Paper 3A Flashcards
What is a cell?
A basic unit of structure and function in an organism
What does a eukaryote have? Example of some
A true nucleus with a nuclear envelope surrounding the chromosome and membrane bound organismsAnimal and plant cells
What does a prokaryote have? Example of one
Don’t have membrane bound organelleFree floating DNA and plasmids, not a nucleus
What does a plant cell have?
ChloroplastsNucleusCell membraneCell wallVacuoleCytoplasm
What does an animal cell have?
NucleusPlasma membraneMitochondriaRibosomesCytoplasmGolgi apparatusSmooth endoplasmic reticulumRough endoplasmic reticulumNuclear envelopeNucleolusNucleoplasmVesicles
What does a bacteria cell have?
FlagellumPlasmidsFree floating DNACytoplasm - containing ribosomes
What does a yeast cell have?
Cell wallCell membraneVacuoleCytoplasmNucleus
Parts of a chloroplast
Double membraneThylakoidGranaStroma
structure of Nucleus
Nucleus surrounded by a nuclear envelope (a double membrane)Nuclear pores allow the passage of large molecules out of the nucleusNucleoplasm jelly makes up a bulk of the nucleusNucleolus within the nucleoplasm manufactures RNAChromosomes
Function of Nucleus
Store genetic informationControl centre of the cell
Structure of Ribosome
2 sub units (one small one big)Each contain ribosomal RNA and protein
Function of ribosome
Site of protein synthesis
Difference between 70S and 80S ribosomes
80S – eukaryotic cells, 25nm diameter70S – prokaryotic cells, mitochondria, and chloroplasts, slightly smaller than 80S
Structure of mitochondria
Bound by a double membraneOuter membrane = MatricInner membrane = CristaeHas its own strand of DNA
Function of mitochondria
Respiration“Powerhouse of the cell”Aerobic RespirationProduction of ATP
Structure of the cell membrane
Around the whole cell
The function of the cell membrane
Controls what diffuses in and out of the cell
Structure of Rough Endoplasmic Reticulum
Ribosomes present
The function of Rough Endoplasmic Reticulum
Protein synthesisPathway for the transport of materials (like proteins throughout the cell)
Endoplasmic Reticulum general info
‘ER’Connected to the outer nuclear membrane
Structure of Golgi Apparatus
Stack of membranes = flattened sacsMembranes contain small hollow structures called vesicles
The function of the Golgi Apparatus
Transport, modify and store proteins and lipids produced by the Endoplasmic ReticulumMolecules transported to and from the Golgi by vesiclesProduces Lysosomes and secretory enzymesCell post office – receives, sorts and delivers
Structure of Smooth Endoplasmic Reticulum
No ribosomes
The function of smooth endoplasmic reticulum
Synthesize, store and transport lipids and carbohydrates
Cytoplasm
Between the membrane and nucleus, made up of mainly water
Lysosome
MembraneContained up to 50 enzymes
Chloroplast
Outer and Inner membraneOpen space in the stromaThylakoid stacks (Grana) provides surface area
Permanent Vacuole
Large membrane bound sacs
Cell wall
On top of the cell membrane, around the whole cell
Cytoplasm
Houses all the organelleWhere chemical reactions take place
Lysosome
Garbage disposal of the cellRemove useless/dangerous materialFormed when vesicles produced by the Golgi contain useful enzymesContain digestive enzymes to break down waste
Chloroplast
Captures light for photosynthesis
Permanent Vacuole
Provides structure and support for the cell and holds sap/water
Cell wall
Provides structure and support for the cell
What are the 3 main adaptations a cell can have?
number of RER and GolgiNumber of mitochondriaSurface area
How does the number of RER and Golgi affect a cell? What cells would need this adaptation?
Increased protein synthesis and production as well as transport for these proteins (and hormones)Useful for cells that need lots of proteins for example cells that produce enzymes
How does the number of mitochondria affect a cell? What cells would need this adaptation?
Increased respiration which in turn increases energy for cells that need a lot of energyFor example muscle of sperm cells
How does surface area size affect a cell? What cells would need this adaptation?
Increases room to diffuse but also space to carry thingsRed blood cells have no nucleus, so, therefore, a bigger surface area, so that it can carry more oxygen and waste products
Which is bigger prokaryotes or eukaryotes?
Eukaryotes
Explain DNA in eukaryotes
Membrane-bound in a true nucleus
Explain DNA in prokaryotes
Free-floating or in plasmids, not membrane-bound
Which organelles are present in prokaryotes?
PlasmidFree-floating DNAFlagellumRibosomes
Which organelles are present in eukaryotes?
NucleusRibosomesMitochondriaGolgi ApparatusSERRERVesiclesLysosomes
Are ribosomes membrane-bound?
No, but RER is
Is there any photosynthetic material present in prokaryotes? Why?
No, chloroplasts are too big, but some big bacteria’s do have some photosynthetic material
Which ribosomes are present in prokaryotes?
70S
Which ribosomes are present in eukaryotes?
80S70S (in mitochondria and chloroplasts)
What are cell walls made of in prokaryotes?
murien
What are cell walls made of eukaryotes?
Cellulose
Describe the basics of an antigen
.On the surface of all cells are chemical markers called antigens.Your body recognises the antigens on your cells as your own.Anything with different antigens to yours stimulates an immune response.In an immune response, your body will recognise the antigen as foreign and will attack it
Which molecules can act as anitgens?
. Proteins. Glycoproteins
Why are antigens important?
. Initiate immune response to pathogens. Allowing recognition of faulty cancer cells. Recognition of cells from other organisms of the same species
How does antigenic variation work?
.Some pathogens can mutate which causes changes in the surface antigens.The memory cells from the first infection won’t recognise the different antigens.The immune system must carry out a primary response against the new antigens
What is phagocytosis?
Phagocytosis is when phagocytes (a type of white blood cell) engulf and break down an invading pathogen in order to protect the body, it is a part of the immune system.
What type of response is phagocytosis?
Phagocytosis is a non-specific response
Describe the steps of phagocytosis
- The phagocyte is attracted to the pathogen by detecting the toxins it is releasing2. The phagocyte moved towards one of the pathogens3. The phagocyte begins to surround the microbe. A vacuole forms around it.4. The phagocyte engulfs the pathogen5. The pathogen is inside a vacuole like phagosome in the phagocyte6. Lysosomes fuse with the phagosome and secrete digestive enzymes into the phagosome7. The pathogen inside the phagosome is digested by these enzymes and destroyed
What are the roles of T cells?
.Produces memory T Cells.Stimulates phagocytosis.Kills infected cells – making holes in their membranes.Stimulates B cells to divide
How does an antigen presenting cell come about?
B cells with an antibody that is complementary to the antigen of invading pathogens takes up the surface antigenThis antigen is presented on the surface of the B cell
What happens to an antigen presenting cell?
