Plants and animals often use color to attract attention.The substances responsible for these colors belong to a class of chemical called antioxidants(抗氧化物).Plants make antioxidant to protect themselves from the sun’s ultraviolet(UV)(紫外线)light.

　　Ultraviolet light causes chemicals called free radicals(自由基)to form within plant cells.They can destroy parts of plant.Free radicals also have damaging effects on human beings.Some of these effects like wrinkled skin can be seen.The damage is caused by the free radicals attacking cells in our bodies.Certain cancers and heart disease are linked to free radicals.

　　Our bodies have natural defences for fighting off free radicals.While we are young,our defences are pretty strong.However,they get weaker as we get older.The body’s built-in defences can only go so far without extra help.

　　The key to fighting free radicals with fruits and vegetables is to mix and match colors.It’s like sunscreen(防晒霜)for the inside of your body.Go for a range of very bright colors.Colorful foods contain hundreds of healthy chemicals not found anywhere else.

　　Research into how chemicals in blueberries affect the brain’s function in rats suggests that these chemicals may help our own brains work more efficiently.

　　Don’t just blame the sun.Ultraviolet light isn’t the only source of free radicals.If you breathe polluted air such as smog,automobile exhaust(废气),or wasted gas from a factory,you take in chemicals that also cause such damage.And,the body itself produces free radicals as it processes food.

【2017届高考英语一轮复习知识梳理练习：必修1 Unit 2 Heroes（北师大版）】相关文章：

★ 【浙江专用】2014届高考英语一轮复习课时作业(二十五)必修5Unit 5《First aid》

★ （安徽专用）2014届高考英语一轮复习方案 作业手册（23）模块8 《Unit 23 Conflict》（含解析） 北师大版必修1

★ 2014届高考英语一轮复习课时作业(三十七)选修7Module 1《Basketball》（外研版）

★ 【北师大版】2014届高考英语一轮复习指导课时作业：Unit 7 B卷 Word版含解析

★ 湖南省汝城二中2014届高考英语一轮复习阅读训练 (9)

★ 湖南省汝城二中2014届高考英语一轮复习阅读训练 (58)

★ （全国通用）2014届高考英语一轮单元复习 限时强化训练十一

★ （安徽专用）2014届高考英语一轮复习方案 作业手册（21）模块7 《Unit 21 Human Biology》（含解析） 北师大版必修1

★ 2017届高考英语二轮复习大题冲关秘籍阅读理解七选五：解题策略（含解析）

★ （安徽专用）2014届高考英语一轮复习方案 作业手册（10）模块4 《Unit 10 Money》（含解析） 北师大版必修1