TOPIC 2 practicals

Question 1

Mitotic index of plant root tips: what must be done to the cells in order to see chromosomes inside cells?

Answer 1

cells must be separated and spread out into a layer that is one cell thick

Question 2

How could you determine the water potential of a plant tissue?

Answer 2

• place equal amounts of (dry) plant tissue into different solutions of different solute concentrations/ water potentials
• measure change in tissue mass after 30 minutes
• plot graph of change in mass against solution concentration
• when change of mass = 0 (when graph crosses x-axis) is the water potential of the tissue

Question 3

How is the ELISA test used to detect presence of an antigen in a sample of patients blood?

Answer 3

• add patients sample (with antigens) to slide, in which antigens will attach
• wash several times to remove any unattached antigens
• add antibody that is specific to antigen we are trying to detect (if antigen is present in sample = antibody attaches to antigen)
• wash surface to remove excess antibody
• add a second antibody (with enzyme attached) that binds to first antibody
• add colourless substrate of the enzyme
• enzyme changes substrate into coloured product
  amount of antigen present is relative to intensity of colour