Correct Answer: Option 3, They recycle chemicals from dead organisms.

Fungi and bacteria are principal decomposers that keep the nutrient balance in ecosystems, which is essential for plant and animal growth. They play an important role in nutrient cycling, or the endless recycling of chemical elements that occurs between organisms and their nonliving surroundings. Fungi and bacteria secrete enzymes that degrade organic material into inorganic nutrients and minerals, which are then returned to the environment, ready to be absorbed by living organisms.

Option 1 is incorrect. The decomposers recycle and break down organic materials, which are returned to the abiotic environment in forms that can be used by plants, but not as energy.

Option 2 is incorrect. They release inorganic products like carbon dioxide and ammonia, not oxygen.

Option 4 is incorrect because what they synthesize are inorganic products from organic nutrients, not the other way around.

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 4 a rapid rise in the number of blood cells

Homeostasis means steady state. Options 1, 2, and 3 are all about homeostasis. All are normal occurrences in the body. The primary function of the red blood cells, or erythrocytes, is to carry oxygen from the lungs to body tissues and to transfer carbon dioxide from the tissues to the lungs. The normal RBC count of adult males is 4.6 - 6.0 million, while for adult female it is 4.2-5.0 million. Normal physiological increases in the RBC count occur at high altitudes or after strenuous physical training. At high altitudes, less atmospheric weight pushes air into the lungs, causing a decrease in the partial pressure of oxygen and hypoxia. With strenuous physical training, increased muscle mass demands more oxygen. Smokers also have a higher number of red blood cells than non-smokers. The normal increase in RBC count is due to body's initiative to maintain homeostasis.

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 2 Gene expression can be influenced by the environment

Cloning is the process of producing populations of genetically-identical individuals that occurs in nature. If there would be variation, this is influenced by the environment in which the organisms are exposed to. For instance, a cloned shade-loving plant is exposed to sunlight, while the other clone is placed in a shaded area during growth stages. The clone exposed to sunlight might develop characteristics that would help it adapt to the intense light.

Meiosis is a two-staged type of cell division in sexually reproducing organisms. That results in gametes with half the chromosome number of the original cell. This causes variation of the offspring from the parent cells.

It is true that differentiated cells are dictated by different genes; but clones will undergo the same differentiation of cells. Hence, option 3 is incorrect.

If cloning is done to produce offsprings, the genetic composition of the parent is not divided but replicated to produce the same organism with the same genetic composition.

Correct Answer: Option 4 recombination of genes within the cell

Genetic recombination is the process by which a strand of genetic material (usually DNA; but can also be RNA) is broken and then joined to a different DNA molecule. In eukaryotes recombination commonly occurs during meiosis as chromosomal crossover between paired chromosomes. This process leads to offspring having different combinations of genes from their parents and can produce new chimeric alleles.

Variation may not be the effect of this kind of change. A change in the base subunit sequence could lead to an alteration of amino acid sequence to be coded to form the proteins of the body.

Evolution cannot take place because the recombination just happened in one organism, not it a population of organisms. Thus, the rate of evolution will not be affected.

Correct Answer: Option 3 The two cells that result will have identical DNA.

Budding is a form of asexual reproduction. The new organism is naturally genetically identical to the primary one (a clone). When yeast buds, one cell becomes two cells.

The simple cell division of a yeast cell is through the pinching of small bud cells from a parent cell. Meiosis is absent because it usually occurs in sexual reproduction. Therefore, option 4 is incorrect.

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 4 liver cells use different genes than muscle cells

Genes are turned on or off for cellular differentiation. For example, to produce the specialized liver cells, only a fraction of the genes are expressed (through transcription with the aid of enzymes) to generate the specific structure and function of the cell. To produce the muscle cell, another set of genes of the DNA are "turned-on" (while the genes coding for the liver are not expressed) to make its specific structure and function.

The other options are invalid.