CHAPTER 2 Plant Cell.ppt

CHAPTER 2 PLANT CELL At the end of this topic, the students should be able to:  Compare and contrast the general characteristics of prokaryotic and eukaryotic cells  Compare and contrast plant and animals cell  Describe the plant cell components (plasma membrane, cell wall, cytoplasm, endopl...

CHAPTER 2 PLANT CELL At the end of this topic, the students should be able to:  Compare and contrast the general characteristics of prokaryotic and eukaryotic cells  Compare and contrast plant and animals cell  Describe the plant cell components (plasma membrane, cell wall, cytoplasm, endoplasmic reticulum, mitochondria, ribosomes, golgi apparatus, plastids, chloroplast)  State and label the distribution of various organelles  Define nucleus and describe function of nucleus  Describe other cellular structures (vacuole, cytoskeleton)  Describe the Cell cycle: Mitosis & Meiosis  Identify the Mitosis and Meiosis stages in plant cell  Explain the importance of Mitosis and Meiosis  Compare and contrast between Mitosis and Meiosis  CELL AND MICROSCOPY  Cell is the basic structural, functional, and biological unit of all known living organisms.  It is the smallest unit of life that can replicate independently.  CYTOLOGY is the study of the cell.  The earliest phase of cytology began with the English scientist Robert Hooke’s microscopic investigations of cork in 1665.  He observed dead cork cells and introduced the term “cell” to describe them  Most plant and animal cells are visible only under a microscope, with dimensions between 1 and 100 micrometres  A short history of cells.  1665--Robert Hooke “discovers” cells with an early microscope (30x)  1675: Anton Von Leeuwenhoek sees microorganisms (300 x)  1855 Theodore Schwann and Mathias Schleiden propose Cell Theory. Discover cell membrane.  1855 Rudolf Virchow shows that cells must come from other cells. (Remember Francesco Redi disproving spontaneous generation, 1650?)  1945 electron microscope show new cell parts  1950’s first stem cells discovered in bone marrow. How do we study cells?  Microscopes opened up the world of cells Robert Hooke (1665) the 1st cytologist cork Drawings by Hooke flea  CELL AND MICROSCOPY…...con  The modern cell theory states that:-  All living organisms are made up of one or more cells.  New cells are formed by the division of pre-existing cells.  Cells contain genetic material of an organism which is passed from parent to daughter cells.  All metabolic reactions take place within cells.  All cell are surrounded by a plasma membrane  The semi-fluid substance within the membrane is the cytosol, and containing the organelles  CELL AND MICROSCOPY…...con  Some organisms are unicellular, made up of just one cell  Other organisms are multicellular and consist of many cells.  A tissue consists of a group of cells and carry out a particular common function, eg: - xylem tissue.  An organ consists of a number of different tissues working together as a functional unit, eg:- vascular bundle.  Different organ work together as organ systems, eg:- the transportation system.  Cell – Tissue – Organ – System – Organism  CELL AND MICROSCOPY…...con  There are two types of cell a) Eukaryotic  contain a nucleus  Single cell or multicellular b) Prokaryotic  do not contain nucleus  The DNA not enclosed by nuclear membranes and the area called the nucleoid region.  The DNA scattered out in the cytoplasm.  Have many ribosomes (synthesized protein)  lack of organelles.  single-celled organisms CELL AND MICROSCOPY…...con  Eukaryotic cellsPLANT CELL ANIMAL CELL CELL WALL Have rigid cellulose No cellulose cell wall, only cell wall and plasma plasma membrane membrane CHLOROPLAS Chloroplasts present in No chloroplasts T photosynthetic cells VACUOLE Large vacuoles Small, temporary vacuoles TONOPLAST Have tonoplast No tonoplast CENTRIOL No centrioles. Have centrioles LYSOSOM No Lysosomes Have Lysosomes CILIA No cilia and flagella Some cells have cilia or FLAGELLA flagella STORANGE Contain starch Contain glycogen granules ORGAN granules for for carbohydrate storage carbohydrate storage PIT Plasmodesmata and No plasmodesmata and pits. pits present in cell Animal Cell vs Plant Cell Animal cell Plant Cell  The plant cell  Angiosperms are complex multicellular organisms  composed of many