Module 2 Cell Structure Flashcards
What is the equation for magnification
Magnification= image size/actual size
Magnification definition
How much bigger the image is than the specimen
Resolution definition
How well a microscope distinguishes between two points that are close together, how detailed the image is.
Light microscope
Maximum resolution of about 0.2 micrometers. Used to look at whole cells or tissues. Maximum magnification is x2000. Inexpensive. Small/portable. Resolving power is 200nm. Specimens can be living/dead. Vacuum not required. Simple sample preparation. Natural colour of sample is seen.
TEM(transmission electron microscope)
Use electromagnets to focus a beam of electrons which is then transmitted through the specimen to produce 2D images. Denser parts of the specimen absorb more electrons which makes them look darker on the image. They provide high resolution images, so can see small organelles e.g ribosomes. Specimens need to be cut thinly sliced, the angles which the specimens are cut can affect how they appear. Has 0.05nm or 0.00005um max resolution. Can be more than x1,000,000 max magnification. Electrons pass through
SEM(scanning electron microscope)
Scan a beam of electrons across the specimen. This knocks off electrons from specimen, which are gathered in a cathode ray tube to form an image. Images produced show surface of specimen and can be 3D but lower resolution than TEMS. Has a 0.002 micro meter max resolution. Less than x500000 max magnification. Electrons bounce of surface
Producing electron micrographs
Treated with solution of heavy metals, this process is equivalent of staining samples that are to be viewed with a light microscope. The metal ions act to scatter the electrons that are fired to the sample and give contrast between different structures. Images produced by electron microscopes are black and white and colour is added after.
What stain can be used for DNA
Methylene blue
What stain can be used for different type of blood cells
Giemsa
Dry mount
Used for observing specimens such as hairs, pollen. Thin slice of specimen to let light through, use tweezers to put in middle of clean slide, put cover slip on top.
Wet mount
Can be used for living samples such as aquatic organisms. Pipette a drop of water on slide, tweezers to put specimen on top, put cover slip on at angle so no air bubbles
How to use a light microscope
- Clip slide onto stage 2. Select lowest powered objective lens 3. Use coarse adjustment knob to bring stage up to just below objective lens 4. Look down eyepiece, use coarse adjustment knob to move stage downwards until image is roughly in focus 5. Adjust focus with fine adjustment knob, until you get a clear image 6. If you need to see slide with greater magnification swap to a higher powered objective lens and refocus.
What is a Eukaryote
Any organism consisting of one or more cells that contain DNA in a membrane bound nucleus e.g animals, plants, fungi, protists, contain specialised membrane bound organelles.
Nucleus
A large organelle surrounded by a nuclear envelope (double membrane) which contains many pores. The nucleus contains chromatin(made from DNA and proteins), which is seen as dark patches on light microscope, and a structure called nucleolus. Controls cells activity’s and genetic material and controls instructions to make proteins. The pores allow substances to move between nucleus and cytoplasm. The nucleolus makes RNA made into ribosomes. In nuclear envelope there is a nucleoplasm. Largest organelles in cell. Nuclear envelope is a dense spherical structure surrounds nucleolus, 2 membranes with fluid separating them. 1. Nuclear envelope 2. Nuclear pores 3. Chromatin 4. Nucleolus
Mitochondria
Energy generating organelle. Surrounded by 2 membranes. Inner layer folds inwards to form cristae. The cristae project into a liquid called the matrix. Inner membrane is coated in enzymes which catalyse the reactions of aerobic respiration to produce ATP. 2-5 micro meter long.
Ribosomes
Tiny organelles which can be found in cytoplasm or bound to rough endoplasmic reticulum. Each ribosome consists of 2 sub units. Site of protein synthesis. Made of proteins and RNA. Not surrounded by a membrane.
Golgi apparatus
A stack of membrane bound flattened sacs. It’s a single membrane is a similar to cell membrane, 2 layers. Membrane surrounds an area of fluid where complex molecules are stored and changed. Receives proteins from ER and modifies them, may add sugar molecules. Then packages proteins into vesicles. Also make lysosomes.
