Biology: Chapter 4: Cell surface membrane: Fluid mosaic structure, it's components and function

Biology: Chapter 4: Cell surface membrane: Fluid mosaic structure, it's components and function

Phospholipids

Phospholipid

• Phospholipids are lipid molecules that consist of a polar head (hydrophilic) and non-polar tail (hydrophobic) because one of the fatty acid groups is replaced with a phosphate group, making the head polar. 
• This means in water or solutions, the water-loving phospholipid heads will be in the liquid whereas the non-polar hydrophobic tails will avoid water or liquid, and are either on the surface of the water (monolayer) or point towards each other, forming a layer. 
• Micelle: Ball-like structure formed by phospholipids, where the polar heads are on the exterior, shielding the hydrophobic tails which point in towards each other.
• Bi-layer: Two layered structure - shown in the diagram below. Basic structure of membranes.

• The phospholipid bilayer forms a membrane-bound compartment where chemicals can be isolated from the external environment, and exchange between the cell/organelles and the outside environment (eg. respiration and excretion) can be controlled.

Diagram of liposomes (vesicles), micelle and the bilayer sheet

Cell surface (plasma) membrane.

Structure of membranes

• The phospholipid bi-layer is visible using the electron microscope on a very high magnification (x100,000 -One hundred thousand)
• Around 7 nm thick

Fluid mosaic model

• Fluid: Because phospholipids and proteins can move around by diffusion - Phospholipids mainly move sideways within their own layer (monolayer) , while some proteins can move within the bi-layer. The fluidity of the bilayer is similar to that of olive oil. 
• Mosaic: Pattern of scattered proteins when the membrane is viewed from above.
• Model: Because we cannot magnify a cell enough to see the cell membrane, so we just have a model of what we predict the membrane looks like.

Features of fluid mosaic model

• Double layer (bi-layer) of phospholipids
• Individual phospholipid molecules move around their own mono-layers by diffusion.
• Phospholipid tails point inward, forming non-polar hydrophobic interior
• Phospholipid heads face outwards, into the aqueous (water-containing) medium that surrounds the membranes.
• Some phospholipid tails are saturated and some are unsaturated (eg. cholesterol).
• The more unsaturated they are, the more fluid the membrane is; this is because unsaturated fatty acid tails are bent, and therefore fit together more loosely.
• Tail length also affects fluidity: the longer the tail, the more fluid the membrane is.
• When temperature decreases, membranes become less fluid because there is less kinetic energy.
  Some organisms, such as bacteria and yeasts, who cannot regulate their own body temperature, respond by increasing the proportion of unsaturated fatty acids in their membranes to maintain fluidity.

Unsaturated tails in the phospholipid bi-layer

Fluid mosaic model

Psychology: Development psychology: Transmission of aggression through imitation of aggressive models

Psychology: Development psychology: Transmission of aggression through imitation of aggressive models

Authors: Bandura et al. (1961)

Key term: Aggression

Background/context: Behaviorists believe that all behavior is learned, through classical conditioning (Pavlov - learned through association) and operant conditioning (Skinner - learned through reward and punishment). Watson (1923) classically conditioned 'Little Albert' to be scared of a white rat.

Behaviorists believed that we could only learn things that happened to us personally. But Bandura outlined observational learning - if behavior of a model (parent, teacher, etc) is observed then it will be copied (imitation learning). To test this theory Bandura designed an experiment trying to teach children aggression through observation.

Aim/Hypothesis: Children would reproduce aggressive behavior even if the model was no longer present

1. If a behavior is observed it will be imitated.
2. If a behavior is not observed it cannot be imitated.
3. Boys will copy a male model more than a female model/ Girls will copy a female model more than a male model.
4. Boys are more predisposed to show aggression than girls.

Method: Laboratory experiment - controlled observation 

Variables:

• Independent variables:

1. Three conditions:
   -Aggressive model group - 6 boys and 6 girls with the male model; 6 boys and 6 girls with the female model.
   -Non-aggressive model group - 6 boys and 6 girls with the male model; 6 boys and 6 girls with the female model.
   -Control group - 12 boys and 12 girls who saw no model at all.
2. Sex of model
3. Sex of child

• Dependent variable: Number of behaviors out of 240 maximum in each response category.

