Notes Biology A-Level

8/10/2019 Notes Biology A-Level

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Photosynthesis light energy from sun into chemical potential energy

Releases oxygen from water

Autotrophsuse light energy or chemical energy and inorganic molecules (co2 + water) to synthesise complex

organic molecules

Chemoautotrophsynthesise organic molecules using energy from exergenoic reactions(e.g. nitrifying

bacteria)

PhotoautotrophsOrganisms that can photosynthesisePlants, Bacteria, Protoctists

Heterotrophsingest and digest complex organic molecules releasing chemical potential energy stored in

them.

6CO2 + 6H20 (+LIGHT ENERGY) C6H12O6 + 602- - - - - - - Photosynthesis

Other way around is respiration

Photosynthesis happens in chloroplasts.

Structure of chloroplasts:

Disc shaped2-10 umlong

Double membrane

Inter membrane space 10-20nmwide

Outer is permeable to small ions

Inner has transport proteins.

Inner folded into lamellaewhich are stackedup to form a granum

Between grana are intergranal lamellae

Stromafluid filled matrixreactions of light independentstage occur here. Necessary enzymes are

located here. Starch grains and oil droplets also in stroma, and DNA and prokaryote type ribosomes too

Granastacks of flattened thylakoid membranes. Light absorption and ATP synthesis in light

dependent stage happen here.

Adaptations

Inner membrane can control entry/exitof substances between cytoplasm and stroma

Grana has 100 stacks of thylakoid membranes so large surface area for photosynthetic

pigments, electron carriers and ATP synthase enzymes

Photosynthetic pigments arranged in photo systems

Proteins in the grana hold the photo systems in place

Stroma has enzymes to catalyse reactions of light independent

Grana surrounded by stroma, so products from dependent stage, which are needed inindependent stage can pass into stroma easily

Chloroplasts have DNA and ribosomes so they can easily make the necessary proteins

Photosynthetic pigments

They tried to capture as much light as possible

Are found in thylakoid membranes, arranged in funnel shaped structuresphoto systems

Chlorophyll is a mixture of pigmentshas a Mg atom, a long phytol and a porphyringroup

Light hits chlorophyll a causing pair of electrons to be exited

Two forms of chlorophyll A one in P680 and other in P700 both are yellow/green Both found at centre of photo systems and are known as primary pigment reaction centres


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P680PSII- absorbs light at 680nm

P700PSIabsorbs light at 700nm

Chlorophyll a absorbs blue light at 450nm

Chlorophyll b absorbs light around 500nm and 640nm , appears blue/green

Accessory pigments

Carotenoids reflect yellow and orange light and absorb blue light

Dontcontain porphyrin and arent involved directly in light dependent

Absorb light which isnt absorbed well by chlorophyll, and pass the energy associated to

chlorophyll A at base of photo system

Carotene(orange) and xanthophylls(yellow) are main Carotenoids pigments

In photo system, main pigment is at the bottom where the light hits

The accessory pigment are located around photo system and absorb light that the main

photosynthetic pigment cantabsorb

The absorbed light energy passed down to the primary pigment reaction centre

Chlorophyll A is located there and energy is supplied there to excite electrons

Light dependent stage

Takes place on thylakoid membrane

PSI is usually on the intergranal lamellae and PSII occurs almost all the time on the granal

lamella

These pigments trap light energy so it can be converted to chemical energy then ATP

PSII has an enzyme that can split water into H+ ions, electrons and oxygen

2h20 4h+ + 4e- + O2

Oxygen produced is used for aerobic respiration and some diffuses out through stomata

Splitting of water forms H+ ions, used in chemiosmosis to produce ATP. H+ accepted by

coenzyme NADP which becomes reduced NADPH. NADPH used in light independent stage toreduce co2 and produce organic molecules.

Water is also a source of electrons to replaces ones lost by oxidised chlorophyll

Photophosphorylation

Light travels in particles called photons

When a photon hits a chlorophyll molecule, the energy of the photon is transferred to two

electrons and they become excited. The electrons are captured by electron acceptors and

passed along a series of electron carries embedded in the thylakoid membranes. Electron

carriers are proteins that contain iron atoms.

Energy is released as the electrons pass the chain of electron carriers. This pumps protons

across the thylakoid membrane in thylakoid space

Proton gradient is formed across thylakoid membrane and protons flow down their

gradients through channels associated with ATP synthase enzymes

Force drives the rotation of part of the enzyme and allows ADP and Pi to be joined forming

ATP.

Kinetic energy from proton flow is converted to energy in ATP molecules used in light

independent stage of photosynthesis.

Flow of protons is called chemiosmosis

Making of ATP using light energy is called Photophosphorylation.

Two typesCyclic and Non-Cyclic


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Cyclic Photophosphorylation

Uses PSI. Excited electrons pass to an electron acceptor and back to the chlorophyll

molecule from which they were lost. No photolysis of water and no generation of NADP, but

little ATP are made.

The ATP may be used in light independent stage reaction of photosynthesis or may be used

in guard cells to bring K ions, lowering water potential and causing water to follow by

osmosis. Cause guard cells to swell and opens the stomata

Non cyclic Photophosphorylation

Involves PSI and PSII

Light hits PSII, excites electrons that leave chlorophyll molecule from PPRC

Electrons pass along electron carriers and energy is released to synthesize ATP

Light has also struck PSI and pair of electrons lost

Electrons along with protons in stroma join NADP to form NADPH

Electrons from oxidised PSII replaced electrons lost from PSI

Electrons from photolysis water replace those lost by oxidised chlorophyll in PSII

Protons from photolysed water take part in chemomeiosis to make ATP and are then

captured by NADP in stroma. This is used in light independent stage

Light independent stage

Calvin Cycle

Takes place in stroma

Products of light dependent stage are required

CO2 from air diffuses into leaf through stomata (bottom of leaf). Diffuses throughout air

spaces in spongy mesophyll and reaches palisade mesophyll layer. Then diffuses through

thin cellulose walls, the cell surface membrane, cytoplasm and then the chloroplastenvelope into the stroma.

In stroma, CO2 combined with 5 carbon RuBP (co2 accepter). Reaction catalysed by rubisco.

RUBP becomes carboxlyated.

Forms 3 carbon glycerate 3 phosphate (GP)CO2 is now fixed

GP is reduced and phosphorylated to triose phosphate (TP)

ATP and NADPH from light dependent are used in this process

5 out of 6 TP are recycled by phosphorylation using ATP from light dependant to 3 molecules

of RuBP

How are they used?

