There are many kinds of worms. Biologists classify worms into three major phyla—flatworms, roundworms, and segmented worms. Worms have long, narrow bodies without legs, and they have bilateral symmetry. They
have tissues, organs, and body systems. Worms are the simplest animals to have a brain. Worms reproduce both sexually and asexually.
Flatworms include planarians, flukes, and tapeworms. Flatworms are flat and as soft as jelly. Many flatworms are parasties.
A parasite is an organism that lives inside or on another organism. The parasite takes its food from its host, the organism in or on which it lives.
There are also free-living organisms, such as planarians, that do not live in or on other organisms. Planarians are scavengers, which means they feed on dead or decaying material.
A tapeworm is a kind of parasitic flatworm. Its
body is adapted to absorbing food from its hostÂ’s digestive system.
Roundworms have cylindrical bodies. Unlike cnidarians or flatworms, roundworms have a digestive system that is like a tube, open at both ends.
Food enters through the mouth. Wastes leave the digestive system through the anus, an opening at the other end of the tube.
Earthworms and other segmented worms have bodies made up of many linked sections called segments. Some organs are repeated in most segments. But other organs, such as the reproductive organs, occur only
once.
Segmented worms have a closed circulatory system. In a closed system, such as your own, the blood flows only through connected tubes called blood vessels. A closed system moves the blood around an animalÂ’s body
more quickly than an open circulatory system can.
7th
The Properties of Water
A water molecule is made up of two hydrogen atoms bonded to an oxygen atom. Each end of a water molecule has a slight electric charge. A molecule
that has electrically charged areas is called a polar molecule. The positive hydrogen ends of one water molecule attract the negative oxygen ends of
nearby water molecules. As a result, the water molecules tend to stick together.
Many of water’s unusual properties occur because of the attraction among its polar molecules. The properties of water include capillary
action, surface tension, the ability to dissolve many substances, and high specific heat.
Capillary action is the combined force of attraction among water molecules and with the molecules of surrounding materials.
Surface tension is the tightness across the surface of water that is caused by polar molecules pulling on each other.
A solution is a mixture that forms when one substance dissolves another.
The substance that does the dissolving is called the solvent. Many substances dissolve in water because water is polar. The charged ends of the water molecule attract the molecules of other polar substances.
Specific heat is the amount of heat needed to increase the temperature of a certain amount of a substance. Compared to other substances, water
requires a lot of heat to increase its temperature.
Water exists in three states, or forms: solid, liquid, and gas. Ice is a solid, the familiar form of water is a liquid, and water vapor in the air is a gas.
Change of state is related to temperature, which is a measurement of the average speed of molecules. When the temperature reaches 0°C, the solid ice
melts and becomes liquid water. At 100°C, liquid water boils and the molecules have enough energy to escape the liquid and become water vapor.
Liquid water also becomes a gas through evaporation, which is the process by which molecules at the surface of a liquid absorb enough energy to
change to the gaseous state.
The process by which a gas changes to a liquid is called condensation.
As the temperature of the gas cools down to 100°C, the molecules slow down
and begin to change back to the liquid state. When water cools below 4°C,
the molecules line up in a crystal structure. Water molecules take up more
space in this crystal structure than as a liquid. This means that ice is less
dense than liquid water, and thus floats on liquid water.
Water on Earth
Earth is unique among the planets in the solar system because its surface is nearly covered with liquid water. The water on Earth is essential to life. All
living things need water in order to carry out their body processes.
Most of the Earth’s water—roughly 97 percent—is found in salty oceans.
Only 3 percent is fresh water. The huge expanses of ice near the North and South Poles account for about three quarters of that 3 percent. The oceans—actually, a single world ocean—cover nearly 71 percent of Earth’s surface. The fresh water that is available for humans to use includes the
water in lakes and rivers. But far more fresh water is located underground.
Groundwater is water that fills the cracks and spaces in underground soil and rock layers.
Water on Earth is naturally recycled through the water cycle. Water moves from bodies of water, land, and living things on Earth’s surface to the atmosphere and back to Earth’s surface. The sun is the source of energy that drives the water cycle.
The water cycle has no beginning or end. It includes evaporation, condensation, and precipitation. Large amounts of water continually evaporate from oceans and lakes. More water vapor is given off through the
leaves of plants in a process called transpiration.
As warm air carries water vapor upward, the air cools. Cold air holds less water vapor than warm air, so the water condenses into droplets, which
clump around dust particles and form clouds. As the droplets grow bigger and heavier, they fall back to Earth as rain, snow, sleet, or hail, also called
precipitation.
The total amount of water on Earth has remained fairly constant for millions of years. In the world as a whole, the rates of evaporation and precipitation are balanced.
8th
Concentration and Solubility
Concentration is the amount of solute dissolved in a certain amount of solvent.
A dilute solution has only a little solute dissolved in the solvent.
A concentrated solution has a lot more solute dissolved in the solvent. You can change the concentration of a solution by adding more solute. You can also change the concentration by adding or removing solvent.
To measure concentration, you compare the amount of solute to the amount of solvent or to the total amount of solution.
Solubility is a measure of how much solute can dissolve in a solvent at a given temperature.
When you’ve added so much solute that no more
dissolves, you have a saturated solution. If you can continue to dissolve more solute, you still have an unsaturated solution.
The solubility of a substance tells you how much solute you can dissolve before a solution becomes saturated. Solubility can be used to help identify a substance because it is a characteristic property of matter.
The solubilities of solutes change when conditions change. Factors that affect the solubility of a substance include pressure, the type of solvent,
and temperature.
Pressure affects the solubility of gases. The higher the pressure of the gas over the solvent, the more gas can dissolve.
Sometimes you can’t make a solution because the solute and solvent will not mix. Ionic and polar compounds dissolve in polar solvents. Nonpolar
compounds do not dissolve in polar solvents.
Many solids dissolve better when the temperature of the solvent increases. Unlike most solids, gases become less soluble when the temperature goes up. When heated, a solution can dissolve more solute than
it can at cooler temperatures. A supersaturated solution has more dissolved solute than is predicted by its solubility at the given temperature. Dropping
a crystal of the solute in a supersaturated solution will cause the extra solute to come out of solution.
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