- Created by: Danniatkinson
- Created on: 16-02-17 17:03
Seeing cells and components
- Cells are seen by using a light microscope; a beam of light is pssed through the cells.
- Electron microscopes pass a bem of electrons through the cells. This lets us see them in much more detail.
- To work out the magnifiction of a light microscope use this calculation: Magnifying power of eyepiece lens x magnifying power of objective lens = total magnifiction.
- The greater the resolving power of a microscope the clearer the image it forms.
- Resolving power depends on the wavelength of the electromagnetic radiation (light or electrons) that is used:wavelength divided by 2 = resolving power
Cells and components
Plant and animal cells have some features in common:
- Cell membrane - seperates the content of the cell and it's surrondings. It controls the movement of substances like oxygen, glucose and carbon dioxide into and out of the cell.
- Cytoplasm - where many of the chemical reactions needed to carry out life proccesses take place. It also contains organelles (tiny structures that carry out specific jobs.)
- Nucleus - An orgenelle that contains DNA, which is the genetic material. the nuclues also controls all the activities of the cell.
- Mitochondria - organelles in which respiration occurs. They are very thin and cannot be seen easily through a light microscope at low magnification.
Plant cells also have some other structures:
- Cell wall- made of tough cellulose to support the cell and allow it to keep its shape.
- Large vacuole - a space in the cytoplasm that is filled with cell sap and helps to support the plant by keeping the cells rigid.
- Chloroplasts- organelles thta contain chlorophyll, a green substance that absorbs light energy used in photosynthesis.
DNA and it's structure
- A cells nucleus contins chrormosomes, which are made up of DNA wrapped around a core of protein molecules.
- DNA is a double stranded molecule twisted into a spirl called a double helix.
- The strands of DNA may consist of thousands of building units called nucleotides.
- Each nucleotide includes one of the four bases: Guanine(G), Thymine(T), Adenine(A),and Cytosine(C).
- These bases can be in any order but A lways bonds with T and C always bonds with G.
- A gene is a section of a strand of DNA which carries the information in the sequence of it's bases, enabling a cell to make a protein or part of a protein.
- DNA can easily be extracted from cells in the following ways:
- Use a detergant/salt mixture to break up the membrane of the cells and release the chromosomes.
- Use a protein-digesting enzyme to break down the protein part of the chrormosomes, releasing their DNA.
- Add cold methanol, which precipitates the DNA. The strands can now clearly be seen.
- The structuyre of DNA was discovered by scientists building upon each others work.
- In 1952 Rosalind Franklin and Maurice Wilkins used X-ray crystallography to discover the arrangement of the atoms of DNA molecules.
- In 1953 James watson and Francis Crick used this information to propose that the structure of a molecule of DNA is double helix.
Complementary base pairing.
- The arrangment where the two stnds of a DNA molecule are joined together by their bases, ( A to T) and (G to C) is called complementary base pairing.
- Weak hydrogen bonds join a base with its complementary partner. Because the bonds are weak they are easily broken, enabling a DNA molecule to seperate into two strands.
- This is important when cells make protein nd when they divide to form new cells.
- The sequences of three bases is called a codon. Each codon specifies a particular amino acid
- This genetic code is universal, it works the same in all living things.
- Genetic engineering invloves transferring genes from one type of organism to another.
- A gene controlling the production of a useful protein such as human insulin can be inserted into bacterial cells,
- The cells grow in a solution called a culture in huge containers called fermeters. They produce large amount of protein very quickly.
- The genes are transferred from cell to cell using bacterial enzymes
- The take a strand of DNA which is carrying a gene which enables cells to produce useful proteins and they cut out that gene using a restriction enzyme. The bacteria cell has its plasmid cut out by the same enzyme. The gene is then inserted into the bacteria cell using the ligase enzyme. The plasmid is then put back into the bacteria cell. Bacteria then mutilplies and creates millions of clones with the same useful gene, all with the coding of the required protein. Bacteria is grown in fermeters and the end product is removed from the fermeter.
