Skip to content
Marlbridge
Free trial

Flashcards · 9700 · A Level Topic 15

Control and coordination (A Level) flashcards

13 cards on A Level Topic 15, subtopics 15.1 to 15.2. Pick a subtopic or study them all.

Study mode needs JavaScript. Every card is listed below, so you can still cover the answers and test yourself.

All 13 cards

For a quick read-through or printing. Cover the right-hand side to test yourself.

15.1 Control and coordination in mammals

Nervous vs endocrine communication
Nervous: action potentials along neurones; fast, short-lived, localised. Endocrine: hormones from ductless glands carried in blood; slower, longer-lasting, often widespread.
Resting potential: value and how it is maintained
About −70 mV, inside negative. The Na⁺–K⁺ pump moves 3 Na⁺ out and 2 K⁺ in; K⁺ diffuses out through leak channels more than Na⁺ leaks in.
Ion movements during an action potential
Depolarisation: voltage-gated Na⁺ channels open, Na⁺ in (to about +40 mV). Repolarisation: Na⁺ channels close, voltage-gated K⁺ channels open, K⁺ out. Hyperpolarisation: K⁺ channels slow to close.
Roles of the refractory period
Keeps action potentials discrete, makes them travel in one direction only, and sets the maximum frequency (1 ÷ refractory period in seconds).
Saltatory conduction
Myelin from Schwann cells insulates the axon, so depolarisation happens only at nodes of Ranvier. Local circuits stretch between nodes and the action potential jumps from node to node, so conduction is faster.
Transmission at a cholinergic synapse
Action potential → voltage-gated Ca²⁺ channels open → Ca²⁺ in → vesicles release ACh by exocytosis → ACh binds receptors → ligand-gated Na⁺ channels open → depolarisation. Acetylcholinesterase hydrolyses ACh; choline is recycled.
Which bands shorten when a sarcomere contracts?
The sarcomere (Z line to Z line), I band and H zone shorten. The A band and the lengths of the actin and myosin filaments stay the same.
Sliding filament mechanism
Ca²⁺ binds troponin, which moves tropomyosin to expose binding sites on actin. Myosin heads bind (cross-bridges), release ADP + Pi and pull actin (power stroke). ATP binds to detach the head, and its hydrolysis re-cocks it.
Troponin vs tropomyosin
Troponin binds Ca²⁺. Tropomyosin blocks the myosin-binding sites on actin until troponin changes shape and moves it.

15.2 Control and coordination in plants

How does a Venus fly trap close?
Bending sensory hairs causes receptor potentials; repeated stimulation within a short time triggers an action potential across the lobes. A rapid change in cell turgor flips the lobes from convex to concave, closing the trap.
How does auxin cause cell elongation?
Auxin stimulates proton pumps, so H⁺ is pumped into the cell wall and acidifies it. Expansins loosen the cellulose; water enters by osmosis and the cell elongates.
Role of gibberellin in seed germination
The embryo releases gibberellin, which acts on the aleurone layer: DELLA proteins are broken down, the amylase gene is transcribed, and amylase hydrolyses starch in the endosperm to maltose for the embryo.
Auxin vs gibberellin
Auxin: elongation by acid loosening of cell walls. Gibberellin: germination (and stem elongation) by removing DELLA proteins so genes are transcribed.

Revise Control and coordination further