Investigate and explain the functions of cellular organelles in eukaryotic cells, and relate the structure of each organelle to the function it performs (TEKS Biology, Reporting Category 1; structure and function).

What this topic is asking

The Biology TEKS treat the cell as a system of parts, each with a job. For STAAR Reporting Category 1 you need to name the major organelles, state what each one does, and above all relate structure to function. Items often show a labeled diagram or describe a cell with a striking feature and ask you to reason about what the cell does. This is the recurring theme of structure and function in action.

The major organelles

• Nucleus. Holds the cell's DNA and directs the cell by controlling which proteins are made. It is bounded by a nuclear envelope with pores.
• Ribosomes. Small structures (free in the cytoplasm or attached to the rough ER) that build proteins by joining amino acids in the order set by the genetic code.
• Endoplasmic reticulum (ER). A network of membranes. The rough ER (studded with ribosomes) makes and folds proteins; the smooth ER makes lipids and helps detoxify substances.
• Golgi apparatus. Modifies, sorts, and packages proteins and lipids into vesicles for delivery inside or outside the cell.
• Mitochondria. The site of cellular respiration, releasing energy from glucose as ATP. Cells with high energy demand have many.
• Chloroplasts. Found in plant cells and algae; the site of photosynthesis, capturing light energy to make glucose.
• Lysosomes. Contain digestive enzymes that break down waste, worn-out parts, and invading material.
• Cell (plasma) membrane. The selectively permeable boundary controlling transport, covered in the cell membrane and transport.
• Cytoplasm. The fluid that holds the organelles and where many reactions take place.

Plant cells versus animal cells

Plant and animal cells share most organelles, but plant cells have three extra features that STAAR tests often:

• A cell wall, a rigid layer of cellulose outside the membrane that gives shape and support.
• Chloroplasts, for photosynthesis.
• A large central vacuole, which stores water and keeps the cell firm (turgid).

Animal cells lack these but often have small vacuoles and other structures. Knowing which structures are plant-only is a frequent multiselect or hot-spot question.

Structure determines function

This is why a cell that secretes protein has abundant rough ER and Golgi, a hard-working muscle cell has many mitochondria, and a green leaf cell has many chloroplasts. The recurring theme of structure and function is the single most reliable way to reason through these items.

Try this

Q1. Identify two structures found in a plant cell but not in a typical animal cell, and state the function of each. [2]

• Cue. Any two of: cell wall (support and shape), chloroplasts (photosynthesis), large central vacuole (stores water, keeps the cell turgid).

Q2. Explain why a cell that secretes large amounts of protein contains a great deal of rough endoplasmic reticulum. [2]

• Cue. The rough ER, studded with ribosomes, is where proteins are built and folded; a cell that exports much protein needs a large amount of this machinery.