- Genetically engineered insulin has many advantages: It is cheap to produce and is avaliable in large quantities. It is human insulin so no one is allergic to it. It doesnt use animal products so vegetarians and religious groups dont have a problem with it.
- However some people are scared tht GM organisms could have unknown effects on other organisms, including humans.
- Developments in GM crops include those that can
- Grow in places with low rainfull
- Produce their own chemicals to kill insects that damage them
- resist diseases
- resist the effects of herbicides farmers can then destroy competing weeds without destroying the crop.
- Produce their own fertiliser.
- Some people are corncered about GM crops. There worries are:
- It's not natural
- GM crops may harm wildlife
- Eating GM crops may affect our health
- Pollen from crops modified to resist herbicides may transfer to weeds.
Vitamin A deficiency is common in poor people and can cause blindness. Golden rice has been genitically modified to produce more beta-carotene in the rice grain. This is converted to vitamin A in our cells.
- Mitosis results in two daughter cells with identical chromosomes to the parent cells. If the parent cells have two sets of chromosomes (diploid) the dughter cells will also be diploid.
- Mitosis is used in order for organisms to:
- repair damage. Damaged or old cells are replaced by mitosis with identical new cells.
- Grow. The mass of a plant root increases because the existing root cells produce more by mitosis.
- Asexual reproduction also happens via mitosis. It invloves only one parent, which produces new cells to form offspring. The offspring are therefore genetically identical to each other and the parent. They are clones.
Diploid- two sets of chromosomes
Haploid- one set of chromosomes
- Meiosis is the process that is used to form gametes.
- In meiosis the four daughter cells each have half the mount of chromosomes of the parent cell, resulting in genetically different haploid gametes.
- When a parent cell is about to divide itself it's chromosomes copy themselves.
- This results in chromosomes with two identical strands called chromatids.
- During meiosis, each chromosome pairs up with it's corresponding partner along the centre of the cell.
- The pairs of chromosome copies exchange pieces of DNA with eachother before the cell divides.
- Another division then takes place where the chromatids are split in half. Each daughter cell receives a different chromosome. This results in gametes that are haploid and genitically different from one another.
- During fertilisation, a haploid male gamete(sperm) fusesa with a haploid female gamete(egg). The chromosomes of each cell combine
- The result is a diploid zygote (fertilised egg). this has inherited a new combination of chromosomes- and therefore genes - contributed 50/50 from the parents.
Cloning plants and animals
- Sometimes parts of the root, leaf or stem can grow into a new plant. This is called asexual reproduction and is sometimes called vegatative reproduction. The plants it produces are genitically identical(clones) to the parent plant. This is useful for farmers who want a stock of plants with preffered charateristics like disease resistant, fruit colour, flower shape. A simple way is to take cuttings.
- Tissue culture is a process that invloves cutting small pieces of tissue from the parent that is to be cloned. The pieces are grown in a sterile liquid or gel, which provides all the substances needed for their development.
- Embryo transplants begin in the laboratory and end in normal births. Donor eggs are taken from female animals and fertilised in the laboratory. Each embryo is formed is split up into it's seperate cells. Some of the seperated cells are transplanted into the womb of the host mother, where they develop into identical embryos. The host mother then gives birth to genetically identical youngsters, they are clones.
- Cloning allows scientists to produce animals is desirable charateristics quikly and reliably. It helps build up a population of rare animals so they don't go extinct.
- There is evidence that clones have medical issues and we shouldn't produce clones that may have short painful lives.
- It's currently illegal but we can clone human cells. This could be used to produce organs for people needing a transplant.
The cells on the inside of the embryo are called embryonic stem cells.They are not meant for any specific job. As the embryo develops the cells begin to differenciate and change into different types of cell. As the cells mature they can no longer differentiate but some of our stem cells remain into adulthood.For example there are adult stem cells in our bone marrow which give rise to new blood cells. If stem cells could be made to mutiply and differentiate we would hve unlimited supply of different types of cells, which could be transplanted into people whose tissues are damaged. This is called stem cell therapy.
