Cumulative Flashcards

Question

What is the difference between saturated and unsaturated fatty acids?

Answer 1

Unsaturated fatty acids contain one or more Carbon-Carbon double bonds, creating kinks in the hydrocarbon chain. Saturated fatty acids contain no Carbon-Carbon double bonds, and therefore all Carbons are fully saturated with Hydrogen.

Answer 2

Triglycerides consist of 1 glycerol molecule and 3 fatty acids, which join via condensation reactions. Therefore, 3 molecules of water are released and 3 ester bonds form.

Answer 3

The hydrolysis of the fatty acid chains releases a lot of energy, meaning that triglyceride molecules are ideal energy stores. Also, the fatty acid chains are hydrophobic, meaning that triglyceride molecules are insoluble in water. Therefore, the molecules do not affect water potential, so no osmotic action occurs, damaging cells.

Answer 4

One of the fatty acids of a triglyceride is substituted for a phosphate group in a phospholipid.

Answer 5

The phosphate group is hydrophilic and the fatty acid chains are hydrophobic. Therefore they can form membranes as they are selectively permeable, allowing certain substances into the cell and not others.

Answer 6

Add ethanol and shake, and then add water. If the test is positive, a milky emulsion will form on top.

Answer 7

Each participant only takes part in one of the conditions. + Order effects will not affect the results - Differences between conditions may be due to participant variables

Answer 8

Each participant takes place in all of the conditions + Participant variables will not affect the results - Order effects may affect the results

Answer 9

Counterbalancing

Answer 10

Each participant takes part in one condition, however each participant is matched according to certain characteristics with another participant in the other condition. + The effect of order effects and participant variables are reduced - Can be time consuming or difficult to match participants

Answer 11

A laboratory experiment is an experiment carried out in a highly controlled environment, such as a laboratory. + Researchers can control for extraneous variables and ensure the procedure is fully standardised and replicable, increasing reliability - Results may lack ecological validity, as the artificial environment may cause unnatural behaviour from the participants

Answer 12

A field experiment is an experiment carried out the participants' natural setting + Results are likely to be high in ecological validity as participants' behaviour will be more natural - Researchers have little control over extraneous variables, therefore decreasing reliability

Answer 13

A quasi experiment is an experiment in which the IV is not directly manipulated by the researcher + Useful for conducting research into naturally occurring variables or variables that would be unethical or impractical to manipulate - Low reliability as the researcher has no control over the IV

Answer 14

A smaller, repeating molecule from which larger polymers are made

Answer 15

A larger molecule which is made up of identical repeating monomers.

Answer 16

A reaction in which two molecules join together, forming a covalent bond and releasing a molecule of water.

Answer 17

A reaction in which the covalent bond between two molecules is broken, which uses up a molecule of water.

Answer 18

Polynucleotides (DNA or RNA)

Answer 19

Polysaccharides

Answer 20

Polypeptides (Proteins)

Answer 21

In α-glucose, the H is above the OH whereas in β-glucose, the OH is above the H

Answer 22

https://static.aqa.org.uk/assets/image/0018/235440/00055366-DA00046397-DB.png

Answer 23

https://static.aqa.org.uk/assets/image/0008/235439/00055366-DA00046396-DB.png

Answer 24

Molecules with the same molecular formula but differently arranged atoms.

Answer 25

A disaccharide is two monosaccharides joined together with a glycosidic bond. They are formed by a condensation reaction, which releases a molecule of water.

Answer 26

Glucose and Glucose

Answer 27

Glucose and Fructose

Answer 28

Glucose and Galactose

Answer 29

Polysaccharides are made up of many (more than 2) monosaccharides, joined together with glycosidic bonds. They are formed by many condensation reactions, releasing water molecules.

Answer 30

Starch acts as an energy source in plant cells. It is a polysaccharide of alpha glucose. It contains both Amylose and Amylopectin. Amylose has 1-4 glycosidic bonds and is therefore unbranched. Amylopectin has both 1-4 and 1-6 glycosidic bonds, meaning that it is branched.

Answer 31

Glycogen acts as an energy store in animal cells. It is a polysaccharide of alpha glucose. It has both 1-4 and 1-6 glycosidic bonds. Therefore, it is branched.

Answer 32

Cellulose acts as structural support in plant cells. It is found in the cell walls of plant cells. It is a polysaccharide of beta glucose, held together by 1-4 glycosidic bonds forming straight unbranched chains. Chains are joined together with hydrogen bonds forming microfibrils.

Answer 33

Starch is helical, so it is compact for storage in cell. Also, it is a large molecule, meaning it can not leave the cell. It is also insoluble in water, meaning that it does not affect the water potential of the cell, so no osmotic action which could damage the cell occurs. Also, it is branched to increase the surface area for faster hydrolysis.

Answer 34

Glycogen is branched are is therefore compact and more molecules can fit in small area. Also, the branching results in a larger surface area for the enzymes to quickly hydrolyse the glycosidic bonds to release glucose. Also, it is a large molecule meaning it can not leave the cell. It is also insoluble in water, meaning that it does not affect the water potential of the cell, so no osmotic action which could damage the cell occurs

Answer 35

Every second β-glucose molecule is inverted in a long, straight, unbranched chain. Many hydrogen bonds link parallel strands (crosslinks) to form microfibrils. Hydrogen bonds are strong in large quantities, so provides strength to plant cell walls

Answer 36

Firstly, add Benedict’s solution, which is blue to the sample. Next, heat the sample in a water bath. A positive test will result in a green, yellow, orange or red precipitate depending upon on the concentration of reducing sugars.

Answer 37

If the result of the Benedict’s test is negative, there still could be non-reducing sugar present. Heat in a boiling water bath and add acid in order to hydrolyse into reducing sugars. Next, neutralise with alkali (e.g. sodium bicarbonate) Now, carry out the Benedicta test as normal by heating sample in a boiling water bath with Benedict’s solution. Positive result = green / yellow / orange / red precipitate.

Answer 38

Carry out a Benedict’s test, then filter and dry the precipitate. Then, measure the mass of the precipitate.

Answer 39

First, make a dilution series of sugar solutions of known concentrations. Next, heat a set volume of each sample with a set volume of Benedict’s solution. Use a colorimeter to quantitively measure the absorbance of each known concentration, and plot a calibration curve with . concentration on the x axis and absorbance on the y axis, and draw a line of best fit. Repeat the Benedict’s test with the unknown sample and find the concentration on the graph which is associated with the absorbance of the unknown sample.

Answer 40

Add iodine dissolved in potassium iodide, which is orange/brown. A positive result will cause a colour change to blue/black

Answer 41

https://cdn.sanity.io/images/p28bar15/green/e7a792fa03f686507301a1d00a82af36777d3f91-960x670.png

Answer 42

There are 20 amino acids that are common in all organisms and they differ only in their R group side chain.

Answer 43

Amino Acids join together via a condensation reaction, removing a water molecule. A Peptide bond is formed between the carboxyl group of one amino acids and the amine group of the other.

Answer 44

2 amino acids joined together with peptide bonds.

Answer 45

More than 2 amino acids joined together with peptide bonds.

Answer 46

Sequence of amino acids in a polypeptide chain, joined by peptide bonds.

Answer 47

The folding of the polypeptide chain into alpha helices or beta pleated sheets due to hydrogen bonding between amino acids (between NH group of one amino acid and C=O group of the other)

Answer 48

The 3D folding of the polypeptide chain due to interactions between the R groups of the amino acids. Therefore, hydrogen bonds, ionic bonds and disulphide bridges are formed.

Answer 49

Made up of more than one polypeptide chain, formed by interactions between polypeptides.

Answer 50

Add Biuret reagent (sodium hydroxide + copper II sulphate), which is blue. A positive result will cause a colour change to lilac. This indicates the presence of peptide bonds and therefore the presence of proteins.

Answer 51

Enzymes catalyse reaction by lowering the activation energy. This speeds up the rate of reaction as less energy is needed to start it.

Answer 52

Substrate binds to the active site, which is completely complimentary to it. They bind to form an enzyme-substrate complex.

Answer 53

The substrate binds to the active site, which is not completely complimentary. This causes the active site to change shape so that it becomes complimentary to the substrate and an enzyme-substrate complex forms. This causes bonds in the substrate to change, lowering activation energy.

Answer 54

Initially, the accepted model of enzyme action was the lock and key model, which stated that the active site is fixed and it is exactly complimentary to the substrate. New molecular evidence has suggested the induced fit model, which states that the active site changes shape slightly in order for the substrate to be able to fit.

Answer 55

The specific tertiary structure determines the shape of the active site. This is dependent on the sequence of amino acids (primary structure). The active site is complimentary to a specific substrate, and only this substrate can bind to the active site. The active site slightly changes shape in order for the substrate to fit, forming an enzyme-substrate complex.

Answer 56

As enzyme concentration increases, the rate of reaction also increases. The rate increases because the concentration of enzymes is increasing, and there are more available active sites for substrate molecules to bind to, and therefore more enzyme-substrate complexes are formed. At this point, enzyme concentration is the limiting factor as there is excess substrate. At a certain point, the substrate concentration becomes the limiting factor, so the rate will stop increasing because all of the substrates will be in use.

