CSET Practice Test Subtest II Science

Conduction, Convection and Radiation - Moving Heat

Conduction, convection and radiation are the three 
major methods of heat transfer. That is, they are three 
different ways that heat can spread. 

Conduction is probably the simplest to understand. If 
you say that something is hot, then what you are really 
saying is that the atoms inside of it are moving around a 
lot. Even in a solid like a metal, the atoms can move 
back and forth quite a bit. When the atoms move, they 
bump into the atoms next to them, making them move. 
This starts a chain reaction and the heat spreads through 
the whole object. This is what's happening if you've ever 
set a pan on the stove. The handle gets warm even 
though only the bottom touches the burner because the 
metal conducts the heat. As it turns out, in metals heat 
is conducted not so much by wiggling atoms, but mostly 
by wiggling electrons (the idea is the same, though). 

Convection is a bit trickier. Convection is a way for heat 
to move through a fluid, like water or air. You may have 
heard of the phrase 'hot air rises.' This is convection. Hot 
air (or hot water, etc.) is less dense than cooler air. So if 
you heat up the air at ground level, it will rise up into the 
sky to be replaced by cooler air moving downwards. This 
creates something called 'convection currents,' which are 
one of the things that birds use to rise up into the air. To 
see this at home, you can get a clear ice-cube and drop 
it into a glass of warm colored water (food coloring is fine). 
You should be able to see how the warm (colored) water 
moves upwards while the cold (clear) water melting off 
the ice cube moves down. 

Radiation has to do with light. Sounds weird? Not really. 
The light that you see is actually made up of something 
called electromagnetic waves. The electromagnetic 
waves that carry the kind of heat that we are most 
familiar with (from a heat lamp, for example) have longer 
wavelengths than the waves that make up visible light 
and hence they are often called "infra-red". When 
something is hot, like the burner on your stove, it releases 
some of its energy in the form of these infrared waves. 
The waves travel through the air until they hit something, 
which gets heated up. This is why you can feel the heat 
from your stove even if your hand isn't actually touching 
it. The burner literally 'radiates' heat.

The Heart

The heart is a unique, muscular, hollow organ located 
under your rib cage to the left of your breastbone. It is 
about the size of your fist and weighs less than one 
pound. The heart constantly pumps blood throughout the 
body-to every cell in each muscle, bone and organ. Like 
any other muscle, the heart requires oxygen-rich blood 
in order to perform its functions. 

HEART CHAMBERS
The heart consists of four separate compartments, or 
chambers. There are two chambers on the left side of 
the heart and two on the right. The upper chamber on 
each side, known as the atria, receive and collect blood. 
The lower chambers, or ventricles, pump the blood to all 
parts of the body and are larger and thicker than the 
atria. 

The left ventricle is the main pumping chamber, pumping 
blood to all parts of the body, except the lungs, while 
the right ventricle pumps blood exclusively to the lungs. 
A thick, muscular wall, the septum, divides the right and 
left sides of the heart and prevents blood from passing 
from one side to the other. 

HEART VALVES
Four valves in the heart keep blood flowing in the proper 
direction through the heart, lungs and into the body. The 
valves are thin, flexible flaps of tissue attached to the 
heart muscle. 

Two of the valves, the atrioventricular valves, regulate 
the flow of blood from the atria to the ventricles. The 
tricuspid valve is located on the right side of the heart, 
and the mitral valve is located on the left. 

The other two valves regulate the flow of blood from 
the ventricles to the lungs and body. From the right 
ventricle, the blood is pumped through the pulmonary 
valve to the lungs, where it picks up oxygen and gets 
rid of waste products such as carbon dioxide. From the 
left ventricle, blood is pumped through the aortic valve 
to all parts of the body. 

BLOOD VESSELS
Several types of blood vessels carry blood to all parts of 
the body. Arteries carry "oxygen-rich blood" away from 
the heart to tissues throughout the body. Veins carry 
"oxygen-poor blood" back to the heart. 

The oxygen-poor blood that returns from the body 
collects in the right side of the heart. It is then pumped 
into the lungs, where it receives a fresh supply of 
oxygen. This oxygen-rich blood then flows into the left 
side of the heart and gets pumped into arteries, which 
carry the oxygen and nutrient rich blood to various 
parts of the body. 

CORONARY ARTERIES
In order to keep pumping blood throughout the body, 
the heart must have a constant supply of oxygen. 
Therefore, the heart has its own set of arteries, the 
coronary arteries, which continuously supply it with 
blood, oxygen and nutrients. 

There are three main coronary arteries and many small 
branches that supply the heart muscle. The right 
coronary artery supplies the bottom and back of the 
heart. The left main coronary artery branches into 
two smaller arteries: the left anterior descending 
artery and the left circumflex artery. The left coronary 
artery system supplies the top, front, left sides and an 
area in the back of the heart. 

BLOOD PRESSURE
Blood vessels maintain pressure at all times to allow 
the blood to flow throughout the body. When the 
ventricles contract, pressure rises, and blood is 
pumped out into the arteries. Between heartbeats, 
while the ventricle is refilling, the pressure falls. 

The two numbers used to measure blood pressure 
are referred to as the systolic and diastolic pressures. 
The systolic blood pressure is the highest pressure 
achieved when the heart is contracting and forcing 
blood into the arteries. The diastolic blood pressure 
is the lowest pressure that occurs when the heart is 
relaxed or when the left ventricle is refilling. A typical 
blood pressure reading is written as a fraction with 
the systolic number over the diastolic rate 
(e.g., 120/80). 

THE HEARTBEAT: THE HEART'S ELECTRICAL SYSTEM
The heart, unlike most other muscles, has its own 
pacemaker, which transmits electrical impulses, signaling 
the heart to beat. The Sinoatrial (SA) node, or 
"pacemaker" of the heart, is a bundle of muscle fibers 
located in the right atrium. The electrical impulse, or 
signal, begins here and travels through the atria, causing 
them to contract and force blood into the ventricles. 

The Atrioventricular (AV) node receives the signal after 
it has traveled through the atria and serves as an 
electrical "gateway" between the atria and ventricles. 
It connects to fibers, which divide into branches along 
the septum and down the ventricles. 

The impulse continues down two bundle branches and 
stimulates the ventricles to contract. The contraction 
forces blood into the lungs and the rest of the body. 
For every impulse that travels this path, the heart 
beats, or contracts.