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(Basic outline) Year 12 Biology - AQA
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Year 12 BiologyDr Esler
Course overview…….Unit 1
Biology and disease
Written paper -Short and long questions
1 hr 15 mins
60 raw marks
33.3% of total AS marks
Unit 2The variety of
living organisms
Written paper –Short questions and data handling question
1 hr 45 mins
85 raw marks
46.7% of total AS marks
Unit 3Practical
assessment
Practical task Either ISA task or practical exam50 raw marks
20% of total AS marks
Term 1 / unit 1 topicsPathogens Absorption
Lifestyle Osmosis
Digestion Active transport
Proteins Lung structure
Enzymes Lung disease
Cells structure/function Heart structure/function/disease
Cell membrane Immunology
Diffusion Data analysis
1.Causes of disease- Pathogens• Define ‘disease’ and pathogens• Describe how pathogens may enter the body• Explain how pathogens produce disease symptoms
disease Caused by…… Infectious?
Microorganisms as pathogens
Are there any other types of organisms that are also pathogens?
(Not these…)
Eg Parasitic worms
How do microorganisms gain entry?• Use page 5 to complete the table..
Entry point Typical diseases Natural defence
Symptoms of disease..• 2 main causes-• Damaging host tissue• Production of toxins
• Often a range of symptoms arise• symptoms of disease
Data, disease and correlationsRecognise how data can be misleading Understand the difference between correlation and causationDevelop a critical approach when examining data in the media
Correlation is not causation!
Use the information on pages 6+7 to explain this statement
Data deception…….
• What would worry you more: being told that cancer kills 25 people out of 100, or that it kills 250 people out of 1000? Dumb question, you might say; both statements mean that a quarter of people die of cancer.
• Yet such differences do matter - not to the risk itself, but to our perception of it. Those wishing to play up or play down a risk, whether to sell newspapers or a medical treatment, can follow the simple rule of "ratio bias". The bigger the number, the riskier the risk appears.
Data deception……
• the Harvard School of Public Health has just produced a study showing the risk of heart disease goes up by 42 per cent with every 56-gram serving of processed meat. It sounds extraordinarily high, but on closer inspection isn't. Compare it with smoking, which raises the risk of cancer by 20 times - that is, 2000 per cent. A 42 per cent rise is small, in epidemiological terms, and could have been thrown up by a bias. But there isn't a bias in the world that could produce a 2000 per cent increase.
• Remember newspapers aim to sell as many copies as possible so will usually aim for the most dramatic headline.
• Imagine a disease that is rare but lethal…….a headline will not say that the number of affected people has increased from 4 to 5 (out of a population of 60 million) But rather will say
‘25% increase in new killer disease’
Be wary of relative data rather than absolute data ie the actual or absolute numbers involved
Why smart people believe dumb things…..• 1. Randomness- seeing patterns where there is only random
noise
We have an innate desire to see order in chaos- faces in clouds, gamblers with ‘runs of luck’ etc Consider a batsman hitting runs. X=hit O=missDoes this sequence indicate a ‘winning streak’…..OXXXOXXXOXXOOOXOOXXOOIn fact this is a random sequence… even though there appears to be some order.
2. Regression to the mean- seeing causal relationships where there are none.
When a certain measurement is at its extreme, it is likely to return to a middle value or ‘regress to the mean’Imagine someone visits a homeopath when their back pain is at its worst. The pain will get better regardless of the visit because when things are at their worst, they generally do. However it is easy to see why the improvement might be ascribed to the treatment…Often we are to oversensitive to spotting causal relationships.
• 3 We are more biased towards positive evidence and our prior beliefs
If we already believe a particular hypothesis, we will look for positive evidence to confirm it. The questions we might ask will elicit information that will confirm our original theory.
Flaws in experimental design are downplayed if the results support existing views. Some alternative medical therapies use vague anecdotal data but ignore systematic reviews carried out by scientists.
4. Availability (when information is made more ‘available’)• Our attention is always drawn to the exceptional and the
interesting. ‘High availability’ stories in the media are dramatic, associated with strong emotion and lend themselves to memorable visual imagery. They are concrete and tangible rather than abstract. Miracle cures, scare stories and distressed parents all add to ‘availability’.
• People are more afraid of sharks at the beach than they are of flying to Florida for example.
