IGCSE Biology Revision Notes PDF

IGCSE 0610 BIOLOGY Revision notes 1  Content overview Unit Page no. 1 Characteristics and classification of living organisms 1 2 Organisation of the organism 16 3 M...

IGCSE 0610 BIOLOGY Revision notes 1  Content overview Unit Page no. 1 Characteristics and classification of living organisms 1 2 Organisation of the organism 16 3 Movement into and out of cells 36 4 Biological molecules 49 5 Enzymes 57 6 Plant nutrition 66 7 Human nutrition 84 8 Transport in plants 99 9 Transport in animals 110 10 Diseases and immunity 128 11 Gas exchange in humans 137 12 Respiration 148 13 Excretion in humans 156 14 Coordination and response 166 15 Drugs 201 16 Reproduction 203 17 Inheritance 230 18 Variation and selection 253 19 Organisms and their environment 264 20 Human influences on ecosystems 278 21 Biotechnology and genetic modification 289  1 Unit.1, Characteristics and classification of living organisms 1.1 Characteristics of living organisms Characteristics of Living Organisms  Movement: an action by an organism or part of an organism causing a change of position or place  Respiration: the chemical reactions that break down nutrient molecules in living cells to release energy for metabolism  Sensitivity: the ability to detect or sense stimuli in the internal or external environment and to make appropriate responses  Growth: a permanent increase in size and dry mass by an increase in cell number or cell size or both  Reproduction: the processes that make more of the same kind of organism  Excretion: the removal from organisms of toxic materials, the waste products of metabolism (chemical reactions in cells including respiration) and substances in excess of requirements  Nutrition: the taking in of materials for energy, growth and development; plants require light, carbon dioxide, water and ions; animals need organic compounds, ions and usually need water  2 1.2 Concept and uses of classification systems How Organisms are classified  There are millions of species of organisms on Earth  A species is defined as a group of organisms that can reproduce to produce fertile offspring  These species can be classified into groups by the features that they share e.g. all mammals have bodies covered in hair, feed young from mammary glands and have external ears (pinnas) The Binomial System  Organisms were first classified by a Swedish naturalist called Linnaeus in a way that allows the subdivision of living organisms into smaller and more specialised groups  The species in these groups have more and more features in common the more subdivided they get  He named organisms in Latin using the binomial system where the scientific name of an organism is made up of two parts starting with the genus (always given a capital letter) and followed by the species (starting with a lower-case letter)  When typed binomial names are always in italics (which indicates they are Latin) e.g. Homo sapiens  The sequence of classification is: Kingdom, Phylum, Class, Order, Family, Genus, Species Linnaeus’s system of classification  3 Dichotomous Keys  Keys are used to identify organisms based on a series of questions about their features  Dichotomous means ‘branching into two’ and it leads the user through to the name of the organism by giving two descriptions at a time and asking them to choose  Each choice leads the user onto another two descriptions  In order to successfully navigate a key, you need to pick a single organism to start with and follow the statements from the beginning until you find the name  You then pick another organism and start at the beginning of the key again, repeating until all organisms are named Example of a dichotomous key #1  4 Example of a dichotomous key #2  5 Reflecting Evolutionary Relationships  Classification systems aim to reflect evolutionary relationships between species  Traditional biological classification systems grouped organisms based on the features that they shared o If organisms shared more similar features, then they were said to be more closely related  In the past, scientists have encountered many difficulties when trying to determine the evolutionary relationships of species based on this method  Using the physical features of species (such as colour/shape/size) has many limitations and can often lead to the wrong classification of species Using DNA to Classify Organisms  Organisms share features because they originally descend from a common ancestor  Example: all mammals have bodies covered in hair, feed young from mammary glands and have external ears (pinnas)  Originally, organisms were classified using morphology (the overall form and shape of the organism, e.g. whether it had wings or legs) and anatomy (the detailed body structure as determined by dissection)  As technology advanced, microscopes, knowledge of biochemistry and eventually DNA sequencing allowed us to classify organisms using a more scientific approach  Studies of DNA sequences of different species show that the more similar the base sequences in the DNA of two species, the more closely related those two species are (and the more recent in time their common ancestor is)  This means that the base sequences in a mammal’s DNA are more closely related to all other mammals than to any other vertebrate groups  6 DNA sequences can show how closely related different species are  The sequences above show that Brachinus armiger and Brachinus hirsutus are more closely related than any other species in the list as their DNA sequences are identical except for the last but one base (B. armiger has a T in that position whereas B. hirsutus has an A)  As DNA base sequences are used to code for amino acid sequences in proteins, the similarities in amino acid sequences can also be used to determine how closely related organisms are 1.3 Features of organisms The Five Kingdoms  The first division of living things in the classification system is to put them into one of five kingdoms. They are: o Animals o Plants o Fungi o Protoctists o Prokaryotes  Main features of all animals: o they are multicellular o their cells contain a nucleus but no cell walls or chloroplasts o they feed on organic substances made by other living things  7 A typical animal cell  Main features of all plants: o they are multicellular o their cells contain a nucleus, chloroplasts and cellulose cell walls o they all feed by photosynthesis A typical plant cell  8 The Animal Kingdom  Several main features are used to place organisms into groups within the animal kingdom Vertebrates  All vertebrates have a backbone o There are 5 classes of vertebrates Vertebrate Table  9 Vertebrate classification Invertebrates  Invertebrates do not possess a backbone  One of the morphological characteristics used to classify invertebrates is whether they have legs or not  All invertebrates with jointed legs are part of the phylum Arthropods  They are classified further into the following classes:  10 Invertebrate Table Arthropod classification  11 The Five Kingdoms  The first division of living things in the classification system is to put them into one of five kingdoms  They are: o Animals o Plants o Fungi o Protoctists o Prokaryotes  Main features of all fungi (e.g. moulds, mushrooms, yeast) o usually, multicellular o cells have nuclei and cell walls not made from cellulose o do not photosynthesize but feed by saprophytic (on dead or decaying material) or parasitic (on live material) nutrition A typical fungal cell  Main features of all Protoctists (e.g. Amoeba, Paramecium, Plasmodium) o most are unicellular but some are multicellular o all have a nucleus, some may have cell walls and chloroplasts o meaning some protoctists photosynthesise and some feed on organic substances made by other living things  12 Two examples of protoctist cells  Main features of all Prokaryotes (bacteria, blue-green algae) o often unicellular o cells have cell walls (not made of cellulose) and cytoplasm but no nucleus or mitochondria A typical bacterial cell  13 The Plant Kingdom  At least some parts of any plant are green, caused by the presence of the pigment chlorophyll which absorbs energy from sunlight for the process of photosynthesis  The plant kingdom includes organisms such as ferns and flowering plants Ferns  Have leaves called fronds  Do not produce flowers but instead reproduce by spores produced on the underside of fronds Ferns Ferns reproduce by spores found in the underside of their fronds  14 Flowering plants  Reproduce sexually by means of flowers and seeds  Seeds are produced inside the ovary found at the base of the flower  Can be divided into two groups – monocotyledons and dicotyledons Wheat plants are monocotyledons Sunflowers are dicotyledons How do you distinguish between monocotyledons and dicotyledons? 