A chemical substance that an organism requires to live. a nutrient that is scarce or cycles slowly through an ecosystem. ensures that nutrients will be circulated throughout the biosphere.
Answer:
Our body cells require oxygen to release energy.
Explanation:
The oxygen that we take in during respiration is used to break down the food we eat to release energy from it. When we breathe in oxygen, it diffuses into blood from the lung, where it is transported by red blood cells to the entire body to be used to produce energy.
D lowering the activation energy of a reaction.
Answer:
Microtubules composed of tubulin protein.
Explanation:
The cytoskeleton is composed of three well defined filamentous structures: microtubules, microfilaments, and intermediate filaments. Each of these filamentous structures is a polymer of proteinic subunits united by weak, not covalent connections.
Microtubules are long hollo cylindric tubes with no ramifications of a diametre near to 25 nanometers. They are constituted by two subunits of tubulin protein which polymerize to form microtubules. These filaments shape the cell and are involved in intracellular transport. Microtubules extend from an organizing center near the nucleus to the cellular surface.
