Cells, DNA and growing up
Cells, DNA and growing up: a chapter of The Human Body Book, with the facts about your own body that are worth knowing.
12 cards · Science
Each Zap teaches up to 5 new cards, so you learn the chapter a few at a time.
Checked by the Brain Zap team · reviewed 27 Oct 2026
Sources: Human body (Encyclopaedia Britannica), Health A to Z (NHS)
Preview
Part of a cell that holds its DNA
Show answerHide answer: Part of a cell that holds its DNA
Nucleus
Learn more: Almost every human cell keeps its DNA in a nucleus; red blood cells lose theirs as they mature.
Parts of a cell that release energy from food
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Mitochondria
Learn more: They turn sugar and oxygen into usable energy, and you inherit them only from your mother.
Number of chromosomes in most human cells
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46
Learn more: One set of 23 comes from each parent; egg and sperm cells carry 23 each.
Sex chromosomes most males have
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XY
Learn more: The Y chromosome carries the gene that starts male development.
Stretch of DNA that codes for a protein
Show answerHide answer: Stretch of DNA that codes for a protein
A gene
Learn more: Genes make up only about 1 to 2% of your DNA; much of the rest helps control when they switch on.
About this topic
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.
This is a chapter of The Human Body Book. Each card asks one question, with a hint before you answer and a short reason after. Once you know most of this chapter, the next one starts arriving in your Daily Zap.
All 12 cards
Part of a cell that holds its DNA
Nucleus
Learn more: Almost every human cell keeps its DNA in a nucleus; red blood cells lose theirs as they mature.
Parts of a cell that release energy from food
Mitochondria
Learn more: They turn sugar and oxygen into usable energy, and you inherit them only from your mother.
Number of chromosomes in most human cells
46
Learn more: One set of 23 comes from each parent; egg and sperm cells carry 23 each.
Sex chromosomes most males have
XY
Learn more: The Y chromosome carries the gene that starts male development.
Stretch of DNA that codes for a protein
A gene
Learn more: Genes make up only about 1 to 2% of your DNA; much of the rest helps control when they switch on.
Number of letters in the DNA code
4
Learn more: The bases A, C, G and T pair up across the double helix: A with T, C with G.
Twins who share the same DNA
Identical twins
Learn more: Fraternal twins come from two eggs and are as alike as any brothers and sisters.
Cell division that makes two identical cells
Mitosis
Learn more: Meiosis is the other kind: it makes egg and sperm cells with half the chromosomes.
Cells that can turn into many kinds of cell
Stem cells
Learn more: They renew blood, skin and gut lining all your life; scientists study them to repair damaged tissue.
Hormone that drives puberty in boys
Testosterone
Learn more: It deepens the voice and builds muscle; in girls, oestrogen drives most of puberty's changes.
Where bones grow longer in children
Growth plates
Learn more: Cartilage near the ends of long bones turns into bone, so growing taller stops once the plates close.
Roughly how many bones a newborn has
About 300
Learn more: Many fuse together as a child grows, leaving an adult with 206.
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