Unit 4 Flashcards

Question

what does the reaction between RuBP and CO2 produce

Answer 1

The resulting 6-carbon (6C) compound is unstable and splits in two This results in two molecules of a 3C compound known as glycerate 3-phosphate (GP)

Answer 2

Energy from ATP and hydrogen from reduced NADP are used to reduce the two 3C molecules of GP to two 3C molecules known as GALP

Answer 3

Some of the carbons in GALP go towards the production of useful organic molecules such as glucose, while the rest remain in the Calvin cycle to allow the regeneration of RuBP Two molecules of GALP contain six carbon atoms

Answer 4

Five sixths of the GALP molecules are used to regenerate RuBP This process requires ATP

Answer 5

Intermediate molecules of the Calvin cycle, such as (GALP), are used to produce hexose sugars e.g. glucose (which react to make sucrose, cellulose...) , glycerol can be used for building lipid molecules, fatty acids, nucleic acids (created by the combination of this product with P of soil), acetyl coenzyme A, amino acids (created by the combination of this product with NO3 of soil), Many of the molecules produced are used to build new plant biomass

Answer 6

Intermediate molecules of the Calvin cycle, such as (GALP), are used to produce hexose sugars e.g. glucose (which react to make sucrose, cellulose...) , glycerol can be used for building lipid molecules, fatty acids, nucleic acids (created by the combination of this product with P of soil), acetyl coenzyme A, amino acids (created by the combination of this product with NO3 of soil), Many of the molecules produced are used to build new plant biomass

Answer 7

Many of the molecules produced are used to build new plant biomass

Answer 8

carbon fixation

Answer 9

a graph showing the amount of light absorbed by a pigment against the wavelenght of the light

Answer 10

a graph demonstrating the rate of photosynthesis against the wavelength of light

Answer 11

Chloroplasts are the organelles in plant cells where photosynthesis occurs

Answer 12

Each chloroplast is surrounded by a double-membrane known as the chloroplast envelope Each of the envelope membranes is a phospholipid bilayer

Answer 13

with a cytoplasm-like fluid found in chloroplasts

Answer 14

The stroma contains enzymes and sugars, as well as ribosomes and chloroplast DNA If the chloroplast has been photosynthesising there may be starch grains or lipid droplets in the stroma

Answer 15

This membrane system consists of a series of flattened fluid-filled sacs known as thylakoids, each surrounded by a thylakoid membrane Thylakoids stack up to form structures known as grana (singular granum) Grana are connected by membranous channels called lamellae (singular lamella), which ensure the stacks of sacs are connected but distanced from each other

Answer 16

ATP synthase enzymes Proteins called photosystems that contain photosynthetic pigments such as chlorophyll a, chlorophyll b, and carotene

Answer 17

The double membrane encloses the chloroplast, keeping all of the components needed for photosynthesis close to each other The transport proteins present in the inner membrane control the flow of molecules between the stroma and cytoplasm

Answer 18

The gel-like fluid contains enzymes that catalyse the reactions of photosynthesis

Answer 19

The chloroplast DNA contains genes that code for some of the proteins used in photosynthesis

Answer 20

Ribosomes enable the translation of proteins coded by the chloroplast DNA

Answer 21

There is a space between the two thylakoid membranes known as the thylakoid space, in which conditions can differ from the stroma e.g. a proton gradient can be established between the thylakoid space and the stroma The space has a very small volume so a proton gradient can develop very quickly

Answer 22

The grana create a large surface area, maximising the number of photosystems and allowing maximum light absorption Grana also provide more membrane area for proteins such as electron carriers and ATP synthase enzymes, which together enable the production of ATP

Answer 23

There are two types of photosystems; photosystem I and photosystem II, containing different combinations of photosynthetic pigments such as chlorophyll a, chlorophyll b, and carotene Each photosystem absorbs light of a different wavelength, maximising light absorption e.g. photosystem I absorbs light at a wavelength of 700 nm while photosystem II absorbs light at a wavelength of 680 nm

Answer 24

Chlorophylls and Carotenoids

Answer 25

wavelengths in the blue-violet and red regions of the light spectrum, reflecting green light and appearing green in colour

Answer 26

wavelengths of light mainly in the blue-violet region of the spectrum, reflecting yellow and orange light Carotenoids often remain in leaves after the breakdown of chlorophyll in the autumn, giving some leaves their yellow, orange, and red autumn colours

Answer 27

Chromatography can be used to separate and identify chloroplast pigments that have been extracted from a leaf

Answer 28

Different components within a mixture travel through materials at different speeds due to their size or charge This causes different components to separate An Rf value can be calculated for each component of the mixture on the basis of its rate of movement

Answer 29

The rate at which producers convert light energy into chemical energy

Answer 30

the rate at which chemical energy is converted into carbohydrates during photosynthesis

Answer 31

Net primary productivity, or NPP, is the GPP minus plant respiratory losses Of the total energy stored in glucose during photosynthesis, 90 % will be released from glucose to create ATP for the plant during respiration 90 % of the energy originally converted by the plant will therefore not be stored as new plant biomass and will not be available to be passed on to herbivores, also known as primary consumers

Answer 32

NPP= GPP - R

Answer 33

NPP is expressed in units of energy per unit area or volume per unit time e.g. Using area: J m–2 yr-1 (joules per square metre per year) Using volume: J m–3 yr-1 (joules per cubic metre per year) Volume would be used when calculating NPP in aquatic habitats

Answer 34

GPP = NPP + R R = GPP - NPP

Answer 35

a group of organisms of the same species, living and breeding together in a habitat

Answer 36

all the populations of all the different species of organisms living in a habitat at any one time

Answer 37

the place where an organism lives

Answer 38

an environment including all the living organisms interacting within it, the cycling of nutrients and the physical and chemical environment in which the organisms are living

Answer 39

biotic and abiotic factors

Answer 40

are living factors that influence populations within their community; biotic factors come about as a result of the activity of other organisms

Answer 41

Predation Food availability Intraspecific competition, arising when individuals of the same species compete for resources Interspecific competition, arising when individuals of different species compete for resources Cooperation between organisms Parasitism Disease

Answer 42

Light intensity and wavelength Temperature Turbidity, or cloudiness, of water Humidity Soil or water pH Soil or water salinity Soil composition Oxygen or Carbon dioxide concentration

Answer 43

are non-living factors that influence populations within their community

Answer 44

What it eats Which other species depend on it for food What time of day a species is active Exactly where in a habitat a species lives Exactly where in a habitat a species feeds