Lysosomes
Spherical sacs surrounded by a single membrane. Specialised vesicles. Contain powerful digestive enzymes and role is to break down materials eg in your tears, protects your eyes.
Rough Endoplasmic reticulum
Consists of flattened membrane bound sacs called cisternae. They are studded with ribosomes. Transports proteins on attached ribosomes. Some proteins will be secreted by cell whilst others on cell membrane.
Smooth endoplasmic reticulum
Don’t have ribosomes, involved in making lipids
Microtubules
Hollow filaments of protein Tubulin, give structural support as part of cytoskeleton and form organelles such as centrioles and cilia. Centrioles involved in cell division. Cilia are hairs.
Plasma membrane
Membrane found on surface of animal cells and inside cell wall of plant cells and prokaryotes, made mainly of lipids and proteins. Regulates movement of substances into and out of cell. It also has receptor molecules on it, which allow it to respond to chemicals like hormones.
Cell wall
A rigid structure that surrounds plant cells, mainly made of carbohydrate cellulose. Supports plant cells.
Vesicle
A small fluid sac in the cytoplasm surrounded by a membrane. Transports substances in and out of cell and between organelles. Some are formed by the Golgi apparatus or endoplasmic reticulum while others are formed at cell surface.
Chloroplast
A small flattened structure found in plant cells. It’s surrounded by a double membrane and also has membranes inside called thylakoid membranes. These membranes are stacked up in some parts of chloroplast to form grana. Grana are linked together by lamellar, thin flat pieces of thylakoid membrane. The site where photosynthesis takes place, some parts of photosynthesis happen in grana and other parts happen in the stroma (thick fluid found in chloroplast). Uses carbon dioxide,water, light to build sugars. Photosynthesis occurs in thylakoid. Stroma diffuses products.
Centriole
Small, hollow cylinders made of microtubules. Found in animal cells and only some plant cells. Involved with separation of chromosomes during cell division.
Cilia
Small hair like structures found on surface of membrane of some animal cells. In cross section they have an outer membrane and a ring of nine pairs of protein microtubules inside with a single pair of microtubules in the middle. The microtubules allow the cilia to move. The movement is used by the cell to move substances along the cell surface.
Flagellum
Flagella on eukaryotic cells are like cilia but longer. They stick out from the cell surface and are surrounded by the plasma membrane. Inside they’re like cilia too, two microtubules in the centre and nine pairs around the edge. The microtubules contract to make the flagellum move. Flagella are used like outboard motors to propel cells forward eg when a sperm cell swims.
How is protein produced
Proteins are made at ribosomes which are on the rough endoplasmic reticulum which make proteins that are excreted or attached to cell membrane, whereas the free ribosomes in the cytoplasm make proteins that stay in the cytoplasm. New proteins that are produced at RER are folded and processed e.g sugar chains in RER. Then they’re transported from RER to Golgi apparatus in vesicles. At the Golgi apparatus, the proteins may undergo further processing e.g sugar chains are trimmed or more are added. The proteins enter more vesicles o be transported around the cell.
Cytoskeleton
Organelles in cells are surrounded by the cytoplasm. It has a network of proteins running through it. These protein threads are called the cytoskeleton. In eukaryotic cells the protein threads are arranged as microfilaments (thin protein strands) and microtubules(tiny protein cylinders). Microtubules and microfilaments support the cells’s organelles, keeping them in position. They strengthen the cell and maintain shape. Responsible for transport of organelles and materials within cells. The proteins of cytoskeleton can cause cell to move e.g flagellum for a sperm cell, the cytoskeleton propels whole cell.
Squash slides
Wet mount prepared, lens tissue to press cover slip. E.g root tip squashes for cell division.
Smear slides
Edge of slide is used to smear sample, creates thin coating e.g blood
What do you need to remember for a scientific drawing
Title, magnification, sharp pencil, plain paper, continuous lines, no shade, label all structures, ensure proportions
Development of cell theory in 1665
Robert Hooke, observed structure of thin sliced cork using light microscope, compartments as cells.
