DIATOM

PARTS AND FUNCTION

Frustule (glassy shell) – consists of two tightly fitting halves often resembling a flat, round, or elongated box. Also has intricate perforations and ornaments such as spines or ribs. The Frustule allows light to pass through so that the conspicuous golden-brown chloroplasts can capture light energy for photosynthesis.

Nucleus

Chloroplast – are the most noticeable internal component of almost all diatoms, giving the diatom its color and photosynthetic capabilities. Diatom chloroplasts are usually yellowish-brown in color, ranging between yellowish-green and dark brown. This coloration is due to the presence of photosynthetic pigments such as chlorophyll, beta carotene, and fucoxanthin. The pigment chlorophyll is also a key component of terrestrial plants. Without this pigment, neither plants nor diatoms grow very well.

Mitochondrion

Oil Droplet

Reproduction – Under the right conditions, diatoms can reproduce very rapidly and a population of a small species can double each day. Diatoms normally reproduce by binary fission, where one ‘mother cell’ splits into two daughter cells. The two halves of the mother frustule become the ‘lids’ for the daughter frustules- the ‘box’ parts are made inside, as the daughters separate. One daughter cell will therefore be the same size as the parent, and the other will be slightly smaller. Over time, a lineage of diatoms will get smaller and smaller, although a few species avoid this problem by having stretchable frustules. When cells get too small, they discard their old frustules and build new, much larger ones. This process can be connected to sex. In many centrics, some individuals will break up into many small sperm-like cells. These ‘fertilise’ other diatoms, which then produce new, large frustules. In pennates, ‘sex’ involves two adult cells lining up alongside each other, dividing and then swapping one daughter cell each. The new pairs of daughter cells fuse, giving two cells that are each half of each ‘parent’. They then produces new, large frustules and glide away.

NAME OF ORGANISM
Scientific Classification
Domain: Eukaryota
Kingdom: Chromalveolata
Phylum: Heterokontophyta
Class: Bacillariophyceae
Order: Centrales and Pennales

HABITAT

Almost all living diatoms require sunlight to survive and photosynthesize, limiting them to the uppermost 200 meters of the water column. This sunlit region of the water column is referred to as the photic zone. Since the entire surface of the ocean is exposed to sunlight at least part of the year, diatoms live practically everywhere at the sea surface. Diatoms are classified into two categories according to their lifestyle: planktonic or benthic. Since all diatoms are photosynthetic, both planktonic and benthic diatoms are restricted to living within the photic zone. Centric diatoms are mostly planktonic, floating near the sea surface, while pennate diatoms are mostly benthic, living on the seafloor, or attached to floating objects.

FOOD SOURCE


DESCRIPTION OF LIFE CYCLE


HOW DOES IT MOVE


UNIQUE CHARACTERISTICS


ROLE IN THE ECOSYSTEM
Like many micro-organisms, diatoms can bloom when conditions of nutrients, light and temperature are ideal. While diatom blooms are a major source of energy for the ocean, which ultimately supports the large predators such as fish and marine mammals and birds, severe blooms can be harmful. One diatom can kill farmed fish because its barbed spines can wound gills. Chemicals present in diatoms can build up in the bodies of animals that eat them and if concentrated enough, can affect people that eat the animals. In Australia, diatom blooms have been responsible for making shellfish unpleasant to taste and unsaleable for long periods of time. One diatom is responsible for Amnesic Shellfish Poisoning, a potentially fatal illness whose symptoms include memory loss. Worldwide outbreaks to date have been very rare, however there is concern that human activities are increasing the frequency of many sorts of micro-organism blooms (see silicoflagellates).

CITES: http://earthguide.ucsd.edu/diatom/d10.html; http://www.reef.edu.au/asp_pages/secb.asp?FormNo=7; http://images.google.com/images?hl=en&q=diatom&gbr=2