Complete notes for A-Levels BiologyCIE according to syllabus objectives - updated 2025
Biology (9700) notes A-Level - Control and coordination (CIE)
Control and Coordination in mammals
● The endocrine gland that produces hormones → collectively
endocrine system.
● The Central Nervous System consists of brain and spinal cords
and the peripheral nervous system consists of all the nerves in
the body.
A2
● Nervous system: Brain, spinal cord, electrical impulse, nerves,
muscle or glands, very fast and short.
● Endocrine system: Glands, chemical hormones, target cells in
specific tissues, slower and longer, until hormones break down.
s
● Sensory neurons carry impulses from CNS to the effector.
am
Relay (intermediate) neurons are found entirely within the CNS
and connect sensory and motor neurons. Motor neurons carry
impulses from CNS to the effector.
Ex
● Motor neurons: Have a large cell body at one end that lies
within the spinal cord or brain. A nucleus that is always that is
always in its cell body. Many highly branched dendrites extend
ck
from the cell body providing a large surface area for the axon
terminals of other neurons.
ra
C
Picture from Biology A-Level CourseBook
CRACK EXAMS A2 1
, Complete notes for A-Levels BiologyCIE according to syllabus objectives - updated 2025
● Sensory neurons: Almost same but has a cell body that
branches off in the middle of the cell (it maybe near the
source of stimuli or in a swelling of a spinal nerve known as
ganglion)
A2
Picture from Biology A-Level CourseBook
s
● Role of sensory receptor cells in detecting stimuli: Cell
responds to stimulus → receptor cell transducers → convert
am
energy in one form into energy in electrical impulse. When
stimulated it's depolarised. If the stimulus is very weak, the
cells are not sufficiently depolarised and the sensory neuron is
Ex
not activated to send impulses. If strong, → activated →
impulse to CNS.
● Sequence of events that result in an action potential in sensory
ck
neurons: (Example of chemoreceptor cell in a human taste bud).
Chemoreceptor in taste buds that detect salt (NaCl) respond
directly to sodium ions. Salt eaten → Sodium ions diffuse
ra
through highly selective channel proteins in the cell surface
membranes of the microvilli of the chemoreceptor cell
C
membrane. The increase in positive charge inside the cell is
known as receptor potential. If sufficient stimulation by
sodium ions and sufficient depolarisation of membrane, the
receptor potential becomes large enough to stimulate
voltage-gated calcium ion channel proteins to open → calcium
ions enter cytoplasm of the chemoreceptor cell and stimulate
exocytosis of vesicles containing neurotransmitter from the
CRACK EXAMS A2 2
Biology (9700) notes A-Level - Control and coordination (CIE)
Control and Coordination in mammals
● The endocrine gland that produces hormones → collectively
endocrine system.
● The Central Nervous System consists of brain and spinal cords
and the peripheral nervous system consists of all the nerves in
the body.
A2
● Nervous system: Brain, spinal cord, electrical impulse, nerves,
muscle or glands, very fast and short.
● Endocrine system: Glands, chemical hormones, target cells in
specific tissues, slower and longer, until hormones break down.
s
● Sensory neurons carry impulses from CNS to the effector.
am
Relay (intermediate) neurons are found entirely within the CNS
and connect sensory and motor neurons. Motor neurons carry
impulses from CNS to the effector.
Ex
● Motor neurons: Have a large cell body at one end that lies
within the spinal cord or brain. A nucleus that is always that is
always in its cell body. Many highly branched dendrites extend
ck
from the cell body providing a large surface area for the axon
terminals of other neurons.
ra
C
Picture from Biology A-Level CourseBook
CRACK EXAMS A2 1
, Complete notes for A-Levels BiologyCIE according to syllabus objectives - updated 2025
● Sensory neurons: Almost same but has a cell body that
branches off in the middle of the cell (it maybe near the
source of stimuli or in a swelling of a spinal nerve known as
ganglion)
A2
Picture from Biology A-Level CourseBook
s
● Role of sensory receptor cells in detecting stimuli: Cell
responds to stimulus → receptor cell transducers → convert
am
energy in one form into energy in electrical impulse. When
stimulated it's depolarised. If the stimulus is very weak, the
cells are not sufficiently depolarised and the sensory neuron is
Ex
not activated to send impulses. If strong, → activated →
impulse to CNS.
● Sequence of events that result in an action potential in sensory
ck
neurons: (Example of chemoreceptor cell in a human taste bud).
Chemoreceptor in taste buds that detect salt (NaCl) respond
directly to sodium ions. Salt eaten → Sodium ions diffuse
ra
through highly selective channel proteins in the cell surface
membranes of the microvilli of the chemoreceptor cell
C
membrane. The increase in positive charge inside the cell is
known as receptor potential. If sufficient stimulation by
sodium ions and sufficient depolarisation of membrane, the
receptor potential becomes large enough to stimulate
voltage-gated calcium ion channel proteins to open → calcium
ions enter cytoplasm of the chemoreceptor cell and stimulate
exocytosis of vesicles containing neurotransmitter from the
CRACK EXAMS A2 2
