I WILL PASS MY EXAMS I KNOW WHAT IS GOING ON

WHAT HAPPENS IN THE ELECTRON TRASNFER CHAIN

EXCITED ELECTRONS FROM CHLOROPHYLL MOVE DOWN ETC

UNDERGO SERIES OF REDOX

GIVE PROTONS ENERGY

how is proton gradient established during chemiosmosis

• energy released as electrons move down the ETC is used to pump protons (H⁺ ions) from the stroma into the thylakoid

• The proton concentration inside the thylakoid , creating a proton gradient across the thylakoid membrane

• This establishes an electrochemical gradient (proton motive force)

• Protons flow back into the stroma through ATP synthase

• The flow of protons drives the synthesis of ATP from ADP and inorganic phosphate

How do plants use the sugars from

Photosynthesis

As respiratory substrates

To synthesis other biological molecules

What is biomass

Total dry mass of tissue or mass of carbon measured over a given time in a specific area

How can chemical energy store in dry biomass be estimated

Using calorimetry

Energy released is specific heat capacity X volume of water X tempyeraykte inc of water

Why is bomb calorimetry preferred tl

Simple calorimetry

Reduces heat loss to surroundings in

How could a student ensure that all water had been removed from sample Before weighing

Keep heating the sample and rewriting until the mass reading is constant

Gross primary production

Total chemical energy in plant biomass working a given volume or area

Net primary production

Total chemical energy available for plant growth for plant growth plant reproduction and energy transfer to other trophic levels after respiratory losses

how does phosphorus cycle occur

plans absorb phosphate into soil

plants are then eaten by animals

animals die or secrete

sapriabionts feed and break down phosphate back in soil

Why can sodium and potassium ions only cross the axon membrane through channel proteins, and not by simple diffusion?

sodium and potassium ions are hydrophilic

sodium and potassium ions are charged

insoluble in lipids

what affects the rate of conduction of an action potential

The bigger the axon diameter the lower the resistance inside the axon and the faster the speed of conductance. A bigger diameter also means that in a given amount of time, fewer potassium ions diffuse out of the axon. This makes it easier to maintain the resting potential inside the axon. This allows action potentials to be triggered more quickly, which leads to a greater speed of conductance

Neurobiologists found that the nerve impulses in the Penaeus shrimp have the fastest speed of conductance in the animal kingdom, with speeds of over 200m/s.200 m/s. Observation of neurones from the Penaeus shrimp under a microscope showed that they were myelinated. Using this information, explain the fast speed of conductance of the Penaeus shrimp neurones.

In myelinated neurones, depolarisation can only occur at the nodes of Ranvier since the myelin sheath is an insulator. This means nerve impulses jump from node to node via saltatory conduction rather than travel across the whole length of the axon. So, in a myelinated axon, a reduced number of action potentials are needed. Therefore, less time is taken up with the repeated formation of action potentials. As a result, myelinated axons have a greater speed of conductance compared to non-myelinated axons. This accounts for the fast speed of conductance of the Penaeus shrimp.

Muscular paralysis is a condition characterised by loss of ability to move some parts of the body. Individuals with muscular paralysis often have damaged myelin sheaths on their neurones.

Explain how this can cause the symptoms of muscular paralysis.

With damaged myelin sheaths on neurones, saltatory conduction cannot occur. This means that depolarisation/action potentials must occur along the whole length of the axon. Therefore, Nerve impulses are slowed down at neuromuscular junctions causing muscular paralysis.

what is the point of the refractory period

to allow ap to be unidirections

and discrete impulses

The venom of the female black widow spider contains a toxin called αα-LTX.

αα-LTX is thought to work by forming a Ca2+Ca2+- permeable ion channel in the presynaptic membrane of cholinergic neurones.

Being bitten by the female black widow spider causes a massive release of neurotransmitters across the synaptic cleft.

Explain how, and include the name of the neurotransmitter in your answer.

By forming a Ca2+Ca2+- permeable ion channel, αα-LTX causes a massive influx of Ca2+Ca2+ into the synaptic knob, even in the absence of an action potential and depolarisation. The influx of Ca2+Ca2+ causes synaptic vesicles to move down the synaptic knob, and to fuse with the presynaptic membrane. This releases acetylcholine, the neurotransmitter found in cholinergic neurones, into the synaptic cleft.

Proteins named SNAREs are involved in helping synaptic vesicles to fuse with the presynaptic membrane.

Some toxins, such as the botulinum toxin produced by the bacteria Clostridium botulinum, cleave SNAREs.

Suggest how the botulinum toxin works on cholinergic synapses.

Cleavage of SNARE proteins means that synaptic vesicles containing acetylcholine cannot fuse with the presynaptic membrane upon the influx of Ca2+Ca2+ caused by the arrival of an action potential. This means the neurotransmitter, acetylcholine, is not released across the synaptic cleft.