Answer 57

As substrate concentration increases, the rate of reaction also increases. The rate increases because the concentration of substrates is increasing, and there are more substrate molecules that can bind to active sites, and therefore more enzyme-substrate complexes are formed. At this point, substrate concentration is the limiting factor as there is an excess of enzyme active sites, but at a certain point, the enzyme concentration becomes the limiting factor, so the rate will stop increasing because all of the enzymes will be saturated.

Answer 58

As temperature increases up to the optimum, the rate of reaction increases because the molecules have more kinetic energy, meaning that more collisions between enzymes and substrate molecules will occur, leading to more enzyme-substrate complexes being formed. After the optimum, the rate of reaction decreases as the enzymes denature. Due to the high temperatures, the hydrogen bonds and ionic bonds in the tertiary structure of the enzyme break, changing the shape of the active site. Therefore, the active site is no longer complimentary, meaning that fewer enzyme-substrate complexes can form.

Answer 59

If the pH decreases or increases too much beyond the optimum, the rate of reaction decreases. This is because the H+ and OH- ions interfere with the hydrogen bonds and ionic bonds in the tertiary structure of the enzyme. Therefore, the shape of the active site changes and is no longer complimentary to the substrate, meaning that fewer enzyme-substrate complexes can form.

Answer 60

As the concentration of competitive inhibitors increases, the rate of reaction decreases. Competitive inhibitors have a similar shape to the substrate, and they therefore compete for the active site. This means that the active site is occupied, so the substrate can’t bind to the active site and fewer enzyme-substrate complexes can form. Increasing the concentration of substrate will reduce the effect of the competitive inhibitor as the substrate will begin to outcompete the inhibitor.

Answer 61

As the concentration of non-competitive inhibitor increases, the rate of reaction increases. Non-competitive inhibitors bind to the allosteric site, away from the active site. This leads to the tertiary structure of the enzyme changing, and the shape of the active site changing. Therefore, the active site is no longer complimentary to the substrate, so the substrate can not bind and fewer enzyme-substrate complexes form. Increasing substrate concentration will have no effect on the rate of reaction as the change to the tertiary structure is permanent.

Answer 62

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Answer 63

Enzyme concentration, Substrate concentration, Temperature, pH, Inhibitor concentration.

Answer 64

Transfers genetic information from DNA to ribosomes.

Answer 65

RNA and Proteins

Answer 66

Carries genetic information, which codes for proteins.

Answer 67

In a DNA nucleotide, the pentose sugar in deoxyribose, whereas in RNA it is ribose. DNA contains the nitrogenous bases A, T, G and C, whereas RNA contains A, U, G and C. DNA molecules are double stranded and much larger than RNA molecules, which are much smaller and usually single stranded.

Answer 68

Nucleotides join via condensation reactions, which remove water molecules. This forms phosphodiester bonds between the phosphate group of one nucleotide and the deoxyribose/ribose of the other.

Answer 69

DNA is a chemically simplistic molecule which consists of very few components. Many scientists believed that the molecule that carries the genetic code would be much more complex.

Answer 70

DNA is a polynucleotide. Each nucleotide is formed from a deoxyribose pentose sugar, a phosphate group, and a nitrogenous base. Adjacent nucleotides are joined by phosphodiester bonds, and the 2 polynucleotide chains are joined by hydrogen bonds between complimentary base pairs (Adenine and Thymine, Guanine and Cytosine) This forms a double helix structure.

Answer 71

RNA is Polynucleotide. Each nucleotide is formed from a ribose pentose sugar, a phosphate group and a nitrogenous base (Adenine, Uracil, Guanine or Cytosine). Phosphodiester bonds join adjacent nucleotides, forming a single helix.

Answer 72

* Double stranded - Both can act as template strands for semi-conservative replication. * Hydrogen bonds between complimentary base pairs are weak - strands can be easily separated for replication. * Complimentary base pairing - Accurate replication * Many hydrogen bonds between complimentary base pairs - strong, stable molecule * Double helix with sugar phosphate back bone - protects the bases and hydrogen bonds * Long molecule - can store lots of genetic information, which codes for proteins. * Coiled double helix - compact for storage

Answer 73

The % of adenine in strand 1 is equal to the % of thymine in strand 2 and vice versa. The % of guanine in strand 1 is equal to the % of cytosine in strand 2 and vice versa. This is because of complimentary base pairing between the 2 strands.

Answer 74

There are 2 Hydrogen bonds between Adenine and Thymine, and 3 Hydrogen bonds between Guanine and Cytosine

Answer 75

It ensures genetic continuity between generations of cells.

Answer 76

Each new DNA molecule consists of one strand from the parent DNA molecule, and one new strand.

Answer 77

1. DNA helicase breaks hydrogen bonds between complementary bases, unwinding the double helix 2. Both strands act as template strands. 3. Free DNA nucleotides in the nucleoplasm are attracted to exposed bases and join by complementary base pairing 4. Hydrogen bonds form between complimentary base pairs (adenine-thymine and guanine-cytosine) 5. DNA Polymerase moves along the polynucleotide chain, joining adjacent nucleotides on new strand by condensation reactions, forming phosphodiester bonds.

Answer 78

DNA has antiparallel strands, so the arrangements of nucleotides on each end are different. DNA Polymerase is an enzyme, and therefore has a specific active site, so it can only bind to substrate with a complimentary shape, which is the Phosphate end of each strand.

Answer 79

Watson and Crick

Answer 80

1. Bacteria was grown in medium containing heavy nitrogen (15N), so nitrogen is incorporated into the DNA bases. The DNA was extracted & centrifuged, so it settled near the bottom, as all DNA molecules contain 2 heavy strands 2. Bacteria that was grown in medium containing heavy nitrogen (15N) and was transferred to medium containing light nitrogen (14N) and was left to divide once - The DNA was extracted & centrifuged, so it settled in the middle, as all DNA molecules contain 1 original heavy strand and 1 new light strand 3. Bacteria in light nitrogen (14N) was allowed to divide again. The DNA was extracted & centrifuged, and half settled in middle, as contains 1 original heavy and 1 new light strand; half settles near top, as contains 2 light strands.

Answer 81

A ribose sugar, Adenine and 3 Phosphate groups.

Answer 82

ATP is broken down via a hydrolysis reaction, using a molecule of water. ATP → ADP + Pi. This reaction is catalysed by the enzyme ATP Hydrolase

Answer 83

* The hydrolysis of ATP releases energy, so this energy can be used to provide energy for energy requiring reactions within cells. * The hydrolysis of ATP releases an inorganic phosphate, which can be used to phosphorylate other molecules in the cell, making them more reactive.

Answer 84

ADP + Pi → ATP. This is a condensation reaction, and therefore releases a molecule of water. This is catalysed by the enzyme ATP Synthase and it occurs during respiration and photosynthesis.

Answer 85

* Releases energy in small, manageable amounts * Hydrolysis of ATP is a single reaction as only one bond is hydrolysed to release energy. This means that the energy is released immediately. * ATP molecules can not exit the cell

Answer 86

Water is a polar molecule. The slightly negatively charged oxygen atoms attract the slightly positively charged hydrogen atoms of other water molecules.

Answer 87

Due to the Hydrogen bonding, water molecules take more energy to separate them, so the boiling point is higher than expected. As water therefore has a higher specific heat capacity, it is a buffer to sudden temperature changes. This is important when organisms are mostly water

Answer 88

The Hydrogen Bonding also means that a lot of energy is required to evaporate 1kg of water. This means that sweat in mammals is a very efficient way of cooling as body heat is used to evaporate water.

Answer 89

Cohesion allows water to be pulled through tubes e.g. xylem vessels. Where water molecules meet the air, they are pulled back to the body of water, resulting in surface tension. This allows water to support small organisms.

Answer 90

* Metabolite - Water is used in hydrolysis and released in condensation, as well as it being a raw material in photosynthesis * Solvent - Water dissolves gasses, wastes, ions and small hydrophilic molecules. * Other - Evaporation cools organisms, isn’t easily compressed so allows turgor in plants, transparent so aquatic plants can photosynthesise.

Answer 91

They maintain pH levels in the body, therefore affecting enzyme action.

Answer 92

They are a component of haemoglobin, therefore allowing oxygen to bind for transport as oxyhaemoglobin.

Answer 93

They are involved in the co-transport of glucose and amino acids into cells. They are also involved in action potentials in neurons and they affect the water potential of cells, causing osmosis into and out of the cell.

Answer 94

A research method in which data is collected by watching participants’ behaviour

Answer 95

- Observational research often produces valid results as we can investigate how people actually behave, rather than how they said they would, like in self report methods. - Observations can be used when it would be unethical or impractical to manipulate the Independent Variable.

Answer 96

- Difficult to replicate as the way people act in a certain scenario may not be exactly the same every time. - Results may be affected by observer bias, reducing the validity of the results.

Answer 97

An observation in which observers collect data by recording the frequency of predetermined behaviours using a coding scheme.

Answer 98

- Produces quantitative data which is easy to analyse and compare between conditions - More objective and reduces chance of observer bias

Answer 99

- May produce invalid results as the behaviours recorded may not be representative of all behaviours that could occur - Produces quantitative data which lacks detail, therefore doesn't provide detail and reasons for behaviour

Answer 100

An observation in which observers collect data by writing down all behaviour that occurs in the observation period

Answer 101

- Collects qualitative data which is rich in detail and can explain reasons for behaviour - Unlike in structured observations, all behaviours will be recorded, so the results will be more valid

Answer 102

- As observers are recording everything that occurs, they may miss certain behaviours, therefore decreasing the reliability of results. - Collects qualitative data, which is difficult to analyse and can be subjective, decreasing the validity of conclusions made.

