Biology

The scientific method is used to solve problems and explain phenomena. The development of the scientific method coincided with changes in philosophy underpinning scientific discovery, radically transforming the views of society about nature. During the European Renaissance, individuals such as Francis Bacon, Galileo, and Isaac Newton formalized the concept of the scientific method and put it into practice. Although the scientific method has been revised since its early conceptions, much of the...

Cell Membranes and Diffusion In order to function, cells are required to move materials in and out of their cytoplasm via their cell membranes. These membranes are semipermeable, meaning that certain molecules are allowed to pass through, but not others. This movement of molecules is mediated by the phospholipid bilayer and its embedded proteins, some of which act as transport channels for molecules that otherwise would not be able to pass through the membrane, such as ions and carbohydrates.

Background Cells represent the most basic biological units of all organisms, whether it be simple, single-celled organisms like bacteria, or large, multicellular organisms like elephants and giant redwood trees. In the mid 19th century, the Cell Theory was proposed to define a cell, which states: Every living organism is made up of one or more cells. The cells are the functional units of all organisms. All cells arise from preexisting cells. All cells share common features such as having a...

Biomolecules Organisms contain a wide variety of organic molecules with numerous functions which depend on the chemical structures and properties of these molecules. All organic molecules contain a carbon backbone and hydrogen atoms. The carbon atom is central in the formation of a vast variety of organic molecules ranging in size, shape and complexity; inorganic molecules on the other hand, generally have simpler structures. The outermost shell of a free carbon atom can accommodate eight...

Homeostasis Conditions in the external environment of an organism can change rapidly and drastically. To survive, organisms must maintain a fairly constant internal environment, which involves continuous regulation of temperature, pH, and other factors. This balanced state is known as homeostasis, which describes the processes by which organisms maintain their optimal internal conditions. To maintain homeostasis, organisms have developed structures with distinct functions. Physiology is the...

Mendelian Genetics Evolution is caused by changes in the genetic composition of populations. In the field of population genetics, scientists model this process as changes in the frequency of alleles at individual genetic loci. This simple representation of how evolution occurs dates to Gregor Mendel’s analysis of trait inheritance patterns in pea plants, first presented in 1865. Mendel determined, using rigorous collection of data, that noticeable traits are controlled by two alleles of each...

The revelation of DNA as the hereditary molecule in all organisms has led to enormous scientific and medical breakthroughs and significantly enhanced our understanding of ourselves and other organisms. DNA isolation and profiling have been the fundamental first steps for many of the advancements in the past century; from identification of gene function, to revolutions of agriculture and forensics. Isolating DNA from Cells DNA isolation is a fairly simple procedure that requires few but...

Background In early 20th century, pneumonia was accountable for a large portion of infectious disease deaths1. In order to develop an effective vaccine against pneumonia, Frederick Griffith set out to study two different strains of the Streptococcus pneumoniae: a non-virulent strain with a rough appearance (R-strain) and a virulent strain with a smooth appearance (S-strain) due to an outer polysaccharide capsule2. This outer layer of the S-strain bacteria enabled them to withstand the host...

Autotrophs Almost all living organisms on Earth depend on photosynthesis, which is the process that converts sunlight energy into a simple sugar called glucose. This molecule can be used as a short-term energy source or to build more complex carbohydrates like starches for long-term energy storage. Autotrophs are organisms that capture light energy using photosynthesis. Also known as primary producers, they provide the energy necessary to the organisms that eat them, which are known as...

Autotrophs and Heterotrophs Living organisms require a continuous input of energy to maintain cellular and organismal functions such as growth, repair, movement, defense, and reproduction. Cells can only use chemical energy to fuel their functions, therefore they need to harvest energy from chemical bonds of biomolecules, such as sugars and lipids. Autotrophic organisms, namely plants, algae, and photosynthetic and chemosynthetic bacteria, convert inorganic materials into such biomolecules by...

