chapter 2

• cell theory states that both plant and animal tissue is composed of cells, cells are the basic unit of life and that they can only develop from existing cells
• light microscopy is easily available, relatively cheap and can observe living and dead organisms and prepared specimens
• a compound light microscope has 2 lenses, the objective lends that is near the specimen and the eyepiece lens which is where the object is viewed, the objective lens produces a magnified image which is magnified again by the eyepiece lens
• illumination is provided by a compound light microscope underneath the sample, opaque specimens can be illuminated from above with some

  
• dry mount


  solid specimens cut into thin slices (sectioning) and placed on the centre of the slide and a cover slip is placed over the sample, hair, pollen and dust can be examined this way
• wet mount


  specimens are suspended in liquid such as water or immersion oil, cover slip placed at an angle, aquatic organisms and other living organisms can be viewed this way

  
• squash slide


  wet mount is first made, then a lens tissue is used to gently press down on the cover slip, good technique for soft samples, need to be careful to not break cover slip when being pressed
• smear slides


  edge of a slide is used to smear the sample, creating a thin, even coating on another slide, a cover slip is then placed on top, good way to view the cells in blood
• resolution is limited by the wavelength of light and diffraction of light as it passes through the sample
• diffraction is the bending of light as it passes close to the edge of an object
• the cytosol of cells and other cell structures are often transparent, stains increase the contrast between different components and allow them to become visible so they can be identified
• crystal violet or methylene blue are positively charged dyes, and are attracted to negatively charged materials in cytoplasm leading to staining of the cell components
• nigrosin or congo red are negatively charged and are repelled by the negatively charged cytosol so they stay outside the cells, and stain the background so they stand out = negative stain technique
• differential staining can distinguish between 2 types of organisms that would be hard to identify, can also differentiate between different organelles of a single organism within a tissue sample
• prokaryotic cells


  cells with no membrane bound nucleus or organelles
• eukaryotic cells


  cells with a nucleus and other membrane bound organelles
• metabolism


  synthesis and the breaking down of molecules
• membranes


  selectively permeable and control the movement of substances into and out of the cell organelles, effective barriers in controlling which substances enter and exit cells, but they are fragile
• eukaryotic cell:

  
• nucleus


  contains coded genetic information in the form of DNA molecules, and the DNA controls the metabolic activities of the cell, and controls the enzymes to allow metabolism to take place
• dna contained within a nuclear envelop to protect it from damage in the cytoplasm, the envelope contains nuclear pores to allow molecules to move in an out
• dna associated with proteins called histones to form chromatin, which coils and condenses to form chromosomes, and only become visible when preparing to divide
• nucleolus


  area within the nucleus and is responsible for producing ribosomes, composed of proteins and RNA, RNA then used to produced ribosomal RNA (rRNA) which combines with proteins to form the ribosomes necessary for protein synthesis
• mitochondria

  site of the final stages of cellular respiration, energy is stored in the bonds of the complex, organic molecules available for use by the production of ATP
• mitochondria have a double membrane and the inner one is folded to form a cristae, and the fluid inside is the matrix is called the cristae, the membrane forming the cristae contains enzymes needed in aerobic respiration
• mitochondria contain small amount of DNA called mitochondrial DNA, mitochondrion can produce their own enzymes and reproduce themselves
• vesicles


  membranous sacs that have storage and transport roles, consist of a simple membrane with fluid inside, used to transport materials inside the cell
• lysosomes


  specialised vesicles that contain hydrolytic enzymes that are responsible for breaking down waste material in the cells such as old organelles, break down pathogens by ingestion in the immune system, and programme cell death or apoptosis
• cytoskeleton


  network of fibres necessary for the shape and stability of a cell, hold organelles in place and it controls cell movement
• cytoskeleton - microfilaments


  contractile fibres formed from the actin protein, responsible for cell movement and cell contraction during cytokinesis,
• cytoskeleton - microtubules


  globular tubulin proteins polymerise to form tubes that determine shape of a cell, act as a track for the movement of organelles around the cell, spindle fibres are composed of microtubules
• cytoskeleton - intermediate fibres

  give mechanical strength to cells and help maintain their integrity
• centrioles


  component of cytoskeleton present in most eukaryotic cells apart from flowering plants and fungi, composed of microtubules and 2 associated centrioles form a centrosome, which assembles spindle fibres in mitosis
• centrioles position flagella and cilia in organisms with these structures
• flagella


  whip like, used to enable cell mobility, sometimes used as a sensory organelle detecting chemical changes in the cell's environment
• cilia


  hair like, can be mobile or stationary, stationary cilia present on surface as a sensory organ such as in the nose, mobile cilia beat in a rhythm that creates a current to cause fluids or objects to move, such as in the trachea to move mucus or in fallopian tubes to move eggs from ovary to uterus
• endoplasmic reticulum (ER)


  network of membranes enclosing flattened sacs called cisternae, connected to outer membrane of nucleus, 2 types
• smooth endoplasmic reticulum


  responsible for lipid and carbohydrate synthesis, used for storage
• rough endoplasmic reticulum


  ribosomes bound to the surface and is responsible for the synthesis and transport of proteins
• secretory cells


  release hormones and enzymes, have more rough endoplasmic reticulum than cells that do not release proteins