GCSE Biology Edexcel B3 Topic 1

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B3 Topic 1 Control Systems
Biological rhythms
Biological rhythms that happen across one day are circadian rhythms.
For example, in human brains there is a timing mechanism called a biological clock which regulates the things
that occur in our body over a 24 hour period and can be influenced by environmental factors such as light
This includes the release of hormones such as Melatonin. This usually happens around 10pm at night as
Melatonin makes us feel sleepy. However, in the morning Melatonin levels drop so we wake up. That is why
we are sleepy at night and alert in the morning.
Our biological clock needs regular exposure to day and night to keep with the 24 hour cycle. When we travel
across the globe the day-night cycle there is different than the one the body was using. This can cause a
person to feel less alert and less able to think clearly which is jet lag.
Flowers, such as daisies, close at night and open during the daytime. This makes sure the insects can visit
them for pollination in the day and the seeds are protected from the wind and cold at night. Flowers only
produce nectar during the daytime when the insects are likely to visit the flowers.
Stomata open in the day and close at night.
This is controlled by plant genes. The way in which living organisms respond to changes in day length.
An example of this is deciduous trees as they lose their leaves in winter as the days become shorter.
The plants use the change in day length to help them grow or flower at the right time. Responses to changing
day length are called photoperiodism.
Plants can tell when it is spring from winter as the days get longer. As a result, their seeds sense this and
germinate even if the plant has already died.
Some plants grow throughout winter but grow faster in lengthening days as a response. In autumn, the days
get shorter and the plants stop growing to prepare for winter.
Plant species are often synchronised when releasing their pollen as it is an important stage for creating the
next generation. For example, millions of crop plants harmonise their life cycles to produce grains at the same
Plant defences
Plants can be attacked by insects or pathogens. If this happens to crops, crop yield can be severely reduced
as the plants are eaten, which will increase the price of the crop in the long run.
As a result, plants can produce chemicals to protect the plant when they are attacked by pathogens. This can
be done in different ways:
o Attract parasites to kill the insects.
o Put the insect off (doesn't taste nice)
o Attract predators to attack the insects eating the plants.
Although the plant may have to use a lot of energy to make the chemicals it is worth it.
Milkweed plant produces a toxic chemical that stops insects from eating due to the taste.
Corn plant, when attacked by caterpillars produces a chemical that attracts a parasitic wasp. The wasp lays
eggs in the skin of the caterpillar. When the larvae hatch they eat the caterpillar from the inside out,
preventing further attack.
Wheat seedlings produce a chemical when attacked by insects which attract aphids that eat the insects.
Young lupin leaves produce poisonous chemicals called alkaloids. These make the leaves poisonous to insect
pests or larger herbivores that might want to eat them.

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Potatoes are often attacked by a fungus-like organism called potato blight that destroys their leaves,
thereby killing the plant. Some varieties of potato produce chemicals that kill it.
Plants are a key source of food for people. If pathogens destroy a crop our food supply is at risk. An example
of this is the famine caused by potato blight in Ireland in 1845 and 1846 that killed over 1 million people.…read more

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Some of these lymphocytes become memory lymphocytes. The way the body responds to infection is called
the immune response. Making someone immune to a disease is called immunisation.
Are vaccines safe?
All young children in the UK are offered vaccinations to dangerous childhood diseases such as measles and
whooping cough. However, sometimes children can get a reaction to the vaccine.
About 20% of children may get a mild fever or a rash from the measles vaccine and 1 in a million get a
dangerous reaction.…read more

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Monoclonal antibodies
Monoclonal antibodies: many identical antibodies.
These were invented for making large quantities of antibodies for identifying particular substances.
A lymphocyte can divide over and again to make identical clones of itself. However, once it starts making
antibodies it becomes a B-lymphocyte and it can't divide anymore.
To get around this problem a B-lymphocyte can be fused with a tumour cell (which divides very quickly) to
produce a hybridoma.…read more

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These are often used in medicine. An example is pregnancy testing. Antibodies are placed on a strip that bind
with the hormone "human chorionic gonadotrophin" (hCG). This is found in the urine of women in the early
stages of pregnancy.
The strip is dipped into some urine and if there is any hCG in it, it binds with the monoclonal antibodies on the
strip and causes a colour change.
Monoclonal antibodies can be made radioactive to find cancer in the body.…read more

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The patient will need life-long medication to prevent the kidney being rejected. This suppresses the immune
system so the patient may catch colds more easily.
How kidneys work
Each kidney contains thousands of tiny, microscopic tubes called nephrons.
Blood flows in a network of capillaries called a Glomerulus which runs inside the Bowman's capsule of the
The high pressure of the blood squeezes small molecules through the tiny holes such as water, urea, ions and
glucose.…read more

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ADH: not enough water
Step 1: The brain senses there is not enough water in the blood.
Step 2: The pituitary gland secrets more ADH.
Step 3: The ADH causes the kidneys to reabsorb more water.
Step 4: A small volume of concentrated urine is produced.
ADH: too much water
Step 1: The brain senses there is too much water in the blood.
Step 2: The pituitary gland secretes less ADH.
Step 3: This makes the kidneys reabsorb less water.…read more

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Progesterone: This maintains the lining of the uterus. It inhibits the production of FSH and LH. When
progesterone levels fall, and there is a low oestrogen level, the uterus lining breaks down. A low
progesterone level allows FSH to increase and the whole cycle starts again.
If the egg is fertilised and is implanted in the uterus (pregnancy) the level of progesterone will stay high to
continue to maintain the uterus lining.…read more

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The main functions of the egg is carry the female DNA and nourish the developing embryo:
o 1) The egg contains nutrients in the cytoplasm to feed the embryo.
o 2) As soon as the egg is fertilised with a sperm, the egg's membrane quickly changes its structure to
prevent any more sperm getting in. This is to ensure the offspring have the correct amount of DNA.…read more

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Sex-linked inheritance
Most of our chromosomes come in matching pairs. The two chromosomes in a pair have the same genes in
the same places but may have different alleles.
However, the X chromosome is much larger than the Y chromosome. As well as this, there are more genes on
the X chromosome than on the Y chromosome. This means that males will only have one copy of most of the
genes on the X chromosome.…read more



very, very useful. tried to rate as 5 stars but unfortunately clicked on 1 star.


An exceptionally detailed and complete set of notes for Edexcel B3 topic containing information on immunology, the kidney, fertility and control systems as some of the topics included. These might be useful to students studying other specifications as well. Try using these alongside the related flashcards or a quiz to test your knowledge.


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Thank you


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Brilliant ! Very helpful . Thank you . Very concise and detailed enough at the same time :) 




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