• 5 Social influencesOur values (what we believe in) are socially reinforced by conformity and by the company we keep. We expose ourselves to situations where are beliefs are confirmed. ‘Communal reinforcement’ is the process by which a claim becomes a strong belief through repeated assertion by members of a community.This partly explains why statements from therapists, celebrities, politicians talk show hosts and so on can become more powerful than scientific evidence.We tend to assume that positive characteristics cluster; people who are attractive must also be good; people who seem kind might also be intelligent and well-informed. (The behaviour of sporting teams which wear black is rated as more aggressive and unfair than teams which wear white)There are many other examples of bias- we have a disproportionately high opinion of ourselves. A large majority of the public think they are more fair-minded, less prejudiced, more intelligent and better drivers that the average.
Lifestyle and health• Define the term ‘risk’• Consider risk factor associated with cancer and CHD
P 8-13
What is risk?
“Risk is a measurement of the probability that damage to health
will occur as a result of given hazards.”
Lifestyle factors that contribute to cancer include:SmokingDiet: what we eat and drink affects risk. A low-fat, High fibre diet, rich in fruit and vegetables, reduce risk.Obesity: being overweightLack of physical activitySunlight
Reducing risk of cancer and CHDGiving up smokingAvoid becoming overweightReducing salt intakeReducing intake of cholesterol and saturated fats in dietRegular aerobic exerciseIncrease intake of dietary fibres and antioxidants.
Evidence……
Epidemiological (correlation) Experimental (causation)
Page 11/12 Use the information to complete the table below
assessment….• Pages 14-17 questions 1-5
Enzymes and the digestive system
What is the purpose of digestion?
Page 18-19
Task
Choose one part of the digestive system.Make a brief presentation to the class on the area you have chosen. What does it do? How is its structure adapted to this function?
What is meant by physical and chemical digestion?
carbohydrases
proteins
Fatty acids +glycerol
Write down as many things as you can remember about carbohydrates…
… or glucose in particular
Carbon, hydrogen and oxygen….Carbohydrates
Carbohydrates 1 Monosaccharides
Give an overview of carbohydrate structure and functionDescribe the structure of monosaccharide carbohydrates
• Monosaccharides
• Disaccharides
• Polysaccharides
C3 triose Triose phosphate
rare
C5 pentose
glucose Energy source
Simple sugars are named according to the number of carbon atoms they possess…
The basic unit or monomer is the monosaccharide eg glucose C6H12O6
Glucose is white, sweet tasting and crystalline, highly soluble
Glucose is an abundant and very important monosaccharide. It contains six carbon atoms so it is a hexose sugar. Its general formula is C6H12O6.
Glucose is the major energy source for most cells. It is highly soluble and is the main form in which carbohydrates are transported around the body of animals. Can be represented in several ways:
Or even simpler…
Glucose exists in different forms called structural isomers. Two common isomers are alpha glucose and beta glucose
The only difference between these two isomers is the position of the –OH group attached to carbon 1. In alpha glucose it is below the carbon and in beta glucose it is above the carbon.
This minor structural difference has a major effect on the biological roles of alpha and beta glucose.
alpha beta
Two other important hexose monosaccharides are fructose and galactose.
Fructose is very soluble and is the main sugar in fruits and nectar. It is sweeter than glucose.
Galactose is not as soluble as glucose and has an important role in the production of glycolipids and glycoproteins
fructose galactose
Testing for reducing sugars– Benedict’s test
All monosaccharides are reducing sugars. This means they can donate electrons, in this case to Benedict’s Reagent which becomes reduced and changes colour. The extent of the colour change can be used to estimate the concentration of the sugar present.
Summarise the practical steps when carrying out the Benedict’s test. p21
You have been provided with 3 unknown samples of glucose solutions. Arrange these in order of relative concentration.
sample Colour change Relative concentration
Carbohydrates2. Disaccharides and Polysaccharides
Describe how monosaccharides join to form disaccharidesExplain how starch may be formed from alpha glucose
OMG!
Disaccharides are formed when two monosaccharides join together. A molecule of water is produced in this CONDENSATION reaction
Maltose (malt sugar) is formed from two glucose molecules joined by an alpha 1–4 glycosidic bond.
