AS LEVEL BIO OCR
Cards (99)
- It states that the cell is the fundamental structure of all living matter, and that cells can only develop from other existing cells.
- All living organisms are composed of cells, and since most cells are too small to see without a microscope, we cannot observe the functions of cells and their organelles without one.
- Before then, microscope magnification was not as powerful, and so scientists were unable to see and identify single cells or cell components.
- 4. Replace the stage micrometer with a specimen to measure.
- How many times larger the image is than the actual size of the object.
- It has two lenses - the objective lens near the specimen, and the eyepiece lens, through which the specimen is viewed.
- A mount used to observe solid specimens, where the specimen is sectioned and a cover slip is placed over the top.
- A mount used to observe specimens suspended in water or immersion oil.
- A mount used to observe living specimens where the sample is squashed gently between the slide and the cover slip.
- A mount used to observe liquid samples by smearing the sample across the slide with a cover slip, creating a thin, even coating of the substance.
- This is used to separate bacteria into gram-positive and gram-negative bacteria. Crystal violet is applied first to a bacterial specimen, then iodine, which fixes the dye, and then the slide is washed with alcohol. Gram-positive bacteria retain the dye while gram-negative lose it as they have thinner cell walls.
- This is used to differentiate Mycobacterium from other bacteria. A lipid solvent carries dye into the cells, which are then washed with a dilute acid-alcohol solution. Mycobacterium retain the stain.
- By providing contrast, it allows us to differentiate between cell organelles that would otherwise be hard to identify.
- The shortest distance between two objects that can still be seen as separate entities.
- A beam of electrons illuminates the specimen, showing a more detailed cell ultrastructure.
- Transmission Electron Microscopy - electrons are transmitted THROUGH a specimen and focused to produce an image.
- Scanning Electron Microscopy - electrons are sent across the SURFACE of a specimen, and the reflecting electrons are collected, giving 3D images.
- Electron = expensive
- Electron = large and must be installed
- Electron = complex sample preparation that often leads to distortion.
- Electron = black and white images are produced but can be coloured digitally.
- Electron = over x500,000
- Electron = TEM: 0.5nm and SEM: 3-10nm
- A visible structural detail caused by processing the specimen, and is not actually a feature of the specimen itself.
- This refers to the chemical reactions of both the synthesis and the breaking down of molecules.
- To contain genetic information in the form of DNA molecules.
- To provide a double membrane to protect DNA from damage in the cytoplasm.
- To allow molecules, such as mRNA, to move in/out of the nucleus.
- DNA associates with proteins called histones, which form complexes known as chromatin. Chromatin then coils and condenses to form chromosomes which only become visible when cells are preparing to divide.
- It is a space within the nucleus made of proteins and RNA, and is responsible for producing ribosomes.
- They are the site of the final stages of cellular respiration.
- They have a double membrane, and the inner membrane is folded to form cristae, which encases the fluid interior known as the matrix.
- They are membranous sacs that have important roles in storage and transportation of substances.
- Lysosomes are specialised vesicles that contain hydrolytic enzymes, used to break down waste material in cells.
- It is a network of fibres necessary for the shape and stability of a cell.
- It has three components: microfilaments, which are contractile fibres made of actin that bring about cell contraction during cytokinesis; microtubules, which are formed from tubulin and form scaffold-like structures used in the movement of organelles; and intermediate fibres, which give mechanical strength to the cell.
- They are components in the cytoskeleton of most eukaryotic cells, and are made from microtubules. Two centrioles form a centrosome, which is involved in the organisation of the spindle fibres during cell division.
- They are used primarily for movement, but in some cells can also be used as sensory organelles to detect changes in the environment.
- These can move to create a current, causing fluids or objects around the cell to move.
- To synthesise lipids and carbohydrates.