BIOLOGY - MAINTAINING A BALANCE

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MAINTIANING A BALANCE QUESTIONS

1. Describe a current theory that plains the movement of materials through xylem

xylem is not alive therefor physical processes are responsible for the upward movement of minerals. The current theory for this is called the cohesion-tension theory which is summarised as 4 processes.

1. cohesion - water molecules stick together within a continuous network of liquid columns which have the ability to instantaneously transfer pressure or tension.

2. transpiration - water is evaporated through the stomates and is replaced by water from cells and xylem tissue

3. tension - water moves up the xylem like a wire b pulled up, due to cohesion. this helps resist the formation of bubbles within the stream

4. adhesion - when the pull stops (eg. at night) wter sticks to the sides of the tubes and does not fall down

another theory proposed by the research school of biological science at australian national university suggests that the stretching and compressing of cells against one anither may cause tissue pressure to promot eupward moveemnt of water through plants

2. Describe a current theory that explains the movement of materials through phloem

movement of material through phloem is called transcolation - materials move bth up and down the stem > the processes responsible for translocation are not known with certainty- current theories into two views

1. view one = includes processes that rely on cytoplsmic streaming and diffusion of sugar in the seiive elements.the conducting tissue generate the moving force. ctoplasmic streaming is the vigorous 'stirring' of nutrients, metabolites, genetic material and even organelles to all parts of the cell > there is o doubt that cytoplasmic streaming occurs but because t involves movement of the solute, not the solvent , it alone cannot account for the rate of movement of sugars in the phloem.

2 view two has more general acceptance but still has limitations because it cannot be demonstrated in all plant species. it includes a number of mass-flow mechanisms and is called the 'source to sink' model - in this theory sieve elements accumulate solutes such as sugars from the leaves (source) - a process that requires metabolic energy. comanon cells also acculmulate solutes and deliver them to sieve elements. t these sites the sugar concentration is high and this causes resulting pressure causes water and dissolved solutes to flow along under the force of turgor pressure to the paces where sugar is being removed (sink)

3. explain the difference between a transverse ad a longitudinal section of a stem

a transverse section of a stem shows the long, narrow cells in both the phloem and xylem whereas the transverse tion shows the ell walls of xylem tubes and the perforated sieve plates in phloem cells.

4. distinguish between cells in xylem and phloem

cells in phloem transport food nutrients such as sugar and amino acids from leaves to storage organ and growing parts of the plant, the moevement of these substances is called translocation. this process occurs in the stems, roots and leaves. the srtucture of phloem cells is an elongated tubular shape with thin walled sieve tubes, the sieve tubes have pores at each end in the cross walls and icrotubules tat extend between sieve elements allowing longitudinal flow of material.

xylem traspors water and minerals from the roots to the aerial parts of the plant, in the roots, stes and teaves and is a tubular shape with no cross walls which allows a continuous column of water and facilitates more rapid transport within the xyle vessels.

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plants and animals regulate the concentration of gases, water and wste products of metabolism in cells in interstitial fluid .

1. justify why water concentration in cells is restricted to a narrow range.

water concentration in cells must be held at a constant narrow range because wator is a major solvent for chemical reactions and the amount of water will affect concentration of materials in the cell.

2. at are metabolic wastes

metabolic wastes are wastes fromt he reactions in cells such as carbon dioxide

3. why must metabolic wastes be removed from cells?

they must be removed from cells use some are poisonous, they take up space and some create problems for osmoregultion. the excretory system is concerned iwth the removal of these waste prodcts. in humans the organs responsible for excreton re the kidneys, lungs and the skin. additionally the excretory system is also resposnsible fining constant blood composition and therefore a constant internal environment.

