Biology GCSE B2

Infections are caused by microogranisms entering your body and reproducing.

There are 3 types of microbes:

• virus (smallest)
• bacteria (middle)
• fungus (largest)

disease causing microogranims are called pathogens which live off their host.(parasites)

Ideal conditions for microbes:

• warmth
• moisture
• nutrients

Once bacteria invade the body they can reproduce every 20minutes 

Effects of an infection = symptoms

microogranisms enter the body --> reproduce quickly --> damage cells when reproducing or secretion of toxins --> symptoms of feeling ill 

Some bacteria produce enzymes which break down material holding cells togetherallowing them to invade more deeply.

however, microbes don't always affect us because...
- most microogranisms don't cause disease
- our bodies have physical barriers keeping them out

physical barriers:
skin-if damaged can repair itself quickly to prevent wounds gettin infected
skin openings-->sweat - forms protective layer on skin and doesnt allow growth of microbes there. 
eyes-->tears- contains enzymes that kill bacteria
stomach-->acid- hyrodchloric acid kills bacteria and stops them spreading 

 white blood cells are part of your immune system. Different types of white blood cells do different things

Phagocytes will sense a foreign microbe in the body and digest and engulf them =  phagocytosis. These also produce inflammatory responses so bloood flow to infected area increases and fluid leaks onto damaged tissue

Other white blood cells will produce antibodies :

• these can mark antigens for other WBC's 
• attach to and neutralise toxins
• attach to the antigens and kill them directly
  
  [memory cells- some white blood cells that made an antibody before remain in the blood,so if the same microbe attacks,white blood cells can produce the correct antibodies very quickly before you feel ill= immunity]. 

Colds are viruses and there are hundreds of them so its hard to become immune. Also they have a high mutation rate(change of DNA)along with the antigens on their surface, so new antibodies are made each time. 

Vaccines allow you to become immune to a disease before you actually catch it

Small amount of dead/inactive microbes injected in the body--> white blood cells recognise it and make correct antibodies --> antibodies make microbes clump together --> phagocytes digest--> memory cells remain in blood. 

mcirobes with a high mutation rate make it difficult to make vaccines for them (influenza) and some viruses like AIDS attack white blood cels so you're immune system won't work that well. 

Pros                                                               Cons
-epidemic can be prevented if large              - never completely safe, people 
% population vaccinated. even people           genetically different , so react who arent vaccinated won't catch it                        differently. 
because less passing on disease                
 - some disease can be wiped out                 -side effects may be painful

There are different opinions on vaccinations.

• some people don't want to be forced to be vaccinated
• others think the right policy is the one that leads to the best outcome for the most people
• there must be enough of the population vaccinated for a disease to be controlled

in poorer countries you are more likely to catch a disease due to crowded living conditions,poor diet, and low access to medical care. This would make it more important for them to be vaccinated. However often developing countries can't afford it so only people on the edge of a community might be vaccinated to stop it spreading outwards.

antiobiotics are antimocrobial chemicals which can kill only bacteria and fungus but NOT viruses.

Bacteria can evolve and become resitant to antiobiotics. These are called superbugs

random mutations in DNA can lead to change in characterisitc of bacterium so they are less affected by an antiobiotic and resist antibiotic. They live longer and reproduce more. This resistance gene is then passed on to offspring -natural selection.

How superbugs spread so quickly...?

• people don't finish their dose of antiobiotics meaning some resistance microbes will be left behind and reproduce a population of antiobitic-resistant bacteria
• people taking antiobiotics when they don't need it because they create a situaiton where resistance bacteria have an advantage and increase.

How can scientists tackle superbugs?