1) Flowers  Flowers from monocotyledons contain petals in multiples of 3  Flowers from dicotyledons contain petals in multiples of 4 or 5 2) Leaves  Leaves from monocotyledons have parallel leaf veins  Leaves from dicotyledons have reticulated leaf veins (meaning that they are all interconnected and form a web-like network throughout the leaf)  15 Comparing monocots and dicots Viruses  Viruses are not part of any classification system as they are not considered living things  They do not carry out the seven life processes for themselves, instead they take over a host cell’s metabolic pathways in order to make multiple copies of themselves  Virus structure is simply genetic material (RNA or DNA) inside a protein coat Structure of a typical virus  16 Unit.2, Organisation of the organism 2.1 Cell structure Animal & Plant Cells Animals  The main features of animals: o They are multicellular o Their cells contain a nucleus with a distinct membrane o Their cells do not have cellulose cell walls o Their cells do not contain chloroplasts (so they are unable to carry out photosynthesis) o They feed on organic substances made by other living things o They often store carbohydrates as glycogen o They usually have nervous coordination o They are able to move from place to place A typical animal cell  17 Plants  The main features of plants: o They are multicellular o Their cells contain a nucleus with a distinct membrane o Their cells have cell walls made out of cellulose o Their cells contain chloroplasts (so they can carry out photosynthesis) o They feed by photosynthesis o They store carbohydrates as starch or sucrose o They do not have nervous coordination A typical plant cell  18 Cell Structures Found in Both Animal and Plant Cells Table An animal and plant cell as seen under a light microscope  19 Cell Structures Found Only in Plant Cells Table Bacteria Cells  Bacteria, which have a wide variety of shapes and sizes, all share the following biological characteristics: o They are microscopic single-celled organisms o Possess a cell wall (made of peptidoglycan, not cellulose), cell membrane, cytoplasm and ribosomes o Lack a nucleus but contain a circular chromosome of DNA that floats in the cytoplasm o Plasmids are sometimes present - these are small rings of DNA (also floating in the cytoplasm) that contain extra genes to those found in the chromosomal DNA o They lack mitochondria, chloroplasts and other membrane-bound organelles found in animal and plant cells  Some bacteria also have a flagellum (singular) or several flagella (plural). These are long, thin, whip-like tails attached to bacteria that allow them to move  Examples of bacteria include:  20 o Lactobacillus (a rod-shaped bacterium used in the production of yoghurt from milk) o Pneumococcus (a spherical bacterium that acts as the pathogen causing pneumonia) A typical bacterial cell Identifying Cell Structures & Function  Within the cytoplasm, the following organelles are visible in almost all cells except prokaryotes when looking at higher magnification (ie using an electron microscope): o Mitochondria (singular: mitochondrion) are organelles found throughout the cytoplasm o Ribosomes are tiny structures that can be free within the cytoplasm or attached to a system of membranes within the cell known as Endoplasmic Reticulum o Endoplasmic reticulum studded with ribosomes looks rough under the microscope; this gives rise to its name of Rough Endoplasmic Reticulum (often shortened to R.E.R.) o Vesicles can also be seen using a higher magnification - these are small circular structures found moving throughout the cytoplasm  21 Structures in an animal cell visible under a light microscope and an electron microscope Structures in a plant cell visible under a light microscope and an electron microscope Organisation of Cells Producing New Cells  The cells in your body need to be able to divide to help your body grow and repair itself  Cells grow and divide over and over again  New cells are produced by the division of existing cells  22 Specialised Cells Specialised cells in animals  Specialised cells are those which have developed certain characteristics in order to perform particular functions. These differences are controlled by genes in the nucleus  Cells specialised by undergoing differentiation: this is a process by which cells develop the structure and characteristics needed to be able to carry out their functions Specialised Cells in Animals Table  23 Diagrams of specialised cells in animals Ciliated cell  24 Nerve cell Red blood cells  25 Sperm cell Egg cell  26 Examples of specialised cells in plants  27 Diagrams of specialised cells in plants Root hair cell Xylem structure  28 Palisade mesophyll cell Levels of Organisation in an Organism  29 Levels of organisation  30  Your syllabus states that you should be able to identify the different levels of organisation in drawings, diagrams and images of familiar material  An example of this is shown in the exam question below:  31 Typical levels of organisation question 2.2 Size of specimens Magnification Formula Calculating magnification and specimen size using millimetres as units  Magnification is calculated using the following equation: Magnification = Image size ÷ Actual size  32  A better way to remember the equation is using an equation triangle: Magnification equation  Rearranging the equation to find things other than the magnification becomes easy when you remember the triangle - whatever you are trying to find, place your finger over it and whatever is left is what you do, so: o Magnification = image size / actual size o Actual size = image size / magnification o Image size = magnification x actual size Remember magnification does not have any units and is just written as ‘x 10’ or ‘x 5000’ To find the actual size of the cell: Worked example using the magnification equation  33 Converting Between Units Using millimetres and micrometres as units  The table below shows how millimetres are related to two other measures of length  What this basically means is that 1mm = 1000µm and 1cm = 10,000µm  This usually comes up in questions where you have two different units and you need to ensure that you convert them both into the same unit before proceeding with the calculation  For example:  34 Example extended magnification question  Remember 1mm = 1000µm  2000 / 1000 = 2 so the actual thickness of the leaf is 2mm and the drawing thickness is 50mm  Magnification = image size / actual size = 50 / 2 = 25  So the magnification is x 25 (NO UNITS) 35  36 Unit.3, Movement into and out of cells 3.1 Diffusion Diffusion  Diffusion is the movement of molecules from a region of its higher concentration to a region of its lower concentration  Molecules move down a concentration gradient, as a result of their random movement Diffusion across the cell membrane  For living cells, the principle of the movement down a concentration gradient is the same, but the cell is surrounded by a cell membrane which can restrict the free movement of the molecules  The cell membrane is a partially permeable membrane - this means it allows some molecules to cross easily, but others with difficulty or not at all  The simplest sort of selection is based on the size of the molecules  Diffusion helps living organisms to: o obtain many of their requirements o get rid of many of their waste products o carry out gas exchange for respiration  37 Examples of diffusion in living organisms  You will need to learn examples of substances that organisms obtain by diffusion  Don’t forget that plants require oxygen for respiration at all times, as well as carbon dioxide for photosynthesis when conditions for photosynthesis are right (e.g. enough light and a suitable temperature) Examples of Diffusion Table Where does the energy for diffusion come from?  All particles move randomly at all times  This is known as Brownian motion  The energy for diffusion comes from the kinetic energy of this random movement of molecules and ions  38 Brownian motion Factors that Influence Diffusion Surface area to volume ratio  The bigger a cell or structure is, the smaller its surface area to volume ratio is, slowing down the rate at which substances can move across its surface  Many cells which are adapted for diffusion have increased surface area in some way - eg root hair cells in plants (which absorb water and mineral ions) and cells lining the ileum in animals (which absorb the products of digestion) Cell adaptations for diffusion  39 The highly folded surface of the small intestine increases its surface area Distance  The smaller the distance molecules have to travel the faster transport will occur  This is why blood capillaries and alveoli have walls which are only one cell thick, ensure the rate of diffusion across them is as fast as possible Temperature  The higher the temperature, the faster molecules move as they have more energy  This results in more collisions against the cell membrane and therefore a faster rate of movement across them Concentration Gradient  The greater the difference in concentration either side of the membrane, the faster movement across it will occur  This is because on the side with the higher concentration, more random collisions against the membrane will occur  40 Water as a Solvent  Water is important for all living organisms as many substances are able to dissolve in it (it is a solvent)  Water is important as a solvent in the following situations within organisms: o Dissolved substances can be easily transported around organisms - eg xylem and phloem of plants and dissolved food molecules in the blood o Digested food molecules are in the alimentary canal but need to be moved to cells all over the body o Toxic substances such as urea and substances in excess of requirements such as salts can dissolve in water which makes them easy to remove from the body in urine o Water is also an important part of the cytoplasm and plays a role in ensuring metabolic reactions can happen as necessary in cells Water as a solvent 3.2 Osmosis Osmosis  All cells are surrounded by a cell membrane which is partially