General Science Study Guide for the ASVAB

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General Information

The General Science section of the ASVAB test is designed to measure your scientific aptitude. Because it is a general science test, students must possess a general knowledge of a variety of scientific areas, including ecology, astronomy, anatomy, geology, and biology. When studying for each of these portions of the general science test, be sure not to focus too heavily on any one area; a basic understanding of and knowledge in these areas is all that is required. Each separate category will be discussed in greater depth here.

The CAT version of the ASVAB contains 15 questions in the General Science section and they must be completed in 10 minutes. The paper-and-pencil test gives you 25 questions and 11 minutes to complete them.

Life Science: Part 1

Health and Nutrition



Macronutrients consist of those larger compounds from which we derive the calories, or energy, necessary to sustain life functions. Carbohydrates, proteins, and lipids (or fats) are the macronutrients from which our energy is derived.

Carbohydrates—Carbohydrates, both simple and complex, can be thought of as immediate and readily accessible energy. These molecules are ultimately broken down into glucose and circulated throughout the blood to support metabolic functions.

Lipids—The body converts and stores unused carbohydrates as lipids, or fats. Lipids function as the source material for hormones. They enable better absorption of micronutrients, and they also serve as an energy source.

Protein—Proteins are necessary for cellular growth, repair, and transport. They are made up of amino acids, which can be thought of as micronutrients.


Micronutrients consist of those vitamins and minerals required by the body to function properly. As indicated by the micro- prefix, these nutrients are only required in small amounts; however, they are not insignificant. If adequate amounts of these micronutrients are not acquired, overall health is potentially compromised, and long-term issues may arise.

Vitamins—There are numerous vitamins found throughout the body, all with a different purpose, to allow for normal cellular function. They can be broken down into two groups: fat-soluble vitamins and water-soluble vitamins. Fat-soluble vitamins (such as vitamins A, D, E, and K) are present in foods with fats and do not dissolve in water. Water-soluble vitamins (such as the B vitamins) are dissolved in water and carried around the body but are not stored.

Minerals—Minerals are found in food that we consume and are essential for cells to function properly. Common minerals are magnesium, potassium, sodium, and calcium.

Other Important Substances

There are various other things that your body needs in order for normal cellular function to occur.

Water—Water is an essential molecule needed for all cellular functions and makes up between 60 and 80 percent of our body mass. In its absence, the metabolic reactions that occur in our body would not be able to exist.

Fiber—Fiber is a plant derivative that cannot be broken down by the body and is essential for bowel health and function. It works by bulking up the stool and allowing for easier passage throughout the body. This can be found in foods such as berries, whole grains, and apples, or as an over-the-counter supplement.

Related terms to know: vitamins, minerals, carbohydrates, lipids, proteins

Nutrition-related diseases are those which arise from either the deficiency or the excess of a micro or macronutrient. Diabetes, hypertension, scurvy, and iron-deficiency anemia are examples of nutrition-related diseases.

The Human Body

Human anatomy is the study of the human body: how it works, what makes up its parts, and what is necessary to keep it functioning well and properly. Human anatomy is included in the General Science section of the ASVAB, requiring students to have a basic knowledge and understanding of the human body and its functions. To prepare, study the basic components of human anatomy, including the bones, muscles, and blood vessels comprising the body, as well as the basic functions of these different systems. Though the questions are not heavy or in-depth due to the “general” nature of the test, you should have some understanding of how the body works and what is required to keep it functioning.

Skeleton and Muscles

The human skeletal system is a collection of bones, composed of a very hard and inflexible phosphate, and cartilage, composed of spongy, flexible collagen. The skeletal system functions as structural support and protection for muscles and organs. It also facilitates locomotion. Blood is created inside of bone marrow.

The muscular system works in conjunction with the skeletal system to facilitate motion. The muscular system is made up of three types of muscle: cardiac muscle, skeletal muscle, and smooth muscle.

The heart is made of cardiac muscle that is involved in regulating contraction and relaxation of the heart.

Skeletal muscles are those connected to bone that enable motion.

Smooth muscle lines organs and aids in digestion.

Related terms to know: bones, cartilage, cardiac, skeletal, smooth


Respiration is a process performed by living organisms that allows for the exchanging of gases between one’s internal and external environment. Cells use these gases as a way to obtain energy for cell processes to take place.

Oxygen—Cellular respiration can occur with or without oxygen. In aerobic processes (those that involve oxygen), oxygen is converted into energy in the form of ATP. In human respiration this is the gas that we inhale.

Carbon dioxide—Carbon dioxide is the gas that oxygen is exchanged for in respiration and therefore the gas that we exhale.

Water Vapor—This is the gas phase of water. It occurs as liquid water is evaporated or solid water (ice) undergoes sublimation.

Nose—The nose allows for both inhalation and exhalation of air via respiration.

Nasal cavity—This is the air-filled space behind the nose.

Pharynx—The pharynx (also known as the throat) is the structure behind the nose and the mouth that connects them to the esophagus. Its main function is to receive and allow for the transmission of air to the lungs and food to the stomach.

Epiglottis—This is the flap behind the tongue that ensures that air goes to the lungs and food goes to the stomach. At rest, the epiglottis sits upright and flips over one way or the other, depending whether food or air enters the mouth/nose.

Trachea—The trachea (also known as the windpipe) is a passageway for air to get moist and warm as it makes its way to the lungs.

Bronchi—The trachea branches into the left and right bronchi. The bronchi are responsible for transporting air that has come through the windpipe to the lungs.

Lungs—After air leaves the left and right bronchi, it dumps into the left and right lungs, respectively. The lungs are spongy organs that can be broken down into smaller divisions to allow for gas exchange to occur.

Bronchioles—Also known as “little bronchi”, these are smaller branches that the left and right bronchi divide into.

Alveolus—These are tiny air sacs that branch off from the bronchioles where gas exchange occurs in the lungs.

Capillaries—These are tiny blood vessels that serve as a connection point between arterioles and venules, allowing nutrients to be transferred between blood and tissues

Diaphragm—The diaphragm is a skeletal muscle that sits below the lungs. As you inhale, the diaphragm contracts and flattens to allow your lungs to fill with more air. As you exhale the diaphragm relaxes so air can be pushed out of the lungs.

Blood and Circulation

The circulatory system is responsible for the transport of blood and nutrients throughout the body. It is made up of arteries, veins, capillaries, the lungs, the heart, the brain, and the kidneys.

The heart functions to pump oxygenated blood to the body and deoxygenated blood to the lungs to become oxygenated. Blood flows through the arteries and veins along with other nutrients, while delivering oxygen to cells throughout the body and carbon dioxide to the lungs to be eliminated.

Blood consists of red blood cells, which facilitate oxygenation, white blood cells, which aid in immunologic defense, plasma, which is the liquid medium inside of the circulatory system, and platelets, which also aid in defense.

Other Terms to Know

Atrium/atria—These are the two receiving chambers of the heart. They appear on both the left and right sides of the heart above the ventricles.

Ventricles—These are the two pumping chambers of the heart. They appear on both the left and right sides of the heart below the atria.

Vena cava(e)—There are two vena cavae in the heart: superior and inferior. The superior vena cava drains the upper part of the body while the inferior vena cava drains the lower half of the body. Both of these dump deoxygenated blood into the right atrium.

Pulmonary artery—This is responsible for carrying deoxygenated blood from the heart to the lungs.

Pulmonary vein—This is responsible for carrying oxygenated blood from the lungs to the heart.

Aorta—This is the largest artery in the body. Oxygenated blood will leave the heart through the aorta to be sent throughout the whole body.

Artery—This is a blood vessel that carries blood away from the heart. You can think “A” and “Away”. Arteries typically carry oxygenated blood with the exception of the pulmonary artery, which carries deoxygenated blood.

Arterioles—Also known as “little arteries,” these are small branches off the arteries that connect arteries to capillaries.

Vein—A vein is a blood vessel that carries blood toward the heart. Veins typically carry deoxygenated blood with the exception of the pulmonary vein, which carries oxygenated blood.

