Final answer:
Horizontal transmission refers to the spread of pathogens between individuals of different species, such as sexually transmitted diseases or those spread by vectors. Vertical transmission involves the direct transfer from parents to offspring, exampled by diseases like HIV and rubella.
Step-by-step explanation:
The statement Transmission occurs between organisms of different species is classified as horizontal transmission. Horizontal transmission involves the spread of pathogens between individuals of different species, whereas vertical transmission refers to the transfer of pathogens from parents to their offspring, either during pregnancy, birth or shortly thereafter.
Examples of diseases that are transmitted horizontally include those spread by sexual activity, like chlamydia and gonorrhea, and those spread by vectors, such as malaria. Diseases like HIV infection and rubella can be transmitted vertically from an infected mother to her child. It's important to understand these transmission routes to prevent the spread of infectious diseases effectively.