Answer 45

No two species can fill the same niche within a habitat The niche filled by a species determines its abundance within a habitat The niche filled by a species determines its distribution

Answer 46

the two species will be in direct competition with each other for resources, and one of the two species will out-compete the other, causing it to die out in that particular habitat

Answer 47

If two species occupy a similar niche within a habitat they will be competing with each other, so their populations will be smaller, and their abundance will therefore be lower

Answer 48

Species can only survive in habitats to which they are well adapted; if they are not well suited to a habitat's biotic and abiotic factors then they will move to a more suitable habitat and their distribution will change

Answer 49

The process of ecosystem change over time

Answer 50

is the process that occurs when newly formed or newly exposed land is inhabited by an increasing number of species

Answer 51

The magma from erupting volcanoes cooling and forming new rock surfaces or new rocky islands in the sea

Answer 52

A landslide that exposes bare rock A glacier that retreats to reveal bare rock

Answer 53

The arrival of organisms on bare land is known as colonisation, and the bare land is said to be colonised

Answer 54

any type of bare land, including sand dunes at the edge of the ocean, and on exposed rock

Answer 55

Seeds and spores that are carried by the wind land on exposed rock and begin to grow The first species to colonise the new land are pioneer species Pioneer species can germinate easily and withstand harsh conditions such as low nutrient and water availability As pioneer species die and decompose, the dead organic matter forms soil Seeds of small plants and grasses land on this soil and begin to grow The plants at this early stage of succession are adapted to survive in shallow, nutrient-poor soils The roots of these small plants form a network that helps to hold the soil in place and prevent it from being washed away As these small plants die and decompose, the soil becomes deeper and more nutrient-rich Larger plants and shrubs, as well as small trees can now begin to grow These larger plants and small trees also require more water, which can be stored in deeper soils Over time the soil becomes sufficiently deep, contains enough nutrients, and can hold enough water to support the growth of large trees The final species to colonise the new land become the dominant species of the now complex ecosystem The final community formed, containing all the different plant and animal species that have now colonised the land, is the climax community A climax community is not always the most biodiverse stage of succession, but it is a stable community

Answer 56

secondary succession takes place on previously occupied land e.g. after a wild fire or deforestation Secondary succession is very similar to primary succession except that soil is already present so the process begins at a later stage

Answer 57

stops a climax community from developing Regular mowing prevents woody plants from establishing themselves in a lawn The grazing activity of livestock such as sheep and cattle prevent new plants from establishing

Answer 58

Climax communities that develop as a result of human intervention; these communities are stable but would not have occurred without human intervention, e.g. heathland

Answer 59

Records of atmospheric carbon dioxide levels Records of average global temperatures Records of changing plant communities gained from sampling of pollen grains preserved in peat over time Records of tree growth gained by analysing the rings in the trunks of trees; known as dendrochronology

Answer 60

Under waterlogged and acidic conditions partly decomposed dead plant matter accumulates and becomes compacted under its own weight over time; this compacted, partially decomposed plant matter

Answer 61

The place where peat accumulates is known as a peat bog, or peatland

Answer 62

Peat builds up in layers, meaning that layers of peat at the top of a bog are recently formed and the peat become older as you dig down into a bog Peat cores can be taken from a bog and the layers can be analysed to assess the pollen grains that have become trapped in the peat

Answer 63

the pollen grains of each plant species are unique to that plant, the plant species that were growing around the bog at different points in time can be identified Different plant species grow under different climatic conditions, so the plants present at different times can be used a measure of the climate at that time

Answer 64

Light coloured rings are produced by fast growth during warmer spring and summer months and dark coloured rings form as a result of slow autumn growth, meaning that one light ring and one dark ring together represent a full year's growth in a tree Trees grow faster when conditions are warmer, so the rings that form during warm years are wider than the rings that form during cool years

Answer 65

Analysis of the width of tree rings can provide a measure of climate during each year of growth

Answer 66

a gas that absorbs this re-radiated radiation, trapping it in the earth's atmosphere so that it is not lost to space

Answer 67

In addition to the burning of fossil fuels, carbon dioxide is also released into the atmosphere when natural stores of carbon are damaged or destroyed by human activities These carbon stores are known as carbon sinks Carbon sinks include trees, soils, peat bogs, and the oceans Deforestation, soil degradation, peat harvesting, and ocean warming all contribute to the addition of carbon dioxide to the atmosphere

Answer 68

Methane is released from the guts of ruminant mammals such as cattle Landfill sites release methane when organic matter such as food waste decomposes Extraction of fossil fuels from underground releases methane Anaerobic bacteria in waterlogged rice paddy fields release methane

Answer 69

Carbon is present in the atmosphere in the form of carbon dioxide Carbon dioxide is removed from the atmosphere by producers during photosynthesis and incorporate carbon into their biomass in the form of carbohydrates and other biological molecules Carbon is transferred to and between consumers as a result of feeding Carbon is transferred back into the atmosphere by both plants and animals as a result of respiration as it releases co2 as a product Carbon dioxide can also be removed from the atmosphere by dissolving in the oceans Dissolved carbon can be taken in by marine plants when they photosynthesise or by other marine organisms as they build calcium carbonate exoskeletons When living organisms die their tissues are broken down by decomposers such as bacteria and fungi When these organisms respire, they too release carbon dioxide back into the atmosphere Any living tissue that is not fully decomposed can go towards the formation of peat or fossil fuels over millions of years; carbon can be stored in these sinks for long periods The combustion of peat and fossil fuels releases carbon dioxide back into the atmosphere The combustion of biomass such as wood also returns carbon to the atmosphere

Answer 70

Reducing the combustion of fossil fuels Reducing the combustion of biomass Reducing disturbance of carbon pools such as soils and peat bogs Increasing rates of photosynthesis by planting trees

Answer 71

Extrapolated data can be used to produce models that show how the climate may change in the future

Answer 72

Building flood defences Funding scientific research into climate change technologies Reduce the burning of fossil fuels Increase the use of renewable energy sources such as solar and wind energy Reduce meat consumption

Answer 73

The IPCC has produced models based on several emissions scenarios, and we do not know which of these scenarios is most likely We do not know whether future technologies will be successful at removing greenhouse gases from the atmosphere It is unknown exactly how atmospheric gas concentrations might affect global temperatures Global climate patterns are complex and therefore predictions are difficult It is possible that a certain tipping point in global temperatures could lead to a sudden acceleration in global warming We don't know exactly how factors other than human activities may affect climate in the future

Answer 74

Weather events becoming more extreme Changes to ocean currents leading to altered local climates Warmer air can hold more moisture, leading to changes in patterns of rainfall; more, heavier rainfall in some places could lead to reduced rainfall in other locations

