Biology

1. Biology Edexcel International GCSE in Biology (4BI0) First examination June 2013

2. The nature and variety of living organisms • Characteristics of living organisms • Variety of living organisms

3. Characteristics of living organisms 1.1 Understand that living organisms share the following characteristics: • Respiration • Reproduction • Growth • Response to stimuli • Maintaining internal environment • Movement • Excretion • Nutrition

4. Variety of living organisms 1.2 describe the common features shared by organisms within the following main groups: plants, animals, fungi, bacteria, protoctists and viruses, and for each group describe examples and their features as follows (details of life cycle and economic importance are not required) • Plants • Multicellular • Contain chloroplasts to carry out photosynthesis. • Make water and carbon dioxide into organic compounds such as cellulose, which plants use for walls and starch. • Animals • Vertebrates: Mammals, birds, reptiles, amphibians and fish. • Invertebrates: Crustaceans, insects, starfish, mollusks, sponges and worms. • Unable to carry out photosynthesis. Gain energy by feeding on other animals or plants.

5. Variety of living organisms • Fungi • Multicellular: Mushrooms, toadstools, molds etc. • Unicellular: Yeasts • Do not contain chloroplasts, cannot photosynthesize. • Have cell walls, made of chitin, not cellulose. • The mushroom is the reproductive structure of the fungi, called a fruiting body. • Under the soil the mushroom has many thread-like filaments called hyphae. • A mold is a mushroom without the fruiting body. The network of hyphae is called mycelium. • Molds feed by absorbing nutrients from dead material. • Many nuclei within one cell in some molds such as Mucor.

6. Variety of living organisms • Protoctists • Most protoctists are microscopic single-celled organisms. • Protozoa look like animal cells, such as Amoeba, which lives in pond water. • Algae have chloroplasts and carry out photosynthesis therefore more like plants. • Most algae are unicellular but some species such as seaweeds are multicellular. • Malaria is caused by the protoctist Plasmodium.

7. Variety of living organisms • Bacteria • Bacteria are small single-celled organisms. A much simpler structure. • Three basic shapes of bacteria: spheres, rods and spirals. • Spheres come in singles, pairs, chains or groups. • Rods come in singles or chains, with or without flagella. • Surrounded by a cell wall, protects the bacterium. Made of polysaccharides and proteins. • Some species have another layer outside the wall called a capsule or slime layer. Both give the bacterium extra protection. • Has no nucleus, instead its DNA is in a single chromosome, loose in the cytoplasm. • Some bacteria can swim using movements from structures called flagella. • Plasmids also contain some of the bacterium’s DNA. • Some bacteria contain a form of chlorophyll, and can carry out photosynthesis. • Most bacteria feed off living or dead organisms. • Important decomposers, other species are pathogens which cause disease.

8. Variety of living organisms 1.3 recall the term ‘pathogen’ and know that pathogens may be fungi, bacteria, protoctists or viruses • A pathogen is a agent that can cause disease and harm, it may be a fungi, bacteria, protoctist or virus.

9. Structures and functions in living organisms • Levels of organization • Cell structure • Biological molecules • Movement of substances into and out of cells • Nutrition • Respiration • Gas exchange • Transport • Excretion • Coordination and response

10. Levels of organization 2.1 describe the levels of organization within organisms: organelles, cells, tissues, organs and systems • Organelles  Cells  Tissue  Organ System • Organelle: Mitochondria • Cell: Sperm Cell • Tissue: Muscle • Organ: Heart • System: Pulmonary System

11. Cell structures 2.2 describe cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

12. Cell structures 2.3 describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole • Nucleus: The nucleus controls the cell, also contains DNA which is important for cell reproduction. • Cytoplasm: Where chemical reactions take place, the mitochondria in the cytoplasm facilitates respiration. It also contains enzymes. • Cell membrane: It controls what goes in and out of the cell. • Cell wall: Made of cellulose, it gives the shape and structure of the cell to provide support. It becomes turgid when it is full of water. • Chloroplast: Contain the green chlorophyll substance that allows it to absorb light energy and convert it to chemical energy in photosynthesis. • Vacuole: Contains cell sap, the storage of the cell and maintains the cell structure.

