2.2B Photosynthesis and cellular respiration Notes

Photosynthesis: Conversion of Light Energy to Chemical Energy

1. Photosynthesis is the process by which autotrophs, organisms such as green plants, algae, and photosynthetic bacteria, convert light energy from the Sun into chemical energy in the form of glucose.
2. This glucose serves as an immediate energy source for cellular processes or can be stored as biomass, forming the foundation of most ecosystems’ energy flow.
3. Photosynthesis occurs in specialized cell organelles called chloroplasts, which contain the pigment chlorophyll, a molecule that captures visible wavelengths of light energy and initiates the chemical transformation.

Inputs, Processes, and Outputs of Photosynthesis

1. Inputs:
   1. Light energy (from the Sun)
   2. Carbon dioxide (CO₂) from the atmosphere
   3. Water (H₂O) from the soil
2. Process:
   1. Occurs inside chloroplasts, where chlorophyll pigments absorb visible light energy.
   2. Energy is transformed and stored in glucose molecules.
3. Outputs:
   1. Glucose (C₆H₁₂O₆): chemical energy stored in biomass
   2. Oxygen (O₂): released into the atmosphere

Transformation of Energy and Matter

1. Photosynthesis transforms light energy into chemical energy stored in the bonds of glucose molecules.
2. This energy can later be used by the plant or transferred to other organisms when they feed on the plant.
3. Glucose can be converted into other carbon compounds such as starch, cellulose, proteins, and lipids, which together form biomass, the total mass of living material in an organism or ecosystem.

Producers: The First Trophic Level

1. Producers (autotrophs) occupy the first trophic level in every food chain.
2. They convert abiotic inputs (CO₂, H₂O, sunlight) into living matter, forming the energy base for all other organisms.
3. Typical producers include plants, algae, and photosynthetic bacteria.
4. The energy captured by producers flows to higher trophic levels through feeding interactions.

Role of Producers in Ecosystems

1. Convert solar energy into biomass, forming the base of energy pyramids.
2. Supply food and oxygen to consumers.
3. Influence ecosystem productivity and nutrient cycling.
4. Support biodiversity by sustaining multiple trophic levels.

Cellular Respiration

1. Cellular respiration is the process by which organisms release energy stored in glucose to power biological activities.
2. This occurs in all living cells, including plants, animals, fungi, and microorganisms.
3. Respiration is essentially the reverse process of photosynthesis, completing the energy cycle within ecosystems.
4. Energy released during respiration is used for growth, repair, movement, active transport, and reproduction.

Inputs, Processes, and Outputs

1. Inputs: Glucose and oxygen
2. Processes: Oxidation reactions occur within cells (usually in mitochondria).
3. Outputs: Carbon dioxide, water, energy (in a usable chemical form)

Aerobic respiration equation:

Glucose + Oxygen → Carbon dioxide + Water + Energy

Energy Transformation in Respiration

1. Stored chemical energy in glucose is converted into usable energy within cells.
2. This usable form drives metabolism, cell division, and muscle contraction.
3. Some of the energy is lost as heat, demonstrating the inefficiency of energy transfer.
4. Thus, respiration transforms:

Chemical energy → Kinetic energy + Heat energy

Relationship Between Photosynthesis and Cellular Respiration

1. Photosynthesis and cellular respiration are interconnected processes that form the basis of energy flow in ecosystems.
2. In plants, photosynthesis creates glucose and oxygen, which are then used by the plant and other organisms in the ecosystem for cellular respiration.
3. Cellular respiration generates ATP, which powers cellular functions, and produces carbon dioxide and water, which are then used in photosynthesis.
4. This cycle is a key part of the energy and matter flow in ecosystems.

Energy Loss as Heat During Cellular Respiration

1. During cellular respiration, energy is released as glucose is broken down into smaller molecules, ultimately producing usable energy for the cell.
2. However, this process is not 100% efficient.
3. Some of the chemical energy from glucose is converted into heat rather than being fully captured as usable energy in the form of chemical bonds.
4. This inefficiency is a normal part of the metabolic process.

Why Is Heat Generated?

1. The transformation of glucose into chemical energy involves several biochemical steps.
2. In each step, some energy is lost as heat due to the inherent inefficiency of the processes.
3. This heat is produced as a byproduct of cellular reactions.

Implications for Ecosystems

1. Continuous energy input from the Sun is required to offset heat loss in ecosystems.
2. Energy flow through ecosystems becomes less efficient with each trophic transfer.
3. Understanding these inefficiencies helps explain pyramid shapes in energy diagrams and limitations in food chain length.