ER.html: 06_12EndoplsmcReticulum.jpg
Endoplasmic reticulum (ER). A membranous system called cisternae, enclosing a compartment called the lumen, the ER is continuous with the nuclear envelope. Rough ER, which is studded on its outer surface with ribosomes, can be distinguished from smooth ER. Transport vesicles bud off and travel to the Golgi apparatus and other destinations.

Golgi.html: 06_13GolgiApparatus.jpg
The Golgi apparatus consists of stacks of flattened sacs, or cisternae. They receive and process the transport vesicles produced in the ER to be delivered to other parts of the cell.

cell.html: 06_cell_brightfield.jpg

cell_confocal.html: 06_cell_confocal.jpg

cell_differential-contrast.html: 06_cell_differential-contrast.jpg
Differential interference contrast (Nomarski) works by separating a polarised light source into two beams taking slightly different paths through the sample. When recombined the two beams interfere and enhance the variation of optical density of the sample.

cell_fluorescence.html: 06_cell_fluorescence.jpg

cell_phase-contrast.html: 06_cell_phase-contrast.jpg
A transparent phase-plate in the microscope enhances phase difference in light as it travels through the transparent specimen.

cell_sizes.html: 06_02CellSizeRange.jpg
Most cells are too small to see with the naked eye.

cell_stained.html: 06_cell_brightfield_stained.jpg

cells.html: 06_01Cell_fluorescence.jpg
A cell and its skeleton viewed by fluorescence microscopy.

cells_animal.html: 06_09aAnimalCell.jpg

cells_eukaryotic.html: 06_09aAnimalCell.jpg

cells_plant.html: 06_09bPlantCell.jpg

central_vacuole.html: 06_15PlantCellVacuole_CL.jpg
The central vacuole, surrounded by a membrane called the tonoplast, holds organic compounds and water in plant cells. It is usually the largest organelle seen under the light microscope.

centrosome.html: 06_22CentrosomeStructur.jpg
Centrosome containing a pair of centrioles.

An animal cell has a pair of centrioles within its centrosome, the region near the nucleus where the cell's microtubules are initiated.

The centrioles are found at right angles to each other, and each is made up of nine sets of three microtubules. The microtubules are made of tubulin subunits.

chloroplast.html: 06_18Chloroplast_CL.jpg
A chloroplast has a double membrane: the inner membrane encloses a compartment containing the fluid stroma as well as ribosomes and DNA. A third membrane called thylakoids contains the photosynthetic pigment chlorophyll and is stacked to form structures called grana (singular, granum).

cilia.html: 06_23Cilia.jpg
Cilia have a back-and-forth motion that moves the cell in a direction perpendicular to the axis of the cilium. A dense nap of cilia, beating at a rate of about 40 to 60 strokes a second, covers this Colpidium, a freshwater protozoan.
Videos: humans

cytoskeleton.html: 06_20Cytoskeleton_CL.jpg
The cytoskeleton. This TEM shows the thicker, hollow microtubules and the thinner, solid microfilaments.

dynein.html: 06_25DyneinWalkingA.jpg
Powered by ATP, the dynein arms of one microtubule doublet grip the adjacent doublet, push it up, release, and then grip again.

dynein_bend.html: 06_25DyneinWalkingB.jpg
In a cilium or flagellum, two adjacent microtubule doublets cannot slide far because they are restrained by proteins, so they bend .

dynein_wave.html: 06_25DyneinWalkingC.jpg
Localized, synchronized activation of many dynein arms probably causes a bend to begin at the base of the cilium or flagellum and move outward toward the tip in successive bends, result in a wavelike motion.

ecm.html: 06_29ExtracellularMatrix.jpg
Extracellular matrix (ECM) of an animal cell. The ECM functions in support, adhesion, movement, and regulation. In this example, three different types of glycoproteins are present: proteoglycans, collagen, and fibronectin.

endomembrane_system.html: 06_16EndomembraneSystem.jpg
The Endomembrane System.

