required practicals: cells Flashcards
(25 cards)
Where in plants can cells undergoing mitosis be found?
Meristem tissue at shoot and root tips.
What is the mitotic index?
The ratio of cells undergoing mitosis to the total number of cells in a sample
Outline the procedure to prepare a root tip slide
- Warm 1M HCl to 60° in water bath
- Cut a root tip using a scalpel and add to the HCl. Leave for 5 minutes
- Remove from HCl and wash with distilled water.
- Cut tip of root tip and place on slide
- Add a few drops of stain to make chromosomes visible
state the formula for the mitotic index
number of cells with visible chromosomes/ number of cells in sample
State the hazards and precautions for reagents used in mitosis practical (HCl, blue stain)
HCl - corrosive, avoid contact with skin, wear eye protection
Toluidine Blue O stain - irritant, avoid contact with skin, wear eye protection
Scalpel - cut away from fingers
What is the purpose of calibration curves?
Used to determine the concentration of an unknown sample by comparing it to a set of standard values with known concentrations
How is a calibration curve used to find the concentration where sucrose in solution = plant tissue?
(potato practical)
Plot a calibration curve of percentage change in mass against concentration. Find the X-intercept where the plant tissue is isotonic to the sucrose solution
What occurs when plant tissue is placed in a hypotonic solution?
Water moves into the plant tissue by osmosis, plant tissue increases in mass
What occurs when plant tissue is placed in a hypertonic solution?
Water moves out of the plant tissue by osmosis, tissue decreases in mass
Why are the potato discs left in solution for 20 minutes?
To allow time for osmosis until the plant tissue reaches equilibrium with its surrounding solution
What is water potential determined by?
The concentration of solutes
The higher the solute concentration the lower the water potential
What is the first step in investigating effect of concentration on osmosis using potato tissue? (HINT: dilutions)
Make a simple dilution of 1M sucrose to produce 5 concentrations. Add 5 cm³ to 5 different test tubes.
What is the second step in the osmosis investigation procedure (potato preparation)?
Cut a potato into equal sized chips and weigh.
What should be done after placing potato chips in the test tubes?
Leave the chips in each test tube for 20 minutes in a water bath
What is the next step after potato chips have been in water bath for 20 minutes?
Take out the chips, dab the excess water, and weigh them again.
What calculation is performed at the end of the osmosis investigation?
Calculate the percentage change in mass.
Why is percentage change used rather than actual change in mass?
Potato chips may have different starting mass. Percentage change allows for comparison.
Why are the potato chips dabbed dry after removing from the sucrose solution?
To remove any excess water clinging to its surface
Controlled variables in the water potential practical
Volume of sucrose solution
size of potato chips
length of time left in solution
dab each potato disc with paper towels
temperature of sucrose solution
State 2 factors that affect the permeability of cell membranes
Temperature
concentration of solvents (ethanol)
How is beetroot used to measure the permeability of cell membranes
The higher the permeability, the more red pigment that leaks out into the surrounding solution within a given time. A colorimeter can be used to determine the absorbance, hence concentration of pigment
Outline the procedure to investigate the effect of temperature on permeability of cell membranes?
- Cut beetroot into 6 cylinders of equal length
- Place each cylinder in a different test tube with equal volumes of distilled water
- Place each test tube into water baths ranging from 30°-80°c. Leave for 20 mins
- Filter each solution out into a cuvette and measure % absorbance using a colorimeter
What are the safety hazards involved in testing the effect of ethanol concentration on membrane permeability?
It is an irritant, flammable. keep away from naked flames, wear eye protection
Handle hot liquid with care
How does temperature effect membrane permeability?
Increasing temperature increases permeability
