What was William Withering’s process of developing a drug for Dropsy in 1785?
identified the medically useful ingredient - tested on a small group of ill patients - tested on a larger group of people to work out the dose - general use
How do we develop a drug today?
identify medically useful substance - active ingredient isolated - make drug synthetically to control dosage, quality and large quantities - pre-clinical tests using computer modelling, tissue culture and animals to find out safety, dosage and efficacy - phase one testing on a small group of healthy volunteers to test for safety and side effects - phase ii testing on a small group of ill patients - matched larger group, placebo controlled and double-blind trials to remove bias and account for psychological effects - statistical analysis and approval - general use
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What was William Withering’s process of developing a drug for Dropsy in 1785?
identified the medically useful ingredient - tested on a small group of ill patients - tested on a larger group of people to work out the dose - general use
How do we develop a drug today?
identify medically useful substance - active ingredient isolated - make drug synthetically to control dosage, quality and large quantities - pre-clinical tests using computer modelling, tissue culture and animals to find out safety, dosage and efficacy - phase one testing on a small group of healthy volunteers to test for safety and side effects - phase ii testing on a small group of ill patients - matched larger group, placebo controlled and double-blind trials to remove bias and account for psychological effects - statistical analysis and approval - general use
What are the similarities between Withering and modern day?
identified medically useful ingredient, tested on small group of ill patients, tested on larger group of people and general use
what do xylem vessels do?
transport of water and minerals, stiffened cell walls help to support plant
what do sclerenchyma fibres do?
forms columns, stiffened cell walls provide support
what are phloem sieve cells used for?
form long tubes for transport of organic solute
How are xylem vessels formed?
lignified - entry of water and solutes is restricted - tonoplast breaks down - autolysis of cell contents (broken down by enzyme action) - dead, empty cells left form a tube
what gives xylem vessels strength?
cellulose microfibrils and lignin in cell walls - a role in supporting plant
What is the process of water movement via. the Xylem vessels?
transpiration - water removed is replaced by water from roots - removal of water from cells provides force need to draw water up plant - capillaries draw water up by capillary action - water moves up xylem vessels and through cell walls within leaf in a transpiration stream.
What is transpiration?
water evaporates from stomata. Diffuses out of stomata, down a concentration gradient.
what is capillary action?
movement of water due to surface tension between water and surface of the cell wall
What would happen during transpiration if xylem cell walls were not lignified?
the xylem vessels would collapse inwards due to water under tension
what is cohesion-tension theory?
water column in xylem vessels does not break due to cohesive forces between water molecules
what does the movement of water in the xylem provide?
a mass-flow system for transport of inorganic ions
what are nitrate ions required for?
to make amino acids, which make up protein which makes up most of the cells cytoplasm (as well as chlorophyll, nucleic acids, ATP and some plant growth substances)
What would happen if inorganic ions aren’t absorbed in sufficient amounts?
the plant will show deficiency symptoms
What does it mean when a plant shows deficiency symptoms?
the plant has not absorbed sufficient amounts of inorganic ions
how are phloem sieve cells formed?
a column of long, narrow cells in growing stem. The nucleus and most cell contents disintegrate during development - most of cell space is lumen (liquid-filled space).
how does phloem allow for the transfer of materials between adjacent cells?
end walls of each sieve tube cells contains holes that are aligned with those of the adjacent cell
what is a sieve-tube element?
section of phloem between sieve plates
what is translocation?
the movement of substances via the phloem - mainly sucrose and amino acids
where do substances in the phloem go?
either from leaves to roots (amino acids and sugars are used for growth or converted to polysaccharide for storage) or from leaves to buds for growth and development of flowers, fruits and seeds
what is the difference in the directions of transport between xylem and phloem?
xylem vessels only transport substances one way, phloem vessels transport substances all around the plant
What are companion cells?
long, thin cells that contain a nucleus, mitochondria, ribosomes and a rough ER - perform the metabolic functions that maintain the sieve tube
what are transport cells?
a specialised type of parenchyma cells that actively help to transport sugars and amino acids and other organic solutes
how are transport cells well adapted to their function?
cell walls and cell surface membranes have many small infoldings increasing surface area, contain many plasmodesmata that link cytoplasm to adjacent cells, contain lots of mitochondria to provide energy needed to load solutes into sieve tubes
what is the function of transport cells?
products of photosynthesis move out of cells they’ve been produced in, pass through plant cells until they reach a transfer cell (next to sieve tube).
what are sinks?
photosynthetic products are actively unloaded from phloem sieve tubes into the parts of the plant where they are being used but not produced
how do plants survive winter and redevelop in the spring?
in a dormant state, starch is stored the roots, bulbs or tubes. Inspires starch to sugar, and for a short time the root becomes the source and buds and developing leaves become the sink.
cellulose in plant cell walls.
a polysaccharide, a polymer of glucose composed of two Beta glucose, in cellulose all 1, 4 glyosidic bonds. A long, unbranched molecule.
how are microfibrils formed?
cellulose molecules remain as straight chains, hydrogen bonds between -OH groups between cellulose chains form bundles - microfibrils.
