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AQA A Level Biology > Paper 3A > Flashcards

Paper 3A Flashcards

1
Q

What is a cell?

A

A basic unit of structure and function in an organism

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2
Q

What does a eukaryote have? Example of some

A

A true nucleus with a nuclear envelope surrounding the chromosome and membrane bound organismsAnimal and plant cells

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3
Q

What does a prokaryote have? Example of one

A

Don’t have membrane bound organelleFree floating DNA and plasmids, not a nucleus

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4
Q

What does a plant cell have?

A

ChloroplastsNucleusCell membraneCell wallVacuoleCytoplasm

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5
Q

What does an animal cell have?

A

NucleusPlasma membraneMitochondriaRibosomesCytoplasmGolgi apparatusSmooth endoplasmic reticulumRough endoplasmic reticulumNuclear envelopeNucleolusNucleoplasmVesicles

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6
Q

What does a bacteria cell have?

A

FlagellumPlasmidsFree floating DNACytoplasm - containing ribosomes

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7
Q

What does a yeast cell have?

A

Cell wallCell membraneVacuoleCytoplasmNucleus

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8
Q

Parts of a chloroplast

A

Double membraneThylakoidGranaStroma

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9
Q

structure of Nucleus

A

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

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10
Q

Function of Nucleus

A

Store genetic informationControl centre of the cell

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11
Q

Structure of Ribosome

A

2 sub units (one small one big)Each contain ribosomal RNA and protein

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12
Q

Function of ribosome

A

Site of protein synthesis

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13
Q

Difference between 70S and 80S ribosomes

A

80S – eukaryotic cells, 25nm diameter70S – prokaryotic cells, mitochondria, and chloroplasts, slightly smaller than 80S

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14
Q

Structure of mitochondria

A

Bound by a double membraneOuter membrane = MatricInner membrane = CristaeHas its own strand of DNA

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15
Q

Function of mitochondria

A

Respiration“Powerhouse of the cell”Aerobic RespirationProduction of ATP

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16
Q

Structure of the cell membrane

A

Around the whole cell

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17
Q

The function of the cell membrane

A

Controls what diffuses in and out of the cell

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18
Q

Structure of Rough Endoplasmic Reticulum

A

Ribosomes present

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19
Q

The function of Rough Endoplasmic Reticulum

A

Protein synthesisPathway for the transport of materials (like proteins throughout the cell)

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20
Q

Endoplasmic Reticulum general info

A

‘ER’Connected to the outer nuclear membrane

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21
Q

Structure of Golgi Apparatus

A

Stack of membranes = flattened sacsMembranes contain small hollow structures called vesicles

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22
Q

The function of the Golgi Apparatus

A

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

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23
Q

Structure of Smooth Endoplasmic Reticulum

A

No ribosomes

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24
Q

The function of smooth endoplasmic reticulum

A

Synthesize, store and transport lipids and carbohydrates

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25
Q

Cytoplasm

A

Between the membrane and nucleus, made up of mainly water

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26
Q

Lysosome

A

MembraneContained up to 50 enzymes

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27
Q

Chloroplast

A

Outer and Inner membraneOpen space in the stromaThylakoid stacks (Grana) provides surface area

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28
Q

Permanent Vacuole

A

Large membrane bound sacs

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29
Q

Cell wall

A

On top of the cell membrane, around the whole cell

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30
Q

Cytoplasm

A

Houses all the organelleWhere chemical reactions take place

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31
Q

Lysosome

A

Garbage disposal of the cellRemove useless/dangerous materialFormed when vesicles produced by the Golgi contain useful enzymesContain digestive enzymes to break down waste

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32
Q

Chloroplast

A

Captures light for photosynthesis

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33
Q

Permanent Vacuole

A

Provides structure and support for the cell and holds sap/water

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34
Q

Cell wall

A

Provides structure and support for the cell

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35
Q

What are the 3 main adaptations a cell can have?

A

number of RER and GolgiNumber of mitochondriaSurface area

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36
Q

How does the number of RER and Golgi affect a cell? What cells would need this adaptation?

A

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

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37
Q

How does the number of mitochondria affect a cell? What cells would need this adaptation?

A

Increased respiration which in turn increases energy for cells that need a lot of energyFor example muscle of sperm cells

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38
Q

How does surface area size affect a cell? What cells would need this adaptation?

A

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

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39
Q

Which is bigger prokaryotes or eukaryotes?

A

Eukaryotes

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40
Q

Explain DNA in eukaryotes

A

Membrane-bound in a true nucleus

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41
Q

Explain DNA in prokaryotes

A

Free-floating or in plasmids, not membrane-bound

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42
Q

Which organelles are present in prokaryotes?

A

PlasmidFree-floating DNAFlagellumRibosomes

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43
Q

Which organelles are present in eukaryotes?

A

NucleusRibosomesMitochondriaGolgi ApparatusSERRERVesiclesLysosomes

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44
Q

Are ribosomes membrane-bound?

