Identify the major cell organelles and relate each structure to its function, showing how organelles work together to support life processes (Virginia 2018 Biology SOL BIO.3.a).

What this topic is asking

Virginia Biology SOL standard BIO.3.a asks you to know the major organelles and, crucially, to relate each structure to its function. The Biology EOC rarely asks for a definition in isolation; instead it gives a labeled diagram or a clue about a cell's job and asks which organelle fits. The deeper idea, that structure determines function and that organelles work together, is a crosscutting theme the test returns to again and again.

The control center: the nucleus

The nucleus is often called the cell's control center because the DNA it holds carries the instructions for every protein the cell makes, and proteins determine what the cell does. Inside the nucleus, the nucleolus makes ribosomes.

Making and shipping proteins

A set of organelles works as a production line for proteins:

• Ribosomes are the sites of protein synthesis, joining amino acids into proteins following the instructions in mRNA. They can float free in the cytoplasm or sit on the rough ER.
• The rough endoplasmic reticulum (ER) is studded with ribosomes and processes and transports the proteins they make. The smooth ER (no ribosomes) makes lipids and helps detoxify.
• The Golgi apparatus receives proteins from the ER, then modifies, packages, and ships them to where they are needed, inside or outside the cell.

This sequence, ribosome to ER to Golgi, is a favorite EOC example of organelles working together.

Releasing energy: mitochondria

If a question describes a cell with a very high energy demand, expect mitochondria to be involved, and expect the cell to have a lot of them. This is the structure-and-function reasoning the EOC rewards.

Plant-cell organelles

Plant cells, being eukaryotic, have all the organelles above, plus three that animal cells lack. Chloroplasts carry out photosynthesis, capturing light energy to make glucose. The cell wall (cellulose) lies outside the membrane and gives the cell support and a fixed shape. A large central vacuole stores water and dissolved substances and keeps the cell firm (turgid). These three are the plant-only organelles you should be ready to identify.

The cell membrane

The cell membrane (covered in detail in the cell membrane and transport) surrounds every cell and controls what enters and leaves. It is selectively permeable, letting some substances through while blocking others, which is essential for keeping the right internal conditions.

Try this

Q1. State the function of the Golgi apparatus. [1]

• Cue. It modifies, packages, and ships proteins (and other molecules) to their destinations.

Q2. Explain why a cell that secretes a lot of protein would have a large amount of rough endoplasmic reticulum. [2]

• Cue. The rough ER carries ribosomes that make proteins and processes and transports them; a high rate of protein secretion needs a lot of rough ER to make and handle those proteins.