Multiple choice

1. A plant sits on a window sill. Over time, the stems of the plant curve toward the light coming in the window. This process is called

A. phototropism. 

B. photoperiodism. 

C. gravitropism.

D. phytochromism.

2. Which of these parts receive nerve impulses from the central nervous system, causing muscle fibers to contract?

A. Interneurons 

B. Motor neurons 

C. Sensory neurons

D. Myelin sheaths

3. In the human immune system, the main function of the _______ is filtering blood.

A. thymus gland 

B. spleen 

C. tonsils

D. appendix

4. In flowering plants, which of these becomes the female gametophyte?

A. Microspore 

B. Pollen grains 

C. Pollen sacs

D. Megaspores