Biology Notes Module 1, Maintaining a Balance, by F.A ... · Biology Notes – Module 1, Maintaining a Balance, by F.A 2 1. Most organisms are active in a limited temperature range

Biology Notes – Module 1, Maintaining a Balance, by F.A

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Maintaining a Balance


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1. 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 Enzyme action

Enzymes - protein molecules acting as biological catalysts, increase the rate of the reactions that occur in living organisms

Intracellular enzymes are used within the cells that produce them (e.g. enzymes in cellular respiration and photosynthesis)

Extracellular enzymes act outside the cells that produce them (e.g. digestive enzymes)

While enzymes participate in reactions as biological catalysts they are not used up and are available for reuse (the activation energy required to start the reaction is lower when an enzyme is present)

Enzyme structure

Enzymes are made up of proteins and the basic building block of proteins is the amino acid. Two amino acids bonded together form a dipeptide. When a number of dipeptides join together a polypeptide chain is formed. Polypeptides form proteins. These chains fold in a specific way forming active sites

Many enzymes require the presence of other factors as well as the protein part before they act. These non-protein parts are called cofactors and include metallic ions like iron, calcium, copper and zinc. If the cofactor is an organic molecule like a vitamin it is called a coenzyme

Figure 9.2.1.1 - (a) From a pool of amino acids form a dipeptide when joined by a peptide bond. (c) A polypeptide is formed when many peptide bonds are formed. (d) Polypeptides fold into specific shapes to act as enzymes. Each has its own specific active site that combines with its substrate

Enzymes and their substrates

The compound acted on by an enzyme is called a substrate

The compounds obtained as a result of the enzymes action on the substrate are called the products

Enzymes are highly specific in their action – each enzyme acts upon a particular substrate

The shape of an enzyme at a region, its active site fits with part of the substrate molecule – this is called the lock & key model

In some cases the active site of the enzyme varies slightly from that of the substrate and the two fit only after contact when the substrate induces a complementary shape at the enzyme’s active site – this is called the induced fit theory of enzyme action

Poisons like cyanide and arsenic work by blocking the active sites of enzymes and stopping their action


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Figure 9.2.1.2 – Each enzyme only reacts with one kind of substrate. The active site of each enzyme is able to bind to part of the specific substrate. Two models of enzyme action are shown: (a) ‘lock and key’ model; (b) ‘induced-fit’ model

The essential role of enzymes in metabolism

There are hundreds of chemical reactions taking place in human body cells every second, most of which would never take place at the temperature and the pH of living things unless they are catalysed by enzymes

Example – respiration: glucose is oxidised and the energy stored in its bonds is released as ATP. Without enzymes this reaction has a very high activation energy reached only at very high temperatures. If the reaction takes place at high temperatures there are two main disadvantages:

- all the energy is released spontaneously and is lost to the cell as it cannot be trapped - high temperatures can damage living molecules

with enzymes present the activation energy is reduced and the reactions can take place at moderate temperatures

Enzymes catalyse steps in metabolic pathways and work in teams to produce an end product needed by the organism. Every enzyme plays an essential role in the process. If one enzyme is missing or defective then the entire pathway is affected

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

The pH of a solution is the measure of the concentration of hydrogen ions per litre of the solution

The pH of a neutral solution, like water is 7.0. A pH below 7.0 indicates an acid – the lower the pH the more acidic the solution. A pH higher than 7.0 indicates a basic solution

Most biological fluids have a pH between 6 and 8 (e.g. blood pH is maintained at about 7.4). However there are a few extremes like gastric juice which has a pH of about 2


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PRACTICAL Identify data sources, plan, choose equipment or resources and perform a first-hand investigation to test the effect of:

- increased temperature - change in pH - change in substrate concentrations

on the activity of a named enzyme Renin is an enzyme found in the stomach of calves and in junket tablets – it causes the proteins in milk to set into semi-solid curds Aim: To demonstrate the effect of temperature, pH and substrate concentration on the ability of renin to solidify milk Part 1 – Temperature

(i) Measure and mark 2.5cm on 4 large test-tubes containing 0.01g of junket powder

(ii) Warm or cool 4 samples of milk in a beaker to 5oC, 40oC, 90oC & room temperature

(iii) Add the milk to the mark on the test-tubes containing 0.01g of junket powder

(iv) Add one test-tube to a water bath at 5oC, another at 40oC and another at 90oC and leave the fourth as a control at room temperature

(v) Time how long it takes for the milk to set Results

Temperature (oC) Time to set

Control (room temp) Over 5 min

5oC Over 5 min

40oC 1 min 48 sec

90oC Over 5 min

Part 2 – pH variation (i) To three preheated test-tubes containing 2.5cm

of milk and 0.01g of junket powder in a 40oC water bath. To one add 2mL of HCl (acid), 2mL of NaOH (base) to another, and the third as a control with no pH alteration

(ii) Time how long it takes for each to set Results:

pH Time to set

Acidic Over 5 min

Alkaline Over 5 min

Control 1 min 48 sec

Part 3 – Substrate concentration

(i) Dilute a milk sample with water, add 0.01g of junket powder, immerse in a 40oC water bath and time how long it takes to set

(ii) Compare this time with the time normal milk takes to set at the same temperature

Results:

Sample Time to set

All milk sample 1 min 48 sec

Diluted milk sample Over 5 min

EXPLANATION:

The rate of an enzymic reaction is affected by several factors including temperature, pH and substrate concentration Temperature:

At high temperatures, enzymes are permanently denatured (their structure is permanently changed and even when the temperature returns to normal, they remain inactive as their active site is damaged and the protein molecule is unwound)

Enzymes that are inactivated in low temperatures become active when the temperature returns to normal

Most human enzymes have an optimal temperature of about 37oC (normal body temp)

Heat-tolerant organisms like bacteria living in hot springs have enzymes with high optimal temperatures


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pH:

Each enzyme has an optimal pH at which it acts best

A change in pH can change the shape of an enzyme’s active site affecting its ability to combine with the substrate. Because the enzyme is less able to combine with its substrate it is unable to act and metabolic reaction declines

Enzymes becomes less efficient if the variable value is greater or less than optimal

Carbonic anhydrase – found in human blood has optimal pH of 7.4 (bloods normal pH)

Pepsin – found in human stomachs has an optimal pH of 2 (acidic – gastric juice)

Trypsin – found in the human small intestine has an optimal pH of 8.0 (basic) Substrate concentration:

The addition of more substrate to an enzyme solution will initially increase the rate of reaction if not all of the active sites of the enzyme present are occupied but then plateau

The solution contains a set amount of enzyme and if no more is added the rate of reaction declines as all of the active sites of the enzyme molecules become occupied

Enzyme concentration:

Only a very small number of enzyme molecules are usually involved in a reaction and these produce a given amount of product per unit time. If the amount of enzyme is increased, the amount of product made per unit time increases but amount of product will still be limited by the amount of substrate

Enzyme molecules are not used up in a reaction and are available for reuse Inhibition:

Other molecules may compete with the normal substrate for active sites of enzymes and this compound may combine with the active site interfering with normal substrate-enzyme reactions and inhibiting formation of the normal product

Enzyme inhibition can cause death

Cyanide acts by inhibiting cytochrome c oxidase, an enzyme important in aerobic respiration (provides ATP needed for life) and for this reason is extremely poisonous

Explain why the maintenance of a constant internal environment is important for optimal metabolic efficiency The external environment can vary greatly. In spite of this living cells can exist in a relatively unchanging stable environment

