Louisiana LEAP 2025 Biology LS1 (Cells and Transport): a complete overview of cell theory, cell types, organelles, membrane transport, mitosis, and meiosis

What the cells and transport content demands

Cells and transport sits at the heart of the LS1 core idea (From Molecules to Organisms) on the Louisiana LEAP 2025 Biology test, with one topic (meiosis) reaching into LS3 (Heredity). This guide runs from the foundational cell theory, through the two cell types and the organelles that do the work, to how the cell membrane controls transport, and finally to the two kinds of cell division. The recurring crosscutting concept is structure and function: across cells, organelles, and membranes, the shape of a thing suits 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 cell types

The 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 from the evidence of many scientists once the microscope made cells visible. All cells share a membrane, cytoplasm, ribosomes, and DNA. The key division is the nucleus: prokaryotes (bacteria) have no nucleus and no membrane-bound organelles; eukaryotes (protists, fungi, plants, animals) have a true nucleus and organelles. Among eukaryotes, plant cells add a cell wall, chloroplasts, and a large vacuole.

Organelles and structure-function

A eukaryotic cell is a system of organelles. The nucleus stores DNA and controls the cell. Mitochondria release energy by respiration, so energy-hungry cells have many. Ribosomes build proteins; the rough ER folds and transports them; the Golgi apparatus packages and ships them; the smooth ER makes lipids. Chloroplasts (plants) carry out photosynthesis, and vacuoles store materials. The exam skill is to predict which organelle a specialized cell needs most from its job.

The cell membrane and transport

The cell membrane is a selectively permeable phospholipid bilayer with embedded proteins (the fluid mosaic model). Passive transport needs no energy and moves substances down the gradient: diffusion (dissolved particles), osmosis (water), and facilitated diffusion (through a protein). Active transport uses ATP and a protein pump to move substances against the gradient. In osmosis, water follows solute, so cells swell in hypotonic, stay the same in isotonic, and shrink in hypertonic solutions; plant cell walls prevent bursting.

The cell cycle and mitosis

The cell cycle is mostly interphase, when the cell grows and copies its DNA. Mitosis then divides the nucleus through prophase, metaphase, anaphase, and telophase, and cytokinesis splits the cytoplasm. The result is two genetically identical daughter cells with the same chromosome number, used for growth, repair, and replacement. Copying the DNA first is what makes the daughter cells identical.

Meiosis and variation

Meiosis makes gametes (eggs and sperm) and halves the chromosome number, so fertilization can restore the full number in the offspring. It produces four genetically varied cells through crossing over (matching chromosomes swap DNA) and independent assortment (pairs separate at random). This variation is the raw material for natural selection, connecting LS3 to LS4.

Check your knowledge

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

1. State the three parts of the cell theory. (3 marks)
2. State one structure found in both prokaryotic and eukaryotic cells, and one found only in eukaryotic cells. (2 marks)
3. A muscle cell has a high energy demand. Name the organelle it would have in large numbers and give its function. (2 marks)
4. Define selectively permeable. (1 mark)
5. State the difference between passive and active transport in terms of energy. (2 marks)
6. A cell is placed in a hypertonic solution. State the direction water moves and what happens to the cell. (2 marks)
7. Name the stage of the cell cycle in which DNA is copied. (1 mark)
8. State the number, chromosome number, and genetic relationship of the cells produced by mitosis. (2 marks)
9. Name one process during meiosis that creates genetic variation and explain how it does so. (2 marks)