BIOLOGY

B1 B2 B3

B1: You and Your Genes

NUCLEUS

Contains

CHROMOSOMES

Made of long strands of DNA

DNA MOLECULES

BASE PAIRS (G=C)(A=T)

A GENE = A section of DNA that has the genetic code for making a particular protein.

These proteins can be:a) STRUCTURAL – muscles/hair etcb) ENZYMES – digestive/proteases etc

3 Base pairs in a DNA molecule are code for an AMINO ACID.

Base pairs: G=C A=T

A human body has 23 PAIRS of chromosomes.

The sex cells of both males and females carry half of the information, 23 individual chromosomes.

MOTHER23 CHROMOSOMES

FATHER23 CHROMOSOMES

ZYGOTE46 CHROMOSOMES

23 PAIRS

EMBRYO46 CHROMOSOMES

23 PAIRS

Gender• A female carries XX• A male carries XY

The SRY (sex determining region Y) is carried on the Y gene. The SRY makes an XY embryo male, through the production of male hormones (ANDROGENS).

Alleles• Each chromosome has genes in the same

places. But different versions of the genes called alleles.

• Genes can be either RECESSIVE or DOMINANT alleles.

R + R -> R

R + D -> D

D + D -> D

Variation• Variation are differences.• Identical twins are not the same even

though they carry the same genetic information, this is because of ENVIRONMENTAL FACTORS.

• Examples of these factors are:

Climate, diet, physical accidents, lifestyle and culture.

Genetic Testing

• Tests are carried out to see if an individual carries certain alleles.

Following are types of testing...

Antenatal:Analysing the babies DNA before birth. This

can’t detect all disorders.Prenatal:Testing for couple’s with an increased risk.

Prenatal for Down’s Syndrome is offered to all women.

Neonatal:Testing the baby just after birth for disorders

which can be treated early. All babies are screened for 3 (heel prick test).

Carrier Testing:Offered to individuals with a family history of

a disorder such as cystic fibrosis which is caused by a recessive allele. If a couple are both carriers they have an increased risk of a baby with the disorder.

Predictive Testing:Looks for progressive disorders which

develop later on in life. Again this is offered to those with relations that suffer from one.

Limits of Genetic Testing

• Currently tests are not available for all genetic disorders.

• The testing is not completely safe.• These tests are not completely reliable and if

the results are taken as the definite then there may be serious consequences..

E.g: false negative abortion

false positive reassurance & continuation of

pregnancy.

Gene TherapyWhat this involves:1. A normal allele is taken and cut out.2. Copies are made of it.3. They are inserted into the chromosomes

of the patient’s cells.

Stage 3 causes difficulty because the information/cells may not work. The cells may naturally be replaced. In this case nose sprays, injections and viruses can be used to get it into the body.

• Gene therapy does not remove the faulty allele and so, it may be passed on to offspring.

• It is currently illegal to use gene therapy to alter sex cells.

Asexual Reproduction• This requires only one parent.• There is no fusion of cells or mixing of

genetic information, which means that a clone of the parent is produced.

• Plants do this by producing side branches, runners or underground food storage organs which develop into the next generation.

• This is unusual in animals, but starfish and anemones reproduce this way.

Cloning• Clones are genetically identical

individuals.• Twins are natural clones.• Embryo transplants and fusion cell cloning

produce clones.• These processes allow the good features

of an individual to be selected & duplicated in offspring.

Embryo Transplants

EMBRYOEMBRYO

EMBRYO is taken before the cells become specialised.

SEPARATED

GROWNHOST MOTHER

HOST MOTHER

HOST MOTHER

COPY OF ANIMAL A

COPY OF ANIMAL A

COPY OF ANIMAL A

ANIMAL A

Fusion Cell Cloning

BODY CELL

ANIMAL A ANIMAL B

ANIMAL CCLONE OF ANIMAL A- ALL THE GENETIC INFO HAS COME FROM ANIMAL A.

OVARY

DNA NUCLEUS REMOVED

FUSED AND GROWN

Stem Cells• These are unspecialised cells that are taken from

embryos.

THERAPEUTIC CLONING:The cells that are needed are grown from stem cells, but if they do not contain the patient’s genetic information then their body will reject them. So a clone is made of the patients own cell. This is used to produce an embryo, the growth of which is stimulated in a lab. Stem cells can then be taken from the embryo to treat many diseases.

B2: Keeping Healthy

Circulatory System

ARTERIESVEINS

DEOXYGENATED OXYGENATED

CAPILLARIES

(BLOOD VESSELS)

VEINS ARTERIES

Under Low Pressure Under High Pressure

Thin Walls Thick Walls

Thin Layers of Muscle & Elastic Fibres

Thick Layers of Muscle & Elastic Fibres

+ One Way Valves

• Coronary arteries supply the heart muscle with blood.

• When these get blocked by fatty deposits, this causes a heart attack.

Hormonal System

• What are hormones?

They are chemicals which are produced by glands to be transported to the organs via the bloodstream.

