What Sets Adult Size: teacher key

How You Grow, grade 12 edition, written for 12th grade and up. Growth slows and stops at an adult size, and nobody has the whole answer. Growth-plate cells, feedback loops, genes, brain energy and environment each add a piece.

Read the book. Print this page for the key.

Questions and answers

1. What does a review of mammal growth say causes the slowdown after early life?
   • Strong suppression of cell division in many tissues (answer)
   • A single signal from the brain
   • The closing of every growth plate at birth
2. What does the growing of hypertrophic cells largely explain?
   • How tall parents are
   • Why different bones grow at different rates (answer)
   • Why bones are made of collagen
3. Which protein holds back skeletal and cardiac muscle growth, with an amount that depends on muscle mass?
   • Collagen
   • Calcium phosphate
   • Myostatin (answer)
4. What is true of the gene variants that scientists have found for height?
   • One gene explains it all
   • Many variants each add a modest effect (answer)
   • Genes play no part
5. Why does brain energy demand help explain slow human childhood growth, according to one idea?
   • Brain energy demand and body growth rate vary inversely (answer)
   • Brains stop using energy in childhood
   • Bodies grow faster when brains grow faster

Words

• hypertrophic: swollen large
• myostatin: muscle growth brake
• variants: gene versions
• synapse: brain link