Chemical composition of the cell; water and salts
Answers are for parents and teachers.
1
Write three biological functions of water with an example each.
Solvent (substances travel in blood); heat regulation (sweating); turgor (a leaf stays firm).
2
How many grams of water are in a 400 g piece of watermelon with 90 % water?
360
3
Write the role of Na⁺, K⁺ and Ca²⁺ ions in the cell.
Excitability and nerve impulses, transport across membranes; Ca²⁺ also takes part in muscle contraction and blood clotting.
4
Why is there little water in tooth enamel but a lot in growing cells?
Enamel is a hard mineral layer; growing cells have intense metabolism and need much water.
5
Why is iodised salt recommended, yet should it not be eaten in excess?
Iodine is needed, but any element in excess can harm the body; a doctor advises the norm.