age structure

Examples of age structure in the following topics:

• Age Structure, Population Growth, and Economic Development

  • With knowledge of this age structure, population growth can be more accurately predicted.
  • This results in a column-shaped age structure diagram with steeper sides.
  • Countries with declining populations, such as Japan, have a bulge in the middle of their age structure diagram.
  • The leftmost diagram (representing the age structure of a rapidly-growing population) indicates that the number of individuals decreases rapidly with age.
  • Explain how age structure in a population is associated with population growth and economic development

• Carbon Dating and Estimating Fossil Age

  • A substantial hurdle is the difficulty of working out fossil ages.
  • There are several different methods for estimating the ages of fossils, including:
  • If a fossil is found between two layers of rock whose ages are known, the fossil's age is thought to be between those two known ages.
  • If rocks of unknown age have traces of E. pseudoplanus, they have a mid-Ordovician age.
  • The layers of sedimentary rock, or strata, can be seen as horizontal bands of differently colored or differently structured materials exposed in this cliff.

• Evolution of Gymnosperms

  • Seed ferns produced their seeds along their branches without specialized structures .
  • What makes them the first true seed plants is that they developed structures called cupules to enclose and protect the ovule (the female gametophyte and associated tissues) which develops into a seed upon fertilization.
  • The Jurassic period was as much the age of the cycads (palm-tree-like gymnosperms) as the age of the dinosaurs.
  • This fossilized leaf is from Glossopteris, a seed fern that thrived during the Permian age (290–240 million years ago).

• Neurodegenerative Disorders

  • Roughly one in every eight people age 65 or older has the disease.
  • Due to the aging of the baby-boomer generation, there are projected to be as many as 13 million Alzheimer's patients in the United States in the year 2050.
  • This rare form of early-onset Alzheimer's disease affects fewer than five percent of patients with the disease and causes dementia beginning between the ages of 30 and 60.
  • Since Alzheimer's disease appears to hijack the normal aging process, research into prevention is prevalent.
  • Parkinson's disease causes the loss of dopamine neurons in the substantia nigra, a midbrain structure that regulates movement.

• Modeling Ecosystem Dynamics

  • Conceptual models describe ecosystem structure, while analytical and simulation models use algorithms to predict ecosystem dynamics.
  • Conceptual models are useful for describing ecosystem structure and dynamics and for demonstrating the relationships between different organisms in a community and their environment.
  • Human combustion of fossil fuels accelerates this conversion by releasing large amounts of carbon dioxide into the atmosphere, which may be a large contributor to the rise of the atmospheric carbon dioxide levels in the industrial age.
  • Conceptual models are useful for describing ecosystem structure, but are limited by their poor prediction of ecosystem changes.

• Evidence of Evolution

  • Scientists calculate the age of fossils and categorize them to determine when the organisms lived relative to each other.
  • Scientists call these synonymous parts homologous structures.
  • These unused structures (such as wings on flightless birds, leaves on some cacti, and hind leg bones in whales) are vestigial.
  • Great ape embryos, including humans, have a tail structure during their development that is lost by birth.
  • Like anatomical structures, the structures of the molecules of life reflect descent with modification.

• Bone and Joint Disorders

  • A key structural characteristic for a synovial joint that is not seen at fibrous or cartilaginous joints is the presence of a joint cavity.
  • Arthritis may arise from aging, damage to the articular cartilage, autoimmune diseases, bacterial or viral infections, or unknown (probably genetic) causes.
  • The most common type of arthritis is osteoarthritis, which is associated with aging and “wear and tear” of the articular cartilage.

• Anatomy of the Eye

  • Many structures in the human eye, such as the cornea and fovea, process light so it can be deciphered by rods and cones in the retina.
  • The lens is a transparent, convex structure located behind the cornea.
  • With age comes the loss of the flexibility of the lens; a form of farsightedness called presbyopia results.
  • The human eye contains structures, such as the cornea, iris, lens, and fovea, that process light so it can be deciphered by the retina.
  • Other structures like the aqueous humor and the vitreous humor help maintain the shape of the eye.

• Types of Synovial Joints

  • Synovial joints are further classified into six different categories on the basis of the shape and structure of the joint.
  • This structure allows rotational movement, as the rounded bone moves around its own axis.
  • RA is more common in women than men; the age of onset is usually 40–50 years of age.
  • This allows the soft tissue structures of joints, such as cartilage, tendons, and ligaments, to be visualized.
  • Differentiate among the six categories of joints based on shape and structure

• Epigenetic Control: Regulating Access to Genes within the Chromosome

  • This can lead twins who look very similar as infants or young children to differ in appearance as they age.
  • Histones package and order DNA into structural units called nucleosome complexes, which can control the access of proteins to the DNA regions.
  • These beads (histone proteins) can move along the string (DNA) and change the structure of the molecule.
  • Nucleosomes can move to open the chromosome structure to expose a segment of DNA, but do so in a very controlled manner.
  • Instead, these changes are temporary (although they often persist through multiple rounds of cell division) and alter the chromosomal structure (open or closed) as needed.