13. Cell structure 2.4 compare the structures of plant and animal cells.

14. Biological molecules 2.5 identify the chemical elements present in carbohydrates, proteins and lipids (fats and oils) • Carbohydrates and lipids: • Carbon, hydrogen, oxygen • Protein: • Carbon, hydrogen, oxygen, sulfur, phosphorous, nitrogen 2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up from smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol • Glucose, maltose  starch, glycogen • Amino acids  protein • Fatty acids, glycerol  lipids, fats

15. Biological molecules 2.7 describe the tests for glucose and starch • Glucose: • To test for glucose, dissolve the sample in water and add drops of Benedict’s reagent until the solution is colored blue. When the solution is heated, it will turn orange-red if glucose is present. • Starch: • To test for starch, add a drop of iodine solution to the sample. The solution will turn blue-black color if starch is present. 2.8 understand the role of enzymes as biological catalysts in metabolic reactions • Enzymes are biological catalysts; they speed up reactions inside cells. • They are proteins.

16. Biological molecules 2.9 understand how the functioning of enzymes can be affected by changes in temperature, including changes due to change in active site • High temperatures denature enzyme by changing the shape of the active site so it is no longer compatible with the substrate. • Low temperatures lower the rate of reaction of the enzyme. 2.10 understand how the functioning of enzymes can be affected by changes in active site caused by changes in pH • A change in pH, whether more acidic or basic, will change the shape of the active site and denature the enzyme. 2.11 describe experiments to investigate how enzyme activity can be affected by changes in temperature. • Refer to experiment section

17. Movement of substances into and out of cells 2.12 understand definitions of diffusion, osmosis and active transport • Diffusion is: • Movement of particles • High concentration  low concentration • Passive: does not use energy • Osmosis is: • Movement of water • Semi-permeable membrane • High concentration  low concentration • Passive: does not use energy • Active transport is: • Movement of particles • Low concentration  high concentration • Across a selectively permeable membrane • Active: uses energy produced by cellular respiration

18. Movement of substances into and out of cells 2.13 understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport • Cell membranes are partially permeable, so osmosis takes place across cell membranes. 2.14 understand the importance in plants of turgid cells as a means of support • The turgor of plant cells is important for to support the plant. • If the plant loses water through osmosis, the cell contents decrease in volume and the cytoplasm no longer pushes against the cell wall. • The cell is flaccid. • The cell cannot support the plant tissues and the plant wilts. • Wilting helps protect the plant from further water loss.

19. Movement of substances into and out of cells 2.15 understand the factors that affect the rate of movement of substances into and out of cells, to include the effects of surface area to volume ratio, temperature and concentration gradient • Surface area: the higher the surface area, the faster the rate of movement. • This is because there is more area of contact for diffusion to occur. • Temperature: the higher the temperature, the faster the rate of movement. • This is because the temperature increases the kinetic energy of the particles. • Concentration gradient: The steeper the con. gradient, the faster the rate of movement. 2.16 describe experiments to investigate diffusion and osmosis using living and non-living systems. • Refer to experiment section

20. Nutrition 2.17 describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy • The leaves of plants make glucose from carbon dioxide and water using the light energy of the sun. The waste product is oxygen. • The light energy of the sun is captured by chlorophyll in chloroplasts in the leaves and converted to chemical energy in glucose. • Glucose is converted into sucrose to be transported around the plant and into starch to be stored. • The glucose from photosynthesis is used to make cellulose for cell walls, proteins and DNA, chlorophyll, lipids as an energy store for seeds 2.18 write the word equation and the balanced chemical symbol equation for photosynthesis • Carbon dioxide + water  glucose + oxygen • 6CO2 + 6H2O  C6H12O6 + 6O2

21. Nutrition 2.19 understand how varying carbon dioxide concentration, light intensity and temperature affect the rate of photosynthesis • The higher each of the factors are, the faster the rate of photosynthesis. • However, the rate of photosynthesis will only increase as long as the limiting factor is increasing. The limiting factor is the component of the reaction that is not in excessive supply and limits the rate at which the reaction can take place. 2.20 describe the structure of the leaf and explain how it is adapted for photosynthesis • They are thin and flat so the surface area to absorb light is as large as possible and the distances that gases need to diffuse are short.

