2.大肠杆菌培养基被污染后,除大肠杆菌外,又滋生了别的细菌和真菌。从生命系统的结 构层次来分析,对应于哪个层次·······································( )
A.种群 B.系统 C.群落 D.生态系统
3.下列选项中,属于动植物细胞共有的糖类是······························( )
A. 淀粉、脱氧核糖、乳糖 B. 葡萄糖、淀粉和果糖
C. 葡萄糖、核糖、脱氧核糖 D. 麦芽糖、果糖、乳糖
4.生物大分子以什么结构为骨架··········································( )
A.肽链 B.碳链 C.核苷酸链 D.磷脂分子
5.大豆根尖细胞所含的核酸中,含有碱基A、C、G、T的核苷酸种类数有·······( )
A.8 B.7 C.5 D.2