Independent variable conditions

Design: Matched pairs - Children were matched for pre-existing aggression levels of aggression, and independent groups as shown in 3 conditions above.

Participants and sampling technique: 

• 72 children (36 boys and 36 girls) aged between 37(just over 3 years) to 69 months (5 years 9 months) from Stanford University nursery school.
• Mean age was 52 months (4 years 4 months)
• Probably opportunity sample
• Quota sampling to achieve 12 participants in each sub-category

Apparatus: 

• Room 1: Potato prints, picture stickers, table and chair, Tinker toy set, mallet and inflatable 5-foot bobo doll (adult-size)
• Room 2: Fire engine, locomotive (train), doll, spinning top
• Room 3: One-way mirror for observations, 3-foot bobo doll, mallet and peg board, two dart guns, tetherball with a face, tea set, 3 bears, cars, farm animals, crayons and coloring paper.

Bobo doll

Controls:

• Children were matched for pre-existing aggression levels by the experimenter and nursery teacher independently rating 51 children on a scale of 0 - 5 (5 being very aggressive). There was very good agreement between the teacher and experimenter (0.89).
   -eg. A child rated as 5 (very aggressive) was matched with another child rated 5 (with one going to the 'aggressive' condition and one going to the 'non-aggressive' condition).
• The toys in room 1, 2 and 3 were always the same and always in the same position when a child entered the room. 
• The actions of the aggressive model was always the same, in the same order and for the same length of time. 
• Observers watching through the two way mirror were unaware of which condition the child was in while observing to prevent bias.
• The 20 minute session was divided into 5 second intervals, giving 240 response 'units'. 
• Observers had a inter-rater reliability rate in the 0.9 range.

Procedure:

1. Each child was shown to room 1. He/She played with the potato prints and stickers to settle in. 
2. The child was taken to the other side of the room where they were shown to either of the two conditions for 10 minutes: aggressive or non aggressive.
    -Aggressive condition: Model would sit on, throw the bobo doll (Verbal aggressive: "throw him in the air") punch in the nose ("sock it on the nose"), hit the bobo doll with the mallet ("hit him down") and kick the bobo doll around the room ("kick him").
    -Non-aggressive condition: Adults assembled toy and did not interact with the bobo doll.
    -Control condition: No adult in the room.
3. Child was then taken to room 2 for Mild aggression arousal (to annoy children and increase aggressive behavior). He/She played with the toys for around 2 minutes before the toys got taken away from the child and he/she was told they were not allowed to play with anymore as they were "the very best toys" and had been reserved for other children.
4. Testing for delayed imitation. Room 3 (test room) contained non-aggressive and aggressive toys (eg. dart guns - aggressive gun play). The experimenter was in the room occupied with paperwork, while two observers watched through a two way mirror. Children were observed playing for the next 20 minutes.

Results:

• Results were in 6 response categories for both female and male children:
  - Imitative physical aggression
  - Imitative verbal aggression
  - Mallet aggression
  - Punches bobo doll
  - Non-imitative aggression
  - Aggressive gun play
• Imitative aggression: Physical and verbal aggression to that modeled in the procedure
• Non-imitative aggression: New aggressive acts not demonstrated by model
• Quantitative data

Results table

• Significant results:
  Male imitative physical aggression with male model: 25.8
  Female imitative verbal aggression with female model: 13.7
  Male mallet aggression with male model: 28.8
  Male Non-imitative aggression with male model: 36.7

Findings:

• Significantly more instances of aggression in the aggressive group than the non aggressive group.
• Boys followed the male model more when it came to physical aggression.
• Girls followed the female model more in verbal aggression.
   This may be because since a young age we are taught that men are meant to be more masculine.
• Children in all groups, boys and girls, showed aggressive gun-play even though this was not observed in Room 1 (exposure) - non-imitative aggression.