Answer 75

Warming climates cause animals to move towards the poles or to higher altitudes these species may not be able to compete with, or may even out-compete, the species already present in these habitats, with either result leading to decreased biodiversity Some species, such as plant species, may not be able to move or change their distribution fast enough to adapt to changing temperatures and may become extinct as a result

Answer 76

Changes to rainfall patterns can be devastating to species that rely on seasonal rains for their survival Some species may no longer be able to survive in their habitat due to a lack of rainfall; such species may migrate to a new habitat or may become extinct

Answer 77

Plant species are producing flowers earlier in the year Animals are producing young earlier in the year Bird migratory patterns may lose their synchronisation with their habitats, leading to a change in migration patterns

Answer 78

The loss of glacier ice from mountain ranges may affect the water supplies of many people and surrounding wildlife

Answer 79

people and animals at risk of being flooded out of their homes Sea levels are rising due to the expansion of warmer water and due to melting polar ice

Answer 80

Enzymes have a specific optimum temperature This is the temperature at which they catalyse a reaction at the maximum rate

Answer 81

prevent reactions from proceeding or slow them down Molecules move relatively slowly as they have less kinetic energy Less kinetic energy results in a lower frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to less frequent enzyme-substrate complex formation Substrates and enzymes also collide with less energy, making it less likely for bonds to be formed or broken

Answer 82

reactions to speed up Molecules move more quickly as they have more kinetic energy Increased kinetic energy results in a higher frequency of successful collisions between substrate molecules and the active sites of the enzymes which leads to more frequent enzyme-substrate complex formation Substrates and enzymes also collide with more energy, making it more likely for bonds to be formed or broken

Answer 83

the enzymes begin to denature The increased kinetic energy and vibration of an enzyme puts a strain on its bonds, eventually causing the weaker hydrogen and ionic bonds that hold the enzyme molecule in its precise shape to start to break The breaking of bonds causes the tertiary structure of the enzyme to change The active site is permanently damaged and its shape is no longer complementary to the substrate, preventing the substrate from binding Denaturation has occurred if the substrate can no longer bind

Answer 84

The temperature coefficient, represented by Q10, calculates the increase in rate of reaction when the temperature is increased by 10 degreeC Q10 = rate at higher temperature divided byrate at lower temperature

Answer 85

Some chemical reactions take place faster at higher temperatures Some chemical reactions are slowed down at higher temperatures The sex of the young inside the egg of some species is determined by temperature, so increasing temperatures can affect the sex ratios in a species Species may have to change their distribution in response to changing temperatures in order to survive

Answer 86

Photosynthesis is essential for converting carbon dioxide into carbohydrates, the process which produces food for producers and other organisms higher up the food chain; it relies on the function of proteins in the electron transport chain and that of enzymes such as rubisco

Answer 87

At high temperatures plants carry out a reaction called photorespiration at a faster rate; this reaction uses the enzyme rubisco and so slows down photosynthesis This can reduce crop yields as temperatures rise Some fish eggs have been shown to develop more slowly at higher temperatures Many species' successful egg development is dependent on temperature, with impacts such as Extreme temperature fluctuations can reduce hatching rates in some invertebrates

Answer 88

Species may migrate to higher altitudes or further from the equator to find cooler temperatures

Answer 89

changes in the heritable characteristics of organisms over generations

Answer 90

Heritable characteristics are determined by the alleles of genes that are present in an individual Alleles may change as a result of random mutation, causing them to become more or less advantageous Heritable characteristics that are advantageous are more likely to be passed on to offspring, leading to a gradual change in a species over time This is the process of natural selection

Answer 91

the process by which organisms that are better adapted to their environment survive, reproduce, and pass on their advantageous alleles, causing advantageous characteristics to increase in frequency within a population

Answer 92

Natural selection can only take place if variation is present

Answer 93

Variation results from small differences in DNA base sequences between individual organisms within a population Sources of variation include Mutation Meiosis Random fertilisation during sexual reproduction

Answer 94

Environmental factors that influence survival chances are said to act as selection pressures

Answer 95

those acquired during the lifetime of an organism

Answer 96

Variation exists between individuals in a population In any habitat there are environmental factors that affect survival chances In any population, due to the variation present, some individuals will have characteristics that make them better adapted for survival in the face of any selection pressures (This is sometimes described as 'survival of the fittest') Individuals that are well adapted and survive into adulthood are more likely to find a mate and reproduce, producing many offspring This means that they are more likely to pass on the alleles that code for these advantageous characteristics to their offspring The number of individuals in a population with a particular favourable characteristic will increase over time; the characteristic is said to increase in frequency Eventually this favourable characteristic will become the most common of its kind in the population; the population can be said to have adapted to its environment by the process of natural selection

Answer 97

the development of new species from pre-existing species over time

Answer 98

two populations of the same species must be isolated from each other in some way When this happens, there can no longer be an exchange of genes between the two populations The exchange of genes is sometimes known as gene flow

Answer 99

Geographical isolation This leads to a type of speciation known as allopatric speciation Random mutations that prevent them from interbreeding with each other This leads to a type of speciation known as sympatric speciation

Answer 100

Populations that are isolated from each other may face different selection pressures in their environment The different environmental conditions for the two populations might mean that different alleles are advantageous, so different alleles are more likely to be passed on and become more frequent in each population; this is the process of natural selection The allele frequencies in the two populations change over time Note that a process known as genetic drift can also affect allele frequencies Over time the two populations may begin to differ physiologically, behaviourally and morphologically to such an extent that they can no longer interbreed to produce fertile offspring; speciation has occurred

Answer 101

Allopatric speciation occurs when populations of a species become separated from each other by geographical barriers The barrier could be natural It can also be man-made

Answer 102

creates two populations of the same species between which no gene flow is taking place Allele frequencies in the gene pools of the two populations may change in different ways due to Different selection pressures acting on them The accumulation of random changes resulting from genetic drift Changing allele frequencies will lead to changes in the phenotypes of the two populations If enough allele frequency differences arise between the two populations, then they will eventually no longer be able to breed with each other and produce fertile offspring, and can be said to be separate species

Answer 103

Isolation occurs when random changes in the alleles and therefore phenotypes of some individuals in a population prevent them from successfully breeding with other individuals in the population. such as: Seasonal changes Mechanical changes Behavioural changes