A T helper cell attaches to the processed antigens on the B cells thereby activating the B cell meaning it produces by mitosis to produce clones
When B cells divide by mitosis what is formed?
They can either become memory cells or plasma cells
Where are memory cells found and what are ready to do?
Memory cells circulate in blood and tissue fluid in readiness to respond to a future infection by the same pathogen whos antigen was used in the process of forming them
What do plasma cells do?
Plasma cells produce antibodies that exactly fit the antigens on the pathogens surface
What do antibodies do?
The antibodies attach to antigens on the pathogen and destroy them
If the same infection occurs again what do memory B cells do?
If the same infection occurs again the memory B cells divide and develop into plasma cells that produce antibodies
List 3 functions of antibodies
.Coat the pathogen with antibodies to make it easier for the phagocyte to engulf it.Coat the pathogen with antibodies to prevent it from entering host cells.Antibodies bind to and neutralise (inactivate) toxins produced by the pathogen
How are B cells and C cells both needed to remove a pathogen from the body?
The responses interact with each other.T cells activate B cells and antibodies coat pathogens making it easier for phagocytes to engulf them
If you see the word humoral in the exam what do you think?
B cells
What produces antibodies?
B cells, more specifically plasma cells
Are antibodies specific?
yes
Name 6 parts of an antibodies structure
- Antigen binding sites2. Variable region3. Constant region4. Light chains5. Heavy chains6. Receptor binding sites
Draw and label antibodies
idk check your revision guide or google if its right?
Why are the variable regions on antibodies called that?
As the binding sites differ
What gives the variable region its specific 3d shape in antibodies?
The sequence of amino acids
In antibodies, where does the constant region bind to?
receptors
Each binding site on an antibodie is c____________ to a specific antigen
complementary
When an antibodies binding site binds to an antigen what is formed?
forms an antigen-antibody complex
Roles of antibodies
.Antibodies do not directly destroy antigens.Agglutination.Markers
What happens in agglutination
Antibodies clump bacteria cells together which is helpful as it means they can be taken in by phagocytes for digestion much more easily since they are easier to locate as they are less spread out
How do antibodies act as markers?
They can act as markers that stimulate phagocytosis
What is a polyclonal antibodie?
.Pathogens can have many antigens on their surface that can activate many B cells.Each of these B cells will clone copies and will produce different antibodies.These are collectively known as polyclonal antibodies
What are monoclonal antibodies?
.It is useful to be able to produce antibodies outside of the human body.It is even better if a single type of antibody can be isolated and cloned on mass.These antibodies are known as monoclonal antibodies
Different between poly and mono clonal antibodies?
Poly - .Made from a variety of B cellsMono - .Made from only one type of B cell
How do pregnancy tests work?
A hormone called HCG is found in the urine of women only when they are pregnant, pregnancy tests can detect these hormones..Monoclonal antibodies that attach to HCG can be mass produced and stuck down to a test strip on a pregnancy test, while on a separate part of the pregnancy test antibodies attached to blue heads can be placed..If your pregnant and wee on it, the HCG in your urine will attach to the antibodies on the blue heads and the urine will carry them down to the test strip where they will attach to the stuck down antibodies and change the colour of the strip – showing a positive result..If you are not pregnant and wee on it, the urine still carries the blue beads and antibodies down the test to the test strip but they won’t attach to the stuck down antibodies, and so a colour change does not occur – a negative result.
How do monoclonal antibodies help diagnose PSA?
.men with prostate cancer tend to have high levels of the protein PSA (prostate specific antigen) in their blood due to the fact they produce so much of it. Through the use of a monoclonal antibody that can interact with it, it is possible to get a measure of the level of PSA in a sample of blood.
Name 3 ethical implications of monoclonal antibodies?
.Use of mice.Death of patients with MS.Drug trials are dangerous
How is the use of mice in the production of monoclonal antibodies an ethical issue? Has any help been put in place?
.Production of monoclonal antibodies includes the use of mice.The formation of tumour cells includes the deliberate inducing of cancer in mice.Guidelines have been drawn up to reduce suffering but many people still believe it is unethical
How is the death of people with MS in treatment with monoclonal antibodies an ethical issue? Has any help been put in place?
.Monoclonal antibodies have saved many lives through diagnosis and treatment.But they have also led to the deaths of some people with multiple sclerosis.Informed consent is needed, where people know all the details of treatment including possible death before they consent to it
How are drug trials with monoclonal antibodies an ethical issue? Has any help been put in place?
.March 2006, 6 healthy volunteers underwent a test for a new monoclonal antibody in London.They all suffered from organ failures, as a result of T cells overproducing chemicals that stimulate an immune response or attack body tissues.All 6 survived, but it still raises questions about the ethics of drug trials
What is immunity?
The ability of an organism to resist immunity
What are the two types of immunity?
.Passive.Active
What is passive immunity, with examples
.Antibodies introduced from an outside source.Abs are not produced by the individual so they are broken down.No memory cells.Short livedFor example – .Anti-venom.Immunity acquired by a foetus from the mother
What is active immunity
.Production of abs is stimulated by the individual.Direct contact with the pathogen/antigen.Takes time to develop.Long lasting
What two forms does active immunity come in?
.Natural – met the disease yourself, normal immune response.Artificial – from a vaccine, induced immune response, few symptoms
How can vaccines be administered?
orally or subcutaneously (injection)
What does a vaccination do?
Generate an immune response
What do vaccines contain and what do they lead to?
.Vaccines contain antigens from the pathogens and lead to the formation of memory cells
When launching an effective vaccine programme, what needs to be thought about?
.Few side effects, as people can be easily discouraged.Should be cheap enough to immunise all vulnerable populations.Ability to produce, store and transport vaccine – requires hi-tech equipment, hygienic conditions and refrigeration.Needs to be administered correctly at the appropriate time – trained staff required.Vaccinate the majority of the population – best at one time so that for a period no individual carries the disease (transmission interrupted) – herd immunity
What is herd immunity?
.When a large enough proportion of a population is vaccinated which makes it difficult for the pathogen to spread.The vaccinated population provide a measure of protection for individuals who have not developed immunity
Basically, what is herd immunity?
.Basically it’s harder for unvaccinated people to come into contact with the pathogen
When is herd immunity best carried out?
.Herd immunity is bet achieved when the vaccinations are carried out at one time.This means that for a short period there are few infected individuals.This interrupts its transmission
Why are vaccinations not 100% effective?
.Vaccinations don’t induce immunity in some individuals (immune system defects).Disease develops immediately after vaccination before immunity is established .Pathogens can mutate frequently, rapidly changing their antigens (like with the flu).Each pathogen has many varieties (100 varieties of the common cold).Some pathogens can ‘hide’ in the immune system, they hide in cells or live in the gut where they are difficult to kill (e.g. cholera).Individuals object to vaccinations- Religious, ethical, medical and safety concerns
What ethical problems arise with vaccinations?