different types of cells  Plant cells have all of the structures that animal cells do but, the they also have some structures that the animal cell does not  Plant cells have a cell wall and chloroplast  The plant cell  The Plant Cell consists of a more or less rigid cell wall and the protoplast (the contents of the cell)  The protoplast consists of the cytoplasm and a nucleus  The cytoplasm includes:  distinct membrane-bound organelles such as plastids and mitochondria;  systems of membranes (endoplasmic reticulum and dictyosomes);  non-membranous entities such as ribosomes, actin filaments and microtubules  liquid matrix (cytosol) in which the nucleus, various entities and membrane systems are suspended.  Plant Cell wall  present in most prokaryotes (algae and bacteria), plants and fungi.  Found surrounding plant cells but NOT in animal cells  Surrounds all the parts of the cell (protoplast)  situated outside the cell membrane.  It is tough, flexible, and rigid.  Consist of one or two layers (primary and secondary wall)  Plant cells wall are made of cellulose.  Middle lamella is a layer of sticky material between walls of adjacent cells  The middle lamella containing calcium and magnesium pectate - join the adjacent cells together  The cell walls have pits (plasmodesmata) that enable cytoplasmic strands to pass through the connecting cytoplasm of one cell and its adjacent cell. Plasmodesmata  pores or channels between plant cell walls that allow molecules and communication signals to pass between individual plant cells. Functions of Cell Wall  Plasma membrane/cell membrane  is a biological membrane that surrounds the cytoplasm of a cell.  made up from three components: 1. Lipid layer called phospholipids bilayer (partly hydrophobic and partly hydrophilic). 2. Protein molecules – Embedded within phospholipid layer (like iceberg on a sea) that act as channels and pumps that move different molecules into and out of the cell 3. Cholesterol – effects the fluidity of the membrane  It is 'semi-permeable’, = allows certain particles to pass through.  it can either let a substance (molecule or ion) pass through freely,  Or pass through to a limited extent  or not pass through at all.  The purpose: to be able to let molecules in the cell needs but to keep particles out that could harm the cell  also contain receptor proteins that allow cells to detect external signaling molecules such as hormones. Plasma Membrane Diagram Functions of Plasma Membrane Cell Components & Functions Cell Components & Functions  Cell Components & Functions Cytoplasm = cytosol + Organelles It is the entire region (a sticky, semi fluid material) between the  nucleus and the cell membrane (material within a living cell, excluding the cell nucleus).  Consist of proteins, lipids, carbohydrates, minerals, salts and water  It comprises cytosol and organelles suspended in it.  Functions of cytoplasm:  Site for many biochemical reactions, example glycolysis.  The place where the organelles scattered out.  Cell Components & Functions Cytosol  is the gel-like substance enclosed within the cell membrane (fills the cell)  contains various components  90% water and solutes such as sugar, amino acids, enzyme, ATP and dissolved gases  Microfilaments and microtubules which form the cytoskeleton, providing support to the cell and are involved in cell motility  Site for many biochemical reactions, for example glycolysis  Functions:  Suspends the organelles within the cell  Fills the cell and gives shape  Allow nutrients to move about the cell  Cell Components & Functions Organelles  Organelles (literally "little organs"), are usually membrane- bound structures inside the cell that have specific functions.  the organelles is the cell's internal sub-structures.  The plant cell organelles are: a. Nucleus b. Mitochondria c. Plastids - Chloroplast d. Endoplasmic reticulum e. Ribosom f. Golgi apparatus Cell Components & Functions a. Nucleus  Most important part of the cell  controlling influence on all cell activities  Usually spherical or oval structure  Located in the centre of the cell  surrounded by the nuclear membrane  Serves as the information processing and administrative center of the cell.  Only the cells of eukaryotes, have a nucleus.  