5.5- Plant and animal responses Flashcards
Describe different types of stimuli plants respond to
- biotic and abiotic components of the environment
- Examples- depositing thicker layers of wax on leaves in response to higher temperatures, signifying vascular tissue more heavily when very windy, chemical responses to herbivores
What is the ultimate purpose of plants responding to the environment
Helps plants survive long enough to reproduce
Name 3 different chemical defences in response to the threat of herbivores
- Tannins
- Alkaloids
- Pheromones
Describe Tannins
- toxic to microorganisms and larger herbivores
- in leaves, found in upper epidermis- make leaf taste bad
- in roots, prevent infiltration by pathogenic microorganisms
Describe Alkaloids
- derived from amino acids
- located in growing tips and flowers, and peripheral cell layers of stems and roots
- Bitter taste- feeding deterrent to animals
Describe pheromones
- chemicals released by 1 individual which can affect the behaviour or physiology of another
Describe different categories of plant responses
- tropisms- directional growth response
- positive tropic- plant responds towards stimulus
- negative tropic- plant responds away from stimulus
- nastic- non-directional to external stimuli
Describe an example of nastic responses
- sensitive plant Mimosa podia responds to touch with sudden falling of the leaves
- response is example of thigmonasty
Name different types of tropisms
- phototropism
- geotropism
- chemotropism
- thigmotropism
Describe phototropism
- shoots grow towards light (positively phototrophic)
- enables them to photosynthesise
Describe geotropism
- roots grow towards pull of gravity
- this anchors them in soil and helps them to take up water- needed for support (keeps them turgid), as a raw material for photosynthesis, to help cool the plant, and to carry minerals e.g. nitrate needed for the synthesis of amino acids
Describe chemotropism
- on a flower, pollen tubes grow down to the style, attracted by chemicals, towards the ovary where fertilisation can take place
Describe thigmotropism
- Shoots of climbing plants, such as ivy, wind around other plants or solid structures to gain support
Describe the role of hormones in plant responses
- coordinate plant responses to environmental stimuli
- chemical messengers that can be transported away from their site of manufacture to act in other parts (target cells or tissues) of the plant
- produced in a variety of tissues in the plant (not endocrine glands)
Describe the action of plant hormones
- when they reach their target cells, they bind to receptors on the plasma membrane
- specific hormones have specific shapes, which can only bind to specific receptors with complementary shapes on the membranes of particular cells
- specific binding means hormones can only act on correct tissues
- some hormones can have different effects on different tissues, some can amplify each other’s effects, and some can cancel out each other’s effects
- can influence cell division, differentiation, or elongation
Name 5 different plant hormones
- Cytokinins
- abscisic acid
- auxins (e.g. IAA- indole 3-acetic acid)
- gibberellins
- ethene
Describe cytokinins (plant hormones)
- promote cell division
- delay leaf senescence
- overcome apical dominance
- promote cell expansion
Describe abscisic acid (plant hormones
- inhibits seed germination and growth
- causes stomatal closure when the plant ios stressed by low water availability
Describe Auxins (plant hormones)
- promote cell elongation
- inhibit growth of site-shoots
- inhibit leaf abscission (fall)
Describe gibberellins (plant hormones)
- promote seed germination and growth of stems
Describe ethene (plant hormones)
Promotes fruit ripening
What is the apex of a plant
The tip
Which plant hormones are responsible for regulating plant growth
Auxins
What happens if you break the shoot tip off a plant
The plant starts to grow side branches from lateral buds that were previously dormant
Describe the scientific research process into auxins
1) Researchers first suggested that auxins from the apical bud prevent lateral buds from growing- when the tip is removed, auxin levels in the shoot drop and the buds grow. To test this, scientists applied paste with auxins to cut end and lateral buds didn’t grow
2) however, scientists manipulation of the plants could have had unexpected effect on exposure to oxygen- cells on end could have produced a hormone that promoted lateral bud growth
3) Because of this, scientists applied a ring of auxin transport inhibitor below the apex- lateral buds still grey
4) Then suggested that a normal auxin level in lateral bids inhibits growth, whereas low levels promote growth
5) however, 2 variables (auxin levels and growth inhibition) may have no effect on eachotehr- could both be affected by 3rd variable
6) Then suggested that auxin levels in lateral bids of kidney bean actually increased when the shoot tip was cut off
7) Now think that 2 other hormones are involved- Abscisic acid and cytokinins
Name 2 hormones other than auxins that are involved in plant growth
- abscisic acid
- cytokinins
Describe the role of abscisic acid in plant growth
- inhibits plant growth
- high auxin in the shoot keeps abscisic acid levels high in the bud
- when the tip (source of auxin) is removed, abscisic acid levels drop and the bud starts to grow
Describe the role of cytokinins in plant growth
- promote bud growth
- directly applying cytokinin to buds can override the apical dominance effect
- high levels of auxin make the shoot apex a sink for cytokinins produced in the roots- most of the cytokinin goes to the shoot apex
- when the apex is removed, cytokinin spreads evenly around the plant
Describe the apical dominance effect
- refers to the inhibition of lateral buds further down the shoot by chemicals produced by the apical bud at the tip of a plant shoot
- The lateral buds are more sensitive to auxin than the apical bud
- There is a concentration of auxin at which the apical bud is stimulated to grow while the lateral buds are inhibited
- When the apical bud is removed, the source of auxin is removed
- Since the auxin concentration is much lower, the lateral buds can now grow
- Thus pruning a shoot will cause it to branch
lateral and apical bud diagram
auxin levels in root, apical bud and lateral bud graph
Describe the role of gibberellins in plant growth
- plant hormones which are responsible for control of stem elongation and seed germination
Describe the effects of differing gibberellin levels in plants
- Researchers found higher levels of GA1 in tall pea plants (homozygous for the dominant Le allele) compared to dwarf pea plants (homozygous for the recessive le allele)
- They worked out that the Le gene was responsible for producing the enzyme that converted GA20 to GA1
Describe the research process investigating the effects of gibberellins of plant growth
1) In japan, a fungus causes disease which makes rice grow very tall- fungal compounds involved are gibberellins and include gibberellic acid (GA3)
2) Scientists tested gibberellic acid on many different plants- when they applied it to dwarf varieties of plants e.g. maize/peas or to rosette plants, they grew taller
