A pathogen is any microorganism that causes disease in a host. Pathogens include bacteria, viruses, fungi, and parasites. Enzymes are proteins that speed up chemical reactions and are not microorganisms. Immune factors are components of the immune system that protect against disease. A vector is an organism, such as a mosquito or tick, that transmits pathogens but does not itself cause disease. The NEX Science exam commonly assesses understanding of infectious disease terminology and distinctions between disease-causing organisms and disease carriers. Recognizing pathogens as the direct cause of illness is a key concept in microbiology and public health.
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Question 13
In which biochemical family do starch and glycogen belong?
Starch and glycogen are both polysaccharides, which are complex carbohydrates composed of many glucose units. Starch is the primary storage form of glucose in plants, while glycogen is the storage form of glucose in animals, particularly in the liver and muscles. Carbohydrates serve as a major energy source for cells. Nucleic acids store genetic information, proteins perform structural and enzymatic functions, and lipids are involved in energy storage and membrane structure. The NEX Science exam often tests classification of biomolecules and their functions, making carbohydrates the correct answer.
Saltatory conduction is the rapid transmission of nerve impulses alongmyelinated axons. In myelinated neurons, the axon is covered with a fatty insulating layer called myelin, which is interrupted at gaps known as nodes of Ranvier. During saltatory conduction, the electrical impulse “jumps” from one node to the next, greatly increasing the speed of signal transmission. Unmyelinated axons conduct impulses more slowly because the signal must travel continuously along the entire membrane. Dendrites receive signals rather than transmit them over long distances, and muscle cells do not conduct nerve impulses in this manner. The NEX Science exam commonly tests nervous system physiology, particularly mechanisms that improve conduction speed, making myelinated axons the correct answer.
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Question 15
What is the result of crossing over during meiosis?
Options:
A.
Homologous pairs of chromosomes have exchanged segments of their DNA.
B.
Non-sister chromatids of homologous pairs of chromosomes have formed a chiasmata.
C.
Members of homologous pairs of chromosomes have lined up along the metaphase plate.
D.
Homologous pairs of chromosomes have been randomly assorted along the metaphase plate.
Crossing over is a key event that occurs during prophase I of meiosis. During this process, homologous chromosomes pair up and exchange corresponding segments of DNA. Specifically, non-sister chromatids exchange genetic material, which results in new combinations of alleles. The primary result of this exchange is increased genetic variation in gametes, which is essential for evolution and diversity within a species. While chiasmata are structures formed during crossing over, they describe the physical points of contact rather than the outcome of the process. Lining up at the metaphase plate and random assortment occur later during meiosis and are separate mechanisms of genetic variation. Therefore, the correct result of crossing over is the exchange of DNA segments between homologous chromosomes. This process ensures that offspring have unique genetic combinations that differ from both parents, which is a core concept tested on the NEX Science exam.