Some GP can be used to make amino acids and fatty acids

Pairs of TP molecules combine to form hexose sugars, e.g. glucose and fructose

Some glucose can be isomerised to form hexose sugar

Glucose and fructose can be combined to form disaccharide sucrose to be translocated in

phloem sieve tubes

Hexose sugars can be polymerised into other carbs such as cellulose and starch

TP can be converted to glycerol and may be combined with fatty acid to form GP to makelipid


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Limiting factors

Light intensity, CO2 conc, Temperature are all limiting factors

Too high temperature will cause proteins to be denatured

Effect of light intensity

Causes stomata to open so CO2 can enter leaves

Light is trapped by chlorophyll where it excites electrons

Splits water molecules to produce protons

Effect of temperature

Between 0-25OC, Photosynthesis doubles for each 10

oC rise

Above 25 it levels off, then falls because enzymes work less efficiently and oxygen

successfully competes for active site of rubisco, stopping CO2 from binding

Causes loss of water from stomata making stress response to close the stomata, limiting CO2

available

Measuring photosynthesis

Measure uptake of substrates or appearance of products per second/minute

Volume of oxygen produced

Rate of CO2 uptake

Rate of increase in dry mass of plants

Usually measured by oxygen produced

-Limitations are that some oxygen produced will be used for respiration by the plant

-There maybe be some dissolved nitrogen in the gas collected.

Photosynthometer/Audus microburette air tight so no bubbles in capillary tubing

Gas collected at flare at end of rube

Gas buble can be meoved into the part of the capillary tube against the scale and its length

can be measured

Volume of gas collected = length of buble x pi R ^2

Compare rates by using the length of gas bubble evolved per unit time, given diameter is

constant

How to measure:

-Fill apparatus with tap water. Remove plunger from synrige and gentle stream of tap water

into the syringe until whole barrel and plastic tube are full of water-Replace synringe plunger and gently push water out of flared end of capillary tubing until

plunger is nearly at the end of the syringe and no air bubbles.

-Cut well illuminated Elodea7cm longmake sure bubbles of gas are emerging from cut

stem. Place cut end upwards into test tube containing the saem water that the pondweed

has been kept in. Add two drops of hydrogen carbonate solution t the water of the test tube.

Stand test tube in a beaker of water at about 20oC. Use thermometer to measure the

temperature of the beaker at intervals during the investigation. Add cold water if necessary

-Place light source as close to the beaker. Measure distance from piece of pondweed to light

source and record. L = 1/d2

-Leave the apparatus with capillary tube postioned so that it is not collection gas given off by

palnt for 5-10 minutes.


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-Postion teh capillary tube over the cut end of the plant and after a known period of time

(5-10 mins) gently pull the syringe plunger so that the bubble of gas collected is in teh

capillary tube near the scale. Note length of bubble and gently push in the plunger so that

the bubble is expelled

-Reposition capillary tube to collect more gas and repeat ^ twice more

-Move light source further from plant and measure distance and calculate the light intensity

or use a light meter to measure light intensity. Allow a 5-10 min acclimatisation period then

repeat ^ and ^^.

-Continue investigation with different light intensity. Tabulate your data and plot graph ofrate of photosynthesis. Calc volume of oxygen evolved per minute against light intesntiy 1/d

2

Investigate rate of temp. Keep all factors same, alter temperature. Note that warmer water

reduces solubility of oxygen gas

Co2everything constant but add more hydrogen carbonate solution

GO THROUGH PROCEDURE PAGE 70

Light intensity

L = 1/d2

It alters light dependant reaction

More light = more excitation of electrons

More electrons excited = greater phosphorylation so more ATP and NADPH produced

ATP and NADPH used in light independent as source of hydrogen and energy to reduce GP

to TP.

ATP used to phosphorylate 5/6 molecules of TP to regenerate RUBP

If theres no light, then GP cant be changed to TP, so GP will accumulate.

Lower amount of RuBP reducing CO2 fixation and formation of more GP

CO2

Increased amount = more CO2 fixation

More molecules of GP and more TP and more regeneration of RuBP.

The number of stomata that open to allow gaseous exchange leads to increased

transpiration and may lead to the plant wilting, if water uptake cant exceed water lost

through transpiration

Leads to release of plant growth regulator (abscisic acid) and stomata close.

This reduces CO2uptake and rate of photosynthesis

Temperature

Increasing temp affects photolysis of water.

Affects rate of light independent as catalyst is used

Over 25Oc, oxygenase activity of rubisco increases more than carboxylase increases

Means photorespiration > photosyntehsis

Consequently, ATP and NADPH from light dependant is wasted

Reduces overall rate of photosynthesis

Very high temp can denature

Increased temp causes an increase in water loss from leaves by transpiration. Can lead to

closure of stomata and reduction in photosynthesis rate


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Explain, using the information in the diagram, why the pH of the thylakoid

space (lumen) is lower than that of the stroma and what significance this has for

ATP production.

.........................................................................................................................

In this question, one mark is available for the quality of use and organisation of

scientific terms.

There are a number of organic molecules in cells whose role is to transfer hydrogen

atoms from one compound to another. Examples include NAD, FAD and NADP.

NAD, FAD and NADP are important molecules in plant cells. Describe, in detail, the

role of these molecules within a palisade mesophyll cell

When plants are grown in glasshouses during autumn and winter, when the

natural light intensities are low, it is important that temperatures are kept

relatively low.

With referenceto respiration and photosynthesis, explain why it is essential to do

this.

.........................................................................................................................

Go through diagram of Chloroplast

Learn about Mesophyll cells

Enzymes need to be under these conditions:

-Suitable PH

-Suitable temp-An aqueous environment that keeps substrates and products in solution


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-Freedom from toxins and excess inhibitors

Stimulus: Change in environment that causes a response

Response: Change in behaviour or physiology as a result of a stimulus

Most multicullular organisms tissues are protected by epithelial tissues (bark and skin).

In animals they are bathed in tissue fluid

Metabolic waste e.g. toxic things diffuse out of cell into tissue fluid

Therefore activity of cell determines the cells own environment

Co2 is a waste product that could disrupt action of enzymes or can change pH

These waste products act as a stimulus to remove these waste productsexcretion

Good communication system:

Cover whole body

Cell communication

Specific communication

Rapid communication

Short and long term responses

Cell signalling

Neuronal systeminterconnected network of neurons that signal to each other across

synapse junctions. Are quick and can enable rapid responses to stimuli changing quickly

Hormonal systemuses blood to transport it signal. Cells in an endocrine organ release

the hormone into the blood. Carried all over body but recognised by specific target cells.

Long term

Homeostasis:

Maintenance of internal environment in a constant stage despite external changes.

This that have to be kept constant: Temp, Blood salt conc, Blood glucose conc, water

potential of blood, blood pressure, co2 conc

Negative feedback

Any change to internal environment must be detected

Change must be signalled to other cells

Must be a response that reverses the change

Negative feedback: Process that brings about a reversal of any change in conditions.

Ensures that an optimum steady state can be maintained as the internal environment is

returned to its original set of conditions after any change.

Stimulus>Receptor>Communication Pathway (cell signalling) > Effector > Response

Sensory receptors such as temperature receptors, glucose conc receptors are internal and

monitor conditions inside the boy

If they detect a change they will send a message

A communication system such as the nervous system or the hormonal system acts by

signalling between cells.

