Topic 6: Organisms respond to changes in their internal and external environments Flashcards
3.6.1.1 Survival and response
Define a stimulus.
- a detectable change in the environment, detected by receptors.
- Organisms can increase chance of survival by responding to a stimuli i.e. taxis and kinesis
3.6.1.1 Survival and response
Define taxes.
- movement of an organism in response to a stimuli.
- towards stimulus = + taxes
- away stimulus = - taxes.
3.6.1.1 Survival and response
Define kinesis.
with an example.
- change in speed of movement or rate of turning.
- i.e woodlouse must be in damp conditions to prevent excess water loss, rate of turning increases in dry conditions.
3.6.1.1 Survival and response
What are the advantges of taxes and kinesis?
- Maintain a mobile organism in a favourable environment.
3.6.1.1 Survival and response
What are plant growth factors and where are they produced?
- Chemicals that regulate plant growth response to directional stimuli that are produced in plant growing regions.
- diffuse from cell to cell.
3.6.1.1 Survival and response
What do plants respond to?
- Light : shoots grow towards light (+PT), roots grow away from light (-PT).
- Gravity : Roots are (+ gravitropic)
- Water : Plants grow towards water (+ hydroptropic)
3.6.1.1 Survival and response
What is a type of growth factor?
- IAA, type of auxin.
- Move around via diffusion or active transport.
- IAA makes cell walls become soft and stretchy OR short and hard.
- shoots = cell elongation
- roots = cell inhibitation.
3.6.1.1 Survival and response
Explain why shoots show positive phototropism.
- Shoots produce IAA which is transported down (diffusion) to the shaded side of the shoot tip.
- High concentration of IAA in shaded side of shoot.
- IAA causes cells on shaded part to elongate more + faster due to higher turgor pressure
- Shoot bends towards light = + PT
3.6.1.1 Survival and response
Describe how roots show negative phototropism.
- High concentration of IAA inhibits cell elongation.
- Cells elongate more on the shaded side.
- Roots bend away from light = - PT
3.6.1.1 Survival and response
Describe how roots respond to gravitropism.
- Cells in the tip of the root produce IAA.
- Transported along root on all sides.
- IAA increases on the lower side of the root due to gravity.
- IAA inhibits cell elongation, cells on this side elongate less.
- Root bends downwards = + gravitropism.
3.6.1.1 Survival and response
Describe how shoots respond to gravitropism.
- Cells in the tip of the shoot produce IAA.
- Transported along shoot on all side.
- IAA increases on the lower side of the shoot due to gravity.
- IAA promotes cell elongation, cells on this side elongate more.
- Shoots grow upwards = - gravitropism.
3.6.1.1 Survival and response
What is a reflex arc?
- A rapid, involuntary, short-lived response to a stimulus
3.6.1.1 Survival and response
Outline what happens in a 3-neurone simple reflex arc.
Receptor detects stimuli -> sensory neurone-> coordinator -> motor neurone -> effector -> response.
Sam = stimuli
Raced = receptor
Susie = sensory neurone
Cause =Coordinator
Mike = Motor neurone
Eats = effector
Rats = response
3.6.1.1 Survival and response
What neurones are involved in the reflex arc?
Motor, sensory and relay neurones
3.6.1.1 Survival and response
What is the role of a sensory neurone?
- To transmit nerve impulses from sensory receptors to the central nervous system
3.6.1.1 Survival and response
What is the role of a relay neurone?
- To transmit impulses between other neurones
3.6.1.1 Survival and response
What is the role of a motor neurone?
- To transmit nerve impulses from the central nervous system to an effector.
3.6.1.1 Survival and response
RP 10 Outline the method for the movement of an animal using either a choice chamber or maze.
Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or maze
Choice chamber:
1. Secure nylon fabric between lid and base to create surface for inverterbrates to move over.
2. Secure the lid.
3. Use teaspoon to add 12 invertebrates into central hole lid of each choice chamber.
4. Leave them for 5 mins to adjust.
5. Remove lid and count n.o of invertebrates in each chamber.
TOP TIP: take a picture before the invertebrates move.
3.6.1.1 Survival and response
What is the aim of RP 10?
Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or maze
- Investigstion into the response of invertebrates (woodlouse) to light/dark and humid/dry conditions in a choice chamber.
3.6.1.1 Survival and response
What is the hypothesis of RP10 ?
Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or maze
Most invertebrates will move into the chamber which is dark and humid.
3.6.1.1 Survival and response
Outline why the following are needed in the experiment:
1. silica beads
2. filter paper and water
3. black paper and cellotape.
Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or maze
- creates a dry chamber } absorbs mositure in air.
- Creates a damp/humid chamber.
- Creates a dark chamber.
3.6.1.1 Survival and response
Outline a conclusion for this practical.
Required practical 10: Investigation into the effect of an environmental variable on the movement of an animal using either a choice chamber or maze.