Conclusion: Behavior that is observed is likely to be imitated - Bandura's 'observational learning' theory is supported. 

Strengths:

• Laboratory experiment - High levels of control - Reliable, can be redone, EVs rare
   -Same toys in the same position for each child
   -Models did the same procedure for each condition for each child
   -All variables besides conditions in the IV controlled
   -Observers did not know which condition they were recording results for, so no bias.
•  -Standardized procedure, can be repeated again to test for reliability of results
• Valid - IV directly affects DV - Observation of models determining child's level of aggression
• Quantitative data - Objective, can be analysed
   -Number of responses marked for each response category to show aggression in children clearly shows that the children who experienced the aggressive condition show more aggression.

Weaknesses:

• Laboratory experiment - Lacks mundane realism - Not normal daily life activity
   -Children do not usually sit there and watch adults play without joining in
   -Children and model are strangers
   -Child and model do not interact
• Quantitative data - We don't know why the children chose to be aggressive
• Snapshot study - Results recorded immediately after experiment, which was also a single experiment - can one experience cause long term effects?

Ethics: 

• Use of children in experiments is unethical because they cannot give consent
• This experiment could have left long term psychological damage on the children
• Children left the experiment psychologically different then before the experiment

Psychology: Social psychology: Case Study 4: Experiments in intergroup discrimination

Psychology: Social psychology: Case Study 4: Experiments in intergroup discrimination

Author: Tajfel (1970)

Key term: Intergroup discrimination

Background: Tajfel believes that we as people categorize everything - including other people. As children, we decide who we like and don't like, putting things into an order that is easier and simpler to understand and deal with. We categorize people into 'us' and 'them', 'we' and 'they' - an 'in-group' and 'out-group'. The implication of this prejudice is we develop a 'generic norm of behavior' - a way of behaving in society and toward other people, favoring people in our in-group (anything can create an in-group; race, age, gender, likes, dislikes, etc) and discriminating against those in the out-group.

Prejudice - Forming an opinion before knowing the facts 

Aim/hypothesis: 

• Study 1: Test the theory that in-group favoritism and out-group discrimination will be shown even in the categorization into minimal groups (over and under estimating number of dots)- will just merely being in different groups cause discrimination?
• Study 2: Validate study 1 using a different criteria for minimal groups (artistic preference)

Method: Laboratory experiment

Variables:

• Independent variables:
  Study 1: Two conditions -
   Groups 'over-estimators of dots' and 'under-estimators of dots'  For half the boys, they were told some boys were more accurate at estimating than others.
  Study 2: Two conditions - groups 'preference for Klee' and 'preference for Kandinsky' (artists)
  However... The boys only thought they were sorted into these two groups - but each boy is in both in-group and out-group.
• Dependent variables: Choice of points made by the boys on each matrix.

Design: Repeated measures - Each boy is in both the in-group and out-group, although they were deceived into thinking that they were in different groups depending on their estimation of dots and preference of Klee and Kandinsky.

Participants/ Sampling technique:

• Study 1: 64 boys aged 14-15 from a comprehensive school in Bristol, UK. All the boys were in the same house and knew each other.
• Study 2: 3 new groups, 16 boys in each group from the same school as Study 1 - 68 boys in total, but only 48 boys did the experiment in the end.
• Probably opportunity sampling because boys were from the same school 

Experimenters: Unknown - probably Tajfel himself.

Apparatus:

• Study 1: Booklet with 18 matrices; 6 different matrices for 3 variables: ingroup choice (ingroup-ingroup), outgroup choice (outgroup-outgroup) and intergroup choice (ingroup-outgroup). In-group was always on the top row.

Example of a matrix used in study 1. 

• Study 2: 12 slides - 6 pictures by the artist Klee, 6 pictures by the artist Kandinsky. Booklet with 4 different matrices for the same 3 variables. One major difference was these matrices were employed to allow experimenters to investigate these three variables;
   Maximum joint profit (giving the largest reward to both groups)
   Largest possible reward to ingroup (largest reward to boy of their group regardless of the reward to outgroup)
   Maximum difference (largest difference in points in favour to the ingroup)
  The outgroup was also the top row in some of the matrices.

