What does the nucleus do?

It stores the cell's DNA as chromatin and is the site of DNA replication and transcription. It is enclosed by a double-membrane nuclear envelope perforated by nuclear pores that control what enters and leaves.

What is the nucleolus and what happens there?

A dense region inside the nucleus, without its own membrane, where ribosomal RNA is transcribed and ribosomal subunits are assembled before being exported to the cytoplasm.

What are ribosomes made of and what do they do?

They are built from ribosomal RNA and proteins, and they are the site of translation, where messenger RNA is read to build polypeptides. They are not membrane-bound, so they are not an exception to the rule that prokaryotes lack membrane-bound organelles — every cell has ribosomes.

How do eukaryotic and prokaryotic ribosomes differ?

Eukaryotic cytosolic ribosomes are 80S, built from 60S and 40S subunits. Prokaryotic ribosomes are 70S, built from 50S and 30S subunits — the difference many antibiotics exploit.

What does the rough endoplasmic reticulum do?

Studded with ribosomes on its cytosolic face, it synthesizes and folds proteins destined for secretion, for the plasma membrane or for lysosomes, and begins adding carbohydrate groups.

What does the smooth endoplasmic reticulum do?

It synthesizes lipids and steroid hormones, detoxifies drugs and other compounds, and stores calcium ions. It has no ribosomes on its surface.

What does the Golgi apparatus do?

It receives proteins and lipids from the ER at its cis face, then modifies, sorts and packages them into vesicles that leave from its trans face for their final destinations.

A membrane-bound vesicle containing acid hydrolase enzymes that work best at low pH. It digests macromolecules, engulfed material and worn-out organelles, the last process being autophagy.

What does a peroxisome do?

It breaks down fatty acids by beta-oxidation and detoxifies various compounds, generating hydrogen peroxide as it does so. Its enzyme catalase then converts that hydrogen peroxide into water and oxygen.

What is the structure and function of a mitochondrion?

It has an outer membrane and a folded inner membrane whose folds are called cristae. The citric acid cycle runs in the matrix and oxidative phosphorylation occurs at the inner membrane, generating most of the cell's ATP.

What is the structure and function of a chloroplast?

Found in plants and algae, it has a double membrane plus internal thylakoid membranes stacked into grana. The light-dependent reactions occur in the thylakoid membranes and the Calvin cycle occurs in the surrounding stroma.

Why do mitochondria and chloroplasts have their own DNA and ribosomes?

The endosymbiotic theory holds that both descend from free-living prokaryotes taken up by an ancestral eukaryotic cell. They retain circular DNA, 70S ribosomes and a double membrane, and divide independently of the cell.

What does the large central vacuole do in a plant cell?

It stores water, ions and waste products, and the pressure it exerts against the cell wall creates turgor pressure, which keeps non-woody plant tissue rigid.

What are the three components of the eukaryotic cytoskeleton?

Microfilaments made of actin, intermediate filaments, and microtubules made of tubulin. Together they give the cell shape, anchor organelles and provide tracks for movement inside the cell.

What is the centrosome and what does it do?

It is the main microtubule-organizing center of an animal cell and contains a pair of centrioles. It organizes the spindle apparatus that separates chromosomes during cell division.

How is the plasma membrane structured?

As a phospholipid bilayer with embedded and attached proteins, cholesterol and carbohydrate chains — the fluid mosaic model. It is selectively permeable, controlling what enters and leaves the cell.

What are cell walls made of in plants, fungi and bacteria?

Cellulose in plants, chitin in fungi and peptidoglycan in bacteria. All three lie outside the plasma membrane and give structural support; animal cells have no cell wall.

How are eukaryotic cilia and flagella built?

From microtubules in a 9+2 arrangement — nine outer doublets surrounding two central singlets — enclosed by the plasma membrane. Bending is driven by dynein motor proteins.

Which eukaryotic structures are bounded by a double membrane?

The nucleus, the mitochondrion and the chloroplast. Lysosomes, peroxisomes, vacuoles, the Golgi apparatus and transport vesicles are each bounded by a single membrane.

Which organelles make up the endomembrane system?

The nuclear envelope, endoplasmic reticulum, Golgi apparatus, lysosomes, vacuoles, transport vesicles and the plasma membrane. Mitochondria and chloroplasts are not part of it.

What is the difference between cytoplasm and cytosol?

Cytoplasm is everything inside the plasma membrane except the nucleus, organelles included. Cytosol is only the fluid portion in which those organelles are suspended.

Where is a prokaryote's DNA located?

In the nucleoid, an irregular region of the cytoplasm with no surrounding membrane, holding a single circular chromosome. Many bacteria also carry small extra circular DNA molecules called plasmids.

Which structures do prokaryotic cells lack?

A membrane-bound nucleus and all membrane-bound organelles, including mitochondria, chloroplasts, endoplasmic reticulum, Golgi apparatus and lysosomes. They do have ribosomes, a plasma membrane and usually a cell wall.

Which structures are found in animal cells but not in the cells of most higher plants?

Centrioles, which organize the spindle in animal cells; the cells of most higher plants build spindles without them.

Which structures do plant cells have that animal cells lack?

A cellulose cell wall, chloroplasts, and a large central vacuole that maintains turgor pressure.

What is the difference between prokaryotic and eukaryotic cells?

Prokaryotic cells have no membrane-bound nucleus and no membrane-bound organelles; their DNA sits in a region called the nucleoid and their ribosomes are 70S. Eukaryotic cells enclose their DNA in a nucleus, contain organelles such as mitochondria and the Golgi apparatus, and use 80S cytosolic ribosomes.

Which organelles do plant cells have that animal cells do not?

Plant cells have a cellulose cell wall, chloroplasts for photosynthesis, and a large central vacuole that maintains turgor pressure. Animal cells in turn have centrioles, which are absent from the cells of most higher plants.

What is the best way to memorize organelles and their functions?

Learn them as structure-function pairs and rehearse both directions, since exams ask 'what does the Golgi do?' as often as 'which organelle packages proteins?'. Cram can turn a biology chapter or your lecture notes into flashcards with AI and schedule spaced reviews so the pairings hold.

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Cell Organelles flashcards

This deck pairs each cell structure with what it does: nucleus and nucleolus, ribosomes, rough and smooth endoplasmic reticulum, Golgi apparatus, lysosomes, peroxisomes, mitochondria, chloroplasts, vacuoles, the cytoskeleton, centrosomes, the plasma membrane and cell walls. It also includes the comparison cards students are most often asked for: which organelles have a double membrane, which structures separate plant cells from animal cells, and how prokaryotic cells differ from eukaryotic ones.

Cell structure is the foundation the rest of an introductory biology course is built on, and exam questions rarely stop at naming a part. They ask you to trace a secreted protein from ribosome to rough ER to Golgi to vesicle, to predict which organelle a given cell type would have in abundance, or to explain why mitochondria and chloroplasts carry their own DNA. Having structure and function locked together is what makes those questions straightforward.

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How to study this deck

Trace the secretory pathway as one sequence rather than as separate cards: ribosome on the rough ER, transport vesicle, Golgi cis face, trans face, secretory vesicle, plasma membrane. Exams test that order far more often than the individual definitions.
For each organelle, ask which cell type would have unusually many — muscle cells and mitochondria, pancreatic acinar cells and rough ER, liver cells and smooth ER, white blood cells and lysosomes. That reasoning step is exactly what applied questions require.
Keep the three double-membrane structures (nucleus, mitochondrion, chloroplast) as one grouped card and connect them to endosymbiotic theory, since the same three facts answer several different question types.

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