Answer 103

An observation carried out in a controlled environment in which extraneous variables can be controlled, for example a laboratory.

Answer 104

- High levels of control over extraneous variables, so causality can be established - Can be replicated easily, so they have high external reliability.

Answer 105

- Low ecological validity as the environment is highly artificial - Participants are more likely to show demand characteristics, decreasing the validity of the results

Answer 106

An observation which takes place in the participants' natural environment

Answer 107

- More ecologically valid as the environment is natural. - Participants are less likely to show demand characteristics, increasing the validity of the results

Answer 108

- Low levels of control over extraneous variables, so it is difficult to establish causality - Can not be replicated easily, so they have low external reliability.

Answer 109

An observation where the observer takes part in the situation they are observing and becomes part of the observed group

Answer 110

- Observer can gain a more in-depth understanding of the participants' behaviour as they are interacting with them - The observer will understand the situation that they are observation better because they take part in it themself.

Answer 111

- Observer will likely have to record behaviours afterwards, and therefore may forget some behaviours, decreasing the reliability of results - May lead to observer bias as the researcher is interacting with the participants - Usually involves deceiving participants, and therefore is unethical

Answer 112

An observation in which the observer doesn't participate in the situation that they are observing and does not become part of the observed group

Answer 113

- Less likely to result in observer bias as the researcher does not interact with the participants - Observer can record behaviours as they happen, therefore not relying on memory

Answer 114

- It may be difficult to understand behaviour of participants if the observer doesn't interact with them - The observer may not understand the situation they are observing if they do not participate in it

Answer 115

An observation in which the participants are not aware that they are being observed

Answer 116

Reduces the chance of demand characteristics, increasing the validity of results.

Answer 117

They are unethical as participants do not give informed consent

Answer 118

An observation in which the participants are aware that they are being observed

Answer 119

They are usually ethical as participants are aware they are being observed and have therefore consented.

Answer 120

Results may be affected by demand characteristics as participants know they are being observed

Answer 121

When observers pick a time interval and only record behaviours that occur at those times.

Answer 122

Observers are more likely to be able to record behaviours accurately and in detail as they have time to write down what they have observed, meaning what they write down will be valid

Answer 123

Any behaviours that occur outside of the time intervals will not be recorded so the results may not be representative of all behaviours, and so are less likely to be valid

Answer 124

When observers observe all behaviour through the entire length of the observation, recording all events that occur using a coding scheme

Answer 125

No behaviours will be missed because the observer records behaviour that occurs throughout the whole length of the observation

Answer 126

It may not be possible for researchers to write down every behaviour that they see without missing some behaviours, therefore results may be invalid.

Answer 127

A measure of agreement between multiple observers in what they have seen

Answer 128

When the observer interprets what they see in a way which is influenced by what they expect to see

Answer 129

Research method which investigates the relationship between two co-variables without the researcher manipulating any of them

Answer 130

As one co-variable increases, the other co-variable also increases

Answer 131

As one co-variable increases, the other co-variable decreases

Answer 132

No significant relationship is found between the co-variables

Answer 133

There will be no significant correlation between (Variable A) and (Variable B). Any correlation will be due to chance.

Answer 134

There will be a significant positive/negative correlation between (Variable A) and (Variable B).

Answer 135

There will be a significant correlation between (Variable A) and (Variable B).

Answer 136

0.7 , 0.8 , 0.9 , 1

Answer 137

-0.7 , -0.8 , -0.9 , -1

Answer 138

0.4 , 0.5 , 0.6

Answer 139

-0.4 , -0.5 , -0.6

Answer 140

0.1 , 0.2 , 0.3

Answer 141

-0.1 , -0.2 , -0.3

Answer 142

- Good as preliminary research. We can investigate if there is a link between variables before investigating them further experimentally - Useful for investigating variables that would be unethical or impractical to manipulate.

Answer 143

- Impossible to establish cause and effect as a relationship is established, but it is unclear which variable causes the effect in the other - There may be a third variable which is affecting the variables, therefore making the results invalid

Answer 144

In interviews, the questions are asked verbally by an interviewer, whereas in questionnaires, questions are written down

Answer 145

Strength: Is a cheaper, easier method of obtaining data about people's thoughts and behaviours Weakness: Results are often affected by social desirability bias, meaning results may be invalid.

Answer 146

Strength: * Easier and cheaper way to collect lots of data as easy to distribute * Results are less likely to be affected by social desirability bias because there is nobody else present when the participant completes the questionnaire Weakness: There is no way for the participants to clarify questions that they don't fully understand. Therefore, results may be less valid as participants may not have answered how the researcher intended

Answer 147

Strength: Participants can ask interviewer to clarify any questions they don't understand. This means the results are likely to be more valid as participants are more likely to answer how the research intended Weakness: * Much more time consuming as each participants needs to be individually interviewed * More likely to be affected by social desirability bias because the interviewer is present, so the participant may give untruthful answers in an attempt to make themself appear more socially desirable

Answer 148

Questions which are answered by the participant choosing from a pre-determined set of answers. + Produces quantitative data, which is easy to analyse and compare across conditions - Lacks detail and doesn't allow researcher to gain an insight into the reasons for behaviour.

Answer 149

Questions that the participant can answer in any way they choose + Provides detail and insight into the reasons for behaviour - Produces qualitative data, which is difficult to analyse and compare across conditions

Answer 150

Questions in which participants indicate on a scale how much they agree with a statement given

Answer 151

Questions in which the participants is given a statement, as well as a scale with two contrasting adjectives on the ends. They have to say where on the scale their opinion on the statement lies between the two adjectives.

Answer 152

* Structured: Interviewers ask a predetermined list of questions in the same order and in the same way * Semi-structured: Interviewers ask a predetermined list of questions but they can deviate from the list and ask follow up questions * Unstructured: The topic of the interview is the only thing that is predetermined. The interviewer asks anything they believe will give them useful answers.

Answer 153

+ As the questions are standardised, the research will be more reliable as it can be easily replicated - The interviewer can't ask follow up questions, meaning they may not be able to gain a full understanding of the participant's thoughts and feelings. Therefore, results may lack validity

Answer 154

+ As the interviewer is able to ask follow up questions, they can gain more valid data - Low reliability as the interview can not be replicated as the questions are not standardised

Answer 155

Respect, competence, responsibility, integrity

Answer 156

Informed consent, right to withdraw, confidentiality

Answer 157

Protection from Physical and Psychological harm, Debrief

Answer 158

* Chi-Squared: Independent Measures Design, Nominal Data. Observed value must be greater than or equal to the critical value for findings to be significant. * Mann-Whitney U Test: Independent Measures Design, Interval/Ordinal Data. Observed value must be less than or equal to the critical value for findings to be significant. * Binominal Sign Test: Repeated Measures Design, Nominal Data Observed value must be less than or equal to the critical value for findings to be significant. * Wilcoxon Test: Repeated Measures Design, Interval/Ordinal Data. Observed value must be less than or equal to the critical value for findings to be significant. * Spearman's Rho: Correlations. Observed value must be greater than or equal to the critical value for findings to be significant.

Answer 159

Mode, Median, Mean

Answer 160

Identify what is the most frequently occurring number in the data set

Answer 161

Arrange the numbers from smallest to largest and find the midpoint.

Answer 162

Add together all numbers in the data set, and divide by how many numbers there are in the data set

Answer 163

* Strength: Not skewed by extreme values * Weakness: Doesn’t take all the scores in the data set into consideration

Answer 164

* Strength: Not skewed by extreme values * Weakness: Doesn’t take all the scores in the data set into consideration

Answer 165

* Strength: Takes all of the scores in the data set into consideration * Weakness: Can be skewed by extreme values

Answer 166

Range, Variance, Standard Deviation

Answer 167

Calculate the largest value minus the smallest value

Answer 168

Subtract the mean from each number in your sample, and square the result of these calculations. Add these numbers together and divide this by how many numbers you have in the sample minus 1. This will give the variance. Square root the variance to find the standard deviation

Answer 169

It is a measure of how dispersed the data is in relation to the mean. A small standard deviation indicates data is clustered tightly around the mean, and a large standard deviation indicates data is more spread out.

Answer 170

* Nominal - Data that is sorted into categories * Ordinal - Data which is on a rating scale * Interval - Data with an exact value

Answer 171

* Qualitative - Data which involves in depth descriptions * Quantitative - Data which involves numerical values * Primary - Data that has been collected directly by the researcher, solely for their research * Secondary - Data that the researcher has not collected themself.

Answer 172

Eukaryotic cells have membrane bound organelles, and their genetic material is enclosed in a nucleus.

Answer 173

The cell surface membrane is a phospholipid bilayer. Phospholipids have hydrophilic phosphate heads and hydrophobic fatty acid tails, so the heads point outwards and the tails point inwards. It also contains intrinsic and extrinsic proteins, glycolipids and glycoproteins on the exterior surface, and cholesterol molecules.

Answer 174

It is selectively permeable, selectively allowing some substances in and out of the cell. It also has receptors on its surface, allowing recognition of foreign and abnormal cells.

Answer 175

The nucleus is surrounded by a double membrane called the nuclear envelope, which has nuclear pores in it. The interior of the nucleus consists of the nucleoplasm, within which is the nucleolus. Also in the nucleoplasm is chromatin.

