Edexcel A2 Biology Unit 5 Revision Cards [Autosaved]

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(4) Oxidative phosphorylation (in the mitochondrial matrix) [1 Glucose= 32 ATP]

Reduced NAD and FAD from other stages release their hydrogen atoms- which split into H+and an electron.

Electrons move along 3 carrier proteins in the electron transport chain on the mitochondrial matrix and lose energy.

Energy used by carriers to pump protons from

mitochondrial matrix to the inter-membrane space. H+

concentration is greater in the inter-membrane space which creates an electrochemical gradient.

Protons move down the gradient- back into the

mitochondrial matrix via ATP synthase on stalked particle. This movement drives the synthesis of ATP- this is called the CHEMIOSMOTIC THEORY or CHEMIOSMOSIS.

At the end of the electron transport chain, in the

mitochondrial matrix H+combine with an electron and O2

from blood to form WATER.







+ 6O




+ 6H



(1) Glycolysis(in the cytoplasm) [Produces: 2 x (3C) Pyruvate, 2NAD(H), 2 ATP]

-Glycogen from muscles and liver cells are converted to hexose sugar (glucose).

-Two phosphate groups P(i) are added to glucose, this makes is UNSTABLE and REACTIVE.

-Splits into 2 molecules of (3C) compound. Each (3) compound is oxidised to produce pyruvate (3C). The two hydrogen atoms lost are collected by coenzyme NAD- forming two reduced NAD. Phosphate groups, P(i) from the pyruvate are given to ADP> two molecules of  ATP are formed through substrate-level phosphorylation.

(2) The Link reaction [Produces: Acetyl coA, 2NAD(H), CO2]

(3C) pyruvate is decarboxylated> so CO2 is released (waste product) AND dehydrogenated so 2 Hydrogen atoms are removed by NAD. Left with a (2C) compound. The (2C) compound combines with the coenzyme A- producing Acetyl-coA.

(3) The Krebs cycle(in the mitochondrial matrix) [Produces: 2CO2, 1ATP, 3NAD(H), 1FAD(H)]

-Acetyl coA combines with (4C) Oxaloacetate to regenerate coA and form (6C) Citrate.

-(6C) Citrate- is decarboxylated and dehydrogenated, forming a (5C) compound.

-The (5C) compound is decarboxylated and dehydrogenated forming a (4C) compound. This time t wo NAD(H) and one FAD(H) are made. There is an intermediate compound- gives a P(i) to ADP> forming ATP. The intermediate then becomes (4C) Oxaloacetate which goes back into the Krebs cycle.

Definition: Splitting of the respiratory substrate (e.g. glucose) to release carbon dioxide as a waste product and reuniting of hydrogen with atmospheric oxygen with the release of a large amount of energy.



(1) The Sino Atrial Node (SAN) is in the wall of the right atrium- it’s the

pacemaker of the heart. The SAN sets the rhythm of the heartbeat by sending out regular waves of electrical activity to the atrial walls. (2) This causes the right and left atria to contract at the same time.

(3) A band of non-conducting collagen tis sue prevents waves of electrical activity from being passed directly from the atria to the ventricles.

(4) Instead, these waves of electrical activity are transferred from the SAN to the AVN.

(5) The AVN is responsible for passing the waves of electrical activity onto the Bundle of His. There is a slight delay before the AVN reacts, to make sure that the ventricles contract only after the atria have expired fully.

(6) The Bundle of His is a group of muscle fibres responsible for conducting the waves of electrical activity to the finer muscle fibres in the right and left ventricle walls- called the Purkeyne fibres.

(7) The Purkeyne fibres carry the waves of electrical activity into the muscular walls of the right and left ventricles, causing them to contract simultaneously, from the bottom to the top.




Controlled by two ventilation centres in the medulla- the inspiratory and the expiratory centre.

• The inspiratory centre in the medulla sends impulses

to intercostal muscles and diaphragm muscles, making them contract= This increases the volume of the

lungs> lowers pressure in the lungs. Inspiratory centre also send impulses to inhibit the expiratory centre.