Answer 104

The populations may still live in the same habitat but they are isolated from each other in the sense that they do not interbreed The lack of gene flow between the two populations means that allele frequencies in the gene pools of the two populations may change in different ways Changing allele frequencies will lead to changes in the phenotypes of the two populations If enough allele frequency differences arise between the two populations, then they will eventually no longer be able to breed with each other and produce fertile offspring, and can be said to be separate species

Answer 105

There is a great deal of scientific evidence that has been tested and checked by other scientists that supports the hypothesis that humans burning fossil fuels causes climate change Climate is highly complex People may have a personal interest; some are especially passionate about the environment, while others depend financially on fossil fuels It is important that we are aware of the personal biases of those making claims about the causes of climate change

Answer 106

Reducing carbon emissions Biofuels Other renewable sources Increasing carbon removal

Answer 107

limiting the rate at which fossil fuels are burned by Burning biofuels instead of fossil fuels The use of other renewable energy resources

Answer 108

Biofuels are often cheaper than oil It is argued that biofuels are 'carbon neutral' meaning that they only release carbon that was recently removed from the atmosphere when the plants were alive They do not release carbon that has been stored away for millions of years as with fossil fuels Biofuels are a renewable source of energy, i.e. they can be regrown quickly

Answer 109

They do still release carbon dioxide into the atmosphere The vast amounts of land required to grow biofuels could otherwise have been used for food production Creating land for biofuel growth often involves the loss of other types of habitats e.g. rainforest; this is bad for biodiversity Cutting down mature trees to create land for biofuel growth reduces the removal of carbon from the atmosphere by photosynthesis

Answer 110

These kinds of technologies are advancing quickly and are becoming cheaper and more efficient to use No carbon dioxide is released when these technologies are used to generate electricity

Answer 111

Geothermal energy can only be used when there is volcanic activity close to the earth's surface Solar energy depends on sunshine hours Wind energy depends on wind speeds and some conservationists are concerned about the impact of wind turbines on birds and bats Some are also concerned about the visual impact of wind turbines on the landscape Tidal energy can only be generated near the coast

Answer 112

Stopping the destruction of forests by deforestation Planting trees, also known as reforestation If trees are allowed to grow to maturity, they can store huge amounts of carbon in their biomass

Answer 113

Nutrients Oxygen Note that anaerobic microorganisms would require the absence of oxygen Optimum pH Favourable temperature

Answer 114

There is always the risk that a mutation could lead to the formation of pathogenic strains Pathogenic bacteria from the environment could contaminate the bacterial culture being investigated

Answer 115

Follow health and safety precautions Ensure that all equipment are sterilised before culturing the bacteria Sterilising involves killing microorganisms, e.g. by heating to a high temperature or the use of antimicrobial chemicals Keep the culture in the laboratory Seal cultures in a plastic bag and sterilise at high temperature and pressure before disposal

Answer 116

Obtain a supply of the type of microorganism to be cultured Provide them with the correct type of nutrients to facilitate growth A nutrient growth medium in the form of a liquid culture or a solid nutrient agar Ensure that the nutrient medium is kept under sterile conditions until use By adjusting the type of nutrients in the medium, conditions will be created for the optimal growth of a certain type of microorganism; this is known as a selective medium Microorganisms are introduced to a growth medium using inoculation with a sterilised inoculation loop Inoculation can be used to transfer microorganisms between media The new medium should be sealed or covered to avoid contamination from microorganisms in the air; if growing aerobic microorganisms any seal or cover should not be airtight Flasks can be sealed with a sterile cotton wool stopper Petri dishes can be covered with a lid Label the medium clearly and incubate at around 20 °C to prevent the growth of pathogenic microorganisms

Answer 117

In order to grow a single type of microorganism, or a pure culture, the specific microorganism must be isolated This can be done by using knowledge about the needs of the microorganism to be cultured or those of microorganisms that may contaminate the culture Being able to isolate pathogenic microorganisms is useful in the diagnosis and treatment of diseases

Answer 118

Cell counts Dilution plating Measuring area and mass Optical methods

Answer 119

A nutrient broth is diluted with an equal volume of trypan blue The chamber of the haemocytometer is filled with the stained nutrient broth The number of living cells in the four corner squares of the grid are counted Each corner square consists of 16 smaller squares Consistency needs to be used when deciding whether to count cells that are on the lines that border the corner squares The mean number of cells from the four corner squares can be calculated

Answer 120

This is a dye that will stain dead cells blue It enables the investigator to only count the living cells

Answer 121

to allow the calculation of the number of cells in a known volume of broth Because the haemocytometer chamber can hold exactly 0.1 mm3 of liquid, it is possible to estimate of the cell count in 1 ml of nutrient broth using the following calculation No. of cells per ml nutrient broth = mean cell count x dilution factor x 10 ^4 Multiplying by the dilution factor enables calculation of the bacterial cell count in the original broth rather than the diluted broth The multiplication by 10 ^4 enables calculation of the bacterial cell count in 1 ml rather than in 0.1 mm3 1 ml = 1 cm3 1 cm3 = 0.1 mm3 x 10 000 10 000 = 1 x 10^4

Answer 122

No. of cells per ml nutrient broth = mean cell count x dilution factor x 10 ^4 The multiplication by 10 ^4 enables calculation of the bacterial cell count in 1 ml rather than in 0.1 mm3 1 ml = 1 cm3 1 cm3 = 0.1 mm3 x 10 000 10 000 = 1 x 10^4

Answer 123

used to determine the total viable cell count in a nutrient broth The nutrient broth is transferred to agar where the bacteria use nutrients in the agar gel to reproduce A single cell that lands on agar reproduces by cloning itself, resulting in a mass of identical cells known as a colony Each microbial colony that grows on agar gel originated with one viable microorganism, so can be counted as one viable cell

Answer 124

this reduces the number of cells in the original sample so that individual colonies are visible on an agar plate

Answer 125

To calculate the total viable cell count, the number of colonies are multiplied by the dilution factor A mean can be determined if more than one plate is used

Answer 126

Measuring the diameter of individual areas of the mycelium can be used to determine the growth of fungi This can be used to compare growth rates in different conditions, e.g. at different temperatures The larger the mean diameter, the greater the growth of the fungi Testing the dry mass of fungi is another effective way to measure fungal growth The higher the mass, the more fungal growth has occurred

Answer 127

Petri dishes of agar are inoculated with fungal spores and incubated at a suitable temperature The resulting areas of fungal mycelia are then measured

Answer 128

A liquid nutrient broth is inoculated with fungal spores Samples of the nutrient broth are removed at set time intervals The fungal mycelia are removed by filtering or centrifugation The material is dried in an oven overnight and its mass measured The higher the mass, the more fungal growth has occurred