Answer 176

Holds and stores genetic information, which codes for proteins. It is also the site of DNA replication as well as the site of transcription, producing mRNA. Also, Ribosomes are produced in the nucleolus.

Answer 177

Made up of ribosomal RNA and 2 subunits of protein. It is not membrane bound.

Answer 178

Site of protein synthesis

Answer 179

Ribosomes on the surface synthesise proteins, which are then processed, in the RER and are then packaged into vesicles for transport around the cell.

Answer 180

Synthesises and processes lipids

Answer 181

Consists of a system of fluid filled channel-like membranes. The RER has attached Ribosomes.

Answer 182

The Golgi modifies and packages proteins and lipids, and also produces lysosomes. The Golgi vesicles transport proteins and lipids around the cell.

Answer 183

They release hydrolytic enzymes called lysozymes, which hydrolyse pathogens.

Answer 184

They are surrounded by a membrane and contain lysozymes, which are digestive enzymes.

Answer 185

Mitochondria consist of an outer membrane, Cristae, which are the inner membrane folds, and the matrix containing small 70S ribosomes and circular DNA

Answer 186

Mitochondria are the site of aerobic respiration, producing ATP for energy release.

Answer 187

Chloroplasts have a double membrane, and stroma, which contain thylakoid membrane, 70S ribosomes, circular DNA, starch granules and lipid droplets. Chloroplasts also contain lamellae, and grana (stacks of thylakoid)

Answer 188

Absorb light energy for photosynthesis

Answer 189

Composed of Cellulose in plants and algae. Composed of Chitin in fungi, and of Murein in bacteria.

Answer 190

Provides structural support to the cell, preventing the cell bursting due to osmotic action.

Answer 191

Contains cell sap and is surrounded by a tonoplast membrane.

Answer 192

Maintains turgor pressure in the cell, stopping the plant wilting. Also contains cell sap which stores sugars, amino acids, pigments and any waste chemicals.

Answer 193

Group of specialised cells with a similar structure working together to perform a specific function.

Answer 194

They lack membrane-bound organelles, and therefore their genetic material is not enclosed in a nucleus

Answer 195

Group of tissues working together to perform a specific function

Answer 196

Group of organs working together to perform specific functions.

Answer 197

They consist of cytoplasm, and within the cytoplasm are 70S Ribosomes and circular DNA, which is free in the cytoplasm and not associated with proteins. Sometimes, this DNA is in the form of plasmids. The cells are surrounded by a cell-surface membrane and a murein cell wall. Some prokaryotic cells are also surrounded by a capsule, and some also have flagella.

Answer 198

* Eukaryotic Cells have membrane bound organelles, whereas Prokaryotic Cells have no membrane-bound organelles. * Eukaryotic Cells have a nucleus which contains DNA, whereas Prokaryotic Cells have no nucleus, so their DNA is free in the cytoplasm. * In Eukaryotic Cells, the DNA is long, linear, and associated with histone proteins, whereas in Prokaryotic Cells, the DNA is short, circular, and not associated with any proteins. * Eukaryotic Cells contain larger (80S) Ribosomes, whereas Prokaryotic Cells contain smaller (70S) Ribosomes. * Prokaryotic Cells have a Cell Wall made of Murein, whereas in Eukaryotic Cells, where present, the Cell Wall is made of Cellulose or Chitin in fungi.

Answer 199

They are acellular because they are not made of cells, and they have no organelles. They are non-living because they can not independently replicate.

Answer 200

Contains Nucleic acids surrounded by a capsid (protein coat) They have attachment proteins on surface to allow attachment to specific host cells. Some also surrounded by a lipid envelope e.g. HIV

Answer 201

The number of times larger the image is than size of the real object

Answer 202

Magnification = Size of Image / Size of real object

Answer 203

Minimum distance apart 2 objects can be to be distinguished as separate objects

Answer 204

* Light focused using glass lenses * Light passes through specimen, different structures absorb different amounts & wavelengths * Generates a 2D image of a cross-section * Low resolution due to long wavelength of light * Can’t see internal structure of organelles * Specimen has to be thin * Low magnification (x 1500) * Can view living organisms * Simple preparation * Can show colour

Answer 205

* Electrons focused using electromagnets * Electrons pass through specimen, denser parts absorb more and appear darker * Generates a 2D image of a cross-section * Very high resolution due to short wavelength of electrons * Can see internal structures of organelles * Specimen has to be very thin * High magnification (x 1,000,000) * Can only view dead / dehydrated specimens as uses a vacuum Can only view dead / dehydrated specimens as uses a vacuum * Complex preparation so artefacts often present * Does not show colour

Answer 206

* Electrons focused using electromagnets * Electrons deflected / bounce off specimen surface * Generates a 3D image of surface * High resolution due to short wavelength of electrons * Can’t see internal structures * Specimen does not need to be thin * High magnification (x 1,000,000) * Can only view dead / dehydrated specimens as uses a vacuum * Complex preparation so artefacts often present * Does not show colour

Answer 207

May result in air bubbles or particles of dust etc. in the slide. This could result in artefacts which could be mistaken for cell organelles and other structures that are not actually present.

Answer 208

Metre (m), Millimetre (mm), Micrometre (µm), Nanometre (nm)

Answer 209

1. Line up scale of eyepiece graticule with scale of stage micrometre 2. Calibrate eyepiece graticule - use stage micrometre to calculate size of divisions on eyepiece graticule 3. Take micrometre away and use graticule to measure how many divisions make up the object 4. Calculate size of object by multiplying number of divisions by size of division 5. Recalibrate eyepiece graticule at different magnifications

Answer 210

1. Homogenise tissue to disrupt cell membrane, breaking open cells and releasing the organelles 2. Place in a cold, isotonic, buffered solution (Cold to reduce enzyme activity → so organelles not broken down / damaged, Isotonic so water doesn’t move in or out of organelles by osmosis → so organelles don’t burst, Buffered to keep pH constant → so enzymes don’t denature 3. Filter homogenate to remove large, unwanted debris 4. Ultracentrifugation - separates organelles in order of density. Centrifuge homogenate in a tube at a relatively low speed. Remove pellet of heaviest organelle and respin supernatant at a higher speed. Repeat at increasing speeds until separated out.

Answer 211

1. Nuclei 2. Chloroplasts and Mitochondria 3. Lysosomes 4. Endoplasmic Reticulum 5. Ribosomes

Answer 212

1. Interphase - DNA undergoes semi-conservative replication, leading to 2 sister chromatids joined at the centromere. Also, the number of organelles and the volume of cytoplasm increases. 2. Mitosis - The nucleus divides to produce 2 nuclei with identical copies of DNA 3. Cytokinesis - The cytoplasm and cell membrane divide to form 2 new genetically identical daughter cells.

Answer 213

The Chromosomes condense, becoming visible. They will appear as 2 sister chromatids joined at the centromere. The nuclear envelope breaks down and the centrioles move to opposite poles, forming the spindle network.

Answer 214

The spindle fibres attach to the chromosomes at the centromere, and chromosomes align along the equator.

Answer 215

The spindle fibres contract and the centromere divides, pulling sister chromatids to opposite poles of the cell.

Answer 216

Chromosomes uncoil, and the nuclear envelope reforms to form 2 new nuclei. Spindle fibres and centrioles are broken down.

Answer 217

Cells divide to produce 2 genetically identical daughter cells for: * Growth * Replacing cells in damaged tissue * Asexual reproduction

Answer 218

Mitosis is a controlled process. Mutations in the gene controlling mitosis (oncogenes) can lead to uncontrolled cell division. This may result in a mass of abnormal cells, forming a tumour. If this tumour metastasises, it becomes malignant and cancerous.

Answer 219

Some cancer treatments disrupt spindle fibre formation and activity, so that the spindle fibres can not attach to the chromosomes at the centromere, and the chromatids can't be separated to opposite poles during anaphase, therefore preventing mitosis. Others prevent DNA replication by inhibiting DNA Polymerase, so that cells can't make 2 copies of each chromosome, so prevents mitosis.

Answer 220

Most cancer treatments kill cells or prevent mitosis, therefore healthy cells will also be destroyed or their cell cycle will be disrupted.

Answer 221

They replicate via Binary Fission: * Replication of Circular DNA and any Plasmids that are present. * Division of the cytoplasm, producing 2 new daughter cells * The 2 new daughter cells each contain a single copy of the Circular DNA and a variable number of copies of plasmids.

Answer 222

1. Attachment proteins attach to the complimentary receptors on host cell 2. They inject viral nucleic acid into host cell 3. Infected host cell replicate the virus particles nucleic acid, producing viral proteins. 4. The virus is assembled then released.

Answer 223

A foreign protein which stimulates an immune response, leading to the production of a complimentary antibody.

Answer 224

Each cell has specific antigen on it’s cell surface. These antigens are proteins and have a specific tertiary structure, which help the immune system to recognise them as self or foreign.

Answer 225

* Pathogens (microorganisms that cause disease) * Cells from other organisms (e.g. organ transplants) * Abnormal body cells (e.g. tumour cells or virus infected cells) * Toxins (Harmful chemicals release by some bacteria)

Answer 226

Phagocytosis

Answer 227

Cellular and humoral response.

