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Intracellular digestion is divided into heterophagic digestion and autophagic digestion. [3] These two types take place in the lysosome and they both have very specific functions. [3] Heterophagic intracellular digestion has an important job which is to break down all molecules that are brought into a cell by endocytosis. [3]
It takes place either in the lumen of the digestive system, in a gastric cavity or other digestive organ, or completely outside the body. During extracellular digestion, food is broken down outside the cell either mechanically or with acid by special molecules called enzymes. Then the newly broken down nutrients can be absorbed by the cells nearby.
Choanocytes (also known as "collar cells") are cells that line the interior of asconoid, syconoid and leuconoid body types of sponges that contain a central flagellum, or cilium, surrounded by a collar of microvilli which are connected by a thin membrane. They make up the choanoderm, a type of cell layer found in sponges.
Extracellular digestion takes place within this central cavity, which is lined with the gastrodermis, the internal layer of epithelium. This cavity has only one opening to the outside that functions as both a mouth and an anus : waste and undigested matter is excreted through the mouth/anus, which can be described as an incomplete gut .
The female lays her eggs on vegetation overhanging water. The larvae hatch and drop into the water where they seek out sponges to feed on. They use their elongated mouthparts to pierce the sponge and suck the fluids within. The larvae of some species cling to the surface of the sponge while others take refuge in the sponge's internal cavities.
Pinacocytes are part of the epithelium in sponges. They play a role in movement (contracting and stretching), cell adhesion, signaling, phagocytosis, and polarity. [ 2 ] Pinacocytes are filled with mesohyl which is a gel like substance that helps maintain the shape and structure of the sponge.
The first stage, the cephalic phase of digestion, begins with secretions from gastric glands in response to the sight and smell of food. This stage includes the mechanical breakdown of food by chewing, and the chemical breakdown by digestive enzymes, that takes place in the mouth.
Illustration of a eukaryotic cell membrane Comparison of a eukaryotic vs. a prokaryotic cell membrane. The cell membrane (also known as the plasma membrane or cytoplasmic membrane, and historically referred to as the plasmalemma) is a biological membrane that separates and protects the interior of a cell from the outside environment (the extracellular space).