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Why do we need enzymes to digest food? Can't our stomach acid just break everything down by itself?

How do really tall trees get water all the way up to their leaves? It seems impossible for water to go against gravity like that.

Why is excretion so important for us? What would happen if our kidneys stopped working properly?

Teacher, why does our heart have four chambers? Wouldn't two be simpler, like in some other animals?

Ma'am, what's the actual difference between breathing and respiration? My friend says they're the same, but I think they're not.

Sir, why do plants need sunlight? I thought they make their own food, so why can't they just do it in the dark?

Why does light bend when it goes from air to water? What's refractive index?

How do I know if a lens or mirror will form a magnified or diminished image?

What are the sign conventions for mirrors and lenses? I always get confused!

Why do we use concave mirrors for shaving and convex mirrors for rearview in cars?

What's the difference between real and virtual images?

Why does a spoon look bent in water?

Why are chemical equations so important? What information do they actually give us?

What's the main difference between exothermic and endothermic reactions? Can you give simple examples?

Why does iron rust, and how can we stop it? Also, what's that smell when food goes bad?

What's the difference between oxidation and reduction? My teacher said something about gaining/losing oxygen or hydrogen, but then also electrons, and I'm lost.

How can I tell what type of reaction it is just by looking at the equation? I always get confused between decomposition and displacement.

Why do we even need to balance chemical equations? Like, what's the point?

What is the Fundamental Theorem of Arithmetic? It sounds important but I don't really get what it means for solving problems.

Can a number be both rational and irrational? And what about numbers like $\pi$ or $e$? Are they always irrational?

How can I tell if a fraction like $13/3125$ will have a terminating or non-terminating decimal expansion without actually dividing it?

How do I prove that numbers like $\sqrt{2}$ or $3 + \sqrt{5}$ are irrational? I always get stuck on the contradiction part.

When should I use prime factorization to find HCF/LCM, and when should I use Euclid's Division Algorithm? Is one better?

What's the difference between Euclid's Division Lemma and Algorithm? And why do we even learn it?

Why does a convex lens form a real and inverted image when the object is placed beyond 2F?