Organelles and compartmentalization

A structure inside a cell that carries out a **specific function** (a 'little organ').

An organelle **surrounded by its own membrane** (e.g. nucleus, mitochondrion, Golgi apparatus).

It **holds the cell's DNA** and **controls** the cell's activities.

It is the site of **aerobic respiration**, releasing **energy (ATP)** for the cell.

It **builds proteins** by joining amino acids (protein synthesis).

The **ribosome** — it is the only organelle without a membrane.

It **makes and transports proteins** (its surface is studded with ribosomes).

It **modifies, packages and sorts proteins** into **vesicles** for transport or export.

The **Golgi apparatus**.

**Ribosomes / rough ER → Golgi apparatus → vesicle** (build → package → transport out).

If it is a **membrane-bound organelle** — prokaryotes have no membrane-bound organelles, only ribosomes.

Its correct **name** AND a **specific function** (a vague function scores no marks).

**Dividing the inside of the cell into separate membrane-bound spaces** (compartments) — most are the membrane-bound organelles.

An organelle surrounded by its own membrane (e.g. nucleus, mitochondrion, lysosome), creating a **compartment** separate from the cytoplasm.

It **separates incompatible reactions** (or: concentrates enzymes/substrates; encloses harmful substances; adds membrane surface; keeps local optimum conditions).

The molecules for a reaction are gathered in a **small space**, so the reaction happens **faster**.

The membrane keeps the enzymes **separate**, so they **cannot digest or damage the rest of the cell**.

They provide extra **membrane surface area** for membrane-bound reactions (e.g. the folded inner membrane of a mitochondrion).

**More of an organelle = more of its job** — a cell that does a lot of a process has a lot of the organelle that carries it out.

A lot of **aerobic respiration** to release **ATP** — so the cell is very **active** (e.g. a muscle cell).

A lot of **making and processing molecules** (proteins, lipids, detoxification) — e.g. a liver cell.

**Link structure to function** — state what organelle X does, then say the cell does a **lot** of that process.

The mark is for the **link** between the feature and the cell's function, not for the label itself.

**No** — they have no membrane-bound organelles, so their reactions share one space (the cytoplasm).

**DNA, cytoplasm, a plasma membrane and ribosomes** — present in both prokaryotes and eukaryotes.

A **structure inside a cell** that carries out a particular job (e.g. nucleus, mitochondrion, chloroplast).

A cell with **no nucleus and no membrane-bound organelles**; its DNA is free in the cytoplasm (e.g. a bacterium).

A cell that keeps its DNA inside a **nucleus** and contains **membrane-bound organelles** (e.g. animal, plant, fungal cells).

The **nucleus** — prokaryotes have none (DNA free in the cytoplasm); eukaryotes enclose their DNA in a nucleus.

A **chloroplast** (also acceptable: large central vacuole, or cellulose cell wall).

**Ribosomes** (also: plasma membrane, DNA, cytoplasm).

A **cellulose cell wall**, **chloroplasts** and a **large central vacuole**.

**Yes** — both are eukaryotic, so both have a nucleus, mitochondria, ribosomes and a plasma membrane.

Because plants (cellulose), fungi (chitin) and most bacteria (peptidoglycan) all have cell walls — the material differs.

A **fungal cell** — eukaryotic with a wall, but no chloroplast (so not a plant).

No nucleus → **prokaryote**; nucleus + chloroplast → **plant**; nucleus, no chloroplast → **animal**.

**Eukaryotic** cells are larger (about 10–100 µm); prokaryotes are smaller (about 1–5 µm).

Mitochondria and chloroplasts began as **free-living prokaryotes** that were **engulfed** by a host cell and **survived inside it**, becoming organelles.

'**Endo**' = inside, '**symbiosis**' = living together — one cell living permanently inside another, with both benefiting.

An **aerobic (oxygen-using) bacterium** — it carries out aerobic respiration to release energy for the host.

A **photosynthetic bacterium** — it makes food using light, in plant and algal cells.

**Engulf** the bacterium -> it **survives** inside -> the relationship **benefits both** -> the bacterium is **kept** and becomes an organelle.

**Endocytosis** — the host membrane folded around the bacterium, so it ended up inside a vesicle.

Each organelle has its **own DNA**, its **own 70S ribosomes**, a **double membrane**, and divides by **binary fission**.

**70S** — the smaller, bacterial type. The host cell's cytoplasm uses larger **80S** ribosomes.

The **inner** membrane is the bacterium's own; the **outer** membrane came from the host's vesicle when the bacterium was engulfed.

The cytoplasm uses **80S** ribosomes, but the chloroplast keeps the **70S** ribosomes of its free-living bacterial ancestor.

By **binary fission** — splitting in two on their own, just like the free-living bacteria they descended from.

Only some cells engulfed the **photosynthetic** partner (-> chloroplast); the **aerobic** partner (-> mitochondrion) was engulfed by the ancestor of nearly all eukaryotes.