3) Suggetss that gibberellic acid is responsible for plant stem growth- however, experiment may not have actually investigated a natural phenomenon just because GA3 CAN cause stem elongation, doesn’t mean that it DOES so in nature- experiment needs to work within concentrations of gibberellins naturally found in plants, and in parts of the plant that gibberellin molecules normally reach
4) To reach this criteria, compared GA1 levels in tall pea plants (homozygous for the dominant Le allele) compared to dwarf pea plants (homozygous for the recessive le allele)- found that plants with her GA1 levels were taller
5) To show that GA1 directly causes stem growth, needed to know how GA1 is formed- worked out the Le gene was responsible for producing the enzyme that converted GA20 to GA1
6) Then research chose pea plant with mutation that blocks gibberellin production between ent-kaurene and GA12-aldehyde- those plants produce no gibberellin and grow to only around 1cm tall
7) Researchers grafted a shoot onto homozygous le plant (which cannot convert GA20 to GA1) and it grew tall- such a shoot, with no GA20 of its own, does have the enzyme to convert GA20 to GA1, and it can use the unused GA2- from the normal plant- as thee shoot grew tall confirmed that GA1 causes stem elongation
8) Further studies have shown that gibberellins cause growth in the internodes by stimulating the production of a protein that controls the cell cycle
Synthesis pathway for gibberellins diagram
Gibberellins stem elongation diagram
What else do gibberellins effect
Seed germination
Describe the effects of gibberellins on seed germination
- promote seed germination
- when the seed absorbs water, the embryo releases gibberellin, which travels to the aleurone layer in the endosperm region of the seed
- the gibberellin enables the production of amylase, which can break down starch into glucose
- this provides a substrate for respiration for the embryo, so it goes
- the glucose is also used for protein synthesis
Branches of the nervous system
Autonomic divided into sympathetic and parasympathetic
Outline the central nervous system
- consists of brain and spinal cord
Describe the brain (brief- CNS)
- contains 86 billion neurones
- much composed of relay neurones
- multiple connections enabling complex neural pathways
- Most cells are non-myelinated and tissue looks grey in colour- grey matter
Describe the spinal cord (brief- CNS)
- spinal cord
- many non-myelinated relay neurones making up the central grey matte
- also contains many myelinated neurons making up outer region of white matter- carry action potentials up/down cord for rapid communication over long distances
- Protected by the vertebral column
- Between each vertebra, peripheral nerves enter and leave the spinal cord carrying action potentials to/from the rest of the body.
What is the role of the peripheral nervous system
- ensures rapid communication between the sesnory receptors, the CNS and the effectors
- composed of sensory and motor neurones- usually bundled together in. collective tossie sheath to from nerves
Describe the somatic nervous system
- motor neurones that conduct action potentials from the CNS to effectors
- under voluntary/conscious control
- e.g. skeletal muscles
- myelinated neurones- rapid responses
- always one single neurone connecting CNS to effector
- can only be stimulatory effect
Describe the autonomic nervous system
- motor neurones that conduct action potentials from the CNS to effectors
- not under voluntary control
- includes glands, cardiac muscle, smooth muscle in the walls of blood vessels, airway, wall of digestive system
- mostly unmyelinated neurones- control of many effectors don’t need to be rapid
- at least 2 neurones involved in the connection between CNS and effector
- neurones connected at small swellings- ganglia
- responsible for controlling majority of homeostatic mechanisms- plays vital role in regulating internal environment of body
- contains sympathetic and parasympathetic system
Describe the action of the sympathetic and the parasympathetic neurones
- sympathetic system prepares the body for activity, and the parasympathetic conserves energy
- differ in both structure and action
- antagonistic system- action of one opposes the other
- at rest, action potentials pass along the neurones of both systems at relatively low frequency
- controlled by subconscious parts of brain
- changes to internal conditions or stress lead to changes in the balance of stimulation between 2 systems- leads to the appropriate response
Compare the structure of the parasympathetic and the sympathetic nervous system
- S consists of many nerves leading out of CNS with each reading to a separate effector, whereas P consisted of just a few nerves leading out if the CNS which divide and lead to different effectors
- S has ganglia just outside the CNSm whereas P has ganglia in the effector tissue
- S has short pre-ganglionic neurones, whereas P has long pre-ganglionic neurones (variable in length, dependent upon position of effector)
- S has long post-ganglionic neuornes (variable in length, dependent upon position of effector), whereas S has short post-ganglionic neuones
- S uses noradrenaline as the neurotransmitter, whereas P uses acetylcholine
Compare the action of the parasympathetic and the sympathetic nervous system
- S increases activity to prepare the body for activity, whereas P decreases activity to conserve energy
- S is most active in times of stress, whereas P is most active during sleep or relaxation
- S increases heart rate whereas P decreases it
- S dilates pupils, whereas P contacts them
- S increases ventilation rate, whereas P decreases it
- S reduces digestive activity, whereas P increases it
- S causes orgasm, whereas P causes sexual arousal
name the 4 main areas of the brain
- cerebrum
- cerebellum
- hypothalamus and pituitary complex
- medulla oblongata
Describe the structure of the cerebrum
- has 2 cerebral hemispheres
- connected via major tracts on neurones- corpus callosum
- outermost layer consists of a thin layer of nerve cell bodies called the cerebral cortex
Describe the functions of the cerebrum
More highly developed in humans than any other organism, controls higher brain functions:
- conscious thought
- conscious actions including the ability to override some reflexes
- emotional responses
- intelligence, reasoning, judgement, decision making
- factual memory
Describe different areas about the cerebral cortex
- sensory areas- receive action potentials from the sensory receptors- size of the regions allocated to receive input from different receptors are related to the sensitivity of the area that inputs are received from
- association areas- compare sensory inputs with previous experience, interpret what the input means, and judges an appropriate response
- moor areas- sen action potentials to various effectors (muscles and glands)- sizes of the regions allocated to deal with different effectors are related to the complexity of the movements needed in the parts of the body. Motot eras on the left side control the effectors on the right side of the body and vice versa.