In healthy people, whether they are eating or fasting their blood glucose is kept within 3.6 - 6.8 mmol/L and regardless of weather conditions their core body temperature is kept around 37oC

Multicellular organisms have mechanisms that enable an enzyme to operate at its optimal capacity by providing an environment that has relatively constant temperature, pH and substrate concentration. Since the activity of enzymes influences the outcomes of metabolism, constant internal environmental conditions equate to optimal enzyme activity and metabolic efficiency

The internal environment of living cells in the human body is a liquid consisting of tissue fluid (liquid that surrounds and bathes the membranes of nearly all cells), plasma (the liquid part of the blood in which blood cells are suspended) and other fluids

Describe homeostasis as the process by which organisms maintain a relatively stable internal environment Homeostasis is the condition of a relatively stable internal environment, maintained within narrow limits

When deviation occurs mechanisms act to restore values to the ‘normal’ state

Factors like infection, trauma, exposure to toxic substances or extreme conditions such as immersion in icy water, auto-immune diseases and inherited disorders may lead to a failure of homeostasis and is potentially life threatening


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Figure 9.2.1.3 – Summary of major variables that are subject to homeostasis in mammals

Variable Normal Range Comments

Temperature 36.1oC – 37.8oC Temperature of internal cells of the body is called the core temperature

Blood glucose 3.6 – 6.8 mmol per L Blood glucose is typically maintained within narrow limits regardless of diet

Water Daily intake must balance daily loss

Body tissues vary in their water content. Bone contains about 20% water and blood about 80% water. In prolonged dehydration, fluid moves from cells and tissue fluid into blood

Ions (e.g. plasma Ca2+) 2.3 – 2.4 mmol per L Specific ions are required by some tissues

pH of arterial blood 7.4 This pH is necessary for enzyme action and nerve cells

Blood pressure – arterial Diastolic (relaxed) Systolic (contracted)

13.3 kPa (1000 mm Hg) 5.33 kPa (40 mm Hg)

Transport of blood depends on maintaining adequate blood volume and pressure

Urea (nitrogen containing wastes) in plasma

< 7 mmol per L Waste products of cellular processes must be removed by the kidneys to prevent toxic effects on cells

Red blood cells (contain haemoglobin)

Haemoglobin values: Females – 135g per L Males – 150g per L

Essential for transport of oxygen - Erythropoietin, a hormone produced by the kidney, acts on red bone marrow and stimulates red blood cell production

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

Stage 1 - Detecting changes from the stable state

In this stage a sensor of some kind detects a change in a specific variable from the desired stable level

The fact that there has been an undesirable change is then transmitted to the next part of the control system

Stage 2 - Counteracting changes from the stable state

An effector receives the message that there has been an undesirable change that must be counteracted and the variable is restored to its desired level (this is a negative feedback mechanism)

In positive feed back mechanisms this stage varies. While in negative feedback mechanisms the process corrects deviation positive feedback mechanisms causes the system to reinforce the deviation and change it further (positive feedback mechanisms are rare though they do exist - e.g. entry of Na+ into neurons, the entry of one ion stimulates entry of more Na+)

Figure 9.2.1.4 – Detecting and counteracting change. A diagrammatic summary of the two interrelated stages of homeostasis. Note that their action relies on negative feedback systems. If a variable slightly overshoots the optimal as a result of effector action, the counter negative feedback system will respond to correct the overshoot. These actions occur continuously in the body so that optimal levels of variables are continually fine-tuned Body systems contribute to homeostasis

Various mechanisms monitor conditions inside the body and, when change is detected, body systems react to restore the balance. In humans, cells form tissues and systems that play an essential role in homeostasis. With the exception of the reproductive system, all body systems play a part in homeostasis


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Figure 9.2.1.5 – Summary of the contribution of some body systems to homeostasis

The hormonal and nervous systems are the major systems responsible for the control and coordination of homeostasis


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

Control of blood pressure – a negative feedback mechanism

The control of blood pressure is an example of a negative feedback mechanism

A fall in blood pressure is detected by pressure receptors in the muscle in the walls of blood vessels

The signal passes to the brain which responds by sending electrical signals to the heart and blood vessels

The heart rate increases, blood vessels constrict and so the blood pressure increases

The response counteracts the initial change Figure 9.2.1.6 – If a change in blood pressure occurs, events take place that counteract the initial change. A fall in blood pressure is followed by events that lead to a restoration of normal blood pressure

Outline the role of the nervous system in detecting and responding to environmental changes

The human body continuously monitors variables and responds to any changes. The nervous system and hormonal systems are the two main controlling systems in the body and play major roles in detection and response processes

In most cases of maintaining homeostasis both the nervous and hormonal systems interact and in many situations the nervous system stimulates the release of hormones

Structure of the nervous system

The nervous system is composed of the brain, spinal cord and all the nerve cells connecting these to other parts of the body

In the nervous system, the passage of a nerve impulse along one neuron involves electrical changes, while the transmission from cell to cell involves the diffusion of chemical substances


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Figure 9.2.1.7 – The nervous system coordinates the action of various kinds of muscles and glands in the human body. While different parts of the system are recognised, it should be noted that the system acts as a whole

Central nervous system (CNS)

The CNS includes the brain and the spinal cord

Bone protects the CNS – the skull surrounds the brain and the vertebrae surround the spinal cord

The largest part of the brain is the cerebrum which has a folded surface called the cerebral cortex

The thalamus and the hypothalamus lie deep in the brain

The thalamus receives impulses from sensory neurons and directs them to various parts of the brain where they are interpreted

The hypothalamus regulates the release of many hormones as well as controlling many other aspects of homeostasis – the hypothalamus is important in maintaining temperature, water balance, blood pressure as well as hunger and thirst

Nerve impulses that pass from sensory detectors to the brain and impulses that pass from the brain to other parts of the body travel along the spinal cord

Figure 9.2.1.8 – Longitudal section through the midline of the brain showing the relative positions of the hypothalamus and the anterior and posterior parts of the pituitary gland


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Nerve cells

Nerve cells are the basic units of the nervous system and are also called neurons

There are three basic kinds of neurons found in the nervous system: - sensory (or affector) neuron – detect change in internal or external environment and transmit info to the CNS

- motor (or effector) neuron – carries impulses away from the CNS to muscle or gland cells - interneuron (or connecting neuron) – are usually found in the CNS and link sensory and motor neurons

Peripheral nervous system (PNS)

The PNS is the remainder of the nerve cells that lie outside the CNS

The PNS has two parts: sensory and motor divisions

The sensory division: - transmits sensory information about the external and internal environment to the CNS where it is processed - monitors and informs the CNS of events happening both inside and outside the body - carried out by somatic sensory neurons and visceral sensory neurons

The motor division: - transmits impulses away from the CNS to muscle and glands (effector organs) - has two distinct systems: somatic nervous system and autonomic nervous system - The somatic nervous system transmits messages to skeletal muscles and is called the voluntary nervous system

because we can control our skeletal muscles - The autonomic nervous system transmits messages to smooth muscle, heart muscle and glands and because we

have no control over these actions the system is also called the involuntary nervous system Figure 9.2.1.9 – Relationship between different kinds of neurons. The junction between two neurons is called a synapse

Hormones – chemical regulators

The hormonal system in the other major controlling system in the body alongside the nervous system

The hormonal system, also called the endocrine system, produces hormones that help maintain homeostasis

Hormones are chemicals produced in special structures called endocrine glands – they are secreted into and transported through the bloodstream and act on other organs and tissues of the body

