plant structure

plant cellular structure

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the structure of a typical plant cell

Plant cells have many mambranes with the same chemical makeup as plant cells (lipoproteins, protein pores and carbohydrates)

  • plants have a ridgid cell wall (not in animals)
  • cell surface membrane beneath allows substances to diffuses in and out
  • tonoplast - cell membrane around the vacuole
  • vacuole keeps the plant tergid shape by water absorbtion
  • chloroplast site for photosynthesis (not in animals)
  • mitochondria produce ATP
  • nucleolus very dense area of almost pure dna
  • nucleus controls protein synthesis in the cells
  • cytoplasm chemical medium
  • rough and smooth endoplasmic reticulum (smooth produces lipids and hormones, rough produces proteins)
  • golgi body(packages, modifies and transports proteins)
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Cellulose - The plant cell wall

  • gives the plant their tergid structure and support
  • pollysaccaride (made of many glucose)
  • made up of largely insoluable cellulose,  (an arrangement of microfibrils within a matrix)
  • made of long chain glucose joined by glycosidic bonds in the form 1,4 (unbranched) as glucose is a isomer (comes in different forms)
  • cellulose is made from B-glucose form.
  • To form long chains the B-glucose moleules turn 180 degrees and form hydrogen bonds between the OH and H groups.
  • The glycosidic bond is between the oxygen in a condensation reaction (removal of H2O) to link the glycosidic chains this is called Cross linking
  • (when H2O is added its a hydrolisis reaction which seperates the glycosidic bonds)
  • cellulose microfibrils in are cross linked making them flexable but strong this makes a composie material (combining 2 features of a material)
  • plants are turgid most of the time due to vacuole filled with water however the can wilt and become flaccid
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Structure of starch

  • used as an energy storage molecule found in fruit and veg, cereals and  carbohydrate rich foods
  • polysaccharid formed by condensation reactions (-H2O) between a-glucose molecules
  • branched amylopectin 1,4 and 1,6 (amylose only has 1,4), makes extracting glucose easier because its branched
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cell wall impregnation

most of the time the cell walls are permiable but as the plant get older and bigger it needs to be stronger the cell walls can become impregnated with lignin producing wood this stops water passing through it

cell walls are made up of layers the first is the middle lamella which is flexable and cells divide from this made largely of pectin and polysaccarides which bind it together. Negatively charged carboxyl (COOH) ions and positivelt charged ions of calcium help bond structure aswell.

cellulose microfibrils build up on either side of the middle lamella forming a flexable primary cell walls  as the plant ages thinkining takes place a secondary cell wall builds up, as it develops lignin is added which hardens it into wood.

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communication between cells - plasmodesmata

despite cells being encapsulated in cellulose cell walls, intercellular exchanges happen, these are through special bridges called plasmodesmata.

Its a product of cell division when the cells don't seperate compleatly and threads of cytoplasm remain between them, the threads pass through gaps in the new cell walls so substances can pass between them

The interconnection of the cytoplasm is called symplast.

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Plant cell organelles

  • Vacuole - fluid filled space inside the cytoplasm surrounded by tonoplast membrane, filled with cell sap it keeps the plant upright and ridgid, it also causes water to move into the cell via osmosis creatin low concentration gradien inside the cell in comparision to surroundings. it can also be used for storage of food or waste products.
  • Chloroplast - enables plants to make its own food via photosynthesis (not present in animal cells) almost all areas of plant have the potential to produce the chlorophyll so if its damaged in one part it can produce it in another area. chloroplasts contain ribosomes, stroma, granum stacks of thylokoid membrane where the light sensitive chlorophyll is (place of photosynthesis) and outer and inner membranes. the majority of the cell consists of chloroplasts and they are at the top just under epidermis to maxamise light absorbtion.
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Structure of plant stem

primary function= support, needs to be strong but flexable so it doesn't brak easily and can move

other function is the transport of substance e.g minerals from one area to another water moves up the steam in a steady stream

