Chapter 20 Cell Division Summary

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1 Chapter 20 Cell Division Summary Bk3 Ch20 Cell Division/1 Table 1: The concept of cell (Section 20.1) A repeated process in which a cell divides many times to make new cells Cell Responsible for growth, repair and reproduction in an organism Usually involves of the nucleus, followed by of the cytoplasm Table 2: Chromosome (Section 20.1; Figs. 20.2, 20.3 and 20.4) Characteristics of s Inside the nuclei of cells Thread-like structures Carry genetic materials which determine the characteristics of the organism Invisible under the microscope when a cell is not dividing (extend into very fine chromatins) Become much shorter and thicker when a cell starts to divide Visible under the microscope as darkly stained threads after treating with a special stain Number of s in body cells of organisms of the same species is always the same Always occur in pairs in a cell Members of a pair of s are known as homologous s Table 3: Types of cell (Section 20.1) Mitotic cell Plays important roles in growth and repair Meiotic cell Involved in reproduction Replication of genetic materials takes place before cell occurs Table 4: Mitotic cell (Section 20.2) Mitotic cell A process by which a cell divides and produces two identical cells New cells formed contain the same number and kinds of s as their parent cell Gives rise to a large number of cells that contain identical genetic materials Found in different parts of the human body Localized in the root tips and shoot tips in plants Mitosis is the process of nucleus 1

2 Bk3 Ch20 Cell Division/2 Table 5: The process of mitosis (Extension Study) (Section 20.2; Fig. 20.6) Chromosomes become shorter and thicker Each appears as a pair of identical chromatids Each chromatid carries an exact copy of genetic materials of the parent Nuclear membrane disappears The second stage Chromosomes line up in the middle of the cell, each attaching to spindle fibres Each pair of chromatids separate from each other and move towards opposite ends of the cell Separated chromatids are now called daughter s Each end of the cell has a complete set of s as the parent cell Daughter s extend into tiny threads and become invisible Nuclear membrane is formed around each set of daughter s, producing two identical daughter nuclei Table 6: Division of cytoplasm after mitosis (Extension Study) (Section 20.2) In plant cells In animal cells Cytoplasm is separated into two halves by new cell membranes and cell walls formed between the two newly formed nuclei (Fig. 20.7(a)) Cytoplasm separates into two halves by constricting inwards between two daughter nuclei (Fig. 20.7(b)) Table 7: Significance of mitotic cell (Section 20.2) Provides new cells for body growth Significance of mitotic cell In humans, it is responsible for the growth of the body from a fertilized egg into the mature organism Produces new cells for replacing dead or worn out cells Produces new cells for repairing wounds or damaged tissues In some organisms, cells are produced for asexual reproduction Table 8: Meiotic cell (Section 20.3) Meiotic cell Produces gametes Four daughter cells are produced from a parent cell Number of s in the daughter cells is reduced by half to that of parent cell Meiosis is the process of nucleus 2

3 Bk3 Ch20 Cell Division/3 Table 9: The process of meiosis (Extension Study) (Section 20.3; Fig. 20.8) First meiotic (separation of homologous s) Second meiotic (separation of chromatids) The second stage The second stage Each pair of homologous s lie side by side Each duplicates to form two identical chromatids Nuclear membrane disappears Paired homologous s line up in the middle of the cell Two members of each homologous pair of s separate from each other and move towards opposite ends of the cell Division of cytoplasm takes place Results in two daughter cells Each appears as a pair of chromatids Chromosomes line up in the middle of the cell Each pair of chromatids separate from each other and move towards opposite ends of the cell Each chromatid becomes a daughter Nuclear membrane is formed and four nuclei are produced Table 10: Division of cytoplasm after meiosis (Extension Study) (Section 20.3) After meiosis Cytoplasm divides to form four haploid daughter cells (gametes) Table 11: Significance of meiotic cell (Section 20.3) Significance of meiotic cell Results in haploid gametes (with halving of numbers) Normal diploid number of s is restored when a male gamete and a female gamete fuse together to form a zygote during fertilization (Fig. 20.9) Each pair of homologous s arranged in the middle of the cell and separated are independent of other pairs of homologous s (independent assortment) (Fig ) Gametes contain different combinations of genetic materials In fertilization, fusion of gametes is a random process and this leads to different combinations of genetic materials in the zygotes Essential for maintaining a constant number in the offspring produced by sexual reproduction Provides genetic variation and is important for evolution of the species 3