Eg. of matrix in booklet for study 2

Example of the variables that experimenters could investigate in the matrices in study 2

No box allows equal marks to be given - the marker has to favour one or the other boy.
Matrices are scored on a scale of 1-14.
Matrices consist of 13 boxes.

Each point was worth 1/10 of a 

Controls:

• All the boys received the same instructions.
• All boys completed the booklet separately in individual cubicles - no conformity or copying.
• Boys did not know who they were allocating rewards to, each boy was given a code name - prevent bias
• Boys could not allocate points to themselves - prevent bias
• In Study 2 signatures of Klee and Kandinsky were removed from the paintings shown to the boys so they would not know they were randomly allocated.
• Study 2 allows investigation of max. diff., max joint profit and max. profit - elimination of EVs
• Some matrices in Study 2 had the outgroup as the top row - elimination of EVs

Procedure:

• Study 1 - Estimating dots:

1. The 64 boys arrived in the laboratory in groups of 8.
2. They were told the experiment was on 'visual judgement' and shown 40 slides of varying numbers of dots and told to estimate the number of dots.
3. They were then divided into groups of  'over-estimators' and 'under-estimators' but the groups were actually randomly allocated
4. Half of the boys (4 groups of 8) were told some people in the group were 'better as estimating' than others.
5. Each boy was given a booklet of the matrices to complete alone. The boys would choose a column in the matrix with two different points they wished to allocate to two boys.
6. Boys were told each point was worth 1/10 of a penny 

• Study 2 - Aesthetic preference:

1. 68 boys arrived in the laboratory in groups of 16. 
2. They were told the experiment was about 'aesthetic preference for two foreign painters' and shown 12 slides of paintings - 6 by Klee, 6 by Kandinky. Autographs of the painters were removed.
3. The boys completed a booklet of the 12 matrices for Study 2.

Data: Quantitative data - the points boys chose in each matrix were totalled; they were not asked why they allocated those points.

Results:

Study 1: 

• The results were scored on a scale of 1-14, 1 being minimum amount of points possible and 14 being the max. amount of points possible to a fellow ingroup member.
   For the ingroup-ingroup and outgroup-outgroup matrices, the average result was 7.5 out of 14.
• This shows that for same group matrices, the boys gave both boys in the matrix points that were as close as possible to being fair. 
• However, when it came to intergroup choices, the boys allocated more points to their ingroup; the average score was 9 out of 14. This difference is statistically significant.

Study 2: 

• Study 2 was to further investigate the findings in Study 1, the relative weightings given to three variables - max. diff., max. joint profit, and max. in-group profit. 
• The boys did not choose the max. joint profit rewards to both in-group and out-group or maximum in-group profit, despite them all knowing each other. 
• Instead, they chose maximum difference, meaning that although the in-group got less overall, the out-group got less than the in-group. 
• Maximumising the difference between the two groups, even if it meant less profit for the group, was more important than maximum profit.

Findings:

• Study 1: The boys showed in-group favoritism and out-group discrimination even on the basis of 'flimsy and unimportant criteria' (in this study, being an over/under-estimator of dots).
• Study 2: The boys discriminated the out-group, choosing to maximise the difference between the two groups instead of maximum profit on the basis of 'flimsy and unimportant criteria' (in this study, artistic preference)

Conclusion:

• When people are placed in a group based on a similar characteristic they share, no matter what kind of characteristic, they will favor those in their group and there will be discrimination towards people who don't have that characteristic.
• If school boys showed this trait even over a small difference, this proves that bigger differences (race, religion) can cause more inter-group conflict.
• Competition vastly increases inter-group conflict as shown in Sherif's Robbers cave experiment.