Sucrose (table sugar) is formed from glucose and fructose joined by an alpha 1–4 glycosidic bond
Lactose (milk sugar) is formed from galactose and glucose joined by a beta 1–4 glycosidic bond
Disaccharides form Polysaccharides
Starch
• Good for storage (it’s compact!)• Starch is insoluble due to its structure so no
osmotic effect.• It is therefore the main plant storage
compound
Cellulose….. A polysaccharide of B-glucose
A structural carbohydrate found in plant cell walls
O
O
O O
O O
OO
O-O--O- -O--O--O-
-O--O--O--O-
O
O
O-O--O-
O
-O-
Hydrogen bonds form between chains
When a molecule of water is lost in a reaction
glycogen
Two glucose molecules reducing sugars
Milk sugar isomers
The bond between monosaccharides
cellulose
All monosaccharides are…. lactose
Animal storage carbohydrate condensation
Different forms of glucose maltose
A structural polysaccharide glycosidic
When a molecule of water is lost in a reaction
condensation
Two glucose molecules maltose
Milk sugar lactose
The bond between monosaccharides
glycosidic
All monosaccharides are…. Reducing sugars
Animal storage carbohydrate glycogen
Different forms of glucose isomers
A structural polysaccharide cellulose
Make a flow diagram to show how non-reducing sugars may be detected. P23
Now use this scheme to test sugar samples A, B and C. Which are non-reducing sugars?
HomeworkFind out what is meant by ‘polysaccharides’Describe the formation and function of STARCH.
Summary questions 23 Q1-3
Using page 24 to assist, make a storyboard to show how starch digestion occurs in humans. Include the location, enzymes involved and the substrates and products.
Carbohydrate digestionDescribe the action of salivary amylase in digesting starch
Summarize the location and action of other carbohydrases
HomeworkResearch the topic of lactose intolerance. What does this mean? What are the symptoms and possible remedies?
Proteins
Describe the structure of amino acids
Explain how amino acids join to form primary, secondary and tertiary proteins
All amino acids (20) have the same general structure: the only difference between each one is the nature of the R group. The R group therefore defines an amino acid.
aminogroup
carboxylic acid group
R group
Make a flow diagram to show how two amino acids join by condensation to make a PEPTIDE bond.
When two or more amino acids join through peptide bonds, a PRIMARY STRUCTURE results.
The primary structure is the sequence of amino acids determined by the base sequence in DNA. The number and type of amino acids will determine protein structure and function.
collagen – the main component of connective tissue such as ligaments, tendons, cartilage.
Secondary structure of proteins occurs when the primary chain undergoes further modifications and strengthening bond formation….
keratin – the main component of hard structures such as hair, nails, claws and hooves
Tertiary proteins- further modifications of the primary and secondary structures results in a 3D tertiary structure….
As well as peptide bonds, there are disulphide bridges, ionic bonds and hydrogen bonds
The chains are usually folded so that hydrophobic groups are on the inside, while the hydrophilic groups are on the outside. This makes many globular proteins soluble in water.
Prac: chromatography of egg albumin; biuret test
Some proteins are made from several chains coiled together or have a non-protein group included eg haemoglobin. These are called Quaternary Proteins
TASKDiscuss the structure of collagen. How is it suited to its function? Use p29 for guidance
Make a dicotymous key to identify carbohydrate and protein molecules. Use features such as elements present, size reaction with Benedicts, type of bond present etc
State that enzymes are globular proteins, with a specific tertiary structure, which catalyse metabolic reactions in living organisms.
Enzyme action
Explain, with the aid of diagrams, the mechanism of action of enzyme molecules with reference to specificity, active site, lock and key hypothesis, induced-fit hypothesis, enzyme–substrate complex, enzyme–product complex and lowering of activation energy.
Pineapple; jelly hydrogen peroxide
What do we mean by METABOLISM?
What do we mean by METABOLISM?The sum of all chemical reactions within a living
organism is known as metabolism.
Metabolism is a combination of catabolism (breaking down) and anabolism (building up)
Catabolism refers to chemical reactions that result in the breakdown of more complex organic molecules into simpler substances.Catabolic reactions usually release energy that is used to drive chemical reactions. Anabolism refers to chemical reactions in which simpler substances are combined to form more complex molecules. Anabolic reactions usually require energy.Anabolic reactions build new molecules and/or store energy.
Enzymes are involved in both branches of metabolism
Enzymes are catalysts that lower activation energy without themselves undergoing any change.
Lock and Key model of enzyme action
How is this different to the Induced Fit model?
