Biology by Bradford
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The subtopic in the middle and 13 tasks round it: label three diagrams, complete three tables, put a process in order and fill 68 gaps. Every box is standard level. Type into the blanks and check them, or print it on A4, Letter or A3 with an answer key.
| Innate system | Adaptive system | |
|---|---|---|
| Responds to | broad categories of pathogen | pathogens |
| Cells | ||
| Over a lifetime | does not change | builds up a of pathogens met, so it becomes more effective |
The adaptive system recognises : mostly on a pathogen's outer surface. Those on red blood cells can trigger antibody production after a transfusion of the wrong .
Lymphocytes circulate in the blood and also collect in . The body has a vast number of B-cells, each able to make one type of antibody. A B-cell is activated only when it binds the molecule it matches and is touched by a lymphocyte activated by that same molecule. It then divides by into a clone.
Disease-causing organisms, or , include viruses, bacteria, and protists. No are known to cause disease in humans. Careful observation drove progress: Semmelweis cut deaths from childbed fever in Vienna by making doctors wash their , and John Snow traced a cholera outbreak in London to one water .
The skin is a barrier: its outer layer is tough, dry and made of dead cells packed with . It is also a barrier, as its secretions are slightly and contain substances that kill bacteria. Mucous membranes line the airways and gut, where sticky traps pathogens.
Immunity is the ability to eliminate an infectious disease. It comes from long-lived : on a second exposure they make the specific antibody and in greater amounts. A vaccine contains , or coding for them, so it builds immunity without causing the disease.
Number the steps in order.
Because each step activates the next, the clot forms , sealing the skin against .
Phagocytes squeeze out of the blood and reach the site of infection by movement. They recognise foreign cells, engulf them by and digest them with .
Antibiotics block processes in bacteria that do not happen in cells, such as building a bacterial cell . They cannot control viruses, which have no of their own and use the host cell's. Each use of an antibiotic resistant bacteria, which survive and multiply, so careful use is needed to slow the rise of strains.
| Disease | Pathogen | How it reaches humans |
|---|---|---|
| Tuberculosis | unpasteurised milk or air breathed out by infected cattle | |
| Rabies | virus | a from an infected mammal, often a dog |
| Japanese encephalitis | virus | the bite of a that fed on infected pigs or birds |
| COVID-19 | virus (SARS-CoV-2) | crossed recently from another species; now spreads between people in airborne |
Infectious diseases that pass to humans from other species are : they are common, and most newly emerging human diseases start this way.
HIV passes between people in body fluids: in semen and vaginal fluid during unprotected , in blood on shared , and from mother to baby during pregnancy or birth, or in . It infects and kills , so fewer B-cells are activated and fewer antibodies are made. Opportunistic infections take hold: develops.
If a high enough of a population is immune, an infected person rarely meets a one, so transmission is impeded and an cannot take hold. This also shields people who cannot be vaccinated. Vaccines are rigorously tested: the risk of side effects is very small, but not .
| Week | New cases in one town | Percentage change on the week before |
|---|---|---|
| 1 | 1600 | (first week) |
| 2 | 2400 | % |
| 3 | 1800 | % |
| 4 | 1440 | % |
Percentage change = change ÷ × 100. In week 4, 30 in every 100 000 vaccinated people caught it, against 120 in every 100 000 unvaccinated: taken relative to the unvaccinated rate, a percentage difference of %.
12345Disease-causing organisms, or pathogens, include viruses, bacteria, fungi and protists. No archaea are known to cause disease in humans. Careful observation drove progress: Semmelweis cut deaths from childbed fever in Vienna by making doctors wash their hands, and John Snow traced a cholera outbreak in London to one water pump.
The skin is a physical barrier: its outer layer is tough, dry and made of dead cells packed with keratin. It is also a chemical barrier, as its secretions are slightly acidic and contain substances that kill bacteria. Mucous membranes line the airways and gut, where sticky mucus traps pathogens.
Because each step activates the next, the clot forms rapidly, sealing the skin against pathogens.
| Innate system | Adaptive system | |
|---|---|---|
| Responds to | broad categories of pathogen | specific pathogens |
| Cells | phagocytes | lymphocytes |
| Over a lifetime | does not change | builds up a memory of pathogens met, so it becomes more effective |
The adaptive system recognises antigens: mostly glycoproteins on a pathogen's outer surface. Those on red blood cells can trigger antibody production after a transfusion of the wrong blood group.
Phagocytes squeeze out of the blood and reach the site of infection by amoeboid movement. They recognise foreign cells, engulf them by endocytosis and digest them with hydrolytic enzymes.
Lymphocytes circulate in the blood and also collect in lymph nodes. The body has a vast number of B-cells, each able to make one specific type of antibody. A B-cell is activated only when it binds the molecule it matches and is touched by a lymphocyte activated by that same molecule. It then divides by mitosis into a clone.
Immunity is the ability to eliminate an infectious disease. It comes from long-lived memory cells: on a second exposure they make the specific antibody faster and in greater amounts. A vaccine contains antigens, or nucleic acid coding for them, so it builds immunity without causing the disease.
HIV passes between people in body fluids: in semen and vaginal fluid during unprotected sex, in blood on shared needles, and from mother to baby during pregnancy or birth, or in breast milk. It infects and kills helper T-cells, so fewer B-cells are activated and fewer antibodies are made. Opportunistic infections take hold: AIDS develops.
Antibiotics block processes in bacteria that do not happen in eukaryotic cells, such as building a bacterial cell wall. They cannot control viruses, which have no metabolism of their own and use the host cell's. Each use of an antibiotic selects for resistant bacteria, which survive and multiply, so careful use is needed to slow the rise of multiresistant strains.
| Disease | Pathogen | How it reaches humans |
|---|---|---|
| Tuberculosis | bacterium | unpasteurised milk or air breathed out by infected cattle |
| Rabies | virus | a bite from an infected mammal, often a dog |
| Japanese encephalitis | virus | the bite of a mosquito that fed on infected pigs or birds |
| COVID-19 | virus (SARS-CoV-2) | crossed recently from another species; now spreads between people in airborne droplets |
Infectious diseases that pass to humans from other species are zoonoses: they are common, and most newly emerging human diseases start this way.
If a high enough percentage of a population is immune, an infected person rarely meets a susceptible one, so transmission is impeded and an epidemic cannot take hold. This herd immunity also shields people who cannot be vaccinated. Vaccines are rigorously tested: the risk of side effects is very small, but not zero.
| Week | New cases in one town | Percentage change on the week before |
|---|---|---|
| 1 | 1600 | (first week) |
| 2 | 2400 | +50 % |
| 3 | 1800 | −25 % |
| 4 | 1440 | −20 % |
Percentage change = change ÷ original value × 100. In week 4, 30 in every 100 000 vaccinated people caught it, against 120 in every 100 000 unvaccinated: taken relative to the unvaccinated rate, a percentage difference of 75 %.