HSC Biology Syllabus dot-point Summary – Maintaining a Balance

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Maintaining a Balance

Contents

Contextual Outline

Multicellular organisms have specialised organ systems that are adapted for the uptake and transport of essential nutrients from the environment, the utilisation or production of energy and the removal of waste products arising from cellular activities.

The basis of healthy body-functioning in all organisms is the health of their cells. The physical and chemical factors of the environment surrounding these cells must remain within narrow limits for cells to survive. These narrow limits need to be maintained and any deviation from these limits must be quickly corrected. A breakdown in the maintenance of this balance causes problems for the organism.

The nervous and endocrine systems in animals and the hormone system in plants bring about the coordinated functioning of these organ systems. They are able to monitor and provide the feedback necessary to maintain a constant internal environment. Enzyme action is a prime example of the need for this balance. Enzymes control all of the chemical reactions that constitute the body’s metabolism. As enzymes normally function only within a narrow temperature range, even a small rise in body temperature can result in the failure of many of the reactions of metabolism that are essential to life.

Most organisms are active in a limited temperature range

Identify the role of enzymes in metabolism, describe their chemical composition and use a simple model to describe their specificity on substrates

Metabolism is the sum of all the biochemical reactions occurring in the cells of the body.

Anabolic reactions involve the building up of large organic molecules. Catabolic reactions involves the breaking down of large molecules

Enzymes are proteins that act as biological catalysts. They:

  • regulate the rates of chemical reactions in an organism (are biological catalysts)
  • are special large proteins
  • contain a functional site called the active site
  • can be used over and over again (only needed in small amounts)
  • are made in the cell where they are needed (manufacture is controlled by the nucleus)
  • vary – different cells make different enzymes depending on the activities and functions of the cell
  • are highly specific for the reactions they catalyse
  • work best under optimum conditions of temperature and pH
  • may need co-factors e.g. ions like magnesium and coenzymes e.g. vitamins to help functioning
  • have names usually ending in “–ase”
  • form a temporary association with the molecules they act on, forming an enzyme-substrate complex

Enzymes are specific. They provide an active site where the reaction can take place. They act on molecules known as substrates.

Induced fit theory

When a substrate binds to an active site, the binding induces a temporary change in the shape of the enzyme (induced fit). A chemical reaction occurs, the substrate is changed and the product(s) is/are released. The enzyme returns to its original form and can be used again.

induced fit theory

AdvantagesLimitations
  • Considered most accurate model of enzyme activity
  • Only a theory – cannot display actual process of enzyme activity for various enzymes
  • Simplifies a biological process that cannot be observed easily
  • Lack of a time frame

Lock and key theory

The active site on the enzyme has a surface groove which fits the substrate perfectly, bringing the active sites of both chemicals into alignment so that the reaction occurs quickly.

lock and key theory

AdvantagesLimitations
  • Aids understanding of enzyme specificity
  • Considered less accurate than induced-fit model
  • Simplifies a biological process that cannot be observed easily
  • Lack of a time frame

Identify pH as a way of describing the acidity of a substance

The pH of a medium refers to the amount of hydrogen ion present and measures acidity or alkalinity. The scale ranges from 0 to 14.

At room temperature, substances of pH 7 are neutral. Below 7 is acid and above 7 is basic.

The optimal pH is different for each enzyme e.g. 2.8 for pepsin, where most other enzymes would be denatured.

Describe the effect of the following on enzyme activity: increased temperature, change in pH and change in substrate concentrations

Temperature
  • increased temperature leads to increase enzyme activity until optimum temperatureo
    • more successful collision
  • high temperatures denature enzymes
    • permanent change to protein structure
    • hydrogen bonds broken, disrupting 3D shape
  • partially denatured enzymes will regain shape after cooling
  • completely denatured enzymes cannot correctly function again
pH
  • enzymes are most effective in a certain pH range (1.5 to 2 in the mammalian stomach)
  • extreme pH will denature enzymes
Substrate concentration
  • increased concentration of substrate will increase the rate of reaction until all enzyme active sites are occupied (saturation point)
  • the reaction will then proceed at its maximum rate

Explain why the maintenance of a constant internal environmental is important for optimal metabolic efficiency

A constant internal environment is essential for optimal metabolic efficiency because:

  • enzymes regulate metabolism by regulating rates of reaction
  • optimal enzyme activity is achieved under certain conditions of temperature and pressure.
  • therefore, optimal metabolic efficiency is achieved in a constant internal environment

Multicellular organisms have the ability to control their internal environment even when their external environment ranges to extremes.

Describe homeostasis as the process by which organisms maintain a relatively stable internal environment

Homeostasis is the process of coordinating body systems to maintain a relatively stable internal environment. Cell activity, requirements and wastes are monitored using feedback systems, involving the nervous and endocrine systems. The organism coordinates the surroundings of its cells as a whole to ensure that the composition of internal body fluid remains within certain limits. A relatively controlled internal environment is achieved.

detecting changes and homeostasis

Explain that homeostasis consists of two stages: detecting changes from the stable state and counteracting changes from the stable state

For a stable internal environment, an organism must pick up information from external and internal environments, interpret this information and react appropriately.

Detecting changes

Environments contain many stimuli (information that provokes a response) which are detected by receptors. Receptors can be a patch of sensitive cells or complex sense organs e.g. ears/eyes in mammals. In plants, the shoot and root tips work together with hormones.

StimulusType of receptorExample
Lightphotoreceptor
  • Retina at the back of eye has rod and cone cells to detect light
Heat, coldthermoreceptor
  • Skin
Sound, touch, pressure, gravitymechanoreceptor
  • Cochlea in the ear has hair cells that detect pressure waves in the cochlear fluid
  • Skin
Oxygen, carbon dioxide, water, pH, inorganic ions, nitrogenous wastes, glucosechemoreceptor
  • Tongue has taste buds
  • Nose has olfactory receptors
Electrical fields, magnetic fieldsother specialised receptors
  • Turtles and homing pigeons use the earth’s magnetic fields to navigate

Counteracting changes

When a change affects the organism’s stable state, a homeostatic response occurs to counteract the change to ensure a stable state is maintained.

In mammals, effectors may be muscles or glands.

  • Muscles contract or relax, bringing movement.
  • Glands respond by secreting a chemical substance e.g. saliva when food is detected

In plants, effectors are hormones.

