Biology Unit 2

  • Created by: Rosa
  • Created on: 23-05-13 14:22

7.1 Investigating Variation

  • Intrespecific Variation = one species differs from another   
  • Intraspecific Variation = members of the same species but differ from eachother     

 Measurements are takne by sampling (individuals selected to represent whole of organisms)however can cause problems as maybe sampling bias as selection choice is biased such as buttercups not as likley to be sampled from a muddy area compared to a dry area and also another problem is chance as just by luck the 50 buttercups may be the tallest in the while population- best way is random sampling , divide area in to grids random numbers and then use those co-ordinates.To reduce chance we can use a large sample size as instead of 50 can use 500 - lower probability of being taller than average - greater sample size more reliable 

Causes of Variation-Genetic Differences arise from a result of :     

Mutations - sudden change of genes and chromosomes may , or may not be passed on to next generation     

Meiosis - this nuclear division forms gametes - mixes up genetic material     

Fusion of Gametes - inherit characteristics from each parent - which gamete fuses with which at fertilisatiob is a random proccess so more variety    

Environmental Influences - for instance buttercup may have genes to grow tall however if seed germinated in an environment with poor light or low soil nitrogen will not grow properly- Climatic conditions, soil conditions , pH , food avalibility- normally varation is due to genetic and environmental influences 

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7.2 Mean and Standard Variation

Mean = the measurment at the maximum height of the curve - it provides and average value and good information when comparing one sample to another - however does not provide information about the range of values in it.

Standard deviation = measurement of the width of the curve - gives an indication of range of values ether side of the mean- its the distance from the mean to the point where the curve changes from being convex to concave 

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8.1 Structure of DNA

DNA is made up of 3 basic components to combine to form a nucleotide:  a sugar called deoxyribose  a phosphate group  an organic base (a) single -ring bases - Cytosine (C) and thymine (T) or b) a double-ring bases adenine (A) and guanine (G)) The three groups combine due to condensation reactions to give a nucleotide (mononucletoide).

The mononuclrotide may combine as a result of a condensation reaction between deoxyribose of one and phosphate group of another - DINUCLEOTIDE- the contiunued joining of mononucleotides form POLYNUCLEOTIDE

DNA is made up of two strands of nucloetides (polynucleotides) - extremely long and joined by hydrogen bonds formed between certain bases  Organic Bases , those with double-ring structure (A &G) have longer molecules than those with a sing ring structure (C &T) - rungs of DNA ladder must be same length - SO ADENINE ALWAYS PAIRS WITH THYMINE BY 2 HYDROGEN BONDS , GUANINE ALWAYS PAIRS WITH CYTOSINE BY 3 HYDROGEN BONDS ( PAIRS COMPLEMENTARY TO EACHOTHER)- (ratio of adennine to thymine to guanine to cystonine varys from species to species)

DNA is responsible for passing genertic material from cell to cell and generation to generation (much variety of sequences along length of DNA) DNA is adapted to carry out function as its very stable and pass from generation to gerneration without change , large molecule so can carry big amount og genetic info - seperate strands joined by hydrogen bonds which allow to seperate during DNA replication and protein synthesis. 

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8.2 The triplet code

What is a gene? They are sections of DNA containing coded information for making polypetides - polypetides combine to make proteins . Enzymes are proteins and control chemical reactions for organisms development and activities - so genes control this

The triplet code - in trying to discover how DNA bases coded for amino acids , scientists suggest their must be a minimum of 3 bases that coded for each amino acid.The reasoning: only 20 amino acisds regulary occur in proteins  each amino acid must have its own code of bases on the DNA only 4 different bases (A,T,G,C) are present in DNA If each base coded for a different amino acid , only 4 amino acids could be coded for 3 bases produce 64 different codes - more than enough to satisfy requirements for 20 amino acids- some amino acids have more than one code

Introns are wherre much of the nuclear DNA does not code for amino acids   

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8.3 DNA & Chromosomes

In eukaryotic cells , DNA molecules are larger and form a line rather than a circle and occur in association with proteins to form stuctures such called CHROMOSOMES

Chromosome Structure - only visible when cell is dividing , appear as 2 threads joined at a single point (centremoere). , each thread is called a chromatid. DNA in chromosomes are held in position by proteins - much DNA is found in each cell and is highly coiled. DNA double helix is wound around around proteins so it fixes into posoitin , the DNA-protein complex is then coiled , it is looped and the further coiled before being packed into chromosome.

Chromosome numbers vary as in humans theres 46 and in potato plants 48.  A homologous pair of chromosomes occur in pairs such as humans one from mother (egg) other from father (sperm) , and the total number of chromoes is referred to as the DIPLOID number - humans = 46. A homologous pair is always 2 chromosomes that determine the same genetic characteritstics BUT this does not mean identical

What is an allele? - each gene exists in 2 (sometimes more) forms - each of these forms is called an allele - each individual recieves one allele from each parent - 2 alleles maybe the same or different - each allele will code for a polypeptide - if base sequence of allele is different it will result in a different sequence of amino acids being coded for , mean different production of polypeptide and hence a different protein - may not function properly-enzyme may have different shape - may not fit to enzyme substrate - may not function and there are serious consequences

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8.4 Meiosis and Genetic Variation

Division of cell involves firstly division of nucleus and then whole cell -

Meiosis division produces 4 daughter nuclei , each with half the number of chromosmes as the parent cell.  In order to maintain a constant number of chromosmes in the adult species , the number of chromosomes must be halved at some stage in the life cycle - MEIOSIS - during meiosis the chromosome pairs seperate so that only one chromosome from each pair enters each gamemte - known as the HAPLOID number of chromosomes which in humans in 23.

