💥 Cambridge O-Level Biology 5090: Coordination & Control + Plant Responses

🧠 14.1 Mammalian Nervous System

Concept Summary
Integration of body functions by nervous system (fast, electrical impulses)
Coordination
or endocrine system (slow, chemical hormones).
Nervous system =
CNS = brain + spinal cord; PNS = nerves connecting CNS to the body.
CNS + PNS
Sensory: sense organ → CNS; Relay: within CNS; Motor: CNS →
Types of neurones
effectors (muscles/glands). (Draw the 3 neurones!)
Along neurones as electrical signals. Direction: receptor → CNS →
Impulse travel
effector.
🧠 Involuntary, fast, protective. Pathway: Stimulus → Receptor → Sensory
Reflex arc neurone → Relay neurone (spinal cord) → Motor neurone → Effector
(muscle/gland) → Response.
Reflex examples Blink reflex, knee jerk, coughing, pupil reflex.
Gap between neurones. Impulse triggers neurotransmitter release →
Synapse diffuses across synaptic gap → binds receptors → impulse in next
neurone.
Neurotransmitter only on one side; receptors only on next neurone → one-
One-way only
way transmission.

🧠 Memory Hack: RSRMER → Reflex Arc order = Receptor → Sensory → Relay → Motor →
Effector → Response

📌 Exam Tip: Always use "rapid and automatic" when defining reflex. Examiner expects
"without conscious control".

👁️ 14.2 Mammalian Sense Organs

Structure Function
Cornea Refracts light onto lens.
Controls pupil size via circular (contract in light) and radial muscles
Iris
(contract in dark).
Pupil Allows light into eye.
Lens Focuses light onto retina.
 Structure Function
Ciliary muscles Contract/relax to change lens shape.
Suspensory
Pull lens flat/thick based on tension.
ligaments
Retina Light receptors (rods for dim light, cones for color).
Fovea Sharp vision – high cone density.
Optic nerve Carries impulses to brain.
Blind spot No receptors – where optic nerve exits.

📌 Pupil Reflex:

 Bright light → circular muscles contract, radial relax → pupil constricts

 Dim light → radial contract, circular relax → pupil dilates
🌀 Antagonistic muscle action

📌 Accommodation:

Object Ciliary muscles Ligaments Lens Light

Near Contract Loosen Thicker More refraction
Distant Relax Tighten Thinner Less refraction

💡Tip: "Closer = Fatter lens" – Think zooming in!

🧠 14.3 Mammalian Hormones

Hormone Gland Function
Fight/flight: ↑HR, ↑BR, dilates pupils, converts glycogen to
Adrenaline Adrenal gland
glucose.
Pancreas
Insulin Lowers blood glucose by converting glucose → glycogen (liver).
(islets)
Pancreas
Glucagon Raises glucose: glycogen → glucose.
(islets)
FSH Pituitary Stimulates follicle to develop and release oestrogen.
LH Pituitary Triggers ovulation + corpus luteum.
Oestrogen Ovary Builds uterus lining; female secondary traits.
Progesterone Ovary Maintains uterine lining.
Testosterone Testes Male secondary sexual traits.
🧠 Hormone = chemical messenger carried by blood, made by glands, affects target organs
only.

📌 Nervous vs Hormonal Control

Feature Nervous Hormonal

Speed Fast Slow
Duration Short Long
Transmission Electrical (neurones) Chemical (blood)
Target Specific Widespread
Reversible Usually Sometimes not

🔁 14.4 Homeostasis
📘 Definition: Maintenance of constant internal environment (e.g., temp, water, glucose).

📌 Negative Feedback: Change detected → corrective action → returns to set point.

🧠 "Body reacts to oppose the change." Example: ↑ glucose → insulin → ↓ glucose.

🌡️ 14.5 Temperature Control

Component Role
Hypothalamus Brain region detecting blood temperature.
Skin receptors Detect external temp.
Hair erector muscles Contract = traps air (insulation). Relax = lose heat.
Sweat glands Produce sweat → evaporates = cools body.
Blood vessels Vasodilation (heat loss), vasoconstriction (retain heat).
Shivering Muscle contractions generate heat.

📌 Mnemonic: SV SHV → Sweat, Vasodilation, Shiver, Hair, Vasoconstriction

🍭 14.6 Blood Glucose Control

Hormone Action
Insulin ↓ Blood glucose – stimulates glucose uptake + conversion to glycogen (liver).
Hormone Action
Glucagon ↑ Blood glucose – stimulates glycogen → glucose (liver).

📌 Type 1 Diabetes:

 Cause: Islet cells don’t produce insulin.

 Signs: High blood glucose, glucose in urine.
 Treatment: Insulin injections.

🧠 Hack: Glucagon = Go ↑, Insulin = Into cells ↓

🌱 15.1 Coordination in Plants

Tropism Description
Phototropism Growth towards light (shoots = positive).
Gravitropism Growth in response to gravity (roots = positive, shoots = negative).

📌 Auxin (Plant Hormone):

 Made in shoot tip.

 Moves down stem.
 Uneven distribution in light/gravity.
 Stimulates elongation (in shoots only).

🧠 Hack: Light side = Less auxin → Slower growth

Shade side = More auxin → Elongates more → Bends towards light

🎯 Past Paper Gold (2020–2024)

PP Question MS Tip / Examiner Report Insight
2023 ON 14.1 (Reflex Must include correct sequence AND key terms “rapid, automatic” to
arc) score full.
2022 JN 14.2 (Pupil Describe muscles by name: circular and radial. Just saying “muscle”
reflex) = 0.
2021 ON 14.3 Use phrases like “prepares body for action”, “fight/flight”, not just
(Adrenaline) “increases heart rate”.
2020 JN 14.4 (Negative
Draw diagram + define “set point” to impress examiner.
feedback)
 PP Question MS Tip / Examiner Report Insight
Always state insulin lowers blood glucose by converting glucose
2021 ON 14.6 (Diabetes)
to glycogen—not just “stores glucose”.

🚀 Final Hacks for Distinction (6/5 Level)

🧠 Mnemonic Vault:

 RSRMER – Reflex arc

 CRaZY HORMONE PEST – Cortisol, Repro (testes, ovaries), Adrenaline, Zzz
(melatonin), Yawn, Progesterone, Estrogen, Serotonin, Testosterone
 VVSHH – Vasodilation, Vasoconstriction, Shivering, Hairs, Hypothalamus

🧠 Experiment Triggers:

 Reflex test → knee-jerk + eye blink

 Pupil reflex → lamp + mirror
 Tropism → rotating clinostat or directional light

⚠️ Examiner Alerts:

 Don’t say “brain controls reflex” → spinal cord!

 Don’t confuse glucose/glycogen/glucagon!
 Always define stimulus, effector, receptor with examples.

Would you like diagrams and visual cheatsheets for each section next (reflex arc, synapse, eye,
tropisms)?