Edexcel IGCSE Revision notes
Written by Tim Filtness
Mercha Merchant nt Taylo aylors rs School
Biology IGCSE Biology IGCSE Revision Workbook Trippple Award Specification (4BIO) Examination in 2011 1
Edexcel IGCSE Revision notes
Written by Tim Filtness
IGCSE Revision Notes Trippple Award Specification
Key words are underlined in red . Practical work is printed in italics.
Section 1: The nature an variety o! living organis"s Characteristics Characteristics of living organisms include;
M ovement R
espitation
S ensitivity
G rowth R eproduction E xcretion N utrition In addition all living organisms contain nucleic acids !"#$% and have the a&ility to control teir internal conditions. 'inally all living organisms can die. (ivi (iving ng orga organi nism smss are are clas classi sifi fied ed into into ) grou groups ps each each of whic which h has has cert certai ainn characteristics characteristics you need to learn #lants: *. ,. -. .
+ult +ultic icel ellu lula larr orga organi nism smss Cells contai containn chloroplast chloroplastss and are a&le to carry carry out photos photosynth ynthesis esis Cells ells have ave cellulose cell walls /hey store car&ohydra car&ohydrates tes as as starch starch or or sucrose sucrose.. Examples include flowering plants such as a cereal !e.g. mai0e% and a her&aceous legume !e.g. peas or &eans%.
$ni"als: 2
Edexcel IGCSE Revision notes
*. ,. -. . ).
Written by Tim Filtness
+ult +ultic icel ellu lula larr orga organi nism smss Cells do not contain chloroplasts and are not a&le to carry out photosynthesis Cells ells have ave no cell walls /hey /hey have have a nervo nervous us syste system m /hey /hey ofte oftenn store store car&o car&ohy hydra drate te as as !l"co!en Examples include mammals !e.g. humans% and insects !e.g. housefly%.
%ungi: *. /hey are saprop"tic and feed &y excreting digestive digestive en0ymes onto food and a&sor&ing the digested products ,. Cells do not contain chloroplasts and are not a&le to carry out photosynthesis -. Cells Cells are 1oine 1oined d togeth together er to form form threads threads called called "pae . 2yphae contain many nuclei &ecause they are made from many cells. . Cell Cell wal walls ls are are mad madee from from citin !a protein% ). /hey /hey stor storee car&o car&ohyd hydrat rates es as as !l"co!en. Examples include +ucor and 3east !which is single celled%.
Bacteria: *. +ade fr from sin!le cells ,. Cells do not contain a nucleus &ut have a small piece of circular "#$ instead !a #acterial cromosome%. -. Some &acteri &acteriaa can carry out out rudimentar rudimentaryy photosynt photosynthesi hesis s &ut most most are saprop"tes . /hey have have the the structur structuree &elow !learn !learn it it it comes comes up4%
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Edexcel IGCSE Revision notes
Written by Tim Filtness
Examples include (acto&acillius &ulgaricus !a rod5shaped &acterium used in the production of yoghurt from milk% and Pneumococcus !a spherical &acterium that causes Pneumonia%
#rotoctisis: 6asically everything that doesn7t fit into the other kingdoms4 +ost are single celled organisms which can either; *. 2ave animal5like characteristics !e.g. $moe&a% ,. 2ave plant5like characteristics !e.g. Chlorella% 2owever some protoctisis are multicellular !e.g. seaweeds yes they7re #8/ plants4%
&iruses: *. ,. -. .
+uch smaller than &acteria. Te" are not made from cells /otally parasitic and reproduce inside host cells. /hey infect every type of living cell /hey have the structure &elow !learn it it comes up4%
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Edexcel IGCSE Revision notes
Written by Tim Filtness
/he En$elope is used to gain entry into host cells. /he %apsid is a protein coat and is used to protect the genetic information and give the virus structure /he "#$ or R#$ !a different type of nucleic acid% contain the code for &uilding new viruses. Examples include the /o&acco +osaic 9irus and the Influen0a virus !which causes :flu%.
Section ': Structures an %unctions in (iving )rganis"s a* (evels o! organi+ation 8rganisms are made from organi0ations of smaller structures. 3ou need to know the following hierarchy of structures. Or!anelles intracellular structures that carry out specific functions within a cell %ells the &asic structural and functional unit from which all &iological organisms are made Tissues a group of speciali0ed cells which are adapted to carry out a specific function. 5
Edexcel IGCSE Revision notes
Written by Tim Filtness
Or!ans a collection of two or more tissues which carries out a specific function or functions Or!an S"stems a group of two or more organs
b* Cell structure 3ou need to know the differences &etween plant and animal cells the functions of the organelles and &e a&le to recogni0e them in a microscope picture or drawing.
"ifferences &etween plant and animal cells< 6
Edexcel IGCSE Revision notes
Written by Tim Filtness
Or!anelle
Animal %ell
&lant %ell
Chloroplast
=
,
Cell >all
=
,
Sap 9acuole
=
,
Chlorophyll
=
Si0e
Roughly )?@m long
Shape
#o fixed shape
'ound in chloroplast Roughly *)?@m long Rectangular
#.6. /he cells are measured in @m ! micrometers%. 8ne micrometer is *A*???th of a millimetre. 'unctions of the 8rganelles< %"toplasm site of chemical reactions in the cell %ell 'em#rane controls what enters A leaves the cell !selectively permea&le% ucleus contains nucleic acids which code for the synthesis of specific proteins. /hese proteins control all activity in the cell 'itocondrion site of respiration %loroplast site of photosynthesis %ell all made from cellulose. Strengthens the cell and allows it to &e tur!id Sap *acuole contains the cell sap. $cts as a store of water or of sugars or in some cases of waste products the cell needs to excrete.
c* Biological "olecules 'ood /ests< (ipids are tested for using the Emulsion test Proteins are tested for using the Biuret test Starch is tested for using Iodine solution
Edexcel IGCSE Revision notes
Written by Tim Filtness
Blucose is tested for using Benedict+s test /he 'ood Broups< ,ood -roup
,unction
(ipids !fats oils%
Dsed as a lon!.term ener!" store !much easier to store than car&ohydrates%. $lso have a role in protection and insulation
Car&ohydrates
+ade from single sugars or chains of sugars. /hey are used in respiration to provide ener!".
Proteins
6roken down into amino acids which our &ody a&sor&s and assem&les into new proteins. /he proteins are used for !rowt and repair. Regulates &owel movement. Sloughs off old lining of intestine.
'i&re >ater
9itamins and +inerals
Essential as a solvent for chemical reactions !e.g. cytoplasm% heat loss !e.g. transpiration% transport !e.g. &lood% etc Essential for the normal function of some en0ymes and proteins e.g. 'e,F is an essential part of /aemo!lo#in and +g,F is part of %lorop"ll
Components of the main 'ood Broups< /he main food groups are car&ohydrates lipids and proteins. $ll three groups are made from smaller molecules. Car&ohydrates are large molecules made from one or more sugars !e.g. &oth Starc and -l"co!en are &oth pol"mers of -lucose% Proteins are polymers of Amino Acids (ipids are made from one !l"cerol molecule and three fatt" acid molecules 1oined together.
!
Edexcel IGCSE Revision notes
Written by Tim Filtness
En0ymes< 5 5 5 5 5
$re proteins $re &iological catal"sts !speed up chemical reactions% $re specific to one particular Su#strate $re affected &y temperature and p2 $re not used up in the reaction they cataly0e
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Edexcel IGCSE Revision notes
Written by Tim Filtness
*. Initially raising the tem perature *. Initially increasing the p2 increases the rate of reaction. increases the rate of reaction. ,. 2owever after the optimum ,. 2owever after the optimum p/ is temperature is reached the reached the en0yme &egins to en0yme &egins to change shape change shape and the acti$e site and the acti$e site stops &eing stops &eing a&le to &ind to the su#strate . su#strate . a&le to &ind to the -. /he en0yme &ecomes denatured -. /he en0yme &ecomes denatured and stop working !the rate of and stop working !the rate of reaction is 0ero at this point%. reaction is 0ero at this point%. 3ou need to &e a&le to recall an experiment you have done that explores the effect of temperature on en0ymes. $n example is the en0yme %atalase which &reaks /"dro!en peroxide into ater and Ox"!en; ,2,8, - 8, F ,2,8 Catalase is found in potatos. /herefore putting potato chips into peroxide will produce 8,. /he rate of reaction is therefore proportional to the volume of 8 , given off. Changing the temperature will alter the volume !i.e. initially increase it reach an optimum then decrease Guickly as the %atalase &ecomes denatured%.
