Bio topic 5

health

a state of complete physical, mental and social well-being and not merely the absence of disease or infirmity

communicable diseases

caused by microorganisms called pathogens which can spread between individuals or individuals and animals

non-communicable diseases

are not caused by pathogens and cannot be passed on between individuals

How can susceptibility of a disease be increased if an individual suffers from a disease

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

pathogen

a disease-causing microorganism

Types of pathogens

Fungi

Bacteria

Viruses

Protists

How do pathogenic bacteria cause harm?

• 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

How do pathogenic fungi cause harm?

• 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

How do pathogenic protists cause harm?

• Protists are a diverse group of eukaryotic (and usually unicellular) organisms

• 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

Why are viruses not considered to be alive?

viruses do not carry out the 8 life processes for themselves

Characteristics of viruses

• 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

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

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

Infections caused by bacteria4

tuberculosis

cholera

stomach ulcers

chlamydia

tuberculosis symptoms

cough

bloody mucus

lung damage

How is tuberculosis transmitted

Airborne 

Via coughing

How can tuberculosis be prevented/reduce transmission

avoid crowded areas

maintain good hygiene

ventilate homes and work spaces

cholera symptoms

vomiting

leg cramps

diarrhoea

How is cholera transmitted

waterborne

in contaminated water sources

How can cholera be prevented

Avoid dirty water

Improve sanitation

Give access to clean water

stomach ulcers symptoms

H. pylori infection often gives no symptoms, but can lead to leads to pains in the abdomen, loss of appetite, bloating and nausea

stomach ulcers transmission

oral transmission

consumption

How can stomach ulcers be prevented

ensure access to clean water

good hygiene

chlamydia symptoms

There may be no symptoms in some patients, others may have pain when they urinate, unusual discharge or bleeding after sex

chlamydia transmission

sexually transmitted - body fluids

How to prevent chlamydia

use condoms

screening after unprotected sex

limiting sexual partners

infection/s caused by fungi

Chalara Ash Dieback

Chalara Ash Dieback symptoms

It causes dark patches on the leaves, early leaf loss and bark lesions

Chalara Ash Dieback transmission

airborne - spores are carried in the wind

Chalara Ash Dieback prevention

Remove infected trees and replace with different species

Restrict imports of Ash species

infection/s caused by protists

malaria

malaria symptoms

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

malaria transmission

By mosquitoes - carried by a vector

malaria prevention

Use insect repellent

mosquito nets

infection/s caused by viruses

Ebola Virus

HIV

Ebola Virus symptoms

Symptoms are flu-like initially

• This includes headaches, high temperature, joint and muscle pains

• Serious cases will also show diarrhoea, sickness, rashes and may lead to haemorrhagic fever (fever and internal bleeding)

Ebola Virus transmission

body fluids

Ebola Virus prevention

isolate infected individuals

sterilise contaminated area

HIV symptoms

• Initial symptoms are flu-like

  • This includes headaches, high temperature, joint and muscle pains

• Can lead to AIDS associated illness

HIV prevention

wear condoms

limit sexual partners

avoid sharing needles

screening after potential exposure

education

medication can stop the spread

What type of cell does HIV destroy?

white blood cells

How does HIV lead to AIDS

• 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)

Examples of STDs

HIV

Chlamydia

Types of transmission

airborne

waterborne

oral transmission

body fluids and sexual transmission

animal vectors

Physical defences of plants(5)

cellulose cell wall

waxy cuticle

bark

leaf loss

thorns/hairy stems

chemical defences of plants(3)

antiseptics/antimicrobial enzymes

chemical poisons

mechanisms to attract other insects as a biological control

How can plant chemicals be useful for humans?

Chemicals with antimicrobial properties can be extracted for human use such as in antibiotics

herbal face creams can use plant extracts such as tea tree oil, mint and witch hazel to have antibacterial effects

pain relief drug aspirin comes from willow tree bark

How does the cell wall act as a defence for plants?

Made of cellulose

Provides protection from microorganisms

How does the waxy cuticle act as a defence for plants?

acts as a barrier to microbes from entering the plant. The only place that they can enter in the leaf is through the stomata

How does bark act as a defence for plants?

provides a tough layer around the stem of the plant to prevent pathogens from entering

How does leaf loss as a defence for plants?