.Animals used in development.Side-effects can cause long term hard – risk against benefit.Who should vaccines be tested on?.Is it fair to test on a population where the target disease is common based on the idea they will gain the most benefit is its success – the vaccination is just a bit of a guess.Is it right to make vaccinations compulsory?.Should expensive vaccination programmes continue when the disease is almost vaccinated?
What is HIV?
human immunodeficiency virus
What does HIV cause?
AIDS – Acquired immune deficiency syndrome
What does HIV do?
Cause aids and HIV gradually destroys the sufferer’s immune system
When did AIDS epidemic start?
1980’s
As of 2015, how many people were living with HIV globally?
36.7 million people
How many people died of HIV last year?
1.1 million
Where did HIV come from?
HIV arose as a human infection:.Western central Africa.The virus ‘jumped’ the species barrier transferred from primates to humans.Possibly due to eating or slaughtering chimpanzees
How can HIV infect us?
The virus can enter the body via infected body fluids:.During sexual intercourse.Drug-taking using infected needles.Blood infection wounds.Blood transfusion and blood products.Mother to child across the placenta during pregnancy and via breast milk or birth
Symptoms of HIV
.Fever.Sore throat.Body rash.Tiredness.Joint pain.Muscle pain.Swollen glands (nodes)
Symptoms of AIDS
.Weight loss.Chronic diarrhoea.Night sweats.Skin problems.Recurrent infections.Serious life threatening illness
Name the 7 parts that make up HIV virus?
- Transmembrane glycoprotein2. Attachment glycoprotein3. Lipid envelope4. Reverse transcriptase5. Matrix6. Capsid7. Genetic material (RNA)
What is reverse transciptase?
enzyme that catalyses the production of DNA from RNA
Because HIV can produce DNA from RNA, what group is it apart of?
retroviruses
Because HIV is a virus what cant it do? So what does it do instead?
.As HIV is a virus, it is unable to replicate on its own.It uses its genetic material to instruct the host cell’s biochemical mechanisms to produce the parts needed to make new HIV
How does HIV infect host cells? (8 steps)
- p120 molecules on the HIV bind to CD4 receptor proteins on T helper lymphocytes and macrophages2. The protein capsid fuses with the cell membrane3. HIV RNA + enzymes enter T cell4. HIV reverse transcriptase converts the viruses RNA to DNA5. The new DNA is moved into the helper T cell’s nucleus where it is inserted into the cell’s DNA6. The HIV DNA in the nucleus creates mRNA using the cells enzymes. This mRNA contains the instructions for making new viral proteins and the RNA from new HIV7. The mRNA leaves the nucleus of the host cell through nuclear pores and uses the cell’s protein synthesis mechanisms to make HIV particles8. The HIV particles bud away from the helper T cell with a piece of its CSM surrounding them which forms their lipid envelope
What does HIV specifically target?
helper T cells
How does HIV lead to aids?
HIV leads to AIDs by destroying/interfering with T cells normal functioning
How many helper T cells does a healthy human have?
800-1200 helper T cells per mm^3 of blood
How many helper T cells does an AIDS sufferer have?
less than 200 helper T cells per mm^3 of blood
If someone doesn’t have enough T cells what problems arise?
- B cells cannot be stimulated to produce Ab - Cytotoxic T cells cannot be stimulated
With AIDS/HIV can memory cells be affected? What effect does this have?
Memory cells are also sometimes infected and destroyedThis results in an inadequate immune response leaving the body vulnerable to infections and cancer
What are AIDS sufferers prone to?
AIDS sufferers are therefore prone to infections of the lungs, intestine, brain and eyesDiarrhoea and weight loss are common
What type of illness is HIV, why?
It is a secondary illness, not HIV that causes death
How to produce monoclonal antibodies
.Irradiate mouse to induce formation of tumours.Tumours form inside mouse, the cells are removed.Inject different mouse with non-self antigens.B-cells which produce antibodies against the antigens are removed from the spleen.Mix tumour cells with B cells and add detergent.Detergent causes cells to fuse.Fused cells are separated and cultured.Fused cells have features of tumour and B cells – ‘immortal’ and produce antibodies.Culture cells to form clones.Test each clone to identify which one is producing the required antibody.Culture the selected cells on a large scale
Define huminisation
making the monoclonal antibodies suitable for human use (since they come from mouse tissue)
Uses of monoclonal antibodies
.Separating chemicals from mixtures.Immunoassay (detecting concentrations of macromolecules in solutions).Cancer treatment.Transplant surgery
What can antibodies be used to identify?
Antibodies can be used to identify flu, hepatitis, chlamydia and types of cancer
What is a non-specific response?
immediate and same for all pathogens
What are the two nonspecific responses?
.Physical Barrier (skin).Phagocytosis
What is a specific response?
slower and pathogen specific
What are the two specific responses?
.Cell – mediated response (T-Lymphocytes).Humoral response (B-Lymphocytes)
Where do T cells mature?
.T Lymphocytes mature in the thymus gland
What do T cells respond to?
own cells altered by viruses/cancers (foreign material inside body cells) or transplanted tissues
How can different cells display antigens on their surface?
- Phagocytes that have engulfed and hydrolysed a pathogen present some of the pathogens antigens on their surface2. Body cells invaded by a virus present viral antigens on their surface as a distress signal3. Cancer cells are different from normal cells and present antigens on their surface4. Transplanted cells from the same species have different antigens on their cell surface
What are cells that display foreign antigens known as?
antigen-presenting cells
How do T cells become activated?
The phagocyte places antigens from the pathogen on its own cell-surface membraneReceptors on certain helper T-cells fit exactly onto these antigensThis activates other T cells to divide rapidly by mitosis and form a clone
What do cloned T-cells do?
.Develop into memory cells that allow a fast future response to the same pathogen .Stimulate phagocytes to engulf pathogens via phagocytosis .Stimulate B-cells to divide and secrete their antibody .Activate cytotoxic T cells
What do cytotoxic T cells do?
.Cytotoxic T cells kill abnormal body cells
How do cytotoxic T cells kill abnormal body cells?
.They produce a protein called perforin that makes holes in the cell surface membrane.This makes the cell freely permeable, killing it
What are cytotoxic T cells effective against?
.This action is very effective against viruses as they replicate inside cells
What is the ELISA test?
