5.5 Flashcards
what do plants respond to
biotic and abiotic factors and external stimuli
give examples of stimuli to plants
-temperature (e.g in a high temperature they will deposit a thick layer of wax on their leaves)
-wind (in very windy conditions they may have vascular tissue which is more heavily lignified)
describe tannins
(chemical defence) toxic to microorganisms and larger herbivores. In leaves, they are found in the upper epidermis, and make the leaf taste bad. In the roots they prevent infiltration by pathogenic microorganisms
describe alkaloids
(chemical defence) they are derived from amino acids. In plants, scientists think they are a feeding deterrent to animals, tasting bitter. They are located in growing tips and flowers, and peripheral cell layers of stems and roots (N containing)
describe pheromones
(chemical defence) chemicals which are released by one individual which can affect the behaviour or physiology of another
what are the types of response in plants ( name the tropisms which are directional growth responses of plants)
-phototropism
-geotropism
-chemotropism
-thigmotropism
what are tropisms
tropisms are directional growth responses of plants. The direction of the response is stimulated by the direction of the external stimulus.
what is geotropism
roots rowing towards the pull of gravity. This anchors them in soil and helps them to take up water, which is needed for support (to keep cells turgid), as a raw material for photosynthesis and to help cool the plant. There will also be minerals such as nitrate in the water needed for synthesis of amino acids
what is chemotropism
on a flower, pollen tubes grow down the style, attracted by chemicals, towards the ovary where fertilisation can take place
what is thigmotropism
shoots of climbing plants such as ivy, wind around other plants or solid structures to gain support
what is phototropism
shoots grow towards light ( they are positively phototropic ) which enables them to photosynthesise
whats a positive tropic response and whats a negative trophic response?
positive tropic response- a plant responding towards a stimulus
negative trophic response- a plant responding away from a stimulus
what are nastic responses
non- directional responses to external stimuli are nastic responses
talk about the sensitive plant Mimosa pudica and its response to touch
it responds to touch with a sudden folding of the leaves, this response is thigmonasty
what is thigmonasty
a non-direct(ional) response, in plants , to the stimulation of contact
what coordinates plant responses and what produces them
hormones (chemical messengers to act on target cells) coordinate responses, they are produced by cells in a variety of tissues in the plant.
state what happens after plant hormones reach their target cells and their effect and their influence
after 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 complimentary shapes on the membrane of particular cells, this specific binding ensures hormones only act upon the correct tissues. Some hormones can have different effects on different tissues; some can amplify each others effects. Hormones can influence cell division, cell elongation or cell differentiation
name the 5 plant hormones
-cytokinins
-abscisic acid
-auxins e.g. IAA (indole-3-acetic acid)
-gibberellins
-ethene
plants- what is the effect of the hormone:
cytokinins
-promote cell division
-delay leaf senescence
-overcome apical dominance
-promote cell expansion
plants- what is the effect of the hormone:
abscisic acid
-inhibit seed germination and growth
-causes stomatal closure when the plant is stressed by low water availability
plants- what is the effect of the hormone:
auxins e.g. IAA (indole-3-acetic acid)
-promotes cell elongation
-inhibits the growth of side-shoots
-inhibits leaf abscission (leaf fall)
plants- what is the effect of the hormone:
gibberellins
-promote seed germination and growth of stems
plants- what is the effect of the hormone:
ethene
-promotes fruit ripening
how do hormones move around the plant (3 ways)
-active transport
-diffusion
-mass flow in the phloem sap or in xylem vessels
what are auxins responsible for
regulating plant growth
what did scientists discover abt auxins when testing plants dk
-firstly scientists stated that if you break the shoot tip (apex of a plant), the plant starts to grow side branches from the lateral buds.
-scientists suggested that auxins from the apical bud prevent lateral buds from growing. when the tip is removed, auxin levels in the shoot drops and the buds grow. they applied an auxin paste to the cut end of the shoot and lateral buds didnt grow. However due to the manipulation, buds may ahve grown due to expose to oxygen/another hormone. auxin transport inhibitor was placed below the apex of the shoot and lateral buds grew. due to this scientists suggested that normal auxin levels in lateral buds inhibit growth , whereas low auxin levels promote growth however auxin levels and growth inhibition may have no effect on each other, but could both be affected by a third variable . later a scientists remarked that auxin levels actually increased when a shoot tip was cut off, scientists now think 2 hormones are involved.
what other 2 hormones are important in regulating plant growth and what do they do apart from auxins
-abscisic acid inhibits bud growth
-cytokinins promote bud growth
what is apical dominance
inhibition of lateral buds further down the shoot by chemicals produced by the apical bud at the tip of the plant shoot
what happens when u apply cytokinins directly to buds
it can override the apical dominance effect
what is the relationship between cytokinins and auxins
And what happens when the apex is removed
High Auxin = Cytokinins accumulate in shoot apex.
