PAGS

Question 1

whats a respirometer

Answer 1

• apparatus used to measure the rate of respiration of living organisms by measuring the rate of exchange of oxygen and carbon dioxide

Question 2

describe the principle behind the respirometer

Answer 2

• organisms that are respiring aerobically absorb oxygen and give out carbon dioxide
• if the carbon dioxide is produced is absorbed by sodium hydroxide solution or solid soda lime then the only volume change within the respirometer is due to the volume of oxygen absorbed by the organisms
• if oxygen is absorbed from the tube containing the organism then that tube has a reduced volume of air in it, exerting less pressure than the greater volume of air in the other tube, as a result the coloured liquid in the manometer tube rises up towards the respriometer tube
• the original level of liquid is in the manometer tube is marked and the radius of the bore in the capillary tube is known, the volume of oxygen absorbed during a specific period can be calculated
• reset the apparatus the syringe is depressed to inject air into the system and reset the liquid in the manometer tube back to its original position, allows reading of the volume of oxygen absorbed by noting the change in level of syringe plunger as measured from the graduated scale on the syringe level

Question 3

how do you set up the respirometer

Answer 3

1. after placing the coloured liquid for example methylene blue solution that has one drop of detergent added to it, into the manometer tube, the apparatus is connected with the tape open, this enables the air in the apparatus to connect with the atmosphere
2. mass of living organisms be used should be found
3. with the taps still open the whole set up with the living organisms in place is placed in a water bath for at least 10 minutes until it reaches the temperature of the water bath
4. the syringe plunger should be the near the top of the scale on the syringe barrel and its level noted
5. the levels of coloured liquid in the manometer tubes marked with a felt tip pen
6. taps are closed and the apparatus left in the water bath for a specific period such as 10 minutes
7. the change in level of manometer liquid can be measured and teh syringe barrel depressed to rest the apparatus, also allows you to measure the volume of oxygen absorbed
8. then you can calculate the volume of oxygen per minute per gram of living organism

Question 4

how do you measure the effect of temperature

Answer 4

• use respirometer
• readings should be taken at each temperature
• organisms need to adjust to the new temperature
• 10-40 degrees for living organisms otherwise fungi

Question 5

respriaiton rate in yeast

Answer 5

• respirometer used so that a suspension of yeast with differing concentrations of glucose in solution is placed in one of the tubes,
• sodium hydroxide solution is omitted then the evolution of carbon dixoide during a specific time period can be measured

Question 6

Practical investigations into respiration rates in yeast

Answer 6

• yeast can oxidise ethanol under aerobic conditions
  1. pour 50cm3 of cider into each of the conical flasks
  2. using a clean pipette, add one drop of yeast suspension to each conical flash make sure before taking the yeast suspension from its flask that the flask is swirled to mix its contents
  3. place four layers of muslin, cheesecloth or tights material over the mouth of each conical flask and secure with an elastic band, this allows oxygen t enter the flask but keeps out dust and contaminants
  4. leave the flask in a warm place for about a week
  5. mix the contents of each flask thoroughly by swirling and using a clean pipette withdraw some of the flask contents and place a drop onto a haemocytometer slide with its coverslip in place
  6. count the number of yeast cells in the centre square and each corner square, in each square where cells are counted some cells may be lying on boundaries, in this case only the cell touching the north and west side of the square are counted as well as cells within the boundaries of that square
  7. each of the five squares where you counted contain 16 smaller squares so out counted cells in 80 very small squares having a total volume of 0.02mm3
  8, if you multiply the cell count you obtained by 50,000 you will find the number of yeast cells per cm3
  9. carry out three counts for each size flash, calculate the mean number of yeast cells per cm3 for each flask
  9. draw the graph

Question 7

Photosynthetic pigments PAG

Answer 7

• easily separate pigments in chlorophyll by scapign or mashing a green leaf
• you can do this using two microscope slides
• then spot the chlorophyll onto a slide coated with TLC material
• chose a suitable solvent such as ethanol
• when a solvent creeps up the slide the pigments separate out because they have different Rf values
• make sure there are no naked flames around ethanol or another highly flammable solution and avoid any leaves that are known to provoke an allergic reaction and wash hands after use

Question 8

How to set up a photosynthometer

Answer 8

• no air bubbles in the capillary tubing
• gas given off is collected in the syringe
• gas bubble can be moved into part of the capillary tube against the scale and its length measured
• if the radius of the capillary tube bore is known then volume can be calculated
• same apparatus has to be used throughout the experiment

Question 9

investigating the effect of light intensity on the rate of photosynthesis

Answer 9

1. remove the plunger from the syringe and allow a gentle stream of tap water into the barrel of the syringe until the whole barrel and plastic tube are full of water
2. replace the syringe plunger and gently push water out of the flared end of the tube until there is no air bubbles in the water of the capillary tube
3. cut a 7cm length of well illuminated Eloeda and make sure that there are no air bubbles in the water of the capillary tube
4. stand the boiling tube in a beaker of water at around 25 degrees, have some cold water ready to add if teh temperature begins to rise during the investigation
5. place the light source as close to the beaker as possible, measure and record the distance between the light source

Question 10

investigating the effect of light intensity on the rate of photosynthesis

Answer 10

1. remove the plunger from the syringe and allow a gentle stream of tap water into the barrel of the syringe until the whole barrel and plastic tube are full of water
2. replace the syringe plunger and gently push water out of the flared end of the tube until there is no air bubbles in the water of the capillary tube
3. cut a 7cm length of well illuminated Eloeda and make sure that there are no air bubbles in the water of the capillary tube
4. stand the boiling tube in a beaker of water at around 25 degrees, have some cold water ready to add if teh temperature begins to rise during the investigation
5. place the light source as close to the beaker as possible, measure and record the distance between the light source and the plant I=1/D2
6. leave the apparatus with the capillary tube positioned so that it is not collecting gas given off by the plant for 5-10 minutes to allow the plant to acclimatise to that light intensity
7. position the capillary tube over the cut end of the plant stem and after a known period of time gently pull the syringe plunger and bring the oxygen bubble into the tube against the scale, read the length
8. repeat
   9, move light source away from the plant, measure and record the distance and repeat steps 6 and 7
9. draw a table and put findings in a table
10. draw a graph

Question 11

rate of carbon dioxide concentration

Answer 11

1. use drinking straw to cut several leaf discs from cress cotyledons
2. place 6 or 8 discs into a 10cm3 syringe and half fill the syringe with dilute sodium hydrogencarbonate solution
3. hold the syringe upright, place your finger over the end of the syringe and gently pull on the plunger, this causes the air in the spongy mesophyll layer of the leaf discs making them more dense, they sink to the bottom of the syringe
4. once all the discs have sunk transfer the contents of the syringe to a small beaker, or keep the discs in the syringe, place the upside down syringe in a boiling tube and position the tube underneath a light source, use the light meter to monitor the light intensity
5. place the beaker of discs directly under a lamp and measure the time taken for one leaf disc to float to the top
6. as the discs carry out photosynthesis, oxygen produced collects in the spongy mesophyll and displaces the sodium hydrogencarbonte solution making the discs less dense and more buoyant
7. repeat steps again