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#	Question	Answer
1	What is the basic unit from which all organisms start life?	A single cell.
2	What are the two important characteristics of cells mentioned in the chapter?	Growth and reproduction.
3	How do cells reproduce?	By dividing into two daughter cells.
4	What allows a single cell to form a structure consisting of millions of cells?	Cycles of growth and division.
5	What is meant by the cell cycle?	The sequence of events by which a cell duplicates its genome, synthesises other cell constituents, and divides into two daughter cells.
6	Which three processes must occur in a coordinated way during cell division?	Cell division, DNA replication, and cell growth.
7	During which stage of the cell cycle does DNA synthesis occur?	During one specific stage of the cell cycle.
8	What controls the events of chromosome distribution during cell division?	Genetic control.
9	Name the two basic phases of the cell cycle.	Interphase and M Phase (Mitosis phase).
10	What does the M Phase represent?	The phase in which actual cell division or mitosis occurs.
11	What does interphase represent?	The phase between two successive M phases.
12	Approximately how long does a human cell take to complete one cell cycle?	About 24 hours.
13	How long can the cell cycle of yeast take?	About 90 minutes.
14	What percentage of the cell cycle is occupied by interphase?	More than 95%.
15	How long does cell division proper last in a human cell cycle?	About one hour.
16	What is karyokinesis?	Nuclear division corresponding to the separation of daughter chromosomes.
17	What is cytokinesis?	Division of the cytoplasm.
18	Why is interphase called the preparation phase?	Because the cell undergoes growth and DNA replication in an orderly manner.
19	Into which three phases is interphase divided?	G1 phase, S phase, and G2 phase.
20	What occurs during G1 phase?	The cell is metabolically active and continuously grows but does not replicate DNA.
21	What occurs during S phase?	DNA synthesis or replication takes place.
22	What happens to the DNA content during S phase?	It doubles from 2C to 4C.
23	Does chromosome number increase during S phase?	No, chromosome number remains the same.
24	What is the chromosome number after S phase if the cell was 2n in G1 phase?	It remains 2n.
25	What happens in animal cells during S phase besides DNA replication?	The centriole duplicates in the cytoplasm.
26	What occurs during G2 phase?	Proteins are synthesised in preparation for mitosis and cell growth continues.
27	What is the quiescent stage of the cell cycle called?	G0 stage.
28	What is characteristic of cells in G0 stage?	They remain metabolically active but do not proliferate.
29	Which animal cells generally do not exhibit division?	Heart cells.
30	In animals, mitotic division is mainly seen in which cells?	Diploid somatic cells.
31	Give an example where haploid cells divide by mitosis in animals.	Male honey bees.
32	Can plants show mitotic division in both haploid and diploid cells?	Yes.
33	Why is mitosis called equational division?	Because the number of chromosomes in parent and progeny cells remains the same.
34	Name the four stages of karyokinesis in mitosis.	Prophase, Metaphase, Anaphase, and Telophase.
35	Which is the first stage of karyokinesis in mitosis?	Prophase.
36	What marks the beginning of prophase?	Initiation of condensation of chromosomal material.
37	What happens to chromatin during prophase?	It condenses and becomes untangled.
38	What happens to centrosomes during prophase?	They move towards opposite poles of the cell.
39	What are asters?	Microtubules radiating from centrosomes.
40	What forms the mitotic apparatus?	Two asters together with spindle fibres.
41	What is the inactive stage entered by cells that no longer divide?	Quiescent stage (G0).
42	What is the condition of cells in G0 stage?	They remain metabolically active but no longer proliferate unless required.
43	In animals, mitotic cell division is generally seen in which type of cells?	Diploid somatic cells.
44	Give an example where haploid cells divide by mitosis in animals.	Male honey bees.
45	Can plants show mitotic divisions in both haploid and diploid cells?	Yes.
46	Why is mitosis called equational division?	Because the chromosome number remains the same in parent and progeny cells.
47	Which phase is considered the most dramatic period of the cell cycle?	M Phase.
48	What major process occurs during M Phase?	Major reorganisation of virtually all cell components.
49	What are the four stages of karyokinesis in mitosis?	Prophase, Metaphase, Anaphase, and Telophase.
50	Which stage is the first stage of karyokinesis in mitosis?	Prophase.
51	Which phases of interphase precede prophase?	S phase and G2 phase.
52	What is the condition of newly formed DNA molecules before prophase?	They are not distinct but intertwined.
53	What marks the beginning of prophase?	Initiation of condensation of chromosomal material.
54	What happens to chromosomal material during chromatin condensation?	It becomes untangled.
55	What happens to the centrosome during prophase?	It moves towards opposite poles of the cell.
56	What are asters?	Microtubules radiating from centrosomes.
57	What forms the mitotic apparatus?	Two asters together with spindle fibres.
58	What is the structure of chromosomes during prophase?	Two chromatids attached together at the centromere.
59	Which cell organelles disappear by the end of prophase?	Golgi complexes, endoplasmic reticulum, nucleolus, and nuclear envelope.