A

No, but RER is

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45
Q

Is there any photosynthetic material present in prokaryotes? Why?

A

No, chloroplasts are too big, but some big bacteria’s do have some photosynthetic material

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46
Q

Which ribosomes are present in prokaryotes?

A

70S

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47
Q

Which ribosomes are present in eukaryotes?

A

80S70S (in mitochondria and chloroplasts)

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48
Q

What are cell walls made of in prokaryotes?

A

murien

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49
Q

What are cell walls made of eukaryotes?

A

Cellulose

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50
Q

Describe the basics of an antigen

A

.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

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51
Q

Which molecules can act as anitgens?

A

. Proteins. Glycoproteins

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52
Q

Why are antigens important?

A

. Initiate immune response to pathogens. Allowing recognition of faulty cancer cells. Recognition of cells from other organisms of the same species

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53
Q

How does antigenic variation work?

A

.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

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54
Q

What is phagocytosis?

A

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.

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55
Q

What type of response is phagocytosis?

A

Phagocytosis is a non-specific response

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56
Q

Describe the steps of phagocytosis

A
  1. 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
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57
Q

What are the roles of T cells?

A

.Produces memory T Cells.Stimulates phagocytosis.Kills infected cells – making holes in their membranes.Stimulates B cells to divide

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58
Q

How does an antigen presenting cell come about?

A

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

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59
Q

What happens to an antigen presenting cell?

A

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

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60
Q

When B cells divide by mitosis what is formed?

A

They can either become memory cells or plasma cells

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61
Q

Where are memory cells found and what are ready to do?

A

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

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62
Q

What do plasma cells do?

A

Plasma cells produce antibodies that exactly fit the antigens on the pathogens surface

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63
Q

What do antibodies do?

A

The antibodies attach to antigens on the pathogen and destroy them

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64
Q

If the same infection occurs again what do memory B cells do?

A

If the same infection occurs again the memory B cells divide and develop into plasma cells that produce antibodies

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65
Q

List 3 functions of antibodies

A

.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

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66
Q

How are B cells and C cells both needed to remove a pathogen from the body?

A

The responses interact with each other.T cells activate B cells and antibodies coat pathogens making it easier for phagocytes to engulf them

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67
Q

If you see the word humoral in the exam what do you think?

A

B cells

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68
Q

What produces antibodies?

A

B cells, more specifically plasma cells

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69
Q

Are antibodies specific?

A

yes

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70
Q

Name 6 parts of an antibodies structure

A
  1. Antigen binding sites2. Variable region3. Constant region4. Light chains5. Heavy chains6. Receptor binding sites
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71
Q

Draw and label antibodies

A

idk check your revision guide or google if its right?

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72
Q

Why are the variable regions on antibodies called that?

A

As the binding sites differ

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73
Q

What gives the variable region its specific 3d shape in antibodies?

A

The sequence of amino acids

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74
Q

In antibodies, where does the constant region bind to?

A

receptors

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75
Q

Each binding site on an antibodie is c____________ to a specific antigen

A

complementary

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76
Q

When an antibodies binding site binds to an antigen what is formed?

A

forms an antigen-antibody complex

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77
Q

Roles of antibodies

A

.Antibodies do not directly destroy antigens.Agglutination.Markers

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78
Q

What happens in agglutination

A

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

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79
Q

How do antibodies act as markers?

A

They can act as markers that stimulate phagocytosis

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80
Q

What is a polyclonal antibodie?

A

.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

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81
Q

What are monoclonal antibodies?

A

.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

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82
Q

Different between poly and mono clonal antibodies?

A

Poly - .Made from a variety of B cellsMono - .Made from only one type of B cell

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83
Q

How do pregnancy tests work?

A

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.

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84
Q

How do monoclonal antibodies help diagnose PSA?

A

.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.

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85
Q

Name 3 ethical implications of monoclonal antibodies?

A

.Use of mice.Death of patients with MS.Drug trials are dangerous

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86
Q

How is the use of mice in the production of monoclonal antibodies an ethical issue? Has any help been put in place?

A

.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

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87
Q

How is the death of people with MS in treatment with monoclonal antibodies an ethical issue? Has any help been put in place?

A

.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

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88
Q

How are drug trials with monoclonal antibodies an ethical issue? Has any help been put in place?

A

.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

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89
Q

What is immunity?

A

The ability of an organism to resist immunity

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90
Q

What are the two types of immunity?

A

.Passive.Active

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91
Q

What is passive immunity, with examples

A

.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

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92
Q

What is active immunity

A

.Production of abs is stimulated by the individual.Direct contact with the pathogen/antigen.Takes time to develop.Long lasting

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93
Q

What two forms does active immunity come in?

A

.Natural – met the disease yourself, normal immune response.Artificial – from a vaccine, induced immune response, few symptoms

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94
Q

How can vaccines be administered?

A

orally or subcutaneously (injection)

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95
Q

What does a vaccination do?

A

Generate an immune response

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96
Q

What do vaccines contain and what do they lead to?