Some sieve tube of vascular plant lack of nuclei at maturity  Composed of several elements:  Nuclear envelope/membrane  Nuclear pore  Nucleoplasm  Nucleolus  Chromatin/DNA  Nuclear pore: regulate the passage of molecules between the nucleus Structure of and cytoplasm, permitting some to pass through the Nucleus membrane. Nuclear envelope: Have an outer membrane and an inner membrane. separates the nuclear material from cytoplasm, contains numerous small holes called nuclear pores. Mainly made up of protein and lipids Nucleolus: Usually one spherical body Lack of membrane Rich in protein and RNA (Ribonucleic acid) Site of transcription Assembles ribosomes Chromatin: Chromosomes consist of the invisible state called chromatin. Nucleoplasm: Mainly consists of DNA Is cytoplasm/fluid of within the nuclear (Deoxyribonucleic acid) membrane in which chromatin and The chromatin strands thicken to form nucleoli is suspended chromosomes which become visible at The nucleoplasm contain chromatin, the time of cell division. nucleotides, enzymes and mineral ions DNA is the hereditary material that carries the genetic code from generation Functions of Nucleus  Cell Components & Functions b. Mitochondria  A double membrane-bound organelle  found in all eukaryotic organisms.  Mitochondria have different shapes and sizes  generally are rod-shaped with a length of about 2.5 - 5µm and a diameter of 1 µm  Contains outer and inner membranes composed of phospholipid bilayers and proteins (two membranes have different properties).  DNA in the mitochondria enables the mitochondria to replicate during cell division.  There are five distinct parts to a mitochondria:  the outer membrane,  the inter-membrane space (the space between the outer and inner membranes),  the inner membrane,  the cristae space (formed by enfolding of the inner membrane)  the matrix (space within the inner membrane). Function of Mitochondria  Cell Components & Functions c. Plastid  The term plastid was derived from the Greek word plastic as meaning formed or moulded. This term was coined by Schimper in 1885.  is a major double-membrane organelle  found in the cells of plants and algae  primarily responsible for activities related to chromopla making and storing food. st  Plastids may differentiate into several forms, depending upon which function they need to play in the cell.  The plastids are classified into two main types namely chromoplasts and leucoplasts.  contain pigments and the types of pigments present can change or determine the cell's colour. TYPES OF PLASTID  c. Plastid: Chloroplasts  General  found in plant cells  conduct photosynthesis.  The word chloroplast (Greek words); chloros, = green, plast, = form or entity.  bounded by a double membrane  Shape:  varies in shape.  spheroid or ovoid or discoid in higher plants.  Size:  Varies from species to species.  In higher plants, 4-5microns (length) and 1- 3microns (thickness).  chroloplasts of plants growing in shady places are larger in size.  Number:  varies from plant to plant,  In higher plants, 20 to 40 chloroplasts per cell or up to 1000 chloroplasts.  Chloroplast structure: A chloroplast comprises of three main components: Envelope, Stroma and Thylakoids. Envelope: * made up of two unit membranes. * These unit membranes are separated by periplastidal space of 10nm. * Exchange Thylakoids: of molecules * consistsbetween of closedchloroplast and and flattened vesicles.cytosol occurs across this * vesiclesdouble membrane are arranged envelope. as a membranous network. * The outer surface of the thylakoid is in contact with the stroma and the inner surface encloses an intra-thylakoid space. * Thylakoids are found to be stacked one Stroma: on other like the pile of coins called * The inner space of chloroplast grana (granum). * It is a colorless matrix. * The number of grana in the matrix of a * Fills most of the volume of the chloroplast may be 40 to 80. chloroplast. * The space within the thylakoid is called * Stroma surrounds the thylakoids as lumen. * Contains almost 50% of the proteins of * The photosynthetic pigments (light- the chloroplast. absorbing pigments) like chlorophylls * Carbon fixation, synthesis of sugars, and carotenoids are present in the  d. Endoplasmic Reticulum (ER)  Present in all eukaryotic cells  Endoplasmic = “within the plasm” ; reticulum = “network”  It is a network of tubular and flat vesicular structures (interconnected with one another) in the cytoplasm which continues with outer membrane of the nuclear envelope.  