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tissue that makes up stems: epidermis parenchyma,

tissue that makes up stems:

Epidermis the outer layer of the stem - role is protection of cells beneath it , secretes cutin a waxy substance which helps prevent water loss some contain hairs which can be stiff for protection or loaded with irritant chemicals

Parenchyma - packing tissue, parenchyma is most common, unspecialised cells which can be modified e.g into collenchyma and sclerenchyma.

collenchyma gives the tissue its strength found around the outside of the stem just under the epidermis give support but remain living ( not lignin)

sclerenchyma develops as plant gets bigger and needs more support makes strong secondary cell walls lignin is depsited on the cell walls making it no longer permiable the cell dies and becomes hollow forming wood. when it becomes compleatly impregnated it forms a sclereids.

in order from inside nucleus, vacuole, cytoplasm, middle lamellum, parenchyma (primary cell wall) collenchyma (extra cellulose), sclerenchyma (secondary cell wall, with lignin), epidermis.

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Transport tissue in plants - xylem and phloem

Xylem- tissue carries water and dissolved inerals from the roots to the photosynthetic parts of the plant. the movement is always upwards, made of mostly dead lignified cells so its hollow

Phloem- living tissue which transport the dissolved products of photosynthesis (sucrose) from  the leaves to anywhere its needed. therefore the flow can go up or down.

Cambium is a layer of unspecialised cells that specialise to become both xylem or phloem cells.

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starts as living tissue called the protoxylem which stretches and grows because the walls aren't fully lignified,

cells are arranged on top of each other ,

cells enlarge as vacuoles take in water lignin is deposited on cell wall stopping permiability

as plant becomes fully lignified the transverse cell walls break down and form a hollow tube

The movemnet of water can be observed by cutting the end of a shoot and placing it in a solution of eosin dye, also if the plants are given a solution of water with radioactive isotopes the movemnt of these can be traced using autoradiography. (plant is given radioactive solution, taken up by plant placed plant against photographic paper shows areas of isotope transport.)

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Translocation - the movement of substances around

Movemnet of water in the xylem depends on transpiration= which is the loss of water vapour from the surface of the plant mainly from leaves.

once in the leaves water moves from the xylem in the veins of the leaves by osmosis into the mesophyll cells and then evaporates to the air space and finally the stomata along the concentration gradient into the outside air where it evaporats. factors which speed up transpiration = windy, dry conditions

the transpiration system-

Molecules of water leaves the xylem to enter cells via osmosis and finally evaporate. They create tension in the water colunm in the xylem, this tension is transmitted down to the root due to coheasion. Coheasion is due to the dipolar nature of water wanting to stick together (due to the hydrogen bonds) this gives the colunm a high tensile strength. Molecules also adhere stongly to the walls of the xylem called adhesion - (a combination of adhesion and coheasion pulls the water up the xylem, water is continiously moved into the roots by osmosis from the soil to replace that lost from the leaves by transpiration.)

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the transpiration stream

  • water moves into the root hair by osmosis
  • water moves across the root by osmosis to maintain the continious colounm in the xylem
  • as water molecules are lost via transpiration / evaporation from the leaves cohesion between the water molecules means the whole colunm is pulled upwards.
  • water moves across the leaves cells by osmosis down the concentration gradient mainly along the apoplast pathway
  • water is lost from leaf surface by evaporation
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uptake of water by plants