4. what role does the kidney play in the fish and mammals.?

the kidney has a dual role of excreting nitrogenous wastes and aintining water balance in mammalls and fish. it is an organ of filtration, reabsorption and secretion. when amino acids are broken down a, a highly toxic substence is produced. in some fsh ammonia may ddiffuse out across the gills and be excreted through the kidneys in dilute urinen mmmals, sharks and some bony fish the liver convers ammonia to ureah is less toxic so that it can be stored briefly but is less soluable. blood carrying nitrogenous wastes brought to the kidneys by renal arteries. urine is formed on the outer cortex and centrl medulla -vis connects the medulla to the ureter which takes the urine to the bladder for short term storage. depending on the environment oh and mammals, the kidneys excrete urine within a range in concentration> by forming concentratd urine kidneys help fihs and mamals living in dehydrating environments to reabsorb wayter into theb lood and maintain water balance - freshwater fish excrete dilute urine to help overcome ater balance problem resulting from an influx of water that diffuses in from their environemnt.

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what is diffusion

diffusion is the process in which ticles move from a reigon where they are in high concentraton to reigon where they are in low concentration.

what is osmosis

osmosis is a selective form of diffusion in which the cell membrane acts as a selectively permeable barrier that allows the passage of water but not largr molecules. it results in the movement of water from a dilte solution tot a stronger solution.

why is it impossible for cells to remove wastes through the processes of diffusion and osmosis ?

it is mpossible because diffusion is too slow and non seelectve of solutes and osmosis would mean ste would stay in the body and water would leave it.

what is the essential difference between active and passive transport?

passive transport is the process which a process occurs spontaneously and requires no expenditure of energy whereas some processes require energy such as the iing nitrogenous wastes, when reabsorbing nutirents some go against the concentration gradient and require active transport.

what role does passive transport play in the mammalian kidney?

water reabsorption in the mammalian kidney is a passive processbecause it goes with the concentration gradient

what role does active transmport play in mammalian kidney?

active transport i sinvolved in the reabsorption of sodium salts, glucose and amino acidswhich is an active process because these substances go against the concentration gradient and require energy to complete. additionaly many drugs are secreted by the kidney tubules actively.

what is a ephron NS HOW DOES ITS SRTUCTURE RELATE TO ITS FUNCTION

the nephron is the structural and funtional unit of the nephron. There are around 1 million nephrons in the human kidneys, e aranged in the outer cortex and central medulla. each nephron iw qmde up of a glimerulus and tubules .blood flows into the nephron under pressure resulting in the plasma being forced through the glomerelus into the bowmans capsule. ructure of the glomerelus means t acts as an ultra filter

what is the role of filtration in the mamalian nephron

what is the role of reabsrption in regulating the composition of bodily fuids.

in wht way is renal dyalisis similar to the function of the kidney

while the artificial kidney does not match th complexity of the natural kidney and hs limits a long term subsititute for the kidney. similarly tot he function of the kidney it regulates concentration of the patients blood by removing substances surea lectively adding substances - a process called dyalisis. the fluid used n dyalisis promotes dffusion of the apporpriate nces into and out of the blood.

in what ways does renal dyalisis differ from the function of the kidney

it differs in that it is an artificial proces that is controlled by computers and done either at a medicl centre or at home, frequently. the process is artificial and occurs when the individual is hoocked upto a machine ch takes blood from the artery and pumps it through coils of dyalisis tubing which blood is pumped and then returns it to the vein. it uses filtration only instead of filtration and reabsorption.

compare the roles of aldosterone and ADH

aldosterone is a steriod hormone that is produced by the adrenal cortex of the kidney. its role is to maintain the balance of water and salts in the body. aldosterone stimulates the nephrons to decrease reabso of potassium and increase reabsorption of sodium into the blood. this leds to an increasedrrption of chloride ions and water. the reabsorption of these substancese a rise in blood volume and blood pressure.

adh or anti diuretic hormone is a hormone produced by the hypothalamus in the brain and stored in the posterior pituitary. ADH stimulates the nephrons to reabsorb more water. it acts to decrease urine volume, increase urine concentration and increase blood volume.

