Ripples, Striders and a Microscope Quiz

Trace sense signals from stimulus to brain to behavior or memory during a pond study week.

The ripple test

Read the passage and Table 1. Then answer questions 1–6.

Pond Week at Fernbrook Nature Center

1Each fall, Ms. Ilse Varga's sixth graders spend a week studying Willow Pond at the Fernbrook Nature Center. The center's educator, Kofi Mensah, helps them collect pond water and small animals, and every animal goes back into the pond at the end of the day. The pond, the people and the numbers here are made up, but they are based on real studies.

2Water striders are insects that stand on the surface of the pond on long, thin legs. When a small insect falls onto the water and struggles, it sends tiny ripples across the surface. Striders have sense receptors in their legs that detect movements of the water's surface. The class noticed that striders often skate quickly toward insects that land on the pond.

3Mr. Mensah put 10 striders in a shallow white tray of pond water, 60 cm long. Student Noor Castellano touched the water at one end of the tray with the tip of a fine paintbrush in four different ways. She ran 3 trials of each way, with a 5-minute rest between trials, and the class counted how many striders skated toward the brush within 5 seconds. In Condition D, a cardboard card stood between the striders and the brush. The card was held 1 cm above the water, so it blocked the striders' view of the brush but not the ripples.

4The class also studied drops of pond water under microscopes. Light from each tiny organism passes through the lenses into a student's eye, where light-sensing cells send signals along nerves to the brain. On Day 1, students used a picture key: rotifers have a crown of hairs that seems to spin, water fleas swim in short jerks, and some algae form long green strands. At the end of each day, Ms. Varga gave a quiz. She showed 10 Willow Pond organisms on a video microscope, and students named them without the key. On Day 4, she also showed 10 organisms from a salt marsh that the class had never studied.

5One morning, Ms. Varga turned the microscope lamps up to full brightness all at once. Several students blinked, and Eli saw the black center of his partner's eye shrink.

Table 1. Skating Toward the Brush (10 striders × 3 trials = 30 tries)
Condition	How the brush moved	Tries with skating
A	Quick taps on the water	27
B	One touch, then held still	6
C	Waved 2 cm above the water	3
D	Quick taps, behind a card	25

In Condition A, what percent of the tries ended with a strider skating toward the brush? %

Condition A had how many times as many tries with skating as Condition B? Do not round. times

Compare Conditions A and C. What do they show?

A. Striders skated toward any brush they could see, whether it touched the water or not.
B. Striders responded far more to ripples on the water than to the sight of a moving brush.
C. Striders skated away from the ripples and toward the brush waving above the water.
D. Striders responded more in Condition C, since a waving brush is easier to notice.

In Condition D, which part of the path from stimulus to behavior did the card block?

A. The signals traveling along nerves from the striders' brains to their leg muscles
B. The signals traveling from the receptors in the striders' legs to their brains
C. The ripples traveling across the water to the receptors in the striders' legs
D. The light from the brush traveling to the light-sensing cells in the striders' eyes

Use Table 1. Which conclusion do Conditions A and D together support best?

A. Striders found the tapping brush about as often when they could not see it.
B. Striders learned where the brush would be, so the card made little difference.
C. Striders found the brush mainly by sight, since the card lowered the count a lot.
D. Striders responded to the card itself, since it stood right next to the water.

Two flies land on the pond near a group of striders. One is dead and lies still. The other is alive and beats its wings against the water. Based on Table 1, which prediction fits best?

A. The striders would skate away from both flies, since a new object on the water often means danger.
B. The striders would more likely skate to the live fly, since it makes ripples like Condition A.
C. The striders would reach both flies at about the same rate, since both can be seen.
D. The striders would reach the dead fly sooner, since a still fly is easier to grab.

The microscope quizzes

Use paragraphs 4 and 5 and Table 2 to answer questions 7–12.

Table 2. Microscope Quiz Results (class averages, 10 organisms per quiz)
Quiz	Named correctly	Time to finish (min)
Day 1, Willow Pond	5	18
Day 2, Willow Pond	7	13
Day 3, Willow Pond	8	10
Day 4, Willow Pond	9	7
Day 4, salt marsh	4	17

By how many minutes did the average time to finish the Willow Pond quiz drop from Day 1 to Day 4? min

What best explains the change in the Willow Pond quiz results from Day 1 to Day 4?

A. The lamps were brighter each day, so the light reached the students' eyes sooner.
B. The brain stored memories of each organism's shape and motion, so naming got faster.
C. The students' eyes grew more light-sensing cells, so they saw each organism more sharply.
D. The organisms grew larger during the week, so they were easier to spot in the field.

Which result is the best evidence that the students improved because of memories of the Willow Pond organisms, and not because their eyes simply got better at seeing through a microscope?

A. On Day 1, students named only half of the Willow Pond organisms.
B. On Day 4, students named 9 of 10 Willow Pond organisms in 7 minutes.
C. On Day 4, students named 4 of 10 salt marsh organisms in 17 minutes.
D. The time to finish the Willow Pond quiz dropped on each new day.

10.

Circle each event from pond week in which the brain mostly used a memory stored from earlier experience.

On Day 4, Noor names a rotifer the moment she sees its spinning crown.Eli blinks when the lamp suddenly turns up to full brightness.Aiyana knows a jerky swimmer is a water flea because she drew one on Day 2.The black center of a student's eye shrinks as bright light floods in.During a quiz with no key, Joaquín says "algae" as soon as long green strands appear.

11.

On Day 4, Noor sees a rotifer on the screen and writes its name. Which order shows the path of the signals?

A. Light from the rotifer → light-sensing cells in the eye → nerves → brain matches a memory → nerves → hand muscles write
B. Light from the rotifer → brain matches a memory → light-sensing cells in the eye → nerves → hand muscles write
C. Hand muscles write → nerves → brain matches a memory → nerves → light-sensing cells in the eye → light from the rotifer
D. Light from the rotifer → light-sensing cells in the eye → hand muscles write → nerves → brain matches a memory

12.

A classmate says, "The striders found the brush by seeing it, the same way we find organisms under the microscope." Do you agree? Write a claim, give evidence from Table 1, and explain your reasoning. Name the stimulus and the sense receptors that most likely led to the striders' behavior.