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Attempt either A or B - Scottish Highers Biology - Question 16 - 2019
Question 16
Attempt either A or B. Write your answer in the space below and on pages 29 and 30. A Write notes on photosynthesis under the following headings. (i) Use of energy... show full transcript
Worked Solution & Example Answer:Attempt either A or B - Scottish Highers Biology - Question 16 - 2019
Step 1
Use of energy absorbed by photosynthetic pigments
Answer
Photosynthetic pigments, primarily chlorophyll and carotenoids, absorb light energy, which excites electrons within their molecules. Here's how the process works:
- Energy Absorption: Light energy, particularly in the blue and red wavelengths, is absorbed by pigments like chlorophyll.
- Excitation of Electrons: This energy causes electrons to become excited and move to higher energy states.
- Electron Transport Chain: The excited electrons are transferred through a series of proteins in the thylakoid membrane known as the electron transport chain. As electrons flow through this chain, they release energy.
- ATP Production: This energy is harnessed by ATP synthase to convert ADP and inorganic phosphate into ATP, a process known as photophosphorylation.
- Role in Water Splitting: Additionally, some of the energy helps in splitting water molecules (photolysis), releasing oxygen as a byproduct.
Step 2
Carbon fixation
Answer
The process of carbon fixation is essential in the Calvin Cycle, which incorporates CO₂ into organic molecules. The steps involved are:
- ATP and NADPH Usage: Carbon fixation begins with ATP and NADPH produced in the light-dependent reactions.
- Joining of Carbon: CO₂ is fixed to a five-carbon sugar, ribulose bisphosphate (RuBP), forming a six-carbon compound that splits into three-carbon molecules called 3-phosphoglycerate (3PG).
- Catalyzed by RuBisCO: The enzyme ribulose bisphosphate carboxylase/oxygenase (RuBisCO) catalyzes this reaction.
- Phosphorylation of 3PG: The 3PG molecules are then phosphorylated using ATP to form glyceraldehyde-3-phosphate (G3P).
- Regeneration of RuBP: Some G3P molecules are utilized to synthesize glucose, while others are recycled to regenerate RuBP, ensuring the cycle can continue.
Step 3
The bottleneck effect
Answer
The bottleneck effect significantly impacts biodiversity through genetic diversity reduction:
- Reduced Genetic Diversity: During a bottleneck event, populations experience drastic reductions in size, leading to low genetic diversity.
- Limited Evolutionary Potential: Smaller populations have limited capacity to adapt to changing environmental conditions.
- Inbreeding Depression: With fewer mating options comes a higher likelihood of inbreeding, which can result in poor reproductive rates and increased vulnerability to diseases.
Step 4
Habitat fragmentation and habitat corridors
Answer
Habitat fragmentation affects biodiversity through the alteration of habitats:
- Isolation of Habitats: Habitats become separated, reducing the area available for species to thrive.
- Examples of Fragmentation: Activities like urban development lead to fragmentation by creating roads, buildings, and farms that interrupt habitats.
- Increased Competition: Fragmentation leads to degradation of remaining habitats and increases competition for resources among species.
- Diminished Genetic Diversity: Isolated populations face lower genetic diversity, further reducing species resilience.
- Role of Habitat Corridors: Habitat corridors can mitigate these effects by connecting separate patches, allowing for movement and genetic exchange between fragments.