  • the uptake of water by roots depends on the concentration gradient across the roots from the soil water to the xylem.
  • water moves from the soil to the root hair cells down the concentration gradient by osmisis.
  • this make the root hair cell more diloute than its neighbour so water moves from cell to cell by osmosis
  • there are 3 alternative routs for water to travel from root hair to xylem:
  • 1 symplast pathway- the plasmodesmata forms a continious pathway between cells, water passes through via diffusion down the concentration gradient
  • 2 apoplast pathway- water passes freely through the cellulose cell wall by attraction of water molecues (hydrogen dipolar)
  • 3 vaculor pathway - water moves through the vacuole by osmosis from the cytoplasm
  • whichever rout taken they reach the casparian strip which is a waterproof barrier causing water to enter the cytoplasm to get across into the xylem
  • root pressure shows transpiration is an active process when during night and low transpiration times the plant force water out called guttering to keep water moving (metabolic inhibiters e.g lack of oxygen effects transpiration = active process)
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plants need minerals

plants need minerals to synthesise substances for growth

Nitrogen - needed for making amino acids and proteins- which include plant enzymes, also needed for plants to make DNA - without - older leaves turn yellow and die, growth is stunted

Calcium - needed in the middle lamella to combine with pectin forming calcium pectin for structure also needed in permiability - without -growing points die, young leaves turn yellow and crinkly

Magnesium- needed to produce green pigment in chlorophyll also activation of plant enzymes - without- yellow areas develope on old leaves growth slows down

Phosphate - needed for phosphate groups ADP and ATP involved in energy transfer also structural support  - without- very dark green leaves and purple veins, growth is stunted

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mineral transport

they move into the cells and into the xylem often moving against the concentration gradient by active transport

dissolved in water absorbed from the soil carried by the apoplast pathway (cell walls) moving through the adjacent cell walls until reaching the endodermis they can also move through the symplath pathway (through the plasmodesmata symplasts) against the concentration gradient by active transport using ATP energy - result is the parenchyma cells are bathed in a dilute solution of mineral ions

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Plants as natrual resources

food - central to human diet making macronutrients of carbohydrates, lipids and protins but also micronutrients in the form of vitimins and minerals, also they provide fibre which helps the gut work

food staples are basic energy suppliers of the diet most are filled with starch storage organelles e.g potato

seeds are used for oil, animals we raise to eact are fed on plants

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plants as construction and clothing material

fibres - have to be extracted from the plant, usually very long sclerenchyma cells and xylem tissue which is very strong. cellulose and lignified cellulose are not easily broken down by enztmes or chemicals, but the matrix and connective pectins can usually be dissilved or removed

plants have tensile strength - not easily broken by pulling along with flexablilty

how they are processed to make product = paper is made from fibres from wood it hard to extract the fibres because it is strongl lignified, so wood is soaked in strong alkali e.g causic soda to produce pulp consisting of cellulose and lignified cellulose in water this is then layed on a thin film to dry. Cotton easy to get at but short fibres spinning pulls out the short single fibres twists them together to make long apparently continious thread which can be woven - synthetic fibres have since been made which were cheap long lasting and hard wearing but they have limitations e.g do not soak up body fluid so do not breath so you sweat, made from chemicals dirived from crude oil so they aren't sustainable (increasingly expensive as used up)

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plant resources continued

wood - composite material made of lignified cellulose fibre has properties of both materials e.g strong but flexable, resistant to compression (squeezing by weight) so its good for weight bearing building.

Sustainability - using materials that can be replaced. plants are vital in sustainable resources they soak up co2 from the atmosphere locking it in their cell structure, they are a renewable resource and are carbon neutral

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Problems with plastic made from polyethene called PVC originate from petrol, non renewable resource, can't be decomposed non biodegradable

biological polymers - based on structures of starch and cellulose, two main benefits :

  • they are sustainable, can be easily grown
  • are biodegradable, usually can be broken down by bacteria

we can burn bioplastics, energy released during burning can be used to generate electrisity and make more plastic.

disadvantages - when bioplastics are brken down by decompositers they produce methane a green house gas 25 times more potent than carbon dioxide, still much more expensive than oil based products partly due to the limited new technology, ethical issues surrounding use of crops e.g maise wheat and sugar for biofules and plastic when people are starving in the world.