A message carried by the nervous system usually follows the stimulus-response model: stimulus-receptor-sensory neuron-interneuron-motor neuron-effector-response.

Outline the role of the nervous system in detecting and responding to environmental changes using temperature change as an example

outline the role of the nervous system

The nervous system works to regulate and maintain an animal’s internal environment and respond to the external environment.

  • central nervous system comprises of brain and spinal cord
    • coordinate all responses
    • received information, interprets it and initiates a response
  • peripheral nervous system comprises of system of nerves branching throughout body to and from receptors and effectors
    • communication channels to pass messages rapidly to the central nervous system and back
    • information transmitted along nerve cells or neurons as electrical impulses

The nervous system works closely with the endocrine system:

  • produces hormones
  • made in special glands in response to certain stimuli
  • transported in blood to areas where their effects will bring a response

Outline the role of a feedback mechanism in maintaining a stable body temperature

  • In a feedback system, the response alters the stimulus.
  • When feedback reduces effect of original stimulus, the case is known as a negative feedback.
    • g. in humans, if receptors detect that the body temperature is raised (stimulus), mechanisms of sweating and heat radiation from the skin occur as a response
    • This lowers the body temperature and the stimulus that originally triggered the response is removed.
  • Negative feedback systems are the major mechanism for homeostasis.
  • Positive feedback increases the stimulus e.g. oxytocin (a hormone) continually dilates the cervix during childbirth.

Identify receptors and responses used by humans to maintain a stable internal temperature across a range of environmental conditions

The human body temperature is maintained around 37°C.

Thermoreceptors exist in the skin and also in the hypothalamus at the base of the brain, which is also the control centre. Special cells constantly monitor the temperature of the blood flowing by.

When receptors send messages to the hypothalamus about temperature, nerve messages are sent to the effectors.

Effectors include blood vessels, sweat glands, endocrine glands, muscles and body hairs.

EffectorResponse to heatResponse to cold
Blood vesselsVasodilation is where the smooth muscle of the arteriole relaxes, and allows more blood to flow near the skin, so that more body heat escapes.Vasoconstriction is where the diameter of surface capillaries shrinks, and causes less blood to flow near the skin, retaining blood in the inner core and thus reducing heat loss through radiation.
Sweat glandsPerspiration is excreted, allowing evaporative cooling as the water evaporates from the skin, taking body heat with it.
Endocrine glandsThyroxine (produced in thyroid gland in the neck) controls that rate of metabolism and thus controls the amount of heat released by metabolic activity e.g. respiration.
MusclesMuscles shiver so that the extra respiration increases heat production.
Body hairsThe hair follicle muscle (erectopili muscle) attached to each hair relaxes, causing hair to lie flat and allowing air to flow close to the skin, so that more heat is removed by convection currents.Erectopili muscle contracts, causing the hair follicle to become upright (i.e. goose bumps are formed) so that air is trapped between the hairs, insulating the skin and reducing convection currents.

Identify the broad range of temperatures over which life is found compared with the narrow limits for individual species

  • Temperature of environment is known as ambient temperature.
  • Some archaea exist in hot volcanic springs when water temperature reaches over 100°
  • Some seeds, lichens and mosses can survive exposure to temperatures below -200°
  • Musk oxen can survive at -40°
  • Many plants can survive temperatures of several hundred degrees in wildfires.
  • But most species can only tolerate a narrow range of temperatures in their local environment due to enzyme specificity.
    • g. sugar cane needs frost-free, tropical (>15°C) environment
    • Tropical fish required temperatures between 25°C and 35°C

Distinguish between the terms ectotherm and endotherm, naming Australian examples

EctothermEndotherm
Most organisms – invertebrates, fish, amphibians and reptilesBirds and mammals
Limited ability to control body temperature – cellular activities generate little heatMetabolism generates heat to maintain internal temperature
Body temperature dependent on external environmentBody temperature independent of external temperature
Less energy requiredMore energy (food) required
Red back spider, great white shark, red-eyed green tree frog, saltwater crocodileCockatoo, red kangaroo

Describe responses of Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation

Ectotherms

Ctenophorus dragon
  • Burrowing beneath salt crust of lake beds and salt flats when conditions are hot – earth is cooler below
  • Walk with toes off the ground – reduce body area exposed to hot ground
Freshwater crocodile
  • Bask in sun when it is cold – gain heat from sun
  • Fill lower jaw with water and gape when it is hot – evaporative cooling
Blue-tongued lizard
  • Lie flat when it is cold – absorbing more heat from the sun
  • Turn facing the sun when it is hot – less body area exposed to sun
  • Seeking shade when it is hot – avoiding the sun
Australian alpine grasshopper
  • Thermocolour grasshopper (adult male)
    • Bright greenish blue at temperatures above 25°C
    • Dull and black at temperatures below 15°C – absorb more heat

Endotherms

Red kangaroo
  • Licking forearms – evaporative cooling
  • Panting – evaporative cooling
  • Seeking shade – avoiding the heat of the Sun
  • Large ears with many blood vessels – increases surface area for heat loss
Fairy penguin
  • Blood shunt – flow of blood from body towards feet is shunted, via a special vein with a valve, back into the body
    • feet, which are poorly insulated, receive nearly no blood, thus reducing heat loss
  • Huddling behaviour – preserve body heat by reducing surface area exposed to cold air
  1. Identify some responses of plants to temperature change.
Australian snow gum
  • Thick, leathery, waxy leaves – prevent heat loss by providing insulation
  • Many oil glands in leaves – oil assists in insulation
  • Multiple palisade cell layers – more photosynthesis to produce more glucose for respiration, which produces heat
Schlerophyll plants
  • small narrow leaves – reduce heat absorption from Sun
  • vertical orientation – avoid Sun at midday but catch light in morning and evening when Sun is rising or setting
  • waxy cuticle – reflective surface reduces the amount of radiation that is absorbed to keep plant cool
Cacti
  • Leaves reduced to spines – reduce surface area exposed to heat from the Sun

Identify data sources, plan, choose equipment or resources and perform a first-hand investigation to demonstrate the effect of: increased temperature, change in pH and change in substrate concentrations on the activity of a named enzyme

The enzyme rennin is found in the gastric juices of mammals. It causes the milk protein casein to clump together. The enzyme rennet is the commercialised form and is found in junket tablet.