Lobes of the brain diagram and explanation
A- Frontal lobe- concerned with higher brain functions such as decision making, reasoning, planning and consciousness of emotions. It includes the motor cortex which stores information about how to carry out different movements
B- Parietal lobe – concerned with orientation, movement, sensation, calculation and types of recognition and memory.
C- Occipital lobe – Visual cortex, concerned with processing information from the eyes including vision, colour, shape and perspective
D- Cerebellum- coordinates movement and balance
E- Temporal Lobe – concerned with processing auditory information i.e. Hearing, sound, and recognition of speech. Also involved in memory
Areas of the cerebral cortex diagram
Why is the human brain wrinkled
- cerebral cortex has become enlarged to enable the higher processes to occur
- cerebral cortex is only thin layer of cells- has become enlarged by increasing its surface area which is around 2.5 m2 to fit inside the head
Describe the cerebellum
- contains over half of all the neurones in the brain
- involved with balance and coordination of movement
- must receive information from many sensory receptors and process the information accurately
- sensory organs that supply information- retina, balance organs in the inner ear, spindle fibres in muscles which give information about muscle length, and joints
- the conscious decision to contract voluntary muscles is initiated in the cerebral cortex, however, the CC doesn’t provide the complex signals needed to coordinate complex movements
- coordinates fine control of muscular movement e.g. maintaining body position/balance, judging the position of objects/limbs, tensioning muscles to use instruments/tools, coordinating contraction and relaxation of antagonistic skeletal muscles when walking/running
Describe pathways in the cerebellum
- fine control of muscular movement often requires learning
- once learnt, such activities may become second nature and involve much unconscious control
- this sort of coordination requires complex nervous pathways which are strengthened by practice
- means the complex activity becomes programmed into the cerebellum, and neurones from the cerebellum conduct action potentials to the motor areas so that motor output to he effectors can be finely controlled
How are the cerebrum and cerebellum connected?
The pons
Where does growth happen in plants
Meristems
Describe different types of meristems
- Apical meristems- at tips or apices (apex) of roots and shoots- responsible for roots.shoots getting longer
- lateral bud meristems- found in buds- can give rise to side shoots
- lateral meristems- form cylinder near the outside of roots and shoots- responsible for roots/shoos getting wider
- intercalary meristems- in some plants, located between the nodes, where the leaves and buds branch off the stem- growth between the nodes is responsible for the shoot getting longer
Describe the action of auxin in shoots when the light is on one side of the plant
- produced at the apex of the shoot
- travels to the shaded side if the sun is on one side of the plant (move away from the sun)
- causes cell elongation in the shaded side
- this causes the plant to grow in a bend towards the light, as the cells on the shaded side are elongating whereas those in the light aren’t
- the extent to which cells elongate is proportional to the concentration of auxins
Describe the action of auxin in shoots when the light ISN’T on one side of the plant
- when light equal on all sides, the auxins simply promote shoot growth evenly
Describe the action of auxin in roots
- involved in geotropic responses in roots
- in a root lying flat, auxin accumulates on the lower side- inhibits cell elongation
- the upper side continues to grow and the root bends downwards
- INVESTIGATED BY WENT
Compare the action of auxin in the shoots and roots
- in shoots, shoot lying flat bends upwards as auxins promote cell elongation
- in roots, root lying flat bends downwards as auxins inhibit cell elongation
- happens because root and shoot cells in the elongation zone exhibit different responses to the same concentrations of auxin- concentrations that stimulate shoot growth inhibit root growth
Briefly outline the investigation of phototrophic and geotropic responses
- phototropic responses can be investigated by using an experimental plant and a control plant with 10 replicates
- control is illuminated on all sides while the experimental has illumination from just one side
- in each plant, shoots and roots are marked every 2mm at the start
- after several days, the standard mean and standard deviation of the lengths between the marks has increased on the shady side
Briefly outline the investigation of geotropic responses
- control plant is evenly spun slowly by klinostat to ensure the effect of gravity is applied equally to all sides of the plant
- experimental plant- klinostat is not switched on so gravity is only applied to one side
-in the experimental plant, the root bends downwards because the upper side of the root has elongated more than the lower side- the shoot bends upwards, because the lower side of the shoot has elongated more than the upper side - in the control plant, both root and shoot grow horizontally
name experiments into the effect of plant hormones on phototropisms
- Darwin
- Boysen-Jensen
- Went
Describe Darwin’s experiments into the effect of plant hormones on phototropisms
- confirmed that the shoot tip was responsible for phototropic responses
Describe Boysen-Jensens experiments into the effect of plant hormones on phototropisms
- confirmed that water and/or solutes need to be able to move backwards from the shoot tip for phototropism to happen
- when a permeable gelatine block was inserted behind the shoot tip, the shoot still showed positive phototropism
- when an impermeable mica block was inserted there was no phototropic response
Describe Went’s experiments into the effect of plant hormones on phototropisms
- to demonstrate that a chemical messenger existed and could stimulate a phototropic effect artificially, Went found Agard block containing auxin stimulates growth, offset blocks containing auxin stimulate curved growth, and blocks containing no auxin have no effect
What experiment confirmed the role of auxin as the chemical messenger
- agar blocks impregnated with different concentrations of auxin gives the same result
- using a series of blocs of different concentrations of auxin created by serial dilution gives shoot curvature in proportion to the amount of auxin
Outline the mechanisms of auxin’s effect
Increases stretchiness of cell wall:
- promotes the active transpory of H+ by an ATPase enzyme on the plasma membrane, into the cell wall