Proccess of Meiosis  1st division of meiosis, the homolgus chromosoems pair up and their chromatids wrap around each other  (equivalent portions of these chromatids may be exchanges in a process called crossing over) - by the end thought the homolgus pair have seperated , with one chromosone from each pair (made up of two chains)  going into one of the 2 daughter cells

In second division the chromatids move apart , and at the end four cells have been formed  Meiosis produces genetic variation among the offspring , allowing an organism to adapt and survive in a changing world - TEXT BOOOOOK!

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9.1 Genetic Diversity

All members of the same species have the same genes , however organisms differ in the alleles they posses - the combination of alleles they posses make species different from one another - greater number of different alleles that all members of a species posses , the greater genetic diveristy of that species , more likley to adapt to some environmental change - as wider range of alleles and therefore wider range of characeristics

Selective Breeding/Artificial selection  - identifying individuals with the desired characteristics and using them to parent the next generation  (offspring with not desored characteristics are killed/not allowed to breed) - variety of alleles in population DELIBRATLEY restricted to small desired alleles - leads to desired qualities in population , but reduced genetic diversity. Selective breeding usd to produce high yielding breeds of domesticated animals and plants (resisance to disease)

The Founder effect = just a few individuals from an area colonise a nw region or area - cary only a small fraction of alleles - new pop. show less genetic diversity than the population from which thy came e,g, new volcanic islands rise out the sea

Genetic Bottlenecks - populations of species from time to time suffer a dramatic drop in numbrs - e.g. such a volcanic eruption - few survivors posses a much smaller variety of alleles than orginial population - genetic diversity will be less - when they breed genetic diversity of population will remain restricted- e.g. elephant seals - hunted only 20 remained - less gentic variety 

Ethical Implications - animals have rights , whos features should be selected for who and who decides, should be allowed to slec just beacuse their desirable , less genetic variability lose some alleles forever that might bnefit animals in the future

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10.1 The Variety of Life / Haemoglobin

Haemoglobin are a group of chemically similar molecules found in a wide of variety of organisms , the strucutre is made up of:

  • primary structure - four poly-peptide chains
  • secondary structure - each polypeptide chains is coiled into a hlix
  • tertiary structure - polypeptide chain is folded into a precise shape- ability to carry oxygen
  • quaternary structure  - 4 polypeptide chains are linked together to form a spehrical molecule- each polypeptide is associated with a haem group - which contains a ferrous ion. Each ferrour ion can combine with an oxygen molecule to make a total of 4 O2 molecules that can be carried by a single haemoglobin molecules in humans

The role of haemoglobin is to transport oxygen , to be efficent the haemoglobin must readily associate with o2 at the surface where has exchange takes place and readily disassociate from oxygen at those tissues requiring it - hey contradict eachother but are a propert of hamroglobin- it can change the amount of o2 undr different conditions (its shape changes in presence of certain substances e.g. CO2). -Different Haemoglobins 

  • Haemoglobins with a high affinity for oxygen - they take up oxygen more easily but release it LESS readily- this is because an organism living in anenvironment with little o2 requires a haemoglobin which combines with oxygen if it is to asorb enough of it - if metabolic rate is not high it is not a problem if o2 is not released as often
  • Haemoglobing with a low affinity for oxygen - take up oxygen less easily but release it more readily - organisms with a high metabolic rate needs to realease oxygen readily into tissues - as long as plent of 02 in organisms environment not a problem 
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10.1/2 Haemoglobin

  • Loading and unloading oxygen- Process where haemoglobin combines with oxygen = LOADING (humans in lungs) 
  • Process where haemoglobin releases its oxygen = UNLOADING (humans in tissues)

Oxygen Dissociation Curves - low partial pressures 4 polypeptide chains of hameoglobin are united and difficult to asorb 1st oxygen molecule - but once loaded this o2 molecule causes the polypeptide to load remianing 3 oxygens molecules easily - REMEMBER : 

  • the further to the left of the curve , the greater is the affinity of haemoglobin for oxygen - oxygen easily readily taken up but released less easily 
  • the further to the right the curve , the lower the affinity of haemoglobin for oxygen - it takes up oxgen less readily but releases it more easily 

Effects of CO2 , Haemoglobin has reduced affinity for oxygen in presence of CO2 , greater the conc of CO2 more readly haemoglobin releass its oxygen - why behaviour of hamoglobin changes in different regions of the body 

  • gas exchange surface - level of CO2 is low as it diffuses across gas-exchange surface and is expelled from organism - afffinity of haemoglobin for O2 is increased and with high conc. of oxygen in the lungs means oxygen is readily loaded by haemoglobin - reduced CO2 level has shifted o2 association curve to left 
  • in respiring tissues - level of CO2 is high-affinity of haemoglobin for O2 is reduced- with low conc of O2 in molecules means O2 is redily unloaded from the haemoglobin - dissociation curve shift to right 
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10.2 Loading , Transporting and unloading of oxyge

  • Gas exchange surface C02 is constantly being removed 
  • pH is raised due to low levels of CO2 
  • higher pH changes the shape of haemoglobin into one that enables it to load oxygen readily
  • shape increases affinity of haemoglobin for oxygen , so it is not released while bing transported in the blood by tissue
  • in tissues ,carbon dioxide is produced by respiring cells 
  • CO2 is acidic in solution so pH of the blood within in the tissue is lowered
  • lower pH changes shape of hameoglobin into one with a lower affinity of oxygen 
  • Hamoglobin releases its oxygen into respiring tissue 

More active a tissue the more oxygen is unloaded

  • higher rate of respiration , more CO2 the tissues produces therefore the lower pH 
  • there is a greater the haemglobin shape change , more readily o2 is unloaded , more 02 avaliable for respiration 

Most hameoglobin molecules are loaded with their maximum of 4 oxygen molecules - when pasisng through the lungs- if it reaches a tissue with a low respiratory rate only one of the o2 molecules will be relaesed so blood returning to the lungs will contain haemolgobin (75% saturated with o2)

