Biology  by Bradford cramly support
BIOLOGY BY BRADFORD · IB BIOLOGY HL C2.1 · AP BIOLOGY UNIT 4

Signal Lab Lite

Five stations. Change the settings, watch the signal, hit the checkpoints.

0 / 5 checkpoints
IB C2.1.1AP 4.1 · 4.2

Lock & ligand

A receptor has a binding site for one specific ligand. Match them, then change the concentration.

RECEPTOR
LIGAND
LIGAND CONCENTRATION
AFFINITY · Kd
lower Kd = tighter binding
CHECKPOINT
    KEY IDEAS
    • Binding site is complementary to one ligand only.
    • More ligand → more receptors occupied.
    • Binding changes the receptor's shape → signal on.
    IB C2.1.2C2.1.14AP 4.1 · 4.5

    Quorum sensing

    Vibrio fischeri glows only when crowded. Compare the squid's light organ with the open ocean.

    ENVIRONMENT
    AUTOINDUCER MADE PER CELL
    POSITIVE FEEDBACK
    CHECKPOINT
      HOW IT WORKS
      • Every cell releases autoinducer; more cells → higher concentration.
      • Above threshold it binds a receptor (LuxR) → lux genes on → light.
      • In open water the autoinducer diffuses away, so no glow.
      IB C2.1.6C2.1.7C2.1.12AP 4.2

      Inside or outside?

      Predict where each ligand's receptor is, then send it.

      LIGAND
      THIS CELL HAS RECEPTORS FOR
      YOUR PREDICTION
      Choose a ligand, make a prediction, then send it.
      CHECKPOINT
        TWO KINDS OF RECEPTOR
        • Hydrophilic ligand → stays outside → transmembrane receptor.
        • Hydrophobic steroid → crosses membrane → intracellular receptor → binds DNA → transcription.
        IB C2.1.7–C2.1.11AP 4.2 · 4.3 · 4.4

        Pathway workshop

        Three receptors, three ways to pass a message inside the cell.

        ACETYLCHOLINE RELEASED
        ACETYLCHOLINESTERASE
        NAME THE HORMONE
        HORMONE MOLECULES BOUND
        BREAK IT
        INSULIN IN BLOOD
        RECEPTOR
        CHECKPOINT
          RECEPTION → TRANSDUCTION → RESPONSE
          • ACh: channel opens → Na⁺ in → depolarisation.
          • Adrenaline: G protein → cAMP (second messenger) → glucose released.
          • Insulin: tyrosines phosphorylated → GLUT4 moves to membrane.
          IB C2.1.13C2.1.14AP 4.5

          Feedback loops

          Negative feedback cancels a change. Positive feedback amplifies it.

          RESPONSE STRENGTH
          HYPOTHALAMUS SENSITIVITY TO OESTRADIOL
          PROGESTERONE
          CHECKPOINT
            TWO KINDS OF FEEDBACK
            • Negative: output reduces the stimulus → back to the set point.
            • Positive: output boosts the stimulus → surge until an event ends it.
            IB C2.1AP Unit 4

            Quick check

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