• continue creating new antiobiotics
• having better hygiene in hospitals to reduce risks of infections
• ensuring people finish their dose of antiobiotic

developments of new drugs:
1. tests done in labs on different body cells to see effectiveness of chemicals
2. drug tested on animals to test effectiveness
3. clinical trials where its tested on humans both for safety and effectiveness.The drugs tested on healthy people first to ensure no harmful side effects and then sick people are tested.

placebos are fake treatments given in drug trials. Sometimes they aren't given because its unfair for people who are seriously sick to miss out on treatment.

blind trials: patients don't know if they're given the drug of placebo because they might feel better for psychological reasons even if there wasnt any improvement or if a patient knows they're not taking the drug wont feel like they're recovering. 

double blind trials: scientist and patients don't know who's got drugs or placebos so scientists monitoring patients analyse results without being influenced by the knowledge of whether a patients actually taken the drug.

open-label trial: both patient & doctor know. 

ARTERIES : take blood from the heart around the body & have thick outer walls, thick layer of muscle and elastic fibres to withstand high pressure of oxygenated blood created by pumping heart 

VEINS: bring deoxygenated blood back to the heart & have thin walls and thin layer of muscle and elastic fibres allowing the vein to be squashed when you move-pushing blood back to heart. Have valves to prevent backflow of blood

CAPILLARIES: one cell thick, allows diffusion of oxygen and food into cells and waste out of cells.

blood travels around the body through the above ^ blood vessels.

 How blood circulates?
  Blood from body -> right atrium--> flows into lower right ventricle--> pumps blood up to lungs to pick up oxygen --> (oxygenated)blood flows back down to left atrium --> flows into left ventricle--> pumped around body delivering oxygen to cells for respiration. 
heart is like a double pump because blood passes through twice in each circuit. 

Heart disease:
plaque builds up in arteries narrowing the lumen of the arteries. This restricts the flow of blood to the heart meaning Heart attacks occur because the heart's muscle cells aren't getting any oxygen or glucose to respire and therefore dying. If arteries are clogged with fat the heart has to pump harder to push blood around the body. You can measure you're blood pressure to see how hard the heart is working.

Causes of Heart disease... ? lifestyle factors

•  diet - saturated fat diets can cause this plaque to build up in arteries
• stress
• smoking (narrows arteries)
• too much alcohol
• not enough exercise ((burns fat and strengthens heart muscle)
• genes
• age

Homeostasis = keeping conditions in your body the same
e.g. keeping correct levels of water and salt, amount of nutrients, getting rid of toxic substances (CO2 + urea)

Control systems have 3 things:

• receptor - detects change
• processing centre - receives information and forms a response
• effector- produces automatic response

Newborn babies are put in incubators because they can't control their temperature. This is also a control system because if it is too cold a heater turns on and if its too hot, then the heater turns off.
This is called negative feedback: any change in the system results in an action that reverses the change 

Our bodies use negative feedback also. For example when we get too hot we sweat to cool ourselves down. We have effectors warming us up and cooling us down.

Water homeostasis is keeping a steady water level in the body .

Kidneys have 2 jobs: water homeostasis + excretion of toxic products. These are linked because you use water to flush out waste products. 

Kidneys control the water balance in your body by changing the amounts of urine you make. The concentration of your blood plasma determines how much water is reabsorbed by kidneys. This concentration can increase if you:

•  sweat excessively 
• don't drink enough water
• eat salty foods

In these cases your kidneys reabsorb water and make less urine

Alcohol causes a larger volume of dilute urine to be produced and causes people to be dehydrated causing dizziness, headaches and tiredness. 

Ecstasy does the opposite.

The control system for water is also negative feedback
1.receptors in brain detect changes in concentration of blood plasma
2. if concentration too high, release of hormon ADH from pituitary gland in brain    
if concentration too low, no ADH released
3. ADH affects amount of water that can be reabsorbed back into blood. The more ADH the more water reabsorbed.

Drugs affect on ADH control:
Alcohol and ecstasy alter the volumes of urine produced because they affect ADH production.

Alcohol suppresses ADH production Less water is reabsorbed in the kidneys so a larger volume of water is made. 

Ecstasy increase production of ADH so less volume of urine is produced as more water is reabsorbed by kidneys. This body fluid build up can lead to brain damage or death.