Topic 4- Biodiversity and Natural Resources

key definitions

cellulose function and structure

cellulose function and structure

structural component of plant cell walls to provide strength and support

made of β-glucose, bonded together by 1,4-glycosidic bonds, joined in a condensation reaction

every alternate β-glucose is inverted, and it is unbranched

alpha and beta glucose- isomers

—> alpha glucose has two hydroxyl groups adjacent

cellulose microfibril structure

• contains β-glucose

• joined by 1,4-glycosidic bonds and alternate glucose molecules are inverted

• microfibril is composed of many (60-70) cellulose molecules held together by hydrogen bonds

structure of the plant cell wall

• made of cellulose molecules

• bundles of cellulose molecules are held together by hydrogen bonds to form cellulose microfibril

• layers of microfibrils are laid down at different angles to form a mesh, which is then embedded in a matrix of hemicelluloses and pectins to form the primary cell wall

• secondary thickening involves lignin being added to form the secondary cell wall

xylem vessels

• cellulose microfibrils in cell walls

• walls thickened with lignin, often in spirals or rings

• continuous column made of hollow, dead cells with no cell contents

• pits in walls

• vessels have open ends

• at the innerpost point of the vascular bundle

function: transport of water and disolved mineral ions from roots to leaves, and provides structural support

phloem

• cellulose cell wall

• seive tube elements have thin peripheral cytoplasm and few organelles

• have seive plates and pores

• a companion cell is linked to each seive tube element by plasmodesmata

• living tissue

• in the middle of the vascular bundle

function: transport of organic solutes eg sucrose or amino acids from source to sink, in translocation

sclerenchyma fibres

• fibres have cellulose cell walls which are thickly lignified

• dead and hollow cells when mature

• often have pits in their walls

• long, narrow cells, usually pointed at both ends

• at the outer point of the vascular bundle

function: structural support only

linking structural components of xylem to its function

• lignin and cellulose microfibrils in cell walls- for strength to prevent the vessel collapsing

• lignin in walls- to make the vessel waterproof

• lignin in rings or spirals- allow stretching and flexibility as plant grows

• no end walls- forms a continuous, dead, hollow tube with no cytoplasm to reduce resistance or obstruction to water flow

• pits in walls- allow lateral/sideways movement of water between xylem vessels

• large cross sectional area- allows a larger volume of water to be transported

transpiration

• water evaporates from the surface of the leaf cells into the air spaces and exits the leaf by transpiration- water vapour diffuses out of the leaves through the stomata down a concentration gradient

• this creates a low hydrostatic pressure in leaves which draws water out of the xylem vessels by osmosis

• a continuous column of water molecule (transpiration stream) is pulled, under tension, up the xylem by capillary action

• due to cohesion- hydrogen bonding between polar water molecules in xylem, and adhesion- hydrogen bonding between water and the cellulose in xylem walls

• water moves into roots by osmosis, creating a high hydrostatic pressure

• water moves along the high hydrostatic pressure gradient, from high pressure in roots to low pressure in leaves, by mass flowrol

role of water in plants

• act as a reactant in photosynthesis

• keep plant turgid for support

• needed for hydrolysis reactions eg breakdown of starch

• as a solvent to dissolve and transport mineral ions

calcium ions

needed to make calcium pectate for making the middle lamella which holds plant cells together, plays a role in permeability

deficiency exhibits symptoms such as young leaves turning yellow and crinkly, growng points die back, stunted growth

magnesium ions

needed for making chlorophyll, which is required for photosynthesis. also needed for nucleic acid synthesis and activation of some plant enzymes

deficiency exhibits symptoms such as less glucose being made and stunted growth (due to lack of chlorophyll synthesis and therefore photosynthesis), yellowing of leaves between the veins

nitrate ions

needed to make amino acids for the synthesis of proteins including enzymes, and also found in chlorophyll, nucleic acids, ATP, growth hormones

deficiency exhibits symptoms such as older leaves turning yellow and dying, lack of side shoots, and stunted growth due to lack of enzymes/proteins

phloem structure related to its function

• transfer cell for loading sucros into the sieve tube at the source, or unloading at the sink