Cell division is fundamental to all living organisms and required for growth and development. As an essential means of reproduction for all living things, cell division allows organisms to transfer their genetic material to their offspring. For a unicellular organism, cellular division generates a completely new organism. For multicellular organisms, cellular division produces new cells for the general development of the organism, as well as produces healthy cells to replace damaged cells from...

Background All living organisms must carry out a set of basic functions in order to maintain themselves. One of these processes involves the transportation of materials throughout the organism. Therefore, organisms need to exchange materials with the environment, which can be seen on the small scale of cells transporting protein and other materials among one another or on a larger scale such as the water cycle, where water is continuously moving on, above, and below the surface of Earth. In...

Biological Catalysts All living organisms continuously perform numerous biochemical reactions to sustain their presence. Most of these reactions require an input of energy to start, which is called the activation energy. Catalysts are chemicals that lower the activation energy. Even though catalysts facilitate a chemical reaction, they are not consumed by it. This means a catalyst can facilitate a specific chemical reaction over and over in succession, increasing the rate of that reaction.

Drosophila as a Model Organism The common fruit fly, Drosophila melanogaster, is a widely used model organism in biology, though it may be more commonly recognized as a fruit-loving pest. There are multiple reasons that make D. melanogaster an excellent experimental organism: their roughly two-week generation time allows studying multiple generations, they are easily maintained in very small tubes, and their sexual dimorphism enables investigators to easily distinguish between males that have...

The Food Chain Energy is one of the most important abiotic factors in an ecosystem and organisms in an ecosystem are connected by the flow of energy and matter among one another. Since energy can be neither created nor destroyed, it can only change form or be transferred to the next organism in a food chain. For example, every time a cow grazes on grass or an osprey hunts and consumes fish, energy is transferred from the consumed organism to the consumer. Each of these interactions in a food...

Diverse ecosystems are important for the health of the planet and our survival as humans; it is therefore incredibly important for us to understand and measure biodiversity, which is defined as the variability among living organisms in an ecosystem. Biodiversity can be measured at many different levels including genetic, species, community, and ecosystem. One way to measure biodiversity is to assess species richness of an ecosystem, which is the total number of distinct species within a local...

The History of Life on Earth Fossils of organisms that were different from anything alive today had been documented as early as the 17th century, but it was not until the early 19th century that scientists began to recognize that the successive layers of fossil bearing rocks were like successive pages in the history of life on earth. Although this recognition gave rise to the birth of the field of paleontology, the idea of complete global extinction of a species had yet to be fully accepted. At...

Species Distribution Biogeography is the study of species distribution across geographic space and the processes that shape these distributions. This discipline is based on the assumption that each species within a location must have immigrated from another geographic area or evolved from a local species. Within each habitat, a variety of biotic and abiotic factors act on individual species to shape birth, death, immigration, and emigration rates. To avoid local extinction, the combined birth...

Population Models An ecological population is a group of individuals of a single species living in an area at the same time. To persist, a population must either grow or maintain its size. Population ecology is the study of how population size and age distribution change over time through interactions with other species and the environment as well as with individuals of their own species. A particularly important feature that is studied by ecologists is the rate at which a population grows or...

Populations do not live in isolation; thus, every population interacts with others in certain ways. These interactions give rise to a network of populations. Hence, an ecological community is composed of such population networks of various species interacting with each other within the same area. These biological, or biotic, components may also closely interact with non-living, or abiotic, components, forming an ecosystem. Ecosystems may be as small as the microbial communities inside the human...

The certainty of climate change remains a public controversy despite the consensus among approximately 97% of active climate researchers, who not only agree that the Earth’s climate is changing but also state that this change is intensified by human activity, predominantly carbon emissions 1. The disconnect between the public and the experts is partly due to poor understanding of the mechanisms involved in climate change as well as the differences among essential concepts such as weather and...

