Human Sexual Reproduction: Stages, Fertilization, and Development
Human Sexual Reproduction
In sexual reproduction, two cells unite (sperm and egg), each from one individual of the opposite sex, to form a zygote. The zygote develops and produces an offspring that is genetically different from the parents.
Puberty and Adolescence
Puberty: The acquisition of sexual maturity during adolescence.
- Primary Sexual Characteristics: Reproductive organs.
- Secondary Sexual Characteristics: Hair, voice changes, etc.
Adolescence: The stage from approximately 9 to 18 years of age,
Read MoreUnderstanding the Human Digestive System: Organs, Glands, and Processes
The Human Digestive System: An Overview
The digestive system is a complex network of organs working together to break down food and absorb nutrients. It consists of the following:
- Mouth: Where digestion begins with saliva.
- Pharynx: The throat, a passageway for food and air.
- Esophagus: A muscular tube that carries food to the stomach.
- Stomach: An organ that churns food and mixes it with gastric juices.
- Small Intestine: The primary site for nutrient absorption.
- Large Intestine: Absorbs water and forms stool.
Cardiac Pacemakers: How They Work and Save Lives
The Cardiac Pacemaker
Normally, the heart carries out its job of pumping blood by means of a built-in system of rhythmic electrical impulses. These impulses are carried through the heart by nerves that lead to its muscle fibers, causing them to contract. Two main nerves lead to the ventricles, which are responsible for pumping blood. If one of these nerves fails to function properly, the heart beats irregularly. If both nerves fail for a few seconds, the brain receives insufficient blood, and the
Read MoreFoundations of Evolutionary Thought
Early Ideas on Species Change
Pierre-Louis Moreau de Maupertuis (1698-1759) suggested that the multiplication of species resulted from accidental recombination of particles from both parents, leading to offspring with varied traits from both parents.
Georges-Louis Leclerc, Comte de Buffon (1707-1788) proposed that animals had not been created as they appeared; rather, modern forms modified from common ancestors. Species change over time.
Jean-Baptiste Lamarck (1744-1829)
Lamarck believed animals possessed
Read MoreFundamentals of Taxonomy, Phylogeny, and Population Evolution
Basic Taxonomy and Phylogeny
Basic taxonomy has its roots in Aristotle’s original 2 Kingdom system. Since that time, modern taxonomy has undergone countless revisions, including important contributions by Linnaeus, Whittaker, Woese (Table 24.2), and others. Be able to recognize and express important historical changes to our taxonomical schemes.
In biology today, modern taxonomy is synonymous with phylogenetic systematics. Understand the basic principles of grouping organisms based on evolutionary
Read MoreFundamentals of Genetics, Heredity, and Human Ecology
Nucleotide Base Pairing in DNA
In DNA, the nucleotide bases pair specifically: Adenine (A) pairs with Thymine (T), and Guanine (G) pairs with Cytosine (C).
What Makes Individuals Unique?
Individuals are unique primarily due to variations in their alleles, which are different versions of the same gene.
Autosomes vs. Sex Chromosomes
Humans typically have 22 pairs of autosomes (homologous chromosomes that are not sex chromosomes) and one pair of sex chromosomes (XX for females, XY for males), totaling 46