1. How long is the typical human digestive tract?
   
2. what are chemicals that break down food into the four basic organic compounds.
   

3.urnine is finally expelled from the body through which of the following?

Bladder

Collecting duct

Kidneys

Urethra

4.What does the hemoglobin in red blood cells do?

It binds carbon dioxide

it binds oxygen

it releases antibodies

it releases carbon dioxide

5.what chamber of the heart pumps blood into the pulmonary artery, which leads to the lungs?

The left atrium

the left ventricle

the right atrium

the right ventricle

6.In which part of the circulatory system is blood brought directly to the tissues?

7.when a cell first takes in a virus, what organelles tries to destroy it?

8.what type of cells engulfs an invading pathogen and displays its antigens?

9.what is keratin?

1. what is the principle component of the thickest layer of the skin?
   

11.what is the tough protein that is one of the primary components of bones?

12.how many bones are contained in the adult body?

13.which of 6the following bones protects the spinal cord?

1. which of the following types of muscles are voluntary?
   

15.what is the role of the proteins actin and myosin?

16.where is insulin produced?

17.which of the following receptors respond best to dim light?

18.what is the hormone that causes secondary characteristics in males?

1. what are eggs produced in the female body?