Hormones contribute to homeostasis by negative feedback mechanisms


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Figure 9.2.1.10 – The endocrine system: its main glands, the hormones they produce and their actions

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

The total temperature range across which living organisms can be found is large – from sub-zero temperatures in Antarctica to hot water springs. However, each species of is usually restricted to a narrow range of temperatures Heat source: external or internal

Reptiles such as snakes and lizards are not found in Arctic regions, only found in temperate and tropical environments. They cannot survive in Arctic environments as they depend on external heat sources to generate body warmth and are called ectotherms. To warm up reptiles absorb heat by exposing their body surface to the sun and to prevent overheating they seek shade or shelter in burrows

Mammals and birds occupy habitats in tropical, temperate and polar regions as they are endothermic – have an in-built body heat source (internal energy releasing reactions that produce body heat – often reactions involving the digestion). As a result, mammals and birds maintain fairly constant body temperatures, regardless of temperature fluctuations

Tolerance

Every organism has a tolerance range for environmental factors, such as temperature and oxygen concentration, light intensity and ultraviolet exposure. A tolerance range identifies the variation within which an organism can survive

Tolerance ranges differ for various species and are influenced by structural, physiological and behavioural features of an organism – for example, the cold tolerance of various mammals is influenced by their structural features such as fur density, shape of body and extremities and extent of insulating fat deposits, and by their behaviours such as hibernating

If an environmental factor has a value above or below the range of tolerance of an organism, that organism will not survive unless it can escape from or somehow compensate for the change – migration is one such escape behaviour

Figure 9.2.1.11 – The temperature ranges of life


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Compare the responses of named Australian ectothermic and endothermic organisms to changes in the ambient temperature and explain how these responses assist temperature regulation PRACTICAL Analyse information from secondary sources to describe adaptations and responses that have occurred in Australian organisms to assist temperature regulation

Organisms that live successfully in a particular habitat would be expected to show particular structural, behavioural or physiological features or characteristics to assist survival in the range of environmental conditions that exist in the habitat

Features that equip organisms for survival within a range of environmental conditions in their habitats are called adaptations Mountain pygmy possum (Burramys parvus)

The mountain pygmy possum is the only Australian mammal that lives permanently in the alpine regions. It lives in two small areas – one in Kosciuszko National Park in NSW and the other near Mt Hotham in Vic

Burramys has behavioural and physiological features that enable it to survive low winter temperatures of its alpine environment

It collects and hides seeds and fruits for use during winter as it has no storage of fat in its tail

At low temperatures during winter, Burramys goes into torpor that is equivalent to hibernation – its heartbeat slows down considerably and body metabolism is significantly reduced and their body temperature drops

Burramys (in captivity) can hibernate at 6oC for 3-7 days at a time. Normal body temperature drops to that of the environment

The body metabolism of Burramys in hibernation is 0.6% - 3.9% of normal metabolic rate of an active Burramys at 6oC

Hibernation and reduced metabolic rate means that the amount of food required to survive the winter period is reduced Bilby (Macrotis lagotis)

The bilby lives among the most arid areas of Australia in northern WA and in pockets of Central Australia - areas of the NT

The bilby does not have to conserve body heat in the day in the desert, instead it must lose heat to avoid overheating

Its large, thin ears make up a large surface area that lets heat escape from blood vessels close to the surface. The large SA:V of the ears can be identified as a structural feature that equips this species to survive successfully in the desert

During the daytime bilbies shelter in deep burrows, away from extreme heat – the claws on its front feet allow the bilby to dig its burrow (structural feature)

Bilbies come out of their burrows at night to feed (nocturnal) when the temperature is a lot cooler (behavioural feature)

The environment of the bilby is dry – access to water is limited. To survive it must conserve its water very efficiently. It cannot afford to waste water by excreting its nitrogenous wastes in solution in large volumes of watery urine. The bilby produces a concentrated urine (physiological feature)

Water holding frogs (Cyclorana platycephala)

The water-holding frogs of central Australia have features and behaviours that equip them to survive and reproduce in the prolonged arid conditions of their central Australian habitat

They are able to burrow underground and enter a state of torpor. Not only does this reduce their core body temperature, metabolic activity is also reduced meaning less energy by the way of food is necessary for survival

The tadpoles of this species can survive in water temperatures of more than 40oC and they mature into adult frogs more quickly than other species – increasing chance of survival

Black snake (Pseudechis porphyriacus)

Body temperature of ectotherms are dependant on the environment and fluctuate with the temperature of the environment

Because snakes often cool down, they tend to be sluggish as their hearts are unable to pump sufficient blood to supply the oxygen needed for vigorous activity. Snakes and other ectotherms use anaerobic respiration during muscular activity, as lactate builds up the time spent in strenuous activity is limited. Hence why snakes generally escape to cover when danger is near

The rate at which a snake heats up as it basks in the sun is influenced by a number of factors: - snakes move in and out of the shade and vary their exposure to sun to control temperature - some change their shape, by flattening out to expose a greater surface area to the sun

- physiological factors include increased blood flow in vessels close to the skin as a snake basks, hence more heat is absorbed and transported to the inner body tissues and organs


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Identify some responses of plants to temperature change Plants tend to maintain their temperature within an optimal range to ensure optimal metabolic action and to minimise damage

that can occur at extremes of heat and cold Hot environment

Green plants depend on radiant energy from the sun to carry out photosynthesis. Only a small amount of the energy absorbed is used. To prevent overheating, a plant must lose much of the radiant energy it absorbs and they do this in the following ways:

Radiation – a plant radiates heat to objects in its environment

Transpiration – plants are cooled when the heat within them is used to evaporate water from cell surfaces. The water vapour exits through the stomata. If water loss continues, guard cells become less turgid and stomata close. Excessive water loss can cause plant death

Convection – air surrounding the plant becomes heated and hence is less dense than the air further away from the plant. The heated air rises carrying heat away from the plant

Other factors that affect heat loss from, or heat gain by a plant are as follows:

Leaf shape – leaves are thinnest where the two surfaces of a leaf come together and lose most heat from that region. The larger the ratio of edge length to surface area of a leaf, the faster the leaf will be cooled

Heat shock proteins – plants in temperate climates produce proteins called heat-shock proteins at about 40oC. It is thought that these proteins may protect enzymes and other proteins in some way so that they are not denatured as the temperature rises

Leaf orientation – in hot weather the leaves of some plants orient themselves so that a minimum surface area is exposed to direct rays of sunlight. Leaves hang so that their flat blade surfaces are parallel with the rays of the sun, and less radiant energy from the sun falls on the leaf – many eucalypts orient themselves in this way

Structure – an Australian native species that survives well in hot conditions is the boab tree. It has a thick bottle shaped trunk which is a structural adaptation for water storage. Boab trees are deciduous and shed all their leaves during the very hot summer months – there are no stomata during the summer to lose water by and a far smaller surface area through which water can be lost. There is also a smaller surface area through which heat can be absorbed

Leaf fall – some eucalypts shed their leaves during the dry season to decrease the surface area through which heat may be gained and water vapour lost through transpiration

Cold environment

Many plants survive in sub-zero temperatures without being damaged. They gradually become resistant to the potential danger of ice forming in their tissues as the temperature falls below 0oC

As temperature drops below freezing surrounding the plant ice forms outside living cells. The inside cells don’t freeze because the concentration of ions in cytosol is greater than the concentration outside the cell (the cytosol has a lower freezing point)

Because ice has formed the concentration of water inside living cells is greater than the concentration outside so the water moves out of the cell. This movement out increases the ion concentration within the cell and further lowers their freezing point