• Air enters the lungs because of the pressure difference

between lung air and the air outside.

• As lungs inflate, stretch receptors in lungs are

stimulated. These send nerve impulses back to the medulla. These impulses inhibit the inspiratory centre.

• The expiratory centre is no longer inhibited- it sends

impulses to the diaphragm and intercostal muscles to relax. This causes lungs to deflate, expelling air. As lungs deflate, stretch receptors become inactive= inspiratory centre is no longer inhibited so the cycle starts again.

Controlled by the Cardiovascular Control Centre in the Medulla.

Decrease in blood pH = Increase in breathing rate

During exercise, CO2level in the blood increases> this

decreases the pH of blood. There are chemoreceptors that are sensitive to pH changes, in the medulla, aortic bodies & carotid bodies.

• Chemoreceptors sense a pH decrease > send impulses

to the medulla> medulla sends MORE FREQUENT impulses to the intercostal muscles and diaphragm > this increases the RATE and DEPTH of breathing.

• This speeds up gas exchange so the CO2level drops

Cardiac output: total volume of blood pumped by a ventricle every minute.

Stroke Volume: volume of blood pumped by one ventricle each time it contracts.

Blood pressure increase> Heart Rate decrease:

-Pressure receptors in the aorta wall and carotid sinuses detect changes in blood pressure.

-If pressure is too high, receptors send impulses to the cardiovascular control central which sends impulses to the SAN to SLOW DOWN the heart rate.

-If pressure is too low, pressure receptors send nerve impulses to the cardiovascular control centre which sends impulses to the SAN to SPEED UP the heart rate.

pH decrease> Heart Rate increase:

A decreases is detected by chemoreceptors. These send impulses to the medulla. The medulla sends impulses to the SAN to increase the heart rate.

Cardiac Output increases with exercise because Heart Rate increases.

Ventilation rate: Volume of air breathed in or out in a period of time e.g. a minute.

Ventilation rate increases during exercise because breathing Cardiac Output cm3/min = Heart Rate b.p.m. x Stroke Volume cm3




When it’s DARK, rod cells are NOT stimulated:

• Sodium ions (Na+), are pumped out of the cell using active

transport. But these can diffuse back in through open (Na+)


• This makes the inside of the cell only slightly negative

compared to the outside- the cell membrane is DEPOLARISED (not much difference in potential.)

• Depolarisation triggers the release of neurotransmitters. • These neurotransmitter inhibit the bipolar neurone- so it

cannot fire an action potential. No information is sent to the brain.

When it’s LIGHT, rod cells ARE stimulated:

• Light energy causes Rhodopsin (purplish pigment) to break

down into Retinal and Opsin- this is BLEACHING.

• Bleaching causes (Na+) channels to close. So (Na+) are

actively transported out of the cell but they cannot diffuse back in.

• This causes (Na+) to build up outside of the cell, making the

inside of the cell much more negative than the outside- the cell membrane is HYPERPOLARISED.

• When a rod cell is hyperpolarised, it stops releasing

neurotransmitters. This means the bipolar neurone is not inhibited so it depolarises.

• If the change in potential difference reaches the threshold,

an action potential is transmitted along the optic nerve to the brain.

Light enters the eye through the pupil. The amount of  light that enters is controlled by the iris muscles.

Light rays are focused by the lens onto the retina, which lies on the inside of the eye. The retina contains

photoreceptor cells. The fovea is the area in the retina that controls lots of photoreceptors. Impulses from the photoreceptors are carried from the retina to the opt ic nerve to the brain. The optic nerve is a bundle of 

neurones. There are no photoreceptors where the optic nerve leaves the eye- the blind spot.

The human eye has TWO types of 


• Rods- Found in the peripheral parts of the retina.

Gives information in black and white (monochromatic vision.)

• Cones- Found packed together in the fovea. Gives

information in colour (trichromatic vision). There are 3 types of cones: red, green and blue- sensitive.



Uses x-rays to produce cross-sectional images of the brain. MoreCT- Computed Tomography dense areas > absorbs more radiation > shows up lighter.

