5.5.5 - Plant And Animal Responses Flashcards
Two types of nervous system
- Central
- Peripheral
Two parts of the CNS
- Brain
- Spinal Cord
Two (necessary) neurones in peripheral Nervous System
- Motor
- Sensory
Function of the motor neurone
Bring about a response
Function of sensory neurone
Detect a change in the environment (stimuli) and transmit an action potential to the CNS.
Function of motor neurone
Bring about a response
Two types of motor neurone response
- Autonomic
- Somatic
Two types of autonomic response
- what are they used for?
- Sympathetic - stressed situations - fight or flight
- Parasympathetic - calm/conserve situations
Examples of sympathetic response
- dilate pupil
- orgasm
- increase blood flow to gut
- decrease digestive activity
- makes liver release more glucose
- increase breathing rate
- increase heart rate
- increase blood flow to skeletal muscle
Examples of parasympathetic response
8 examples
- constricts pupils
- sexual arousal
- increase blood flow to gut (smooth muscle)
- increases digestive activity
- makes liver take up more glucose and convert to glycogen
- decreases breathing rate
- decreases heart rate
- decrease blood flow to skeletal muscle
Role of the CNS
- Its role is for coordinating nervous responses
- contains many synapses
What is the brain mostly made up of (tissues)?
Mostly made of non‐myelinated relay neurones - called grey matter
What is the spinal cord made up of (tissues)?
- Contains grey matter and white matter - Contains myelinated relay neurones for more rapid communication.
What is the PNS (Peripheral)made up of (tissues)?
- mostly of sensory and motor neurones
- connects receptors (which sense stimuli) to the CNS and then connect them to effectors (muscles and glands)
- this brings about a response
Sensory nervous system info
- Connects receptors to the CNS
- Dendrons of the neurones enters the spinal cord at the dorsal root where the cell body also is.
- The short axon connects to relay neurones in the CNS
Motor neurone system info.
- Connects the CNS to effectors
- Split into the autonomic and somatic nervous systems
Somatic nervous system info
- made of motor neurones under voluntary control, e.g. controlling skeletal muscles
- made mostly of myelinated neurones
- this makes responses fast
- single motor neurones connect CNS and effectors
Autonomic nervous system info
- What processes does it control?
- motor neurones under involuntary control, examples:
- controlling glands
- controlling cardiac muscle
- controlling smooth muscle in the gut
- controlling muscle in eyes
- controlling muscle in blood vessels or airways
- Mostly made of non-myelinated neurones
- this means responses are slower
- as least 2 neurones between CNS and effector connected at ganglia (swellings) containing their cell bodies
What is the significance of the autonomic system being antagonistic?
- Antagonistic means:
- depending on certain internal conditions or stress, balance between the -para and sympathetic systems will change to bring about an appropriate response
When is the parasympathetic system more active?
Times of rest/calm
When is the sympathetic system more active?
In times of stress - fight or flight
Sympathetic system structure and info
- Short preganglionic neurone
- ganglia near CNS
- many nerves leave CNS
- noradrenaline is neurotransmitter
- active in fight/flight or stress
Parasympathetic system structure and info
- long preganglionic neurone
- ganglia near organs
- a few nerves leave CNS then split up to go to effectors
- acetylcholine is neurotransmitter
- active is calm/rest - conserve
Autonomic nervous system def
Part of the nervous system responsible for controlling the involuntary motor activities of the body
Central Nervous system def
Central part of the nervous system composed of the brain and spinal cord
Peripheral nervous system def
The sensory and motor nerves connecting the sensory receptors and effectors to the CNS
Somatic nervous system def
The motor neurones under conscious control
Four main parts of the brain and their functions
- Cerebrum - the largest part and organises most of our higher thought processes, such as conscious thought and memory
- Cerebellum - which coordinates movement and balance
- Hypothalamus and Pituitary Complex - which organises homeostatic responses and controls various physiological processes
- Medulla Oblongata - which coordinates many of the autonomic responses
Cerebellum def
Region of the brain coordinating balance and fine control of movement
Cerebrum def
Region of the brain dealing with the higher functions such as conscious thought
It is divided into two cerebral hemispheres
Hypothalamus def
The part of the brain that coordinates homeostatic responses
Medulla oblongata def
Region of the brain that controls physiological responses
Pituitary gland info
- What do the anterior and posterior lobe do?
