Compare and contrast paragraph writing

Hi,

I have done a short paragraph writing on fresh foods versus convenience foods. Would you mind helping me to grade it in terms of language,tenses and content?

Fresh foods and convenience foods differ vastly from each other.The first difference would be the freshness of the food. Fresh foods are often consumed daily to maintain the freshness of the food, whereas convenience foods are often kept for long period. Another difference is the use of additives in foods. Convenience foods are preserved through the use of additives. The large amount of chemicals used is detrimental to people lives as it can cause certain illnesses such as, Cancer, in the long term. On the other hand, fresh foods do not contains chemicals in it as they are consumed daily or within a few days.

Besides the two differences, the third difference is the cost of the food. Convenience foods are much more expensive due to the packaging and the use of chemicals in order to prolong their shelve life. In contrast, fresh foods are relatively cheaper since it does not require any packaging and chemicals. Therefore, people would prefer fresh foods as it has less detrimental effects on humans as compared to convenience foods.

Thanks!

Cheers,

Jennifer Unagi:)