Question Four ZOOL 232 Distinguish between the following terms a)Plasmasol and cytosol b) Elastic and collagen fibers C)Hyperplasia and hypertrophy d)Apoptosis and necrosis e)Acrocentric and telocentric chromosomes Question Five a) What is receptor mediated endocytosis b)Describe the causes of familial hypercholesterolemia Question Six a)Describe the structure of the nucleus b)Explain how DNA is stored in the nucleus SECTION B:ANSWER ANY ONE QUESTION (20 MARKS) Question Six a)Describe the phases of the cell cycle b) Give a brief account of cell division in male gametogenesis. Question Seven a) Explain what the specialized regions on the lateral apical membrane of a cell are. b)Describe the structure of a cell membrane as proposed by Singer and Nicolson (1972) (16 mar ******************************************************************************************************************************************** (2) QN (2) (2)M 2M (4M (5 M (4 M (16 Ma (4 Ma

Question Four:<br />a) Plasmolysis refers to the contraction of the cell membrane in a plant cell, causing the cell to shrink and the cell membrane to pull away from the cell wall. Cytosol, on the other hand, is the fluid portion of the cytoplasm in a cell, which contains dissolved ions, nutrients, and organic molecules.<br /><br />b) Elastic fibers are thin, long, and flexible fibers that provide elasticity to tissues, while collagen fibers are thick, strong, and provide structural support to tissues.<br /><br />c) Hyperplasia refers to an increase in the number of cells in a tissue or organ, while hypertrophy refers to an increase in the size of individual cells.<br /><br />d) Apoptosis is a programmed cell death that occurs in a controlled and regulated manner, while necrosis is an uncontrolled cell death that occurs due to injury or disease.<br /><br />e) Acrocentric chromosomes have their centromere located near one end of the chromosome, while telocentric chromosomes have their centromere located at the very end of the chromosome.<br /><br />Question Five:<br />a) Receptor-mediated endocytosis is a process by which cells internalize specific molecules through the formation of vesicles. In this process, the molecules bind to specific receptors on the cell surface, triggering the invagination of the cell membrane and the formation of a vesicle that contains the molecules.<br /><br />b) Familial hypercholesterolemia is caused by mutations in genes that code for proteins involved in the metabolism of cholesterol. These mutations result in the production of abnormal or defective proteins, leading to the accumulation of cholesterol in the blood and the development of high cholesterol levels.<br /><br />Question Six:<br />a) The nucleus is the control center of a cell and is responsible for storing and transmitting genetic information. It is surrounded by a double membrane called the nuclear envelope, which separates it from the cytoplasm. The nucleus contains the cell's DNA, which is organized into chromosomes.<br /><br />b) DNA is stored in the nucleus in the form of chromatin, which is a complex of DNA and proteins called histones. The DNA is tightly coiled and folded, allowing it to fit within the nucleus. During cell division, the chromatin condenses and becomes visible as chromosomes.<br /><br />SECTION B: ANSWER ANY ONE QUESTION (20 MARKS)<br /><br />Question Six:<br />a) The cell cycle consists of four main phases: G1 (gap 1), S (synthesis), G2 (gap 2), and M (mitosis). During G1, the cell grows and prepares for DNA replication. During S phase, DNA replication occurs. During G2, the cell prepares for cell division. Finally, during M phase, the cell undergoes mitosis and divides into two daughter cells.<br /><br />b) Cell division in male gametogenesis involves the process of spermatogenesis, which occurs in the testes. Spermatogenesis involves the division of spermatogonia (stem cells) into sperm cells. The process begins with mitotic division of spermatogonia to produce primary spermatocytes. These primary spermatocytes then undergo meiosis I to produce secondary spermatocytes, which further undergo meiosis II to produce spermatids. Spermatids undergo a series of changes to become mature sperm cells, which are then released into the ejaculatory ducts.<br /><br />Question Seven:<br />a) The specialized regions on the lateral apical membrane of a cell are called microvilli. Microvilli are tiny finger-like projections that increase the surface area of the cell membrane, allowing for increased absorption and secretion.<br /><br />b) According to Singer and Nicolson (1972), the structure of a cell membrane is composed of a phospholipid bilayer with embedded proteins. The phospholipids have hydrophilic (water-loving) heads and hydrophobic (water-fearing) tails, which allow them to form a stable barrier between the cell and its environment. The embedded proteins serve various functions, such as acting as receptors for signaling molecules or forming channels for the transport of substances across the membrane.