Strengths

• Laboratory experiment - High levels of control - Confidence that IV directly affects DV
  Autographs removed from paintings so boys did not know they were randomly assigned into groups
   -Each boy did his experiment individually so there was no copying and bias
   -Boys knew they were not allocating points to themselves
   -Names were not used in the booklets - boys only saw code names, not the real names of the boys they were allocating points to
• Laboratory experiment - High levels of control - Reliable, can be repeated and results should be the same 
• Quantitative data - Easy to analyze and objective - Results show clearly that boys favored the in-group from the points allocated

Weaknesses

• Laboratory experiment - Lacks ecological validity  - A laboratory where boys have to sit in a cubicle and mark matrices is not normal in real life 
• Quantitative data - We don't know why those boys allocated the points the way they did, there could be another reason besides grouping
• Reductionism - This study generalizes the world from a bunch of boys in a school in UK, maybe only teenagers in UK act like this.
  - All the boys knew each other - Strangers may behave differently in the same experiment 

Ethics

• Use of money is considered unethical
• Deception
   -Boys did not know the experiment was on inter-group discrimination - They were told the experiment was on "visual judgement" and "aesthetic preference", and the booklets were on "judgement". This is unethical because the boys were not told the real intention of the experiment.
   

Psychology: Social psychology: Case study: 3: Good Samaritan

Psychology: Social psychology: Case study: 3: Good Samaritan

Authors: Piliavin et al. (1969)

Key term:  Subway Samaritans

Background: In 1964, Kitty Genovese was brutally stabbed and murdered in a neighborhood with apparently approximately 38 witnesses, where no-one called the police or went out to help, causing psychologists to conduct research into this behaviour which later become known as the bystander effect - when individuals do not offer help in the presence of other bystanders; and diffusion of responsibility - the bigger the group, the less likely people are to help.

Aim/Hypothesis: There are four aims to this experiment:

1. Test diffusion of responsibility in a real-life setting.
2. The effect of the type and race of victim on the speed, frequency and race of helper. Would someone who was ill more likely to get help than someone's who was drunk (at their own fault)? Are people more likely to help someone of their own race?
3. Effects of modelling - Are people more likely to help when they see someone else helping?
4. Examine relationship between size of group, frequency and time of helping response.

Method: Field experiment and non-participant, naturalistic observation (conductor of experiment not in the experiment).

Variables: 

• Independent variables:

1. Type of victim (ill/drunk)
2. Race of victim (black/white)
3. Model conditions
   -Critical-early: Model in same carriage as victim, helps 70 seconds after victim falls.
   -Critical-late: Model in same carriage as victim, helps 150 seconds after victim falls.
   -Adjacent-early: Model in adjacent carriage as victim, helps 70 seconds after victim falls.
   -Adjacent-late: Model in adjacent carriage as victim, helps 150 seconds after victim falls. 

• Dependent variables:

1. Frequency of helping
2. Speed of helper
3. Race of helper
4. Gender of helper
5. Comments made by passengers

Design: Independent groups - people on the subway only experienced an ill black trial, ill white trial, drunk black trial or drunk white trial. 

Setting: 

• New York City 
• 7 1/2 minute train journey 
• IND (independent line) from 59th street station to 125th street station.

Experimenters: Students from Columbia University. 

4 teams of 4; 1 male victim, 1 male model, 2 female observers. In total; 

• 4 male victims (1 black and 3 white, aged 26-35)
• 4 male models (all white, aged 24-29) 
• 8 female observers. 

Participants/ Sampling technique: 

• 4450 men and women traveling between 11am and 3pm. 
• Unaware they were in an experiment. 
• 45% black and 55% white. 
• Sample was self-selecting because it consisted of participants who were on the train at that time.

Apparatus: 

• Subway train (old model which observers could sit in the same place each time) which only had 13 seats. 
• All victims dressed in Eisenhower jackets and old slacks (no tie). 
• Victim in ill condition: black cane
• Victim in drunk condition: smelled of alcohol, had a liquor bottle in a brown bag. 

Controls:

• Same 7 1/2 train journey for all trials
• Victims wore same clothes and fell over at the same time (after 70 seconds) in the same place and the same way.
• Started the journey in the same place (observer 1 in adjacent carriage near exit, observer 2 in adjacent carriage in far corner.