The living cells are able to withstand further drops in the external temperature because the more concentrated cytosol acts as an anti-freeze


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2. Plants and animals transport dissolved nutrients and gases in a fluid medium Identify the form(s) in which each of the following is carried in mammalian blood:

- carbon dioxide - oxygen - water - salts - lipids - nitrogenous wastes - other products of digestion

The transport of substances in blood plasma

Plasma is the extracellular fluid which is the main component of blood (blood cells are suspended within the plasma)

Carbon dioxide is produced as a waste product of respiration in body cells. Because its concentration is higher in cells than in blood, it diffuses into the blood. After entering the blood stream it may:

- be dissolved in the plasma - bind to haemoglobin forming carbaminohaemoglobin - be converted into carbonic acid and then hydrogen carbonate ions in red blood cells and move to the plasma in

which form it is transported (most common form)

Oxygen is transported attached to haemoglobin in red blood cells

Water is the solvent of plasma and comprises about 60% of the volume of blood

Salts are transported dissolved in plasma. They are composed of positive and negative ions (i.e. Na+, K+, Ca2+, Cl-, HCO3-)

Lipids enclosed in protein packages called chylomicron are transported in lymph vessels and then in blood plasma

Nitrogenous wastes in the form of urea, uric acid and creatinine, are transported dissolved in blood plasma

Other products of digestion include amino acids, nitrogenous bases, sugars (monosaccharides), glycerol and vitamins. They are mainly water soluble and are transported dissolved in the plasma

PRACTICAL Perform a first-hand investigation to demonstrate the effect of dissolved carbon dioxide on the pH of water Aim: To demonstrate the effect of dissolved carbon dioxide on the pH of water Method:

1. In a 100mL beaker pour in 50mL of distilled water 2. Add a few drops of universal indicator to the distilled water 3. Using a straw blow bubbles into the water 4. Record your observations

Results:

As exhaled air (CO2) is breathed into the water the water changes colour

Using the pH chart it is found that CO2 gas makes the water acidic

The pH of the water became acidic because the CO2 reacted with water to form carbonic acid


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

1. Set up the prepared slide on the microscope 2. Place a piece of millimetre graph paper or a ruler under the microscope at low power 3. Calculate the field of view (i.e. if you can see 1.6 mm across the diameter then the field of view is 1600μm) 4. Now that the field of view for the low power has been found the field of view for high power must be calculated (i.e. if low

power is 100X and high power is 400X, the magnification is 4X larger and therefore the field of view is 4X smaller – the field of view for high power is 400μm)

5. Now under high power estimate how many red blood cells can be lined up across the diameter and hence find the approximate size of the red blood cells (i.e. if approx 50 red blood cells can fit across the diameter the size of the cells is 400μm/50 = 8μm in length)

6. Repeat step 5 for white blood cells (white blood cells are slightly larger than red blood cells, length will be approx 12μm) 7. Using the results draw a scaled diagram of each type of blood cell

Explain the adaptive advantage of haemoglobin The majority of cells in blood are red blood cells

Red blood cells contain haemoglobin, a red, iron-containing protein that combines readily with oxygen to form oxy-haemoglobin

The functions of haemoglobin include: - transport of oxygen from lungs to body cells - transport of some carbon dioxides from body cells to the lungs - buffering H+ that are produced in ionisation of carbonic acid (produced when carbon dioxide reacts with water)

The major role of haemoglobin is transport of oxygen. Oxygen is not very soluble in water (plasma) and most of is carried by haemoglobin in RBCs. The interaction of Fe ions with oxygen binds oxygen to haemoglobin forming oxyhaemoglobin

Hb + O2 HbO2

Haemoglobin + oxygen oxyhaemoglobin

As altitude increases the air becomes thinner and the concentration of oxygen decreases. In response to this mammals may increase their breathing rate, increase their heart rate and synthesise more red blood cells (more haemoglobin)

High oxygen concentration

Low oxygen concentration

12μm

8μm

Scale: 1μm = mm


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

Arteries are thick-walled vessels that carry blood away from the heart (two main arteries – pulmonary artery carries blood from the heart to lungs, aorta carries blood to the rest of the body)

Arteries have three main layers: - the inner layer is an endothelium that is in direct contact

with the blood and a very thin layer of connective tissue - the second layer consists of elastic fibres and smooth

muscle. This layer gives strength to arteries and gives them the ability to stretch and recoil as the heart beats

- the outer layer is non-elastic connective tissue that anchors the arteries in place in the body

Arteries branch repeatedly into smaller and smaller arteries and give rise to arterioles (same structure as arteries but with much smaller thickness)

Arterioles enter tissues and branch into microscopic vessels - capillaries

The muscle in the second layer of arterioles allows them to constrict and dilate and control the rate of flow into the capillaries

Capillaries

Although blood flow is controlled by arterioles, smooth muscle cells control blood flow into capillaries by acting as sphincters

Capillaries are thin walled vessels (one cell thick), materials either pass through or between cells as they leave or enter bloodstream

O2 diffuses thru endothelial cells into surrounding tissue fluid and cells

Carbon dioxide leaves surrounding tissues and enters blood stream

Water and water-soluble molecules like glucose and inorganic ions diffuse through gaps between the endothelial cells

Some proteins leave the capillaries through endothelial spaces or across cells in vesicles (most proteins stay in blood vessels)

Phagocytic white blood cells can squeeze between the endothelial cells Veins

Blood moves from capillaries into venules which combine to form larger vessels called veins

The walls of veins have a basic structure similar to that of arteries but have thinner walls – the muscle and connective tissue layers of veins are thinner than those in arteries, hence veins are more flexible and distensible than arteries

Blood flow slows as it branches from larger vessels into many small vessels. This leads to a reduction in blood pressure. Although pressure increases as blood flows from venules into veins the pressure is still insufficient to return all the blood to the heart from the extremities. To counter this deficiency veins have valves that prevent the backflow of blood. The contraction of muscles near veins also helps to squeeze veins and move the blood along

Veins transport deoxygenated blood (O2 is exchanged for CO2 in capillaries) back to the heart which pumps this blood into the lungs which exchange CO2 for O2 returning oxygenated blood to the heart to be pumped back around the body

Describe the main changes in the chemical composition of the blood as it moves around the body and identify the tissues in which these changes occur As capillaries pass alveoli oxygen diffuses from alveoli into blood and carbon dioxide diffuses from capillaries into the alveoli.

These capillaries lead back to the pulmonary vein which supplies the heart with oxygenated blood to be pumped around the body. As the blood leaves the heart via the aorta it branches into arterioles and finally capillaries around tissue where the oxygen diffuses out of the bloodstream and carbon dioxide diffuses into it. The deoxygenated blood then travels to venules and veins and finally the pulmonary artery where it once again goes back to the lungs to be oxygenated again

Urea is a nitrogenous waste product produced by the liver and removed by the kidneys. The concentration of urea in the blood entering the kidneys is higher than the urea concentration leaving the kidneys


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Glucose levels in blood rise after a meal but as glucose is removed by the liver and muscle and sometimes stored as glycogen (under hormonal control) its concentration returns to the normal range

PRACTICAL Analyse information from secondary sources to identify current technologies that allow the measurement of oxygen saturation and carbon dioxide concentrations in blood and describe and explain the conditions under which these technologies are used Pulse oximeter

Used by hospitals to monitor blood oxygen and carbon dioxide levels in patients during heavy sedation or anaesthesia. Also used when a patient is on a ventilator, artificial breathing machine, during stress testing, in sleep labs, when checking the body’s response to different medications or to monitor a person with asthma or who is having trouble breathing