permeable  Water can move in and out of cells by osmosis  Osmosis is the diffusion of water molecules from a dilute solution (high concentration of water) to a more concentrated solution (low concentration of water) across a partially permeable membrane  In doing this, water is moving down its concentration gradient  The cell membrane is partially permeable which means it allows small molecules (like water) through but not larger molecules (like solute molecules)  41 Osmosis and the partially permeable membrane How osmosis works  42 Osmosis Experiments Immersing plant cells in solutions of different concentrations  The most common osmosis practical involves cutting cylinders of root vegetables such as potato or radish and placing them into distilled water and sucrose solutions of increasing concentration  The cylinders are weighed before placing into the solutions  They are left in the solutions for 20 - 30 minutes and then removed, dried to remove excess liquid and reweighed Potatoes are usually used in osmosis experiments to show how the concentration of a solution affects the movement of water, but radishes can be used too  If the plant tissue gains mass: o Water must have moved into the plant tissue from the solution surrounding it by osmosis  43 o The solution surrounding the tissue is more dilute than the plant tissue (which is more concentrated)  If plant tissue loses mass: o Water must have moved out of the plant tissue into the solution surrounding it by osmosis o The solution surrounding the tissue is more concentrated than the plant tissue (which is more dilute)  If there is no overall change in mass: o There has been no net movement of water as the concentration in both the plant tissue and the solution surrounding it must be equal o Remember that water will still be moving into and out of the plant tissue, but there wouldn’t be any net movement in this case Investigating osmosis using dialysis tubing  Dialysis tubing (sometimes referred to as visking tubing) is a non-living partially permeable membrane made from cellulose  Pores in this membrane are small enough to prevent the passage of large molecules (such sucrose) but allow smaller molecules (such as glucose and water) to pass through by diffusion and osmosis  This can be demonstrated by: o Filling a section of dialysis tubing with concentrated sucrose solution o Suspending the tubing in a boiling tube of water for a set period of time o Noting whether the water level outside the tubing decreases as water moves into the tubing via osmosis  Water moves from a region of higher water potential (dilute solution) to a region of lower water potential (concentrated solution), through a partially permeable membrane An example setup of a dialysis tubing experiment  44 Osmosis in Plant Tissues  When water moves into a plant cell, the vacuole gets bigger, pushing the cell membrane against the cell wall  Water entering the cell by osmosis makes the cell rigid and firm  This is important for plants as the effect of all the cells in a plant being firm is to provide support and strength for the plant - making the plant stand upright with its leaves held out to catch sunlight  The pressure created by the cell wall stops too much water entering and prevents the cell from bursting  If plants do not receive enough water the cells cannot remain rigid and firm (turgid) and the plant wilts Osmosis in Animals & Plants Plant cells in solutions of different concentrations  When plant cells are placed in a solution that has a higher water potential (dilute solution) than inside the cells (e.g. distilled water) then water moves into the plant cells via osmosis  These water molecules push the cell membrane against the cell wall, increasing the turgor pressure in the cells which makes them turgid A turgid plant cell  45  When plant cells are placed in a concentrated solution (with a lower water potential than inside the cells) water molecules will move out of the plant cells by osmosis, making them flaccid o If plant cells become flaccid it can negatively affect the plant's ability to support itself  If looked at underneath the microscope, the plant cells might be plasmolysed, meaning the cell membrane has pulled away from the cell wall A plasmolysed plant cell Animal cells in solutions of different concentrations  Animal cells also lose and gain water as a result of osmosis  As animal cells do not have a supporting cell wall, the results on the cell are more severe  If an animal cell is placed into a strong sugar solution (with a lower water potential than the cell), it will lose water by osmosis and become crenated (shrivelled up)  If an animal cell is placed into distilled water (with a higher water potential than the cell), it will gain water by osmosis and, as it has no cell wall to create turgor pressure, will continue to do so until the cell membrane is stretched too far and it bursts  46 Effect of osmosis on animal cells 3.3 Active transport Active Transport  Active transport is the movement of particles through a cell membrane from a region of lower concentration to a region of higher concentration using energy from respiration  47 The process of active transport Importance of Active Transport  Energy is needed because particles are being moved against a concentration gradient, in the opposite direction from which they would naturally move (by diffusion)  Active transport is vital process for the movement of molecules or ions across membranes  Including: o uptake of glucose by epithelial cells in the villi of the small intestine and by kidney tubules in the nephron o uptake of ions from soil water by root hair cells in plants Protein Carriers  Active transport works by using carrier proteins embedded in the cell membrane to pick up specific molecules and take them through the cell membrane against their concentration gradient:  48 1. Substance combines with carrier protein molecule in the cell membrane 2. Carrier transports substances across membrane using energy from respiration to give them the kinetic energy needed to change shape and move the substance through the cell membrane 3. Substance released into cell Carrier proteins in active transport  49 Unit.4, Biological molecules 4.1 Biological molecules Chemical Elements  Most of the molecules in living organisms fall into three categories: carbohydrates, proteins and lipids  These all contain carbon and so are described as organic molecules Chemical Elements Table Large Molecules are made from Smaller Molecules Carbohydrates  Long chains of simple sugars  Glucose is a simple sugar ( a monosaccharide)  When 2 glucose molecules join together maltose is formed (a disaccharide)  When lots of glucose molecules join together starch, glycogen or cellulose can form (a polysaccharide)  50 Glycogen, cellulose and starch are all made from glucose molecules Fats  Most fats (lipids) in the body are made up of triglycerides  Their basic unit is 1 glycerol molecule chemically bonded to 3 fatty acid chains  The fatty acids vary in size and structure  Lipids are divided into fats (solids at room temperature) and oils (liquids at room temperature) Structure of a triglyceride  51 Proteins  Long chains of amino acids  There are about 20 different amino acids  They all contain the same basic structure but the ‘R’ group is different for each one  When amino acids are joined together a protein is formed  The amino acids can be arranged in any order, resulting in hundreds of thousands of different proteins  Even a small difference in the order of the amino acids results in a different protein being formed General amino acid structure Amino acids join together to form proteins  52 Food Tests Test for glucose (a reducing sugar)  Add Benedict's solution into sample solution in test tube  Heat at 60 - 70 °c in water bath for 5 minutes  Take test tube out of water bath and observe the colour  A positive test will show a colour change from blue to orange or brick red The Benedict's test for glucose Test for starch using iodine  We can use iodine to test for the presence or absence of starch in a food sample. The iodine test for starch  53  Add drops of iodine solution to the food sample  A positive test will show a colour change from orange-brown to blue-black Testing a potato to prove the presence of starch Test for protein  Add drops of Biuret solution to the food sample  A positive test will show a colour change from blue to violet / purple The Biuret test for protein Test for lipids  Food sample is mixed with 2cm3 of ethanol and shaken  The ethanol is added to an equal volume of cold water  A positive test will show a cloudy emulsion forming  54 The ethanol test for lipids Test for vitamin C  Add 1cm3 of DCPIP solution to a test tube  Add a small amount of food sample (as a solution)  A positive test will show the blue colour of the dye disappearing The DCPIP test for vitamin C  55 Structure of a DNA Molecule  DNA, or deoxyribonucleic acid, is the molecule that contains the instructions for growth and development of all organisms  It consists of two strands of DNA wound around each other in what is called a double helix DNA, chromosomes and the nucleus  The individual units of DNA are called nucleotides A nucleotide  All nucleotides contain the same phosphate and deoxyribose sugar, but differ from each other in the base attached  There are four different bases, Adenine (A), Cytosine (C), Thymine (T) and Guanine (G)  The bases on each strand pair up with each other, holding the two strands of DNA in the double helix  The bases always pair up in the same way: o Adenine always pairs with Thymine (A-T) o Cytosine always pairs with Guanine (C-G)  56 DNA base pairs  The phosphate and sugar section of the nucleotides form the ‘backbone’ of the DNA strand (like the sides of a ladder) and the base pairs of each strand connect to form the rungs of the ladder The DNA helix is made from two strands of DNA held together by hydrogen bonds  It is this sequence of bases that holds the code for the formation of proteins  57 Unit.5, Enzymes 5.1 Enzymes What Are Enzymes?  