• The glands are:

Brain, Pituitary gland, Thyroid, Adrenal gland, Kidney, Pancreas, Testis, Ovary

Nervous System

• The nervous and the hormonal systems were developed because cells need to communicate.

• Cells communicate with electrical impulses.

• The nervous system is made up of:

The brain, spinal cord and also neurones.

• Neurones are nerve cells.

NUCLEUS

DENDRITE (These are like branches)

AXON

ENDING NERVE

Nervous System

• RECEPTORS are groups of specialised cells.

• They detect environmental changes called STIMULI.

• These are then turned into electrical impulses.

• The EFFECTORS produce the response.

• The receptors are in the SENSE ORGANS.

• There are position, light, sound, chemical, touch, pressure, pain and temperature receptors.

• The brain co-ordinates some of the responses, but REFLEX ACTIONS are instant and do not need the brain.

DETECTION OF STIMULUS

SENSORY NERVE

RELAY NERVE

MOTOR NEURONE

EFFECTOR

RESPONSE PRODUCED

Homeostasis

• This is how the body maintains constant internal conditions.

1. Water Content

Water is lost through urine, exhaling, sweat.

2. Temperature

Controlled by blood flow to skin, sweating and shivering.

3. Salts

Lost through sweat and urine.

4. Sugar Levels

Glucose can be released and stored.

This is controlled by the hormone INSULIN, as it removes glucose from the blood.

Disease

• Pathogens cause disease.• Bacteria and viruses are pathogens.

Immune System

• PASSIVE IMMUNITY

(The first line of defence)

Natural Barriers: Skin, Tears, Sweat, Stomach Acid.

• ACTIVE IMMUNITY

(The second line of defence)

White Blood Cells

• The white blood cells recognise the foreign markers on the pathogen cells.

• Antibodies are produced.• They stick to the markers on the micro-

organisms.

• Other white blood cells engulf and ingest the marked cells.

Vaccinations

• Vaccines establish antibodies before the disease is present.

• The memory cells can then remember which antibodies need to be produced and this can be done so quickly if the disease does attack in the future.

• This makes the immune system stronger when fighting the disease.

VACCINATIONS

Small amount of inactive form of pathogens injected

Stimulates white blood cells

Antibodies produced

Type of antibody is stored in the memory cells

Antibiotics

• Overuse and misuse can lead to resistant strains of the disease.

• Resistance can be caused by random mutations.

• The course must be completed or the remaining bacteria may multiply again.

Drug Testing

1. Tests on laboratory grown cells or computer models.

2. Tests on animals.

3. Clinical Trials:

Firstly healthy volunteers & then patients.

Clinical Trials:

BLIND TRIALS

Volunteers don’t know what they are receiving but the doctors/researchers do.

May give unreliable results due to observer bias.

DOUBLE BLIND

Volunteers & researchers/doctors don’t know. This will give more reliable results but is more complex in setting it up.

PLACEBO- FAKE DRUG WITHOUT EFFECT

B3: Life On Earth

Evolution

• The Earth is approximately 4.5 billion years old.

• Life has been present for the last 3.5 billion years.

• There are no records of when life began• We can only have theories. No one will

ever be certain…

The Theories

• Life developed from molecules that like DNA, could copy themselves.

• Earth could have been very different and these molecules could have only been present on the planet then.

• Or these starter molecules many have been in rock from another planet.

• As the molecules joined they became more complex organisms.

Darwin’s Theory of Evolution

• 19th century, Darwin’s explanation was very controversial as it conflicted with religious beliefs.

• He noticed that finches on the Galapagos islands had different beaks that differed with their food sources.

Darwin’s “Natural Selection”

• This is the process of the best adapted individuals in a species surviving.

• The offspring inherit the successful characteristics.

• “Survival of the fittest”

• The poorly adapted individuals will eventually die out and become extinct.

• They will not survive to reproduce.

• This means that only the successful genes are kept in the gene pool.

EXTINCTION

ENVIRONMENTAL CHANGESE.G. CHANGE IN CLIMATE NEW DISEASES

NEW PREDATORS

NOT SUCCESSFULLY ADAPTED SO DO NOT SURVIVE TO REPRODUCE

NEW COMPETITION ON THE FOOD CHAIN

EXAMPLE: THE DODO

• Flightless• Hunted• Caught easily• Humans arrived in

and upset their environment

• Imported animals like rats, pigs and cats ate their eggs.

CONCLUSION:1. The dodo was

poorly adapted because it could not escape predators.

2. Humans were new predators.

3. Humans introduced animals from abroad which upset food chain.

Evidence Of Variation

• He saw that individuals in a species show a wide range of variation.

• Variation is due to differences in genes.

• The variation is for survival and suits different environments.

Evidence of Evolution

• FOSSILS- although some have not yet been discovered.

Human Evolution• Humans DID NOT evolve from apes.• They shared a common ancestor.

Humans had a better chance of survival because:

1. They could stand upright- improving visibility of prey and predators.

2. They had a larger brain- allowing the abilities of planning, speaking & working together.