- results in low pH
- this low pH provides optimum conditions for wall-loosening enzymes (expansins) to work
- these enzymes btreak bonds within he cellulose 9at the same time, the increased hydrogen ions also disrupt hydrogen bonds within cellulose)
- this means the walls become less rigid and cen expand as the cell taken in water
Comparison of autonomic and somatic nervous system diagram
What part of the brain controls homeostatic mechanisms, briefly outline this
the hypothalamus- contains its own sensory receptors and acts by negative feedback to maintain a constant internal environment
Describe the roles of the hypothalamus
Temperature regulation:
- the hypothalamus detects changes in core body temperature
- also receives sensory input from temperature receptors in the skin
- it will initiate responses to temperature change that regulate body temperature within a narrow range
- these responses may be mediated by the nervous system or by the hormonal system (via the pituitary gland)
Osmoregulation:
- contains osmoreceptors that monitor the water potential in the blood
- when the water potential changes, the osmoregulatory centre initiates responses that bring about a reversal of this change
- the responses are mediated by the hormonal system via the pituitary gland
Briefly outline the role of the pituitary gland
- acts in conjunction with the hypothalamus
- consists of 2 lobes- posterior and anterior lobe
Describe the posterior lobe of the pituitary gland
- links to the hypothalamus by specialised neurosecretory cells
- hormones such as ADH which are manufactured in the hypothalamus pass down the neurosecretory cells and area released into the blood from the pituitary gland
Describe the anterior lobe of the pituitary gland
- produces its own hormones which are released into the blood in response to releasing factors produced by the hypothalamus s
- releasing factors are hormones that need to be transported only a short distance from the hypothalamus to the pituitary
- hormones from the anterior pituitary control a number of physiological processes in the body including response to stress, growth, reproduction and lactation
Describe the medulla oblongata
- controls the non-skeletal muscles (the cardiac muscles and involuntary smooth muscles)
- sends action potentials through the autonomic nervous system
- contains centres for regulating several vital processes which receive sensory information and coordinate vital functions by negative feedback
Describe the centres of the medulla oblongata
- cardiac centre- regualtes heart rate
- vasomotor centre- regulates circulation and blood pressure
- respiratory centre- controls the rate and depth of breathing
Outline reflex actions
- responses to changes in the environment that don’t involve any processing in the brain to coordinate the movement
- the nervous pathway is as short as possible so that the reflex is rapid
- most consist of just 3 neurones- sensory to relay to motor
- the brain may be informed that the reflex has happened but is not involved in coordinating the response
- always have a survival value- may be used to get out of danger to avoid damage to part of the body, or it may be used to maintain balance
name examples of reflexes
- blinking reflex
- corneal reflex
- optical reflex
- knee jerk reflex
Outline the initiation/purpose of the blinking reflex
- causes temporary closure of the eyelids to protect eyes from damage
- may be stimulated by sudden changes in the environment e.g. a foreign object touching the eye (corneal reflex)
- a sudden bright light (optical reflex)
- sudden movements close to the eye
Describe the pathway of the blinking reflex
- cranial reflex- passes through the brain
- direct pathway- doesn’t involve any thought processes in the higher parts of the brain
- receptor and effect are in the same place- reflex arc
Outline the optical reflex
- protects light-sensitive cells of the retina fro. damage
- stimulus is detected by the retina and the reflex is mediated by the optical centre in the cerebral cortex
- the optical reflex is a little slower than the corneal reflex
What is another word for auxin
Indole-3-acetic acid- IAA
Outline the corneal reflex
- mediated by a sensory neurone from the cornea, which enters the pons
- a synapse connects the sensory neurone to a relay neurones, which passes the action potential to the motor neurone
- the motor neurone passes back out of the brain to the facial muscles, causing the eyelid to blink
- this is a very short and direct pathway, so the corneal reflex is very rapid- takes around 0.1 seconds
- usually causes both eyes to blink even if only 1 cornea is affected
Can the corneal reflex be inhibited by conscious control
yes
Describe how the corneal reflex be inhibited by conscious control
- the sensory neurone involved in the corneal reflex also passes the action potential to myelinated neurones in the pons
- these myelinated neurones carry the action potential to the sensory region in the cerebral cortex, to inform the higher centres of the brain that the stimulus has occurred
- this allows the reflex to be overridden by conscious control, as the higher parts of the brain can send inhibitory signals to the motor centre in the pons
- the myelinated neurones carrying g impulses to and from the cerebral cortex transmit action potentials much more rapidly than the non-myelinated neurone in the pons
- therefore the inhibitory action potentials can prevent the formation of an action potential in the other motor neurone
Describe stimulus and response in mammals
- have complex sensory mechanisms that monitor changes in both the internal and external environment
- these provide input to the brain, which must assimilate the inputs and coordinate a response which ensures survival
- e.g. simple task like standing up requires input from range of receptors (eyes, balance, organs, muscle stretch receptors)
- more complex activities/responses receive input from a wider range of receptors (e.g. information about blood glucose levels from islets of langerhans in the pancreas or information from stretch receptors in the stomach or pain receptors in the skin and joints)
- responses may be short term e.g. homeostatic mechanisms of temperature control, or long term e.g. behaviours associated with reproduction
name different responses (outputs to effectors coordinated to the brain)
- action potentials in the somatic nervous system
- action potentials in the sympathetic and parasympathetic parts of the autonomic nervous system
- release of hormones via the hypothalamus and pituitary gland
What are the different responses to threats in the fight or flight responses
- running away
- challenge to perceived threat