Uses to transmit message from receptor cells to effectors cells

The message may or may not pass through a coordination centre such as the brain


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Effector cells such as liver or muscle cells will bring about the response and reverse the

change

Positive feedback

Increases the original change and usually harmful. Example: when body is too cold,

enzymes become less active. If less active, exergonic reactions that release heat are slow

and so less heat released. This cools down body more and releases less heat Definition: Process that increases any change detected by the receptor. Tends to be

harmful and doesnt lead to homeostasis

Sometimes beneficial. Example pregnancy when dilation of cervix. Begins to stretch and

change is signalled to anterior pituitary gland stimulating secretion of oxytocin. Oxytocin

increases contractions and stretches cervix more

Meaning of constant

Negative feedback will maintain a reasonably constant set of conditions, but will never

remain perfectly constant

Will be some variation around mean

Need to maintain a body temp

Enzymes are globular proteins and structure is specific to function

Enzyme activity is affected if they are not kept at optimum temp.

Endotherms: Maintain body temperature within fairly strict limits, independent of

external temperaturehumans

Ectotherms: Organism that relies on external sources of heat to regulate its bodytemperature

Advantages of ectotherm:

-Use less food for respiration

-Find less food and may be able to survive for longer without eating

-More energy from food goes for growth

Disadvantages

-Less active in cool temperatures. Need to warm up. Higher risk of predation

-Incapable of activity during winter so they need food to survive them for a long time

Temperature regulation in ectotherms

Do not use internal energy sources to maintain their body

Muscle contractions generate some heat from increased respiration

When ectotherm is cold, itllchange behaviour or physiology to increase absorbption of heat

from environment

Adaptation How it helps regulate temp Example

Expose body to sun Enables more heat to be

absorbed

Snake

Orientate body to sun Exposes large S.A for more heat Locusts


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absorption

Orientate body away from sun Exposes lower S.A so less heat

absorbed

Locusts

Hide in burrow Reduce heat absorption by

keeping out of sun

Lizards

Alter body shape Expose more less S.A to sun Horned lizards

Increase breathing movements Evaporates water Locusts

Endotherms

Use internal sources of heat to maintain body temp.

Many chemical reactions are exergonicrelease energy in form of heat

Can increase rate of respiration in liver ot release heat

Advantages

-Constant body temp regardless of external temp

-Active in cold and night

-Can inhabit colder parts of the planet

Disadvantages:

-A lot of energy from food is used to respire-More food required

-Less of energy from food put towards growth

Component of body involved Response if temp high Response if temp low

Sweat glands Secret more sweat on skin,

water in sweat evaporates

using heat from body to supply

latent heat of vaporisation

Less sweat secreted. Less

evaporation of water

Lungs, mouth and nose Panting increases evaporation

of water from lungs, tongue

and other moist surfaces usinglatent heat as above

Animal doesnt pant

Hairs on skin Hairs lay flat, little insulation.

More heat lost by convection

and radiation

Hairs stick up, increases

insulation, reducing loss of heat

from skin

Arterioles leading to capillaries

in skin

Vasodilatation allows more

blood into capillaries near the

skin. More heat can be radiated

from skin, which in pale skinned

people may look red

Vasoconstriction reduces flow

of blood through capillaries.

Liver cells Rate of metabolism reduced.

Less heat generated fromexergonic reactions

Rate of metabolism increases..

Respiration generates moreheat.

Skeletal muscles No spontaneous contractions Spontaneous contractions

(shivering) generate heat as

muscle cells respire more

Behavioural mechanismsmove into shademove into sun light

Orientate body to increase/decrease S.A exposed

Remain inactive and spread out limbs to increase S.Aor active and ball up


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Endotherms monitor temperate of blood via Hypothalamus.

If change, then hypothalamus sends signal

1) Increase rate in metabolism to release more heat through exergonic reactions

2) Release of heat through extra muscular contraction

3) Decreased loss of heat to the environment

-------------------------------------------------------------------------

--------------Rise in core temp Thermoregulatory centre in hypothalamus detects change Nervous system

and hormonal system carry signals to skin, liver and muscles Less heat generated and more

heat lost Temperature falls

Role of peripheral temperature receptors

An early warning that body temp may change could help hypothalamus respond quicker

If extremities start to cool down, may eventually affect core body temp

Peripheral temp receptors in skin monitor temperature in extremities.

Info is fed to the hypothalamus and can initiate behavioural mechanisms

Sensory receptors

Specialised cellsenergy transducers, convert one form of energy to another

Each type of transducer is adapted to detect changes for a specific form of energy

Change in energy levels in environment called stimulus

Sensory receptors convert energy into a form of electrical energy called nerve impulse

PAGE 12 sensory receptor table

Generating nerve impulses

Some protein channels allow movement of ions across membrane

Ions keep diffusing until concentration is equal on both sides

Neurones (nerve cells) have specialised channel proteins specific to K and Na ions

They have a gate which controls the permeability of the membrane.

Channel is usually kept closed

Neurones also contain carrier proteins that actively transport Na out of cell, K into cell.

Called sodium/potassium ion pumps.

More sodium ions are transported out, than potassium is trasnrpoted in

Inside is negatively charged polarised membrane

Nerve impulse is created by altering permeability to sodium ions

As sodium ion channels open, sodium ions move across membrane down their conc gradient

into cell

Movement of ions creates a change in P.D across membrane

Inside becomes less negative than outsidedepolarisation


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Generator potentials

Receptor cells respond to changes in environment

Gated sodium ions channels open allow Sodium to diffuse across membrane into cell.

A small change in potential caused by 1 or 2 sodium ion channels opening is called a

generator potential

Larger the stimulus, the more gated channels open

If enough sodium ions enter the cell, potential difference changes and will initiate an

impulse or action potential

Once stimulus detected and energy converted to depolarisation of receptor cell membrane,

impulse must be transmitted to other parts of body. Impulse transmitted across neurone as

an action potential

Different types of neurones:

SensoryCarry action potential from sensory to CNS

MotorCNS to effector RelayConnect sensory and motor

Function of neurone is to transmit AP from one part of body to another

Structure to function of neurone

Long so can transmit AP over long dstance

Plasma membrane has many gated ion channels that control entry/exit of Na/K or C ions

Na/K pumps that use ATP to actively transport Na ions out cell, and K into cell

Maintain P.D across plasma membrane

Surrounded by fatty sheath called myelin sheath (group of Schwann cells) that insulates

neurone from electrical activity from nearby cells.

There are gaps between where the Schwann cells meet called nodes of ranvier

Have a cell body that contains nucleus, many mitochondria and ribosomes Motor have cell body outside CNS, and have long axon

Sensory have long Dendron, positioned outside CNS.

Sensory have short axon

Sensory and Motor have many dendrites connected to other neurones

Resting neurone

When a neurone is not transmitting = rest

Always actively transporting ions across its plasma membrane.


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Na/K pumps use ATP to mum 3 Na out/2 K in.

