Protists
The protist kingdom is very diverse. All protists are eukaryotes that cannot be classified as animals, plants, or fungi. All live in moist surroundings. Most
are unicellular, but some are multicellular. Some are heterotrophs, some are autotrophs, and some are both. Protists can be divided into three categories:
animal-like, funguslike, and plantlike protists.
Like animals, animal-like protists are heterotrophs, and most are able to move from place to place to obtain food. Animal-like protists are also
called protozoans. Protozoans can be divided into four types: sarcodines, ciliates, flagellates, and those that are parasites. Sarcodines move and feed
by using pseudopods. Pseudopods are temporary bulges of the cell. Pseudopods form when cytoplasm flows toward one location and the rest of the organism follows. Protozoans that live in fresh water, such as amoebas, have a contractile vacuole, which collects the extra water and expels it from the cell. Ciliates have structures called cilia, which are hairlike projections that move with a wavelike motion. Flagellates move using whiplike flagella.
Some flagellates live inside the bodies of other organisms in a state of symbiosis. Symbiosis is a close relationship between two species where at
least one of the species benefits. Sometimes, flagellates harm their hosts. In other cases, their relationship is one of mutualism, in which both partners benefit. Protozoans that are parasites feed on their hosts’ cells and body fluids.
Plantlike protists are called algae. Like plants, algae are autotrophs. Algae can exist in a variety of colors because they contain many types of
pigments—chemicals that produce color. Plantlike protists include diatoms, dinoflagellates, euglenoids, red algae, green algae, and brown algae.
Diatoms have beautiful, glasslike cell walls. Dinoflagellates are covered by stiff plates and move using two flagella. Euglenoids can be heterotrophs
when sunlight is not available. Red algae and brown algae live in the oceans. Green algae live in fresh water, salt water, and moist places on land.
Like fungi, funguslike protists are heterotrophs, have cell walls, and use spores to reproduce. Spores are tiny cells that are able to grow into new
organisms. All funguslike protists are able to move at some point in their lives. The three types of funguslike protists are slime molds, water molds,
and downy mildews. Slime molds live in moist soil and on decaying plants. Water molds and downy mildews grow as tiny threads in water or moist places.
7th
The Outer Planets
The first four outer planets—Jupiter, Saturn, Uranus, and Neptune—are much larger and more massive than Earth, and they do not have solid surfaces. Because these four planets are all so large, they are often called the gas giants. The fifth outer planet, Pluto, is small and rocky, like the terrestrial planets.
Like the sun, the gas giants are composed mainly of hydrogen and helium. Because they are so massive, they exert a much stronger gravitational force than the terrestrial planets. This prevents their gases from
escaping, so they have thick atmospheres. All of the giants have many moons and are surrounded by a set of rings. A ring is a thin disk of small particles of ice and rock. Jupiter is the largest and most massive planet. Jupiter has a thick atmosphere made up mainly of hydrogen and helium. An interesting feature
of Jupiter’s atmosphere is its Great Red Spot, a storm that is larger than Earth. Jupiter probably has a dense core of rock and iron at its center,
surrounded by a thick mantle of liquid hydrogen and helium.
Galileo discovered Jupiter’s four largest moons: Io, Europa, Ganymede, and Callisto.
Saturn is the second-largest planet in the solar system. Its average density is less than that of water. The rings around Saturn are made of chunks of ice and rock. Saturn has the most spectacular rings of any planet.
Uranus is about four times the diameter of Earth and is twice as far from the sun as Saturn. Uranus looks blue-green because of traces of methane in
its atmosphere. Uranus’s axis of rotation is tilted at an angle of about 90 degrees from the vertical. It rotates from top to bottom instead of from side
to side.
Neptune is a cold, blue planet. Its atmosphere contains visible clouds. Neptune was discovered as a result of a mathematical prediction. Astronomers have discovered at least 13 moons orbiting Neptune.
Pluto has a solid surface and is much smaller and denser than the other outer planets. Pluto has a single moon, Charon. Because Charon is more
than half the size of Pluto, some astronomers consider them to be a double planet instead of a planet and a moon. Pluto revolves around the sun only once every 248 Earth years.
8th
Organizing the Elements
In 1869, the Russian scientist Dmitri Mendeleev discovered a set of patterns in the properties of the elements.He noticed that a pattern of properties
appeared when he arranged the elements in order of increasing atomic mass. The atomic mass of an element is the average mass of all the isotopes of that element.
Mendeleev published the first periodic table. In the periodic table, the properties of the elements repeat in each period, or row, of the table. Mendeleev left three blank spaces in the table. He predicted that these spaces would be filled by elements that had not yet been discovered. He even predicted the properties of those elements. Those elements were soon discovered. Their properties are close to those predicted by Mendeleev. The periodic table has been updated since Mendeleev’s time as scientists
discovered new elements. After protons were discovered, elements were rearranged according to atomic number. Some elements changed positions
and the patterns of properties became more regular.
The modern periodic table contains over 100 squares, one for each element. Each square includes the element’s atomic number, chemical symbol, name, and atomic mass. The chemical symbol for an element
usually consists of one or two letters, such as Fe, the chemical symbol for iron.
The properties of an element can be predicted from its location in the periodic table. Each horizontal row of the table is called a period. As you move across a period from left to right, the properties of elements change in a predictable pattern. There are seven periods of elements. The elements in a column are called a group, or family. The groups are
numbered from Group 1 on the left to Group 18 on the right.The family name of a group is typically the name of the first element in the column. Elements in each group have similar characteristics.
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