table of physiological changes and survival value caused by the fight or flight response
Outline how light causes the redistribution of auxin
- 2 enzymes identified whose activity are promoted by blue light- phototropin 1 and 2
- blue light is main component of white light that causes the phototropic response
- means there is lots of phototropin 1 activity on the light side but progressively less activity towards the dark side
- this gradient causes redistribution of PIN proteins- transmembrane proteins that can be found dorsally, ventrally or laterally on the plasma membrane of cells, control the efflux of auxin from each cell, essentially sending auxin in different directions in the shoot, depending upon their location on the plasma membrane
- activity of PIN proteins is controlled by PINOID molecule
- suggested that phototropins affect activity of PINOID- then affects PIN activity
- however recent evidence from Arabidopsis suggests this may only work for pulse-induced phototropism (short bursts of light), with another independent mechanism able to operate in continuous light
Describe commercial uses of auxins
- can be used to prevent leaf and fruit drop and can promote flowering for commercial flower production (but in high concentrations can also promote fruit drop)- useful if too many small fruit that will be difficult to cell as the plant then produces fewer
- taking cuttings- dipping the end of a cutting in rooting powder before planting it encourages root growth- rooting powder contains auxins and talcum powder
- seedless fruit- treating unpollinated flowers with auxin can promote growth of seedless fruit (parthenocarpy)- applying auxin promotes ovule growth, which triggers the automatic production of auxin by tissues in the developing fruit, helping to complete the developmental process
- herbicides- kill weeds- as they are man-made, plants find them harder to break down- can act within the plant for longer- promote shoot growth so much that the stem cannot support itself, buckles, and dies
Describe commercial uses of auxins
- can be used to prevent leaf and fruit drop and can promote flowering for commercial flower production (but in high concentrations can also promote fruit drop)- useful if too many small fruit that will be difficult to cell as the plant then produces fewer
- taking cuttings- dipping the end of a cutting in rooting powder before planting it encourages root growth- rooting powder contains auxins and talcum powder
- seedless fruit- treating unpollinated flowers with auxin can promote growth of seedless fruit (parthenocarpy)- applying auxin promotes ovule growth, which triggers the automatic production of auxin by tissues in the developing fruit, helping to complete the developmental process
- herbicides- kill weeds- as they are man-made, plants find them harder to break down- can act within the plant for longer- promote shoot growth so much that the stem cannot support itself, buckles, and dies
Shoot tip diagram
Cytokinins
- delay leaf senescence- used to prevent yellowing of lettuce leaves after they have been picked
- used in tissue culture to help mass-produce plants- promote bud and shoot growth from small pieces of tissue taken from a parent plant- this produces a short shoot with a lot of side branches which can be split into many small plants which can then be grown separately
name commercial uses of gibberellins
- fruit production
- brewing
- sugar production
- plant breeding
Describe use of gibberellins in fruit production
- delay senescence in citrus fruit, extending the time fruits can be left unpicked, and making them available longer in the shops
- can act with cytokinins to make apples elongate to improve their shape
- can make bunches of grapes less compact to prevent growth of individual grapes being restricted- causes grape stalks to elongate which means grapes get bigger
Describe use of gibberellins in brewing
- malt is needed to make beer- which is produced in malt-house at brewery
- when barley seeds germinate, the aleurone layer of the seed produces amylase enzymes that break down starch into maltose
- usually, the genes for amylase production are switched on by naturally occurring gibberellins
- adding gibberellis can speed up the process
- malt is then produced by dying and grinding the seeds
Describe use of gibberellins in sugar production
- spraying sugar cane with gibberellins stimulates growth between the nodes, making the stems elongate
- useful as sugar cane stores sugar in the cells of the internodes (subsections of stems)
- makes more sugar available from each plant
Describe use of gibberellins in plant breeding
- breeders job is to produce plants with desired characteristics by breeding together other plants, usually over many generations
- in conifer plants, this can take a particularly long time, because they spend a long time as juveniles before becoming reproductively active
- can speed up the process by inducing seed formation on young trees
-seed companies that want to harvest seeds from biennial plants (which flower only in their second year of life) can add gibberellins to induce seed production - can also stop plants from making gibberellins- spraying with gibberellin inhibitors can keep flowers short and stocky (desirable in plants like poinsettias), and ensures that the internodes of crop plants stay short, helping to prevent lodging (happen in wet summers stems bend over because of the weight of water collected on the ripened seed heads, making the crop difficult to harvest)
Describe the commercial use of ethene
- as ethene is a gas and cannot be sprayed directly, scientists developed 2-chlroroethyphosphonic acid- that can be sprayed in solution
Commercial uses include:
* speeding up fruit ripening in apples, tomatoes and citrus fruits
* promoting fruit drop in cotton, cherry and walnut
* promoting female sex expression in cucumbers, reducing the chance of self-pollination (pollination makes cucumbers taste bitter) and increasing yield
* promoting lateral growth in some plants, yielding compact flowering stems
- restricting ethenes effects can also be useful- storing fruit at a low temperature and high carbon dioxide levels prevents ethene synthesis and thus prevents fruit ripening - this means fruits can be stored for longer- essentials when shipping unripe bananas from the Caribbean- other inhibitors of ethene synthesis such as silver salts, can increase the shelf life of cut flowers
Outline the muscles involved/ function of the knee-jerk reflex
- involved in coordinated movement and balance
- quadriceps (muscle at front of thigh) contracts to straighten leg
- this muscle is attached to the lower leg via the patella tendon that connects the patella to the lower leg bones at the front of the know
