Coordination & Control
Coordination & Control (Plants and Animals)
Coordination in Animals – Why Nervous and Endocrine Systems?
Coordination means making all organs of the body work together in a smooth, orderly and purposeful way. Animals use two main systems for coordination:
- Nervous system – fast, electrical and chemical messages (nerve impulses).
- Endocrine system – slower, chemical messages (hormones) carried by blood.
| Need for coordination | Examples in daily life |
|---|---|
| To respond to changes in environment (stimuli). | Withdrawing hand from hot vessel, closing eyes to bright light. |
| To maintain internal balance (homeostasis). | Keeping body temperature nearly constant, controlling sugar level in blood. |
| To control complex activities. | Walking, running, speaking, studying, playing games. |
Memory Line: “Nerves act fast, hormones act last long.” – Nerves give quick responses, hormones give slower but long-lasting effects.
Exam Tip: If the question has words like “instant, reflex, immediate” → answer usually involves nervous system. If it has words like “growth, development, puberty, metabolism” → answer usually involves hormones.
Nervous System – Neuron, CNS, PNS and Reflex Action
Basic unit: The working unit of nervous system is the neuron (nerve cell).
| Part of neuron | Structure | Function |
|---|---|---|
| Cell body (cyton) | Contains nucleus and cytoplasm. | Controls activities of neuron. |
| Dendrites | Short, branched processes. | Receive impulses from other neurons or receptors. |
| Axon | Single, long fibre, may be covered by myelin sheath. | Conducts impulses away from cell body to other neurons or muscles. |
Organisation of human nervous system:
| Division | Sub-parts | Main role |
|---|---|---|
| Central nervous system (CNS) | Brain and spinal cord. | Processing, control and integration of information. |
| Peripheral nervous system (PNS) | Cranial nerves (from brain) and spinal nerves (from spinal cord). | Carry messages between CNS and rest of body. |
| Autonomic nervous system (ANS) | Sympathetic and parasympathetic divisions. | Controls involuntary actions – heartbeat, breathing rate, gut movements. |
Brain – major parts:
- Cerebrum – thinking, memory, intelligence, voluntary actions.
- Cerebellum – balance, posture, coordination of movements.
- Medulla oblongata – controls heartbeat, breathing, swallowing.
Reflex action: Quick, automatic, involuntary response to a stimulus, controlled by spinal cord in many cases.
| Element | Role in reflex arc (example: hand from hot object) |
|---|---|
| Receptor | Skin detects heat (stimulus). |
| Sensory neuron | Carries impulse from skin to spinal cord. |
| Relay neuron | Connects sensory and motor neuron in spinal cord. |
| Motor neuron | Carries impulse from spinal cord to muscles of arm. |
| Effector | Muscles contract and pull hand away. |
Memory Line: “RSRME” – Receptor → Sensory → Relay → Motor → Effector helps remember the order of reflex arc.
Exam Tip: If question uses word “reflex arc”, always draw or imagine this chain. Brain may know later, but spinal cord gives the first quick response.
Endocrine System – Major Human Glands and Hormones
Endocrine glands are ductless glands which release chemical messengers called hormones directly into blood.
| Gland | Location | Main hormone(s) | Key function / effect |
|---|---|---|---|
| Pituitary (master gland) | Base of brain. | Growth hormone, TSH, FSH, LH, etc. | Controls growth and regulates other endocrine glands. |
| Thyroid | Neck region. | Thyroxine. | Controls metabolic rate and proper growth. Needs iodine. |
| Parathyroid (4) | Embedded in thyroid. | Parathormone. | Controls calcium and phosphate balance. |
| Pancreas (endocrine part) | Near stomach. | Insulin and glucagon. | Regulate blood sugar level. |
| Adrenal glands | On top of each kidney. | Adrenaline (epinephrine). | Prepares body for “fight or flight” in emergency (increases heart rate, breathing rate). |
| Testes (in males) | Scrotal sac. | Testosterone. | Controls development of male secondary sexual characters. |
| Ovaries (in females) | Pelvic region. | Estrogen, progesterone. | Control female secondary sexual characters and menstrual cycle. |
Memory Lines:
- “Pituitary directs, thyroid speeds, pancreas sugars, adrenal speeds heart.”