A

.Vaccines contain antigens from the pathogens and lead to the formation of memory cells

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97
Q

When launching an effective vaccine programme, what needs to be thought about?

A

.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

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98
Q

What is herd immunity?

A

.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

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99
Q

Basically, what is herd immunity?

A

.Basically it’s harder for unvaccinated people to come into contact with the pathogen

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100
Q

When is herd immunity best carried out?

A

.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

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101
Q

Why are vaccinations not 100% effective?

A

.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

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102
Q

What ethical problems arise with vaccinations?

A

.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?

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103
Q

What is HIV?

A

human immunodeficiency virus

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104
Q

What does HIV cause?

A

AIDS – Acquired immune deficiency syndrome

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105
Q

What does HIV do?

A

Cause aids and HIV gradually destroys the sufferer’s immune system

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106
Q

When did AIDS epidemic start?

A

1980’s

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107
Q

As of 2015, how many people were living with HIV globally?

A

36.7 million people

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108
Q

How many people died of HIV last year?

A

1.1 million

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109
Q

Where did HIV come from?

A

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

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110
Q

How can HIV infect us?

A

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

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111
Q

Symptoms of HIV

A

.Fever.Sore throat.Body rash.Tiredness.Joint pain.Muscle pain.Swollen glands (nodes)

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112
Q

Symptoms of AIDS

A

.Weight loss.Chronic diarrhoea.Night sweats.Skin problems.Recurrent infections.Serious life threatening illness

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113
Q

Name the 7 parts that make up HIV virus?

A
  1. Transmembrane glycoprotein2. Attachment glycoprotein3. Lipid envelope4. Reverse transcriptase5. Matrix6. Capsid7. Genetic material (RNA)
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114
Q

What is reverse transciptase?

A

enzyme that catalyses the production of DNA from RNA

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115
Q

Because HIV can produce DNA from RNA, what group is it apart of?

A

retroviruses

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116
Q

Because HIV is a virus what cant it do? So what does it do instead?

A

.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

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117
Q

How does HIV infect host cells? (8 steps)

A
  1. 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
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118
Q

What does HIV specifically target?

A

helper T cells

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119
Q

How does HIV lead to aids?

A

HIV leads to AIDs by destroying/interfering with T cells normal functioning

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120
Q

How many helper T cells does a healthy human have?

A

800-1200 helper T cells per mm^3 of blood

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121
Q

How many helper T cells does an AIDS sufferer have?

A

less than 200 helper T cells per mm^3 of blood

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122
Q

If someone doesn’t have enough T cells what problems arise?

A
  • B cells cannot be stimulated to produce Ab - Cytotoxic T cells cannot be stimulated
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123
Q

With AIDS/HIV can memory cells be affected? What effect does this have?

A

Memory cells are also sometimes infected and destroyedThis results in an inadequate immune response leaving the body vulnerable to infections and cancer

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124
Q

What are AIDS sufferers prone to?

A

AIDS sufferers are therefore prone to infections of the lungs, intestine, brain and eyesDiarrhoea and weight loss are common

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125
Q

What type of illness is HIV, why?

A

It is a secondary illness, not HIV that causes death

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126
Q

How to produce monoclonal antibodies

A

.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

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127
Q

Define huminisation

A

making the monoclonal antibodies suitable for human use (since they come from mouse tissue)

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128
Q

Uses of monoclonal antibodies

A

.Separating chemicals from mixtures.Immunoassay (detecting concentrations of macromolecules in solutions).Cancer treatment.Transplant surgery

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129
Q

What can antibodies be used to identify?

A

Antibodies can be used to identify flu, hepatitis, chlamydia and types of cancer

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130
Q

What is a non-specific response?

A

immediate and same for all pathogens

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131
Q

What are the two nonspecific responses?

A

.Physical Barrier (skin).Phagocytosis

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132
Q

What is a specific response?

A

slower and pathogen specific

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133
Q

What are the two specific responses?

A

.Cell – mediated response (T-Lymphocytes).Humoral response (B-Lymphocytes)

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134
Q

Where do T cells mature?

A

.T Lymphocytes mature in the thymus gland

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135
Q

What do T cells respond to?

A

own cells altered by viruses/cancers (foreign material inside body cells) or transplanted tissues

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136
Q

How can different cells display antigens on their surface?

A
  1. 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
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137
Q

What are cells that display foreign antigens known as?

A

antigen-presenting cells

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138
Q

How do T cells become activated?

A

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

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139
Q

What do cloned T-cells do?

A

.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

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140
Q

What do cytotoxic T cells do?

A

.Cytotoxic T cells kill abnormal body cells

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141
Q

How do cytotoxic T cells kill abnormal body cells?

A

.They produce a protein called perforin that makes holes in the cell surface membrane.This makes the cell freely permeable, killing it

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142
Q

What are cytotoxic T cells effective against?

A

.This action is very effective against viruses as they replicate inside cells

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143
Q

What is the ELISA test?

