Triple Biology GCSE AQA Grade 9 Unit 5 Homeostasis Notes
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Course
Science
Institution
GCSE
Biology GCSE AQA Grade 9 Unit 5: Homeostasis notes made by Grade 9 student, now studying A level Biology. Includes all relevant details adhering to the specification and visual aids, such as diagrams, pictures, coloured notes, etc.. Similar quality notes available for all units for each triple scie...
Unit 5: Homeostasis
Introduction
Internal environment: the conditions inside our bodies.
Homeostasis: maintaining a constant internal environment.
FACTORS TO BE CONTROLLED
FACTOR CAUSE FOR INCREASE CAUSE FOR DECREASE IMBALANCE PROBLEMS
Water Drinking and eating Urinating and sweating Osmoregulation
Glucose Eating Respiration, excess stored Osmoregulation, risk of
as glycogen diabetes
Ion Drinking and eating Drinking lots of water Osmoregulation
concentratio
n
Temperature Exercising, sickness, being in Being in a cold place Impact on enzyme activity
a warm place
Control Systems
Homeostasis is regulated by automatic control systems:
- Receptors are cells that detect stimuli (changes in the environment).
- The coordination centre (e.g. brain, spinal cord, pancreas) receives and processes
information from receptors.
- Effectors evoke responses restoring optimum levels.
E.g. glands and muscles cause muscle contractions or hormone release.
STIMULUS RECEPTORS COORDINATION EFFECTORS
CENTRE
Receptors
Are specialised cells SENSE ORGAN STIMULI
Detect stimuli Skin touch, temperature, pain
Stimulate electrical impulses in Tongue chemicals (in food/drink)
response Nose chemicals (in the air)
Sense organs contain receptors to Eye light (rod and cone cells in the retina)
detect specific stimuli: Ear sound, position of head
Negative FeedbackA mechanism used to restore
optimum bodily conditions.
1. Optimum level 4. Coordination
centre receives/
processes the
2. Level changes information and
from optimum organises response
3. Receptors detect 5. Effectors respond
change
, The Nervous System
Enables us to react to surroundings and coordinate our behaviour.
Composed of millions of neurones carrying electrical impulses.
Relays messages about internal changes.
Parts of the nervous system
. Central Nervous System (CNS)- Brain and spinal cord (in Effectors- Muscles and glands that respond
vertebrates). - Connected to body by sensory neurones and to nervous impulses
motor neurones.
STIMULUS RECEPTOR SENSORY NEURONE CNS MOTOR NEURONE EFFECTOR RESPONSE
Peripheral Nervous System (PNS)- Sensory neurones: carry information as electrical
impulses from receptors to CNS.- Motor neurones: carry electrical impulses from CNS to
effectors.
Reflex actions (reflexes)
Automatic and rapid responses to stimuli
Avoid danger and protect the body
Occur without using our brains’ conscious part
Reflex arc: passage of electrical impulses in a reflex (from receptor to effector)
Reflex Arc Example:
5. MOTOR NEURONE: impulses travel
Spinal Cord along motor neurone to effector.
(transverse view)
6. EFFECTOR: when impulse
reaches the muscle it contracts.
4. TRANSFER: impulses
passed along a relay
neurone via a synapse. 2. RECEPTOR: pain
stimulation is detected.
3. SENSORY NEURONE:
impulse from receptor
travels to CNS. 1. STIMULUS (hot candle)
PART OF REFLEX ARC DESCRIPTION
Stimulus what your body is reacting to.
Receptors the cells which detect the stimulus.
Sensory neurone the neurone that carries the impulse to the CNS.
Relay neurone carries impulse from sensory neurone to motor neurone.
Motor neurone the neurone that carries the impulse to the effector(s).
Effector the part of the body which reacts to the stimulus.
, Response what your body does in reaction to the stimulus.
Synapse a tiny gap between neurones.
Neurones (nerve cells)
Three types are:
- Sensory
- Motor
- Relay
Specialised cells
Adapted to carry electrical impulses at extremely fast speeds
Structure (motor neurone):
direction of impulse
Adaptations:
ADAPTATION PURPOSE:
Long axons carry messages quickly to distant parts of body
Tiny branches (dendrons) branch further with dendrites at each end and receive
incoming impulses from other neurones.
Myelin sheath fatty layer of insulation to prevent the electrical impulse from
being lost.
Synapses: gaps between neurones
- Neurones aren’t directly connected
- They communicate with each other via synapses
Nerve impulses cause Neurotransmitters Receptors generate Neurotransmitters are
vesicles to move to the released into synaptic new nerve impulse, it released from
synaptic space’s edge. space, diffuse and bind travels to next receptors, either
to receptors in next synapse. broken down by
nerve cell’s dendrite. enzymes or return to
axon terminal, and
reform as vesicles.
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