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10.3 Starch , glycogen and cellulose

Starch - a polysaccharide found in many parts in a plant as small grains , forms good compnents of food and a major energy source. Made up of a-glucose monosaccharides linked by glydosidic bonds that are formed by CONDENSATION reactions - the chain is wound into a tight coil so is very compact. Main role of starch is energy storage and is suited as it is insouluble and therefore does not tend to draw water into the cells by osmosis and does not diffuse easily out of cells. Its compact and so a lot of it can be in a small space , and when hydrlysed it forms a-glucose which is eaily transported and readily used in respiration 

Glycogen - similar to strach but has shorter chains and more highly branched - it is the major carbohydrate storage product of animals , in animals it is stored in small grannules mainly in muscles and liver. Structure suited for storage same reasons as starch. However due to shorter chains is evn more hydrolysyed to a-glucose . Only found in animal cells 

Cellulose - made of monomers of B-glucose - results in many differences - as in b-glucose POSITION OF H GROUP AND OH GROUP ON A SINGLE CARBON ATOM ARE REVERSED, OH IS ABOVE THE RING. In order to form glydosidic links each b-glucose molecule must be rotated 180 degrees - this means CH2OH group on each b-glucose alternats , between above and below the chain. They have straight unbranced chains, which run parrallel to one another allowing hydrogen bonds to form between adjacent chains- strengthening ceelulose all together. Cellulose molecules are grouped together are arranged in groups called fibres. Cellulose is a component of plant cell wall and provides ridigity of the cell wall  and prevents cell from burstin when water entes by osmosis as it exerts an inard pressure that stops any nflux of water- important stems and leaves are turgid so provide max surface for photsynthesis

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10.4 Plant Cell Structure

Plant cells are eukarotic cells . 

Leaf palisade cells - carry out photosynthesis  - main features to suit its function is long , thin cells that form a continous layer to absorb sunlight , numerous chlorplasts that arrange themselves in the best position to collect the max. amount of light , a larg vaculoe that pushes the cytoplasm and chloroplasts to the edege of the cell. 

Chlorolasts also carry out photosynthesis , they vary in shape and size but normally are disc shaped . Their main feature are: 

  • Chloroplast envelope- a double plasma membrane that surrounds the organelle - highly selective in what can exit and enter the chloroplast 
  • The grana are stacks of up to 100 disc-like structures called THYLAKOIDS , within these is chlorophyll. Grana can link with other grana in thylakoids by tubular extensions - 1st stage of photosynthesis 
  • stoma - fluid filled matrix where the 2nd stage of photosynthesis takes place  - within there are other structures such as grains 

Chloroplasts are adapted to their function of harvesting sunlight and carrying out photosynthesis by: 

  • granular membranes provide a large SA for attachment of chlorphyll 
  • fluid of stoma posseses all the enzyme needed to carry out 2nd stage of photosynthesis ]
  • chloroplasts contain both DNA and ribosomes so they quickly and easily manufacture proteins needed for photosy
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10.4 Cell Wall

Cell wall consists of microfibrils of the polysaccharide cellulose , embedded in a matrix. Cellulose microfibrils have considerable strength , so strengthen cell wall , they have the following features:

  • have a number of polysaccharides , such as cellulose
  • thin layer called middle lamella , marks the boundary between adjacent cell wall and cements adjacent cells together

Functions of the cellulose cell wall : 

  • provide mechanical strength in order to prevent the cell from bursting under the pressure of osmotic pressure - by water
  • give mechanical strength to the plant as a whole 
  • allow water to pass along and so conribute to the movement of water through the plant 

Difference between plant and animal cells 

  • Plants have a cell celluolse cell wall surounds the cells as cell-surface membrane , as only a cell-surface membrane surrounds the cell (plants starch grains used for storage as glycogen granules are used in animals)
  • chloroplasts are present in large numbers in most cells , not found in animal cells 
  • Plant cells normally have a large single cenral vacuole filled with cell sap, animal vaculoes are small and scattered throughout the cell
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11.1 DNA Replication

Before a nucleus divides its DNA it must be replicated (copied) , this is to ensure that all daughter cells have genetic information to produce the enzymes and other proteins that they need    

Semi-conservative replication 

  • four types of nucleotide ,each with their bases Adenine , Guanine , Cytosine ,Thymine present
  • two strands of DNA , both act as a template for attachment of these nucleotides
  • DNA polymerase is needed to  catalyse the reaction  - chemical energy to drive reaction 
  • The enzyme DNA helicase breaks the hydrogen bonds linking the base pairs of DNA
  • As a result the double helix seperates into its two strands and unwinds
  • Each exposed polynucleotide strand then acts as a template to which complementary nucleotides are attracted
  • energy is used to acivate these nucleotides 
  • activated nucleotides are joined together by the enzyme DNA polymerase to form the 'missing polynuclotde strand on each of the two original polynucleotide strands of DNA - all nucleotides are joined to form a complete polynuclotide chain using DNA polymerase - in this way to identical strands of DNA are formed , each strand retains half of the original DNA material
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11.2 Mitosis

Nuclear Division - Mitosis produces 2 daughter nuclei have the same number of chromosomes as the parent cell and eachother 

Mitosis is the division of the nucleus of a cell that results in each of the daughter cells having an exact copy of the DNA of the parent cell, the genetic make-up of nuclei is also identical as parent unless there is a mutation. After mitosis interphase always follows which is period during where the cell is not dividing (it includes proccess of DNA replication) Mitosis is split into 4 stages : 

  • INTERPHASE - cell is activley synthesising proteins - chromosomes invisibe - DNA replicates
  • PROPHASE - chromosomes become visible and nuclear envelope disappears
  • METAPHASE - spindle forms ,where the chromosomes arrange themselves at the centre of the cell 
  • ANAPHASE - ispindle fibres attached to chromatids (centre of chrmosome)contract and chromatid are pulled towards opposite poles 
  • TELOPHASE - where the nuclear envelope reforms and spindle fibres disintergrate 

