Frozen Miracle Reading Passage
Grade 5 Science & Reading Lexile: 820L • Informational Text
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Animal Adaptations Spotlight
Frozen Alive: The Wood Frog’s Miracle
How a tiny North American amphibian survives being frozen solid all winter long
Subarctic Lab
[1] As autumn winds sweep across the dense forests of Alaska and Canada, most creatures prepare for the brutal winter ahead. Bears retreat into insulated dens, and birds fly thousands of miles south toward tropical warmth. The North American wood frog (Lithobates sylvaticus), however, stays behind on the chilly forest floor. It does not dig deep beneath the frost line. Instead, it tucks beneath a shallow blanket of decaying autumn leaves and prepares for one of the most astonishing biological feats on Earth: it allows itself to freeze completely solid.
[2] When sub-zero temperatures arrive, ice crystals touch the wood frog's moist skin, triggering an immediate shutdown of its physical body. Soon, ice fills the frog’s abdominal cavity, wrapping around its internal organs. The frog’s lungs stop breathing, its brain activity goes completely quiet, and its heart stops beating entirely. Touch the hibernating frog, and it feels as hard as a hockey puck. Drop it, and it would clatter like a piece of frozen glass. By all normal medical definitions, the frog appears dead.
[3] How does the wood frog survive conditions that would kill almost any other vertebrate? The secret lies in a special chemical defense. When freezing begins, the frog’s liver immediately shifts into overdrive, releasing massive amounts of glucose (a natural sugar) into its bloodstream. This sugar acts as a biological cryoprotectant—nature’s version of automotive antifreeze. While ice forms safely in the spaces between organs, the dense sugar syrup protects the insides of individual cells. This prevents water inside cells from turning into jagged ice crystals that would slice cell walls to ribbons.
[4] For up to seven freezing months, the frog remains in this suspended state, enduring temperatures as low as zero degrees Fahrenheit. Then, when the warm spring sunshine melts the winter snow, a second miracle unfolds. The frog does not thaw from the outside in; it warms up from its very core. Within a few short hours, the heart mysteriously sparks back to life. Blood begins circulating, the lungs refill with air, and the frog takes its first tentative hop toward a nearby vernal pond to mate and lay eggs.
[5] Today, human scientists and medical doctors are closely examining the wood frog’s frozen secret. Currently, donated human organs like hearts and kidneys can only survive outside the human body for several hours on ice before cellular damage occurs. If researchers can unlock how the wood frog preserves its living tissues during freezing, doctors might one day freeze and store human transplant organs for weeks or months, ultimately saving thousands of human lives.
Cryoprotectant:
A substance that prevents biological tissue and cell walls from freezing damage.
Suspended State:
A temporary pause in living functions where heartbeat and breathing stop completely.
Super Fast Fact:
Up to 65% of the total water in a wood frog’s body turns to solid ice during deep winter!
Wilderness Science Series • Reading Comprehension Turn page for comprehension questions → Page 1 of 2
Comprehension Check: Frozen Miracle
Read each question carefully. Select the best answer or write your response in the space provided.
10 Questions Total
Section 1: Main Idea 2 Questions
- Which sentence best states the central main idea of the entire passage?
A. Wood frogs migrate hundreds of miles south every autumn like songbirds.
B. The wood frog uses a special sugar defense to survive being frozen solid in winter.
C. Sub-zero temperatures in Alaska cause irreversible damage to all living creatures.
D. Human doctors have successfully discovered how to freeze all human organs.
- What is the main idea of paragraph 3?
A. Glucose acts as a cellular shield that stops dangerous ice crystals from forming inside cells.
B. Automotive antifreeze is dangerous to frogs living in northern woodlands.
C. The frog’s heart stops beating when sub-zero air chills the ground.
D. Vertebrate animals require warm weather to produce energy from sugars.
Section 2: Supporting Details 3 Questions
- According to paragraph 2, what physical changes happen to the frog during a freeze?
A. Its breathing speeds up and its skin turns completely white.
B. Its lungs stop breathing, brain activity pauses, and its heartbeat ceases.
C. It burrows six feet underground beneath the deep frost line.
D. It shivers continuously to maintain a normal body temperature.
- Which internal organ releases large amounts of glucose into the frog’s bloodstream?
A. The lungs
B. The brain
C. The liver
D. The stomach
- How long can the wood frog remain in this frozen state during northern winters?
