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Biology B3 Revision What’s in a cell? Cytoplasm where many chemical Cell membrane controls reactions happen the movement of substances in and out of the cell Genetic information is carried on chromosomes Nucleus carries genetic information DNA • Chemical found inside the nucleus. • Forms structures called chromosomes. • Section of a chromosome is called a gene. • Each gene is a code for making a protein. • Proteins are needed for growth and repair. • Everyone has their own unique DNA code. • The production of proteins is called protein synthesis. • Any time your body needs a particular protein, like an enzyme, a new one is made using the code on the DNA strand. DNA Fingerprinting • Used to identify people from a fragment of DNA in a blood or hair or skin or semen sample. Fragments of DNA are placed on a gel and separated by an electric current. Banding of DNA fragments can be matched. So….. Who did it? DNA Replication • Every time a cell divides by mitosis, the DNA must replicate itself first. DNA Replication- Higher New bases pair up with their complementary base to form two new double strands. End up with two identical DNA strands. Used for mitosis to make genetically identical cells for growth and repair. Enzymes • Biological catalysts. • Protein that speeds up a chemical reaction. • Used in all sorts of reactions: – Making cheese photosynthesis – Respiration – Photosynthesis – Protein synthesis enzymes are specific because their active site will only fit one type of substrate. • Enzyme –controlled reactions are affected by: – pH (measure the acidity of a solution) – temperature Lock and Key- Higher 1. The enzyme acts like 2. The substrate fits into 3. Once the substrate a lock, and the the active site. The has broken down, the substrate fits in like a substrate gets broken enzyme releases it. key down. The enzyme is not changed so can be used again. Denaturing Enzymes- Higher • Enzyme is a protein, which is made up of a chain of amino acids. • At too high temperatures or the wrong pH, the structure of the enzyme is changed, so the substrate no longer fits into the active site. Diffusion • Diffusion is the movement of a substance from a region of high concentration to a region of low concentration. Semi-permeable membrane Where diffusion occurs in the body • There is more oxygen in the alveoli than in the blood, so oxygen moves by diffusion into the blood stream. • There is more carbon dioxide in the blood than in the alveoli, so it moves by diffusion into the alveoli and it is breathed out. Digestive system • After eating there is a high concentration of food molecules in the small intestine compared to the blood stream. • Food molecules move by diffusion into the blood. Diffusion and the placenta A foetus growing inside its mother’s uterus needs food and oxygen to stay alive. It also needs to be able to get rid of waste products. In the placenta the mother’s blood and the baby’s blood is separated by a semi-permeable membrane. Substances are exchanged between the two types of blood by diffusion. Diffusion and the leaf • Plants use diffusion to exchange gases through the special holes in their leaves called stomata. Leaf cells Xylem vessels Water enters air bring water from space by roots into leaf cells evaporation Water diffuses out through stomata to the outside because of the high concentration of water in the air space. Diffusion- Higher • The rate of diffusion can be increased by: – Increasing the surface area – Decreasing the diffusion distance – Increasing the concentration difference Small Intestine Increasing the surface area: Decreasing the diffusion distance: The surface of the small Villus is only one cell thick intestine is covered with villi that increase its surface area A greater concentration difference: A good blood supply means the digested food is carried away quickly to maintain the concentration difference Lungs Increased surface area: Large number of alveoli inside the lungs Greater concentration difference: Decreasing the diffusion distance: Breathing makes sure there is a higher concentration of O2 in the Alveolus wall is only one cell thick alveoli Placenta • It is important to move substances across the placenta as quickly as possible. • To speed up this movement, the placenta has: – A very large surface area – A very thin semi- permeable membrane so substances only have a short distance to diffuse across. The Leaf To increase the rate of gas exchange, the leaf has a large surface area. The under-surface of the leaf also has many stomata through which the gases can diffuse. Guard cells stomata Synapses • A synapse is a gap between two neurones (nerve cells). • To carry a signal from one neurone to the next, the synapse releases a transmitter substance. • This is a special chemical that can diffuse across the gap between the two neurones. • When it reaches the other side of the synapse, it causes an impulse to travel along the neurone. neurotransmitter Direction of impulse Transport around the body • Blood is made up of 4 things: – Plasma- a yellow liquid that transports carbon dioxide, nutrients, hormones and other things around the body. – Red Blood cells- contain a chemical called haemoglobin which binds with oxygen and transports it around the body. – White blood cells- used for