The Importance of Mitosis 

  • Growth- 2 haploid cells fuse to form a dipoloid cell- needed to form a new organism- mitosis ensures it happens
  • Differentation - cells divide by mitosis to give tissues made of identical cells which peform a particular function
  • Repair- if cells are damaged or die , need new identical cells , strucuture and function- need exact copies 
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11.3 The cell cycle

Cells do not divide continously , but undergo a regular cycle of division seperated by periods of cell growth- known as the cell cycle and has 3 stages

  • interphase - which occupies most of the cell cycle - known as the resting phase as no division takes place - it is split into 3 parts - a) first growth (G1) , when the protein from which cell organised and synthesised are produced. b)Synthesis phase , when DNA is replicated c) Second Growth (G2) phase , when organelles grow and divide and energy stores are increased
  • nuclear division - nucleus divides either into 2 (mitosis) or four meiosis 
  • cell division - where the whole cell divided in to two (mitosis) or four meiosis 

Typically for a mammalian cell takes about 24 hours for a cell cycle and 90% are int interpahse

Cancer is caused by a growth disorder of cells , due to damage to the genes that regulate mitosis and the cell cycle , it leads to uncontrolled growth of cells , as a result a growth of abnormal cells called tumour develops , to treat cancer involves blocking some part of the cell ccle , in this way the cell cycle is disrupted and cell division stops. Drugs used to treat cancer (chemotherapy) disrupt the cell cycle by preventing DNA from replicaing and inhibiting the metaphase stage of mitosis by interphering with spindle formation - however also disrupt cell cycle of normal cells 

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12.1 Cellular Organisation

Cell Differenation - No one cell can provide the best conditions for all functions , they are adapted in different ways to peform a particular role. A cell starts the same but becomes specialised in structure to suit the role that they will carry out . Every cell contains the genes needed for it to develop into any one of the many different cells in an organism  , however only a few of the different genes are switched on in each type of differentiated cell , the rest of the genes are switched off.It is not just the shape of different cells that varies , but also numbers of each organelles. Cells of multicellular oraganism have therefore evolved to become more and more suites to one specialised function , in doing so they have lost the ability to carry out other functions- so each cell are specially adapted so whole organism functions effecivley 

Tissue - collection of similar cells that perform a particular function is known as a tissue e.g. epithelial cells which line surfaces of organs and have a protective or secretory function - there are many types such as cilited epithelium that lines trachea ,and cilia which move mucus over epithelial surface. Another example is xylem - occurs in plants and made up of a numver of cell types - used to transport water and minerals throughout the plant and gives mechanical support 

Organs - it is a combination of tissues that are co-ordinated to perform a variety of funcions although normally is a predominant funcion  such as in animal he stomach is an organ which carries out digestion and is made up of tissues such as muscle to churn and mix up stomach content , epithelium to protect the stomach wall , connective tissue to hold together oher tissues 

Organ Systems - when organs work together as a single unit known as an organ system - grouped together to perform particuar functions more efficently. e.g. Digestive system , digests and proccesses food - includes organs such as the salivary glands, oesphagus , stomach , pancreas and liver- (respiratory system - breathing and gas exchnge-trachea/lu

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13.1 Exchange and Transport

Examples of things which need to be interchanged between an organism and its environment , include , respiratory gases (O2 CO2) , nutrients (glucose , fatty acids , minerals) , excretory products (urea , CO2) and heat. The exhange can take place passivley by diffusion and osmosis or activley by active transport. 

For exchange surfaces to be effective , the surface are of an organism must be large compared with its volume. Small organisms have a large SA:volume however as animals become bigger volume grows rapidly so to overcome this they have to have a flattened shape so no cell is ever far from the surface , and specialised exchange surfaces with large areas to increase the SA:vol (lungs in mammals , gills in fish). 

To allow effective transfer of material across by diffusion or active transport , exchange surfaces have the following characteristics: 

  • large SA : VOL RATIO - to increase rate of exchange 
  • very thin so diffusion distance is short - materials transfer rapidly 
  • partially permeable to allow selected materials to cross without obstruction 
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13.2 Gas Exchange in insects and single celled org

Single celled organisms are small and have a large SA : VOL RATIO. Oxygen is absorbed by diffusion across their body surface (covered only by cell-surface membrane) - CO2 also diffuses from respiration across the body surface - living cell surrounded by cell wall so is completley permeable 

Insects - the insect has to balance the opposing needs of exchanging respiratory gases with reducing water loss. To reduce water loss the insects have 2 features: 

  • Waterproofing coverings - over their bodys surface , it is a rigid outer skeleton covered with a waterproof cuticle 
  • Small surface are to vol ratio - minimise area over which water is lost 

The features mean they cannot use their body to diffuse respiratory gases instead they have developed a internal network of tubes called tracheae (supported by rings so dont collapse) - trahcea is divided into smaller tubes called tracheoles , which extend throughout body tissue - means atmospheric air is brought directly to respiring tissues. Respiratory gases move in and out of tracheal system in 2 ways:  1. Along a diffusion gradient - when cells are respiring , oxygen is used up and so its concentration towards the end of the tracheoles falls - causes a diffusion gradient causing oxygen to diffuse from cells antomsphere along tracheae and tracheoles to cells. Carbon dioxide is produced by cells during respiration which creates a diffusion gradient in the opposite direction - causing co2 to diffuse along tracheae/tracheoles from cells to atmosphere 2. Ventilation - movement of muscles in insects create mass movement of air in and out of tracheae - speeds up exchange 

Gases enter and exit tracheae through tiny pores called spiracles on body surface- open or closed by valve- normally closed to prevent water loss (when open water evaporates)- open for gas exchange 

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13.3 Gas exchange in Fish

Fish have a waterproof , gas tight outer covering. They have a small SA : vol ratio  - body not adequate to supply and remove their respiratory gases so they have develpoed an internal gas exchange surface gills. 

