Topic 4 Two Star LOs 2024 PDF

4.2) Explain the negative impact that some human activities (give 3 examples) have on the diversity of species 1. Climate change – our lifestyles are leading to a rise in the temperature of the atmosphere, which will impact on ecosystems, such as melting of Arctic...

4.2) Explain the negative impact that some human activities (give 3 examples) have on the diversity of species 1. Climate change – our lifestyles are leading to a rise in the temperature of the atmosphere, which will impact on ecosystems, such as melting of Arctic ice. 2. Deforestation – this may be done to increase the area of land for agriculture, or for timber. Species living in the forests will be negatively affected. 3. Over-fishing – some fish species numbers have crashed as we remove too many in an unsustainable way. 4.7) Explain how the concept of niche accounts for distribution and abundance of organisms in a habitat Niche - the role an organism plays in its environment. Any description must refer to where the organism lives and how it fits into its environment (e.g. what its position in a food chain is). Two species competing for the same resources cannot stably coexist. In other words, only one species can exist in any one niche. Within a niche the members of the species have intraspecific competition with each other. Where niches overlap there is interspecific competition between the different species. 4.8) Define the terms “natural selection”, “evolution” and “selection pressure”  Natural selection is the mechanism by which organisms change over time as they adapt to their changing environments. Evolution is a change in allele frequency in a population over time (generations). Selection pressure is the force driving the natural selection Natural selection is the mechanism that allows evolution to occur. 4.11) Explain the importance of meiosis to natural selection and evolution (mentioning genetic variation) If evolution is to occur, by natural selection, there needs to be genetic variation in a population. Sexual reproduction adds genetic variation as the process of gamete production involves meiosis, which ensures that the gametes are genetically variable. This variation is achieved though crossing over / formation of chiasmata, and independent assortment of homologous pairs of chromosomes. 4.13) Explain how reproductive isolation can lead to a change in allele frequencies, possibly leading to the formation of a new species E.g. a flock of sparrows get accidentally blown out to sea and colonise a distant island. If this new ecosystem (the island) has different environmental conditions, the sparrows will evolve to suit these new conditions, but no longer interbreed with the mainland sparrows. The allele frequencies in this new gene pool on the island change, and eventually a new species is formed. These two groups individuals cannot interbreed to produce fertile offspring. This is how Charles Darwin explained what he found on the Galapagos Islands, whereby 14 bird finch species alive today evolved from one single ancestral finch species, over many thousands of years. 4.14) Quote the equation for the Hardy-Weinberg calculation, and use it to calculate the frequencies of alleles and genotypes in a population p2 + 2pq + q2 = 1 (genotype frequencies) Hardy-Weinberg equation p + q = 1 (allele frequencies) 1. Work out the frequency of the recessive homozygote (q2) 2. The square root of q2 will give us the value of q 3. We can now find out p (using p + q = 1) 4. Now put the values of p and q into the Hardy-Weinberg equation  4.17) Explain the benefit of greater genetic diversity in a population, and state how it is measured by calculating the heterozygosity index Genetic diversity serves as a way for populations to adapt to changing environments. With more variation, it is more likely that some individuals in a population will possess variations of alleles that are suited for the environment. Those individuals are more likely to survive to produce offspring bearing that allele. However, if a population falls below the level of 50 breeding adults, there is likely to be genetic inbreeding, usually resulting in the accumulation of harmful recessive alleles. So newer species are less genetically diverse than older species, and so less resilient to diseases. Heterozygosity index (H) A measure of the genetic diversity in a population. The heterozygosity index is a useful measure of genetic diversity because it is a proportion rather than an absolute number, so it is unaffected by the sample size. heterozygosity index (H) = number of heterozygotes number of individuals in the population 4.18) Describe what tends to happen to genetic diversity over time and explain why  Genetic diversity tends to increase over time As random mutations increase in number, and accumulate in the population 4.23) Define the terms “classification” and “taxonomy” Classification is a means of organising the variety of life based on relationships between organisms using differences and similarities in phenotypes and genotypes, and is built around the species concept. Taxonomy – the scientific study of classification. 4.24) Describe what is meant by a “hierarchical” classification and a “phylogenetic” classification Hierarchical – we can keep breaking everything down into smaller and smaller groups (no overlaps). All living organisms belong to one of five kingdoms; each Kingdom (large group) is divided into a number of smaller Phyla (smaller groups); each Phylum is broken down into Classes etc. Phylogenetic – based on common structures / similar characteristics, reflecting patterns of evolutionary history. Molecular phylogeny – how the study of DNA base sequences, and amino acid sequences in proteins, can help us understand how closely related different species are / how recently they shared a common ancestor. 4.30) Explain what occurs in the “peer review” process (including publication of a scientific paper), and in scientific conferences Research is published in some form that other scientists can easily access (journal, internet, conference). Other scientists who work in the same field (anonymously) check their data (by repeating the experiment), and interpretations of the data. The peer review process then helps to detect invalid claims and adds weight to valid ones. 4.32)  List 3 similarities and 3 differences between plant cells and animal cells Differences The plant cell has a rigid cell wall made of cellulose. The plant cell contains chloroplasts The starch is found in the vacuoles in the cytoplasm, called amyloplasts There is often a large central vacuole surrounded by a membrane (the membrane is called a tonoplast) in plant cells Plasmodesmata – narrow, fluid-filled channels making the cytoplasm of one plant cell continuous with the cytoplasm of the adjoining cell Pits – in some places the cell wall is thin because only the first layer of cellulose is deposited, and there is no lignin. These places are called pits. Middle lamella – the region found between the cell walls of adjacent plant cells Similarities Both have nucleus, membrane-bound organelles, cell surface membrane, cytoplasm, linear DNA, 4.33) Recognise the following plant cell structures from EM images: cell wall, chloroplasts, amyloplasts, vacuole, tonoplast, plasmodesmata, pits and middle lamella Cell wall with plasmodesma Chloroplast Amyloplast with starch grains Vacuole with tonoplast Middle lamella Pit (narrowing of cw) 4.34) Describe the difference in structure between alpha- glucose and beta-glucose Notice then position of the hydroxyl group on carbon 1. It either points up or down.  4.35) Explain why alpha-glucose links together to form starch whereas beta-glucose links together to form cellulose  It is down to the arrangement of atoms on the C1 of each glucose. Which way does the OH group face – is it up (beta glucose) or down (alpha glucose)? Starch (amylose) forms spirals, whilst cellulose is a straight chain. 