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Lab examv questions [11 26-13]

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  • cell cycle, the ordered sequence of events that occur in a cell in preparation for cell division. The cell cycle is a four-stage process in which the cell increases in size (gap 1, or G1, stage), copies its DNA (synthesis, or S, stage), prepares to divide (gap 2, or G2, stage), and divides (mitosis, or M, stage). The stages G1, S, and G2 make up interphase, which accounts for the span between cell divisions. On the basis of the stimulatory and inhibitory messages a cell receives, it “decides” whether or not it should enter the cell cycle and divide
  • The seminiferous tubules, in which the sperm are produced, constitute about 90 percent of the testicular mass. In the young male the tubules are simple and composed of undeveloped sperm-producing cells (spermatogonia) and the Sertoli cells. In the older male the tubules become branched, and spermatogonia are changed into the fertile sperm cells after a series of transformations called spermatogenesis. The Sertoli cells found in both young and adult males mechanically support and protect the spermatogonia. Each seminiferous tubule of the adult testis has a central lumen, or cavity, which is connected to the epididymis and spermatic duct (ductus deferens). Sperm cells originate as spermatogonia along the walls of the seminiferous tubules. The spermatogonia mature into spermatocytes, which mature into spermatids that mature into spermatozoa as they move into the central lumen of the seminiferous tubule. The spermatozoa migrate, by short contractions of the tubule, to the mediastinum testis; they are then transported through a complex network of canals (rete testis and efferent ductules) to the epididymis for temporary storage. The spermatozoa move through the epididymis and the spermatic duct to be stored in the seminal vesicles for eventual ejaculation with the seminal fluid. Normal men produce about one million spermatozoa daily. In animals that breed seasonally, such as sheep and goats, the testes regress completely during the nonbreeding season and the spermatogonia return to the state found in the young, sexually immature males. Frequently in these animals the testes are drawn back into the body cavity except in the breeding season, when they again descend and mature; this process is known as recrudescence.
  • Spermatocytogenesis(also called Mitosis): Stem cells (Type A spermatogonia; singular = spermatogonium) divide mitotically to replace themselves and to produce cells that begin differentiation (Type B spermatogonia).  Spermatogonia have spherical or oval nuclei, and rest on the basement membrane. (You are not responsible for distinguishing between Type A and Type B spermatogonia in lab.)  Meiosis: Cells in prophase of the first meiotic division are primary spermatocytes.  They are characterized by highly condensed chromosomes giving the nucleus a coarse chromatin pattern and an intermediate position in the seminiferous epithelium. This is a long stage, so many primary spermatocytes can be seen.  Primary spermatocytes go through the first meiotic division and become secondary spermatocytes.  The cells quickly proceed through this stage and complete the second meiotic division. Because this stage is short there are few secondary spermatocytes to be seen in sections. You are not responsible for identifying secondary spermatocytes in lab.  Meiosis is the process by which the diploid number of chromosomes present in spermatogonia (the stem cells) is reduced to the haploid number present in mature spermatozoa.The products of the second meiotic division are called spermatids. They are spherical cells with interphase nuclei, positioned high in the epithelium.  Since spermatids go through a metamorphosis into spermatozoa, they occur in early through late stages.  You are not responsible for distinguishing the different stages of spermatids, but you are required to identify a spermatid.All of these progeny cells remain attached to each other by cytoplasmic bridges. The bridges remain until sperm are fully differentiated.Spermiogenesis: This is the metamorphosis of spherical spermatids into elongated spermatozoa. No further mitosis or meiosis occurs.  During spermiogenesis,  the acrosome forms, the flagellar apparatus forms, and most excess cytoplasm (the residual body) is separated and left in the Sertoli cell. Spermatozoa are released into the lumen of the seminiferous tubule. A small amount of excess cytoplasm (the cytoplasmic droplet) is shed later in the epididymis. Spermiogenesis:  a process of metamorphosis from a round cell with typical organelles to a highly specialized, elongated cell well adapted for traversing the male and female reproductive tracts and achieving fertilization of an egg.Sertoli Cell & Developing Sperm Cells: an interactionThe Interaction  At all stages of differentiation, the spermatogenic cells are in close contact with Sertoli cells which are thought to provide structural and metabolic support to the developing sperm cells.  A single Sertoli cell extends from the basement membrane to the lumen of the seminiferous tubule although its cytoplasm is difficult to distinguish at the light microscopic level. They are characterized by the presence of a vesicular, oval, basally positioned nucleus which contains a prominent nucleolus. The nuclear envelope often contains a definite fold.  The significance of the very close association of the two types of cells is unknown. Sertoli cells are endocrine cells - they secrete the polypeptide hormone, inhibin. Inhibin acts at the level of the pituitary to reduce the secretion of follicle stimulating hormone.