Answer 228

1. Phagocyte is attracted to chemicals made by pathogen or recognises it’s foreign antigens on cell surface membrane. 2. Phagocyte engulfs pathogen by endocytosis, surrounding it with its cell membrane. 3. Pathogen contained in phagosome within the cytoplasm of the phagocyte. 4. Lysosome fuses with phagosome to produce a phagolysosome and releases lysozymes. 5. Lysozymes hydrolyse the pathogen and the products are absorbed into the phagosome if they are soluble, but are expelled from the cell if they are insoluble.

Answer 229

Phagocytosis leads to presentation of antigens, where antigens are displayed on the phagocyte cell-surface membrane, stimulating the specific immune response (cellular and humoral response).

Answer 230

T-Lymphocytes recognise antigens on the surface of antigen presenting cells. Specific T-Helper cells with complimentary receptors on their cell surface bind to the antigen on the antigen-presenting cell, causing the T-Helper cells to divide rapidly by mitosis, which then stimulate the production of Cytotoxic T Cells (which produce chemicals such as perforin to kill infected cells and pathogens), Specific B Cells (which stimulate the humoral response, including the production of antibodies) and Phagocytes (which engulf pathogens by phagocytosis).

Answer 231

B Lymphocytes can recognise free antigens. When they come across a foreign antigen, specific B-Lymphocytes with complimentary receptors bind to the antigens, and is stimulated by T-Helper cells to divide rapidly by mitosis. Some of these clones differentiate into B-Plasma cells, which secrete large amounts of antibodies, which are specific to the foreign antigen. Others differentiate into B-Memory cells, which remain in the blood until the secondary immune response.

Answer 232

Antibodies are quaternary structure proteins and they consist of 4 polypeptide chains. They are secreted by B-Plasma cells in response to specific antigen. They are complimentary to their specific antigen, and when bind to it, they form an antigen-antibody complex.

Answer 233

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Answer 234

Antibodies bind to complimentary antigens on the surface of pathogens . Each antibody can bind to 2 pathogens at a time, causing agglutination. This allows the antibodies to attract phagocytes, which destroy the pathogens via phagocytosis.

Answer 235

The primary response refers to the immune response which occurs upon the first exposure to an antigen. Antibodies are produced slowly and at a lower concentration as it takes time for specific B-Plasma cells to be stimulated to produce the specific antibodies. Memory cells are produced in the primary response. The secondary response refers to the immune response that occurs upon the second exposure to an antigen. In the secondary response, antibodies are produced faster and at a higher concentration. This is because B memory cells are present in the blood, and they rapidly undergo mitosis in order to rapidly produce specific antibodies.

Answer 236

The injection of antigens from dead, weakened or inactive pathogens, stimulating a weak immune response, producing memory cells.

Answer 237

1. Specific B lymphocyte with complementary receptor binds to antigen 2. Specific T helper cell binds to antigen-presenting cell and stimulates B cell 3. B lymphocyte divides by mitosis to form clones 4. Some differentiate into B plasma cells which release antibodies 5. Some differentiate into B memory cells 6. On secondary exposure to antigen, B memory cells are already present, so they can rapidly divide by mitosis to produce B plasma cells 7. These release antibodies faster and at a higher concentration

Answer 238

Herd Immunity - If a large proportion of the population is vaccinated, then the majority of people will not become ill from infection. This results in fewer infected people to pass the pathogen, and therefore unvaccinated people are less likely to come into contact with someone with the disease. This helps to protect vulnerable people such as young children and elderly people, as well as other people who do not get vaccinated due to personal or medical reasons.

Answer 239

* In active immunity, the person is exposed to the antigen, either natural (via primary infection) or artificially (via vaccination), whereas in passive immunity, the person has not been exposed to the antigen. * In active immunity, the antibodies were produced and secreted by the person’s own B-plasma cells, but in passive immunity the antibodies that are introduced into the body were produced by another organism (e.g. through breast milk) * Active immunity is slower as it requires a full immune response. Passive immunity is much quicker as the antibodies can act immediately.

Answer 240

The tertiary structure of the antigens on the surface of pathogens changes due to a mutation, causing a change in shape. Therefore, the B-memory cells can no longer bind to the antigen when exposed to the antigen, and the specific antibodies are no longer complimentary so can not bind to the antigen. Therefore, there is no more immunity.

Answer 241

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Answer 242

1. HIV attachment proteins attach to receptors on helper T cell. 2. Lipid envelope fuses with T-Helper cell-surface membrane, releasing capsid into cell. 3. Capsid breaks down, releasing RNA and reverse transcriptase into the cell. 4. Reverse transcriptase converts viral RNA to DNA. 5. Viral DNA is inserted into helper T cell DNA, so it is replicated when cells replicate. 6. DNA is used to make HIV RNA and proteins at the host ribosomes. 7. Virus particles are assembled, which bud off from the cell membrane and continue infecting other cells.

Answer 243

HIV infects and kills T-Helper cells. Therefore, T-Helper cells can’t stimulate Cytotoxic T Cells , B-Cells and Phagocytes. This means that B Plasma cells can’t release as many antibodies, leading to the deterioration of the immune system. This makes the patient more susceptible to opportunistic infections, leading to many of the patient’s healthy body cells being destroyed.

Answer 244

* Having unprotected sex with an infected person. * Close contact with the blood of an infected person (via the sharing of needles for drug use or the use of infected blood in blood transfusions) * Mother to child (Shared through the placenta or through breast milk).

Answer 245

Viruses do not have structures and processes that antibiotics inhibit. Viruses do not have metabolic processes and they do not have bacterial enzymes or a murein cell wall.

Answer 246

Monoclonal antibodies have a specific tertiary structure and therefore their antigen binding site is complementary to the receptor of an antigen found only on a specific cell type (e.g. cancer cell). Therapeutic drugs can be attached to the monoclonal antibodies, so the antibody will bind to the specific cell, forming antigen-antibody complex, delivering the drug to the specific cell.

Answer 247

Monoclonal antibodies have a specific tertiary structure and therefore their antigen binding site is complementary to the receptor of the antigen associated with diagnosis. Fluorescent markers can be attached to the monoclonal antibody, and if the antibody binds to the receptor of the specific antigen, it will form an antigen-antibody complex which will be visible so that scientists can diagnose diseases by identifying which antigen is present.

Answer 248

1. Attach sample with potential antigens to well 2. Add complementary monoclonal antibodies with enzymes attached. They will bind to antigens if present. 3. Wash well to remove unbound antibodies (to prevent false positive) 4. Add substrate so that the enzymes create products that cause a colour change (positive result)

Answer 249

1. Attach antigens to well that are complimentary to the antibody you are testing for. 2. Add sample with potential antibodies, wash to remove unbound antibodies. 3. Add complementary monoclonal antibodies with enzymes attached, which will bind to antibodies if present, 4. Wash well to remove unbound antibodies. 5. Add substrate so that enzymes create products that cause a colour change (positive result).

Answer 250

So that you can compare it to the test well to ensure that only the enzyme caused the colour change and that all unbound antibodies had been washed away.

Answer 251

1. Mobile monoclonal antibodies that are complimentary to the hCG protein are attached to a coloured bead. 2. If there is any hCG in the urine (indicating pregnancy) then it will bind to the antibodies, forming a HCG-antibody complex. 3. The urine moves up the strip, until in reaches a line of immobilised monoclonal antibodies which only binds to the HCG-antibody complex. If the test is positive, this first this line will change colour. 4. The urine continues up the test strip to a line of immobilised monoclonal antibodies which only bind to the mobile monoclonal antibodies, regardless of whether there in hCG attached or not. This line indicates that the test worked.

Answer 252

* Was the sample size large enough to be representative? - Were participants diverse in terms of age, sex, ethnicity and health status? * Were placebo / control groups used for comparison? * Was the duration of the study long enough to show long-term effects? * Was the trial double-blind to reduce bias?

Answer 253

* What side effects were observed, and how frequently did they occur? * Was a statistical test used to see if there was a significant difference between start & final results? * Was the standard deviation of final results large, showing some people did not benefit? * Did standard deviations of start & final results overlap, showing there may not be a significant difference? * What dosage was optimum? Does increasing dose increase effectiveness enough to justify extra cost? * Was the cost of production & distribution low enough? * What are the ethical issues surrounding the use of vaccines and monoclonal antibodies?

Answer 254

As size increases, surface area to volume ratio decreases.

Answer 255

Surface area (for regular shapes: side length x side width x number of sides) divided by volume (length x width x depth)

Answer 256

Metabolic rate is the amount of energy used up by an organism within a given period of time. It is often measured by oxygen uptake because oxygen is used in aerobic respiration to make ATP for energy release.

Answer 257

They have a large surface area to volume ratio, so they can absorb any substances required. They have a short diffusion distance between the outside of the organism to the centre of it, so they can quickly absorb substances from the environment. An advantage of this is that they can exchange materials with their environment. A disadvantage is that they lose heat energy and water quickly, so they can not survive extreme temperatures

Answer 258

They have a small surface area to volume ratio so can not absorb enough substances through small outer surface to support large volume. They have a large diffusion distance between the outside and the centre of the organism so diffusion through outer surface is too slow to supply cells efficiently. An advantage of this is that they lose less heat energy, so can survive in cold environments. A disadvantage is that they often need internal mass transport systems in order to supply the body with vital substances.

