Most jellyfish undergo two distinct life history stages (body forms) during their life cycle. The first is the polypoid stage, when the animal takes the form of a small stalk with feeding tentacles. Very often, this polyp is attached to the sea floor, or to another hard surface; it rarely moves around. A polyp that lives that way is called sessile. In some cases, the polyp is free-floating. Polyps generally have a mouth surrounded by upward-facing tentacles. Polyps may be on their own or in groups, and some bud asexually, making more polyps. Most are very small, measured in millimeters.
In the second stage, the tiny polyps asexually produce jellyfish, each of which is known as a medusa. Tiny jellyfish swim away from the polyp and then grow and feed in the plankton. Jellyfish reproduce both sexually and asexually. Well-fed adult jellyfish spawn daily. In most species, spawning is controlled by light, so the entire population spawns at about the same time of day, often at either dusk or dawn. Jellyfish are usually either male or female (with occasional hermaphrodites). In most cases, adults release sperm and eggs into the surrounding water, where the (unprotected) eggs are fertilized and mature into new organisms.
Medusae have a radially symmetric, umbrella-shaped body called a bell, which is usually supplied with marginal tentacles that capture prey. A few species of jellyfish do not have the polyp portion of the life cycle, but go from jellyfish to the next generation of jellyfish through direct development of fertilized eggs. Jellyfish at the medusa stage usually lives only up to six months, after which it dies.
Jellyfish eat plankton and small fish, which they catch using their venomous tentacles. Jellyfish may live in symbiosis with algae. The jellyfish transports them into sunlight and get nutrients from the algae's photosynthesis. Both forms of jelly fish have small tentacles with nematocysts (stinging cells) that sting and can hurt people on contact.
Medusozoans differ from anthozoans in having a medusa stage in their life cycle. Their mitochondrial DNA molecules are linear rather than circular as in anthozoans and almost all other animals. The cnidae, the explosive cells of the Cnidaria, are of a single type. There are nematocysts but no spirocysts or ptychocysts.
A group of jellyfish is called a current; an occurrence of many jellyfish simultaneously is sometimes called a "bloom".
Tilapia
Tilapia is a fish that is often farmed for food, or kept as pets in aquariums. They live in warm, fresh water, but some species live in brackish water. The fish are found in Africa, North and South America, India, and Sri Lanka.
They are listed as one of the worlds worst introduced species. They can quickly take over from native fish in rivers. This has happened in places like in the Endeavour River, in Queensland, Australia. These fish are thought to have been released into the river from an aquarium.
Sardine
Sardine is a name of several kinds of fish, especially oily fish. Another name for these fish is Pilchard. All of those fish are quite small and are related to the herring. The Latin name of the family of these fish is Clupeidae. However, the naming is not precise. Fishbase, a database about all kinds of fish, has six species just named "pilchard". There are over a dozen with the name of "sardine". Many more exist, with the basic names qualified by adjectives.
The fish are named after the Island of Sardinia. In the past, they could easily be fished there.
Many shops and supermarkets sell canned (or tinned) "sardines". The can is filled in liquids like water or oil. Very often, those fish are not sardines, but rather sprats or round herrings.
Bone
Bones are parts of the skeleton of vertebrates. They also protect organs inside our body.
The bones are the framework of the body. Without them we would be a pile of organs on the ground and would not be able to move.
Bones also protect. The skull protects the brain and the ribs protect the heart and lungs. The jaw and cheekbones support the facial muscles, which help us eat and smile. The pelvis protects the reproductive organs, and vertebrae protect the spinal cord.
Bone is living tissue, and must be maintained by taking regular exercise and by having calcium from foods like milk, and dark leafy greens such as spinach. The bone marrow in the middle of the bigger bones makes our red blood cells.
Long bones are hollow, with a central core which is not strong like the rest of the bone. It contains the bone marrow, one of the most important tissues in the vertebrate body. It produces blood cells for the blood system, and lymphocytes for the immune system.
Osteons are the small units of which the hardest parts of human bones are made. They are roughly cylindrical, and about 0.2mm wide and a few millimeters long. They are found in the bone in most mammals, and many reptiles, birds and amphibians. Inside the osteons are bone cells called osteocytes, each living in its own small space. Osteocytes make contact with each other by cytoplasmic processes through a network of tiny canals. This allows the exchange of nutrients and metabolic waste. Collagen fibers in each ring of cells ('lamellae') give them structure.
Osteons have a hole down the middle, called the haversian canal. This canal contains the bone's blood supply. It also contains capillaries, and nerve fibres.
The details of osteon structure varies between bones and parts of bones, from species to species, between sexes, and by age and environmental factors.
Anteater
An anteater is a mammals of the family Myrmecophagidae and the suborder Vermilingua. Anteaters live in South America and Central America.
Anteaters eat ants and termites. They have long, sharp claws and a long, sticky tongue. The tongue can be up to 60 cm long, as long as a person's arm. The anteater opens an ant nest with its claws. Then it licks up the ants with its tongue.
Large anteaters that move on the ground knuckle-walk, bending their front toes under when they move the way gorillas do. Small anteaters that live in trees do not do this.
Sorghum
Sorghum is a genus in the grass family "Poaceae". The plants are grown in warmer climates. Species grow naturally in tropical and subtropical regions of all continents in addition to Oceania and Australasia. Because many species of Sorghum are resistant to drought and high temperatures, it is a very important food source in the desert areas of Africa.
Polar bear
The polar bear ("Ursus maritimus") is a large bear which lives in the Arctic. It is also called white bear or northern bear. It has black skin under the white fur. They are strong and fast, and can run as fast as 25 miles (40 km) an hour for a short distance.
Polar bear fur is made up of a layer of dense underfur and an outer layer of "guard hairs", which appear white to tan but are actually translucent. The fur keeps them very warm. The skin is not white; it is black. Therefore, they can absorb sunlight efficiently. They are strong and can swim very well. Polar bears are similar in size to a normal bear but have a slimmer neck, longer legs and fur.
They are mostly carnivorous. Polar bears are apex predators. They eat mostly seals and fish. They also eat sea lions, walruses, reindeer, arctic hares, penguins, seagulls, small whales, lemmings, crabs and carrion. When polar bears hunt, they often wait at holes in the ice, where the seals come up to breathe. They can live off of one seal for many days, but it will make them hungry if they do.
Polar bears live alone.
Young Polar bears stay with their mothers for 1–2 years, and they become mature when they are 5–6 years old. People think polar bears can become 25–30 years old in nature, but in captivity (for example, in zoos), they can become up to 45 years old.
Polar bears live in countries in the Arctic Circle, including these: