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CHEMICAL SIGNALLING

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Endocrine system Animals have two systems of internal communication &

regulation – the nervous system and the endocrine system.

The nervous system conveys high-speed signals along neurons, functioning in movement of body parts, etc.

The endocrine system is the collection of an animal’s hormone-secreting cells.

Exocrine glands (not part of the endocrine system) secrete chemicals like mucus, sweat, digestive enzymes into ducts that

convey the products to locations.

Endocrine glands are hormone-secreting organs.

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Chemical signals Chemical signals play major roles in coordinating animal function.

Pheromones carry messages between different individuals.

Hormones convey information via the bloodstream to targets

cells throughout the body.

Target cells have specific receptors for the chemical signal.

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Hormone types Peptides & proteins

Glycoproteins

Steroids Amines

Insulin – blood glucose regulation.

Oxytocin – uterine contractions. Follicle-stimulating

hormone – ova & sperm production.

Adrenaline & noradrenaline – fight or flight

response.

Oestrogen & testosterone.

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Signal transduction pathways Signal molecules (eg hormones) have specific 3D

conformations that can be recognised by target cells.

The signal is received when the molecule binds to a specific receptor. Then signal transduction within the target cell

results in a response, a change in the cell’s behaviour.

Surface receptor.

Intracellular receptor.

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NERVOUS SYSTEM

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Cells of the nervous system Neurons – functional and structural unit of the nervous system.

Glia – supporting cells of the nervous system. Essential for nervous system structural integrity.

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Impulse propagation All cells have a voltage across their plasma membrane, maintained by differential concentrations of ions.

Nerve impulses (electrical signals) propagated down processes by

sequential polarity reversal.

Myelin sheaths make the signal jump, allowing faster conduction.

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Impulse propagation

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Central nervous system

Brain – responsible for processing complex signals.

Underlies vertebrate complexity.

Spinal cord – simple responses to certain stimuli. Also conveys

information to the brain.

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Peripheral nervous system PNS – everything outside the CNS.

Peripheral nervous system

Sensory division

Motor division

Sensing external

environment

Sensing internal

environment

Autonomic nervous system

Somatic nervous system

Sympathetic division

Parasympathetic division

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SENSORY MECHANISMS

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Taste & smell Taste and smell are both based on chemoreception.

Chemoreceptor cells recognise particular chemical groups on molecules that give the molecules their characteristic qualities.

This stimulus is converted into a nerve signal for transmission to the brain for processing.

Chemoreceptor cells

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Touch Touch receptors are mechanoreceptors and convert

mechanical stimuli to nerve signals.

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Hearing Hearing & balance involve

mechanoreceptors with hairs producing impulses when hairs are disturbed.

Cochlea, uncoiled.

Different places along the cochlea vibrate with different

frequencies/pitches. 2004 Biology Olympiad Preparation Program 17

Lateral line system Many fish & amphibians augment their ear hearing with a

lateral line system along both sides of the body.

Mechanoreceptors pick up low-frequency waves carried into the system by water.

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Sight Light detectors, e.g. eyes, contain photoreceptors that

contain pigment molecules that absorb light.

125 million rod cells.

More sensitive to light. Cannot distinguish colours.

6 million cone cells.

Distinguish colours in daylight.

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ANIMAL MISC.

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Skeletal systems 3 functions of skeletal systems:

Support – most land animals would sag from their own weight if they had no skeleton to support them.

Protection – many animals have hard skeletons that protect soft tissues – e.g. skull, ribcage.

Movement – skeletons aid in movement by providing muscles something firm to work against.

Hydrostatic skeleton – fluid held under pressure

in a closed body compartment.

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Skeletal systems

Exoskeleton – hard encasement deposited on the body surface. Muscles

attach to inside of the exoskeleton. Requires periodic moulting for growth.

Endoskeleton – consists of hard supporting elements, e.g. bone, embedded within soft tissues of

animals. Muscles attach via tendons. Joints provide flexibility.

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Asexual reproduction Asexual reproduction is the creation of new individuals whose

genes all come from one parent without the fusion of egg & sperm.

Fission – equal division of parent.

Budding – new individuals splitting

off parent. Fragmentation –

breaking of parent body into parts, followed by

regeneration. Parthenogenesis – egg develops

without fertilisation. 2004 Biology Olympiad Preparation Program 23

Sexual reproduction Sexual reproduction is the creation of offspring by the fusion of haploid gametes to form a diploid zygote (fertilised egg).

Increases genetic variability among offspring to possibly enhance the

reproductive success of parents when environmental pressures exist.

More costly than asexual reproduction – finding/attracting

a mate, timing, parental protection, etc.

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