Yeh the pressure really got to me. I also put thought process as a system because they weren't shown on the diagram. Is this right???(Original post by Greg Lewis)
It's cool man, in the pressure of exams you just don't think of these things. I suppose you could use garlic dough-balls at a push although they have a smaller surface area.
Turn on thread page Beta
IGCSE EDEXCEL BIOLOGY PAPER 1 12TTH MAY...are you ready?! watch
- 12-05-2015 22:12
- 12-05-2015 22:17
- 12-05-2015 22:19
Was the second last question, % change or % yield?
- 12-05-2015 22:22
- 12-05-2015 22:28
No, please don't think that Why would you think such a thing? Stereotypes are horrible
And I'm sure you didn't fail.Last edited by TastyPinkHair; 12-05-2015 at 22:29.
- 12-05-2015 22:30
(Original post by Deano1)
- 12-05-2015 22:47
I can't believe it...
I drew a line graph/frequency polygon sort of thing when it said in the question draw a bar chart...
Someone please please help me...
(Original post by Deano1)
- 12-05-2015 22:48
I can't believe it...
I drew a line graph/frequency polygon sort of thing when it said in the question draw a bar chart...
Someone please please help me...
- 12-05-2015 22:50
If you do single science then chill, you still have the chance to bring ur grade up
If not, dont worry 5% seems like alot but it isnt really, besides u'll get atleast half the marks for that question
Oh and tbh stop worrying about this, whats done is done, you cant change it so why worry?
Just focus on your upcoming exams
Posted from TSR Mobile
- 12-05-2015 22:53
Hey, how many marks do you need for a C? Really need this C cuz a D isn't good enough. Think I've probably got 45-55 on this paper....
(Original post by reelsalah)
- 13-05-2015 07:41
I didn't write in such a detail but i just wrote place it in a fermenter so that bacteria produces the growth hormone.
the previous subdivision said that the growth harmone was a protein.
Proteins are amino acids joined together. DNA codes for amino acids therefor i think we have to use genetic engineering by using plasmid.
(Original post by ChloexCharlotte)
- 13-05-2015 07:53
Yeah don't worry... I put immunity system haha :') which doesn't even exist
- 13-05-2015 08:32
As the picture shows, all the particles in a solid are touching. Another feature of a solid is that the particles aren't moving, the particles have no energy.
Liquid particles are, like solids, all touching. The difference is that liquid particles are moving- they flow to fit the space- this means that they have some energy.
In gasses the particles aren't all touching; they are far apart. They move freely and have a high energy level.
Spoiler:Show1.50 understand why ionic compounds conduct electricity only when molten or in solutionSpoiler:Show
- 13-05-2015 08:33
When ionic compounds are molten or in solution, the positive and negative ions separate this means that there are ions free to flow, and so they can conduct electricity.
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Labels: 1.50, Electrolysis, Section 1
1.49 understand why covalent compounds do not conduct electricity
In covalent compounds there are no electrons free to move, this means there can be no transfer of electricity through a covalent compound
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Labels: 1.49, Electrolysis, Section 1
1.48 understand that an electric current is a flow of electrons or ions
An electric current is a flow of electrons, although it can also be a flow of ions (as they have a charge.)
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Labels: 1.48, Electrolysis, Section 1
1.47 explain the electrical conductivity and malleability of a metal in terms of its structure and bonding.
Metals have delocalised electrons, electrons carry electricity; so because there are free electrons charge can pass easily through a metal.
The structure of a metal is with rows of atoms on top of one another, in pure metals as all the atoms will be the same size, the layers can slide easily over one another making them easy to bend.
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Labels: 1.47, Metallic crystals, Section 1
1.46 understand that a metal can be described as a giant structure of positive ions surrounded by a sea of delocalised electrons
In a metal atoms come together into a lattice, the electrons become detached from their atoms- delocalised- making the atoms positive ions.Last edited by Puddles the Monkey; 13-05-2015 at 09:42.
- 13-05-2015 08:34
2.39 describe tests for the gases
- burns with a 'squeaky pop' sound
- will relight a glowing splint
iii carbon dioxide
- Turns lime water cloudy
- Damp red litmus paper blue
- Damp universal indicator purple
- bleaches damp litmus paper white
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Labels: 2.39, Section 2, Tests for ions and gasses
2.38 describe tests for the anions
i) Cl-, Br-and I-, using dilute nitric acid and silver nitrate solution
- Chloride ions + nitric acid + silver nitrate > white precipitate (silver chloride)
- Bromide ions + nitric acid + silver nitrate > cream precipitate (silver bromide)
- Iodide ions + nitric acid + silver nitrate > yellow precipitate (silver iodide)
ii) SO4 2- (sulphate ions) using dilute hydrochloric acid and barium chloride solution
- SO4(2-) + HCl + Ba(2+) > white precipitate (barium sulphate)
iii) CO3 2-, using dilute hydrochloric acid and identifying the carbon dioxide evolved
- Carbonate + acid > salt + water + carbon dioxide
- Carbon dioxide produced will turn lime water cloudy
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Labels: 2.38, Section 2, Tests for ions and gasses
2.37 describe tests for the cations
i) Li+, Na+, K+, Ca2+ using flame tests
- Lithum: red
- Sodium: orange (so strong can mask other colours)
- Potassium: lilac
- Calcium: brick red
ii) NH4+, using sodium hydroxide solution and identifying the ammonia evolved
- NH4 + OH > NH3 + H2O
- ammonium ions + hydroxide ions > ammonia + water
- ammonia (pungent smelling gas) turns red litmus paper blue
iii) Cu2+, Fe2+ and Fe3+, using sodium hydroxide solution
- Copper(ii) sulphate + sodium hydroxide > blue precipitate
- Iron(ii) sulphate + sodium hydroxide > green precipitate
- Iron(iii) sulphate + sodium hydroxide > brown precipitate
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Labels: 2.37, Section 2, Tests for ions and gasses
Wednesday, 15 May 2013
2.36 understand the sacrificial protection of iron in terms of the reactivity series.
Sacrificial is covering a metal with a more reactive metal. What this means is water and/or air will react with the more reactive metal instead of the one underneath.
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Labels: 2.36, Reactivity series, Section 2
2.35 describe how the rusting of iron may be prevented by grease, oil, paint, plastic and galvanising
Grease, oil, paint and plastic prevent air and/or water from coming into contact with iron. This means the reaction that rusts iron can't occur.
Galvanising is coating in zinc. This Zinc react in the air to form ZnCO3 which prevents air and/or water from coming into contact with the iron.
Posted by Hannah A at 10:33 No comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.35, Reactivity series, Section 2
2.34 describe the conditions under which iron rusts
Water and oxygen are needed to rust iron: iron that reacts with these becomes hydrated iron(iii) oxide.
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Labels: 2.34, Reactivity series, Section 2
2.33 understand the terms redox, oxidising agent, reducing agent
In a redox reaction, a more reactive metal gains an oxygen from a less reactive metal which looses it.
i.e. a more reactive metal is oxidised and a less reactive metal is reduced.
The reducing agent is the more reactive metal which reduces the other metal.
The oxidising agent is the less reactive metal which allows the other metal to be oxidised.
Posted by Hannah A at 01:25 No comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.33, Reactivity series, Section 2
2.32 understand oxidation and reduction as the addition and removal of oxygen respectively
oxidation is the gain of oxygen,
reduction is the loss of oxygen.
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Labels: 2.23, Reactivity series, Section 2
2.31 deduce the position of a metal within the reactivity series using displacement reactions between metals and their oxides, and between metals and their salts in aqueous solutions
A metal oxide or a metal salt dissolved in water:
- introduce a more reactive metal and it will displace the current one
- introduce a less reactive metal and no displacement will take place
From this you can deduce which metals are more and less reactive.
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Labels: 2.31, Reactivity series, Section 2
2.30 describe how reactions with water and dilute acids can be used to deduce the following order of reactivity: potassium, sodium, lithium, calcium, magnesium, zinc, iron and copper
potassium, sodium, lithium and calcium all react with water and acids
magnesium, zinc and iron all react with acids (and very slowly with water.)
copper doesn't react with either.