- Endocrine gland at the base of the brain, below but attached to the hypothalamus
- the anterior lobe secretes many hormones
- the posterior lobe stores and releases hormones made in the hypothalamus
Cerebrum structure
- Has two central hemispheres - connected by major tracts of neurones called the corpus callosum
- Outermost layer of the cerebrum consists of a thin layer of nerve cell bodies called the cerebral cortex
What does cerebrum control
- Conscious thought
- Conscious actions (incl. the ability to override some reflexes
- emotional responses
- intelligence, reasoning, judgement and decision-making
- factual memory
Function of motor area subdivision in the cerebral cortex
- Motor areas: send action potentials to various effectors (muscles and glands)
- Size of the regions are proportional to the complexity of the area it controls
- Motor areas on the left side of the brain control right side of the body, vice versa
Function of sensory area subdivision in the cerebral cortex
- These areas receive action potentials directly from the sensory receptors
- sizes of the areas are related/proportional to the sensitivity of the area inputs are received from
Function of association area subdivision in the cerebral cortex
- Compare sensory inputs with previous experience
- they can interpret what the input means and judge an appropriate response
Sensory receptors that provide a stimulus for the cerebellum
- Retina in the eye
- Balance organs in the inner ear
- Spindle fibres in the muscles - give information about muscle length and the joints
Where does the conscious decision to contract voluntary muscles come from?
Initiated in the cerebral cortex
List examples of functions of the cerebellum
- Maintaining body position and balance
- Judging the position of objects and limbs while moving about or playing sport
- Tensioning muscles - in order to use tools and play musical instruments effectively
- Coordinating contraction and relaxation of antagonistic skeletal muscles when walking and running
How do you strengthen the pathways in the cerebellum?
- Practice of the same movements and coordinations can strengthen complex neural pathways
- Complex activity becomes “programmed” into cerebellum
- So neurones from the cerebellum conduct action potentials to the motor areas, so that motor output to effectors can be finely controlled
How are cerebellum and cerebral cortex controlled?
They are connected by the “pons” (?)
Function of hypothalamus
- Controls homeostatic mechanisms in the body
- it contains its own sensory receptors and acts by negative feedback to maintain a constant internal environment
Examples of hypothalamus homeostatic control:
- Temperature regulation:
- Osmoregulation:
Pituitary gland and hypothalamus
Hdhdh
Medulla Oblongata function
- Controls the non-skeletal muscles (cardiac muscles and involuntary smooth muscle)
- It does this by sending action potentials out through the autonomic nervous system.
- The medulla Oblongata contains multiple centres for regulating several vital processes
Different centres of the medulla Oblongata and what they control/regulate
- Cardiac centre: regulates heart rate
- Vasomotor centre: regulates circulation and blood pressure
- Respiratory centre: controls the rate and depth of breathing
How do centres in the medulla oblongata receive information?
They receive sensory information and coordinate vital functions by “negative feedback”
What is grey matter?
Non-myelinated neurones
What is white matter?
Myelinated relay neurones - allow faster responses/action potentials
Knee jerk reflex def
A reflex action that straightens the leg when the tendon below the knee cap is tapped
Reflex action def
A response that does not involve any processing or coordination by the brain
Short reflex pathway
- Impulse received at sensory neurone
- Impulse goes to relay neurone
- Travels to a motor neurone which stimulates response from the effector
Why do we need reflex actions?
- They have survival value
- A reflex may be used to get out of danger
- To avoid damage to part of the body
- to maintain balance
What is the blinking reflex
Causes temporary closure of the eyelids to protect the eyes from damage
Pathway for blinking reflex
- passes through the brain - is a cranial reflex
- pathway does not involve any conscious movements or brain coordination
How may blinking be stimulated?
- a foreign object touching the eye (the corneal reflex)
- sudden bright light (the optical reflex)
- loud sounds
- sudden movements close to the eye
Corneal reflex mechanism
- the reflex is mediated by a sensory neurone form the cornea
- this enters the pons.
- a synapse connects the sensory neurone to a relay neurone
- this passes the action potential to the motor neurone.
