STANDARD SET 6. Chemistry of Living Systems

6. Principles of chemistry underlie the functioning of biological systems. As a basis for understanding this concept:

6.a. Carbon, because of its ability to combine in many ways with itself and other elements, has a central role in the chemistry of living organisms.

6.b. Living organisms are made of molecules consisting largely of carbon, hydrogen, nitrogen, oxygen, phosphorus, and sulfur.

6.c. Living organisms have many different kinds of molecules, including small ones, such as water and salt, and very large ones, such as carbohydrates, fats, proteins, and DNA.

Because all living organisms are made up of atoms, chemical reactions take place continually in plants and animals , including humans. The uniqueness of organic chemistry stems from chain polymers. Life could not exist without the ability of some chemicals to join together, repetitively, to form large, complex molecules. Concepts learned in this standard set are critical for understanding fully the chemistry of the cells of organisms, genetics, ecology, and physiology that will be taught in the high school biology/life sciences standard sets.


Carbon is unique among the elements because it can bond to itself and to many other elements. This attribute makes possible many different kinds of large, carbon-based molecules. Typically, carbon will make four separate covalent bonds (to other carbon atoms), but double and triple bonds are also possible. The variety of bonds allows carbon-based molecules to have a wide range of shapes and chemical properties. Key shapes include tetrahedral (e.g., methane and carbon tetrachloride), planar (e.g., formaldehyde and ethylene), and linear (e.g., acetylene and carbon dioxide). Students can research the nomenclature, composition, and structure of organic molecules by using textbooks and supplemental instructional mate-rials. They can also construct models of carbon-based molecules by using commercial modeling kits or inexpensive alternatives (e.g., gumdrops and tooth-picks).


Living organisms are made up of a great variety of molecules consisting of many atoms (with carbon atoms playing the main roles), but the number of different elements involved is quite small. Carbon and only five other elements make up most of Earth’s biomass. Those six elements, however, can combine in many different ways to make large, organic molecules and compounds. To demonstrate this idea, teachers may burn organic material, such as bone, leaves, wood, or a variety of candles. They may hold a cold glass or plate above the flame to condense droplets of water, one of the combustion products. They may also hold a heat-treated glass in the flames to collect carbon deposits in the form of soot. Students can discuss what elements were in the organic material. Teachers may draw students’ attention to the black material that forms when meat is roasted or grilled or when toast is charred.

6. c.

Living organisms require a variety of molecules; some molecules contain carbon and some do not. The molecules that make up organisms and control the biochemical reactions that take place within them are usually large molecules, such as DNA, proteins, carbohydrates, and fats. Organisms also require simple substances, such as water and salt, to support their functioning. Teachers may encourage students to research why plants and animals need simple molecules such as water. Other activities for teachers may include squeezing the water from celery or turnips to demonstrate the presence of water. Or they may ask students how they can demonstrate that water is in fruits and vegetables (e.g., dried fruit). Teachers may also ask students how they know that there is salt in their bodies. Most students know that their perspiration tastes salty.


The Structure and Composition of the Universe
Review from STANDARD SET 2
  • 2.g. Students know the role of gravity in forming and maintaining the shapes of planets, stars and the solar system.



      Gravity, an attractive force between masses, is responsible for forming the Sun, the planets, and the moons in the solar system into their spherical shapes and for holding the system together.

It is also responsible for internal pressures in the Sun, Earth and other planets, and the atmosphere. Newton asked himself whether the force that causes objects to fall to Earth could extend to the Moon.

      Newton knew that the Moon should travel in a straight line (getting farther and farther from earth.) unless a force was acting on ot to change its direction into a circular path.He worked out the mathematics that convinced him that the force between all massive objects is directly proportional to the product of their masses and inversely proportional to the square of the distance between their centers.

      This relationship was then extended to explain the motion of Earth and other planets about the Sun.



      Initially, the universe consisted of light elements, such as hydrogen, helium, and lithium, distributed in space. The attraction of every particle of matter for every other particle of matter caused the stars to form, making possible the “stuff” of the universe.

      As gravity is the fundamental force responsible for the formation and motion of stars and of the clusters of stars called galaxies, it controls the size and shape of the universe.

STANDARD SET 4.  The structure and composition of the universe

The structure and composition of the universe can be learned from studying stars and galaxies and their evolution. As a basis for understanding this concept:

a. Students know galaxies are clusters of billions of stars and may have different shapes.

b. Students know that the Sun is one of many stars in the Milky Way galaxy and that stars may differ in size, temperature, and color.

c. Students know how to use astronomical units and light years as measures of distances between the Sun, stars, and Earth.

d. Students know that stars are the source of light for all bright objects in outer space and that the Moon and planets shine by reflected sunlight, not by their own light.

e. Students know the appearance, general composition, relative position and size, and motion of objects in the solar system, including planets, planetary satellites, comets, and asteroids originally thought to be stars are now known to be distant galaxies.

STANDARD SET 4. Framework


  • Galaxies them-selves appear to form clusters that are separated by vast expanses of empty space.

  • As galaxies are discovered they are classified by their differing sizes and shapes.

  • The most common shapes are spiral, elliptical, and irregular. Beautiful, full-color photo-graphs of astronomical objects are available on the Internet, in library books, and in popular and professional journals.

  • Astronomers have inferred the existence of planets orbiting some stars.


  •  The Sun is a star located on the rim of a typical spiral galaxy called the Milky Way and orbits the galactic center.