describe some symptoms of people who cannot secrete aldosterone nd how hormone replacement therapy cn help them

the innability to secrete dosterone is a symptom of addinsons disease which is caused mostly b the shrinking or desrtuction of the adrenal corte. adrnal cortex produces two hormones;rtisol and aldosterone. if the body acannot secrete aldosterone then water and salt levels cannot be maintained. when this balance is upsete volume of blood falls dangerously low, there is a drop in blood pressure and severe dehydration. when levels of both cortisol and aldosterone odily functions are severely disrupted. the hormone replacement s called fludrocortisone. the treatment itself corrects the levels of hormones our body isnt producing.

enantiostasis important in estuarine environments

what is the difference in urine concentration of marine fish, freshwater fish and terrestrial mammals

marine fish

- oncentration is highly conentrated because aquatic organisms face the problem of osmosis. in seawater the concentrations of dissolved substances re usually lower in the body of the organism than in the sewater environment. r, therefore will tend to move out by osmosis and salts wil diffuse in. marine organisms excrete salt through the gills and very little urine is excreted. marine fish drink large amounts of seawater to replace water loss.

freshwater fish

- have a dlute urine ( urine has a lot of water relative to solutes) - in fresh water fsh the concentrations of dissolved substances are usually hgher in the body of the organism than they are in the environment. water, therefore will tend to move into the organism by osmosis. freshwter fish must rid themselves of excess water. the waste product is large amounts of dilute urine.

terrestrial mammals.

- concentration and volume varies according many factors. for example in mammals that live in the desert uine s highly concentrated however herbivorous mammals such as cattle ecree urine that is less concentrated. the reason for this is that teresstral organisms face the sisue of conserving whater and at the same time removing nitrogenous wastes.

why does he concentration of urine vary across fish in freshwater and marine environment and animals in terrestrial environments

identify how differents plants regulate the concentration of salt in their tissues in saline environments

plants in salne envronments such as mangroves and coastal marshes use three main processes for keeping the growing stems and leaves mostly free of salt. these include

- salt barries which are special tissues in the roots and lower stems which stop salt from entering the plant but allow water uptake,

- secretion - some plants are able to concentrate salt and get rid of it though special glands on the leaves for example the grey mangrovealt is then washed off by the rain

- salt deposits - some plants deposit salt in older tissues which are then disguarded such as the mangrove rhizophora which concentrates salt in its old leaves which it sheds.

how do australan insects conentrate and excrete nitrogenous waste to ensure water is conserved

insects do this through converting nitrogenous products into almost insoluable substace called uric acid . uric acid has low ttoxicity and if it is excreted then no water is lost. the acid is excreted through cial tuubules or uric acid crystals are deposited in various parts of the body. the white scales on the wings of some butterflies are uric acid deposits.

what iis the relationship between the concentration of nitrogenous waste and the need to conserve water by austalian terrestrial mammals.

Terrestrial organisms face the issue of conserving water and at the same time removing nitrogenous wastes in a form that is concentrated but not toxic. Desert mammals provide good examples of how teresstrial mammals overcome em of conserving wter and excreting ous wastes - some australian examples include the red angaroo whose kidneys produce higly concentrated urine and the mulgara, a small carnivorous mouse like marsupial that inhabits sand hill deserts in central australia. the mulgara does not drink but moisture is provided in foohe large amounts of urea produced by a carnivorous diet are exceted in highly concentrated urine. additionally the murid hoppng mouse lives on dry seeds and has no drinking water - it has the greatest ability to produce concentrated urine.

describe some adaptions of australian plants thatminimise water loss

australian trial plants range of adaptions that assist in minimising water loss and at the same time allow for gass exchange. plants in sclerophyll forests (meaning hard leaf) such as eucalyptmiimise water loss through the waxy cuticle on their leaves as well as sunken stomates located only on the under surface of the leaf, and eaves hanging almost vertically to reduce area exposed to sunlight. The saltbush reduces water loss through the salt crystals on the leaves which reflect heat so less transpiration occurs and thus less water lost.

describe how first hand observation can assist informaation gatheting about structures that assist water loss.

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