Essential Biology: Life Processes, Viruses, and Species

Characteristics of Living Things

MRS GREN is an acronym used to remember the seven life processes: Movement, Respiration, Sensitivity, Growth, Reproduction, Excretion, and Nutrition.

• Movement: Observed in living things through actions like jumping or processes like photosynthesis.
• Respiration: A chemical reaction in cells that breaks down nutrient molecules and releases energy for metabolism (e.g., plants release oxygen that is absorbed by other living things).
• Sensitivity: The ability to respond to stimuli, such as touch or light.
• Growth: The process of increasing in size, such as plants getting bigger.
• Reproduction: Male and female members of the same species producing offspring, which can be asexual (e.g., breaking in half) or sexual.
• Excretion: The process that removes waste products from the body, such as urine and sweat.
• Nutrition: The intake of nutrients; for example, plants require light, carbon dioxide, and water.

Understanding Viruses

What are Viruses?

A virus is a non-cellular particle made up of genetic material and protein that can invade living cells. Viruses have no nucleus, no organelles, no cytoplasm, or cell membrane.

The common types of viruses include helical, polyhedral, spherical, and complex structures. Their primary components are:

1. Nucleic acids: DNA or RNA.
2. Protein coat (capsid): Surrounds the DNA or RNA for the protection of genetic material.
3. Lipid membrane (envelope, spikes): The protein coat found only in some viruses.

How do Viruses Reproduce?

Viruses cannot replicate on their own; rather, they depend on the host cell's protein synthesis pathways to reproduce.

What are the Structures of Viruses?

Viral Structure: In simpler viruses, the virion consists of a single molecule of nucleic acid surrounded by a protein coat, the capsid; the capsid and its enclosed nucleic acid together constitute the nucleocapsid. In some of the more complex viruses, the capsid surrounds a protein core.

Defining Biological Species

What is a Species?

A species is a group of living organisms consisting of similar individuals capable of exchanging genes or interbreeding. A species is often defined as a group of individuals that actually or potentially interbreed in nature. In this sense, a species is the biggest gene pool possible under natural conditions.

Interbreeding is key to the biological species concept, which defines a species as members of populations that can interbreed with each other to produce viable offspring. To be considered "viable," the offspring must themselves be able to reproduce.