Cell Continuity + Diversity

• Cells are grouped into tissues, tissues into organs and organs into systems.
• All cells arise from pre-existing cells. This is called cell continuity.
• A chromosome is a section of DNA and protein.
• Chromosomes are found in the nucleus of a cell.
• Chromatin is a mass of chromosomes which occurs when a cell is not dividing.
• A haploid cell has one set of chomosomes. e.g. sperm and egg
• A diploid cell has two sets of chromosomes e.g. human cells
• Homologous chromosomes are matching pairs of chomosomes.
• Somatic cells are associated with growth and go through mitosis.
• Gametes are associated with sexual reproduction and go through meiosis.
• The cell cycle includes the phases interphase and mitosis.
• Interphase takes up 90% of the cell cycle and is the phase where the cell is not dividing. Chromosomes form chromatins and DNA replication occurs.
• Mitosis is a form of nucleus division that results in two identical daughter nuclei.
• Mitosis is an asexual form of reproduction and functions in the growth and repair of cells.
• The stages of mitosis are prophase, metaphase, anaphase, and telophase.
• In prophase, chromatin contract and the nucleolus disappears. Spindle fibers appear in the cytoplasm and the nuclear membrane begins to break down.
• In metaphase, the nuclear membrane completely breaks down and spindle fibers attach to each chromosome. They pull the chromosomes to line up at the equator of the cell.
• In anaphase, the spindle fibers contract and pull one strand of each double-stranded chromosome to each end.
• In telophase, the spindle fibers break down and the chromosomes at each pole begin to form chromatin. A nuclear membrane forms around each mass of chromatin and the cell divides in two.
• This is a diagram of prophase.

  
• This is a diagram of metaphase.

  
• This is a diagram of anaphase.

  
• This is a diagram of telophase.

  
• Cell division in animals occurs by a process called cleavage furrow. It becomes deeper until the cell splits.
• In plant cells, vesicles gather between the two nuclei. They form a structure called the cell plate which then forms a middle lamella.
• Meiosis is a form of nuclear division in which the daughter nuclei contain half the chromosome number of the parent nucleus.
• This is a diagram of meiosis.

  
• Cancer is when a cell loses the ability to control the rate of mitosis. This results in a mass of cells called a tumor.
• Tumors can be benign or malignant. Benign tumors are inactive and appear as skin tags, moles, or warts. Malignant tumors are active and life-threatening.
• Carcinogens are cancer-causing agents. e.g. cigarette smoke, UV radiation, or asbestos.
• An example of a multi-cellular organism in animals is the red blood cell. Its function is to transport oxygen and it has a bi-concave shape with no nucleus.
• An example of a multi-cellular organism in an animal is the root hair cell. This absorbs water and minerals from the soil and is only one cell thick.
• Simple tissue is composed of one cell only e.g. dermal. Complex tissue is composed of many cells e.g. blood
• Dermal tissue in plants is found covering stems, roots, and leaves. It protects the plant.
• Vascular tissue in plants has two branches. Xylem transports water while phloem transports food.
• Ground tissue in plants is responsible for storing carbohydrates produced by the plant.
• Meristematic tissue is responsible for the growth of the plant
• Epithelial tissue in animals lines internal organs. It is used for protection. e.g. mucus membrane in the esophagus.
• Connective tissue in animals links the body structure together. e.g. ligaments
• Nervous tissue in animals sends messages to and from the brain and spinal cord.