a system of membrane channels and saccules.  It is internal delivery system in cell  It often appears as two interconnected sub-compartments, namely rough ER and smooth ER.  Both types consist of membrane enclosed, interconnected flattened tubes/sacs called cisternae (reservoir for liquid).  Cisternal space is the ER membrane that separates the internal compartment of the ER from the cytosol.  The space in the endoplasmic reticulum, is Lume called the lumen. n  1. Rough Endoplasmic Reticulum (rough ER)  Rough ER is continuous with the outer nuclear membrane.  studded with millions of ribosomes that give it a rough appearance. Functions:  Involved in the synthesis, packing and transport of protein  folding of protein molecules in sacs called cisternae and the transport of synthesized proteins in vesicles to the Golgi apparatus  2. Smooth endoplasmic reticulum  System of membranous tubules and sacs  It is NOT studded with ribosomes thus it is “smooth” ER  Form transport vesicles  Smooth ER is more tubular than rough ER and forms an interconnecting network sub-compartment of ER. Functions:  Synthesis and transport lipids  Metabolism of carbohydrates  Detoxification of drugs and poisons  It contains enzymes and produces and digests lipids (fats) and membrane proteins  moving the newly-made proteins and lipids to the Golgi body and membranes  e.Ribosomes  Found in both prokaryotes and eukaryotes  are the “cellular machines” that produce (synthesis) protein.  important biological molecules  are small, dense granules with a diameter of about 20 – 25 nm  can be found free floating within the cytoplasm or attached to the endoplasmic reticulum. Functions:  serves as the site of protein synthesis (translation)  The protein synthesized on the free ribosomes are released into the cytosol, where they perform their functions as enzymes  The protein synthesized by ribosomes attached to rough ER pass into the cisternal to the Golgi apparatus. They are finally secreted from the cell in the form of digestive enzymes  f. Golgi apparatus  It was identified in 1897 by the Italian biologist, Camillo Golgi and named after him in 1898  A series of a stack of flattened, membrane-bound sacs called cisternae - looking like a sac of pita bread  The membrane of each cisterna separates its internal space from the cytosol  One side of the Golgi, the cis side – receives material from ER by fusing with vesicles,  the trans side – buds off vesicles that travel to other sites  gathers simple molecules and combines them to make molecules that are more complex.  then packages them in vesicles or stores them for later use or sends them out of the cell. Functions:  Formation of secretory vesicles.  Formation of glycoproteins & lipoproteins.  Formation of lysosomes.  Formation of Acrosome.  Storage of secretions.  Location of enzymes  Working with Rough ER…  The Golgi complex works closely with the rough ER.  When a protein is made in ER, something called a transition vesicle is made.  The vesicle/sac floats through the cytoplasm to the golgi apparatus and is absorbed.  After the golgi does it work on the molecules inside the sac , a secretory vesicle is created and released into the cytoplasm.  From there the vesicle moves to the cell membrane and the molecules are released out of the cell.  OTHER CELLULAR STRUCTURE Vacuole/ Central vacuole fluid filled organelles enclosed by a membrane called tonoplast regulates ion, water and nutrient movement between the cytosol and the vacuolar lumen through the activity of its membrane proteins. The relative abundance of these proteins and their respective activities/regulation determine the specific function of plant vacuoles. Plant cells usually have a large central vacuole (90% volume of cell) which contains a liquid called cell sap Cell sap contains dissolved substances such as sugars, mineral salts and amino acids  Vacuole/ Central vacuole Functions:  provides support  Storage - store materials such as food, water, sugar, minerals and waste products (proteins, amino acids and organic acids, ions, sugars, pigments)  Digestion (acid hydrolases – proteases, nucleases, glycosidases, lipases)  pH and ionic homeostasis (serve as reservoirs of protons and metabolically important ions)  Defense against microbial pathogens and herbivores (cell wall‐degrading enzymes, phenolic compounds, alkaloids, etc.)  