  • A. The gametogenic function of the testes is to produce the male gametes or spermatozoa. This process is termed, spermatogenesis. The sites of spermatozoa production are the seminiferous tubules. The spermatozoa originate from precursor cells that are called spermatogonia, and these cells line the basement membrane of the seminiferous tubule. Spermatogenesis can be divided into three portions:spermatocytogenesis -- proliferative phase meiosis -- production of the haploid gamete spermiogenesis -- "metamorphosis" of spermatids into spermatozoaDiscussion of spermatogenesis will be based on the adult male mammal that is a continuous breeder. The stages are outlined in Figure 2. B. Spermatocytogenesis and Meiosis This phase begins with the division of the spermatogonia, that line the seminiferous tubule, near the basement membrane. Spermatogonia originate at puberty by the proliferation of the gonocytesand are the descendants of the primordial germ cells. One or two divisions of spermatogonia occur to maintain their population in a stem cell pool. Of the cells resulting from these mitotic divisions, some spermatogonia stay in the "resting" pool, while the remaining type A spermatogonia proliferate several times and undergo 1 to 5 stages of division and differentiation. After the last division, the resulting cells are termed primary spermatocytes and this ends spermatocytogenesis. The primary spermatocytes then undergo the first of the two division that constitute meiosis. The first meiotic division produces two secondary spermatocytes. Division of the secondary spermatocytes completes meiosis and produces the spermatids (Figure 2). 2. The "resting" or stem cell spermatogonia remain dormant for a time and then join a new proliferation of spermatogonia. Since this new wave of spermatogonial divisions does not wait for the previous generation of cells to complete spermatogenesis, the result are an overlapping of generations in any one area of the seminiferous tubules. The purpose of this phenomena is to ensure a residual population of spermatogonia, without which the testis would exhaust its ability to produce sperm. The time required for one spermatogonium to divide and form spermatozoa requires about 4.5 to 5 times that time span between divisions of the stem cell spermatogonial. C. SpermiogenesisThis part of spermatogenesis is defined as the nuclear and cytoplasmic changes in the spermatid that results in the spermatozoa. Some aspects of the restructuring of the cell are: condensation of nuclear material formation of the acrosome formation of tail structures mitochondrial spiral formation removal of extraneous cytoplasm. The process of spermiogenesis ends in the testis with release of the spermatozoa from the Sertoli cell. The spermatozoa has been embedded up until now in the Sertoli cell. The process by which spermatozoa are shed into the lumen of the seminiferous tubule for transport out of the testis is spermiation. The overall results of spermatogenesis is: cell proliferation maintenance of a reserve germ cell population reduction in chromosome number genetic variation through meiosis shaping of the spermatid into the spermatozoa
  • 1. Early in embryogenesis, primordial germ cells migrate from the yolk sac endoderm to the genital ridge (developing ovary) where they take up residence and are called oogonia. 2.These diploid oogonia undergo several mitotic divisions prior to or shortly after parturition, thus providing the developing ovary with a large supply of future ova (eggs). 3. When oogonia begin the first meiotic division, they are called primary oocytes.4. Primary oocytes are arrested in prophase of Meiosis I until the female reaches sexual maturity. They grow in size during this arrested phase, but do not divide. A human female is born with about 2 million primary oocytes in her ovaries, but by the time of puberty only about 400,000 are left due to atresia (degeneration).. When the female reaches sexual maturity and under the influence of follicle stimulating hormone (FSH), a small number of primary oocytes are stimulated to continue through Meiosis I.6.During this process the number of chromosomes is reduced from the diploid number (2N) to the haploid number (1N). 7. This division is uneven in that although the chromosomes are divided equally, most of the cytoplasm stays with the oocyte. The smaller polar body contains half the chromosomes but only a small amount of cytoplasm and will eventually degenerate. 8.After a primary oocyte completes the first meiotic division, it is called a secondary oocyte (1N).  In most species Meiosis I is completed just before ovulation (release of the ovum from the ovary).  However, in horses and dogs Meiosis I is completed after ovulation.  9. If a secondary oocyte is not penetrated by a sperm, it will degenerate. 10. If fertilization and pregnancy do not occur, a new cycle will begin in which FSH from the pituitary gland will stimulate a few more primary oocytes to continue through Meiosis I.  11. The process is the same as previously described and a secondary oocyte is formed.12. However, some of the time a sperm will penetrate the zonapellucida and the secondary oocyte is stimulated to continue   through Meiosis II, forming a second polar body and a mature ovum (1N).  Again, the polar body contains half of the chromosome material, but little cytoplasm, and it eventually degenerates. 13. After a sperm enters the cytoplasm of the ovum, two pronuclei form, containing genetic material from the ovum or the sperm.  14.Fertilization is complete when the two pronuclei fuse and restore the diploid chromosome number.  15. If fertilization is completed, the zygote undergoes several mitotic changes to become an embryo; otherwise it degenerates.
