Introduction of sponges

Sponges 

 1. Sponges are marine animals that live in a widely diverse range of ocean habitats, with some making poisons to keep other fauna from growing on them or to allow their own spreading growth.

2. Most live in quiet, clear waters, because sediment stirred up by waves or currents would block their pores, making it difficult for them to feed and breathe.[2] The greatest numbers of sponges are usually found on firm surfaces such as rocks, but some sponges can attach themselves to soft sediment by means of a root-like base.

3. their very porous construction enables them to extract food from these resource-poor waters with the minimum of effort.

4.Many sponges shed spicules, forming a dense carpet several meters deep that keeps away echinoderms which would otherwise prey on the sponges.[1] They also produce toxins that prevent other sessile organisms such as bryozoans or sea squirts from growing on or near them, making sponges very effective competitors for living space.Glass sponges produce no toxic chemicals, and live in very deep water where predators are rare.

Collaboration with other organisms

In addition to hosting photosynthesizing endosymbionts,[7] sponges are noted for their wide range of collaborations with other organisms. The relatively large encrusting sponge Lissodendoryx colombiensis is most common on rocky surfaces, but has extended its range into seagrass meadows by letting itself be surrounded or overgrown by seagrass sponges, which are distasteful to the local starfish and therefore protect Lissodendoryx against them; in return the seagrass sponges get higher positions away from the sea-floor sediment.[

body of sponge forms a wall around a hollow cavity

body has openings or pores which water moves through

water propelled by flagella (collar cells)

water delivers food and oxygen to the cells and removes wastes out the top opening (osculum).gametes are transported through the water.

spiney spicules interlock forming the skeleton

amebocytes produce spicules from calcium carbonate or silica

softer sponges are made up of a protein called sponging

are filter feeders

ameobocytes digest food

digestion is intracellular

chemical defenses.4)All are sessile, (live attached to something as an adult). Throughout this body run canals through which water flows, there is considerable variation in the complexity of these canals. The canals have openings to the outside which are called pores, where the water enters the sponge system these pores are usually small and are called 'ostia' and where the water leaves the sponge system the pores are larger, often singular and are called 'oscula' (singular osculum). Many if not most of these canals are lined with special flagellated cells called 'choanocytes'

. These choanocytes keep the water flowing through the canals in the correct direction by beating their flagellum, they are also important in trapping food items.

The fertilised ova are retained within the adult sponge until some unknown signal indicates it is time for their release. They are then set free into the surrounding waters.

Sponges are strong animals with dense skeletons that are well adapted to their environments. As they may live almost everywhere, they adapt to the regions and surfaces they grow in. Certain sponge species are adapted to freshwater environments. Their skeleton types allow them to live in either hard or soft sediments. Their pores allow them to filter the water around them for food. Inside the sponge, there are flagella that create currents so their collar cells may trap the food. Sponges may have adapted to these feeding habits from a long time ago when food sources may have been scarce.

Sponges have strong structures that are able to handle the high volume of water that flows through them each day. By constricting certain of their openings, sponges are able to control the amount of water that flows through them. Scientists believe that sponges are colourful because the colours act as a protection from the sun’s harmful UV rays.

Sponges have been around for a very long time.  This is because although the world is constantly changing, sponges are still able to respond to these changes through adapting to their environment. Sponges are also able to release toxic substances into the environment around them to make sure they have a good place to grow in.

 

Plant Science; Biochemistry; Ecology

Plant Science; Biochemistry; Ecology

Understanding the mechanisms controlling whole-plant and foliar nitrogen isotope composition will advance our knowledge of plant nitrogen acquisition and allocation. Nitrogen is the element that most often limits plant growth in many terrestrial ecosystems 1. Anthropogenic activity has altered the amount and relative abundance of the forms of nitrogen (NH4+, NO3− and amino acids) that are available for plant absorption [1] and [2]. The forms of nitrogen absorbed by plants can have different isotope compositions 3, and many studies now routinely measure foliar δ15N (Box 1) in an attempt to understand differences in patterns of nitrogen use among co-occurring species. Many studies assume that 15N at natural abundance levels acts as a tracer (i.e. the isotope ratio of source nitrogen is preserved during nitrogen absorption, assimilation and translocation, and that the δ15N of leaf tissues reflects that of the nitrogen source in the soil). This assumption is important because although the reported variation in plant δ15N can be between −10‰ and +10‰, the difference among co-occurring species is often less (0–10‰), and biologically significant differences can be ∼1‰ (Ref. 4). However, it is clear that this assumption could be invalid because physiological factors, such as different nitrogen uptake mechanisms, different pathways of assimilation, and recycling of nitrogen in the plant, can discriminate against 15N. This review addresses how physiological transformations of nitrogen can influence whole-plant and leaf δ15N. Ecological aspects of δ15N measurements and δ15N of plant nitrogen sources are addressed in [3] and [5].

Nitrogen exists as two naturally occurring stable isotopes, 15N and 14N. Variation in the absolute abundance of 15N is small , therefore nitrogen isotope composition is expressed using δ notation in parts per thousand.

(I)Where δ15N is the isotope ratio relative to the atmospheric air standard, and Rsample and Rstandard are the molar ratios of the heavier to the lighter isotope. The value for Rstandard is 0.0036765. Differences in δ15N between a substrate and product will occur when 15N and 14N react at different rates. The ratio of the rate constants (k14/k15) is the isotope effect (α), and is equivalent to (Rsubstrate/Rproduct)a. Discrimination (Δ) is the deviation of α from unity (Δ=α–1)(Ref. a). Discrimination can be stated in relation to the δ15N of the substrate (δ15Ns) and product (δ15Np)

(II)The term (1+δ15Np/1000) does not differ significantly from 1, therefore an approximation is (Eq. (III)):

(III)Discrimination is positive in most biological systems, therefore, the product should have a lower δ15N value than the substrate.

 Abstract :

Whole-plant and leaf nitrogen isotope composition are determined by the isotope ratio of the external nitrogen source and physiological mechanisms within the plant. Whole-plant isotope composition can reflect that of the nitrogen source when plant demand exceeds nitrogen supply. Uptake by mycorrhizae can cause the isotope ratio of the plant to deviate from the source. Intra-plant variation in isotope composition can be caused by multiple assimilation events, organ-specific loss of nitrogen, and resorption and reallocation of nitrogen. Future work must address acquisition of organic nitrogen from the soil solution, the role of mycorrhizae, and internal transformations within the plant.