ORGANISMS RESPOND TO CHANGES IN THEIR INTERNAL + EXTERNAL ENVIRONMENTS Flashcards
TOPIC 6
STIMULUS
change in internal or external environment
RESPONDING TO ENVIRONMENT HELPS ORGANISMS TO SURVIVE BY
.Animals respond to changes in external environment eg. Avoid harmful environments
.Animals respond to changes in their internal environment to maintain optimal conditions for internal chemical reactions
.Plants show tropisms to grow towards or away from stimuli
RECEPTORS
specialised cells or proteins in cell membranes which detect stimuli – they are specific to one type of stimulus
EFFECTOR
Cells which bring about response to stimulus
SENSORY NEURON
Transmit impulses from receptors to CNS or relay neurone
RELAY NEURON
Transmit impulses from sensory to motor neurones
MOTOR NEURON
Transmit impulses from CNS/relay to effectors
AUTONOMIC NERVOUS SYSTEM
controls unconscious activities eg. reflex responses and response of heart rate to changes in carbon dioxide concentration or pressure
DENDRTIES
Receive and carry impulses towards cell body
CELL BODY
Contains nucleus and granular cytoplasm containing ribosomes grouped together into Nissl granules for making neurotransmitter
AXON
Long, membrane covered cytoplasmic extension which generates action potentials and transmits impulses away from cell body-Has nerve endings which form synapses w/effector
SCHAWANN CELLS
Grow around axon forming myelin sheath around cell membrane
MYELIN SHEATH
electrically insulates neurone, speeding up transmission of impulse
NODES OF RAVNIER
Thin areas between Schwann cells causing gaps in myelin sheath important in speeding rate of transmission of impulse
EXAMPLES OF SIMPLE REFLEXES
.Blinking
.Contraction of pupils when exposed to light.
.Withdrawal of hands when one touches an hot object
.Sneeze reflex when nose is irritated
EXAMPLE OF REFLEX ARC: TOUCHING VERY HOT OBJECT
.Stimulus: hot object
.Receptor: temperature and pain receptors in skin
.Sensory neurone sends an impulse to spinal cord via dorsal root
.Relay neurone connects sensory neurone to motor neurone
.Motor neurone sends impulse to an effector via ventral root
.Effector: arm muscles that contract to move hand away
GIVE THE IMPORTANCE OF REFLEX ARC
1.Rapid
2.Protect against damage to body tissues
3.Do not have to be learnt
4.Help escape from predators
5.Enable homeostatic control
KINESIS
organisms movement is affected by non-directional stimulus eg. humidity
TAXIS
organisms move towards or away from directional stimulus eg. light
positive taxis-Whole organism moves towards favourable stimulus
negative taxis-whole organisms moves away from unfavourable stimulus
ADVANTAGES OF TAXIS + KINESIS TO ORGANISM
.Move them away from other organisms to reduce competition
.Move them away from predators/into better camouflage to avoid predators
.Prevent them from drying out
.Help them find mate
.Ensure organism remains near food source
RP10-EFFECT OF ENVIRONMENTAL VARIABLE USING WOODLICE
10 woodlice for 10 minutes
Dark and dry, dark and damp, light and dry, light and damp by using dark paper to block out to block out light on one half use wet paper towel to make area damp
TROPISM
Response of plants to stimuli via growth
can be positive-towards stimulus or negative-away from stimulus controlled by specific growth factors-IAA
PHOTOTROPISM
If shoot is exposed to an uneven light source, IAA is transported to more shaded part
positive phototropism-eg.leaves so that they can capture more light for photosynthesis
negative phototropism- roots to grow to soil
GRAVITROPISM
growth in response to direction of gravity
positive gravitropism-roots so that they grow into soil to absorb water and mineral ions