Parkinson’s Disease (PD) is a neurodegenerative condition caused by the loss of functional dopaminergic neurones in the brain.

The image below shows how dopamine is synthesised in presynaptic neurones.
Levodopa is the first line treatment for PD. Levodopa is the synthetic version of L-DOPA.

Using the information given, suggest how levodopa can treat PD.

Dopamine diffuses across the synaptic cleft and binds to receptor sites on sodium channels on the postsynaptic neurone. This leads to the diffusion of sodium ions into the postsynaptic neurone. This causes depolarisation and the generation of an action potential if the threshold potential is reached.

Levodopa has the same structure as L-DOPA so levodopa is converted by DOPA decarboxylase into dopamine in the brain. This means more dopamine is available in dopaminergic presynaptic neurones to be released into the synaptic cleft. This restores some of the function of the dopaminergic

List the similarities and differences between cholinergic synapses and neuromuscular junctions.

Similarities:

∙  ∙ Both involve neurotransmitters packaged in vesicles that diffuse across a synaptic cleft when they are released.

∙  ∙ Ca2+Ca2+ channels are involved in both.

∙  ∙ In both, there are sodium channels on the postsynaptic membranes with two receptor sites.

∙  ∙ In both, enzymes are involved in catalysing the reformation of the neurotransmitter, which is then packed back into vesicles in the presynaptic membrane using energy from ATP.

∙  ∙ In both, there is depolarisation of the postsynaptic membrane.



Differences:

∙  ∙ The presynaptic neurone of cholinergic synapses can be a motor or relay neurone but in neuromuscular junctions, the presynaptic neurone is always a motor neurone.

∙  ∙ Cholinergic synapses link motor/relay neurones to other neurones or effector organs while neuromuscular junctions link neurones to muscles cells.

∙  ∙ Acetylcholine is the only neurotransmitter in cholinergic synapses. In neuromuscular junctions, many different neurotransmitters can be used.

∙  ∙ Nerve impulses end at a neuromuscular junction, as a muscle contraction occurs. In cholinergic synapses, the nerve impulse continues.

WHAT DO NEUROMUSCULAR JUNCTION DO

LINK MOTOR NEURONE TO MUSCLES

WHAT DO CHOLINERGIC SYNAPSES LINK

Cholinergic synapses link motor/relay neurones to other neurones, or motor neurones to effector organs.

Cholinergic synapses link motor/relay neurones to other neurones, or motor neurones to effector organs.

First, glucagon or adrenaline activates the enzyme adenylate cyclase, which converts ATP into cyclic AMP.

 

This new molecule acts as a second messenger and binds to the enzyme protein kinase, activating it. 

 

This enzyme then catalyses glycogenolysis.

Describe the process of ultrafiltration.

There is high hydrostatic pressure in the capillaries that form the glomerulus. This forces out small molecules within blood to pass through the endothelium, the basement membrane, and podocytes into the Bowman’s capsule to form the glomerular filtrate. Small molecules that pass through include urea, water, glucose, and sodium ions, while larger molecules such as red blood cells are left behind in the blood.

WHAT HAPPENS DURING SELECTIVE REABSORPTION

During selective reabsorption, SODIUM

ions are transported from the epithelial cell into the blood via

ACTIVE

TRANSPORT

. Sodium ions and other substances in the lumen are then transported into the epithelial cell via

FACILLITATED

DIFFUSION

using

CO TRANSPORT

proteins. These substances then travel down their concentration gradient into the blood.

Describe how sodium ions and water are reabsorbed in the loop of Henle.

n the loop of Henle, sodium ions are actively transported out of the ascending limb and into the medulla. This decreases the water potential in the medulla, creating a water potential gradient. So, water moves out of the descending limb and into the medulla by osmosis. This is an example of a countercurrent mechanism. In the medulla, both sodium ions and water are reabsorbed into the blood.

People with diabetes are unable to remove glucose from their blood. Therefore, one of the symptoms of diabetes is the presence of glucose in urine. Explain why a person with untreated diabetes will have glucose in their urine.

A person with untreated diabetes will have a high concentration of glucose in their blood. This means that a lot of glucose will be filtered out of the blood during ultrafiltration, giving a filtrate with a high concentration of glucose. During selective reabsorption in the proximal convoluted tubule, the co-transport proteins that are responsible for reabsorbing glucose will be saturated. This means not all of the glucose from the filtrate can be reabsorbed, and some will remain in urine.

Describe the body’s response to a decrease in the water potential of the blood.

First, the decrease in water potential is detected by osmoreceptors.

Osmoreceptors then send impulses to the posterior pituitary and stimulate it to release more ADH.

