Topic 2 - Cells

• What is the cell theory?

  All life on earth exists as cells, as eukaryotic (plant, animal, fungi) and prokaryotic (bacterial) cells. viruses are acellular and non-living. in complex, multicellular organisms, eukaryotic cells become specialised for specific functions.

  Specialised cells are organised into tissues, tissues into organs, organs into systems.
• What are the main organelles in an animal cell?

  Gogli apparatus, lysosomes, mitochondrion, cell surface membrane, cytoplasm, SER, RER, ribosomes, nucleus - nucleolus, nuclear envelope, nuclear pores, chromatin.
• What is the purpose of the nucleus?


  Nuclear pores control entrance and exit of substances such as ribosomes and RNA, nucleoplasm full of chromatin which condenses into chromosomes during cell division. The nucleus also controls all genetic information in the cell.
• What is the purpose of the mitochondrion?

  Site of aerobic respiration, inside folded into cristae (LSA).
• What is the purpose of the ribosomes?

  Site of protein synthesis.
• What is the purpose of the SER?

  Series of membrane bound channels - synthesises and transports mainly lipids via the golgi.
• What is the purpose of the RER?

  series of membrane bound channels - studded with ribosomes. synthesises and transports proteins via the golgi.
• What is the purpose of the golgi apparatus?

  A series of flattened vesicles which transports proteins and lipids from the SER and RER to the cell membrane for export.
• What are the main organelles in a plant cell?

  Lysosomes, permanent vacuole, SER, RER, nucleus, golgi, ribosomes, mitochondria, cell wall, cell membrane, chloroplasts
• What is the purpose of lysosomes?


  membrane bound vesicles which contain many digestive enzymes, they break down unwanted chemicals, toxins, organelles and whole cells.
• What is the purpose of the permanent vacuole?

  Fluid filled sac, containing mineral salts, sugars, amino acids etc. keeps the cell turgid and temporary food stores.
• What is the purpose of the cell wall?

  Give the cell strength and rigidity.
• What is the purpose of the chloroplasts?

  Site of photosynthesis
• What are the main organelles in a prokaryotic cell?

  Smaller ribosomes, cytoplasm, genetic material, flagellum, slime capsule, murein cell wall, cell surface membrane, plasmids, circular DNA loop.
• What is the structure of a virus?

  genetic material surrounded by a protein capsid with attachment proteins to bind onto host cells.
• Are viruses living or non-living?

  Non-living because they cannot divide on their own.
• What is the definition of magnification?


  Number of times greater the size of an image is than the size of the real object.
• What is the formula for magnification?


  Magnification = image size / size of real object
• What is the definition of resolution?

  Ability to distinguish between two adjacent points that are very close together - a higher resolution means more detail.
• How does an image form from a light microscope?

  Uses light to form an image - light that passes through or reflects from the surface of the specimen is seen.
• What are some advantages of using a light microscope?

  Can examine both alive and dead specimen, can examine specimen of variable size (whole or sectioned), cheap and can see colour/ observe staining.
• What are some disadvantages of using a light microscope?

  Low resolution, low magnification compared to the electron microscope.
• How does a TEM form an image?

  Uses electrons to form an image - electrons that pass through specimen are detected to form a 2D image.
• What are some advantages of the electron microscope?

  Much higher magnification and resolution compared to light microscope, high quality images, 3D images produced by SEM.
• What are some disadvantages of the electron microscope?

  Cannot analyse live specimen, only black and white images produced, artefacts may be present in the image produced, expensive.
• What are artefacts in microscopy?


  Artefacts are details in the image caused by the processing of the specimen such as air bubbles, folds in thin slices of the specimen, chemical changes due to stains and contamination from other cells or tissue.
• What are stains used for?

  to colour different components of a cell to give a clear indication of what substances are present in the cell and their distribution.
• Is staining invasive or non-invasive?

  Non-invasive (it does not destroy the cell) and the results can be viewed under a light microscope. e.g. starch grains in plant cells stained black using iodine in KI.
• What is cell fractionation?

  The process of separating cell components by mass for analysis
• What are the stages of cell fractionation?

  Tissue is cut up and kept in a cold, buffered, isotonic solution.

  Cut up tissue is further broken up in a homogeniser where large debris is filtered out.

  Homogenised tissue is then spun in an ultracentrifuge at a low speed for 10 minutes.

  A pellet forms of the heaviest organelles which is then removed, and the solution is then spun again at a higher speed.

  This process repeats.
• What does the pellet contain after being spun at a low speed?

  Whole cells, nuclei, unbroken tissue, cytoskeleton
• What does the pellet contain after being spun at a medium speed?

  Mitochondria and chloroplasts
• What does the pellet contain after being spun at a high speed?

  Ribosomes
• What are the two types of division that eukaryotic cells undego?

  Mitosis and meiosis
• What is mitosis?


  When a parent cell divides to produce two identical daughter cells with the same copies of DNA and the same number of chromosomes as the parent cell.
• What is meiosis?


  When a parent cell divides into four non-identical daughter cells (gametes) that contain half of the number of chromsomes to a parent cell.
• Can all cells divide?

  No, Not all cells in multicellular organisms retain the ability to divide as they mature (e.g neurones).
• What are the stages of the cell cycle?

  Interphase - gap phase 1, synthesis phase, gap phase 2.

  Mitotic phase - prophase, metaphase, anaphase, telophase.

  Cell division - cytokinesis.
• What happens in interphase?


  Cell prepares for division; DNA replicates, new organelles are manufactured, cell grows, chromatin condenses
• What happens in prophase?

  Chromosomes spiralise and condense into two sister chromatids joined at the centromere.

  Centrioles move to opposite poles of the cell.

  Spindle fibres begin to form.