• sieve tube has sieve plates with sieve pores, so fluid and flow through

• companion cell has organelles including mitochondria that provide metabollic support for the sieve tube element cells

• peripheral cytoplasm of sieve tube has few organelles so less resistance to fluid flow

translocation

• at the source eg leaf, sucrose is produced from glucose and fructose

• transfer cells actively pump sucrose into phloem sieve tubes against a concentration gradient, using energy in the form of ATP from respiration

• there is a high sucrose concentration in the sieve tube at the source

• this draws water into the sieve tube by osmosis from adjacent xylem vessels, increasing hydrostatic pressure at the loading end of the sieve tube

• fluid in the sieve tube flows from high to low hydrostatic pressure by mass transport

• sucrose is activeky unloaded using ATP in sinks where the sugars are needed, so solute concehtration decreases in the sieve tube at the sink.

• water moves back into the xylem by osmosis, decreasing hydrostatic pressure

bacterial growth- optimum temperature (varies with species)

for optimum enzyme activity, rate of reaction and growth metabolism

bacterial growth- optimum pH

for optimum enzyme activity, rate of reaction and growth metabolism

bacterial growth- optimum oxygen concentration

for respiration to release energy

bacterial growth- optimum concentrations of glucose, nitrogen, etc

glucose for respiration to release energy

nitrogen for making amino acids to make proteins for growth and DNA

bacterial growth- moisture/water

for cell function eg hydrolysis reactions g

growth of a bacterial culture graph

• lag phase- no change/increase in number of cells as they adjust to conditions

• log phase- number of cells increases as cells divide at the fastest rate possible for the conditions, doubling each time

• stationary phase- no change/increase in number of cells as glucose is depleted and waste products build up, causing a change in pH

• death phase- number of cells decreases as cells dying are more than cells being formed

starch structure

alpha-glucose joined by glycosidic bond in condensation reactions

made of amylose and amylopectin

• amylose: 1,4- glycosidic bonds, straight chained, spiralled

• amylopectin: 1,4 and 1,6- glycosidic bonds, branched

uses of starch from seeds

• stiffening agents eg fabric or paper

• thickning agents for custard or wallpaper paste

• starch foam for packaging

• superabsorbants eg for nappies

sustainable resource

a resource that is renewable and will not run out so s therefore available for future generations

plastic/petrol sustainability

come from crude oil which is a fossil fuel, so is non-renewable and will run out

why is starch renewable

made from plants, which are a renewable resource as more plants are grown to replace those used

they biodegrade/decompose more quickly, so will not contribute to landfill

drug testing: William Withering’s protocol

• potentially useful plant chemical/ substance identified

• trial on a small group of patients with the disease- side effects recorded

• trial on a larger group to discover the effective dose

• results recorded and published

pre-clinical trials

lab testing on animals or cells/tissue cultures to assess safety/side effects and determine if drug is effective against the disease

clinical trials phase 1

small group of healthy human volunteers are given the drug to look for side effects in humans. different doses are trialled to find one which is both safe and effective. is the drug absorbed, distributed, metabolised, excreted as expected?

clinical trials phase 2

does the drug work?- it is tested on a small group (100-300) of volunteer human patients who have the disease

clinical trials phase 3

a double blind randomised controlled trial

a larger group (1000-3000) of patients are assigned randomly either to either a test group, who are given a new drug or a control group, who are given the existing drug (or a placebo/sugar pill if no existing drug is available)- checks for effectiveness (efficacy) and side effects

control group is for comparison with the test rgroup, to prove any improvement is due to the new drugs to improve validity

statistical analysis of data- checks if drug is effective by seeing if there is significant difference/improvement in patients taking it compared to those taking the existing drug

clinical trials after licensing

drug licenced. data on efficacy and safety continues to be collected and monitored

placebo

an inactive substance which does not contain the drug. used as a control to compare to the actual drug and removes the psychological effect taking a drug

double-blind trial

some people are given the drug and sme are given a placebo, or existing drug, and neither the patient nor the doctor know who has been given the actualy drug and who has been given the placebo, removing bias from the trial