Introduction to Life Sciences, Semester 1

The first semester of the Introduction to Life Sciences course introduces students (in grade 8, 9, or 10) to the concepts of cell biology and heredity and provides a foundation for further study in biology or other related science disciplines. Within this course, there are three themes from which to develop standards-based learning cycle lessons:

• Characteristics and structure of life
• Heredity
• Evolutionary theory

Characteristics and Structure of Life

• The cell theory states that the cell is the basic unit of life; organisms are made of one or more cells; and all cells come from pre-existing cells. Cells are composed of a small number of key chemical elements.
• There are important differences among animal, plant, and bacterial cells. For example, bacteria, which are simple prokaryotic cells, have no membrane-bound organelles. Animal and plant cells, which are eukaryotic, have membrane-bound organelles.
• The structure of each organelle determines how it will support cell function. Animal cells contain many organelles such as the endoplasmic reticulum, Golgi bodies, ribosomes, mitochondria, and a nucleus. Plant cells have chloroplasts along with the other organelles. Animal, plant, and other eukaryotic cells contain many of the same organelles.
• Complex multicellular organisms are composed of tissues, organs, organ systems, and differentiated cell structures that work simultaneously to keep an organism alive and healthy.
• Many biological processes occur within cells. Such processes include, but are not limited to osmosis, diffusion, photosynthesis, cellular respiration, homeostasis, and synthesis of organic molecules.
• Eukaryotic cells undergo nuclear divisions and cytokinesis. Mitosis occurs when somatic cells divide. Meiosis occurs in germ cells and produces gametes. Cell division and differentiation enable cells to become specialized for given functions. Prokaryotic cells reproduce through prokaryotic fission.

Heredity

• The structure and function of DNA is related to the process of protein synthesis and, ultimately, the characteristics of an organism. DNA directs all the activities of the cell.
• The unit of hereditary information is a gene. Genes may occur in different forms called alleles. Traits are inherited by alleles being passed from parents to offspring.
• Chromosomes are made of DNA and proteins. Genes, also made of DNA, are small segments of chromosomes.
• Spontaneous changes in DNA are known as mutations. Some mutations are harmful, some have no effect, and some are beneficial. When mutations occur in sex cells, they may be passed on to future generations. Mutations that occur in body cells may affect the functioning of that cell or the organism in which that cell is found.
• Gregor Mendel determined the basic laws of genetics through controlled experiments with pea plants. He discovered the presence of dominant and recessive alleles. Later studies building on Mendel’s work revealed that Punnett squares could be used to predict the probability that offspring will express given traits.
• Mendelian and non-Mendelian genetics principles (i.e., segregation, independent assortment, jumping genes) help provide a more complete picture of heredity.

Evolutionary Theory

• Charles Darwin proposed that natural selection provides the mechanism for evolution to occur. Natural selection involves a change in gene frequency (genetic composition) in a population over time.
• Major points in Darwin’s theory include:
  • Variations exist within species.
  • In a particular environment, some individuals of a species are genetically better-suited for survival and reproduction. The offspring of such individuals are more likely to survive and reproduce.
  • Over time, change within species may lead to the evolution of a new species.
  • Within a population more offspring are produced than can survive, resulting in competition for resources.
  • Natural selection is the process through which species evolve.
• Genetic drift, gene flow, and mutation are mechanisms for genetic change within a population.
• Evolution is still occurring.
• Natural selection and other evolutionary mechanisms and their consequences provide a scientific explanation for the diversity and unity of past life-forms, as depicted in the fossil record, and in present life-forms.
• The earliest traces of life are found as cyanobacteria fossils dated at 3.5 billion years old.
• Prokaryotic ancestral cells gave rise to the Kingdoms Archaebacteria and Eubacteria. Eukaryotic cells descended from the Archaebacteria, and eventually gave rise to the Protista, Fungi, Plantae, and Animalia kingdoms.