Temperature

Method summary
  • Water baths of various temperatures were prepared using icy water, tap water and warm water.
  • Two test tubes, labelled A and B were placed in each water bath, each containing 30 mL of milk.
  • 3 drops of rennet solution (made with one junket tablet crushed with 10mL water) were added to all test tubes labelled A.
  • The time taken for the milk in each test tube to clot was recorded
Results
  • Test tubes in water baths of 30°C and 40°C clotted the fastest.
  • Milk in test tubes kept at 10°C and 70°C did not clot at all.
  • None of the test tubes labelled B These were the controls and demonstrate that the milk clotting was actually an effect of the enzyme rennet.
Processing results

A graph was drawn with Temperature (°C) on the x-axis and Enzyme activity (1/clotting time) on the y-axis. A slightly skewed bell-shaped curve was achieved.

Discussion

At low temperatures, particles have little energy and successful collision is rare, and thus chemical reactions involving rennin are slow. At high temperatures, enzymes are denatured and thus enzyme activity is similarly low.

Conclusion

The enzyme rennin has the greatest activity in a certain temperature range (30-40°C), and any deviation from these temperatures decreases enzyme activity.

pH

Method
  • 30mL of milk was added to each of three test tubes.
  • 2mL of 0.01M HCl was added to one of them and 2mL of 0.001M NaOH was added to another. 2mL of water was added to the last one.
  • Warm and cold water were combined to achieve a water bath kept at 37°C, in which all test tubes were placed.
  • 13mL of rennet solution (one junket tablet and 10mL water) was added to each test tube.
  • The time taken for the milk in each test tube to clot was measured and recorded.
Results
AdditionpHTime for clotting (min)Activity (1/clotting time)
hydrochloric acidlow2.250.444
waterneutral1.001.000
sodium hydroxidehigh1.330.750
Discussion

The enzyme rennet appears to have an optimal pH of around the pH of water. Rennet’s optimal pH is usually given as 5.5-6.0, which is closer to the pH of water than to that of hydrochloric acid and that of sodium hydroxide. Although rennin is a digestive enzyme and has an optimal pH of 2, the commercial rennet is used for cheese and has an optimal pH of 5.5 to 6.0, as demonstrated in the investigation.

Enzyme activity was lower at extremes of pH as the enzyme denatured and lost its 3D shape.

Conclusion

The enzyme rennet has an optimal pH at which peak of activity is achieved. Any deviation from this pH results in a decrease in enzyme activity.

Substrate concentration

Method
  • Test tubes were prepared as follows:
    • 5mL milk and 25mL water
    • 15mL milk and 15mL water
    • 30mL milk
  • All test tubes were placed in a water bath kept at 37°
  • 15mL of rennet solution (one junket tablet and 10mL water) was added to each tube.
  • The time taken for milk to clot was recorded.
Results
Volume of milk (mL)% (v/v) of milkClotting time (min:sec)Relative clotting time(clotting time/volume (mL))Activity (1/relative clotting time)
516.672:110.43672.29
15502:130.14786.77
301002:310.083911.92
Processing results

Although total volume of solution was kept constant, the amount of milk wasn’t a controlled variable (concentration was the independent variable). Therefore more milk took longer to be visibly seen to be clotting, but this was due to the volume of milk, not low enzyme activity. Therefore to make results more valid, the relative clotting time was calculated, relative to substrate amount.

Results were graphed with Substrate concentration (% v/v) on the x-axis and Activity (1/clotting time) on the y-axis. The graph was increasing quite constantly.

Discussion

As substrate volume was not controlled, even though the independent variable (substrate concentration) was varied, the experiment was not valid.

With processing of results to calculate activity relative to substrate volume, the graphs shows that maximum activity (where all active sites are occupied) may not have been achieved yet as the graph has not levelled out.

Conclusion

Increased substrate concentration increases the activity of the enzyme rennin (theoretically up to a maximum – but the experiment did not show this).

Gather, process and analyse information from secondary sources and use available evidence to develop a model of a feedback mechanism

Negative feedback is a like a see-saw that maintains balance:

negative feedback is a like a see-saw that maintains balance

An electric hot water system works similarly in keeping the room as a constant temperature:

an electric hot water system

Stimulus: change in temperature, receptor: thermostat, effector: heater, response: water is heated

Gather, process and analyse information from secondary sources to distinguish between ectotherms and endotherms, name Australian examples and use available evidence to describe adaptations or responses of these organisms that assist temperature regulation

Ectotherms

Australian alpine grasshopper
  • Thermocolour grasshopper (adult male)
    • Bright greenish blue at temperatures above 25°C
    • Dull and black at temperatures below 15°C – absorb more heat
Copperhead Snake and Corroboree Frog
  • Seek shelter underground and become dormant in winter
    • slowed heartbeat and breathing
    • body temperature drops to just above freezing

Endotherms

Brush-tailed possum
  • Nocturnal – avoid hottest parts of daytime to be active at night instead
    • Prominent eyes assist with seeing in the dark
    • Large ears assist with hearing
  • Large ears – help to radiate heat from the body
  • Queensland possums are smaller – less body area exposed to sun as Queensland is a warm area
  • Tasmanian possums are larger and furrier – no need to reduce body area exposed to the sun, extra fur helps insulation as Tasmania is a cool region
Australian fur seal
  • Blubber – insulation
  • Woolly underfur and long, coarse outer hairs – outer hairs reduce convection currents and assist waterproofing and dense underfur traps air to insulate the seal
  • Countercurrent heat exchange in flippers (heat gradient between arteries and veins allows heat to flow from artery to vein before reaching end of flipper) – keeps flippers warm by spreading heat
Fairy penguin
  • Blood shunt – flow of blood from body towards feet is shunted, via a special vein with a valve, back into the body
    • feet, which are poorly insulated, receive nearly no blood, thus reducing heat loss
  • Huddling behaviour – preserve body heat by reducing surface area exposed to cold air

Plants and animals transport dissolved nutrients and gases in a watery medium

Identify the form(s) in which each of the following is carried in mammalian blood: Carbon dioxide, oxygen, water, salts, lipids, nitrogenous waste and other products of digestion

plants and animals transport dissolve nutrients and gases

Carbon dioxide

  • 70% combines with water to form hydrogen carbonate ions in the red blood cells
    • then carried as ions dissolved in plasma
    • CO2 + H2O ® H2CO3 ® H+ + HCO3
    • carbon dioxide + water ® carbonic acid ® hydrogen ion + hydrogen carbonate ion
  • 23% combines with haemoglobin to form carbaminohaemoglobin
  • 7% is dissolved directly in the plasma