- when the muscles at the front of the thigh are stretched, specialised stretch receptors- muscle spindles- detect an increase in length of the muscle
- if the stretching is unexpected, a reflex action causes contraction of the same muscle
- part of the mechanism that allows us to balance on 2 legs- e.g. if standing, the muscle in front of the thigh will stretch if the knee is bending or body is starting to lean beackwards- contraction of the muscles straightened the knee or beings body back front of legs
- the response must be rapid so body can remain balanced
Outline the pathway of the knee-jerk reflex
- spinal reflex- nervous pathway passes through spinal cord rather than through the brain
- only consists of 2 neurones- sensory to motor
- one less synapse so response is quicker
- higher parts of brain informed that reflex is happening, however, as there is no relay neurone, the brain cannot inhibit the reflex, as inhibition relies on rapid myelinated neurones carrying the inhibitory action potential to the synapse before the motor neurone is stimulated
- in the absence of a relay neurone, the motor neurone is stimulated directly by the sensory neurone and there is insufficient delay to enable inhibition
- this is why doctors test reflexed by tapping the tendon below the knee cap- causes immediate response that cannot be inhibited
Describe receptors that can detect a threat (fight or flight response)
- eyes, ears and nose can detect external threat
- internal receptors may detect therat e.g. pain or sudden decrease in blood pressure
Describe the initiation of the fight or flight response
1) inputs feed into the sensory centres in the cerebrum
2) the cerebrum passes signals to the association centres
3) if a threat is recognised, the cerebrum stimulates the hypothalamus
4) The hypothalamus increases activity in the sympathetic nervous system and stimulates the release of hormones from the anterior pituitary gland
Describe the role of the sympathetic nervous system in the fight or flight response
- increasing it’s stimulation increases the activity of the effectors
- nervous communication is used for rapid response- impulses activate glass and smooth muscles
-for a prolonged response, endocrine system is needed- sympathetic NS stimulates the adrenal medulla- adrenaline secreted from the adrenal medulla travels In blood stream to cells
Outline the mechanism of adrenaline action
Adrenaline is first messenger- amino acid derivate and therefore can’t enter target cell- must cause effect inside the cell, without entering the cell itself:
1) bind to adrenaline receptor on plasma membrane
2) This receptor is associated with a G protein on the inner surface of the plasma membrane, which is stimulated to activate the enzyme adenyl cyclase
3) Adenyl cyclase converts ATP to cyclic AMP (cAMP) - second messenger
4) cAMP causes an effect inside the cell by activating enzyme action- precise effect depends upon the cell that adrenaline has bound to
Describe the hormones secret by the hypothalamus in the fight or flight response
- secretes releasing hormones (AKA releasing factors) into the blood
- these pass down a portal vessel to the pituitary gland and stimulate the release of tropic hormones from the anterior pituitary
- these stimulate a wide variety of endocrine gland
name the 2 releasing hormones secreted by the hypothalamus in the fight or flight response
- Corticotropin-releasing hormone (CRH)
- Thyrotropin-releasing hormone (TRH)
Describe the effects of CRH (fight or flight)
- causes the release of adrenocorticotropic hormone (ACTH)
- ACTH passes around the blood system and stimulates the adrenal cortex to release a number of different corticosteroid hormones
- These include glucocorticoids e.g. cortisol that regulate the metabolism of carbohydrates- causes more glucose to be released from glycogen stores, new glucose may also be produced from fat and protein stores
Describe the effects of TRH (fight or flight)
- causes the release of thyroid-stimulating hormone (TSH)
- TSH stimulates the thyroid gland to release more thyroid hormone (thyroxine)
- thyroxine acts on nearly every cell of the body, increasing the metabolic rate and making the cells more sensitive to adrenaline
Fight or flight pituitary hypothalamus hormones diagram
Fight or flight response pathway diagram
Describe the roles of the heart
The heart pumps blood around the circulatory system-circulation has several important roles:
* Transport of oxygen and nutrients, such as glucose, fatty acids and amino acids to the tissues.
* Removal of waste products, such as carbon dioxide from the tissues to prevent accumulation that may become toxic.
* Transport of urea from the liver to the kidneys.
* Distribute heat around the body or deliver it to the skin to be radiated away
Describe the requirements of cells and tissues when one is physically active
- muscle cells need more oxygen and glucose so they can respire more, releasing more energy for contraction
- heart muscle cells need more oxygen and fatty acids
- all the muscles will need to remove more carbon dioxide and heat
Hw can the circulatory system adapt to meet the needs of the tissues
- raising/lowering hear rate- number of beats per minute
- altering the force of contractions of the ventricular walls
- altering the stroke volume
Define stroke volume
Volume of blood pumped per beat of the heart
Describe the standard coordination of heart rate
- cardiac muscle is myogenic- can initiate its own beat at regular intervals
- atrial muscle has a higher myogenic rate than ventricular muscle
- these 2 pairs of chambers must contract in a coordinated fashion or the heart action will be ineffective- coordination mechanism is essential
- SAN is own pacemaker- region of tissue that can initiate action potential- initiates waves of excitation that usually override the myogenic action of the cardiac muscle
- wave of excitation travels over the atrial walls, through the AVNm and down the purkyne fibres to the walls of the ventricles- causing them to contract
- heart muscle also responds directly to hormone adrenaline in blood- increases heart rate (frequency of contractions not beats themselves)
Describe heart rate at rest
- controlled by the SAN
- set frequency at which it initiates waves of excitation- varies by person
- frequency pf excitation is typically 60-80 per minute
What alters the frequency of the excitation waves of the SAN
Output from the cardiovascular centre in the medulla oblongata
Describe how the cardiovascular centre in the medulla oblongata can alter the frequency of waves of excitation from the SAN
- nerves from the cardiovascular centre in the medulla oblongata supply the SAN
