Tennessee Biology I EOC LS1 (Cells and Transport): a complete overview of cell theory, cell types, organelles, the membrane, the cell cycle, and meiosis

What the cells-and-transport part of LS1 demands

From Molecules to Organisms (LS1) is the largest content area on the Tennessee Biology I EOC. This guide covers its cellular core: what a cell is, the parts inside it, how things cross the membrane, how cells divide, and how meiosis creates variation. (The biochemistry and energy part of LS1, with water, macromolecules, enzymes, photosynthesis, and respiration, is in the biochemistry and energy guide, and the body-systems part is in the human body and homeostasis guide.) 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.

This guide ties together the matching topic pages, each with its own practice questions: cell theory and the types of cells, comparing prokaryotic and eukaryotic cells, cell structure and organelles, the cell membrane and transport, the cell cycle and mitosis, and meiosis and genetic variation.

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 compartmentalization: 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. 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 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 through membrane proteins. 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.

The cell cycle and cancer

The cell cycle 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 and repair. 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.

Meiosis and variation

Meiosis makes gametes: one diploid cell ($2n$) produces four haploid cells ($n$), halving the chromosome number so that fertilization restores it. It differs from mitosis by making four genetically different haploid cells instead of two identical diploid ones. Meiosis creates genetic variation through crossing over (homologous chromosomes swap segments), independent assortment (pairs line up and separate randomly), and random fertilization. This variation is the raw material for evolution.

Check your knowledge

A mix of recall and reasoning questions covering the cells-and-transport part of LS1. 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 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. A body cell has 38 chromosomes. State the number in a gamete produced by meiosis. (1 mark)