A

Enzyme linked immunosorbent assay.It uses antibodies to detect the presence and amount of protein in a sample.Highly sensitive

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144
Q

ELISA test method

A

.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

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145
Q

Define pathogen

A

Disease causing microbe

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146
Q

Define phagocyte

A

WBCs that travel in the blood and tissues, destroying pathogens

147
Q

Define phagocytosis

A

Mechanism where phagocytes engulf pathogens and hydrolyses them using enzymes

148
Q

Define immune

A

Resistant to a particular infection or toxin owing to the presence of specific antibodies

149
Q

Define antigen

A

Molecule that triggers an immune response

150
Q

Define antibody

A

A protein made by lymphocytes in response to the presence of an antigen

151
Q

Define t lymphocyte

A

Type of WBC produced in the bone marrow but matures in the thymus. Coordinates immune response and kills infected cells – cell mediated response

152
Q

Define helper t cell

A

Bind to antigens presented by antigen presenting cells. This binding stimulates T cell to divide rapidly.

153
Q

Define antigen presenting cell

A

Cells that display foreign antigens on their cell-surface membrane.

154
Q

Define b lymphocyte

A

Type of WBC produced by and matures in the bone marrow. Present in bodily humour. Humoral immunity. Produce antibodies.

155
Q

Define memory cell

A

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

156
Q

Define plasma cell

A

Secrete antibodies into blood plasma. Survive for only a few days. Destroy pathogens and toxins. Immediate defence only - primary immune response

157
Q

Define cytotoxic T cell

A

Kills infected cells by introducing perforin molecules into their CSM, causing them to take in water and burst.

158
Q

Define vaccination

A

Introduction of a vaccine subcutaneously or orally that contains pathogen antigens capable of initiating an immune response.

159
Q

Define biodiversity

A

The range and variety of genes, species and habitats within a particular region.

160
Q

What are the 3 types of biodiversity?

A

Species diversity, genetic diversity and ecosystem diversity

161
Q

What is species diversity?

A

the number of different species and the number of individuals of each species within any one community

162
Q

What is genetic diversity?

A

the variety of genes possessed by the individuals that make up any one species

163
Q

What is ecosystem diversity?

A

the range of different habitats within a particular area

164
Q

What is species richness?

A

Species richness is the number of different species in a particular area at a given time (community)

165
Q

Equation for species diversity index? With meaning for each letter

A

d = species diversityN = total number of organisms of all speciesn = total number of organisms of each speciesΣ = the sum of

166
Q

Human factors affecting biodiversity

A

.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

167
Q

How does agriculture affect biodiversity?

A
  1. 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)
168
Q

How do monocultures affect biodiversity?

A

reduction in species and genetic diversity directly and indirectly as fewer food sources and habitats

169
Q

how does lack of intercropping affect biodiversity?

A

Drains the soil of nutrients, results in monoculture

170
Q

How does competition for space affect biodiversity?

A

Natural species habitats cannot grow/are outcompeted by dominant

171
Q

How does use of pesticides and herbicides affect biodiversity?

A

Can be toxic to species, enters water cycle, eutrophication

172
Q

How does cattle in the field where species may grow affect biodiversity?

A

Over grazing, trampling, reduction in species diversity

173
Q

How does draining wetland and marches affect biodiversity?

A

Removes nutrients and moisture from soil so species cannot grow

174
Q

How does removing hedgerows affect biodiversity?

A

Removes habitats and food sources

175
Q

What is deforestation?

A

The permanent clearing of forests and the conversion of land to other uses, such as agriculture, grazing or settlement

176
Q

How many species are being lost each year due to deforestation?

A

50,000

177
Q

How does deforestation reduce biodiversity?

A

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.

178
Q

How can maintaining biodiversity bring economic benefit?

A
  1. 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.
179
Q

How can you reduce human impacts of deforestation?

A

.Eco charges.Increased taxes/fines

180
Q

What are nerve cells (also called neurones)?

A
  • Highly specialised cells- Adapted to rapidly carry electrochemical changes (nerve impulses)- Amongst the largest cells in the body (especially in length)
181
Q

Draw and label a basic nerve cell

A

check notes or google

182
Q

Function of cell body

A

Contains the nucleus and large amount of rough endoplasmic reticulum. Nucleus holds DNA and controls the cell, large amounts of RER to form neurotransmitters

183
Q

Function of axon

A

Collect and carry the nerve impulse away from the cell body

184
Q

Function of myelin sheath

A

Multiple cells wrapped around the axon; they increase the speed of the impulse, wrapped around to form Myelin layer

185
Q

Function of nodes of ranvier

A

Gaps where there is no myelination, increases speed

186
Q

Function of shwan cells

A

Individual cells protect the neurone, provide electrical insulation

187
Q

Function of dendrite

A

Extensions of the cell body, carry impulses towards the cell body, increase action potential

188
Q

Function of dendrons

A

Extensions of the cell body, thickest part of the branches, they subdivide into dendrites

189
Q

How are motor neurones different? Why?

