Exams

The main excretory organs of insects and spiders are Malpighian tubules.

Yes, plant cells have Mitochondria.

While plant cells have chloroplasts to photosynthesize, they also require ATP for cellular functions, and do use oxygen to break down some of the sugar they produce in order to generate that ATP. They need mitochondria for this.

In particular, at night when there is no light, plants undergo cellular respiration since there is no sunlight to photosynthesize.

They do, however, produce far more sugar and oxygen through photosynthesis than they use up in respiration.

Footsteps. 

Yes, as you walk forward, you will leave the footstep behind you.

Veins carries Blood back from the body parts to the Heart.

We know that The circulatory system of our body is a loop. The Heart is the pump, the arteries and their smaller branches (arterioles) carry oxygen rich blood all through your body and the veins and their smaller branches (venules) carry oxygen depleted blood and waste products back.

In each row, the third figure is a collection of the common elements (line segments) of the first and the second figures.

A nanosecond (ns) is an SI unit of time equal to one thousand-millionth of a second or one billionth of a second.

• That is, 1/1,000,000,000 of a second, or 10^−9 seconds.