Enzymes are: o Catalysts that speed up the rate of a chemical reaction without being changed or used up in the reaction o Proteins o Biological catalysts (biological because they are made in living cells, catalysts because they speed up the rate of chemical reactions without being changed) o Necessary to all living organisms as they maintain reaction speeds of all metabolic reactions (all the reactions that keep an organism alive) at a rate that can sustain life How Do Enzymes Work? Enzyme substrate specificity  Enzymes are specific to one particular substrate (molecule/s that get broken down or joined together in the reaction) as the enzyme is a complementary shape to the substrate  The product is made from the substrate(s) and is released  58 Enzyme specificity: lock and key model of enzyme activity Investigating the Effect of Temperature on Amylase  Starch solution is heated to a set temperature  Iodine is added to wells of a spotting tile  Amylase is added to the starch solution and mixed well  Every minute, droplets of solution are added to a new well of iodine solution  This is continued until the iodine stops turning blue-black (this means there is no more starch left in the solution as the amylase has broken it all down)  Time taken for the reaction to be completed is recorded  Experiment is repeated at different temperatures  The quicker the reaction is completed, the faster the enzyme is working  59 Investigating the effect of temperature on enzyme activity  60 Investigating the Effect of pH on Amylase  Place single drops of iodine solution in rows on the tile  Label a test tube with the pH to be tested  Use the syringe to place 2cm3 of amylase in the test tube  Add 1cm3 of buffer solution to the test tube using a syringe  Use another test tube to add 2cm 3 of starch solution to the amylase and buffer solution, start the stopwatch whilst mixing using a pipette  After 10 seconds, use a pipette to place one drop of mixture on the first drop of iodine, which should turn blue-black  Wait another 10 seconds and place another drop of mixture on the second drop of iodine  Repeat every 10 seconds until iodine solution remains orange-brown  Repeat experiment at different pH values - the less time the iodine solution takes to remain orange-brown, the quicker all the starch has been digested and so the better the enzyme works at that pH  61 Investigating the effect of pH on enzyme activity Enzyme Action & Specificity  Enzymes are specific to one particular substrate(s) as the active site of the enzyme, where the substrate attaches, is a complementary shape to the substrate  This is because the enzyme is a protein and has a specific 3-D shape  This is known as the lock and key hypothesis  When the substrate moves into the enzyme’s active site they become known as the enzyme-substrate complex  After the reaction has occurred, the products leave the enzyme’s active site as they no longer fit it and it is free to take up another substrate  62 How enzymes work 1. Enzymes and substrates randomly move about in solution 2. When an enzyme and its complementary substrate randomly collide - with the substrate fitting into the active site of the enzyme - an enzyme-substrate complex forms, and the reaction occurs. 3. A product (or products) forms from the substrate(s) which are then released from the active site. The enzyme is unchanged and will go on to catalyses further reactions.  63 Enzymes & Temperature  Enzymes are proteins and have a specific shape, held in place by bonds  This is extremely important around the active site area as the specific shape is what ensures the substrate will fit into the active site and enable the reaction to proceed  Enzymes work fastest at their ‘optimum temperature’ – in the human body, the optimum temperature is 37⁰C  Heating to high temperatures (beyond the optimum) will break the bonds that hold the enzyme together and it will lose its shape -this is known as denaturation  Substrates cannot fit into denatured enzymes as the shape of their active site has been lost  Denaturation is irreversible - once enzymes are denatured they cannot regain their proper shape and activity will stop Effect of temperature on enzyme activity  64  Increasing the temperature from 0⁰C to the optimum increases the activity of enzymes as the more energy the molecules have the faster they move and the number of collisions with the substrate molecules increases, leading to a faster rate of reaction  This means that low temperatures do not denature enzymes, they just make them work more slowly Graph showing the effect of temperature on the rate of enzyme activity Enzymes & pH  The optimum pH for most enzymes is 7 but some that are produced in acidic conditions, such as the stomach, have a lower optimum pH (pH 2) and some that are produced in alkaline conditions, such as the duodenum, have a higher optimum pH (pH 8 or 9)  If the pH is too high or too low, the bonds that hold the amino acid chain together to make up the protein can be destroyed  This will change the shape of the active site, so the substrate can no longer fit into it, reducing the rate of activity  Moving too far away from the optimum pH will cause the enzyme to denature and activity will stop  65 Effect of pH on enzyme activity Graph showing the effect of pH on rate of activity for an enzyme from the duodenum  66 Unit.6, Plant nutrition 6.1 Photosynthesis Photosynthesis  Green plants make the carbohydrate glucose from the raw materials carbon dioxide and water  At the same time oxygen is made and released as a waste product  The reaction requires energy which is obtained by the pigment chlorophyll trapping light from the Sun  So photosynthesis can be defined as the process by which plants manufacture carbohydrates from raw materials using energy from light Photosynthesis Word Equation Photosynthesis Chemical Equation Balanced chemical equation for photosynthesis  67 Chlorophyll  Chlorophyll is a green pigment that is found in chloroplasts within plant cells  Chlorophyll transfers energy from light into energy in chemicals, for the synthesis of carbohydrates Use & Storage of Carbohydrates How are the products of photosynthesis used?  The carbohydrates produced by plants during photosynthesis can be used in the following ways: o Converted into starch molecules which act as an effective energy store o Converted into cellulose to build cell walls o Glucose can be used in respiration to provide energy o Converted to sucrose for transport in the phloem o As nectar to attract insects for pollination  Plants can also convert the carbohydrates made into lipids for an energy source in seeds and into amino acids (used to make proteins) when combined with nitrogen and other mineral ions absorbed by roots Minerals in Plants  Photosynthesis produces carbohydrates, but plants contain many other types of biological molecule; such as proteins, lipids and nucleic acid (DNA)  Carbohydrates contain the elements carbon, hydrogen and oxygen but proteins, for example, contain nitrogen as well  Other chemicals in plants contain different elements as well, for example chlorophyll contains magnesium and nitrogen  Plants obtain these elements in the form of mineral ions actively absorbed from the soil by root hair cells  68 Mineral Deficiencies Table Investigating the Need for Chlorophyll, Light & Carbon Dioxide for photosynthesis Investigating the Need for Chlorophyll  Starch is stored in chloroplasts where photosynthesis occurs so testing a leaf for starch is a reliable indicator of which parts of the leaf are photosynthesising.  