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Summary of Lab 6 for BIOL 112 (Winter 2011). Week of Feb 14, 2011. It was a lovely week.

Photosynthesis.

Unique to plants (and some bacteria and protists lol)
Pigments capture light energy, convert to chemical energy
- Principal pigments: green chlorophylls
- Two forms: chlorophyll a (blue-green) and b (yellow-green)
- Primarily absorb blue and red light (narrow range of the light spectrum)
- Accessory pigments: less efficient (carotenoids)
  - Absorb blue-green light
  - Examples: carotene, xanthophylls; can come in various colours
- Pigments found in organelles called chloroplasts (where photosynthesis takes place)
The basis process: 6 carbon dioxide + 12 water --> sugar + 6 water + 6 oxygen (from original water molecule)
- The water molecules are split by light
- Measurement of the amount of oxygen evolved can indicate the rate of photosynthesis under different conditions

Procedure:
- Overhead lights turned off
- Assemble manometer
- Fill test tube with sodium carbonate solution (source of carbon dioxide)
- Obtain sprig of Elodea, cut 1cm off broken end, place rest of sprig in test tube (should be no air in test tube)
- Place test tube in rack, fill beaker with cold water, place in front of rack (heat sink, prevent heat from killing Elodea lol)
- Make a light barrier around three sides of the test tube rack
- Start the 30cm mark, leave for 15 minutes; record change in volume
- Same for 5cm mark
- Now, still at 5cm, repeat for three filters: green, red, blue (only the desired colour will pass through)
- Make sure to normalise for 5 minutes to white light before moving to next colour filter
Results:
- Distance: more oxygen evolved when plant is closer to light (greater light intensity)
- Colour: green least, red and blue best
  - Chlorophyll a and b reflect green, but accessory pigments can absorb green etc
  - Absorb red and blue, but blue is better because it has a higher frequency, so more energy etc

Alcohol/acetone (?) extract of leaves provided (pigment solution)
Chlorophyll fluorescence: hold it up to light, intense red colour emitted
- Substance absorbs radiant energy, immediately re-emits some of it (longer wavelength)
Process:
- Use a glass slide, draw pigment onto the filter paper strip many times until dark
- Add petroleum ether: acetone (a bit) to test tube; place paper in it (streak should be above)
- Allow the solvent to move up the paper, 20 mins; pigments separate into 4 distinct bands
  - Top: carotenes (yellow-orange)
  - Xanthophylls (yellow)
  - Chlorophyll a (blue-green)
  - Chlorophyll b (yellow-green)
  - Also, brown bands of photo-degraded chlorophyll and translucent bands of lipid may be seen
- Note: if we had used a pigment that was not soluble in the solvent, it wouldn't have moved at all
- Also, if we used a different solvent, the bands would be different (because of different solubility in the solvent)
More soluble substances move up more (more soluble in the mobile phase etc)

Chlorophyll formation almost always requires light
Demonstration: seedlings of peas, grown in either light or total darkness
Light inhibits growth of the stem in length, but stimulates growth of leaves
Those grown in the dark are longer, but no leaves, and
Red or blue light but not green light are effective for inducing greening
Some plants can form chlorophyll even without light
Chlorophyll formation also requires a certain temperature range and certain ions
A plant grown in the dark might lack chlorophyll because photochlorophyll can only become chlorophyll in the presence of light
- The reaction is quick, so if we leave something in light for a short while, will quickly become green

Geranium plants kept in darkness for 3 days, ensure that reserve food materials (mostly starch) were used up
In leaves, starch is readily degraded to sugar, which then is respired, producing chemical energy
After the starvation period, leaves partly covered with foil
Anyways, results:
- Starch molecules: don't diffuse from light-receiving parts of leaves to covered parts
- Because they are too large
- In some plant parts, starch can be formed even in darkness ... from high concentrations of glucose; energy comes from glucose respiration

Lab 6 summary