4.48) Describe the patterns that are created when lignin is laid down, and the importance of lignin for plants  Lignin is laid down in rings and spirals. To transport water the cells walls need to be waterproof. This is achieved using lignin. This polymer impregnates the cell walls of the xylem vessels (they become lignified), which restricts the entry of water, oxygen and ions into them. As they become lignified, the tonoplast (the membrane surrounding the vacuole) also breaks down, and there is enzyme destruction of cell contents, leaving an empty tube. Sclerenchyma fibres also have lignin. 4.49) State 4 ways in which water is important to plants 1. Polar molecule so forms hydrogen bonds with other polar molecules (e.g. glucose dissolves in water) 2. Cohesion to other water molecules, adhesion to other polar molecules 3. Good for transporting molecules and ions 4. Water has a high specific heat capacity, so it takes of lot of energy to heat it up (good for ponds not over-heating) 4.60) Describe how William Withering discovered a way of treating dropsy with extracts from foxglove 1. He observed that a patient of his cured herself of the symptoms of dropsy (congestive heart failure) by drinking a herbal remedy. 2. Mrs Hutton’s drink was a mixture of 20 or so herbs, one of which was foxglove. Withering suspected that the foxglove contained the active ingredient (must be identified) 3. Withering realised the importance of getting the dose right. 4. He slowly increased the dose until the patient started to have diarrhoea and vomiting, then reduced it slightly – this would be the most effective dose. 4.63) Describe what a “double-blind trial” is and explain its significance for producing valid and reliable results  In phase III of the clinical trials, it is crucial that neither the patients nor the doctors know who is having the compound under investigation, and who is receiving the placebo or standard treatment. This is known as a “double-blind randomised control trial” and is the most valid method of testing available. These trials are an important way of testing to see if the new drug actually works, and reduces bias in the results 4.64)  Describe the placebo effect and explain how it can affect the validity of results A placebo is a substance that contains no active ingredients but which is designed to appear exactly the same as the treatment normally used / being researched. All medicines induce the placebo effect. It is only those treatments that have an effect above and beyond that produced by a placebo that are classed as efficacious (having the capacity to produce an effect). As such a placebo can help assess the validity of a drug’s effect. A placebo can be used as a control experiment. It may have a psychological effect. 4.71) Explain why the use of plant-based products can alleviate some of the problems of using oil-based fuels and plastics The use of plant-based products can help. Although burning fuel from vegetable oils also releases CO2 this CO2 has only been removed from the atmosphere recently during photosynthesis, when the crop was grown - the oil is thus described as being “carbon-neutral”. All of these products are also biodegradable. 4.72)Describe 3 of the difficulties associated with using plant-based products to replace oil-based plastics 1. Due to lack of space, biofuel crops are being growing instead of food crops, or at the expense of tropical rainforests 2. The intensive agriculture of developed countries is very energy-demanding (machinery to plant, harvest and plough, fertilisers, pesticides etc) 3. The human population is still rapidly increasing globally 4. Some of the plant alternatives do not have the same desirable qualities as the oil-based products 5. Some plant alternatives may require the consumption of as much or more energy in production and transport of the product, compared with oil-based products. 4.75)  Explain how zoos use studbooks to conserve genetic diversity Small gene pool in individual zoos (so exchanges need to occur on a regular basis – encourage outbreeding, which means animals not allowed to mate with closely-related individuals). Each species has an appointed coordinator / studbook holder who advises on which animals should or should not breed, and on the movement of animals between partner zoos. In this way the genetic diversity within captive populations is maximised (prevents in-breeding effects). Genetic drift – in small populations only – reduction in genetic diversity due to chance, as a result of in-breeding. Inbreeding depression – only in small populations – close relatives are reproducing so in-breeding. Ability to survive and reproduce declines. 4.77) State the problems associated with reintroduction programmes 1. Animals may not behave as in the wild – reluctant to breed, dependent upon keepers for food (predators may not know how to hunt), do they need to migrate? 2. Their habitat may have been destroyed, so little point in reintroducing 3. Small gene pool in individual zoos, so individuals may lack the required genetic diversity to survive 4. Is there enough food available in the wild? 5. Too few individuals to produce a viable breeding population 6. Could they be susceptible to a disease in the wild? 4.79) State the objectives of seed banks  The Millennium Seed Bank (MSB) aims to provide an insurance policy against the extinction of plants in the wild. The current phase of the project is to conserve 25% of the world’s plant species by 2020. This is important because plants provide food, building materials, fibres for clothing, medicines and fuel, but also it is preserving our botanical heritage for generations. Collecting seeds and preserving them ex situ (away from their natural habitat) offers an economical and effective way to save seeds and keep them for posterity. In the future, if required, they can be germinated and reintroduced to the wild or used in scientific research.