2.1 Cell structure

• Magnification is the number of times larger the size of an image is in comparison to the actual size of the object.
• Resolution is the ability to differentiate between two objects at a close range.
• The higher the resolution, the higher clarity of the image.
• Ultrastructure of a cell: detailed structure of the contents of a cell, shown by an electron microscope at high resolution.
• Magnification = size of image/actual size.
• Light (optical) microscopes are cheap, easy to use, and are used to study whole specimens.
• The maximum resolution of light microscopes is 200nm, with a magnification of x2000.
• Specimens can be alive or dead, so vacuum is not needed for light (optical) microscopes.
• Natural colour is seen in light (optical) microscopes.
• Transmission electron microscope (TEM) is very expensive to buy and operate, requires trained staff to use, and a vacuum is required for dead specimens.
• The maximum resolution of a transmission electron microscope (TEM) is 0.2nm, with a magnification of x2,000,000.
• Scanning electron microscope (SEM) is expensive to buy and operate, has a maximum magnification of x500,000, and a resolution of 10nm.
• Laser scanning (conofocal) microscope is used for living specimens, has a higher resolution than light, and shows structures at different depths.
• Sample preparation for microscopy includes dry mount, wet mount, squash sample, and smear.
• Staining in microscopy helps to distinguish between different components of the cell, made more visible.
• Nucleus is comprised of nucleolus, nuclear envelope (pores) and chromatin, holds nearly all the cells genetic material, and is the largest organelle in the cell.
• Mitochondrion has two membranes, smooth outer, folded (cristae) inner.
• Aerobic respiration is the site of energy release from food to make ATP.
• The endoplasmic reticulum (ER) consists of two types: rough, which has flattened membrane sacs - cisternae, and is studded with ribosomes (roughness), and smooth, which has the same structure but no ribosomes, and is the site of lipid synthesis.
• Cilia and flagella are essential for locomotion of organisms in single celled eukaryotes, and help move fluid or materials, moving a cell or group of cells in multicellular organisms, and are not found in plant cells.
• Lysosomes are specialised vesicles that contain digestive enzymes to break down materials, found inside phagocytes and sperm cells.
• The cellulose cell wall contains plasmodesmata that allow molecules to pass between cells, provides mechanical support and structure for the cell, and is found in plant cells.
• The site of aerobic respiration contains DNA, endosymbiotic theorem, and is possibly once a prokaryotic cell.
• Ribosomes are organelles found free in the cytoplasm or RER and are the site of protein synthesis.
• The Golgi apparatus is made of membrane stacks and is the site of processing of complex molecules.
• Eukaryotes are larger and more complex, have membranes around complex organelles, are part of a multicellular organism, and have a cell wall sometimes present, with DNA in the nucleus, larger ribosomes, rough and smooth endoplasmic reticulum, and cytoplasm.
• Prokaryotes are smaller and simpler, have no nucleus and no membrane bound organelles, and are found in bacteria and animals, with a cell wall made of peptidoglycan, a plasma membrane, flagella for locomotion, a nucleoid where DNA is, pilli for sexual reproduction, ribosomes, the site of protein synthesis, and cytoplasm.
• Ribosomes are not membrane bound.
• Centrioles are made up of nine bundles of microtubules and help in organising cell division, and are only present in animal cells.
• The large permanent vacuole is tonoplast- a partially permeable membrane surrounding the vacuole, keeping the cell firm (structural support), storing cell sap (sugars, enzymes water etc.), and is found in plant cells.
• Some proteins go to the plasma membrane for exocytosis (secretory vesicles).
• Chloroplasts contain some DNA, have a double membrane structure, thylakoids stack to make grana, and are the site of photosynthesis, with stroma being the fluid filled matrix in the chloroplast.
• The Golgi apparatus receives proteins from the ER, modifies and repackages them into transport vesicles.
• interrelations of organelles in protein synthesis: nucleus - contains DNA and instructions for the cell. ribosome - site of protein synthesis (translation) located in the cytoplasm or on RER. RER - transports newly made proteins. Golgi apparatus - site of protein modification and packaging. Vesicles - secretory vesicles transport proteins to the plasma membrane to fuse for exocytosis, transport vesicles for transporting molecules around the cell.