Embryonic stem cells can differentiate into many more types of cell than adult cells, they are more ideal for therapies that that repair damaged tissues. Sourcing embryonic stem cells kills the embryo and some people think that it is unethical to destroy embryo's.
- Risk of stem cell therapy includes:
- rejection of the embryonic stem cells
- the possibility that the adult stem cells carry genetic mutations for disease or may become defective
- Side effects and complications in the recipient, eg development of cancer.
- treatment to the side effects may be dangerous.
The human genome
- Genome refers to all DNA in each cell of an organism.
- The human genome project begn in 1989. A group of scientists all over the world collaorated to work out the human genome project. The result was announced in April 2003.
- The scientists broke up the chromosomes of cells to get at their DNA. Thousands of copies of the DNA was placed inside machines called sequencers, which display the most likely order of the bases.
- Powerful computers were used to match the base sequences of genes with the proteins in which they code for.
- Understanding the human genome enbkles scientists to look at how genes control our vunerability to a particular diseases and to personalise drug treatments to work with an individuals genome.
- The human genome revealed that some races are more or less vunerable to certain diseases than others. Some people are concerned that if this information was revealed it will encourge discrimination towards certin groups of people.
- Cells make or or synthesis proteins by joining together amino acid units in the correct order.
- Proteins have a complicated shape that helps them to carry out their jobs. Protein molecules that are the wrong shape cannot perform their functions correctly.
- DNA makes sure that the correct number of amino acid units joins together in the right order .
- The more amino acid units joined together, the larger the molecule: pepcides are chains of 2-20 amino acids; polypepcides contain 21-50; proteins contain more than 50 amino acid units.
- Ribonuceic acid (RNA) is a chemical like DNA however RNA is a single strand and has U instead of a T.
- Messanger RNA (mRNA) crries the protein making information from the DNA inside the nuclues of the cell to the ribosomes in the cytoplasm, where the protein is made.
- Transfer RNA (tRNA) carries the amino acids needed to form the protein to the ribosomes.
- 1.The strands of DNA seperate
- 2. Strands of mRNA form as the bases of RNA nucleotides combine with their complementary bases of the single-stranded DNA
- 3.The strands of mRNA seperate from their respective completmentary strands of DNA. They pass from the nuclues through the gaps.
- 4. Each strand of mRNA binds to a ribosome, forming an mRNA- ribosome complex.
- 5. Each type of tRNA molecule binds to a particular amino acid dissolved in the cytoplasm depending on the triplet of bases (codon) it carries.
- 6.tRNA/amino acid combinations pass to the mRNA-ribosome complex. The exposed bases of each tRNA bind to their complementary bases on the mRNA. Chemical bonds form between the amino acids next to eachother
- 7. Once the bonds form each tRNA seperates from it's amino acid and the mRNA strand.
- 8.The linked amino cids form a polypeptide.
- If a sperm or an egg carries a mutated gene, the mutation will be inherited by it's offspring.
- Mutations can be harmful as altering the proteins produced can disturb the activity of cells. Affected organisms are therefore less liekly to survive.
- Some genes that are now normal were once mutants. The mutations added genetic variation that happened to be beneficial.
- This meant that the organisms carrying the mutated gene survived. Their descendants inherited the genes and now they are the normal versions.
- Some mutations are neutral - they do not effect an organisms chances of surviving one way or another.
- Mutations occur because of copying errors in the sequence of bases during DNA replication.
- A base may be deleted or inserted. This changes the sequence of bases along the gene from where the mutation occurs.
- A normal DNA base sequence can be mutated by a deletion (removal of a base) and an insertion (addition of a base).
- The order of amino acid units from where the mutation occurs changes in each mutated gene. This affects the structure of the protein.
