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Additional Biology – Revision notes A. Cells. Cells are the basic units of living things Animal and Plant cells All cells contain a nucleus, cytoplasm and cell membrane Plant cells contain a cell wall, permanent vacuole and chloroplasts Cells that have a specific function have special adaptations How do substances get in and out of cells? Particles in liquids and gases move randomly Liquids and gases move in and out of cells randomly by diffusion Diffusion is a process whereby substances move from an area of high concentration into an area of lower concentration, which causes mixing Diffusion is a passive process Osmosis Osmosis is the passage of water from an area of high concentration into an area of lower concentration across a semi permeable membrane Osmosis is important in plants maintaining the shape and integrity of cells. Dissolved substances can move into and out of cells by diffusion. Water can move by Osmosis www.cellsalive.com B.How plants produce food During photosynthesis light energy is absorbed by a green substance called chlorophyll, which is found in chloroplasts of plant cells The light energy is used to convert carbon dioxide and water into sugar (glucose) and oxygen is released as a by-product Limiting factors The rate of photosynthesis is determined by the supply of carbon dioxide, temperature and availability of light These factors interact, but if one of these factors is in short supply the rate of photosynthesis is limited How plants use glucose The glucose produced in photosynthesis may be converted into insoluble starch for storage Plant cells use some of the glucose produced in respiration Why do plants need minerals? Plants absorb mineral salts for healthy growth Nitrate is used to produce protein, plants lacking nitrate are stunted Magnesium is used to produce chlorophyll; plants lacking magnesium have yellow leaves Pyramids of biomass The ultimate source of all energy for living things is the sun The mass of living material at each stage of a food chain is less than the previous stage The amount of biomass at each stage can be drawn to scale and shown in a pyramid of biomass Energy losses The amount of biomass and energy contained in organisms is reduced at each stage of a food chain because During respiration heat is lost to the surroundings Respiration supplies the energy for all life processes including movement Some materials and energy are lost as waste materials Maintenance of a constant body temperature (mammals & birds) which is usually higher than their surroundings means high energy losses Energy in food production At each stage in a food chain, less material and less energy are contained in the biomass of the organisms This means that the efficiency of food production can be improved by (i) reducing the number of stages in a food chain (ii) restricting energy loss by food animals by limiting their movement (iii) by controlling the temperature of their surroundings Decay Living things remove the materials that they need for life processes from their environment These materials are returned to the environment either in waste materials or when they die & decay Materials decay because they are digested by micro-organisms. Warm moist conditions with plenty of oxygen are the best conditions for microbe activity The Carbon cycle The constant recycling of carbon is called the carbon cycle. Plants remove carbon dioxide from the atmosphere during photosynthesis Respiration, death & decay returns carbon dioxide to the atmosphere Organic /intensive farming There are advantages and disadvantages of organic and nonorganic farming techniques Compromises need to be struck to ensure production of enough high quality foodstuffs There is a compromise between efficient food production and the practical mechanisms of animal husbandry/ making it work www.soilassociation.org and www.rhs.org.uk C. Enzymes Enzyme structure Catalysts alter the rate of chemical reactions Enzymes are proteins Enzymes are catalysts produced by cells Enzymes have a special shape which allows other chemicals to fit into them Factors affecting enzyme action Enzymes are proteins their shape is important to their functioning. Changes in pH, high temperatures alter protein shape Enzymes in digestion Digestive enzymes are produced by specialised cells in glands & in the lining of the gut The enzymes pass out of the cells and into the gut; they catalyse the breakdown of large molecules into smaller ones Amylase is produced in the salivary glands and pancreas and catalyses the breakdown of starch into sugar Protease is produced by the stomach and pancreas it catalyses the breakdown of proteins into amino acids Lipase is produced by pancreas & small intestine and catalyses the breakdown of fats into fatty acids and glycerol Speeding up digestion Protease enzymes are produced by the stomach, the stomach produces Hydrochloric acid. The enzymes in the stomach work most effectively in these conditions