Pigmentation  Detoxification - Sequestration of toxic compounds  protection  OTHER CELLULAR STRUCTURE Cytoskeleton It is a network of fibers. It organized cell structures and activities, anchoring many organelles Maintain cell shape Composed of three types of molecular structures: a. Microtubules b. Microfilaments c. Intermediate filaments This structure is responsible for both cell movement and stability.  a.Microtubules  small tubes made from the protein tubulin.  found in cilia and flagella,  structures involved in cell movement.  provide pathways for secretory vesicles to move through the cell,  involved in cell division as they are a part of the mitotic spindle, which pulls homologous chromosomes apart.  b.Microfilaments  the thinnest part of the cytoskeleton,  made of actin (a highly-conserved protein that is actually the most abundant protein in most eukaryotic cells).  Actin is both flexible and strong,  a useful protein in cell movement.  c. Intermediate Filaments  Smaller than the microtubules, but larger than the microfilaments,  made of a variety of proteins such as keratin and/or neuro-filament.  very stable, and help provide structure to the nuclear envelope and anchor organelles. Cell cycle & cell division MITOSIS VS MEOSIS  Cell Division & cell cycle  Cells of living organisms divide and reproduce genetically in a process called the cell cycle  The cell cycle is the series of events that take place in a cell leading to its division and duplication of its DNA (DNA replication) to produce two daughter cells.  The cell cycle encompasses:  the growth of a cell during the cell division cycle,  the replication of its genomes  the formation of two daughter cells containing all the necessary information to repeat the cycle.  Cell Division & cell cycle  the cell cycle is divided into three periods:  interphase (G₁, S, and G₂ phases)  mitotic (M) phase (mitosis)  cytokinesis.  During interphase, the cell grows, accumulating nutrients needed for mitosis, preparing it for cell division and duplicating its DNA.  During the mitotic phase, the chromosomes separate.  During cytokinesis, the chromosomes and cytoplasm separate into two new daughter cells. Cell Division & cell cycle  Cell division is the process by which a parent cell divides into two or more daughter cells.  Cell division usually occurs as part of cell cycle.  There are two types of cell division:  MITOSIS  MEIOSIS Cell division: MITOSIS  one cell (the mother) divides to produce two new cells (the daughters) that are genetically identical to itself.  OR a single cell divides into two identical daughter cells.  Daughter cells have same number of chromosomes as does parent cell.  Mitosis occur in somatic cell (a body cell; a cell whose genes will not be passed on to future generations)  Somatic cell have 2 set of chromosome (2n)/diploid = 46 chromosomes  1 set from male (n) and 1 set from female (n)  The division of the cell is initiated by division of the nucleus (Karyokinesis) followed by division of cytoplasm (Cytokinesis).  The stages of karyokinesis are: 1. Prophase 2. metaphase, 3. anaphase, 4. telophase. MITOSIS - Prophase  the nucleus migrate into the center of the cell  The nucleolus disappears.  The chromatin condenses into discrete chromosomes by tightly coiling (chromosomes visible under a microscope).  The nuclear envelope breaks down.  Chromatin fibers become coiled into chromosomes with each chromosome having two chromatids joined at a centromere.  The mitotic spindle (composed of microtubules and proteins), forms in the cytoplasm.  MITOSIS – LateProphase  the spindle fibers, reach from each cell pole to the cell's equator.  Kinetochores (specialized regions in the centromeres of chromosomes), attach to a type of microtubule called kinetochore fibers.  The kinetochore fibers "interact" with the spindle polar fibers connecting the kinetochores to the polar fibers.  The chromosomes begin to migrate toward the cell center  Each chromosome has two chromatids and are identical  The two chromatids are joined at the centromere.  