A
  • 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
190
Q

How are sensory neurones different? Why?

A
  • 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
191
Q

How are intermediate neurones different? Why?

A
  • Short axon- Lots of dendrites
192
Q

What is a nerve impulse?

A
  • 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
193
Q

What are the two states of a nerve impulse?

A
  • Action potential- Resting potential
194
Q

What is resting potential?

A
  • Negative inside- Positive outside
195
Q

What is action potential?

A
  • A nerve impulse occurs when there is a temporary reversal of these charges- The reversal is then propagated along the axon
196
Q
  • Neurones send messages ________
A

electrochemically

197
Q
  • Chemicals in the body are _____ charged
A

electrically

198
Q

The important ions in the nervous system are:

A
  • Sodium (1+ charge)- Potassium (1+ charge)
199
Q

What controls nervous system ions movement?

A
  • Phospholipid bilayer- Intrinsic proteins- Gated channels
200
Q

How is ion movement controlled?

A
  • 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
201
Q

Value of resting potential

A

= -65mV

202
Q

describe the Formation of a Resting Potential

A
  1. 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
203
Q

• The energy of a stimuli causes ________________________ on the axon membrane

A

a temporary reversal of the charge

204
Q

• Resting potential value meaning?

A

the difference in charge across the membrane

205
Q

What is the change in charge from resting potential to action potential?

A

• The temporary reversal causes the charge of -65mV difference in the resting potential to become a +40mV difference

206
Q

What happens to the membrane when it goes from -60mV to +45mV?

A

It is depolarised

207
Q

Where is negative and positive in action potential?

A

outside negative, inside positive

208
Q

Voltage-Gated Ion Channels, what are they?

A
  • Channels in the membrane change shape- Open or close, depending on the voltage across the membrane
209
Q

At rest, which voltage gated ion channels are open on the axon?

A

.Some potassium gated channels are open.Sodium channels are closed

210
Q

Draw the graph for resting potential to action potential

A

CHECK NOTES OR GOOGLE

211
Q

How is an action potential produced and restored along an axon?

A
  1. 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
212
Q

Describe the passage of action potentials

A

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

213
Q

HOw is an impulse passed along an axon in an unmyleinated sheath?

A
  1. 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)
214
Q

The myelin sheath is an electrical insulator, what does this cause?

A
  • Prevents action potentials forming- Action potentials can only occur at nodes of ranvier- Results in ‘node hopping’ (saltatory conduction)
215
Q

Draw the diagram of saltatory conduction

A

CHECK NOTES OR GOOGLE

216
Q

Describe and explain saltatory condcution

A
  1. 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
217
Q

Action potential propagation along myelinated axons from what to what?

A

one node of ranvier to the next node

218
Q

Key points of saltatory conduction

A
  • Energy is not lost between action potentials- Each action potential is the same size
219
Q

What factors effect the speed of an impulse?

A

Myleination, temperature, diameter of the axon

220
Q

How does temperature effect the speed of an impulse?

A

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

221
Q

How does diameter effect speed of an impulse?

A

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

222
Q

What is the refractory period?

A

The refractory period is the time that it takes for Na+ influx to be possible again.

223
Q

Where is the refractory period on the graph?

A

The refractory period is the portion of the graph that leads back to the resting potential.

224
Q

For an action potential to occur, it needs to reach ________ – if it does not it is called a _______.

A

a threshold valuefailed initiation

225
Q

Why are refractory periods important?

A
  1. Ensures action potentials are in one direction2. Ensures action potentials are discreet (separate)3. Ensures action potentials are limited in number at one time
226
Q
  • The area before the action potential will be in refractory period, so how does this allow the impulse to travel in one direction?
A

o A new action potential cannot occuro Axon must be at resto Travels in the correct direction (brain or effector)

227
Q

How is a refractory period discrete? Why is this good?

A
  • Area behind means AP cannot occur- Refractory period takes time- Messages sent to the brain are discrete (not muddled)
228
Q

How can there only be a certain number of action potentials? Why is this good?

A
  • 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’
229
Q

What is the synapse

A

The synapse is the point where a neurone communicates with the dendrite of another neurone or with an effector.

230
Q

Draw and label a diagram of a synapse

A

check notes

231
Q

What does the synaptic knob contain? Why are each required?

A
  • 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
232
Q

What are neurotransmitters?

A

Neurotransmitters are:- Chemical messages- Specific- Enable synaptic transmission

233
Q

The response to the arrival of a neurotransmitter will however depend on what?

A
  • The cell- The cells location- The neurone
234
Q

A synapse that relies on the neurotransmitter acetylcholine, it is made of what?

A
  1. Acetyl (ethanoic acid)2. Choline
235
Q

Which synapse relies on the neurotransmitter actylcholine?

A

cholinergic synpase

236
Q

Describe the sequence of events leading to the release of acetylcholine and its binding to the postsynaptic nerve.

A
  1. 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
237
Q

What are neuroreceptors?

A

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

238
Q

What is acetylcholinesterase?