Leaves can be tested for starch using the following procedure: o A leaf is dropped in boiling water to kill the cells and break down the cell membranes o The leaf is left for 5-10 minutes in hot ethanol in a boiling tube. This removes the chlorophyll so colour changes from iodine can be seen more clearly o The leaf is dipped in boiling water to soften it o The leaf is spread out on a white tile and covered with iodine solution o In a green leaf, the entire leaf will turn blue-black as photosynthesis is occurring in all areas of the leaf o This method can also be used to test whether chlorophyll is needed for photosynthesis by using a variegated leaf (one that is partially green and partially white) o The white areas of the leaf contain no chlorophyll and when the leaf is tested only the areas that contain chlorophyll stain blue-black o The areas that had no chlorophyll remain orange-brown as no photosynthesis is occurring here and so no starch is stored  69 Testing a variegated leaf for starch  70 Investigating the Need for Light  The same procedure as above can be used to investigate if light is needed for photosynthesis  Before starting the experiment the plant needs to be destarched by placing in a dark cupboard for 24 hours  This ensures that any starch already present in the leaves will be used up and will not affect the results of the experiment  Following destarching, a leaf of the plant can be partially covered with aluminium foil and the plant placed in sunlight for a day  The leaf can then be removed and tested for starch using iodine  The area of the leaf that was covered with aluminium foil will remain orange- brown as it did not receive any sunlight and could not photosynthesise, while the area exposed to sunlight will turn blue-black  This proves that light is necessary for photosynthesis and the production of starch Investigating the Need for Carbon Dioxide  Destarch two plants by placing in the dark for a prolonged period of time  Place one plant in a bell jar which contains a beaker of sodium hydroxide (which will absorb carbon dioxide from the surrounding air)  Place the other plant in a bell jar which contains a beaker of water (control experiment), which will not absorb carbon dioxide from the surrounding air  Place both plants in bright light for several hours  Test both plants for starch using iodine  The leaf from the plant placed near sodium hydroxide will remain orange-brown as it could not photosynthesise due to lack of carbon dioxide  The leaf from the plant placed near water should turn blue-black as it had all necessary requirements for photosynthesis An example setup for an experiment to test whether carbon dioxide is necessary for photosynthesis in plants.  71 Investigating the Rate of Photosynthesis  The plants usually used are Elodea or Camboba - types of pondweed  As photosynthesis occurs, oxygen gas produced is released  As the plant is in water, the oxygen released can be seen as bubbles leaving the cut end of the pondweed  The number of bubbles produced over a minute can be counted to record the rate  The more bubbles produced per minute, the faster the rate of photosynthesis  A more accurate version of this experiment is to collect the oxygen released in a test tube inverted over the top of the pondweed over a longer period of time and then measure the volume of oxygen collected  This practical can be used in the following ways: Investigating the effect of changing light intensity  This can be done by moving a lamp different distances away from the beaker containing the pondweed Investigating the effect of changing light intensity on the rate of photosynthesis  72 Investigating the effect of changing temperature  This can be done by changing the temperature of the water in the beaker Investigating the effect of changing temperature on the rate of photosynthesis Investigating the effect of changing carbon dioxide concentration  This can be done by dissolving different amounts of sodium hydrogen carbonate in the water in the beaker  73 Investigating the effect of changing carbon dioxide concentration on the rate of photosynthesis  Care must be taken when investigating a condition to keep all other variables constant in order to ensure a fair test  For example, when investigating changing light intensity, a glass tank should be placed in between the lamp and the beaker to absorb heat from the lamp and so avoid changing the temperature of the water as well as the light intensity Investigating Gas Exchange  Plants are respiring all the time and so plant cells are taking in oxygen and releasing carbon dioxide as a result of aerobic respiration  Plants also photosynthesise during daylight hours, for which they need to take in carbon dioxide and release the oxygen made in photosynthesis  At night, plants do not photosynthesise but they continue to respire, meaning they take in oxygen and give out carbon dioxide  74 Photosynthesis and respiration in plants  During the day, especially when the sun is bright, plants are photosynthesising at a faster rate than they are respiring, so there is a net intake of carbon dioxide and a net output of oxygen  We can investigate the effect of light on the net gas exchange in an aquatic plant using a pH indicator such as hydrogencarbonate indicator  This is possible because carbon dioxide is an acidic gas when dissolved in water  Hydrogencarbonate indicator shows the carbon dioxide concentration in solution  The table below shows the colour that the indicator turns at different levels of carbon dioxide concentration  75  Several leaves from the same plant are placed in stoppered boiling tubes containing some hydrogencarbonate indicator  The effect of light can then be investigated over a period of a few hours  Results from a typical experiment are shown in the table below:  76 Limiting Factors:  If a plant is given unlimited sunlight, carbon dioxide and water and is at a warm temperature, the limit on the rate (speed) at which it can photosynthesise is its own ability to absorb these materials and make them react  So a limiting factor can be defined as something present in the environment in such short supply that it restricts life processes  There are three main factors which limit the rate of photosynthesis: o Temperature o Light intensity o Carbon dioxide concentration  Although water is necessary for photosynthesis, it is not considered a limiting factor Temperature  As temperature increases the rate of photosynthesis increases as the reaction is controlled by enzymes  However, as the reaction is controlled by enzymes, this trend only continues up to a certain temperature beyond which the enzymes begin to denature and the rate of reaction decreases The effect of temperature on the rate of photosynthesis  77 Light intensity  The more light a plant receives, the faster the rate of photosynthesis  This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply The effect of light intensity on the rate of photosynthesis  At low light intensities, increasing the intensity will initially increase the rate of photosynthesis. At a certain point, increasing the light intensity stops increasing the rate. The rate becomes constant regardless of how much light intensity increases as something else is limiting the rate  The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough carbon dioxide. Carbon dioxide concentration  Carbon dioxide is one of the raw materials required for photosynthesis  This means the more carbon dioxide that is present, the faster the reaction can occur  This trend will continue until some other factor required for photosynthesis prevents the rate from increasing further because it is now in short supply  78 The effect of carbon dioxide concentration on the rate of photosynthesis  The factors which could be limiting the rate when the line on the graph is horizontal include temperature not being high enough or not enough light  79 6.2 Leaf structure Leaf Structure & Adaptations for Photosynthesis Leaf structure Diagram showing the cross-section of a leaf  80 How photosynthesising cells obtain carbon dioxide  Pathway of carbon dioxide from the atmosphere to chloroplasts by diffusion: Atmosphere → air spaces around spongy mesophyll tissue → leaf mesophyll cells → chloroplast Leaf Structure Table  81 Adaptations of Leaf Structure for Photosynthesis Table  82 Identifying Leaf Structures in a Dicotyledonous Plant  You will be expected to identify the following structures in the leaf of a dicotyledonous plant: o Chloroplasts o Cuticle o Guard cells o Stomata o Upper and lower epidermis o Palisade mesophyll o Spongy mesophyll o Air spaces o Vascular bundles (xylem and phloem)  83 Diagram showing the cross-section of a leaf An electron micrograph of a leaf.  84 Unit.7, Human nutrition 7.1 Diet Balanced Diet  A balanced diet consists of all of the food groups in the correct proportions  The necessary food groups are: o Carbohydrates o Proteins o Lipids o Vitamins o Minerals o Dietary Fibre o Water Food Groups Table Vitamin and Mineral Requirements Table  85 Varying Dietary Needs of Individuals Table  86 Scurvy & Rickets Scurvy  Scurvy is the name for a severe vitamin C deficiency o It is caused by a lack of vitamin C in the diet for over 3 months  Its symptoms include: o Anemia o Exhaustion o Spontaneous bleeding o Pain in the limbs o Swelling o Gum ulcerations o Tooth loss  It is a condition that was commonly seen in sailors between the 15th to 18th centuries o Long sea voyages made it very hard to access a ready supply of fresh produce  Scurvy can be treated with oral or intravenous vitamin C supplements Rickets  Rickets is a condition in children characterised by poor bone development  Symptoms include: o Bone pain o Lack of bone growth o Soft, weak bones (sometimes causing deformities)  Rickets is caused by a severe lack of vitamin D o Vitamin D is required for the absorption of calcium into the body  Calcium is a key component of bones and teeth  Vitamin D mostly comes from exposure to sunlight but it can also be found in some foods (fish, eggs and butter)  The treatment for rickets is to increase consumption of foods containing calcium and vitamin D o Alternatively vitamin D supplements can be prescribed  87 7.2 Digestive System Identifying Organs of the Digestive System The human digestive system  88 Organs of the Digestive System: Function Stages of food breakdown  Food taken into the body goes through 5 different stages during its passage through the alimentary canal (the gut): o Ingestion - the taking of substances, e.g. food and drink, into the body through the mouth o Mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules o Chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules o Absorption - the movement of small food molecules and ions through the wall of the intestine into the blood o Assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells o Egestion - the passing out of food that has not been digested or absorbed, as faeces, through the anus Functions of the Digestive Organs Table  89 7.3 Physical Digestion Physical Digestion  Physical digestion (sometimes referred to as mechanical digestion) is the breakdown of food into smaller pieces without chemical change to the food molecules  The processes that take place during physical digestion help to increase the surface area of food for the action of enzymes during chemical digestion  It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum  90 Teeth Types of Human Teeth  Mechanical digestion is the breakdown of food into smaller pieces without chemical change to the food molecules  It is mainly carried out by the chewing action of the teeth, the churning action of the stomach and the emulsification of fats by bile in the duodenum  Teeth are held firmly in the bone of the jaw o They are used for chewing to increase the surface area of the food so that it can be exposed to saliva and other digestive juices and broken down more quickly  The differing shapes and sizes of teeth enable them to perform slightly different functions: o Incisors - chisel-shaped for biting and cutting o Canines - pointed for tearing, holding and biting o Premolars and molars - larger, flat surfaces with ridges at the edges for chewing and grinding up food Types of teeth Structure of a Tooth Structure of a typical tooth  91 The Stomach  The stomach is one of a number of organs that make up the digestive system  The role of the digestive system is to break down large insoluble molecules into smaller, soluble food molecules to provide the body with nutrients  The stomach lining contains muscles which contract to physically squeeze and mix the food with the strong digestive juices that are present o Also known as "stomach churning"  Food is digested within the stomach for several hours Three types of tissue found in the stomach are muscular, epithelial and glandular. These tissues work together to allow the stomach to carry out its role.  92 Emulsification of Fats & Oils  Cells in the liver produce bile which is then stored in the gallbladder Bile production and secretion Bile has two main roles:  It is alkaline to neutralise the hydrochloric acid which comes from the stomach  The enzymes in the small intestine have a higher (more alkaline) optimum pH than those in the stomach  It breaks down large drops of fat into smaller ones. This is known as emulsification. The larger surface area allows lipase to chemically break down the lipid into glycerol and fatty acids faster  93 7.4 Chemical Digestion Chemical Digestion Stages of food breakdown  Food taken into the body goes through 5 different stages during its passage through the alimentary canal (the gut): o Ingestion - the taking of substances, e.g. food and drink, into the body through the mouth o Mechanical digestion - the breakdown of food into smaller pieces without chemical change to the food molecules o Chemical digestion - the breakdown of large, insoluble molecules into small, soluble molecules o Absorption - the movement of small food molecules and ions through the wall of the intestine into the blood o Assimilation - the movement of digested food molecules into the cells of the body where they are used, becoming part of the cells o Egestion - the passing out of food that has not been digested or absorbed, as faeces, through the anus  The role of chemical digestion is to produce small soluble molecules that can be absorbed Enzymes in Digestion Amylases  Amylases are produced in the mouth and the pancreas (secreted into the duodenum)  Amylases digest starch into smaller sugars The digestion of starch  94 Proteases  Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas) The digestion of proteins Lipases  Lipase enzymes are produced in the pancreas and secreted into the duodenum  They digest lipids into fatty acids and glycerol The digestion of lipids Hydrochloric Acid  The stomach produces several fluids which together are known as gastric juice  One of the fluids produced is hydrochloric acid  This kills bacteria in food and gives an acid pH for enzymes to work in the stomach  95 How is a low pH helpful in the stomach?  The low pH kills bacteria in food that we have ingested as it denatures the enzymes in their cells, meaning they cannot carry out any cell reactions to maintain life  Pepsin, produced in the stomach, is an example of an enzyme which has a very low optimum pH - around pH 2  The hydrochloric acid produced in the stomach ensures that conditions in the stomach remain within the optimum range for pepsin to work at its fastest rate Digestion of Starch  Amylases are produced in the mouth and the pancreas (secreted into the duodenum)  Amylases digest starch into smaller sugars The digestion of starch  Amylase is secreted into the alimentary canal in the mouth and the duodenum (from the pancreas) and digests starch to maltose (a disaccharide)  Maltose is digested by the enzyme maltase into glucose on the membranes of the epithelium lining the small intestine Digestion of Protein  Proteases are a group of enzymes that break down proteins into amino acids in the stomach and small intestine (with the enzymes in the small intestine having been produced in the pancreas)  96 The digestion of proteins  Protein digestion takes place in the stomach and duodenum with two main enzymes produced: o Pepsin is produced in the stomach and breaks down protein in acidic conditions o Trypsin is produced in the pancreas and secreted into the duodenum where is breaks down protein in alkaline conditions Bile in chemical digestion o Bile is an alkaline mixture that neutralises the acidic mixture of food and gastric juices entering the duodenum from the stomach, to provide a suitable pH for enzyme action. 7.5 Absorption Absorbing Nutrients  Absorption is the movement of digested food molecules from the digestive system into the blood (glucose and amino acids) and lymph (fatty acids and glycerol)  Nutrients are absorbed in the small intestine Absorbing Water  Water is absorbed in both the small intestine and the colon, but most absorption of water (around 80%) happens in the small intestine Adaptations of the Small Intestine  The ileum is adapted for absorption as it is very long and has a highly folded surface with millions of villi (tiny, finger like projections)  These adaptations massively increase the surface area of the ileum, allowing absorption to take place faster and more efficiently  97 Adaptations of the small intestine  98  Microvilli on the surface of the villus further increase surface area for faster absorption of nutrients  Wall of villus is one cell thick meaning that there is only a short distance for absorption to happen by diffusion and active transport  Well supplied with a network of blood capillaries that transport glucose and amino acids away from the small intestine in the blood  Lacteal runs through the centre of the villus to transport fatty acids and glycerol away from the small intestine in the lymph  99 Unit.8, Transport in plants 8.1 Xylem and phloem The Xylem & Phloem  Plants contain two types of transport vessel: o Xylem vessels – transport water and minerals from the roots to the stem and leaves o Phloem vessels – transport food materials (mainly sucrose and amino acids) made by the plant from leaves to regions in the roots and stem  These vessels are arranged throughout the root, stem and leaves in groups called vascular bundles Vascular tissue in a dicotyledonous plant  100 Adaptations of Xylem Vessels Xylem cells lose their top and bottom walls to form a continuous tube through which water moves through from the roots to the leaves  Function: transport tissue for water and dissolved mineral ions  Adaptations: o Cells joined end to end with no cross walls to form a long continuous tube o Cells are essentially dead, without cell contents, to allow free passage of water o Outer walls are thickened with a substance called lignin, strengthening the tubes, which helps support the plant 8.2 Water uptake Root Hair Cells  Root hairs are single-celled extensions of epidermis cells in the root  They grow between soil particles and absorb water and minerals from the soil  Water enters the root hair cells by osmosis  This happens because soil water has a higher water potential than the cytoplasm of the root hair cell  101 Structure of the root  The root hair increases the surface area of the cells significantly  This large surface area is important as it increases the rate of the absorption of water by osmosis and mineral ions by active transport Pathway Taken by Water  Osmosis causes water to pass into the root hair cells, through the root cortex and into the xylem vessels: Pathway of water into and across a root  102  Once the water gets into the xylem, it is carried up to the leaves where it enters mesophyll cells  So the pathway is: Root hair cell → root cortex cells → xylem → leaf mesophyll cells Investigating Water Movement in Plants  The pathway can be investigated by placing a plant (like celery) into a beaker of water that has had a stain added to it (food colouring will work well)  After a few hours, you can see the leaves of the celery turning the