Revision Pack BIOLOGY

Transcription

1 Revision Pack BIOLOGY CB1 Overarching Themes in Biology CB2 Cells and Control CB3 Genetics CB4 Natural Selection & Genetic Modification When we tackle obstacles, we find hidden reserves of courage and resilience we did not know that we had. -A.P.K Abdul Kalam Be kind, for everyone you meet is fighting a battle. Plato Just be yourself man, be proud of who you are. Eminem

2 CB1 Overarching Themes in Biology Light microscopes are used to see small objects such as cells They use light and lenses to magnify images This triangle is used to calculate the size of a sample from image size and magnification. Electron microscopes are more powerful, and use electron beams to see even smaller objects. The sample must however be dead, and the images are always in black and white As things are so small, we sometimes use standard form to measure them. For example, a cell would be measured in micrometres (1 x 10-6 m) The sub-cellular structures in a cell are called organelles A cell with a nucleus is called a eukaryote (i.e. a plant/animal cell) A cell without a nucleus is called a prokaryote (i.e. a bacteria) The diagrams below show which organelles are found in each cell type. Specialised cells have a different shape/adaptation as they have a specific function Examples are given below: Cell Adaptation Function Haploid (half the DNA) Acrosome full of enzymes Tail Lots of mitochondria Sperm (animal cell) Ovum (animal cell) Ciliated Epithelial (animal cell) Nerve (animal cel) Red blood cell (animal cell) Root hair cell (plant cell) Palisade cell (plant cell) Haploid (half the DNA) Full of nutrients Small cilia (hairs) Long axon Myelinated sheath Many dendrites No nucleus Disc shaped Large surface area Lots of chloroplasts To fuse with the ovum nucleus To break through the ovum cell membrane To swim to the ovum To produce lots of energy for swimming To fuse with the ovum nucleus To help develop the foetus To brush away mucus full of bacteria To carry electrical signals long distances To speed up the nerve signal (insulator) To reach other nerve cells More room for haemoglobin (to carry oxygen) Larger surface area to diffuse gases To absorb more water To absorb sunlight for photosynthesis

3 Enzymes are biological catalysts that speed up chemical reactions inside living things. They are proteins. Enzymes either break down large molecules or put smaller molecules together to make longer ones. Enzymes have a specific active site that only matches one substrate. When the enzyme is bonded to its substrate, it is called an enzyme-substrate complex If an enzyme gets too hot / acidic / alkaline, it will change shape and stop working (denature). Increasing the amount of substrate can increase the rate of enzyme action. Common enzymes involved in digestion are; Lipase; Lipids à fatty acids Protease; Proteins à amino acids Amylase; Starch à glucose Diffusion is the movement of particles from a high concentration to a low concentration Osmosis is the movement of water from a high concentration of water to a low concentration of water through a semi-permeable membrane This is how water gets into red blood cells, root hair cells and why sweets swell in a glass of water Diffusion and osmosis are called passive transport because they do not require energy DIFFUSION OSMOSIS If you place potato in a solution of concentrated sugar, that is more concentrated with sugar than the potato, the water will come out of the potato into the solution. The potato will decrease in mass. If you place a potato in pure water, where there is a lower concentration of sugar, the water will instead move into the potato and it will increase in mass. To calculate the percentage mass lost, you use this equation; Final mass starting mass x 100 Initial mass Active transport is the movement of particles from a low concentration to a high concentration; this requires energy and normally occurs through a special channel in the membrane.

4 CB2 Cells and Control The cell cycle includes the growth and replication of living cells Interphase = cell grows and replicates Mitosis = nucleus splits into two Cytokinesis = the cytoplasm splits into two Cells do mitosis / cell replication for; growth, repair, reproduction (prokaryotes) and cancerous tumours The stages of mitosis are; Prophase DNA organises into chromosomes Metaphase chromosomes lines up down the centre of the cell Anaphase chromosomes get pulled to either side of the cell by spindles Telophase new nuclear membranes form around the chromosomes Cytokinesis cytoplasm splits in two to make two identical cells Living organisms can grow in the following ways; Increase the size of cells Increase the number of cells Elongation cells getting longer Differentiation cells changing type and specialising We measure the expected growth of humans on Percentile Growth Charts, that show if a person is following a normal growth pattern. It also helps us to compare their size (mass and height) with the national average. Plants also grow through cell elongation, differentiation and cell division The meristem at the tip of the shoot and the root is a site of rapid replication and differentiation Stem cells can differentiate into many types of specialised cells. Embryonic stem cells can differentiate into all cell types of that species, whilst adult stem cells can only differentiate into a limited number of cell types. Stem cells can also be found in the umbilical cord. There is lots of potential for stem cells to be used in medicine, repairing tissues and organs. Some people think it is wrong to produce embryos for stem cell research, and in the UK we only use un-implanted embryos originally developed for IVF for research.

