Section H — Coach Light — Light and Your Body Clock
This section covers Chapter 2, Lessons 2.1 through 2.4.
Part A — Vocabulary (20 points, 2 points each)
Select the best answer for each question.
1. The retinohypothalamic tract is:
A) A muscle in the eye B) The nerve pathway that carries light signals from ipRGCs in the retina to the SCN C) A blood vessel in the brain D) A bone in the skull
2. Phase advance is:
A) A clock pulled later B) A shift of the body clock to an earlier time — caused by light in the first hour or two after waking C) The same as melatonin D) Only relevant for travel
3. Phase delay is:
A) A clock pulled earlier B) A shift of the body clock to a later time — caused by light in the late afternoon and evening C) The same as a phase advance D) A type of sleep
4. A zeitgeber is:
A) A bone in the brain B) An environmental cue that synchronizes a biological clock — light is the strongest in humans C) A meal D) A vitamin
5. Vitamin D is:
A) A vitamin you can only get from supplements B) A fat-soluble vitamin produced in the skin when UVB light interacts with a cholesterol-related compound; also obtainable from some foods C) A type of bone D) A type of fat
6. UVB is:
A) Visible blue light B) Ultraviolet light with wavelengths from about 280-315 nm — drives vitamin D production in skin and also causes sunburn C) The same as UVA D) Always harmful
7. Melanin is:
A) The pigment in skin that absorbs UV light — more melanin = more protection from UV damage and slower vitamin D synthesis B) A type of vitamin C) A muscle protein D) A bone
8. Latitude is:
A) Distance from the equator, measured in degrees — affects how directly sunlight hits the ground B) The temperature of the air C) Speed of walking D) A type of food
9. Free-running rhythm is:
A) Running on a track B) The clock's natural cycle length without outside cues — about 24.2 hours in humans, slightly longer than 24 C) A type of sleep D) Only present in adolescents
10. Peripheral clocks are:
A) Clocks on a wall B) Local circadian clocks present in cells throughout the body (liver, gut, muscle, fat) — synchronized by the SCN C) Only in the brain D) A type of bone
Part B — Concept Comprehension (20 points, 2 points each)
Select the best answer for each question.
11. The master clock of the human body is the:
A) Heart B) Pituitary C) Suprachiasmatic nucleus (SCN), in the hypothalamus D) Pineal gland
12. The phase response curve (PRC) shows that:
A) Light has no effect on the body clock B) Morning light tends to phase-advance the clock; evening light tends to phase-delay it C) Only midnight light affects the clock D) Light only affects vision, never timing
13. Outdoor light on a cloudy day is approximately:
A) Less bright than a kitchen light B) Roughly 1,000-10,000 lux — still many times brighter than typical indoor light C) Dimmer than a phone screen D) The same as moonlight
14. UVB intensity at the ground depends most on:
A) Wind direction B) The angle of the sun in the sky (which depends on latitude, season, and time of day) C) Whether you are wearing sunglasses D) Recent rainfall only
15. In Boston (about 42° N) in December at noon:
A) UVB is plentiful and vitamin D production is high B) The sun is too low in the sky for meaningful UVB to reach the ground; vitamin D synthesis from sun is essentially absent C) UVB is stronger than in June D) The sun does not rise
16. People with darker skin (more melanin):
A) Cannot make vitamin D B) Make vitamin D more slowly at the same UV exposure but are more protected from UV damage — a trade-off, not a defect C) Always need supplements D) Have no melanin
17. Coach Light at Grade 7 does not tell you to:
A) Step outside in morning light B) Stare directly at the sun for several seconds each morning C) Notice the lux differences between rooms D) Pay attention to seasonal light variation
18. Looking directly at the sun:
A) Sets the body clock more effectively B) Causes solar retinopathy — permanent retinal damage from intense light, possible in seconds, even at sunrise C) Is fine if the sun looks "soft" D) Only a problem for adults
19. Coach Light says morning circadian signal comes from:
A) Staring at the sun B) The bright environment reaching the eyes from the sky, trees, buildings, and ground — peripheral vision is enough C) Phone screens at 4 a.m. D) Reading by candlelight
20. Coach Light's main message at Grade 7 is:
A) Light is just for seeing B) The body clock runs on light timing; morning light anchors the clock earlier, evening light pushes it later, and vitamin D depends on latitude/season/skin C) Stare at the sun every morning D) Never go outside
Part C — Application (30 points, 6 points each)
Write 2-4 complete sentences for each question.
21. Trace what happens when morning light enters your eye. Use the words ipRGCs, retinohypothalamic tract, SCN, and peripheral clocks in your answer.
22. Why is morning light a phase advance (pulling the clock earlier) while evening light is a phase delay (pushing it later)? What does this mean for someone trying to fall asleep at a reasonable hour?
23. Use what you learned about latitude. About how much vitamin D production from sun is available in Orlando (28° N) in June compared to Boston (42° N) in December? Why such a big difference?
24. Explain the trade-off between melanin (skin pigmentation) and vitamin D production. Why is this an example of evolution to local UV environments rather than a defect of any one population?
25. Safety recognition. A video tells you to "view the rising sun within 30 seconds of waking for several minutes each morning." Why is the direct sun-viewing part of this practice unsafe, and what would the correct application of the morning-light principle look like instead?
Continue to Section I — Coach Water.