Ohio Biology EOC B.C (Cells): a complete overview of cell theory, cell types, organelles, the membrane, the cell cycle, photosynthesis, and cellular respiration

What the Cells strand demands

Cells (B.C) is one of the four Biology strands on Ohio's EOC, and it is a large share of the test. This guide covers it end to end: what a cell is, the parts inside it, how things cross the membrane, how cells divide, and the two energy processes that sustain life. The recurring crosscutting concept is structure and function: nearly every item rewards connecting the shape or contents of a structure to the job it does. The four content statements are B.C.1 (cell division and differentiation for growth, maintenance, and repair), B.C.2 (cells carry on functions that sustain life), B.C.3 (each cell structure corresponds to its function), and B.C.4 (the organization of cells, tissues, organs, organ systems, and the whole organism).

This guide ties together the matching topic pages, each with its own practice questions: cell theory and the types of cells, cell structure and organelles, the cell membrane and transport, the cell cycle and mitosis, photosynthesis, and cellular respiration.

Cell theory and how we know it

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. It was built over more than 150 years (Hooke named cells, Leeuwenhoek saw living single-celled organisms, Schleiden and Schwann generalized to plants and animals, Virchow added that cells come from cells) as the microscope improved. The EOC uses this history to teach the nature of science: a theory is a well-supported explanation that gets refined as new evidence and tools appear, not a guess.

Two kinds of cell

All cells share a membrane, cytoplasm, ribosomes, and DNA. The split is between prokaryotes (bacteria, archaea), 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. The advantage of the eukaryotic design is compartmentalisation: membranes wall off reactions so the cell can run many at once. Among eukaryotes, plant cells add a cell wall, chloroplasts, and a large central vacuole that animal cells lack.

The organelles

Each organelle is a worked example of structure fitting function (B.C.3). The nucleus stores DNA and directs the cell; ribosomes build proteins; the rough ER folds and transports proteins while the smooth ER makes lipids; the Golgi apparatus modifies and packages them into vesicles; mitochondria release energy by respiration; chloroplasts (plants) carry out photosynthesis; lysosomes digest waste; and the cell membrane controls transport. 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, a phospholipid bilayer with embedded proteins, controls what crosses. Passive transport needs no energy and moves substances down a gradient: diffusion spreads particles, osmosis is the diffusion of water, and facilitated diffusion uses a protein channel. Active transport uses energy (ATP) to move substances against a gradient. In osmosis, water moves toward the side with more solute, so a cell swells in a hypotonic solution, stays the same in an isotonic one, and shrinks in a hypertonic one. Controlling transport keeps the cell in homeostasis.

The cell cycle and cancer

The cell cycle (B.C.1) is the orderly sequence a cell follows to grow and divide: interphase (growth and DNA copying) then mitosis (PMAT: prophase, metaphase, anaphase, telophase) and cytokinesis. Mitosis produces two genetically identical cells with the full chromosome number, used for growth, maintenance, and repair. After dividing, cells differentiate into specialized types. The cycle is regulated by genes at checkpoints. A mutation in those genes can remove the controls, so the cell divides without stopping, forming a tumor and possibly cancer.

Photosynthesis and cellular respiration

These are the cell processes that sustain life (B.C.2), and they are mirror images. Photosynthesis (in the chloroplast) converts light energy into the chemical energy of glucose: $6\,CO_2 + 6\,H_2O \xrightarrow{\text{light}} C_6H_{12}O_6 + 6\,O_2$, releasing oxygen. Cellular respiration (in the mitochondrion) releases that energy as ATP: $C_6H_{12}O_6 + 6\,O_2 \to 6\,CO_2 + 6\,H_2O + \text{ATP}$. When oxygen is short, cells switch to anaerobic respiration (fermentation), making lactic acid (muscle) or ethanol (yeast) and releasing far less energy. The products of one process are the reactants of the other, so together they cycle carbon and energy.

Check your knowledge

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

1. State the three parts of cell theory. (3 marks)
2. State the one feature that defines a eukaryotic cell. (1 mark)
3. Name the three structures found in plant cells but not in typical animal cells. (3 marks)
4. Put these in the order a protein passes through them: Golgi apparatus, ribosome, vesicle, rough ER. (2 marks)
5. State the difference between diffusion and active transport in terms of energy. (2 marks)
6. A cell is placed in a hypertonic solution. State which way water moves and what happens to the cell. (2 marks)
7. List the four phases of mitosis in order. (2 marks)
8. Explain how a mutation can lead to cancer. (2 marks)
9. Write the word equations for photosynthesis and aerobic respiration, and name the organelle for each. (4 marks)