Answer 129

Turbidimetry

Answer 130

Turbidimetry is a specialised form of colorimetry that can be used as an alternative method to measure the number of cells in a sample Turbidity is a measure of how cloudy a solution is More turbid = more cloudy Less turbid = less cloudy Colorimetry uses a machine called a colorimeter to shine a beam of light at a sample and measure the amount of light that is either transmitted through or absorbed by the sample

Answer 131

The higher the number of cells the more turbid the solution becomes More turbid solutions will absorb more light and allow less light through; this can be measured by a colorimeter This provides an indirect measure of the number of microorganisms present A calibration curve can be constructed by measuring the turbidity of a series of control cultures while also counting the cells in each culture using a haemocytometer; the results are plotted in a graph of turbidity against cell count This curve can then be used to estimate the cell count of unknown samples by measuring their turbidity and then reading their cell count from the graph

Answer 132

The single, circular DNA molecule undergoes DNA replication Any plasmids present undergo DNA replication The parent cell divides into two cells, with the cytoplasm roughly halved between the two daughter cells The two daughter cells each contain a single copy of the circular DNA molecule and a variable number of plasmids

Answer 133

The growth of a bacterial population follows a specific pattern over time

Answer 134

Lag phase Exponential phase Stationary phase Death phase

Answer 135

The population size increases slowly as the microorganism population adjusts to its new environment and gradually starts to reproduce

Answer 136

With high availability of nutrients and plenty of space, the population moves into exponential growth; this means that the population doubles with each division This phase is also known as the log phase

Answer 137

The population reaches its maximum as it is limited by its environment, e.g. a lack of resources and toxic waste products. During this phase the number of microorganisms dying equals the number being produced by binary fission and the growth curve levels off

Answer 138

Due to lack of nutrients and a build up of toxic waste build up, death rate exceeds rate of reproduction and the population starts to decline This phase is also known as the decline phase

Answer 139

Logarithmic scales allow for a wide range of values to be displayed on a single graph

Answer 140

kt Nt = N0 x 2 Nt = the number of organisms at time t N0 = the number of organisms at time 0 k = the exponential growth rate constant t = the time for which the colony has been growing

Answer 141

number of times the population doubles in a given time period

Answer 142

log10 (Nt) - log10(N0) k=_____________________ log10 (2) x t

Answer 143

single-celled prokaryotes

Answer 144

A cytoplasm that lacks membrane-bound organelles Ribosomes that are smaller (70 S) than those found in eukaryotic cells (80 S) No nucleus, instead having a single circular bacterial chromosome that is free in the cytoplasm and is not associated with proteins A cell wall that contains the glycoprotein murein (peptidoglycan)

Answer 145

Loops of DNA known as plasmids Capsules-It helps to protect bacteria from drying out and from attack by cells of the immune system of the host organism Flagella (singular flagellum)- Long, tail-like structures that rotate, enabling the prokaryote to move (Some prokaryotes have more than one) Pili (singular pilus)-Thread-like structures on the surface of some bacteria that enable the bacteria to attach to other cells or surfaces (Involved in gene transfer during sexual reproduction) A cell membrane that contains folds known as mesosomes; these infolded regions can be the site of respiration

Answer 146

non-cellular infectious particles

Answer 147

A nucleic acid core Their genomes are either DNA or RNA, and can be single or double-stranded A protein coat called a ‘capsid’ made of repeating units known as capsomeres

Answer 148

Some viruses have an outer layer called an envelope formed from the membrane-phospholipids of the cell they were made in Some contain proteins inside the capsid which perform a variety of functions Viruses also contain attachment proteins, also known as virus attachment particles, that stick out from the capsid or envelope

Answer 149

infecting living cells and using the protein-building machinery of their host cells to produce new viral particles

Answer 150

DNA viruses RNA viruses Retroviruses

Answer 151

They contain DNA as genetic material Viral DNA acts as a direct template for producing new viral DNA and mRNA for the synthesis of viral proteins Examples: smallpox, adenoviruses, and bacteriophages Bacteriophages are viruses that infect bacteria, such as the λ (lambda) phage

Answer 152

They contain RNA as genetic material Most have a single strand of RNA They do not produce DNA at all Mutations are more likely to occur in RNA viruses than DNA viruses Examples: tobacco mosaic virus (TMV), ebola virus

Answer 153

Special type of RNA virus that does produce DNA They contain a single strand of RNA surrounded by a protein capsid and lipid envelope Viral RNA controls the production of an enzyme called reverse transcriptase This enzyme catalyses production of viral DNA from the single strand of RNA The new viral DNA is incorporated into the host DNA using integrase enzymes where it acts as a template to produce viral proteins and RNA Example: HIV (Human Immunodeficiency Virus)

Answer 154

Lysogenic Lytic

Answer 155

Bacteriophages inject their genetic material into bacteria Some animal viruses enter the cell via endocytosis by fusing their viral envelope with the host cell surface membrane Plant viruses will often use a vector such as an insect to breach the cell wall

Answer 156

Some viruses will not immediately cause disease once they infect a host cell Viral DNA known as a provirus is inserted into the host DNA, but a viral gene coding for a repressor protein prevents the viral DNA from being transcribed and translated Every time the host DNA copies itself, the inserted viral DNA will also be copied This is called latency and the time during which it occurs is known as a period of lysogeny Viruses in a lysogenic state may become activated and enter the lytic pathway Activation may occur as a result of, e.g. host cell damage or low nutrient levels inside a cell

Answer 157

The viral genetic material is transcribed and translated to produce new viral components These components are assembled into mature viruses that accumulates inside the host cell Eventually the host cell bursts which releases large numbers of viruses, each of which can infect a new host cell Cell bursting is known as cell lysis This typically results in disease

Answer 158

When infected people with the active form of TB cough or sneeze, the Mycobacterium tuberculosis bacteria enter the air in tiny droplets of liquid released from the lungs TB is transmitted when uninfected people inhale these droplets Once inside the lungs, TB bacteria are engulfed by phagocytes The bacteria may be able to survive and reproduce while inside phagocytes Individuals with a healthy immune system will not develop TB at this stage This is known as the primary infection Over time the infected phagocytes will become encased in structures called tubercles in the lungs where the bacteria will remain dormant It is possible for the bacteria to become activated and overpower the immune system at a later stage, such as during an HIV infection when the immune system is compromised; the person will then develop TB This is known as the active phase of TB The length of time between infection and developing the disease can vary from a few weeks to a few years