Life in a Population Organisms in populations interact with one another in complex ways, where individuals compete for resources such as food, shelter, and mates. These interactions are costly since individuals invest energy to acquire the resource, therefore there are a variety of strategies that organisms adopt to gain an advantage over their competitors. This is observed clearly with polymorphic mating systems, in which one sex, predominantly males, display multiple mating strategies. For...

Optimal Foraging Organisms must acquire and use resources in their environment to survive. While food is one of the primary resources organisms must search for, individuals also need to seek habitats, shelter, and mates. This process of searching for resources is known as foraging, which involves a series of costs and benefits. More specifically, acquiring a resource provides the organism with a benefit, however, searching and capturing the resource requires expenditure of time and energy.

Choosing Mates Evolutionary fitness is largely determined by the ability of an organism to survive and successfully produce offspring. Critical to this process is sexual selection, which plays a large role in the determination of mating pairs, and thus which genes are passed on to the next generation. Often, intense competition for mates within a population places selective pressure on traits related to courtship and copulation. Natural selection that results from these pressures is called...

Social Organization Varying levels of social organization are observed within the animal kingdom, ranging from simple to highly complex. These systems can greatly enhance the survival and reproductive success of an individual or a population. Of these, eusociality is the highest level of social organization, involving divisions of labor based on social castes. However, this system is rarely observed in nature, as it requires individuals to help others in the population at great survival or...

Fitness Widespread variation of phenotypes in natural populations provides the raw material for evolution, which is the change in the inherited traits of populations over successive generations. Natural selection is one of the main mechanisms of evolution and requires variable traits to be heritable and associated with differential survival and/or reproductive success. Phenotypes that correlate with greater success will have more offspring that survive to reproduce in the next generation, and...

Natural Selection and Adaptive Evolution In natural settings, adaptive evolution takes place by natural selection, a process in which differences in traits lead to differences in survival and reproductive success between individuals. This happens because individuals with certain phenotypes have a higher probability of survival and/or produce more surviving offspring than individuals with other phenotypes. A classic example of this was demonstrated by Rosemary and Peter Grant studying the...

Evolutionary change is interesting and important to study, but changes in populations occur over long periods of time and in huge physical spaces and are therefore very difficult to measure. In general, studying phenomena like this requires the use of mathematical models which are built using parameters that can be conveniently measured. These models are then used to make predictions about how changes to the system might affect the outcome. For example, changes to the frequency of genetic...

Humans have been attempting to properly classify living things since Aristotle made the first attempt during the 4th century BC. Aristotle’s system was improved upon during the Renaissance and then, subsequently, by Carolus Linnaeus in the mid 1700’s. These more formal classification and organization systems grouped species by their physical similarity to one another. For example, all vertebrates have a backbone, but invertebrates do not. Traits like the backbone are called synapomorphies,...

From Water to Land Kingdom Plantae first appeared about 410 million years ago as green algae transitioned from water to land. Though challenging, this transition benefited early colonizers in several ways. Initially, most living organisms (including plants and animals) were ocean dwelling, making aquatic environments crowded and highly competitive. In contrast, land was a relatively uncolonized environment with ample resources and little to no predators or competitors. Terrestrial environments...

Kingdom Animalia is composed of a range of organisms united by a set of common characteristics. Barring a few exceptions, animals are multicellular eukaryotes that move, consume organic matter, and reproduce sexually. Although these attributes are shared, species within this kingdom are also extremely diverse. This diversity is due to adaptation of each species to a different niche. The niche of a species includes the area, function, and interrelationship of that species with other biotic and...

Bacteria and fungi are two highly diverse groups of organisms that can have significant beneficial or detrimental impacts on human health. For this reason, it is important to understand and distinguish between individual species of these groups. As you will recall, biological taxonomists group organisms based on their phylogenetic relatedness. The three domains of life, Bacteria, Archaea, and Eukaryota segregate life into three distinct groupings. While all bacteria fall within the domain...