Oxygen

  • Small amount dissolved directly in the plasma
  • Mostly combined with haemoglobin, forming oxyhaemoglobin
  • Each haemoglobin molecule in red blood cells contains 4 active sites (four haem groups) where oxygen molecules can be attached
  • In lungs (high O2 concentration), oxygen diffuses from lungs into the blood
    • Hb + 4O2 ® Hb(O2)4
    • haemoglobin + oxygen ® oxyhaemoglobin
  • At body tissues (low O2 concentration), oxygen is released from haemoglobin
    • Hb(O2)4 ® Hb + O2
    • oxyhaemoglobin ® haemoglobin + oxygen

Water

  • Plasma is 90% water
  • Water exists as H2O molecules in the plasma

Salts

  • Water dissolves ionic substance as water is polar.
  • Ions are dissolved in the plasma.

Lipids

  • enclosed in a package of protein to form a structure called chylomicron
  • transported in blood (and lymph) as fatty acids and glycerol

Nitrogenous wastes

  • Mostly as urea dissolved in the plasma

dissolved in plasma of nitrogenous wastesUrea

  • Also as uric acid and creatinine dissolved in the plasma

uric acid and creatinine dissolved in the plasma of nitrogenous wastesUric acid

Other products of digestion

  • May include amino acids, sugars, vitamins
  • Dissolved in plasma
  1. Explain the adaptive advantage of haemoglobin and discuss physiological responses of mammals to decreased oxygen concentrations experienced at high altitudes.

If oxygen was simply dissolved in the plasma, 100mL of blood would only be able to carry 0.2mL of oxygen. Haemoglobin increases the blood carrying capacity of oxygen by 100 times so that 100mL of blood can carry 20mL of oxygen.

Each haemoglobin complex contains 4 haem groups so that 4 molecules of oxygen can attach to it.

The extra oxygen allows a higher respiration rate and generation of more heat.

Inhabitants of areas of high altitude where oxygen concentration in the air is low generally have:

  • more red blood cells to hold on to more of the oxygen that is inhaled (normally 16% of exhaled air is oxygen)
  • higher breathing and heart rates to absorb more oxygen and also distribute oxygen faster, so that body cells receive the required amounts of oxygen
  • more dense capillaries to more effectively distribute oxygen

Compare the structure of arteries, capillaries and veins in relation to their function

Vessel StructureFunction
Arteries vessel of arteries
  • Thick, elastic fibre
  • Smooth muscular walls
  • Smaller lumen (space within walls) than veins
  • Main arteries branch to form arterioles

 

  • To take the blood away from the heart
  • High pressure of blood keeps it travelling in one direction
  • Needs to expand and recoil with each heart beat (pulse)
Veins vessel of veins
  • Thinner elastic fibre, smooth muscle and connective tissue
  • Wide lumen
  • Valves
  • Small venules unite to form veins
  • To take blood back to the heart
  • Lower pressure than arteries
  • Valves required to stop blood flowing the wrong way
  • Muscles press on veins to help blood keep moving
Capillaries vessel of capillaries
  • Very thin walls
  • Small lumen (7-10µm) – one red blood cell at a time, may be bent as they pass through
  • No valves
  • Large surface area over which exchange of materials occurs
  • Immediate contact with cells and transport of substances between blood and cells
  • Connect arteries to veins

Describe the main changes in the chemical composition of the blood as it moves around the body and identify tissues in which these changes occur

Organ that blood has just passed throughBlood composition
Lungsless CO2, more O2
Muscle tissueless O2, more CO2, less glucose, less amino acids
Liverless glucose, less amino acids, less poisons, more urea
Kidneyless urea, less salts, less water
Small intestinemore glucose, more amino acids, more fatty acids and glycerol, more vitamins, less O2
Endocrine glands (e.g. pancreas, testes, adrenal glands, thyroid gland)more hormones

Outline the need for oxygen in living cells and explain why removal of carbon dioxide from cells is essential

Oxygen is an essential reactant in cellular respiration which is the process by which living cells unlock energy from glucose (in the form of ATP). Energy is required for growth, maintenance, reproduction and heat production (in endotherms).

glucose + oxygen ® carbon dioxide + water + energy (in the form of ATP)

C6H12O6 + 6O2 ® 6CO2 + 6H2O ΔH<0

Carbon dioxide is a waste product in cellular respiration. If allowed to accumulate, it will react with water to form carbonic acid which would lower pH. This would create an overly acidic environment in which enzymes would denature and metabolic processes would be under-regulated.

Instead, excessive CO2 is removed through the lungs (or other respiratory organ). At normal levels, the bicarbonate ion (HCO3) formed from carbonic acid is important in buffering the blood to maintain a constant pH.

Outline the body’s response to increased carbon dioxide concentration in the blood as an example of maintaining the balance in blood composition concentrations

In mammals, changes in pH are monitored by the medulla of the brain and the walls of the aorta and carotid arteries in the neck.

Nerves send messages to the breathing control centre in the medulla. The rate and depth of breathing are altered.

  • Too much CO2 causes an increase in rate and depth of breathing
  • Low levels of CO2 cause a decrease in rate and depth of breathing

Describe current theories about processes responsible for the movement of materials through plants in xylem and phloem tissue

transpiration cohesion adhesion

 

Xylem

The current theory is the transpiration-cohesion-adhesion mechanism. This is passive transport.

  • Transpiration – evaporation of water from stomates in leaves
    • As water is lost through transpiration, water molecules from further down in the xylem are drawn up to replace this loss
    • This is the initiation of the transpiration stream
  • Cohesion – hydrogen bonding of water molecules are strong intermolecular forces
    • Water molecules attract each other and pull each other up
  • Adhesion – water molecules are attracted to the cellulose cell walls
    • This force assists in pulling the water molecules up the xylem tubes

forces of cohesion and adhesion are together known as capillary action

Forces of cohesion and adhesion are together known as capillary action

There is also root pressure, which contributes little to the transport of water.

