June 2015 wjec unit 1 Flashcards
Describe a biochemical test for presence of glucose in the solution?
equal volumes of benedicts reagent and glucose
heat to at least 70 degrees
if glucose is present - solution will change colour from blue through green, yellow and orange until finally a brick red precipitate forms
Explain why a positive result is seen with glucose but not for sucrose?
glucose is a reducing sugar whilst sucrose is a
non reducing sugar
reducing sugars are sugars that can donate an electron
reducing sugar donates an electron to reduce copper (II) ions in copper sulfate solution which is blue
Cu(II) ions - reduced to Cu(I) ions in red copper (I) oxide
if the double helix takes 3.4nm to make 1 complete turn and base pairs are 0.34 nm apart, how many base pair would you expect to find in 5 complete turns?
3.4/0.34 = 10 x 5
50 base pairs
Why the diagram shown above must be DNA rather than RNA?
DNA is double stranded whereas RNA is single stranded
How would an intrinsic protein?
intrinsic proteins extend across both layers of phspholipid bilayer
include transport proteins which would use active transport to more molecules and ions across cell membrane
Use your knowledge of the structure and properties of plasma membranes to explain the results seen one hour after fusion?
Fluid mosaic model
where the proteins are free to move within membrane after fusion, there is new arrangement of proteins
Describe changes that happens to a plant cell during prophase?
envelope disintegrates and nucleolus disappears
chromosomes shorten, thicken and condense
appears as 2 chromatids
chromatids are joined at centromere
spindle forms
Student observed 100 cells and found 5 undergoing prophase
if the total length of the cell cycle = 24 hours calculate length of prophase in minutes?
5/100 x 100 x 24/60 / 20 = 72
= 5 in 24 hours
Vincristine is a chemical which inhibits mitosis by preventing the formation of the spindle fibres
use your knowledge of the cell cycle, explain how the results of the experiment show that vincristine inhibits mitosis?
both show interphase, dna doubles
with vincristine, no halving dna
lack of spindle fibres prevents chromatids, being pulled to poles, therefore no cytokinesis
daughter cells not produced
2 other ways in which cells produced by meiosis would differ from those produced by mitosis?
mitosis produces genetically identical cells whereas meiosis produces genetically different cells
meiosis halves chromosome number + mitosis maintains chromosome number
Definition of water potential?
tendency of water molecules to move out of a system
Why did the student conclude that the water potential of the epidermal tissue was -1120 kPa?
cells - turgid
cells = plasmolysed
50% of cells is plasmolysed - incipient plasmolysis
pressure potential - 0
no net movement of water
solute potential = water potential
so molarity of solution = molarity of tissue
Explain the role of the plant cell wall in maintaining turgidity?
as water enters cell by osmosis
cytoplasm expands
cell wall won’t stretch
cell wall pushes against cytoplasm
generating pressure potenital
Biological catalyst definition?
speeds up the rate of reaction
without being used up
protein produced by cells