- The structure of a protein affects it's function. Chnages in structure can therefore affect how well the protein works or may even prevent it from working at all.
- A codon is a section of DNA and RNA that codes for an amino acid. Almost all amino acids are specified by more than one codon (there are two acceptions to this)
- If a mutation changes a codon to an alternative that still specifies the same amino acid, and the sequence of codons is unchanged, then the amino acid sequence and the structure of the protein remains unchanged.
- This is known as a silent mutation.
- Enzymes are biological catalysts. They increase the rate of chemical reactions inside and outside cells.
- Enzymes are specific in their action - each enzyme only catalyses a particular chemical reaction or type of chemical reaction.
- During digestion enzymes brek down large insouble food molecules into smaller soluble ones that can dissolve into the blood.
- The substrate binds with part of the enzyme called the active site. They fit together like a lock and key. An enzyme will only catalyse a particular reaction when the shape of it's active site matches the shape of the substrate molecule.
- The enzyme catalyses the breakdown of the substrate into the products, which then leave the enzyme. The enzyme is then free to join to another substrate molecule.
- Examples of enzymes in the body include:
- DNA polymerase, which breaks up the double helix before DNA replication. It is also involved in checking the copying of the DNA strand.
- Speeding up the rate of joining together the individual amino acids during protein synthesis.
- Because most enzymes are proteins, they are sensitive to changes in temperature and pH.
- The activity of the enzymes increases as the temperature goes up. When the activity of the enzyme is at a maximum, we say this is the optimum temperature. This is around 37 degrees for enzymes that exist in the human body. After this point, as the temperature increases the activity will decrease.
- Different enzymes have different optimum pH's.
- Enzyme activity is also affected by substrate concentration.
- 1. When there is more than enough enzyme, the rate of reaction is proportional to the concentration of substrate.
- 2. When all the enzyme's active sites are filled with subrate molecules the rate of reaction levels off
- 3. Adding more enzymes increases the rate of reaction because the more active sites are available to substrate molecules, which fill them.
- Protein systhesis
- At extremes of temperature of pH an enzyme will become denatured.
- Denaturing is a permanant change of shape of the protein molecule. It is caused by the breaking up of the hydrogen bonds that hold the structure together.
- A change in the proteins shape will affect it's activity because the active site will change, so the substrate will no longer fit.
Respiring cells and diffusion
- We exhale less oxygen and more carbon dioxide then we inhale. This results in cells carrying out the chemical reaction aerobic respiration. This uses oxygen to break down glucose molecules to release energy, carbon dioxide and water.
- glucose+water>carbon dioxide+water+energy
- All of the available energy is released from a glucose molecule during aerobic respiration.
- Anaerobic respiration does not use oxygen for example in muscle tissue:
- gluose>lactic acid+energy
- The energy released in anaerobic respiration is much less than in aerobic respiration as the glucose is not fully broken down.
- The energy released during aerobic respirtion is to keep us warm and drive life processes, such as movement and reproduction.
- Exercising hard results in the muscles carrying out anaerobic respiration, as the heart and lungs cannot work fast enough to get the required amount of oxygen for aerobic respiration.
- The lactic acid produced in anaerobic respiration accumulates in the muscles and makes them tired and sore.
- After exercise, rapid breathing draws more air into the lungs and the fast beating heart sends the oxygen to the muscle cells where it helps break down lactic acid into carbon dioxide and water.
- The time taken for the lactic acid to be removed and breathing and heart rates to return to normal is the recovering period.
Respiring cells and diffusion
- Molecules in liquids and gases are in a constant random motion. Some molecules will spread from areas where they are highly concentrated to areas of lower concentration, meaning there is a net movement of molecules in this direction. This is called diffusion.
- The greater the difference between the regions of high and low concentration, the faster the substances rate of diffusion.
- Substances move into and out of cells of living things by diffusion.
- Capillary vessels supply body tissue with body via the circulatory system.
