During the aging process, not all hormone levels decrease; some actually increase. Which of the following is a hormone that may increase as a person ages?

Skeletal muscle: This muscle cell is striated, long, and cylindrical. There are many nuclei in a skeletal muscle cell. Attached to bones in the body, skeletal muscle contracts voluntarily, meaning that it is under conscious control.

Smooth muscle: This muscle consists of nonstriated muscle cells that are spindle-shaped. Like cardiac muscle cells, smooth muscle cells contain one nucleus. This muscle type is found in the walls of internal organs like the bladder and stomach. Smooth muscle contraction is involuntary and controlled by the autonomic nervous system.

Cardiac muscle: This muscle consists of muscle cells that are striated, short, and branched. These cells contain one nucleus, are branched, and are rectangular. Cardiac muscle contraction is an involuntary process, which is why it is under the control of the autonomic nervous system. This muscle is found in the walls of the heart.

The primary organ of the urinary system is the kidney. Blood from the heart flows through the kidneys via the renal artery. As blood drains from the kidney, it exits through a series of veins, the most prominent of which is the renal vein. When urine is produced, it does not drain through the tubes through which blood flows. Rather, urine flows through two ureters before emptying into the urinary bladder.

The following steps outline how the urinary system works:

• Kidney filters and excretes wastes from blood, producing urine.
• Urine flows down the ureters.
• Urine empties into the bladder and is temporarily stored.
• Bladder, when filled, empties urine out of the body via the urethra.

The number of protons, 28, gives the atomic number, which identifies this atom as nickel. The mass is the number after the dash in the isotope name, which is determined by adding the numbers of protons and neutrons (28 + 32 = 60).

The main male reproductive organs are thepenisand thetesticles, which are located external to the body. The penis is composed of a long shaft and a bulbous end called the glans penis. The glans penis is usually surrounded by an extension of skin called the foreskin.

Thetestes(analogous to the female ovaries), or testicles, are retained in a pouch of skin called thescrotum, which descends from the base of the penis. The scrotum contains nerves and blood vessels needed to support the testicles’ functions. Each testicle (or testis) produces sperm (analogous to the female ova), which are passed into a series of coiled tubules called theepididymis. The epididymis stores and nurtures sperm until they are passed into thevas deferens, a tubule that is about 30 centimeters long, extending from the testicle into the pelvis and ending at the ejaculatory duct.

The epididymis and vas deferens are supported by several accessory glands (the seminal vesicles, the prostate gland, and the Cowper glands) that produce fluid components of semen and support the sperm cells.

The protein disc that holds two sister chromatids together is what collectively makes a chromosome. A gene is a segment of DNA, deoxyribonucleic acid, which transmits information from parent to offspring. A single molecule of DNA has thousands of genes. A chromosome is a rod-shaped structure that forms when a single DNA molecule and its associated proteins coil tightly before cell division.

Chromosomes have two components:

• Chromatids: two copies of each chromosome
• Centromeres: protein discs that attach the chromatids together

Human cells have 23 sets of different chromosomes. The two copies of each chromosome are called homologous chromosomes, or homologues. An offspring receives one homologue from each parent. When a cell contains two homologues of each chromosome, it is termed diploid (2n). A haploid (n) cell contains only one homologue of each chromosome. The only haploid cells humans have are the sperm and eggs cells known as gametes.

The duodenum is the first part of the small intestines, located between the stomach and the middle part of the small intestines (jejunum). Once food has mixed with acid in the stomach, it moves into the duodenum, where it then mixes with bile from the gallbladder and digestive juices secreted from the pancreas. In the duodenum, absorption of vitamins, minerals, and nutrients begins.

The phenotype is the physical appearance of an organism, and the genotype is the set of alleles.

Mendel’s Theory of Heredity

To explain his results, Mendel proposed a theory that has become the foundation of the science of genetics. The theory has five elements:

• Parents do not transmit traits directly to their offspring. Rather, they pass on units of information calledgenes.
• For each trait, an individual has two factors: one from each parent. If the two factors have the same information, the individual ishomozygousfor that trait. If the two factors are different, the individual isheterozygousfor that trait. Each copy of a factor, orgene, is called anallele.
• The alleles determine the physical appearance, orphenotype. The set of alleles an individual has is itsgenotype.
• An individual receives one allele from each parent.
• The presence of an allele does not guarantee that the trait will be expressed

Because this is a positive correlation, if the nutrient concentration increases or decreases, plant height will either increase or decrease accordingly.

While analyzing data, scientists tend to observe cause-and-effect relationships. These relationships can be quantified using correlations.Correlationsmeasure the amount of linear association between two variables. There are three types of correlations:

Positive correlation:
As one variable increases, the other variable also increases. This is also known as a direct correlation.

Negative correlation:
As one variable increases, the other decreases. The opposite is true if one variable decreases. A negative correlation is also known as an inverse correlation or an indirect correlation.

No correlation:
There is no connection or relationship between two variables.

One step of the scientific method is to analyze information or data collected from the experiment to conclude whether the hypothesis is supported.

Recall that these make up thescientific method,described below:

• Problem:The question created because of an observation.Example: Does the size of a plastic object affect how fast it naturally degrades in a lake?
• Research:Reliable information available about what is observed.Example: Learn how plastics are made and understand the properties of a lake.
• Hypothesis:A predicted solution to the question or problem.Example: If the plastic material is small, then it will degrade faster than a large particle.
• Experiment:A series of tests used to evaluate the hypothesis. Experiments consist of anindependent variablethat the researcher modifies and adependent variablethat changes due to the independent variable. They also include acontrol groupused as a standard to make comparisons.
  • Example: Collect plastic particles both onshore and offshore of the lake over time. Determine the size of the particles and describe the lake conditions during this time period.
• Observe:Analyze data collected during an experiment to observe patterns.
  • Example: Analyze the differences between the numbers of particles collected in terms of size.
• Conclusion:State whether the hypothesis is rejected or accepted and summarize all results.
• Communicate:Report findings so others can replicate and verify the results.

There are two major types of receptor molecules that respond to an intercellular chemical signal:

• Intracellular receptors: These receptors are located in either the cytoplasm or the nucleus of the cell. Signals diffuse across the cell membrane and bind to the receptor sites on intracellular receptors, of the same cell.
• Membrane-bound receptors: These receptors extend across the cell membrane, with their receptor sites on the outer surface of the cell membrane. They respond to intercellular chemical signals that are large, water-soluble molecules that do not diffuse across the cell membrane.