3.6 Flashcards

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1
Q

Survival and Response

A
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2
Q

Why do organisms respond to changes in their environment

A

to increase their chances of survival
e.g. by preventing extinction through potential danger

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3
Q

What are taxis and kinesis

A

simple responses that enable mobile organisms to stay in a favourable environment
taxis is a directional response to stimuli
kinesis is a non-directional response to stimuli

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4
Q

What is kinesis affected by and give an example

A

The rate of movement of an organism is affected by the intensity of the stimulus
Flatworms called planarians possess a network of neurones and simple eye-like structures that have light-sensitive cells
Planarians display kinesis when removed from their usual dark environment
Planarians are found on the underside of stones, hidden from daylight
When a stone is removed or turned over the planarians begin to move in random directions
Once these random movements eventually bring them back into the darkness they stop moving
This type of responsive behaviour helps them to protect themselves from predators
In the scenario above, the light-sensitive cells are detecting light when the stone is overturned but the planarian has no way of detecting the nearest shaded space, therefore it moves randomly until the eye detects a low level or no light
The planarian uses kinesis to ensure it is in its favourable environment - darkness

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5
Q

What is taxis affected by and give an example

A

The organism moves directly away from or towards the stimulus
A single-celled organism called Euglena which is commonly found in ponds exhibits taxis
It has chloroplasts for photosynthesis and a flagellum to help it swim
The flagellum has a receptor close to its base that is sensitive to light
Euglena swims directly towards the light, this is known as phototaxis
This behaviour is highly valuable as it brings the organism towards the light where it can photosynthesise

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6
Q

investigating taixs and kinesis

A

Taxes and kineses behaviour in small animals can be studied using special apparatus
Choice chambers and mazes are common pieces of apparatus that are used
Woodlice and maggots are often the organisms studied
It can be difficult to distinguish taxis from kinesis in these experiments
The animals need to be observed during the experiment to see if turning frequency or movement rate changes in different environments
If movement is directional then the turning frequency would decrease when the organism detects the stimulus
Choice chambers
An experiment was conducted to investigate whether maggots exhibited negative phototaxis
This would mean that they moved away from bright light (not randomly)
One half of the transparent choice chamber was covered in an opaque material to prevent light from entering
30 maggots were placed into the chamber via the hole in the centre of the lid
10 minutes later the number of maggots found in each half of the chamber were counted
This was repeated several times
The results showed that there was always more maggots in the shaded half of the chamber at the end of the experiment
As the maggots were not observed during the experiment it can not be said whether kinesis or taxis has occurred
However, the results do conclude that maggots have the ability to detect bright light and respond by moving until they reach a more favourable environment

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7
Q

6.1.1 sme

A

Organisms must respond to changes in their environment in order to survive
They can only survive if they are successful at:
Finding favourable conditions for living
Finding food
Avoiding being eaten
If these vital requirements are not met then a species will die out or go extinct
For example, a red robin must find worms and insects to feed on and at the same time, they must also be watching out for predators such as crows
Detecting and responding to change
Responses to change can vary in complexity depending on the type of organism involved and the specific circumstances they are responding to
Responding to change requires detection
Detection involves a stimulus being detected by a receptor cell
There are different types of receptors
Some receptor cells produce electrical activity in nerve cells in response to stimuli
Other receptor cells secrete substances in response to stimuli
The nerve impulses sent by receptor cells travel to a coordinator
This is either the brain or the spinal cord
From the coordinators, the impulse is conducted to the specific effector that will produce the appropriate response
Using the earlier example of the red robin staying alert to predators:
A sudden movement by a crow (the stimulus) is detected by the receptors in the robin’s eye
The receptor cells send an impulse along the nerves and to the brain (coordinator)
The brain sends an impulse to the wing muscles (effectors) of the red robin so it can fly away (response)

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8
Q

protective effect of a simple reflex

A
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9
Q

effect of different concentrations of indoleacetic acid (IAA) on cell elongation in the roots and shoots of flowering plants as an explanation of gravitropism and phototropism in flowering plants.

A
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10
Q

basic structure of a Pacinian corpuscle.

A

-not a separate cell, as they are found at the ends of sensory neurone axons

-made of many layers of membrane separated by a gel

-gel between the layers contains positively charged sodium ions (Na+)

-the section of axon surrounded by layers of membrane contains stretch-mediated sodium ion channels

  • these open when sufficient pressure is applied
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11
Q

how does deformation of stretch-mediated sodium ion channels in a Pacinian corpuscle leads to the establishment of a generator potential.

