What do you think selectively permeable means? A. The membrane lets nothing in or out.

B. The membrane lets certain substances move across it freely, while others must move through a “gate”.

C. The membrane lets everything in and out.

B. The membrane lets certain substances move across it freely, while others must move through a “gate”.

Explanation:

Selective permeability is a property of cellular membranes that only allows certain molecules to enter or exit the cell. This is important for the cell to maintain its internal order irrespective of the changes to the environment. For example, water, ions, glucose and carbon dioxide may need to be imported or exported from the cell depending on its metabolic activity. Similarly, signaling molecules may need to enter the cell and proteins may need to be released into the extracellular matrix. The presence of a selectively permeable membrane allows the cell to exercise control over the quantum, timing and rate of movement of these molecules.

B. The membrane lets certain substances move across it freely, while others must move through a “gate”.

hormones in blood stream

image: dtc.ucsf.edu

endocrine glands secrete hormones into the blood stream near them; the hormones then travel in our bloodstream until it reaches its destination, called a target cell, in distance parts of the body. in the target tissue, hormones lock onto the target’s plasma membrane, called the receptor site.

it cools slower in the earth meaning the crystals have more time to form than lava on the surface