22. Nutrition

23. Nutrition 2.21 understand that plants require mineral ions for growth and that magnesium ions are needed for chlorophyll and nitrate ions are needed for amino acids • Plants need mineral ions, which they take from the soil to survive and grow. • Nitrates ions are used to make amino acids. • Magnesium ions are used to make chlorophyll. 2.22 describe experiments to investigate photosynthesis, showing the evolution of oxygen from a water plant, the production of starch and the requirements of light, carbon dioxide and chlorophyll • Refer to experiment section 2.23 understand that a balanced diet should include appropriate proportions of carbohydrate, protein, lipid, vitamins, minerals, water and dietary fiber • A balanced diet should include carbohydrate, protein, fats / lipids, vitamins, minerals, water and dietary fiber.

24. Nutrition 2.24 identify sources and describe functions of carbohydrate, protein, lipid (fats and oils), vitamins A, C and D, and the mineral ions calcium and iron, water and dietary fiber as components of the diet • Carbohydrates are the main fuel of the body. • Cell release energy from glucose. • Most of the carbohydrate that forms our diet is from starch. • Plant cells are made of cellulose that is made from carbohydrates, it is used as fiber or roughage because we cant digest it. • Simple sugar is glucose, fructose, sucrose, etc. • Complex carbohydrates such as starch, glycogen, cellulose, etc. are made of simple sugar joined together. • Carbohydrates are found in bread, pasta and rice.

25. Nutrition • Proteins are used for growth and repair of tissues. • They are made up long chains of amino acids. • They contain carbon, hydrogen and oxygen, but have nitrogen and sulfur as well. • Proteins are found in meat, fish and cheese. • Lipids (fats and oils) are made of glycerol and fatty acids. • They are made up of the same elements as carbohydrates – oxygen, carbon, hydrogen, but there is much less carbon. • They contain a lot of energy and are used as energy stores. • It is used as insulation, also to protect organs. • Lipids are found in butter, corn oil and eggs.

26. Nutrition • Vitamins

27. Nutrition • Minerals

28. Nutrition • Water is important in the body as a solvent for breaking up large molecules by hydrolysis. • Fiber is important in the body as a bulk for the muscles of the gut to move. It assists peristalsis. 2.25 understand that energy requirements vary with activity levels, age and pregnancy • People need more energy in the early – mid sections of their life due to higher activity levels and energy is used for growth. • A pregnant woman not only has to supply energy for herself, but also for her baby.

29. Nutrition 2.26 describe the structures of the human alimentary canal and describe the functions of the mouth, esophagus, stomach, small intestine, large intestine and pancreas • The alimentary canal is the muscular tube that runs from the mouth to the anus. • Mouth: Physically breaks down the food to make it easier to digest. Saliva lubricates the food and also contains the enzyme amylase. • Esophagus: The pipe by which food enters the stomach from the mouth. • Stomach: Acidic conditions kills bacteria in the food and provides the optimum pH for enzyme pepsin. Muscular contractions in the stomach mix the food up with gastric juices. The mixture is now called chyme. • Small intestine: At the duodenum, the acidic chyme is made alkaline with bile from the gall bladder. It also emulsifies fats. In the small intestine, absorption takes place. • Large intestine: This is where the water is reabsorbed leaving behind feces. • Pancreas: Produces enzymes and pancreatic juice which digests lipids.

30. Nutrition

31. Nutrition 2.27 understand the processes of ingestion, digestion, absorption, assimilation and egestion • Ingestion is the intake of food via the mouth (eating). • Digestion is the breakdown of macromolecules into smaller, soluble molecules. • Absorption is the products of digestion being absorbed into the bloodstream. • Assimilation is the distribution of digested food products into the cells . • Egestion: The removal of water from the matter coming out of the small intestine. After the removal of water, it is passed out through the anus as feces. 2.28 explain how and why food is moved through the gut by peristalsis • Peristalsis is the way in which the bulk of food is moved through the alimentary canal. • The muscles before the bulk of food contracts, pushing the food forward. • The muscles after the bulk of food relaxes, letting the food through. • Fibers help with peristalsis, they give more bulk so it is easier to push it forward as it fills up the entire channel.