Answer 259

Organisms with a larger surface area to volume ratio (smaller organisms) have a higher metabolic rate as they lose heat more easily. Therefore, more energy and a higher metabolic rate is required to maintain a constant internal temperature. Per unit of body mass, metabolic rate is higher in small organisms.

Answer 260

* Behavioural: Small mammals with a large surface area to volume ratio will lose heat easily so they need to eat high energy foods such as nuts and seeds to help maintain body temperature. They may also hibernate during winter. * Physical: Adapted animals will have a compact body shape, giving a smaller surface area to volume ratio. Small mammals with larger surface area to volume ratio may have thick layers of fur to insulate and reduce heat loss.

Answer 261

* Behavioural: Large organisms such as hippos spend much of the day in water to help lose heat. Some other organisms may be nocturnal so that they are only active in cold temperatures (at night). * Physical: Large organisms with low surface area to volume ratio often have large ears which increase their surface area allowing them to lose more heat.

Answer 262

* Behavioural: Organisms may be nocturnal so that they are most active in cooler temperatures, reducing the need for cooling by evaporative water loss (sweating), therefore conserving water. * Physical: Small mammals with a high surface area to volume ratio have structural kidney adaptations so that they produce less urine to conserve water.

Answer 263

It is waterproof to prevent water loss by evaporation, and transparent to allow light to pass through.

Answer 264

It protects the leaf and is 1 cell thick to allow the light to pass through

Answer 265

It is a layer of cells containing large amounts of chloroplasts for photosynthesis.

Answer 266

It has air spaces which increases the surface area for gas exchange. The cells within the spongy mesophyll also contain lots of chloroplasts.

Answer 267

Transports water from the roots up the plant to the leaves.

Answer 268

Transports nutrients, sugars and respiratory products up and down the plant

Answer 269

Gases enter and exit via the stoma, which opens and closes

Answer 270

Stomata control how much water leaves the plant by transpiration. If there is a higher water potential outside than there is inside the cell, water will move in via osmosis, and if there is a lower water potential outside than inside , water will move via osmosis. When plants have enough water, guard cells are turgid which keeps the pores open, and when plants don't have enough water, guard cells become flaccid causing the pores to close.

Answer 271

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Answer 272

Air enters the trachea through pores on the surface of the exoskeleton called spiracles, which can open and close. Carbon Dioxide and Oxygen will diffuse in and out of the spiracles down the concentration gradient. The tracheae divide into smaller tubes called tracheoles which continue to divide until they branch off into individual body cells. The tracheoles are permeable to allow gas exchange

Answer 273

* Tracheoles have thin walls, so short diffusion distance to cells * High numbers of highly branched tracheoles, so larger surface area for gas exchange * Rhythmic contraction of abdominal muscles changes pressure in body, causing air to move in / out, maintaining concentration gradient for diffusion * Fluid in end of tracheoles drawn into tissues by osmosis during exercise increases rate of diffusion * Spiracles can open and close to maintain the concentration gradient

Answer 274

By contracting muscles between each body segment, the insect can compress the trachea and therefore pump gases in and out of its body.

Answer 275

Each gill is made of lots of thin gill filaments which are attached to a bony gill arch. The gill filaments a covered in small, thin folds called lamellae, which have lots of blood capillaries and a thin layer of cells.

Answer 276

* Blood and water flow over the lamellae in opposite directions * So blood is always flowing next to water that has a higher oxygen concentration * So maintains a concentration gradient of oxygen between water and blood * For diffusion happens along whole length of lamellae

Answer 277

* Gills made of many filaments covered with many lamellae, increasing surface area for diffusion * Thin lamellae wall / epithelium, so short diffusion distance between water and blood * Lamellae have a large number of capillaries which remove O2 and bring CO2 quickly so maintains concentration gradient * Counter current flow system to maintain concentration gradient across the full length of the gill lamellae.

Answer 278

They have many stomata , resulting in a large surface area for gas exchange. The spongy mesophyll contains air spaces, allowing a large surface area for gases to diffuse through. The leaves are thin, resulting in a short diffusion distance

Answer 279

* Leaves are spikes and therefore have a small surface area, reducing evaporation rate * Sunken stomata trap water to maintain maintain humid air around the stomata to reduce the water potential gradient * Stomatal hairs trap water to maintain maintain humid air around the stomata to reduce the water potential gradient * Extensive root systems maximise water uptake. Some xerophytes have wide, shallow roots to collect rainwater, and other have deep roots to collect groundwater * Reduced amount of stomata, reducing the amount of places water can evaporate from * Thicker waxy cuticle to waterproof leaves and stem to reduce evaporation

Answer 280

The Trachea spits into Bronchi, when then split into smaller Bronchioles. At the end of each Bronchiole is an Alveolus, surrounded by a capillary network

Answer 281

* 1 cell thick → short diffusion distance * Folded → large surface area * Permeable → allows diffusion of gases * Moist → gases can dissolve for diffusion * Good blood supply from large network of capillaries → maintains large concentration gradient

Answer 282

Oxygen diffuses from the alveoli, across the alveolar epithelium and the capillary endothelium into blood down its concentration gradient. Carbon dioxide diffuses from the blood, across the capillary endothelium and the alveolar epithelium into the alveoli down its concentration gradient.

Answer 283

Brings in air containing higher concentration of oxygen and removes air with lower concentration of oxygen, maintaining concentration gradients

Answer 284

1. Diaphragm muscles contract and the diaphragm therefore flattens 2. External intercostal muscles contract, and the internal intercostal muscles relax, so the ribcage is pulled up and out 3. This increases volume and decreases pressure in thoracic cavity 4. Air moves into lungs down pressure gradient

Answer 285

1. Diaphragm muscles relax and the diaphragm therefore moves upwards 2. External intercostal muscles relax, and the internal intercostal muscles contract, so the ribcage moves down and in 3. This decreases volume and increases pressure in thoracic cavity 4. Air moves out of lungs down pressure gradient

Answer 286

Internal intercostal muscles do not normally need to contract, and expiration is aided by elastic recoil in alveoli

Answer 287

* Thickened alveolar tissue (eg. fibrosis) → increases diffusion distance * Alveolar wall breakdown → reduces surface area * Reduced lung elasticity → lungs expand / recoil less → reduces concentration gradients of O2 / CO2

Answer 288

* Some lung diseases reduce lung elasticity (eg. fibrosis which is a build-up of scar tissue) → lungs expand / recoil less. This reduces volume of air in each breath (tidal volume) and also reduces the maximum volume of air breathed out in one breath (forced vital capacity) * Some lung diseases narrow airways or reduce airflow in & out of lungs (e.g. asthma, which is inflamed bronchi) Therefore, reduces maximum volume of air breathed out in 1 second (forced expiratory volume) * Some lung diseases reduce rate of gas exchange, resulting in increased ventilation rate to compensate for reduced oxygen in blood

Answer 289

Cells receive less oxygen, so the rate of aerobic respiration is reduced and less ATP made

Answer 290

Large insoluble biological molecules are hydrolysed into smaller soluble molecules that are small enough be absorbed across cell membranes into the blood

Answer 291

* Amylase (produced by salivary glands and pancreas) hydrolyses starch into maltose * Membrane-bound maltase (attached to cells lining ileum) hydrolyses maltose to glucose * Hydrolysis of glycosidic bond

Answer 292

* Bile salts (produced by liver) emulsify lipids causing them to form smaller lipid droplets * This increases surface area of lipids for increased hydrolysis * Lipase (made in pancreas) hydrolyses lipids into monoglycerides and fatty acids by hydrolysing the ester bonds

Answer 293

* Endopeptidases hydrolyse internal peptide bonds within the polypeptide chain. This results in the polypeptide chains being broken into shorter chains, so there are therefore more terminal ends for exopeptidases * Exopeptidases hydrolyse peptides bonds at the terminal ends of the polypeptide chains, releasing singular amino acids * Membrane bound dipeptidases hydrolyse the peptide bond between dipeptides, releasing 2 amino acids

Answer 294

Membrane bound enzymes are located on the cell membrane of the epithelial cells lining the ileum. By hydrolysing molecules at the site of absorption, they maintain concentration gradients for higher absorption rates

Answer 295

1. Sodium ions are actively transported from the epithelial cells lining ileum to blood, establishing a concentration gradient of Sodium ions, as the concentration is now higher in lumen than the epithelial cell 2. Sodium ions enter the epithelial cell down its concentration gradient with co-transported glucose or amino acids. This occurs via a co-transporter protein. This establishes a concentration gradient of Glucose or Amino Acids, as the concentration is higher in the epithelial cell than in the blood 3. The Glucose or Amino Acids move down the concentration gradient into blood via facilitated diffusion

Answer 296

* Micelles carry bile salts, monoglycerides and fatty acids to the epithelial cells of the ilium and breakdown, allowing monoglycerides and fatty acids to diffuse across membrane because they are lipid-soluble. * The monoglycerides and fatty acids are transported to the Endoplasmic Reticulum where they recombine to form triglycerides again. * Inside the Golgi, the triglycerides bind with cholesterol and proteins to form chylomicrons. * Chylomicrons travel in a vesicle to the cell membrane and leave the epithelial cell via exocytosis. * The Chylomicrons enter lymphatic capillaries called lacteals which transport them away from the small intestine to tissues around the body, where the triglycerides can be hydrolysed and the fatty acids are used by the tissues.