Procedure

1. Members of the team of four position themselves in the specific locations on the train.
2. Subway leaves the station, 70 seconds later, victim (black/white and ill/drunk) staggers forward, collapses and remains on the floor, staring at the ceiling of the carriage.
3. If no one helps, the model intervenes. One of the four model conditions used (above in independent variables).
4. Observer 1 records: Gender, race and location of passengers (seated or standing) in critical carriage, total number of passengers, total number who went to help.
   Observer 2 records: Gender, race and location of passengers in adjacent area, time taken for first passenger to help, time taken for someone to help the model.
   Both observers record comments by passengers sitting next to them. 
5. If no one helps, the model helps the victim to his feet. At the next station the team of four get off the train, cross over and repeat procedure on the train going in the opposite direction. 6-8 trials completed in a day.

Data:

• Quantitative data: Demographic characteristics (gender, race), frequency of helping, speed of helping, etc.
• Qualitative data: Comments made by passengers

Findings:`

• 43 people present in each carriage
• Total 103 trials
• 78% of victims received spontaneous help
• Ill victim: Spontaneous help on 62 out of 63 trials - model only helped 3 times. Median helping time was 5 seconds.
• Drunk victim: Spontaneous help on 19 out of 38 trials. Median helping time was 109 seconds.
• When spontaneous help was given, on 60% of the 81 trials two, three or more helpers joined. No difference between black or white, ill or white victim. If one person helped others join.
• 60% of first helpers in critical area were male; 90% of people helping were male 
• No significant difference in race of helpers - 64% of first helpers white.
• Same race helping:
  When victim was white, 68% of first helpers were white; when victim was black, only 50% of first helpers were white - Tendency for same race helping
  Ill condition - no difference in race of helpers.
  Drunken condition - mainly members of the same race
• People left the critical area only 20% of the time - 34 people; more people left when the victim was drunk than ill.
• Most comments happened during drunk trials - especially when no one helped after 70 seconds.
  - May be due to discomfort of not helping, needing to justify inaction eg. "It's for men to help", "I'm not strong enough".

No diffusion of responsibility - In this study, helping was faster when there were more people.

• Victim and witnesses were face to face; unlike laboratory experiments. 

Conclusion

• Individuals who appear to be ill receive more help than a drunk person.
• Men are more likely to help than women - however, this could be a weakness of generalization, because in 1969, gender roles were different; women were still not seen as completely equal to men.
• Same-race helping is more likely, especially when victim is drunk.
• No strong relationship between number of bystanders and speed of helping - expected diffusion of responsibility not observed.
• The longer the emergency continues without help, the less impact a model has, and people are more likely to leave the immediate area.

Study results

Model of response in emergency situations

• Observing any emergency situation causes arousal in a bystander.
• Arousal: Unpleasant feeling (eg. sympathy, fear) that a bystander feels a need to reduce. Arousal can be higher if witness can relate to victim (eg. same race), the bigger the emergency, and the longer the situation continues.
• Arousal can be reduced by helping, going to get help, leaving the scene or concluding the victim doesn't deserve help.

Cost-reward matrix

• Determines response - People weigh up the costs and benefits before making a decision to help.
• Costs of helping - eg. possible physical harm
• Benefits of helping - eg. social approval 
• Benefits of not helping - eg. getting to work on time

Strengths

• Ecological validity - Could happen in real life.
• Behaviour is valid - Passengers did not know they were in an experiment, so behaviour is natural, although this is unethical, because passengers are deceived and there is no informed consent.

Weaknesses

• IV may not be affecting the DV - Situational variables are difficult to control in a field experiment, and it could be an EV affecting the DV - Eg. Positioning of people in carriage could not be controlled, so some people may not have noticed the incident, which could affect the level of helping.
• Unethical - Participants did not know they were in a study - no informed consent and deception.

