The best answer is D.
Hormones are chemical messengers secreted mostly into blood and also extracellular fluid by specialized tissue of the endocrine system and affect the functioning of other tissues or cells.
Most hormones circulate in blood and come in contact with essentially all cells, but a particular hormone will only affect a limited number of cells, which are termed as target cells to that hormone.
A target cell responds to a particular hormone because it bears receptors for that hormone.
For example the red blood cells have receptors for the hormone called insulin which is produced by the pancreas. The red cells are able to take in glucose when their receptors bind to insulin.
Answer and Explanation:
The steps of the sliding filament theory are:
Muscle activation: breakdown of energy (ATP) by myosin.
Before contraction begins, myosin is only associated with a molecule of energy (ATP), which myosin breaks down into its component molecules (ADP + P) causing myosin to change shape.
Muscle contraction: cross-bridge formation
The shape change allows myosin to bind an adjacent actin, creating a cross-bridge.
Recharging: power (pulling) stroke
The cross-bridge formation causes myosin to release ADP+P, change shape, and to pull (slide) actin closer to the center of the myosin molecule.
Relaxaction: cross-bridge detachment
The completion of the pulling stroke further changes the shape of myosin. This allows myosin and ATP to bind, which causes myosin to release actin, destroying the cross-bridge. The cycle is now ready to begin again.
The repeated cycling through these steps generates force (i.e., step 2: cross-bridge formation) and changes in muscle length (i.e., step 3: power stroke), which are necessary to muscle contraction.
The smallest item in the list would be organelles. Organelles are tiny structures within a cell, that help it to function. Example of organelles are-- nucleus, mitochondria, cell membrane to name a few. Cells are the basic unit of structure and function of all living things, therefore, cells would have to be placed second. They are microscopic. A group of similar cells that work together to perform a specific function, is known as a tissue. Therefore, tissue is next largest. Examples of tissues include, muscle tissue, epithelial tissue, adipose tissue. When different types of tissues work together to perform a function in the body, this group of tissues forms an organ. An example of an organ is the heart. Inside the heart are many types of tissue-- cardiac muscle,nerve, blood, connective, etc. The job it performs is to pump blood. When various organs work together to perform a specific function in the body, this makes up a system. An example is the circulatory system. In this system are many organs that work together. Arteries, veins, capillaries and heart are all part of the circulatory system. Its job is to circulate blood containing nutrients and oxygen to cells and to pick up cellular wastes. All the systems of the body comprise the organism. An organism is a living thing. It can be as tiny as a microbe, or a complex as a human. When referring to a multicellular organism, the correct order from smallest to largest is-- organelle, cell, tissue, organ, system, organism
