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Class/Subject: 9th Class Biology
Chapter Name: Cell Cycle
Board: Federal Board
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FBISE 9th Class Biology Chapter 5 Cell Cycle Short Questions Answers
The series of events from the time a cell is produced until it completes mitosis and produces new cells is called the cell cycle.
Interphase is the time when a cell’s metabolic activity is very high, as it performs various functions.
Sometimes mutations occur in genes that control the timing and number of mitosis and the cells continue to divide. It results in the growth of abnormal cells called tumors. As long as these tumors remain in their original location, they are called benign.
The process through which living organisms produce offsprings of their kind is called reproduction.
When the uncontrolled division of cells leads to the growth of abnormal cells, then this is called the tumor.
The phenomenon in which non-sister chromatics of homologous chromosomes exchange that segments are known as crossing over.
In this phase, the cell duplicates its chromosomes. As a result, each chromosome consists of two sister chromatids is called S-phase.
In the G2 phase, cells prepare proteins that are essential for mitosis, mainly for the production of spindle fibers.
Cells that have temporarily or permanently stopped dividing are said to have entered a state of quiescence, called the G0 phase. In multicellular eukaryotes, cells enter the G0 phase from G1 and stop dividing.
Budding is the type of asexual reproduction in which an outgrowth is formed which is ultimately separated and grows in size e.g. yeast (Fungi).
1.Cell increases its supply of proteins.
2. Increases the number of organelles (such that mitochondria, ribosomes)
3. Cells grow in size.
The chromosomes which are similar in morphology (size, structure, and position of centromere) are known as homologous chromosomes.
1. Number of chromosomes remains constant from species to species.
2. Variations are produced.
3. Resistance power is produced due to meiosis.
4. Meiosis takes place in gamete formation and spore formation.
5. Each zygote will have a unique genetic makeup.
Meiosis is the process by which one diploid eukaryotic cell divides to generate four haploid daughter cells. Diploid means the cell in which chromosomes are in pairs (homologous pairs) while haploid means the cell with half the number of chromosomes i.e. chromosomes are not in the form of pairs.
The nuclear membrane seeks during cell division so there is no distinct nucleus. In an interphase nuclear material is in the form of fine chromatin which condenses during prophase to get into the shape of chromosomes.
The type of cell division in which a cell divides into two daughter cells, each with the same number of chromosomes as were present in the parent cell is called mitosis
Prokaryotic cells undergo a process similar to mitosis is called binary fission.
Centrosomes give rise to microtubules by joining tubulin proteins present in the cytoplasm. The microtubules thus formed are called spindle fibers.
Each chromosome has a kinetochore at the centromere. The kinetochore is a complex protein structure that is the point where spindle fibers attach.
1. It occurs by a process known as cleavage.
2. A cleavage furrow develops where the metaphase plate (a part of the cytoskeleton) used to be.
3. The ring contracts deeping the furrow and eventually pinching the parent cell into two.
The tumors can send the cancer cells to the other parts of the body where new tumors may form. This phenomenon is called metastasis.
Tubulin is a type of protein present in the cytoplasm. The tubulin monomers give rise to microtubules by polymerization.
The two non-sister chromatids of chromosomes become “zipped” together, forming complexes known as chiasmata, in a process known as synapsis.
The two centrosomes give rise to microtubules by polymerizing the tubulin proteins present in the cytoplasm. The microtubules thus formed are called spindle fibers and the complete set of the spindle fibers is known as a mitotic spindle.
The phase of mitosis and meiosis in which each kinetochore fiber pulls toward the originating centrosome and divides the sister chromatids (in mitosis and meiosis-II) or divides the homologous pair (in meiosis-I).
The programmed cell death during which cell membrane makes blebs which break from the cell and are phagocytosed by other cells.
The accidental death of cells and living tissues is called necrosis.
causes of necrosis: Injury, Infection, Cancer, Hypoxic environment, Lack of proper care to a wound site, Spider bites.
Cell membrane makes irregular buds known as blebs. Blebs break off from the cell and are now called apoptotic bodies, which are then phagocytosed by other cells.
After meiosis, I, both haploid daughter cells enter a period of rest, known as interkinesis or interphase II.
In 1911, the American geneticist Thomas Hunt Morgan observed the phenomenon of crossing over in fruit fly Drosophila melanogaster.
Diploid means the cells in which chromosomes are in pairs (homologous pairs) while haploid means the cells with half the number of chromosomes i.e. chromosomes are not in the form of pairs.
As long as tumors remain in their original location, they are called benign tumors. But if they invade other tissues, they are called malignant (cancerous) tumors and their cells are called cancer cells.
The process in which an organism can be regenerate its lost parts through mitosis is called regeneration.
Cytokinesis in plant cells occurs differently. Vesicles derived from the Golgi apparatus move to the middle of the cell and fuse to form a membrane-bounded disc called a cell plate or phragmoplast.
1. Telophase is the reversal of prophase.
2. A new nuclear envelope forms around each set of separated chromosomes.
3. Both sets of chromosomes, now surrounded by new nuclear envelopes, unfold back into chromatin, Nuclear division is completed.
The two chromatids of the same chromosome are called sister chromadits. They are attached at the same centromere.
Chiasmata is the region where crossing over occurs. It is a cross-like link between two homologous chromosomes. After crossing over, homologous chromosomes separate from one another but remain tightly packed at chiasmata.
During metaphase, a kinetochore fiber attaches to kinetochores of the centromeres of the chromosomes arrange themselves along the equator of the cell forming a metaphase plate.
After the G2 phase of interphase, the cells enter the division phase i.e. M-phase. It is characterized by mitosis, in which the cell divides into two daughter cells and the number of chromosomes remains the same as that of the parent cell.
Cell division of prokaryotes is not called mitosis because prokaryotes do not have proper nuclei and do not form spindles during division that is why their division is not called notes is, instead they under a similar process to mitosis called, binary fission.
During Anaphase I, chromosomes separate and go to opposite poles, while during anaphase II, sister chromosomes separate. This is called a disjunction.
1. Condensation of chromatin
2. Duplication of chromosomes
3. Formation of the mitotic spindle
4. Disappearance of the nucleolus
5. Ans nuclear envelope
In this phase, the cell duplicates its chromosomes. The DNA molecules of each chromosome are copied, and new protein molecules are attached.
Cytokinesis is the division of cytoplasm is known as Cytokinesis.
1. Apoptosis can occur when a cell is damaged or undergo stress conditions. Apoptosis removes the damaged cell. preventing it from getting further nutrients.
2. Apoptosis prevents the spread of infection.
3. Apoptosis also gives advantages during development.
The mitosis in which the spindle fibers are formed outside the nuclear envelope is called open mitosis.
The condition in which there is one more chromosome than the usual 2N number.