The ultrastructure of a cell is the detailed internal structure that can only be seen with an electron microscope. A light microscope shows the nucleus and cytoplasm; the electron microscope reveals the membranes and organelles inside.
• nucleus with a double nuclear envelope, nuclear pores and a darker nucleolus
• rough endoplasmic reticulum (flattened sacs lined with ribosomes) and smooth endoplasmic reticulum (tubes without ribosomes)
• Golgi apparatus, a stack of curved flattened sacs with vesicles
• mitochondria, with a double membrane and folded cristae
• ribosomes, tiny dots free in the cytoplasm or on RER
• lysosomes, small dense vesicles, and centrioles near the nucleus
• the cell surface membrane, sometimes with microvilliPlant cells show all of these (apart from centrioles in most plants), plus a cellulose cell wall, chloroplasts and a large permanent vacuole.A key idea is compartmentalisation: membrane-bound organelles separate different reactions, so each can have its own conditions and enzymes. The organelles also work together; for example, a protein for secretion is made on ribosomes on the RER, modified in the Golgi apparatus and released in vesicles, using ATP from mitochondria.In the exam you should be able to identify organelles in electron micrographs and use scale bars to calculate their actual sizes.
• nucleus with a double nuclear envelope, nuclear pores and a darker nucleolus
• rough endoplasmic reticulum (flattened sacs lined with ribosomes) and smooth endoplasmic reticulum (tubes without ribosomes)
• Golgi apparatus, a stack of curved flattened sacs with vesicles
• mitochondria, with a double membrane and folded cristae
• ribosomes, tiny dots free in the cytoplasm or on RER
• lysosomes, small dense vesicles, and centrioles near the nucleus
• the cell surface membrane, sometimes with microvilliPlant cells show all of these (apart from centrioles in most plants), plus a cellulose cell wall, chloroplasts and a large permanent vacuole.A key idea is compartmentalisation: membrane-bound organelles separate different reactions, so each can have its own conditions and enzymes. The organelles also work together; for example, a protein for secretion is made on ribosomes on the RER, modified in the Golgi apparatus and released in vesicles, using ATP from mitochondria.In the exam you should be able to identify organelles in electron micrographs and use scale bars to calculate their actual sizes.