Membrane is more permeable to K that it is to Na, and so many K diffuse back out

Cytoplasm has anions and interior of cell is maintained at a negative potential

Potential difference across cell membrane is about -60mV. = Resting potential

Action potential

At rest, Na ion channels kept closed

Na/K pump uses ATP to pump in K to the axon

A few K diffuse back out and some K channels are still open

If some Na are open, Na will quickly diffuse down conc gradient into cell from surrounding

tissue fluid

Causes depolarisation of membrane

In generator region of receptor cells the gated channels are opened by changes in

environment

E.g. pacinian corpuscle which detects pressure changes are opened by deformation

The gates further along neurone are open by changes in PD across membrane. They are

voltage gated channels.

Generator potentials in sensory are depolarisaitons of ccell membrane A small depolarisation has no effect but if it reaches the threshold potential of -50mV , itll

open up nearby voltage gated channels causing influx of Na ions and Depolarisation of the

membrane will now reach +40mV causing an action potential

Once action potential starts, itll continue till end of neurone

Action potential consist of a set of ionic movements across cell membrane when correct

channels are open

1) Membrane starts in resting state polarised - -60mV compared to outside

2)

Sodium ion channels open and some sodium ions diffuse into cell

3)

Membrane depolarises, becomes less negative and reaches threshold value of -50mV

4) Voltage gated Na ion channels open and Na come in.Becomes positively charged in

respect to outside

5)

Potential difference across plasma membrane reaches +40mV. Inside of cell is positive

compared with outside

6) Na ion channels close, K channels open

7) K ions diffuse out of cell, bringing PD back to negative. Repolarisation

8)

PD overshoots slightly making cell hyperpolarised

9)

Original PD is restored so cell returns to resting state After AP, Na and K are in wrong placerestored by Na/K pumps

Refractory period = time taken to recover from an action potential

Also makes sure AP are transmitted in 1 direction

Local Currents

Opening of Na ion channels at one particular point upsets balance of Na and K ions created

by Na/K pumps

Creates a local current in cytoplasm of neurone. These cause Na channels along membrane

to open


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Channels made out of 5 polypeptide molecules. 2 have a special receptor site specific to

acetylcoline

When acetylcholine binds to the two receptors, Na ion channels open.

Transmission across synapse

1)

AP arrived at synaptic knob

2) Voltage gated Ca channels open

3) Ca diffuse into synaptic knob causing synaptic vesicles to move and fuse with

presynaptic membrane

4)

Acetylcholine released by exocytosis and diffuse across cleft

5) Binds to receptor sites on Na ion channels in post synaptic membrane

6) Na ion channels open and Na diffuses across postsynaptic membrane into postsynaptic

neurone

7) A generator potential or excitatory postsynaptic potential (ESPS) is created

8) If sufficient generator potentials combine, then potential across postsynaptic membrane

reaches the threshold potential

9) A new AP is created in post synaptic neurone

Acetylcholineesterade in synaptic cleft.

Hydrolyses acetylecholine to ethanoic acid and coline

Stops trasnmsisions of signals so synapse doesnt continue to produce AP

They are recycled and renter synaptic knob by diffusion where they are recombined to

acetylcholine using ATP

Action potentials are all or nothing responses

Other roles of synapses

Presynaptic neurones might converge to one postsynaptic neurone allowing signals from

different parts of the nervous system to create the same response. Useful when several

different stimuli

One presynaptic neurone might diverse to several postsynaptic neurones. Allow one signal

to be transmitted to several places. Useful in the reflex arc

Synapses ensures it is in correct direction and one direction

Synapses can filter out low level signals

Low level signals can be amplified by summation. If a low level signal happens a lot, it will

generate several successive action potentials. Post synaptic generator signals combine to

form AP. Summation can also occur when several presynatpic neurones each release small

numbers of vesicles into one synapse

AcclimatisationSynapse = fatigued when its run out of transmitter substance. Means that

our nervous system no longer responds to stimulus, for example a smell of perfume or

background noise. Helps avoid overstimulation of an effecter which could damage it

Creation of specific pathways of conscious thought and memory

The pathways created by synapses enable nervous system to convey a wide range of

messages


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Frequency of transmission

When a stimulus is at higher intensity, more generator potentials produced

Causes more frequent AP in sensory

Our brain can determine intensity of stimulus through frequency of signals arriving

Myelinated and non myelinated neurones

1/3 of peripheral neurones are myelinated

Sheath consists of several layers of membrane and thin cytoplasm from the Schwann Cell Nodes of ranvier occur at intervals of 1-3mmnode is roughly (2-3um long)

Remainder of peripheral neurones are most of the neurones in CNS are not myelinated.

Non myelinated at still associated with Schwann cells but will only have the odd one or so.

Means that action potential travels along neurone as a wave and doesnt jump

Advantage of myelination

Myelinated travels at 100-120ms-1non myelinated travels at 2-20ms -1

Carry signals from sensory to CNS and CNS to effectors over long distances

Longest neurone in human is about 1metre Enables a rapid response to a stimulus

Non-myelinated neurones are shorterused to coordinate functions such as breathing and

action of digestive system so speed isnt important

Endocrine System

Uses blood circulation to transport signals

Hormones

Released from endocrine glandsductless glands.

Consist of group of cells that produce and release the hormone into blood capillaries running

through the gland

Exocrine gland

These dont release hormone, they have small duct or tube that carries their secretion to

another place. E.g. salivary gland secrete saliva into a duct and flows into mouth

Targeting the signal

Cell receiving hormone must have a complementary receptor

This means hormone can travel around blood without affecting cells that dont have a

complementary receptor

Target cell: cells that possess specific receptor on their plasma membrane. Shape is

complementary to the hormone molecule. Many cells form together to form a tissue

Nature of hormones

2 types of hormone:

-protein and peptide hormone (insulin and glucagon) and derivatives of amino acids

(adrenaline)

-Steroid hormones (sex hormones)


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Protein hormones are not soluble in the phospholipid membrane and dont enter the cell

Steroids can pass through membrane and enter the cell to have direct effect on DNA

Adrenalineamino acid derivativeunable to enter target cells

Must cause effect inside the cell without entering itthe binds onto receptor of cell surface

membrane

Receptor is associated with an enzyme on inner surface of cell membrane called Adenyl

Cyclase

Adrenaline binds to receptor. Adrenaline is called the first messenger

When it binds it activates enzyme adenyl cyclise which converts ATP to cyclic AMP (cAMP).

Camp is the second messenger and causes an effect inside cell by activating enzyme action

Functions of adrenal gland

Lying above kidneys, one on each side of the bond. Can be divided into medulla region and

cortex region

Medulla:

-Found in centre of gland. Release adrenaline when pain/shock. Most cells have adrenaline

receptors. Effect is to prepare body for activity:

-Relax smooth muscle in bronchioles

-Increase stroke volume of heart. Increase heart rate. Vasoconstriction to raise blood

pressure. Stimulate conversion of glycogen to glucose. Dilate pupils. Mental awareness.

Inhibit action of gut. Body hair erect

Adrenal cortex:

-Uses cholesterol to produce certain steroid hormones

-Mineralcorticoids (ladosterone) to help control conc of K/Na in blood

-Glucocorticoids (cortisol) help to control metabolism of carbohydrates and protein in liver

Regulation of blood glucose

Pancreas is a small organic under stomachhas exo and endocrine system

Releases digestive enzymesexocrine part

Cells found in small groups surrounding tubules into which they secret digestive enzymes

the tubules join up to form pancreatic duct.

