LIGORES, DANIKA TONI B. 22

1. In a woody plant such as a tree, which parts have cells that live only briefly and die quickly? Which parts have cells that live for several years?

Answer: Gland cells, bark, and leaf cells live briefly and die quickly. Growing points at the tips of roots live for several years

2. Some cells never stop dividing. Give two examples of cells like this.

Answer: Cells at the growing points of tips of roots and shoots.

3. Interphase is also called the resting phase of the cell cycle. Why was it given that name?

Answer: The researchers assumed that between division cells were “resting”, so the growth phase was called the resting phase, or interphase.

4. What are the main activities of a cell while it is in G1 phase?

Answer: The cell grows in size and synthesizes mRNA and proteins in preparation for subsequent steps leading to mitosis. G1 phase ends when the cell moves into the S phase of interphase.

5. What is the main activity of the S Phase of the cell cycle? What does “S” stand for?

Answer: The main activity is when the genes in the nucleus are replicated. “S” stands for synthesis.

6. Table 4-2 gives the number of chromosomes in a haploid set of chromosomes. What is the lowest number in the table?

Answer: -2What is the highest number?

Answer: -24Most cells in plants are diploid, having two sets of chromosomes, so the number per nucleus should be doubled.How many chromosomes are present in each diploid potato nucleus?

Answer: -48If a potato plant has 1 million cells, each with one diploid nucleus, how many chromosomes are present in the entire plant?

Answer: -2 million chromosomes.

7. How many chromatids does a chromosome have before S phase of the cell cycle? (B) How many does it have after S phase?

Answer: Before S phase, each chromosome has one chromatid and one copy of each gene.

Answer: After replication in S phase, each chromosome has two chromatids and two copies of each gene.

8. Examine Table 4-1. How many hours does the cell cycle last in the root tips of corn and in onion?

Answer: -9.9 and 17.5 hours.

Which plant has cells that divide more quickly?

Answer: -Daucus Carota (carrot)

How many cell cycles could corn and onion roots undergo in 4 weeks (the cell cycles in Table 4-1 are given in hours, not days)?

Answer: Carrot: 89.6 cell cyclesAnswer: Corn: 67.87 cell cycles

If after a cell divides both daughter cells could divide and then their daughter cells could divide, how many corn cells and how many onion cells would be present at the end of 4 weeks if you started with just one cell of each?

Answer: Carrot: 716.8 cellsAnswer: Corn: 543.03 cells

9. What are the four phases of the cell cycle? What is the principal activity in the cell during each phase? Can any phase be eliminated or bypassed?

Answer: Prophase – compressing of chromatins into coiled chromosomes, disappearance of the nuclear wall, moving of organelles at the side and development of spindle fibers, made of tubulin proteins.Metaphase – the thickened chromosomes align at the middle at what is called the “metaphase plate” in a horizontal fashion. The spindle fibers are attached to the kinetochores at this point, each chromosome being attracted to two spindle fibers.Anaphase – spindle fibers pull the chromosome apart, breaking them into two. The chromosomes migrate to the two ends of the cell at what are called the spindle poles.Telophase – in the most comprehendible sense, telophase is the reverse of prophase: a.) Chromosomes become thinner again turning into two spindle fibers. b.) The nuclear walls reappear. The organelles move normally around the cytoplasm of the new cell wall. d.) Spindle fibers disappear.No it can’t be eliminated or bypassed.

10. Why is mitosis called duplication division and meiosis called reduction division? What is reduced and what is duplicated: chromosomes, number of chromosomes, or number of sets of chromosomes?

-Mitosis is called duplication division because the nuclear genes are first copied; then one set of genes is separated from the other, and each is packed into its own nucleus. Each daughter nucleus is basically a duplicate of the original mother nucleus and a twin of the other. -Meiosis is called reduction division because because it results in the reduction of the chromosome number from diploid to haploid.-Chromosomes are duplicated and reduced.

11. What does it mean when chromosomes are said to condense during prophase of mitosis? How long are chromosomes after condensation is complete? How big is a typical dividing cell in a root or shoot? If a chromosome were still 20 micrometre long after condensation, would it be possible for division to pull half of it to one end of the cell and the other half to the other end?

Answer: It means to undergo a change in the way the histones associate.Chromosome condensation continues until chromosomes are only 2 to 5 micrometre long.Long chromosomes may tangle somewhat, but microtubules exert sufficient pull to untangle them and drag them to the ends of the spindle. Because the spindle is shaped like a football, as chromosomes on each side get closer to the end, they are pulled together into a compact space.

12. What is the name of the set of microtubules that pull chromosomes apart? What is the name of the attachment point between microtubules and chromosomes? What is the name of the ends of the cells where chromosomes are pulled?

Answer: Spindle FibersKinetochorePoles

13. What is a metaphase? What is duplicated at the end of the metaphase? When this is duplicated, chromatids become free of each other. How many chromatids are there per chromosome in prophase? How many chromatids per chromosome after metaphase?

Answer: Metaphase – the thickened chromosomes align at the middle at what is called the “metaphase plate” in a horizontal fashion. The spindle fibers are attached to the kinetochores at this point, each chromosome being attracted to two spindle fibers.The number of chromosomes is doubled, but the size of each chromosome is halved.In prophase of mitosis, the chromosomes condense to facilitate easy separation into the daughter cells. Here there are still 2 chromatids per chromosome.The number of chromosomes is doubled.

