Diatoms

1⃣ Dinoflagellates (Sections 11.1 & 11.2)

Dinoflagellates are microscopic algae that live in oceans and freshwater. Some of them produce oxygen through photosynthesis, while others eat other organisms.

Important Terms

• Alveolata → A group of single-celled organisms (including dinoflagellates, ciliates, and parasites) that have small sacs (alveoli) under their outer membrane.

• Plastids → Structures inside cells that perform photosynthesis (like chloroplasts in plants).

• Endosymbiosis → A process where one organism lives inside another. Dinoflagellates got their plastids from ancient red algae through endosymbiosis.

• Flagella → Whip-like tails that help dinoflagellates move.

  • Transverse flagellum → Located in a groove around the middle of the cell (cingulum), helps the cell spin.

  • Longitudinal flagellum → Sticks out from the sulcus and pushes the cell forward.

• Cingulum → A groove that wraps around the cell, where the transverse flagellum is located.

• Sulcus → A groove that runs along the bottom part of the cell.

• Chromosomes → DNA structures inside the nucleus. In dinoflagellates, they stay condensed (packed tightly) all the time, unlike in other organisms where they loosen up for DNA reading.

• Nucleoproteins (DVNPs) → Proteins that help package DNA in dinoflagellates (instead of histones, which are used by most eukaryotes).

2⃣ Diatoms (Section 12.2)

Diatoms are a type of algae with glass-like shells made of silica (SiO₂). They are very important for Earth's oxygen supply.

Important Terms

• Frustule → The hard outer shell of a diatom, made of silica (like glass).

  • Epitheca → The larger top half of the shell.

  • Hypotheca → The smaller bottom half of the shell.

• Mitosis → Asexual reproduction where a single cell splits into two identical cells.

• Sexual Reproduction → When diatoms get too small after multiple mitotic divisions, they create special reproductive cells (gametes) to restore their original size.

• Carbon Fixation → The process where diatoms take in CO₂ (carbon dioxide) from the atmosphere and turn it into organic matter (like sugar) through photosynthesis.

• Sediment → When diatoms die, their silica shells sink to the bottom of the ocean and form layers of deposits(used in climate studies).

• Primary Producers → Organisms (like diatoms) that produce energy-rich compounds (like sugars) using sunlight. They are the base of the food chain