IGCSE Biology(生物)

IGCSE Biology 2012http:/www.s-cool.co.uk/gcse/biology/biology/revision.htmhttp:/www.bbc.co.uk/schools/gcsebitesize/biology//gcse/biology.phpCharacteristics of living things1 List and describe the characteristics of living organisms.Assimilation is a much better word than nutrition (because plants taking in and using CO2 and H2O is not nutrition but is assimilation). The word assimilation in biology means taking in substances from the surrounding environment and building them into your own structures.Sensitivity leads to a response.Respiration is one of the biochemical reactions of cell metabolism.So we can produce an alternate list.GrowthAssimilation (replaces nutrition)Metabolism (includes respiration)ExcretionResponse (sensitivity)ReproductionGAMER2AssimilationTaking in inorganic and organic chemicals from the surrounding environment, and using them for cell construction and cell metabolism.MetabolismAll the chemical reactions that occur in a cell and result in what we call life.ExcretionRemoval of the waste products of metabolism from a cell.SensitivityUsing the sense organs to notice change.ResponseReacting to external change from the environment.ReproductionProducing new cells from pre-existing cells.To be a living thing something must exhibit all of GAMER2 and be made of cells.Cell structure and organisation1 State that living organisms are made of cells. Everything, from bacteria to plants to insects to animals are all made of one (unicellular) or more cells (multicellular)Cell TheoryLiving organisms are composed of cells.Cells are the smallest unit of life.Cells come from pre-existing cells.2 Identify and describe the structure of a plant cell (palisade cell) and an animal cell (liver cell), as seen under a light microscope. 3 Relate the structures seen under the light microscope in the plant cell and in the animal cell to their functions.(a) cell surface membrane, which controls what enters and leaves the cellThe cell membrane allows diffusion of simple substances without control (passive transport), e.g. movement of oxygen into the cell, carbon dioxide out of the cells and ions into or out of the cells. Additionally the membrane proteins can control movement of substances into or out of the cell and against a concentration gradient (if needed). The cell uses ATP energy to do this (active transport)(b) nucleus, which contains DNA which is inherited, and which controls the activities of the cell Nuclear DNA contained within the cell carries the messages of life (genes).Genes tell the cell how to build specific proteins needed for all the functions of a cell.(c) chloroplasts, in which photosynthesis takes placeChloroplasts are membrane bound organelles found in green plants. Each chloroplast contains a green pigment protein molecule called chlorophyll, which is capable of using the energy from sunlight to produce glucose during photosynthesis.(d) cell wall, provides support to the cell so it can maintain its shape. It also help to prevent damage to the cell membrane.The cell wall has large spaces in it allowing anything to pass easily, it is fully permeable.4 Describe the differences in structure between typical animal and plant cells. Animal CellsPlant cellsNo cell wallCell wallNo vacuoleMay have a vacuole, but not alwaysNo chloroplastsChloroplasts in photosynthesizing cellsHeterotrophic must take in organic molecules from the surrounding environmentAutotrophic can make their ownOrganic molecules from inorganicMolecules using photosynthesis.Use the organic molecules- Glucose- Lipids- Amino acids- Nucleic acidsUse the inorganic molecules- Water- Carbon dioxide- Nitrates- PhosphatesRely on plants for foodSelf sufficient5 Calculate magnification and size of biological specimens using millimetres as units.Magnification = Drawing or image size for the specimen biological(mm)Actual size of the biological specimen (mm) How big is a cell?/howbig.htm/biology/ketcham/microscope/scope.htmlMovement in and out of cells1 Define diffusion as the net movement of molecules from a region of their higher concentration to a region of their lower concentration down a concentration gradient, as a result of their random movement.Diffusion, Brownian motion/sites/0072495855/student_view0/chapter2/animation_how_diffusion_works.htmlO2, CO2, and small ions can diffuse in or out of cells.2 Describe the importance of diffusion of gases and solutes and of water as a solvent.ing organisms Water (H2O) is not an organic compound but it is essential for life on Earth. Cell membranes are shaped into hollow spheres because of the polar nature of water and the way it interacts with lipid molecules that make up the bilipid layer. Water has a high thermal capacity. This means it takes a lot of energy to change the temperature of water. This keeps temperature stable in living cells. Water dissolves many chemicals allowing chemical reactions to occur more easily. Water allows gases such as oxygen and carbon dioxide to diffuse and dissolve into the water making the transport of these gases much faster across cell membranes. Water flows and is therefore a great transporter of substances.Enzymes1 Define enzymes as proteins that function as biological catalysts.Catalysts speed up chemical reactions, without themselves being part of the reactants or the products.Enzymes are specially folded proteins. The folding depends on the exact order of the amino acids that make up the protein. The folded protein then has one side of its 3D shape called