Distribute diagrams of an enzyme colliding with a substrate through to the products being formed. Students must summarise the stages as a series of bullet points.
Give students a series of cards to play snap with. A snap pair consists of a diagram on one card and a corresponding explanation on the other.
P32 summary questions
Describe and explain the effects of: pH, temperature, enzyme concentration and substrate concentration on enzyme activity
Apply the lock and key model to explain experimental findings
Factors affecting enzyme action
P33-35
Why are enzymes in washing powder are often obtained from thermophilic bacteria (bacteria that live in hot springs).
Remember…….Many think that all enzymes work best at 35 - 40 °C and denature above 40 °C. This isn’t true. Many enzymes work best at well above 40 °C – pepsin works best at 60 °C and phosphatase from bean sprouts works best at 55 °C. However they can also work at lower temperatures and it is not efficient to run bodies at 60 °C and it would damage other structures – other proteins and phospholipids. What sort of bonds would you expect to find holding the tertiary structure of a heat stable enzyme in place (A: S–S bonds).
Enzyme inhibition
Explain the effects of competitive and non-competitive inhibitors on the rate of enzyme-controlled reactions
Describe one role of enzyme inhibition in metabolism
P36 In pairs, convert a written description of each type of inhibition into a set of labelled diagrams
(Km is the concentration of substrate that leads to half-maximal velocity. Km = 1/2 Vmax)
Uses of enzyme inhibition….
1. Controlling metabolic pathways ( end point inhibition)
Q 1-4 p37
Find out about how enzyme inhibitors have been used in drugs and poisons
Cell structure and organisation
Investigating cell structure
Clarify the difference between magnification and resolution
Explain the technique of cell fractionation
Cells alive
The magnification of an object is how many times bigger the image is compared to the original object. X 10 X3000 X0.5 etc
Before any calculations are performed, make sure all the units are the same.
Resolution is the minimum distance apart two objects can be in order for them to appear as separate structures.
The wavelength of light used to illuminate the specimen determines resolving power. Increasing magnification does not increase resolution.
What is the resolving power of a light and an electron microscope?
Cell fractionation- a technique used to isolate cell components (organelles)
What is a cold isotonic buffered solution ? P41
Summarize the steps on page 41 in flow diagram
Summary questions 1-7
The electron microscope
Outline how an electron microscope functions
Distinguish between different types of electron microscope
Describe limitations of producing images using these tools.
Summarize the main differences between transmission and scanning electron microscopes. What are the main limitations of both?
Scanning or transmission?
Cell structure
Describe the structure and function of major cell organelles
Use headings from your text book to makes notes on the organelles listed. Include their size and function..eukaryotes
H/W p143 Q1-4
Prokaryotes…cells without a nuclear membrane
Prokaryotes do not have a nucleus, mitochondria, or any other membrane-bound organelles. In other words, all their intracellular water-soluble components (proteins, DNA and metabolites) are located together in the same volume enclosed by the cell membrane, rather than in separate cellular compartments. Prokaryotes include two major classification domains: the bacteria and the archaea. Archaea were recognized as a domain of life in 1990. These organisms were originally thought to live only in inhospitable conditions such as extremes of temperature, pH, and radiation but have since been found in all types of habitats.The genome in a prokaryote is held within a DNA/protein complex in the cytosol called the nucleoid, which lacks a nuclear envelope. The complex contains a single, cyclic, double-stranded molecule of stable chromosomal DNA, in contrast to the multiple linear, compact, highly organized chromosomes found in eukaryotic cells. In addition, many important genes of prokaryotes are stored in separate circular DNA structures called plasmids.
Comparing eukaryotes and prokaryotesSee table p 65
Lipids
Describe the structure of a triglyceride
State how phospholipids differ in structure and property to triglycerides
What are the main functions of lipids in living organisms?
Summary questions 1-3 p51
How do these diagrams explain the differences between butter and margarine?
Cell-surface membraneDescribe the structure of the cell surface membrane with reference to the ‘Fluid mosaic model’
State the functions of the membrane components
Write out the meaning of as many terms as possible from the diagram……
How could the phospholipid molecules arrange themselves so that a stable layer is formed that can interact with the water-based environment inside and outside the cell?
What do the proteins do?
Fat soluble molecule
Charged or large molecule
Intact membrane 8.1 7.2
Protein component removed
8.0 0.3
Relative rate of substances crossing a cell membrane
How do hormones ‘know’ which cells to target?