Answer 297

* Red blood cells contain lots of haemoglobin, which binds with Oxygen at gas exchange surfaces where partial pressure of Oxygen is high * This forms oxyhaemoglobin which transports Oxygen (each haemoglobin protein can carry 4 oxygen molecules as it has 4 haem groups * The haemoglobin unloads the oxygen near cells and tissues where the partial pressure of oxygen is low, so that the cells and tissues can respire

Answer 298

Haemoglobin is a protein with a quaternary structure. It is made up of 4 polypeptide chains, and each chain contains a Haem group containing an iron ion

Answer 299

When each Oxygen molecule binds, the tertiary structure of the Haemoglobin changes, exposing more Haem group binding sites, meaning it is easier for Oxygen to bind to the Haemoglobin

Answer 300

* At lower partial pressures of oxygen, as oxygen increases there is a slow increase in % saturation of Haemoglobin with oxygen * At higher partial pressures of oxygen, as oxygen partial pressure increases, there is a faster increase in % oxygen saturation of Haemoglobin, showing it has become easier for oxygen molecules to bind

Answer 301

* Partial pressure of Oxygen * Haemoglobin saturation * Partial pressure of Carbon Dioxide

Answer 302

An increase in blood carbon dioxide levels due to increased rate of respiration results in the formation of Carbonic Acid, lowering the pH of the blood. This changes the tertiary structure of the Haemoglobin, meaning the Oxygen is unloaded more easily at any given partial pressure of oxygen.

Answer 303

Oxygen is unloaded more quickly, meaning that the respiring tissues have access to more oxygen so they can aerobically respire at a faster rate. Therefore, more ATP is produced.

Answer 304

Different types of Haemoglobin are made up of polypeptide chains with different amino acid sequences, resulting in different tertiary structures, and therefore different affinities for oxygen

Answer 305

* Left shift - Oxygen with bind with Haemoglobin at a lower partial pressure. For example, organisms in high altitude or underground environments and foetuses * Right shift - Oxygen will dissociate from haemoglobin more easily. For example, organisms with high metabolic rate such as small mammals with a larger SA:V ratio, so will lose heat more easily)

Answer 306

Closed double circulatory system

Answer 307

* Deoxygenated blood in right side of heart is pumped to the lungs, and the oxygenated blood returns to left side * Oxygenated blood in left side of heart pumped to rest of body and the deoxygenated blood returns to right side

Answer 308

* Prevents mixing of oxygenated / deoxygenated blood, so blood pumped around the body is fully saturated with oxygen for aerobic respiration * Blood can be pumped to body at a higher pressure, so oxygen can reach the body cells more efficiently

Answer 309

* Vena cava – Transports deoxygenated blood from the respiring body cells to the heart * Pulmonary artery - Transports deoxygenated blood from the heart to the lungs * Pulmonary vein – Transports oxygenated blood from the lungs to the heart * Aorta – Transports oxygenated blood from heart to the respiring body cells

Answer 310

The coronary arteries

Answer 311

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Answer 312

The left side has thicker muscle to contract with greater force, so it can generate higher pressure to pump blood around entire body

Answer 313

* Atrial systole - The atria contract, so the volume decreases, increasing the pressure. The atrioventricular valves open when the pressure in the atria exceeds the pressure in the ventricles, so the blood is pushed into the ventricles * Ventricular systole - The ventricles contract, so the volume decreases, increasing the pressure. The semilunar valves open when the pressure in the ventricles exceed the pressure in the arteries, so blood is pushed into the arteries * Diastole - The atria and ventricles relax, so the volume increases, so the pressure decreases. The semi-lunar valves shut when the pressure in the arteries exceeds the pressure in the ventricles, so the blood enters the atria.

Answer 314

* Semi-lunar valves close when the pressure in the artery is higher than the pressure in the ventricles * Semi-lunar valves open when the pressure in the ventricle is higher than the pressure in the artery * Atrioventricular valves close when the pressure in the ventricle is higher than the pressure in the atrium * Atrioventricular valves open when the pressure in the atrium is higher than the pressure in the ventricle

Answer 315

Cardiac output (volume of blood pumped out of heart per minute) = stroke volume (volume of blood pumped in each heart beat) x heart rate (number of beats per minute)

Answer 316

Heart rate (beats per minute) = 60 (seconds) / length of one cardiac cycle (seconds)

Answer 317

Their function is to carry blood away from the heart at high pressures. Adaptations include: * Thick muscular walls - can withstand high pressure, muscles can contract and relax to control blood flow * Narrow lumen - maintains high pressure

Answer 318

Their function is to carry blood towards the heart at lower pressures. Adaptations include: * Wide lumen - Maintains blood flow * Valves - To prevent backflow of blood

Answer 319

Their function is to allow efficient exchange of substances between blood and tissue fluid . Adaptations include: * Walls are one cell thick - reduces diffusion distance * Capillary bed is a large network - increases surface area for diffusion

Answer 320

At the arteriole end of capillaries, there is a higher hydrostatic pressure inside the capillaries than outside the capillaries. This forces water and dissolved substances out of the capillaries into the surrounding tissues, and large plasma proteins remain in the capillary

Answer 321

The water potential outside the capillary is higher than the water potential inside the capillary. Therefore, water enters the capillary via osmosis down a water potential gradient. Excess fluid enters the lymphatic system to become lymph, containing lymphocytes

Answer 322

* Low concentration of protein in blood plasma or high salt concentration will result in higher water potential, so the water potential gradient is reduced. This will mean more tissue fluid will be formed at arteriole end and less water absorbed at venule end by osmosis * High blood pressure will result in high hydrostatic pressure. Therefore more tissue fluid will form at arteriole end and less water will be absorbed at venule end by osmosis

Answer 323

A risk factor is an aspect of a person's lifestyle, body or environment which has been shown to increase their likelihood of getting a certain disease. Examples for cardiovascular disease include age, salt and fat concentration in diet, smoking, lack of exercise

Answer 324

Transports water and mineral ions up the stem to the leaves

Answer 325

* Cells are joined together with no end walls, forming a long continuous tube, so water can flow as a continuous column * Made up of dead cells which contain no cytoplasm or nucleus, allowing for easier water flow * Thick walls made of lignin which provides support and allows the xylem to withstand tension * Pits in side walls → allow lateral flow of water

Answer 326

Water evaporates from the mesophyll due to heat from the sun (Transpiration). This results in the cells having a negative water potential, causing more water to diffuse in through osmosis. This increase in water tension pulls more water into the leaf (transpiration pull). Water molecules are cohesive due to the fact they form Hydrogen bonds, so when some are pulled into the leaf, others follow. This along with adhesion of the water molecules to the xylem pulls the whole column of water in the xylem up from the roots to the mesophyll tissue, and water enters the stem through the roots via osmosis.

Answer 327

* If a trunk or stem is damaged and a xylem cell is broken, water does not leak out. Once air enters, the tree can no longer draw up water because the continuous column of water has been broken * The trunks of trees reduce in diameter during the daytime when transpiration is at its greatest rate. This is because adhesion of water molecules to the walls of the xylem results in tension, pulling the xylem walls in.

Answer 328

* Light Intensity - As light intensity increases, the rate of photosynthesis increases. This means that the stomata open to allow CO2 for photosynthesis to enter. This also results in more water being lost. * Temperature - As temperature increases, the kinetic energy of the water molecules increases. This results in the water evaporating at a faster rate * Wind intensity - As wind intensity increases, wind blows water molecules away from the stomata, increasing the water potential gradient, so water evaporates at a faster rate * Humidity - At higher humidity levels, there is more water in the air, so there is a lower water potential gradient between the leaf and the air, so water evaporates at a slower rate

Answer 329

Transports products of photosynthesis in plants

Answer 330

The sieve tubes have no nucleus and very few organelles, to maximise space for easier flow of substances. The end walls between the phloem cells are perforated to allow substances to pass between the individual cells. The companion cells contain many mitochondria, to allow a high rate of respiration to make ATP for active transport of substances

Answer 331

The movement of solutes such as sucrose from sources to sinks

Answer 332

At the source, sucrose is actively transported into the phloem cells by the companion cells. This lowers water potential in the phloem cells, so water enters laterally from the xylem via osmosis. This increases the hydrostatic pressure in phloem, creating a hydrostatic pressure gradient. So mass flow occurs, as the solute moves from the source to the sink. At the sink, sucrose is removed by active transport to be used by respiring cells or stored in storage organs

Answer 333

Hydrogen ions are actively transported out of the companion cell into the cells of the source tissue using the hydrolysis of ATP. This creates a hydrogen concentration gradient across the companion cell membrane. This means that the Hydrogen ions diffuse down the gradient through co-transporters, and they bring a co-transported sucrose molecule with them. This increases the concentration of sucrose in the companion cells, so the sucrose diffuses into the phloem cell

Answer 334

When sieve tubes are cut, sap is released. This demonstrates that the sap is under pressure within the phloem

Answer 335

Sucrose travels to many different sinks and does not always travel to the one with the highest water potential first, which it should according to the mass flow hypothesis

Answer 336

* Nucleotide structure is identical - deoxyribose attached to phosphate and a base * Adjacent nucleotides joined by phosphodiester bonds and complementary bases joined by hydrogen bonds

Answer 337

* Eukaryotic DNA is longer * Eukaryotic DNA is linear, prokaryotic DNA is circular * Eukaryotic DNA is associated with histone proteins, prokaryotic DNA is not * Eukaryotic DNA contain introns, prokaryotic DNA does not

Answer 338

Long, linear DNA and its associated histone proteins, found in the nucleus of eukaryotic cell

Answer 339

A sequence of DNA bases that codes for a amino acid sequence of a polypeptide or a functional RNA (e.g. ribosomal RNA or tRNA)

Answer 340

Fixed position a gene occupies on a particular DNA molecule.

