Mendel discovered the pattern associated with _____after developing a series of rules in genetics.

Human intercourse consists of the male introducing sperm into the female’s reproductive system. Sperm may then pass through the female’s reproductive system to the Fallopian tubes where one sperm fertilizes an ovum, creating azygote. The zygote passes out of the Fallopian tube and implants into the uterine wall to begin gestation. Over nine months, the zygote develops and grows into an embryo and then a fetus. An infant is the baby that is born.

In solids, particles are usually closer together than in other states of matter because of the strong cohesive forces between the particles.

• Solids, liquids, gases, and plasmas differ from one another in the amount of energy that the particles have and the strength of the cohesive forces that hold the particles together.
• Cohesion is the tendency of particles of the same kind to stick to each other.
• A solid has the lowest amount of energy because its particles are packed close together. Liquids have more energy than a solid, and gases have more energy than solids or liquids because the cohesive forces are very weak.

In this reaction, two elements are trading places hence double-replacement. In the reactants, zinc and bromide ions are together, and potassium and hydroxide ions are together. In the products, zinc and hydroxide ions are together, and potassium and bromide ions are together.

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.

Theaging processaffects hormone activity in one of three ways: their secretion can decrease, remain unchanged, or increase.

Hormones thatdecrease secretioninclude the following:

• Estrogen (in women)
• Testosterone (in men)
• Growth hormone
• Melatonin

Inwomen, the decline in estrogen levels leads to menopause. Inmen, testosterone levels usually decrease gradually. Decreased levels of growth hormone may lead to decreased muscle mass and strength. Decreased melatonin levels may play an important role in the loss of normal sleep-wake cycles (circadian rhythms) with aging.

Hormones that usually remainunchangedorslightly decreaseinclude the following:

• Cortisol
• Insulin
• Thyroid hormones

Hormones that mayincrease secretionslevels include the following:

Parathyroid hormone

• Follicle-stimulating hormone (FSH)
• Luteinizing hormone (LH)
• Norepinephrine
• Epinephrine, in the very old

Taxonomy is the process of classifying, describing, and naming organisms. There are seven levels in the Linnaean taxonomic system, starting with the broadest level, kingdom, and ending with the species level. For example, in the image the genus level contains two types of bears, but the species level shows one type. Additionally,organisms in each level are found in the level above it. For example, organisms in the order level are part of the class level. This classification system is based on physical similarities across living things. It does not account for molecular or genetic similarities.

Both litmus paper and a pH scale can be used to indicate whether a solution is acidic. However, a pH scale can also determine the strength of an acid.

Researchers can determine the strength of an acid or a base by measuring the pH of a solution. The pH value describes how acidic or basic a solution is. On pH scale, shown below, if the number is less than 7 the solution is acidic. A pH greater than 7 means the solution is basic. When the pH is exactly 7, the solution is neutral.

The cell cycle is an organized process divided into two phases:interphaseand theM (mitotic) phase. During interphase, the cell grows and copies its DNA. After the cell reaches the M phase, division of the two new cells can occur. The G1, S, and G2phases make up interphase.

• G1:The first gap phase, during which the cell prepares to copy its DNA
• S:The synthesis phase, during which DNA is copied
• G2:The second gap phase, during which the cell prepares for cell division

It may appear that little is happening in the cell during the gap phases. Most of the activity occurs at the level of enzymes and macromolecules. The cell produces things like nucleotidesfor synthesizing new DNA strands, enzymes for copying the DNA, and tubulin proteins for building the mitotic spindle. During the S phase, the DNA in the cell doubles, but few other signs are obvious under the microscope. All the dramatic events that can be seen under a microscope occur during the M phase: the chromosomes move, and the cell splits into two new cells with identical nuclei.

Before mitosis or meiosis occurs, interphase must happen. This is when the cell cycle takes place. The cell cycle is an organized process divided into two phases:interphaseand theM (mitotic) phase. During interphase, the cell grows and copies its DNA. After the cell reaches the M phase, division of the two new cells can occur. The G1, S, and G2phases make up interphase.

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.