NDA Biology · Cell Biology
Cell Organelles and Functions — the Chapter's Core
Organelles are the tiny working compartments of a eukaryotic cell — the mitochondrion makes energy, the lysosome digests, the endoplasmic reticulum transports and builds lipids, and three organelles (mitochondria, chloroplasts, nucleus) carry their own DNA.
Why this matters
This is the single biggest cluster in Cell Biology — 17 of 44 PYQs. Master the organelle table and you win a third of the chapter. The bank's three favourite facts: which organelles have their own DNA (mitochondria + chloroplast/plastid + nucleus), which one is the cell's digestive/suicide bag (lysosome), and the ER's split roles (rough = transport, smooth = lipids + detox). All EASY or MODERATE — pure named-fact recall.
Concept 1 of 7
The organelle map — who does what
Intuition
Before the detail, fix the one-line job of each organelle on a labelled cell. Almost every organelle question reduces to 'which one does X?' — so the map below is the highest-leverage thing in the chapter.
Definition
The working organelles and their signature jobs:
- Mitochondrion — the powerhouse; makes ATP (cellular respiration). Has its own DNA.
- Chloroplast / plastid — photosynthesis (plants); has its own DNA.
- Nucleus — holds the DNA; controls the cell.
- Ribosome — builds proteins (rRNA, no own DNA).
- Endoplasmic reticulum — transport network; smooth ER also makes lipids.
- Golgi body — packages and ships secretions.
- Lysosome — digests waste (hydrolytic enzymes).
- Vacuole — storage; osmoregulation in unicellular organisms.
Powerhouse (mitochondrion), digestion (lysosome), transport (ER), packaging (Golgi), control (nucleus).
| Organelle | Job |
|---|---|
| Mitochondrion | Makes ATP — the powerhouse |
| Chloroplast | Photosynthesis (plant cells) |
| Nucleus | Stores DNA, controls the cell |
| Ribosome | Protein synthesis |
| Endoplasmic reticulum | Transport; smooth ER makes lipids |
| Golgi body | Packaging and secretion |
| Lysosome | Intracellular digestion |
| Vacuole | Storage; water expulsion in unicellulars |
Practice this concept4 quick reps
Concept 2 of 7
Organelles with their own DNA
Intuition
Most organelles have no genome of their own — but three do: the mitochondrion, the chloroplast (plastid), and the nucleus. The mitochondrion and chloroplast also have their own ribosomes, because they were once free-living bacteria (endosymbiotic theory). This is the bank's most-repeated organelle fact.
Definition
Which organelles carry genetic material:
- Have their own DNA: mitochondria, chloroplasts / plastids, and the nucleus.
- Mitochondria + chloroplasts also have their own ribosomes and can make some of their own proteins (endosymbiotic theory).
- No own DNA encoding proteins: ribosomes (carry rRNA only — structural), Golgi bodies, plasma membrane, ER, lysosomes.
- The plasma membrane has NO nucleic acid at all (it is lipid + protein).
| Organelle | Own DNA? | Note |
|---|---|---|
| Mitochondrion | Yes | Own DNA + ribosomes; makes some proteins Mitochondria + chloroplasts are the 'has its own DNA AND ribosomes' pair. |
| Chloroplast / plastid | Yes | Own DNA + ribosomes (plant cells) |
| Nucleus | Yes | Holds the cell's main DNA |
| Ribosome | No | Carries rRNA (structural), not its own genome |
| Plasma membrane | No | No nucleic acid at all — lipid + protein 'Which organelle does NOT possess nucleic acid?' → plasma membrane. |
| Golgi body / ER / lysosome | No | No own genome |
Practice this conceptself-check · 4 quick reps
From the bank · past-year question
Which of the following organelles have their own DNA and ribosomes ?
[Q140 · Sep · 2025]
Ribosomes have rRNA, but no DNA genome
A ribosome contains rRNA, so 'does it have nucleic acid?' is yes — but it has no DNA genome encoding proteins. When the question asks which organelle lacks 'its own genetic material encoding proteins', the answer is the ribosome.