- “Too little thyroxine + lack of iodine → goitre (neck swelling).”
Exam Tip: Many questions ask “name the gland/hormone for…”. Always link:
- Blood sugar problem → insulin (pancreas).
- Stress, fear situation → adrenaline (adrenal).
- Iodine deficiency → thyroid / thyroxine.
Plant Hormones – Auxin, Gibberellin, Cytokinin, ABA, Ethylene
Plants also show coordination using plant hormones (phytohormones). They control growth, development and responses to environment.
| Plant hormone | Main role | Simple examples |
|---|---|---|
| Auxins | Cell elongation, growth of stem, root formation, bending towards light. | Higher auxin on dark side of stem → stem bends towards light. |
| Gibberellins | Stem elongation, seed germination, breaking dormancy. | Used to increase length of grapes and sugarcane internodes. |
| Cytokinins | Cell division, delay ageing of leaves. | Used in tissue culture to promote shoot formation. |
| Abscisic acid (ABA) | Inhibits growth, promotes dormancy, closes stomata during water stress. | Helps plant to survive drought by reducing water loss. |
| Ethylene | Ripening of fruits, falling of leaves and fruits. | Used commercially for artificial ripening of fruits. |
Memory Line: “A G C E are mostly growth promoters; ABA is growth stopper.” – Auxin, Gibberellin, Cytokinin, Ethylene promote some aspects of growth, while Abscisic Acid mainly inhibits.
Exam Tip: If the question speaks about fruit ripening → think ethylene. If about stomata closing and drought → think ABA. For bending towards light → think auxin distribution.
Tropic Movements in Plants – Directional Responses
Tropic movement is a growth movement of a part of plant in response to a stimulus which comes from one direction. It can be towards (positive) or away from (negative) the stimulus.
| Type of tropism | Stimulus | Response / example |
|---|---|---|
| Phototropism | Light. | Stem bends towards light (positive phototropism); root shows negative phototropism. |
| Geotropism (gravitropism) | Gravity. | Root grows downwards (positive geotropism); stem grows upwards (negative geotropism). |
| Hydrotropism | Water. | Roots bend towards region of higher moisture. |
| Thigmotropism | Touch of solid object. | Tendrils of climbers (pea, money plant) coil around support. |
| Chemotropism | Chemical substances. | Pollen tube grows towards ovule due to chemical attractants. |
Role of auxin in phototropism (simple view):
- Light falling on one side of stem causes auxin to accumulate on darker side.
- Cells on darker side elongate more due to higher auxin.
- Stem bends towards light, helping plant to receive more sunlight.
Memory Line: “Shoots love light and air; roots love water and earth.” – Shoots show positive phototropism and negative geotropism; roots show positive geotropism and hydrotropism.
Exam Tip: If direction of stimulus is clearly mentioned (light from one side, gravity from below, water on one side) → answer is a type of tropism. Use proper prefix: photo, geo, hydro, thigmo, chemo.
Nastic Movements in Plants – Non-Directional Responses
Nastic movement is also a response to stimulus, but it does not depend on direction of stimulus. It is usually caused by changes in turgor (water pressure) of cells or by growth.
| Type | Stimulus | Example |
|---|---|---|
| Thigmonasty / Seismonasty | Touch or shock. | Leaves of Mimosa pudica (touch-me-not plant) fold up when touched. |
| Photonasty | Light (not directional). | Opening of petals in morning and closing at night in many flowers. |
| Nyctinasty | Day–night rhythm. | Sleeping movements of leaves in some plants in evening. |
Mechanism example – Mimosa leaf movement:
- Touch stimulus reaches the swollen region at base of leaf called pulvinus.
- Water moves out of cells in pulvinus → cells lose turgor → leaf droops and folds.
- After some time, water returns and leaf opens again.
Memory Line: “Tropism cares for direction; nastic cares for stimulus only.” – Tropic movement depends on direction of stimulus, nastic movement does not.
Exam Tip:
- Leaf movements of Mimosa and flower opening–closing are usually asked under nastic movement.
- If the question stresses “growth towards or away from stimulus” → it is tropic, not nastic.