Fluid mosaic model
Diffusion
State what we mean by ‘diffusion’Describe the factors that affect the rate of diffusionExplain the special case of facilitated diffusion
The movement of particles in a gas or liquid from a region of high concentration to a region of lower concentration. Since no energy input is involved, the movement is PASSIVE.
(Multimedia for sci)
In what direction will the perfume particles move?
(permanganate demo
What affects the rate of diffusion?
P55 Can you give an example of how one organ system in the body optimises each of these factors?
Facilitated diffusion- helping diffusion to occur by means of protein channels and carrier molecules in the cell membrane
Osmosis…diffusion of water molecules• Define what is meant by water potential• Explain osmosis using water potential gradients
How is this cell dependent on osmosis in order to perform its function?
How do plant and animal cells behave as a result of osmosis?
What will happen in plant cells?
Describe and explain, using labelled diagrams, the effect on a plant cell of placing tissue in a hypertonic and hypotonic solutions.Use the terms turgid, flaccid, plasmolysed and incipient plasmolysis
summary
Movement using energy….Active TransportDefine the process of active transport and the role of ATPIdentify the parts of the cell membrane involved with active transport
Explain what is happening in each of these 3 diagrams…
Absorption in the small intestine• Identify the location and structures involved in mammalian
glucose absorption• Describe and explain the mechanism involved in glucose
absorption
Use page 63 to identify how the structures above increase the efficiency of absorption.
microvilli
Active transport is also involved in glucose transport. P64 summarize the steps involved in this mechanism. Summary questions 1-3.
Cholera• Recall the structure of prokaryotes• Describe and explain the causes and symptoms of the disease, Cholera
Vibrio cholerae
What are the main features of prokaryotes?
The main symptoms are watery diarrhea and vomiting. This may result in dehydration and in severe cases grayish-bluish skin. Transmission occurs primarily by drinking water or eating food that has been contaminated by the faeces (waste product) of an infected person, including one with no apparent symptoms.The severity of the diarrhea and vomiting can lead to rapid dehydration and electrolyte imbalance, and death in some cases. The primary treatment is oral rehydration therapy, typically with oral rehydration solution, to replace water and electrolytes. If this is not tolerated or does not provide improvement fast enough, intravenous fluids can also be used. Antibacterial drugs are beneficial in those with severe disease to shorten its duration and severity.Worldwide, it affects 3–5 million people and causes 100,000–130,000 deaths a year as of 2010.
Cholera toxin (also known as choleragen and sometimes abbreviated to CTX, Ctx, or CT) is a protein complex secreted by the bacterium Vibrio choleraeHow does producing this toxin help the survival of the bacterium?
Use the information on pages 66+67 to make a flow chart showing how the symptoms of cholera are produced. Summary questions 1-4 p67
Oral rehydration therapy• Descibe the need for rehydration following diarrhoea• Explain the components of rehydration medicines and their testing
prior to release
Make a table to show the ingredients of a rehydrating solution. Why is giving water alone insufficient? p68
component function
What were the problems associated with developing rehydrating solutions?Summarize the steps involved in testing a new drug.
Summary questions 1-4 p69
Lungs and lung disease• Describe the structures involved in human gas exchange (lungs)
Use the information on page 75 to describe the main parts of the lungs.Summary questions 1-3
Mechanism of breathing• Identify the muscles and movements involved in lung movements• Calculate pulmonary ventilation
Ventilation of the lungs occurs as a result of pressure changes. These changes are brought about by the intercostal muscles and the diaphragm
Summarize the steps taken during inspiration and expiration p76/77
Lung ventilation
Summary questions 1-4 p77
Tidal volume (dm3) Ventilation rate (min-1)
Pulmonary ventilation (dm3 min-1)
0.5 12
.63 14
Exchange of gases in the lungs• Summarize the features of gas exchange surfaces• Recall the structure and function of the alveoli
What are the features of these external gills that allow for efficient gas exchange?
