<< Chapter < Page Chapter >> Page >

Physiological processes in sponges

Sponges, despite being simple organisms, regulate their different physiological processes through a variety of mechanisms. These processes regulate their metabolism, reproduction, and locomotion.

Digestion

Sponges lack complex digestive, respiratory, circulatory, reproductive, and nervous systems. Their food is trapped when water passes through the ostia and out through the osculum. Bacteria smaller than 0.5 microns in size are trapped by choanocytes, which are the principal cells engaged in nutrition, and are ingested by phagocytosis. Particles that are larger than the ostia may be phagocytized by pinacocytes. In some sponges, amoebocytes transport food from cells that have ingested food particles to those that do not. For this type of digestion, in which food particles are digested within individual cells, the sponge draws water through diffusion. The limit of this type of digestion is that food particles must be smaller than individual cells.

All other major body functions in the sponge (gas exchange, circulation, excretion) are performed by diffusion between the cells that line the openings within the sponge and the water that is passing through those openings. All cell types within the sponge obtain oxygen from water through diffusion. Likewise, carbon dioxide is released into seawater by diffusion. In addition, nitrogenous waste produced as a byproduct of protein metabolism is excreted via diffusion by individual cells into the water as it passes through the sponge.

Reproduction

Sponges reproduce by sexual as well as asexual methods. The typical means of asexual reproduction is either fragmentation (where a piece of the sponge breaks off, settles on a new substrate, and develops into a new individual) or budding (a genetically identical outgrowth grows from the parent and eventually detaches or remains attached to form a colony). An atypical type of asexual reproduction is found only in freshwater sponges and occurs through the formation of gemmules. Gemmules are environmentally resistant structures produced by adult sponges wherein the typical sponge morphology is inverted. In gemmules, an inner layer of amoebocytes is surrounded by a layer of collagen (spongin) that may be reinforced by spicules. The collagen that is normally found in the mesohyl becomes the outer protective layer. In freshwater sponges, gemmules may survive hostile environmental conditions like changes in temperature and serve to recolonize the habitat once environmental conditions stabilize. Gemmules are capable of attaching to a substratum and generating a new sponge. Since gemmules can withstand harsh environments, are resistant to desiccation, and remain dormant for long periods, they are an excellent means of colonization for a sessile organism.

Sexual reproduction in sponges occurs when gametes are generated. Sponges are monoecious (hermaphroditic), which means that one individual can produce both gametes (eggs and sperm) simultaneously. In some sponges, production of gametes may occur throughout the year, whereas other sponges may show sexual cycles depending upon water temperature. Sponges may also become sequentially hermaphroditic, producing oocytes first and spermatozoa later. Oocytes arise by the differentiation of amoebocytes and are retained within the spongocoel, whereas spermatozoa result from the differentiation of choanocytes and are ejected via the osculum. Ejection of spermatozoa may be a timed and coordinated event, as seen in certain species. Spermatozoa carried along by water currents can fertilize the oocytes borne in the mesohyl of other sponges. Early larval development occurs within the sponge, and free-swimming larvae are then released via the osculum.

Locomotion

Sponges are generally sessile as adults and spend their lives attached to a fixed substratum. They do not show movement over large distances like other free-swimming marine invertebrates. However, sponge cells are capable of creeping along substrata via organizational plasticity. Under experimental conditions, researchers have shown that sponge cells spread on a physical support demonstrate a leading edge for directed movement. It has been speculated that this localized creeping movement may help sponges adjust to microenvironments near the point of attachment. It must be noted, however, that this pattern of movement has been documented in laboratories, but it remains to be observed in natural sponge habitats.

Watch this BBC video showing the array of sponges seen along the Cayman Wall during a submersible dive.

Section summary

Animals included in phylum Porifera are Parazoans because they do not show the formation of true tissues (except in class Hexactinellida). These organisms show very simple organization, with a rudimentary endoskeleton. Sponges have multiple cell types that are geared toward executing various metabolic functions. Although these animals are very simple, they perform several complex physiological functions.

Art connections

[link] Which of the following statements is false?

  1. Choanocytes have flagella that propel water through the body.
  2. Pinacocytes can transform into any cell type.
  3. Lophocytes secrete collagen.
  4. Porocytes control the flow of water through pores in the sponge body.

[link] B

Got questions? Get instant answers now!

Questions & Answers

is the law of independent assortment same as the law of dominance?
Danny Reply
explain the process of digestion in animal
Lephetha Reply
discuss the ueses of human cell
Oghenesuvwe Reply
what is hormone
Gift Reply
they are liquid substance which are essential for different body functions
Ed
the meaning of warm classroom
Musasaidutaiwo Reply
How is an image formed at the retina
Tarisai Reply
what is gland
Chinwe Reply
what's cells?
Santino Reply
hi santino Cells is a basic unit of life
Yohannes
the structural and functional units of life is known as cell
Rathod
good night all friends
Rathod
u too
Papaye
y do plants have a single respiratory system?
Papaye
hey
Chinwe
please is endocrine cell
Chinwe
what is a meiosis
Mercy Reply
what is a mitosis
Mercy
meiosis is a cell division that produces 4 daughter cell that doesn't look alike
Damilola
mitosis is a cell division that produces two daugther cell that looks alik
Damilola
what is call division
Ajak Reply
mitosis
Damilola
what are the effects of transpiration
Noah Reply
Are extraterrestrials mostly sited on land or in the sea also?
Golden Reply
what's sperm
Juma Reply
what is gaseous exchange
khang Reply
what is respiration
Lubna
hi lubna respiration is the breakdown of food with or without the use of oxygen to produce energy, carbon dioxide and water and it takes place in cells
caleb
fart😥😂
Golden
what is the structure of a cell
Blessing Reply
cell membrane, nucleus and cytoplasm lie upon the two
Jamiu
is a cell membrame
KIHEMBO
types of diffusion
KIHEMBO
two types of transpiration
KIHEMBO
Passive and active transport
Dillenia
nidhi
Nidhi

Get Jobilize Job Search Mobile App in your pocket Now!

Get it on Google Play Download on the App Store Now




Source:  OpenStax, Biology. OpenStax CNX. Feb 29, 2016 Download for free at http://cnx.org/content/col11448/1.10
Google Play and the Google Play logo are trademarks of Google Inc.

Notification Switch

Would you like to follow the 'Biology' conversation and receive update notifications?

Ask