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B2 Topics- What do you want to revise? • Plant and Animal Cells • Specialised Cells • Bacterial and Fungal Cells • Diffusion • Animal Tissues, Organs and Organ Systems • Photosynthesis • Plant Tissues and Organs • Sampling Techniques • Mean, mode median • Enzymes Respiration Mitosis Meiosis Inheritance Mendel Genetic diseases Embryo Screening, Stem Cells and DNA Fingerprinting • Fossil record • Extinction • Forming a New Species • • • • • • • Animal and Plant Cells In Both Animal and Plant Cells Part Function contains genetic material, which controls the activities of nucleus the cell most chemical processes take place here, controlled by cytoplasm enzymes cell membrane controls the movement of substances into and out of the cell mitochondria most energy is released by respiration here ribosomes protein synthesis happens here Part cell wall Plant Cells Only chloroplasts permanent vacuole Function strengthens the cell contain chlorophyll, which absorbs light energy for photosynthesis filled with cell sap to help keep the cell turgid Specialised Cells • You are likely to be given information, perhaps in a diagram, to help you to explain the adaptations of a particular cell type to its function. • You should be able to name specialised cells, state their function and explain how they are adapted to carry out their function Red Blood Cells Carry Oxygen to the Cells Adaptations - Thin outer membrane, to allow quick diffusion of oxygen - Large surface area, to allow diffusion quicker - No nucleus, so whole cell is full of haemoglobin Sperm Cell • Fertilises the female egg cell Adaptations • The head contains genetic information and an enzyme to help penetrate the egg cell membrane. • The middle section is packed with mitochondria for energy. • The tail moves the sperm to the egg. Root Hair Cell • Absorbs water and mineral ions from the soil Adaptations • Long 'finger-like' process with very thin wall, which gives a large surface area. Palisade Cell • Absorbs light energy for photosynthesis Adaptations • Packed with chloroplasts. • Regular shaped, closely packed cells form a continuous layer for efficient absorption of sunlight. Bacterial and Fungal Cells Bacteria • A bacterium is a single-celled organism. • It has cytoplasm, a membrane and a surrounding cell wall, but the genetic material in a bacterial cell is not in a distinct nucleus. Fungi • Yeast is a single-celled organism. • Like bacterial cells, yeast cells have cytoplasm and a membrane surrounded by a cell wall. • Unlike bacterial cells, yeast cells have a nucleus. Diffusion Key Points • From a high concentration to a low concentration • If answering about movement through cells, you must say “through a cell membrane” or “through a partially permeable membrane” Two examples of diffusion down concentration gradients Location Particles move From To Small intestine Digested food products Small intestine Blood in capillary of villus Lungs Oxygen Alveolar air space Blood circulating around the lungs Animal Tissues and Organs Cells are the basic units of life. Groups of cells work together to form tissues. Groups of tissues work together to form organs. Digestive System The pancreas secretes enzymes but food does not travel through the pancreas so don’t state it as a “site of digestion” The liver produces bile. The bile is stored in the gall bladder. After the stomach, food travels to the small intestine. in the small intestine work best in alkaline conditions, but the food is acidic after being in the stomach. Bile is an alkaline it is secreted into the small intestine, where it emulsifies fats. This is important, because it provides a larger surface area in which the lipases can work. Plant Tissues Tissue Epidermal tissue Palisade Mesophyll Xylem and phloem Stomata Function Covers the plant Carries out photosynthesis Transport of substances around the plant To allow CO2 to diffuse into the leaf Photosynthesis • Examples of plant organs include: – Roots – Stems – Leaves- site of photosynthesis • Factors that can limit the rate of photosynthesis; – – – – CO2 concentration Light intensity Water availability Temperature Light Intensity • Without enough light, a plant cannot photosynthesise very quickly, even if there is plenty of water and carbon dioxide. Increasing the light intensity will boost the speed of photosynthesis. Can you explain what is happening here? CO2 • Sometimes photosynthesis is limited by the concentration of carbon dioxide in the air. Even if there is plenty of light, a plant cannot photosynthesise if there is insufficient carbon dioxide. Something other than CO2 concentration is acting as a limiting factor Temperature • If it gets too cold, the rate of photosynthesis will decrease. Plants cannot photosynthesise if it gets too hot. Why? Respiration • Site of respiration- mitochondria Aerobic- “in the presence of oxygen” Glucose + oxygen Carbon Dioxide + water (+Energy) C6H12O6+O2 CO2 + H2O (+energy) The energy made is used to make larger molecules from smaller molecules. It is also used in muscle contraction and maintaining body temperature. Good for long distance. Anaerobic Respiration- no oxygen Glucose →Remember Lactic acidin(+yeast energy) anaerobic respiration produces ethanol and This type of respiration may be used carbon dioxide (which when, for example, an animal is being is why we used it to chased by a predator (short bursts). make beer and bread) Less energy is produced less than from aerobic respiration. Sampling Techniques- Quadrats • A square made of wire. It may contain further wires to mark off smaller areas inside. The organisms underneath, usually plants, can be identified and counted. Quadrat Key Points Random sampling canso that a • It should be placed randomly be achieved representative sample isby taken assigning numbers to the area being • The validity and reproducibility of the using a from results sampled increases and as the results random more quadrats are number analysed generator Transects • A transect is a line across a habitat or part of a habitat. It can be as simple as Transects can a string or rope placed in a line on the be used ground. together with quadrats to • The number of organisms of each create a belt species transect.can be observed and recorded at regular intervals along the transect. Mean • Add the numbers together and divide the total by the