Valves—There are four valves of the heart: the bicuspid (mitral) valve, tricuspid valve, aortic valve, and pulmonary valve. The tricuspid and bicuspid valves are also known as the atrioventricular (AV) valves as these are the two valves that separate the atria from the ventricles. The bicuspid (or mitral valve) separates the left atrium from the left ventricle, and the tricuspid valve separates the right atrium from the left atrium. The aortic valve connects the left ventricle to the aorta (hence the name), and the pulmonary valve connects the right ventricle to the lungs.

Diffusion—This is the movement of molecules from an area of high concentration to low concentration.

Venules—Also known as “little veins”, these are small branches off the veins that connect veins to capillaries.

Heart Disease (Cardiovascular Disease)

Heart diseases, also known as cardiovascular diseases, stem from difficulties in pumping blood throughout the body by way of arterial blockage, high blood pressure, and other issues.

Blood Types

There are four main blood types: A, B, AB, and O. These blood types are dependent on the antigens present on one’s red blood cells (also known as erythrocytes). Each blood type is also classified as either positive or negative depending on if the Rhesus (Rh) factor is present or not.

Antigens—These are what the cells recognize as “self”. For example, if someone has a blood type A, they will have A antigens on the surface of their red blood cells. If they have AB blood, then they will have both A and B antigens. O blood is the absence of any antigens.

Rh factor—Rhesus (Rh) factor is an inherited protein that is found on the surface of red blood cells. Presence of this protein makes you Rh positive, and absence of this protein makes you Rh negative.

Universal donor—This is someone who can donate blood to someone with any blood type. The universal blood donor is blood type O since there are no antigens on the surface of its cells.

Universal recipient—This is someone who can receive blood from someone with any blood type. The universal blood recipient is blood type AB since there are both A and B antigens on the surface of its cells.

Digestion and Excretion

The digestive system functions to break food down into usable micro and macronutrients. Upon ingestion of food, the digestive process begins.

The saliva in our mouths contains enzymes that begin breaking down food. Mastication, or chewing, helps reduce the food to a bolus that is easy to swallow.

Smooth muscle in the esophagus undergoes peristalsis to pass the bolus to the stomach where the bolus is treated with strong acids to create chyme, which is then passed onto the small intestine.

The small intestine primarily serves to absorb the nutrients from the chyme before passing it on to the large intestine (colon). In the large intestine, further absorption of nutrients and water takes place, before passing the remaining matter, termed feces, to the rectum where it is excreted through the anus.

The excretory system serves to expel waste, primarily urine, from the body. This system helps maintain homeostasis through the regulation of internal fluids. Its major components are: kidneys, lungs, skin, ureter, urethra, and the urinary bladder.

The kidneys function to remove waste from the bloodstream through a filtration system resulting in the production of urine.

The lungs, in addition to providing oxygenated blood, remove carbon dioxide from the blood.

The skin is the organ through which perspiration (sweat) is released. It plays a minor role in excretion; its primary role is temperature regulation.

The ureter, urethra, and urinary bladder all work in conjunction to remove and expel urine from the body.

Salivary amylase—This is an enzyme found in the mouth that is responsible for the initial breakdown of starches from complex carbohydrates to monosaccharides (simple sugars).

Gastric acids—Gastric acid, also known as stomach acid, is the acidic fluid within the stomach. The pH of the stomach lies between 1 and 3 and is essential for activating digestive enzymes as well as breaking down proteins.

Pepsin—Pepsin is an enzyme found in the stomach that breaks down proteins into polypeptides.

Pancreas—The pancreas is an organ found below the liver. One of its main functions is to produce enzymes that break down food into a usable form for our body. One pancreatic enzyme is lipase, which is responsible for breaking down fats. Another pancreatic enzyme, pancreatic amylase, similar to salivary amylase, is responsible for breaking down starches. Finally, trypsin in the pancreas allows for the digestion of protein.

Liver—The liver is a large organ that is situated on the right side of the abdomen. It serves as producer of bile, metabolizer of nutrients, and an enzyme activator. It also helps with the excretion of drugs and hormones.

Bile—Bile is a green-brown fluid that is produced in the liver and stored in the gallbladder. It functions to carry wastes away and break down fats.

