Question

Why is it that during transportation of carbohydrates in plants it is in the form of Sucrose but in animals it is in the form of Glucose?

Answer 1

Sucrose transport is more efficient for plants. Furthermore, plants and animals have different enzymes and transporters.

Explanation:

`color(blue)"The difference between glucose an sucrose"`

• Glucose = a monosaccharide, a single building block of sugars
• Sucrose = a disaccharide, build from the monosaccharides glucose and fructose.

`color(blue)"Why plants use sucrose instead of glucose"`
Sucrose is formed in the cytosol of photosynthesizing cells from fructose and glucose and is then transported to other parts of the plant. This process is favorable for two reasons:

1. Sucrose contains more energy than a monosaccharide, so it is more energy efficient, both in transport as in storage.

2. Secondly, sucrose is a so called non-reducing sugar. This means that it is not oxidized i.e. no intermediate reactions with other molecules occur. This in contrast to glucose that is reactive and can form other products during transport.

`color(blue)"Why animals use glucose instead of sucrose"`
The question arises why animals don't use sucrose instead of energy considering the above mentioned advantages.

This has to do with the fact that animal cells do not have the same transport mechanisms and enzyme distribution as plants do:

1. In plants sucrose is converted back to glucose and fructose by an enzyme called sucrase. Animals produce less sucrase, the presence of these enzymes is limited to certain tissues.

2. Animals have specific mechanisms to transport glucose to the target tissues. However, they have no sucrase transporters

3. Some cells convert sucrose into glucose and fructose. Glucose can go into glycolysis in almost all tissues. Fructolysis is limited to the liver, so most cels don't have the enzymes to deal with fructose.

So for animals, sucrose is not an efficient energy source.