Structure of Gills - located in the body behind the head , made up of gill filaments which are stacked up in a pile. Right angle to fillaments are gill lamellae which increases SA of the gills. Water taken in through mouth , forced over gills and out through opening of the side body. The flow of water over the gill lamellae and the flow of blood within them are in opposite directions - COUNTERCURRENT FLOW- ensures maximum possible gas exchange 

Countercurrent exchange principle - the blood within lamellae and water over the lamellae flow in opposite directions, this means that , blood that is loaded well with oxygen meets water which also has max conc of oxygen , therefore diffusion of oxygen from the water to the blood takes place . Also blood with little or no oxygen meets water which has most oxygen removed , again it means diffusion of oxygen from the water to blood takes place. Therefore there is a constant rate of diffusion across the entire length of the lamellae

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13.4 Gas exchange in the leaf of a plant

In plants cells take in oxygen and produce carbon dioxide during respiration . However in photsynthesis they take in carbon dioxide and produce oxygen . This means that the volumes and types of gases that are being exchanged by a plant leaf change , it depends on the balance between rates of photosynthesis and respiration. 

  • When photosynthesis is occuring most co2 is obtained from the air , little from respiring cells. In the same way oxygen from photosyntheis is used in respiration but most diffuses out of the plant 
  • When photosynthesis is not occuring - (dark) - oxygen diffuses into the leaf because it is constantly being used by the cells during respiration - carbon dioxide produced in resporation diffuses out 

Structure of a plant leaf and gas exchange - gas exchange in plants similar to animals as no living cell is far from the external air and therefor always a source of O2 and CO2. Diffusion takes place in air so is rapid than if it was in water. 

In plants there is a short , fast diffusion pathway , the plant leaf also has a large SA compared with volume of living tissue , therefore there is no special transport system - gases simply move through plant by diffusion. Leaves have adaptations for diffusion , a thin flat shape which provides a large SA , may small pores called stomata in lower epidermis and numerous interconnecting air spaces that occur throughout mesophyll. 

Stomata - minute pores which occur mainly on the leaves (underside) , each stomata is surrounded by a pair of special cells - guard cells. These cells can open and close the stomata pore , in this way they can control the rate of gaseous exchange- important as can lose water by evaporation - plants have to balance gas exchange and water loss- by partly closing stomata  

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13.5 Circulatory system of a mammal

With increasing size SA:VOL RATIO decreases to a point where the needs of organism cannot be met by bidy surface alone, a special echange surface is needed to absorb nutrient and respiratory gases. A transport sytem is required to take materials from cells to exchange surfaces and from exchange surfaces to cells , materials have to be transported between exchange surfaces and the environment and between different parts of the organism - organisms evolved into larger and more complex structures. It depends on the SA to Vol ratio and how active organism is e.g. lower SA to Vol ratio and more active organism need for a specialised  transport system with a pump. 

Features of a transport system: 

  • a suitable medium to carry materials e.g. blood - normally liquid based on water as dissolves and moved easy
  • a form of mass transport in which the transport medium is moved in bulk over long distances 
  • a closed system if tubular vessels which contain transport medium and network to distribute it to all parts body 
  • A mechanism for moving the transport medium within vessels - requires pressure difference between on epart of system and another - animals used muscular contraxtion either body muscles or organ such as heart - plants rely on passive natutral physical proccesses such as the evaporation of water
  • a mechanism to maintain flow movement in 1 direction e.g. valves 
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13.5 Circulatory system of a mammal / Blood Vessel

Transport system in mammals - close blood system blood confines to vessels - muscular pump heart circulates blood round the body- mammals have double circulatory system , blood passes twice through heart for each complete circuit of the body as when passed through lungs pressure is reduced - pass immediatley to rest of body circulation woul dbe very slow - returned to heart to boost pressure- delivered quickly good body has high temp and metablolism - vessels divided into 3 types atreries veins capliiaries - final part o fjourney intio cells is by diffusion though from blood vessels into cells is rapis as large SA  , short distance , steep diffusion gradient 

Blood vessels and their functions. There are different types of blood vessels: 

  • Arteries - carry blood away from the heart and into arterioles
  • Arterioles - are smaller arteries that control blood flow from arteries to capillaries
  • Capillaries - are tiny vessels that link arterioles to veins 
  • Veins - carry blood from capillaries back to the heart 

ARTERIES , ARTERIOLES & VEINS have same basic layered structure - from outwards , inwards: 

  • tough outer layer - resists pressure changes from both within and outside
  • muscle layer - that can contract and so control the flow of blood
  • elastic layer - helps to maintain blood pressure by stretching and springing back 
  • thin inner lining - that is smooth to prevent friction and thin to allow diffusion 
  • lumen - not actually a layer but is the central cavity of the blood vessel through which the blood flows  
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13.6 Blood vessels and functions

Artery Structure related to function - their function is too transport blood rapidly under high pressure from heart to tissues

  • the muscle layer is thinck compared to veins - smaller arteries can be constricted and dialates-control vol. of blood 
  • elastic layer is thick compared to veins - important blood pressure in arteries is kept high if blood is to reach around whole body - elastic wall stretched at each beat of heart and springs back when heart is relaxes (diastole) - stretching and recoiling action maintains high pressure and smooth pressure surges created by beating of heart
  • The overall thickness of wall is large - resists the vessel bursting under pressure 
  • There are no valves - as blood is underconstant high pressure and therefore soed not tend to flow backwards (except in arteries leaving the heart) 

Arteriole Structure related to function - they carry blood under lower pressure than arteries , from arteries to capillaries- also control the blood flow between the two 