- Substances such as glucose, oxygen and hormones pass between the blood and tissues via diffusion.
- Gaseous exchange is the process by which oxygen enters the blood and carbon dioxide leaves. It takes place across the walls of the alveoli (air sacs) in the lungs.
- The concentration gradient is the difference in concentration of a substance between high and low concentration regions.
- The greater the difference between the regions the greater the concentration gradient. A s a result the rate of diffusion is maximised.
- The diffusion of glucose and oxygen to respiring cells relies on a high concentration gradient between the cells and the blood capillaries.
- This is maintained because the cells are constantly respiring, breaking down the glucose and oxygen and lowering their concentration inside the cells.
Effects of exercise
- Exercise increases the heart rate and breathing rate.
- During exercise aerobic respiration in the muscle cells releases energy, enabling muscles to contract quickly and strongly.
- Respiration produces carbon dioxide, which passes from the muscle cells to the blood, raising its acidity and lowering its pH below 7.
- The lowered pH stimulates an increase in the heart rate and breathing rate.
- Heart and brething rates remain high for some minutes after exercising. As a result more blood (with a load of carbon dioxide) is passed to the lungs where it is exhaled.
- The concentration of carbon dioxide in the blood decreases, restoring the pH of the blood to it's normal value of 7.4. Heart and brething rate return to normal.
- Breathing rate can be investigated by using limewater to test for carbon dioxide.
- An easy way to measure your carbon dioxide output is to place a straw in limewater and note the time taken for the limewater to turn cloudy as you breathe out through the straw.
- Counting the number of times your back rises and falls in a minute gives the breathing rate.
- Taking your pulse is an easy way of measuring heart rate.
Effects of exercise
- The more air we breathe in, the more oxygen reaches the muscles and the more energy is released through aerobic respirtion.
- The muscles contract more vigorously enbling us to exercise more.
- The increased rate of aerobic respiration in the muscle cells produces more carbon dioxide. The increased breathing rate tapidly removes the carbon dioxide from the lungs.
- The larger the volume of air moving in and out of our lungs with each breath, the higher the volume of oxygen that can reach the muscles.
- The following equation can be used to calculate this:
- number of breaths in a min x volume of air per breath = volume of air exchange per minute
- One complete contraction and relaxation of the heart prodcuces one heartbeat.
- The volume of blood pumped from the heart each minute (called the cardic output) depends on the heart rate and volume of blood pumped out with each beat (stroke volume)
- Heart rate, stroke volume and cardiac output measure the heart's effectiveness and fitness. Each can be calculated using the equation:
- Cardiac output = stroke volume x heart rate
- Plants use sunlight, carbon dioxide and water to produce glucose, through the process of photosynthesis. light energy
- Carbon dioxide + water > glucose + oxygen
- Plants are green because of the green pigment chlorophyll inside the chloroplasts in their cells.
- Chlorophyll absorbs the light energy required to drive photosynthesis.
- Leaves are thin and flat, exposing a large surface area maximising the absorption of light.
- The palisade cells, just under the upper surface of the leaf where the light is brightest, are packed with chloroplasts containing chlorophyll for maximum rate of photosynthesis.
- Air spaces enable gases including water vapour to circulate within the leaf, so the reactants for photosynthesis can reach the cells that need them.
- Oxygen, carbon dioxide and water vapour diffuse between the leaf's air spaces and the atmosphere through the gaps called stomata that perforate the underside of the leaf.
- The rate at which plants make glucose is affected by conditions of:
- temperature, light intensity, carbon dioxide, water
- If any of these factors drop too low photosynthesis slows even if the others are in abundant supply. This is called a limiting factor.
- You can measure the rate of photosynthesis by putting a water weed in a inverted tunnel and put that in a beaker full of water, then put a test tube upside down over the inverted tunnel. You shine a light onto the water weed. The rate of photosynthesis is measured by counting the mount of bubbles of oxygen the water weed produces in a given time.