at the late prophase, the nuclear envelope completely disappears  the paired chromatids are moving toward the equator of the cell. Mitotic spindle a structure made of microtubules, strong fibers that are part of the cell’s “skeleton.” organize the chromosomes and move them around during mitosis. The spindle grows between the centrosomes as they move  MITOSIS - Metaphase  The spindle fully develops.  Chromosomes align at the metaphase plate.  Chromosomes move randomly until they attach (at their kinetochores) to polar fibers from both sides of their centromeres.  At the metaphase checkpoint, cells make sure that all the replicated chromosomes are attached to the mitotic spindle before continuing to anaphase.  MITOSIS - Anaphase  The shortest stage of mitosis.  The paired centromeres in each distinct chromosome begin to move apart.  attachments between the two sister chromatids of each chromosome break  The sister chromatids separate from one another and are pulled towards opposite poles of the cell.  the movement of chromatid is due to the shorten contraction of spindle (kinetochore microtubules)  by end of the anaphase, the chromosomes have reached opposite poles of the cell and form densely packed  The separated sister chromatids are now referred to as daughter chromosomes.  MITOSIS - Telophase  formation of two daughter nuclei.  Nuclear membrane and nucleoli reappear and surround the chromosomes.  The nuclear envelopes of these nuclei are formed from remnant pieces of the parent cell's nuclear envelope.  The chromosomes also start to de-condense (uncoil and diffuse)  the spindle fibers disappear.  The newly formed nucleus contains the same numbers of chromosomes as in parent nucleus.  After these changes, telophase/mitosis is largely complete and the genetic "contents" of one cell have been divided equally into two.  CYTOKENESIS  Cytokinesis is not a phase of mitosis but a separate process, necessary for completing cell division onto form two new cells.  After nuclear division ends, it divides its cytoplasm into two parts by forming new plasma membrane and cell wall down the middle of the cell between the daughter nuclei.  The cytoskeleton moves small vesicles derived from the Golgi apparatus  The vesicles fuse together, bringing together the vesicle membranes and the wall material that was inside the vesicles into a line in the middle of the cell.  The vesicle membranes form the new plasma membranes for each cell.  The wall material joins together to form the cell plate.  The two new cells then secrete cellulose and other materials to build a primary cell wall on either side of the cell plate, which is now called the middle lamella  When the cell plate is fully formed, cytokinesis is complete.  Following cytokinesis, the cell returns to interphase.  Mitotic daughter cells enlarge, reproduce organelles, and resume regular activities. Importance of Mitosis 1. Increase the number of cell for growth (production new cells) 2. Replace the damage tissue or died (wound healing/repair) 3. Asexual reproduction: Produce the daughter cells which genetically identical with mother cells that have same number of chromosome and genetic information via: a) Binary fission – reproduce by splitting into two bacteria b) Budding – bud on parent organism (yeast) c) Vegetative reproduction – plant send out stolon, rhizomes which become new individuals  Cell division: MEIOSIS  Is a type of cell division that results in four daughter cells each with half the number of chromosomes of the parent cell, as in the production of gametes and plant spores.  OR Is a division of the nucleus that reduces chromosome number by half.  OR Meiosis is a mode of cell division specific to eukaryotic organisms whereby four haploid (n) daughter cells are produced from a single  Meiosis occurs in the reproductive cells or germ cell (a cell that is diploid (2n) parent cell destined to become a gamete): pollen (anther) and eggs(ovary)  Involve two successive nuclear division that produce four haploid cells  The first division (meiosis I) is the reduction division; consists of prophase I, metaphase I, anaphase I, and telophase I.  the second division (meiosis II) separates the chromatids; consists of prophase II, metaphase II, anaphase II, and telophase II.  genetic content is different than mother cell  Features of Meiosis  Meiosis includes two rounds of division – meiosis I and meiosis II.  