Biology B1 (part 1)

A Balanced Diet

• Carbohydrates release energy
• Fats keep us warm and release energy
• Protein is for growth, cell repair and cell replacement
• Fibre helps the disgestive system
• Vitamins and Mineral ions keep the skin, bones and blood healthy

Metabolic Rate -  the speed at which chemical reactions (metabolism) in the body occur

Factors that affect metabolic rate:

• Age                                           - Exercise/ physical activity
• Gender                                     - Inherited factors (genes)
• Proportion of muscle to fat

Malnourished = unbalanced diet

Obesity - excess fat - bad diet - overeating - lack of exercise

^ health problems: arthritis, type 2 diabetes, high blood pressure, heart disease,cancer

Lack of food: slow growth, fatigue, poor resistance to infection, irregular periods (in women)

Deficiency diseases (lack of vitamins or minerals)

Exercise- more energy used, less stored fat, builds muscle- boosts metabolic rate

Inherited Factors can affect metabolic rate and blood cholesterol

Pathogens - Bacteria and Viruses

Bacteria (tiny living cells) 

•  reproduce rapidly inside your body
•  damage your cells
•  produce toxins (poisons)

Viruses (tinier than bacteria, not cells)

• invade your cells and replicate themselves
• the cell will then burst and release the viruses
• this cell damage makes you feel ill

Defence System

• Skin, hairs and mucus in the respiratory tract
• Platelets help blood clot quickly (to seal wounds)

Immune system: WHITE BLOOD CELLS can....

• ENGULF foreign cells and DIGEST them
• PRODUCE ANTIBODIES (proteins) that lock onto and kill ANTIGENS

• ANTIBODIES are specific to ANTIGENS
• If infected with same previous pathogen > white blood cells rapidly produe the correct antibodies to kill it _ naturally IMMUNE to that pathogen (won't get ill)
• ANTITOXINS counteract TOXINS produced by INVADING BACTERIA

Vaccination - protects from future infections

Infected by new micorooganism, takes whiteblood cells a while to learn how to deal with it, by this time you become quite ill

Vaccination - INJECTED with small amounts of DEAD or INACTIVE microorganisms, these carry ANTIGENS which cause your body to produce ANTIBODIES to attack them. If the same LIVE microorganisms appear again, the WHITE BLOOD CELLS can rapidly produce the right ANTIBODIES to kill the PATHOGEN 

MMR vaccine - contains weakened versions of measles, mumps, rubella

PROS: control infectious diseases (polio, measles, whooping cough, tetanus...) and prevent epidemics (big outbreaks of disease)

CONS: don't always work and sometimes you can get a bad reaction (rare)

PAINKILLERS - relieve symptoms (aspirin)

ANTIBIOTICS - prevent the growth of bacteria, without damaging body cells. They don't destroy viruses

If antibiotics are over-used, bacteria can mutate and become resistant

Investigating Antibiotics...

• Microorganisms can be cultured (grown) in a 'culture medium' (usually agar jelly)
• Hot agar jelly is poured into a petri dish
• Inoculating loops are used to transfer the microorganisms, which then multiply
• Paper disks are soaked in various antibiotics and placed on the jelly
• Antibiotic-resistant bacteria will grow around them (the others will die)
• All equipmetn must be sterilised and a lid must be put on the dish (prevent other microorganisms)

Semmelweis Cut Deaths by Using Antiseptics

Ignaz Semmelweis realised that women were dying in huge numbers after childbirth from a disease called puerperal fever. He believed that doctors were spreading the disease on their unwashed hands, so he made doctors wash their hands with antiseptic before entering his ward > this cut the death rate from 12% to 2%

The antiseptic solution killed bacteria on the doctors' hands (though Semmelweis didn't know this - existence of bacteria not discovered yet ). Therefore he couldn't prove why his method worked > when he left, his methods were dropped and death rates rose again.

Nowadays we know that basic hygiene is essential in controlling disease (although MRSA spread recently in some modern hospitals, due to a lack of basic hygiene).

Antibiotic Resistance is Becoming More Common

We're now able to deal with bacterial infections quite easily by using antibiotics > death rate from infectious bacterial diseases (eg. pneumonia) has fallen drastically.

But bacteria can develop antibiotic resistance, eg. MRSA bacteria are already resistant to certain antibiotics. And the overuse of antibiotics is making the problem worse > increasing the likelihood of people getting infected by antibiotic-resistant strains.

People infected by these bacteria can't easily get rid of them (because antibiotics don't work) and may pass on the infection to others.

So antibiotic resistance is a big problem > drug companies are encouraged to develop new antibiotics that are effective against these resistant strains.

Meanwhile, bacteria resistant to most known antibiotics ('superbugs') are becoming more common.