1#
Edexcel IGCSE Revision notes
Written by Tim Filtness
* Move"ent o! substances into an out o! cells iffus ion the movement of molecules from high concentration to low concentration down a concentration gradient. Osmosis the movement of water molecules from high concentration to low concentration through a partially permea&le mem&rane Acti$e Transport the movement of molecules from low concentration to high concentration against the concentration gradient. Energy is reGuired for movement to occur.
"iffusion and osmosis occur &ecause molecules have inetic ener!". /he molecules constantly &ounce off each other all the time gradually spreading out. Eventually there will &e an even mixture of molecules which is called an euili#rium . "iffusion can &e affected &y; 5 5 5 5 5 5
temperature !increases Kinetic energy% stirring !increases Kinetic energy% surface area for diffusion thickness A distance molecules have to diffuse the si0e of the concentration gradient the surface area to $olume ratio Plant cells are normally tur!id !swollen full of water%. /his is important &ecause it provides strength to plants. Plant cells have a cell wall to stop them &ursting when turgid. >hen plant cells start to lose water they &ecome flaccid. 'laccid plants lose their strength and start to wilt. Eventually flaccid cells &ecome plasmol"sed as the cell mem&rane &egins to peel away from the cell wall. /his kills the cell. 3ou need to give examples of diffusion and osmosis living and nonliving situations. Bood examples of diffusion are ink chromatography or the diffusion of K+n8 crystals !purple% into water. "iffusion of gases in the lung or leaf are also good examples. 8smosis can &e shown artificially using visking tu&ing or potato chips in salt solutions of different concentrations.
e* Nutrition utrition in ,lowerin! &lants3
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Edexcel IGCSE Revision notes
Written by Tim Filtness
Plants are potoautropic !i.e. they generate their own Hfood using energy from the Sun.% /hey do this through photosynthesis. Car&on "ioxide JC8,
F F
>ater J2,8
-
8xygen J8,
F F
Blucose CJ2*,8J
/hrough photosynthesis light energy is converted into chemical energy in the &onds in glucose. Plants use glucose for the following; 5 5 5 5
espiration Stored as Starc /urned into %ellulose !cellulose is a polymer of glucose% Dsed to make fats and oils
$t any point the rate of photosynthesis can &e increased &y adding more C8 , more water more light or heating towards optimum temperature !photosynthesis is cataly0ed &y en0ymes%. 2owever at a certain point the addition of more e.g. light will not increase the rate of photosynthesis any further. /his is &ecause a second factor is limiting the rate of photosynthesis. $dding more of the ratelimitin! factor will increase the rate further until another factor &ecomes limiting.
Rate o! ./s
(ight is the rate 0
li"iting !actor $ secon !actor is li"itinge2g2 C) * '
(ight intensity
3ou need to know the parts of the leaf and their adaptations.
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Edexcel IGCSE Revision notes
5eaf Structure
Written by Tim Filtness
Adaptation for potos"ntesis
Cuticle
Stops the leaf from losing water !remem&er water is used in photosynthesis%
Epidermis
/ransparent protective layer. Protects the leaf without inhi&iting photosynthesis.
Palisade cells
$re packed full of chloroplasts. $re long and thin so light has to pass through as many chloroplasts as possi&le.
$ir Spaces
Increase the surface area inside the leaf to maximise gas exchange across the surface of the Spongy +esophyll cells
Stoma
$llow exchange of C8, and 8,
Buard Cells
$llow the stoma to open and close to stop the leaf losing too much water
9ein !containing 6"lem%
6rings a steady supply of water to the leaf.
In addition to water and C8, plants also need specific minerals; itrate used to make amino acids for use in plant proteins 'a!nesium forms part of the chlorophyll molecule &otassium 5 essential for cell mem&ranes &ospate 5 essential part of "#$ and cell mem&ranes
3ou need to know an experiment that shows how the rate of pAs is affected &y rate5 limiting factors. /he &est example is using pond weed ! Elodea% which produces &u&&les of 8, as it photosynthesi0es. /he rate of &u&&le production is approximately 13
Edexcel IGCSE Revision notes
Written by Tim Filtness
proportional to the rate of photosynthesis. /herefore when you add light or give it more C8, the rate of &u&&le production increases. 3ou also need to know an experiment that proves that light and C8 , are essential for the production of starch. $ good example is the -eranium plant. It7s leaves normally turn &lue5&lack in the presence of iodine solution showing starch is present !you have to &oil it in ethanol first to remove the chlorophyll to show the colour%. 2owever if one leaf is put in aluminum foil and another is kept with lime water &oth do not turn &lue5&lack implying &oth C8 , and light are essential for starch production and therefore essential for pAs. utrition in /umans3 2umans need to eat a #alanced diet. /his really means some of every food !roup &ut not too much or too little of a particular one. /he two groups that provide energy !through respiration% are lipids and car#o"drates. Per mass lipids have a&out *?x more energy in them than car&ohydrates. /he energy in food is measured in %alories !eGuivalent to ., k%. In order to keep our &odies functioning !i.e. heart &eating &asic respiratory reGuirement% 5 5
+ales need to consume 2700 Calories a day 'emales need to consume 2000 Calories a day 2owever this will change if;
5 5 5 5 5
3ou exercise 3ou are growing 3ou are ill 3ou are pregnant 3ou are old 3ou need to know an experiment that can show how much energy there is in food. /he easiest way of doing this is to &urn a sample of food and use it to heat a fixed volume of water. If you record the change in temperature of the water you can use the eGuation &elow to find out the energy the food gave to the water; Energy L change in temp. x volume of water x .,AgA 3C $ potential pro&lem is that not all the food will &urn. /o control this you measure the start and end mass of the food and calculate the mass that actually &urned. /o standardi0e this you can divide your calculated energy value &y the change in mass to give you the change in mass per !ram of food !which will allow you to compare values fairly &etween different food samples%
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Edexcel IGCSE Revision notes
Written by Tim Filtness
3ou need to know the specific sources and functions of the following minerals and vitamins *itamin 8 'ineral
,unction
9itamin $
Present in fis ceese and e!!s. It forms an essential part of the pigment in rods and cones that detects light. (ack of 9itamin $ can lead to &lindness.
9itamin C
Present in citrus fruit. It forms an essential part of colla!en protein which makes up skin hair gums and &ones. (ack of 9itamin C causes scurvy.
9itamin "
Present in fis &ut made naturally &y our &ody when sunlight shines on the skin. It is essential for regulating the growth of &ones. (ack of 9itamin " can cause rickets.
Calcium
Present in mil ceese dairy foods. It is essential for &one growth and muscles. (ack of calcium can lead to osteoporosis.
Iron
Present in red meat and some $e!eta#les !e.g. spinach%. Is part of aemo!lo#in. (ack of iron causes anaemia.
i!esti$e S"stem3
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Edexcel IGCSE Revision notes
Written by Tim Filtness
/he purpose of digestion is to &reak food into molecules that are small enough to &e a&sor&ed into the &loodstream. /here are two types of digestion; 'ecanical i!estion < digestion &y physically &reaking food into smaller pieces !i.e. not using en0ymes%. Carried out &y;
5 5
mouth and teeth chewing food stomach churning food %emical i!estion <
digestion using en0ymes
3ou need to know the following en0ymes; ere it is made ere it wors
Salivary Blands Stomach cells (iver
Pancreas Small Intestine
+outh
En9"me
Su#strate
&roducts
$mylase
Starch
+altose
Stomach
Protease
Protein
$mino $cids
Small Intestine
6ile Salts
'at
'at droplets
Small Intestine
$mylase Protease (ipase
Starch Protein 'at
+altose $mino $cids Blycerol 'atty acids
+altase Protease
+altose Protein
Blucose $mino $cids
Small Intestine
Bile salts are not technically en0ymes. /hey are made in the li$er and stored in the !all #ladder. /hey help &y emulsif"in! lipid !i.e. turning large fat droplets into lots of tiny droplets%. /his increases the surface area which helps lipase actually &reak the lipid down.
6ile also has a second 1o&. 6ile is alali which is important for neutrali9in! stomac acid as soon as it leaves the stomach. Stomach acid is important &ecause it kills any &acteria that enter the stomach. Stomach acid does not play a significant role in digestion. :e" Ideas3 In!estion<
taking food into the digestive system 16
Edexcel IGCSE Revision notes
Written by Tim Filtness
i!estion <
&reaking food down into molecules small enough to &e a&sor&ed into the &loodstream.
A#sorption <
taking molecules into the &loodstream. /his happens almost entirely in the small intestine !ileum%
Assimilation <
using food molecules to &uild new molecules in our &odies. I.e. the food molecule physically &ecomes part of our &ody.