4 Bk3 Ch20 Cell Division/4 Glossary Vocabulary 詞彙 Page Description 解釋 asexual reproduction 無性生殖 63, 83 reproduction involving one parent, without the fusion of gametes cell 細胞分裂 63 the process of dividing a cell into two or more new cells after replication of cell materials, include two modes: mitotic cell and meiotic cell chromatin 染色質 64 a material inside the nucleus; during cell the chromatin is transformed into genetic 遺傳 64 the scientific study of genes and the inheritance of characters homologous meiotic cell mitotic cell 同源染色體 64, 168 減數細胞分裂有絲細胞分裂 s in the cells of sexually reproducing organisms which contain identical sets of genes, the two s of each pair are identical in shape and size and will line up during meiosis 65 the process of cell in which s of germ cells are reduced from the diploid number to the haploid number during oogenesis and spermatogenesis 65 the process of cell in which each splits into two, leaving each new cell with the same number of s as the parent cell mitosis 有絲分裂 66 the process by which a cell divides into two cells, each with exactly the same number and type of s as the original cell replication 複製 66 the synthesis of an exact copy of a structure from a template of the same structure 只涉單一親本, 不涉配子融合的繁殖模式細胞在進行物質複製後, 分成兩個或以上新細胞的過程 ; 包括兩種模式 : 有絲細胞分裂和減數細胞分裂細胞核內的物質細胞分裂期間, 染色質轉化成染色體以科學方法研究基因, 以及特徵如何從一代遺傳給下一代進行有性生殖的生物的細胞中, 兩條含相同基因且形狀及大小相同的染色體, 每對的兩條染色體會在減數分裂時並列細胞分裂的過程, 當中生殖細胞染色體的數目由二倍體減至單倍體, 而遞減的過程在卵子發生與精子發生的期間出現細胞分裂的過程, 當中每條染色體一分為二, 結果形成的每個新細胞的染色體數目, 是與親本細胞相同的細胞一分為二, 形成兩個新細胞的過程, 每個新細胞擁有跟原來細胞種類和數目相同的染色體根據某個結構的模板, 製造出完全相同的結構作為複製品 4

5 Vocabulary 詞彙 Page Description 解釋 chromatid 染色單體 67 one of two DNA molecules and its associated proteins of a duplicated ; remain attached to its sister chromatid until they are separated from each other during nuclear, becoming a separate spindle fibre 紡錘絲 67 fibres that form during nuclear, which attach themselves to s and attract them towards the two poles daughter cell 子細胞 68 the cells formed after cell gamete 配子 70 sex cell; reproductive cell that must fuse with another before it can develop into a new individual meiosis 減數分裂 70 the process by which a cell divides to form sex cells, each with half the number of the parental s diploid 二倍體 71 the status of having two sets of s in the nucleus; usually in non-reproductive cells haploid 單倍體 71 to describe the status of having only a single set of s in nucleus; such as the sex cells fertilization 受精作用 75, 100, 121 the fusion of male and female gametes Bk3 Ch20 Cell Division/5 一對已複製的染色體的其中一條 DNA 分子與有關的蛋白質, 在分離前與另一染色單體相連, 細胞核分裂後會形成個別的染色體細胞核分裂時形成的纖維, 負責連接染色體, 並把它們拉向兩極細胞分裂後所形成的細胞即性細胞或生殖細胞, 須先與其他生殖細胞融合, 才可發育成新的個體過程中, 細胞分裂成性細胞, 結果每個性細胞的染色體數目比親本染色體減少一半形容細胞核中有兩組染色體的狀態, 通常在非生殖細胞中出現形容細核中只有一組染色體的狀態, 例子有性細胞雄性與雌性的配子融合的過程 zygote 合子 75, 85 the fertilized ovum 已受精的卵 independent assortment 獨立分配 76, 190 Mendelian principle that each gene pair tends to assort into gametes independently of other gene pairs located on non-homologous s 孟德爾的理論, 指出每對基因不受處於其他染色體上的基因的影響, 分別分離進配子中 5

0 0 = 1 0 = 0 1 = = 1 1 = 0 0 = 1

0 0 = 1 0 = 0 1 = = 1 1 = 0 0 = 1 0 0 = 1 0 = 0 1 = 0 1 1 = 1 1 = 0 0 = 1 : = {0, 1} : 3 (,, ) = + (,, ) = + + (, ) = + (,,, ) = ( + )( + ) + ( + )( + ) + = + = = + + = + = ( + ) + = + ( + ) () = () ( + ) = + + = ( + )( + ) + = = + 0