Enzyme linked immunosorbent assay.It uses antibodies to detect the presence and amount of protein in a sample.Highly sensitive
ELISA test method
.Apply sample to surface.The antigens in the sample will attach to this surface.Wash the surface to remove any antigens that aren’t attached.Add the antibody that is specific to the antigen we are trying to detect.Leave to allow binding.Rinse to remove excess antibody.Add a second antibody that will bind with the first antibody.The second antibody has an enzyme attached to it.Add the substrate to the enzyme (must be colourless).The enzyme acts on the substrate.The substrate is converted into coloured products.The amount of antigen present is relative to the intensity of colour that develops
Define pathogen
Disease causing microbe
Define phagocyte
WBCs that travel in the blood and tissues, destroying pathogens
Define phagocytosis
Mechanism where phagocytes engulf pathogens and hydrolyses them using enzymes
Define immune
Resistant to a particular infection or toxin owing to the presence of specific antibodies
Define antigen
Molecule that triggers an immune response
Define antibody
A protein made by lymphocytes in response to the presence of an antigen
Define t lymphocyte
Type of WBC produced in the bone marrow but matures in the thymus. Coordinates immune response and kills infected cells – cell mediated response
Define helper t cell
Bind to antigens presented by antigen presenting cells. This binding stimulates T cell to divide rapidly.
Define antigen presenting cell
Cells that display foreign antigens on their cell-surface membrane.
Define b lymphocyte
Type of WBC produced by and matures in the bone marrow. Present in bodily humour. Humoral immunity. Produce antibodies.
Define memory cell
Produced by B cells. Live for decades. Provide long-term immunity. When they encounter the same pathogen again they divide rapidly into more plasma and memory cells to immediately fight the infection - secondary immune response
Define plasma cell
Secrete antibodies into blood plasma. Survive for only a few days. Destroy pathogens and toxins. Immediate defence only - primary immune response
Define cytotoxic T cell
Kills infected cells by introducing perforin molecules into their CSM, causing them to take in water and burst.
Define vaccination
Introduction of a vaccine subcutaneously or orally that contains pathogen antigens capable of initiating an immune response.
Define biodiversity
The range and variety of genes, species and habitats within a particular region.
What are the 3 types of biodiversity?
Species diversity, genetic diversity and ecosystem diversity
What is species diversity?
the number of different species and the number of individuals of each species within any one community
What is genetic diversity?
the variety of genes possessed by the individuals that make up any one species
What is ecosystem diversity?
the range of different habitats within a particular area
What is species richness?
Species richness is the number of different species in a particular area at a given time (community)
Equation for species diversity index? With meaning for each letter
d = species diversityN = total number of organisms of all speciesn = total number of organisms of each speciesΣ = the sum of
Human factors affecting biodiversity
.Agriculture – demand for food has more than doubled.Increased use of herbicides and pesticides.Use land for homes and industry.Increased waste and land fill.Deforestation
How does agriculture affect biodiversity?
- Monoculture (growing only one species) 2. Lack of intercropping (not rotating what is grown each season)3. Competition for space4. Use of pesticides and herbicides5. Cattle in the field where species may grow6. Draining wetland and marshes7. Removing hedgerows (replacing hedge borders with fences)
How do monocultures affect biodiversity?
reduction in species and genetic diversity directly and indirectly as fewer food sources and habitats
how does lack of intercropping affect biodiversity?
Drains the soil of nutrients, results in monoculture
How does competition for space affect biodiversity?
Natural species habitats cannot grow/are outcompeted by dominant
How does use of pesticides and herbicides affect biodiversity?
Can be toxic to species, enters water cycle, eutrophication
How does cattle in the field where species may grow affect biodiversity?
Over grazing, trampling, reduction in species diversity
How does draining wetland and marches affect biodiversity?
Removes nutrients and moisture from soil so species cannot grow
How does removing hedgerows affect biodiversity?
Removes habitats and food sources
What is deforestation?
The permanent clearing of forests and the conversion of land to other uses, such as agriculture, grazing or settlement
How many species are being lost each year due to deforestation?
50,000
How does deforestation reduce biodiversity?
by clearing the forests you are not only killing the trees (a species) and so reducing the species diversity index directly but the trees may also act as a habitat or food source to other animals so by killing the trees you are killing the animals that rely on the tree as well – thereby indirectly reducing biodiversity as well.
How can maintaining biodiversity bring economic benefit?
- By maintaining biodiversity, you can keep biodiverse areas (like the coral reef or forests) which attract tourists and people for days out, thereby benefiting the economy. Also extracts of plants can be used for medicine, so you keep the biodiversity and keep the money.
How can you reduce human impacts of deforestation?
.Eco charges.Increased taxes/fines
What are nerve cells (also called neurones)?
- Highly specialised cells- Adapted to rapidly carry electrochemical changes (nerve impulses)- Amongst the largest cells in the body (especially in length)
Draw and label a basic nerve cell
check notes or google
Function of cell body
Contains the nucleus and large amount of rough endoplasmic reticulum. Nucleus holds DNA and controls the cell, large amounts of RER to form neurotransmitters
Function of axon
Collect and carry the nerve impulse away from the cell body
Function of myelin sheath
Multiple cells wrapped around the axon; they increase the speed of the impulse, wrapped around to form Myelin layer
Function of nodes of ranvier
Gaps where there is no myelination, increases speed
Function of shwan cells
Individual cells protect the neurone, provide electrical insulation
Function of dendrite
Extensions of the cell body, carry impulses towards the cell body, increase action potential
Function of dendrons
Extensions of the cell body, thickest part of the branches, they subdivide into dendrites
How are motor neurones different? Why?
- Lots of dendrites, to make sure it gathers as much information as possible- Axons split into 3 at the end, to make sure a response occurs by carrying the impulse to different places- Cell body at basic position, to pick up neurone and carry it- Long axon length, to carry the signal far- Nerve endings at muscle or gland
How are sensory neurones different? Why?
- Nerve endings in tissue, like skin- Cell body not at end, mid-way- Dendrites come off the end in different places, so it can send different messages to coordinate a response
How are intermediate neurones different? Why?
- Short axon- Lots of dendrites
What is a nerve impulse?
- A self-propagating wave of electrical disturbance that travels along the surface of the axon membraneSpecifically, it is a temporary reversal of the electrical potential difference across the axon membraneNOT in the neuroneNOT an electrical current
What are the two states of a nerve impulse?
- Action potential- Resting potential
What is resting potential?
- Negative inside- Positive outside
What is action potential?
- A nerve impulse occurs when there is a temporary reversal of these charges- The reversal is then propagated along the axon
- Neurones send messages ________
electrochemically
- Chemicals in the body are _____ charged
electrically
The important ions in the nervous system are:
- Sodium (1+ charge)- Potassium (1+ charge)
What controls nervous system ions movement?
- Phospholipid bilayer- Intrinsic proteins- Gated channels
How is ion movement controlled?