Answer 159

TB spreads more quickly among people living in overcrowded conditions

Answer 160

The first symptoms of TB will include developing a fever, fatigue, coughing and lung inflammation If left untreated the bacteria will cause extensive damage to the lungs which can result in death due to respiratory failure TB may also spread to other parts of the body where it can lead to organ failure if not treated promptly

Answer 161

HIV contains RNA and is a retrovirus -Sexual intercourse -Blood donation -Sharing of needles used by intravenous drug users -From mother to child across the placenta -Mixing of blood between mother and child during birth -From mother to child through breast milk

Answer 162

It enters the helper T cells by attaching to a receptor molecule on the host cell membrane The capsid enters the helper T cell and releases the RNA it contains The viral RNA is used as a template by reverse transcriptase enzymes to produce a complementary strand of DNA Once this single-stranded DNA molecule is turned into a double-stranded molecule it can be successfully inserted into the host DNA From here it uses the host cell's enzymes to produce more viral components which are assembled to form new viruses These bud from the host cell and enter the blood, where they can infect other helper T cells and repeat the process At this stage, the individual is HIV positive and may experience flu-like symptoms

Answer 163

These bud from the host cell and enter the blood, where they can infect other helper T cells and repeat the process At this stage, the individual is HIV positive and may experience flu-like symptoms This is known as the acute HIV syndrome stage After the initial infection period, during which HIV replication is rapid, the replication rate drops and the individual enters the asymptomatic or chronic stage During this period the person will not show any symptoms, often for years Gradually the virus reduces the number of helper T cells in the immune system B cells are no longer activated No antibodies are produced The patient begins to suffer from HIV-related symptoms and are now in the symptomatic disease stage of the infection The lack of T helper cells decreases the body’s ability to fight off infections, eventually leading to the final stage of an HIV infection, which is known as advanced AIDS (Acquired immune deficiency syndrome)

Answer 164

As a patient can no longer produce antibodies against pathogens, they are immunocompromised and unable to fight off infections They begin to suffer from diseases that would usually cause very minor issues in healthy individuals These diseases are described as opportunistic

Answer 165

An individual starts suffering from constant opportunistic infections The helper T cell count drops below a critical level

Answer 166

Initially an AIDS sufferer will only have mild infections of the mucous membranes due to the low helper T numbers Over time, however, infections will become more severe e.g. diarrhoea, TB During the final stages of AIDS a person will suffer from a range of more serious opportunistic infections It is these opportunistic diseases that cause an individual with advanced AIDS to die

Answer 167

The number of existing infections The strain of HIV the person is infected with Their age Access to healthcare

Answer 168

Vectors Inhalation Ingestion Indirect contact Direct contact Inoculation

Answer 169

These are living organisms that carry pathogens and transmit them between hosts Insects, such as flies and mosquitoes, are common vectors for diseases

Answer 170

Droplets from the respiratory tract will be suspended in the air when an infected person coughs, sneezes or talks These droplets contain pathogens that can be inhaled by healthy people The airways provide an entry point into the respiratory system of a new host and another infection occurs, e.g. flu, measles, tuberculosis

Answer 171

Pathogens can enter through the digestive system when we ingest contaminated food or drink This is especially probable if food is undercooked, as heat destroys most of the pathogens These pathogens can make their way through the lining of the gut and cause disease (e.g. cholera, Salmonella poisoning)

Answer 172

Inanimate objects can contain large numbers of pathogens that may be transferred between hosts An infected individual may touch or cough on an object which is later touched by a healthy individual who transfers the pathogens to their mouth or nose by touching their face Examples include bedding, towels, and surfaces

Answer 173

Pathogens that spread this way will require some part of the host, e.g. skin, body fluids, to come into direct contact with a healthy individual Pathogens that spread by this route can then pass through the mucous membranes and enter the bloodstream, e.g. When shaking hands with another person who then puts their hand to their nose or mouth During sexual transmission Examples include HIV, ebola, syphilis

Answer 174

This typically occurs when a pathogen enters the body through broken skin, providing it with a direct route into the bloodstream Transmission could be through sexual contact, sharing needles during drug use, or bites or scratches from infected animals Examples include hepatitis B, HIV, tetanus, and rabies

Answer 175

Skin Microorganisms of the gut and skin Stomach acid Lysozyme

Answer 176

The skin provides a physical barrier against infection If the skin is damaged it leaves the exposed tissue beneath vulnerable to pathogens The blood clotting mechanism of the body plays an important role in preventing pathogen entry in the case of damage to the skin Blood clotting takes time, however, so a few pathogens may still enter before a clot forms

Answer 177

Collectively these harmless microorganisms are known as the gut or skin flora They compete with pathogens for resources, thereby limiting their numbers and therefore their ability to infect the body

Answer 178

The hydrochloric acid that makes up a large part of the gastric juices in the stomach creates an acidic environment that is unfavourable to many pathogens present on food and drink Sometimes a few of these pathogens may survive and make their way to the intestines where they infect the gut wall cells and cause disease

Answer 179

Secretions of the mucosal surfaces, e.g. tears, saliva, and mucus, contains an enzyme called lysozyme This enzyme will damage bacterial cell walls, causing them to burst, or lyse

Answer 180

Non-specific Specific

Answer 181

This response is the same, regardless of the pathogen that invades the body

Answer 182

This is a response specific to a particular pathogen The immune system is able to recognise specific pathogens due to the presence of antigens on their cell surface Pathogens have non-self antigens, so the immune system recognises them as not belonging to the body

Answer 183

Inflammation Interferons Phagocytosis

Answer 184

Body cells called mast cells respond to tissue damage by secreting the molecule histamine Histamine is a chemical signalling molecule that enables cell signalling, or communication between cells

Answer 185

Vasodilation increases blood flow through capillaries Capillary walls become 'leaky', or more permeable, allowing fluid to enter the tissues and creating swelling Some plasma proteins leave the blood when the capillaries become more permeable Phagocytes leave the blood and enter the tissue to engulf foreign particles Cells release cytokines, another cell signalling molecule that triggers an immune response in the infected area

Answer 186

Cells infected by viruses produce anti-viral proteins called interferons Interferons prevent viruses from spreading to uninfected cells They inhibit the production of viral proteins, preventing the virus from replicating They activate white blood cells involved with the specific immune response to destroy infected cells They increase the non-specific immune response e.g. by promoting inflammation