an active site.The active site is a specific match for specific substrate/s (reactant/s) in a chemical reaction.If an enzyme is affected by high temperature or by a different pH then the protein may unfold and lose its active site, the protein is said to be denatured./biology/lab/proteinfolding/index.htmlEach enzyme will ONLY catalyse ONE specific chemical reaction.Most cellular reactions are multiple step reactions requiring a number of specific enzymes, each one unique in its job.Watch the following animations on enzymes:/sites/0072495855/student_view0/chapter2/animation_how_enzymes_work.html/thelifewire/content/chp06/0602001.html/college/pratt/0471393878/student/animations/enzyme_kinetics/index.html/AP%20Biology%20II;jsessionid=357EDFCC9EC3C03ADAF019857B9EF8362 Investigate and describe the effect of changes in temperature and pH on enzyme activity.3 Explain the effect of changes in temperature and pH on enzyme activity.As heat energy increases the kinetic energy of the particles increases.Greater kinetic energy = more probability of an enzyme-substrate collision.Enzyme-substrate collisions = more product produced = faster rate of reactionAs the optimum temperature is reached, further increase in heat energy leads to atoms in the protein molecule vibrating too much. Too much vibration within the protein molecule can break the chemical bonds, which help to fold the protein into its specific shape. The protein loses its shape = denatured = less enzyme-substrate complexes = slower rate of reaction.When the correct specific pH of an enzyme changes it can cause denaturing of the enzyme. On both sides of the optimum pH enzyme denaturing occurs.Protein denaturing/biology/lab/proteinfolding/index.htmlNutrition1 List the chemical elements that make up: carbohydrates, fats, proteins. Biological organic molecules all contain C, H, O as the base set of elementsCarbohydratesCHOLipids (fats, oils, waxes)CHOProteinsCHONDNA and RNACHONP2 Describe the structure of large molecules made from smaller basic units, i.e. simple sugars to starch and glycogen, amino acids to proteins, fatty acids and glycerol to fats and oils. Carbohydrates (C, H, O) are built around the molecule of glucose, C6H12O6One glucose moleculemonosaccharideTwo glucose molecules disaccharideMany glucose moleculespolysaccharide (starch, cellulose, glycogen) Glucose is the main source of fuel for cells during respiration in mitochondria.Lipids (C, H, O) are fats, oils and waxes. They are made of a hydrophilic head called glycerol and three hydrophobic tails called fatty acids. Each 1 gram of lipid contains twice the chemical energy of 1 gram of carbohydrate. Lipids are used for cell membranes, insulation and energy.Proteins (C, H, O, N) have a variety of jobs in cells. Proteins are built from amino acids. Amino acids (AA) Peptides 2 or 3 AA joinedPolypeptides (proteins) many AA joined and folded a special way Structural proteinsHormonesEnzymes Help to build cell membranes Chemical Speed up and other cell structures signalschemical reactions3 Describe tests for starch (iodine solution), reducing sugars (Benedicts solution), protein (biuret test), fats (ethanol). Starch + yellow/brown iodine liquid Iodine changes to blue black colourSugar + Benedicts solution clear blue liquid (gently heat) Benedicts changes to orange precipitate.Protein + Biuret solution clear blue liquid Biuret changes to a purple gel precipitate.Fats + ethanol (shake well to dissolve fats) + water A milky white substance appears.4 List the principal sources of, and describe the importance of: carbohydrates, fats, proteins, vitamins (C and D only), mineral salts (calcium and iron only), fibre (roughage), water.Carbohydrates come from vegetables, fruits and grains, needed for energyFats (lipids) come from animal fats and plant oils, needed for energy, insulation and membrane building.Proteins come from beef, pork, chicken, fish, eggs, nuts, milk, needed for energy, structural proteins, hormones and enzymes. Fibre is undigested plant cell walls. Our bodies digestive system cannot break down the chemical cellulose that make sup cells walls, needed to clean the digestive system and keep things moving.5 Describe the use of microorganisms in the manufacture of yoghurt.Yogurt is made by putting certain bacteria Streptococcus thermophilus and Lactobacillus bulgaricus, into milk. This is called the starter culture. You can make it at home, if you place a tablespoon of yogurt in a glass of milk, the bacteria will reproduce and spread through the milk, and within 6 to 12 hours, transform the milk to yogurt. But yogurt cultures are fussy - the milk must be boiled first in order to remove any competing bacteria and then cooled to a lukewarm temperature so that the yogurt bacteria wont be killed by high heat. You could also use sterile powdered milk, or a combination of the two (boiled and sterile)The bacteria use the lactose sugar in the milk in anaerobic respiration and produce lactic acid.Lactose sugar lactic acidThe acid lowers the pH of the milk causing milk proteins to denature and become more solid like, the acid also gives the yogurt its tangy taste.6 Describe the deficiency symptoms for: vitamins (C and D only), mineral salts (calcium and iron only).Vitamin C is found mostly in citrus fruits like oranges, lemons etc. It is a strong antioxidant preventing chemical damage to cells.It is essential for healthy skin (collagen), strong gums and immune system.Scurvy is a disease resulting from lack of vitamin