Question

directions: read the passage and answer questions 1 - 7. write the letter of the correct answer on the line. experimental design: photosynthesis in elodea a group of biology students wanted to investigate how light intensity affects the rate of photosynthesis in elodea, a common aquatic plant. the students placed equal lengths of elodea in three test tubes filled with the same amount of water and a small amount of baking soda to provide carbon dioxide. each test tube was placed under a light source at different distances: 10 cm, 30 cm, and 50 cm from the light. the students observed the number of oxygen bubbles released from the cut end of the elodea stems over five minutes. they predicted that the closer the light source was to the plant, the more bubbles would be produced. after collecting data, the students plotted their results to determine the relationship between light intensity and photosynthesis rate. 1. what was the independent variable in the students experiment? a. the amount of water in each test tube b. the distance of the light source from the plant c. the number of bubbles produced d. the species of plant used 2. what was the dependent variable in this investigation? a. the distance of the light source b. the amount of baking soda added c. the number of oxygen bubbles produced d. the type of water used 3. which factor was controlled to ensure a fair test? a. the length of elodea used b. the distance from the light c. the amount of bubbles counted d. the time of day 4. what hypothesis did the students most likely test? a. elodea grows faster in dark conditions. b. the rate of photosynthesis increases as light intensity increases. c. oxygen is not produced during photosynthesis. d. carbon dioxide decreases the rate of photosynthesis. 5. what is the most reliable way to improve the accuracy of the results? a. use a different plant species for each trial. b. measure the light intensity with a sensor instead of using distance. c. count bubbles for a shorter period of time. d. use water without baking soda. 6. which type of microscope would be used to study the internal structures of elodea cells in great detail? a. dissecting microscope b. compound light microscope c. scanning electron microscope d. transmission electron microscope 7. which statement correctly describes a difference between prokaryotic and eukaryotic cells? a. prokaryotic cells have a nucleus, while eukaryotic cells do not. b. eukaryotic cells have membrane - bound organelles, while prokaryotic cells do not. c. both prokaryotic and eukaryotic cells contain mitochondria. d. prokaryotic cells are larger and more complex than eukaryotic cells.

Explanation:

1. In an experiment, the independent variable is what is changed. Here, the distance of the light source from the plant (which affects light intensity) is changed.
2. The dependent variable is what is measured. The number of oxygen bubbles (related to photosynthesis rate) is measured.
3. Controlled variables are kept the same. The length of Elodea is kept equal.
4. The students' prediction about light - distance (related to light intensity) and bubble production (related to photosynthesis rate) aligns with the hypothesis that photosynthesis rate increases with light intensity.
5. Measuring light intensity directly (with a sensor) is more accurate than using distance as a proxy.
6. A transmission electron microscope (TEM) allows for detailed study of internal cell structures.
7. Eukaryotic cells have membrane - bound organelles (like mitochondria, nucleus etc.), prokaryotic cells do not.

Answer:

1. B. The distance of the light source from the plant
2. C. The number of oxygen bubbles produced
3. A. The length of Elodea used
4. B. The rate of photosynthesis increases as light intensity increases.
5. B. Measure the light intensity with a sensor instead of using distance.
6. D. Transmission electron microscope
7. B. Eukaryotic cells have membrane - bound organelles, while prokaryotic cells do not.