A

Acetylcholinesterase is:- A hydraulic enzyme (hydrolysis)- Located on the membrane- Breaks up acetylcholine into acetyl (ethanoic acid) and choline

239
Q

What happens after hydrolysis of acetylcholine?

A
  • 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
240
Q

Define neurotransmitter

A

Chemical messenger released form the pre-synoptic neurone and involved in the communication between adjacent neurones or cells

241
Q

Define cholinergic synapse

A

The gap where a neurone that produces acetylcholine sends messages to other neurones, or to muscle cells

242
Q

Define synapse

A

A junction between two neurones in which they do not touch but have a narrow gap, across which neurotransmitters cross

243
Q

Define refractory period

A

Period during which the membrane of an axon of a neurone cannot be depolarised and no new action potential can be initiated

244
Q

Define saltatory conduction

A

The propagation of a never impulse along a mylenated neurone in which the action potential jumps from one node of Ranvier to another

245
Q

Synapses transmit impulses in ___ direction to a ______ location

A

oneprecise

246
Q

Synapses prevent ____________

A

overstimulation

247
Q

Synapses act as a junction between, allowing what to what?

A

a. A single impulse to multiple neuronesb. A number of impulses to be combined at a synapse

248
Q

What is summation?

A

The additive effect of low frequency action potentials to produce sufficient neurotransmitters to trigger an action potential across the synapse.

249
Q

What are the two forms of summation?

A
  • Spatial- Temporal
250
Q

What is spatial summation?

A

Different presynaptic neurones come together to trigger one action potential.

251
Q

What is the number of pre and post synaptic neurones with spatial summation?

A

o Multiple pre-synaptic neurones at one synapse

252
Q

How does spatial summation reach the threshold value?

A

o A single neurone does not release enough neurotransmittero Multiple neurones release neurotransmittero Threshold is exceeded

253
Q

What is temporal summation?

A

Single presynaptic neurone release neurotransmitters many times over a short period to exceed the threshold.

254
Q

What is the number of presynaptic neurones for temporal summation?

A

o One neurone per post synaptic neurone

255
Q

What is the amount of neurotransmitters for temporal summation?

A

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

256
Q

What is an inhibitory synapse?

A

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.

257
Q

How does an inhibitory synapse inhibit?

A
  1. 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)
258
Q

How do some drugs create fewer action potentials? with example

A

o Inhibiting the release of neurotransmittero Blocking the sodium/potassium channelso For example: Gaba• Inhibits or slows the brain’s function• Promotes sleepiness

259
Q

How do some drugs stimulate the nervous system?

A

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

260
Q

Define tendon, ligament and cartilage

A

Tendon – connect bone to muscleLigament – connective tissue that connects bone to boneCartilage – connective tissue found between bones, a ‘shock absorber’

261
Q

What are muscles?

A
  • Bundles of fibres- Different structures- Different jobs
262
Q

What is a cardiac muscle?

A

a. Present in the heartb. Acts involuntarilyc. Myogenicd. Strong and continuous contraction

263
Q

What is a skeletal muscle?

A

a. Attached to bonesb. Vast majority of musclec. Discontinuous contractiond. Controlled voluntarily

264
Q

What is a smooth muscle?

A

a. Involuntary muscleb. Found in the gut, blood vessel walls, and in the iris of the eyec. Slow and weak contraction

265
Q

How do muscles act?

A
  • Receiving a nerve impulse- Working in antagonistic pairso You cannot stimulate the contraction of two antagonistic muscles at the same time- Pulling bones
266
Q

What is antagonistic?

A

one muscle (prime mover) contracts and the other (antagonistic) relaxes

267
Q

What happens in flexion and extension of the arms?

A

Flexion:Biceps contracted, triceps relaxed (extended). The prime mover is the biceps.Extension:Triceps contracted, biceps relaxed. The prime mover is the triceps.

268
Q

Structure of skeletal muscle with analogy

A

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).

269
Q

What is the structure of skeletal muscles?

A
  • Individual muscle cells are fused together- Form muscle fibres (myofibrils)- Lie parallel to each other- Increases strength
270
Q

What are the two types of fibres found in muscles?

A
  • Slow twitch fibres - Fast twitch fibres
271
Q

How can muscles fibres be grouped?

A

Group based on two properties:- Resistance to fatigue- Speed of contraction

272
Q

Slow twitch, speed of contraction, power of contraction, type of activity, type of respiration, and example of muscle containing fibre

A

SlowLow but prolongedEndurance: walking, posture, standing, long distance runningAerobicCalf muscles

273
Q

Fast twitch, speed of contraction, power of contraction, type of activity, type of respiration, and example of muscle containing fibre

A

FastHighIntense activity over a short period: weight lifting, sprintingAnaerobicBiceps

274
Q

Slow twitch fibres adaptations

A
  • 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
275
Q

Why is each slow twitch fibre adaptation beneficial?

