolved in water (gives off CO2)
- Experiment can be repeated with different conc. of sodium hydrogencarbonate
What is reaction time?
Time it takes to respond to a stimulus
Describe how you could investigate the effect of caffeine on reaction time (be detailed)
- Person being tested = sit with their arm resting on table edge
- Hold ruler vertically between thumb and forefinger + 0 end of ruler = level with their thumb and finger
- Then let go without warning
- Person tested: catch ruler as soon as possible
- Reaction read from top of thumb
- Repeat test several times & calculate mean distance that ruler fell
- Person being tested = drink caffeinated drink, after 10 mins, repeat steps 1-5
When investigating the effect of caffeine on reaction time, what variables do you need to control? (name 4)
- Same person catches ruler each time
- Person should use same hand
- Ruler should be dropped from same height
- Person tested should have no caffeine beforehand
When investigating reaction time, name 3 benefits of using a computer in oppose the ruler test
- Computers give more precise reaction time
- Using computer removes possibility of person predicting when to respond
- Computers give more accurate measurement
Explain how a computer gives a more accurate reaction time
Computer can record reaction time in milliseconds
Explain how a computer gives a more precise reaction time
It removes possibility of human error from measurement (e.g. on ruler)
