Texas STAAR Biology Reporting Category 1 (Cell Structure and Function): a complete overview of cells, organelles, transport, and homeostasis

What Reporting Category 1 actually demands

Reporting Category 1, Cell Structure and Function, is the foundation of STAAR Biology and about a fifth of the test points. It runs from the smallest idea (cell theory and what a cell is) through the parts inside a cell, how things move across the membrane, how cells build up into organisms, and how a cell stays in balance. The recurring theme throughout is structure and function: nearly every item rewards connecting the shape or contents of a structure to the job it does.

This guide ties together the matching dot-point pages, each with its own practice questions: cell structure and organelles, prokaryotic and eukaryotic cells, the cell membrane and transport, levels of cellular organization, viruses and cell theory, and homeostasis and cellular regulation.

Cell theory and viruses

Cell theory has three parts: all living things are made of one or more cells; the cell is the basic unit of structure and function; and all cells come from pre-existing cells. A virus sits outside this: it is genetic material in a protein coat, with no organelles and no metabolism, and it cannot reproduce on its own. Because a virus must infect a host cell to make copies, it is not classified as living. STAAR likes to test the reasoning here, because having genetic material is not enough to count as alive.

Two kinds of cell

All cells share a membrane, cytoplasm, ribosomes, and DNA. The split is between prokaryotes (bacteria), which have no nucleus and no membrane-bound organelles, and eukaryotes (plants, animals, fungi, protists), which have a true nucleus and organelles and are larger and more complex. The advantage of the eukaryotic design is compartmentalization: membranes wall off reactions so the cell can run many of them at once under different conditions.

The organelles

Each organelle is a worked example of structure fitting function. The nucleus stores DNA and directs the cell; ribosomes build proteins; the rough ER makes and folds proteins while the smooth ER makes lipids; the Golgi apparatus modifies and packages them; mitochondria release energy by respiration; chloroplasts (plants) carry out photosynthesis; lysosomes digest waste; and the cell membrane controls transport. Plant cells add a cell wall and a large central vacuole. When an item shows a striking feature (many mitochondria, abundant rough ER), the answer connects that structure to a function.

The cell membrane and transport

The selectively permeable membrane controls what crosses. Passive transport needs no energy and moves substances down a gradient: diffusion spreads particles from high to low concentration, and osmosis is the diffusion of water. Active transport uses energy (ATP) to move substances against a gradient through membrane proteins. The membrane's control of transport is how a cell maintains homeostasis.

Organization and homeostasis

Cells build up into a hierarchy: cell, tissue, organ, organ system, organism. Cells become specialized by expressing different genes (differentiation), so structure matches function across the body. Through it all, the cell maintains homeostasis, a stable internal environment, mainly by controlling transport across the membrane and by feedback responses that reverse changes. A loss of homeostasis (from disease, toxins, or extreme conditions) stops enzymes working and harms the cell.

Check your knowledge

A mix of recall and reasoning questions covering Reporting Category 1. Attempt them under timed conditions, then check against the solutions.

1. State the three parts of cell theory. (3 marks)
2. Give one reason a virus is not classified as a living cell. (1 mark)
3. State two features that prokaryotic and eukaryotic cells have in common. (2 marks)
4. Name the organelle that is the site of cellular respiration. (1 mark)
5. Explain why a cell that secretes a lot of protein has abundant rough endoplasmic reticulum. (2 marks)
6. State the difference between diffusion and active transport in terms of energy. (2 marks)
7. A cell is placed in pure water. State what happens to the water and name the process. (2 marks)
8. List the levels of organization from smallest to largest. (2 marks)
9. Define homeostasis. (1 mark)