A
  • 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)
276
Q

Fast twitch fibre adaptations

A
  • Thicker and more myosin filaments- High concentration of enzymes involved in anaerobic respiration- A store of phosphocreatine – provide energy (energy buffer)
277
Q

Why do fast twitch fibres tire quickly?

A
  • Fewer blood vessels- Run out of oxygen quicker- Thicker; larger diffusion distance
278
Q

Individual myofibrils are fused together into one long cell, what do they share? What is it called?

A

o Nuclei = multinucleatedo Cytoplasm = sarcoplasmo Cell membrane = sarcolemma

279
Q

Why do nucleic need to be dotted all over the sarcoplasm?

A
  • Transcription- All muscle cells controlled
280
Q

Which organelle will be in large number in the sarcoplasm and why?

A
  • Mitochondria: ATP for contraction and protein synthesis- RER: protein synthesis
281
Q

Myofibrils consist of two types of protein filaments, what are they?

A

Actin and myosin

282
Q

Descibe actin

A

a. Thinnerb. Made up of two strands coiled around each other

283
Q

Describe myosin

A

a. Thickerb. Consists of rod-shaped fibres with ‘bulbed’ heads which project outwards

284
Q

What do myofibrils consist of?

A
  • Multiple sarcomeres- Actin and myosin filaments
285
Q

Why do myofibrils appear stiped? What are the dots?

A

Banding patternCauses myofibrils to appear stripedThin dots = actinThick dots = myosin

286
Q

What are the two main components of the sarcomere?

A
  1. Dark bandsa. Actin and myosin overlapb. Anisotropic bands (A-bands)c. Depends on myosin length2. Light bandsa. No overlapb. Isotropic bands (I-bands)
287
Q

Label a sarcomere

A

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

288
Q

Where is one sarcomere, in terms of z-lines?

A

One sarcomere is z-line to z-line

289
Q

What is a neuromuscular junction?

A

Where a motor neurone meets skeletal muscle fibres

290
Q

Often there are multiple neuromuscular junctions connected to different muscle fibres, why?

A

o Multiple fibres stimulatedo Speeds up the responseo Contraction is quicker and more powerfulo Threshold is met

291
Q

What is the all or nothing principle?

A

the strength by which a nerve or muscle fibre responds to a stimulus is independent of the strength of the stimulus

292
Q

How do neuromuscular junctions affect contraction strength?

A
  • 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
293
Q

Neuromuscular junctions are always cholinergic synapses, therefore:

A
  • The neurotransmitter is acetyl choline- The enzyme that hydrolyses the neurotransmitter is acetyl choline esterase
294
Q

How do action potentials travel to the muscle fibre?

A
  • 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
295
Q

As well as actin and myosin, there are two other proteins found in muscle fibres - name and describe them

A
  • Tropomyosino Long and thin fibrous strandso Wrap around the actin filament- Troponino Globular protein involved in muscle contraction
296
Q

What is the sliding filament theory?

A
  1. 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
297
Q

What is speciation?

A

The formations of two populations from one

298
Q

What are the types of speciation?

A

Allopatric speciation and sympatric speciation

299
Q

Explain how oxygen is loaded, transported and unloaded in the blood. (6 marks)

A

.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);

300
Q

Selection pressures are …

A

… environmental factors that limit the population of a species

301
Q

Stabilising selection is caused by …

A

… selection pressure against both extremes, and so the mean remains the same

302
Q

Directional selection is caused by …

A

… selection pressure for an extreme, and so the mean changes

303
Q

Tell me about disruptive selection

A
  • Selects against the average phenotype- Favours the extreme phenotypes- Can lead to speciation
304
Q

.Speciation is what?

A

the evolution of new species from existing species

305
Q

What does speciation enable?

A

.It enables evolutionary change and diversity

306
Q

Speciation occurs due to:

A
  • Reproductive isolation- Genetic differences (mutations)- Geographical isolationo Differences in two populations gene pools
307
Q

What are the two forms of speciation?

A

Allopatric Speciation:Sympatric Speciation:

308
Q

WHat is allopatric speciation?

A

.More common.Different locations.Geographic separation

309
Q

WHat is Sympatric Speciation:

A

.Less common than allopatric.Same location.Reproductive isolation

310
Q

How does allopatric speciation occur –

A

.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

311
Q

Define Adaptive radiation

A

The diversification of a species into forms adapted to different ecological niches

312
Q

Allopatric Speciation key points

A

.More common than sympatricDifferent locations.Geographic seperation .Physical barrier i.e. Lake, desert, mountain area.Takes millions of years

313
Q

Sympatric Speciation key points

A

.Less common than allopatric.Same locations.Reproductive isolation .Breeding seasons or food preference

314
Q

Apple maggot fly sympatric specxiation example explanation

A
  1. 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
315
Q

two examples of sympatric speciation

A

apple maggot fly, seasonal breeding

316
Q

Why is speciation more likely in small populations?

A

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

317
Q

What is genetic drift?

A

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

318
Q

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)

A
  1. 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
319
Q

What is disruptive selection?