Low Auxin = Cytokinins spread around plant and so allow side shoot growth..
-when the apex is removed, cytokinin spreads evenly around the plant.
what are gibberellins
plant hormones which are responsible for the control of stem elongation and seed germination
in japan, there is a fungus that causes a disease which makes rice grow very tall, what are the fungal compounds involved
gibberellins and gibberellic acid
what is gibberellic acid responsible for
plant stem growth ( they applied this to dwarf varieties of pants and they grew taller).
what do gibberellins cause growth in and how
in the internodes by stimulating cell elongation (by loosening cell walls) and cell division (by stimulating production of a protein that controls the cell cycle)
in terms of growth, what does the plant cell wall limit
it limits the cells ability to divide and expand.
where does growth happen in plants
at the meristems
talk abt apical meristems
- are at the tips or apices (singular: apex) of roots and shoots, and are responsible for the roots and shoots getting longer
talk abt where lateral bud meristems are found and what they can give rise to
found in the buds
give rise to side shoots
talk abt what lateral meristems form and what they are responsible for
form a cylinder near the outside of roots and shoots
responsible for roots and shoots getting wider
intercalary meristems are found in some plants, where are they located and what are they responsible for
located between nodes, where the leaves and buds branch off the stems.
growth between the nodes is responsible for the shoot getting longer
whats a klinostat
a machine that causes something to spin very slowly so that the effect of gravity is applied equally to all sides of the plant.
whats a klinostat and what can it investigate?
a machine that causes something to spin very slowly so that the effect of gravity is applied equally to all sides of the plant.
-this can investigate geotropic responses
what would you expect to see when one plant has been in a kilostat and one plant hasn’t
plant with kilostat: both root and shoot grow horizontally
plant without kilostat: (gravity is only applied to one side) 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 soot has elongated more than the upper side
in terms of growth, what happens to a plant where its given light but only from one side
the shoot has bent towards the light as the shady side of the shoot has elongated more than the illuminated side,
what did Darwins experiments confirm that the shoot tip was responsible for
confirmed the shoot tip was responsible for phototrophic responses by causing cell elongation on the shaded side of the shoot which makes the shoot bend towards the light
for phototropism to occur, what did Boysen-Jensen remark
he confirmed that water and/or solutes need to be able to move backwards from the shoot tip for phototropism to happen- he showed that the signal was a mobile chemical as when a permeable block (e.g, gelatin) was inserted, the shoot tip still showed positive phototropism, whereas with an impermeable block (e.g. mica), no phototropism occured
when a permeable gelatine block was inserted behind a shoot tip, what did it show
still showed positive phototropism
in terms of phototropic response, was there one when an impermeable mica block was inserted on a shoot tip
no phototropic response
what is the role of auxins
auxins:
-promote cell elongation
-regulate plant growth
-inhibit growth of side shoots
-inhibit leaf abscission (leaf fall)
what is senescence
the gradual decline of all organ systems leading inevitably to death
how did scientists experiment on auxins
-applied auxin paste to a cut shoot, this prevented side shoot growth (contributes to apical dominance)
-applied auxin paste and a ring of auxin transport inhibitor to a cut shoot. This allowed lateral growth
what did scientist conclude on auxins
-normal auxin levels inhibit lateral bud growth, but low levels promote growth
-however scientists now think 2 other hormones are involved
what is the role of abscisic acid
-inhibits bud growth and seed germination
-causes stomatal closure when the plant is stressed by low water availability
what is the relationship between auxins and abscisic acid
high auxin= high abscisic acid= low lateral bud growth
-when the apical bud is removed, (removing auxins) the level of abscisic acid also drops.
