BIOLOGY GCSE

structure of bacteria

small and reproduce very quickly

lytic pathway for virus

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

properties of viruses

non living, no cellular structure, small particles, can reproduce inside living cells, need a host cell to replicate

lysogenic pathway for the virus

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 particle

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)

Physical defences of Plants

• The cellulose cell wall provides protection from microorganisms

• The waxy cuticle of the leaf and stems acts as a barrier to microbes from entering the plant.

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

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

• Thorns or hairy stems also makes it more difficult for pests to access the plant tissue to feed

Chemical defences of plants

• Plants have chemical adaptations to prevent herbivores from eating them

  • Antiseptics or antimicrobial enzymes

  • Chemical poisons to deter pests that might eat them

  • Mechanisms to attract other insects as a biological control

Human Physical defence

Cilia in trachea - prevents pathogens from entering the stomach and the lungs

Hair in nose - prevents pathogens from travelling up from the nose to the lungs

Skin- forms a scab, sweat to trap pathogens, barrier to organs

Chemical Human defence

• Stomach acid - 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

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

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

• Sebum on the surface of the skin - kills bacterial and fungal pathogens

Phagocyte structure

Multi lobe nucleus and granular cytoplasm

Blymphoctyes

Have a large nucleus and a non granular cytoplasm

Aseptic techniques

What do you test new drugs for

• Toxicity – does it have harmful side effects?

• Efficacy – does the drug work?

• Dose – what dose is the lowest that can be used and still have an effect?

How Monoclonal antibodies treat cancer cells

Trigger immune response, block receptors which stops them growing and dividing, carry radioactive substances to the site of the tumour

advantages of monocolonal antibodies

Only bind to a specific cell and do not damage host cells, highly specific used to be treat a range of conditions

disadvantages of monoclonal antibodies

expensive to produce, may cause a lot of side effects

Use of monoclonal antibodies

The monoclonal antibodies are specific to a hormone produced in pregnancy,HCG. The monoclonal antibodies are specific to the antigens found on the surface of the pathogens, blood clots or cancer cells.They also contain the marker that helps in detect the cells. Monoclonal antibodies with a fluoroscent dye attached can be used by the scientist to detect specific molecules in tissue.Monoclonal antibodies can also be used in the treatment of cancers(block receptors,trigger immune cells, carry radioactive substances to the site )