Nitrogen enters the food 1. primarily through soil-dwelling bacteria that "fix" nitrogen by attaching it to other atoms 2. from the atmosphere when "fixed" by the photosynthetic machinery of plants 3. when rocks dissolved by rainwater become soil, which is then utilized for plant growth 4. through soil erosion followed by runoff into streams and ponds 5. through methane, produced by herbivores as a by-product of the breakdown of plant material.

The correct answer will be Option-1.

Explanation:

Nitrogen fixation is the process by which the atmospheric nitrogen enters the living sphere of the earth. The atmosphere is the largest reservoir of nitrogen in which nitrogen accounts for 78% of the total gases.

The atmospheric nitrogen is fixed through three pathways: lightning, man-made a method like Haber's process and the Biological fixation.

Biological fixation accounts fro 92% of the total nitrogen fixation which is performed by the few bacteria which contains the Nitrogenase enzyme and break down the N₂ to NH₃. The bacteria like Rhizobium is the leguminous bacteria which fixes the nitrogen.

Thus, Option-1 is the correct answer.

question#1

ans:

cell is the basic unit of organization of all living things. cells are often called the building block of life and it is the smallest unit of life. the study of cell is called cell biology. cell consists of cytoplasm enclosed within membrane, which contain bio-molecules such as proteins and nucleic acid.

two third of cell is water, which means that two-third of your whole body is water. the rest is the mixture of molecules, mainly proteins, lipids and carbohydrates.

question#2

ans:

organ:

an organ is a group of tissues specialized to form a functional unit. an example is the heart in animals.

organ system:

an organ system is a group of several organs whose functions are synchronized to release an effective action in a living organism. an example is digestive system.

question#3

different systems perform different function at tissue level. for example, the respiratory system facilitates breathing. in the alveoli tissue of the lungs, the exchange of oxygen and carbon dioxide molecules between the air and the bloodstream occurs by passive transport, so that oxygen is taken in and carbon dioxide and water are removed. different systems of the body carry out different functions. for example, your digestive system is responsible for taking in and processing food, while your respiratory system working with your circulatory system is responsible for taking up oxygen and getting rid of carbon dioxide.

question#4

different systems perform different function at tissue level. for example, the respiratory system facilitates breathing. in the alveoli tissue of the lungs, the exchange of oxygen and carbon dioxide molecules between the air and the bloodstream occurs by passive transport, so that oxygen is taken in and carbon dioxide and water are removed. different systems of the body carry out different functions. for example, your digestive system is responsible for taking in and processing food, while your respiratory system—working with your circulatory system is responsible for taking up oxygen and getting rid of carbon dioxide.

question#5

our body works because of the interactions that happen between organs and organ systems.  

for example:  

the heart to regulate blood flow throughout the body. the blood carries oxygen and nutrients to the cells and carries carbon dioxide and waste away from the cells. body systems work together in maintaining a constant internal environment. when this balance is disrupted, the body systems may not function properly, and human health can suffer.   you start to feel bad.