Pancreatic duct carries fluid containing enzyme into first part of small intestine

Fluid: Amylase (carbohydrase) , Trypsinogen (Inactive protease) , Lipase

Fluid contains sodium hydrogen carbonate ions making itt alkaline helping neutralise

contents of digestive system that have left stomach acid

Pancreas has Islet of Langerhans containing different types of cells.

2 typesAlpha cellsSecrete hormone glucagon

Beta cellsManufacture and secret Insulin

Islets are well supplied with blood capillaries and these hormones go into capillaries

Endocrine function


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Blood glucose is carefully regulated

Islets of langerhans monitor conc of glucose in blood. Normal blood conc is 90mg 100cm-3.

OR 4 and 6mmol dm-3

If conc rises or falls, alpha and beta cells detect change and respond by releasing hormone

If blood conc. too high

Too highbeta cells secrete insulin into bloodtarget cells hepatocytes, muscle cells and

other body cells including those in brainpossess specific membrane bound receptors for

insulinBlood passes these cells and the insulin binds to receptors2nd

messenger

system activates a series of enzyme controlled reactions in cell Effects of insulin on liver cells:

-More glucose enters cell through glucose channels

-Glucose in cell is converted to glycogen for storage (glycogenesis)

-Glucose converted to fats

-Glucose used in respiration

Increase in entry of glucose through channels reduces blood glucose conc

If blood glucose conc too low:

Detected by Alpha cells and they secrete hormone glucagon

Target cells are the hepatocytes

Effects are:

1)conversion of glycogen to glucose (glycogenolysis)

2) use of fatty acids in respiration

3) Production of glucose by conversion from amino acids and fats (gluconeogenesis)

Overall effect is to increase blood glucose conc

Insulin secreted when blood glucose is highwhen its low secretion needs to stop

Control of insulin secretion

1) Cell membrane of B cells contain Ca and K ion channels

2) K ion channels are normally open and CA normal closed. K diffuses out of cell, making

inside more negative. PD of membrane = -70mV

3) When glucose conc outside is high, glucose molecules diffuse into cell

4) Glucose is quickly used in metabolism to produce ATP

5)

Extra ATP closes K ion channels

6) K cant diffuse out no more and so PD across membrane becomes less negative

7)

Change in PD opens CA ion channels


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8) CA ions enter and cause the secretion of insulin by making the vesicles containing insulin

move to cell surface membrane and fuse with it releasing insulin by exocytosis

Diabetes Mellitus

Body can no longer control its blood glucose conc

Can lead to very high conc. of glucoseHyperglycaemia

Hypoglycaemiablood glucose conc too low

Type 1 diabetes

Insulin dependentstarts in child hood

Result of autoimmune reponse in which bodys own immune system attacks beta cellas and

destroys them. Results from a viral attackbody is no longer able to manufacture sufficient

insulin and cannot tore excess glucose and glycogen

Type 2 diabetes

Non insulin dependent Happens in older ageresponsiveness to insulin declines

Specific receptors on the surface of the liver and muscle cells decline and cells lose ability to

respond to insulin in blood

Levels on insulin secreted by Beta cells may decline.

Factors contributing to this: obesity, high sugar diet, Asian or Afro Caribbean, family history.

Treatment

Type 2Minotiring and control of diet. Match carbohydrate intake and use. Eventually be

supplemented by insulin injections or use of other drugs which slow down the absorption ofoff glucose from digestive system

Type 1insulin injections. Blood glucose conc must be monitored and correct dose of

insulin must be administered to ensure glucose conc remains fair stable

Advantages of genetically engineered bacteria to produce insulin instead of using ones from animals

Exact copy of humanmore effective

Less chance of developing tolerance

Less chance of rejection

Lower risk of infection

Cheaper to manufacture than of animals

Adaptable to demand

No moral objections as its not from animals

Blood supplies oxygen, nutrients, glucose, fatty acids, amino acids to cells

Removes waste products such as Co2 and urea so they dont inhibit cell metabolism

The heart adapts to body to supply more oxygen and glucose by: increasing/decreasing

heart rate...Increase strength of contractions....Volume of blood pumped per beat (stroke

volume)


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Rate at which heart beat is affected by many factors

Heart = myogenicinitiate its own contractions

Own pacemakersinoatrial node. Can initiate its own action potential by sending a wave of

exication over atria walls through AVN down purkyne fibres to ventricles causing

contractions

Heart is supplied by nerves from medulla oblongata of brain. These connect to SAN and do

not initiate a contraction but can affect frequency of contractions. AP sent down accelerator

nerve increase the heart rate. AP sent down vagus nerve reduce heart rate

Under resting conditions, heart rate is controlled by SAN

60-80 per minute usuallyfrequency controlled by cardiovascular centre in medulla

oblongata.

Factors affecting heart rate:

1) Movement of limbs detected by stretch receptors in muscles send impulses to

cardiovasulcar centre informing that extra oxygen may be needed, usually increasing

heart rate

2)

When we exercise, CO2 produced. Some reacts with water in blood plasma reducing PH,

which is detected by chemoreceptors in carotid arteries, aorta and the brain.

Chemoreceptors send impulses to cardiovasulcafr centre which increases heart rate

3) When we stop exercising, CO2 conc falls reducing activity of accelerator pathway

reducing heart rate

4)

Adrenaline secreted in response to stress, shock, anticipation or excitement. Presence of

adrenaline increases heart rate helping prepare the body for activity

5) Blood pressure monitored by stretch receptors in walls of carotid sinus, which is a small

swelling in carotid artery. If blood pressure is too high, stretch receptors send signals to

cardiovascular centre which responses by reducing heart rate

DIAGRAM PAGE 29

Artificial pacemakers deliver impulses via electrode pad on skin. Similar method to electrical

chair, was very painful

1950patient wear small plastic box with wires inserted through skin to act as electrons on

heart muscle

Modern pacemakers only 4cm long and implanted under skin and fat on chest and are

responding on activity of patient

Some deliver impulses to ventricle walls. This deals with conditions where AVN normally

relays the impulse from atria to ventricles, via purkyne fibres, is not functioning but the SAN

maybe.

Respiration is where energy stored in complex organic molecules(carbs, fats, proteins) is

used to make ATP

Exists as potential energy and kinetic energy


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Molecules have kinetic energy that allows them to diffuse down a concentration gradient

Energy cant becreated or destroyed, but converted to another. Measured in Joules.

Types of energy: sound, light, heat, electrical, chemical and atomic

Anabolicmetabolic reactions which build large molecules

Catabolicbreak large molecules into smaller ones

Metabolic process:

Active transportmoving ions and molecules across a membrane against concentration

gradient. Sodium-Potassium pumps use this

Secretionlarge molecules made in cells exported by exocytosis

Endocytosisbulk movement of large molecules into cells

Synthesis of large molecules from smaller ones, such as proteins from amino acids,

steroids from cholesterol and cellulose from B glucose.Example of anabolism

DNA replication and synthesis of organelles

Movementsbacterial flagella, eurkaryotic cilia and undulipdia, muscle contraction and

microtubule motors moving organelles.