what is the role of cytokinins
-promote cell division
-overcome apical dominance
-delay leaf senescence
-promote cell expansion
what is the relationship between auxins and cytokinins
high auxin= cytokinins accumulate in shoot apex
low auxin= cytokinins spread around plant and so allow side shoot growth
what is the role of gibberellins
-promote seed germination
-promote growth of stems
How did scientists experiment on Gibberellins
found GA1 existed at higher levels in taller pea plants (Le) than shorter pea plants (le)
How did scientists conclude on Gibberellins
they worked out the Le gene was responsible for producing the enzyme that converted GA20 to GA1
what happens when grafting an Le plant with no GA20 onto an le plant
the Le plant uses the spare GA20 from the normal plant, and contains the enzyme to convert GA20 to GA1, and therefore grew tall
how do gibberellins stimulate seed germination
when the seed absorbs water, the gibberellins enable the production of amylase, which can break down starch into glucose
this provides substrate for respiration and protein synthesis
whats the role of ethene
promotes fruit ripening
auxin is produced in the tip, what happens when the tip is cut
when the tip is cut, auxin levels drop and the bud grows
what happened when auxin paste was applied to the cut shoot
the lateral buds didn’t grow ( this is cus the conc is too HIGH)
what role does the secondary hormone of abscisic acid play a part of
- high abscisic acid= lateral bud growth inhibition
-it is thought that high auxin levels encourage high abscisic acid levels thus when tip is cut, abscisic acid levels drop and growth is uninhibited
what role does the secondary hormone of cytokinins play a part of
cytokinin= bud growth promotion
-produced in the roots, cytokinins travel to where auxin is most concentrated. when the apical tip is cut, cytokinins are spread more evenly and promote growth
talk abt auxin to abscisic acid to cytokinins and what that leads to when plant tip is intact
high auxin levels
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high abscisic acid levels
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low cytokinins in lateral bud
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inhibit lateral bud growth
talk abt auxin to abscisic acid to cytokinins and what that leads to when plant tip is removed
low auxin levels (more normal levels)
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low abscisic acid levels
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higher cytokinin levels in lateral buds
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lateral buds grow
what are gibberellins responsible for
stem elongation (by loosening cell walls) and seed germination (cell division by stimulating production of a protein that controls the cell cycle)- this happens in internodes
what are the 4 steps of seed germination
- the seeds absorb water
- the embryo releases gibberellin (GA) which travels to the aleurone layer in the endosperm of the seed.
- gibberelin aids the production of amylase that breaks down starch into glucose
- glucose is used for respiration
how did scientists test for GA1 levels
they found that plants with higher GA1 levels were taller- they found that the La gene was responsible for producing an enzyme converting GA20 to GA1
what happened when gibberellic acid was added to dwarf plants
they grew taller
what caused lengthening? GA1 or GA20
GA1
where does growth in length occur
apical meristems
where does growth in side shoots occur
lateral bud meristems
auxin is produced at the apex of the shoot, auxin travels to the cells in a zone of elongation, what doe this lead to
when moving to the zone of elongation this causes them to elongate and making the shoot grow
what does auxin do when light is equal on all sides
auxin promotes shoot growth evenly
when light is shone from one direction onto a plant, there is a light side and a shaded side, where do auxins move o and what does this cause
they move to the shaded side, this causes the cells there to elongate more quickly, this makes the shoot bend towards the light (the extent at which the cells elongate is dependent on the conc of auxins)
talk abt the mecanism of auxin
Auxin increases the stretchiness of the cell wall by promoting the active transport of H+ by an ATPase enzyme on the plasma membrane, into the cell wall. The resulting low pH provides optimum conditions for wall- loosening enzymes (expansins) to work. these enzymes break bonds within the cellulose ( at the same time, the increased hydrogen ions also disrupt hydrogen bonds within cellulose), so the walls become less rigid and can expand as the cell takes in water.
what is the main component of white light that causes phototrophic responses
blue light
what two enzymes are promoted by blue light
phototropin 1 and photropin 2
where is there lost of phototropin activity and what redistribution cause
lots on the light side but not a lot on the dark side, this gradient causes the redistribution of auxins through their effect on PIN proteins
where can PIN proteins be found and what can they do
these transmembrane proteins are found dorsally, ventrally or laterally on the plasma membrane of cells and they control the efflux of auxin from each cell, essentially sending auxin in different directions in the shoot, depending on their location on the plasma membrane
describe how is auxin involved in geotropic responses of roots
when a root is lying flat, auxin accumulates on the lower side, where it inhibits cell elongation . The upper side continues to grow and the root bends downwards
talk abt how the effects on auxin in roots and shoots contrast each other
they are the direct opposite as root and shoot cells in the elongation zone exhibit different responses to the same conc. of auxin (look at graph)
what can artificial auxins do
can be used to prevent leaf and fruit drop (this can occur in high conc. of auxin) and to promote flowering for commercial flower production.