  • In similar spiral galaxies this galactic center appears as a bulge of stars in the heart of the disk.

  • The bright band of stars cutting across the night sky is the edge of the Milky Way as seen from the perspective of Earth, which lies within the disk of the galaxy.

  • Stars vary greatly in size, temperature, and color. For the most part those variations are related to the stars’ life cycles.

  • Light from the Sun and other stars indicates that the Sun is a fairly typical star. It has a mass of about 2 × 1030 kg and an energy output, or luminosity, of about 4 × 1026 joules/sec.

  • The surface temperature of the Sun is approximately 5,500 degrees Celsius, and the radius of the Sun is about 700 million meters.

  • The surface temperature determines the yellow color of the light shining from the Sun. Red stars have cooler surface temperatures, and blue stars have hotter surface temperatures.

  • To connect the surface temperature to the color of the Sun or of other stars, teachers should obtain a “black-body” temperature spectrum chart, which is typically found in high school and college textbooks.


  • Distances between astronomical objects are enormous.

  • Measurement units such as centimeters, meters, and kilometers used in the laboratory or on field trips are not useful for expressing those distances. Consequently, astronomers use other units to describe large distances.

  • The astronomical unit (AU) is defined to be equal to the average distance from Earth to the Sun: 1 AU = 1.496 × 1011 meters.

  • Distances between planets of the solar system are usually expressed in AU.

  • For distances between stars and galaxies, even that large unit of length is not sufficient.

  • Interstellar and intergalactic distances are expressed in terms of how far light travels in one year, the light year (ly):

  • 1 ly = 9.462 × 1015 meters, or approximately 6 trillion miles.

  • The most distant objects observed in the universe are estimated to be 10 to 15 billion light years from the solar system.  


  •  The energy from the Sun and other stars, seen as visible light, is caused by nuclear fusion reactions that occur deep inside the stars’ cores.

  • By carefully analyzing the spectrum of light from stars scientists can determine the composition of stars (and other distant objects)

  • Most stars are composed primarily of hydrogen, a smaller amount of helium, and much smaller amounts of all the other chemical elements.

  • Most stars are born from the gravitational compression and heating of hydrogen gas.

  • A fusion reaction results when hydrogen nuclei combine to form helium nuclei.

  • Hydrogen fusion in stars releases energy and establishes a balance between the inward pull of gravity and the outward pressure of the fusion reaction products.

  • Ancient peoples observed that some objects in the night sky wandered about while other objects maintained fixed positions in relation to one another (i.e., the constellations). Those “wanderers” are the planets.

  • Through careful observations of the planets’ movements, scientists found that planets travel in nearly circular (slightly elliptical) orbits about the Sun.

  • Planets (and the Moon) do not generate the light that makes them visible.

  • The fact that planets do not generate the light that makes them visible is demonstrated during eclipses of the Moon or by observation of the phases of the Moon and planets when a portion is shaded from the direct light of the Sun.

  • Various types of exploratory missions have yielded much information about the reflectivity, structure, and composition of the Moon and the planets.

  • Explopratory missions to the moon and planets have included

    • spacecraft flying by and orbiting those bodies

    • the soft landing of spacecraft fitted with instruments on them

    • the visits of astronauts to the Moon during the 1970's


  • Nine planets are currently known in the solar system:

    • Mercury

    • Venus

    • Earth

    • Mars

    • Jupiter

    • Saturn

    • Uranus

    • Neptune

    • Pluto

  • Planets greatly in size and appearance.

    • the mass of Earth is 6 × 1024 kg and the radius is 6.4 × 106 m.

    • Jupiter has more than 300 times the mass of Earth, and the radius is ten times larger

  • The planets drastically vary in their

    • distance from the Sun

    • period of revolution about the Sun

    • period of rotation about their own axis

    • tilt of their axis

    • composition

    • appearance

  • Composition

    • The inner planets (Mercury, Venus, Earth, and Mars) tend to be relatively small and are composed primarily of rock.

    • The outer planets (Jupiter, Saturn, Uranus, and Neptune) are generally much larger and are composed primarily of gas.  commonly referrred to as 'Gas Giants'

    • Pluto is composed primarily of rock and is the smallest planet in the solar system.

    • All the planets are much smaller than the Sun


    • All objects are attracted toward one another gravitationally, and

    • The strength of the gravitational force between objects depends on their masses and the distance that separates them from one an-other

    • They are all being acted on by the graviational attraction of each other and the Sun  


    • Before Newton formulated his laws of motion and the law of universal gravitational attraction, German astronomer Johannes Kepler deduced from astronomical observations three laws (Kepler’s laws) that describe the motions of the planets.


    • Planets have smaller objects orbiting them called satellites or moons.

    • Earth has one moon that completes an orbit once every 28 days (approximately).

    • Mercury and Venus have no moons, but Jupiter and Saturn have many moons.


    • Very small objects composed mostly of rock (asteroids) or the ice from condensed gases (comets) or both also orbit the Sun.

    • The orbits of many asteroids are relatively circular and lie between the orbital paths of Mars and Jupiter (the asteroid belt).

    • Some asteroids and all comets have highly elliptical orbits, causing them to range great distances from very close to the Sun to well beyond the orbit of Pluto.

Things to do...

  • visit a planetarium would be another way to observe the sky.
  • observe the motion of Jupiter’s inner moons as well as the phases of Venus.



Copyright © 2005 -  S. B. EglI