- the motor neurone passes back out of the brain to the facial muscles
- this causes the eyelid muscles to blink
- this is a short and direct pathway
- so the reflex is very fast - takes about 0.1 seconds
- signal is sent to brain to notify it about the change/movement
Optical reflex mechanism
- protects the light sensitive cells of the retina from damage
- stimulus is detected by the retina
- reflex is mediated by the optical centre in the cerebral cortex
- optical reflex is slightly slower than the corneal reflex
Knee jerk reflex info
- it is a spinal reflex - nervous pathway passes through the spinal cord rather than through the brain
Knee jerk reflex mechanism
Hhhh
Examples of fight or flight responses and reasons
- Increased heart rate
- increased rate of blood flow - more oxygen and glucose to respiring cells to release more energy
- increased breathing rate and depth
- Faster rate of gas exchange = more oxygen in blood = more aerobic respiration to release more energy
- arterioles to skin and digestive system vasoconstrict and ones to muscle vasodilate
- Less oxygen to skinand digestive system (not needed in response) and more to muscles = more aerobic respiration in muscles to release more energy for muscle contraction
- pupils dilate
- allow more light on retina to see better
- increase in Glycogenolysis in the liver
- more glucose in blood for higher rate of respiration to release more energy
- metabolic rate increases
- More glucose converted to ATP for energy for response
- erector muscles in skin contract
- Make hairs stand up ‐ appear bigger to warn off individuals to avoid conflict and injury
- endorphins are released in the brain
- these negate some pain when an injury is inflicted upon the animal - it can keep on fighting
How brain coordinates response in fight or flight response
- Receptors sense threatening stimulus
- Action potential sent to sensory centres in cerebrum and then to association centres which coordinates the response
- Cerebrum stimulates hypothalamus in response to threat
- Hypothalamus stimulates sympathetic nervous system and the anterior pituitary gland
Role of sympathetic nervous system in fight or flight response
- increases activity of effectors via nervous impulses for rapid response
- stimulates the adrenal medulla to release adrenaline (bringing about response in effectors) for longer response
Action/Mechanism of adrenaline on fight or flight response
- Adrenaline acts as a first messenger by travelling through the blood and binding to receptors on the cell surface membrane of its target cells
- Binding causes a G-protein on the membrane to activate the enzyme adenyl cyclase
- this converts ATP to cyclic AMP - a second messenger.
- this brings about the effect in the cell
Main role of anterior pituitary gland
- causes hypothalamus to secrete more hormones (factors) into the blood to the pituitary gland
Hormones released in the anterior pituitary gland
- CRH (Corticotropin-releasing hormone)
- ACTH (adrenocorticotropic hormone)
- TRH (Thyrotropin-releasing hormone)
- TSH (Thyroid-stimulating hormone)
Three parts of the anterior pituitary gland
- Hypothalamic-pituitary-gonadal gland
- Hypothalamic-pituitary-thyroid gland
- Hypothalamic-adrenal-? gland
Effect of adrenocorticotropic hormone (ACTH)
Stimulates the adrenal cortex to release corticosteroid hormones
- e.g. cortisol
Effect of Corticotropin‐releasing hormone (CRH)
Causes the release of ACTH into the blood
Effect of Thyrotropin‐releasing hormone (TRH)
Dundee
Effect of thyroid‐ stimulating hormone (TSH)
DJ DJ
Thyroxine effect
- Increases metabolic rate
- Makes cells more sensitive to adrenaline
Effect of cortisol
- Increases metabolism of carbohydrates‐‐>glucose = increases blood glucose levels. - hence why some people lose weight
- Also increases blood pressure and suppresses immune system
What does it mean when the heart is myogenic?
It initiates its own contractions/beats
What part of the brain controls the frequency of the wave of excitations (controls heart rate) which occur from the heart?
Medulla Oblongata
- via the autonomic nervous system
Medulla oblongata and changing heart rate mechanism
- Chemoreceptors and pressure receptors detect changes in pressure and pH in the aorta and carotid artery
- more on lesson slides…
Describe how the medulla oblongata responds to an increase in CO2 concentration in the blood during exercise
Explain how this response leads to a decrease in the concentration of CO2 in the blood
(6 Marks)
Increase in CO2 levels increases levels of hydrogencarbonate ions in blood
Lower pH is detected by chemoreceptors in the carotid artery
Sympathetic nerve sends a signal to the heart to initiate impulses more frequently This also increases breathing rates and stroke volume
SAN is stimulated to initiate more waves of excitation
This causes the heart to beat faster
So there is an increase in stroke volume, increased blood flow in the arteries to the respiring tissues
So there is a faster removal of carbon dioxide
Blood CO2 levels fall to normal levels
This happens via a negative feedback response
How does heart rate decrease via neural pathways after exercise stops?
- Conc. of CO2 decreases - pH rises
- higher pH detected by chemoreceptors in carotid arteries, aorta and brain
- decreased action potential frequency in sensory neurone to medulla oblongata
- cardiovascular centre sends fewer sensory impulses to SAN vis the sympathetic nerve
- heart rate decreases
How does heart rate decrease via neural pathways after an increase in blood pressure?
- Blood pressure monitored by baroreceptors (pressure receptors) in carotid sinus
- if blood pressure is too high (e.g. exercise) sensory nerves carries signal to medulla oblongata
- cardiovascular centre sends nervous impulses to SAN via the vagus nerve (parasympathetic nervous system)
- acetylcholine (neurotransmitter) released at SAN
- causes heart rate to decrease which causes blood pressure to decrease
3 main types of muscle
- Cardiac
- Skeletal
- Smooth
What two protein filaments cause contractions in muscles?