- these nerves are part of the autonomic nervous system
- the nerves don’t initiate a contraction but can affect the frequency of contractions
Describe the 2 different nerves from the cardiovascular centre in the medulla oblongata and how they alter the frequency of waves of excitation from the SAN
ACCELERANS NERVE:
- sympathetic nerve
- cause the release of noradrenaline at the SAN
- causes increase in heart rate
VAGUS NERVE:
- release neurotransmitter acetylcholine
- reduces heart rate
Describe how environmental factors affect heart rate
- input from sensory receptors is fed to the cardiovascular centre in the medulla oblongata
- some inputs increase heartrate, whereas others decrease it
- the interaction of these inputs is coordinated by the cardiovascular centre to ensure that the output to the SAN is appropriate for overall conditions
Name different sensory inputs to the cardiovascular centre in the medulla oblongata
- stretch receptors in muscles
- chemoreceptors in carotid arteries, aorta and brain
- concentration of CO2 in the blood
- stretch receptors in walls of carotid sinus
Describe the role of stretch receptors in muscles in regulating heart rate
- detect movement of the limbs
- send impulses to the CV centre, informing that extra oxygen may soon be needed
- leads to an increase in heart rate
Describe the role of chemoreceptors in carotid arteries, aorta and brain in regulating heart rate
- monitor pH of blood
- when exercising, muscles produce more carbon dioxide
- some of this reacts with the water in the blood plasma to form carbonic acid
- this reduces the pH of blood, which will affect the transport of oxygen
- the change in pH is detected by the chemoreceptors, which send action potentials to the CV centre
– this will tend to increase heart rate
Describe the role of the concentration of CO2 in the blood in regulating heart rate
- when we stop exercising, the concentration of CO2 in the blood falls
- this reduces the activity of the accelerator pathway
- therefore, heart rate declines
Describe the role of stretch receptors in walls of carotid sinus in regulating heart rate
- small swelling in the carotid artery- monitors blood pressure
- an increase in blood pressure e.g. during vigorous exercise, is detected by these stretch receptors
- if pressure rises too high, the stretch receptors send action potentials to the CV centre
-this leads to reduction in heart rate
Control of heart rate diagram
What happens if the mechanism controlling heart rate fails
An artificial pacemaker must be fitted
Describe artificial pacemakers
- delivers an electrical impulse to the heart muscle
- implanted under the skin and fat on the chest (or sometimes within the chest cavity itself)
- may be connected to the SAN or directly to the ventricle muscle
Describe artificial pacemakers
- delivers an electrical impulse to the heart muscle
- implanted under the skin and fat on the chest (or sometimes within the chest cavity itself)
- may be connected to the SAN or directly to the ventricle muscle
briefly outline the structure of muscle
- composed of cells arranged to form fibres
- these fibres can contract to become shorter, which produces a force
- contraction is achieved by the interaction between 2 protein filaments (actin and myosin) in the muscle cells
- muscle can’t elongate without an antagonist
- therefore, muscles are usually arranged in opposing pairs, so that one contracts as the other elongates
- in some cases, the antagonist may be an elastic recoil or hydrostatic pressure in a chamber
Name 3 different types of muscle
- involuntary (smooth)
- cardiac (also involuntary)
- voluntary (skeletal or striated)
Describe the cells of involuntary (smooth) muscle
- consists of individual cells, tapered at both ends (spindle shaped)
- at rest, each cell is around 500um long and 5um wide
- each cell has a nucleus and bundles of actin and myosin
Describe the nature of contraction of involuntary (smooth muscle)
- contracts slowly and regularly
- doesn’t tire quickly
- controlled by the autonomic nervous system
Describe where involuntary (smooth) muscle is found
- walls of tubular structures e.g. digestive system and blood vessels
- usually arranged in longitudinal; and circular layers that oppose each other
involuntary (smooth) muscle diagram
involuntary (smooth) muscle microscopy
Describe the cells of cardiac muscle
- individual cells form long fibres
- this fibres branch to form cross-bridges between the fibres
- these cross-bridges help to ensure that electrical stimulation spreads evenly over the walls of the chambers
- when the muscle contracts, this arrangement also ensures that the contraction is a squeezing action rather than one-dimensional
- cells are joined by intercalated discs- specialised cell surface membranes fused to produce gap junctions that allow free diffusion of ions between the cells
- action potential pass easily and quickly between the cardiac muscle fibres
Describe the nature of contraction of cardiac muscle
- contracts and relaxes continuously throughout life
- can contract powerfully and doesn’t fatigue easily
- some muscle fibres in heart (Purkyne fibres) are modified to carry electrical impulses- coordinate the contraction of the chamber walls
- myogenic- can initiate own contraction
- rate of contraction normally controlled by SAN
Where is cardiac muscle found
Forms muscular part of heart
Cardiac muscle diagram
cardiac muscle microscopy
appears striated when viewed under microscope
Describe the location of voluntary (skeletal/striated) muscle
- occurs at the joints in the skeleton
Describe nature of contraction of voluntary (skeletal/striated) muscle
- contraction causes movement of the skeleton by bending or straightening the joint
- the muscles are arranged in antagonistic pairs- when one contracts, the other elongates
Describe the cells of voluntary (skeletal/striated) muscle
- muscle cell cytoplasm is sarcoplasm- specialised to contain many mitochondria and an extensive sarcoplasmic reticulum (specialised endoplasmic reticulum)
Describe the arrangement of voluntary (skeletal/striated) muscle
- muscle cells form fibres of around 100um in diameter- each fibre is multinucleate (contains many nuclei), and is surrounded by a membrane called the sarcolemma
- the contents of the fibres are arranged into a number of myofibrils, which are the contractile elements
- these myofibrils are divided into a chain of subunits called sarcomeres
- sarcomeres contain the protein filaments actin and myosin
- actin and myosin are arranged in a particular banded pattern, which gives the muscle a striped or striated appearance
- dark bands are known as A bands, and lighter bands are known as the I bands