The woodlice prefer dark/damp environments } greater number of woodlice to be in side of chamber with damp paper. In unfavourable environements they move quickly + change directions often, stop moving once they reach dark/damp area.
3.6.1.2 Receptors
What features are common to all sensory receptors and what is used as an example of a receptor to illustrate that?
- Respond to specific stimuli
- stimulation of a receptors lead to the establishment of a generator potential.
- Pacinian corpuscle.
3.6.1.2 Receptors
Describe the basic structure of a pacinian corpuscle.
- Has a single sensory neurone wrapped with connective tissue (lamellae) sepearated by gel.
- stretched-mediated Na+ channels on plasma membrane.
- capillary runs along base layer of tissue.
3.6.1.2 Receptors
What stimulus does a pacinian corpuscle respond to? How?
- Stimuli = pressure
- Pressure deforms membrane, causing stretched mediated Na+ ion channels to open.
- If influx of Na+ ions raises membrane to threshold potential, generator potetial is produced.
- Action potential moves along the sensory neurone.
3.6.1.2 Receptors
Name two types of photoreceptor cell located in the retina.
- Cone cells
- Rod cells
3.6.1.2 Receptors
Where are the cone and rod cells located?
CONE
mainly in the central fovea where it can receive high light intensity.
ROD
evenly distrubted around the periphery NOT in fovea.
BLIND SPOT
No photoreceptors located here (no cone or rod cells).
No light is detected here.
3.6.1.2 Receptors
Compare and contrast cone and rod cells.
CONE
pigment: Iodopsin = red, green, blue
visual acuity / reason: High = each cone cell synapses with 1 bipolar neurone = no retinal convergence.
colour sensitivity: Tricolour = red, green, blue wavelengths are absorbed by different types of iodopsin.
density in fovea: High
density out of fovea: Low
light intensity: High
light sensitivity: less sensitive = not involved in night vision.
ROD
pigment: Rhodopson = black, white
visual acuity / reason: low = many rod cells synapse with 1 bipolar neurone.
colour sensitivity: Monochromatic = black, white, all wavelengths of light detected.
density in fovea: Low
density out of fovea: High
light intensity: Low
light sensitivity: Very sensitive = spatial summuation of subthreshold impulses.
3.6.1.3 Control of heart rate
Define myogenic.
- Contraction of heart is initiated within the muscle itself rather than by nerve impulses.
3.6.1.2 Receptors
Outline a pathway of light from a photoreceptor to the brain.
- Photoreceptor -> bipolar neurone -> ganglion cell of optic nerve -> brain.
3.6.1.3 Control of heart rate
State the name and location of the two nodes which are involved in heart contraction.
- Sinoatrial node (SAN): within the wall of the right atrium
- Atriventricular node (AVN): near lower end of right atrium in the wall that seperates the 2 atria.
3.6.1.3 Control of heart rate
Outline the role of SAN.
- acts as a pacemaker by transmitting waves of electrical activity along the walls of the atria at regular intervals.
3.6.1.3 Control of heart rate
Describe how heartbeats are intiated and coordinated.
- SAN initates waves of depolarisation (WOD).
- WOD spreads across atria and atrial systole.
- Layer of fibrous, non-conducting tissue delays impulses while ventricles fill and valves close. Creates a delay to ensure the atria are empty before the ventricles begin to contract.
- AVN carries WOD down septum via Bundle of His, which branches into purkinje fibres along ventricles.
- Causes ventricles to contract from apex upwards.
3.6.1.3 Control of heart rate
What is the role of the Bundle of His?
- a collection of conducting tissue that transmits the electrical activity to the apex (bottom) of the heart and around the ventricle walls along fibres called the Purkyne fibres.
3.6.1.3 Control of heart rate
What is the role of AVN?
- Waves of electrical activity cannot pass from the atria to the ventricles due to a collection of non-conducting tissue.
- Delay is created to ensure atria is empty before ventricles contract.
- Electrical activity pass through the AVN to the bundle of His.
3.6.1.3 Control of heart rate
Outline the role and location of chemoreceptors.
ROLE
* sensitive in changes in CO2 concentration.
* If CO2 is high, heart rate increases.
LOCATION
* found in aortic body = wall of aorta
* found in carotid body = wall of the carotid artery in the neck.
3.6.1.3 Control of heart rate
Outline the role and location of baroreceptors.
ROLE
* sensitive to changes in blood pressure.
* If blood pressure increases, heart rate decreases.
LOCATION
* found in walls of various arteries but mainly in carotid sinus (in wall of carotid artery.)
3.6.1.3 Control of heart rate
What is the autonomic nervous system?
- System that controls involuntary actions of muscles and glands
- Consists of: sympathetic and parasympathetic
3.6.1.3 Control of heart rate
State the difference between sympathetic and parasympathetic.
SYMPATHETIC:
* involved in flight or fight response = stimulates effectors to speed up activity.
