Edexcel GCSE Biology PDF Past Paper Notes

Head to www.savemyexams.com for more awesome resources Edexcel GCSE Biology Your notes 5.1 Disease Contents 5.1.1 Health & Disease 5.1.2 Pathogens 5.1.3 Common Infections...

Head to www.savemyexams.com for more awesome resources Edexcel GCSE Biology Your notes 5.1 Disease Contents 5.1.1 Health & Disease 5.1.2 Pathogens 5.1.3 Common Infections Page 1 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 5.1.1 Health & Disease Your notes Defining Health The World Health Organisation (WHO) defines health as 'a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity' This means that health is not just dependent on whether an individual is physically sick or not There are lots of factors that should be considered when assessing the health of an individual which includes mental health as well as the level of social support in place Page 2 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Communicable & Non-Communicable Disease Communicable Diseases Your notes Communicable diseases are caused by microorganisms called pathogens which can spread between individuals or individuals and animals E.g. chickenpox, a common childhood disease, is caused by a viral pathogen called the varicella- zoster virus whereas Covid-19 is caused by the SARS-CoV-2 virus Communicable Diseases Table Non-Communicable Diseases Non-communicable diseases are not caused by pathogens and cannot be passed on between individuals Their effects on health tend to be longer-lasting; examples are asthma, CHD and most cancers However, the risk of developing non-communicable diseases may be increased by certain factors (including diet, stress and life situations) as these factors may have a profound effect on both physical Page 3 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources and mental health Eating a balanced diet that provides the right amount of energy and nutrients helps maintain good health whereas a poor diet can lead to deficiencies, obesity, diabetes and poor mental health Your notes Constantly being under stress can lead to cardiovascular issues (such as high blood pressure, increasing the risk of CHD) and poor mental health Where a person lives and their income can have a profound impact on health - this affects the standard of healthcare that is accessible to them (and what they can afford), what food they buy etc. Risk Factors in Non-Communicable Diseases Table Page 4 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 5 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Susceptibility If an individual suffers from one disease, they are likely to be more susceptible to other diseases This is because the immune system may be compromised in some way or the different types of disease may interact in ways that negatively affect the health of the individual Defects in the immune system mean that an individual is more likely to suffer from infectious diseases; individuals infected with HIV eventually end up with reduced numbers of lymphocytes circulating around the body which reduces the ability of the immune system to fight opportunistic infections like pneumonia Viruses living in cells can be the trigger for cancers; the HPV virus can infect cells of the cervix in women resulting in cervical cancer developing in some cases, whereas some strains of the hepatitis virus can cause liver cancer Immune reactions initially caused by a pathogen can trigger allergies such as skin rashes and asthma - these often develop as a result of an overactive immune response Severe physical ill health can lead to depression and other mental illness; both can negatively impact the immune system and lifestyle choices made by the individual, further compounding the effects of poor health Page 6 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 5.1.2 Pathogens Your notes Types of Pathogen Communicable diseases are spread by pathogens A pathogen is any microorganism that causes disease in another organism (e.g. in plants or animals) Many microorganisms are pathogens including: Bacteria Fungi Protists (protoctists) Viruses Not all species within these groups (apart from the viruses) are pathogens, as many bacteria, fungi and protists are harmless and do not cause disease However, all viruses are pathogenic as they can only exist by living inside the living cells of other organisms (or by using these cells to create more viruses) Pathogenic bacteria Pathogenic bacteria do not always infect the hosts of cells, they can remain within body cavities or spaces Toxins produced by the bacteria also damage cells They are small and can reproduce very quickly Bacterial infections include: M. tuberculosis causes tuberculosis (TB) in humans N. meningitidis causes bacterial meningitis in humans Helicobacter Pylori causes stomach ulcers V. Cholerae causes cholera in humans Pathogenic fungi Fungal diseases are much more common in plants than animals Fungi can be single-celled or multicellular (with threads of hyphae) The spores they produce allow them to infect other organisms In plants, fungal diseases tend to be much more serious and can threaten entire crops Fungal diseases include: Cattle ringworm and athletes foot are fungal diseases in animals Black Sigatoka is a fungal disease in bananas Chalara Ash Dieback is a fungal disease that affects ash trees Pathogenic protists Protists are a diverse group of eukaryotic (and usually unicellular) organisms Page 7 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources They are parasites which means they need a host in order to survive Only a small number of protists are pathogenic, but the diseases they cause are often serious Examples of diseases caused by protists are: Your notes Plasmodium falciparum is a protist that causes severe forms of malaria in humans P. infestans causes the infamous potato blight Page 8 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Lifecycle of a Virus Viruses are not usually included in the classification of living organisms as they are not considered to Your notes be alive This is due to the fact that viruses do not carry out the 8 life processes for themselves In fact, the only life process they seem to display is reproduction but even to carry out this process they must take over a host cell’s metabolic pathways in order to make multiple copies of themselves Viruses, which have a wide variety of shapes and sizes, all share the following biological characteristics: They are small particles (always smaller than bacteria) They are parasitic and can only reproduce inside living cells They infect every type of living organism They have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA Structure of a typical virus Page 9 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Examples of viruses include: Tobacco mosaic virus (TMV) causes discolouring of the leaves on tobacco plants by preventing the formation of chloroplasts Your