are chemical messengers secreted by glands. Exocrine glands, such as sweat glands, secrete fluids through ducts. glands secrete hormones directly into the bloodstream. The gland plays an important role in puberty and growth. Epinephrine, triggering the "fight or flight" response, is produced by the glands, which sit on top of the kidneys. Most glands that secrete hormones operate using feedback mechanisms. When hormone concentrations are high, the gland will produce of the hormone. Many cells produce chemicals called , hormone-like substances that impact inflammation and reproduction. The gland that helps regulate growth, body temperature, and the level of calcium in the blood is called the . Describe the function and compare steroidal and nonsteroidal hormones. How does each type of hormone interact with the cell? What other molecules are required for or involved in their function? ANSWERS:

1. Hormones

2. endocrine

3. pituitary

4. adrenal

5. less

6. prostaglandins

7. thyroid

8. Steroidal hormones enter the cell directly and interact with DNA inside the nucleus. These hormones change gene expression, affecting the RNA that is produced and the proteins that are translated in a cell. Nonsteroid hormones do not enter the cell. Instead, they bind to specific receptors on the outside of the cell membrane. This triggers molecules called secondary messengers, such as cAMP, to begin their work of relaying information in the cell, where other chemicals, messengers, and proteins are involved to create a cellular response.

Answers:

Hormones are chemical messengers

Endocrine glands secrete hormones...

The pituitary gland plays...

is produced by the adrenal glands...

the gland will produce fewer amounts of the hormone...

produce chemicals called paracrine factors...

blood is called the thyroid.

Steroid hormones are synthesized from cholesterol, while nonsteroid hormones are synthesized from modified amino acids and small peptides. Non-steroid hormones are not lipid-soluble and therefore they need to bind to a receptor on a cell membrane; while steroid hormones can diffuse through the cell membrane.

Explanation:

Hormones are signaling molecules synthesized by glands. The endocrine glands include the adrenal glands, pineal gland, thyroid gland, parathyroid gland, pituitary gland, ovaries, testes, pancreas and hypothalamus. The pituitary gland is an endocrine gland that secretes hormones capable of stimulating the adrenal glands in order to produce steroid hormones. Hormone levels are often modulated by negative feedback, by which high-hormone levels reduce their own production. Paracrine factors (also known as growth and differentiation factors) are proteins that can diffuse across small distances in order to induce responses in neighboring cells. The thyroid gland secretes hormones involved in regulating metabolism and growth. Moreover, the thyroid gland also secretes calcitonin that regulates calcium levels in the blood.

1) gene flow

- it is described as the transfer of genes from one population to another population so that frequency of gene is increased.

-a zebra migrates to join a different herd of zebras.

2) natural selection

- a mechanism of evolutionary change in which individuals with advantageous traits survive and reproduce whereas the others ( those that can not adapt) eliminate from the population.

-competition for sunlight leads to taller trees.

3) mutation

- permanent change in the nucleotide sequence of dna ( genetic material) that could have harmful or useful consequences.

-the dna of a snake changes to make its venom stronger.

4) genetic drift - it is a random phenomenon ( that occurs by chance such as fire) that results in change in the gene frequency in a small population.    

-a grassfire randomly sweeps through a population of buffalo and kills most of the animals.

explanation:

they deliver oxygen to the blood