why are artificial auxins useful in terms of fruit growth
they can be used to produce fewer but larger fruit instead of many small fruit
what are the three commercial uses of auxins
- Auxin and cuttings
-dipping the end of a cutting in rooting powder encourages root growth - Auxin and seedless fruit
-treating unpollinated flowers with auxin can promote the growth of seedless fruit (parthenocarpy). Applying auxin promotes ovule growth, which triggers automatic production of auxin by tissues in the developing fruit, helping it complete the developmental process. - Auxin and herbicides
- auxins are used as herbicides to kill weeds. Because they are an made, plants find them more difficult to break down, and they can act within a plant for longer. They promote stem growth so that the stem cant support itself, buckles and dies
what are the commercial uses of cytokinin’s
- cytokinin’s can delay leaf senescence thus they are used to prevent the yellowing of lettuce leaves after they have been picked.
-cytokinin’s are used in tissue culture to help mass produce plants.
-cytokins promote bud and shoot growth from small pieces of tissue taken from a patient plant. This produces a short shoot with a lot of side branches, which can be split into lots of small plants. each of these is then grown separately.
what 4 things are gibberellins used in (commercial)
- fruit production
-brewing
-sugar production
-plant breeding
how are gibberellins used in fruit production
- they delay senescence in citrus fruit, extending the time fruits can be left unpicked, and making them available for longer in the shops
-gibberellins acting with cytokinin’s can make apples elongate to improve their shape.
-without gibberellins, bunches of grapes are very compact: this restricts the growth of individual grapes. with gibberellins, the grape stalk elongate, they are less compacted, and the grapes get bigger
how are gibberellins used in brewing
during germination, the seed produces amylase that breaks down starch to maltose, usually due to gibberellin. By adding gibberellin, the process is sped up, malt is then produced by drying and grinding the seeds ( germinated cereal grains)
how are gibberellins used in sugar production (SPRAYING)
spraying sugar cane with gibberellins stimulates growth between the nodes, making the stems elongate. this is useful as sugar cane stores sugar in the cells of the internodes ( subsections of the stems), making more sugar available from each plant.
how are gibberellins used in plant breeding
sometimes breeding can take a long time (esp in conifer plants). gibberellins ca speed up the process by inducing seed formation on young trees.
stopping plants making gibberellins is also useful, spraying plants with gibberellin synthesis inhibitors can keep flowers short and stocky and ensures that internodes of crop plants stays short, helping to prevent lodging
whats lodging
it occurs in wet summers where stems bend over because of the weight of water collected on the ripened seed heads, making the crop difficult to harvest
ethene
ethene
what are the 4 commercial uses of ethene
-speeding up fruit ripening in apples
-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
why can restricting ethenes effects be useful
storing a fruit at a low temperature , with little oxygen and high carbon dioxide levels prevents ethene synthesis and thus prevents fruit ripening, this means fruits can be stored for longer and is essential for shipping. Other inhibitors such as silver salts can increase shelf life of cut flowers
what 4 things must a communication system enable
- detection of changes in environment
-cell signaling to occur between all parts of the body
-coordination of a range of effectors to carry out responses to the sensory input
-suitable responses
to ensure survival when there is a change in environment, what should responses be
rapid and well coordinated
what are some examples of the role of the nervous system
-coordinated muscle action
-control of balance and posture
-temperature regulation
-coordination with the endocrine system
what is the most obvious division of the nervous system
the central nervous system (CNS) and the peripheral nervous system (PNS)
what is the PNS further divided into
the sensory system and the motor system
what is the motor system divided into
into the somatic nervous system and the autonomic nervous system
what is the CNS divided into
the brain and the spinal cord
much of the brain is composed of which types of neurons
-relay neurons which have multiple connections enabling complex neural pathways
are relay neurons myelinated or non- myelinated and what does this mean it looks like
mostly non-myelinated cells and the tissue looks grey in colour, this is known as grey matter.
what’s the autonomic nervous system
part of the nervous system responsible for controlling the involuntary motor activities of the body.
what’s the central nervous system
the central part of the nervous system composed of the brain and spinal cord
whats the peripheral nervous system
the sensory and motor nerves connecting the sensory receptors and effectors to the CNS. The sensory and motor neurons are usually bundled together in a connective tissue sheath to form nerves
what’s the somatic nervous system
the motor neurones under conscious control.