5 Nerves (neurones) carry electrical signals around the body. There are three main types described below. Neurone type Location Function Sensory neurone From sense organ à relay neurone To sense things Relay neurone From sensory neurone à motor neurone Often found in the spinal cord To pass on messages to the motor neurone or the brain Motor neurone From relay neurone à muscles (effectors) To make us react to a stimulus These three neurone types sometimes work without the brain. This is called a reflex and is much quicker than reactions that involve your brain. Examples include your pupil dilating in dim light, or your hand quickly moving away from a hot surface Synapses are the gaps between nerves, where they meet each other. Chemicals called neurotransmitters pass over these gaps to start an electrical signal in the next nerve. Some drugs cause more/less neurotransmitter to be released, therefore they speed up or slow down reactions in the nervous system. The structure of each nerve (neurone) helps the body carry electrical signals around the body quickly. They have a myelin sheath to speed up the impulse, a long axon to carry the signal long distance, and dendrites to reach other nerve cells. QUESTIONS TO TEST YOURSELF CB1 & CB2 1. What organelles are only found in a plant cell? 2. Which type of microscope is more powerful? 3. What is the difference between a eukaryote and a prokaryote? 4. What does a cell wall do? 5. What is the acrosome in a sperm cell? 6. What is the adaptation of a root hair cell? 7. Why do enzymes only work on one substrate? 8. What happens to an enzyme in an alkali solution? 9. What does denature mean? 10. What happens to a potato cube in pure water? Why? 11. Does diffusion require energy? 12. How do you calculate percentage mass loss? 13. Why are embryonic stem cells more useful than adult stem cells? 14. What does differentiate mean? 15. Where do you find a relay neurone?

6 CB3 Genetics Meiosis is the production of gametes (sperm or ovum) from a diploid (two copies of each chromosome) cell. Meiosis produces 4 daughter cells that are haploid (contains one copy of each chromosome). All the haploid daughter cells are genetically different, so all offspring are genetically different. The genome is the entire DNA of an organism. A gene is a small section of DNA that codes for a protein. DNA is a polymer, made up of 4 bases; A, C, G, T The strand of DNA coils into a double-helix shape, as complimentary bases bond together with weak hydrogen bonds. A bonds to T, C bonds to G. An allele is a different version of the same gene. For example blue eyed and the brown eyed are both alleles of the eye colour gene. Every person has two copies of each gene; one from their Mother and one from their Father. If both copies are the same allele, it is called homozygous. Two different alleles are called heterozygous. A dominant allele is expressed in the phenotype (physical attribute) A recessive allele is only expressed is both copies are recessive. Genotypes: H = dominant h = recessive HH = homozygous dominant Hh = heterozygous hh = homozygous recessive If you know the genotype (which alleles) of the mother and father, you can calculate the chance of their offspring s DNA. A Punnett square is used to calculate this as seen above. A genetic diagram like this can also be used to calculate the chances of offspring being male or female. Most phenotypes (physical attributes) are the result of multiple genes working together, instead of just one gene. Differences within a species is called variation. Variation is caused by genes from sexual reproduction, environmental factors and genetic mutations.

7 CB4 Natural Selection & Genetic Modification The primary source of evidence for human Evolution is fossils. Famous fossils include: Ardi 4.4mya (million years ago) Lucy 3.2mya Leakey s discovery of fossils from 1.6mya The discovery of stone tools also shows how species prior to humans began to form and use tools to aid survival. This is considered an important step in our evolutionary history. Darwin developed the theory of natural selection, after observing how populations changed over time. 1. There is variation within a species 2. Some of these variations are beneficial 3. Living organisms with the beneficial mutation are more likely to survive and reproduce 4. The beneficial variation is passed on genetically to the next generation 5. Less beneficial mutations are not passed on 6. Over many generations, the species changes to be increasingly well adadpted For example: 1. Some giraffes have short necks. By a genetic mutation, some have longer necks 2. Having a longer neck is more useful for obtaining food 3. The giraffes that can reach more food will more likely survive and reproduce 4. The genetic mutation for a longer neck will be passed on 5. The shorter neck gene is not passed on as much 6. Over time, more giraffes have longer necks the species has changed over time 7. We can see this happening today with the increase in antibiotic-resistant bacteria. The bacteria that are resistant to antibiotics are surviving and replicating more successfully changing the species over time. Other evidence for this theory of evolution is the pentadactyl limb many species that all seem to have a five-digit limb, This suggests we all share a common ancestor, but have adapted over time to match environments, locomotion and lifestyle. Living things used to be classified into 5 kingdoms, based on their cellular structure. However, genetic analysis showed distinct differences in the DNA of some prokaryotes, so living things are now classified into 3 domains, based on this genetic analysis. 1. Archaea Prokaryotes 2. Bacteria Prokaryotes 3. Eukaryotes; including Funghi, Plantae and Animalia Selective breeding is a method of purposefully reproducing organisms with desired traits, to increase the chance of passing on desired genes to their offspring. For example, breeding two cows with large muscle mass to produce cattle for beef. This process is repeated over many generations to increasingly produce the best change over time. Genetic engineering however, involves the direct manipulation of DNA in the nucleus, for example: 1. To make crops resistant to herbicides, 2. To increase the amount of Vitamin A in rice (golden rice) 3. To increase the size of fruit/vegetables Bacteria plasmids are often used for this, as restriction enzymes can cut a small section of DNA out of the plasmid, and replace it with the desired gene. This is how human insulin is now manufactured for diabetics.

8 QUESTIONS TO TEST YOURSELF CB3 & CB4 1. What does diploid mean? 2. How many cells are produced in meiosis? 3. How is a gene different to a genome? 4. What are the 4 bases of DNA? 5. Which base pairs with A? 6. How would you describe the genotype HH? 7. What is a phenotype? 8. When do scientists think Ardi was alive? 9. Give an example of a species changing because of natural selection. 10. How have antibiotic resistant bacteria developed? 11. What is the pentadactyl limb? 12. What are the 3 domains? 13. How have we used Genetic Engineering to help people?