32. Nutrition 2.29 understand the role of digestive enzymes, to include the digestion of starch to glucose by amylase and maltase, the digestion of proteins to amino acids by proteases and the digestion of lipids to fatty acids and glycerol by lipases

33. Nutrition 2.30 understand that bile is produced by the liver and stored in the gall bladder, and understand the role of bile in neutralizing stomach acid and emulsifying lipids • Bile is produced in the liver, stored in the gall bladder. • It neutralizes stomach acid and emulsifies fats, making them easier for lipase to digest. 2.31 describe the structure of a villus and explain how this helps absorption of the products of digestion in the small intestine • Shape gives a large surface area • A good blood supply to maintain high concentration gradient • Microvilli extensions to further increase surface area • Lacteal allows absorption of fats • Capillaries only one cell thick to facilitate fast diffusion

34. Nutrition 2.32 describe an experiment to investigate the energy content in a food sample. • Refer to experiment section

35. Respiration 2.33 understand that the process of respiration releases energy in living organisms • Respiration is used to produce energy for muscle contraction, active transport, building up large molecules and cell division. 2.34 describe the differences between aerobic and anaerobic respiration • Aerobic respiration requires oxygen, anaerobic respiration does not. 2.35 write the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms • Carbon dioxide + water  glucose + oxygen • C6H12O6+ 6O2 6CO2 + H2O 2.36 write the word equation for anaerobic respiration in plants and in animals • Glucose  lactic acid (+ some energy)

36. Respiration 2.37 describe experiments to investigate the evolution of carbon dioxide and heat from respiring seeds or other suitable living organisms. Refer to experiment section

37. Gas exchange 2.38 understand the role of diffusion in gas exchange • In humans, gas exchange depends on the efficient diffusion of gases. 2.39 understand gas exchange (of carbon dioxide and oxygen) in relation to respiration and photosynthesis • Plants respire all the time, using oxygen and producing carbon dioxide. • The rate of photosynthesis is not constant, which uses carbon dioxide and produces oxygen. 2.40 understand that respiration continues during the day and night, but that the net exchange of carbon dioxide and oxygen depends on the intensity of light • Respiration occurs constantly, but photosynthesis is dependent on light levels. • Therefore, the volume of carbon dioxide used up and the volume of oxygen produced is variable throughout a 24 hour period.

38. Gas exchange 2.41 explain how the structure of the leaf is adapted for gas exchange • Spongy mesophyll cells have air space for gas diffusion. • Palisade mesophyll cells are tightly packed with chloroplasts. • Lower epidermis has more stoma and guard cells. 2.42 describe the role of stomata in gas exchange • The stoma is a pore that controls gas exchange. • The light intensity stimulate the stoma to open and close. 2.43 describe experiments to investigate the effect of light on net gas exchange from a leaf, using hydrogen-carbonate indicator • Refer to experiment section

39. Gas exchange 2.44 describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes • The lungs are enclosed in the cheat by the ribcage or thorax and a muscular sheet of tissue called the diaphragm. Joining each rib to the next are two sets of muscles called intercostal muscles. • The bronchial tree is the air passages of the lungs. Enters our nose or mouth and passes down the trachea. This then splits into two tubes called the bronchi, one leading to each lung. Each bronchus divides into smaller tubes called bronchioles, eventually ending at microscopic air sacs celled alveoli. Here is where gas exchange takes place. • The walls of the trachea and bronchi contain rings of cartilage to support the airways and keep them open when we breathe in. The inside of the thorax are separated from the lungs by two thin membranes called the pleural membrane. They make an envelope around the lungs, forming an airtight seal.

40. Gas exchange

41. Gas exchange 2.45 understand the role of the intercostal muscles and the diaphragm in ventilation • Inhalation: • External intercostal muscles contract pulling ribs up and out. • Muscles in the diaphragm contract pulling the diaphragm down. • Increase in volume in the thorax  Lower concentration of air  Air enters. • Exhalation: • Internal intercostal muscles contract pulling ribs downand in. • Muscles in the diaphragm relax to let diaphragm return to a dome shape. • Decrease in volume in the thorax  Higher concentration of air  Air exits.

42. Gas exchange 2.46 explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and blood in capillaries • Alveoli are wrapped in capillaries; to keep a constant fresh blood flow. • The steep concentration gradient facilitates maximum diffusion. • Alveoli are ball shaped; to create maximum surface area. • The larger surface area allows it to absorb more oxygen at any given time. • Capillaries are only 1 cell thick; short diffusion distances between air and blood. • This means they have to travel a less, allowing a faster diffusion rate.