  • "antibiotic." Encyclopaedia Britannica. Encyclopaedia Britannica Online Academic Edition. Encyclopædia Britannica Inc., 2013. Web. 26 Nov. 2013. <http://www.britannica.com/EBchecked/topic/27751/antibiotic>.
  • Question: is this a complete answer?
  • Sexual reproduction in Rhizopus: hyphae meeting (far left) and making a zygospore (far right).
  • Spores may be produced either directly by asexual methods or indirectly by sexual reproduction. Sexual reproduction in fungi, as in other living organisms, involves the fusion of two nuclei that are brought together when two sex cells (gametes) unite.
  • Transcript

    • 1. Lab Exam: Questions
    • 2. Why choose an embryonic mass of cells to study the stages of mitosis • Unlike most cells in an adult body, an embryonic mass of cells is always dividing. Most cells in the adult body is quiescent and will not divide unless signals have been given to them to divide, and many cells such as muscle and nerve cells have even lost the ability to divide.
    • 3. What stage of mitosis of often associated with the beginning of cytokinesis? telophase
    • 4. Does the cell cycle have a beginning and an end? • cell cycle, the ordered sequence of events that occur in a cell in preparation for cell division. The cell cycle is a four-stage process in which the cell increases in size (gap 1, or G1, stage), copies its DNA (synthesis, or S, stage), prepares to divide (gap 2, or G2, stage), and divides (mitosis, or M, stage). The stages G1, S, and G2 make up interphase, which accounts for the span between cell divisions. On the basis of the stimulatory and inhibitory messages a cell receives, it “decides” whether or not it should enter the cell cycle and divide
    • 5. • spermatogenesis • • The seminiferous tubules, in which the sperm are produced, constitute about 90 percent of the testicular mass. In the young male the tubules are simple and composed of undeveloped spermproducing cells (spermatogonia) and the Sertoli cells. In the older male the tubules become branched, and spermatogonia are changed into the fertile sperm cells after a series of transformations called spermatogenesis. The Sertoli cells found in both young and adult males mechanically support and protect the spermatogonia. Each seminiferous tubule of the adult testis has a central lumen, or cavity, which is connected to the epididymis and spermatic duct (ductus deferens). Sperm cells originate as spermatogonia along the walls of the seminiferous tubules. The spermatogonia mature into spermatocytes, which mature into spermatids that mature into spermatozoa as they move into the central lumen of the seminiferous tubule. The spermatozoa migrate, by short contractions of the tubule, to the mediastinum testis; they are then transported through a complex network of canals (rete testis and efferent ductules) to the epididymis for temporary storage. The spermatozoa move through the epididymis and the spermatic duct to be stored in the seminal vesicles for eventual ejaculation with the seminal fluid. Normal men produce about one million spermatozoa daily. In animals that breed seasonally, such as sheep and goats, the testes regress completely during the nonbreeding season and the spermatogonia return to the state found in the young, sexually immature males. Frequently in these animals the testes are drawn back into the body cavity except in the breeding season, when they again descend and mature; this process is known as recrudescence.
    • 6. Spermatogenesis • Spermatogenesis: the process by which stem cells develop into mature spermatozoa. There are three phases: (1) Spermatocytogenesis (Mitosis), (2) Meiosis, and (3) Spermiogenesis
    • 7. Spermatogenesis in the Sexually Mature Male • A. The gametogenic function of the testes is to produce the male gametes or spermatozoa. This process is termed, spermatogenesis. The sites of spermatozoa production are the seminiferous tubules. The spermatozoa originate from precursor cells that are called spermatogonia, and these cells line the basement membrane of the seminiferous tubule. Spermatogenesis can be divided into three portions: • spermatocytogenesis -- proliferative phase • meiosis -- production of the haploid gamete • spermiogenesis -- "metamorphosis" of spermatids into spermatozoa
    • 8. oogenesis • in the human female reproductive system, growth process in which the primary egg cell (or ovum) becomes a mature ovum.