ADH travels in the blood to the kidneys, where it binds to receptors on cells lining the distal convoluted tubule and collecting duct.

This binding increases their permeability to water, which increases the reabsorption of water by osmosis.

This causes the water potential of the blood to increase back to the optimum.

Describe how the permeability of the cells lining the collecting duct is increased.

ells in the collecting duct have vesicles containing aquaporins.

When ADH binds to receptors on the surface of cells lining the collecting duct, it triggers the production of cAMP.

cAMP phosphorylates the vesicles containing aquaporins. This causes the vesicles to move to the cell membrane next to the lumen of the collecting duct. The vesicles fuse with the cell membrane and add aquaporins to it.

what does methyl group bind to

dna

what does acetyl group bind to

histones

define epigenetics

Epigenetics involves heritable changes in gene function, without changes to the base sequence of DNA.

Tumour suppressor genes are responsible for preventing the development of cancer.

Explain how increased methylation of the tumour suppressor gene could lead to cancer.

Methyl groups can be added to tumour suppressor genes. This inhibits the transcription of tumour suppressor genes, leading to uncontrolled cell growth.

Epigenetic changes have been linked to the development of autism. An increase in expression of a specific gene, Shank3, is found in people with autism.

Describe how a reduction in DNA methylation may be linked to autism.

A reduction in DNA methylation would cause an increase in Shank3 gene transcription. This leads to an increased expression of Shank3 within autistic individuals.

Fragile X syndrome is a condition which causes intellectual disability. It has been shown that hypermethylation of the FMR1 gene is a contributing factor for this syndrome.

How can epigenetic therapy be used to combat fragile X syndrome?

To reverse the epigenetic changes, drugs can inhibit the enzyme responsible for adding methyl groups to the FMR1 gene. This will lead to less methylation of FMR1 gene and stimulate transcription again.

Outline how siRNA inhibits translation.

siRNA first joins to a protein complex, forming an RNA-induced silencing complex. The protein complex removes one strand from the siRNA molecule, forming single-stranded RNA. The single-stranded RNA then binds to complementary bases on an mRNA molecule. This binding can prevent translation in one of two ways:

First, it can prevent a ribosome from attaching to mRNA.

Second, an enzyme in the RNA-induced silencing complex can destroy the mRNA.

Suggest why the siRNA molecule would only affect gene expression in the HCV cells, and not other cells within the human body.

the siRNA base sequence would only be complementary to the RNA molecule inside the HCV virus. Therefore, it would only prevent translation of genes inside the HCV virus.

A tumour suppressor gene may undergo a deletion mutation, in which a base is removed. State the role of tumour suppressor genes. Explain how a deletion mutation in a tumour suppressor gene could result in the formation of a tumour.

Tumour suppressor genes encode for proteins that actively prevent tumours from forming. A deletion mutation in the tumour suppressor gene removes one or more bases, meaning that triplets are read incorrectly during transcription.

This changes the sequence of amino acids in the primary structure, which in turn changes the bonding between the side groups.

This changes the protein’s tertiary structure so it ends up with a different shape and does not function properly.

As a result, the protein is unable to carry out its role in preventing tumours. By, for example, slowing down cell division.

This allows a tumour to form.

Describe and explain how changes to a tumour suppressor gene could lead to cancer.

umour suppressor genes prevent the formation of tumours by encoding for proteins that slow down or prevent cell division, repairing mistakes in DNA, and telling abnormal cells to die.

A tumour suppressor gene can become inactive in two ways.

First, a mutation could change the sequence of amino acids in the primary structure of the protein encoded by the gene. This in turn changes the protein’s tertiary structure, which prevents the protein from functioning correctly.

Second, a tumour suppressor gene can become inactive through increased methylation. This prevents transcription of the tumour suppressor gene so the protein is not produced.

In both cases, the inactivation of the tumour suppressor gene can lead to uncontrolled cell division which can form tumours.

Describe fully how a gene machine can be used to produce a DNA fragment.

A gene machine uses the DNA sequence to build the DNA fragment from scratch. Starting from a protein of interest, first, the amino acid sequence of the protein is identified. From this, scientists work backwards to identify the corresponding mRNA sequence.

Using the mRNA sequence, the complementary DNA sequence can be identified.

This DNA sequence is entered into a computer that checks whether the DNA is safe.

Finally, the gene machine assembles short strands of the DNA, one nucleotide at a time, which are then assembled into one complete DNA fragment.

In order to make enough tPA for medical use, geneticists take the gene coding for tPA and place it into a bacterium. The bacterium then produces tPA which is collected.

There are three possible methods for obtaining the tPA gene.

