Question

question 19
enzymes speed up biochemical reactions by lowering the activation energy. what does this refer to?
a less energy is needed to start the reaction
b less energy is needed to finish the reaction
c the reaction must be energy - absorbing
question 20
what is hydrogen bonding?
a weak bonds between the hydrogen atoms of water molecules
b strong bonds between the oxygen atom and a hydrogen atom in a water molecule
c weak bonds between the oxygen atom of one water molecule and a hydrogen atom of another water molecule

Explanation:

Question 19

Activation energy is the minimum energy required to start a reaction. Enzymes lower this, meaning less energy is needed to start the reaction. Option B is wrong as activation energy is about starting, not finishing. Option C is incorrect as enzymes work on both energy - absorbing and releasing reactions.

Hydrogen bonding is a weak bond. In water, it is between the oxygen atom of one water molecule (which is slightly negative due to oxygen's higher electronegativity) and a hydrogen atom of another water molecule (which is slightly positive). Option A is wrong as it's not between hydrogen atoms of the same molecule. Option B describes a covalent bond (strong) within a water molecule, not hydrogen bonding.

Answer:

A. less energy is needed to start the reaction

Question 20