60	What marks the start of metaphase?	Complete disintegration of the nuclear envelope.
61	Why can chromosomes be clearly observed during metaphase?	Because chromosome condensation is completed.
62	What is a metaphase chromosome made up of?	Two sister chromatids held together by the centromere.
63	What are kinetochores?	Small disc-shaped structures at the surface of centromeres.
64	What is the function of kinetochores?	They serve as attachment sites for spindle fibres.
65	Where do chromosomes align during metaphase?	At the equator of the cell.
66	What is the metaphase plate?	The plane of alignment of chromosomes at metaphase.
67	How are sister chromatids attached during metaphase?	Each chromatid is connected by its kinetochore to spindle fibres from opposite poles.
68	What are the key features of metaphase?	Attachment of spindle fibres to kinetochores and alignment of chromosomes at the metaphase plate.
69	What happens at the onset of anaphase?	Each chromosome splits simultaneously.
70	What are daughter chromatids called after separation in anaphase?	Daughter chromosomes.
71	Towards where do daughter chromosomes move during anaphase?	Opposite poles of the cell.
72	Which part of the chromosome leads during movement in anaphase?	The centromere.
73	What happens to chromosome arms during anaphase movement?	They trail behind.
74	What are the key events of anaphase?	Centromeres split, chromatids separate, and chromatids move to opposite poles.
75	Which is the final stage of karyokinesis?	Telophase.
76	What happens to chromosomes at the beginning of telophase?	They decondense and lose their individuality.
77	Can individual chromosomes be seen clearly during telophase?	No, they cannot be seen as discrete elements.
78	What happens to chromatin material during telophase?	It collects at the two poles of the cell.
79	What are the key events of telophase?	Chromosomes cluster at opposite poles, nuclear envelope reforms, and nucleolus, golgi complex, and ER reappear.
80	What forms around chromosome clusters during telophase?	Nuclear envelope forming two daughter nuclei.
81	What is cytokinesis?	Division of the cytoplasm into two daughter cells.
82	What process does mitosis accomplish before cytokinesis?	Segregation of duplicated chromosomes into daughter nuclei (karyokinesis).
83	How does cytokinesis occur in animal cells?	By formation of a furrow in the plasma membrane.
84	What happens to the furrow during cytokinesis in animal cells?	It deepens and joins in the centre to divide the cytoplasm.
85	Why is cytokinesis different in plant cells?	Because plant cells have a relatively inextensible cell wall.
86	How does cytokinesis occur in plant cells?	By cell wall formation starting from the centre and growing outward.
87	What is the precursor formed during cytokinesis in plant cells?	Cell plate.
88	What does the cell plate represent?	The middle lamella between walls of two adjacent cells.
89	Which organelles get distributed between daughter cells during cytokinesis?	Mitochondria and plastids.
90	What is syncytium?	A multinucleate condition formed when karyokinesis is not followed by cytokinesis.
91	Give an example of syncytium mentioned in the text.	Liquid endosperm in coconut.
92	To which cells is mitosis usually restricted?	Diploid cells.
93	Can haploid cells also divide by mitosis?	Yes, in some lower plants and social insects.
94	What type of daughter cells are produced by mitosis?	Diploid daughter cells with identical genetic complement.
95	What is responsible for growth in multicellular organisms?	Mitosis.
96	Why must cells divide as they grow?	To restore the nucleo-cytoplasmic ratio.
97	What is one important contribution of mitosis?	Cell repair.
98	Which cells are constantly replaced through mitosis?	Epidermal cells, gut lining cells, and blood cells.
99	Which plant tissues show continuous mitotic divisions?	Apical meristem and lateral cambium.
100	What is meiosis?	A type of cell division that reduces chromosome number by half to produce haploid daughter cells.
101	Why is meiosis important in sexual reproduction?	It produces haploid gametes.
102	What restores the diploid phase in sexually reproducing organisms?	Fertilisation.
103	During which process does meiosis occur in plants and animals?	Gametogenesis.
104	How many cycles of DNA replication occur in meiosis?	Only one.
105	When is meiosis I initiated?	After parental chromosomes replicate during S phase.
106	What important event occurs between homologous chromosomes during meiosis?	Pairing and recombination between non-sister chromatids.