A small clip with a sensor is attached to the patient’s finger, earlobe or toe. A cable connects the sensor to the pulse oximeter machine. The colour of blood changes according to the amount of oxygen that is dissolved in it. Blood high in oxygen is bright red while blood low in oxygen is a darker colour. The sensor emits a light signal that passes through the skin and measures the amount of light absorbed as it passes through tissue and blood, and transmits the information to the pulse oximeter – the reading is given in percentage form

Arterial Blood Gas (ABG) Analysis Machines

These measure the amount of oxygen and carbon dioxide in a sample of blood by monitoring the rate of diffusion of these gases through artificial membranes which are permeable to these gases

When moving through a membrane, oxygen produces an electrical current while carbon dioxide changes the pH of the solution

Outline the need for oxygen in living cells and explain why the removal of carbon dioxide from cells is essential Respiration is the breakdown of glucose using oxygen to produce energy in the form of ATP:

Glucose + oxygen carbon dioxide + water + energy (as ATP)

Respiration without oxygen is called fermentation

All living cells that metabolise glucose require oxygen which is supplied by the haemoglobin in red blood cells

Carbon dioxide and water are by-products of respiration. Carbon dioxide has no further use and must be removed as it can have a damaging effect on body chemistry:

- increased carbon dioxide concentration decreases blood pH (carbon dioxide combines with water forming carbonic acid) which can then affect enzyme activity

- excess carbon dioxide can change the ability of haemoglobin to bind to oxygen molecules

Carbon dioxide is removed in three ways: as dissolved gas in the blood plasma, attached to haemoglobin and as hydrogen carbonate ions in the blood plasma (most common)

For cells to respire efficiently oxygen must be continually supplied and carbon dioxide removed

Blood transports carbon dioxide and oxygen. Oxygen is supplied to and carbon dioxide is removed from body cells by the blood

PRACTICAL Analyse information from secondary sources to identify the products extracted from donated blood and discuss the uses of these products Each sample of blood collected is tested for viruses, and types for blood groups and blood group antibodies

Although some whole blood is retained, much of it is further subdivided into its constituent parts for specialised use

A single blood donation contributes to the making up of up to 20 life-saving products, these include: - Red blood cells for treatment of anaemia and bleeding after trauma or surgery - Filtered red cells for patients who have antibodies against white cells - Platelets for the control of haemorrhage, often in patients with leukaemia and the treatment of many cancers - White cells occasionally used for patients who are not producing their own white cells or who have a very low

white cell count and a serious bacterial infection - Rh(D) Immunoglobulin for prevention of haemolytic disease in newborn babies from Rh(D) negative mothers


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- Hyper-immune Globulins treatment of specific infections like tetanus, hepatitis B or chickenpox - Fresh Frozen Plasma to treat patients who have bleeding problems after trauma or liver transplants

PRACTICAL Analyse and present information from secondary sources to report on progress in the production of artificial blood and use available evidence to propose why such research is needed Blood transfusions have been researched for centuries. In early 1900s, successful transfusions were carried out but up until

the HIV crisis in the 1980s, there was little interest in artificial blood, as there did not seem a great need. With the transmission of the virus during transfusions, there was nothing to replace donor blood, so artificial blood became a research priority

Sensitive screening tests have been developed for potential infective organisms, such as HIV and hepatitis, making donor blood safe. Also, there are safe and effective blood substitutes for certain applications, although they are still not ready for widespread use. There is a continuing shortage of donor blood to help the victims of emergencies, civil and international conflicts and natural disasters, and there is no guarantee that something similar to the HIV crisis will not occur in the future

There are often shortages of blood available in blood banks and this was heightened in September 2000 when Australia’s health ministers were forced to ban donations from people who had lived in the UK for six months or more from 1980 to 1996 because of the BSE (“mad cow” disease) outbreaks and the potential that individuals who ate beef during that period could have been exposed to the BSE agent which causes a variant to Creutzfeldt-Jakob disease, a degenerative brain disease. This decision meant more than 50 000 blood donors could no longer give blood which depleted the replenishment of reserves even more – artificial alternatives were investigated even more so than before

Perfluorocarbon-based substitutes

Oxygen and carbon dioxide are highly soluble in perfluorocarbons (PFC), inert compounds that carry more oxygen than blood plasma. PFCs must be combined with lipids to form an emulsion that can be mixed with blood. One product being tested at the moment, Oxycyte can carry at least five times more oxygen than haemoglobin

Red blood cells are 70 times larger than a PFC microdroplet, therefore PFCs can penetrate areas that red blood cells cannot

Advantages of PFC-based substitutes: - can be stored at room temp so it can be carried in emergency vehicles for use at accident sites - has a prolonged shelf life of 12 months or more, compared with one month for whole blood - can be used universally with all blood types (no blood antigens) so no matching of blood is required - can be used temporarily during open-heart surgery. A patient’s blood could be partially withdrawn, replaced by the

substitute during the surgery, then returned after the operation – this minimises blood loss during surgery

However blood does more than just carry carbon dioxide and oxygen around the body. Its vital functions include the transport of nutrients, clotting agent and the initiation of immune reactions. Although current substitutes being tested will be valuable they have a long way to go before they can be considered true blood substitutes rather than oxygen and carbon dioxide carriers

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

Plants transport materials in vascular tissue which is made up of xylem and phloem

Xylem transports water and dissolved minerals. Minerals required in large amounts for normal growth are called macro-nutrients while those needed in relatively small amounts are called micronutrients (also called trace elements)

Phloem transports sucrose, produced in photosynthetic tissue, hormones and any other organic material made by the plant Movement of water through xylem

Water is absorbed by root hairs by osmosis, moves through the cortex into the xylem where it is transported throughout a plant

Water moves up the xylem (only upward movement) by transpiration pull. The energy of the sunlight gives the water molecules at the surface of the leaf enough energy to move out into the air. This loss of water through the stomata is called transpiration

Transpiration creates tension (negative pressure of pull) on water further down xylem column. Cohesion (attraction of water molecules for each other) causes water further up to attract water below them to fill space left by water lost in transpiration

Xylem tubes are narrow so some water is in contact with walls of the xylem. The walls of the xylem contain both cellulose and lignin. There is a strong adhesion (attraction between molecules of different types) between the cellulose in the xylem walls and the water in contact with it. In narrow tubes this is called capillarity or capillary action and it also helps drag water up


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This mechanism is called the evaporation (transpiration)-tension-cohesion mechanism because the evaporation (or transpiration) from the top of the plant lead to tension on water further down xylem and cohesion then draws the water up. Mineral ions are carried up the xylem dissolved in the water. They supply leaves and may by redistributed later (in the phloem)

Figure 9.2.2.2 – (a) Water transport in stems and leaves – transpiration stream (b) The pressure-flow mechanism for translocation

Movement of organic substances in phloem

The movement of sugars and small amounts of other nutrients in phloem from sugar sources (where sugar is made or in abundance) to sugar sinks (where sugar is required) is called translocation

Unlike transpiration, translocation requires cellular energy and can take place in any direction within the plant

At the sugar source sucrose is loaded into the phloem vessels (from nearby cells) against concentration gradient, by active transport using ATP. This increases solute concentration in the phloem so water moves into the phloem from cells by osmosis

At the sugar sink sucrose is removed from the phloem into the plant cells that require it. This also occurs by active transport. Water follows the sucrose from the phloem into the cells by osmosis

