What is the difference between a prokaryotic and a eukaryotic cell?

Both cell types have a cell membrane, cytoplasm, ribosomes, and DNA. The defining difference is that a eukaryotic cell keeps its DNA in a membrane-bound nucleus and has other membrane-bound organelles (such as mitochondria and, in plants, chloroplasts), while a prokaryotic cell has no nucleus and no membrane-bound organelles, with its DNA as a single loop free in the cytoplasm. Prokaryotes are smaller and simpler and include the bacteria and archaea; eukaryotes are larger and include animals, plants, fungi, and protists.

What is the difference between passive and active transport?

Passive transport moves a substance down its concentration gradient, from high to low concentration, and needs no energy. It includes diffusion, osmosis (the diffusion of water), and facilitated diffusion (down the gradient through a protein channel). Active transport moves a substance up its gradient, from low to high concentration, and requires energy in the form of ATP and a protein pump. Endocytosis and exocytosis, which move bulk material, also require energy.

How do enzymes speed up reactions?

An enzyme is a biological catalyst, usually a protein, that lowers the activation energy of a reaction so it proceeds faster at the cell's normal temperature, without the enzyme being used up. Each enzyme has an active site whose shape fits only its substrate (the lock-and-key model), which makes it specific. Activity rises with temperature up to an optimum, then falls sharply as heat denatures the enzyme; each enzyme also has an optimum pH, and the wrong pH denatures it.

What happens to a cell in a hypertonic solution?

In a hypertonic solution the surrounding fluid has a higher solute concentration than the cell, so water moves out of the cell by osmosis. An animal cell loses water and shrinks (crenates). A plant cell loses water from its central vacuole, and the contents pull away from the cell wall (plasmolysis), so the plant wilts. In a hypotonic solution the opposite happens: water moves in, and an animal cell may burst while a plant cell becomes firm (turgid).

North CarolinaBiology

North Carolina Biology EOC: Cells and Cellular Processes - a complete overview of cell theory, cell types, organelles, membranes and transport, macromolecules, and enzymes

Q: What does the cells and cellular processes content on the North Carolina Biology EOC cover?

It covers the cell theory and the difference between unicellular and multicellular organisms; the comparison of prokaryotic and eukaryotic cells (the nucleus and membrane-bound organelles are the defining difference); the structure and function of organelles such as the nucleus, mitochondria, chloroplasts, ribosomes, ER, and Golgi; the cell membrane and how it controls transport by diffusion, osmosis, facilitated diffusion, and active transport; the four macromolecules (carbohydrates, lipids, proteins, nucleic acids) and their monomers and roles; and enzymes as catalysts that lower activation energy, including how temperature and pH affect them. These align to the LS.Bio.1 standards in the North Carolina Standard Course of Study.

A deep-dive guide to the cell biology of the From Molecules to Organisms strand on the North Carolina Biology EOC: cell theory, prokaryotic and eukaryotic cells, organelles, the cell membrane and transport, the four macromolecules, and enzymes, with the item types the EOC uses.

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What the cells and cellular processes content demands
Cell theory and cell types
Prokaryotic and eukaryotic cells
Organelles and structure-function
The cell membrane and transport
The four macromolecules
Enzymes
Check your knowledge

What the cells and cellular processes content demands

The From Molecules to Organisms strand opens the North Carolina Biology course and supplies a large share of the EOC. This guide runs from the foundational cell theory, through the two cell types and the organelles that build a eukaryotic cell, to how the membrane controls transport, the macromolecules that cells are made of, and the enzymes that run their chemistry. The recurring crosscutting concept is structure and function: at every level, shape suits the job.

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 macromolecules of life, and enzymes and biochemical reactions.

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. Improving microscopes made it possible, from Hooke naming "cells" in cork to Leeuwenhoek seeing living cells. A unicellular organism is one cell doing everything; a multicellular organism is many specialized cells working together.

Prokaryotic and eukaryotic cells

All cells share a membrane, cytoplasm, ribosomes, and DNA. The defining difference is the nucleus: eukaryotic cells have a membrane-bound nucleus and organelles and are larger; prokaryotic cells have neither and keep their DNA as a free loop, and are smaller. Bacteria and archaea are prokaryotic; animals, plants, fungi, and protists are eukaryotic.