107	How many haploid cells are formed at the end of meiosis II?	Four haploid cells.
108	Name the stages of meiosis I.	Prophase I, Metaphase I, Anaphase I, and Telophase I.
109	Name the stages of meiosis II.	Prophase II, Metaphase II, Anaphase II, and Telophase II.
110	How is prophase I of meiosis different from prophase of mitosis?	It is longer and more complex.
111	Into how many stages is prophase I subdivided?	Five stages.
112	Name the five stages of prophase I.	Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
113	What happens during leptotene?	Chromosomes gradually become visible under the light microscope.
114	What continues throughout leptotene?	Compaction of chromosomes.
115	What occurs during zygotene?	Chromosomes start pairing together.
116	What is synapsis?	The pairing of homologous chromosomes.
117	What are homologous chromosomes?	Paired chromosomes during synapsis.
118	Which structure forms during synapsis?	Synaptonemal complex.
119	What is a bivalent?	A complex formed by a pair of synapsed homologous chromosomes.
120	What is another name for a bivalent?	Tetrad.
121	During which stage are tetrads clearly visible?	Pachytene.
122	What becomes distinct during pachytene?	The four chromatids of each bivalent chromosome.
123	What appears during pachytene indicating crossing over?	Recombination nodules.
124	Between which chromatids does crossing over occur?	Non-sister chromatids of homologous chromosomes.
125	What is crossing over?	Exchange of genetic material between homologous chromosomes.
126	Which enzyme is involved in crossing over?	Recombinase.
127	What is the result of crossing over?	Recombination of genetic material.
128	By the end of which stage is recombination completed?	Pachytene.
129	What marks the beginning of diplotene?	Dissolution of the synaptonemal complex.
130	What are chiasmata?	X-shaped structures where homologous chromosomes remain attached after crossing over.
131	How long can diplotene last in vertebrate oocytes?	Months or years.
132	What marks diakinesis?	Terminalisation of chiasmata.
133	What happens to chromosomes during diakinesis?	They become fully condensed.
134	What forms during diakinesis to prepare chromosomes for separation?	Meiotic spindle.
135	What disappears by the end of diakinesis?	Nucleolus and nuclear envelope.
136	Diakinesis represents transition to which stage?	Metaphase I.
137	What happens during metaphase I?	Bivalent chromosomes align on the equatorial plate.
138	Where do spindle microtubules attach during metaphase I?	To kinetochores of homologous chromosomes.
139	What occurs during anaphase I?	Homologous chromosomes separate.
140	What remains associated during anaphase I?	Sister chromatids remain attached at centromeres.
141	What reappears during telophase I?	Nuclear membrane and nucleolus.
142	What follows telophase I?	Cytokinesis.
143	What is formed after cytokinesis in telophase I?	Dyad of cells.
144	What is interkinesis?	The stage between the two meiotic divisions.
145	Does DNA replication occur during interkinesis?	No.
146	How is prophase II compared to prophase I?	It is much simpler.
147	When is meiosis II initiated?	Immediately after cytokinesis.
148	Which process does meiosis II resemble?	Normal mitosis.
149	What happens to the nuclear membrane during prophase II?	It disappears.
150	What happens to chromosomes during prophase II?	They become compact again.
151	What occurs during metaphase II?	Chromosomes align at the equator.
152	To what do spindle microtubules attach in metaphase II?	Kinetochores of sister chromatids.
153	What initiates anaphase II?	Splitting of the centromere of each chromosome.
154	What happens after centromere splitting in anaphase II?	Sister chromatids move toward opposite poles.
155	How do chromatids move to opposite poles during anaphase II?	By shortening of microtubules attached to kinetochores.
156	With which stage does meiosis end?	Telophase II.
157	What happens to chromosomes during telophase II?	They get enclosed by a nuclear envelope.
158	What follows telophase II?	Cytokinesis.
159	What is formed after cytokinesis in telophase II?	A tetrad of four haploid daughter cells.
160	What is the significance of meiosis in sexually reproducing organisms?	It conserves the specific chromosome number across generations.
161	How does meiosis maintain chromosome number despite reducing it by half?	Fertilisation restores the diploid chromosome number.