Meiosis II resembles mitosis  During meiosis I, homologous chromosomes (homologues) become closely associated with each other. This is synapsis.  Proteins between the homologues hold them in a synaptonemal complex.  Crossing over: genetic recombination between non-sister chromatids  Physical exchange of regions of the chromatids  chiasmata: sites of crossing over  The homologues are separated from each other in anaphase I.  Results in a reduction of the chromosome number from diploid 62 to haploid. The Process of Meiosis I In Prophase I, Chromosomes condense Synapsis occurs: homologous chromosomes come together to form pairs called bivalents or tetrads Tetrad is two chromosomes or four chromatids (sister and non-sister chromatids) each bivalent has two chromosomes and four tetrads. In Metaphase I, bivalents align randomly on the equatorial plate, both chromosomes still attached to another at chiasma each daughter cell has an equal chance of getting either the chromosome from the sperm or one from the egg. In Anaphase I, the chromosomes separate, each with two chromatids, move to opposite poles; each of the two daughter cells is now haploid (n).  MEOSIS II Meiosis II is the second meiotic division, and usually involves equal segregation, or separation of sister chromatids. Meiosis II begins with two haploid cells (dividing the two haploid nuclei formed in meiosis I) and ends with four haploid daughter cells. Meiosis II is the same as mitosis, The four main steps of Meiosis II are: Prophase II, Metaphase II, Anaphase II, and Telophase II and are identical to the stages of mitosis MEOSIS II In prophase II disappearance of the nucleoli and the nuclear envelope shortening and thickening of the chromatids. Centrosomes move to the polar regions and arrange spindle fibers for the second meiotic division. In metaphase II, the centromeres contain two kinetochores that attach to spindle fibers from the centrosomes at opposite poles. The new equatorial metaphase plate is rotated by 90 degrees when compared to meiosis I, perpendicular to the previous plate In anaphase II, the remaining centromere cohesion is cleaved allowing the sister chromatids to segregate. The sister chromatids are now called sister chromosomes. In telophase II, similar to telophase I, marked by de-condensation and lengthening of the chromosomes and the disassembly of the spindle. Nuclear envelopes reform and cleavage or cell plate formation eventually produces a total of four daughter cells, each with a haploid set of chromosomes. Meiosis is now complete and ends up with four new daughter cells. Important of Meiosis 1. Production of gametes.  Meiosis enable the production of gametes, fertilization cannot take place without the presence of male and female gametes and new organisms cannot be produced. 2. Reduction in chromosome number.  Each gamete has only half of the number of chromosomes of the parent cell.  Embryo contains chromosomes from both the male and female gamete. 3. Maintenance of chromosome number in somatic cells.  Meiosis enable us to maintain the number of chromosomes in our somatic cells (46 chromosomes). 4. Production of variation.  It is importance because basis of sexual reproduction  Crossing over during meiosis can produce the variation in the chromosome of gamete  fusion of gamete will increase the variation in the characteristic of individual. MEIOSIS vs MITOSIS  MITOSIS VS MEIOSIS MITOSIS MEIOSIS Occur in all somatic cells Occur in reproductive cells The number of chromosomes of The number of chromosomes of daughter cells is similar to daughter cell is half of mother cell parent cell (diploid) (haploid) In late prophase, the In late prophase I, the homologous homologous chromosomes do chromosomes synapse to form not synapse to form bivalent bivalent No chiasmata and crossing over Chiasmata formed and crossing thus no genetic exchange over occur thus genetic information exchanged Genetic content of daughter Genetic content of daughter cells is cells same as mother cells half of mother cells 2 daughter cells formed 4 daughter cells formed Cytokenesis occur once Cytokenesis occurs 2 times Daughter cells can undergoes Daughter cells cannot undergoes mitosis meiosis but can do mitosis