- This set-up works for investigating the effects of changing light intensity, carbon dioxide concentration and temperature on the rate of photosynthesis.
- Most plants grow best in warm, light conditions and when there is a high concentration of carbon dioxide and plenty of water. Growing plants in greenhouses can help maximise these conditions.
- The higher the temperature, the faster the rate of photosynthesis and the faster the production of materials that enable plants to grow.
- If the temperature continues to increase beyond optimum, photosynthesis slows because the enzymes controlling the different reactions of photosynthesis are denatured.
- Plants grow more vigorously in bright sunlight because high light intensity maximises the rate of photosynthesis. The rate of increase is up to a maximum value. Even though light intensity increses futher, the rate of photosynthesis does not.
Transport in plants and root hairs.
- Transport in plants
- Xylem tissue consists of columns of hollow, dead cells. It carries water and dissolved mineral salts from the roots, through the stem and out into every leaf and flower.
- Phloem tissue runs by the side of the xylem. It's tube-like cells carry dissolved glucose and other substances to all parts of the plant.
- Water evaporates from stomata in a process called transpiration.
- As water is lost from the leaves, more is drawn up through the xylem tissue from the roots, which absorb more water from the soil. This continuous movement of water is called the transpiration stream.
- Root hairs
- Root hair cells are fine, hair-like extensions of the root.
- Water flows into the root hair cells by osmosis. Their large surface area is an adaption that enables plants to maximise their absorption of water from the soil.
- Root hairs also take up mineral salts in solution. The solutions are much more concentrated in the cells of root tissue than in the soil. Therefore mineral salts cannot pass into the roots by diffusion. Active transport is used, which requires energy from aerobic respiration.
Osmosis and organisms and their environment
- Osmosis is the movement of water from a high water concentration to a lower one across a partially permeable membrane (one that will only let water molecules across.)
- You can investigate osmosis by studying cells under a micrscope. Cells left in a concentrated salt or sugar solution will lose water by osmosis. They will become flaccid (limp.)
- Visking tubing is a partially permeable membrane that can be used to investigate the movement of substances into and out of cells.
- Fieldwork investigations are designed to find out more about where organisms live and why they live where they do.
- Techniques used include:
- Pooters, nets and traps to collect animals in order to estimate their distribution.
- Quadrats to count the number of animals or plants in a known area.
- Probes to measure temperature, pH and light intensity.
- Ecosystems and their populations are usually too large for us to study everything about them. Instead we study small parts called samples.
- Erros in sampling techniques can be reduced by taking a number of random samples and standardising the samples taken.
- Fossils are the remains of dead organisms. They are usually found in sedimentary rocks. They are preserved over millions of years as rock particles from ancient seas fell on dead organisms on the seabed.
- Each layer of fossils records life on earth at the time the layer formed. This helps us trace the history and evolution of life. Fossils provide evidence for Darwins theory of natural selection.
- Fossil records do not show a continuous series of chnages between ancestors and their desecendants. These are gaps. This is because:
- Most organisms decompise quickly when they die; not all of them find their way into a environment where they will be preserved and so only a few fossils form.
- Many fossils are yet to be found
- Even if a fossil forms it may not survive geological cycles.
- Most vertebrates today have a pentadactyl limb - a forelimb with five fingers or toes.
- The discovery of pentadctyl limbs in fossils has led to scientists to believe that all vetebrates directly descend from a common ancestor. They use this as evidence of evolution.
- Growth is measured as an increase in an organisms size, length and mass. The increaseis the result of:
- Cell division- the number of cells increases
- Cell elongation- the length of cells increases
- Synthesis of organic materials (carbohydrates, proteins, fats and oils) the mass of cells increases.
- Plants grow throughout their life from cell division in tissues called meristems.
- Behind the meristems are regions where cells elongate and increase in size by water and other organic materials flowing into them.
