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B3.1 - Rhythms
· Circadian rhythm: biological processes that follow 24h cycle.
· E.g. chemical patterns (e.g. hormone production)/physiological
patterns (e.g. body temp.)/patterns of behavior (e.g. sleeping).
· All organisms have circadian rhythms.
· Controlled by internal biological clock but external factors can
affect it too (e.g. light).
· Photoperiodism/photoperiodicity: response of a plant to a change
of light/dark in 24h. Examples of photoperiodism:
Germination: some seeds (e.g. Arctic plants) germinate in spring
when day length is longer; usually growth conditions are better.
Growth: plants stop growing over winter; some trees lose leaves.
Reproduction (flowering): plants in seasonal areas produce flowers at
particular time of year; some produce flowers in response of days
increasing in length (spring/summer); others plants flower when day
length decreases (autumn).…read more

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Circadian Examples
· Sleep patterns: "master clock" (group of nerve cells in brain) gets
info about light intensity from eyes; uses this to control
melatonin production. In dark; melatonin increases; sleepy.
· Urine production: master clock controls ADH production; ADH
levels increase at nights; reduced urine production (so sleep isn't
· Stomata opening: stomata responds to light intensity; opens at
day; close at night. Opens to carry out photosynthesis; closes at
night to reduce water loss when photosynthesis stops.
· Flower opening: plants respond to light intensity by
closing/opening their flowers at different times of day. Only need
to open for when pollination is active (e.g. for tobacco flowers it'
s at night; pollinated by moths).…read more

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B3.2 Plant defences
· To protect themselves, plants produce chemicals. This can be:
· Poison in their cells to deter pests that want to eat them.
· Chemicals that kill pathogens (e.g. bacteria/fungi).
· We use plant's defence chemicals as medicines:
· Quinine ­ cinchona tree ­ treats human diseases e.g. malaria.
· Digoxin ­ foxglove ­ treats human disorders e.g. heart disorders.
· Aspirin ­ willow tree ­ relieves symptoms e.g. pain/fever.
· Taxol ­ Pacific yew tree ­ anti-cancer drug.
· Louis Pasteur ­ showed microorganisms were responsible for spoiling food
and some diseases; proposed idea of keeping microorganisms away from
people; aseptic techniques; pasteurization process (heat briefly before stored
to kill bacteria).
· Pests can reduce crop yield:
· Fruit flies ­ feed on fruit ­ ruin entire fruit crops.
Weeds ­ near plants to compete for nutrients in soil - plants wont grow as well
­ crop yield will be lower.
· Plants infected with pathogens ­ energy taken away by pathogen ­ less
energy to produce useful thins ­ lower yield ­ heavy infestation = whole field
produces no food at all.
Add to cost of food production ­ must buy pesticides + diseases resistant crops.
· Drives up price for consumers due to low crop yields (low availability).…read more

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B3.4 - Vaccination
· Avoid getting ill = be immunised.
· Immunisation = inject dead/inactive microorganism into body; they're antigenic (carry
antigens) = harmless but body still creates antibodies to attack them.
· Antigens; trigger memory lymphocytes to be made (if same microorganism appears; killed by
antibodies which have already been developed).
· Edward Jenner ­ gave boy cowpox pathogen ­ boy developed cowpox + recovered ­ Jenner
later gave him smallpox cowpox ­ boy didn't develop cowpox; cowpox vaccine made him
immune to smallpox. Because smallpox has some of the same antigens as cowpox; immune
system quickly produced antibodies when infected with smallpox
1. Vaccine containing dead/weakened pathogen; injected into body; has antigens (surface
proteins that identify a cell) on surface.
2. Lymphocyte (type of white blood cell) produces antibody which fits antigen.
3. Lymphocyte will divide multiple times to produce clones of identical lymphocytes.
4. Some of lymphocytes; secrete large amounts of antibodies; stick to antigens + destroy
pathogen. Other lymphocytes; remain in blood as memory lymphocytes ­ ready to respond
immediately if same antigen turns up again.
5. Sometimes get bad reaction e.g. swelling/something more serious e.g. seizure.
6. Doesn't always work; doesn't always give you immunity.
7. Epidemics can be prevented if a lot of people are immunised.
8. Lasts a long time (often for life).
9. If most people are immune = unlikely people w/o immunisation will be infected.…read more

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B3.5 - Antibodies
· Entry of pathogen = known as infection.
· 1st time pathogen infects person; only 1 or 2 lymphocytes recognize antigens
on it; a while to multiply + secrete enough antibodies to destroy pathogens
(primary response).
· After infection/immunisation = memory lymphocytes remain in blood; can
immediately make right antibodies if same pathogen re-enters (secondary
· Lymphocytes - produces enough antibodies to destroy pathogens before
making person ill.
· Because antibodies are specific = used to identify substances; scientists need
large quantities of identical antibodies (monoclonal antibodies).
· Lymphocyte can divide multiple times to make clones of itself; once it has
started to make antibodies it becomes a B lymphocyte; cant divide anymore;
hybridoma cell solves this problem:
Antigen e.g. HGH injected into mouse ­ will produce lymphocytes that make
antibodies against HGH ­ same time, myeloma (cancer) cells grow in culture
medium ­ take the B lymphocyte from mouse and the cancer cell; fuse together
to create a hybridoma cell that can divide + make antibodies against HGH.
· Monoclonal antibodies are useful as they will target one particular molecule.…read more

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This is really useful!

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