Actin and myosin
What word describes the mechanism of the muscle
They work as antagonistic pairs
Involuntary smooth muscle description
- Consists of individual cells tapered at both ends (spindle shaped)
- At rest, each cell is about 500 micrometres long and 5 micrometres wide
- Each cell consists of a nucleus and bundles of actin and myosin
- This type of muscle contracts slowly and regularly
- It does not tire quickly
- It is controlled by the autonomic nervous system
What changes occur during contraction of a strained muscle?
A band - stays unchanged in length
H zone - shortens
I band - shortens
Cardiac muscle def
Muscle found in the heart walls
Involuntary smooth muscle def
Smooth muscle that contracts without conscious control
Neuromuscular junction def
The structure at which a nerve meets the muscle.
It is similar in action to a synapse
Skeletal (striated muscle) def
Muscle under voluntary control
How is contraction achieved in muscle cells?
- Interaction occurs between actin and myosin, two protein filaments in muscle cells.
- Muscles are usually arranged in opposing pairs; anatgonistically.
- When one contracts the other elongates
Cardiac muscle information
- lots of information about structure
- Forms muscular part of the heart
- Individual cells form long fibres
- fibres branch to form cross-bridges
- this ensures electrical stimulation spreads evenly over walls of the chambers
- also ensures that contractions in heart act as squeezing motions, as opposed to one-dimensional
- cells are joined by intercalated discs
- these are specialised cell surface membranes fused to produce gap junctions
- gap junctions allow free diffusion of ions between cells
- allows action potentials to pass easily and quickly along and between cardiac muscle fibres
How is contraction stimulated at a neuromuscular junction?
- Action potentials arriving at end of axon open Ca+ ion channels allowing Ca+ ions to flood into an axon tip
- Vesicles of acetylcholine move towards membrane and fuse, releasing ACh by exocytosis
- Acetylcholine molecules diffuse across gap and bind to receptors on the sarcolemma
- Na+ ion channels open and diffuse into the muscle fibre, causing depolarisation of the sarcolemma
- Wave of depolarisation passes along sarcolemma and down transverse tubules into the muscle fibre
- The action potential reaches the sarcoplasmic reticulum and causes it to release ACh
- Release of acetylcholine causes contraction of the muscle
What is the sarcolemma?
Muscle cell plasma membrane
What is the sarcoplasm and how is it adapted?
- Sarcoplasm is a muscle cell cytoplasm
Adaptations: - Many mitochondria -increased ATP production
- extensive sarcoplasmic reticulum
What are myofibrils?
The contractile elements of muscle fibres.
Structure of myofibrils
- They are divided into a chain of subunits called sarcomeres
Function of sarcomeres?
They contain protein filaments of actin and myosin
Parts of nervous system present in neuromuscular junction
- Skeletal muscle is under voluntary control - controlled by the somatic system
Which types of muscle are striated?
- Skeletal muscle
- Cardiac muscle
Where, precisely, are acetylcholine receptors found?
HINT: near muscle cells/sarcomeres
Post-synaptic membrane in the neuromuscular junction
Describe how three named components of the elbow joint interact to bring about hinge
movement (bending of the arm).
(3 Marks)
- Muscles work as antagonistic pairs
- Tendons connect to and pull on bone
- Ligaments hold bones together (prevent dislocation)
- Cartilage reduces friction /wear
- Synovial membrane secretes fluid
- Synovial fluid is a lubricant - allows smooth movement
Outline the organisation and roles of the autonomic nervous system in mammals
(8 Marks)
(Mark scheme)
- Two parts of the autonomic nervous system are sympathetic and parasympathetic
- Sympathetic has short preganglionic neurone, long postganglionic neurone and ganglia nearer the spinal cord
- Parasympathetic has long preganglionic neurone, short postganglionic neurone and ganglia near the target organ
- Sympathetic uses noradrenaline, wheareas parasympathetic uses acetylcholine as neurotransmitter
- List of differences in what they do:
- e.g. parasympathetic active in times of calm/relaxation and sympathetic is active in fight/flight and stress responses.
- Sympathetic increases heart rate, whereas parasympathetic decreases heart rate
- etc.
Describe the events that occur after adrenaline reaches the cell surface membrane that then result in changes in metabolism inside the cell cytoplasm.
• ACh acts as a first messenger
• Binds to complementary receptor on target cell surface membrane
• Activates G- proteins
↳ these activate adenyl cyclase
• adenyl cyclase converts ATP into cAMP (cyclic AMP)
• cAMP activates enzymes /proteins by altering 3D structure
Where are calcium ions produced?
In the sarcoplasmic reticulum
What are sarcomeres?
