How does an enzyme speed up a chemical reaction?

By lowering the activation energy needed for the reaction

Why does enzyme activity fall sharply above its optimum temperature?

The enzyme is denatured and the active site changes shape

Its active site has a shape that fits only that substrate

$6 \text{CO}_2 + 6 \text{H}_2\text{O} \rightarrow \text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2$

Chloroplasts, using chlorophyll

Light is no longer the limiting factor; another factor now limits the rate

$\text{C}_6\text{H}_{12}\text{O}_6 + 6 \text{O}_2 \rightarrow 6 \text{CO}_2 + 6 \text{H}_2\text{O}$

It only partly breaks glucose down, so less energy is released as ATP

The products of one are the reactants of the other, so carbon and oxygen cycle

Photosynthesis builds the carbon of glucose from carbon dioxide in the air

Energy is lost as heat at each transfer and cannot be reused, while matter is conserved and cycles

14questions. Pick an answer and you'll see why right away.

How does an enzyme speed up a chemical reaction?
Why does enzyme activity fall sharply above its optimum temperature?
What makes an enzyme specific to its substrate?
What is ATP broken down into when a cell releases its energy?
Where in the cell is most ATP produced?
Which equation represents photosynthesis?
In which organelle and pigment does photosynthesis capture light?
A graph of photosynthesis rate against light intensity rises then plateaus. What does the plateau indicate?
Which equation represents aerobic cellular respiration?
Why does anaerobic respiration release less energy than aerobic respiration?
What does anaerobic respiration produce in human muscle cells?
How are photosynthesis and respiration related in terms of matter?
Why does the dry mass a plant gains as it grows come mostly from the air?
Why must energy keep entering an ecosystem while matter does not?