← The Human Body

Chapter 7

Cells, DNA and growing up

You began as a single cell, and you are now made of trillions. Each one holds your DNA in its nucleus, written in a code of just four letters and packed into 46 chromosomes. This chapter covers how cells get their energy, how they divide to help you grow and heal, what genes and stem cells are, and what changes as a child grows up: growth plates, bones that fuse and the hormones of puberty.

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  1. Part of a cell that holds its DNANucleus
  2. Parts of a cell that release energy from foodMitochondria
  3. Number of chromosomes in most human cells46
  4. Sex chromosomes most males haveXY
  5. Stretch of DNA that codes for a proteinA gene
  6. Number of letters in the DNA code4
  7. Twins who share the same DNAIdentical twins
  8. Cell division that makes two identical cellsMitosis
  9. Cells that can turn into many kinds of cellStem cells
  10. Hormone that drives puberty in boysTestosterone
  11. Where bones grow longer in childrenGrowth plates
  12. Roughly how many bones a newborn hasAbout 300