At one end of the phloem vessel (near the sugar source) there is a large amount of solute (sugar and other nutrients) and high water content. This exerts a high water pressure or hydrostatic pressure. Further along the phloem (at the sugar sink) there is lower water content and lower levels of solute. Water flows along the phloem from the area of high hydrostatic pressure to the area of low hydrostatic pressure (sugar source to sugar sink). Therefore pressure flow drives the sugars in the phloem from photosynthetic to storage sites for use at that time or later

The mechanism is called the pressure-flow mechanism and involves sucrose being loaded into phloem by active transport and water following by osmosis at the sugar source. The opposite occurs at the sugar sink. This produces a difference in hydrostatic pressure in the phloem, causing the sugar solution to move from source to sink

PRACTICAL 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 Aim: To draw transverse and longitudal sections of phloem and xylem tissue Method:

1. Let a stick of celery (stalk with the leaves) stand overnight in a beaker of water which is coloured using food colouring 2. The next day it can be seen that the coloured water has risen through the xylem vessels, staining them strongly. The water

has also travelled down through phloem vessels

(a) (b)


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3. Using a sharp blade cut a very thin slice across the stalk (transverse section) and then cut another down the length of the stalk (longitudinal section)

4. Take the slices of celery and prepare them separately as wet mounts on two separate slides 5. View the slides under your light microscope and draw the image that you see

Results:


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3. Plants and animals regulate the concentration of gases, water and waste

products of metabolism in cells and interstitial fluid PRACTICAL Perform a first-hand investigation of the structure of a mammalian kidney by dissection, use of a model or visual resource and identify the regions involved in the excretion of waste products Aim: To investigate the structure of a mammalian kidney by dissection Method:

1. Consider safe working practices – wear gloves, a lab coat and some protective eyewear 2. Take the sheep kidney and make a longitudinal cut with the scalpel along the convex side. Do not cut the tubes and leave

the two halves of the kidney attached to the them 3. After opening the kidney identify the major parts including the ureter, renal pelvis, medulla, cortex and blood vessels 4. Draw a labelled diagram of the kidney

Results:


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Explain why the concentration of water in cells should be maintained within a narrow range for optimal function Water as a solvent

Water is an excellent solvent. Thousands of inorganic and organic molecules dissolve in water or are suspended in it. Water is a polar molecule and therefore can attract ionic compounds and this leads to the separation of the ions forming true solutions

Water can also dissolve other polar molecules like sugars. For large molecules such as proteins, water can form a hydration layer preventing them from coming out of the solution (colloid)

A number of important features of cell biochemistry follow from this solvent property of water: - the solution of substances is essential to maintain osmotic balance in cells - some important body lubricating fluids such as mucus are colloidal mixtures with water - metabolic reactions only take place between chemicals in solution and water is the solvent - water is the body’s major transport medium – nutrients, gases and wastes are transported dissolved in blood

plasma (mainly composed of water) Water as a reactant/product in metabolism

Water is an important reactant or product in many metabolic reactions


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The digestion of food is a hydrolysis reaction (reaction where a molecule is broken or lysed and a molecule of water is added for each bond broken)

When large polymers such as starch, glycogen or proteins are synthesised from small monomers, bonds are formed and a molecule of water is removed for each bond formed – condensation polymerisation

Photosynthesis and respiration involve water as a reactant or product Water and its relationship with heat

Water has a relatively high specific heat (can absorb or release large amounts of heat without appreciably changing in temperature). Because it is abundant in the body and its high specific heat, it prevents large fluctuations in body temperature

Water has a high heat of vaporisation (when it changes from liquid to gas large amounts of heat are absorbed). This property accelerates heat loss from the body – as we perspire water evaporates from our skin and a large amount of heat leaves

Water as a shock absorber

Water solutions in body cells and tissues form a cushion around many body organs (e.g. cerebrospinal fluid cushions the brain) Water concentration must be maintained

Water maintains the shapes of the cell membrane – too much water can cause the cell to burst

Changes in water concentration are typically accompanied by changes in concentrations of dissolved substances. The concentrations must be kept constant to maintain optimum metabolic functioning, e.g. if amount of water in blood decreases, dissolved carbon dioxide concentration increases, lowering the pH

The kidney is the major homeostatic regulator for water

Explain why the removal of wastes is essential for continued metabolic activity When nutrients enter the blood and then the body cells, they are involved in numerous biological reactions of metabolism. The

majority of these reactions are catalysed by enzymes and a complex interaction of factors enables these reactions to proceed so that the body can function effectively

Sometimes metabolic products are formed that have no use to the body - they are called wastes. Another source of wastes is the ingestion and absorption of compounds that cannot be used and that can be damaging (e.g. caffeine and alcohol)

These wastes can affect some enzymes and disrupt metabolism and homeostasis. They may damage cellular components and at the very least take up space required by the normal structural and functional chemicals

An example of a waste that affects body function is excess hydrogen ions, which reduce pH. This can affect the activity of enzymes and the oxygen saturation of haemoglobin

The brain is especially vulnerable to some wastes such as ammonia and urea, toxins and many drugs. Hence the blood capillaries in the brain are less permeable than other capillaries. This is known as the blood-brain barrier

Because of the importance of eliminating unwanted chemicals, the body has an organ system with the specific function of removing wastes – excretory system

The two main wastes removed by the body are carbon dioxide and nitrogenous wastes Carbon dioxide

Carbon dioxide is a waste product of cellular respiration

It is transported by the blood to the lungs where it is expelled from the body

If carbon dioxide accumulated in cells, the pH of the cells and their environments become acidic

Metabolic processes can cease because enzymes become inactive in acidic environments Nitrogenous wastes

When animals metabolise protein, nitrogen-containing wastes are produced as waste. If these are left to accumulate, vital tissues become damaged and the animal dies

When protein is metabolised in a cell, ammonia is formed. Ammonia is a colourless gas that is highly soluble in water – a solution of ammonia is highly alkaline. If ammonia is not removed it remains in cell solution and its highly alkaline nature causes metabolic activities to cease because enzymes can no longer function and the organism dies

Because ammonia is so toxic it must be excreted immediately in large quantities of water or converted into less toxic compounds for removal

The way of excretion is dependant upon how much water is available:


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- in fish nitrogenous wastes are excreted as ammonia in large amounts of water - in terrestrial mammals, ammonia is converted to urea (less water for removal) - in reptiles and birds, ammonia is converted to uric acid (least toxic of the nitrogenous wastes, little water required)

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

The kidneys, ureters, bladder and urethra form the excretory system

Lungs are also excretory organs, excreting carbon dioxide

The kidney is the major organ responsible for stabilising the internal environment of an animal. Some its roles include: - removal of nitrogenous wastes - regulating the water concentration of blood therefore contributing to water balance in the body - removing or maintaining certain ions in the blood - in some organisms it is also important role in osmoregulation (the maintenance of constant osmotic concentration

in internal fluids in spite of different or varying osmotic concentrations in their external environments) The kidneys of fish

There are three different types of aquatic environment: - freshwater - marine (salt water) - estuarine (an environment of varying salt concentrations)

Excretion of nitrogenous wastes is no problem for fish as they have an abundant supply of water and are able to excrete nitrogenous waste without damage to their tissues although freshwater and saltwater fish deal with the matter in different ways

Freshwater Fish Marine (Saltwater) Fish

Tissues hypertonic (higher concentration of solutes) to surroundings Tissues hypotonic (lower concentration of solutes) to surroundings

Concentration gradient results in loss of salts and uptake of water Concentration gradient results in loss of water and uptake of salts

