Summer 2015 selection (b)

Explanation/disclaimer: click to expand/contract

Luteinising hormone (LH) ...

stimulates the unfertilised ovum to develop into the corpus luteum

matures the eggs

causes a follicle to leave the ovary

causes egg to move down fallopian tube

works with FSH to release the follicle from its casing, allowing it to bond with the uterus lining

stimulates evolution

When LH breaks down it forms a corpis luteum

Testosterone feedback loop

This feedback loop ensures that less testosterone is produced by the kidneys

Inhibition of these hormones causes chemical reactions to be slower and fewer

Therefore there is less activity in the testes

This causes the hypothalamus to reduce the stimulus to the pituitary gland which stops release of testosterone

The body then turns off the organelle that produces testosterone

This results in a decrease in secretion of LH and FSH to the testes

This will cause the hypothalamus to stop releasing testosterone

Therefore the testes are inhibited

If the concentration of testosterone rises too high it will be inhibited by the pituitary gland

If testosterone is not used to make sperm cells it enters the blood stream

LH and FSH stimulate the testes to produce either sperm cells or testosterone

Too much testosterone causes inhibition which is a message directed towards the pituitary gland

FSH is reduced so follicles are not stimulated

Possible male contraceptive pill

It inhibits the release of FSH and LH into the testes

How a mutated tumour suppressor gene can result in a tumour

There is now a mutated gene with tumour-coding bases

The tumour suppressor gene will divide uncontrollably

Explain why not all mutations result in a change to the amino acid sequence of the encoded polypeptide

The last allele of a triplet does not affect the coding of an amino acid

Amino acids are degenerate

Amino acids can be coded for by multiple codons

This is due to the degenerate codon

The amino acid sequence could still code for the same gene

Different amino acids can still code for the same polypeptide

How DNA methylation can prevent gene expression

The gene is not a functional protein and is not expressed

How a Pacinian corpuscle produces a generator potential when stimulated

A pacinian corpuscle has a general negative on the outside ... when pressure is applied it pushes the negative ions inside

When the impulse hits it it will bounce off and rapidly travel

Reason why damage to myelin sheath can lead to muscle contraction problems

Myelin sheaths are electrical conductors

This could cause the action potential to travel along the entire length of the neurone instead of along the nodes of Ranvier

Shorter distance for impulses to jump means slower impulse

Myelin sheath can't act as an impulse and cannot limit impulses

Why do cannabinoids (hydrophobic molecules) easily pass into neurones?

Because there is no water in neurones

How cannabinoids could prevent muscle contraction

Synaptic vesicles cannot bind to acetylcholine

Vesicles are taken into the synaptic cleft

The vacuoles may not fuse with pre-synaptic membrane

Vesicles containing neurotransmitter will not be able to bind to receptors on the post-synaptic membrane

Similarity between a taxis and a tropism:

Both are responses to a positive or negative stimulus

They both involve a directional change in the behaviour of an organism

If the stimulus is favourable both responses will cause the organism to get closer to the stimulus

An example is in animals like worms which would move towards light to get above ground

Both require a stimulus such as environment

Difference between a taxis and a tropism:

effect is immediate with taxis whereas tropism takes a longer time

taxis is full, tropism is partial movement

Why scientists used the same restriction endonuclease enzymes on each DNA sample

So they allow themselves to cut DNA at equal lengths

So the same bases are cut

Why scientists used cells that were in mitosis:

When DNA is dividing you can clearly see the alleles as you can see chromosomes

Other cells have loose DNA that is not arranged in chromosomes

As they contain two copies of the alleles which may be seen on the microscope

These cells would be stretched out into 'chromosome shapes' rather than the DNA being all mixed together

The DNA probe is radioactively marked, and this makes it more visible under the microscope

Chromosomes become visible under the microscope, which would allow the scientists to attach a DNA probe

Scientific inaccuracy

A homologous pair is when a chromosome has the same gene but different alleles

Respiration rats also increase in animals

Plants have negative phototropism and positive geotropism in their roots

This impulse tells the brain that the external temperature is too high and pushes the body to make changes to itself in order to oppose the change

This increased heart rate allows more oxygen to be carried around the body than carbon dioxide

We control our glucose concentration in the blood by the use of certain humans

A reflex arc uses a sensory neurone, intermediate neurone and motor neurone to move something like an arm away from something like fire

The reflex arch is the simplest response tool

Plant roots stretch towards the soil in the direction of gravy

The body needs to be in homeostasis in order for it to work properly.

When insulin binds to receptors glucose is broken down to glycogen

The plant moves towards the sun by the axons in the stem of the plants.

This causes the heart to beat faster so that CO2 can dissolve out of the blood more rapidly

In the cold the blood will leave the arms and legs

Increasing heart rate flushes out the high pH

Genes respond to their environment by producing proteins

Responses to cold weather: hairs moving up on skin

When an organism moves away from or towards a stimulus it is called a tactical response (taxis)

Tropism is when plants grow directional to compete for light and nutrients

Body fluid (lymph) is forced out under hydrostatic pressure and reabsorbed into the lympathetic system

The process of taxis is where an organism has a directional response to a positive or negative stimuli

Taxis are responses to stimuli in the environment

Arterioles widen to press the blood against the capillaries

Animals will migrate north to follow the plants

Plants can for example open and close their leaves

If a male/female touches a hot pan, a reflex arc is involved

During photosynthesis, when light is available, the photoreceptors in the chlorophyll in the leaf is stimulated

This (vasodilation) allows blood to be presented to the skin's surface for evaporation.

Humans reproduce by meiosis and is very important as the genetics from the parents is different to the child.

The child is not a clone. The child gets random genetics from both parents.

The variation in reproduction means we have a large genetic diversity and therefore we are less likely to all be susceptible to the same disease.

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