There is an estimated 10-100 trillion bacteria and other microorganisms living in the human digestive system, forming a mutualistic relationship in which all species benefit. Recently, much research has been done on the role of these microorganisms in the development of disease, the brain, and behavior. Drag the terms on the left to the appropriate blanks on the right to complete the sentences. Not all terms will be used.
The is a layer of cells lining the blood vessels within the brain, acting as a filter that controls the molecules that pass between the blood and the brain.
An organism's is the collection of all the microorganisms (e. g. bacteria, phages, fungi) that live inside the digestive system of that individual.
Ais a type of intercellular protein connection between animal cells that prevents leakage of materials through the space between the cells.
The transmembrane protein is one of the component proteins of a tight junction.
lack all microorganisms in their digestive systems, a state achieved by delivering them through cesarean section and raising them in sterile incubators.
are raised under sterile conditions to limit their exposure disease-causing microorganisms.
tight junction
gut microbiota gap junction
germ-free mice pathogen-free mice
blood brain barrier adhesion plaque
occludin

- The blood brain barrier is a layer of cells lining the blood vessels within the brain, acting as a filter that controls the molecules that pass between the blood and the brain.

- An organism's gut microbiota is the collection of all the microorganisms (e.g. bacteria, phages, fungi) that live inside the digestive system of that individual.

- A gap junction is a type of intercellular protein connection between animal cells that prevents leakage of materials through the space between the cells.

- The transmembrane protein occludin is one of the component proteins of a tight junction.

- Germ-free mice lack all microorganisms in their digestive systems, a state achieved by delivering them through cesarean section and raising them in sterile incubators.

- Pathogen-free mice are raised under sterile conditions to limit their exposure disease-causing microorganisms.

Explanation:

The blood-brain barrier is a layer of cells made up of endothelial cells that act to limit the passage of substances from the bloodstream in a more selective manner than endothelial cells of capillaries located in other parts of the body. Gut microbiota can be defined as all the microorganisms (i.e., bacteria) inhabiting the mammalian gastrointestinal tract, which helps to ferment non-digestible substrates (e.g., dietary fibers). A gap junction is a class of cell junction that is formed between cells contacting each other which allows small molecules (e.g., water, ions, metabolites, microRNA sequences, etc) to pass through this intercellular communication.  In vertebrate animals, cell junctions can be divided into 1-gap junctions (communication between cells), 2-tight junctions (occludin junctions), and 3-adherens junctions, hemidesmosomes and desmosomes (anchor junctions). Tight Junctions are composed of multiple proteins including transmembrane proteins such as occludin, tricellulin, junctional adhesion molecule (JAM), and one member of the claudin protein family. Germfree animals are research animals that have no microorganisms living in or on them, which are housed in controlled/isolated conditions to prevent any type of contamination. Finally, pathogen-free animals are research animals that are guaranteed to be free of particular pathogenic (harmful) microorganisms.

cells use diffusion to get substances in and out of themselves. that diffusion will occur across the cell membrane or the outer covering of the cell. because we are talking about the surface of the cell, surface area and volume are  important factors here. as a cell increases in size, its surface area and volume increase as well.  we call that the surface area to volume ratio (sa: vol).  but the catch is that  volume increases at a greater rate than surface  area. in other words, as a cell gets bigger, the sa: vol gets smaller. so a really small cell like bacteria is mostly cell membrane (surface) with very little contents (volume). a really big cell like an egg, is mostly insides with a super thin membrane. so what ends up happening is that the cell cannot efficiently diffuse all of the stuff it needs in/out to survive. therefore cell size is limited to about 100mm. so how do we make organisms bigger than 100mm? cells divide! by dividing and becoming multicellular, organisms are able to grow!   check out the diagrams i attached to see the effect of sa: vol. i hope this ! good luck!