  • Mineral ions may be actively taken up through the roots at night.
  • However, transpiration is low, so there is no transpiration stream to transport water and mineral ions up xylem.
  • Pressure builds up and water is pushed up the stem. This is known as guttation.

the pressure flow mechanism of phloem

Phloem

The pressure-flow mechanism (or source-to-sink mechanism) is widely accepted. Movement is called translocation.

  • Sugar is loaded into the phloem tube from the sugar source (e.g. leaf) by active transport.
  • Water enters by osmosis due to high solute concentration in the phloem tube. Water pressure is now raised at this part of the tube.
  • At the sugar sink, where sugar is taken to be used and stored, sugar is actively unloaded. Water follows the sugar, leaving by osmosis, and water pressure in this part of the tube is lowered.

Therefore the high water pressure at the source causes water and dissolved sugar to flow to the low water pressure at the sink.

Sieve cells join end-to-end to form a series of connecting elongated cells, divided by specialised membranes containing pores (sieve plates). They allow movement of phloem sap.

  1. Identify data sources, plan, choose equipment or resources and perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water.

Method

  • Two test tubes containing limewater (Ca(OH)2) and universal indicator were prepared.
  • Hydrochloric acid and calcium carbonate were combined in a side-arm tube, with rubber tubing leading into one of the test tubes containing limewater. Carbon dioxide was bubbled into the limewater.

2HCl + CaCO3 ® H2O + CaCl2 +CO2

  • Colour changes and corresponding pH changes were observed.
  • A straw was used to blow into the other test tube containing limewater. Exhaled air containing carbon dioxide was bubble through the limewater.
  • Colour changes and corresponding pH changes were observed.

Results

Both sources of CO­­­2 caused limewater to become more acidic. It also became more opaque. The solutions in both test tubes turned form purple to blue to green.

Discussion

CO2(g) + Ca(OH)2(aq)­­ ® CaCO3(s) + H2O

Carbon dioxide reacted with limewater formed a precipitate of calcium carbonate, which caused the limewater to become milky and opaque. This reaction decreased the number of OH ions in the solution of limewater, thus raising the pH. In plain water, this reaction would not take place.

But also: CO2(g) + H2O(l) ® H+(aq) + HCO3(aq)

The carbonic acid (existing as hydrogen ions and bicarbonate ions) resulted from a reaction between the carbon dioxide gas and the water that was the solvent for calcium hydroxide. This reaction would have taken place in plain water and also contributed to the lower pH.

The results were taken qualitatively using acid-base indicator. More accurate, quantitative results could have been obtained using a calibrated pH probe. A pH probe would also be a non-destructive form of testing, whereas indicators are a destructive form of testing.

Conclusion

Dissolved carbon dioxide lowers the pH of water.

Perform a first-hand investigation using a light microscope and prepared slides to gather information to estimate the size of red and white blood cells and draw scaled diagrams of each

dissolved carbon dioxide lowers the ph of water of conclusion

The use of a prepared slide prevented the spread of blood-borne diseases.

Gather, process and analyse information from secondary sources to identify current technologies that allow measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and explain the conditions under which these technologies are used

Pulse oximeter

non invasive probe that goes over the patien't finger

  • non-invasive probe that goes over the patient’s finger, earlobe or toe
  • measuring pulse and oxygen concentration as a percentage of haemoglobin saturated with oxygen
  • measures transmission of light through the tissues (oxygenated blood is bright red, while deoxygenated blood is dull red)
  • readings under 90% set off alarm signal
  • used when:
    • patients are undergoing procedures requiring anaesthesia or sedation
    • patients are on a ventilator or artificial breathing machine
    • patients have abnormal breathing or circulation
    • patients are undergoing stress testing
    • patients are in sleep laboratories
    • checking response to different medications

Arterial blood gas analysis

  • invasive
  • sample of blood taken from an artery (usually in the arm) for laboratory analysis with arterial blood gas analysis machine
  • monitor amount of oxygen and carbon dioxide diffusing across artificial membranes
  • oxygen in the blood produces an electric current when diffusing
  • carbon dioxide changes pH
  • measures oxygen saturation, partial pressure of oxygen (diffusion of air from lungs into blood), CO2 level, pH and bicarbonate ions
  • used when:
    • assessing effectiveness of breathing in patients with respiratory diseases
    • patients show signs of dangerously low oxygen levels or high carbon dioxide levels
    • symptoms of low oxygen levels
      • cyanosis (blue-tinging of skin)
      • visual hallucinations
    • symptoms of high carbon dioxide levels
      • drowsiness
      • bounding pulse
      • headache
      • tremors

Gather, process and analyse information from secondary sources to identify and describe the products extracted from donated blood and the uses of these products

There are three types of blood donations:

  • Whole blood donation – red blood cells, plasma and platelets are collected
    • can be done every 12 weeks
  • Plasma donation – plasma only is collected through apheresis (where other blood components are returned to patient)
    • can be done every 2 weeks as red blood cells are returned
  • Platelet donation – platelets only are collected through apheresis
    • can be done every 2-4 weeks as platelets are replaced within a few days

Blood products include:

  • Red blood cells
    • when greater oxygen-carrying capacity is required
    • replacing cells lost following significant bleeding
    • can be refrigerated for up to 42 days
  • Platelet concentrate
    • treatment of bleeding caused by conditions or diseases where platelets are not function properly e.g. thrombocytopenia (shortage of platelets)
    • stored at room temperature for up to 5 days
  • Clinical fresh frozen plasma (FFP)
    • provide blood components that coagulate the blood
    • contains all coagulation factors in normal amounts
    • used to increase blood volume or for patients requiring immediate clotting effects e.g. warfarin therapy (blood thinning) or when massive transfusions have taken place
  • Cryoprecipitate anti-haemophilic factor
    • concentrate of clotting proteins – for treatment of severe bleeding
    • treatment of haemophilia and von Willebran disease (similar to haemophilia)
    • replacement of clotting proteins, fibrinogen, Factor XIII and Factor VIII when no other option is successful
    • liver transplants
  • Other plasma products
    • immunisations against chicken pox, hepatitis B and tetanus
    • protein products for the treatment of patients with burns, liver and kidney diseases
    • immunoglobin products for the treatment of patients with antibody deficiencies (e.g. for Hepatitis A) and other immune disorders

Gather, process, analyse and present information from secondary sources to report on progress in the production of artificial blood and use available evidence to propose reasons why such research is needed

Types of artificial blood:

  • Modified haemoglobin (Polyheme)
    • developed as a military project with a focus on keeping trauma patients alive in remote areas when donated blood is not available
    • trying to duplicate oxygen-carrying capacities of blood
    • effectively replaces blood function with a circulation half-life of 24 hours
      • manufactured using human haemoglobin (especially outdated red blood cell products) – donors are still required
    • reached Phase III clinical trials
      • may be related to cases of high blood pressure
    • Perfluorocarbons
      • using oxygen-carrying capacity of these compounds
      • manufactured entirely artificially – cheap to produce, no risk of infection
      • not soluble in water, but carries 50% more oxygen than plasma (oxygen dissolved directly)
        • still carries nowhere near as much as haemoglobin
        • needs to be attached to another molecule e.g. lipid to be transported in blood (i.e. emulsified)
      • Stem cell research
        • extraction of haematopoietic stem cells from umbilical cord
        • trying to duplicate differentiation process into red blood cells in vitro
        • mixing with plasma or fluid for transfusion
          • expensive
          • umbilical cord stem cells are not in abundant supply
          • still undergoing trials
        • Plasma Substitutes
          • widely used to increase blood volume and blood pressure
            • No oxygen-carrying abilities

Why research is needed:

In the 1980s the HIV crisis triggered research into artificial blood, as suddenly natural blood transfusions could lead to fatal infections.

  • artificial blood is far from perfection – still under trial
    • can only substitute one function of natural blood (mostly targeting transport – not clotting or immune defence)
    • modified haemoglobin has short circulation time – research into enclosure with membrane to prevent oxidation or breakdown by enzymes may be beneficial
    • PFCs do not combine well with the patient’s blood
    • Clinical applications are essential to find out long-term side effects on humans.
    • further research required to be economically viable
  • artificial blood has many benefits over natural blood:
    • no risk of blood-borne diseases being transferred
    • no need to identify blood type (saving time in emergencies)
    • no problem with supply in case of war, terrorism or natural disaster when masses of victims require blood transfusions
    • avoiding cultural or religious objectionsg. Jehovah’s witness
    • longer shelf life

Choose equipment or resources to perform a first-hand investigation to gather first-hand data to draw transverse and longitudinal sections of phloem and xylem tissue

Transverse

transverse of arterial blood gas analysis

 

Longitudinal

 

longitudinal of arterial blood gas analysis

Toluidine Blue used to stain celery. A wet mount was used.

Gather, process and analyse and present information from secondary sources to compare the movement of materials through mammals and flowering plants

 MammalsFlowering Plants
VesselsArteries, veins and capillariesXylem and phloem
OxygenAttached to haemoglobin, a small amount dissolved directly in bloodDirect diffusion from air
Carbon dioxideDissolved in blood, some attached to haemoglobinDirect diffusion from air
Transport of nutrientsThrough blood vesselsTranslocation through phloem
Transport of waterThrough blood vesselsTranspiration-cohesion-adhesion through xylem
Carbon dioxideTransported through blood to lungsDiffusion to and from air

Plants and animals regulate the concentration of gases, water and waste products of metabolism in cells and in interstitial fluid

Recall the role of the respiratory and excretory systems in maintaining humans as functioning organisms

respiratory system and excretory system of plants and animals

Respiratory system

  • providing oxygen for respiration
  • removing carbon dioxide as a waste product

Excretory system

  • removing nitrogenous wastes, which result from the breakdown of proteins and nucleic acids

Identify the role of water as a solvent for metabolic reactions in living cells and explain why the concentration of water in cells must be held constant

Water is the solvent for metabolic reactions in living cells. It is known as the universal solvent, dissolving ionic substances, polar molecules, and non-polar molecules to some degree. Water is also a transport medium for substances because of its properties as a solvent. Water is a reactant in many reactions and a product in others.

Living cells work best in an isotonic environment – solute concentration is the same both inside and outside the cell. Cells die if water content is changed significantly e.g. through osmosis, as solute concentration is not held in balance. Water also provides structure.

Water also moistens cell membranes for ease of diffusion of materials.

Explain why the removal of wastes is essential for continued metabolic activity

  • Metabolic wastes inhibit the reactions that produce them if allowed to accumulate (Le Chatelier’s principle), thus slowing metabolism.
    • Products of metabolic reactions hinder reversible reactions.
  • Nitrogenous wastes are toxic. They can change pH (so enzymes are denatured) and interfere with membrane transport
    • They are produced by the breakdown of proteins and nucleic acids.
  • Carbon dioxide lowers pH.
  • Excess salts can affect osmotic pressure.

Therefore wastes must be removed to promote metabolism and to prevent cells from being poisoned by accumulating wastes.

Compare the waste products of a range of terrestrial and aquatic organisms and explain why these differences occur

OrganismWaste productEnvironmental factors
Terrestrial mammals, adult amphibians, some cartilaginous fishUrea
  • Need to conserve water – ammonia is converted into urea.
  • This process takes energy, but less than for uric acid.
  • Urea is less toxic than ammonia.
  • Urea is highly soluble in water.
  • Its limited toxicity allows concentrated urine to be formed.
Terrestrial insects, birds, reptilesUric acid
  • Need to conserve water – ammonia is converted into uric acid.
  • This process takes a lot of energy.
  • Uric acid is less toxic that urea and ammonia.
  • Uric acid is insoluble in water.
  • It can be released as a paste, requiring very little water to expel it.
  • Its low toxicity also allows for embryos (in eggs) to not be poisoned.
FishAmmonia
  • Ammonia takes little energy to produce – it is the direct product of breakdown of proteins and amino acids.
  • Ammonia is highly toxic – but fish can excrete it continuously through the gills directly into the water where it quickly disperses.
  • Ammonia is highly soluble in water and it takes a lot of water to excrete it – but there is plenty of water available.

Identify the role of the kidney in the excretory system of fish and mammals

identify the role of the kidney in the excretory system of fish and mammals

  • The kidney in fish primarily plays the role of osmoregulation. Nitrogenous wastes are excreted across the gills. Fish urine is mainly water and salt.
  • In freshwater fish, the kidneys excrete large amounts of dilute urine, to get rid of excess water in an environment where osmotic balance causes them to constantly absorb water. Gills and kidneys actively absorb salts.
  • In marine fish, the kidneys excrete small quantities of concentrated urine, to preserve water in an environment when osmotic balance causes them to constantly lose water. Gills and kidneys actively excrete salts.
  • In mammals, the kidneys excrete urea and also have the role of osmoregulation.
  • Excess amino acids are transported to the liver, where they are deaminated to form urea. Kidneys excrete urea. They also reabsorb water and mineral ions and secrete substances to maintain osmotic balance.