Plasma membrane has NO nucleic acid
Unlike the nucleus, chloroplast or ribosome, the plasma membrane is purely lipid + protein. In 'which does NOT possess nucleic acid', it is the answer.
Concept 3 of 7
Lysosomes — the digestive 'suicide bags'
Intuition
The lysosome is the cell's stomach and waste-disposal unit, packed with hydrolytic (digestive) enzymes. It breaks down ORGANIC material and worn-out parts, and can self-destruct the cell — earning the nickname 'suicide bag'.
Definition
Key lysosome facts the bank tests:
- Lysosomes are rich in hydrolytic (digestive) enzymes — lipases, proteases, nucleases.
- They perform intracellular digestion and are the cell's waste-disposal system.
- Nicknamed 'suicide bags' because their enzymes can digest the whole cell.
- They break down organic material — NOT 'all inorganic materials' (a false-statement trap).
| Fact about lysosomes | Correct? |
|---|---|
| Rich in hydrolytic (digestive) enzymes | True |
| Waste-disposal system of the cell | True |
| Called 'suicide bags' | True |
| They break down all INORGANIC materials | False Lysosomes digest ORGANIC matter — 'breaks down all inorganic materials' is the wrong statement. |
Practice this conceptself-check · 4 quick reps
From the bank · past-year question
Which one of the following organelles of mammalian cell is rich in hydrolytic enzymes?
[Q149 · Apr · 2019]
Lysosomes digest ORGANIC, not 'all inorganic'
A statement saying lysosomes 'break down all inorganic materials' is FALSE — their hydrolytic enzymes act on organic macromolecules (proteins, lipids, nucleic acids). Watch for this in 'which statement is NOT correct' questions.
Concept 4 of 7
Endoplasmic reticulum — transport, lipids, detox
Intuition
The endoplasmic reticulum (ER) is the cell's internal highway, moving materials around the cytoplasm. It comes in two flavours: rough ER (studded with ribosomes) and smooth ER. The smooth ER builds lipids and, in liver cells, detoxifies poisons.
Definition
The ER's roles, split by type:
- General role — the ER is the cell's transport system, moving materials through the cytoplasm and to the nucleus.
- Smooth ER (SER) — synthesises lipids; a defect here blocks lipid synthesis. Its specialised extra function is detoxification of toxic substances (e.g. in liver cells).
- Rough ER (RER) — studded with ribosomes; involved in protein synthesis.
| ER role | Which type | Note |
|---|---|---|
| Transport of materials | ER (general) | Moves substances through cytoplasm/nucleus |
| Lipid synthesis | Smooth ER | A cell that can't make lipids has a defective SER Can't synthesise lipids → the smooth ER is defective. |
| Detoxification | Smooth ER | The SER's 'additional' function (liver cells) SER's extra job = detoxification, not protein synthesis. |
| Protein synthesis | Rough ER | Ribosome-studded surface |
Practice this conceptself-check · 4 quick reps
From the bank · past-year question
One of the additional functions of Smooth Endoplasmic Reticulum (SER) is
[Q58 · Sep · 2018]
Smooth ER detoxifies; rough ER does proteins
The SER's 'additional function' is detoxification — NOT protein synthesis (that's the rough ER). Don't pick 'protein synthesis' for a smooth-ER question.
Concept 5 of 7
Vacuoles — storage and osmoregulation
Intuition
The vacuole is the cell's storage tank. In plants a single large central vacuole fills most of the cell and keeps it turgid; in unicellular organisms a contractile vacuole pumps out excess water. Vacuoles exist in animal cells too — just smaller.
Definition
Vacuole facts the bank tests:
- In plant cells, a large central vacuole may occupy up to 90% of the cell volume and provides turgidity and rigidity.
