IB Notes
Ultrastructure of cells
* DEVELOPMETNS IN SCIENTIFIC RESEARCH FOLLOW IMPROVEMENTS IN APPARATUS- THE INVENTION OF ELECTRON MICROSCOPES LED TO GREATER UNDERSTANDING OF CELL STRUCTURE.
- A shard of clear glass that is thick at the middle and thin at the edge can magnify things.
- The compound microscope has two or more lenses and it can largely increase magnification.
- Small lenses with great curvatures produced even greater magnification (up to x240).
Modern light microscopes
- They are compound for greater magnification. The upper lens is called the eyepiece lens, the lower lens is called the objective lens.
- Focusing knobs (coarse and fine) to change focus.
- Diaphragm to adjust light intensity going through the speciment.
- Light condenser concentrates the light onto the specimen.
- Light source may be internal or external.
* USE OF LIGHT MICROSCOPE TO INVESTIGATE THE STRUCTURE OF CELLS AND TISSUES, WITH DRAWING OF CELLS.
* CALCULATING MAGNIFICATION
- 1000 nanometers = 1 micrometer
- 1000 micrometers = 1 millimeter
- 1000 millimeters = 1 centimeter
- Magnification = image / actual
* ELECTRON MICROSCOPES HAVE A MUCH HIGHER RESOLUTION THAN LIGHT MICROSCOPES.
- Light microscopes have a resolution of 200nm, anything less than 200nm apart will apear as one thing.
- Electron microscopes relies on a stream of electrons to visualize the specimen (instead of light).
- Electrons have a smaller wavelength so the resloution is around 50pm.
Prokaryotic cells
- They are mostly small in size compared to other cells and can be found in the soil, water, in or on other organisms, etc.
- They do not have a nucleus, genetic information is found in the cytoplasm.
* PROKARYOTES HAVE A SIMPLE CELL STRUCTURE WITHOUT COMPARTMENTALIZATION.
- Cell wall: Protects the cell, maintains its shape and prevents bursting. Made from peptidoglycan.
- Pili: Fine hair like projections on the surface which are used to attatch to surfaces and exchanges genetic material.
- Flagellum: Helps to propel the cell through the medium in which it is found.
- Plasma membrane: Regulates what goes in and out of the cell.
- Cytoplasm: Spread continuously throughout the cell. Where metabolism takes place and is filled with proteins.
- 70S ribosomes: Makes protein molecules.
- Nucleoid: Contains naked DNA. It is the lighter area of the cytoplasm as it doesn't contian proteins.
* PROKARYOTES DIVIDE BY BINARY FISSION.
- The cell theory states that all cells arise from pre-existing cells and prokaryotes do so through binary fission.
- Genetic material replicates and moves to opposite ends of the cell.
- The cytoplasm doubles, cell membrane invaginates, meets in the middle, and produces two daughter cells.
* DRAWING OF THE ULTRASTRUCTURE OF PROKARYOTIC CELLS BASE ON ELECTRON MICROGRAPHS.
Eukaryotic cells
* EUKARYOTES HAVE A COMPARTMENTALIZED CELL STRUCTURE
- There are small compartments call organelles, each with a distinctive structure and function.
- Compartmentalization allows each compartment to perform specific functions without interference from other cell functions.
- Organelles with their contents can be moved around within the cell.
- Conditions such as pH can be maintained at an ideal level for a particular process. This may be different to the levels needed for other processes.
- Substances that could damage the cell can be kept inside the membrane of an organelle (digestive enzymes of a lysosome).
- Enzymes and substrates for a particular process can be more concentrated than if they were spread throughout the cytoplasm.
* STRUCTURE AND FUNCTION OF ORGANELLES WITHIN EXOCRINE GLAND CELLS OF THE PANCREAS AND WITHIN PALISADE MESOPHYLL CELLS OF THE LEAF.
- Nucleus: A store for the cell's chromosome which are made from chromatin. It is bounded by a double membrane.
- Nucleolus: Inside the nucleus, where ribosomes are made.
- Nuclear pore: They are large protein complexes which is the doble membrane surounding the cell nucleus.
- Mitochondrion: Enzymes in the cytoplasm produces ATP for the cell by cellular respiration. Fat is digested here if it is being used as an energy source for the cell. Has an inner membrane which folds in for more surface area.
- Cytoplasm: A semi-fluid which helps to suspend the organelles. Most of the chemical reactions take place here for metabolism. It acts as a medium of transport.
- Golgi apparatus: Processes materials sent from the smooth and rough ER. Can add biochemical groups to the materials and then packed back into the vesicles for export from the cell.
- Rough endoplasmic reticulum: Covered with 80s ribosomes (protein synthesis). Proteins are packed into vesicles and sent to the Golgi apparatus. If the protein being made is being exported outside the cell, it will be made on the rough ER. If the protein being made is being used inside the cell, it will be made in the cytoplasm.
- Smooth endoplasmic reticulum: Involved in lipid synthesis. Lipids are packaged into vesicles and sent to the Golgi apparatus.
- Lysosome: Spherical with a single membrane. Contains digestive enzymes (hence, a lot of proteins) which can be used to break down ingested food, organelles or even the entire cell.
- Chloroplast: Contains chlorophyll. Produces glucose and a wide variety of other organic compounds by photosynthesis. Starch grains may be present if they have been photosynthesizing rapidly.
- Free ribosomes: These are not attatched to anything and are free to move. Involved in protein sythesis but most are used by the cell itself.
- Cilia: Whip-like projections that create a current in the fluid near the cell. Help with movement / response.
- Flagella: Similar to cilia, but are larger in size. Used to propel the cell.
- Vacuoles: Membrane bound sacs containing fluid. Vacuoles are much bigger than vesicles and it can be found in plant cells.
- Vesicles: Membrane bound sacs containing fluid. These are found in animal cells and is used to transport materials around the cell.
- Centrioles: Contains two groups of 9 microtubule triplets and are involved in moving chromosomes during cell division. Centrioles form an anchor point for the microtubules.
- Cell membrane: It is semi-permeable to selectively allow materials in and out of the cell.
* DRAWING OF THE ULTRASTRUCTURE OF EUKARYOTIC CELLS BASED ON ELECTRON MICROGRAPH.
* THE STRUCTURE AND FUNCTION OF ORGANELLES WITHIN EXOCRINE GLAND CELLS OF THE PANCREAS.
- The pancrease has 2 types of gland cells- endocrine and exocrine. They both secrete substances through their plasma membranes.
- Endocrine gland cells secrete hormones into the blood stream.
- Exocrine gland cells secrete digestive enzymes into a duct leading to the small intestines (for food digestion).
- Exocrine gland cells have organelles which can synthesise protein in large quantities, process them to make them ready for secretion, transport them to the plasma membraane and then release them.
- Exocrine gland cells have lysosomes, mitochondrion, rER, nucleus, plasma membrane, Golgi apparatus and vesicles.
* THE STRUCTURE AND FUNCTION OF ORGANELLES WITHIN PALISADE MESOPHYLL CELLS OF THE LEAF.
- The main function of a leaf is to produce organic compounds from carbon dioxide and other simple organic compounds using light energy.
- The palisade mesophyll carrues out most of the photosynthesis in a cell.
- The palisade mesophyll cell has a cell wall, plasma membrane, chloroplast, cytoplasm, nucleus, mitochondrion and vacuole.
* INTERPRET ELECTRON MICROGRAPHS AND DEDUCE THE FUNCTION OF SPECIALIZED CELLS.
- Identify the organelles and their functions in a eukaryotic cell.
- Deduce the cell type with this information.