notes HIV virus causes AIDS Influenza virus causes the ‘flu’ Ebola virus causes haemorrhagic fever When a virus infects a host cell, it can then reproduce using two different pathways, known as: The lytic pathway The lysogenic pathway The lytic pathway 1. The virus infects the host cell and injects its DNA into the cytoplasm 2. Next, the virus uses proteins and enzymes within the host cell to produce new virus particles 3. Finally, the cell bursts, releasing the virus particles into the host organism to infect more cells The lysogenic pathway 1. The virus injects its DNA into the host cell and the DNA becomes incorporated into the host DNA 2. As the host cell replicates, the viral DNA replicates also, but no new virus particles are made during this time (the virus is dormant) 3. Changes in the environment (e.g. a chemical trigger) cause the viral DNA to move to the lytic pathway to make new virus particles Page 10 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes A virus can follow two different pathways after infecting the host cell Page 11 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources 5.1.3 Common Infections Your notes Common Infections Infections caused by bacteria Myobacterium Tuberculosis causes tuberculosis (TB) in humans The bacteria infect the lungs, causing a chronic cough and bloody mucus It is a disease often associated with poor hygiene and sanitation M. bovine in cows can also transmit to humans to cause TB Vibrio Cholerae causes Cholera Bacteria infect the intestines causing diarrhoea, vomiting and leg cramps Cholera can lead to death if not treated quickly It is a disease often associated with poor hygiene and sanitation Helicobacter Pylori causes stomach ulcers Infection of the stomach commonly occurring during childhood H. Pylori infection often gives no symptoms, but can lead to leads to pains in the abdomen, loss of appetite, bloating and nausea Chlamydia Trachomatis causes chlamydia This is a sexually transmitted infection There may be no symptoms in some patients, others may have pain when they urinate, unusual discharge or bleeding after sex Chlamydia can cause infertility if left untreated Infections caused by fungi Chalara Ash Dieback This fungal infection originated in Asia and affects ash trees of all ages with devastating effects It causes dark patches on the leaves, early leaf loss and bark lesions Spores travel large distances in the wind Infections caused by protists Plasmodium Falciparum is a protist that causes severe forms of malaria in humans The parasite is spread by mosquitoes It cases damage to the blood and the liver Infected individuals experience fever, chills and fatigue Malaria can progress with more serious symptoms eventually leading to death Infections caused by viruses Page 12 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Ebola Virus infects and kills body cells Symptoms are flu-like initially This includes headaches, high temperature, joint and muscle pains Your notes Serious cases will also show diarrhoea, sickness, rashes and may lead to haemorrhagic fever (fever and internal bleeding) Human Immunodeficiency Virus (HIV) destroys white blood cells in the immune system Initial symptoms are flu-like This includes headaches, high temperature, joint and muscle pains If untreated, the virus compromises the immune system leading to the onset of Acquired Immune Deficiency Syndrome (AIDS) AIDS is used to refer to several life-threatening illnesses which may result from having a compromised immune system More about HIV The virus infects a certain type of lymphocyte of the body's immune system Normally lymphocytes seek out and destroy pathogens that enter the body, producing antibodies that attach to pathogens, enhancing phagocytic activity However, HIV avoids being recognised and destroyed by lymphocytes by repeatedly changing its protein coat It then infects a certain type of lymphocyte and uses the cells’ machinery to multiply This reduces the number of lymphocytes of the immune system, and also the number of antibodies that can be made This decreases the body’s ability to fight off infections, eventually leading to AIDS (Acquired immunodeficiency) Page 13 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 14 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources How HIV affects lymphocytes Your notes Page 15 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources The Spread of Common Infections Diseases that are caused by pathogens that pass from one host to another are described as Your notes transmissible diseases Transmission can occur through several different mechanisms: Airborne - droplets travelling in the air (maybe as a result of wind or sneezing/coughing) lead to infection e.g. Colds, influenza, tuberculosis, Chalara ash dieback These types of infection in animals can be prevented by: Avoiding crowded areas Good hygiene generally Ventilation of homes or workspaces These types of infection in plants can be prevented by: Preventing imports of trees from countries known to carry the disease Cutting down infected trees as soon as possible and replacing with an alternative species which is unaffected Waterborne - pathogens that live in dirty water are transmitted to organisms that come into contact with it e.g. Cholera This can be prevented by avoiding poor quality water and making sure that people have access to clean water Oral transmission - pathogens are ingested and transmitted to the host e.g. Stomach ulcers This can be prevented by having access to clean water and good hygiene standards Body fluids and sexual transmission - Exchange of saliva, blood or semen can carry pathogens from one host to another e.g. HIV, Chlamydia, Ebola Generally, body fluid transmission is prevented by: Isolating infected individuals Cleaning and sterilising contaminated areas Sexual transmission of chlamydia and HIV can be reduced by: Wearing condoms Screening to detect cases and particularly after unprotected sex Medications Drug users with HIV should also avoid sharing needles Limiting the number of sexual partners Raising awareness by education programmes Animal vectors - Animals carry pathogens between hosts Page 16 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources e.g. Malaria Animal vectors can be prevented by Using insect repellent Your notes Mosquito nets Preventing the vector from reproducing Transmission of Common Infections Table Page 17 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Page 18 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers  Head to www.savemyexams.com for more awesome resources Your notes Exam Tip Know the symptoms and how the pathogen causing each disease is spread. Typically, this topic appears as data analysis questions in the exam where you may be given a graph to analyse and interpret. Page 19 of 19 © 2015-2024 Save My Exams, Ltd. · Revision Notes, Topic Questions, Past Papers