Practical Skills Flashcards
What is an independent variable
This is the characteristic or condition you change intentionally to observe the effect on the dependent variable
What is a dependent variable
This is the phenomenon or condition you aim to observe or measure as a result of the experiment.
What is a controlled variable
This is the condition kept constant to ensure that changes in the dependent variable are due to the manipulation of the independent variable
What is differential staining
This is when multiple stains are used and each stain binds to a specific cell structure, staining each structure differently so the structure can be easily identified
What does acetic orcein do
It binds to DNA and stains chromosomes red
What does eosin do
Eosin stains cytoplasm dark red or pink
What does iodine do
Iodine stains starch blue-black (appears violet under the microscope)
What does iodine in potassium iodide solution do
It stains cellulose yellow
What does haematoxylin do
Stains RNA/DNA a purple/blue colour
What does methylene blue do
It is an all-purpose stain often used to stain DNA blue
How do you mount a wet mount sample
this is used for a variety of live specimens, such as aquatic animals
Use a pipette to put a drop of water on the slide.
Use tweezers to place the specimen in the water.
Put the cover slip on by standing it upright on the slide, next to the water droplet, then carefully tilt it down onto the specimen. Be careful to not add bubbles – these will obstruct the view of the image.
Add a stain. Put a drop on one edge of the cover slip. Put a paper towel on the opposite edge. The paper towel will absorb the stain, drawing it under the coverslip, staining the specimen. (You want to make sure the stain used is not toxic to the live specimen)
How to mount a dry sample
this is used for specimens such as hairs, parts of insects, pollen, parts of flowers etc.
Slice the specimen into a thin piece so light can pass through
Use tweezers to pick it up and put it in the middle of the slide
Put a cover slip on top of it.
How do you calculate the actual length of the species being measured
the number of divisions should be multiplied by the length of one division (you calculated this when you calibrated the graticule).
How do you calibrate a graticule
- Set up the microscope to the required magnification to view the sample.
- Place a stage graticule on the stage.
- Line up the two scales (the stage and eyepiece graticules) similar to the diagram.
- Count the number of divisions on the eyepiece graticule equivalent to each division on the stage micrometre.
- As the length equivalent to each division on the stage micrometer are known, it is possible to calculate the length of one eyepiece division.
What are the rules for drawings
● No shading. Areas that should be shaded should be labelled instead.
● The drawing should take up at least half of the page.
● Label lines must be completely horizontal, drawn with a ruler, exactly touch the object that they’re labelling and must not overlap each other.
● Drawing lines should completely connect and should not be broken
● A scale should be given e.g. for the magnification of the image size.
● They should be drawn in pencil and look like the actual image.
How do you identify the four main vessels attached to the heart during dissection
Identify the four main vessels attached to the heart. Arteries are thick and rubbery, whereas veins are thinner. Identify the coronary artery on the external surface. Locate where the coronary artery connects to the aorta
How do you cut across a stem
You cut the section as perpendicular to the length of the stem as possible and as thinly as possible
What colours does toluidine blue stain tissues
Phloem- red
Xylem- green/blue-green
Sclerenchyma- blue-green/sometimes green
Collenchyma- red-purple
Parenchyma- red-purple
What colour is toluidine blue in non-lignified tissue and lignified tissue
Non-lignified: pink/purple
Lignified: green/blue
When examining a kidney, what is the renal capsule covered in
It is covered in renal capsule
What is below the renal capsule
The cortex
Which part of the kidney is indented
The renal hilium
What are the tubes
The renal vein, renal artery and the ureter
Which tube is likely to have the most adipose (fatty) tissue
The ureter
How does the cortex appear
It appears dense and grainy and it is a lighter shade than the medulla
What are the renal pyramids
These are the many cone-shaped structures in the medulla. They appear stripy because they contain straight sections of the nephrons (loops of Henle and collecting ducts)
What are in between the renal pyramids
Renal columns
What are renal calyces
These are the hollow cavities visible leading from the base of the renal pyramids
What are renal pelvis
Large hollow structure that connects to the ureter
What is random sampling
This is where sample sites are selected randomly
What are the advantages of random sampling
This prevents selective sampling,ensuring the data is not biased
What are the limitations of random sampling
Not all the areas/types of habitat may be sampled equally, leading to inaccurate data. Also, species with a small population may be missed, leading to an underestimate of biodiversity
What is a stratified sampling (non-random sampling)
In this method, the habitat is divided into groups that appear different, and each area is sampled separately. Each group should be mutually exclusive (each population can only be in one group) and collectively exhaustive (no population must be left out).
What are the advantages of the stratified sampling
This ensures that all areas are sampled and prevents small populations from being missed out.
It also allows areas of different population levels in the same habitat to be sampled equally
What are the disadvantages of stratified sampling
This may lead to some over-representation of some areas in the study, for example small areas may be sampled more than necessary because they look different from other areas.
What is opportunistic sampling
This method is when areas are chosen to sample by the researcher either using their prior knowledge, or choosing areas that interest them as they are collecting data.
What are the advantages of opportunistic sampling
This is easier and quicker than random sampling and produces more data
What are the disadvantages of opportunistic sampling
This method has a potential for bias. Species which are more noticeable may be included more often than less noticeable species, leading to an overestimation of their importance, and an inaccurate estimate of biodiversity.
What is systematic sampling
This is when samples are taken at set distances e.g.using a transect
What are the advantages of systematic sampling
This is good to view a change in biodiversity or population along a line
What are the disadvantages of systematic sampling
This method has the risk of missing species as only a small area is sampled. This could cause biodiversity to be underestimated
What is species diversity
This is a measure of the number of different species in a given community
What is a community
A community is the sum of the populations of different species living in the same place and time
Is simpson’s index of diversity
D=1-[sum of(n/N)^2]
What is species abundance
This is a measure of the amount of a certain in a specific habitat
What is species distribution
Species distribution is a measure of where species are located / how species are distributed
When investigating the effect of temperature on catalase activity, what are the independent and dependent variables
Independent variable= temperature
Dependent variable= rate of reaction
When investigating the effect of enzyme (amylase) concentration on the rate of reaction, what are the independent and dependent variables
Independent variable= the concentration of amylase (enzyme concentration)
Dependent variable= rate of reaction
When starch is present what colour does iodine solution change to
It turns dark blue-black when starch is present but remains orange-brown when there’s no starch
When investigating the effect of substrate concentration on the rate of an enzyme-controlled reaction, what are the independent and dependent variables
Independent variable= the concentration of hydrogen peroxide (substrate concentration)
Dependent variable= rate of reaction
How does serial dilution occur
Most methods of serial dilution have a factor of 2, meaning with each dilution the concentration halves.
1. Set up 5 boiling tubes
2. Starting with a 2.00% catalase solution, add 4cm^3 to the first boiling tube.
3. Using a syringe, add 2cm^3 of the solution in the first tube to the next tube. This makes a 1.00% catalase solution
4. Repeat this process to make 0.50%, 0.35% and 0.13% solutions.
Each successive solution is half the concentration of the previous one.