Activation chemicalsglucose is phophorlated at beginning of respiration so its unstable

and can be broken down to release energy Some energy from catabolic reactions is released in heat form.

Where does energy come from?

Plants, Protoctists and bacteria - - - Photoautotrophs

Respiration releases energy to phosphorylate ADP to make ATP

Role of ATP

ATP is a nucleotideAdenosine (adenine and ribose) + 3 phosphate

Can be hydrolysed to ADP and Pi releasing 30.6kj energy per mol. Described as universal energy currency

ATP + H20 ADP + H20AMP + H2OADENOSINE

The H2O added is the substance being hydrolysed

1st

step produces 30.6kJ mol, 2nd

step 30.6kJ mol, 3rd

step 14.2kJ mol

Pi is produce at each step. Its a condensation reaction, the other way. ATP Synthase is used here

4 stages of respiration

GlycolysisHappens in cytoplasm. Doesnt need oxygen, can be aerobic or anaerobic.

Glucose is broken down to 2 molecules of pyruvate

Link reactionhappens in mitochondrial matrix, Pyruvate is dehydrogenated and

decarboxlyated and converted to acetate

Krebs cycleHappens in mitochondrial matrixacetate is decarboxylated and

dehydrogenated

Oxidative phosphorylationTakes place on folded inner membrane (crisate) of

mitochondria ADP is phophorylated to ATP

Krebs, Link and Oxidative take place under aerobic conditions If its anaerobic, pyruvate is converted to either Ethanol or Lactate


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Coenzymes

In link, glycolysis and krebs, H atoms are removed from substrate molecules in oxidation

reactionscatalysed by dehydrogenase

Enzymes arent good at catalysing oxidation or reduction reactions so coenzymes help

Hydrogen atoms are combined with coenzymes such as NAD which carry hydrogen atoms, to

the inner mitochondrial membranes, to be split into hydrogen ions + electrons

Oxidation phosphorylation happens now to produce a lot of ATP.

When Hydrogen atoms arrive, the coenzymes are reoxidised so they can combine with more

hydrogen from first three stages of respiration

NAD

Non organic, non protein molecule helping the dehydrogenase enzyme carry out oxidation

reactions

Made out of 2 nucleotides from nicotinamide, ribose, adenine and 2 phopsphate.

The nicotinamide acceots hydrogens

When NAD has accepted 2 hydrogens, it becomes NADH

NAD used in glycolysis, link, krebs and anaerbobic ethanol and lactate pathways

Coenzyme A

Adenosine, 3 phosphate, pantothenic (vitamin B5) acid and a small cystemaine group

(amine and sulphur)

Glycolysis

Happens in cytoplasm4 stages:

Phosphorylation

-Glucose is stable and needs to be activated before it can be split into two-One ATP molecule is hydrolysed and phosphate group released attaches to the glucose at

carbon 6 forming Glucose 6-phosphate

-Glucose 6-phosphate turned into fructose 6-phosphate

-Another ATP is hydrolysed and phosphate attaches to the fructose at carbon 1.

-Fructose 1,6 biphosphate is now formed

-The energy from hydrolysed ATP activates hexose sugar and prevents it from being

transported out of the cell. Its now called Hexose 1,6 biphosphate

-2 ATP molecules have been used for ONE glucose molecule

Splitting of hexose 1,6 biophsphate

-

Split into two molecules of triose phosphate

Oxidation of triose phosphate

-Anaerobic process involving oxidation

-2 hydrogens are removed from each triose phosphate

-Involves dehydrogenase enzymes

-Aided by NAD which accepts the hydrogen atoms forming NADH

-So far, 2 molecules of NAD are reduces for each molecule of glucose

- 2 molecules of ATP are formed called substralte level phosphorylation


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Conversion of triose phosphate to pyruvate

-4 enzyme catalysed reactions convert triose phosphate to pyruvate (3 carbon compound)

-2 molecules of ADP are phospohorylated to two molecules of ATP by substrate level

phospohorlyation

Products of glycolysis (per each glucose molecule)

2 molecules of ATP ( 2 used, 4 gained, net = 2)

2 molecules of NADHcarry hydrogen to the inner mitchodnrial membrane and be

used to generate more ATP during OP

2 molecules of pryvuateactively tansported to mitochondrial matrix for next stage

of aerobic respiration.

Mitochondria

Have an inner and outer phospholipid membrane making up an envelope

Outer membrane is smooth and inner folded into cristae (gives a larger surface area)

The matrix is enclosed by the inner membrane

Matrix is semi-rigid, gel like consisting of lipids and proteins. Also has mitochondrial DNA,

Ribosomes and enzymes

Rod or thread like. Most are 0.5-0.1um in diameter and 2-5um.

Athletes have larger mitochondria

Metabolically active cells have larger demand for ATP and so more mitochondria

These usually are longer and have more densely packed cristae for more electron transport

chains and more ATP synthase enzymes.

Can be moved around by cytoskeleton.

Synaptic knobs have lots of mitochondria around them permanently as it has a high ATP

demand.

Structure to function (matrix)

Matrix is where link reaction and Krebs cycle

Molecules of NAD

Oxaloacetate4 carbon compoundaccepts acetate from link

Mitochondrial DNA codes for mitochondrial enzymes and other proteins

Mitochondrial ribosomes where proteins are assembled

Structure to function (outer membrane)

Contains proteins to form channels to allow pyruvate to pass. Has enzymes too

Structure to function (Inner membrane)

Different lipid composition and is impermeable to small ions and hydrogen ions

Folded to cristae to increase surface area

Electron carriers an ATP synthase enzyme


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Electron carriers are protein complexes arranged into ETC

Each EC is an enzyme with a cofactor non protein, haem group with n Fe atom

Co factors accept and donate electrons as Fe reduces to Fe2+

by accepting an electron and

oxidised to Fe3+

donating an electron to next electron carrier

Haem group acts as oxidoreductase enzymes as they are involved in oxidation and reduction

Some EC have coenzyme that pumps protons from matrix to inter membrane space

Inner membrane is impermeable to small ions and so protons accumulate in intermembrane

space. Causes a lower pH in the space than in the matrix

ATP Synthase enzymes

Large and protrude from inner membrane into the matrix

Known as stalked particles

Allow protons to pass through them

Protons flow down proton gradient, through ATP synthase, into matrix from inter membrane

Chemiosmosis Force drives the rotation of part of the enzyme and allows ADP and Pi to be joined forming

ATP.

