B2 Topic 1 revision The building blocks of life Class revision with exam questions
Animal cells
What is aerobic respiration? Aerobic respiration is the process of releasing energy through the oxidation of glucose molecules. carbon glucose + oxygen dioxide + water ( + energy) C 6 H 12 O 6 + 6O 2 6CO 2 + 6H 2 0 ( + ATP) This reaction releases energy in the form of ATP a compound that can readily be used in cellular processes.
Plant cells
What is photosynthesis? Photosynthesis is a chemical reaction where light energy is used to convert carbon dioxide and water into glucose and oxygen. carbon dioxide + water light energy chlorophyll glucose + oxygen 6CO 2 + 6H 2 0 C 6 H 12 O 6 + 6O 2 The reaction uses light energy from the Sun and takes place in chloroplasts of plant cells.
What organelles are present in a bacterial cell? Cytoplasm Slime layer flagella Plasmid DNA Cell wall Cell membrane Chromosomal DNA
What organelles are present in a bacterial cell? Chromosomal DNA Plasmid DNA Plasmid DNA are just loops of DNA.
Light Microscopes The magnification can be worked out by using a simple formula: Total magnification = magnifying power x magnifying power of eyepiece lens of objective lens Total magnification = x10 x x50
How did Watson and Crick develop their model of DNA? Started with ideas and a hypothesis Written and published a paper on their model. Conducted various experiments Gathered evidence from other sources
Extracting DNA Action Why? Finely chopped kiwi fruit tissue is added to saline/detergent solution The mixture is kept warm at 50 C for 15 mins, then filtered. Cooled methanol is carefully added to the filtrate in equal volumes. Look for a change at the boundary. Membranes of the cell brake up, releasing chromosomes. Protein-digesting enzymes in the cells digest the protein part of the chromosomes, releasing DNA. DNA precipitates from the filtrate. DNA strands are visible in the methanol layer.
What happens to DNA in cell division? Before cell division takes place, the chromosomes duplicate. How does this affect DNA? Each chromosome is made of a DNA molecule, so DNA also needs to replicate. DNA is a very interesting molecule because it is able to copy itself. It is able to do this because it is double stranded.
How does DNA replicate? The replication of DNA is a continuous process but can be broken down into several stages: The DNA helix unwinds. The two strands separate. New bases bond to each strand, creating two new molecules of DNA. Each molecule of DNA winds up again, creating two new helices.
Mitosis Mitosis results in two daughter cells. Most cells contain 2 set of chromosomes (1 from mum and 1 from dad) The DNA replicates and make chromatids The cell splits apart creating two identical cells
Meiosis Mitosis results in four daughter cells. Most cells contain 2 set of chromosomes (1 from mum and 1 from dad) The DNA replicates and make chromatids The cell splits apart The cell splits apart again
Mutation! DNA is able to copy itself very accurately for every 1 billion bases replicated, only 1 will be wrong! Sometimes, however, mistakes do happen. When this happens, it is called a mutation. Most mutations are harmful and many have no effect, but sometimes a mutation results in a new, beneficial characteristic for the individual. How important are mutations in natural selection and evolution?
Replicating micro-organisms Genetically-engineered micro-organisms, such as bacteria and yeast, can easily be replicated on a large scale. Tanks called fermenters or bioreactors are used. These enable the micro-organisms to be grown, or cultured, at optimum ph, temperature and nutrient levels. The product can be continuously removed and purified.
GM crops Crops can be given extra genes for new and useful characteristics. They are genetically modified (GM). What characteristics might be useful in crops? pest resistance frost resistance disease resistance herbicide resistance drought resistance longer shelf life
Plants with extra vitamins Rice can be genetically modified to make beta-carotene, a substance that is converted into vitamin A in the body. The colour of the rice is an indication of how much more betacarotene it contains. The GM rice is called Golden Rice and is being developed to help fight vitamin A deficiency and blindness in developing countries.
Taking cuttings A plant can easily and quickly be cloned by taking a cutting. This is a fast way of cloning. stem cut from parent plant cutting dipped in rooting powder and planted The problem with this method is that it cannot produce many clones at once.
Tissue culture
Embryo transplantation It is more difficult to clone animals than plants. A technique used to create clone animals is embryo transplanting. For example, a cattle farmer would follow this process: 1. Sperm is taken from the best bull and used to fertilize an egg from the best cow. 2. The fertilized egg divides to form an embryo containing several cells. 3. The embryo is separated into individual cells, which go on to form new embryos. Each embryo contains the same genes. 4. The embryos are implanted into surrogate cows. 5. The cows give birth to calves, which are all clones of each other.
Human therapeutic cloning The DNA of an embryo cell can be replaced with the DNA from a patient s cell. patient s DNA inserted embryo cell nucleus removed 5 day-old embryo stem cells removed the embryo dies The embryo produces stem cells containing the patient s genes. The cells will not be rejected, so immune-suppressing drugs are not needed. This process is therapeutic cloning.
Higher only
What are stem cells? Stem cells are unspecialized cells that can develop into any type of cell. Early embryos are good sources of stem cells. stem cells red blood cells liver cells muscle cells
Using stem cells Stem cells could be injected into damaged organs to rebuild the tissues. This would reduce the need for organ transplants. injected into patient with diseased liver stem cells liver is repaired The stem cells would need to have the same genes as the patient, otherwise they would be rejected by the patient s immune system. They would need to be clones. How could you make an embryo that only contained your genes?
What happens at the active site? In the same way that a key fits into a lock, so a substrate is thought to fit into an enzyme s active site. The enzyme is the lock, and the reactant is the key. + + enzyme + enzyme-reactant complex enzyme + reactant products
Factors affecting enzymes The rate of enzyme catalyzed reactions depends on several factors. What are some of these? Factors that affect the rate of a reaction include: temperature ph enzyme concentration substrate concentration surface area pressure. All enzymes work best at only one particular temperature and ph: this is called the optimum. Different enzymes have different optimum temperatures and ph values.
EXAM TIP: NEVER say that the enzyme is destroyed or has died or is killed. It is DENATURED as it loses its shape only, meaning that it cannot match up to the substrate correctly. denatured