Georgia Milestones Biology EOC, Cells (SB1): a complete overview of organelles, prokaryotic versus eukaryotic cells, transport, macromolecules, enzymes, and the energy processes

What the Cells domain demands

Cells (SB1) is the foundation of the Georgia Milestones Biology EOC and about 20 percent of the test. The standard asks you to treat the cell as a system: organelles that interact to maintain homeostasis, the molecules they are built from, how materials cross the membrane, and how energy is captured and released. The recurring theme is structure and function: nearly every item rewards connecting the shape or makeup of a structure to the job it does.

This guide ties together the matching topic pages, each with its own practice questions: cell structure and organelles, prokaryotic and eukaryotic cells, cellular transport and homeostasis, the macromolecules of life, enzymes and cellular processes, and photosynthesis and cellular respiration.

The cell as a system of organelles

A eukaryotic cell is a cooperative set of organelles, each a structure fitting a function. The nucleus stores DNA and directs the cell; ribosomes build proteins; the rough endoplasmic reticulum folds and ships them while the smooth ER makes lipids; the Golgi apparatus modifies and packages molecules into vesicles; mitochondria release energy by respiration; chloroplasts (plants) carry out photosynthesis; lysosomes digest waste; vacuoles store materials; the cell membrane controls transport; and the plant cell wall supports. The point SB1.a stresses is interaction: the secretory pathway (nucleus to ribosome to rough ER to Golgi to vesicle to membrane), powered by mitochondria and kept tidy by lysosomes, is the organelles working together to maintain homeostasis.

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. The advantage of the eukaryotic design is compartmentalization: internal 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 macromolecules

Cells build from four macromolecules. Carbohydrates (monomer: monosaccharide) are quick energy and include sugars and starches; lipids (not a single repeating monomer) store energy long term and form membranes; proteins (monomer: amino acid) are the workhorses, including enzymes, structure, and transport; and nucleic acids (monomer: nucleotide) are DNA and RNA, which store and carry genetic information. Structure fits function: a protein's folded shape is its active site or channel, and a phospholipid's water-loving head and water-fearing tails make the membrane bilayer.

Transport across the membrane

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 (particles), osmosis (water), and facilitated diffusion (through a protein). Active transport uses energy (ATP) to move substances against a gradient. In osmosis, water moves toward the higher solute concentration, so a cell swells in a hypotonic solution, shrinks in a hypertonic one, and stays the same in an isotonic one. Regulating this traffic is how the cell maintains homeostasis.

Enzymes

An enzyme is a protein that lowers the activation energy of a reaction, speeding it up without being used up. Its active site fits one substrate (lock and key), so enzymes are specific. Activity rises with temperature and substrate concentration to an optimum, then falls: too high a temperature or the wrong pH changes the active site's shape (denaturation), so the substrate no longer fits. Reading an enzyme-activity graph (rise from more collisions, peak at the optimum, fall from denaturation) is a recurring EOC skill.

The energy processes

Photosynthesis (in chloroplasts) uses carbon dioxide and water plus light to make glucose and oxygen: $6CO_2 + 6H_2O + \text{light} \rightarrow C_6H_{12}O_6 + 6O_2$. Cellular respiration (in mitochondria) is the reverse, using glucose and oxygen to release energy (ATP) plus carbon dioxide and water. The products of one are the reactants of the other, so energy flows one way (sunlight to ATP to heat) while matter cycles between the two processes. Respiration occurs in almost all cells, plant and animal; photosynthesis only in producers.

Check your knowledge

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

1. State the function of the mitochondrion. (1 mark)
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 hypotonic solution. State which way water moves and what happens to the cell. (2 marks)
7. Name the monomer of a protein and of a nucleic acid. (2 marks)
8. State what an enzyme does to the activation energy of a reaction. (1 mark)
9. Write the word equation for photosynthesis. (2 marks)
10. State which process (photosynthesis or respiration) occurs in the mitochondrion. (1 mark)