These are the contractile elements of muscle muscle cells made of sarcomeres
Function of ATPase in each end of the mysosin heads
Breaks down ATP into ADP and Pi to provide energy to return the myosin head to its original position
Different parts in structure of a sarcomere and their location
Not done yet…
Z band:
M band:
Actin bundle:
Myosin bundle:
Muscle contraction - model mechanism
- Calcium ions bind to troponin
- This causes troponin to change shape
- This moves tropomyosin away from the actin, exposing the myosin head binding sites on the actin
- Myosin heads (with ADP and Pi attached) bind to actin to form actin-myosin cross-bridges
- Binding causes the myosin head to move
- It slides past the stationary myosin
- This is known as the “power stroke”
- ADP and Pi are released from the myosin head during the power stroke
- ATP attaches to myosin head, causing it to detach from the actin
- ATP is hydrolysed (by ATPase on the myosin head) into ADP and Pi
- This provides the energy to return the myosin head to its original position
- Myosin can then reattach further up the actin and repeat
- When the stimulus stops Ca2+ ions are actively transported back into the sarcoplasmic reticulum
- The Calcium conc. will fall to the point where troponin and tropomyosin move back to cover the binding sites
Function of the t/transverse tubules in muscle cells
Vgvgv
Function of anti-acetylcholinesterase
- Prevents the breakdown of ACh
- Allows ACh to bind to receptors for longer for longer contractions
- Can be used to treat Myasthenia Gravis
What is Myasthenia Gravis?
What are the symptoms?
- It is an inheritable autoimmune disease
- There are auto-antibodies to the ACh receptors at the neuromuscular junction
- So less impulses can be sent to muscles
- So less muscle contractions can occur/weaker contractions/less frequent contractions
Symptoms include: - Droopy eyelids
- Slurred speech
- Weak arms and muscles
- Double vision (diplopia due to weaker eye muscles)
Name the part of a synapse that secretes ACh
Synaptic knob
What is the role of the sarcoplasmic reticulum?
Stores calcium ions and releases it over the muscle fibres to cause contraction
What is rigor mortis?
How does it occur?
- Myosin heads continue binding with the active sites of actin proteins via adenosine diphosphate (ADP)
- The muscle is unable to relax until further enzyme activity degrades the complex.
- Normal relaxation would occur by replacing ADP with ATP, which would destabilize the myosin-actin bond and break the cross-bridge.
- However, as ATP is absent, there must be a breakdown of muscle tissue by enzymes (endogenous or bacterial) during decomposition.
- As part of the process of decomposition, the myosin heads are degraded by the enzymes, allowing the muscle contraction to release and the body to relax.
Effect of Calcium ions in myosin head
Calcium ions act as a cofactor for ATPase, and helps it function in the myosin head
Difference between slow and fast twitch muscle fibres
Slow: more mitochondria - ATP produced slower as oxidative phosphorylation takes place for aerobic respiration - longer distance exercise
Fast: less mitochondria - ATP produced quicker as anaerobic respiration occurs, only glycolysis occurs - shorter distance exercise
Outline three reasons why plants need to be able to respond to their environment and describe how they go about it
- To respond to/avoid abiotic stress
- To respond to and protect against predation or invasion by pathogens, avoid against grazing by herbivores
- To ensure germination occurs in suitable conditions e.g. photropism, geotropism, gravitropism, hydrotropism, etc, caused by auxins at tip of roots and shoots
- To gain resources - maximise photosynthesis to obtain more light/water/minerals
List different plant hormones and their function
Cytokinins - promote cell division
- delay leaf senescence(loss of chlorophyll)
- overcome apical dominance
- promote cell expansion
Abscisic acid - inhibits seed germination + growth
- cause stomata to close in low water availability
- inhibit bud growth
Auxins - promote cell elongation
- inhibit growth of side shoots
- inhibit leaf abscission
- inhibit growth of roots
Gibberellins - promote seed germination
- promote growth of stems
Ethene - causes leaf abscission (leaf fall)
- causes fruit ripening
How do plants respond to their environments?
Abiotic stress
Higher Temperatures - thicker waxy cuticle/layer
Very windy - more lignigication of xylem vessels
Drought - root growth slows, stomata close(abscisic acid)
Tropisms to maximise photosynthesis
Different types of tropism
Geotropism/Gravitropism - move roots lower down soil to gain more water for photosynthesis
Hydrotropism - roots move towards water to obtain more water for photosynthesis
Phototropism - point towards sun to maximise light absorption for photosynthesis
Chemotropism - help pollen grain move towards ovule
Thigmotropism - support and anchor, obtaining reactants for photosynthesis
How do plants avoid being eaten by herbivores/grazing?
