Unit 4: Cell Communication and Cell Cycle

Direct contact (junctions or surface molecules), short-range local signaling (paracrine, synaptic), and long-distance signaling (hormones).

Channels between adjacent animal cells that let ions and small molecules pass directly from one cytoplasm to the next, as in heart muscle.

Channels through plant cell walls connecting the cytoplasm of neighboring plant cells, allowing direct exchange of signals and molecules.

Surface molecules on one cell bind receptors on another, as when an antigen-presenting cell displays antigen on MHC proteins to a helper T cell.

A cell secretes local regulators (e.g., growth factors) that diffuse to and affect nearby target cells.

A neuron releases neurotransmitter into a synapse, where it diffuses a very short distance to bind receptors on the target cell.