Related term to know: organs

The Nervous System

The nervous system enables communication between cells throughout the body. Its major components are the brain, the spinal cord, and neurons, or nerve cells.

The brain acts as the central information processing unit of the body. It is composed of many billion neurons and it is where information received by the senses is processed. The brain contains two hemispheres (left and right) and three major parts: the cerebrum, the cerebellum, and the brain stem.

The cerebrum, the largest portion of the brain, is responsible for numerous things such as (but not limited to) speech, judgment, problem-solving, and emotions. The cerebellum aids in balance and coordination. The brainstem connects with the spinal cord and regulates involuntary movements such as breathing and digestion.

The neurons that make up the brain contain a nucleus and long branches that extend to other neurons. Chemical signals pass from one neuron to the next to transmit information.

The spinal cord connects the brain to the rest of the body. It is a bundle of nerves that runs vertically through the spine that branches throughout the body. Signals received by the senses travel through the spinal cord to be processed in the brain.

Together, the brain and the spinal cord form the central nervous system. The peripheral nervous system is the collection of nerves residing outside of the central nervous system, coordinating voluntary and involuntary movement.

Related terms to know: neurons, brain, spinal cord, somatic nervous system, autonomic nervous system, medulla, simple reflexes


Reproduction exists in two forms: asexual and sexual. Asexual reproduction requires no partner, and the offspring produced inherits the same genes as the parent. This differs from sexual reproduction, in which there are usually two partners who both contribute equally to the genetic makeup of the offspring.

Asexual Reproduction

Asexual reproduction is the method by which somatic (or body) cells divide. Through mitosis, a cell divides, and both daughter cells possess the exact DNA of the parent cell.

(Human) Sexual Reproduction

During sexual intercourse, sperm is ejaculated into the vagina of a female. The sperm makes its way to the fallopian tubes where it tries to find an egg to fertilize. If fertilization occurs, a zygote will form and the cells will continue dividing as the fertilized egg travels to the uterus with the intention of implanting in the uterine wall to form an embryo.

Meiosis— This is the process by which sex cells divide. This process results in cells that contain genetic material that is partially from one parent cell and partially from a different parent cell.

Ovulation—Ovulation occurs in females when an egg is released from the ovary. This occurs approximately two weeks after a female’s menstruation.

Ovum—The ovum is the mature female reproductive cell.

Oviduct (Fallopian Tube)—Fallopian tubes are responsible for connecting the ovaries to the uterus. This is also where fertilization of the egg occurs.

Uterus—The uterus is an organ found internally in a female that functions to nourish a fetus during pregnancy.

Endometrial lining—This is the lining of a female’s uterus that gets shed once a month during her menstrual cycle.

Penis—This is the external sex organ of a male that allows for the passage of both urine and sperm.

Testes—Testes are responsible for making testosterone and sperm in a male.

Vagina—The vagina is the canal that runs from the uterus to the outside of a woman’s body. It has several functions, including acting as a passageway for a fetus during childbirth and receiving the penis during sexual intercourse.

Zygote—This is another name for a fertilized ovum.

Prolactin—Prolactin is a hormone produced by the pituitary gland inside the brain that causes milk production in postpartum women. However, this hormone is found in both males and females, but in different quantities.

Lactation—Lactation is the release of milk from the mammary glands.

Menstruation—This is also known as a period—when a woman sheds her endometrial lining causing bleeding to occur during the menstrual cycle.

Menstrual cycle—This is a monthly cycle that pre-menopausal/post-pubescent women go through, during which ovulation occurs.

Related terms to know: mitosis, cellular division

Human Pathogens

A pathogen, in general, is anything that can cause a disease. Human pathogens are specifically those that can cause diseases in humans and can either be bacterial, fungal, or viral.

Bacteria—Bacteria are unicellular, prokaryotic microorganisms that can serve to benefit humans or can be pathogenic.

Viruses—Viruses are non-living, pathogenic microorganisms.

Vaccination/Immunization—These are a weakened form of a virus that allows for one to become immune to an infection caused by either a virus or a bacteria.


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