- Phospholipid bilayero Non-polar fatty acid tails repel charged molecules- Intrinsic proteinso Ion channels allow specific ions to pass- Gated channelso Na+ and K+ gated channels control amount of movement
Value of resting potential
= -65mV
describe the Formation of a Resting Potential
- Na+ are actively pumped out of the axon by sodium-potassium pumps2. K+ are actively pumped into the axon by sodium-potassium pumps3. For every 3Na+ pumped out, 2K+ move in4. There are more Na+ outside (tissue fluid), than there are inside the axon cytoplasm, a chemical gradient is formed5. Due to the gradient, Na+ try to move back in and K+ try to more out, down there concentration gradient6. However, the Na+ gates are shut, and the K+ gates are open7. So only the K+ can move, and so they leave the axon8. At this point the membrane is 100x more permeable to K+9. This causes K+ to diffuse out faster than Na+ can move in, causing the outside of the axon to become positively polarised, and the inside of the axon to become negatively polarised10. But now, due to the massive positive charge outside of the axon (electrical gradient), some K+ are compelled to move back inside, they are attracted to the negative charge and repelled by the positive outside11. Some of the K+ do move back in, but an equilibrium is formed, where there is no more net movement of ions12. The electrical and chemical gradient becomes balanced, and the resting potential is established
• The energy of a stimuli causes ________________________ on the axon membrane
a temporary reversal of the charge
• Resting potential value meaning?
the difference in charge across the membrane
What is the change in charge from resting potential to action potential?
• The temporary reversal causes the charge of -65mV difference in the resting potential to become a +40mV difference
What happens to the membrane when it goes from -60mV to +45mV?
It is depolarised
Where is negative and positive in action potential?
outside negative, inside positive
Voltage-Gated Ion Channels, what are they?
- Channels in the membrane change shape- Open or close, depending on the voltage across the membrane
At rest, which voltage gated ion channels are open on the axon?
.Some potassium gated channels are open.Sodium channels are closed
Draw the graph for resting potential to action potential
CHECK NOTES OR GOOGLE
How is an action potential produced and restored along an axon?
- At resting potential (-65mV) the potassium voltage-gated channels are both open and closed, while the sodium voltage-gated channels are closed2. A stimuli causes the sodium voltage-gated channels to open3. The sodium ions move in (facilitated diffusion) down there electrochemical gradient, this causes more sodium voltage-gated channels to open so more sodium ions can move in4. This causes a change in voltage from -65mV resting to +40mV action, depolarisation has occurred5. This new voltage causes the sodium voltage-gated channels to close and the potassium voltage-gated channels to open6. The potassium ions move out (facilitated diffusion), down its electrochemical gradient, this is called repolarisation, this causes more potassium voltage-gated channels to open so more potassium ions can move out7. Too many potassium ions have moved out and the charge has gone past -65mV to -70mV, this is called hyperpolarisation8. As the neurone cannot react to a stimulus when not at resting potential, the sodium-potassium pump pumps 3 sodium ions out and 2 potassium ions in so the charge difference increases from -70mV to the resting potential of -65mV
Describe the passage of action potentials
Passage of an action potential along a non-mylenated neurone.After initiation of the ‘start’ of an axon, it ‘moves’ rapidly down itKey Points:- Nothing physically moves- The reversal of charge is reproduced
HOw is an impulse passed along an axon in an unmyleinated sheath?
- Sodium outside, potassium inside: polarised (-65mV)2. Influx of sodium ions: reversal of charge (+40mV)3. Acts as a stimuli causing sodium gated channels to open further along: depolarisation4. Behind, sodium gated channels close and potassium open5. Removal of K+ returns membrane to resting potential (-65mV)
The myelin sheath is an electrical insulator, what does this cause?
- Prevents action potentials forming- Action potentials can only occur at nodes of ranvier- Results in ‘node hopping’ (saltatory conduction)
Draw the diagram of saltatory conduction
CHECK NOTES OR GOOGLE
Describe and explain saltatory condcution
- Stimuli causes an influx of sodium ions through the open sodium ion gates into the axon (facilitate diffusion)2. Reversal of charges, action potential occurs3. Sodium ions diffuse from a high concentration to a low concentration in the cell4. A build up of positive ions causes the next sodium ion voltage gated channel to open5. Sodium ions diffuse in6. New action potential occurs7. Action potential moves along the axon
Action potential propagation along myelinated axons from what to what?
one node of ranvier to the next node
Key points of saltatory conduction
- Energy is not lost between action potentials- Each action potential is the same size
What factors effect the speed of an impulse?
Myleination, temperature, diameter of the axon
How does temperature effect the speed of an impulse?
o High temperature increases speed of nervous impulse, particles have more kinetic energy, diffuse quicker, also increased enzyme action, and more energy available for active transporto Too high, enzymes and proteins denature, doesn’t worko Low is opposite effect of high
How does diameter effect speed of an impulse?
o Smaller axon causes the ions to leave easilyo Harder to build up ions in the axono Harder to establish electrical and chemical gradientso Membrane potentials are difficult to maintain
What is the refractory period?
The refractory period is the time that it takes for Na+ influx to be possible again.
Where is the refractory period on the graph?
The refractory period is the portion of the graph that leads back to the resting potential.
For an action potential to occur, it needs to reach ________ – if it does not it is called a _______.
a threshold valuefailed initiation
Why are refractory periods important?
- Ensures action potentials are in one direction2. Ensures action potentials are discreet (separate)3. Ensures action potentials are limited in number at one time
- The area before the action potential will be in refractory period, so how does this allow the impulse to travel in one direction?
o A new action potential cannot occuro Axon must be at resto Travels in the correct direction (brain or effector)
How is a refractory period discrete? Why is this good?
- Area behind means AP cannot occur- Refractory period takes time- Messages sent to the brain are discrete (not muddled)
How can there only be a certain number of action potentials? Why is this good?
- Action potentials are a fixed distance apart- Cannot occur ‘behind’ one another- Axon is a fixed length, thereforeo Only a certain number of action potentials will ‘fit’
What is the synapse
The synapse is the point where a neurone communicates with the dendrite of another neurone or with an effector.
Draw and label a diagram of a synapse
check notes
What does the synaptic knob contain? Why are each required?
- Many mitochondriao Release energy for movement of vesicles toward the synaptic clefto Release energy for protein synthesis- Large amounts of ERo Synthesise chemical messengers (neurotransmitters)- Vesicles containing neurotransmitterso Package up the neurotransmitterso Move neurotransmitters to the membrane
What are neurotransmitters?
Neurotransmitters are:- Chemical messages- Specific- Enable synaptic transmission
The response to the arrival of a neurotransmitter will however depend on what?
- The cell- The cells location- The neurone
A synapse that relies on the neurotransmitter acetylcholine, it is made of what?
- Acetyl (ethanoic acid)2. Choline
Which synapse relies on the neurotransmitter actylcholine?
cholinergic synpase
Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic nerve.
