The Ultimate Biology Gauntlet: Are You a True Biologist? #2

Humans have 46 chromosomes. Each parent contributes 23 chromosomes in a gamete (sex cell). When the gametes combine to form an embryo, the embryo then contains two sets of chromosomes, equal to a total of 46 chromosomes.

Multicellular organisms include organisms with more than one eukaryotic cell. Animals and plants are all multicellular. All prokaryotic organisms are unicellular, meaning the entire organism consists of a single cell. There are some unicellular eukaryotic organisms, such as protists and some fungi (yeast).

Algae bodies that are plantlike, such as the structure of brown algae, are referred to as a thallus. Where plants have roots, stems and leaves, a thallus consists of a hold fast (rootlike part), stipe (stem like part), and blades (leaf like parts).

Organisms in Kingdom Protista include eukaryotes that do not share all of the characteristics of organisms in the kingdoms Animalia, Fungi or Plantae. Within Kingdom Protista are a group of protists that behave like animals. These single-celled organisms are in the Phylum Protozoa.Protozoa include flagellates, ciliates, amoeba and sporozoans.

The three major body parts of all insects (Class Insecta) are the head, thorax and abdomen. Many animals that are similar in size and appearance are mistaken for insects, such as ticks, mites and spiders. However, these creatures are in the Class Arachnida, not Class Insecta.

Honey bees live in a colony with a division of labor. The worker bees form the largest group of bees in the hive. They serve many different roles, such as removing dead bees, feeding baby drones, packing pollen, building the honeycomb, and taking care of the queen bee. The queen bee is the only fertile female bee in the colony. Worker bees remain infertile as long as the queen bee is alive.

Vertebrates are multicellular organisms in Kingdom Animalia. Vertebrates are animals with a backbone, and include mammals, birds, fish, reptiles and amphibians. Insects, earthworms and sea stars belong to a group of animals without a backbone, invertebrates.

Exoskeletons are skeletons located on the outside of an animal's body. They are used for protection and to support the animal. Mollusks and insects are examples of animals with endoskeletons. Birds, turtles and snakes are all animals with endoskeletons. Endoskeletons are internal skeletons.

Organisms in Kingdom Animalia have muscles and nerves. If an animal can move from one place to another (known as locomotion), it is doing so by contracting its muscles. Not all animals have skin and/or a skeleton.

Gametes are haploid cells, which means they contain half the number of chromosomes that body cells contain. Gametes are used in sexual reproduction to form an offspring. When two gametes fuse together during sexual reproduction, they form a zygote.

In humans, there are two sex chromosomes, referred to as “X” and “Y.” Females have two X chromosomes in each body cell and in each sex cell (gamete). Males have one X chromosome and one Y chromosome. If a person inherits two X chromosomes, one from each parent, that person will develop into a female. If a person inherits an X chromosome from the mother and a Y chromosome from the father, that person will develop into a male.

There are three ways genetic variation may take place: New combinations of chromosomes result from sexual reproduction; chromosome mutation and gene mutation occur during mitosis and/or meiosis.

“Survival of the fittest” is an expression used to describe natural selection. Natural selection takes place when organisms with the characteristics best suited for their environment survive and produce fertile offspring. The “fittest” in the phrase is referring to the organisms that have the characteristics that allow them to survive in their environment. In theory, these organisms will not only survive, but will also reproduce. Their offspring will also have the characteristics that allowed the parent to successfully survive. Over time, these characteristics will continue to be passed on to future generations. Organisms that lack the characteristics to survive will die before reproducing, and therefore, not pass on the less desirable characteristics.

Genetic evidence is the most direct type of evidence used to support the theory of evolution. Since adaptations are passed along genetically, from one generation to another, evidence for evolution can be collected by examining the genome of individuals of the same species and comparing it to genetic information of ancestral species, species of the same phylogenetic groups and/or common ancestors between several species.

Hybridization occurs when individuals of different species mate and form offspring. The offspring are referred to as hybrids. In order for hybridization to occur, the parents must be similar to each other. For example, a horse and a donkey can reproduce to form a mule. However, a fly cannot mate with a bird to create a new organism. When hybridization occurs, the offspring are typically sterile.