Biology 1a-Human Biology

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Plant Hormones

Hormones make sure plants grow in a useful direction--towards light

  • Auxin is a Plant Hormones
  • It controls growth near the tips of shoots and roots
  • It controls the growth of a plant in response to light(phototropism), gravity(gravitropism or geotropism) and moisture
  • Auxin is produced in the tips and moves backwards to stimulate the cell elongation process which occurs in the cells just behind the tips
  • If the tip of a shoot is removed, no auxin is available and the shoot may stop growing
  • Extra auxin promotes growth in the shoot but inhibits growth in the root
  • Plant Hormones have uses in Agriculture
  • They can be extracted and used by people or artificial versions can be made
  • Most weeds in crop fields are broad-leaved. Selective weedkillers are made of plant growth hormones. They disrupt their normal growth patterns, which soon kills them but leaves the crops untouched
  • Plant cuttings won't always grow in soil so by adding rooting powder which contains auxin, it'll produce roots rapidly and start growing as new plants.
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Plant Hormones 2

  • Shoots grow towards light
    •  When a shoot tip is exposed to light, more auxin accumulates on the side that's in the shade than the side that's in the light
    • This makes the cells grow faster on the shaded side, the shoot bends towards light
  • Shoots grow away from gravity
    • When a shoot is growing sideways, gravity produces an unequal distribution of auxin in the tip, with more auxin on the lower side
    • This causes the lower side to grow faster, bending the shoot upwards
  • Roots grow towards gravity
    • A root growing sideways will also have more auxin on its lower side
    • But in a root the extra auxin inhibits growth. This means the cells on top elongate faster, and the root bends downwards
  • Roots grow towards moisture
    • An uneven amount of moisture either side of a root produces more auxin on the side with more moisture
    • This inhibits growth on that side, causing the root to bend in that direction, towards the moisture
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Homeostasis

Homeostasis is all the functions in your body trying to maintain a constant internal environment

  • Your body needs some things to be kept constant
    • to keep all your cells working properly certain bodily levels need to be controlled
    • Ion content, water content, sugar content, temperature
  • Ion Content is regulated by the Kidneys
    • Ions are taken into the body in food, then absorbed into the blood
    • If the food contains too much of any kind of ion then the excess ions need to be removed
    • Some ions are lost in sweat
    • The kidneys will remove the excess from the blood--its gotten rid of in the urine
  • Water is lost from the body in various ways
    • Water is taken into the body as food and drink and is lost from the body:
      • through the skin as sweat
      • via the lungs in breath
      • via the kidneys as urine
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Homeostasis 2

Body Temperature is controlled by the Brain

  • All enzymes work best at a certain temperature. The enzymes within the human body work best at about 37*C- so the body tries to maintain that temperature
  • A part of the brain acts as your own personal thermostat. It's sensitive to the blood temperature in the brain and it receives messages from the skin to provide information about skin temperature

Blood Sugar Level needs to be controlled

  • Eating foods containing carbohydrate puts glucose into the blood from the gut
  • The normal metabolism of cells removes glucose from the blood. If someone does a lot of vigarous, then much more glucose is removed
  • A hormone called insulin helps to maintain the right level of glucose in your blood, so your cells get a constant supply of energy
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Drugs

Drugs change your Body Chemistry

Some of the chemical changes caused by drugs can lead to the body becoming addicted to the drug. If the drug isn't taken, the addict can suffer unpleasant withdrawal symptoms

  • Drugs can be Medicinal,Recreational or Performance-Enhancing
    • Medicinal drugs are medically useful like antibiotics. For some you don't need a prescription but for others like morphine you do as they can be dangerous if misused
    • Recreational drugs are used for fun. These can be legal or illegal
    • Performance-enhancing drugs can improve a person's performance in sport
  • Performance-enhancing drugs have health and ethical impacts
    • There are several different types including anabolic steroids (increase muscle size) and stimulants (increase heart rate)
    • They have negative health effects (steroids can cause high blood pressure)
    • Some of these drugs are banned by law, some are prescription only, but all are banned by sporting bodies
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Drugs 2

There are also ethical problems with taking performance-enhancing drugs

  • Against drugs
    • It's unfair if people gain an advantage by taking drugs, not just through training
    • Athletes may not be fully informed of the serious health risks of the drugs they take
  • For drugs
    • Athletes have the right to make their own decision about whether taking drugs is worth the risk or not
    • Drug-free sport isn't really fair anyway--different athletes have access to different training facilities, coaches, equipment