How are microfibrils arranged in cell? What does this do?
wound in helical arrangement, stuck together with polysaccharide glue. Laid at angles to each other (composite structure) which results in them being strong and flexible.
what is polysaccharide glue composed of?
hemicelluloses and pectin’s (middle lamella, act as cement and holds cells together)
what does polysaccharide glue do?
short polysaccharides bind both to surface of celullose and to each other. Hold cellulose microfibrils together.
How do pectins and hemicelluloses make the cell wall strong?
arrangement of cellulose microfibrils within matrix of hemicelluloses and pectins - makes strong but pliable structure.
what does the plasmodesmata do in the plant?
makes cytoplasm of one cell continuous with cytoplasm of the next - aids movement of substances between cells
what are pits?
a thin point in the cell wall where only the first layer of cellulose if deposited - plasmodesmata often located in these pits
what does the lignification of xylem do?
waterproofs cell walls and makes them much stiffer - gives plants much higher tensile strength
how is lignin arranged within xylem?
laid down in spirals or in rings
what does lignin do in sclerenchyma fibers?
they die once lignified, leaving hollow fibers. Strength of fibers vary in different plant species depending on length of fibers and degree of lignification.
how does the height of the plant affect its strength?
the taller the plant grows, the greater its lignification
what do plant stems rely on to maintain shape and keep erect? What happens when this is not the case?
rely on tightly packed, fully turgid parenchyma cells. If water is lost, turgor is lost. If high proportion of a plants cells lose turgidity, plant wilts.
what is a turgid cell?
one that is completely full with cell contents pressing out on cell wall
what do humans use plant fibers for?
clothing, rope, floor covering and paper
what are plant fibers useful?
they’re long, thin, flexible and strong
how can plant fibers be extracted?
plant can be taken apart by pulling out fibers or by digesting surrounding tissue
why is it easy to extract fibers through digesting of surrounding fibers?
cellulose (particularly when combined with lignin) is very resistant to chemical and enzymic degradation, polysaccharide glue can be dissolved away
what are the chemical defenses of plants?
produce a chemical that’s either distasteful (animal deterred from further consumption) or toxic (if predator killed, plant avoids future attacks)
what are the natural antibacterial of mint?
produces menthol and carvone - toxic to microbes and some insects
what are the natural antibacterial of garlic?
active ingredient is allicin which interferes with RNA production and lipid synthesis. When plant is damaged or cut, inactive precursor (alliin) is converted to active form (allicin) by enzyme (alliinase).
what parts of the plant have the greatest antibacterial properties?
seed coat, fruit coat bulb and roots
what is a medicine?
a chemical that kills pathogenic microbes at a level that leaves humans alive
what is a poison?
relative and relates to the dose needed to cause harm to organism
what are seeds adapted to ensure?
they protect the embryo - aid dispersal - provide nutrition for the new plant
how is the ovule fertilised in a flowering plant?
from a pollen grain - develops ovule into a seed
how does the ovule develop into a seed?
outer layers become lignified to form tough seed coat, protects embryo in seed, surrounding ovary develops into fruit (often has important role in dispersal of seed)
what is the endosperm?
a storage tissue. In some species, commonly monocotyledons, stored food remains outside the embryo in the endosperm
what happens in many dicotyledons?
the embryo absorbs stored nutrients from endosperm and food is stored in the seed leaves (cotyledons) - swell to fill seed
where is food stored in seeds such as Brazil nuts?
no apparent cotyledons, food is stored in hypocotyls (developing stalk)
why do plants disperse their seeds?
helps offspring avoid competition with parent plant and each other as well as allowing plants to colonise new habitats
what is the testa?
the seed coat
what are the plumule and radicle?
young shoots
what is the endosperm?
storage tissue
what is a cotyledon?
seed leaf
what is starch from seeds used for?
adhesives, paints, textiles, plaster, insulating material and toiletries
how is starch used in paper coatings and cloth treatment?
starch mixture is applied to surface, gelanised and cooled, allowing bonds to form between starch molecules. Addition of water reverses stiffening.
what are super-absorbents? What are they formed from? How?
starch is chemically cross-linked before gelatinisation, particles are formed that can be dried. When rehydrated, particles take up large amounts of water.
what is starch-foam?
is pressure is raised at the same time as gelatinisation, starch forms a plastic mass. If the pressure is suddenly released, steam forms and starch ‘puffs’ into expanded structure
what does the temperature of gelatinisation of starch depend on?
amount of water present