As deciduous trees lose leaves in the winter the infection can be taken with them

How does poison work as a defence?

Acts as a deterrent

Animals will avoid eating plants that make them feel unwell

example of poisons

foxglove

deadly nightshade

yew

How does thorns work as a defence?

make it painful/unpleasant for large herbivores to eat them

examples of thorns as a defence

brambles

cacti

How does hairy stems work as a defence?

They deter insects + larger animals from feeding on them and

How does drooping and curling when touched work as a defence?

can dislodge insects and frighten off larger species

How does mimicry work as a defence?

Plants can droop to look as if they are diseased

Tricks animals into not eating them

symptoms of plants(7)

stunted growth

spots on leaves

areas of decay or rot

visible pests

discolouration of the leaves

growths

malformed stems and leaves

How can plant diseases be detected and identified in the field?

Observations based on symptoms

For example Chalera ash dieback causes leaf loss and aphids can cause physical damage to the stems of plants

Determining any environmental issue which may be the cause of the symptom

Assessing the distribution of plants can indicate the type of pathogen involved and its transmission

Patches of diseased plants may suggest infection via the soil

random distributions may suggest airborne distribution, such as the spores which cause chalera ash dieback

How can plant diseases be detected and identified in the lab?

Chemical analysis

Culturing pathogen may lead to accurate identification of the disease

Monoclonal antibodies - antibodies which are specific to the pathogen antigens, if the antigen is present the antibodies will bind to them and allow accurate diagnosis of the disease

DNA analysis can help identify the problem-causing pathogen

physical barriers

structures that make it difficult for pathogens to get past them and into the body

3 physical barriers of body

skin

hair and mucus in nose

mucus and cilia in trachea and bronchi

How does skin act as a physical barrier?

covers almost all parts of your body to prevent infection from pathogens. If it is cut or grazed, it immediately begins to heal itself, often by forming a scab.

How do hairs and mucus in the nose act as a physical barrier?

these make it difficult for pathogens to get past them further up the nose so they are not inhaled into the lungs

How do mucus and cilia in the trachea and bronchi act as a physical barrier?

pathogens get trapped in mucus produced by cells in the airways of the lungs. Other cells lining the trachea and bronchi have cilia (microscopic hair-like structures) that waft mucus up to the back of the throat so it can be removed from the body (by coughing, blowing the nose, swallowing etc.)

chemical barriers

substances produced by the body cells that trap or kill pathogens before they can get further into the body and cause disease

4 chemical barriers of body

stomach acid

lysozymes

natural flora

sebum on skin surface

How does stomach acid act as a chemical barrier?

contains hydrochloric acid which is strong enough to kill any pathogens that have been caught in mucus in the airways and then swallowed or have been consumed in food or water

How do lysozymes act as a chemical barrier?

enzymes produced by the eyes and released in tears will breakdown and kill bacteria on or around the eye

How do natural flora act as a chemical barrier?

Natural bacterial flora in the gut and vagina - protect against infection from pathogenic bacteria by outcompeting the pathogen

How does the skin surface act as a chemical barrier

Sebum on the skin’s surface kills fungal and bacterial pathogens

2 types of white blood cells

phagocytes

lymphocytes

How do phagocytes defend against pathogenic microorganisms?

Phagocytes carry out phagocytosis by engulfing and digesting pathogens

Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells

Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it

This is a non-specific immune response as the response is the same for any pathogenic cell

antibodies

Y-shaped proteins with a shape that is specific (complementary) to the antigens on the surface of the pathogen

How do lymphocytes defend against pathogenic microorganisms?

produce antibodies specific to antigens on pathogens

clones itself to produce lots of lymphocytes that produce the specific antibody required

produce specific antitoxins to neutralise toxins released by pathogens

antitoxin

a protein that neutralises the toxins produced by bacteria

How do antibodies work to kill pathogens

Antibodies attach to the antigens and cause agglutination (clumping together)

This means the pathogenic cells cannot move very easily

At the same time, chemicals are released that signal to phagocytes that there are cells present that need to be destroyed

How does the primary immune response work?