New Threats 

• Bacteria can mutate to produce new strains
• New strains can be antibiotic-resistant (current treatments no longer clear an infection)
• A new strain, could be one we've not encountered before (no-one'd be immune to it)
• Therefore it could spread rapidly in a population of people > possibly cause an epidemic (big outbreak of disease)

• Viruses also often mutate 
• This makes it hard to develop vaccines against them because of changes in their DNA which lead to them having different antigens
• There'd be a problem if a virus evolved which was deadly and very infectious (eg. Flu Viruses evolve quickly > so it is possible)
• If so, precautions could be taken to stop the virus spreading in the 1st place (difficult due to people often travelling by plane) and vaccines and antiviral drugs could be developed (though these take time to mass produce).
• But in the worst-case scenario, a flu pandemic (when a disease spreads all over the world) could kill billions of people

Sense Organs detect stimuli (a change in environment)

Receptor - groups of cells, sensitive to a stimuli, they change stimulus energy (eg light energy) into electrical impulses

• EYES -light receptors (sensitive to light)
• EARS -sound receptors (sensitive to sound) -balance receptors (sensitive to position change)
• NOSE -smell receptors (sensitive to chemical stimuli)
• TONGUE -taste receptors (sensitive to chemical stimuli)
• SKIN - sensitive to touch, pressure, pain and temp. change

CENTRAL NERVOUS SYSTEM (CNS) > coordinates a response

• The CNS is where all the info from the sense organs is sent
• It's where reflexes and actions are coordinated
• It consists of the BRAIN and SPINAL CORD
• NEURONS (nerve cells) transmit info as ELECTRICAL IMPULSES to and from the CNS
• 'Instructions' from the CNS are sent to the EFFECTORS (muscles & glands), which respond accordingly

Sensory Neurons - The nerve cells that carry signals as electrical impulses from the receptors in the sense organs to the CNS

Relay Neurons - The nerve cells that carry signals from sensory neurons to motor neurons

Motor Neurons - The nerve cells that carry signals from the CNS to the effector muscles or glands

Effectors - Muscles and glands are known as effectors, they respond in different ways. Muscles contract in response to a nervous impulse, whereas glands secrete hormones

• SYNAPSE- the connection between 2 neurones
• The nerve signal is transferred by chemicals which diffuse across the gap
• These chemicals then set off a new electrical signal in the next neurone

• REFLEXES- automatic responses to certain stimuli (reduce chance of injury)
• The passing of info in a reflex (from receptor to effector) is called a reflex arc

The REFLEX ARC goes through the CNS

1) Stimulus (e.g. heat)                                  Sometimes

2) Pain receptor stimulated                          Raphael

3) Impulse sent along sensory neurone       Smells

4) Impulse passed along relay neurone        Really

5) Impulse sent along motor neurone           Mingin

6) Effector muscle contracts (response)       Especially (when) Running

• HORMONES are chemicals released directly into the blood.
• They're carried in the blood plasma to other parts of the body
• Control things in organs & cells that need constant adjustment
• Produced in, and secreted by, various glands ▿
  
• Pituitary Gland- FSH, LH (menstrual cycle)
• Ovaries- Oestrogen (menstrual cycle)

NERVES

• Very FAST action
• Act for a very SHORT TIME
• Act on a very PRECISE AREA

HORMONES

• SLOWER action
• Act for a LONG TIME
• Act in a more GENERAL way

The Menstrual Cycle - A recurring process in which the lining of the uterus (womb) is prepared for pregnancy. If pregnancy doesn't occur, the lining is shed at menstruation.

Stage 1. Menstruation (bleeding), the uterus lining breaks down (about 4 days)

Stage 2. Lining of uterus builds up, into a thick spongy layer full of blood vessels ready to recieve a fertilised egg    (day 4 to day 14)

Stage 3. Egg is released from ovary   (day 14)

Stage 4. Wall is maintained for around 14 days, until day 28. If egg isn't fertilised by then, the lining starts to break down... and the cycle starts again

FSH: produced by pituitary gland - causes egg to mature in ovary - stimulates ovaries to produce oestrogen

Oestrogen: produced in ovaries - causes pituitary to produce LH - inhibits further release of FSH

LH: produced by pituitary gland - stimulates release of egg (around day 14)

Progesterone: produced by ovaries

Hormones can be used to Reduce Fertility

• Oestrogen can be used to prevent the release of an egg (method of contraception)
• Naturally oestrogen helps stimulate the release of eggs, but if it's taken every day the level is kept perminently high which inhibits the production of FSH

• Progesterone reduces fertility by stimulating the production of cervical mucus > prevents sperm getting through and reaching egg

• The pill is an oral contraceptive (1st version had high levels of oestrogen & progesterone but caused blood clots > the pill now contains less oestrogen)
  • PROS - Pill is over 99% effective in preventing pregnancy - reduces risk of some cancer
  • CONS - Not 100% (can still get pregnant) - side effects (headaches, nausea etc.) - doesn't protect against STDs

• Progesterone-only pill > fewer side effects (but not as effective)

Hormones can be used to Increase Fertility

• Some women's FSH levels are too low for eggs to mature (no eggs released > no pregancy)
• FSH and LH can be injected into these women, to stimulate egg release in their ovaries
  • PROS - Helps women get pregnant
  • CONS - Doesn't always work - expensive - too many eggs may be stimulated (unexpected twins, triplets etc.)