  • Muscle layer is relativley thicker than in arteries - contraction of this muscle layer allows constriction of the lumen of the arteriole , this restricts the flow of blood and so controls its movement into the capillaries that supply tissue with blood 
  • Elastic Layer is relativley thinner than in arteries - as blood is at a lower pressure
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13.6 Blood vessels and their functions

Vein Structure related to function - transport blood slowly , under low pressure from the tissues to the heart 

  • Muscle layer is relativley thin - compared to arteries as veins carry blood away from the tissue and therefore there constriction and dialation cannot control blood flow to tissues
  • Elastic layer is relativley thin - compared to arteries as low pressure of blood within the veins will not cause them to burst and pressure to low to create recoil action 
  • Overall thickness of the wall is small - no need for a thick wall as within the veins pressure is low - so no risk of bursting - allows them to be flattened easily , aiding blood flow 
  • There are valves throughout - to ensure blood does not flow backwards , which it might otherwsise do as pressure is low - when body contracts veins are compressed , pressuring blood within them - valves ensure that this pressure directs the blood in one direction only 

Capillary structure related to function - to exchange metabolic materials between blood and cells of the body - flow of blood is slow and allows more time for the exchange of materials : 

  • walls consist of only lining layer- extremely thin distance over diffusion takes place is short - rapid diffusion 
  • numerous and highly branched - a large SA for diffusion - (have narrow diameter no cells far from capillary)
  • lumen is narrow - red blood cells squeezed flat against side of capillary-even closer to cells which they supply02
  • spaces between the endothelial cells - allow white blood cells to escape in order to deal with infections 
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13.6 Blood vessels and their functions

Tissue fluid is a watery liquid that contains glucose , amino acids, fatty acids ,salts , O2 - it supplies all of these substances to tissues- it recieves CO2 and waste materials form tissue- provides a constant environment for the cells it surrounds 

Formation of tissue fluid- blood pumped by heart passes along arteries then narrower arterioles and finally narrower capillaries - creates a pressure called HYDROSTATIC PRESSURE at the arterial ends of capillaries - this pressure forces tissue fluid out of blood plasma - however the outward pressure is opposed by other forces , hydroststic pressure of the tissue fluid outside the capillaries which prevents outward movement of liquid and the lower water potential of the blood due to the plasma proteins that pulls water back into the blood within the capillaries. Combined affect of all forces and pressures pushes tissue fluid out of capillaries - pressure onloyo enough to push out small molecules - leaving cells and proteins in blood 

Return of tissue fluid to the circulatory system - after it has exchanged metabolic materials it must return to circulatory system - most returns to the blood plasma directly via the capillaries ; loss of the tissue fluid from capillaries reduces hydrostatic pressure inside them- as a result by the time the blood has reached the venous end the of the capillary network its hydroststic pressure is less than the tissue fluid outside therefore the tissue fluid is forced back into the capillaries by the higher hydrostatic pressure outside them- also the osmotic forces resulting from proteins in the blood plasma pull water back into capillaries

Not all tissue can return to capillaries , remainder is carried back by LYMPHATIC SYSTEM- system of vessels that begin in tissue- start like capillairs but gradually merge to bigger vessels that form a netwrok throughouth the body- larger vessels drain their contents back into bloodstream via two ducts that join veins close to heart. Content of lymphatic system are moved by hydroststic pressure of the tissue fluid that has left the capillaries and contraction of body muscle that squeeze lymph cells - valves in lymph vessels ensure the movement in rigth direction 

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13.7 Movement of water through roots

Root hairs - they are the exchange surfaces in plants and are responsible for the absorption of water and mineral ions. Each root hair is a long , thin extenision of a root epidermal cell. They are efficent surfaces for the exchange of water because: 

  • they provide a large SA as they are very long and occur in thousands
  • they have a thin surface layer across whoch material can move easily 

These hairs grow in space around soil particles , damp conditions are surrounded by a soil soolution which contains small quantatites of mineral ions- the soil solution is mostly water and has a high water potential- root hairs have sugars and amino acids dissolved in them so have a lower water potential - as a result water moves by osmosis from the soil solution into root hair cells - after being absorbed into root hair cells water continues its journey across the root in 2 ways - apoplastic pathway or symplastic pathway  

Apoplastic pathway - water drawn in to endodermal cells , it pulls more water along behin it due to cohesive properties of water molecules- creates a tension that draws water along the cell walls of the cells of the root cortex- has a mesh like structure of the cellulose cell walls of these cells has many water-filled spaces and so there is no or little resistance to the pull of water 

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13.7 Symplastic Pathway

Takes place across cytoplams of cells as a result of osmosis. Water passes through cell walls along tiny openings called plasmodesmata - each filled with tiny strand of cytoplasm- therefore there is acontinu ous coloumn of cytoplasm from rooty hair to xylem at centre of root- water moves along this coloumn by:

  • water entering by osomosis increases water potenital in the root hair cell
  • root hair cell now has a higher water potential than the first cell in the cortex
  • water therfore moves from root hair cell to first cell in cortex by osmosis
  • 1st cell now has a higher water potenital than its neighbour to the inside of the stem
  • water therefore moves into neighbouring cell by osmosis along water potenital gradient
  • 2nd cell has high water potential than 3rd cell - so moves from 2nd to 3rd by osmosis
  • at same time the loss of water from first cell lowers water potential so more water enters from root hair cell - water potential gradient set up across all cells of cortex-carries water aong cytoplasm from root hair cell to endodermis 
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13.7 Passage of water into the xylem

Passage of water into xylem- when water reaches endodermis theres a waterproof band prevents it progressingalong - this pont water is forced into living protoplast of cell where it joins with water that has arrived there by the sympastic pathway. Active transport of salts is most likley way which water now gets into xylem- endormal cells activley transport salts into xylem-requires energy only occur within living tissue - takes place along carrier proteins in cells surface membrane- if water eneters xylem must 1st enter cytoplasm of endodermal cells- why water from apoplastic pathway is forced into cytoplasm of endodermal cells by waterproofstrip. Active transport of mineral ions into xylem creates a low water potential in xylem-water move sin by osmosis-this water potential causes a root pressure which helps to force water up the plant - especially in small plants (pressure increases in rise in temp) - metabolic inhibitors e.g. cyandine cause root pressure to cease. 