- In unicellular organisms (e.g. Amoeba, Paramecium), the contractile vacuole expels excess water and wastes — osmoregulation.
- Vacuoles are present in animal cells too (smaller and more numerous) — saying they are 'absent in animal cells' is FALSE.
| Vacuole fact | Correct? |
|---|---|
| Large central vacuole can be ~90% of a plant cell | True |
| Provides turgidity and rigidity in plants | True |
| Expels excess water in unicellular organisms | True (contractile vacuole) |
| Vacuoles are absent in animal cells | False Animal cells DO have vacuoles (smaller) — 'absent in animal cells' is the wrong statement. |
Practice this conceptself-check · 3 quick reps
From the bank · past-year question
Which one of the following cell organelles may play a role in expelling excess water and wastes in case of unicellular organisms?
[Q98 · Apr · 2020]
Vacuoles are NOT absent in animal cells
A common false statement says 'vacuoles are absent in animal cells'. Animal cells have vacuoles too — just smaller and more numerous than the plant central vacuole. Mark this statement as incorrect.
Concept 6 of 7
Plastids — chloroplast, chromoplast, leucoplast
Intuition
Plastids are plant-only organelles, and they come in three colours of job: green chloroplasts photosynthesise, coloured chromoplasts give flowers and fruits their hue, and colourless leucoplasts store food (starch, oil, protein).
Definition
The three plastid types:
- Chloroplast — green; carries out photosynthesis (has chlorophyll + its own DNA).
- Chromoplast — coloured (red/yellow/orange); gives colour to flowers and fruits.
- Leucoplast — colourless; stores starch, oil and protein granules.
| Plastid | Colour | Function |
|---|---|---|
| Chloroplast | Green | Photosynthesis |
| Chromoplast | Red/yellow/orange | Colour of flowers and fruits |
| Leucoplast | Colourless | Stores starch, oil and protein Stores starch + oil + protein granules → leucoplast (not chloroplast). |
Practice this concept3 quick reps
From the bank · past-year question
Which one of the following plant plastids stores starch, oil and protein granules?
[Q72 · Apr · 2022]
Storage plastid = leucoplast, not chloroplast
The colourless leucoplast is the storage plastid (starch, oil, protein). The green chloroplast photosynthesises. Don't pick chloroplast for a storage question. (There is no 'xanthoplast' — a distractor.)
Concept 7 of 7
Red blood cells — a cell with almost no organelles
Intuition
The mature mammalian red blood cell is a famous exception: to pack in as much haemoglobin as possible, it throws out its nucleus, mitochondria and endoplasmic reticulum. It is essentially a bag of haemoglobin.
Definition
Mature mammalian RBC facts:
- A mature RBC has no nucleus, no mitochondria and no endoplasmic reticulum.
- Losing these organelles maximises space for haemoglobin and oxygen-carrying capacity.
- Because it has no mitochondria, the RBC makes its energy by anaerobic glycolysis — it doesn't consume the oxygen it carries.
| RBC component | Present? |
|---|---|
| Nucleus | Absent |
| Mitochondria | Absent |
| Endoplasmic reticulum | Absent Mature RBC = NO nucleus, NO mitochondria, NO ER — maximises haemoglobin. |
| Haemoglobin | Present — the cell is packed with it |
Practice this concept3 quick reps
From the bank · past-year question
Red blood cells (RBCs) have
[Q67 · Apr · 2017]
Mature RBC = no nucleus AND no mitochondria
Distractors say the RBC keeps a nucleus or mitochondria. The mature mammalian RBC has neither, nor an ER — it sacrifices organelles for maximum haemoglobin.
Summary — formulas & gotchas at a glance
A revision cheat-sheet for the formulas and gotchas above. Click any concept name to jump back to its full explanation.