1.    1. Use a restriction enzyme to cut out a DNA fragment containing the gene
2.    2. Use reverse transcriptase to convert the mRNA coding for tPA into cDNA
3.    3. Use a gene machine to create the tPA gene

Explain why the bacterium wouldn’t be able to make tPA using the DNA produced by method 1.1.

The DNA fragment produced in method 11 would contain introns. Bacteria are unable to carry out splicing, meaning that these introns would be present in the final mRNA strand. Translation of this mRNA strand would result in a non-functional protein.

During in vivo gene cloning, bacteria are grown on a plate containing an antibiotic (kanamycin).

The surviving bacteria are then transferred to a plate containing a second antibiotic (ampicillin).

Explain the purpose of this step.

To identify the bacteria that have taken up the recombinant plasmid, rather than a plasmid without a DNA fragment.

The addition of the DNA fragment into the plasmid disrupts the function of the ampicillin resistance gene. This means that when plated on ampicillin, bacteria that contain the recombinant plasmid (i.e. contains the DNA fragment) will die.

Here are some of the steps required to carry out gel electrophoresis on samples of DNA:

 

Add the DNA samples to different wells in the gel.

2. Apply a voltage across the gel.

3. The DNA fragments move down the gel, forming bands.

4. Transfer the DNA fragments to a membrane (or paper) to preserve them.

5. Add DNA probes with a stain to make the bands easier to see.

6. Take a photo to preserve the results for longer.

the breeders expected the actual number pf pffspring phenotype to differ from number predicted WHY

THE PREDICTED OFFSPRING NUMBERS ARE BASED ON PROBABILITY

GAMETES ARE NOT PRODUCES IN EQUAL NUMBERS

CROSSING OVER OR MUTATIONS CAN OCCUR DURING MEIOSIS

SAMPLE SIZE IS SMALL

RANDOM FERTILISATION

MOST OFFSRPINGS HAVE PARENTAL PHENOTYPE

GgNn produce mostly GN and gn

crossing over during meiosis

produces GN gN gametes

how does speciation occur

reproductive isolation/ via georgaphical/ different mating seasons/ courtship behaviours

creates seperate gene pools

variation due to mutations

directional/ disruptive selection

selected organisms survive and reproduce

change in allele frequency over a long period of time

different species

what can lead to reproductive isolation

geographical seperation

variation causedd by random mutations differences in flowering season or courtship behaviour

sympatric speciation

occurs in the same habitat

mutations cause differences in egg laying locations

reproductive seperatiom or gene pools remain seperate

different alleles pass on/ selected or change in frequency of alleles over time

disruptive natural selection

eventually different species cannot breed

SLIDING FILAMENT THEORY

CALCIUM IONS CAUSE TROPOMYOSIN TO MOVE AWAY FROM THE ACTIN BINDING SITE

MYOSIN HEAD ATTACHES TO BINDING SITE ON ACTIN FORMING A CROSS BRIDGE

ADP AND PI ARE RELEASED FROM THE MYOSIN HEAD

ATP BINDS TO MYOSIN HEAD AND DETACHES FROM ACTIN

MYOSIN HEAD HYDROLYSES ATP AND MYOSIN HEAD RETURNS TO STARTING POSITION

WHAT IS A POWER STROKE

DURING MUSCLE CONTRACTION THE MYOSIN HEAD MOVES ALONG THE ACTIN CAUSING THE ACTIN TO END UP CLOSER TO THE M LINEOF THE SARCOMERE THIS IS KNOW AS A POWER STROKE

Using your knowledge of aerobic respiration, suggest how athletes are able to run for longer than two hours

After glucose stores have been used up in aerobic respiration, triglycerides and amino acids can be used in respiration. Triglycerides are broken down into glycerol and three fatty acids. Glycerol is converted into triose phosphate which can take part in glycolysis. The fatty acids are converted into acetyl CoA molecules that can take part in the Krebs cycle. The majority of amino acids with three carbons are converted into pyruvate which is used in the link reaction, whereas 4−4− and 5−5− carbon amino acids are converted into intermediates in the Krebs cycle. By using amino acids and triglycerides, ATP continues to be produced in the absence of glucose stores. This means ATP is available for use as an energy source for the contraction of muscles that allows the athlete to keep running.

Describe the stages of the phosphorus cycle.

Rocks contain phosphate.

Harsh weather conditions break down rocks, releasing phosphate into the soil.

Some of this phosphate is absorbed by plants to make phosphate-containing compounds like ATP.

Plants are eaten by animals, which can then make their own phosphate-containing compounds. Plants and animals die, and animals also excrete. The waste of animals and plants is broken down by saprobionts, releasing phosphate back into the soil.

Some phosphate moves throughout the soil to bodies of water, like the sea.

Over thousands of years phosphate is used to form new rocks - after which the phosphorus cycle repeats.