The liver produces bile. The bile is stored in the gall bladder. Bile neutralises the acid that was produced in the stomach. The enzymes of the small intestine work best in alkaline conditions. Bile emulsifies fats ( breaks them into small droplets) Aerobic respiration Aerobic respiration occurs in the mitochondria of cells It is controlled by enzymes and is the slow controlled release of energy from the reaction of glucose with oxygen Glucose + Oxygen The energy from respiration is used for life processes Carbon Dioxide + Water Making use of enzymes Some micro-organisms produce enzymes that pass out of the cells. These microbes can be cultured to obtain the enzymes. These enzymes have many uses including (i) Biological detergents – protein and fat digesting enzymes (ii) Food industry - baby foods (proteins “pre-digested”). (iii) Isomerase converts glucose into fructose syrup which is much sweeter and used in smaller quantities in slimming foods- Carbohydrases convert starch into sugar syrup. D. Controlling internal conditions The internal conditions of the body which are controlled include water content of body, ion content, and temperature and sugar levels Waste products need to be removed; these include carbon dioxide from respiration, urea from the break down of amino acids The monitoring and control of the body’s internal environment is called homeostasis Controlling body temperature The Body temperature is monitored and controlled by thermoregulatory centre in the brain All cellular reactions are controlled by enzymes Changes in temperature affect the rate at which enzyme controlled reactions occur If the core body temperature falls, blood vessels supplying the skin capillaries constrict, to reduce heat loss. Muscles may “shiver” to generate heat If the core body temperature rises, blood vessels supplying the skin capillaries dilate, causing increased blood flow and heat is lost. Sweat glands release sweat which cools the body as it evaporates Controlling blood sugar Blood glucose levels are monitored and controlled by the pancreas The pancreas produces 2 hormones, Insulin and glucagon Insulin allows blood to be taken up by liver and muscle cells to be stored as an Glycogen, which is an insoluble carbohydrate Glucagon converts the glycogen back into glucose Diabetes is a disease in which a person cannot control there blood glucose levels www.diabetes.org.uk E. Cell division and growth (Mitosis) In body cells the chromosomes are found in pairs. (homologous pairs) Body cells divide by mitosis to produce additional cells during growth, repair or replacement Most animal cells differentiate (specialise) at an early stage. Stem cells Cells from human embryo’s and adult bone marrow, called stem cells, can be made to differentiate into many different types of cells Treatment with these cells can be used to help conditions such as leukaemia www.christopherreeve.org Cell division in sexual reproduction (Meiosis) A www.stemcellresearchfoundation.org Body cells contain two sets of chromosomes (Diploid) Gametes contain one set ( Haploid) Cell division to produce gametes is called Meiosis ( reductive division) simplified outline of the process Copies of chromosomes made Cell divides twice to form 4 gametes When gametes join at fertilisation, the new cell has 2 sets of chromosomes, with information from each parent this gives rise to variation From Mendel to DNA Chromosomes are made up of large molecules of DNA (deoxyribose nucleic acid). The DNA molecule looks like a spiral stair case (called a double helix) The rungs are made of base pairs There are 4 bases. Adenine (A) pairs with Thymine (T), Cytosine (C) pairs with Guanine (G) The combination of the bases codes for particular amino acids which make up proteins Each chromosome consists of Genes Some characteristics are controlled by a single gene Each gene may have different forms called Alleles Some alleles are dominant (Capitol letter L ) others are recessive (lower case l) www.mendelweb.org Inheritance in action (simple genetics) Humans have 23 sets of chromosomes The 23rd set determines gender In females the chromosomes are the same (XX) males the chromosomes are different (XY) www.newbyte.co.uk Inherited conditions in humans Some diseases are inherited Cystic fibrosis is inherited through a recessive allele Huntington’s is inherited through a dominant allele Genetic counselling allows a couple to work out the probability of a child inheriting a disease Embryo screening will determine if an unborn child has inherited a disease Stem cells and embryo’s – an ethical minefield What do we mean by something being ethical? When we say something is a minefield, what do we mean? There are many opposing views on use of stem cells and embryo’s in research Guidelines and rules for use of human cells are strictly controlled There are many valid reasons for use and very strongly held views against the use of human materials in research www.hdfoundation.org www.cftrust.org www.cff.org www.welcome.ac.uk