162	What is another important significance of meiosis?	It increases genetic variability in populations.
163	Why are variations important?	They are important for evolution.
164	According to cell theory, cells arise from what?	Pre-existing cells.
165	What is the process by which new cells are formed from pre-existing cells called?	Cell division.
166	From what does every sexually reproducing organism begin its life cycle?	A single-celled zygote.
167	Does cell division stop after formation of a mature organism?	No, it continues throughout life.
168	What is the cell cycle?	The stages through which a cell passes from one division to the next.
169	Into which two phases is the cell cycle divided?	Interphase and Mitosis (M phase).
170	What is interphase?	The preparation phase for cell division.
171	What is M phase?	The actual period of cell division.
172	Into which phases is interphase subdivided?	G1, S, and G2 phases.
173	What occurs during G1 phase?	Cell growth and normal metabolism.
174	During which phase does most organelle duplication occur?	G1 phase.
175	What occurs during S phase?	DNA replication and chromosome duplication.
176	What occurs during G2 phase?	Cytoplasmic growth.
177	Name the four stages of mitosis.	Prophase, Metaphase, Anaphase, and Telophase.
178	What major event occurs during prophase?	Chromosome condensation.
179	What happens to centrioles during prophase?	They move to opposite poles.
180	Which structures disappear during prophase?	Nuclear envelope and nucleolus.
181	What begins to appear during prophase?	Spindle fibres.
182	What characterises metaphase?	Alignment of chromosomes at the equatorial plate.
183	What happens during anaphase of mitosis?	Centromeres divide and chromatids move to opposite poles.
184	What happens after chromatids reach opposite poles?	Chromosomal elongation starts.
185	What reappears during telophase?	Nucleolus and nuclear membrane.
186	What follows nuclear division in mitosis?	Cytoplasmic division or cytokinesis.
187	Why is mitosis called equational division?	Because chromosome number is conserved in daughter cells.
188	In which cells does meiosis occur?	Diploid cells destined to form gametes.
189	Why is meiosis called reduction division?	Because it reduces chromosome number by half.
190	What restores chromosome number after meiosis?	Fusion of gametes during sexual reproduction.
191	Into which two phases is meiosis divided?	Meiosis I and Meiosis II.
192	What happens during meiosis I?	Homologous chromosomes pair to form bivalents and undergo crossing over.
193	Name the five stages of prophase I.	Leptotene, Zygotene, Pachytene, Diplotene, and Diakinesis.
194	What happens during metaphase I?	Bivalents arrange on the equatorial plate.
195	What occurs during anaphase I?	Homologous chromosomes move to opposite poles with both chromatids.
196	What chromosome number reaches each pole during anaphase I?	Half the chromosome number of the parent cell.
197	What reappears during telophase I?	Nuclear membrane and nucleolus.
198	Which meiotic division resembles mitosis?	Meiosis II.
199	What happens during anaphase II?	Sister chromatids separate.
200	How many haploid cells are formed at the end of meiosis?	Four haploid cells.
201	What is the average cell cycle span for a mammalian cell?	About 24 hours.
202	What is cytokinesis?	Division of the cytoplasm into two daughter cells.
203	What is karyokinesis?	Nuclear division involving separation of daughter chromosomes.
204	What are the main events during interphase?	Cell growth and DNA replication.
205	What is the G0 phase of the cell cycle?	Quiescent phase where cells remain metabolically active but do not proliferate.
206	Why is mitosis called equational division?	Because chromosome number remains the same in daughter cells.
207	During which stage are chromosomes moved to the spindle equator?	Metaphase.
208	During which stage do centromeres split and chromatids separate?	Anaphase.
209	During which stage does pairing between homologous chromosomes occur?	Zygotene of prophase I.
210	During which stage does crossing over occur?	Pachytene of prophase I.
211	What is synapsis?	Pairing of homologous chromosomes.
212	What is a bivalent?	A pair of synapsed homologous chromosomes.
213	What are chiasmata?	X-shaped structures formed at sites of crossing over.
214	How does cytokinesis differ in plant and animal cells?	Animal cells form a cleavage furrow, while plant cells form a cell plate.
215	In which stage of meiosis do homologous chromosomes separate?	Anaphase I.
216	In which stage of mitosis do sister chromatids separate?	Anaphase.
217	What is the main difference between anaphase of mitosis and anaphase I of meiosis?	In mitosis sister chromatids separate, while in meiosis I homologous chromosomes separate.
218	What is the significance of meiosis?	Conservation of chromosome number and generation of genetic variation.
219	Can mitosis occur without DNA replication in S phase?	No.
220	Can DNA replication occur without cell division?	Yes.
221	What happens to chromosome number (N) during mitosis?	It remains constant.
222	What happens to DNA content (C) during S phase?	It doubles.
223	What happens to DNA content after mitosis?	It returns to the original amount in daughter cells.
224	What type of cells are formed at the end of meiosis?	Four haploid daughter cells.
225	Which process restores diploid chromosome number after meiosis?	Fertilisation.