paper 1 practicals

Question 1

outline how you would conduct a fish dissection

Answer 1

1. place fish on dissection tray
2. push back operculumn and use scissors to carefully remove the gills
3. cut each gill arch through the bone at the top and bottom
4. view gill filaments
5. draw and label

Question 1

outline how you would conduct an insect dissection

Answer 1

1. fix insect to a dissection board, place dissecting pins through legs to hold in place
2. to examine trachae cut and remove piece of exoskeleton from along the length of the abdomen
3. using a syringe, fill abdomen with saline solution, should be able to see the network of silvery grey tubes
4. can mount trachae on a wet mount microscope slide and examine
5. draw and label

Question 2

outline how you would conduct a heart dissection

Answer 2

1. wear apron, lab coats and gloves
2. place heart on dissecting tray, observe outside of heart, identifying the 4 main vessels
   - arteries are thick and rubbery, veins are thin
3. identify the left and right atrium and ventricles, left ventricle will be the thickest.
4. using clean scalpal cut along lines on right and left side, can measure and record thickness of ventricle walls
5. cut open atria, note thickness
6. identify atrioventricular and semilunar valves
   7 draw and label

Question 3

outline how you would conduct a plant dissection

Answer 3

1. using scalpal cut crossection of a stem, cut thinly as possible
2. using tweezers, gently place cut sections in the water to prevent drying out.
3. add drop of water to micrscope slide, add plant specimen and add TBO and leave for 1 min
4. apply cover slip at an angle and press down lightly to remove air bubbles
5. view using lowest objective magnification first and draw

Question 4

what colour will the xylem go in TBO

Answer 4

blue

Question 5

what colour will the phloem go in TBO

Answer 5

pink

Question 6

outline how you could investigate pigments in leaves

Answer 6

1. grind up leaves to a pulp with anhydrous sodium sulfate and add drops of propanone (extraction solvent)
2. transfer to test tube and add petroleum ether and gently shake (so non polar components dissolve)
   2 layers will form
3. transfer top layer containing the pigment to second test tube
4. draw start line in pencil, build up a concentrated spot using capillary tube
5. place into glass beaker with solvent so origin is above solvent. place lid on top
   calculate RF

Question 7

these questions are about precautions to take when carrying out chromatography, explain why

1. hold TLC plate by edges
2. make sure plate does not touch the sides of the jar
3. why should you work quickly when extracting the pigments

Answer 7

1. to avoid contamination of the TLC plate with fingerprints
2. condensation on the jar could affect movement of spots
3. propanone quickly evaporates

Question 8

outline how you would view a specimen under a microscope

Answer 8

1. clip slide onto stage
2. select lowest powered objective lens
3. use coarse adjustment knob to move the objective lens to just above the slide
4. look down eyepiece and adjust by moving lens away from sline using the fine adjustment knob
5. if higher magnification needed move to a higher powered objective lens

Question 9

outline how you would carry out a blood smear

Answer 9

1. shake sample to resuspend cells
2. dip glass rod into blood and place a drop of blood a quarter way along the slide
3. hold second slide at an angle of 45 degrees, push backwards until just touches drop of blod and then pull forwards dragging smear of blood
4. leave to air dry
5. pour ehtanol onto dry smear and leave (this fixes and dehydrates the cells)
6. add stain