- Functions of pseudopods
- Examples
- Types and their characteristics
- Lobopodio
- Amoeboza
- Philopodia
- Axopodia
- Radiolaria
- Reticulopid
- Foraminifera
- References
The pseudopods or pseudopodia are filled temporary projections cytoplasmic membrane of a eukaryotic cell or a unicellular protist. Pseudopods can be used for mobility, or to ingest nutrients and particulate matter.
The cells that make up the pseudopods are generally referred to as amoeboids. Pseudopodia expand and contract by the reversible process of actin subunits in many microfilaments.
Image Source: reference.com
The filaments near the cell interact with myosin, causing a contraction. The pseudopodia spread until the actin regroups itself in a channel.
Pseudopods are made up of filament structures and microtubules. The functions of the pseudopods include locomotion and the capture of prey. Pseudopods are key to feeling prey that can be swallowed.
Many pseudopods arise from the surface of the body (as in the amoeba); in other cases, a single pseudopod may form on the surface of a body (as in entamoeba histolytica).
Pseudopods do not always look like amorphous masses; rather they can be classified by their distinctive appearances. They can be classified into the following varieties: lobopodia, filopodia, reticulopodia and axopodia.
Functions of pseudopods
They generally have two functions: locomotion and capturing prey or swallowing food. For example, amoeba can crawl by expanding the cytoplasm and contracting the filaments.
On the other hand, they are also used to capture and ingest prey. They can ingest particulate matter while providing mobility during hunting for food.
They are also needed to sense prey nearby, helping organisms like the amoeba ingest matter through the process of phagocytosis.
In this process, these projections envelop the food particle. In this way they create a sac trapped in a squeezing membrane; creating a food vacuole before the food is fully digested.
Examples
Many genera of the Kingdom Protista use pseudopods to move and ingest food. While pseudopodia are often classified as characteristics of protists, they are not actually restricted to that classification.
The cells of some animals form pseudopods. For example, white cells in vertebrate animals use pseudopods to ingest foreign particles, such as bacteria and viruses, in a process called phagocytosis.
Pseudopods are a feature of a group of organisms called rhizopods. White cells of the immune system use pseudopods to crawl inside bodies.
Types and their characteristics
Lobopodio
They are pseudopods that look like fingers; it is the most common type observed in nature. They are characterized by being bulbous and short projections, containing endoplasm and ectoplasm.
An example of a lobopod is the loose amoeba, which is considered the largest pseudopod.
Amoeboza
They are a large taxonomic group containing about 2,400 species of amoeboid protists. They often contain tubular and wolfish pseudopodia.
This group includes many of the more well-known amoeboid organisms, such as Chaos, Entamoeba, Pelomyxa, and Amoeba itself.
Many of the species in this genus are commonly found in fresh and salt water; as well as on the ground, moss and leaves. Some live as parasites of other organisms, or can cause disease in organisms.
Amebiasis, a common infection in humans, is caused by amoebae of the Entamoeba group. Around 480 million people are infected; between 40,000 and 110,000 people die each year from this infection.
Most amoboezas are unicellular, but some types have multicellular life stages in which aggregated cells produce spores. This species varies in size: from 10mm in diameter to 800mm.
Philopodia
They are thin cytoplasmic projections that extend above the border of the lamellipodia in migrating cells. These projections are backed by microfilaments. Filopodia are threadlike and have sharp edges that are made of ectoplasm.
Filopodia have roles in sense, migration, and interaction between cells. To close a wound in vertebrates, growth factors stimulate the formation of filopodia in fibroplasts to direct fibroplast migration and wound saturation.
Filopodia are also used for the movement of bacteria between cells, to evade the host's immune system.
Some examples include Lecithium and Euglypha. Interestingly, this type of filopodia can have variations.
For example, granulopodia is similar to filopodia, but has a granular structure called an extrusome that specializes in capturing prey and not in mobility.
Axopodia
They are thin pseudopods that contain complex groups of microtubules and are surrounded by cytoplasms.
Axopodia are primarily responsible for phagocytosis and the ingestion of food particles, as they rapidly retract in response to physical contact.
Protists of the genus Radiolaria and Heliozoa are examples of this type of pseudopod.
Radiolaria
They are 0.1-0.2 mm diameter protozoa that produce mineral skeletons, typically with a central capsule that divides the cell into the inner and outer portions of the endoplasm and ectoplasm. The mineral skeleton is usually made of silica.
They can be found in zooplankton throughout the ocean; its skeletal remnants make up a large part of the ocean floor deck. They represent important diagnostic fossils found from the Cambrian Period onwards.
Radiolaria have many needle-like pseudopods; they also have clumps of microtubules that make radiolaria appear abundant and leafy.
Reticulopid
They are complex formations where the pseudopods are combined to form irregular networks and communicate with other pseudopods. The primary function of reticulopide is the ingestion of food; locomotion is the secondary function.
Reticulopods are typical foraminifera
Foraminifera
They are members of the amoeboid protists characterized by: channeling granular ectoplasms to trap food and by having an outer shell of different shapes and materials.
Most of the foraminifera are marine; they live in or in marine sediment. A small amount floats in the water column at various depths.
References
- Pseudopod. Recovered from biologydictionary.net
- Pseudopodia. Recovered from wikipedia.org
- Radiolaria. Recovered from wikipedia.org
- Foraminifera. Recovered from wikipedia.org
- Amoebozoa. Recovered from wikipedia.org
- Filopodia. Recovered from wikipedia.org
- Axopodium. Recovered from merriam-webster.com.