PARASYMPATHETIC:
* involved in normal resting conditions = inhibits effectors to slow down activity.
3.6.1.3 Control of heart rate
Name the receptors and their location and how they are involved in changing heart rate.
CHEMORECEPTORS
* detect changes in pH e.g. increase concentration in CO2
* Carotid and aortic body.
BARORECEPTORS
* detect changes in blood pressure.
* Carotid body.
3.6.1.3 Control of heart rate
How does the body respond to an increase in blood pressure?
BARORECEPTORS
* baroreceptors send more impulses from the medulla oblongata to the SAN via parasympathetic nervous system
* acetylcholine is released (neurotransmitter)
* heart rate slows down = blood pressure decreases.
3.6.1.3 Control of heart rate
How does the body respond to a decrease in blood pressure ?
BARORECEPTORS
* baroreceptors send more impulses from medulla oblongata to SAN via sympathetic nervous system
* noradrenaline is released (neurotransmitter)
* Heart rate increases = blood pressure increases.
3.6.1.3 Control of heart rate
How does the body respond to an increase in CO2 concentration (low O2) ?
CHEMORECEPTORS
* Chemoreceptors detect pH decrease and send more impulses from the medulla oblongata to the SAN via sympathetic nervous system
* Noradrenaline is released
* Heart rate rises and O2, rate of blood flow to lungs increases = CO2 level decrease.
3.6.1.3 Control of heart rate
How does the body respond to a decrease in CO2 concentration (high O2)?
CHEMORECEPTORS
* chemoreceptor sends more impulses from the medulla oblongata to the SAN via a parasympathetic nervous system
* Acetylcholine is released (neurotransmitter)
* Heart rate slows down and O2 levels decrease = CO2 levels increase.
3.6.1.3 Control of heart rate
Medulla obolongata:
- when stimulated baro and chemoreceptors send a signal to a part of the brain called medulla oblongata.
- Part of the medulla oblongata that modifies heart rate is cardiovascular centre
CARDIOVASCULAR CENTRE has two regions:
1. Cardio-inhibitory centre
2. Cardio-acceleratory centre
- Nerve impulses sent from theses centres via the autonomic nervous system to SAN.
3.6.1.3 Control of heart rate
State the formula for cardiac output.
- Cardiac output = stroke volume x heart rate
CO = V x R
3.6.1.3 Control of heart rate
What is cardiac output?
- term used to describe the volume of blood that is pumped by the heart (the left and right ventricle) per unit of time
3.6.1.3 Control of heart rate
What is stroke volume?
- volume of blood pumped out of the left ventricle during one cardiac cycle.
- cm3
3.6.1.3 Control of heart rate
What is heart rate?
- number of times a heart beats per minute
This can also be described as the number of cardiac cycles per minute
3.6.1.3 Control of heart rate
WORKED EXAMPLE It took a woman 1 second to complete a single cardiac cycle. Their stroke volume was measured at 73cm3. Calculate their cardiac output, give your answer in dm3.
Step 1: Find the heart rate
1 cardiac cycle (atrial systole, ventricular systole and diastole) takes 1 second
To find the number of cardiac cycles completed in a minute, multiply by 60
60 x 1 = 60 bpm
Step 2: Insert relevant figures into the equation
Cardiac output = heart rate x stroke volume
Cardiac output = 60 x 73 = 4,380 cm3
CO = 4.38 dm3
1dm3 = 1000cm3
3.6.2.1 Nerve impulses
Describe the structure of a myelinated motor neurone.
6 structures.
- CELL BODY: contains usual cell organelles (nucleus, mitrochondria) and large amounts of R.E.R Produces proteins and neurotransmitters.
- DENDRONS: extension of cell body which divides into dendrites. Carry nerve impulses towards cell body.
- AXON: single fibre carrying nerve impulses away from cell body. Can be myelinated.
- SCHWANN CELLS: surround axon for electrical insulation & protection. Wrap around axon many times so layers of their membrane build up around it.
- MYELIN SHEATH: made from myelin-rich membranes of schwann cells.
- NODES OF RANVIER: short gaps between schwann cells that are next to each other when there is no myelin sheath.
3.6.2.1 Nerve impulses
Name 3 processes schwann cells are involved in.
- electrical insulation.
- phagocytosis.
- nerve regeneration.
3.6.2.1 Nerve impulses
How is a resting potential established?
- Sodium-potassium pumps move Na+ ions outof the axon = electrochemical gradient is created = more Na+ ions outside and the membrane is not permeable to Na+ ions.
- Sodium-potassium pumps actively transports K+ ions in the axon.
3.BUT K+ ions move out of the axon via FD due to potassium ion channels being opened and Na+ ion channels are closed.
- Outside of membrane is positively charged due to the imbalance of positive charged ions.
- 3Na+ ions = pumped out of axon.
2K+ ions = pumped in axon.
PROCESS REQUIRES ATP - active transport.