Pract pt 3 Flashcards
What is the purple pigment in beetroots?
Betalain
What happens when the cell membrane of a beetroot is damaged? 2
Membrane becomes more fluid and more pigment is released
If proteins become denatured, large gaps in the membrane cause pigment to flood out and darken surrounding liquid
What would an investigation using betalain look like? 3
Investigating effect of temperature, alcohol concentration or pH on beetroot cells
Measuring the amount of betalain pigment released in a set period of time
Would use discs of freshly cut beetroot all of a standardised length and diameter
How would you measure the quantity of betalain released by beetroot cells in an investigation?3
Remove discs from solutions
Use the liquid left behind and measure absorbance or percentage transmission of liquids
Using a blue/green filter, colorimeter or colour standards from serial dilution from known concentrations
What does quantitative mean?
measured by the quantity of something rather than its quality
How do you prepare visking tubing? 2
Wet it and rub together to open it
Tie knot at the end once it’s filled with solution
What is investigated using visking tubing? 3
Which substance can move across the membrane
For example a solution may contain a large molecule like starch and a small molecule like glucose or iodine
Small molecules will move across and big ones will stay put
How can you measure the results of a visking tubing investigation? 4
An indicator can be used to detect the presence of substances
Samples can be taken at short intervals & results recorded
Or an indicator can be placed in solutions at the beginning
Will be looking for colour change to indicate movement of one of the solutions
What happens to the cell membranes of beetroot cells at lower temperatures? 3
The cell membrane remains intact
phospholipid molecules move closer together & permeability is decreased
Very little betalain passes through
What happens to the cell membranes of beetroot cells at medium temperatures? 2
Phospholipid molecules are more fluid & spread further apart
So betalain pigment can cross the membrane more easily
What happens to membranes of beetroot cells at high temperatures? 3
The kinetic energy of molecules is too high and the membrane proteins denature
This increases permeability by creating gaps in the cell membrane
Pigment can flood through the gaps
Why are beetroot cells washed with distilled water/dried before experiment begins? 2
This removes excess surface pigment that’s leaked out of cells that are damaged from cutting
excess pigment would cause an error in absorbance & would distort results
In an experiment where visking tubing filled with starch solution was placed in a boiling tube willed with iodine solution, what was moving across the membrane? the starch or the iodine?3
The starch molecules are too big to move across membrane
The iodine particles are very small & can diffused between phospholipds
iodine moves from area of high concentration to area of low concentration & turns blue/black when it reaches starch
What are the features of a substance that affect it’s ability to pass through a cell membrane? 3
charge/polarity
Solubility
shape- for use of carrier/channel proteins
Why is it necessary to wash the outside of visking tubing before starting the experiment? 2
Removes substances that may have leaked out of visking tubing
which would react with substance that the visking tubing is surrounded by and affect results
In an experiment where visking tubing filled with starch solution was placed in a boiling tube willed with iodine solution why did the starch suspension gradually change colour?
The iodine passes through membrane and reacts with the starch inside the tubing to turn blue/black
How is visking tubing different from cell membranes? 4
Made of a mesh of cellulose fibres, cell membrane has no cellulose
No fluid characteristic
No proteins
No cholesterol
Why is agar jelly used in diffusion investigations?
It’s permeable
How do you prepare agar jelly for an experiment?4
IMPREGNATE the jelly with an indicator and allow it to set
Can pour it into plates and change the temperature and acid concentrations to test their affect on diffusion
cut wells/holes in the jelly and then add acid
can change the surface area:volume ratio by cutting it into cubes of different sizes and investigate its effect on diffusion
How do you measure diffusion in agar jelly?2
Use a universal indicator to test time it takes for cube colour to change from green to red
Or can use phenolphthalein and measure time it takes for cube to change from pink to colourless in presence of acid
How do you work our surface area?
Add the area if each face together
What is the area formula of a rectangle/square? 3
Length x width
How do you calculate volume of a rectangle/square?
length x breadth x height
How do you calculate SA:V ratio?
Surface area/volume and then SD on calculator to get decimal value
What are errors when doing surface area diffusion experiment with agar jelly?3
Hard to tell when centre of cube is completely colourless
Hard to see centre of smallest cube
If cube sits on bottom of beaker, some surface area isn’t available for the acid
Regarding surface area diffusion experiment, why is it important for organisms to have a mass transport system? 5
Larger volume =smaller SA:V ratio
Increased volume= decreased time taken for diffusion
Time taken for essential substances like glucose to diffuse to respiring cells would take too long
Mass transport system allows oxygen & glucose to move around the body faster
This provides substances to respiring tissues at life-sustaining rate