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13.8 Movement of water up stems

Movement of water out through stomata - provided stomata are open , water vapour molecules diffuse out of air space sinto surrounding air - watert lost from air space sis replaced by water evaporating from the cells wall - surrounding mesophyll cells - can control rate of transpiration ny changin size of stomatal pores 

Movement of water across a leaf - water is lost from mesophyll cells by evaporation from their surfaces to the air spaces of the leaf- replaced by water reaching mesophyll cells from xylem by apoplastic or symplastic pathways - for symplastic water movement occurs because mesophyll cells lose water to air spaces , these cells have a lower water potential so wanter enters by osmosis from neighbouring cells - loss of water lowerd their water potential so they in turn take water from their neighbours 

Movement of water up the stem in xylem - 2 main factors coheison-tension and root pressure - cohesion tension theory:

  • water evaporates from leaves due to transpiration , water molecules from hydrogen bonds between one another hence stick together - COHESION- water forms a continuous , unbroken pathway across mesophyll cells and down the xylem- water evaporates from mesophyll cells in leaf into air spaces beaneath the stomata more molecules of water are drawn up behind it as a result of this cohesion 
  • water is hence pulled up the xylem as a result of transpiration - TRANSPIRATION PULL- which puts the xylem under tension - negative pressure within xylem and hence COHESIO-TENSION THEORY

(if xylem vessel broken and air enters no longer tree can draw up water - continous coloumn of water is brokem)

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13.9 Transpiration and factors affecting it

Transpiration - (movement of water up the xylem)materials such as mineral ions and sugards are moved around the plant in dissolved water , the water is carried up the plant by the transpiration pull , without transpiration water would not be so plentiful and transport of materials would not be so rapid.

Factors affecting Transpiration : 

Light - stomata are openings in leaves through which CO2 needed for photosynthesis diffuses - photosynthesis occurs in light and stomata only open in light , when open water moves out of lwaf into atmposhere - increases in ligth = increase in transpiration 

Temperarture - afeects how much water the air can hold (water potenial of air) and speed which molecules move. A rise in temp. increases kinetic energy and hence increase speed of movenment of molecules , which also increases rate of evaporation - which menas water evaporates more rapidly from leaves and so rate of transpiration increases. also rise in temp decreases the amount of water air can hold - decrease water potential 

Humidity - meausre of no. of water molecules in the air - air humidity affects the water potential gradient between the air outside the leaf and air inside the lead - when air outside leaf has high humidity the gradient is reduced and rate of transpiration is lower - lower humidity increases transpiration rate 

Air Movement - water diffuses through stomata it accumulates vapour around the stomata on outside of leaf. Water potential around the stomata is therefore increased - reduces the water potential gradient between the moist atmoshpere in the air spaces within the leaf and the drier air outside-transpiration rate is therefore reduced- any air movement arounf the leaf will desperse humid layer at the leaf surface and decrease water potential of air - increases water potential gradient and rate of transpiration - faster air , faster humid air removed , faster and greater transpiration

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14.1 Classification

Classification is the organisation of living organisms in to groups. Organisms are identified by two names and it is called the bionomal system. As there are so many species past and present they are organised into manageable groups , such as artificial classification which divides species by their differences such as colour & size , as natural classification is based on revolutionary species between organisms and their ancestors.  Each group within a natural biological classification is called a taxon and taxonomy is the study of these groups and their positions in a hierachy order. 

  • Kingdom 
  • Phylum     
  • Class    
  • Order
  • Family     
  • Genus    
  • Species    

Problems with defining species - species change and evolve over time - develop into new species - variations within the species - many species are extinct 

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15.1 Evidence of Relationships between organisms

DNA hybridisation - when DNA is heated its double strand seperates into to 2 complementary single strands , when cooled the complementary bases on each strand recombine with eachother to form the original strand - given time all strands in a mixture of DNA will pair up with parteners - using this property DNA hybirdisation can be used to compare 2 species: 

DNA from 2 species is extracted DNA from 1 specie is labelled by attaching a radioactive or fluroecscent marker to it - then mixed with other unlabelled DNA ,DNA from both species is heated to seperate their strands - micxture is cooled and to allow strands to combine with other strands which have complementary bases  some double strands will reform made up od one strand of each species - called hybirdisation and new strands are hybird strands - identified because 50% labelled hybird strands seperated out and the temperature is increased in stages - the degree to which the two strands are still linked together is measured if two species are closely related they will share many complentary nucleotide bases greater number of hydrogen binds , stronger hybird will be  stronger hybird strand , higher the temperature needed to seperate into to two single strands  higher the the temp at which the strand splits the more closely related they are 

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15.1 Immunological comparison on proteins

Proteins of different species can also be compared using immunological techniques- principle behind the method is that antibodies of one species will only respond to specific antigens on proteins - Proccess carried out as follows : 

  • Human (species A) serum injected into rabbit (species B)   
  • Species B produces antibodies specific to all antigens sites on species A  
  • Rabbit serum with anti-human atibodies is extracted  
  • Serum from species B is mixed with serum of the blood of a third species (C)  
  • Antibodies respond to antigens , response is a formation of a precipitate greater the number of similar antigens the more precipitate is formed and more closely species are related 
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15.2 Courtship behaviour