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different types of bioplastics

different types of bioplastics -

  • cellulose bioplastics
  • made of wood pulp
  • used for plastic wrapping of food e.g cellophane


  • starch extracted from potatos and maize
  • main use capsuls for drugs because its easily digested

polylactic acid (PLA)

  • similar properties to polyethene
  • made from maize or sugar
  • makes drinking cups 
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Plant pharmacies

Salicylic acid - a modified version of asprin, derived from willow, previously people would chew or drink willow bark or chew the anal glands of dead beavers to ease pain (beavers eat the willow bark and the salicylic acid becomes concentrated in the anal gland.) now scientists take a closely measured does of a compound closely related but safer version of the compound acetylsalicylic acid

Advantages of extracting and purifying bennificial drugs from plants is it makes it possible to give a known, repeated dose of the active ingredient. impact of drugs are that people are ill less often and have a longer life

disadvantages - enourmous amounts of plant material is needed (which is why scientist isolate healing chemical analyse the chemical structure the synthesise the drug) - the discovery of quinine wasused to prevent and treat malaria however it now enables loggers and developers to work in the amazon basen destroying mosses and floria which could contain bennificial healing chemicals.

Digitalin - found in foxgloves helps cure dropsy when the circulation fails and the organs start to sut down also the right does helps patients with heart conditions , side feffects included vomiting but lare amounts of urine are produced and heart beats stronger and more regularly.

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modern drug development drug trials

new medicen has to Be :

  • effective - it cures or prevents the disease desease designed for or relieves some symptoms
  • safe - non - toxic and without unacceptable side effects
  • stable - able to be stored under normal conitions
  • easily taken in and removed from the body got rid of once its done its job
  • capable of being made on a large scale - manufactured in a pure form on large scale relatively cheaply
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stages of developing a new drug

  • to look for new mediciens scientists investigate the chemicals that bind to our protein receptors or to the active site on our enzymes

  • computer modles

  • testing on cell or tissue culture in the lab making sure the compound is stable and doesn't break down into something inactive or toxic before doing its job

  • whole organism testing on animals showing effect on enire body and if it can be safly excreated- usually must be done on  two types of animals rodents and non rodents

  • human clinical trials - Phase 1 - tested on a small group of healthy volunteers to make sure it doesn't effect any other part of body and has no adverse side effects in general ( at the same time in the animal experiments the long term exposure to the drug is monitered. Phase 2 - 100 - 500 patents effected by the target disease are given the drug to see if its effective on the target problem also helps determin dosage and adeverse side effects. Phase 3 - larger group of 500 volunteers with the target disease are given the drug

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Volunteers placebos and double blind

volunteers are altruistic - doing something which benifits others without any direct bennifit to themselves. However because of the calculated risk they are often paied for their time.

to keep it fair and obtain the most accurate results-

Placebo's are given along side the drug to measure actual effects of drugs against a control not containing the active ingredient. patents often appear to respond to treatment because they believe it is doing them good (mind effects the body)

control mediciens can also be given these are the most effective drug on the market already so as not to deprive a sufferer from getting any medication

in phases 2 and 3 trailes are normally carried out as double blind tests - where neither the doctor of patient knows is the patient is recieveing the new medicine, a control medicien or the placebo. - data is collected and analised to see if there is any difference in the placebo control medication and the new drug to assess effects.

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Difficult to achieve a full set of results as people are unreliable many patioents stop taking the drug after a certain time or don't take it regularly

Some trials are so successful they have to be ended early, as there is no point wasting money and resources running it after you have the data you want also if evidence shows there is a particularly effective traetment it becomes unethical to deprive certain control patients with the condition who are taking the old treatment. Howveer this means its hard to see long term detrimental effects of drugs.

Often the way a drug reacts on animals and tissue is very different from what it does on the human body.

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its really helpful, but i think there is a mistakes e.g starch is made of B glucose. i think starch is made of alpha glucose and cellulose is made of B glucose.

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