Fish must counter these changes to maintain homeostasis Fish must counter these changes to maintain homeostasis

(i) Does not drink (i) Drinks seawater

(ii) Kidney contains glomeruli and secretes copious amounts of very dilute urine that contains ammonia. Tubules actively reabsorb NaCl

(ii) Minimal urine produced. Kidneys lack glomeruli. Tubules actively secrete MgSO4

(iii) Gill membranes permeable to water (iii) Gill membranes are relatively impermeable to water

(iv) Gills actively absorb ions Some ammonia leaves gills at same time

(iv) Gills actively secrete sodium from chloride cells chloride ions follow


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The mammalian kidney - human

The kidneys in humans are towards the back of the abdominal cavity

A renal artery enters and a renal vein leaves the kidney. Each kidney releases the urine it produces into a tube called the ureter which leads to the bladder which stores the urine until enough is formed to be excreted

Each kidney has over a million functional units called nephrons. Each nephron extends across the cortex and medulla. Each nephron has three main parts:

- Glomerulus: a ball of blood capillaries hat has a large surface area. Capillaries continue out of the glomerulus and run alongside the kidney tubule. They eventually collect into venules and into the renal vein

- Bowman’s capsule: a fist-like structure surrounding the glomerulus, it is continuous with the kidney tubule - Kidney tubule: the fluid that has been filtered from the blood (called the glomerular filtrate and later urine) flows in

the tubule. Substances are added or removed from the glomerular filtrate to ensure homeostasis in the body while excreting wastes. The tubules of a number of nephrons join to form a collecting duct and a number of collecting ducts collect into the ureter

Figure 9.2.3.1 – The form of nitrogenous waste excreted by any

organism, in this case fish, is dependant on the availability of water

Figure 9.2.3.3 – The mammalian kidney


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

Dialysis is a process used to filter nitrogenous waste from the bodies of people whose kidneys no longer function efficiently

Dialysis acts like the nephrons of the kidney – separates molecules from the blood removing some and returning others

The patient’s blood is pumped from an artery through tubes made of a semi-permeable membrane. The artificial tubing allows only water and small molecules to pass through it into a dialysing solution that surrounds the tube – the dialysing solution is similar to the interstitial fluid found around nephrons

Blood circulates through the dialysis tubing, urea and excess salts diffuse out instead of by pressure filtration as in the nephron

Substances needed by the body like bicarbonate ions (HCO3-) diffuse from the dialysing solution into the blood (reabsorption)

The machine continually discards used dialysing solution as wastes build up in it

Two healthy kidneys filter the blood volume about once every half-hour but dialysis is much slower and a less efficient process but it’s a lifesaver for those with damaged kidneys

Kidney function Renal dialysis

A natural body process An artificial process to replace damaged kidneys

Performed by two fist-sized organs Performed by a large machine attached to a variety of computer and other equipment

Removes waste continuously Performed intermittently under hospital conditions (two or three times a week, for several hours at a time)

Varies output automatically, depending on concentrations of wastes in blood

Concentrations of substances in blood and dialysis fluid monitored by computers so that most wastes are removed during treatment

Wastes may be removed by both diffusion and active transport Wastes removed by diffusion only

Figure 9.2.3.4 – Summary of urine formation in mammals. Material forced through the glomerulus into the Bowman’s capsule passes along the tubule of the nephron. Some material and much of the water is reabsorbed from the nephron tubule by the blood; other material is added to the filtrate in the tubule


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

Terrestrial mammals must work to find water and are surrounded by air into which water quickly evaporates. Water conservation is of prime concern and they cannot afford to excrete large quantities of water in the removal of metabolic waste. The nitrogenous waste is converted to urea before excretion, urine is fairly concentrated

Marine fish have to deal with the loss of water to the external environment. The environment they live in is hyperosmotic to their internal environment (higher salt concentration outside than inside) which result results in an osmotic gradient in which water is lost and ions are gained. Therefore little urine but in very concentrated form is produced in order to conserve water

Freshwater fish live in an environment, which is hypo-osmotic (more salt inside than outside) to their internal environment. The results in an osmotic gradient where water is gained without drinking and salts are lost by diffusion. This means that these fish can afford to produce copious amounts of urine with dilute ammonia

PRACTICAL 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

There are three main types of nitrogenous wastes, ammonia, urea and uric acid Ammonia

Ammonia is the most toxic form of nitrogenous waste and must be removed immediately, either by diffusion or in dilute urine

It is the waste product of most aquatic animals including many fish and tadpoles

Ammonia is the immediate product of break down of amino acids – no energy is required to make it

It is highly soluble in water and diffuses rapidly across cell membranes

Ammonia needs large quantities of water to be constantly and safely removed Urea

Urea is toxic but not as toxic as ammonia, so it can be safely stored in the body for a limited time

It is the waste product of mammals, some other terrestrial animals, but also of adult amphibians, sharks and some bony fish

Urea is made from amino acids but requires more steps and energy to make than ammonia

It is highly soluble in water but being less toxic it can be stored in a more concentrated solution and so requires less water to remove than ammonia

Uric Acid

Uric acid is the least toxic of the nitrogenous wastes, so can be safely stored in the body for extended periods of time

It is the waste product of terrestrial animals such as birds, many reptiles and insects

Uric acid is a more complex molecule than urea so requires even more energy to produce

It is a lot less soluble than ammonia or urea and has low toxicity, which means little water is expended to remove it – this is a great advantage for survival in arid environments

Organism Organism Type

Nitrogenous Waste

Explanation

Spinifex hopping mouse (Central Australia)

Terrestrial mammal

Concentrated urine (urea)

Living in an arid environment it drinks little water and excretes urea in a concentrated form so that water can be saved

Euro Wallaroo Terrestrial mammal

Concentrated urine (urea)

Have an efficient excretory system that recycles nitrogen and urea to make very concentrated urine. This allows them to survive in very arid environments

Desert grasshopper Insects Uric acid Insects are covered with a cuticle impervious to water and therefore conserve it by producing a dry paste of uric acid


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Some insects excrete ammonia as a vapour across the body surface rather than as a solution of urine, an adaptation for water conservation. More commonly uric acid (a dry urate waste requiring no water to remove and with low toxicity – it can be kept in the body for long periods of time) is produced

The type of nitrogenous waste produced by an organism is related to the amount of water they have available. Ammonia can be excreted by freshwater organisms because they have an abundance of water and have no need to waste energy in producing a less toxic waste. Similarly mammals living in arid environments (e.g. Bilby) must conserve water and therefore produce concentrated urine with high concentrations of urea in order to conserve water

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

Diffusion is the movement of a substance from high concentration to low concentration – down the concentration gradient

Osmosis is the diffusion of water across a semi-permeable membrane

Both diffusion and osmosis (diffusion of water) are forms of passive transport – no cellular energy is expended

In general, diffusion is slow and only useful across distances such as from one cell to the next or from one cell to extracellular fluid. It is dependant on the random movement of molecules and would be too slow over long distances or in situations where blood is flowing quickly and substances are being removed – nitrogenous wastes are toxic and need to be removed quickly

Diffusion occurs in the kidney when small molecules are filtered out of the glomerulus into the Bowman’s capsule but is assisted by the blood pressure

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

Passive transport (i.e. diffusion) is the net movement of a substance, typically in solution from a region of high concentration of a substance to a region of low concentration, the process requires no cellular energy

Active transport is the net movement of dissolved substances in or out of cells against the concentration gradient, this process requires cellular energy

Active transport enables maintenance of stable internal conditions despite variation in external surroundings