Organelles and structure-function

The nucleus stores DNA and controls the cell. Mitochondria release energy (ATP) by respiration, with a folded inner membrane for surface area, so high-energy cells have many. Ribosomes build proteins; the rough ER (with ribosomes) makes and transports them; the Golgi packages them. Chloroplasts do photosynthesis. Plant cells also have a cell wall and a large central vacuole. Each structure suits its function.

The cell membrane and transport

The membrane is a phospholipid bilayer with proteins (the fluid mosaic model) and is selectively permeable. Passive transport (diffusion, osmosis, facilitated diffusion) moves substances down the gradient with no energy; active transport moves them up the gradient using ATP. Tonicity decides water movement: hypotonic (water in, cell swells), isotonic (no change), hypertonic (water out, cell shrinks).

The four macromolecules

Carbohydrates (sugars) are quick energy; lipids (glycerol and fatty acids) are long-term storage and membranes; proteins (amino acids) are the versatile workhorses whose shape sets their function; nucleic acids (nucleotides) store and carry genetic information as DNA and RNA. Nitrogen marks proteins and nucleic acids; phosphorus marks nucleic acids.

Enzymes

An enzyme is a protein catalyst that lowers activation energy and is not used up. Its active site fits only its substrate (lock and key), making it specific. Rate rises with temperature to an optimum, then falls as heat denatures the enzyme; each enzyme has an optimum pH too. More substrate raises the rate until all active sites are busy.

The cells and cellular processes content on the North Carolina Biology EOC covers the three-part cell theory and the difference between unicellular and multicellular life; the comparison of prokaryotic cells (no nucleus, no membrane-bound organelles, small) with eukaryotic cells (membrane-bound nucleus and organelles, larger), noting that all cells share a membrane, cytoplasm, ribosomes, and DNA; the structure and function of organelles (the nucleus controlling the cell, mitochondria releasing ATP with a folded inner membrane, ribosomes and rough ER making proteins, the Golgi packaging them, chloroplasts doing photosynthesis, and the plant-only wall and large vacuole); the fluid mosaic membrane and how it controls transport by passive means (diffusion, osmosis, facilitated diffusion, down the gradient, no energy) versus active transport (up the gradient, using ATP), with tonicity setting the direction of water movement; the four macromolecules (carbohydrates from sugars for quick energy, lipids from glycerol and fatty acids for storage and membranes, proteins from amino acids whose folded shape sets their function, and nucleic acids from nucleotides storing genetic information); and enzymes as protein catalysts that lower activation energy, are not used up, fit their substrate by a lock-and-key active site, and have an optimum temperature and pH beyond which they denature. The recurring theme is that structure suits function at every level.

Check your knowledge

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

State the three parts of the cell theory. (3 marks)
Name the one feature that defines a eukaryotic cell and is absent from a prokaryotic cell. (1 mark)
State two features that all cells share. (2 marks)
A cell uses a lot of energy. Which organelle is abundant, and what does it do? (2 marks)
Name two structures found in a plant cell but not an animal cell. (2 marks)
State whether osmosis is active or passive transport, and why. (2 marks)
A cell is placed in a hypertonic solution. State the direction of water movement and the effect on the cell. (2 marks)
Name the monomer of proteins and of nucleic acids. (2 marks)
Explain how an enzyme speeds up a reaction and why high temperature reduces its activity. (2 marks)

Solutions

Q1: All living things are made of one or more cells; the cell is the basic unit of structure and function; all cells come from pre-existing cells.
Q2: A membrane-bound nucleus (eukaryotes also have other membrane-bound organelles).
Q3: Any two of: a cell membrane, cytoplasm, ribosomes, and DNA.
Q4: Mitochondria; they carry out cellular respiration, releasing energy as ATP.
Q5: Any two of: cell wall, chloroplasts, and a large central vacuole.
Q6: Passive, because it moves water down its concentration gradient (toward higher solute) and needs no energy.
Q7: Water moves out of the cell; the cell loses water and shrinks (an animal cell crenates).
Q8: Protein, amino acid; nucleic acid, nucleotide.
Q9: It lowers the activation energy (and is not used up), so the reaction proceeds faster. High temperature above the optimum denatures the enzyme, changing the active site's shape so the substrate no longer fits, reducing activity.

Sources & how we know this

North Carolina Standard Course of Study for Science — North Carolina Department of Public Instruction (2023)
End-of-Course (EOC) program — North Carolina Department of Public Instruction (2024)