A

-Pacinian corpuscles are stimulated by pressure on the skin, which establishes a generator potential
-this happens due to the movement of charged ions across the membrane

-an excess of positively charged sodium ions surrounds the axon
-pressure is exerted on the Pacinian corpuscle
-the layers of membrane become distorted and the stretch-mediated sodium channels in the axon membrane open
-sodium ions enter the axon via facilitated diffusion
-changes the electrical potential difference across the membrane
-leads to depolarisation
-establishes a generator potential

-the generator potential triggers impulses (action potentials) that travel along the sensory neurone to the central nervous system

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12
Q

What are Pacinian corpuscles

A

-receptors that respond to changes in pressure
-are present in the skin of fingers, soles of the feet, joints, tendons and ligaments
-stimulating these receptors with excess pressure on skin leads to a generator potential

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13
Q

Function of:
cornea
retina
iris
optic nerve
pupil
lens

A

cornea
transparent layer that retracts light as it enters eye

retina:
contains light receptors
-rods: detect light intensity
-cones: detect colour

iris:
controls how much light enters pupil

optic nerve
sensory neurone that carries impulses between the eye and brain

pupil
hole that allows light to enter the eye

lens
transparent disc that can change shape to focus light onto retina

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14
Q

Sensitivity to light and colour

A
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15
Q

Visual acuity

A
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16
Q

Cone cells provide higher visual acuity

A

-one cone cell synapses with a single bipolar cell
-one bipolar cell synapses with a single ganglion cell

-if two cones are stimulated to send an impulse the brain is able to interpret these as two different spots of light

-cone cells detect only one of three colours (red, green or blue) , so the brain will receive information about the colour of light detected by the stimulated cone cell and where this light is

-this is because the brain knows which bipolar cell connects to which cone cell

17
Q

Rod cells provide lower visual acuity

A

-multiple rod cells synapse with a single bipolar cell

-multiple bipolar cells synapse with a single ganglion cell

-brain is not able to interpret which impulses are sent by specific rods

-if multiple rod cells connected to the same bipolar cell detect light, only one impulse from the bipolar cell is sent

-hence the brain receives a general, not specific, understanding of the fields of vision that are light or dark

18
Q

what is summation and the benefit of it

A

There is a benefit to how the rods are connected to the optical nerve
Each rod is very sensitive to light however a single stimulated rod is unlikely to produce a large enough generator potential to stimulate the bipolar cell for the conduction of nerve impulses
When a group of rods are stimulated at the same time the combined generator potentials are sufficient to reach the threshold and stimulate the bipolar cell for the conduction of nerve impulses onwards towards the optic nerve
This additive effect of rods is known as summation
Summation produces a less sharp image but enables organisms to see in much dimmer light than cones allow
Nocturnal animals tend to have mostly or solely rods present in their eyes

19
Q

Explain why the heart is considered myogenic

A

It contracts without any external stimulus

20
Q

Outline how heart rate is controlled and coordinated
How does exercise affect it?

A

-sinoatrial node (SAN) is a group of cells in the wall of the right atrium
-SAN initiates a wave of depolarisation that causes the atria to contract
-the depolarisation is carried to the atrioventricular node (AVN - region of conducting tissue between atria and ventricles)
-after a slight delay, the AVN is stimulated and passes the stimulation along the bundle of His
-delay means that the ventricles contract after the atria
-the bundle of His is a collection of conducting tissue in the septum (middle) of the heart.
-the bundle of His divides into two conducting fibres, called Purkyne tissue, and carries the wave of excitation along them
-the Purkyne fibres spread around the ventricles and initiate the depolarization of the ventricles from the apex (bottom) of the heart
-makes the ventricles contract and blood is forced out of the pulmonary artery and aorta

q2:
the Medulla Oblongata in the brain can increase or decrease heart rate
receives nerve impulse from chemoreceptors (respond to blood pH) in the carotid arteries and pressure receptors (respond to blood pressure) in the carotid arteries and aorta
sends impulse in sympathetic nerves to SAN to increase HR and sends impulse in parasympathetic nerves to SAN to decrease HR

q3:
exercise = muscle contraction, which requires respiration

therefore, waste product CO2 is released into blood

this lower pH of blood (acidic)

this is detected by chemoreceptors in carotid arteries

sends impulses to medulla oblongata

then medulla oblongata sends impulses to SAN via the sympathetic nerves causing the heart rate to increase

benefit = increase blood flow to lungs to remove CO2 and take in O2

21
Q

Outline the role and location of chemoreceptors and baroreceptors

A

Chemoreceptors detect the concentration of oxygen in the blood. They are also sensitive to changes in pH resulting from the carbon dioxide dissolved in the blood (its reacts with the water to form carbonic acid), which is an indication of oxygen availability

Baroreceptors detect changes in blood pressure

Both types of receptors are found in the aortic and carotid bodies.