Biology: Chapter 3: Enzymes: Immobilizing enzymes

Biology: Chapter 3: Enzymes: Immobilizing enzymes

• Immobilized enzyme: Enzymes attached to an inert, insoluble molecule so they do not get mixed in the solution of substrates and product, which is cost-effective because enzymes are not wasted.
• Using immobilized enzymes means you can re-use the enzymes while the product is enzyme free.

Lactase

1. Lactase is mixed with sodium alginate.
2. Droplets of this mixture is added to a solution of calcium chloride.
3. Each droplet instantly reacts with the calcium chloride to form a jelly bead, containing the enzyme.
4. These beads can be packed into a column, where milk, containing Lactases' substrate, lactose, is poured over them. 
5. Lactase in the alginate beads convert the lactose into glucose and galactose, and trickles down the column, where it can be collected as lactose-free milk.

• This is necessary for producing lactose-free dairy products for people who are lactose-intolerant. Without immobilizing the lactase, the milk would be contaminated with lactase, which we also will be unable to re-use. 
• Another advantage of immobilization is that immobilized enzymes are more tolerant of different pH and temperature changes, because their molecules are held more firmly in place by the alginate they are embedded in and less exposed to the external environment, which means they are less likely to denature.

English lang weekly writing #3

Review of Oryx and Crake by Margaret Atwood

Oryx and Crake is a post-apocalyptic science fiction story told from the point of view of a man who refers to himself the 'Snowman'. It is told in both present and past tense since the Snowman recalls many flashbacks of his past life before the pandemic that wiped out the majority of the population.

Snowman's flashbacks of his life explain the hardships of his childhood, his best friend and mad genius Crake, the complicated love triangle between him, Oryx and Crake. and the dystopian nature of the society and world of this book.

Summary

We learn that the Snowman's name used to be Jimmy, and his parents worked at a compound called OrganInc, where they breed animals for organ farming. His mother was against this way of treatment of the animals, and runs away shortly after Jimmy meets Crake. Because this was illegal in the compound Jimmy's parents worked in, he gets frequent interrogations from the Corpsecorps officers to see if Jimmy knew any information on her whereabouts.

Jimmy's father starts seeing one of his co-workers called Ramona, who becomes Jimmy's supposed stepmother. Jimmy is distant from his family and spends most of his time with Crake, who Jimmy's father loves because of his high intelligence. Crake and Jimmy spend most of their time playing games and watching videos until both of them part ways when Jimmy goes to Martha Graham academy for arts and Crake goes to Watson Crick institute, a very prestigious university. The two grow distant but still remain friends, and when Jimmy visits the Watson Crick institute, he is amazed by the advanced facilities compared to his academy, since arts is seen as undervalued and Jimmy could not get into a better school because of his incompetent grades. After graduating Jimmy works as an advert designer for a small company called Anooyoo.

After a few years of working there the Corpsecorps come back to Jimmy and show him a video of an execution in another country. Jimmy recognizes his mother as the executionee but refuses to admit it to the Corpsecorps, but falls into a state of depression afterwards. Crake comes to visit and seeing Jimmy in such a state, he offers Jimmy a job at his company as an advert designer for an anti aging pill.

Crake also shows Jimmy his personal creation; a humanoid creature, the "Crakers", that lacks all flaws of the normal human being, and added features of useful abilities other animals have. He believes that he has created a superior race that will soon rule the earth when the humans become extinct. Here Jimmy meets Oryx, Crake's girlfriend and the person responsible for teaching the Crakers botany. Oryx and Jimmy start having a sexual relationship behind Crake's back, though we are unsure if Crake is aware or not. One day, a worldwide pandemic breaks out, and Jimmy locks himself in the Crakers enclosure to protect himself from the virus, and when Crake comes, he is unable to get in. When Jimmy lets Crake in, Crake slits Oryx's throat in front of him and Jimmy shoots him.

