Which choice best describes homeostasis?
A functional system of the body
Blood flow to every cell in the body
A relatively constant environment within the body
Neural pathways that have integrated into the body
Correct Answer : C
Homeostasis is the existence and maintenance of a relatively constant environment within the body. Each cell of the body is surrounded by a small amount of fluid, and the normal functions of each cell depend on the maintenance of its fluid environment within a narrow range of conditions, including temperature, volume, and chemical content. These conditions are known as variables. For example, body temperature is a variable that can increase in a hot environment or decrease in a cold environment.
There are two types of feedback mechanisms in the human body: negative and positive.
- Negative Feedback: Most systems of the body are regulated by negative feedback mechanisms, which maintain homeostasis. Negative means that any deviation from the set point is made smaller or is resisted. The maintenance of normal blood pressure is a negative-feedback mechanism. Normal blood pressure is important because it is responsible for moving blood from the heart to tissues.
- Positive Feedback: Positive-feedback mechanisms are not homeostatic and are rare in healthy individuals. Positive means that when a deviation from a normal value occurs, the response of the system is to make the deviation even greater. Positive feedback therefore usually creates a cycle leading away from homeostasis and, in some cases, results in death. Inadequate delivery of blood to cardiac muscle is an example of positive feedback.
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Correct Answer is C
Explanation
Theaging processaffects hormone activity in one of three ways: their secretion can decrease, remain unchanged, or increase.
Hormones thatdecrease secretioninclude the following:
- Estrogen (in women)
- Testosterone (in men)
- Growth hormone
- Melatonin
Inwomen, the decline in estrogen levels leads to menopause. Inmen, testosterone levels usually decrease gradually. Decreased levels of growth hormone may lead to decreased muscle mass and strength. Decreased melatonin levels may play an important role in the loss of normal sleep-wake cycles (circadian rhythms) with aging.
Hormones that usually remainunchangedorslightly decreaseinclude the following:
- Cortisol
- Insulin
- Thyroid hormones
Hormones that mayincrease secretionslevels include the following:
Parathyroid hormone
- Follicle-stimulating hormone (FSH)
- Luteinizing hormone (LH)
- Norepinephrine
- Epinephrine, in the very old
Correct Answer is D
Explanation
In solids, particles are usually closer together than in other states of matter because of the strong cohesive forces between the particles.
- Solids, liquids, gases, and plasmas differ from one another in the amount of energy that the particles have and the strength of the cohesive forces that hold the particles together.
- Cohesion is the tendency of particles of the same kind to stick to each other.
- A solid has the lowest amount of energy because its particles are packed close together. Liquids have more energy than a solid, and gases have more energy than solids or liquids because the cohesive forces are very weak.
Correct Answer is A
Explanation
The protein disc that holds two sister chromatids together is what collectively makes a chromosome. A gene is a segment of DNA, deoxyribonucleic acid, which transmits information from parent to offspring. A single molecule of DNA has thousands of genes. A chromosome is a rod-shaped structure that forms when a single DNA molecule and its associated proteins coil tightly before cell division.
Chromosomes have two components:
- Chromatids: two copies of each chromosome
- Centromeres: protein discs that attach the chromatids together
Human cells have 23 sets of different chromosomes. The two copies of each chromosome are called homologous chromosomes, or homologues. An offspring receives one homologue from each parent. When a cell contains two homologues of each chromosome, it is termed diploid (2n). A haploid (n) cell contains only one homologue of each chromosome. The only haploid cells humans have are the sperm and eggs cells known as gametes.
Correct Answer is B
Explanation
The sequence of amino acids in a gene determines the primary structure of a protein. The components necessary fortranslationare located in the cytoplasm. Translation is the making of proteins by mRNA binding to a ribosome with the start codon that initiates the production of amino acids. Apeptide bondforms and connects the amino acids together. The sequence of amino acids determines the protein’s structure, which determines its function.
Correct Answer is A
Explanation
Robert Hooke discovered the first cells in the mid-eighteenth century. The cell theory is a theory because it is supported by a significant number of experimental findings. The cell theory took many years to be developed because microscopes were not powerful enough to make such observations.
This theory, or in-depth explanation, about cells consists of three parts:
- All living things are composed of one or more cells.
- Cells are alive and represent the basic unit of life.
- All cells are produced from pre-existing cells.
Correct Answer is B
Explanation
Blood continually flows in one direction, beginning in the heart and proceeding to the arteries, arterioles, and capillaries. When blood reaches the capillaries, exchanges occur between blood and tissues. After this exchange happens, blood is collected into venules, which feed into veins and eventually flow back to the heart’s atrium. The heart must relax between two heartbeats for blood circulation to begin.
Two types of circulatory processes occur in the body:
Systemic circulation
- The pulmonary vein pushes oxygenated blood into the left atrium.
- As the atrium relaxes, oxygenated blood drains into the left ventricle through the mitral valve. 3. The left ventricle pumps oxygenated blood to the aorta.
- Blood travels through the arteries and arterioles before reaching the capillaries that surround the tissues.
Pulmonary circulation
- Two major veins, the Superior Vena Cava and the Inferior Vena Cava, brings deoxygenated blood from the upper and lower half of the body.
- Deoxygenated blood is pooled into the right atrium and then sent into the right ventricle through the tricuspid valve, which prevents blood from flowing backward.
- The right ventricle contracts, causing the blood to be pushed through the pulmonary valve into the pulmonary artery.
- Deoxygenated blood becomes oxygenated in the lungs.
- Oxygenated blood returns from the lungs to the left atrium through the pulmonary veins.
Correct Answer is A
Explanation
Atissueis a group of cells with similar structure and function and similar extracellular substances located between the cells. The table below describes the four primary tissues found in the human body.
body.
Correct Answer is C
Explanation
The particles in a sample of gas are farther apart than in solids or liquids and therefore have the lowest amount of cohesion.
- Cohesion is the tendency of particles of the same kind to stick to each other.
- A solid has the lowest amount of energy because its particles are packed close together. Liquids have more energy than a solid, and gases have more energy than solids or liquids because the cohesive forces are very weak.
Correct Answer is D
Explanation
The autonomic nervous systemis responsible for activities that arenonvoluntaryand under unconscious control. This system controls glands and the smooth muscles of internal organs, heart rate, breathing, and digestion. The autonomic nervous system is further divided into the following:
- Sympathetic nervous system: The sympathetic nervous system focuses on emergency situations by preparing the body forfight or flight. (Sympathetic = Stress)
- Parasympathetic nervous system: The parasympathetic nervous system controls involuntary processes unrelated to emergencies. This system deals with “rest or digest” activities. (Parasympathetic = Peace)
Thesomatic nervous systemprimarily controlsvoluntaryactivities such as walking and riding a bicycle. Thus, this system sends information to the CNS and motor nerve fibers that are attached to skeletal muscle.
Correct Answer is D
Explanation
Human intercourse consists of the male introducing sperm into the female’s reproductive system. Sperm may then pass through the female’s reproductive system to the Fallopian tubes where one sperm fertilizes an ovum, creating azygote. The zygote passes out of the Fallopian tube and implants into the uterine wall to begin gestation. Over nine months, the zygote develops and grows into an embryo and then a fetus. An infant is the baby that is born.
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