same colour as the dyed water, proving that water is being taken up by the celery  If a cross-section of the celery is cut, only certain areas of the stalk is stained the colour of the water, showing that the water is being carried in specific vessels through the stem - these are the xylem vessels Investigating water movement in plants using a stain  103 8.3 Transpiration Transpiration  Water travels up xylem from the roots into the leaves of the plant to replace the water that has been lost due to transpiration  Transpiration is defined as the loss of water vapour from plant leaves by evaporation of water at the surfaces of the mesophyll cells followed by diffusion of water vapour through the stomata  Xylem is adapted in many ways: o A substance called lignin is deposited in the cell walls which causes the xylem cells to die o These cells then become hollow (as they lose all their organelles and cytoplasm) and join end-to-end to form a continuous tube for water and mineral ions to travel through from the roots o Lignin strengthens the plant to help it withstand the pressure of the water movement  Movement in xylem only takes place in one direction - from roots to leaves (unlike phloem where movement takes place in different directions) Water uptake, transport and transpiration  104 Transpiration in plants  Transpiration has several functions in plants: o transporting mineral ions o providing water to keep cells turgid in order to support the structure of the plant o providing water to leaf cells for photosynthesis o Keeping the leaves cool (the conversion of water (liquid) into water vapour (gas) as it leaves the cells and enters the airspace requires heat energy. The using up of heat to convert water into water vapour helps to cool the plant down) Investigating the Effect of Temperature & Wind Speed on Transpiration Rate Investigating the role of environmental factors in determining the rate of transpiration from a leafy shoot  Cut a shoot underwater to prevent air entering the xylem and place in tube  Set up the apparatus as shown in the diagram and make sure it is airtight, using vaseline to seal any gaps  Dry the leaves of the shoot (wet leaves will affect the results)  105  Remove the capillary tube from the beaker of water to allow a single air bubble to form and place the tube back into the water  Allow the plant to adapt to the new environment for 5 minutes  Record the starting location of the air bubble. Leave for a set period of time  Record the end location of air bubble  Change the wind speed or temperature (only one - whichever factor is being investigated)  Reset the bubble by opening the tap below the reservoir. Repeat the experiment  The further the bubble travels in the same time period, the faster transpiration is occurring and vice versa An experimental setup for testing the effect of light intensity on transpiration rates. The apparatus can be modified to test the effects of temperature and wind speed.  106  Environmental factors can be investigated in the following ways: o Temperature : Temperature of room (cold room and warm room)  As temperature increases the rate of transpiration also increases o Wind speed : Use an electric fan to mimic different wind speeds  As wind speed increases the rate of transpiration also increases Explain how water vapour loss  Evaporation takes place from the surfaces of spongy mesophyll cells  The many interconnecting air spaces between these cells and the stomata create a large surface area  This means evaporation can happen rapidly when stomata are open Explain the mechanism by which water moves  upwards in the xylem Water molecules are attracted to each other by cohesion - creating a continuous column of water up the plant  Water moves through the xylem vessels in a continuous transpiration stream from roots to leaves via the stem  Transpiration produces a tension or ‘pull’ on the water in the xylem vessels by the leaves  As water molecules are held together by cohesive forces (each individual molecule ‘pulls’ on the one below it), so water is pulled up through the plant  If the rate of transpiration from the leaves increases, water molecules are pulled up the xylem vessels quicker  107 The generation of the transpiration stream. Explaining the Effects of Temperature, Wind Speed & Humidity  Wind speed, humidity and temperature all have an effect on the rate at which transpiration occurs  The table below explains how these factors affect the rate of transpiration when they are all high; the opposite effect would be observed if they were low Transpiration Rate Factors Table  108  A potometer can be used to investigate the effect of environmental factors on the rate of transpiration Wilting  If more water evaporates from the leaves of a plant than is available in the soil to move into the root by osmosis, then wilting will occur  This is when all the cells of the plant are not full of water, so the strength of the cell walls cannot support the plant and it starts to collapse A wilted plant cannot support itself and starts to collapse 8.4 Translocation Translocation  The soluble products of photosynthesis are sugars (mainly sucrose) and amino acids  These are transported around the plant in the phloem tubes which are made of living cells (as opposed to xylem vessels which are made of dead cells)  The cells are joined end to end and contain holes in the end cell walls (called sieve plates) which allow easy flow of substances from one cell to the next  The transport of sucrose and amino acids in the phloem, from regions of production to regions of storage or use, is called translocation  Transport in the phloem goes in many different directions depending on the stage of development of the plant or the time of year; however dissolved food is always transported from the source (where it’s made) to sink (where it’s stored or used):  During winter, when many plants have no leaves, the phloem tubes may transport dissolved sucrose and amino acids from the storage organs to other parts of the plant so that respiration can continue  During a growth period (ex. during the spring), the storage organs (ex. roots) would be the source and the many growing areas of the plant would be the sinks  After the plant has grown (usually during the summer), the leaves are photosynthesizing and producing large quantities of sugars; so they become the source and the roots become the sinks – storing sucrose as starch until it is needed again  109 Translocation through the phloem Comparison between Xylem and Phloem Tissue Table  110 Unit.9, Transport in animals 9.1 Circulatory systems Circulatory System  The circulatory system is a system of blood vessels with a pump and valves to ensure one-way flow of blood An example of a circulatory system.  111 Circulatory Systems of Fish & Mammals Circulatory systems in Fish  Fish have a two-chambered heart and a single circulation  This means that for every one circuit of the body, the blood passes through the heart once The single circulatory system in fish Circulatory systems in Mammals  Mammals have a four-chambered heart and a double circulation  This means that for every one circuit of the body, the blood passes through the heart twice  112  The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs (the pulmonary circulation)  The left side of the heart receives oxygenated blood from the lungs and pumps it to the body (the systemic circulation) The double circulatory system in mammals Advantages of Double Circulation  Blood travelling through the small capillaries in the lungs loses a lot of pressure that was given to it by the pumping of the heart, meaning it cannot travel as fast  By returning the blood to the heart after going through the lungs its pressure can be raised again before sending it to the body, meaning cells can be supplied with the oxygen and glucose they need for respiration faster and more frequently  113 9.2 Heart The Mammalian Heart  The heart is labelled as if it was in the chest so what is your left on a diagram is actually the right hand side and vice versa  The right side of the heart receives deoxygenated blood from the body and pumps it to the lungs  The left side of the heart receives oxygenated blood from the lungs and pumps it to the body  Blood is pumped towards the heart in veins and away from the heart in arteries  The two sides of the heart are separated by a muscle wall called the septum  The heart is made of muscle tissue which are supplied with blood by the coronary arteries Structure of the heart  114 Identifying Structures in the Heart  The ventricles have thicker muscle walls than the atria as they are pumping blood out of the heart and so need to generate a higher pressure  The left ventricle has a thicker muscle wall than the right ventricle as it has to pump blood at high pressure around the entire body, whereas the right ventricle is pumping blood at lower pressure to the lungs  The septum separates the two sides of the heart and so prevents mixing of oxygenated and deoxygenated blood Structure of the heart showing the different valves The function of valves  The basic function of all valves is to prevent blood from flowing backwards  There are two sets of valves in the heart: o The atrioventricular valves separate the atria from the ventricles o The valve in the right side of the heart is called the TRICUSPID and the valve in the left side is called the BICUSPID  115 o These valves are pushed open