    • 9. oogenesis • The egg cell remains as a primary ovum until the time for its release from the ovary arrives. The egg then undergoes a cell division. The nucleus splits so that half of its chromosomes go to one cell and half to another. One of these two new cells is usually larger than the other and is known as the secondary ovum; the smaller cell is known as a polar body. The secondary ovum grows in the ovary until it reaches maturation; it then breaks loose and is carried into the fallopian tubes. Once in the fallopian tubes, the secondary egg cell is suitable for fertilization by the male sperm cells
    • 10. Oogenesis Dr. Charlotte Ownby
    • 11. • Stages of mitosis • Prior to the onset of mitosis, the chromosomes have replicated and the proteins that will form the mitotic spindle have been synthesized. Mitosis begins at prophase with the thickening and coiling of the chromosomes. The nucleolus, a rounded structure, shrinks and disappears. The end of prophase is marked by the beginning of the organization of a group of fibres to form a spindle and the disintegration of the nuclear membrane. The chromosomes, each of which is a double structure consisting of duplicate chromatids, line up along the midline of the cell at metaphase. In anaphase each chromatid pair separates into two identical chromosomes that are pulled to opposite ends of the cell by the spindle fibres. During telophase, the chromosomes begin to decondense, the spindle breaks down, and the nuclear membranes and nucleoli re-form. The cytoplasm of the mother cell divides to form two daughter cells, each containing the same number and kind of chromosomes as the mother cell. The stage, or phase, after the completion of mitosis is called interphase
    • 12. • meiosis • Prior to meiosis, each of the chromosomes in the diploid germ cell has replicated and thus consists of a joined pair of duplicate chromatids. Meiosis begins with the contraction of the chromosomes in the nucleus of the diploid cell. Homologous paternal and maternal chromosomes pair up along the midline of the cell. Each pair of chromosomes—called a tetrad, or a bivalent— consists of four chromatids. At this point, the homologous chromosomes exchange genetic material by the process of crossing over (see linkage group). The homologous pairs then separate, each pair being pulled to opposite ends of the cell, which then pinches in half to form two daughter cells. Each daughter cell of this first meiotic division contains a haploid set of chromosomes. The chromosomes at this point still consist of duplicate chromatids. In the second meiotic division, each haploid daughter cell divides. There is no further reduction in chromosome number during this division, as it involves the separation of each chromatid pair into two chromosomes, which are pulled to the opposite ends of the daughter cells. Each daughter cell then divides in half, thereby producing a total of four different haploid gametes. When two gametes unite during fertilization, each contributes its haploid set of chromosomes to the new individual, restoring the diploid number
    • 13. Rhizobium and legumes • Rhizobium organisms in the soil recognize and invade the root hairs of their specific plant host, enter the plant tissues, and form a root nodule. This process causes the bacteria to lose many of their freeliving characteristics. They become dependent upon the carbon supplied by the plant, and, in exchange for carbon, they convert nitrogen gas to ammonia, which is used by the plant for its protein synthesis and growth. In addition, many bacteria can convert nitrate to amines for purposes of synthesizing cellular materials or to ammonia when nitrate is used as electron acceptor
    • 14. rhizobidium • Nitrogen Fixation by Legumes • Legume nitrogen fixation starts with the formation of a nodule. A common soil bacterium, Rhizobium, invades the root and multiplies within the cortex cells. The plant supplies all the necessary nutrients and energy for the bacteria. Within a week after infection, small nodules are visible with the naked eye. In the field, small nodules can be seen 2-3 weeks after planting, depending on legume species and germination conditions. When nodules are young and not yet fixing nitrogen, they are usually white or grey inside. As nodules grow in size they gradually turn pink or reddish in color, indicating nitrogen fixation has started. The pink or red color is caused by leghemoglobin (similar to hemoglobin in blood) that controls oxygen flow to the bacteria.