IVF Can Also Help Couples Have Children

• In vitro fertilisation - eggs collected from womans ovaries > fertilised in lab with man's sperm > grown into embryos > once they're tiny balls of cells, 1 or 2 are transferred into the woman's uterus > improve chance of pregnancy
• FSH and LH given before egg collection to stimulate egg production
  • PROS - Helps women get pregnant
  • CONS - Can have reaction to hormones (pain, vomiting etc.) - possible increased risk of cancer - possible multiple births

• AUXIN is a plant hormone - controls growth in tips of shoots & roots
• Controls growth of plant in response to light (phototropism), gravity (gravitropism) and moisture
• Auxins stimulate cell elongation
• If the tip of a shoot is removed > no auxins available > no growth
• Extra auxin in shoot = more growth,      extra auxin in roots = inhibits growth

• Shoots grow towards light
  • Shoot tip exposed to light > more auxin accumulates on the side in the shade > cells grow faster on shaded side > shoot bends towards light
• Shoots grow away from gravity
  • When a shoot grows sideways > gravity produces more auxin on lower side > lower side grows faster > shoot bends upwards
• Roots grow towards gravity
  • When a root grows sideways > gravity produces more auxin on lower side > in a root extra auxin inhibits growth > cells on top elongate faster > root bends downwards
• Roots grow towards moisture
  • More moisture on one side of root > more auxin produced on this side > inhibits growth on that side > root bends towards moisture

Plant Hormones in Agriculture

They can be extracted for use  or  artificial versions can be made

• Most weeds are broad-leaved > can be targeted with selective weed-killers 

• These contain plant growth hormones > disrupt normal growth > kills weed (crops remain)

• Plant cuttings won't always grow in soil > add rooting powder (contains auxin) > roots are produced rapidly and the cutting starts growing as a new plant

• Helps growers to produce lots of clones of a good plant quickly

Homeostasis: maintaining a constant internal environment in your body

Bodily levels to be kept constant: Ion levels, water levels, blood sugar levels and temperature

Ion content > regulated by kidneys

• Ions consumed from food (eg. sodium) and absorbed into blood
• Excess ions can be removed by sweating
• Kidneys remove excess ions from blood > got rid of in urine

Water is taken in from food & drink > and lost through SKIN as SWEAT, via the LUNGS in BREATH, via the KIDNEYS as URINE.

Body Temp > controlled by brain (enzymes optimum temp 37ºC > body maintains this)

Blood sugar levels controlled by insulin (eating carbohydrates > glucose into blood, metabolism of cells removes glucose from blood, lots of exercise > even more removed)

Drugs > change your body chemistry > lead to addiction & if not taken > withdrawal symptons (E.g. heroin, cocaine, nicotine and caffiene > all very addictive)

• Medicinal > health (eg. antibiotics: paracetamol, morphine)
• Recreational drugs > for fun, can be illegal/legal

• Performance-enhancing drugs > improve sport performance (health & ethical impacts)
  • Anabolic steriods > muscle, stimulants > heart rate
  • Negative health effects (eg. high blood pressure)
  • Some banned by law, always banned by sporting companies
  • AGAINST: unfair in sport, health risks.  FOR: right to personal choice, everyone has dif. facilities anyway

• Statins- prescribed drugs used to lower risk of heart disease and blood cholesterol
  • Gov. scientists did research and proved this with evidence
• Cannabis- illegal drug, been investigations on mental health problems
  • Results vary, no definite evidence found

Three Main Stages in Drug Testing:

• 1) Tested on human cells/tissues in lab

• 2) Tested on live animals, to find out if it works, how toxic it is and the right dosage. In UK, tested on 2 different animals.

• 3) Tested on healthy human volunteers in clinical trial.Check for harmful side effects. Start with low dosage.
• Then tested on people suffering with the illness, find optimum dose.
• See how well drug works: 2 groups, one given drug, other given placebo > Placebo Effect
• Clinical trials are often double-blind, neither doctor nor patient knows.

Things Gone Wrong in Past

• Thalidomide (1950s) - intended & tested as sleeping pill. Later found to relieve morning sickness in pregnant women (wasn't tested for this)
• It could affect the fetus in pregnant women > causing abnormal limb development.
• Recently used to treat leprosy and some cancers (tested)

They can be LEGAL or ILLEGAL

• Illegal drugs can be categorised into soft or hard > hard drugs are very addictive and are more harmful (not scientific, some soft drugs can be dangerous too)
• Most drug users say they do drugs for enjoyment, relaxation or stress-relief.  Can also be to do with the user's background/ personal life
• Cannabis (soft drug) studies:
  • Stepping stone > create desire to try harder drugs
  • Gateway drug > bring people into contact with drug dealers
  • Genetics > some people more likely to take drugs, cannabis users likely to try other drugs

• Some legal drugs have big impacts: Tobacco & alcohol
  • Smoking causes disease in heart, blood vessels and lungs. Can cause cancer. Nicotine makes it addictive.
  • Alcohol affects the nervous system, slows body reactions. Lead to impaired judgement, poor coordination and unconsciousness. Can cause liver disease & brain damage. It's also addictive.
• Tobacco & alcohol big impact in UK (legal) > affect NHS, economy and society socially