 

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Drugs 3

Claims about drugs need to be carefully looked at

  • Statins-They are prescribed drugs used to lower the risk of heart and circulatory disease
  • There's evidence that statins lower blood cholesterol and significantly lower the risk of heart disease in diabetic patients
  • The original research was done by government scientists with no connection to the manufacturers
  • It compared two groups of patients-those who had taken statins and those who hadn't

Research findings are not always so clear

  • Cannabis-It's an illegal drug. Scientists have investigated whether the chemicals in cannabis smoke cause mental health problems. The results vary, and are open to different interpretations
  • Until more definite scientific evidence is found, no-one's sure
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Testing Medicinal Drugs

There are three main stages in Drug Testing

  • 1) Drugs are tested on human cells and tissues in the lab.
    • However, you can't use human cells and tissues to test drugs that affect whole or multiple body systems e.g. testing a drug for blood pressure must be done on a whole animal because it has an intact circulatory system
  • 2) The next step is to test the drug on live animals. This is to see whether the drug works, to find out about its toxicity and the best dosage
    • The law in Britain states that any new drug must be tested on two different live mammals. Some people think it's cruel to test on animals, but others believe this is the safest way to make sure a drug isn't dangerous before it's given to humans
  • 3) If the drug passes the tests on animals then it's tested on human volunteers in a clinical trial
    • First the drug is tested on healthy volunteers. This is to check it doesn't have any harmful side effects when the body is working normally. At start low dose is given, it gradually increases
    • If the results of the tests on healthy volunteers are good, the drugs can be tested on people suffering from the illness. The optimum dose is found- this is the dose of the drug that is the most effective and has few side effects
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Testing Medicinal Drugs 2

  • 3) To test how well the drug works, patients are put into two groups. One is given the new drug, the other is given a placebo. This is so the doctor can see the actual difference the drug makes- it allows for the placebo effect (they'll feel better even though the treatment isn't doing anything)
    • Clinical trials are blind- the patient in the study doesn't know whether they're getting the drug or the placebo. They're often double-blind- neither the patient nor the doctor knows until all the results have been gathered. This is so the doctors monitoring the patients and analysing the results are subconciously influenced by their knowledge
  • Things have gone wrong in the past
    • Thalidomide-a drug developed in the 1950's
    • Thalidomide was intended as a sleeping pill, and was tested for that use but was later found effective in relieving morning sickness in pregnant women
    • Unfortunately, thalidomide hadn't been tested as a drug for morning sickness so it wasn't known that it could pass through the placenta to the fetus causing abnormal limb development. In some cases, babies were born without arms or legs at all
    • About 10,000 babies were affected and about only half survived
    • The drug was banned and more rigorous testing procedures were introduced
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Recreational Drugs

  • Recreational Drugs can be Illegal or Legal
  • Illegal drugs are often divided into two groups- soft and hard. Hard drugs are usually thought of as being seriously addictive and generally more harmful
  • You can have problems with soft drugs too. Heroin and ecstasy are hard drugs and cannabis is a soft drug. All three cause heart and circulatory system problems
  • Some studies link Cannabis and Hard Drug use-others don't
    • Cannabis is a 'stepping stone'-the effects of cannabis create a desire to try harder drugs
    • Cannabis is a 'gateway drug'-brings people into contact with drug dealers
    • It's all down to genetics-certain people are more likely to take drugs generally, so cannabis users will also try other drugs
  • Some Legal Drugs have more of an impact than Illegal Drugs
    • Smoking-causes disease of the heart, blood vessels and lungs
    • Tobacco smoke also causes cancer
    • Nicotine is the drug found in cigarettes-it's addictive so hard to stop smoking
    • Alcohol-it affects the nervous system and slows down the body's reactions
    • Too much alcohol leads to impaired judgement, poor coordination, unconsciousness
    • Excessive drinking can cause liver damage and brain damage
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Recreational Drugs 2

Tobacco and alcohol have a bigger impact in the UK than illegal drugs, as so many people take them.

The National Health Service spends loads on treating people with lung diseases caused by smoking.

It's the same with alcohol. The costs of the NHS are huge.

In addition to the financial costs, alcohol and tobacco cause sorrow and anguish to people affected by them, either directly or indirectly.


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