- Thigmonasty - folding in response to touch, e.g, in Mimosa pudica
- Chemical Defences:
- tannins - make leaves taste bad and defend roots against pathogens
- alkaloids - make tips of roots and shoots and flowers taste bitter - animals are less likely to eat it
- pheromones - can be produced when one leaf is eaten - communicates with other leaves to produce chemical defences
Define leaf senescence
Ageing of leaves - chlorophyll degrades (causes leaves to change to autumnal colours - yellowing of leaves)
Define seed germination
Growth from the seed
Define apical dominance
- Inhibits lateral buds growing further down the shoot
- So shoots will grow upwards, no shoots growing outwards
- More light absorbed - phototropism
Define leaf abscission
Leaf fall, leaves start to die and fall off trees
Plant Hormones action and info
- Made in many plant tissues and act on a very wide range of target tissues
- Move in xylem vessels and phloem tissues by mass flow up and down the plant (and then diffusion or active transport from cell to cell)
- Bind to receptors (complementary in shape to the hormone) on cell surface membrane on target cells
- Binding causes a series of enzyme controlled reactions (sometimes causing genes to be switched on/off) that will bring about the response
Similarities between plant and animal hormone action
- Hormone binds to complementary receptor
- Causes cascade of events/enzyme reactions
- May involve switching on/off genes
- Only present in small concentrations/quantities (to have an effect)
- May have effect on more than one target tissue
- The effect may involve interactions of more than one hormone
Differences between plant and animal hormone action
Animal:
- Made in endocrine system
- Move in blood to location target tissue/ receptor
- Act on a few specific target tissues
- Animal hormones act more rapidly than plant hormones to produce effect on target tissue/cell
Plant:
- Made in many plant tissues
- Hormones move in xylem/phloem by mass flow, and by active transport and diffusion from cell to cell
- Act on most plant tissues
- Can act in cells where produced
- Act less rapidly to produce an effect on cells
State two ways in which the control of plant growth by growth substances differed from the control of blood sugar concentration by mammalian hormones
growth substances produced by, dividing cells / meristems ; ora hormones produced by, islets of Langerhans / alpha cells /beta cells / endocrine gland / pancreas
> growth substances move, in phloem / in xylem / from cell to cell ; – ora hormones / named hormone(s), move in blood
> growth substances usually produce a permanent change in the plant ; – ora hormones produce reversible change in blood sugar
> (GS) not homeostatic / no negative feedback ; ora for hormones – R positive feedback A description of negative feedback
> (GS) not protein / not polypeptide ; ora insulin / glucagon, are proteins
Effect caused by auxins
- Promote cell elongation in shoots - causing shoots to grow
- High concentrations inhibit root growth (inhibits elongation)
- Maintains apical dominance - inhibits growth of side (lateral) shoots (buds)
- Inhibit leaf and fruit abscission
- Prevents ethene production from increasing
- In short: auxin causes apical dominance, tall shoots and Abscission
Commercial use of auxins
- Cuttings of plants are dipped in rooting powder containing low concentrations of auxin (promotors root growth)
- Weedkiller - promotors rapid shoot growth - plant can’t support itself and falls and dies
- Can help make seedless fruits
Effect of abscissic acid
- Inhibits seed germination and growth
- this ensures seeds only germinate in optimal conditions
- Cause stomata to close in low water availability
- Inhibit lateral bud growth (apical dominance)
- High auxin levels keep abscisic acid levels high - prevents lateral bud growth
Effect of cytokinins
- Overcome apical dominance (promote lateral bud growth)
- High levels of auxin inhibit cytokinin effects
- Low levels of auxin allows cytokinins to promote lateral bud growth
- Delay leaf senescence (ageing causing loss of chlorophyll)
- Promote cell division/cytokinesis (and cell expansion)
Commercial use of cytokinins
- Prevent yellowing of lettuce leaves (senescence)
- In tissue culture (artificial I cloning of plants) cytokinins added to promote many side shoots - can be grown into new plants - higher production of new plants
Gibberellins effects
- Promotes seed germination
- When seed absorbs water, embryo releases gibberellin
- Gibberellin travels to aleurone layer - causing production of amylose
- Starch —> maltose
- Maltose is hydrolysed to glucose for aerobic respiration enabling growth
- Promotes internodal growth of stems
- Promotes cell elongation and cell division
- In short:
Giberrellins for germination and Internodal growth
Commercial uses of gibberellins
- Elongate internodal cells in stalks of grapes - grapes spread out and get bigger
- Elongation of internodal cells in sugar cane - more sugar
- Beer production needs malt. Gibberellins added to encourage barley seed to make amylose so starch converted to maltose
- Germination then stopped by drying
Ethene effect of plant cells
- Promotes leaf abscission (leaf fall and death)
- Promotes fruit ripening
Commercial uses of ethene hormone
Spraying fruit with an ethene based compound can:
- Speed up ripening in bananas and other fruits
- promote fruit abscission in cherries and other fruits
- Cold conditions, little oxygen and high CO2 prevents ethene synthesis and can prevent fruit ripening during shipping
In short:
- Ethene for fruit ripening
Mechanism - Method for a practical investigation into the effect of IAA (Indole Acetic Acid (IAA - Auxin)) on growth of shoots
- Take 15 seedlings, cut off the tip and measure them
- To 5 seedlings cover the end of the tip with lanolin (wax) (A)
- To another 5, cover the end with the lanolin infused with IAA (B)
- Leave the final 5 untreated (C)
- After 3 days re-measure them
- A and C won’t grow - no auxins
- B will grow, IAA (auxins) cause cell elongation in shoots
- C shows IAA is causing the effect
- A shows lanolin alone is not causing the effect
Measure the growth of each of the shoots and calculate the percentage growth
Variables that should be controlled in investigation into the effect of IAA on growth of shoots
- Temperature
- Light intensity
- Age of seedlings
- Species of seedlings
- pH of soil
- O2/CO2 conc.
