Diatoms are unicellular microalgae belonging to the domain Eukaryota, known for their silica-based cell walls and significant role in the earth's biomass and carbon fixation. They are vital ecological indicators and contribute to atmospheric oxygen while being classified into two main orders: centrales and pennales. Reproduction occurs through vegetative division, producing smaller new cells within the parent cell.

1. By- RISHIKA PASEBAND
VOLUNTEER OF APPLIED FORENSIC
RESEARCH SCIENCES
PART 1

2.  Introduction of Diatoms
-Definition of diatoms
-Classification of diatoms
-Structure of diatoms
-Types of diatoms
-Reproduction in diatoms
-Question

3. Diatoms are a major group of
algae, specifically microalgae
found in the oceans, waterways
and soils. They make up a
significant portion of the earth’s
biomass. They are among the
most common types of
phytoplankton.
Diatoms are unicellular(single
celled) organisms.

4. • Domain: Eukaryota
• Kingdom: Chromalveolata
• Phylum: Ochrophyta
• Class: Bacillariophyceae
• Order: Centrales
Pennales

5. Diatoms require high levels of silicon as an
essential nutrient and since they are
photosynthesizing organisms, diatoms also
require sunlight. They are a major source of
atmospheric oxygen responsible for 20-30% of
all carbon fixation on the planet and also act as
environmental indicators of climate change.

6. In ecology, diatoms are used to monitor the
water quality of large water bodies.
Diatomaceous Earth:
It is a powdery substance made from the
fossilized remains of a single-celled algae.

7.  Diatoms are Protists.
 This class of organism is distinguished by the
presence of an inorganic cell wall that is
composed of silica.

8. -Endoplasmic cysts
-They store oil rather than starch
-A bipartite(consisting of two parts) cell wall
-Secretion of silica

9. 1.Size:About 2-200 micrometers.
2.Cells are typically circular, some cells may be
triangular, square or elliptical.
3.In diatoms, the site of photosynthesis is
yellowish brown chloroplasts.
4.They are often referred as jewels of the sea or
‘living opals’ due to their ornate silica outer
shell, known as frustule.
5.Frustule can be defined as the hard and porous
cell wall or external layer of diatoms.

10. This cell wall is primarily composed of
silica(hydrated silicon dioxide)made from
silica acid, and is coated with a layer of
organic substance called pectin, a fiber most
commonly found in cell walls.
6.Pores,ribs,marginal ridges, minute spines
and elevations can be seen on this siliceous
wall, all of which can be used to describe
genera and species.
7.Diatom cell consists of two halves where
each half essentially contains a valve(a flat
plate) and girdle(marginal connecting).

11. Two halves are:
•Hypotheca
•Epitheca
-hypotheca is slightly smaller than epitheca

12. nucleus
nucleolus
cell wall
pyrenoid
mitochondria
valves
vacuoles

13. Diatoms are divided into two main Orders, which are
Centrales and Pennales.
Centrales(Centric Diatoms)
They are also referred as Biddulphiales.They are
radially symmetrical.
Pennales(Pennate Diatoms)
They are also referred as Bacillariales.They are
bilaterally symmetrical.

15. Diatoms divide and reproduce by a process called
as vegetative division, which involves the
division of a single cell into two new cells.
During the reproduction cycle, the new cell is
formed inside the parent cell. The new cell is
smaller in size given that it forms within the
mother cell that has a rigid cell wall that does not
expand.

17. Golden brown colour of diatoms is due to
presence of__________?
A. Mycoxanthin, mucoxanthin and
myxoxanthophylls
B. Alpha and beta carotenes and myxoxanthin
C. Fucoxanthin , diatoxanthin, diadinoxanthin
D. None of the above