Explain why the processes of diffusion and osmosis are inadequate in removing dissolved nitrogenous wastes

Diffusion and osmosis rely on random movement of particles and a concentration gradient. They both occur in the kidney.

However, diffusion cannot select useful substances to retain or lose, and it is too slow for normal body function. Osmosis only deals with water, not salts, and again, it is a slow process.

Distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney

Active transport requires the expenditure of energy to transport materials across a membrane. These might otherwise be blocked because of concentration gradient or its own properties, such as size. Passive transport requires no energy and relies on random movement of particles against a concentration gradient.

Both active transport and passive transport occur in the mammalian kidney.

Active transport includes:

  • secretion of substances into the nephron e.g. poisons, potassium ions, hydrogen ions
  • selective reabsorption of all useful nutrients and salts back into the blood e.g. in the distal convoluted tubule

Passive transport includes:

  • osmosis of water being reabsorbed
  • diffusion of salts reabsorbed in the proximal convoluted tubule

distinguish between active and passive transport and relate these to processes occurring in the mammalian kidney

Explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid composition

Filtration occurs in the Bowman’s capsule.

  • The network of capillaries called the glomerulus forces blood at a high pressure into the Bowman’s capsule.
  • Small soluble molecules pass through by passive filtration into the glomerular filtrate.
    • water
    • nitrogenous wastes such as urea
    • food materials e.g. glucose, amino acids, vitamins, minerals
    • other ions e.g. bicarbonate
    • other ingested substances e.g. penicillin, aspirin
    • hormones
  • Blood cells and proteins are too large to be removed
  • Filtration is non-selective and many valuable components of blood must be recovered through reabsorption.

explain how the processes of filtration and reabsorption in the mammalian nephron regulate body fluid composition

Reabsorption occurs in the tubule.

  • proximal convoluted tubule
    • bicarbonate ions, water and potassium ions reabsorbed passively
    • glucose and amino acids (and other nutrients) reabsorbed actively
    • secretion of hydrogen ions
    • secretion of drugs and poisons
  • loop of Henle (descending)
    • walls are permeable to water but not salt
    • water reabsorbed by osmosis
  • loop of Henle (ascending)
    • walls are permeable to salt but more water
    • salt reabsorbed passively through a thin-walled section, then actively through a thick-walled portion
  • distal convoluted tubule
    • selective reabsorption and secretion
    • adjust pH and levels of salts, especially sodium and potassium ions
  • collecting duct
    • walls are permeable to water but not salt
    • water passes out by osmosis
    • final filtrate is urine

Outline the role of the hormones, aldosterone and ADH (vasopressin), in the regulation of water and salt levels in blood

Aldosterone is a steroid hormone released by the adrenal gland (one above each kidney).

  • regulates transfer of sodium and potassium ions in the kidneys
  • low sodium ion levels and/or low blood volume cause more aldosterone to be released
    • increases permeability of distal convoluted tubule to sodium ions
      • more sodium ions are reabsorbed, more potassium ions are secreted
      • water follows by osmosis
    • assisting homeostatic balance of blood pressure

ADH (antidiuretic hormone) controls water reabsorption in the nephron.

  • when fluid levels in the blood drop, the hypothalamus produces ADH which is stored in and released from the posterior pituitary gland
  • released when:
    • dehydration occurs
    • haemorrhaging causes loss of body fluids
  • increases permeability of distal convoluted tubule and collecting duct to water
  • more water is reabsorbed into the blood
  • urine becomes more concentrated

Define enantiostasis as the maintenance of metabolic and physiological functions in response to variation in the environment and discuss its importance to estuarine organisms in maintaining appropriate salt concentrations

Enantiostasis is the maintenance of normal metabolic and physiological functioning in response to changes in the external environment.

An estuary experiences rapid changes in salt concentration with tidal movement and mixing of fresh and salt water.

Osmoconformers allow the body’s osmotic pressure to vary with that of the environment, changing it to match that of the environment.

  • most marine invertebrates
  • as salt concentration affects activity of enzymes, another function is changed to compensate
  • for example, pH is increased to make up for increased salt concentration to increase the reduced efficiency of an enzyme

Halophytes are plants adapted to living in salty environments.

  • exclusion
    • grey mangrove, red mangrove, orange mangrove
    • salt is prevented from entering root systems by filtration
    • passive process relies on transpiration stream
  • excretion
    • grey mangrove, river mangrove, saltbush
    • special salt glands, usually in the leaves
    • salt concentrated in these leaves and is actively excreted
    • often seen and tasted as crystals on leaves – washed off by rain
  • accumulation
    • milky mangrove (old leaves), samphire plant (swollen leaf bases)
    • salt accumulates in a part of plant, usually bark or old leaves
    • these parts are shed
  • pneumatophores
    • obtain oxygen used in respiration from the air, not from the salty water

Describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss

Xerophytes are plants adapted to dry conditions.

  • hard, leathery, needle-shaped leaves with reduced surface area – Hakea sericea, coastal tea trees
  • leaf scales rather than leaves – casuarina
  • phyllodes (flattened leaf stems) rather than leaves – acacias (wattle)
  • change reflectiveness of leaves during development (highly reflective in summer) – Atriplex (salt bush)
  • sunken stomates into pits or grooves or reduced number of stomates – hakea and eucalyptus
  • vertical orientation of leaves – eucalypts
  • rolled up leaves to minimise water loss – porcupine grass, spinifex
  • leaves with thick, waxy cuticle – eucalypts, mangroves
  • dormancy period (lignotubers instead of above-ground parts) – Mallee eucalypts
  • tough, hard seeds to survive long, dry periods – banksia

Perform a first-hand investigation of the structure of a mammalian kidney by dissection, use of a model or visual resources and identify the regions involved in the excretion of waste products

describe adaptations of a range of terrestrial australian plants that assist in minimising water loss

Gather, process and analyse information from secondary sources to compare the process of renal dialysis with the function of the kidney

