The immune System – HSC Biology


The role of the immune system is to protect and defend the body against infectious diseases.

The immune system is broken into two branches, the innate immune system and the adaptive immune system.

The innate immune system is a general immune response which is not specialised to fight against a particular pathogen. A pathogen is just a disease causing microbe such as the virus SARs-CoV-2 which causes covid-19 or the bacteria cholera which causes severe diarrhoea.

For example, the skin is apart of the innate immune system since it prevents entry of microbes into the body. However, if the skin is scratched the body physical barrier to infection is breached allowing for infectious microbes to enter the body.

If this happens the next line of defence in the innate immune system is required to fight the infection. This includes a range of cells, which may be overwhelming at first, however, just think of them as soldiers defending the body. You can use the flashcards below to memorize the cells and their function.

The Adaptive immune system is the specialised immune system which learns to fight infection. This is what we are training when we are given a vaccine. The two key players in our adaptive are the B cells and the T cells. We refer to the pathogen causing the disease to be a antigen. The B cells produce antibodies to fight and neutralise the antigen as well as flag it to be killed by the T cells. The T cells are like the cells trained to fight and kill pathogens.

The adaptive immune system is called in when the pathogen over runs the innate immune system. Typically this will be done by dendritic cells. You may have heard of people or even experienced swollen glands when you are infected with a cold or flu. This is due to the rapid replication of these B and T cells.

Once you encounter a pathogen, you develop memory B and T cells, this means when you encounter this pathogen again, you will be better equipped to fight and kill the infection.



HSC Questions.

2019 HSC

2018 HSC


Future Questions.

Question 1.

Compare and contrast the innate and adaptive immune response. [3 marks]

Question 2.

Outline the sequence of events which lead to the body mounting an immune response and defending against a pathogen. [3 marks]

Question 3.

Explain why vaccine or naturally acquiring an infection can mean we can not get the infection as severe if we encounter this pathogen again. [4 marks]

Question 4.

Compare an contrast B and T cells. [3 marks]


2019: 2: A, 5:B

2018: 3: D, 16 D

2017: 4A, 6C

Question 1.

Innate and adaptive immunity is similar in that they both are driven by cellular process’ to fight and neutralise pathogens – these are disease causing microbes. Innate immune system is unique that it is non specialised response to a multitude of pathogens, for example dendritic cells detect a pathogen and initiate cellular signalling to recruit more cells to the site of infection. In this process natural killer cells will be brought in to attack the pathogen. The skin is also apart of the innate immune system – the innate immune system is what we were born with. Whereas, the adaptive immune system has to encounter the pathogen in order to mount a specialised response to the pathogen. The cells in this response include the B and T cells. The dendritic cells will activate these cells. The B cell produces antibodies, which will bind to and mark the pathogen. The T cells can then go through and kill this pathogen.

Question 2.


There is a break in the skin, allowing virus to enter the deeper parts of the skin. Dendritic cell will get itself infected by the virus. Dendritic cell produces the viral proteins and displays them on its outside. It will migrate to the lymph vessel and go into a lymph node. It will go to a T cell and activate it. This will result in clonal selection of T cell forming many cytotoxic T Cell and T helper cells. T helper cells will activate B cells and result in the B cell producing antibodies. This will help cells to fight infection. Additionally, antibodies will deactivate the virus – hence stopping infection. Cytotoxic T cells will bind to infected cells and cause it to commit apoptosis.

Question 3.

When an individual first acquires an infection it can take up to 5-10 days in order for their body to mount an adaptive immune response. This is due to the time it takes for B and T cells which are antigen specific to multiply. However, after initial infection, B and T cells will survive the contraction phase resulting in long lived memory B and T cells. As a result, these long lived memory cells will be able to mount a response faster upon reinfection – taking up to 3 days. Hence the infection is shorter lived and less severe second time round.

Question 4.

  • Both produce memory cells
  • Both start in the bone marrow

B cell:

  • Plasma cells that produce antibodies
  • Can release antibodies from the lymph nodes
  • B cell mature in bone marrow

T cell:

  • Usually attracted to the site of infection after being activated
  • Cytotoxic T cell will kill infected cell
  • Helper T cells provide cytokines to encourage and sustain macrophage
  • T cells will mature in the thymus.

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