Correct Answer: Option 2 cells→tissues→organs→organ systems

Cells are the basic unit of organization is an organism. Tissues are made up of cells with similar structure and function. Organs are made up of tissues that work together to perform a specific activity. An organ system is composed of organs working together that carry out a biological process.

Correct Answer: Option 1 receptor molecules

A receptor is a protein molecule, embedded in either the plasma membrane or cytoplasm of a cell, to which a mobile signaling (or "signal") molecule may attach. A molecule which binds to a receptor is called a "ligand," like the protein from the surface of HIV and when such binding occurs, the receptor goes into a conformational change which ordinarily initiates a cellular response.

Genetic codes are not attachment sites but a set of rules by which information encoded in genetic material (DNA or RNA sequences) is translated into proteins (amino acid sequences) by living cells. Thus, option 2 is incorrect.

Option 3 is incorrect because molecular bases are not attachment sites as well.  These are the excited complexes of biological systems.

Option 4 is incorrect because inorganic catalysts change the rate of reaction unconsumed but are not attachment sites.

Correct Answer: Option 4 structures found in single-celled organisms can act in a manner similar to tissues and organs in multicellular organisms

All the given statements are correct in their own sense; however the best answer in linking the relationship of the two structures is mentioned in option 4. Options 1-3 focused on the multicellular organism. In option 4, homeostasis occurring in both the single-celled and multi-celled organisms are compared.

Correct Answer: Option 4 chains folded differently and  different sequence of amino acids.

The function of a protein (except when it is serving as food) is absolutely dependent on its three-dimensional structure. For two proteins to perform different functions, they must have different structure and composition. Amino acids are the building blocks of proteins. Proteins are never composed by sugars because it is different from carbohydrates.

Correct Answer: Option 3 chemical bonds

Chemical bonds contain free energy (energy that can be harnessed to do work) which can be released when the bonds are broken. Free energy from chemical bonds is 100% efficient when converted to work.

Atoms like carbon, oxygen and nitrogen are just some of the elements which are bonded chemically and stores chemical energy. Thus, options 1, 2, and 4 are incorrect.

Correct Answer: Option 1Cellular respiration

Cellular respiration is the set of the metabolic reactions and processes that take place in organisms' cells to convert biochemical energy from nutrients into adenosine triphosphate (ATP), and then release waste products.

Option 2 and 3 are incorrect. Cellular reproduction and diffusion are two biological processes but does not yield ATP.

Option 4 is also incorrect. Though energy is gathered through digestion of food materials, digestion is not the specific processes used to generate ATP from organic molecules.

Correct Answer: Option 2 a receptor and a hormone

A given hormone affects different target cells within an animal differently, or it may affect different species differently. The diversity of responses of target cells to hormones is seemingly endless and depends on the number and affinity of receptor proteins within the target cells. The hormone-receptor complex enters the nucleus and binds to specific regulatory sites, stimulating the expression of specific genes.

Correct Answer: Option 4 d

In the hierarchy of classification, the highest and biggest classification is domain, followed by kingdom, phylum, class, order, family, genus and species, respectively. Since option 4 and the species Felis domestica are both under the same genus, therefore, they are most closely related than the other species in the animal kingdom.

Insulin is secreted by the beta cells of the pancreas (organ X) in response to high blood sugar, although a low level of insulin is always secreted by the pancreas. After a meal, the amount of insulin secreted into the blood increases as the blood glucose rises. Likewise, as blood glucose falls, insulin secretion by the pancreatic islet beta cells decreases. In response to insulin, cells (muscle, red blood cells, and fat cells) take glucose in from the blood, which ultimately lowers the high blood glucose levels back to the normal range.

Correct Answer: Option 3 Molecules moved across the membrane without additional energy being supplied

There was no energy added in the setup (e.g. heat) for the change in color to take place. The changes happened because of passive transport of molecules.

An enzyme or a carbohydrate was not added in the setup for the change to take place.