- Action potential in the neurone causes depolarisation of the pre-synaptic neurone which leads to the calcium ion gated channels to open2. This causes an influx of calcium ions into the synaptic knob via facilitated diffusion3. The 2+ charged calcium ions cause a change in the voltage of the synaptic knob and moves the vesicles containing neurotransmitters to the membrane of the synaptic knob4. The vesicles fuse to the membrane5. The neurotransmitters diffuse across the synapse and attach to the neuroreceptors of the post-synaptic membrane6. This changes the tertiary structure of the neuroreceptors, opening them and allowing an influx of tissue fluid – which contains sodium ions – and so causing an impulse if the threshold is met
What are neuroreceptors?
Chemical gated ion channels in the post synaptic neuron membraneThey are:- Specific, binding site for the neurotransmitter involved- Usually closed- When neurotransmitter bind they undergo a conformational change- Cause the influx of sodium ions
What is acetylcholinesterase?
Acetylcholinesterase is:- A hydraulic enzyme (hydrolysis)- Located on the membrane- Breaks up acetylcholine into acetyl (ethanoic acid) and choline
What happens after hydrolysis of acetylcholine?
- Acetyl and choline diffuse back across the cleft into the presynaptic neurone- Neurotransmitters are recycled and repackaged- Generation of a new action potential is prevented
Define neurotransmitter
Chemical messenger released form the pre-synoptic neurone and involved in the communication between adjacent neurones or cells
Define cholinergic synapse
The gap where a neurone that produces acetylcholine sends messages to other neurones, or to muscle cells
Define synapse
A junction between two neurones in which they do not touch but have a narrow gap, across which neurotransmitters cross
Define refractory period
Period during which the membrane of an axon of a neurone cannot be depolarised and no new action potential can be initiated
Define saltatory conduction
The propagation of a never impulse along a mylenated neurone in which the action potential jumps from one node of Ranvier to another
Synapses transmit impulses in ___ direction to a ______ location
oneprecise
Synapses prevent ____________
overstimulation
Synapses act as a junction between, allowing what to what?
a. A single impulse to multiple neuronesb. A number of impulses to be combined at a synapse
What is summation?
The additive effect of low frequency action potentials to produce sufficient neurotransmitters to trigger an action potential across the synapse.
What are the two forms of summation?
- Spatial- Temporal
What is spatial summation?
Different presynaptic neurones come together to trigger one action potential.
What is the number of pre and post synaptic neurones with spatial summation?
o Multiple pre-synaptic neurones at one synapse
How does spatial summation reach the threshold value?
o A single neurone does not release enough neurotransmittero Multiple neurones release neurotransmittero Threshold is exceeded
What is temporal summation?
Single presynaptic neurone release neurotransmitters many times over a short period to exceed the threshold.
What is the number of presynaptic neurones for temporal summation?
o One neurone per post synaptic neurone
What is the amount of neurotransmitters for temporal summation?
o Low frequency action potentials means they do not release enough neurotransmitter so there is no threshold meto High frequency action potentials means neurotransmitters are released multiple times over a short period which means the threshold is met
What is an inhibitory synapse?
A synapse in which the nerve impulse in a presynaptic cell results in reduced likelihood of an action potential initiation in the post synaptic cell.
How does an inhibitory synapse inhibit?
- Neurotransmitters diffuse across2. Causes chloride ion channels in the post synaptic membrane to open3. Chloride ions diffuse across the post synaptic membrane4. Membrane becomes more negative than at resting (hyperpolarisation)
How do some drugs create fewer action potentials? with example
o Inhibiting the release of neurotransmittero Blocking the sodium/potassium channelso For example: Gaba• Inhibits or slows the brain’s function• Promotes sleepiness
How do some drugs stimulate the nervous system?
o They create more action potentials by: Mimicking the neurotransmitter Stimulating the release of more neurotransmitter Inhibiting the break down of neurotransmitter (block the enzyme) For example:• Serotonino Believed to help regulate mood and social behaviours, digestion, sexual and sleep desire, and function
Define tendon, ligament and cartilage
Tendon – connect bone to muscleLigament – connective tissue that connects bone to boneCartilage – connective tissue found between bones, a ‘shock absorber’
What are muscles?
- Bundles of fibres- Different structures- Different jobs
What is a cardiac muscle?
a. Present in the heartb. Acts involuntarilyc. Myogenicd. Strong and continuous contraction
What is a skeletal muscle?
a. Attached to bonesb. Vast majority of musclec. Discontinuous contractiond. Controlled voluntarily
What is a smooth muscle?
a. Involuntary muscleb. Found in the gut, blood vessel walls, and in the iris of the eyec. Slow and weak contraction
How do muscles act?
- Receiving a nerve impulse- Working in antagonistic pairso You cannot stimulate the contraction of two antagonistic muscles at the same time- Pulling bones
What is antagonistic?
one muscle (prime mover) contracts and the other (antagonistic) relaxes
What happens in flexion and extension of the arms?
Flexion:Biceps contracted, triceps relaxed (extended). The prime mover is the biceps.Extension:Triceps contracted, biceps relaxed. The prime mover is the triceps.
Structure of skeletal muscle with analogy
Muscles are composed of small units, bundled into progressively larger units. Myofibrils (individual threads) are bundled into individual muscle fibres (string), which are bundled together into a bundle of muscle fibres (thin rope), which are then bundled together to form the whole muscle (thick rope).
What is the structure of skeletal muscles?
- Individual muscle cells are fused together- Form muscle fibres (myofibrils)- Lie parallel to each other- Increases strength
What are the two types of fibres found in muscles?
- Slow twitch fibres - Fast twitch fibres
How can muscles fibres be grouped?
Group based on two properties:- Resistance to fatigue- Speed of contraction
Slow twitch, speed of contraction, power of contraction, type of activity, type of respiration, and example of muscle containing fibre
SlowLow but prolongedEndurance: walking, posture, standing, long distance runningAerobicCalf muscles
Fast twitch, speed of contraction, power of contraction, type of activity, type of respiration, and example of muscle containing fibre
FastHighIntense activity over a short period: weight lifting, sprintingAnaerobicBiceps
Slow twitch fibres adaptations
- Large amount of myoglobin (red molecule that stores oxygen)- Good supply of glycogen- Good blood vessel network- Many mitochondria- Small diameter (diffusion)- Tend to be darker in colour
Why is each slow twitch fibre adaptation beneficial?
- Large amount of myoglobin (red molecule that stores oxygen)o For oxygen for aerobic respiration for energy and ATP- Good supply of glycogeno For glucose for aerobic respiration for energy and ATP- Good blood vessel networko For a good supply of oxygen and glucose for aerobic respiration for energy and ATP and removes carbon dioxide from aerobic respiration- Many mitochondriao For aerobic respiration to take place for energy and ATP- Small diameter (diffusion)o To allow glucose and oxygen to diffuse in easily, allowing for a good supply of them for aerobic respiration for energy and ATP reduce diffusion pathway- Tend to be darker in colouro Because of the large amount of myoglobin (a red molecule that store oxygen)
Fast twitch fibre adaptations
- Thicker and more myosin filaments- High concentration of enzymes involved in anaerobic respiration- A store of phosphocreatine – provide energy (energy buffer)
Why do fast twitch fibres tire quickly?