Newt larva
Lung disease- pulmonary tuberculosisDescribe the causes, transmission and control of TB
TB is caused by one of two species of rod shaped bacteria- Mycobacterium tuberculosis or Mycobacterium bovis
Use information from the video and from pages 80 and 81 to make a brief summary of important points on TB.Use the headings…Causes/symptomsTransmissionDevelopment of the diseaseControl
Bacillus Calmette–Guérin (historically Vaccin Bilié de Calmette et Guérin commonly referred to as BCG) is a vaccine against tuberculosis that is prepared from a strain of the attenuated (virulence-reduced) live bovine tuberculosis bacillus, Mycobacterium bovisThe UK introduced universal BCG immunization in 1953, and until 2005, the UK policy was to immunize all school children at the age of 13, and all neonates born into high-risk groups.
Lung disease- fibrosis, asthma and emphysema
Describe and explain the causes and symptoms of specific non-infectious lung diseases
Summarize the causes and symptoms of these 3 lung diseases. Include data on frequency. Include table 1 page 84. Questions 1-3 p 84. Questions 1-4 page 85
Structure of the heartDescribe the structure of the heart and associated blood vessels
Look at fig 1 page 88. What causes the fluctuations at the start of the graph?
Blood flowSummary questions 1-4 p89
The cardiac cycleDescribe the events of the cardiac cycleExplain pressure changes in a cardiac cycle graphDescribe the nerve signals that initiate and regulate the cycle.
How will you remember that diastole means relax and systole means contract?
Heart valves prevent the backflow of blood…..
Heart sounds!
Graph of the cardiac cycle showing pressure and volume changes…
Summary questions 1-5 p93
Heart disease Identify common heart diseasesExplain the effect of risk factors on the onset of heart disease
Myocardial infarction (MI; or acute myocardial infarction (AMI) is the medical term for an event commonly known as a heart attack. An MI occurs when blood stops flowing properly to a part of the heart, and the heart muscle is injured because it is not receiving enough oxygen. Usually this is because one of the coronary arteries that supplies blood to the heart develops a blockage due to an unstable build up of white blood cells, cholesterol and fat. The event is called "acute" if it is sudden and serious.
Summarize the 4 main heart conditions p94/5
Atheroma…build up of fatty deposit in the wall of an artery in the heart.An atheroma is an accumulation of degenerative material in the tunica intima (inner layer) of artery walls. The material consists of (mostly) macrophage cells, or debris, containing lipids (cholesterol and fatty acids), calcium and a variable amount of fibrous connective tissue. The accumulated material forms a swelling in the artery wall, which may intrude into the channel of the artery, narrowing it and restricting blood flow.
Atheroma can then lead to two further conditions- thrombosis and aneurysmWhy does atheroma increase the risk of these developing?
Thrombosis..a blood clot develops that eventually blocks the artery
Aneurysm...balloon-like swelling due to a weakening of artery walls
Risk factors associated with heart disease….
• Smoking• High blood pressure• Blood cholesterol• Diet
Uses pages 95 +96 to fully explain how these factors increase the risk of developing heart disease
Summary questions 1-2 p96; page 97 questions 1-3 and 1
ImmunityDescribing our non-specific and specific defence mechanisms
Use fig 2 page 101 to become familiar with some of the main terms involved in understanding immunity
Organisation of cells, tissues , organs and organ systems
Clarify some examples of tissue specialisationOutline the organisation of named organ systems in the human body
A tissue consists of cells of a similar type.
4 main types:• Epithelial cells• Connective tissue• Muscle tissue • Nervous tissue
Tissue type Location and function
Squamous epithelium
Complete the table on epithelial tissues using p144 include a diagram
Summary questions 1+2 P145
One becomes two…..Describe the structure a chromosome following DNA replication
Explain events of the cell cycle
See someone grow
46
46 46
If the chromosome number remains the same at the end of cell division, what must be happening to the DNA in the parent cell?
Different species have different numbers of chromosomes. Humans have 46, chickens have 78, goldfish have 94 and fruit flies, 8.
Why are the chromosomes arranged in pairs?
Homologous pairs• Chromosomes come in pairs with the same size,
shape and banding pattern.• These homologous pairs are the result of sexual
reproduction and the homologous pairs are the maternal and paternal versions of the same chromosome so they have the same sequence of genes.
Chromosome structure
DNA replication
• Now each chromosome consists of a pair of identical chromatids joined at the centromere. The amount of DNA has doubled prior to cell division.