43. Gas exchange 2.47 understand the biological consequences of smoking in relation to the lungs and the circulatory system, including coronary heart disease • Carbon monoxide binds to hemoglobin and takes the place of oxygen. This will lower oxygen levels in the blood. • Cilia is destroyed so dirt, bacteria and mucus is not swept away. This clogs the air passages. • Irritates the cell linings, causing them to produce more mucus. Can lead to bronchitis. • The walls of the alveoli are damaged and break down to form large irregular air spaces, this makes less surface area and gas exchange is made less effective. This is called emphysema. • Tar and other chemicals cause cells to mutate and form cancers in the lungs and throat. 2.48 describe experiments to investigate the effect of exercise on breathing in humans. • Refer to experiment section

44. Transport 2.49 understand why simple, unicellular organisms can rely on diffusion for movement of substances in and out of the cell • Unicellular organisms such as fungi can rely on diffusion because they have high surface area to volume ratio and are small, thus diffusion occurs quickly. 2.50 understand the need for a transport system in multicellular organisms • Multicellular organisms such as animals cannot rely on diffusion, and need a transport system because they have a small surface area to volume ratio and are large, thus diffusion occurs slowly. • Therefore, transport systems such as ventilation and circulatory systems are developed to speed up diffusion to support themselves.

45. Transport 2.51 describe the role of phloem in transporting sucrose and amino acids between the leaves and other parts of the plant • Phloem tissue is made of living cells. • It transports sugars for energy and amino acids for cell building all around the plant. • It travels upwards and downwards 2.52 describe the role of xylem in transporting water and mineral salts from the roots to other parts of the plant • Xylem tissue is made of cell walls of dead cells. • It transports water and mineral ions up from the roots to the rest of the plant. • It is waterproofed with lignen. • It only travels upwards.

46. Transport

47. Transport 2.53 explain how water is absorbed by root hair cells • In the uptake of water: • The root hair cells greatly increase the surface area for the uptake of water. • Water enters the root cells through osmosis, it moves across root cells to the xylem along a concentration gradient. • In the uptake of minerals: • Mineral ions are at a very low concentration in the soil water. • They are moved into root hair cells against a concentration gradient. • This is done using active transport. 2.54 understand that transpiration is the evaporation of water from the surface of a plant • Transpiration is the evaporation and removal of water from the surface of the plant, namely the leaf. • Transpiration is a process of pulling the water up from the xylem and out of the stoma through the plant. This is called the transpiration stream and runs by osmosis.

48. Transport 2.55 explain how the rate of transpiration is affected by changes in humidity, wind speed, temperature and light intensity • Light intensity stimulates the stoma to open and close. • Temperature affects the rate of evaporation. • Humidity affects how long it takes for the water vapor to diffuse. • Wind blows the wind vapor away and replaces it with drier air. 2.56 describe experiments to investigate the role of environmental factors in determining the rate of transpiration from a leafy shoot • Refer to the experiment section

49. Transport 2.57 describe the composition of the blood: red blood cells, white blood cells, platelets and plasma • Blood is made of: • Red blood cells • White blood cells • Phagocytes • Lymphocytes • Platelets • Plasma 2.58 understand the role of plasma in the transport of carbon dioxide, digested food, urea, hormones and heat energy • Plasma is the yellow liquid which transports, dissolved food molecules, carbon dioxide, urea, hormones, and heat. • It is mainly made of water.

50. Transport 2.59 explain how adaptations of red blood cells, including shape, structure and the presence of hemoglobin, make them suitable for the transport of oxygen • Biconcave, disc-shape maximizes surface area. • It is flexible and elastic, so it fits into thin capillaries. • Presence of hemoglobin allows it to carry oxygen. • Thin cell membrane allows for a quicker exchange of oxygen. • Containing no nucleus means there is more space for hemoglobin. 2.60 describe how the immune system responds to disease using white blood cells, illustrated by phagocytes ingesting pathogens and lymphocytes releasing antibodies specific to the pathogen • Lymphocyte has a large spherical nucleus and it produces antibodies to destroy organisms. Lymphocytes form memory cells that if the pathogen infects the body again it can be dealt with quickly before the body experiences symptoms. • Phagocyte is a large cell with a lobed nucleus and engulfs the bacteria and other organisms that are tagged by antibodies.