coordination and response

stimulus definition

change in internal and external environment

what two systems help us respond to stimuli in the environment

nervous system

endocrine system

why do organisms respond to changes in their environment

to increase their chances of survival and reproduction

avoid danger

maintain homeostasis

how does information travel through nerve cells

through neurons they travel as electrical impulses

across synapses they travel as chemical messages

then transforms back into electrical impulses through neurons again

neurotransmitters definition

chemical signaling molecules used to transfer the signal between neurons at a synapse

features of the nervous system

impulses travel along neurons at very high speeds

duration of effect is short-lived

is highly specific and affects certain cells / nerves

features of the endocrine system

chemicals travel through the bloodstream at slower speeds

duration of effect is long-term

is not specific and affects multiple organs and tissues

CNS function

process information from body / environment

sends instructions to muscles and organs

controls thoughts reflexes and emotions

organs of the CNS

brain

spinal cord

3 types of neurons

sensory neurons

relay neurons

motor neurons

sensory neuron function

to transfer a signal from a receptor to the CNS

adaptations of sensory neuron

long and has a cell body branching off the middle of the axon

relay neuron function

to transfer a signal from the sensory neuron to the motor neuron

adaptations of relay neuron

small cell body at one end with many dendrites branching off it

motor neuron function

to transfer a signal from the CNS to an effector

adaptations of motor neuron

long and have a large cell body at one end with long dendrites branching off it

pathway of a reflex arc from stimulus to response

stimulus —> receptor —> sensory neuron —> relay neuron —> motor neuron —> effector —> response

how does an impulse pass across a synapse

impulse travels along the first axon

triggers it to release neurotransmitters from vesicles

they diffuse across the synaptic cleft and bind with receptor molecules

triggers an impulse which travels along the postsynaptic neuron

neurotransmitters are recycled or destroyed once an impulse is sent

how do neurotransmitters move

via diffusion

reflex arc definition

pathway of a reflex response

taken by an electrical impulse

conjunctiva function

lubricates and protects the surface of the eye

sclera function

tough outer layer that protects the eye

cornea function

refracts light into eye

transparent and has no blood vessels

what is the disadvantage of the cornea having no blood vessels

no blood vessels = no supply of oxygen

oxygen diffuses from the outer surface

iris function

controls the diameter of the pupil

therefore how much light enters the eye

lens function

focuses the light onto the retina

is a transparent disc

retina function

contains light receptor cells

rods and cons

what do the rods cells in the retina do

detects light intensity

what do the cone cells in the retina do

detects color

optic nerve function

sensory neuron that carries impulses from the receptors in the eye to the brain

ciliary muscle function

ring of muscle that contracts and relaxes to change the shape of the lens

suspensory ligaments function

connects the ciliary muscle to the lens

fovea function

region in the retina with the highest density of cones

vitreous humour function

liquid filling the eyeball

accommodation definition

eyes ability to adjust its focus

what happens when an object is near

ciliary muscles contracts

causing suspensory ligaments to slacken

stops the suspensory ligaments from pulling on the lens which allows the lens to become fatter (more curved)

light is refracted more

what happens when an object is far

ciliary muscles relax

causing suspensory ligaments to pull tight

the suspensory ligaments pulls on the lens causing it to become thinner

light is refracted less

what happens the eye is in a dark environment

photoreceptors detect change in environment

radial muscles contract

circular muscles relax

pupil dilates

diameter of pupil widens

more light enters the eye

what happens to the eye in a bright environment

photoreceptors detect change in environment

radial muscles relax

circular muscles contract

pupil constricts

diameter of pupil narrows

less light enters the eye

cooling mechanisms in the skin

vasodilation - blood vessels near the skin widen to allow more blood to flow near the surface to transfer more energy via radiation to surroundings

sweating - cools the skin by evaporation, using heat energy to convert liquid water into water vapour

flattening of hairs - which causes them to stop forming an insulating layer by trapper air and allows air to circulate over skin and heat to leave by radiation

warming mechanisms in the skin

vasoconstriction - blood vessels near the skin constrict to allow less blood to flow near the surface so less energy is transferred to the surroundings

shivering - muscles contract rapidly, increasing rate of respiration which transfers more energy to warm the body

exercise does the same

erection of hairs - traps an insulating layer of air and stops heat being lost via radiation, helping to keep us warm

where are thermoreceptors located

in the hypothalamus and skin

what happens when there is an increase in body temperature

thermoreceptors detect change

increases sweating, vasodilation, hairs lie flat

decrease in body temperature

body temperature becomes normal again

what happens when there is a decrease in body temperature

thermoreceptors detect change

increase shivering, vasoconstriction, hairs erect

increase in body temperature

body temperature becomes normal again

why do smaller organisms cool down quicker

they have a bigger surface area to volume ratio

there is more area for the heat to transfer across

smaller organisms survive in the heat because their big surface area to volume ratio reduces chance of overheating

larger organisms survive in the cold because their small surface area to volume ratio reduces heat loss

hormone definition

a chemical substance produced by a gland and carried by blood

it alters the activity of one or more specific target organs

adrenaline function

readies body for a fight or flight response

adrenaline source

adrenal glands

adrenaline effect

increases heart rate

increases blood flow to muscles

increases blood sugar level

insulin function

controls blood glucose level

insulin source

pancreas

insulin effect

stimulates liver to turn glucose into glycogen

what happens if there is a high level of glucose

leads to cells in body losing water by osmosis

what happens if there is a low level of glucose

not enough for respiration

how does the body react to high concentration of blood glucose

cells in pancreas detect change

pancreas produces insulin

insulin stimulates muscles and liver to take up glucose from bloodstream and store it as glycogen

reduces the concentration of glucose in blood back to normal

pancreas stops secreting insulin

how does the body react to low concentration of blood glucose

cells in pancreas detect change

pancreas produces the hormone glucagon

it causes glycogen stored in liver to convert into glucose and released into blood

increases concentration of glucose in the blood back to normal level

pancreas stops secreting glucagon

testosterone function

main male sex hormone

testosterone source

testes

testosterone effect

promotes male secondary sexual characteristics

examples of male secondary sexual characteristics

facial hair

sperm production

deepening of voice

progesterone function

supports pregnancy

progesterone source

ovaries

progesterone effects

maintains uterine lining

oestrogen function

main female sex hormone

oestrogen source

ovaries

oestrogen effect

controls menstrual cycle

promotes female secondary sexual characteristics

examples of female secondary sexual characteristics

hips widen

development of breasts

ovum release and start of periods

ADH function

control water content

ADH source

pituitary gland

ADH effects

controls permeability of collecting duct in nephron

FSH function

female sex hormone

causes egg to mature in ovary

stimulates ovaries to produces oestrogen

FSH source

pituitary gland

LH function

female sex hormone

stimulates release of egg from ovary

LSH source

pituitary gland

why do plants need to respond to stimuli

increases their chance of survival

when they respond to the presence of predators

auxin function

plant hormones which control growth at tips of shoots and roots

they diffuse backwards to stimulate the cell elongation process which occurs in the cells behind the tips

how do plants respond to light

shoots are positively phototropic

roots are negatively phototropic

how do plants respond to gravity

shoots are negatively geotropic

roots are positively geotropic

how do plants respond to water

roots are positively hydrotropic