Answer 187

Chemicals released by pathogens, as well as chemicals released by the body cells under attack, e.g. histamine, attract phagocytes to the site where the pathogens are located They move towards pathogens and recognise the antigens on the surface of the pathogen as being non-self The cell surface membrane of a phagocyte extends out and around the pathogen, engulfing it and trapping the pathogen within a phagocytic vacuole This part of the process is known as endocytosis Enzymes are released into the phagocytic vacuole when lysosomes fuse with it These digestive enzymes, which includes lysozyme, digest the pathogen After digesting the pathogen, the phagocyte will present the antigens of the pathogen on its cell surface membrane The phagocyte becomes what is known as an antigen presenting cell The presentation of antigens initiates the specific immune response

Answer 188

Antibodies bind to specific antigens that trigger the specific immune response Pathogens enter host cells by binding to them using receptors on their surface; antibodies can bind to these receptors, preventing pathogens from infecting host cells Antibodies can act as anti-toxins by binding to toxins produced by pathogens, e.g. the bacteria that cause diphtheria and tetanus; this neutralises the toxins Antibodies cause pathogens to clump together, a process known as agglutination; this reduces the chance that the pathogens will spread through the body and makes it possible for phagocytes to engulf a number of pathogens at one time

Answer 189

T cells B cells

Answer 190

T cells are produced in the bone marrow and finish maturing in the thymus Mature T cells have specific cell surface receptors called T cell receptors These receptors have a similar structure to antibodies and are each specific to a particular type of antigen

Answer 191

T cells are activated when they encounter and bind to their specific antigen on the surface of an antigen presenting cell These activated T cells divide by mitosis to increase in number Dividing by mitosis produces genetically identical cells, or clones, so all of the daughter cells will have the same type of T cell receptor on their surface

Answer 192

T helper cells T killer cells T memory cells

Answer 193

Release chemical signalling molecules that help to activate B cells Release chemical signalling molecules that help to activate T killer cells Release chemicals called opsonins that label pathogens and infected cells for phagocytosis

Answer 194

Bind to and destroy infected cells displaying the relevant specific antigen

Answer 195

Remain in the blood and enable a faster specific immune response if the same pathogen is encountered again in the future

Answer 196

If the corresponding antigen enters the body, B cells with the correct cell surface antibodies will be able to recognise it and bind to it When the B cell binds to an antigen it forms an antigen-antibody complex The binding of the B cell to its specific antigen, along with the cell signalling molecules produced by T helper cells, activates the B cell Once activated the B cells divide repeatedly by mitosis, producing many clones of the original activated B cell

Answer 197

Effector cells, which differentiate into plasma cells -Plasma cells produce specific antibodies to combat non-self antigens Memory cells -Remain in the blood to allow a faster immune response to the same pathogen in the future

Answer 198

Active immunity Passive immunity

Answer 199

Natural; acquired through exposure to pathogens Artificial; acquired through vaccination

Answer 200

Natural-Foetuses receive antibodies across the placenta from their mothers -Babies receive antibodies in breast milk Artificial-People can be given an injection / transfusion of antibodies e.g. the tetanus antitoxin The antibodies will have been collected from people or animals whose immune system had been triggered by a vaccination to produce antibodies As the person’s immune system has not been activated, there are no memory cells that can enable antibody production in a secondary response; if a person is reinfected they would need another infusion of antibodies

Answer 201

The immune system is activated when a new antigen is encountered, launching a primary immune response consisting of a non-specific immune response followed by a specific immune response the numbers of T and B cells with the correct membrane receptors present in the blood will be low It will take time for the correct T and B cells to be activated and to divide and differentiate into different cell types It can take several days before plasma cells develop and are able to start producing antibodies against an antigen This is the reason why an infected person will experience symptoms of the disease the first time they contract it Both T and B cells produce memory cells during the primary response, which will remain in the blood after an infection is over The presence of memory cells means that a person is said to be immune to the pathogen Should the immune system encounter the same antigen again in the future it will launch a secondary immune response which will be much faster and stronger than the primary response

Answer 202

Memory cells are present in larger quantities than the mature lymphocytes at the start of the primary response, so the correct memory cells are able to detect an antigen, activate, divide by mitosis, and differentiate much more quickly Antibodies are produced more quickly and in larger quantities in a secondary response This will often eliminate the pathogen before the infected person can show symptoms

Answer 203

HIV shows antigenic variability due to the high mutation rate in the genes coding for antigen proteins The virus prevents infected cells from presenting their antigens on the cell surface membrane, making it very difficult for the relevant white blood cells to recognise and destroy the infected cells

Answer 204

Once engulfed by phagocytes in the lungs the bacteria produce substances that will prevent a lysosome from fusing with the phagocytic vacuole This prevents the bacteria from being broken down by digestive enzymes, leaving them to multiply within the phagocyte As with HIV the bacteria can disrupt antigen presentation in infected phagocytes, making it difficult for the immune system to recognise and destroy these cells

Answer 205

Bactericidal; they kill bacterial cells Bacteriostatic; they inhibit bacterial growth processes

Answer 206

Staff and visitors must wash hands regularly while visiting patients If a person contracts a HAI they should be moved to an isolation ward to prevent spread of the infection Surfaces and equipment must be disinfected after every use

Answer 207

No antibiotic prescriptions for minor infections or viral diseases No use of antibiotics as a preventative measure against infections Prescription of a narrow-spectrum antibiotic to treat the infection -Narrow-spectrum antibiotics are active against a narrow range of bacterial infections, as opposed to broad-spectrum antibiotics which are effective against many types of bacteria The advantage of using narrow-spectrum antibiotics is that any resistance genes that arise will not cause problems if they are transferred to other types of bacteria Rotate the use of different antibiotics to decrease the chance of bacteria developing resistance against one antibiotic

Answer 208

These decomposers secrete enzymes that break large organic molecules, such as cellulose, down into smaller ones These small molecules, such as glucose, can be broken down further during respiration During decomposition they also release waste products which provides nutrients to plants The microorganisms involved in decomposition produce CO2 and methane which are released into the atmosphere Carbon dioxide can then be absorbed by green plants which will fix the carbon back into carbohydrates during photosynthesis

Answer 209

forensic science as it provides a way to identify individuals DNA profiling can also be used to determine the genetic relationships between different organisms e.g. Paternity and maternity testing Ancestry kits Determining evolutionary relationships between different species

Answer 210

Isolating a sample of DNA e.g. from saliva, skin, hair, or blood Producing more copies of the DNA fragments in the sample using the polymerase chain reaction (PCR) Carrying out gel electrophoresis on the DNA produced by PCR Analysing the resulting pattern of DNA fragments

