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.

All Cell Biology notes NDA Biology strategy

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

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

1.
Which organelle is the powerhouse of the cell?
2.
Which organelle digests waste?
3.
Which organelle is the cell's transport network?
4.
Which organelle controls the cell and stores DNA?

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

Try it yourself

Which two organelles have BOTH their own DNA and their own ribosomes?

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

1.
Name three organelles with their own DNA.
2.
Which two organelles have their own DNA AND ribosomes?
3.
Which organelle has NO nucleic acid at all?
4.
Mitochondria can produce their own ___.

From the bank · past-year question

Example 2Cell BiologyEASY

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.

Drill 6 more on organelles with their own dna

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

Try it yourself

Which statement about lysosomes is NOT correct: (a) waste-disposal system, (b) they break down all inorganic materials, (c) called 'suicide bags'?

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

1.
Which organelle is rich in hydrolytic enzymes?
2.
Where in the cell are digestive enzymes found?
3.
What is the lysosome's nickname?
4.
Do lysosomes break down organic or inorganic material?

From the bank · past-year question

Example 3Cell BiologyEASY

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.

Drill 2 more on lysosomes — the digestive 'suicide bags'

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

Try it yourself

A cell cannot synthesise lipids. Which organelle is most likely defective, and what is that organelle's other special function?

Practice — Level 1 (4 reps)

Quick reps to lock in the method. Try each, then check.

1.
Which organelle moves materials around the cytoplasm and nucleus?
2.
Which ER synthesises lipids?
3.
What is the smooth ER's additional function?
4.
Which ER is involved in protein synthesis?

From the bank · past-year question

Example 4Cell BiologyMODERATE

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.

Drill 2 more on endoplasmic reticulum — transport, lipids, detox

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

Try it yourself

Which organelle helps a unicellular organism expel excess water and wastes?

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

1.
Which organelle expels excess water in unicellular organisms?
2.
What gives a plant cell turgidity?
3.
Are vacuoles absent in animal cells?

From the bank · past-year question

Example 5Cell BiologyMODERATE

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.

Drill 1 more on vacuoles — storage and osmoregulation

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

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

1.
Which plastid stores starch, oil and protein?
2.
Which plastid carries out photosynthesis?
3.
Which plastid colours flowers and fruits?

From the bank · past-year question

Example 6Cell BiologyMODERATE

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

Practice — Level 1 (3 reps)

Quick reps to lock in the method. Try each, then check.

1.
Does a mature RBC have a nucleus?
2.
Which three organelles does a mature mammalian RBC lack?
3.
Why does the RBC shed its organelles?

From the bank · past-year question

Example 7Cell BiologyEASY

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

Mastery check — 5 interleaved questions

Try each one before clicking. Questions are interleaved across the concepts above, not grouped — interleaving sharpens transfer.

Example 1Cell BiologyEASY

Mitochondria are able to produce their own

[Q79 · Sep · 2019]

Example 2Cell BiologyEASY

Which one of the following statements about lysosomes is NOT correct ?

[Q51 · Sep · 2024]

Example 3Cell BiologyEASY

Movement of materials to different parts of cytoplasm and nucleus is generally carried out by

[Q69 · Apr · 2021]

Example 4Cell BiologyMODERATE

Which one of the following statements about 'vacuoles' is

\textbf{\text{not}}

correct?

[Q73 · Apr · 2022]

Example 5Cell BiologyMODERATE

Which one of the following cell organelles does NOT possess its own genetic material encoding proteins?

[Q52 · Apr · 2019]

Drill every past-year question on this subtopic

17 questions from the bank — paginated, with cart and Word-export support.

Drill the 17 questions