- These cells are undifferentiated. As growth continues, differentiation of cells begins producing the types of cell that make up the tissues and organs of the plant.
- Cell division in animals occurs in al of the tissues of the body.
- In young animals, tissues grow because cell division produces more cells than die through age or damage.
- Animals continue to grow until the gain of cells balances the loss of cells.
- Growth then stops, marking the start of becoming an adult. However, the mass of an individual may continue to increase as protein synthesis adds more mass to cells and the tissues that the cells form.
Cells, tissues and organs
- Cells are the building blocks from which humans and all other living things are made.
- Tissues are a group of similar cells with a particular function.
- An organ is a group of different tissues that work together. An organ has a particular function.
- An organ system is a group of different organs that work together. Organ systems also have a specific function.
- All the different types of human cell are the result of cell division (mitosis) and differentiation during the development off the egg to the embryo to the foetus.
- Each type of human cell is specialised to enable it to carry out a particular function. For example, neurones transmit nerve impulses and muscle cells contrast.
- The process of mitiois produces daughter cells. These are genetically identical to one another and to their parent cell. However, most adult cells are differentiated.
- Genetically the cells may be the same, but the pattern of genes switching on and off (gene activity) is different.
- This process occurs in the developmennt of all living things.
- Red blood cells contain a red pigment called haemoglobin. They do not have a nucleus.
- White blood cells have a nucleus. They contain cytoplasm, which allows them to access tissues so they can protect the body by destroying bacteria and viruses.
- Platelets are fragments of cells with no nucleus. Platelets contain proteins.
- Plasma is a straw-coloured liquid that transports carbon dioxide, soluble food products and urea (and waste products from the liver) in solution. Plasma also circulates the heat released by the chemical reactions in the body cells, and this helps to maintain the body temperature.
- The function of red blood cells is to transport oxygen from the lungs to respiring tissues.In the lungs, where oxygen concentration is high, haemoglobin combines with oxygen to form oxyhaemoglobin.
- Oxyhaemoglobin breaks down to release oxygen to respiring tissues where the concentration of oxygen is low.
- When platelets are damaged by a cut or torn tissue, they release a substance that starts a chain of chemical reactions in the blood. These reactions end with the soluble plasma protein called fibringogen changing into insoluble fibrin.
- Fibrin forms a mesh of fibres across the wound and traps red blood cells, forming a clot.
- The clot plugs the wound and stops bleeding, this stops bacteria & viruses entering the body.
- The heart lies inside the chest cavity, protected by the ribcage. Much of the wall of the heart is made of cardiac muscle. This muscle contracts and relaxes to pump blood through the circulatory system.
- The heart has four chambers: two atria (atrium) and two ventricles.
- The wall of the left ventricle is thicker than the right ventricle because it has to pump blood to all parts of the body whereas the right ventricle only pumps blood to the lungs so less effort is required.
- The heart also has four major blood vessels: pulmonary artery, pulmonary vein, vena cava and aorta.
- The heart is a double pump: each side pumps blood along a different route.
- The left atrium and ventricle pump oxygenated blood from the lungs around the rest of the body.
- The right atrium and ventricle pump deoxygenated blood to the lungs where it can be oxygenated.
- When the muscular walls of the heart relax, blood fills the chambers. When the muscles contract blood is forced from the chambers.
- The valves control the flow of the blood throught the heart and into the arteries leading from the heart, preventing backflow (flow in the opposite direction).
The circulatory system
- The circulatory system is a network of tube-like vessels called arteries and veins.
- The heart pumps blood through the arteries to body tissues.
- Blood drains from the tissue through the veins, back to the heart.
- Smaller vessels branch from arteries and veins. The smallest are callee capillaries, they link arteries and veins.
- Blood in veins flows more slowly than blood in arteries because it is at lower pressure. The large diameter of a vein enables the blood to flow easily.
- Blood flow through the veins is helped by the contractions of the muscles in the arms and legs through which veins pass.