A

Selective pressures against the intermediate trait

320
Q

Examples of disruptive selection

A

fur length (medium against)Colour or rabbit (white against)

321
Q

What is speciation?

A

Speciation is the formation of two species from one

322
Q

Where is sympatric speciation?

A

Sympatric Speciation = Same place

323
Q

Exampels of sympatric speciation?

A

Examples are mayflies or seasonal breeding

324
Q

Where does allopatric speciation?

A

away from species

325
Q

Key points of allopatric speciation

A
  1. 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.
326
Q

What is genetic drift? What does it do?

A

• Genetic Change due to CHANCE dissapearance of certain alleles• In small populations • Increases liklihood of speciation

327
Q

Steps of genetic drift?

A
  1. Smaller population, fewer alleles, less diversity2. By chance, one allele is not passed on3. By chance fewer decedents of one phenotype are left
328
Q

What is an isolating mechanism?

A

• Way in which a population becomes separated• Required for speciation to occur

329
Q

How does ecological (habitat choice) act as isolating mechanism?

A

Inhabit different areas (within the same area), individuals rarely meet or cross paths/mating grounds

330
Q

How does temporal (breeding seasons) act as isolating mechanism?

A

Breeding seasons do not coincide, may not be fertile at the same time, no interbreeding

331
Q

How does hybrid sterility act as isolating mechanism?

A

Different chromosome number, fusion of gametes cannot produce viable gametes, horse (2n = 64), donkey (2n = 62) = mule 63 – no pairing

332
Q

How do behavioural differences act as isolating mechanism?

A

Courtship behaviors are different, no attracted to one another scent, different mating rituals

333
Q

Define genepool

A

all the alleles of all the genes of all the individuals in a population at a given time at a given time

334
Q

What is natural selection?

A

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.

335
Q

Phenotypic variation is a result of:

A
  1. Genetic factors 2. Environmental factors
336
Q

Why does genetic variation occur?

A
  1. Meiosis 2. Sexual reproduction 3. Main factor – MutationsAll can result in selection occuring
337
Q

.Most traits are normally distributed, what does this mean?

A

.The most common result (mode) is near the average (mean) and the middle value (mode)

338
Q

.When selection occurs, the normal distribution curve may what?

A

Change shape

339
Q

Directional Selection, what is it with example

A

• Change in environment • Changes the mean• Extreme is selected for• Antibiotic Resistance

340
Q

Stabilizing Selection, what is it with example

A

• Selection against both extremes• Phenotypic variation decreases• Environment has remained stable• Birth Weight

341
Q

Differences between the reproductive successes of individuals affects the allele frequency in populations, explain how. (6 marks)

A
  1. 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
342
Q

Selection pressures are what?

A

environmental factors that limit the population of a species

343
Q

Give the features of selection pressures

A

• Determine the frequency of all the alleles within the gene pool • Vary from time to time and place to place

344
Q

Every organism is subject to selection so …

A

… certain factors may increase the chances of selection occurring

345
Q

Examples of selection pressures

A

dation, competition, disease, natural disasters

346
Q
  1. 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
  1. 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.
347
Q

All species have the potential to increase their number ________

A

exponentially

348
Q

’The rate increases in proportion to …

A

… the growing total number or size’

349
Q

Evolution only occurs by natural selection if ….

A

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)

350
Q

In order for populations to survive and increase exponentially they must …

A

have a high reproductive success and a suitable population size to minimise intraspecific competition

351
Q

Factors that make exponential growth unlikely could be …

A

high death rates from predators, low parental investment and lack of resources

352
Q

Death rates are not random, how are the following death rates influenced:TurtleArctic foxHedgehogeaglehuman

A

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

353
Q

.Death rates within a population will not be completely random / exponential growth is unlikely to occur because organism will…

A
  • Be better adapted to the environment i.e. Camoflagued - Suited to prevailing conditions i.e. Catch food - Resit disease
354
Q

Variation is essential because …

A
  • Changing environments - New diseases - New predators - New competitors
355
Q

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)

A
  1. 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;
356
Q

Selection pressures are what?

A

environmental factors that limit the population of a species

357
Q

Difference between directional and stabilizing selection?

A

Stabilizing Selection –.Selection pressure against both extremes.(Mean remains the same)Directional Selection –.Selection pressure for an extreme.(Mean changes)

358
Q

The selection pressure may change too frequently for _____to occur, so both must be over prolonged periods

A

evolution

359
Q

What is disruptive selection?

A

.Least common form of selection.Opposite to stabilizing selection.Favors the extremes at the expense of the intermediate phenotypes

360
Q

When will disruptive selection occur?

A

When an environmental factor i.e. temperature takes two or more distinct forms. Summer – warm, Winter = cold

361
Q

Explain the example: Fur Length, in disruptive selection

A

• 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

362
Q

Why is it important/what impact will it have? (disruptive selection)

A

• Most important for causing evolutionary• Could result in two distinct species

363
Q

Coho salmon example disruptive selection

A

• 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

AQA A Level Biology (19 decks)

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