BIOLOGY B - (3.6.1 - 3.6.4) ORGANIMS RESPOND TO CHANGES IN THEIR INTERNAL/EXTERNAL CONDITIONS

3.6.1.1 SURVIVAL AND RESPONSE

3.6.1.1 SURVIVAL AND RESPONSE

What is a stimulus

A detectable change in the environment

What cells are these changes detected by

Receptor cells

What do organisms increase by responding to stimuli via different respone mechanisms

Their chance of survival

What are taxes and kinesis

Simple responses which keep organisms with the favourable conditions of their environment

What are taxes

This is a simple response in which an organism will move its entire body towards a favourable stimulus or away from an unfavourable stimulus

What is it known as when an organism moves towards a stimulus

Positive taxis

What is it known as when an organism moves away from a stimulus

Negative taxis

What kind of taxis do earthworms show

Negative phototaxis (They move away from light)

What does this help earthworms to avoid

Dehydration and predators

What kind of taxis do Bacteria show

Positive chemotaxis (move towards certain chemicals)

What is kinesis

When an organism changes the speed of movement and the rate it changes direction

If an organism moves from an area where there are beneficial stimuli to an area with harmful stimuli, what will its kinesis response be

To increase the rate it changes direction to return to the favourable conditions quickly

If an organism is completely surrounded by negative stimuli, what will its kinesis response be

To decrease the rate of turning to keep it moving in a relatively straight line to increase the chances of it finding a new location with favourable conditions

What a woodlice’s kinesis response be to moving from a damp area to a dry area

To turn rapidly to increase the probability that it will end up back in the damp area

What about if the woodlice was in a completely dry area

The turning rate would decrease so that it would move in a straight line to increase the chances of finding a new damp area

What is a tropism

The term given to when plants respond, via growth, to a stimuli

What can tropisms be

Either positive or negative (growing towards or away from a stimulus)

What are the three factors that plants respond to

Light

Gravity

Water

What are tropisms controlled by

Specific growth factors such as indoleacetic acid (IAA)

What is IAA

A type of auxin that can control cell elongation in shoots and inhibit growth of cells in the roots

How does IAA travel

Via diffusion

What is it called when shoots bend towards the light

Positive phototropism

What is it called when shoot tips bend away from the light

Negative phototropism

What happens if there is unilateral sunlight (sunlight on only one side of the shoot)

The IAA diffuses to shaded side of the shoot resulting in a higher concentration of IAA there

What does this result in in SHOOTS

The cells on the shaded side (where the IAA is in higher conc) to elongate more which causes the plant to bend towards the light source

What do roots NOT do nor require

Photosynthesise

Do not require light

What are roots better able to do if they grow away from light, deep into the soil

Anchor the plant better

What does IAA do in both roots AND shoots

Diffuses towards the shaded (side with less light) part of the root or shoot

What does IAA do DIFFERENTLY in roots and shoots

In roots, IAA inhibits cell elongation on the side it is on

In shoots, IAA stimulates cell elongation on the side it is on

What does this result in in roots and shoots

In roots, the side with the most light elongates, causing the root to grow downwards

In shoots, the shaded side elongates more, causing the shoot to bend upwards and grow up

What is this response called in roots

Negative phototropism

What does gravity cause the IAA to do in a shoot

To diffuse from the upper side to the lower side of a shoot

What does this result in if the shoot is vertical

The plant will grow upwards

What does this result in if the shoots is on its side AND what is it called

The shoot will bend upwards (Negative gravitropism)

What does gravitropism do in roots

The IAA moves to lower side of the roots so that upper side elongates and the root bends downwards to anchor the plant in

What is this called

Positive gravitropism because the plant grows down towards the gravity source

3.6.1.2 RECEPTORS

3.6.1.2 RECEPTORS

Outline the general response flow chart to a stimulus

Stimulus —→ Receptor —→ Coordinator —→ Effector —→ Response

What is the nervous system made up of

Peripheral (PNS) and central nervous system (CNS)

What is the PNS made up of

The receptors, sensory and motor neurones

What is the CNS made up of

The brain and spinal chord

What does each receptor respond to

A specifc stimuli

What does this stumulation of a receptor cell lead to

The establishment of a generator potential which can cause a response

What are the three receptors you must know

Pacinian corpuscle

Rods

Cones

What must happen for an action potential to occur

Sodium ions must move into the neuron and cause the voltage to be above (-55mV)

Where are the pacinian corpuscle receptors found

Deep in skin (mainly in fingers and feet)

What stimulus does the pacinian corpuscle respond to

Pressure changes

What does the pacinian corpuscle consist of

A single sensory neurone wrapped with layers of tissue separated by gel

What does the sensory neurone in the Pacinian corpuscle have in its plasma membrane

Special channel proteins

Why are these channel proteins ‘special’

Because they are stretch - mediated sodium channels

What does stretch mediated mean

That they will open and allow Na⁺ ions into the sensory neurone only when they are stretched and deformed

What happens during the resting state, when the sodium ion channels are too narrow for sodium ions to diffuse into the sensory neurone

The resting potential is maintained

What happens when pressure is applied (ie pressing your finger down on table)

The neurone plasma membrane deforms, stretches and widens the sodium ion channels so that sodium ions diffuse in

What does this diffusion of Na⁺ ions into the neurone cause

The establishment of a generator potential

Name the two types of photoreceptors found in the retina

Rods and cones

What colour do rods process light in and why

Black and white because they cannot distinguish between different wavelengths of light

What is an important feature however of Rods which makes them very important and why