- Fewer blood vessels- Run out of oxygen quicker- Thicker; larger diffusion distance
Individual myofibrils are fused together into one long cell, what do they share? What is it called?
o Nuclei = multinucleatedo Cytoplasm = sarcoplasmo Cell membrane = sarcolemma
Why do nucleic need to be dotted all over the sarcoplasm?
- Transcription- All muscle cells controlled
Which organelle will be in large number in the sarcoplasm and why?
- Mitochondria: ATP for contraction and protein synthesis- RER: protein synthesis
Myofibrils consist of two types of protein filaments, what are they?
Actin and myosin
Descibe actin
a. Thinnerb. Made up of two strands coiled around each other
Describe myosin
a. Thickerb. Consists of rod-shaped fibres with ‘bulbed’ heads which project outwards
What do myofibrils consist of?
- Multiple sarcomeres- Actin and myosin filaments
Why do myofibrils appear stiped? What are the dots?
Banding patternCauses myofibrils to appear stripedThin dots = actinThick dots = myosin
What are the two main components of the sarcomere?
- Dark bandsa. Actin and myosin overlapb. Anisotropic bands (A-bands)c. Depends on myosin length2. Light bandsa. No overlapb. Isotropic bands (I-bands)
Label a sarcomere
diagram found in bookletlabelled as follows:1. This area appears light, because only thin, actin filaments are present – I-band2. This area appears dark because there is overlapping of both filaments – A-band3. This area, where there is only myosin is present, is called the H-zone4. Z-line
Where is one sarcomere, in terms of z-lines?
One sarcomere is z-line to z-line
What is a neuromuscular junction?
Where a motor neurone meets skeletal muscle fibres
Often there are multiple neuromuscular junctions connected to different muscle fibres, why?
o Multiple fibres stimulatedo Speeds up the responseo Contraction is quicker and more powerfulo Threshold is met
What is the all or nothing principle?
the strength by which a nerve or muscle fibre responds to a stimulus is independent of the strength of the stimulus
How do neuromuscular junctions affect contraction strength?
- Follow the all or nothing principle BUTo Multiple neurones = one muscle unito Slight force = few fibres stimulatedo Large force = multiple fibres stimulatedo Contraction strength will vary
Neuromuscular junctions are always cholinergic synapses, therefore:
- The neurotransmitter is acetyl choline- The enzyme that hydrolyses the neurotransmitter is acetyl choline esterase
How do action potentials travel to the muscle fibre?
- Action potentials travel into the muscle fibre through:o T-tubuleo Branch through the sarcoplasmo To the sarcoplasmic reticulumo Releases calcium ions from sarcoplasmic reticulum
As well as actin and myosin, there are two other proteins found in muscle fibres - name and describe them
- Tropomyosino Long and thin fibrous strandso Wrap around the actin filament- Troponino Globular protein involved in muscle contraction
What is the sliding filament theory?
- The myosin filament has an ADP attached to it as a myosin head. It needs to attach to the binding site on the actin filament, but there is a tropomyosin molecule blocking the binding site.2. Calcium ions (which have diffused into the myofibrils from the sarcoplasmic reticulum) binds to the troponin, causing the tropomyosin to move out of the way of the binding site3. The ADP (myosin head) binds to the binding site on the actin filament, forming cross-bridges4. The ADP (myosin head) changes angle, which moves the actin filament along5. ATP replaces the ADP in the binding site, and is released from the binding site6. ATPase hydrolyses the ATP into ADP, causing the myosin head to resume the normal position7. This means there is a new point of attachment for the myosin head, and so it can bind to the actin again
What is speciation?
The formations of two populations from one
What are the types of speciation?
Allopatric speciation and sympatric speciation
Explain how oxygen is loaded, transported and unloaded in the blood. (6 marks)
.Haemoglobin carries oxygen / has a high affinity for oxygen / oxyhaemoglobin;. Loading / uptake / association in lungs;.at high p.O2; .Unloads / dissociates / releases to respiring cells / tissues.at low p.O2;.Unloading linked to higher carbon dioxide (concentration);
Selection pressures are …
… environmental factors that limit the population of a species
Stabilising selection is caused by …
… selection pressure against both extremes, and so the mean remains the same
Directional selection is caused by …
… selection pressure for an extreme, and so the mean changes
Tell me about disruptive selection
- Selects against the average phenotype- Favours the extreme phenotypes- Can lead to speciation
.Speciation is what?
the evolution of new species from existing species
What does speciation enable?
.It enables evolutionary change and diversity
Speciation occurs due to:
- Reproductive isolation- Genetic differences (mutations)- Geographical isolationo Differences in two populations gene pools
What are the two forms of speciation?
Allopatric Speciation:Sympatric Speciation:
WHat is allopatric speciation?
.More common.Different locations.Geographic separation
WHat is Sympatric Speciation:
.Less common than allopatric.Same location.Reproductive isolation
How does allopatric speciation occur –
.Each species will have its own range, within which there will be a number of other populations of that species.Populations can still interact and interbreed.Unless a barrier occurs, preventing migration between populations of the same species.The environments of each new range may be different.Different mutations occur in each range.Due to different selection pressures, different mutations are favoured.No gene flow can occur and so changes in allele frequency occur.Eventually they will be unable to interbreed even if the barrier is removed
Define Adaptive radiation
The diversification of a species into forms adapted to different ecological niches
Allopatric Speciation key points
.More common than sympatricDifferent locations.Geographic seperation .Physical barrier i.e. Lake, desert, mountain area.Takes millions of years
Sympatric Speciation key points
.Less common than allopatric.Same locations.Reproductive isolation .Breeding seasons or food preference
Apple maggot fly sympatric specxiation example explanation
- Only lay eggs inside Hawthorns Fruits (native to North America) 2. Apple trees introduced3. Some flies lay eggs in apples4. Mates are found by searching site where they were raised5. Raised in apples, mate with flies raised in apples 6. Mutations may result in two new species
two examples of sympatric speciation
apple maggot fly, seasonal breeding
Why is speciation more likely in small populations?
In a small populations there will be:- A small variety of alleles (lower genetic diversity)- Not equal chance of each allele being passed on OR if a muation occurs….- One allele/mutation is passed on very quickly - Increase in allele frequency - Speciation is more likely
What is genetic drift?