Reference tables (7)
The organelle map — who does what8 rows
| Organelle | Job |
|---|---|
| Mitochondrion | Makes ATP — the powerhouse |
| Chloroplast | Photosynthesis (plant cells) |
| Nucleus | Stores DNA, controls the cell |
| Ribosome | Protein synthesis |
| Endoplasmic reticulum | Transport; smooth ER makes lipids |
| Golgi body | Packaging and secretion |
| Lysosome | Intracellular digestion |
| Vacuole | Storage; water expulsion in unicellulars |
Organelles with their own DNA6 rows
| Organelle | Own DNA? | Note |
|---|---|---|
| Mitochondrion | Yes | Own DNA + ribosomes; makes some proteins Mitochondria + chloroplasts are the 'has its own DNA AND ribosomes' pair. |
| Chloroplast / plastid | Yes | Own DNA + ribosomes (plant cells) |
| Nucleus | Yes | Holds the cell's main DNA |
| Ribosome | No | Carries rRNA (structural), not its own genome |
| Plasma membrane | No | No nucleic acid at all — lipid + protein 'Which organelle does NOT possess nucleic acid?' → plasma membrane. |
| Golgi body / ER / lysosome | No | No own genome |
Lysosomes — the digestive 'suicide bags'4 rows
| Fact about lysosomes | Correct? |
|---|---|
| Rich in hydrolytic (digestive) enzymes | True |
| Waste-disposal system of the cell | True |
| Called 'suicide bags' | True |
| They break down all INORGANIC materials | False Lysosomes digest ORGANIC matter — 'breaks down all inorganic materials' is the wrong statement. |
Endoplasmic reticulum — transport, lipids, detox4 rows
| ER role | Which type | Note |
|---|---|---|
| Transport of materials | ER (general) | Moves substances through cytoplasm/nucleus |
| Lipid synthesis | Smooth ER | A cell that can't make lipids has a defective SER Can't synthesise lipids → the smooth ER is defective. |
| Detoxification | Smooth ER | The SER's 'additional' function (liver cells) SER's extra job = detoxification, not protein synthesis. |
| Protein synthesis | Rough ER | Ribosome-studded surface |
Vacuoles — storage and osmoregulation4 rows
| Vacuole fact | Correct? |
|---|---|
| Large central vacuole can be ~90% of a plant cell | True |
| Provides turgidity and rigidity in plants | True |
| Expels excess water in unicellular organisms | True (contractile vacuole) |
| Vacuoles are absent in animal cells | False Animal cells DO have vacuoles (smaller) — 'absent in animal cells' is the wrong statement. |
Plastids — chloroplast, chromoplast, leucoplast3 rows
| Plastid | Colour | Function |
|---|---|---|
| Chloroplast | Green | Photosynthesis |
| Chromoplast | Red/yellow/orange | Colour of flowers and fruits |
| Leucoplast | Colourless | Stores starch, oil and protein Stores starch + oil + protein granules → leucoplast (not chloroplast). |
Red blood cells — a cell with almost no organelles4 rows
| RBC component | Present? |
|---|---|
| Nucleus | Absent |
| Mitochondria | Absent |
| Endoplasmic reticulum | Absent Mature RBC = NO nucleus, NO mitochondria, NO ER — maximises haemoglobin. |
| Haemoglobin | Present — the cell is packed with it |
Watch out for (7)
- Ribosomes have rRNA, but no DNA genome→ Organelles with their own DNA
- Plasma membrane has NO nucleic acid→ Organelles with their own DNA
- Lysosomes digest ORGANIC, not 'all inorganic'→ Lysosomes — the digestive 'suicide bags'
- Smooth ER detoxifies; rough ER does proteins→ Endoplasmic reticulum — transport, lipids, detox
- Vacuoles are NOT absent in animal cells→ Vacuoles — storage and osmoregulation
- Storage plastid = leucoplast, not chloroplast→ Plastids — chloroplast, chromoplast, leucoplast
- Mature RBC = no nucleus AND no mitochondria→ Red blood cells — a cell with almost no organelles
Drill every past-year question on this subtopic
17 questions from the bank — paginated, with cart and Word-export support.