- The heart pumps blood into arteries at high pressure, as the blood needs to reach the extremities of the body.
- Elastic fibres in the artery wall help maintain the flow of blood away from the heart and prevent backflow, so no valves are needed.
- Capillaries form dense networks, called capillary beds, in the tissue of the body.
- They provide a large surface area for the efficient exchange of materials between the blood and tissues
- The blood is at a higher pressure at the artery end of the capillary bed.The higher pressure forces plasma through the thin capillary wallas. The liquid, called tissue fluid, carries nutrients and oxygen to the surrounding cells.
The digestive system
- The digestive system is made up of the alimentary canal (a tube which food passes through from mouth to anus). liver and pancreas.
- The different parts of the digestive system are:
- mouth- food is taken in (ingestion), chewed into smaller pieces and mixed with saliva. This begins the brekdown of food.
- Oesophagus- this muscular tube pushes food into the stomach.
- Stomach- muscles in the stomach contract and relax to mix food with digestion juices.
- Pancreas- produces pancreatic juice containing digestive enzymes that pass to the small intestine.
- Small intestine- where digestion (breaking food down into soluble products) and absorbtion (diffusion of soluble products into the blood) takes place.
- Liver- processes the nutrients from the small intestine and produces bile, which helps digest fat.
- Large intestine- absorbs water from the remaining indigestible food matter.
- Anus- undigested food is removed as faeces.
- Contraction and relaxation of the muscles layers in the wll of the alimentary canal moves food through the digestive system. This muscular action is called peristalsis.
- The gall bladder is a small sac-like structure connected to the small intestine by the bile duct. It stores the greenish alkaline liquid called bile produced by the liver.
The digestive system
- Enzymes break down large insoluble molecules of carbohydrates fats and protein into smaller molecules which the body can absorb.
- Visking tubing can be used as a model of the small intestine.
- Add a mix of enzymes and large food molecules into the tubing and suspend it in warm water (which acts like the blood supply). You can then detect the presence of the soluble products of digestion in the water.
- Bile breaks down fats into small droplets, which increases the surface area, speeding up the action of lipase.
- Bile also neutralises the stomach acid present in the food, which enters the small intestine to allow enzymes to work at their optimum pH of around 8.
- Tiny projections called villi line the small intestine. They increase it's surface area, allowing more efficient absorption of the soluble products of digestion.
- Functional foods are foods that have a health-promoting benefits over and above their basic nutritional value.
- Probiotic foods contain bacteria such s bifidobacteria and lactic acid and bacteria Lactobacillus that are believed to maintain a healthy digestive system.
- Prebiotic foods contain added sugars called oligosaccharides. These cannot be digested, but act as food suppky to the good bacteria in the alimentary canal.
- Plant stanol esters have been clinically proven to reduce the absorption of harmful cholesterol.
- The bacteria we carry in our digestive system can be divided into:
- Bad bacteria, which can lead to diseases of the alimentary canal.
- Good bacteria, which suppress the activities of the bad bacteria.
- Poor diet, stress, food poisoning and the use of antibiotics can disturb the balance so there are more bad bacteria than good.
- Prebiotics and probiotics are foods which aim to boost the amount of good bacteria.
- The margarine benecol has had plant stanol ester added
- Studies have shown that people who include plant stanols in their diet over a year might expect the cholesterol levels in their blood to fall by up to 10%.
- Lowering blood cholesterol reduces a persons risk of heart disease
- In the past the publics interest has led to food producers making health claims for their products that were unsupported by clear scientific evidence.
- However, there are concerns about the effectiveness of functional foods. The use of lactobacillus and bifidobacterium bacteria in some dairy products is an example. There are concerns involving:
- How well the bacteria survives the manufacture and storage of probiotics before sale
- Their passage through the digestive system
- Competition with the trillions of other microorganisms already in the gut.
- The health claims made for most fuctional foods remains in doubt. Much more research is still needed.