Jobs that are related to stem cells are scientists in lab creating stem cells and doctors that secure the safety of the stem cells.

This relates to the human body because respiratory is one of the 3 main systems of our body, others are circulatory and digestive system. The human body needs the respiratory system to live and breathe. without air,  there wouldn't be blood produced. If there isn't any blood produced, the human would not function. That's why choking someone is the easiest way to kill someone without a weapon, choking someone stops the supplying of air into the body.  

Acids are sour materials that have a PH scale under 7, the less the pH scale the higher the acidity. Acids can eat away metals and minerals (1). Acids can either give off a proton (hydrogen ion) to another compound, or get a pair of electrons.  

Bases are the opposite of acids, it donates a pair of electrons and accepts protons from hydrogen atoms. That's why they have a higher pH (potential of hydrogen). Bases can neutralize acids, it's usually used in cleaning solutions (like bleach), it has slippery textures and bitter flavors, can also conduct electricity. 

Our body have acids and bases to help us maintain a healthy human body. Hydrochloric acids (HCL) are found in our stomach, this gastric juice helps us digests the proteins and minerals we eat by activating the digestive enzymes to break down the amino acids. In our muscles, we have lactic acids, which is produced when we exercise. Lactic acids are when there's a lack of oxygen in our muscles, and the muscles produce lactic acids to break down glucose and generate energy. Bases appears in the small intestine, when the foods from the stomach are acidic, and when it travels to the small intestine, there must be neutralization before going further into the large intestine, or our tissues will break up from the hydrochloric acid. A sodium bicarbonate solution (a pH of 8.8)  is released from the pancreas and travels towards to small intestine to neutralize the acids. 

 Ionic bonds are when and metal and a non-metal bonds together together to  get electrons from each other to obtain a full octet. The metal atoms lose electrons to form positive ions (cations). The non-metal atoms gain electrons to form negative ions (anions). This way they are easily attracted to each other, for example, Sodium Chloride (NaCl) is when a metal (sodium) loses one valence electron, and a non-metal (chlorine) gains one so both atoms can form a full octet to become stable. 

 Covalent Bond forms one bond when two non metals share valence electrons to satisfy a full octet,  this creates a molecule, hence the name. For example, H2O, or water as we know, is formed when one oxygen atom, which has 6 valence electrons, needs 2 more to satisfy the octet rule. This is where hydrogen comes in, the 2 hydrogen atoms comes in and helps the oxygen atom to become a full octet.