Photosynthesis

Overview of Photosynthesis

Photosynthesis is the process by which plants, algae, and some bacteria convert light energy into chemical energy, producing simple sugars and oxygen from carbon dioxide and water. This process occurs in the chloroplasts, which are green due to the presence of chlorophyll.

• Photosynthesis Equation: Simple sugar is produced as the main product.

• Location: Photosynthesis takes place in the chloroplast.

Pigments in Photosynthesis

Pigments are molecules that absorb specific wavelengths of light, enabling photosynthesis.

• Chlorophyll a & b: Absorb red and blue light; reflect green light, giving plants their green color.

• Carotenoids: Absorb blue and green light; reflect orange, yellow, and red light. They help protect the plant from excess light energy.

Photosystems and Energy Production

Photosystems are complexes of chlorophyll molecules that work together to capture light energy and convert it into chemical energy.

• Photosystem I and II: Chlorophyll molecules form groups called photosystems (I & II).

• Electron Transport Chain: Photosystem II uses the electron transport chain to produce ATP.

• NADPH Production: Photosystem I produces NADPH, an electron carrier essential for the next steps of photosynthesis.

Calvin Cycle

The Calvin Cycle is the set of biochemical reactions that take place in the stroma of chloroplasts during photosynthesis. It uses ATP and NADPH to convert CO2 into glucose.

• Main Steps:

  1. Fixation

  2. Reduction

  3. Regeneration

• Calvin Cycle Equation: G3P (glyceraldehyde-3-phosphate) is a three-carbon sugar produced in the cycle.

Cell Division (Mitosis)

Overview of Mitosis

Mitosis is the process by which a single parent cell divides to produce two genetically identical daughter cells. This is essential for growth, repair, and asexual reproduction in eukaryotic organisms.

• Purpose: To produce two genetically identical daughter cells.

DNA Structure

DNA contains the genetic information necessary for cell function and division. Its structure varies between prokaryotes and eukaryotes.

• Prokaryotic DNA: Single, circular DNA molecule, often with plasmids.

• Eukaryotic DNA: Long, linear, double helix DNA, organized into chromosomes and associated with proteins called histones.

• Chromatin: The complex of DNA and proteins (histones) in eukaryotic cells.

Chromosome Terminology

Chromosomes are structures that organize and package DNA for cell division.

• Chromosome: A single DNA molecule.

• Duplicated Chromosome: Consists of two sister chromatids joined at the centromere.

• Centromere: The constricted region where sister chromatids are joined.

• Kinetochore: Protein structure on the centromere where microtubules attach to pull chromatids apart during anaphase.

Cell Cycle Stages

The cell cycle is the series of events that cells go through as they grow and divide. It consists of interphase and mitosis (M phase).

• Interphase:

  • G1: Cell grows, organelles and mitochondria are made, enzymes for S phase are produced.

  • S (Synthesis): DNA replication occurs.

  • G2: Cell continues to grow, more proteins made for cell division.

• Mitosis (M phase):

  1. Prophase: Chromatin condenses into visible chromosomes.

  2. Prometaphase: Nuclear envelope breaks down, microtubules attach to kinetochores.

  3. Metaphase: Chromosomes align at the metaphase plate.

  4. Anaphase: Sister chromatids separate and move to opposite sides.

  5. Telophase: Chromosomes decondense, nuclear envelopes reform.

  6. Cytokinesis: Cytoplasm divides, forming two daughter cells.

Chromosome Counting

Chromosome number is determined by counting the number of centromeres present in a cell.

Key Comparison Table

Additional info:

• Light absorption in photosynthesis occurs through visible light, with photons as packets of energy (wavelengths 400 nm – 710 nm).

• Chromosome counting is important for understanding genetic inheritance and cell division errors.