PROBLEM I . The Composition of Living Things 1 1 5 



are looking through the microscope; then move it to the left. Now state 

 in your notebook what the microscope seems to do to the motion of the 

 object. With your eye at the eyepiece, move the object away from you 

 and then toward you. Describe in your notebook what you notice. Com- 

 pare vour statements with those of your classmates so that all can agree 

 on the best one. 



5. How can you see the three parts of a cell? Mount some of the cells 

 of the lining of your mouth (mucous membrane). Gently rub the inside 

 of your cheek with a clean tongue depresser. Mount the material in a 

 drop of water on a slide, cover, and examine under high power. Stain 

 with dilute iodine solution (Lugol's). Find a place where the cells are 

 separated from one another. What structure now shows more clearly? 

 Where does the nucleus lie? Since you can see the nucleus in a cell of 

 three dimensions what characteristic must the protoplasm have? The firm 

 edge of the cytoplasm is the cell membrane; it shows as a line. Draw 

 and label several cells. 



6. What is the structure of onion skin cells? Cut an onion lengthwise. 

 Separate some of the layers. With forceps peel off some of the thin skin 

 from the inner side of one of the layers. Mount a piece about one quarter 

 of an inch square in a drop of water on a slide. Lay a cover glass over it. 

 Examine under the low power of the microscope. If there are too many 

 black-rimmed circles (air bubbles) mount another piece. Compare with 

 the cells from the mouth studied in Exercise 5. How do the onion skin 

 cells differ? Draw what you see. 



Now study the cells carefully under the high power. Permit a drop of 

 red ink or a weak solution of iodine to run under the cover glass. What 

 more do you see? Draw and label. 



7. To see the cell membrane of a plant cell prepare cells of onion skin 

 mounted in a drop of weak salt solution. Use the low and high powers 



^ of the microscope. What is happening within the cell? Can you see the 

 membrane? Why were you unable to see the cell membrane before? 



8. Answer the following questions: {a) If you can see the nucleus in- 

 side of a cell what must be one characteristic of cytoplasm, cell mem- 

 brane, and cell wall? {b) Can you explain how your idea of a cell is quite 

 different from Hooke's? {c) What are the important facts given in the 

 paragraph on the structure of a cell? This will summarize a difficult para- 

 graph. 



9. The structure of protoplasm. Use the high power of the microscope 

 to examine protoplasm in an ameba or a slime mold. What is the color 

 in bright light? What is the color in dim light? Is the color the same 

 throughout the organism? Do all parts of the protoplasm contain small 

 particles? Are you sure that all protoplasm looks like this? Explain. 



10. Can you devise an experiment in which you get two elements to 

 combine to make a compound? (Hifit: Charcoal is almost pure carbon. 

 Carbon dioxide is a compound consisting of carbon and oxygen. You can 

 detect the presence of carbon dioxide because it turns clear limewater 