Reproduction is important to oraganisms as it means tehir species can survive over time , wants DNA to be passed on. Females of most species only produce eggs at a specific part of the year , therefore important to ensure mating is successful  and off spring have maximum chance of survival , courtship helps to achieve this by:  recognise members of own species - mating only takes place between members of same species - can produce fertile offspring  identify a mate that is capable of breeding - both partners need to be sexually mature,fertile form a pair bons - lead to successful mating and raising of offspring  syncrohnise mating - takes place when max. probability of sperm and egg meeting  Courtship behaviour used by males to determine whether a female is a receptive stage where the can concieve and produce eggs - if she responds in manner than courtship continues - if she dosent respond , male turn satention elsewhere. During courtship animals use signs to communicate with a potential mate- typically male carries out an action , action acts as a stimulus for female , who responds with specific action of her own , male then carry sown with further action (stimulus-response chain)- longer courtship continues more likley to mate- anyone point one of the pair does not responf courtship sequence ends

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16.1 Genetic Variation in bacteria

Bacteria adapts to a changing environment can be seen by their ability to develop resistance to antibiotics. Genetic varaition can arise in bacteria by changing the quantity or structure of the DNA of an organism - MUTATION- or recombining the exisiting DNA of two individuals , occurs during sexual reproduction. 

Mutations - are changes in DNA which result in different characteristics - arise in many ways such as one or bases in DNA may be added, delteted or replaced by others during replication - differences in base sequences mean different sequence in amino acids being coded for - mean different polypetptide & different protein , or no protein- alter organisms characteristics

Conjuation - occurs when one bacterial cell transfers DNA to another bacterial cell , and takes place as follows: 

  • one cell produces a thin projection that meets another cell and forms a thin conjuation between the 2 cells 
  • donor cell replicates one of its small circular pieces of DNA (plasmid) - then broken to make linear before being passed along the tube to recipient cell 
  • contact between cells is brief leaving only time for a portion of the donors DNA to be transferred
  • therefore reciepent cell aquires new characteristic from the donor DNA - linear strand form a circle new plasmid 
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16.3 Antibiotic use and resistance

Antibiotic resistance & turberculosis - bacterial disease in the lungs treated by antibiotics - 1 problem is that antibiotcs have to be taken over a long period of time 6-9 months when ill people take antiobiotics as keen to recover , the antibiotics initially destroy least resistant strains of Mycobacterium- after a few months patient feel better as most mycobacterium has been destroyed - people think are cured and stop taking them- however the few bacteria that remian are those most resistant to bacteria , they survive and multiply and spread to others - this means strains of mycobacterium do not respond to the antibiotic - strains can interchange genes for resitance with other strains by conjutaion- then multiple antibiotic resistant strains of TB have developed - overcome problem 3 or 4 antibiotics is used to be sure it is effective - need to complete course of treatment

Antibiotic resistance MRSA- bacterium in the throat - if it becomes a major health risk can be treated with antibiotics - MRSA name given to any strain of bacterium that is resistant to antibiotics - can be a danger especially in hospitals as proplr in hospitals ten dto be older , sicker and weaker making them more vunreable to infection , many live closer togeteher and examined by same doctors and nurses- transmission of infection (touch other patients)- many antibiotics used in hospitals strains can easil develop multiple resistance

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16.2 Antibiotics

Antibiotics are substances produced by living organisms that can destroy or inhibit the growth of microrganisms. Antibotics work by preventing bacteria from making normal cell walls. they inhibit the synthesis and assemly of important peptide cross-linkages in bacterial cell walls, which weakens the wall so they cannot withstand pressure and are therfore unable to prevent watering entering and so osmotic lysis occurs (water would normally cause cell to burst), killing the bacterium- however antibiotics only effcetive when bacterium is growing - penecillin works in this way- viruses not killed in this way 

Antibiotic resistance - some bacteria is resistance to antibiotics due to a mutation within the bacteria- in case of resistance to penecillin the mutation resulted in certain bacteria being able to make a new protein, new protein was an enzyme which broke down the antibiotic penecillin before it killed the bacteria . Mutation occur randomly and are not due to presence of antibiotics. Many mutations will not benefit the bacterium - only mutant type of bacteria will survive and divide - then new bacteria will be resistant to antibiotic- bacterium only survives in presence of certain type of antibiotic. The allele for antibitic resistance is carried on the small circular loops of DNA called plasmids- which can be transferred from cell to cell by conjugation - resistance can therfore find its way to other bacterial species by horizontal gene transmission - lead to bacteria accumulating DNA to resist range of antibiotics

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17.1 - Species Diversity

Biodiversity , has 3 components

  • Species Diversity - no. of different species and no. of individuals of each species in 1 community
  • Genetic Diversity - variety of genes possessed by the individuals that make up 1 species
  • Ecosystem Diversity - range of different habitats within a particular area

Species diversity can be measured using formula- d= N(N-1) / En(n-1) 

  • N = the total no. of organisms of all species 
  • n= total no. of organisms of each species 

The higher the species diversity index , the more stable an ecosystem is and less fragile to climate change - as if a drought in a community with a high species diversity index at least one species able to tolerate the drought - maintain some community - in arid areas few species adapted to harsh climate so species index is low.

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17.2 - Species Diversity & human activities

Mankind has had a considerable impact on natural world and has led to a reduction in biodiversity. 

Impact of Agriculture - agricultural ecosystems are controlled by humans - farmers select species which of particular qualities , as a result no. of species and genetic variety of alleles is reduced- no. of desirable species tend to be large which means most area is taken up for desirable species and nor much area left for other species , they have to compete for little space and resources - many not survive the competition - pesticides are also used to exclude these species

Impact of Deforestation - many habitats in forests - species diversity is high - most deforestation is deliberate human actions - deforestation is a pernament clearing of forests for land for housing and agriculture - some forests destroyed due to man-made pollutants causing acid rain- due to deforestation has meant loss of biodiversity- loss greatest in rainforests (rainforest size of uk cleared every year)

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