14. Imagine a nucleus that has 10 chromosomes. How many chromosomes does it have before prophase begins? How many chromosomes does each daughter nucleus have after telophase has been completed? How many chromatids are present in the other mother nucleus before prophase begins? How many chromatids are present in each daughter nucleus after telophase has been completed? How many chromatids are present if you add together all chromatids in both daughter nuclei after telophase has been completed?

Answer: 10 chromosomes20 chromosomes20 chromatids

20 chromatids40 chromatids

15. What are the 4 phases of mitosis, and what is the principal activity in the nucleus during each phase?Answer: Prophase – compressing of chromatins into coiled chromosomes, disappearance of the nuclear wall, moving of organelles at the side and development of spindle fibers, made of tubulin proteins.Metaphase – the thickened chromosomes align at the middle at what is called the “metaphase plate” in a horizontal fashion. The spindle fibers are attached to the kinetochores at this point, each chromosome being attracted to two spindle fibers.Anaphase – spindle fibers pull the chromosome apart, breaking them into two. The chromosomes migrate to the two ends of the cell at what are called the spindle poles.Telophase – in the most comprehendible sense, telophase is the reverse of prophase: a.) Chromosomes become thinner again turning into two spindle fibers. b.) The nuclear walls reappear. The organelles move normally around the cytoplasm of the new cell wall. d.) Spindle fibers disappear.

16. Draw a single. Imaginary chromosome as it would appear just as mitosis is ending. Now describe what happens to it during interphase and then during mitosis. Be especially careful to consider how many chromatids and how many copies of each gene it has at its stage.

17. How does cytokinesis occur in plants? Which organelle produces vesicles that fuse to form the cell plate? What membrane is transformed into new plasma membrane?

Answer: Cytokinesis in plants involves formation of a phragmoplast, a set of short microtubules aligned parallel to the spindle microtubules. Phragmoplast microtubules trap dictyosome vesicles that then fuse the cell plate. Cell plate.

18. Many people consider algae to be plants even though algae do not have roots, stems, and leaves, but in many algae, cell division is different from that in true plants. Do most algae have a phragmoplast? What is the name of the structure they use?

Answer: After telophase, a phragmoplast forms, and dictysome vesicles establishes a cell plate, which then grows radially outward- centrifugal growth- until it meets and fuses with the wall of the parent cell. Phycoplast.

19. Sex cells are also called GAMETES. If a species has males and females (not all species do), males produces sex cells called SPERMATOGENISIS cells, and females produce sex cells called OOGENESIS cells.

20. How many sets of chromosomes des each sperm cell carry? How many does each egg cell have? Gametes such as sperm cell and egg cell are said to be (circle one: diploid, haploid). After a sperm and an egg have fused, the new cell is called a ZYGOTE, and it is (circle one: diploid, haploid).

Answer: Both have just one set of chromosomes.

21. If a plant has diploid cells with 20 chromosomes in each nucleus, how many chromosomes does each of is gametes have? What is the name of the division that reduces the number of chromosomes from 20?

Answer: 20. Reduction division, also called meiosis.

22. What are the five stages of prophase I, and what is the principal activity of the nucleus and chromosomes during each stage?

Answer: Leptotene- chromosomes begin to condense and become distinguishable, although they appear to be indistinct.

Zygotene- a remarkable pairing of chromosomes occurs. Each chromosome of one set finds and pair with the equivalent chromosome of the other set; this pairing is synapsis.

Pachytene- chromosomes continue to condense, they become shorter and thicker.

Diplotene- homologous chromosome of each bivalent begin to move away from each other nut do not separate completely because they are held in together at their paired centromeres and at points where they appear to be tangled together.

Diakinesis- homologs continue to separate, and chiasmata are pushed to the ends of the chromosome.

23. During zygotene stage of meiosis I, a remarkable pairing of chromosomes occurs. Look at the bottom part of Figure 4-19 in which “mitosis: growth of the body” has reproduced cells with four different types of chromosomes. The black ones came from the sperm nucleus. The red ones came from the egg nucleus. If one of these nuclei were to undergo meiosis, which chromosomes would pair during zygotene (which are homologous)- the long black one with short black one or the long black one with the lone red one?

Answer: The long black one with short black

24. What is the name of the structure that holds homologous chromosomes together after they have paired during zygotene?

Answer: Synaptonemal complex.

25. During pachytene, crossing over occurs. Do chromosomes actually break during this process?

Answer: Chromosomes break.

26. How does anaphase I of meiosis differ from anaphase of mitosis? Does the number of chromosomes per nucleus change in anaphase I?

Answer: In mitosis, separase degrades cohesin, releasing centromeres from each other, and each chromosomes divides into two chromosomes, each with just one chromatid. However, in the metaphase

I- anaphase I transition, homologous chromosomes separate from each other, and each still has two chromatids. No.

27. Draw all stages in the cell cycle and meiosis for a nucleus that has just one pair of homologous chromosomes, and then do the same for a nucleus that has three different types of chromosomes ( six chromosomes in three sets of homologs). Draw all sets.

28. If a cell undergoes nuclear division but not cell division, it becomes multinucleate. If it has hundreds of nuclei, it is called COENOCYTE.

29. Do prokaryotes undergo meiosis or mitosis? How do their cells divide?

Answer: Meiosis and mitosis only occurs in eukaryotes. Their cell divides with cytokinesis.

30. Describe the process of division that produces more plastids and mitochondria.

Answer: Division of the organelles is accomplished either by infurrowing or by being pulled into two.