Development of cell theory in 1674-1683
Anton van Leeuwenhoek, developed technique for powerful glass lenses and used handcrafted microscopes to examine samples of pond water. First to observe bacteria, ‘little animals’ later found as microorganisms.
Development of cell theory in 1832
Barthelemy dumortier, first to observe cell division in plants, evidence against theories, new cells arise from old cells.
Development of cell theory in 1837-1838
Matthias schleiden, proposed all plant tissues are composed of cells. Theodor schwam, declared all living things are composed of cells and cell products, created birth cell theory.
Development of cell theory, 1884
Robert remark, first to observe cell division in animal cells, disproving theory, new cell origin from old cells. He was not believed at the time. Rudolf Virchow, published these findings as his own in 1855.
Development of cell theory in 1860
Louis Pasteur, theory of spontaneous generation of cells, bacteria only grow in sterile nutrient broth after it had been exposed to air.
Differential staining
Can distinguish between 2 types of organisms
Gram stain technique
Used to separate bacteria into 2 groups, gram positive and gram negative bacteria. Crystal violet is applied, then iodine, which fixes dye. Then washed with alcohol. Gram positive retain crystal violet stain, appear blue/purple . Gram negative, thinner cell walls, lose stain. Then stained with safranin dye, called counter stain, red. Gram positive susceptible to antibiotic penicillin, inhibits formation of cell walls. Gram negative, thinner not susceptible to penicillin.
Acid fast technique
Used to differentiate species of micro bacterium from other bacteria. Lipid solvent used to carry carbolfuchsin dye into cells. Cells then washed with dilute acid alcohol solution. Micro bacterium not affected by acid, alcohol and retain stain, bright red. Other bacteria lose stain, exposed to a methylene blue stain.
Fixing
Chemicals like formaldehyde used to preserve specimens in near natural state.
Sectioning
Specimens dehydrated with alcohols, placed in mould, form block.
Risk management for stains and practical work
Stains used are toxic/irritants. Risk assessment carried out before practical started. CLEAPSS, organisation provides support for practical work, in schools e.g use of chemicals, right equipment, provides safety sheets for risks.
Electron microscope
Expensive, large, complex sample preparation, vacuum required, black and white images, over 500,000 magnification, specimens dead. Max resolution 0.002 um
EQ- care must be taken in interpreting electron micrographs. Some features visible in an electron micrograph may not be present in a living cell. Explain why
Process involved in preparation alter/distort cell contents, introduction of artefacts
Vacuole
Permanent only in plants, consists of membrane called tonoplast, filled with cell sap. Keeps cell firm. When vacuole is full of sap it’s said to be turgid. Tonoplast selective permeable to small molecules.
Prokaryote
Single celled organism,without nucleus, do not have membrane bound organelles eg bacteria.
Slime capsule
Protection
Mesosome
Helps with cell division, creation of new cell walls
Pili
Attachment reproduction and genetic exchange
Prokaryotic v eukaryotic
P- 0.1-10 um, ribosomes 70s-18nm, no nucleus, cell wall made of peptidoglycan, binary fission, cell membrane, dna is circular, flagella made of flagellin E- 10-100um, ribosomes 80s-22nm, nucleus, cell wall made of cellulose in plants, asexual/sexual, cell membrane, dna is linear, flagella is made of microtubules
Endosymbiosis
Mitochondria and other organelles, were formerly free living bacteria, that is prokaryotes. Prokaryotes were taken inside another cell as an endosymbiont -organism lives within body/cells of another organism. Led to evolution of eukaryotic cells.
Eyepiece graticule
In lens
Stage micrometer
Scale on cover slip
Mm to um
X1000
Um to nm
X1000
Images in transmission and scanning electron
Scanning electron=shows surface of sample, more blurry,3D. Transmission=more detailed clear.
How does a light microscope work
Focuses a beam of light through a series of lenses
Artefact
Visible structural detail caused by processing specimen and not a feature of the specimen. Both light and electron.
