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Cell Organelles

The job of each organelle, how plant and animal cells differ, and how organelles work together to make and export a protein.

Module 1: Cells as the Basis of Life 4 min read Updated 13 questions Jump to quiz Feedback

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In short: Organelles are the small structures inside a cell that each do a job. The nucleus holds the DNA and controls the cell, mitochondria release energy by respiration, and ribosomes make proteins. Plant cells also have a cell wall, chloroplasts and a large vacuole.

Starting point: what you already know

  • Cells are the basic unit of life (see the previous chapter).
  • Eukaryotic cells have a nucleus. Prokaryotic cells do not.
  • Plants make food by photosynthesis and all living things release energy by respiration.

The organelles and their jobs

An organelle is a small structure inside a cell with a particular job.

Organelle Job City match
Nucleus Holds DNA, controls the cell. The nucleolus inside makes ribosomes City hall
Cell membrane Controls what enters and leaves Walls and gates
Cytoplasm (cytosol) Jelly-like fluid where many reactions happen The streets and air
Mitochondria Aerobic respiration: release energy from glucose as ATP Power stations
Ribosomes Make proteins Factories
Rough endoplasmic reticulum (RER) Membranes covered in ribosomes. Carries and folds proteins Factory roads
Smooth endoplasmic reticulum (SER) Makes lipids (fats) and breaks down toxins Chemical plant
Golgi body (Golgi apparatus) Modifies, packs and sends out proteins in vesicles Post office
Vesicles Small membrane bags that carry substances Delivery vans
Lysosomes Hold enzymes that break down worn-out parts and invaders Recycling centre
Cytoskeleton Protein fibres that give shape and move things around Scaffolding and rail lines

Only in plant cells

Structure Job
Cell wall (made of cellulose) Strong outer layer. Supports the cell and stops it bursting
Chloroplasts Photosynthesis. Contain green chlorophyll
Large central vacuole Stores water and salts. Pushes outward to keep the cell firm (turgid)

Animal cells may have small vacuoles, and they have centrioles, which help in cell division. Most plant cells do not.

Animal cell vacuole Plant cell
The plant cell has a thick cell wall (the outer frame), a large vacuole and chloroplasts (green). Both cells have a nucleus, a membrane and mitochondria (orange).

Working together: making and exporting a protein

Cells in your pancreas make the hormone insulin and send it into the blood. Follow its path:

  1. Nucleus: the gene for insulin is copied into a message (mRNA), which leaves through a nuclear pore.
  2. Ribosomes on the RER: read the message and build the protein.
  3. RER: the protein is folded and carried along inside the membranes.
  4. Vesicle: buds off and carries it to the Golgi body.
  5. Golgi body: finishes and packs the protein into a new vesicle.
  6. Cell membrane: the vesicle joins the membrane and releases insulin outside the cell (exocytosis).
  7. Mitochondria supply the energy (ATP) for every step.
Organelles
Control
  • Nucleus: DNA
  • Nucleolus: makes ribosomes
Energy
  • Mitochondria: respiration
  • Chloroplasts: photosynthesis
Making things
  • Ribosomes: proteins
  • Rough ER: folds and carries
  • Smooth ER: lipids
  • Golgi: packs and ships
Other
  • Membrane: gatekeeper
  • Lysosomes: digest
  • Cell wall and vacuole: support

Quick summary

  • The nucleus holds DNA and controls the cell. Mitochondria release energy by respiration. Ribosomes make proteins.
  • Proteins for export go: ribosome on RER, to vesicle, to Golgi, to vesicle, to the membrane.
  • Plant cells also have a cellulose cell wall, chloroplasts and a large central vacuole.
  • Plants have mitochondria too.
  • Cells have more of the organelles their job needs.

Quiz

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  1. Which organelle releases energy from glucose in aerobic respiration?

    1. A Chloroplast
    2. B Mitochondrion
    3. C Ribosome
    4. D Golgi body
    Show answer

    B: Mitochondrion

    Mitochondria carry out aerobic respiration and make ATP.

  2. Where are proteins made?

    1. A Nucleus
    2. B Lysosomes
    3. C Ribosomes
    4. D Vacuole
    Show answer

    C: Ribosomes

    Ribosomes join amino acids into proteins.

  3. Which organelle packages proteins into vesicles to leave the cell?

    1. A Smooth ER
    2. B Golgi body
    3. C Nucleolus
    4. D Cell wall
    Show answer

    B: Golgi body

    The Golgi body modifies and packs proteins for export.

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