E!estion<
Removing unwanted food from the digestive system !having a poo4%. /his is not excretion &ecause the unwanted food has never technically &een inside the &ody.
&eristalsis<
the contraction of muscle in the intestine wall #eind a #olus of food !&all of food%. /his pushes the &olus through the intestine.
Small intestine adaptations3
Adaptation
Explanation
/hin wall
/he intestine wall in thin which speeds the rate of diffusion of molecules into the &lood
Rich &lood supply
/his helps carry a&sor&ed molecules away from the intestine Guickly. /his means there is always a low concentration of food molecules in the &lood which maintains a high concentration gradient
Intestine length
Roughly Mm long which increases the surface area
Surface $rea
*illi and micro$illi increase the surface area of the small intestine &y *???x 1
!* Res.iration
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Edexcel IGCSE Revision notes
Written by Tim Filtness
Respiration is the process that releases energy into every living cell of every organism. /he energy is essential for keeping the cell alive as it powers processes like protein synthesis growth repair division etc. 8xygen J8,
Blucose CJ2*,8J -
F F
Car&on "ioxide F JC8, F
>ater J2,8
Some cells have the a&ility to respire without using oxygen. /his is called anaero#ic respiration . 8nly liver and muscle cells can do this in humans. $naero&ic respiration allows the cell to carry on working despite there &eing a shortage of oxygen !this is very useful in muscle cells particularly if you are running for your life4% Blucose CJ2*,8J -
(actic $cid ,C2-C282C882
!interest only don+t learn%
$naero&ic respiration produces 5actic Acid which is poisonous. (actic acid &uilds up inside muscle cells and Guickly leads to muscle fatigue and cramp. Eventually the muscle cell will stop working. "uring recovery the lactic acid is transported to the liver via the &loodstream. /he liver &reaks the lactic acid into C8 , and water. 8xygen is reGuired for this which is called the Ox"!en e#t. ;east also respire anaero&ically except they do not produce lactic acid like humans. Instead they make ethanol. /his type of anaero&ic respiration is also called alcoolic fermentation. It is used in the &aking and &rewing processes. Blucose CJ2*,8J -
Ethanol ,C2-C2,82
F F
Car&on "ioxide ,C8, !interest onl"%
3ou need to know an experiment that shows that living organisms produce C8 , through respiration. /he &est example is to suspend some maggots or seeds near the top of a test tu&e sealed with a &ung !suspend the maggots A seeds in a wire mesh%. $ small amount of lime water in the &ottom of the test tu&e will turn milky over time indicating that C8 , has &een produced.
g* Gas e4change -as Excan!e in ,lowerin! &lants3 emind "ourself of te structure of te leaf (Section 2e < utrition in ,lowerin! &lants)=
1!
Edexcel IGCSE Revision notes
Written by Tim Filtness
Remem&er that C8, and 8, diffuse in and out of leaves through stomata. Remem&er that C8, is used in photosynthesis and produced &y respiration whereas 8, is used in respiration and produced in photosynthesis4 Bot processes run all te time . So the net amount of glucose the plant produces !i.e. the amount it gets to use for growth etc% is governed &y the formula;
#et Blucose
L
/otal production
$mount used in respiration
/he amount the plant uses in respiration in nearly constant. 2owever the total production is not. It is dependent on the ratelimiting factors !i.e. li!t intensit" C8, level water availa&ility temperature etc%. In winter the net glucose production is virtually 0ero whereas in summer the net glucose production is large. Terefore> plants !row a lot durin! te summer and not muc durin! winter?
5eaf Structure
Adaptation for !as excan!e
$ir Spaces
Increase the surface area inside the leaf to maximise gas exchange across the surface of the Spongy +esophyll cells
Stoma
$llow exchange of C8, and 8,
+esophyll cells
2ave a large surface area and moist surfaces which speeds gas exchange
(eaf shape
(eaves are thin which increases diffusion speeds and leaves also have a very large surface area which also increases diffusion speed.
Stomata distri&ution
Stomata are spread out over leaves which means waste gases produced &y the leaf can diffuse away Guickly this stops the &uild5up of excreted products which would slow gas exhange
1"
Edexcel IGCSE Revision notes
Written by Tim Filtness
3ou need to know an experiment which will show the effect of light intensity on the rate of gas exchange. /he &est example is to seal two leaves !still attached to the plant% in separate plastic &ags with some &icar&onate indicator solution. 8ne of the &ags is &lack and the other is translucent. /he leaf in the &lack &ag produces C8, via respiration and the colour of the &icar&onate indicator changes Guickly to yellow. /he leaf in the translucent &ag produces 8 , via photosynthesis and the &icar&onate indicator solution changes to red slowly. 6icar&onate Indicator colours< Red in the presence of 8, 3ellow in the presence of C8,
-as Excan!e in /umans3
2#
Edexcel IGCSE Revision notes
Written by Tim Filtness
2ow &reathing works Breatin! in (inalin!)
*. Intercostal muscles contract pulling the ri#ca!e forwards and out ,. iapra!m contracts moving down -. /he volume of the Toracic %a$it" increases . /he pressure in the /horacic Cavity decreases ). $ir is drawn into the lungs to eGuali0e the pressure
Breatin! out (exalin!)
*. Intercostal muscles relax the ri&cage moves inwards and down ,. "iaphragm relaxes moving up -. /he volume of the /horacic Cavity decreases . /he pressure in the /horacic Cavity increases ). $ir lea$es the lungs to eGuali0e the pressure
/he entire process is passive i.e. no energy Inhaling is an active process i.e. it reGuires is reGuired as there is no muscle energy for muscle contraction contraction.
$lveoli and their adaptations< $daptations for gas exchange< 5
$lveolus is one cell thick
5
Capillary wall is one cell thick
5
+any alveoli produce a huge surface area
5
$lveoli wall is moist
5
6reathing maintains a high concentration gradient for 8, and C8,
5
6lood movement maintains a
high concentration gradient for 8, and C8, 21
Edexcel IGCSE Revision notes
Written by Tim Filtness
Smoking< Cigarette smoke contains tar nicotine carcino!ens %O and poisons %emical
Effect
/ar
6locks up alveoli making gas exchange more difficult. $lso clogs up cilia !little hairs lining the lungs whose 1o& is to Hwave and remove mucus and trapped &acteria out of the lungs%.
#icotine
Speeds heart rate and damages arteries causing furring of artery walls !aterosclerosis%. /his leads to heart disease and vascular diseases. It is also addicti$e.
Carcinogens
"amages the "#$ of alveoli cells. /his can lead to them reproducing faster than normal which will cause a tumour to form. /he tumour is the start of cancer.
Car&on +onoxide
$ttaches permanently to haemoglo&in reducing the a&ility of the &lood to carry 8,
Poisons
/he list is endless. /here are over )??? poisonous chemicals in cigarette smoke !e.g. &en0ene arsenic lead cyanide etc%
3ou need to know an experiment that will show the effect of exercise on humans. /he easiest experiment is to take your own heart rate &reathing rate and skin temperature at rest. "o some exercise then take the same measurements again. 3ou7ll find they7ve all increased. /he reason for this is that your rate of respiration has increased !to supply the muscles with extra energy for contraction%. In order to get respiration to happen faster you need more 8, so the &reathing and heart rate increase. Dnfortunately you also release more waste heat energy so your &ody heats up and you might have to start sweating to cool it down again.
h* Trans.ort $ll organisms respire !well nearly all &ut according to your sylla&us they all do%. /herefore all organisms need to excan!e !ases with their environment. Dnicellular organisms< exchange gases directly through their cell mem&rane. /hey can do this &ecause their surface area is large compared to their volume !lar!e SA3*ol ratio%. /hey do not need a circulatory system. 22
Edexcel IGCSE Revision notes
Written by Tim Filtness
+ulticellular organisms< cannot exchange gases directly through their skin. /heir surface area is very small compared to their volume ! small SA3*ol ratio%; therefore they need to have speciali0ed gas exchange organs !e.g. leaf lung and gill% and a circulator" s"stem. Transport in ,lowerin! plants3
Plants have two different networks of tu&es inside them; &loem< transports sucrose and amino acids up and down the stem 6"lem< transports water and minerals up the stem
Phloem and =ylem are arranged in separate &undles ! $ascular #undles% inside the stem. /he xylem is on the inside and the phloem is on the outside . /his arrangement is different in roots !&ut you don7t need to know it% /ransport in the phloem is tricky &ut fortunately not on your sylla&us. It is not the same as transport in the xylem which occurs &y the process of transpiration. Transpiration is te mo$ement of water up a plant> from te roots> trou! te stem and finall" out of te lea$es=
In the Roots< >ater enters root hair cells &y osmosis. /he roots are full of minerals which artificially lower the concentration of water inside the root cells so water is always drawn into them from the soil. /his ena&les transpiration to happen 23
Edexcel IGCSE Revision notes
Written by Tim Filtness
even if the soil is $er" dr". /he roots take the minerals up against the concentration gradient and is therefore an example of acti$e transport.