A All the chromosomes displayed 1 histone
B All the material in a nucleus 2 chromatids
C Matching chromosomes 3 6 feet
D Enzyme used in DNA replication 4 karyoytpe
E The length of DNA in a human cell 5 Homologous chromosomes
F Sister…. 6 chromatin
G Cell dividing 7 DNA polymerase
H Protein beads on a chromosome 8 cytokinesis
A All the chromosomes displayed 4 karyoytpe
B All the material in a nucleus 6 chromatin
C Matching chromosomes 5 Homologous chromosomes
D Enzyme used in DNA replication 7 DNA polymerase
E The length of DNA in a human cell 3 6 feet
F Sister…. 2 chromatids
G Cell dividing 8 cytokinesis
H Protein beads on a chromosome 1 histone
Cell Cycle• The process of Mitosis refers to the chromosomes dividing and
moving to opposite ends of the cell. Before this can happen, the cell must prepare itself and check for copying errors.
• The cell cycle is the series of events that take place as the cells grow and divide. In average this process takes about 24 hours for cells in mammals.
Mitosis• Describe the cellular events of mitosis• Describe how to prepare a root tip for mitosis examination
Cytokinesis in plant cells
Asexual reproduction…making natural clones
• Outline advantages and disadvantages of asexual reproduction
• State examples of asexual reproduction producing natural clones
1. Binary fission….two new individuals formed. Occurs in simplest organisms such as bacteria and Amoeba
2. Producing spores… common in fungi and mosses
3. Regeneration…animals that can regrow parts that have been lost eg lizards regenerating a tail
4. Budding…a small outgrowth or bud develops from a mature cell. This breaks off and grows into a new individual (clone) Common in Yeast and Hydra. (the bud is asymmetrical to distinguish the process from budding)
5. New plant structures…vegetative reproduction. Only involves mitotic divisions.Can develop from a range of plant parts such as stems, leaves etc. commonly used by gardeners to increase plant numbers.
• Some animals are able to reproduce without fertilisation. This is called . One example relates to the Komodo dragon…
Growth.. permanent increase in cell number, size or mass
• Outline the difficulties in measuring growth in living organisms• Describe a range of growth patterns
Because organisms do not grow uniformly, measuring height, head circumference etc can be misleading. Dry mass is the most accurate method.
(1) A reliable measure of the biomass (as opposed to fresh mass).
(2) The dry matter of a sample or of an object when completely dried (lacks or excluding water).
Dry mass is a more reliable measure of mass than fresh mass because the former excludes the fluctuating water concentrations in the biological material measured which is present in the fresh mass.
Main disadvantage is that the organism must be killed.
Insects grow in stages as they undergo moulting at each stage
Humans grow in stages that merge together. Rapid growth by mitosis occurs in the early stages and puberty.
Meiosis…halving chromosome number to make gametes• Outline the events of meiosis• Describe how meiosis results in genetic variation
In meiosis, there are two phases of chromosome movement each with 4 stages.Meiosis 1 separatesHomologous pairs which have come together, while meiosis 2 separates the chromatids as in mitosis.
During metaphase 1, homologous chromosomes come together and exchange genetic material.
Gametogenesis…making gametes• Describe and compare the process of gametogenesis in
males and females• Explain structural adaptations in sperm and ova
spermatogenesis oogenesis
location
When gametogenesis starts
Number of gametes made per primary spermatocyte/oocytePolar bodies made?
When is meiosis completed
Use the information on page 160 to complete the table below
Sperm cells
Zona pellucida -This structure binds sperm and is required to initiate the acrosome reaction. It surrounds the egg cell membrane
Gametogenesis in plants…
Pollen is produced by meiosis in the anthers…a pollen microspore mother cell undergoes meiosis to form haploid microspores.
The male gamete is produced by mitosis of the generative nucleus.
Inside the ovule, the female gamete develops. Following meiosis, one haploid cell divides 3 times by mitosis to produce 8 haploid cells. One of these is the female gamete.Double fertilisation
Fertilisation...in humans•Recall the events at fertilisation•Describe the role of the acrosome
1. Released ovum is known as a secondary oocyte
2. Protected by the zona pellucida3. Several sperm complete the
acrosome reaction p1654. Penetration of the sperm
stimulates second meiotic division producing haploid egg nucleus.
5. Ion channels open so the inside of the egg becomes positively charged
6. As a result, no further sperm gain entry
7. Fertilisation membrane blocks further sperm entry
8. Tail is left outside while the head swells with water releasing its chromosomes
Following fertilisation.....
