Ocr As Biology - The Immune System (Part 2)

Front 1

How do antibodies help clear an infection?

Back 1

• Agglutinating pathogens - each antibody has two binding sites, so an antibody can bind to two pathogens at the same time - the pathogens become clumped together. Phagocytes then bind to the antibodies and phagocytose a lot of the pathogens all at once. Antibodies that behave like this are known as agglutinins.
• Neutralising toxins - like antigens, toxins have different shapes. Antibodies called antitoxins can bind to the toxins produced by pathogens. This prevents the toxins from affecting human cells, so the toxin is neutralised. The toxin-antibody complexes are also phagocytosed.
• Preventing the pathogen binding to human cells - when antibodies bind to the antigens on pathogens, they may block the cell surface receptors that the pathogens

Front 2

The primary response is...

Back 2

... slow

Front 3

Explain what the primary response is and why is slow/fast, and why it is harder to get ill again.

Back 3

• When a pathogen enters the body for the first time, the antigens on its surface activate the immune system. This is called the primary response.
• The reason why the primary response is slow is because there aren't enough B lymphocytes that can make the antibody needed to bind to it.
• Eventually, the body will produce enough B lymphocytes and antigens to overcome the infection. But while this occurs, the carrier will show symptoms of the infection.
• After being exposed to the antigen, the T and B lymphocytes produce memory cells. These memory cells remain in the body for a long time.
• Memory T lymphocytes remember the specific antigen and will recognise it a second time round.
• Memory B lymphocytes record the specific antibodies needed to bind to the antigen.
• This process makes the person immune - their immune system knows how to respond to a section infection.

Front 4

The secondary response is...

Back 4

...fast

Front 5

Explain what the secondary response is and why is slow/fast and what occurs during the secondary response.

Back 5

• In a secondary response, the immune system will produce and quicker, stronger immune response.
• This is due to clonal selection happening faster.
• Memory B lymphocytes are activated and divided into plasma cells that produce the right antibody to the antigen.
• Memory T lymphocytes are activated and divide into the correct type of T lymphocytes to kill the cell carrying the antigen.
• The secondary response often gets rid of the pathogen before you begin to show any symptoms.

Front 6

Summarise into a table the primary and secondary responses.

Divide the table into Pathogen, Speed of response, cells activated and symptoms.

Back 6

Front 7

Draw a graph showing the concentration of the right antibody against the y-axis and the time and days during the x-axis. Show the primary and secondary examples.

Back 7