Roo
t hair cells increase the root7s surface area
In
the Stem<
*. ,. -. .
>ater evaporates out of the top of the xylem /his generates a low pressure at the top of the xylem !a mini vacuum if you like% /his sucks water molecules up the xylem /his is called transpiration pull
Extension !not on sylla&us &ut very interestingN% >ater molecules are slightly charged ! polar%. /he oxygen atom is slightly negative and the hydrogens are slightly positively charged. /his means that water molecules tend to stick to each other. /herefore when transpiration pull sucks at the water molecules in the top of the xylem the entire column of water moves up the xylem not 1ust the molecules at the top4
In the leaf< >ater enters the leaf in xylem vessels in veins !&asically another name for a leaf vascular &undle%. /he water moves &y osmosis into leaf mesophyll cells where it e$aporates into the air spaces and finally diffuses out of the stomata into the air. 'actors affecting the rate of transpiration< ,actor
/emperature !increases transpiration% 2umidity !decreases transpiration%
Effect on transpiration rate
Increasing temperature increases the inetic ener!" of molecules. /his makes diffusion osmosis and evaporation happen faster >hen the air is humid then there is more water vapour in it. 2umid air is less a&le to accept more water molecules &y evaporation. 24
Edexcel IGCSE Revision notes
Written by Tim Filtness
>ind !increases transpiration%
>ind &lows water vapour away from the stoma keeping the concentration gradient high.
(ight intensity !increases transpiration%
(ight causes stoma to open. >ider stoma can allow faster diffusion of water vapour out of the leaf.
3ou need to know an experiment that can show the effect of the a&ove factors on the rate of transpiration. /he &est experiment is a potometer which measures how Guickly a little &u&&le of air moves up a glass tu&e attached to the &ottom of the stem. $dding a fan changing the humidity increasing the temperature etc will all change the speed the &u&&le moves up the tu&e.
>hy do plants need water !why do they &other to transpire%O 5
Dsed in photosynthesis !*?Q%
5
$ solvent for transporting other things !e.g. minerals% !*?Q%
5
Dsed in chemical reactions !)Q%
5
$ site of chemical reactions !)Q%
5
%oolin! te plant (@0)
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Edexcel IGCSE Revision notes
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Transport in /umans3
6lood consists of main parts;
&lasma mostly water used for transportin! things around the &ody !i.e. %O2 !lucose amino acids other products of digestion urea ormones and eat ener!".
ed Blood %ells adapted to carry 8, around the &ody. 8, attaches to aemo!lo#in protein which the R6Cs are filled with. 8ther adaptations of R6Cs include;
5 5 5 5
Smooth edges Biconca$e shape !increases surface area and allows folding% +ade in huge Guantities #o nucleus !so more room for haemoglo&in%
&latelets help clot the &lood. /his stops &lood loss and also prevents microorganisms entering the &ody.
ite Blood %ells are part of the immune system. /here are two main types; macropa!es and l"mpoc"tes. 'acropa!es
!sometimes called Phagoctyes%
5"mpoct"es
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Edexcel IGCSE Revision notes
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/ravel in the &lood. /hey detect foreign &odies !i.e. foreign cells toxins cells infected with virus and cancerous cells% and en!ulf and destro" them.
Stay in the lymph system !you don7t need to know what this is%. /hey make anti#od" proteins in large num&ers. $nti&ody proteins travel in the &lood and stick to foreign o&1ects. /his helps &ecause; *. foreign o&1ects are stuck to each other stopping them spreading ,. +acrophages can engulf many foreign o&1ects at the same time speeding up the killing process
Engulfing and destroying is called pa!oct"osis
Extension !not technically on sylla&us &ut not sureN% Plasma carries C8, around the &ody. 2owO C8, F
2,8
-
2C8-5
F
2F
/he C8, reacts with water molecules to produce the /"dro!en %ar#onate ion. In the lungs the reaction reverses to produce C8 , again. C8, is therefore carried as an aueous ion in the &lood plasma.
Te /uman /eart3
3ou need to know; *. the names of the cam#ers of the heart ,. the names of the , arteries and , $eins attached to the heart -. /he names of the two sets of $al$es in the heart
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Edexcel IGCSE Revision notes
&ena Cava
Written by Tim Filtness
$orta
#ul"onary $rtery
Se"i0
lunar &alve
Cus.i &alve
&ena Cava
%ontraction in te eart3 emem#er> te atria contract first= Te 5 C atria contract at te same time= Te $entricles contract second= Te 5 C *entricles contract at te same time=
*. 6lood enters the atria ,. 6oth atria start to contract pushing the &lood into the ventricles through the open cuspid valves -. >hen the ventricles are full they &egin to contract . /he cuspid valves shut to stop #acflow ). 6lood is forced out of the heart into the circulatory system through the open semi5 lunar valves J. >hen the ventricles finish contracting the S5( valves shut stopping &ackflow. 2!
Edexcel IGCSE Revision notes
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6lood has to pass through the heart twice to complete a full circuit of the &ody !takes a&out *? ,?sec%. /his is called a dou#le circulation. "uring exercise adrenaline is released from the adrenal !lands. $drenaline has two effects of the heart; *. +akes it &eat faster ,. +akes each &eat arder /he com&ined effect is to massi$el" increase the volume of &lood pumped &y the heart per minute. Extension !summari0es point a&ove mathematically % Cardiac 8utput
L
2eart Rate
x
Stroke 9olume
C8 L 9olume of &lood pumped per minute 2R L #o of &eats per minute S9 L 9olume of &lood e1ected per &eat $drenaline increases &oth 2R S9 therefore increasing C8 lots Arter"> *ein and %apillar"3 $rtery<
collagen & connective tissue smooth muscle & elastic tissue lumen (blood)
*. 1-10mm $rteries carry i! pressure #lood awa" from the heart. Key Points< ,. /hick muscle layer to withstand high pressure &lood -. Elastic tissue allows artery to stretch when &lood is forced into it . Protective collagen layer 2"
Edexcel IGCSE Revision notes
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). Round shape J. Relatively small lumen
9ein< collagen & connective tissue smooth muscle & elastic tissue semilunar valve lumen (blood)
*. 1-20mm 9eins carry low pressure #lood towards the heart. Key Points< ,. -. . ). J.
/hin muscle layer !low pressure &lood% 9alve to stop #acflow Protective collagen layer #ot a round shape !wall not thick enough to hold shape% (arge lumen !decreases effect of friction%
Capillary< basement membrane(collagenSmall hole) endothelium cell red blood cell 8 µm
Capillaries are adapted for excan!e they are not connected directly to the heart. Key Points< *. >alls are one cell tic !cells are called endothelial cells% 3#
Edexcel IGCSE Revision notes
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,. (umen is the same width as one R6C !therefore more of R6C in contact with wall therefore smaller diffusion distance% -. #o muscle or elastic tissue . /iny !compare the scales and remind yourself what a @m is% Something extra you7re supposed to know< /he vessel taking &lood to the kidneys is the renal arter" /he vessel taking &lood away from the kidneys is the renal $ein /he vessel taking &lood to the liver is the epatic portal $ein /he vessel taking &lood away from the liver is the epatic $ein /epatic &ortal *einO /he &lood that goes to the liver comes directly from the gut not from te eart therefore it7s not an artery &ut a portal $ein. " does tis appen O It makes sense to send all &lood from the gut directly to the liver &ecause if there are any poisons in what you7ve eaten they get &roken down &y the liver #efore going around the &ody. Cunning ehO
i* E4cretion Excretion3 te remo$al of waste products of meta#olism from li$in! or!anisms Excretion in ,lowerin! plants3
C8, and 8 , are excreted &y leaves via the stomata. 8, is excreted during photosynthesis and C8 , is excreted during respiration Excretion in /umans3
2umans have - main excretory organs; *. (ungs excrete %O2 and /2O ,. Skin excretes /2O -. Kidneys excrete /2O urea excess minerals and other wastes. Extension 5 wat+s urea O !not technically on sylla&us%
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Edexcel IGCSE Revision notes
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>e need to have a certain amount of protein in our diet to supply the amino acids we need to make our own &ody proteins. 2owever we usually eat far more that we need so we must excrete the rest. &ro#lem< when amino acids are &roken down they make ammonia which is very toxic. Solution< the li$er turns the ammonia into urea which is harmless. Terefore urea is a product of te meta#olism of amino acids=
Te :idne"3
/he functional unit of the kidney is the nepron. /here are millions of nephrons in a single kidney.