1. The pathogen enters the blood stream and multiplies

2. A release of toxins (in the case of bacteria) and infection of body cells causes symptoms in the patient

3. Phagocytes that encounter the pathogen recognise that it is an invading pathogen and engulf and digest (non-specific response)

4. Eventually, the pathogen encounters a B-lymphocyte which recognises its antigens

5. The lymphocyte starts to produce specific antibodies to combat that particular pathogen

6. The lymphocyte also clones itself to produce lots of lymphocytes (all producing the specific antibody required)

7. Antibodies cause agglutination of pathogens

8. Phagocytes engulf and digest the agglutinated pathogens

How does the secondary immune response work?

After the patient has recovered, they retain antibodies specific to the disease as well as memory lymphocytes (lymphocytes that recognise the pathogen)

If the patient encounters the same pathogen again, it will trigger a secondary immune response

Memory lymphocytes can produce much larger quantities of the required antibody in a much shorter time to fight off the pathogen before the patient suffers any symptoms

What do vaccines contain?

harmless versions of a pathogen

How can scientists ensure pathogens in vaccines are harmless?(3)

• Killing the pathogen

• Making the pathogen unable to grow or divide (attenuated vaccine)

• Using fragments of pathogens, which include the necessary antigens (rather than whole cells)

How may a vaccine be administered

injection

nasally

orally

how do vaccines work?

• Once in the bloodstream, the antigens contained within the vaccine can trigger an immune response in the following way:

  • Lymphocytes recognise the antigens in the bloodstream

  • The activated lymphocytes produce antibodies specific to the antigen encountered

  • Memory lymphocytes and antibodies subsequently remain circulating in the blood stream

  • Future infection by the same pathogen will trigger a response that is much faster and much larger compared to the initial response

  • Due to the rapid nature of the response, the pathogen is unable to cause disease and the individual is said to be immune

Advantages of vaccinations

Diseases that were once common are now fairly rare due to widespread vaccinations

epidemics can be prevented if large number of the population are vaccinated

Disadvantages of vaccinations

vaccine doesn’t always give immunity, for example mutations in the pathogens D/RNA can result in significant changes to the antigen of the pathogen meaning that lymphocytes can no longer recognise the pathogen

Side effects of the vaccine can occur for example swelling or a rash ti more severe reactions such as seizures

antibiotics

medicines that help to cure bacterial disease by killing infective bacteria inside the body

How do antibiotics work?

They inhibit processes in the cell such as cell wall production, this ruptures the cell and it dies when it tries to grow

Will antibiotics harm host cells?

They target bacteria so no

Will antibiotics work against viruses and why?

Antibiotics will not work against viruses, as viruses reproduce inside cells. It is difficult to develop drugs that kill viruses without also damaging the host’s tissues

How can bacteria be grown?

in a nutrient broth solution or as colonies on an agar gel plate

6 aseptic techniques

1.All work should be carried out with a yellow flame Bunsen burner

2. Hot agar jelly poured into a sterilised petri dish. The agar is left to cool and set

3. Inoculating tube passed through a flame before it is used to transfer bacteria to culture medium

4. petri dish opened as little as possible, at the side facing the b burner

5. Lid of petri dish should be taped at points around the dish and stored upside down

6. cultures shouldn’t be incubated > 25 degrees in a school laboratory

Why must all work should be carried out with a yellow flame Bunsen burner?

prevents contamination of microorganisms in the air

Why must the petri dish and agar jelly be at a high temperature?

To kill any potential microorganisms that might contaminate the experiment

Why is an inoculating loop used?

Any microorganisms on the loop are killed to prevent contamination

Why must petri dishes be as closed as possible?

reduces risk of microorganism contamination

Why must lid of petri dish be secured?

drops of condensation dropping onto agar surface and contaminating

Why must culture incubation not exceed 25 degrees

Otherwise harmful pathogens may grow as they are more likely to be grown at higher temperatures

How to calculate inhibition zone area

Area = πr²

inhibition zone

an area where no bacterial growth has occurred; the larger the zone, the more effective a substance tested is against the bacteria