C, since without this vitamin, the synthesized collagen is too unstable to perform its function. Scurvy leads to the formation of brown spots on the skin, spongy gums, and bleeding from all mucous membranes. The spots are most abundant on the thighs and legs, and a person with the disease looks pale, feels depressed, and is partially immobilized. In advanced scurvy there are open, infected wounds and loss of teeth and, eventually, death.Vitamin D can be produced by the skin when it is exposed to sunlight.The vitamin allows the body to use calcium to build strong bones. It is appears to have a role in keeping the immune system healthy and in preventing some cancers.Vitamin D causes osteomalacia (called rickets when it occurs in children), which is a softening of the bones. In the developed world, this is a rare disease. Rickets, a childhood disease characterized by slowed growth and deformity of the long bones, can be caused by calcium or phosphorus deficiency as well as a lack of vitamin D; today it is largely found in low income countries in Africa, Asia or the Middle East.Iron is obtained in the diet mostly from red meat, e.g. beef (especially liver). It is also found in some dark green leafy vegetables, e.g. spinach. Iron is used to build haemoglobin molecules in red blood cells, which then carry oxygen to respiring cells. It is also used to make myoglobin, a protein that helps muscle cells use oxygen.Anemia (low red blood cell level) caused by not enough iron in the diet and/or iron loss from intestinal bleeding, parasitic infection, menstruation, etc. Red blood cells contain iron and are not formed when iron is deficient. Deficiency can lead to tiredness, weakness, pale skin and hair loss.Calcium has the main function of muscle contraction (magnesium for muscle relaxation). The secondary use by the body is to build strong, dense bones. Calcium can be obtained from dairy products, seaweeds and nuts.Calcium deficiency leads to osteoporosis which causes brittle and weak bones that fracture more easily.For calcium to be used effectively by the body there must be sufficient vitamin D.Plant nutrition1 Define photosynthesis as the fundamental process by which plants manufacture carbohydrates from raw materials using energy from lightYou should know that not all plant cells contain chloroplasts.All leaf cells contain chloroplasts.The energy from the sunlight is used to split the water (producing H+ ions and oxygen)Plants at the base of the food chain produce most of the organic molecules for life. Photosynthesis Glucose Starch Cellulose Lipids ProteinsStored for Builds cell walls Wax Oils Structure Hormones Enzymeslater use cuticle e.g. chlorophyll e.g. adrenaline tease2 Explain that chlorophyll traps light energy and converts it into chemical energy for the formation of carbohydrates and their subsequent storage.The light energy is used to build the glucose molecule. The light energy is converted to chemical energy stored in the chemical bonds of the glucose molecule.3 State the word equation for the production of simple sugars and oxygen.Carbon dioxide + water glucose + oxygen (the arrow must have the words light and chlorophyll on it)4 State the balanced equation for photosynthesis in symbols6CO2 + 6H2O C6H12O6 + 6O2 (the arrow must have the words light and chlorophyll on it)5 Investigate the necessity for chlorophyll, light and carbon dioxide for photosynthesis, using appropriate controls.6 Investigate and state the effect of varying light intensity on the rate of photosynthesis (e.g. in submerged aquatic plants).Photosynthesizing plants in water (like land plants) will produce oxygen gas. The oxygen gas will leave through the stomata and be seen as bubble coming from the leaf. In an experiment we could count those bubbles. (Dependent variable)To see the effect light intensity has on the number of oxygen bubbles produced per minute we could change the distance of a light source from the plant. (Independent variable)Of course, all other things must be kept the same. (Controlled variables)7 Describe the intake of carbon dioxide and water by plants. During respiration Oxygen enters through the stomata.Carbon dioxide and water gas leave through the stomata. During photosynthesis Carbon dioxide enters through stomata Oxygen and water gas leave through stomata. Both processes are called gas exchange. Gas exchange occurs by diffusion. The plant can control gas exchange by opening or closing stomata.Water (liquid) enters the plant by osmosis through the roots.8 Identify and label the cuticle, cellular and tissue structure of a dicotyledonous leaf, as seen in cross-section under the light microscope.Animal Nutrition1 State what is meant by the term balanced diet and describe a balanced diet related to age, sex and activity of an individual.A balanced diet contains the correct proportions of carbohydrates, proteins, lipid, vitamins and minerals.There is debate about what percentage of the diet should be carbohydrate versus protein.The basic rule for food intake isKilojoules in = kilojoules burnedIf this simple formula is followed then weight gain or loss will not occurExample nutritional needs for different ages/sexAgeBody needsDiet needsBabyHigh growthHigh protein and high fat milkChildHigh growthHigh metabolismCalicum for bonesVit D for bonesLarge balanced food intakeTeenagerGrowth spurtsBrain reorganizationMale muscle growthFemale menstruationCalicum for bonesVit D for bonesLarge balanced food intakeFish oilsProteinIronAdultSlow