#ephrons have , 1o&s; Excretion 5 filtering the &lood and reclaiming the Hgood &its Osmore!ulation 5 &alancing the water level of the &ody !water homeostasis%
$ #ephron<
Blomerulus
PC/
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Edexcel IGCSE Revision notes
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2ow the nephron works< *. "irty &lood enters the kidney via the afferent artery ,. /he artery splits up into a &all of capillaries called the glomerulus -. /he &lood is under high pressure so all small su&stances are forced out of the holes in the capillary walls. 8nly large proteins and cells stay &ehind. . /he small su&stances !glucose minerals urea water etc% move into the &owman7s capsule which wraps around the glomerulus
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Edexcel IGCSE Revision notes
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). /he capsule leads into the PC/ which re5a&sor&s all glucose via acti$e transport !i.e. it selectively removes the glucose from the nephron and returns it to the &lood% J. /he PC/ leads to the (oop of 2enl which re5a&sor&s the water my osmosis M. /he (oop leads to the "C/ which re5a&sor&s all minerals amino acids and other Huseful su&stances &y acti$e transport . /he remaining fluid !containing excess water excess minerals and urea% passes into the collecting duct T. /he collecting ducts from other nephrons 1oin and form the ureter which leads to the &ladder *?. /he fluid is now called urine and is stored in the &ladder for excretion **. /he &ladder takes the urine to the outside world via the uretra /his is the first role of the nephron !it7s role in excretion%. Remem&er the nephron has a second role in osmore!ulation. 6lood water levels are sensed &y the "potalamus in the &rain. >hen water levels are too low the hypothalamus tells the pituitar" !land !also in the &rain% to release the hormone $nti5"iuretic 2ormone ! A/% >hen &lood water levels are too low; *. /"potalamus detects ,. &ituitar" gland releases $"2 into &loodstream -. A/ travels all over the &ody . 8nly the cells in the collectin! duct of the nephrons of the kidney have receptors for $"2 so only they respond to the hormone ). /he collecting duct &ecomes more permea#le J. >ater is draw out of the collecting duct &ack into the &lood 34
Edexcel IGCSE Revision notes
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M. >ater levels return to normal >hen water levels are too high exactly the opposite happens !i.e. the pituitary releases less $"2%
5* Coorination an res.onse /omeostasis3 te maintenance of a constant internal en$ironment $ll organisms try and maintain a constant internal environment. /his is called omeostasis. Examples of homeostasis include the regulation of water levels !see a&ove% and the regulation of &ody temperature !see &elow%.
2umans have two systems which carry out homeostasis; er$ous S"stem immediate responses to stimuli !sec 5 hours% Endocrine S"stem long term responses to stimuli !hours 5 months% 6oth systems respond to stimuli !i.e. events that change the internal environment%. 6oth systems have a detector !which detects the stimulus% and an effector which carries out a response to correct the effect of the stimulus. /he message from detector to effector is carried either via an electrical nerve impulse or as a hormone depending which homeostatic system is &eing used. %oordination in /umans3
#erves the #ervous system< /he nervous system consists of the #rain and the spinal cord. Sense organs !e.g. pain receptors in skin or photoreceptors in the eye% are linked to the &rain via ner$es. Stimulation of the sense organs results in an electrical signal !a ner$e impulse% &eing sent along the nerve to the &rain. #erve impulses are very Guick !*,?mAs% allowing rapid responses to the stimulus Some sense organs are not connected directly to the &rain. /his is a defense mechanism allowing almost instant responses to threatening or dangerous stimuli !e.g. pain%. /hese instant responses are controlled &y nerves in the spine rather than the &rain and are called reflexes $ reflex arc< 35
Edexcel IGCSE Revision notes
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*. $ stimulus is detected &y a receptor ,. /he receptor initiates a nerve impulse in the sensor" ner$e -. /he sensory nerve !which runs from the receptor to the spine% passes the message onto an interneurone in the spine . /he interneurone passes the message on the a motor ner$e ). /he motor nerve !which runs from the spine to a muscle in the same lim& as the receptor% passes the message onto the effector muscle J. /he effector muscle carries out the response. /he entire process !stimulus to response% happens in less than a second and does not involve the &rain. /he purpose of the interneurone is to inform the &rain of what has happened. Reflexes in the eye<
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Edexcel IGCSE Revision notes
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Structure
,unction
Cornea
Refracts !&ends% light entering the eye.
Iris
Controls the amount of light entering the eye &y ad1usting the si0e of the pupil.
Pupil
2ole which allows light into the eye.
(ens
$llows fine focusing &y changing shape.
Ciliary muscle
Changes the shape of the lens &y altering the tension on the suspensory ligaments.
Retina
Contains light5sensitive rod and cone cells which convert light energy into a nerve impulse !i.e. transduce energy%.
'ovea
$rea where most light is focused very sensitive to colour !most cones here%.
8ptic nerve
/ransmits nerve impulses to the &rain where they are interpreted.
Sclera
Choroid
8uter protective layer of eye Contains &lood vessels
(ight is detected &y potoreceptors in the eye. /hese receptors form the retina !the inner lining of the eye%. /here are two types of photoreceptor; 3
Edexcel IGCSE Revision notes
5 5
Written by Tim Filtness
ods which see only in &lack white %ones which see in either red &lue or green !- types of cone%
/here are two types of reflex you need to know a&out in the eye; *. Responding to different light levels ,. 'ocusing the eye Responding to different light levels< In the dar *. Photoreceptors detect ,. Reflex occurs -. +uscles in the Iris are the effectors 5 adial muscles in Iris contract 5 %irculator" muscles in Iris relax . Pupil diameter opens ). +ore light enters the eye
In the li!t J. Photoreceptors detect M. Reflex occurs . +uscles in the Iris are the effectors 5 adial muscles in Iris relax 5 %irculator" muscles in Iris contract T. Pupil diameter closes *?. (ess light enters the eye
'ocusing the eye<
,ar 8&1ect
ear 8&1ect
3!
Edexcel IGCSE Revision notes
Written by Tim Filtness
*. Incoming light is parallel ,. %iliar" muscles relax
). J. M. . T.
-. Suspensor" li!aments are tight . (ens is pulled tin ). (ight is refracted less
Incoming light is di$er!ent %iliar" muscles contract Suspensor" li!aments are loose (ens &ecomes fat (ight is refracted more
(ight converges on the retina
(ight converges on the retina
Controlling Skin temperature< /oo ot >hen you are hot the following !controlled &y reflexes%;
/oo cold happen >hen you are cold the following happen !controlled &y reflexes%;
*. 2airs on skin lie flat !less insulatin! air trapped%
,. Sweatin! starts -. 6lood is diverted close to the surface of the skin !more heat radiation %
*. 2airs on skin stand up !more insulatin! air trapped% ,. Sweatin! stops -. Si$erin! starts so muscles respire more producing more heat . 6lood is diverted away from the surface of the skin !less heat radiation%
/ow is #lood di$ertedD
$rterioles in the skin can open and close in response to nerve messages. *asoconstriction arteriole closes
3"
Vasodilation 6 arteriole o.ens
Edexcel IGCSE Revision notes
Written by Tim Filtness
vasoconstriction
vasoilation
vasodilation vasoconstriction
Te net effect is to open arterioles under te surface of te sin wen ot and close tem wen cold=
Random 2ormones you need to know< /ormone Source
Effect
$"2
Pituitary
Regulated &lood osmolarity !see a&ove%
$drenaline
$drenal glands
Increases heart rate and &reathing rate during exercise !more 8, for respiration%
Insulin
Pancreas
"ecreases &lood glucose level after a meal
/estosterone
/estes
/riggers pu&erty in &oys !see next section%
Progesterone
8varies
+aintains uterus menstruation
8estrogen
8varies
/riggers pu&erty in girls !see next section% Stimulates growth of uterus lining each month and !indirectly% causes o$ulation
lining and !indirectly% causes
It mi!t #e wort "our wile looin! tese up in more detail %oordination in ,lowerin! plants3
4#
Edexcel IGCSE Revision notes
Written by Tim Filtness
Plants also respond to stimuli. $s plants don7t have nerves their responses are limited to hormones only. Plants respond to the following stimuli 5
-ra$it" . Roots grow towards gravitational pull and stems grow away. /his is -eotropism.
5
ater. Roots grow towards water. /his is /"drotropism.
5
5i!t. Shoots grow towards light. /his is &ototropism.
