A Level Biology B Edexcel

This subject is broken down into 66 topics in 10 modules:

  1. Classification and Biodiversity 10 topics
  2. Biological Molecules 7 topics
  3. Cells, Viruses and Reproduction of Living Things 8 topics
  4. Exchange and Transport 7 topics
  5. Energy for Biological Processes 7 topics
  6. Microbiology and Pathogens 7 topics
  7. Modern Genetics 4 topics
  8. Origins of Genetic Variation 3 topics
  9. Control Systems 9 topics
  10. Ecosystems 4 topics
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  • 66
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  • 24,251
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This page was last modified on 28 September 2024.

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Biology B

Classification and Biodiversity

Defining and Understanding Biodiversity

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Defining and Understanding Biodiversity

Understanding Biodiversity

  • Biodiversity refers to the variety of life at different levels of biological organization. This encapsulates genetic diversity, species diversity, and ecosystem diversity.

Genetic Diversity

  • Genetic diversity is the variety of genes possessed by the individuals making up a population, species, or community.
  • More genetic diversity ensures long-term viability of a species because it provides more opportunities for adaptation to changing environments.
  • Inbreeding reduces genetic diversity; conversely, a wide gene pool promotes it.

Species Diversity

  • Species diversity includes two components: species richness (the number of different species in an area) and species evenness (does one species dominate the area or are species numbers fairly equal).
  • A higher degree of species diversity generally contributes to the stability of an ecosystem, as a variety of species can compensate for changes in the environment.

Ecosystem Diversity

  • Ecosystem diversity refers to the variety of different ecosystems on the Earth.
  • Each ecosystem contains unique combinations of species, interactions between these species, and physical conditions under which these species live.

Defining and Identifying Species

  • The biological species concept binds species as groups of organisms that can breed together to produce fertile offspring.
  • This definition has limitations, particularly for organisms that reproduce asexually, don’t currently have the opportunity to interbreed, or for extinct groups of organisms.
  • The phylogenetic species concept identifies species based on the evolutionary history of the population.
  • The morphological species concept categorizes species based on observable physical features.

The Importance of Biodiversity

  • Biodiversity contributes to everything from ecosystem services such as decomposition, water purification, and pollination, to cultural, spiritual, recreational, and aesthetic values.
  • Biodiversity is important to human survival as it provides food, fibres, and medicinal resources; it also ensures the availability of a healthy gene pool for future use.

Threats to Biodiversity

  • Threats to biodiversity include habitat loss, overexploitation, invasive species, pollution, and climate change.
  • Conserving biodiversity requires understanding threats and their impacts as well as taking action to mitigate or limit those threats.
  • Conservation strategies may include establishing protected areas, restoring degraded habitats, reintroducing species, and implementing laws and regulations.

Course material for Biology B, module Classification and Biodiversity, topic Defining and Understanding Biodiversity

Biology B

Energy for Biological Processes

Glycolysis

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Glycolysis

Glycolysis Process

  • Glycolysis is a cytoplasmic pathway which breaks down glucose into two three-carbon compounds and generates energy.
  • The process involves the conversion of glucose (six-carbon) to pyruvate (three- carbon). This conversion happens in ten steps and is catalyzed by different enzymes.
  • The first five steps of glycolysis require energy, thus are called the energy investment phase. They include phosphorylation of glucose and its conversion to fructose and further phosphorylation.
  • Steps six to ten release energy, hence they are the energy payoff phase. Here, D-Glyceraldehyde-3-phosphate (G3P) is formed and two molecules of G3P are converted to pyruvate.
  • Conversion of G3P to pyruvate, in the presence of enzymes, releases energy which is utilized to form ATP (Adenosine Triphosphate) and NADH (Nicotinamide adenine dinucleotide ).

Importance of Glycolysis

  • Glycolysis is considered the universal energy extraction process, as it occurs in all organisms from simple bacteria to complex eukaryotes.
  • It serves as the initial process in fermentation. The anaerobic conversion of glucose to lactate when oxygen is scarce provides a valuable mechanism for muscles and other tissues.
  • The ATP generated during glycolysis is utilized for other biological processes while the NADH contributes to further ATP synthesis in the oxidative phosphorylation process.

Factors Affecting Glycolysis

  • Glycolysis depends on the availability of glucose. The more glucose available, the more ATP can be generated.
  • Certain hormones, such as insulin and glucagon, also regulate glycolysis. Insulin stimulates glycolysis in the liver and muscle cells while glucagon has an inhibitory effect.
  • Enzymes involved in glycolysis act as catalysts, so a change in enzyme activity can significantly change the rate of glycolysis.

Regulation of Glycolysis

  • Glycolysis is audited at the phosphofructokinase stage to ensure that glucose is converted to fructose-1,6-biphosphate only when it is needed.
  • This process is regulated through feedback inhibition, where the end product of glycolysis (ATP) inhibits the early stages of the process when its concentration is high.
  • In the presence of oxygen and the cell has enough ATP, glycolysis is inhibited and glucose is stored in the form of glycogen. However, when ATP levels decrease and ADP levels increase, glucose is broken down to produce ATP.

Course material for Biology B, module Energy for Biological Processes, topic Glycolysis

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