 KidneyRenal dialysis
Filtering unitNephronMachine
FilterWalls of glomerulusArtificial membrane or peritoneal membrane
TransportActive and passivePassive
HormonesADH and aldosteroneNone
OsmoregulationHighly effectiveSmall ions (sodium, potassium and phosphate ions) tend to accumulate in the blood as they do not move out quickly by diffusion. Dialysis in only capable of removing limited amounts of fluid from the blood.No reabsorption.
LifestyleCompletely naturalVisits to a hospital/use of machine for 2-3 hours at a time, 3-4 times a week or overnight every night and possible during the day

Gather, process, analyse and present information to outline the general use of hormone replacement therapy in people who cannot secrete aldosterone and use available evidence to discuss the importance of this therapy

Aldosterone is a hormone released by the adrenal gland. The human body has two of these glands with one above each kidney. Aldosterone causes the kidneys to increase the amount of sodium ions (Na+) reabsorbed into the bloodstream and the amount of potassium ions (K+) removed in the urine, thus maintaining the sodium-potassium balance in the blood. In addition, aldosterone causes water to be reabsorbed with sodium, thus increasing blood volume and maintaining blood pressure.

When there is a decrease of sodium ion levels in the blood, rennin is secreted by the kidneys. Rennin stimulates a series of chemical reactions which in turn to lead the release of aldosterone, which increases sodium ion and water reabsorbed into the blood and restores blood pressure. When these factors are correctly in balance, the level of rennin in the bloodstream falls and thus the amount of aldosterone released also falls. Therefore, aldosterone release is based on a negative feedback system to achieve homeostasis.

Addison’s disease affects about 1 in 100 000 people and is a rare endocrine disorder. Addison’s disease results from the deficiency of glucocorticoid or cortisol, which is nearly always accompanied by a lack of aldosterone. These deficiencies result from the reduced ability of the adrenal glands to produce these hormones, which often occurs when the immune system attacks and damages the adrenal cortex (outside of adrenal glands) over time. Other causes include infection, cancer or surgical removal of tumours in the adrenal or pituitary glands or the hypothalamus.

Symptoms of Addison’s disease include chronic fatigue, nausea, vomiting, diarrhoea, muscle weakness, low blood pressure, salt cravings, dehydration, hypoglycaemia, loss of appetite and weight, increased pigmentation of skin, irregular menstrual periods in women and mood swings or mental confusion. In children and adolescents, these symptoms can develop quickly and in adults, it can take decades. Many of the symptoms are similar to those of other diseases, rendering diagnosis difficult. In severe cases, Addison’s disease can lead to death if it is not treated.

Hormone Replacement Therapy

Addison’s disease is managed using hormone replacement therapy for life. Often corticosteroids, such as fludrocortisone acetate (Florinef), are prescribed as oral medication to be taken daily, with the dose adjusted according to the needs of the patient. An alternative is available for patients who suffer vomiting and cannot retain oral medications. In such an instance, corticosteroid injections are used.

Perform a first-hand investigation to gather information about structures in plants that assist in the conservation of water

PlantStructureEffect
CasuarinaLeaves are reduced to scales with green twig (branchlet) performing photosynthesis instead. Stomata are hidden in grooves.Minimises surface area and thus limits water loss through transpiration
EucalyptusThick waxy cuticleMinimises water loss through transpiration, reflects heat
Vertically hanging leavesMinimises exposure to sun at noon, thus minimising transpiration by controlling temperature around the leaf
CactusThick fleshy stemStorage of water
Leaves are reduced to spikes. Green stem takes over photosynthesis.Minimises surface area and thus limits water loss through transpiration
Dune grassSunken stomataTrap moist air in a humid cavity to reduce water loss through transpiration
Coiled leafMicroclimate of humid air around automates
BottlebrushThick waxy cuticleMinimises water loss through transpiration, reflects heat
HairsReflect heat and trap a humid layer of air around stomates

Gather, process and analyse information from secondary sources to compare and explain the differences in urine concentration of terrestrial mammals, marine fish and freshwater fish

OrganismUrine concentrationsEnvironmental factors
Terrestrial mammalsConcentrated
  • Water is not necessarily readily available on land.
  • The medium is air, so water evaporates.
  • Organisms aim to conserve water.
  • Producing concentrated urine allows nitrogenous waste to be excreted without losing too much water.
Marine fishConcentrated
  • Surrounding environment has a high solute concentration – concentration gradient causes fish to constantly lose water to the environment.
  • Marine fish aim to preserve water.
  • Producing concentrated urine allows nitrogenous waste to be excreted without losing too much water.
  • Ions are excreted by specialised glands
Freshwater fishDilute
  • Surrounding environment has a low solute concentration – concentration gradient causes fish to constantly absorb water to the environment.
  • Freshwater fish aim to maintain reasonable amounts within their bodies.
  • Producing dilute urine allows nitrogenous waste to be expelled along with excess water.
  • Ions are absorbed by specialised glands.

Process and analyse information from secondary sources and use available evidence to explain the relationship between the conservation of water and the production and excretion of concentrated nitrogenous wastes in a range of Australian insects and terrestrial mammals

Meat ants (insect)

  • Malpighian tubules are excretory organs
    • collect water and uric acid from the haemolymph and empty it into the gut
  • Useful substances and water are reabsorbed.
  • Uric acid released in dry paste.

Wallaroo (mammal)

  • concentrated urine (nitrogen and urea are recycled to make it)
  • very arid environments

Spinifex hopping mouse (mammal)

  • lives in the desert and drinks very little water
  • concentrated urine (urea)
  • kidneys have extensive renal medulla and long loop of Henle for reabsorption

Process and analyse information from secondary sources and use available evidence to discuss processes used by different plants for salt regulation in saline environments

Halophytes are plants adapted to living in salty environments.

  • exclusion
    • grey mangrove, red mangrove, orange mangrove
    • salt is prevented from entering root systems by filtration
    • passive process relies on transpiration stream
  • excretion
    • grey mangrove, river mangrove, saltbush
    • special salt glands, usually in the leaves
    • salt concentrated in these leaves and is actively excreted
    • often seen and tasted as crystals on leaves – washed off by rain
  • accumulation
    • milky mangrove (old leaves), samphire plant (swollen leaf bases)
    • salt accumulates in a part of plant, usually bark or old leaves
    • these parts are shed
  • reduction of transpiration
    • some mangroves
    • vertically hanging leaves reduce uptake of water and dissolved salts