Structure: Shows the major brain structures.

Function:Doesn’t show brain function directly but unusual scan can be compared with patient’s loss of function- it would imply that the function loss is due to damage to that area.

Diagnosis: Useful e.g. bleeding after a stroke- blood shows up lighter as it has different density to brain tissue. Can show location and extent of bleeding. Used to work out which blood vessels are damaged> which functions will be affected.

MRI- Magnetic Resonance Imaging

Uses a magnetic field and radio waves to produce cross-sectional images of the brain. More expensive than CT.

Structure: More detailed than CT- can clearly see the difference between normal & abnormal tissue.

Function: Same with CT. Scan compared with condition.

Diagnosis: Useful e.g. tumour- tumour cells respond to a magnetic field differently- show up lighter. Can show the exact location and size of the tumour so the correct/ most effective treatment can be given. Any resulting loss of function can be predicted.

fMRI- Functional Magnetic Resonance Imaging

Same as MRI but shows changes to brain activity as they happen. More oxygenated blood flows to active brain regions= molecules in this respond differently to those in deoxygenated- appears lighter. Structure: Similar to MRI- good detail.

Function: Function is carried out whilst in the scanner- brain

regions involved will be more active & COLOURED so they show up more easily.

Diagnosis: Very useful. Shows abnormal brain regions & allows scientists to study conditions caused by abnormalities- some

Functions of the lobes:

-Frontal- Reasoning, planning, decision-making, consciousness of emotions. Forming associations and ideas. Also includes the primary motor cortex.

-Parietal- Orientation, sensation, calculation, movement, some recognition, memory.

-Occipital- Visual cortex- vision, shape, colour, recognition, perspective.

Cerebrum-See, think, learn, feel emotions. The heaviest part of the brain, making up 2/3 of  brain mass. Divided into two parts called the left and right hemispheres. Each hemisphere

contains four lobes. Surrounded by a thin layer- the cerebral cortex which is highly folded= large surface area.

Medulla- Controls breathing rate & heart rate. Ventilation and Cardiovascular Control Centre. Located at the base of  the brain and at the top of the spinal cord.

Hypothalamus- Controls body temperature (thermo regulation) automatically maintains body temperature at the normal level. Produces hormones that control the pituitary gland just below it.

Cerebellum- Co-ordinates movement. Located under the cerebrum. Also has a folded cortex. Controls movement and balance.





• L-Dopa is a drug used to treat Parkinson’s disorder. • It’s structure is very similar to that of dopamine. • When given, it is absorbed in the brain and

converted to dopamine by the enzyme Dopa-Carboxylase. This increases dopamine levels in the brain.

• Dopamine is not given directly as it cannot pass the

blood-brain barrier.

• Increased dopamine level means that more nerve

impulses are transmitted in synapses in the parts of  the brain that control movement.

• So, L-Dopa gives Parkinson’s sufferers more control

MDMA (Ecstasy)

• Increases serotonin level in the brain.

• Usually serotonin is taken back into the presynaptic

neurone after use, to be used again.

• MDMA increases serotonin level by inhibiting it ’s

reuptake by binding to receptor molecules that woul d take it back up.

• MDMA also triggers the release of serotonin from

presynaptic neurones.

• This means that nerve impulses are CONSTANTLY

triggered in the parts of the brain that control mood.

• So, the effect of MDMA is mood elevation. • Parkinson’s is a brain disorder which destroys

neurones in the parts of the brain that control movement.

• So Parkinson’s affects the person’s motor skills. • Because of the loss of these neurones which usua lly

release the neurotransmitter dopamine, there is a lack of dopamine in the brain.

• This causes fewer nerve impulses to be transmitted

in the part of the brain that controls movement.

• Because scientists know that this is due to low

dopamine levels, they have developed drugs to increase dopamine levels in the brain.

• Scientists think that there is a link between depression

and low levels of Serotonin (a neurotransmitter) in the brain.

• Serotonin transmits nerve impulses across synapses in the

parts of the brain that control mood.

• So scientists have developed drugs to increase serotonin




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