    • 15. • • Steps of Gram stain • • • Lab 6: Gram Stain 1. The bacteria are first stained with the basic dye crystal violet. Both Gram-positive and Gramnegative bacteria become directly stained and appear purple after this step. 2. The bacteria are then treated with Gram's iodine solution. This allows the stain to be retained better by forming an insoluble crystal violet-iodine complex. Both Gram-positive and Gram-negative bacteria remain purple after this step. 3. Gram's decolorizer, a mixture of ethyl alcohol and acetone, is then added. This is the differential step. Gram-positive bacteria retain the crystal violet-iodine complex while Gramnegative are decolorized. 4. Finally, the counterstain safranin (also a basic dye) is applied. Since the Gram-positive bacteria are already stained purple, they are not affected by the counterstain. Gram-negative bacteria, which are now colorless, become directly stained by th e safranin. Thus, Gram-positive appear purple, and Gram-negative appear pink.
    • 16. What happens when milk is pasteurized? • heat-treatment process that destroys pathogenic microorganisms in certain foods and be • The times and temperatures are those determined to be necessary to destroy the Mycobacterium tuberculosis and other more heat-resistant of the non-spore-forming, diseasecausing microorganisms found in milk. The treatment also destroys most of the microorganisms that cause spoilage and so prolongs the storage time of food.verages.
    • 17. • Pasteurization • Pasteurization is most important in all dairy processing. It is the biological safeguard which ensures that all potential pathogens are destroyed. Extensive studies have determined that heating milk to 63° C (145° F) for 30 minutes or 72° C (161° F) for 15 seconds kills the most resistant harmful bacteria. In actual practice these temperatures and times are exceeded, thereby not only ensuring safety but also extending shelf life.
    • 18. antibiotics • chemical substance produced by a living organism, generally a microorganism, that is detrimental to other microorganisms. • Antibiotics produce their effects through a variety of mechanisms of action. A large number work by inhibiting bacterial cell wall synthesis; these agents are referred to generally as β-lactam antibiotics. Production of the bacterial cell wall involves the partial assembly of wall components inside the cell, transport of these structures through the cell membrane to the growing wall, assembly into the wall, and finally crosslinking of the strands of wall material. Antibiotics that inhibit the synthesis of the cell wall have a specific effect on one or another phase. The result is an alteration in the cell wall and shape of the organism and eventually the death of the bacterium.
    • 19. antibiotics • Unlike bacteria, viruses mimic the metabolic functions of their host cells. Antibiotics are not effective against viruses.
    • 20. Fungi
    • 21. How can you tell whether Rhizopus is reproducing sexually or asexually? Fungi - Biology • Rhizopus stolonifer (bread mold) is a zygomycete. • Asexual reproduction in Rhizopus: Sporangia – note the root like hyphae (rhizoids) and horizontallygrowing hyphae (stolons) at the base • Sexual reproduction in Rhizopus: hyphae meeting (far left) and making a zygospore (far right).
    • 22. Rhizopus: Asexual reproduction in Rhizopus: Sporangia – note the root like hyphae (rhizoids) and horizontally-growing hyphae (stolons) at the base
    • 23. Describe the relationship found in lichen. Lichens • lichen is not a single organism the way most other living things are, but rather it is a combination of two organisms which live together intimately.
    • 24. Describe the relationship found in lichen. Lichens • Most of the lichen is composed of fungal filaments, but living among the filaments are algal cells, usually from a green alga or a cyanobacterium
    • 25. Describe the relationship found in lichen. Life History and Ecology of Lichens • Lichens are formed from a combination of a fungal partner (mycobiont) and an algal partner (phycobiont). • A lichen may absorb certain mineral nutrients from any of these substrates on which it grows, but is generally selfreliant in feeding itself through photosynthesis in the algal cells.
    • 26. Describe the relationship found in lichen. Life History and Ecology of Lichens • Lichens growing in trees are simply using the tree as a home. Lichens growing on rocks, though, may release chemicals which speed the degradation of the rock into soil, and thus promote production of new soils.
    • 27. Fungi: Benefits Symbiotic Fungi • Lichens are symbioses involving fungi and unicellular algae • Mycorrhizae are symbioses involving fungi and the roots of plants Multiclavula mucida, a lichenized basidiomycete (left) and Parmelia sp., a lichenized ascomycete (right)
    • 28. The only distinction between a fungi spore and gamete is function • Following a period of intensive growth, fungi enter a reproductive phase by forming and releasing vast quantities of spores. Spores are usually single cells produced by fragmentation of the mycelium or within specialized structures (sporangia, gametangia, sporophores, etc.). Spores may be produced either directly by asexual methods or indirectly by sexual reproduction. Sexual reproduction in fungi, as in other living organisms, involves the fusion of two nuclei that are brought together when two sex cells (gametes) unite. Asexual reproduction, which is simpler and more direct, may be accomplished by various methods.

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