Outline the events following animal fertilisationExplain the terms totipotent and pluripotent
216 different cell types must develop from a single fertilised egg.
Totipotency is the ability of a single cell to divide and produce all of the differentiated cells in an organism; a zygote is one example. Totipotency represents the cell with the greatest differentiation potential.
1. Cleavage. Occurs by mitosis although no interphase exists at this early stage.
2. Small mass of identical cells develops resulting in a hollow sphere called blastocyst. Develops as the zygote moves along the oviduct.
3. The cells can now be referred to as embryonic stem cells. The outer cells of the blastocyst form the placenta. The inner cells can now form many of the required cell types- but not all. These cells are pluripotent.
Cell determination means the process that decides what type of cell an embryonic cell will eventually become. Depends on its position in the blastocyst.
Cell differentiation depends on which parts of the DNA moleule are expressed to make proteins. Transcription factors will determine the genes to be expressed.
Totipotent cells..•Describe the uses of totipotent cells in plants and animals
Plant cells remain totipotent throughout their life.
Plant cell cloning is commonplace. Rare plants such as orchids are reproduced from cuttings/ tissue culture. Animal cells remain totipotent for a short time only before becoming pleuipotent. Once fully differentiated their lose all ability to form different cell types.
and animal cells.....
Embryo splitting is a technique of increasing the numbers of favoured breeds.Unrelated species can be used as surrogate mothers for a short time before the developing embryo is removed
Embryo splitting in cattle
Cell differentiation• Describe how gene expression is controlled to produce
differentiated cells
Controlling expression usually involves switching genes ‘on’ or ‘off’. This requires transcription factors that cause unwinding of specific parts of the DNA molecule. Hormones in development can influence the activity of transcription factors.If transcription does occur, the M-RNA can be inactivated using siRNA molecules.
p173
Stem cells
• Outline the properties and sources of human stem cells• Describe the possible uses of stem cells in stem cell therapy
Stem cells have the potential to develop into many different cell types in the body during early life and growth. In many tissues they serve as a sort of internal repair system, dividing essentially without limit to replenish other cells as long as the person or animal is still alive. When a stem cell divides, each new cell has the potential either to remain a stem cell or become another type of cell with a more specialized function, such as a muscle cell, a red blood cell, or a brain cell.
Human embryonic stem cells (hESCs) are generated by transferring cells from a preimplantation-stage embryo into a laboratory culture dish that contains a nutrient broth known as culture medium. The cells divide and spread over the surface of the dish. Embryonic stem cells that have proliferated in cell culture for for a prolonged period of time without differentiating, are pluripotent, and have not developed genetic abnormalities are referred to as an embryonic stem cell line.
To generate cultures of specific types of differentiated cells—heart muscle cells, blood cells, or nerve cells, for example—scientists try to control the differentiation of embryonic stem cells. They change the chemical composition of the culture medium, alter the surface of the culture dish, or modify the cells by inserting specific genes. Through years of experimentation, scientists have established some basic protocols or "recipes" for the directed differentiation of embryonic stem cells into some specific cell types
D. How are embryonic stem cells stimulated to differentiate?
An adult stem cell is thought to be an undifferentiated cell, found among differentiated cells in a tissue or organ that can renew itself and can differentiate to yield some or all of the major specialized cell types of the tissue or organ. The primary roles of adult stem cells in a living organism are to maintain and repair the tissue in which they are found.
Scientists have found adult stem cells in many more tissues than they once thought possible. This finding has led researchers and clinicians to ask whether adult stem cells could be used for transplants. In fact, adult hematopoietic, or blood-forming, stem cells from bone marrow have been used in transplants for 40 years. Scientists now have evidence that stem cells exist in the brain and the heart. If the differentiation of adult stem cells can be controlled in the laboratory, these cells may become the basis of transplantation-based therapies.
Stem cell cloning…• Used as a possible therapy in diseases such as Type 1 diabetes
or Alzheimer’s disease• Nucleus removed from patients body cell• Nucleus transferred to ‘empty’ egg cell followed by a small
electric shock to initiate embryo development.• Stem cells harvested from the developing embryo and
following differentiation into the required cells, given to patient without risk of rejection.
Interactions between genes and the environment
•Describe examples of how the environment can affect gene expression
Use the information on page 186 to help explain the typical colouring of Siamese cats. How is the environment affecting coat colour?