Phototropism is controlled &y hormones released &y the !rowin! tip of the shoot. 8nly the tip makes the hormone. If you remove the tip the shoot stops growing. /he hormone made &y the tip is called Auxin. 3ou need to know an experiment that demonstrates Beotropism. /he &est example is to grow a runner &ean seed in a 1am 1ar. (et the root start to grow downwards then rotate the seed T?3. /he root will then start growing at T? 3 to its original direction. $ more advanced !and less practical% experiment that shows geotropism is that seeds germinating inside spacecraft have roots that grow randomly4 3ou also need to know an experiment that demonstrates Phototropism. /he &est example is to repeat the example a&ove &ut look at the growth of the shoot4
Section 7: Re.rouction an inheritance a* Re.rouction /here are two types of reproduction;
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Edexcel IGCSE Revision notes
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Sexual < reproduction in which two !ametes !sex cells% fuse to create a new offspring that is !eneticall" different to the parents. /wo parents are involved. Asexual < reproduction witout fusion of gametes. It involves one parent only and produces offspring that are !eneticall" identical to the parent. Two definitions to learn3 ,ertili9ation< the process in which a male and a female gamete fuse to form a 0ygote F"!ote< a cell that is the result of fertili0ation. It will divide &y mitosis to form an em#r"o. eproduction in ,lowerin! plants3
Part
'unction
Petal
Colourful part of the flower. $ttracts insects in insect5 pollinated plants
$nther
+ale part of the plant. +akes pollen.
'ilament
oins the anther to the rest of the flower.
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Edexcel IGCSE Revision notes
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Stigma
'emale part of the plant. Receives pollen.
8vary
Contains the ovules
8vule
Eggs female gametes
Pollen
+ale gamete
#ectary
+akes nectar to attract insects in insect5pollinated plants
Sepal
Protects the flower when it is in &ud ind &ollinated
5 5
Pollen made in huge Guantities #o nectary Insect &ollinated
5
$nthers are large and outside
5
the flower 5
Stigma is large and outside the flower
5
/iny colourless petals
5 5 5
$nthers are small and inside the flower Stigma is small and inside the flower (arge colourful petals 2as a nectary
&ollination< the deposition of pollen from the anther of one flower onto the stigma of a different flower of the same species.
>hen pollination occurs the pollen grows a pollen tu#e down the stigma of the flower. /he pollen tu&e carries the nucleus of the pollen into the ovary where it fuses with an o$ule !fertilisation%.
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Edexcel IGCSE Revision notes
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>hen fertili0ation has happen the flower will change in the following ways; *. Petals die and fall away ,. 'ertili0ed ovule turns into a seed -. 8vary may fill with sugars and turn into a fruit In order to !erminate !grow into a new plant% seeds need the following conditions; 5 5 5
Presence of water Presence of 8, !seed needs to respire% Correct temperature !recall en0ymes work at optimum temp% >hen a seed germinates the cells inside it start to grow rapidly and form the new shoot and root. /he seed contains a limited store of car#o"drate and lipid which it uses as a fuel for respiration to provide the energy for growth. "uring this stage the seed must produce leaves so it can &egin to photosynthesi0e. /he danger is that the seed will run out of stored energy &efore it makes leaves. If this happens it will die. Plants can also reproduce asexually; atural methods
Artificial methods
unners a root from one plant grows a %uttin!s a &ranch from one plant is separate shoot which grows into a new removed and planted in soil. It will grow new roots and &ecome a new plant. plant. Eventually the original root
connecting the two
plants &reaks down
See also !raftin! !not mentioned on sylla&us%
separating the plants See also ri9omes corms #ul#s and tu#ers !not mentioned on sylla&us% 44
eproduction in /umans3
+ale reproductive System<
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Edexcel IGCSE Revision notes
'emale system<
Written by Tim Filtness
reproductive
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Edexcel IGCSE Revision notes
Written by Tim Filtness
Pregnancy< >hen the egg and sperm fuse !fertilisation% the resulting 9"!ote &egins to divide &y mitosis !see next section% and &ecomes an em#r"o. /he em&ryo Guickly develops a placenta which &rings the mother7s &lood supply very close to the foetus7 &lood supply. /he two &lood streams ne$er mix !otherwise the mother7s white &lood cells would attack the foetus4% &ut they are close enough for diffusion to occur "iffuse from foetus to mother 5 C8 , water urea "iffuse from mother to foetus5 8 , glucose amino acids minerals /he placenta is adapted for diffusion in much the same way as other exchange organs i.e. it has; 5 5 5 5
2uge surface area !it has lots of villi5like pro1ections% 8nly a few cells thick 6lood supplies keep the concentration gradients high Counter5current system !this one7s an $5level ideaN look it upO4% $s well as the placenta the em&ryo also develops an amnion !mem&rane sac which fills up with amniotic fluid%. /his helps cushion the em&ryo and protects it. Reproductive 2ormones< "uring pu&erty &oys make testosterone in their testes and girls make oestro!en in their o$aries. Testosterone3
5 5 5 5 5
Causes testes to drop penis to enlarge /riggers spermatogenesis !sperm manufacture% Causes growth of pu&ic and &ody hair Causes larynx to enlarge !voice deepens% Causes muscles to grow
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Edexcel IGCSE Revision notes
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Oestro!en3
5 5 5 5 5
/riggers menstruation to &egin Causes maturation of vagina Causes &reasts to grow Causes growth of pu&ic and &ody hair Causes hips to widen 'S2 no longer inhi&ited. +enstrual Cycle<
Causes the endometrium !uterus lining% to grow.
'S2 +ade &y the
Oestro!en
pituitar" .
Causes the ova !egg% to
&ro!esterone (2
Inhi&its the release of
+ade &y the '2S !so no more eggs instead of 'S2
ripen inside a follicle in ripen% the ovary.
pituitary
Causes the egg to &e released !o$ulation% on "ay *
8va starts to release oestrogen as it ripens
B=
Period Corpus luteum dies. Progesterone levels fall Endometrium is no longer maintained and it falls away !this is a
3ou only need to know a&out Oestro!en &ro!esterone
8vulation Egg is released into the fallopian tu#e where it stands the &est chance of &eing fertilised
period%
Corpus (uteum +aintains endometrium. /he empty follicle turns Inhi&its 'S2 release into a corpus luteum !don7t want an egg which starts to make released as there is progesterone already one waiting4%
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Edexcel IGCSE Revision notes
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b* Inheritance /he nucleus of every cell contains A. "#$ is a !enetic code. Each instruction in the code is called a !ene. Each gene tells the cell how to make a specific protein. /he proteins are what control the cell !e.g. en0ymes are proteins so are structural proteins like collagen%. Sometimes more than one version of a gene occur. /he different versions are called alleles !i.e. we all have the gene for iris pigment &ut there are different colours of iris pigment same gene &ut different alleles% "#$ is a very long molecule. /o stop it from &reaking it is coiled up inside the nucleus. /he coiled up "#$ forms a cromosome. 2umans have ,- different chromosomes inside their cells. >e have two copies of each chromosome therefore each cells contains J chromosomes. /he aploid num#er is the num&er of different chromosomes !i.e. ,-% and the diploid num#er is the total num&er of chromosomes in the cell !i.e. J% Key >ord Summary< Tis topic> more tan an" oter> confuses people= 5earn tese torou!l"? A< $ genetic code -ene< 8ne instruction in the code telling a cell how to make a specific protein Allele< $ different version of a gene %romosome< Coiled up "#$ /aploid num#er< the num&er of different chromosomes in a cell !,-% iploid num#er< the total num#er of chromosomes in a cell !J%
Cell "ivision< /here are two types of cell division; 5 5
'itosis used for growth repair asexual reproduction 'eiosis used to produce gametes for sexual reproduction 4!
Edexcel IGCSE Revision notes
Written by Tim Filtness
'itosis
'eiosis
*. Produces 2 dau!ter cells
*. Produces 4 !ametes
,. "aughter cells are diploid !i.e. only
,. "aughter cells are aploid !i.e. have ,- pairs of chromosomes%
have ,- chromosomes% -. "aughter cells are !eneticall" identical to each other
. "aughter cells are !eneticall" identical to parent cell
-. Bametes are !eneticall" different to each other . Bametes are !eneticall" different to parent cell
). 8ccurs in one stage ). 8ccurs in two stages J. 2appens e$er"were in the &ody J. 2appens in reproducti$e or!ans only Haploid Gamete
23
23
Haploid Gamete
Fertilisation
46
Dipl oid Zygote
/herefore fertili0ation produces a diploid cell !which will grow &y mitosis% from two haploid gametes.