Devise an experiment to show the positive phototropism of plants
- Collect 20 seedlings
- Mark their stems every 20mm
- Plant 10 plants in one pot and 10 in another
- Set up lamps so one pot (A) light from all directions
- Make sure the other 10 only get light from one side
- Leave the plants to grow for 4 days
- Review and analyse the results
Tropism def
- When plants respond, via growth, to stimuli
- Tropisms can be positive or negative, growing away form or towards a stimulus
- Plants respond to light, gravity and water
Why do plants need light
- Shoots need light for LDR in photosynthesis
- This is why plants grow and bend towards light.
- This is controlled by the IAA.
- This is positive phototropism
Where is IAA produced?
Shoot tip cells
Mechanism for cell elongation/apical shoot growth (7 points)
- Auxins are produced at the apex (tip) of the shoot
- These diffuse down the shoot to the zone of elongation and bind to complementary receptors of the cells
- This causes protons (H+) ions to be actively transported into the cell wall
- This causes lower pH conditions - more acidic
- This causes wall loosening enzymes to work by breaking bonds with cellulose
- This makes cell walls more flexible
- Eater enters the cell and flexible wall allows cell to elongate
Mechanism for phototropism (5 points)
- Auxins are produced at the apex (tip) of the shoot
- If more light is coming from one side, phototropism enzymes are activated more on this side
- Phototropins cause PIN proteins to transport more auxins to shaded side
- Cells on the shaded side of the shoot elongate more quickly
- This causes the shoot to bend towards the light
Describe two similarities in the action of plant and animal cell signalling.
(2 Marks)
- Hormone binds to a complementary shaped receptor
- Binding causes a cascade of events/enzyme reactions
- May involve the switching on/off genes
- Hormones may have an effect on more than one target cell/tissue
Asexual reproduction and the ability to prodcue natural reprodcutive clones is common in plants but rare in animals.
Explain why plants are able to form more natural reproductive clones than animals.
(2 Marks)
- Most plant cells are totipotent / retain the ability to differentiate into any cell type
- Plants have meristems/meristematic tissue
- Whereas most animal cells are not totipotent - they are multipotent - only able to divide into the same type of cell
Human shields his eyes from bright light.
Cress seedling grows towards the light 24 hours after being planted.
Describe the mechanism that produces the responses to light in cress seedlings and in the human.
(7 Marks)
Plant - cress seedling:
- Apical cells at tip of shoot produce IAA/auxins
- IAA actively transported down the shoot
- Greater auxin concentration on the shaded side of the leaf
- Auxins bind to complementary receptors on cell surface of plant cells
- H+ ions pumped into the cell wall - low pH to allow cell wall loosening enzymes to work - bonds broken within cellulose wall
- This causes cell elongation on shaded side of the plant
Human:
- retina in eyes detect light
- Action potentials sent along sensory neurone
- Travels to the neuromuscular junction
- This allows synaptic transmission across to the muscle cells
- This causes depolarisation/contraction of muscle fibres (myofibrils)
- Actin and myosin slide over each other
What can be shown by different experiments on phototropism of plants
- different experiments done over history
Darwin:
- Showed the tip was responsible for phototropism
Boysen-Jensen:
- Shows a substance responsible for phototropism (auxins) must pass down from the tip to cause a response
- Gelatin is permeable and mica is impermeable
Went’s Work:
- Showed that a chemical from the tip caused the response (auxin)
- This effect could be caused artificially if the chemical was allowed to diffuse into an agar block
Direction of movement of shoots and roots in geotropism
Shoots - negative geotropism (grow away from gravity)
Roots - positive geotropism (grow down with gravity)
Investigation to prove geotropism mechanism
- Collect 10 seeds
- Embed 5 in one Petri dish of moist cotton wool
- Embed the other 5 in another Petri dish
- Place one group (A - control) in the klinostat and allow it to turn very slowly for 4 days
- With the other group (B) place them in the klinostat and do not turn it for the same length of time
- Observe the results
Auxins - mechanism for geotropism
- Auxins are produced at the apex (tip) of the roots
- If roots are lying flat, auxin collects in the other side
- Auxins inhibit cell elongation in the roots
- Upper side cells elongate and so roots bend downwards
Suggest how hormones affect a plant’s growth if the top of the plant shoot is eaten by an animal.