Jimmy spends a long period of time in the enclosure with the Crakers before he realizes that when the electricity runs out the electrically controlled doors will lock him in. He leads the Crakers into the new, post apocalyptic and deserted world and tells him he is a messenger of Oryx and Crake, here to be there teacher and caretaker, but under the new name, "Snowman". The Snowman shows them a jungle next to a beach and helps them set up a new way of living here. He sets up a hideout in a tree nearby and slowly wastes away from lack of a proper lifestyle and isolation.

At the end of the Snowman's flashback, the crakers mention seeing a few human beings at the shore of the beach. Ecstatic, snowman goes forward to approach these few survivors of the pandemic, though we never get to know the outcome as the story ends here.

Themes

Loneliness is one of the major themes shown in the present part of Snowman's life. The closest companions that he has are the Crakers, who he cannot relate to nor have a proper relationship or conversation with as they are not the same species. All he can do is relive his past memories, although he evidently does not want to as the story of his life we see in his flashbacks indicates a not very pleasant past. This is also shown in Jimmy's indifference towards his dysfunctional family life, although there are indications that his upbringing affects him, as he finds comfort in his platonic friendship with Crake and his complicated yet obvious deep romantic feelings for Oryx, as he frequently hears her voice even after she died. His obsession with Oryx shows that this is the first time he has experienced real love as he never felt it from his parents.

Margaret Atwood shows her satirical view of our modern day society through many of the themes the story is based around. The company Jimmy's parents and Crake worked at made large amounts of money from curing diseases and sickness, although they made more money from beauty products. People who were more academically advanced at science and maths lived comfortable, disease free lives, while people who were not so scientific minded but loved writing (like Jimmy) and arts lived in disease and crime infested areas. The "nature vs technology" drive of scientists trying to defy nature to become immortal and godlike with their battle against sickness and deformities. These are all features of our real life society, and the extremities of these themes in the book gives the reader a satirical perspective of the world we live in.

Biology: Chapter 3: Enzymes: Enzyme affinities

Biology: Chapter 3: Enzymes: Enzyme affinities 

Vmax: Maximum theoretical rate (velocity); all enzymes binded with a substrate. However, in theory, there needs to be an infinite substrate concentration, but this is impossible to measure.
Km (Michaelis-Menten constant): Substrate concentration at which an enzyme works at half its maximum rate (1/2 Vmax). Measure of enzyme affinity. Inverse measure; a higher Km means that more substrates need to be present for enzymes to be saturated (binded with a substrate), which means low affinity. However, a low Km means only a small amount of substrate is needed to saturate the enzymes - high affinity. So the lower the Km, the faster the reaction will proceed to its maximum rate.

• It is impossible to find the Vmax by reading results from a graph, because in reality there isn't an infinite substrate concentration. 
• However, since 1/infinity = 0, which can be plotted, Vmax can be found by plotting 1/[S] (inverse substrate concentration) on the x-axis and 1/velocity (inverse rate). This is called a double reciprocal plot.

• Vmax: On the double reciprocal graph, you can find 1/Vmax on the y-axis. To find Vmax, you can calculate it like this (let's pretend that 1/Vmax is 20 in this example): 
• 1/Vmax = 20
  1= 20 x Vmax
  Vmax = 1/20
  Vmax = 0.05
  

• Km: On the double reciprocal graph, you can find -1/Km on the x-axis. To find the Km, you can calculate it like this (let's pretend -1/Km is -10 in this example):
• -1/Km = -10
  -1= -10 x Km
  Km = -1/-10
  Km = 1/10
  Km= 0.1

• Km for enzymes can vary depending on many factors, eg temperature, pH, presence of particular ions, substrate, ion concentration and the presence of poisons, pollutants or inhibitors.

Significance of Vmax and Km values

• Helps scientists make computerized models of biochemical pathways or even the behaviour of whoe cells by predicting how each reaction in a proposed pathway will proceed, and therefore how enzymes interact, and then the consequences of changing factors such as pH and temperature can be built into models.
• By understanding what affects enzyme efficiency, scientists in the future may be able to design better catalysts, which is linked to genetic engineering.
• Knowing the Km means we can calculate active sites occupied by substrates for any substrate concentration.
• We can compare performances of different enzymes.