They can detect light of a very low intensity because many rod cells connnect to one sensory neurone (bipolar cell in this case)

What is this connection known as

Retinal convergence

What happens if a generator potential is too weak (ie does not reach -55mV)

No action potential will be triggered

DIFFERENCE BETWEEN ACTION POTENTIAL AND GENERATOR POTENTIAL TO BE STUDIED

DIFFERENCE BETWEEN ACTION POTENTIAL AND GENERATOR POTENTIAL TO BE STUDIED

What must happen to the pigment of the rod cells (Rhodopsin) to create a generator potential

It must be broken down by light energy

What must happen for the threshold for an action potential to be met in a bipolar cell

Enough pigment has to be broken down

Why can this threshold be reached even in low light

Because so many rod cells are connected to a single bipolar cell

What is this process an example of

Summation

What does the retinal convergence (multiple rod cells being linked to one bipolar cell which is a type of sensory neurone) mean we cannot do

Distinguish between the separate sources of light that stimulated it

Two light sources close together cannot be seen as separate - what is this known as

Rod cells giving low visual acuity

How many types of cone cells are there

3

What do each of these 3 types of cone cells have that is different from eachother

Different types of iodopsin pigment (Red, Green and Blue) which all absorb different wavelengths of light

How do we perceive colour images using these

Depending on the proportion of each cone cell that is stimulated

When is Iodopsin broken down

Only if there is a high light intensity, so action potentials can only be generated with enough light

Explain why cone cells only respond to high light intensity hence we can’t see colour in the dark

Becuase only one cone cell connects to a bipolar cell, therfore no spatial summation occurs

Why does colour vision using cone cells have high visual acuity

Because each cone cell is connected to one bipolar cell so the brain can distinguish between the separate sources of light detected

How are rods and cones distributed in the retina

Unevenly

What part of the retina is light focused on by the lens and what does this area receive

The fovea

The highest intensity of light

Therefore, where are most cone cells located

Near the fovea as they only respond to high light intensities

Where are rod cells found

Further away from the fovea because they can respond at lower light intensities

3.6.1.3 CONTROL OF THE HEART RATE

3.6.1.3 CONTROL OF THE HEART RATE

What is the rate if contraction of the heart controlled by

A wave of electrical activity

What is the Sinoatrial node (SAN) and where is it located

Located in the right atrium and acts as the pacemaker

Where is the atrioventricular node (AVN) located

Near the border of the right and left ventricle but still in the atria

What is the bundle of his and where is it

What comes after the bundle of his

Conductive tissue that runs down septum of heart and up the ventricles

Prukyne fibres come after

What are the steps in the control of the heart (simple)

SAN depolarisation

After a short delay, the AVN releases secondary wave of depolarisation

Bundle of His conducts this wave down septum and into purkyne fibres in wall of ventricles

Ventricles contract after short delay due to non conductive tissue and wave having to travel down bundle of His

This allows time for atria to empty all blood into ventricle

Cells repolarise and cardiac muscle relaxes

What are the steps in the control of the heart (After medulla oblongata has sent signals down parasympathetic / sympathetic nerves)

The SAN releases a wave of depolarisation across the atria, causing it to contract

The AVN then releases another wave of depolarisation once the first reaches it. There is a non conductive layer between the atria and ventricles which prevents wave of depolarisation travelling down to ventricles

Bundle of His can conduct and pass this wave of depolarisation down the septum and the Purkyne fibres in the walls of the ventricles

As a result, the apex (bottom tip) and then walls of the ventricles contract. There is short delay before this happens whilst the AVN transmits the second wave of depolarisation down bundle of His

This allows for enough time for the atria to pump all the blood into the ventricles. Cells then repolarise and cardiac muscle relaxes

What part of the brain controls the heart rate

The medulla oblongata via the autonomic nervous system

What are the two nervous systems, what are they attached to and what does each one do

Sympathetic nervous system - Increases heart rate

Parasympathetic nervous system - Decreases heart rate

Attached to the SAN

What do factors does heart rate change according to

pH

Blood pressure

What is the name of the chemical receptors

Chemoreceptors

What is the name of the blood pressure receptors

Baroreceptors

Where are both of these receptors found

Carotid Artery

Aorta

Why can high blood pressure be harmful

Can damage the walls of the arteries

Why can low blood pressure be harmful

Can lead to insufficient supply of oxygenated blood to respiring cells and insufficient removal of waste

Why can a lower pH due to increased C02 and lactic acid production lead to increased heart rate

To remove excess acid in order to prevent enzymes in blood from denaturing

For all LARGE MARK QUESTIONS TO RESPONSE TO STIMULUS IN HEART follow this framework of structure

Stimulus (To do with blood pressure or pH)

Receptor (Pressure or chemo)

Coordination (More electrical impulses sent to medulla oblongata AND THEN Sympathetic or parasympathetic nervous stimulation of SAN)

Effector (Cardiac muscle)

Response (Reduced or increased heart rate)

How are pressurereceptors triggered (baroreceptors)

Increased blood pressure stretches the pressurereceptors

3.6.2 NERVOUS COORDINATION

3.6.2 NERVOUS COORDINATION

What does the cell body of a neurone contain

The typical organelles found in an animal cell including the nucleus

What do dendrites do

They carry action potentials to cells surrounding the Myelinated motor neurone

What is the axon

The long, conductive fibre that carries the nervous impulse along the motor neurone

What are Schwann cells

Cells that wrap around the axon to form the myelin sheath, which is a lipid and therefore does not allow charged ions to pass through it