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Cell Division. Cell Division allows for reproduction and growth of organisms. Learning Outcomes. state that mitosis occupies only a small percentage of the cell cycle and that the remaining percentage includes the copying and checking of genetic information. Chromosomes.
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Cell Division Cell Division allows for reproduction and growth of organisms.
Learning Outcomes • state that mitosis occupies only a small percentage of the cell cycle and that the remaining percentage includes the copying and checking of genetic information
Chromosomes • Are found in the nucleus of eukaryotic cells • Are made up of DNA and histone proteins • Hold instructions for making new cells • Specific lengths of DNA are called genes • The number of chromosomes in each cell is characteristic of each species • There are 46 chromosomes in humans • Daughter cells must contain a full set of chromosomes • Before a cell divides the DNA of each chromosome must be replicated
Structure of a chromosomes Chromatid A replica strand of DNA Each one will end up in a different daughter cell Centromere Holds the two copies together. Chromatin is supercoiled to form visible chromosomes, this allows them to be moved around..
The Cell Cycledescribes the events that take place as one parent cell divides to produce new daughter cells which then each grow to full size. • M • Nuclear division (mitosis) • Cytokinesis (cleavage of cytoplasm) • Interphase • G1 • Biosynthesis – proteins are made and organelles replicate, • S • Synthesis of new DNA • Replication of chromosomes • G2 - growth
The Cell Cycle (recap) • The cell cycle has 3 main phases • Interphase • cell grows to normal size • carries out normal biochemical functions • DNA replication takes place • Nuclear division • mitosis, this has 4 stages; • prophase, metaphase, anaphase and telophase • Cell division • cytoplasm divides by cytokinesis
Learning Outcomes • Recap • state that mitosis occupies only a small percentage of the cell cycle and that the remaining percentage includes the copying and checking of genetic information • explain the meaning of the term homologous pair of chromosomes; • describe, with the aid of diagrams and photographs, the main stages of mitosis (behaviour of the chromosomes, nuclear envelope, cell membrane and centrioles);
Nuclear Division • looking at the Karyotype of a human male, you can see: • Homologous pairs – each pair has distinctive banding when stained. • 22 pairs of autosomes • 1 pair of sex chromosomes (female XX; male XY)
Human body cells are diploid (2n), meaning that they have 2 sets of chromosomes. Human gametes are haploid (n), where n is the number of chromosomes in a single set
Learning Outcomes • describe, with the aid of diagrams and photographs, the main stages of mitosis (behaviour of the chromosomes, nuclear envelope, cell membrane and centrioles);
Mitosis • Nucleus of a cell divides resulting in two nuclei which are genetically identical to the parent nucleus. • 4 stages • Prophase • Metaphase • Anaphase • Telophase
ProphaseChromosomes become visible and the nuclear envelope disappears
MetaphaseChromosomes arrange themselves at the centre (equator) of the cell.
Learning Outcomes • explain the significance of mitosis for growth, repair and asexual reproduction in plants and animals; • state that cells produced as a result of meiosis are not genetically identical (details of meiosis are not required);
Requirements of Nuclear Division • There are two requirements of nuclear division • Growth (Mitosis); • where a diploid zygote grows into a multi-cellular adult, all daughter cells have the same number of chromosomes as the parent cell. • sexual reproduction (Meiosis); • the number of chromosomes is halved so that gametes are haploid
Human Life Cycle Diploid Zygote 46 Haploid Sperm 23 Adult 46 Haploid Egg 23 fertilisation
Meiosis • Chromosome number is halved so human gametes have 23 chromosomes • This reduction in chromosome number ensures that when gametes fuse to form a zygote (fertilisation) the diploid chromosome number is restored.
Learning Outcomes • outline, with the aid of diagrams and photographs, the process of cell division by budding in yeast;
Cell Division • In most cells, the nucleus divides first then the cytoplasm (cytokinesis). • This is mitosis and can be used for: • Growth and repair • Replacement of cells • Asexual reproduction • In bacteria, cell division takes place by binary fission • DNA replicates • Cell divides
Cell division in yeast • Yeast is a single celled fungus • It reproduces asexually by budding • Cell produces a swelling (bud) • Nucleus divides into two – the bud gains a nucleus • The bud breaks off leaving a bud scar • Sometimes buds produce their own buds before separating.
Learning outcomes • To define the term stem cell • Explain the meaning of the terms tissue, organ and organ system; • explain, with the aid of diagrams and photographs, how cells are organised into tissues, using as examples • squamous and ciliated epithelia, • xylem and phloem • discuss the importance of cooperation between cells, tissues, organs and organ systems
Stem Cell • Stem cells are omnipotent or totipotent • The are cells which contain a full set of genetic information, and are capable of becoming any one of the different cell types found in a fully grown organism.
Stem Cells • There are a small number of stem cells found in adult mammals in the bone marrow, these are responsible for the formation of bone cells and blood cells. • Stem cells are currently being used in medical research.
Differentiation • Unspecialised cells which show totipotency include • Stem cells in animals • Meristematic cells in plants • These cells divide and then specialise, this is differentiation.
Differentiation and organisation • There is a physical limit to the size a single cell can reach, therefore multicellular organisms need specialised cells. • These specialised cells are organised into tissues which carry out a specific function. • Tissues are organised into organs.
Differentiation of cells • Cells differentiate in a number of ways, by changing: • The number of a particular organelle • Muscle and liver cells contain many mitochondria • The shape of the cell • Red blood cells are a biconcave shape • Some of the cell contents • Red blood cells do not contain a nucleus • Differentiation means to specialise to carry out a particular role or function.
Structure of specialised cellsTry to write out the specific function of each specialisation
Tissues, organs and systems • Tissue • a group of similar specialised cells in a many celled organism, that carries out a specific function or several related functions • Organ • group of different tissues forming a distinct structure and functioning together • animal – lungs, heart, kidneys • plant – roots, stems, leaves • System • collection of organs with a particular function • cardiovascular and digestive systems
Tissues • A tissue is a group of similar, specialised cells which carry out a specific function, or several related functions. • Animal tissues • squamous and ciliated epithelium • Plant tissues • Xylem and phloem
Animal Tissues • Tissues that form sheets covering surfaces are called epithelial tissues, epithelial tissues are one cell thick and rest on a basement membrane (a network of collagen and glycoproteins), which holds the cells in position. • Two examples of animal tissues are squamous and ciliated epithelium.
This tissue is found lining the ends of the bronchioles in the lungs. Ciliated Epithelium
Squamous Epithelium • This tissue covers many surfaces in the human body including the inner lining of cheeks and lining the walls of the alveoli in the lungs. • In the alveoli, the thinness of cells allows rapid diffusion of gases between alveoli and blood.
Plant Tissues • Examples of plant tissues include xylem and phloem, which are transport tissues in plants. • Xylem transports water and ions, phloem transports sugars and other compounds made by plants. • Tissues can be presented in plan diagrams, plan diagrams DO NOT show any individual cells.
