The food group is fats (sweets and oils)
Sand is granular and coarse meaning that water and nutrients can flow through it quite easily. Clay on the other hand has very fine particles that cling together to form a waterproof substance which traps/ stops any nutrients or water from moving down. Clay's also quite difficult for plants to get their roots into. Silt has a texture between clay and sand, meaning that it is the ideal substance as it allows the best water and nutrition movement in the soil. Most plants will grow best in silt, but there are some plants who are more adapted to living in sand (e.g. Marram grass) or clay.
Hemoglobin has tetrahedral structure containing four heme groups that surround a globin group.
Heme is ringlike organic compound also known as a porphyrin to which an iron atom is attached. There are four iron atoms that bind four oxygen atoms and transport them to tissues.
The answer is: An air conditioner that turns on if the temperature gets too hot.
Even though they hurt you emotionally, Negative feedbacks serve their own important function. They keep your feet on the ground and prevent you from getting too arrogant.
This function is similar as a cooling air conditioner. Hot temperature in the comparison above represent your arrogance and the air conditioner represent the negative feedback.
