TEAS Science: Cell Structure, Organelles, and Cell Division Explained

Every living thing is built from cells, which makes cell biology one of the most reliable topics on the TEAS Science section. Questions test whether you can identify organelles, describe their functions, distinguish cell types, explain how substances cross the cell membrane, and recall the stages of cell division. The good news: this material is highly memorizable once it is organized clearly.

This review walks through the cell from the outside in, then covers transport and division. Read it actively—cover the function and try to recall it from the organelle name, then check yourself.

Prokaryotic vs. Eukaryotic Cells

The first big distinction the TEAS tests is between the two fundamental cell types.

• Prokaryotic cells: NO membrane-bound nucleus and no membrane-bound organelles. DNA floats freely in the cytoplasm. These are bacteria and archaea—small and simple.
• Eukaryotic cells: HAVE a true, membrane-bound nucleus and membrane-bound organelles. These make up animals, plants, fungi, and protists—larger and more complex.

The Major Organelles and Their Functions

Think of the cell as a tiny factory. Each organelle is a department with a specific job. These are the ones the TEAS asks about most:

• Nucleus: The control center. Stores DNA and directs all cell activities, including growth and reproduction.
• Mitochondria: The 'powerhouse' of the cell. Produces ATP (energy) through cellular respiration.
• Ribosomes: The protein factories. Assemble proteins from amino acids; can float freely or attach to the ER.
• Endoplasmic reticulum (ER): A transport network. ROUGH ER (with ribosomes) makes proteins; SMOOTH ER (no ribosomes) makes lipids and detoxifies.
• Golgi apparatus: The packaging and shipping center. Modifies, sorts, and ships proteins and lipids in vesicles.
• Lysosomes: The cleanup crew. Contain digestive enzymes that break down waste and worn-out cell parts.
• Cytoplasm: The gel-like fluid that fills the cell and suspends the organelles.
• Cell (plasma) membrane: The selective barrier controlling what enters and exits the cell.

Plant Cells vs. Animal Cells

Both are eukaryotic, but plant cells have three structures animal cells lack:

• Cell wall: A rigid outer layer (made of cellulose) outside the membrane that provides structure and support.
• Chloroplasts: Contain chlorophyll and carry out photosynthesis to make food from sunlight.
• Large central vacuole: Stores water and helps maintain the cell's rigidity (turgor pressure).

Animal cells generally have small, multiple vacuoles and contain centrioles (used in cell division), which most plant cells lack.

The Cell Membrane and Transport

The cell membrane is a phospholipid bilayer that is 'selectively permeable'—it lets some things through and blocks others. The TEAS frequently asks how substances cross it, which falls into two categories.

• Passive transport: Movement that requires NO energy, moving substances from HIGH to LOW concentration (down the gradient). Includes diffusion, osmosis (diffusion of water), and facilitated diffusion (through protein channels).
• Active transport: Movement that REQUIRES energy (ATP), moving substances from LOW to HIGH concentration (against the gradient), often using protein 'pumps' such as the sodium-potassium pump.

Know the tonicity terms too: in a HYPOtonic solution water moves INTO the cell (it may swell or burst); in a HYPERtonic solution water moves OUT (the cell shrinks); in an ISOtonic solution there is no net movement.

The Cell Cycle and Mitosis

Cells reproduce by dividing. Mitosis produces two identical 'daughter' cells for growth and repair. Before division, the cell spends most of its life in interphase, where it grows and copies its DNA.

The four stages of mitosis, in order, are Prophase, Metaphase, Anaphase, and Telophase.

• Prophase: Chromosomes condense and become visible; the nuclear membrane begins to break down.
• Metaphase: Chromosomes line up along the MIDDLE (the metaphase plate) of the cell.
• Anaphase: Sister chromatids are pulled APART to opposite ends of the cell.
• Telophase: Two new nuclear membranes form; the cell prepares to split.
• Cytokinesis: The cytoplasm divides, producing two separate daughter cells (often listed as the final step).

Mitosis vs. Meiosis

Do not confuse the two types of division—the TEAS often pairs them in a question.

• Mitosis: Produces 2 identical diploid cells; used for growth and repair of body (somatic) cells.
• Meiosis: Produces 4 genetically unique haploid cells (gametes—eggs and sperm); essential for sexual reproduction and genetic variation.

Common Cell Biology Mistakes to Avoid

• Confusing prokaryotic and eukaryotic (remember: only eukaryotes have a true nucleus).
• Mixing up the ribosome (makes protein) with the Golgi (packages/ships it).
• Calling osmosis 'active transport'—it is passive and involves water.
• Reversing hypotonic and hypertonic effects on a cell.
• Forgetting the correct order of mitosis stages (PMAT).
• Confusing mitosis (2 identical cells) with meiosis (4 unique gametes).

How to Study Cell Biology for the TEAS

Make flashcards with the organelle name on one side and its function on the other. Draw and label a cell from memory until you can do it without looking. Quiz yourself on transport types and tonicity, and recite the PMAT stages out loud. This material is pure recall—spaced repetition is your best friend.

Cell biology is one of the highest-yield, most learnable topics on the TEAS Science section. Lock in the organelles, transport, and division stages, and you will pick up easy points that boost your overall science score.