when the atria contract but when the ventricles contract they are pushed shut to prevent blood flowing back into the atria o The semilunar valves are found in the two blood arteries that come out of the top of the heart o They are unusual in that they are the only two arteries in the body that contain valves o These valves open when the ventricles contract so blood squeezes past them out of the heart, but then shut to avoid blood flowing back into the heart Functioning of the Heart  Deoxygenated blood coming from the body flows into the right atrium via the vena cava  Once the right atrium has filled with blood the heart gives a little beat and the blood is pushed through the tricuspid (atrioventricular) valve into the right ventricle  The walls of the ventricle contract and the blood is pushed into the pulmonary artery through the semilunar valve which prevents blood flowing backwards into the heart  The blood travels to the lungs and moves through the capillaries past the alveoli where gas exchange takes place (this is why there has to be low pressure on this side of the heart – blood is going directly to capillaries which would burst under higher pressure)  Oxygen-rich blood returns to the left atrium via the pulmonary vein  It passes through the bicuspid (atrioventricular) valve into the left ventricle  The thicker muscle walls of the ventricle contract strongly to push the blood forcefully into the aorta and all the way around the body  The semilunar valve in the aorta prevents the blood flowing back down into the heart Monitoring Activity of the Heart  Heart activity can be monitored by using an ECG, measuring pulse rate or listening to the sounds of valves closing using a stethoscope  Heart rate (and pulse rate) is measured in beats per minute (bpm)  To investigate the effects of exercise on heart rate, record the pulse rate at rest for a minute  Immediately after they do some exercise, record the pulse rate every minute until it returns to the resting rate  This experiment will show that during exercise the heart rate increases and may take several minutes to return to normal  116 Investigating Effect of Physical Activity on Heart Rate  It is relatively simple to investigate the effects of exercise on the body in the classroom  Breathing rate can be measured by counting the number of breaths per minute, while heart rate can be measured by taking a pulse  Either can be measured before and after an activity is performed and the results plotted on a bar chart o It is important that the time over which breathing rate and pulse rate are measured is consistent, and that individuals fully recover (rest) before starting a new activity  Increased physical activity results in an increased heart rate and breathing rate o Heart rate remains high for a period of time after physical has stopped, there is a gradual return to resting heart rate Explaining the Effect of Physical Activity on Heart Rate  So that sufficient blood is taken to the working muscles to provide them with enough nutrients and oxygen for increased respiration  An increase in heart rate also allows for waste products to be removed at a faster rate  Following exercise, the heart continues to beat faster for a while to ensure that all excess waste products are removed from muscle cells  It is also likely that muscle cells have been respiring anaerobically during exercise and so have built up an oxygen debt  This needs to be ‘repaid’ following exercise and so the heart continues to beat faster to ensure that extra oxygen is still being delivered to muscle cells  The extra oxygen is used to break down the lactic acid that has been built up in cells as a result of anaerobic respiration Coronary Heart Disease The coronary arteries  117  The heart is made of muscle cells that need their own supply of blood to deliver oxygen, glucose and other nutrients and remove carbon dioxide and other waste products  The blood is supplied by the coronary arteries  If a coronary artery becomes partially or completely blocked by fatty deposits called ‘plaques’ (mainly formed from cholesterol), the arteries are not as elastic as they should be and therefore cannot stretch to accommodate the blood which is being forced through them - leading to coronary heart disease  Partial blockage of the coronary arteries creates a restricted blood flow to the cardiac muscle cells and results in severe chest pains called angina  Complete blockage means cells in that area of the heart will not be able to respire and can no longer contract, leading to a heart attack Buildup of plaque in the coronary arteries  118 Effect of narrowing of arteries Risk Factors for CHD Table  119 Diet, Exercise & Coronary Heart Disease Reducing the risks of developing coronary heart disease  Quit smoking  Diet - reduce animal fats and eat more fruits and vegetables - this will reduce cholesterol levels in the blood and help with weight loss if overweight  Exercise regularly - again, this will help with weight loss, decrease blood pressure and cholesterol levels and help reduce stress 9.3 Blood vessels Arteries, Veins & Capillaries Arteries  Carry blood at high pressure away from the heart  Carry oxygenated blood (other than the pulmonary artery)  Have thick muscular walls containing elastic fibres  Have a narrow lumen and speed of flow is fast Veins  Carry blood at low pressure towards the heart  Carry deoxygenated blood (other than the pulmonary vein)  Have thin walls and a large lumen  Contain valves and speed of flow is slow Comparing arteries and veins  120 Capillaries  Carry blood at low pressure within tissues  Carry both oxygenated and deoxygenated blood  Have walls that are one cell thick  Have ‘leaky’ walls  Speed of flow is slow Structure of a capillary Main Blood Vessels in the Body  Blood is carried away from the heart and towards organs in arteries  These narrow to arterioles and then capillaries as they pass through the organ  The capillaries widen to venules and finally veins as they move away from the organs  Veins carry blood back toward the heart  121 The circulatory system Important Blood Vessels Table  122 How Structure of Blood Vessels is Adapted to their Function Arteries  Have thick muscular walls containing elastic fibres to withstand the high pressure of blood and maintain the blood pressure as it recoils after the blood has passed through  Have a narrow lumen to maintain high pressure Veins  Have a large lumen as blood pressure is low  Contain valves to prevent the backflow of blood as it is under low pressure Capillaries  Have walls that are one cell thick so that substances can easily diffuse in and out of them  Have ‘leaky’ walls so that blood plasma can leak out and form tissue fluid surrounding cells  123 Adaptations of blood vessels Arterioles and venules As arteries divide more as they get further away from the heart, they get narrower  The narrow vessels that connect arteries to capillaries are called arterioles  Veins also get narrower the further away they are from the heart  The narrow vessels that connect capillaries to veins are called venules The blood vessel network Blood Vessels & the Liver  You must be able to identify the main blood vessels to and from the liver o The hepatic artery brings oxygenated blood from the heart to the liver o The hepatic vein brings deoxygenated blood from the liver back to the heart o The hepatic portal vein transports deoxygenated blood from the gut to the liver Mammalian circulatory system  124 9.4 Blood Components of Blood  Blood consists of red blood cells, white blood cells, platelets and plasma Composition of human blood Components of the Blood Table  125 Identifying Red & White Blood Cells Blood micrograph Components of Blood: Function  Plasma is important for the transport of carbon dioxide, digested food (nutrients), urea, mineral ions, hormones and heat energy  Red blood cells transport oxygen around the body from the lungs to cells which require it for aerobic respiration o They carry the oxygen in the form of oxyhaemoglobin  White blood cells defend the body against infection by pathogens by carrying out phagocytosis and antibody production  Platelets are involved in helping the blood to clot Lymphocytes & Phagocytes  White blood cells are part of the body’s immune system, defending against infection by pathogenic microorganisms  There are two main types, phagocytes and lymphocytes  126 Phagocytes  Carry out phagocytosis by engulfing and digesting pathogens Phagocytosis  Phagocytes have a sensitive cell surface membrane that can detect chemicals produced by pathogenic cells  Once they encounter the pathogenic cell, they will engulf it and release digestive enzymes to digest it  They can be easily recognised under the microscope by their multi-lobed nucleus and their granular cytoplasm Lymphocytes  Produce antibodies to destroy pathogenic cells and antitoxins to neutralise toxins released by pathogens  They can easily be recognised under the microscope by their large round nucleus which takes up nearly the whole cell and their clear, non-granular cytoplasm Blood Clotting  Platelets are fragments of cells which are involved in blood clotting and forming scabs where skin has been cut or punctured  Blood clotting prevents continued / significant blood loss from wounds  Scab formation seals the wound with an insoluble patch that prevents entry of microorganisms that could cause infection  It remains in place until new skin has grow