①细胞核的实际直径约

1.6cm

2*103 =0.8*10-3cm=8*10-6m;

②∵1min=

1

60 h，∴45min=45*

1

60 h=0.75h;

∵1min=60s，∴45min=45*60s=2700s;

③正常情况下，人的心脏1min跳动75次左右，跳动10次的时间约12s=0.2min;

④人正常步行的速度在1.1m/s左右，10min=600s，通过的路程大约1.1m/s*600s=660m，接近700m.

故答案为：

8*10-6;0.75;2700;min;m.