Coenzyme FAD becomes reduced in Krebs cycle, is bound to a dehydrogenase enzyme which

is embedded in the intermembrane. The hydrogen atoms accepted by FAD dont get

pumped into the inertmembrane space. They pass back into the matrix instead

FAD = Riboflavin, adenine, ribose and two phosphate

Link reaction and krebs cycle

Pyruvate produced in glycolysis is transported across inner and outer mitochondrial

membranes into the matrix

Link reaction - - -( 2pyruvate + 2CoA2Co2 + 2NADH + 2CoA

Decarboxylation and dehydrogenation of pyruvate to acetate are catalysed

Pyruvate dehydrogenase removes H atoms

Pyruvate hydrogenase also removes carboxyl group which becomes Co2

NAD accepts H atoms

Coenzyme A accepts acetate forming Acetyl Coenzyme A. CoA carries acetate to krebs

No ATP is produced, but the NADH will take a pair of H atoms to inner mitochondrial

membrane and will be used to make ATP in oxidative phosphorylation

Krebs Cycle

Takes place in mitochondrial matrix

Acetate from Acetyl Coenzyme A joins with Oxaloacetate forming citric acid. Coenzyme A is

released and goes back to collect more acetate


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Citrate is decarobxylated and dehydrogenated to form a 5 carbon compound. Pair of

hydrogen atoms is accepted by NAD which becomes reduced

5 carbon compound is decarboxlyated and dehydrogenated to form 4 carbon compound and

another NADH

4 carbon is changed to another 4 carbon and ADP is phosphorylated to produce a molecule

of ATPSubstrate level phosphorylation

The second 4 carbon compound is changed to another 4 carbon compound. Pair of hydrogen

atoms is removed and accepted by FAD forming FADH.

The 4 carbon compound is dehydrogenated and regenerates oxaloacetate. Another NAD isconverted to NADH

Product per glucose Link reaction Krebs cycle

NADH 2 6

FADH 0 2

Co2 2 4

ATP 0 2

Oxygen isnt used but these stages wont occur without oxygen so are aerobic

Other food substrates that are glucose can be respired Fatty acids broken down to acetate can enter Krebs

Amino acid can be demainated (NH2 removed) and the rest of the molecule can enter Krebs,

or can be changed to Pyruvate or Acetate.

Final stage of aerobic respiration

Involves EC embedded in inner mitochondrial membranes NADH and FADH are reoxidised when they donate Hydrogen atoms which are split into

protons and electrons, to the electron carriers

The first EC to accept electrons from NADH is called NADH Dehydrogenase ( NADH-

Coenzyme Q reductase)

Protons go into the solution in the matrix

ETC

Electrons are passed along a chain of electron carriers and then donated to molecular

oxygen, the final electron acceptor

Chemiosmosis

As electrons flow along the ETC, energy is released and used by coenzymes associated with

the EC to pump protons across the inter membrane space

Builds up a proton/ph gradient and a electrochemical gradient

Potential energy therefore builds up in the intermembrane space

H ions cannot diffuse through lipid part of the inner membrane bbut can diffuse through ion

channels in it. These channels are associated with ATP synthase.

Oxidative phosphorylation


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Formation of ATP by addition of inorganic phosphate to ADP in presence of oxygen.

Protons flow thorugh ATP synthase, drive rotation of enzyme and join ADP and Pi = ATP

Electrons passed from last EC in the chain to molecular oxygen which is final electron

acceptor

Hydrogen ions also join so oxygen is reduced to water.

-4h+ + 4e- + o22H2O

For each glucose molecule, 2 ATP have been gained in glycolysis, 2 ATP have been made in

Krebs.

More ATP will be made in oxidative phosphorylation, where NADH and FADH are reoxidised

Name of molecule Glycolysis Link Krebs

NADH 2 2 6

FADH 0 0 3

NADH and FADH provide electrons to ETC used in oxidative phosphorylation

NADH provides H ions that contribute to the build up of proton gradient for chemiosmosis.

FADH stay in matrix but combine with oxygen to form water

10 molecules of MADJ can produce 26 molecules of ATP during oxidative......

Total yield of ATP molecules per glucose = 30

This is rarely achieved because:

-Some protons leak across mitochondrial membrane reducing proton to generate proton

motive force

-ATP used to actively transport pyruvate into mitochondria

-ATP is used to bring hydrogen from NADH made during glycolysis into mitochondria

PAGE 92 -93

If oxygen is absent, ETC cant function and so Krebs and link will sotp.

Only way to produce ATP is then glycolyisis.

Reduced NAD generated from oxidation of glucose has to be reoxidised for glycolysis

to keep occurring

For eukaryotic cells, there are to pathways to reoxidise NAD

Fungi , yeast, use ethanol fermentation

Animals use lactate fermentation

Lactate Fermentation

Mammalian tissue during vigorous activity when demand for ATP is high


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NADH has to be oxidised to NAD

Pyruvate is hydrogen acceptor accepting from NADH

NAD is now oxidised and is available to accept more hydrogen atoms from glucose

Glycolysis can continue, generating AWTP

Enzyme lactate dehydrogenase catalyses the oxidation of NADH as well as reduction of

pyruvate to lactate

Lactatecarried from muscles to liver where more oxygen is available so it can be converted

back to pyruvate to respire again, or recycled to glucose and glycogen

The reduction in pH that reduces enzyme activity causes muscle fatigure

Alcohol fermentation

Pyruvate loses CO2 moleculeDecarboxylated to ethanal

Catalysed by pyruvate decarboxylase and has a coenzyme (thiamine dipohsophate) bound

to it

Ethenall accepts H atoms from NADH which reoxdisesas Ethenal is reduced to Ethanol

(catalysed by ethanal dehydrogenase)

NAD can accep more Hydrogen atoms now from glucose during glycolyisis

Yeast is a facultative anaerobecan live without oxygen Dies with Ethanol conc 15%

Yeast is grown until aerobic then anaerobic to undergo alcoholic fermentation

More protons = More ATP

More Hydrogen atoms in a molecule of respiratory substrate, the more ATP can be

generated when it is respired.

More hydrogen = more oxygen needed to respire

Animals store glucose as glycogen, plants as starch

Fructore/Galactose are changed to glucose for respiration

Theoretical yield for glucose is 2870 kJ mol-1

Takes 30.6kJ to produce 1 mol ATP

Theoretically, respiration of 1 mol of glucose should produce nearly 94mol of ATP

Actual yield is 30mol ATP, 32% efficiency

Remaining energy released as heat which helps maintain a suitable body temp

Excess amino acids released after protein digestion may be deaminated. Involves removal of

amine group and its conversion to urea. Rest is changed to glycogen or fat

Useful when fasting/starvation/exercise, protein from muscle can be hydrolysed to amino

acids which can be respired

Some can be converted to pyruvate or to acetate and be carried to krbes

Number of H atoms per mole accepted by NAD and then used in oxidative phosphorylate is

slight more than number of hydrogen atoms per mole of glucose, so protein release slightly

more energy than equivalent masses of carbohydrate


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Triglycerides are hydrolysed by lipase to fatty acids and glycerol

Glycerol can be converted to glucose then respired, fatty acids cnat

Fatty acids have many proteins for oxidative phosphorylation so they produce a lot of ATP