flagella.html: 06_23Flagella.jpg
A flagellum usually undulates, its snakelike motion driving a cell in the same direction as the axis of the flagellum.
Propulsion of a human sperm cell is an example of flagellate locomotion.
Videos: sperm

flagellum_structure.html: 06_24FlagellumStructure.jpg
Ultrastructure of a eukaryotic flagellum or cilium. Both cilia and flagella have a "9 + 2" arrangement of microtubules arising from a basal body of 9 triplets. The 9 doublets have attached motor proteins, the dynein arms.

junction.html: 06_31IntercellJunctions.jpg

lysosome_autophagy.html: 06_14Lysosomes_A.jpg
Autophagy. Top: a lysosome engulfs 2 disabled organelles, a mitochondrion and a peroxisome.
Bottom: a lysosome fuses with a vesicle containing a damaged mitochondrion.

lysosome_phagocytosis.html: 06_14Lysosomes_P.jpg
Phagocytosis. Lysosomes digest (hydrolyze) materials taken into the cell and recycle intracellular materials.
Top: a macrophage can ingest bacteria and viruses and destroy them using lysosomes.
Bottom: a lysosome can fuse with a food vacuole during phagocytosis.

microfilament.html: 06_01CytoskeletonStructur_microfilaments.jpg
Microfilaments from fibroblast cells. Microfilaments are made of actin and myosin subunits that slide past each other to cause contraction.

microtubule.html: 06_01CytoskeletonStructur_microtubules.jpg
Microtubules from fibroblast cells.

Microtubules are made of tubulin subunits and help maintain cell shape and guide the movement of cell components. The centrosome in amimal cells is a "microtubule-organizing center" and contains a pair of centrioles.

mitochondrion.html: 06_17Mitochondrion_CL.jpg
The mitochondrion, site of cellular (aerobic) respiration.
A mitochondrion has a double membrane: an outer membrane and an inner membrane folded into cristae enclosing a lumen called the matrix which contains circular DNA and ribosomes.

motility.html: 06_27MotilityB.jpg
Amoeboid movement. The cytoplasm can fluctuate between a fluid state called sol, or endoplasm, and a stiffer state called gel, or ectoplasm. Interaction of actin filaments with myosin near the cell's trailing end (right) squeezes the fluid forward (left) into the psudopodium. _Vid_Campbell7e/Amoeba-V.swf

motor_protein.html: 06_21MotorProteins.jpg

muscle.html: 06_27MotilityA.jpg
Myosin motors in muscle cell contraction. The "walking" of myosin arms drives the parallel actin and myosin filaments past each other so that the actin filaments approach each other in the middle, shortening the cell. nucleus.html: 06_10Nucleus.jpg
The nucleus and its envelope. In the nucleus are chromatin (DNA and proteins), and one or more nucleoli (singular, nucleolus), which synthesize ribosomes. The double membrane of the nuclear envelope is perforated with nuclear pores and lined by the nuclear lamina made of protein filaments.

plasmo.html: 06_28PlantCellWalls_CL.jpg
Plasmodesmata between plant cells. The cytoplasm of one plant cell is continuous with the cytoplasm of its neighbors via plasmodesmata, channels through the cell walls.

plasmodesmata.html: 06_30Plasmodesmata_LP.jpg
Plasmodesmata between plant cells. The cytoplasm of one plant cell is continuous with the cytoplasm of its neighbors via plasmodesmata, channels through the cell walls.

ribosome.html: 06_11Ribosomes_CL.jpg
Ribosomes. This electron micrograph of part of a pancreas cell shows many ribosomes, both free (in the cytosol) and bound (to the ER). Ribosomes are composed of two subunits each made of ribosomal RNA (rRNA) and protein.

sa.html: 06_07SurfaceVolumeRatio_L.jpg

streaming.html: 06_27MotilityC.jpg
Cytoplasmic streaming in plant cells. A layer of cytoplasm cycles around the cell, moving over a carpet of parallel actin filaments. Myosin motors attached to organelles in the fluid cytosol drive the streaming by interacting with the actin.

surface_volume.html: 06_07SurfaceVolumeRatio_L.jpg
The surface area to volume ratio of an object decreases when its size increases.