fighting diseases. – Platelets- fragments of red blood cells used for clotting blood. Blood Vessels • Three types: – Artery carries blood Away from the heart. – Vein carries blood In to the heart. – Capillaries join arteries to veins. It is through capillary membranes that substances are exchanged between the blood and cells. Blood Vessels- Higher Level • Artery- thick muscular and elastic wall to help it withstand high blood pressure as blood leaves the heart. • Vein- large lumen to help blood flow at low pressure; valves stop blood from flowing the wrong way. • Capillaries- thin, permeable wall to allow exchange of material with body tissue. Heart The heart pumps blood around the body. The right side of the heart pumps the blood to the lungs to collect oxygen and drop off carbon dioxide. The left side of the heart has much more muscle than on the right side because it pumps the blood to the rest of the body. Valves in the heart prevent the blood flowing in the wrong direction. The heart beats faster when you exercise to supply your muscles with the oxygen and glucose it needs for respiration to make energy. Double Circulation- Higher One circuit links the heart and lungs called the pulmonary circulation. The other circuit links the heart and the body. The left side of the heart has more muscle so it is able to pump the blood at much higher pressure to the rest of the body. Heart Disease • Saturated animal fats such as cholesterol can stick to the walls of arteries slowing down or blocking the flow of blood. • If this happens in a main blood vessel it can cause a heart attack or a stroke. • A blockage in a coronary artery (this supplies the heart itself with food and oxygen) can cause serious heart problems. Treating heart disease Heart transplants- patients must take drugs to stop their body rejecting their new heart Pacemakers- attached to a heart to help it beat. Cell Division (Mitosis) • Used for: – Growth – Repair damaged tissue – Replace worn out cells • A human body cell contains 46 chromosomes arranged in 23 pairs. • These cells are called diploid cells, because they contain the full amount of DNA. Mitosis- Higher Level Eggs and Sperm (Gametes) • Egg – Much larger than a sperm because it contains a food store for the growing embryo • Sperm – Much smaller than an egg to help it swim – Tail to help it swim – Millions are released to increase the chance of one reaching the egg – Head contains an acrosome that releases enzymes to help digest the egg cell membrane. – Contains a large number of mitochondria to release energy for motion. • Gametes are made by a special type of cell division called meiosis that produces cells with half the amount of DNA in it. • These cells are called haploid. • When two haploid cells meet, they make a diploid cell. • Meiosis makes every sperm and egg different, as they each contain a different combination of genes. • This is why brothers and sisters look different. Meiosis- Higher Level Animal and Plant Growth • Animals grow to a certain size then stop. • Plants can continue to grow. • Plant cells elongate rather than divide. • Plants do cell division at the tips of shoots and roots. Stem Cells • After an egg is fertilised it contains a group of cells called stem cells. • Stem cells are able to grow into any type of cell. • Once the cells have become differentiated into skin or bone or blood etc. they cannot grow into any other cell. • In adults, bone marrow contain stem cells that turn into different types of blood cells. What is a Stem Cell? Human Growth 1. Infancy 2. Childhood 3. Adolescence (puberty) 4. Adulthood (maturity) 5. Old age • Gestation is the length of time form fertilisation to birth. • Different parts of the foetus and baby grow at different rates. • The brain and head develop quickly to coordinate the complex human structure and chemical activity. Growth problems- Higher Level Poor weight can indicate problems with baby’s digestive system. Larger than normal head size can indicate fluid collection on the brain or the separate skull bones not fusing together. Controlling Plant Growth • Special chemicals called hormones control different processes in a plant: – Growth of shoots towards light (phototropism) – Growth of roots downwards in direction of gravity (geotropism) – Growth of flowers – Ripening of fruit Auxin- Higher Level • Plants grow towards the sun. • Why? • Auxin is destroyed by sunlight, so is found on the side of the stem in the shade. • It causes only those cells in the shade to elongate. • This tips the stem over towards the Sun. Commercial Uses of Plant Hormones • Weedkiller- makes weeds grow too fast and they die • Growing roots- taking cuttings from plants to clone them • Seedless fruits- cause fruit to grow even when the flowers have not been fertilised • Transporting fruits- hormones slow down ripening of fruit so they do not get as damaged during transportation • Sleeping seeds- hormones can be used to force seeds to germinate • Slowing down growth- so fruit does not fall off the tree before the harvest Selective Breeding • Farmers choose the animals and plants with the characteristics they want. • They then breed them together to produce the offspring with the desired characteristics. Selective Breeding -Higher • Often involves breeding animals that are closely related. • This is called