Each fatty acid is combined with CoA. Required energy from hydrolysis of a molecule of ATP

to AMP and 2 inorganic phosphate

Fatty acid CoA complex is transported into the mitochondrial matrix where it is broken

down into 2-carbon acetyl group that are attached to CoA

During ths breakdown, by the Beta oxidation pathway, NADH and FADH formed

Acetyle groups released from CoA enter krebs 3 Molecules of NADH, One FADH and one ATP are formed for each acetate here

Large amount of NADH is reoxidised at ETC during OP, producing large ATP

Respiratory substrate Mean energy value kj g-1

Carbohydrate 15.8

Lipid 39.4

Protein 17

Role of loop of Henle is to create a low water potential in the tissue of the medulla

Ensures more water can be reabsorbed from the fluid in the collecting duct

Loop of Henle

Consists of descending limb descending into the medulla

(Ascending limb into the cortex)

Arrangement allows salts (Cl and NA ions) to be transferred from ascending to descending

Overall effect is to increase conc. of salt in the tubule fluid and consequently they diffuse out

of thin walled ascending limb into the surrounding medulla tissue, giving tissue fluid in

medulla very low water potential

As fluid descends deeper into medullawater potential becomes lower because:

-Loss of water by osmosis to surrounding tissue fluid

-Diffusion if Na and Cl ions into tubule from surrounding tissue fluid

As fluid ascends back, water potential becomes higher because:

-Base of tubule, Na and Cl diffuse out of tubule into tissue fluid

-Higher up tubule, Na and Ck are actively transported out into the tissue fluid

Arrangement of loop of Henle is known as a hairpin counter current multiplier

Effect of this arrangement is to increase efficiency of salt transfer from ascending limb ot

descending limb.

Causes a build up of salt conc. in surrounding tissue fluid

Movement of salts from ascending limb into medulla creates high salt conc in tissue fluid so

low water potential

Removal of ions from ascending limb means at the tp of ascending limb the urine is dilute

Water may then be reabsorbed from urine in teh distal tubule and collecting duct

Amount of water reabsorbed depends on needs of body

Kidney is also an organ of osmoregulation

Collecting duct


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Top of ascending limb the tubule fluid passes along a short distal convulatoed tubule where

active transport is used to adjust the cconc of various slats

Then goes to collecting duct and atm tubule fluid contains a lot of water high water potent

Collecting duct carries fluid back down medulla into pelvis

Tissue fluid in medulla has a low water ptent that becomes even lower deeper int the

medulla

As tubule fluid passes down collecting duct, water moves by osmisos from tissue to

surrounding fluid

Then tners the blood capillaries by osmosis and is carried away Amount of water reabsorbed depnds on permeability of walls in collecting duct

By time urine reaches pelvis, it has lower wwater potential and conc of urea and salts in

urine is higher htran that of blood plasma

Osmoregulation

Control of water levels and salt levels in the body Water gained from food, drink, metabolism (respiration)(

Water lost from urine, sweat, water vapour in exhaled air, faeces

Cool daya lot of drinklarge volume conc urine

Hot daylittle drinksmall concentrated urine

Walls of collecting duct can be made more/less permeable depending on needs

Hot day, more permeable walls so more water is kept in

Walls respond to ADH levelCells in walls have ADH receptors

ADH binds, causing enzyme controlled reactions

Causes vesicles containing water permeable channels (aquaporins) into the cell surfacemembrane. Makes the walls more permeable to water. More ADH = More Aquaporins

If less ADH, cell surface membrane folds inwards to create new vesciles that remove water

permeable cahnnels from the membrane. Makes the wals less permeable and less water is

reabsorbed by osmosis.

Water potential is monitored by osmoreceptors in the hypothalamus of the brain

Cells probably respnd to the effects of osmosis when the water potential of the blood is low,

the osmoreceptor cells lose water by osmosis. This causes them to shrink and stimulate

neurosecretory cells in hypothalamus.

The neuersecretory cells are neurones producing ADH. ADH is manufacted in teh cell body

which lies in the hypothalamus

ADH flows down aaxon to terminal bulb in posterior pituiraty gland and stored till needed

When the neuerosecretory cells are stimulated they send action potentials down their axosn

and cause release of ADH

ADH enters blood capillaries running through posterior pituitary gland and it is transported

around body and acts on cells of the collecting ducts

Once water potent of blood rises again ADH released

ADH broken downhalf like 20mins. Therefore collecting ducts will receive less stimulation

Page 49 diagram


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Kidney failure

Can occur by diabetes mellitus

Hypertension

Infection

Means youre unable to remove excess water and certain waste products from blood e.g.

urea and salt

Cant regulate water and salt levels either

Dialysistreatment

Removes wastes, excess fluid and salt from blood by passing over a dialysis partially

permeable membrane allowing exchange of substances between fluid and blood

Dialysis fluid contains correct conc of salt, urea, water and other substances in blood plasma

Excess substances in blood diffuse across membrane into dialysis fluid

Too low conc substances diffuse into blood from fluid

Haemodialysis

Blood is passed into machine that contains an artificial dialysis membrane. Heparin is

added to avoid clotting, and any bubbles are removed before blood returns to body.

Usually performed at a clinic 3 times a week for several hours

Peritoneal dialysis

Filter is the bodys own abdominal membrane

A permanent tube is implanted in abdomen Diaylsysis solution is pour thorugh tube and fills space between abdominal walls and organs

After several hours the used solution is drained out

Performed in consevutive sessions daily at home or work

Kidney transplant

Patient is under anaesthesia, new organ is planted into lower abdomen and attatches it to

blood supply and bladder. Patients feel much better after transplant

Immune system will recognise new organ as foreign and produce a reaction so

immunosuppressant drugs are given to prevent rejection

Advantages:

-Freedom from time consuming dialysis

Diet is less limited

Feel better

Better quality of life

No longer seeing as chronically ill

Disadvantages

Immunosuppressant drugs are needed for lifetime of kidney


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Major surgery

Risk of surgeryinfection, bleeding, damage to surrounding orangs

Frequent checks of organ rejection

Anti rejection medicines cause fluid retention and high blood pressure, more susceptibility

to infections.

Pregnancy test:

HCG is small glycoprotein with molecular mass of 36700.

Found in urine 6 days after pregnant.

Monoclonal antibodies.

Antibody only binds with HCG. Anti body has blue bead. Mobilised anti bodies at the

bottom.

HCG anti body complex moves up to the strip until it sticks to a band of immobilised

antibodies

Top line is a test with mobile and immobilised antibody complex

Testing for anabolic steroids

Increase protein synthesis within cells

More cell tissue in muscles and give advantage in sports

Half life of 16 hours and remain in blood for daystime taken for substance for its conc to

drop to half

Small molecules and can enter nephron easily

Testing it requires gas chromatography/mass spectrometry/ urine sample

Gas is vaporised in presence of gaseous solvent and passed down a long tube lined by anabsorption agent. Each substance dissolves differently in teh gas and stays there for a

unique specific time, retention time

Susssbstance comes out of gas absorbed onto lining then analysed to create chromatogram.

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Notes Biology A-Level