Each parent gives only one of each of the pairs of chromosomes to their gametes. $ pair of chromosomes will have exactly the same genes on them &ut not necessarily the same alleles4 /his is the source of genetic variation in gametes. $lleles for the same gene can &e; 5
ominant always affect the penot"pe !allele represented with capital letter% 4"
Edexcel IGCSE Revision notes
Written by Tim Filtness
5
e cess ece ssi$ i$e e never affect the phenotype in the presence of a dominant allele !allele represented with lower case letter%
5
%o .dom %o.d omin inan antt affect the phenotype eGually in the presence of another co5dominant allele !&oth alleles have capital letters%
Inheritance< Inheritance patterns are always given using a !enetic dia!ram. If this comes up you get loads of marks for it &ut only if you use the genetic diagram4 $ -enetic ia!ram
$
%
Parents7 Phenotype< Phenotype<
6rown eyes
6rown eyes
Parents7 Benotype<
6&
6&
Bametes<
6
'* Benotype<
6
&
6&
&&
6 66
&
6
&
6& &
'* Phenotype<
- < * 6rown eyes < &lue eyes ote te !ametes are alwa"s put in circles
+ore Key >ords< &enot"pe < physical appearance -enot"pe< the com&ination of alleles an individual possesses /etero9"!ous< two different alleles in genotype !i.e. 6 &% /omo9"!ous< &oth alleles the same in genotype !i.e. 6 6 or & &% 5#
Edexcel IGCSE Revision notes
Written by Tim Filtness
Inheritance of gender is governed &y the ,- rd chromosome. 6oys have an = and a 3 girls have two = chromosomes $ -enetic ia!ram
$
%
Parents7 Phenotype< Phenotype<
+other
'ather
Parents7 Benotype<
==
=3
Bametes<
=
'* Benotype<
=
=
==
==
3
=3
=3
'* Phenotype<
,<, L *<*
=
=
3
=
6oy < Birl
ote te !ender of te #a#" is determined #" te sperm?
9ariation< *ariation within a species is produced &y two factors
*. /he /he envi enviro ronm nmen entt ,. /he /he geno genoty type pe.. #ew alleles arise in the population through mutation 'utation 5 a rare random change in the genetic code of a gene. /he mutated gene will therefore produce a slightly different protein to the original non5mutant gene. /he new protein might; *. >ork >ork 1ust 1ust as as well well as as it did &efore &efore !neutral mutation% ,. >ork >ork &et &ette terr than than &ef &efor oree !#eneficial mutation% -. >ork >ork wor worse se A not not at all all !armful mutation%
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Edexcel IGCSE Revision notes
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6enefici 6eneficial al mutations mutations give a selecti$e ad$anta!e to the individual. Individuals with this kind of mutated allele are more likely to survive reproduce and pass their alleles on. /his is the &asis of atural Selection #atural Selection< "arwin came up with this theory. "arwin7s *st 8&servation< "arwin7s ,nd 8&servation<
#ot all individuals survive /here is variation in a species
"arwin7s Conclusion< /he &etter adapted individuals survive !the H fittest % and reproduce passing their alleles onto the next generation. 8ver time this process leads to e$olution. E$olution< the formation of a new species from an original species
+utations can &e inherited or happen on their own. /he freGuency that mutation occurs naturally can &e increased &y exposure to radiation !e.g. gamma rays =5rays and ultraviolet rays% and some chemical muta!ens !e.g. chemicals in to&acco%.
Section 8: Ecology an the environ"ent environ"ent a* The organis" in the environ"ent +ore lovely definitions for you to learn4 &opulation < all the individuals of a particular species within a defined area %ommunit"< a group of different populations living in the same area /a#itat < the physical chemical and &iological environment in which an organism lives Ecos"stem< a community of living things and the environment in which they live 52
Edexcel IGCSE Revision notes
Written by Tim Filtness
Uuadrat
2ow it is used
$ Guadrat can &e used to calculate the total population of a species !e.g. snails%. Simply count the num&er of individuals in the Guadrat. /his techniGue only works for large organisms which can &e distinguished as individuals !not always easy for plants e.g. grass4%
$ Guadrat can &e used to calculate the percenta!e co$er of a species !e.g. moss%. /he Guadrat is divided into *?? smaller sGuares. /he percentage cover of the Guadrat is simply the num&er of sGuares filled with the species.
$ Guadrat can &e used to calculate the percenta!e freuenc" of a species !e.g. daisies in a field%. /he Guadrat is divided into *?? smaller sGuares. 3ou simply count a * for each sGuare the species is in and a ? for those where it is a&sent. /his gives you an indication of the freGuency of the species it does not tell you the total population. 53
In ecology we usually need to sample !this is &ecause it is not practical to count all of the species we7re interested in e.g. one cannot count all of the grass plants in a field4%. Ecologists use uadrats to sample from. Uuadrats can &e any si0e you like !e.g. )km &y )km sampling 0e&ra heards in $frica or )cm &y )cm sampling lichen on a tree% &ut there are - different methods of using a Guadrat. 3ou need to &e a&le to explain how you would use Guadrats to find out information a&out specific species in their ha&itat.
b* %eeing relationshi.s 'ood chains are used to show the relationships &etween species in a ha&itat. E.g. 'ox /he secondar" %onsumer !eats the Primary Consumer% Rabbit
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Edexcel IGCSE Revision notes
Written by Tim Filtness
/he &rimar" %onsumer !eats the producer%
Brass
/he &rimar" &roducer !all food chains start with this%
Each level in a food chain is called a Tropic 5e$el 'ood chains can &e &uilt up into complex food we#s. /he difference &etween food chains and food we&s is that food we&s have #rances chains never do. $ &"ramid of um#ers %o4es Rabbits Grass
/his shows the populations !to scale% of the species in the chain Sometimes a Pyramid of num&ers can &e inverted !i.e. have a tiny &ase%. /his occurs if there is a parasitic relationsip in the food chain i.e. one tree &ut many caterpillars eating the leaves4 /o stop this a pyramid of &iomass is more freGuently used. /his always has a pyramidal shape. $ &"ramid of Biomass Bats Cater.illars Tree
Biomass the mass of the organic material an organism is made from !i.e. dry it out totally and weigh it water doesn7t count4%
>e can also represent the energy flow in a food chain using a &"ramid of Ener!" Transfer. $ &"ramid of Ener!" Transfer
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Edexcel IGCSE Revision notes
Written by Tim Filtness
%o4
Rabbits Grass The Sun
/his gives an indication of the huge amount of ener!" that is not passed on to the next trophic level. /his is &ecause at each level energy is wasted on; 5 5 5
Respiration !most of it as waste heat% Dndigested A egested food Dsed in movement
c* Cycles 9ithin ecosyste"s Edexcel IGCSE Revision notes /he >ater Cycle<
Key ideas E$aporation %ondensation &recipitation Transpiration !rather unhelpfully not shown on this diagram%
/he Car&on Cycle<
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Edexcel IGCSE Revision notes
Written by Tim Filtness
Key ideas espiration &otos"ntesis ecomposition %om#ustion /he #itrogen Cycle<
#itrogen in air !, !as%
"enitrifying 6acteria
#itrogen5'ixing 6acteria
#itrogen in soil
"ecomposition
#itrogen in
!Ammonium < /G%
!&acteria F fungi%
animals !protein%
#itrifying 6acteria
$ssimilation
#itrogen in soil
$ctive
#itrogen in plants
!itrate < O-.%
/ransport
!protein%
/his is not particularly easy to understand. 3ou need to know the roles of all the different &acteria. /here are ; 56
Edexcel IGCSE Revision notes
Written by Tim Filtness
5
ecomposers turn nitrogen in protein into ammonium !#2 F%
5
enitrif"in! Bacteria turn ammonium !#2F% into #,
5
itrif"in! #acteria turn ammonium !#2F% into nitrate !#8-5%
5
itro!en.fixin! #acteria turn #, into ammonium !#2F%
Extension 5 le!uminous plants !not technically on sylla&us% $ll of the a&ove &acteria are naturally present in the soil. /he only exception to this is that some #itrogen5fixing &acteria !e.g. Rhi0o&ium% live in the roots of some plants. /hese plants are called le!umes !e.g. peas clover etc%. /hey have a s"m#iotic relationship with the &acteria i.e. &oth the &acteria and the plant &enefit from working together.