Genetic drift is genetic change due to chance, eg. By chance fewer decesendents of one phenotype are left behind after some organisms of a species get stamped on
On islands in the Caribbean, there are almost 150 species of lizards belonging to the genus Anolis. Scientists believe that these species evolved from two species found on mainland USA. Explain how the Caribbean species could have evolved. (6 marks)
- Geographic(al) isolation;2. Separate gene pools /no interbreeding/gene flow 3. Variation due to mutation;4. Different selection pressures / different abiotic / biotic conditions / environments / habitats5. Different(ial) reproductive success / selected organisms (survive and) reproduce6. Leads to change / increase in allele frequency
What is disruptive selection?
Selective pressures against the intermediate trait
Examples of disruptive selection
fur length (medium against)Colour or rabbit (white against)
What is speciation?
Speciation is the formation of two species from one
Where is sympatric speciation?
Sympatric Speciation = Same place
Exampels of sympatric speciation?
Examples are mayflies or seasonal breeding
Where does allopatric speciation?
away from species
Key points of allopatric speciation
- Geographic(al) isolation2. Separate gene pools / No gene flow 3. Variation caused by a mutation4. Different selection pressures 5. Different(ial) reproductive success6. Change in allele frequency.
What is genetic drift? What does it do?
• Genetic Change due to CHANCE dissapearance of certain alleles• In small populations • Increases liklihood of speciation
Steps of genetic drift?
- Smaller population, fewer alleles, less diversity2. By chance, one allele is not passed on3. By chance fewer decedents of one phenotype are left
What is an isolating mechanism?
• Way in which a population becomes separated• Required for speciation to occur
How does ecological (habitat choice) act as isolating mechanism?
Inhabit different areas (within the same area), individuals rarely meet or cross paths/mating grounds
How does temporal (breeding seasons) act as isolating mechanism?
Breeding seasons do not coincide, may not be fertile at the same time, no interbreeding
How does hybrid sterility act as isolating mechanism?
Different chromosome number, fusion of gametes cannot produce viable gametes, horse (2n = 64), donkey (2n = 62) = mule 63 – no pairing
How do behavioural differences act as isolating mechanism?
Courtship behaviors are different, no attracted to one another scent, different mating rituals
Define genepool
all the alleles of all the genes of all the individuals in a population at a given time at a given time
What is natural selection?
the process by which organisms that are better adapted to their environment tend to survive and breed at the expense of those less well adapted.
Phenotypic variation is a result of:
- Genetic factors 2. Environmental factors
Why does genetic variation occur?
- Meiosis 2. Sexual reproduction 3. Main factor – MutationsAll can result in selection occuring
.Most traits are normally distributed, what does this mean?
.The most common result (mode) is near the average (mean) and the middle value (mode)
.When selection occurs, the normal distribution curve may what?
Change shape
Directional Selection, what is it with example
• Change in environment • Changes the mean• Extreme is selected for• Antibiotic Resistance
Stabilizing Selection, what is it with example
• Selection against both extremes• Phenotypic variation decreases• Environment has remained stable• Birth Weight
Differences between the reproductive successes of individuals affects the allele frequency in populations, explain how. (6 marks)
- Random mutation of alleles within the gene pool 2. The new allele has an advantage in a SPECIFIC environment3. The individuals are better adapted/obtain resources4. These individuals grow rapidly and live longer compared to other alleles5. Reproduce passing on this allele. 6. Offspring survive better and reproduce 7. The advantageous allele increases at the expense of the individuals with the less advantageous allele. 8. Change in the allele frequencies in a population occurs = Evolution
Selection pressures are what?
environmental factors that limit the population of a species
Give the features of selection pressures
• Determine the frequency of all the alleles within the gene pool • Vary from time to time and place to place
Every organism is subject to selection so …
… certain factors may increase the chances of selection occurring
Examples of selection pressures
dation, competition, disease, natural disasters
- The bacteria population’s normal distribution curve shifted in the direction of a population that has a greater resistance to antibiotics. Explain why. (6 marks)
- A spontaneous mutation results in a different protein structure, a new enzyme breaks down the antibiotic. Bacteria with the mutation survived. Antibiotic resistance bacteria multiply, this creates an increased frequency of antibiotic resistant alleles at the expense of the non-resistant population.
All species have the potential to increase their number ________
exponentially
’The rate increases in proportion to …
… the growing total number or size’
Evolution only occurs by natural selection if ….
organisms reproduce and have sufficient resources and genetic variation is present within the population and phenotypic variation is present within the population (greater diversity = adapt to change)
In order for populations to survive and increase exponentially they must …
have a high reproductive success and a suitable population size to minimise intraspecific competition
Factors that make exponential growth unlikely could be …
high death rates from predators, low parental investment and lack of resources
Death rates are not random, how are the following death rates influenced:TurtleArctic foxHedgehogeaglehuman
Turtle – some food sources, some camouflageArctic Fox – Not camouflaged, too warm in summer, some possible foodHedgehog – lots of food sources, camouflage, hibernation, adapted to predatorsEagle – plenty of food sources, adapted to hunt, suitable habitatsHuman – not camouflaged, ability to hint but possible limited food sources
.Death rates within a population will not be completely random / exponential growth is unlikely to occur because organism will…
- Be better adapted to the environment i.e. Camoflagued - Suited to prevailing conditions i.e. Catch food - Resit disease
Variation is essential because …
- Changing environments - New diseases - New predators - New competitors
Great tits are small birds. Natural selection influences the number of eggs laid by the Great tits. Explain why great tits that lay fewer than 3 eggs per nest or more than 14 eggs per nest are at a selective disadvantage. (3 marks)
- When high number of eggs, each individual young will receive less food; reference to mortality rates to disease / predators for2. low numbers of eggs; so in both cases low number of offspring will reach maturity / survive; 3. so less likely to pass on genes / alleles;
Selection pressures are what?
environmental factors that limit the population of a species
Difference between directional and stabilizing selection?
Stabilizing Selection –.Selection pressure against both extremes.(Mean remains the same)Directional Selection –.Selection pressure for an extreme.(Mean changes)
The selection pressure may change too frequently for _____to occur, so both must be over prolonged periods
evolution
What is disruptive selection?
.Least common form of selection.Opposite to stabilizing selection.Favors the extremes at the expense of the intermediate phenotypes
When will disruptive selection occur?
When an environmental factor i.e. temperature takes two or more distinct forms. Summer – warm, Winter = cold
Explain the example: Fur Length, in disruptive selection
• 5 degrees in winter (long fur). 15 degrees in summer (Short fur) • Result: Two different species, each activie in each season• One active in summer so only breed with others active in summer, producing short haired cubs. • One active in winter only breed with those active in winter
Why is it important/what impact will it have? (disruptive selection)
• Most important for causing evolutionary• Could result in two distinct species
Coho salmon example disruptive selection
• Large males and small males have a selective advantages • Small males sneak up to females so reproduce and pass on their alleles• Large males’ fierce competitors so attract the females and reproduce passing on their alleles • Intermediate sized is selected against as has no selective advantage