22
Q

Nervous coordination

A
23
Q

Outline the structures of the three types of neurones

A

sensory neurone has its cell body in the middle and has a dendron and axon

motor neurone has its cell body at the start and only has a long axon

24
Q

Describe the two types of motor neurones

A

Somatic supplies skeletal muscle = under conscious control

Autonomic supplies cardiac muscle, smooth muscle, glands = under subconscious control

25
Q

Define action potential

Define nerve impulse

A
26
Q

Outline what happens during an action potential

A

stimuli causes Na+ ions to enter the start of the neurone

makes membrane potential less negative

if it reaches threshold (-50mV), Na+ channels open

therefore more Na+ ions diffuse into the neurone, therefore membrane potential becomes positive (depolarised)

the membrane potential reaches +40mV

then the Na+ channels close, the K+ channels open

therefore K+ ions diffuse out, therefore membrane potential becomes negative (repolarised)

too many K+ ions move out, so the membrane potential becomes more negative than normal (hyperpolarised)

27
Q

What affects action potentials

A

frequency of impulses
high frequency = larger stimuli
Low frequency = smaller stimuli

28
Q

Factors affecting speed of nervous impulses

A

temperature = higher temp, higher kinetic energy, faster rate of diffusion of ions (faster nerve impulse)

axon diameter = wider diameter, neurone less leaky (faster nerve impulse)

myelination = schwann cells wrap around axon, insulates axon preventing AP, therefore AP only occurs in gaps – called node of ranvier, so AP jumps from node to node = saltatory conduction (faster nerve impulse)

29
Q

What is a synapse
outline the stages of synaptic transmission

A

connection between 2 different neurones

sends nerve impulse across the gap (synaptic cleft) using neurotransmitters (e.g. acetylcholine)

AP arrives in end of presynaptic neurone

Ca2+ channels open

Ca2+ ions enter presynaptic neurone

causes vesicles containing neurotransmitter to move to presynaptic membrane

vesicle binds to membrane releasing neurotransmitter into cleft

neurotransmitter diffuses across cleft

binds to complementary receptors on postsynaptic membrane

Na+ channels open, Na+ ions enter

if threshold is reached, AP occurs

(to return to rest: enzyme used to breakdown neurotransmitter, e.g. acetylcholinesterase breaksdown acetylcholine into ethanoic acid and choline, diffuses back into presynaptic neurone, ATP used to reform neurotransmitter into vesicle and actively transport Ca2+ ions out)

30
Q

Properties of synapses

A

unidirectionality = AP/nerve impulse travels in one direction, from pre to post, pre has the neurotransmitter, post has the receptors

filters out low level stimuli = low level stimuli do not release enough neurotransmitter, therefore not enough Na+ ion channels open, therefore not enough Na+ ions enter postsynaptic neurone for threshold to be reached, therefore no AP produced

summation = low level stimuli add together to release enough neurotransmitter to produce an AP in postsynaptic neurone, can be temporal or spatial

temporal = low level stimuli present for extended period of time

spatial = a low level stimuli from a few presynaptic neurones add together

inhibitory = normal synapses are excitatory (cause AP), some can be inhibitory – prevent action potential from occurring by making postsynaptic neurone hyperpolarised

31
Q

Skeletal Muscle

A
32
Q

types

A

Skeletal

Smooth

Cardiac

33
Q

structure

A

basic structure = sarcomeres

made up of actin and myosin, actin is thin and has tropomysosin wrapped around it, myosin is thick and has heads, when the sarcomere contracts the whole muscle contracts, contracts/shortens by the sliding filament mechanism

many sarcomeres = myofibril

many myofibrils = muscle fibre

surrounded by a membrane called sarcolemma

contains myofibrils, fluid called sarcoplasm and tubes called sarcoplasmic reticulum

many muscle fibres = bundle

many bundles = whole muscle

Locations in a Sarcomere?
A band = location of myosin [no change in contraction]
I band = location between the myosin [shortens in contraction]
H zone = location between the actin [shortens in contraction]
Z line = end line of sarcomere [moves closer together in contraction]

34
Q

Overall function of skeletal muscles?

A

-moves the body skeleton
-when the muscle contracts (shortens) the tendon pulls on joints causing movement

35
Q

what occurs in Sliding Filament Mechanism?

A

how the sarcomere shortens

the myosin heads pull the actin inwards

the somatic motor neurone connects to the skeletal muscle via a neuro-muscular junction

one motor neurone connects to a few muscle fibres = motor unit

  (benefit = simultaneous muscle contraction and can control strength of contraction) 

releases acetylcholine that binds to complementary receptors on the muscle fibre membrane (sarcomere)

Na+ channels open, Na+ ions enter the muscle fibre causing depolarisation

wave of depolarisation travels through sarcoplasmic reticulum

causes release of Ca2+ ions into the sarcoplasm (fluid surrounding sarcomeres/myofibril)

this moves the tropomyosin on the actin

exposes binding sites on the actin

myosin heads now bind to the actin (form actin-myosin cross bridge)

a power stroke occurs, the myosin pulling the actin inwards

ATP attaches to myosin head so it detaches

ATP brokendown by ATPase to release energy

causes myosin head to go back to its original position

so it reattaches, pulling the actin further inwards