Answer 211

DNA or RNA to be amplified Primers( short sequences of single-stranded DNA that have base sequences complementary to the 3’ end of the DNA or RNA being copied; they define the region that is to be amplified, identifying where the DNA polymerase enzyme needs to bind) DNA polymerase The enzyme used to build the new DNA or RNA strand. Taq polymerase does not denature at the high temperature required during the first stage of the PCR reaction Free nucleotides (Enable the construction of new DNA or RNA strands) Buffer solution (Ensures the optimum pH for the reactions to occur in)

Answer 212

Denaturation Annealing Elongation / Extension

Answer 213

The double-stranded DNA is heated to 95 °C which breaks the hydrogen bonds that hold the two DNA strands together

Answer 214

The temperature is decreased to 50-60 °C so that primers can anneal to the ends of the single strands of DNA

Answer 215

The temperature is increased to 72 °C, as this is the optimum temperature for Taq polymerase to build the complementary strands of DNA to produce the new identical double-stranded DNA molecules

Answer 216

After PCR is completed the DNA is treated with restriction endonuclease enzymes and a fluorescent tag can be added; both in preparation for gel electrophoresis Restriction endonucleases break the DNA up into fragments of different length Fluorescent tags enable the DNA fragments to be seen under UV light

Answer 217

DNA fragments are created, e.g. using enzymes known as restriction endonucleases that cut DNA at specific restriction sites The resulting fragments are inserted into a well at the end of a piece of agar gel, before a current is passed through the gel

Answer 218

Positively charged molecules will move towards the cathode (negative pole) while negatively charged molecules will move towards the anode (positive pole) DNA is negatively charged due to the phosphate groups and so when placed in an electric field the molecules move towards the anode

Answer 219

The molecules are separated according to their size / mass Different sized molecules move through the gel at different rates The tiny pores in the gel allow smaller molecules to move quickly, whereas larger molecules move more slowly

Answer 220

An agarose gel plate is created and wells are cut into the gel at one end The gel is submerged in a tank containing electrolyte solution which conducts electricity The DNA samples are transferred into the wells using a micropipette, ensuring that a sample of DNA standard is loaded into the first well (control group) The negative electrode is connected to the end of the plate with the wells and the positive anode is connected at the far end The DNA fragments move towards the anode due to the attraction between the negatively charged phosphates of DNA and the anode The smaller mass / shorter pieces of DNA fragments move faster and therefore further from the wells than the larger fragments Probes are then added, after which an X-ray image is taken or UV-light is shone onto the paper producing a pattern of bands which can be compared to the control, or standard, fragments of DNA

Answer 221

Probes are single-stranded DNA sequences that are complementary to the regions of interest; they can be A radioactive label which causes the probes to emit radiation that makes the X-ray film go dark, creating a pattern of dark bands A fluorescent dye which fluoresces when exposed to UV light, creating a pattern of coloured bands

Answer 222

The fragments were produced after PCR by cutting the DNA samples into pieces using restriction endonuclease enzymes Restriction endonucleases cut DNA at specific locations in the DNA base sequence, so will always cut in between sections of repeated bases known as variable number tandem repeats (VNTRs) VNTRs are known as micro- or mini-satellites depending on the number of repeats that occur Different people have different numbers of repeats in their VNTR regions, so the fragments will differ in length depending on whether there are few or many repeats

Answer 223

Different individuals will have different lengths of DNA fragments, so a different pattern of banding will form on each profile Every banding pattern will be unique to an individual, so comparisons of DNA from crime scenes with that of suspects is a reliable way of finding out who was present at a crime scene

Answer 224

DNA profiles of the particular organisms can be compared to determine which are genetically the most different from each other These organisms will then be crossbred, ensuring that the individuals that breed together are not closely related

Answer 225

inbreeding, and can cause genetic problems at an individual and population level such as: In individuals there can be an accumulation of harmful recessive alleles that might otherwise have been masked by healthy dominant alleles Inbreeding leads to a smaller gene pool within a population, which can reduce a population's ability to adapt to change

Answer 226

Extent of decomposition Stage of succession Forensic entomology Body temperature of the deceased The degree of muscle contraction

Answer 227

Decomposers break down cells and tissues over the course of a few days At this stage in decomposition the appearance of the skin can be a helpful indication of time since death; skin will often appear greenish in colour

Answer 228

breakdown of tissues and organs by micro-organisms over the course of a few days or weeks This process produces gases, such as methane, which will lead to bloating The skin will blister and fall off the rest of the body

Answer 229

A few weeks after death the remains of the soft tissues will turn to liquid which becomes visible as it leaves the body This process will continue over the course of months or years until only a skeleton remain After a few decades or centuries, the skeleton will disintegrate until nothing remains

Answer 230

temperature and availability of oxygen Decomposition would be slower in anaerobic conditions and at lower temperatures but would be faster at high temperatures

Answer 231

in an ecosystem the early pioneer species are out-competed and disappear as the system matures, while in a dead body all of the newly arriving species remain as decomposition progresses

Answer 232

Bacteria will be found in and on the dead body immediately after TOD As tissue decomposition sets in it creates ideal conditions for flies to lay eggs and their larvae to hatch As more soft tissue is consumed by the fly larvae it creates favourable conditions for beetles to establish When tissue dries out over time flies will leave the body as they prefer a moisture-rich environment Beetles, however, can decompose dry tissue so they will remain on the body Once all tissues have been decomposed most organisms will leave the body

Answer 233

accessibility to insects and availability of oxygen will be affected e.g. Buried in soil Buried in a coffin Under water

Answer 234

Drugs that may be present in the body Humidity of the surroundings Oxygen availability Temperature

Answer 235

Once a person dies metabolic reactions will eventually come to an end Since no more heat is produced the body temperature drops until it reaches the temperature of the surrounding environment

Answer 236

Air temperature Surface area : volume ratio Presence of clothing Percentage body fat

Answer 237

Muscles in the body begin to contract about 4-6 hours after TOD, leading to a general stiffening of the body

Answer 238

changes to the proteins in muscle cells after death Since no more oxygen reaches the muscle cells after death they will start to respire anaerobically, producing lactic acid The accumulation of lactic acid decreases the pH in the muscle cells, denaturing the enzymes that produce ATP Without ATP the myosin heads cannot be released from the actin filaments, locking the muscles in a contracted state Muscles contract due to the action of two protein filaments; myosin and actin The binding of myosin heads to actin proteins followed by the bending of the myosin heads causes muscle contraction ATP is required to allow the myosin heads to detach from the binding sites on actin

Answer 239

Rigor mortis will begin in the smaller muscles of the head and end in the larger muscles of the lower body

Answer 240

level of muscle development and the temperature of the surroundings Higher temperatures will speed up the rate of rigor mortis

Unit 4 Flashcards

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