Answer 341

* Universal: The same base triplets code for the same amino acids in all organisms * Non-overlapping: Each base is part of only one triplet so each triplet is read as a discrete unit * Degenerate: An amino acid can be coded for by more than one base triplet

Answer 342

Because each amino acid is coded for by 3 DNA bases

Answer 343

Exon: Base sequence of a gene coding for amino acid sequences (in a polypeptide) Intron: Base sequence of a gene that doesn’t code for amino acids, in eukaryotic cells

Answer 344

The complete set of genes in a cell

Answer 345

The full range of proteins that a cell can produce, coded for by the cell’s DNA

Answer 346

* Transcription: Production of messenger RNA from DNA, happens in the nucleus * Translation: Production of polypeptides from the sequence of codons carried by mRNA, happens at ribosomes

Answer 347

* tRNA is folded into a ‘clover leaf shape’, whereas mRNA is linear / straight * tRNA has hydrogen bonds between paired bases, mRNA doesn’t * tRNA is a shorter, fixed length, whereas mRNA is a longer, variable length (more nucleotides) * tRNA has an anticodon, mRNA has codons * tRNA has an amino acid binding site, mRNA doesn’t

Answer 348

1. Hydrogen bonds between DNA bases break, catalysed by DNA Helicase 2. One DNA strand acts as a template 3. Free RNA nucleotides align next to their complementary bases on the template strand. In RNA, uracil is used in place of thymine (pairing with adenine in DNA) 4. RNA polymerase joins adjacent RNA nucleotides 5. This forms phosphodiester bonds via condensation reactions 6. Pre-mRNA is formed and this is spliced to remove introns, forming mRNA

Answer 349

1. mRNA attaches to a ribosome and the ribosome moves to a start codon (AUG) 2. tRNA brings a specific amino acid 3. tRNA anticodon binds to complementary mRNA codon 4. Ribosome moves along to next codon and another tRNA binds so 2 amino acids can be joined by a condensation reaction forming a peptide bond. Using energy from hydrolysis of ATP 5. tRNA released after amino acid joined polypeptide 6. Ribosome moves along mRNA to form the polypeptide, until a stop codon is reached

Answer 350

* ATP: Hydrolysis of ATP to ADP + Pi releases energy, so amino acids join to tRNAs and peptide bonds form between amino acids * tRNA: Attaches to and transports specific amino acids in relation to its anticodon. tRNA anticodon complementary base pairs to mRNA codon, forming hydrogen bonds. 2 tRNAs bring amino acids together so peptide bond can form. * Ribosomes: mRNA binds to ribosome, with space for 2 codons. Allows tRNA with anticodons to bind and catalyses formation of peptide bond between amino acids. It then moves along to the next codon

Answer 351

A change in the base sequence of DNA, can occur spontaneously during DNA replication in interphase

Answer 352

A factor that increases rate of gene mutation, e.g. ultraviolet (UV) light or alpha particles.

Answer 353

1. Changes sequence of base triplets in DNA (in a gene) so changes sequence of codons on mRNA 2. So changes sequence of amino acids in the polypeptide 3. So changes position of hydrogen / ionic / disulphide bonds (between amino acids) 4. So changes protein tertiary structure (shape) of protein 5. Enzymes - active site changes shape so substrate can’t bind, enzyme-substrate complex can’t form

Answer 354

1. DNA base is replaced by a different base 2. This changes one triplet so changes one mRNA codon. 3. So one amino acid in the polypeptide chain changes. Tertiary structure may change if position of hydrogen/ionic/disulphide bonds change.

Answer 355

1. One nucleotide / base removed or added from DNA sequence 2. Changes sequence of DNA triplets from point of mutation (frameshift) 3. Changes sequence of mRNA codons after point of mutation 4. Changes sequence of amino acids in primary structure of polypeptide 5. Changes position of hydrogen / ionic / disulphide bonds in tertiary structure of protein 6. Changes tertiary structure / shape of protein

Answer 356

Diploid cells have 2 complete sets of chromosomes, and Haploid cells have a single set of unpaired chromosomes

Answer 357

1. Meiosis I separates homologous chromosomes * Chromosomes arrange into homologous pairs * Crossing over between homologous chromosomes * Independent segregation of homologous chromosomes 2. Meiosis II separates sister chromatids, resulting in 4 genetically varied haploid daughter cells

Answer 358

Homologous chromosomes are separated during meiosis I

Answer 359

Alleles are exchanged between chromosomes, creating new combinations of maternal and paternal alleles on chromosomes

Answer 360

Homologous pairs randomly align at equator, so it is random which chromosome from each pair goes into each daughter cell, creating different combinations of maternal & paternal chromosomes in daughter cells

Answer 361

Random fertilisation / fusion of gametes, creating new allele combinations

Answer 362

* Mitosis produces 2 daughter cells, whereas meiosis produces 4 daughter cells, as there is 1 division in mitosis but 2 divisions in meiosis * Mitosis maintains the chromosome number (results in diploid cells) whereas meiosis halves the chromosome number (results in haploid cells). As homologous chromosomes separate in meiosis but not mitosis * Mitosis produces genetically identical daughter cells, whereas meiosis produces genetically varied daughter cells, because crossing over and independent segregation happen in meiosis but not mitosis

Answer 363

The 2 divisions creates haploid gametes, so that the diploid number is restored at fertilisation and the chromosome number is maintained between generations. Also, independent segregation and crossing over creates genetic variation.

Answer 364

Mitosis occurs between stages where chromosome number is maintained, and Meiosis occurs between stages where chromosome number halves

Answer 365

Occurs spontaneously by chromosome non-disjunction during meiosis. Homologous chromosomes (meiosis I) or sister chromatids (meiosis II) fail to separate during meiosis, so some gametes have an extra copy of a particular chromosome and others have none

Answer 366

A group of organisms that can (interbreed to) produce fertile offspring

Answer 367

Different species have different chromosome numbers, so homologous pairs cannot form and meiosis cannot occur to produce gametes for reproduction

Answer 368

It allows recognition of member of the same species, so that fertile offspring is produced

Answer 369

Species are arranged into groups, called taxons, based on their evolutionary origins (common ancestors) and relationships. They use a hierarchy in which smaller groups are placed within larger groups and there is no overlap between groups

Answer 370

Domain, Kingdom, Phylum, Class, Order, Family, Genus, Species

Answer 371

Each species is given a Latin name using the binomial naming system. The name consists of their genus and species. An advantage of this is that it avoids confusion as scientists using different languages can have one universal name for the species

Answer 372

Each branch point represents a common ancestor and each branch represents an evolutionary path. Species with a more recent common ancestor are more closely related

Answer 373

Advances in genome sequencing has allowed comparison of DNA base sequences. The more differences in DNA base sequences there are, the more distantly related the organisms are and the earlier their common ancestor is because mutations build up over time

Answer 374

A measure of the variety of living organisms

Answer 375

All populations of different species that live in an area.

Answer 376

A measure of the number of different species in a community

Answer 377

Describes the relationship between: The number of species in a community (species richness) and the number of individuals in each species (population size)

Answer 378

Index of diversity also takes into account number of individuals in each species, so takes into account that some species may be present in small or large numbers

Answer 379

1. Calculate the total number of organisms (N) 2. Multiply N by (N - 1) 3. For each species, multiply the number of organisms (n) by (n - 1) 4. Add up all the values of n(n - 1) to get Σn(n - 1) 5. Divide N(N - 1) by Σn(n - 1)

Answer 380

* High - There are many species present and each species is evenly represented * Low - The community is dominated by one or a few species

Answer 381

* Deforestation and removal of hedgerows, monoculture (growing one type of crop) and use of herbicides reduces the variety of plants, so there are less habitats and less variety in food sources. * Use of pesticides means that the predator population of the pest will also decrease as they have less food

Answer 382

Conservation is required to increase biodiversity, but when implemented, yield can be reduced, decreasing profit and income for farmers. To offset loss, financial incentives and grants are offered.

Answer 383

* Reintroduction of hedgerows * Reduce use of pesticides

Answer 384

* Comparing frequency of measurable or observable characteristics * Comparing base sequence of DNA * Comparing base sequence of mRNA * Comparing amino acid sequence of a specific protein encoded by DNA and mRNA

Answer 385

The more differences in the sequence, the more distantly related the organisms are and the earlier their common ancestor is, as mutations build up over time. The more mutations there are, the more changes there are in the amino acid sequence

Answer 386

* Collect data from random samples (use a random number generator) → removes bias * Use large sample size to ensure sample is representative of whole population * Ethical sampling → must not harm organisms * Calculate a mean value of collected data and standard deviation of that mean * Interpret mean values and their standard deviations. If standard deviations overlap, the difference is not statistically significant * Use statistical tests → analyse whether there is a significant difference between populations

Answer 387

In Eukaryotic Cells, the pre-mRNA undergoes splicing to remove introns, whereas in Prokaryotic Cells the mRNA is produced directly, so no splicing occurs because prokaryotic DNA contains no introns

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