Kidney tubules function to remove the body of unwanted wastes, such as nitrogenous wastes. This has the danger of being accompanied by the loss of water and other substances if kidney tubules relied only on diffusion and osmosis in the removal of wastes – avoiding this loss of water is vital, for this active transport is necessary

Passive and active transport are both important processes in the production of urine by nephrons

Explain how filtration and reabsorption in the mammalian nephron regulate body fluid composition Waste products are filtered from the blood in the glomerulus. The arteriole leaving the glomerulus is smaller in diameter then

the arteriole entering – the blood in the glomerulus is under pressure and therefore substances are forced through holes in capillary walls into the Bowman’s capsule. About 1/5 of plasma passing through the glomerulus is filtered through the capsule into the tubule, only large compounds like proteins and the blood cells do not pass

The filtrate that moves into the tubule from the glomerulus contains water, nitrogenous wastes, nutrients and salts – some can be used by the body and need to be retained in some way to prevent dehydration and starvation

As fluid moves along the nephron tubule some useful substances are reabsorbed into the capillaries, some diffuses from the tubule back to the bloodstream while others are reabsorbed by active transport


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Some materials are added to the filtrate by the cells of tubules like: drugs such as penicillin, certain ions (help control the pH of the blood and other tissues – as hydrogen ions are secreted sodium ions are displaced and reabsorbed by the body)

The fluid at the end of the nephron tubule is urine and because of the reabsorption that has taken place along the tubules, only about one percent of the fluid filtered by the glomeruli actually leaves the kidney

Outline the role of the hormones aldosterone and ADH in the regulation of water and salt levels in blood Water conservation in the body is associated with blood pressure

because increased water raises blood pressure, decreased water lowers blood pressure

The processes of osmoregulation and blood pressure interact and are controlled by two main hormones:

- ADH (antidiuretic hormone) - Aldosterone

Anti-diuretic hormone (ADH)

Vasopressin is an ADH produced by the hypothalamus (brain), it is activated when osmoreceptors detect a rise in blood solutes (a drop in water concentration) which could be a result of insufficient water intake, excessive sweating or diarrhoea

Vasopressin is transported by blood to the kidneys where it increases permeability of distal tubules and collecting ducts to water. The amount of water reabsorbed increases and the concentration of solutes in the blood declines. Negative feedback then leads to a decreased secretion of ADH

Aldosterone

When dehydration begins blood volume decreases and blood pressure falls, reducing glomerular filtration. This is registered by pressure-sensitive receptors in the kidney causing arteriole cells to secrete renin. Renin initiates chemical reactions that cause adrenal gland to release aldosterone

Aldosterone affects nephron distal tubules – sodium ions are actively reabsorbed, water follows and blood pressure rises

PRACTICAL Present information to outline the use of hormone replacement therapy in those who cannot secrete aldosterone

Addison’s disease is where people fail to secrete aldosterone – symptoms include high urine output with a resulting low blood volume. Eventually, as blood pressure falls, it can lead to heart failure

A replacement hormone, fludrocortisone (Florinef) is used to treat this condition but careful monitoring must be maintained to avoid fluid retention and high blood pressure

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

Estuaries are areas where the freshwater meets and mixes with the sea. As the tide flows in, the concentration of salt increases and, during winter, when river flow increases, the concentration of salt decreases

Estuarine organisms such as fish, other invertebrates and mangroves must maintain homeostasis in their internal environment so that metabolism and other processes can proceed efficiently – so they carry out enantiostasis

To survive fluctuating salinities estuarine organisms must either be able to function with fluctuating internal salt concentrations (osmoconformer) or must have physiological mechanisms that control the concentration of salt in their bodies (osmoregulator)


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Estuarine fish maintain a solute concentration in their cells that is similar to the external salt concentration in the estuarine water (osmoconformer), they move small molecules in and out of their tissues depending on the salt concentration of the water

Mangroves (osmoregulators) maintain the salt concentration of their cells by three methods: - exclusion – endodermis in roots form a barrier against salt, so xylem contains fresh desalinated water - accumulation of salt – accumulate excess salt in bark and leaves and this is lost when leaves fall - salt secretion – thru secretory glands on leaf surfaces, salt crystallises by evaporation and is blown/washed away

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

Most plants cannot tolerate high salt concentrations in the root zone - leads to water stress, salt accumulation in leaves is toxic

Enzymes are inhibited by Na+ ions

Plants that can tolerate high levels of salt in their environment are called halophytes

The grey mangrove has special glands in its leaves that secrete salt. Other mangroves exclude salt at the roots using ultrafiltration, a third mechanism is to store salt in leaves and then drop the leaves. Another mechanism used by mangroves involves controlling transpiration by having small leaves that hang vertically to reduce the surface area presented to the sun thus reducing transpiration and therefore the need for more water which will contain high levels of salt

Salt marsh plants accumulate salt in the swollen leaf bases which fall off and others have salt glands on their leaves

Another form of salt stress occurs in salt laden air such as in coastal environments. Some coastal plants like the Norfolk Island Pine have a mesh cuticle over their stomates which prevents small water droplets from entering the leaf

Describe adaptations of a range of terrestrial Australian plants that assist in minimising water loss PRACTICAL Perform a first-hand investigation to gather information about structures in plants that assist in the conservation of water Xerophytes - plants that have adapted to low ground-water levels and have specific features to enable them to retain water

Adaptations of Australian plants to arid conditions are shown in the table below

Adaptation Advantage Examples

Needle-like leaves Reduced surface area and water loss Acacias, casuarinas, hakeas, grass trees Photosynthetic stems Reduced surface area and water loss Casuarinas

Woody fruits Less water loss than in fleshy fruits (also often fire resistant) Banksias, hakeas

Waxy leaves/cuticle Reduced water loss as cuticle prevents evaporation but also reflects infrared radiation from sun, reducing heat gain

Saltbush

Ephemeral growth Have a short life cycle growing and reproducing in a short period in response to rain

Paper daisies, yellow tops

Partially deciduous Some eucalypts lose most of their leaves during extended dry spells reducing water loss

Eucalypts

Leaf curling Leaves roll up forming a cylinder, which reduces surface area and traps a humid layer of air, which reduces water loss

Hummock grass

Sunken stomates Stomates lie in a cavity in the leaf, which results in humid air being concentrated above the stomate, which reduces water loss

Hakeas

Water storage Water is stored in trunk, leaves or roots Baobab tree – stores water in its trunk Parakeelyas – succulent stems & roots

Hanging leaves Leaf hangs down rather than being held horizontal to the ground, which reduces exposure to the sun

Eucalypts

Hairy or shiny leaves

Hairy surfaces on under surface reduce air movement and increase humidity over stomates, reducing water loss; on upper leaf the hairy or shiny surface reflects radiation from the sun reducing heat gain

Banksias, paper flowers

Water-directing leaves and stems

Stems and leaves are shaped so that water runs down them towards the roots

Acacia, grass trees


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Reduced flower size or flowers with few or no petals

Acacia flowers are small and clustered in small heads or spikes. Eucalyptus flowers are enclosed in a bud cap and when revealed have no petals. The presence of petals requires metabolism and therefore water, so water is saved

Acacia, eucalypts

No leaves Acacias have phyllodes (flattened petioles – leaf stem) that carry out photosynthesis for the plant but lack the stomata of real leaves and therefore reduces water loss

Acacia

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Biology Notes Module 1, Maintaining a Balance, by F.A ... · Biology Notes – Module 1, Maintaining a Balance, by F.A 2 1. Most organisms are active in a limited temperature range