inbreeding. • It reduces the gene pool, so there is not as much variation in a species. • The less variation in a species, the less chance that species has of surviving a change in the environment or a new disease. Mutations- Higher Level • A mutation is a change in the DNA base sequence. original base code mutation CACTTGGTCAAA CACTTGTCAAA • Mutation means a different amino acid is coded for, so a different protein is made. • This can cause all sorts of problems for the living organisms. • Mutations can be caused by radiation, chemicals or chance Genetic Engineering • Scientists can take genes form one organism and put them into a different organism. • These changes are called genetic engineering or genetic modification (GM). • Genetic engineering involves adding a gene to the DNA of an organism. • The altered organism is described as genetically modified (GM). Rice does not Rice now contain vitamin produces Inserted A vitamin A into rice Carrots do contain vitamin A Vitamin A gene extracted from carrot Advantages and disadvantages Advantages • Developing crops resistant to herbicides, frost and disease. • Large supplies of insulin can be made using bacteria. • Rice can have vitamin A added to it using a gene from carrots. Vitamin A is needed for night blindness. Disadvantages • Both methods could cause unexpected problems, for example, some people are concerned how our bodies will react to GM foods in the future. • Some people believe that mixing different animal genes is like ‘playing God’. How Genetic Engineering Works- Higher Level • Select the characteristic • Identify and isolate the gene • Insert the gene into the chromosome of a different organisms • Replicate (copy) the gene in the organism and produce the protein DNA in ring Insulin added DNA cut using ligase shape, enzyme open GM E.coli E.Coli bacterium added enzyme starts making insulin Chromosome DNA DNA cut open from human extracted to get insulin pancreas cell from human gene Cloning • Cloning produces copies of animals and plants that are genetically identical to each other. • Cloning involves one parent and is called asexual reproduction. • Natural clones are identical twins. • Animals can be cloned by embryo transplantation. A cow is artificially inseminated with Sperm is collected the sperm form bull When the fertilised egg divides into an 8-cell embryo, it is collected and split into four 2-cell Each embryo is then embryos implanted into a surrogate cow where it grows into a calf. Cloning Sheep- Higher • Animals can be cloned using a different technique called nuclear transfer. Cells taken from the Egg cell taken udder of sheep B and from sheep A the nucleus removed and nucleus removed Nucleus from sheep B is put into egg of Egg cell is put into a sheep A female sheep to grow Cell grows into a clone of sheep B Risks and Benefits of Cloning Risks • Low rate of success with cloning animals • Cloning humans raises ethical and moral questions Benefits • Human embryos could be cloned to provide stem cells to help cure diseases • Cloned pigs could be used to help with the shortage of organ donors Asexual Reproduction in Plants Plants are able to reproduce sexually (using flowers) or asexually (cloning themselves). Asexual reproduction produces a new plant that is a genetically identical copy to the original plant- a clone. Lots of plants use asexual reproduction because: • it produces lots of new plants quickly • plants do not need to spend lots of energy making flowers and gametes • it is guaranteed to produce new offspring unlike sexual reproduction Taking Cuttings • To clone a plant artificially we can use the technique of taking cuttings. • First the plant we want to clone is cut into smaller sections. • Then each section is dipped into rooting powder. • Each cutting is potted into its own container. • Lastly a plastic bag is placed over each cutting to limit water loss. Tissue Culture- Higher Level Small sections of plant tissue can be cloned using tissue culture. It must be carried out using aseptic technique (sterile conditions). First plants with the desired characteristics are chosen. Then a large number of small pieces of tissue are taken from the parent plant. They are then put into sterile test tubes that contain growth medium. The tissue pieces are left in suitable conditions to grow into plants. Advantages and disadvantages of cloning plants Advantages – All the plants are genetically identical. All the cuttings taken from a red rose will grow into red roses. – Plants can take a long time to grow from seeds. Cloning produces lots of identical plants more quickly. – Cloning enables growers to produce plants that are difficult to grow from seed such as bananas. Disadvantages – The plants are all genetically identical. If the environment changes or a new disease breaks out it is unlikely that any of the plants will survive. – Cloning plants over many years has resulted in little genetic variation. Why can plant cuttings grow into new plants but cuttings from an animal could not grow into a new animal? • Many plant cells retain the ability to differentiate into different cells. Root cells used in tissue culture have to change into all the different types of cells found in a plant. • Most animal cells have lost the ability to differentiate.
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