* u"an in;uence on the environ"ent 3ou need to know a&out the following environmental pro&lems; 5 5 5 5
$cid rain Breenhouse effect Eutrophication "eforestation
$cid rain< S8, C8, and #8x !oxides of nitrogen% dissolve in rain to form Sulphuric $cid Car&onic $cid and #itric $cid. /his falls as acid rain which destroys soil pollutes waterways and causes erosion Breenhouse Effect<
5
Edexcel IGCSE Revision notes
Written by Tim Filtness
Incoming radiation passes through the atmosphere and hits the Earth where it is a#sor#ed. /he Earth re.emits the radiation as longer5wavelength Infra5Red radiation. /his is the pro&lem. IR radiation is a&sor&ed &y !reenouse !ases on its way out of the atmosphere. /his traps the heat in the atmosphere. /he greenhouse gases are< water $apour %O2 O6 metane and %,%s Breenhouse Bas Source >ater 9apour
2umans haven7t had much effect on this its a naturally occurring greenhouse gas
C8 ,
Released from &urning fossil fuels
#8 =
Released from &urning fossil fuels
+ethane
Produced &y cows !yes cow farts% and rice paddy fields. $s agriculture &ecomes more and more intensive methane emissions rise
C'Cs
Dsed to &e used as coolant in fridges and propellant in aerosols. #ow &anned &ut there are still lots of old fridges in scrap yards leaking C'Cs
/he theory goes that the !reenouse effect is causing !lo#al warmin! which is &ad. Blo&al warming might cause; 5 5 5 5 5
Polar ice cap melting Sea levels rising Extinction of species living in cold climates Changes in rainfall !&oth droughts and flooding% Changes in species distri&ution !i.e. tropical species spreading like mosGuitoes% 5!
Edexcel IGCSE Revision notes
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Eutrophication< *. itrate enters a waterway ! sewa!e or fertili9er run.off% ,. #itrate causes al!al #loom -. $lgae &lock out light for plants living on the waterway &ed . /hese plants respire as they can7t photosynthesi0e ). 8, levels fall J. 'ish die M. "ead fish are decomposed &y &acteria which themselves respire using up more 8, . p2 levels fall as decomposition produces acids T. Everything dies. >aterway is incapa&le of supporting life "eforestation< Cutting down trees and not replacing them is &ad. It causes; 5 5 5 5 5 5
(eaching of soil minerals Soil erosion !no roots holding soil together% "esertion !new deserts forming% "istur&ance of the water cycle !less transpiration can lead to flooding and A or drought% Increase in C8, levels "ecrease in 8, production
O$er.fisin! and o$er.!ra9in! can cause food chains to collapse.
Section <: The use o! Biological resources a* %oo .rouction 5"
Edexcel IGCSE Revision notes
Written by Tim Filtness
,ood &roduction usin! %rop plants3 -reenouses and pol"tene tunnels raise the temperature !&y the greenhouse effectN guess why it7s called that% which increases the rate of photosynthesis which increases crop "ield ;ield 5 /he total mass of the edi&le part of crop
If the level of C8, in the greenhouse is increased the yield will further increase !remem&er C8, is a limiting factor in pAs% If fertili0ers are added !specifically those that contain &otasium itrate and &ospate :& fertilisers% then the yield will increase even more4 &otassium essential for plant mem&ranes itrate essential for making plant proteins &ospate essential for "#$ and mem&ranes
Pest Control can also &e used to increase 3ield. /his can &e done either using pesticides or &iological controls. &esticide a chemical that kills pests !anything that eats your crop% &ut does not harm the crop plant Biolo!ical control introducing a &iological organism which will eat the pest &ut not the crop plant !e.g. &irds are sometimes encouraged inside greenhouses &ecause they eat caterpillars% ,ood &roduction usin! 'icroor!anisms3
3east< Remem&er that "east are capa&le of respiring aero#icall" !producing C8, and water% and anaero#icall" !producing C8, and ethanol%. 3east are therefore used in the &rewing industry. In order to make &eer #arle" seeds are allowed to germinate &y soaking the &arley seeds in warm water. /his is called maltin!. /he germinating &arley seeds &reak down their car&ohydrate stores releasing sugar. $fter a couple of days the &arley seeds are gently 6#
Edexcel IGCSE Revision notes
Written by Tim Filtness
roasted !which kills them% and put into a fermenter with yeast. /he yeast use the sugar for anaero#ic respiration and produce &eer. 3ou need to know an experiment that shows the production of C8 , &y yeast in different conditions. /he &est example is to mix a yeast suspension with a sucrose solution and place in a &oiling tu&e with a delivery tu&e attached. $ny C8 , produced can &e collected over water or &u&&led through lime water. (acto&acillus< (acto&acillus &acterium is /his &acterium is used to turn milk into yoghurt. It uses lactose sugar in the milk to produce lactic acid &y anaero#ic respiration . /he lactic acid affects the milk proteins making the yoghurt curdle !go solid% and giving it the characteristic tart taste. $ 'ermenter<
Important details< %oolin! Hacet keeps the microorganisms at optimum temperature. /hey will produce lots of heat through respiration therefore need to &e cooled4 &addles keep stirring the mixture. /his stops waste products from &uilding up and keeps the air evenly mixed utrient medium supplies the microorganisms with fuel for respiration 61
Edexcel IGCSE Revision notes
Written by Tim Filtness
Sterile Air suppl" supplies clean 8, for respiration !note< this is not reGuired in anaero&ic fermentation processes% ata.lo!!er monitors temperature and p2 keeps the fermenter at optimum conditions ;ou don+t need to #e a#le to draw tis out> #ut "ou could #e ased to la#el a dia!ram of a fermenter or #e ased to explain te function of te $arious parts of a fermenter=
,ood &roduction usin! ,is ,armin!3
'ish are farmed in fis farms &ecause they are a good source of protein. 'ish farms keep lots of fish in very small tanks to minimi0e space reGuirements. /o stop the fish fighting with each other these precautions are taken; 5
"ifferent fish species are kept in separate tanks. /his stops competition #etween species of fish ! intraspecific competition %
5
'ish of different genders are kept separately !unless they are &eing &red%
5
'ish of different ages are kept separately. /his stops competition &etween fish of the same species !interspecific competition%
$s with the fermentation the Guality of the water is closely monitored and the fish are continuously supplied with fresh sterile water so that wastes are washed out constantly. /he fish are kept in sterile water to limit disease which would spread very Guickly in the cramped ponds. /he fish are often over5fed or fed with protein.ric food. Sometimes ormones are added to the water to speed !rowt. In addition to this only the &iggest and most healthy fish are allowed to &reed. /his is an example of selecti$e #reedin!.
b* Selective Breeing Selecti$e Breedin! individuals with desired characteristics are &red together to produce offspring which express &oth desired characteristics.
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Edexcel IGCSE Revision notes
Written by Tim Filtness
Examples of this are< increased yield and reduction of stem length in weat and increased yield of meat and milk in cattle .
c* Genetic Moi=cation Genetic engineering* /he structure of "#$<
"#$ is a dou#le.stranded molecule. /he strands coil up to form a dou#le.elix. /he strands are linked &y a series of paired #ases. T"mine !/% pairs with Adenine !$% -uanine !B% pairs with %"tosine !C%
/he &ases are a crucial part of "#$. /he seGuence of &ases is what created the !enetic code4 Process of genetic engineering< Te example "ou need to now is te creation of E coli #acteria tat maes uman insulin= 2owever a more fun example is $l&a the glow5in5the5dark &unny that makes the protein luminol !taken from a 1ellyfish4% 63
Edexcel IGCSE Revision notes
Written by Tim Filtness
*. Extract target gene !human insulin gene% from /his is done &y cutting the gene out of human "#$ restriction en9"me
donor using
cell. a
,. Cut open the &acterial "#$ also using the restriction en9"me -. Insert the gene and Hstitch the "#$ together using A 5i!ase en0yme . Bet the new "#$ into the &acterium. /his is done using a $ector Common vectors include *iruses and &lasmids ow "our trans!enic #acterium is complete= All "ou need to do is !row it in a fermenter and it maes lots of insulin for "ou? Trans!enic Or!anism 8rganism containing "#$ from two or more sources !i.e. an organism that7s &een genetically engineered to express a foreign gene%
Scientists are experimenting with genetic engineering all the time. Plants are good to genetically engineer &ecause they are more simple and there are fewer ethical issues. Benetically modified !B+% crops are engineered to; 5 5 5 5 5 5 5 5 5
2ave &igger yields 6e frost resistant !e.g. frost resistant straw&erries% 2ave resistance to disease Brow in harsher environments !e.g. drought5resistant rice% 2ave vitamins in them that they would not normally have !e.g. golden corn% 2ave a longer sell5&y date !e.g. non5sGuash tomatoes% 6e a different colour A taste to normal !e.g. chocolate carrots% 2ave stronger taste !e.g. chilis% 6e easier to eat !e.g. easy5peel oranges%
* Cloning
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