(3 Marks)
- Less auxins will be produced
- Less apical dominance occurs
- Plants shoots grow sideways/lateral buds develop
- Plant becomes bushy
Describe two ways in which hormones may alter a plants growth in response to overcrowding by other plants.
(4 Marks)
- Auxins are produced
- They cause positive phototropism
- Plant shoots grow/bend towards light
- Plants may grow taller/etiolation
- Climbing plants climb/grow over other plants
- Positive phigmotropism/sense of touch
- Roots May grow towards water/minerals
- Positive hydrotropism
- Alleopathy (?)
The distribution and abundance of plants in a habitat can show how a physical factor varies across the habitat.
Describe how you would measure the distribution and abundance of plants over a distance of 100 metres.
(6 Marks)
- Set grid/area to be sampled
- Tape measure/rope laid
- Record all species touching the line at selected intervals only - interrupted
- Use a quadrat to measure percentage cover of plants
- Use quadrat with ACFOR scale
- Point quadrat use described
- Use of a key to identify species
- Data recording sheets prepared in advance;
Outline the hormonal and nervous mechanisms involved in the control of heart rate.
(5 Marks)
- Adrenaline increases heart rate
- Cardiovascular centre in the medulla oblongata
- Nervous connection with the SAN - Sino-atrial node
- This controls the frequency at which the waves of excitation are sent out across heart
- Vagus/parasympathetic nerve decreases heart rate
- Accelerator/sympathetic nerve increases heart rate
- High blood pressure is detected by baroreceptors in the carotid artery
- Low blood pH/low blood CO2 levels are detected by chemoreceptors in the aorta
State two commercial uses of plant growth substances (not what hormones are involved)
(2 Marks)
- Faster ripening of fruits
- Rooting powder/tissue culture
- Preserve healthy flowers/green vegetables
- Seedless fruits
- Weedkillers
- Restrict hedge growth
- Controls fruit drop
- Producing malt in brewing
In a practical experiment, explain why all the lettuce seeds were kept at 25 Degrees Celsius.
(2 Marks)
- So that temperature doesn’t affect the results - constant temperature
- Since temperature affects enzyme activity
- 25 Degrees is the optimum temperature for lettuce germination/enzyme activity
Describe and explain how the activation of the ‘fight of flight’ response affects voluntary, involuntary and cardiac muscle.
(6 Marks)
- MS photo on laptop
- Outline mechanism behind acetylcholine
- Outline different fight or flight responses, e.g. dilated pupils, increased heart rate etc.
- Which type of muscle, e.g. smooth muscle in blood vessels near skin vasodilate etc.
Suggest how hormones alter a plant’s growth if the top of the plant shoot is eaten by an animal.
(3 Marks)
• less auxin produced
- Apical Dominance stopped
- side shoots grow /lateral buds develop
- plant becomes bushy
Medulla Oblongata increasing heart rate mechanism
- High CO2 levels are detected by CHEMORECEPTORS in the carotid body and Aorta.
- Nerves relay the information to the Medulla oblongata
- The Cardiac nerve runs from the cardiac control centre in the Medulla to the SAN
- It releases noradrenaline which stimulates the SA node to fire faster.
- Adrenaline hormone also acts on the SA node in the same way
Medulla Oblongata decreasing heart rate mechanism
- High pressure detected by BARORECEPTORS in the carotid body and Aorta
- The Vagus Nerve runs from the cardiac control centre in the Medulla and directly to the SAN
- Vagus nerve releases Acetylcholine
- It inhibits the SA node and slows the heart rate
Describe similarities between the action of plant and animal hormones.
(2 Marks)
- bind to target receptors on cells
- May involve switching genes on/off
- only needed in small quantities/concentrations to have effect
- May cause cascade of events/enzyme reactions to occur
- May have effect on more than one target tissue