A. Up to 7 days
B. Up to 3 weeks
C. Up to 7 months
D. Over 3 full years
Section 3: General Comprehension 5 Questions
- Vocabulary: As used in paragraph 3, what does the word cryoprotectant mean?
A. A poison that deters predators in the forest
B. A biological substance that prevents freeze damage
C. A pigment that helps the frog camouflage in leaf litter
D. A hormone that speeds up heart rate during exercise
- Inference: Why can wood frogs live farther north in the Arctic than other frog species?
A. They possess thick fur coats that insulate them from blizzards.
B. They can tolerate freezing temperatures without dying.
C. They only hunt insects underneath deep, warm lake beds.
D. They stay awake all winter feeding on frozen tree seeds.
- Sequence: When spring arrives, how does the wood frog thaw out?
A. From its outer skin first, slowly moving toward its belly
B. From its legs and feet inward toward its chest
C. From its core inside out, with the heart reviving first
D. Only after entering warm water in a river or pond
- Author’s Craft: Why did the author compare the frog to a "hockey puck" and "frozen glass"?
A. To help readers visualize how rock-hard and rigid the frog becomes
B. To explain that children frequently play games with frozen frogs
C. To suggest that the wood frog is dangerous and sharp to the touch
D. To prove that frogs are made of artificial non-living materials
- Written Response: Based on paragraph 5, explain how studying the wood frog could help human patients.
Wilderness Science Series • Reading Comprehension Assessment Check your answers before submitting Page 2 of 2
Frozen Miracle Answer Key
Teacher Guide & Scoring Key CCSS: RI.5.1, RI.5.2, RI.5.4, RI.5.8
Frozen Miracle: Answer Key & Explanations
Total Points: 11 pts
Q1–9: 1 pt each • Q10: 2 pts
Section 1: Main Idea (Questions 1–2) 2 pts
Question 1: Overall Main Idea Correct: B
Text Evidence: Paragraphs 1–4 detail how wood frogs survive winter by freezing solid using glucose. Options A and D are factually inaccurate; Option C is too broad.
Question 2: Paragraph 3 Main Idea Correct: A
Text Evidence: Paragraph 3 focuses directly on how glucose released from the liver protects internal cellular structures from sharp ice crystal destruction.
Section 2: Supporting Details (Questions 3–5) 3 pts
Question 3: Physical Changes Correct: B
Text Evidence: Paragraph 2 states: "The frog’s lungs stop breathing, its brain activity goes completely quiet, and its heart stops beating entirely."
Question 4: Glucose Organ Correct: C
Text Evidence: Paragraph 3 states: "the frog’s liver immediately shifts into overdrive, releasing massive amounts of glucose into its bloodstream."
Question 5: Freeze Duration Correct: C
Text Evidence: Paragraph 4 directly states: "For up to seven freezing months, the frog remains in this suspended state..."
Section 3: General Comprehension (Questions 6–10) 6 pts
Question 6: Vocabulary (Cryoprotectant) Correct: B
Paragraph 3 explains that the sugar acts like antifreeze that keeps cells from freezing damage.
Question 7: Inference (Arctic Range) Correct: B
Most frogs freeze and perish in northern winters; the wood frog's freeze tolerance allows it to thrive in subarctic climates.
Question 8: Sequence & Thawing Process Correct: C
Paragraph 4 explains that the frog warms from the inside out, starting with the heart reviving first.
Question 9: Author’s Craft (Figurative Language) Correct: A
The author uses vivid tactile similes to emphasize how solid, rigid, and completely frozen the frog becomes.
Question 10: Constructed Response Rubric 2 Points Max
2 Points: Explains that human transplant organs survive only hours on ice, and understanding the frog's cellular preservation could allow doctors to freeze and store organs for weeks or months, saving lives.
1 Point: Mentions preserving human organs or freezing organs, but omits the time benefit (hours vs. weeks/months) or medical impact.
Sample 2-Pt Response: "Right now, donor organs like hearts only survive a few hours on ice. If doctors learn how wood frogs protect their cells from ice damage, they could freeze transplant organs for weeks or months to save many patients."
Common Student Misconceptions
Students often assume the frog freezes in a pond or underground burrow. Remind students of paragraph 1: it stays right in the leaf litter on the surface of the forest floor!
Instructional Extension & Discussion
Have students research other cryotolerant animals (e.g., tardigrades, woolly bear caterpillars) and compare how their cellular antifreeze adaptations work.
Wilderness Science Series • Educator Answer Key Standards: CCSS.ELA-LITERACY.RI.5.1, RI.5.2, RI.5.4 Teacher Resource
