Unit A science

• All living things are composed of cells
• Cells are the basic units of structure and function in living things
• all cells are produced from other cells
• cell division allows all multicellular organisms to grow, maintain and repair themselves, and reproduce.
• Cell is the basic unit of life
• Cell cycle is the process by which the parent cell grows, duplicates itself, and divides to produce new daughter cells, usually two.
• during interphase a cell performs its normal cell functions, grow and prepares for cell division
• in mitosis, the nucleus divides to produce an exact copy of itself
• during cytokinesis the rest of the cell contents divides to produce two separate daughters
• each double-stranded DNA molecule is packaged into a structure called chromosome
• interphase -

  In preparation for cell division, the chromosomes are duplicated.

  once the chromosomes are duplicated, each chromosome is made up of two identical, copies of the DNA
• mitosis is a continuous process
• during mitosis the nucleus divides
• mitosis has four stages: prophase, metaphase, anaphase and telophase
• Mitosis

  1. Prophase: the chromosomes condense and shorten. The nuclear envelope begins to dissolve.
  2. Metaphase: the doubled chromosomes line up in the middle of the cell and the membrane around the nucleus is dissolved
  3. Anaphase: The chromosome strands separate and move to opposite ends of the cell.
  4. Telophase: A new nuclear envelope begins to form around the chromosomes.
• Cytokinesis - Last phase of the cell cycle

  The cell membrane pinches in to divide the nuclei, cytoplasm, and organelles to form two daughter cells
• In sexually reproducing specie, the body cells contain two sets of chromosomes
• Cells that have a double set of chromosomes are called diploid cells.
• Cells that contain a single set of chromosomes are called haploid cells
• Benign tumours grow quickly but do not cause any damage
• The cells of the malignant tumours can separate from the main tumour and spread to a different part of the body by the bloodstrea, growing a new tumour
• Cancer results from uncontrolled cell division of specific cells
• Carcinogens are chemicals or toxins that can damage DNA in cells and cause cancer.
• • Chemotherapy: combination of drugs that kill fast-growing cells, such as cancer cells
  • Radiation therapy: use of radiation energy and o damage cancer cells in order to prevent them from reproducing
• Assexual reproduction: involves only one parent, and the offspring is genetically identical to it (clones)
• Species that reproduce asexually invest energy to produce as many identical copies of themselves as possible to build large population quickly
• Binary fission - A type of cell division that involves the division of a single cell into two identical daughter cells.
• Budding - the parent produces a small miniaturized clone
• Parthenogenesis- egg develops in a female without fertilization
• Spores - haploid cells that can develop into new organisms
• vegetative reproduction - the production of new plants from a parent plant by the growth of new shoots from the root, they are clones and it does not involve the formation of a seed.
• Fragmentation - offsprings are formed from a piece of the existing parent organism being identical clones of the parent
• Grafting - part of one plant is joined with another plant
• plant tissue cultures - plant cells can be placed in a petri dish or in a bottle containing nutrients and other chemicals and grow into new individuals
• Sexual reproduction - the union of two sex cells (gametes) to produce a new individual
• The union of the sperm cell with the egg is called fertilization
• Gametes are produced through the cell division process called meiosis
• Meiosis produces four daughter cells that have half the number of chromosomes of the parent cell
• The joining of two gametes creates a zygote
• A zygote has a full set of chromosomes and is the first cell of a new individual