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level: Responding to the environment 2

Questions and Answers List

level questions: Responding to the environment 2

QuestionAnswer
what are the two types of synapses?excitatory and inhibitory
excitatory synapsesmake the postsynaptic membrane more permeable to Na+ only one excitatory sysnapses is not enough to generate an acton potential
inhibitory synapsesmake it less likely for an action potential to generate in the postsynaptic cell Cl- ions move into the cell whilst K+ ions move out of the cell causing the membrane to be hyperpolarised more exitatory neurones are needed to depolarise the membrane
what are the two types of summation?spatial summation and temporal summation
what is summation?the fact that each impulse adds to the effect of others
spatial summationimpulses are from different synapses usually from different neurons producing an action potential in the postsynaptic neurone
temporal summationseveral impulses along the same neurone generate an action potential in the postsynaptic neurone
structue of a rod cellouter segment inner segment synaptic region
outer segment of the rod cellcontains closely pack membrane disks containing rhodopsin
inner segment of the rod cellcontains cell organelles and the nucleus also where lots of mitochondria are found
synaptic region of the rod cellwhere the rod cell and the bipolar neurone synapse
what is rhodopsin?light sensitive pigment made up of opsin and retinal
what is retinal?in cis form in the dark in trans form in the light
the role of mitochondria in rod cellsproduces ATP to provide energy for the ion pumps
what happens in our eyes in the dark?Na+ flow into the outer segment of the rod cell Na+ moves down the concentration gradient into the inner segment where pumps transport them back out the cell the influx of Na+ produces a slight depolarisation of the rod cell this triggers the release glutamate from the rod cells glutamate binds to the bipolar cell stopping it from depolarising
what happens in our eyes in light?light is absorbed by rhodopsin breaking it down into opsin and trans-retinal opsin activate the hydrolysis of a cyclic molecule attached to the cation channel in the outer segment the breakdown of the molecule results in the closure of the cation channel so less Na+ enters the cell and the inner segment keeps pumping Na+ out so the inside of the cell is more negative the cell becomes hyperpolarised so the release of glutamate stops and the bipolar cell can depolarise
glutamateneurotransmitter released when there is no light present inhibits the depolarisation of the bipolar cell so an impulse is not passed along the optic nerve to the brain
what is IAA?a type of auxin made in meristems promotes cell growth and elongation diffuses away from the cells in the light to cells in the shade a plant hormone
define growthan increase in plant volume or mass with or without the formation of new structures such as organs, tissues, cells or cell organelles
how is IAA transported around the plant?long distances in the phloem shorter distances between cells via specific carrier proteins
what is the effect of IAA on gene transcription?auxins bind to protein receptors on their target cell this activates intracellular second messenger signal molecules these molecules activates transcription factors
define phototropismthe mechanism for plants growing towards the light
what is the effect of IAA on cell elongation?process of phototropism IAA attaches to specific receptor site in the cell membranes causing the active pumping of H+ into the cell wall the influx of H+ into the cell wall causes the pH in the cell wall to fall this provides an optimum acidic environment for expansins already present in the cell wall ions move into the cell due increased permeability and water enters by osmosis the cell swells as the vacuoles get larger so the wall grows to accommodate this the cells in the shade grow whilst the cells in the light do not grow causing the bending of the shoot towards the unilateral light source as the cell matures the auxin is destroyed and pH rises so the bonds reform between the cellulose microfibrils
role of expansinsbreak bonds between adjacent cellulose microfibrils and hemicelluloses causing the walls to become more flexible
why is auxin destroyed when the cell matures?it is only found in growing tips
Darwin and Went's investigation into auxin and oat coleoptile growthDarwin cut the tip of an oat coleoptile plant he relplaced the tip back and the plant started growing towards the light again Went cut the tip of the plant then placed it on an agar jelly block he then put the block with tip on top on the rest of the plant the plant started to grow again Went then placed the agar on one side of the tip in the dark the plant bent away from the side the agar was on
what does Darwin's and Went's investigation prove?the presence of auxin in tips of plants the importance of auxin in the growth of plants the reason why plants grow towards the light auxin is able to diffuse through agar jelly
define photoperiodismthe response of an organism(plants) to the changes in the length of days
define photomorphogenesisdevelopmental and morphological changes that are induced by light
define gravitropismthe important plant growth response to the environment that directs shoots upwards and roots downwards
define thigmotropismoriented growth of an organism in response to mechanical contact e.g - plant coiling around its wooden support
what are phytochromes?photoreceptors that detect direction quantity and wavelength of light Pr and Pfr are photoreversible
Prphytochrome red absorbs red light is converted to Pfr in sunlight
Pfrphytochrome far red absorbs far red light is converted into Pr in the dark or presence of far red light
how do phytochromes trigger germination?the sun emits red light red light is absorbed by Pr so it gets converted into Pfr Pfr stimulates responses that lead to germination
how do plants know when to flower?the ration of Pr to Pfr enables it to determine the length of day and night
long day plantsonly flower when the day long and night short as they need Pfr to grow e.g. strawberries
short day plantsflower when the period of uniterrupted darkness is more than 12 hours they need to convert all the Pfr back to Pr Pfr inhibits flowering in short day plants
how does Pfr work?light shines and Pr converts into Pfr by changing its shape Pfr can now bind to proteins these proteins may act as transcription factors or activate transcription factors that bind to DNA so light regulated genes are transcribed the transcription and translation of proteins result in the plants response to light
greeningwhen the shoot has broken through soil into the sunlight the plant undergoes changes in form and biochemistry
nervous systemspeed of transmission is fast mode of transmission by neurones made up of electrical impulses influences muscles and glands
hormonal systemslow speed of transmission mode of transmission is by glands chemicals are released into the blood alters the expression of genes influences growth and development
similarities in plant and animal hormonal systemsinvolve chemical messages chemicals are produced by cells transported away from the site of production influences gene expression has a long term/permanent effect
hormonal system in animalstransported in the blood slow action doesnt just affect growth responds is to stimuli like CO2 conc in blood
hormonal system in plantsdiffuses through and between cells slower action affects only growth responds to stimuli like light