amount of numbers Example Mean = (2 + 4 + 5 + 3 + 4) ÷ 5 = 18 ÷ 5 = 3.6 Quadrat sample 1 2 3 4 5 Number of dandelion plants 2 4 5 3 5 Mode • The median is the middle number. To calculate a median: • Put all the numbers in numerical order • If there is an odd number of results, the median is the middle number • If there is an even number of results, the median will be the mean of the two middle numbers • Example : 23455 The median is 4. Median • The mode is the number which occurs most often in a set of data. • Example : • 2345 5 • The number 5 occurs twice, so it is the mode. (Note that you can have more than one mode.) Enzymes- biological catalysts (speed up reactions) When the enzyme and substrate are together this is called an enzymesubstrate complex Key Points • Enzymes are reusable • They are affected by pH and temperature- these can cause them to denature • They are proteins (made by ribosomes) • Enzymes have an optimum temperature and pH (faster rate of reaction) Enzymes and Temperature Describing the changes; The rate of reaction increases up to 40°c. The optimum is 40°c. After 40°c the rate of reaction decreases to 0 at approximately 63°c. Explaining the changes; At 0°c the rate of reaction is slow, this is because there is a small amount of kinetic energy and the number of successful collisions between the enzymes active site and the substrate are low. After 40°c the enzymes start to denature and are no longer complimentary to the substrate. pH and enzymes • Different enzymes have different optimum temperatures. • Above or below the optimum the enzymes denature. Enzymes are specific and complimentary to their substrates Enzyme Amylase Reaction catalysed Starch Protease Proteins Lipase Lipids → → Where the enzyme is produced Glucose salivary glands, pancreas, small intestine Amino acids stomach, pancreas, small intestine → Fatty acids + Glycerol pancreas, small intestine Enzymes in Industry Enzyme Use Pre-digest proteins during the manufacture Protease Remember when talking of babyabout foods Together with protease - in biological enzymes you should describe detergents to break down - digest - the the reactants and the Lipase substances in stains into smaller, water products. soluble substances Convert starch syrup, which is relatively cheap, into sugar syrup, which is more Carbohydrase When lipase down valuable -breaks for example, as an ingredient in sportslower drinks fats, fatty acids will Convert glucose syrup into fructose syrup the pH Isomerase fructose is sweeter than glucose, so it can be used in smaller amounts in slimming foods Mitosis 1. Parent cell 2. Chromosomes make identical copies of themselves 3. They line up along the centre 4. They move apart 5. Two daughter cells form with identical chromosomes to the parent cell (46 chromosomes) Meiosis • Creates 4 daughter cells • Genetically unique • Gametes (sperm and egg cell) • 23 chromosomes Inheritance Vocabulary • Alleles -different forms of the same gene • Homozygous- 2 of the same allele e.g. bb • Heterozygous- 2 different versions of the same gene e.g. Bb • Genotype- the genes present • Phenotype- the genes that are expressed e.g. Bb, brown eyes • Recessive- only expressed when homozygous • Dominant- expressed when either heterozygous or homozygous Mendel • Gregor Mendel (1822-1884) studied the inheritance of different characteristics in pea plants • He was the first person to come up with the idea that “factors” are passed on through generations and sometimes they skip a generation (recessive genes) Generation 1 Generation 2 Cystic Fibrosis • Affects the cell membranes, causing the production of thick and sticky mucus. It is caused by a recessive allele. Punnett Square Polydactyly • Polydactyly is an dominant inherited condition in which a person has extra fingers or toes. • This means it can be passed on by just one parent if they have the disorder. DNA fingerprinting By cutting a sample of DNA into fragments and comparing it with other samples it's possible to work out if the DNA has come from the same person. Embryo Screening • Embryos can be screened for the alleles that cause polydactyly, cystic fibrosis and other genetic disorders. • Note that you do not need to know or understand how embryo screening works for the examination but your need to be able to discuss the pros and cons Discussing Ethical Issues • Science can answer the question, 'What are the chances of my child having cystic fibrosis?'. However, it cannot answer the question, 'Should I have my pregnancy terminated?‘ • Clearly state the issue • Summarise the different views • Identify arguments that are based on the right decision, ie a decision that produces the best outcome for most of the people involved. • Identify when certain actions are very hard to justify because they are considered unnatural or wrong. Stem Cells • Human stem cells can come from human embryos or from adult bone marrow. • They are able to develop into any kind of human cell. • Note that you do not need to know any details of how this happens for the examination. • They have the potential to be used in new treatments for conditions such as Parkinson's disease and paralysis. • There are social and ethical issues concerning the use of human embryonic stem cells in medical research and treatments. Fossil Record Fossil remains have been found in rocks of all ages. Fossils of the simplest organisms are found in the oldest rocks, and fossils of more complex organisms in the newest rocks. This supports the theory of evolution. Many early forms of life were soft-bodied - and have left few traces behind. Forming a New Species • New species can arise as a result of isolation. This is where two populations of a species become geographically separated. • Genetic variation - where each population has a wide range of alleles that control their characteristics • Natural selection - where the alleles which help an organism to survive are selected in each population • Speciation - where the populations become so different that successful interbreeding cannot happen anymore Extinction • Some of the factors that can cause a species to become extinct: • New diseases • New predators • New, more successful competitors • Changes to the environment over geological time - such as a change in climate • A single catastrophic event - such as a massive volcanic eruption or a collision between an asteroid and the Earth