Describe the nature of contraction of voluntary (skeletal/striated) muscle
- contracts quickly and powerfully
- fatigues quickly
- under voluntary control
- stimulated by somatic nervous system
voluntary (skeletal/striated) muscle diagram
voluntary (skeletal/striated) muscle microscopy
Comparison of different muscle types microscopy
What is the junction between the nervous system and a muscle called
neuromuscular junction
Describe the events at a neuromuscular junction
1) Action potentials arriving at the end of the axon open calcium ion channels in the membrane
2) Calcium ions flood into the end of the axon
3) Vescicles of acetylcholine move towards and fuse with the end of the membrane
4) acetylcholine molecules diffuse across the gap and fuse with receptors in the sarcolemma
5) those open sodium ion channels, which allow sodium ions to enter the muscle fibre
6) This causes depolarisation of the sarcolemma
7) a wave of depolarisation spreads along the sarcolemma and down transverse tubules into the muscle fibre
What is a motor unit
- some motor neurones stimulate single muscle fibres
- all these muscle fibres contract together, providing a stronger contraction- called a motor unit
How can the electrical activity of muscles be measured
Electromyograph (EMG)
Describe the use of an EMG
- when a muscle is stimulated, motor neurone creates action potential in the muscle fibres
- electrodes applied to the surface of the skin detect the combined effects of these action potentials
- a simple contraction of the muscle is seen as a series of apparently disorganised peaks on a trace
- amplitude of EMG recording reflects the number and size of the motor units involved in the contraction- more powerful contraction is seen as a higher amplitude
Comparison of muscle types table
What are myofibrils
- The contractile units of skeletal muscles
What is the sarcolemma
the membrane surrounding skeletal muscle cells
What is the sarcoplasm
The cell cytoplasm of muscle cells
What is the sarcoplasmic reticulum
The specialised endoplasmic reticulum of skeletal muscle cells
What are sarcomeres
A chain of subunits made up of myofibrils
Describe the stricture of the myofibril
- thin filaments- made up by actin- make up the light band (I-band)
- thick filaments- made up my myosin- make up the dark band (A-band)
- Z-Line- holds together thin filaments
- H-Zone- middle of dark band where ether is no overlap between thin and thick filaments
- sarcomere- distance between 2 Z-lines- functional unit of the muscle- at rest around 2.5um
- M-band- where myosin attaches (darker on micrograph)
Describe the thin filaments
- each consists of 2 chains of actin sub-units twisted around each other
- tropomyosin- molecule wound around each actin molecule
- tropomyosin is attached to globular molecules of troponin
- each troponin consists of 3 polypeptides- one bind stop actin, one to tropomyosin, one to calcium when it is available
- at rest, the tropomyosin covers the binding site (actin-myosin binding site) to which the thick filaments can bind, and it is herd in place by troponin
Describe the thick filaments
- consists of bundle of myosin molecules
- each myosin occult has 2 porting heads, which stick out at the end of the molecule
- these heads are mobile and can bind ti actin wen the binding sites are exposed
Briefly outline the sliding filament hypothesis
- during contraction, the light band and the H-zone get shorter
- therefore, the Z lines more closer together and the sarcomere gets shorter
- during contraction, the thick and thin filaments slide past one another
Sliding filaments diagram
Outline the process of muscle contraction
1) When the muscle is stimulated, the action potential passes along the sarcolemma down the t-tubules (transverse tubules) into the muscle fibre
2) The action potential is carried to the sarcoplasmic creticulumn, which stores calcium ions- and causes the release of calcium ions into te sarcoplasm
3) The calcium ions bind to the troponin, which alters the shape pulling the tropomyosin aside- exposes to binding sites on the actin
4) Part of the myosin head acts as ATPase and can hydolyse ATP to ADP and Pi- releasing energy
5) This causes the myosin head to attach to the actin filament, forming a cross-bridge- millions of cross-bridges can be formed between the two filaments
6) The myosin head moves (tilts backwards), causing the thin filament to slide past the thick filament- this is the power stroke
7) During the power-stroke, ADP and Pi are released from the myosin head
8) After the power-stroke, a new ATP molecule attaches to the myosin head, breaking the cross-bridge
9) The myosin egad then returns to its original position (swings forward again) as the ATP is hydrolysed (provides the energy tome this movement occur)
10) The myosin head can now make a New Cross-bridge further along the actin filament
What happens once muscle contraction has occurred
The calcium ions are rapidly pumped back into the sarcoplasmic reticulum- allows the muscle to relax
Describe the needs for the supply of ATP in muscle contraction
- millions of myosin heads involved- makes huge requirement of ATP
- the ATP available in muscle tissue is only enough to support at most most 1-2 seconds of contraction
- means ATP must be generated very quickly in order to allow continued contraction
- 3 mechanisms involved- aerobic respiration oil the mitochondria, anaerobic respiration in the sarcoplasm of the muscle tissue, and creatine phosphate
Describe aerobic respiration in mitochondria as a way of maintaining supply of ATP for muscle contraction
- muscle tissue contains a large number of mitochondria in which aerobic respiration can occur
- the Bohr effect helps to release more oxygen from the haemoglobin in the blood
- however, during intense activity, the rate at which ATP can be produced will be limited by the delivery of oxygen to the muscle tissue
Describe anaerobic respiration in the sarcoplasm of muscle tissue as a way of maintaining supply of ATP for muscle contraction
- anaerobic respiration can release a little more ATP from the respiratory substrates
- however, it leads to the production of lactate (lactic acid) which is toxic
- anaerobic respiration can only last a few seconds before lactic acid build-up starts to cause fatigue
Describe creatine phosphate as a way of maintaining supply of ATP for muscle contraction
- in the sarcoplasm
- acts a reserve store phosphate group[s
- the phosphate can be transferred from the creatine phosphate to ADP molecules, creating ATP molecules very rapidly
- the enzyme creatine phosphotransferase is involved
- he supply of creatine phosphate is sufficient to support muscular contraction for a further 2-4 seconds