what in the spinal cord makes up the central grey matter
the spinal cord has many non-myelinated relay neurons which make up central grey matter
what makes up a region of white matter in the spinal cord
there is a large number of myelinated neurons making up an outer region of white matter
what allows for rapid communication over long distances in the spinal cord
myelinated neurons carrying action potentials up and down the spinal cord
what is the spinal cord protected by
the vertebral column
what is between each vertebrae in the spinal cord
between each vertebrae in the spinal cord, peripheral nerves enter and leave the spinal cord carrying action potentials to and from the rest of the body
what is the role of the PNS
is to ensure rapid communication between the sensory receptors, the CNS and the effectors
what are the sensory fibers of entering the CNS referred to and what do they do/what do they conduct
sensory fibers entering the CNS are dendrons of the sensory neurons. these neurons conduct action potentials from the sensory receptors into the CNS. These neurons have their cell body in the dorsal root leading into the spinal cord and a short axon connecting to other neurons in the CNS.
Simply, what does the motor nervous system do?
The motor nervous system conducts action potentials from the CNS to the effectors.
what are the two further subdivisions of the motor nervous system (the two functions of the motor nerves)
-the somatic nervous system
-the autonomic nervous system
one subdivision of the motor nervous system is the somatic nervous system , describe this system
- consists of motor neurons that conduct action potentials from the CNS to the effectors that are under voluntary (conscious) control, such as the skeletal muscles. these neurons are mostly myelinated, so that responses can be rapid. There is always one single motor neuron connecting the CNS to effector
difefernce between nerrve and nurone
wdwsd
one subdivision of the motor nervous system is the autonomic nervous system , describe this system
consist of motor neurons that conduct action potentials from the CNS to effectors that are not under voluntary control. The control of many of these effectors does not require rapid responses, and the neurons are mostly non-myelinated. There are at least two neurons involved in the connection between the CNS and the effector. These neurons are connected at small swellings called ganglia.
which effectors are involved in the autonomic nervous system that are not under voluntary control
this includes glands, the cardiac muscle and smooth muscle in the walls of blood vessels, the airway and the wall of the digestive system. (bronchi)
define autonomic
‘self-governing’
what is the autonomic nervous system responsible for ( roles it plays in the body )
for controlling the majority of homeostatic mechanisms and so plays a vital role in regulating the internal environment of the body. ( it acts independently of conscious control)
what is the autonomic nervous system further divided into
the sympathetic system (prepares body for activity)
the parasympathetic system. (conserves energy)
in general in both the sympathetic system and the parasympathetic system, how would u describe the action potentials at rest and what are they controlled by
at rest, action potential are passed along both neurons at low frequencies- this is controleld by the brain
how is the the sympathetic system and the parasympathetic system related to each other
they are antagonistic (the action of one system opposes the other).
what alters the balance of stimulation for the sympathetic system and the parasympathetic system
information from external or internal receptors or stress
compare the nerves in the sympathetic system and the parasympathetic system
sympathetic system:
- consist of many nerves leading out of the CNS, each leading to a separate effector.
parasympathetic system:
-consists of a few nerves leading out of the CNS, which divide up and lead to different effectors
compare where the ganglia is in the sympathetic system and the parasympathetic system
sympathetic system:
- ganglia just outside the CNS
parasympathetic system:
-Ganglia in the effector tissue
what is the ganglia
ddss
compare the length of the post-ganglionic neurons in the sympathetic system and the parasympathetic system
sympathetic system:
-long post-ganglionic neurons (variable in length, dependent upon the position of the effector)
parasympathetic system
-short post-ganglionic neurons
compare what neurotransmitter is used in the sympathetic system and the parasympathetic system
sympathetic system:
-uses noradrenaline as the neurotransmitter
parasympathetic system:
-uses acetylcholine as the neurotransmitter
what does kind of activity does the sympathetic system promote compared to the parasympathetic system
sympathetic system:
-increases activity- prepares the body for activity
parasympathetic system:
-decreases activity- conserves energy
compare when the sympathetic system and the parasympathetic system is most active
sympathetic system:
-most active at times of stress
parasympathetic system:
-most active during sleep or relaxation
what are the effects of the sympathetic system
sympathetic system effects:
-increases heart rate
-dilates pupils
-increases ventilation rate
-reduces digestive activity
-orgasm