The more vigorous the reaction the more reactive the metal. The more things a metal will react with, the more reactive the metal.
Posted by Hannah A at 01:09 3 comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.30, Reactivity series, Section 2
2.29 understand that metals can be arranged in a reactivity series based on the reactions of the metals and their compounds
Posted by Hannah A at 00:47 4 comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.29, Reactivity series, Section 2
Tuesday, 7 May 2013
2.28 describe a physical test to show whether water is pure.
If water is pure it will boil at exactly 100° and freeze at exactly 0°
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Labels: 2.28, Hydrogen and water, Section 2
2.27 describe the use of anhydrous copper(II) sulfate in the chemical test for water
anhydrous copper sulphate will become hydrous copper sulphate when it is reacted with water.
So if anhydrous copper sulphate goes from white to blue in the presence of a liquid it will be water.
Posted by Hannah A at 02:50 6 comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.27, Hydrogen and water, Section 2
2.25 describe the reactions of dilute hydrochloric and dilute sulfuric acids with magnesium, aluminium, zinc and iron
acid + metal > salt + hydrogen
magnesium + hydrochloric acid > magnesium chloride + Hydrogen
Mg + 2HCl > MgCl2 + H2
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Labels: 2.25, Hydrogen and water, Section 2
2.26 describe the combustion of hydrogen
The combustion of hydrogen is its reaction with oxygen.
Water is created. and a lot of energy.
2H2 + O2 > 2H2O
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Labels: 2.26, Hydrogen and water, Section 2
2.24 understand that carbon dioxide is a greenhouse gas and may contribute to climate change
Carbon dioxide prevents heat leaving the earth's atmosphere in rays that the earth emits.
Significant amounts of green house gasses will warm up the earth, changing the climate.
Posted by Hannah A at 02:37 No comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.24, Oxygen and oxides, Section 2
2.23 explain the use of carbon dioxide in carbonating drinks and in fire extinguishers, in terms of its solubility and density
Carbon dioxide is dissolved into drinks at a high pressure, this makes CO2 bubbles in fizzy drinks.
Some fire extinguishers have CO2 in, because it is denser than air it will fall over the fire creating a barrier between the air and fire: the fire can't burn with out the oxygen in the air.
Posted by Hannah A at 02:36 2 comments: Email ThisBlogThis!Share to TwitterShare to FacebookShare to Pinterest
Labels: 2.23, Oxygen and oxides, Section 2
2.22 describe the properties of carbon dioxide, limited to its solubility and density
It is denser than air.
It is soluble in water at a high pressure.
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Labels: 2.22, Oxygen and oxides, Section 2
2.21 describe the formation of carbon dioxide from the thermal decomposition of metal carbonates such as copper(II) carbonate
When metal carbonates are heated they become carbon dioxide and a metal.
copper carbonate > copper oxide + carbon dioxide
CuCO3 > CuO + CO2
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Labels: 2.21, Oxygen and oxides, Section 2
2.20 describe the laboratory preparation of carbon dioxide from calcium carbonate and dilute hydrochloric acid
calcium carbonate + hydrochloric acid → calcium chloride + water + carbon dioxide
CaCO3 + 2HCl → CaCl2 + H2O + CO2
Last edited by Puddles the Monkey; 13-05-2015 at 09:43.
Spoiler:ShowTurtles are reptiles of the order Testudines (or Chelonii) characterised by a special bony or cartilaginous shell developed from their ribs and acting as a shield. "Turtle" may refer to the order as a whole (American English) or to fresh-water and sea-dwelling testudines (British English).
- 13-05-2015 08:38
The order Testudines includes both extant (living) and extinct species. The earliest known members of this group date from 157 million years ago, making turtles one of the oldest reptile groups and a more ancient group than snakes or crocodilians. Of the 327 known species alive today, some are highly endangered.
Turtles are ectotherms—their internal temperature varies according to the ambient environment, commonly called cold-blooded. However, because of their high metabolic rate, leatherback sea turtles have a body temperature that is noticeably higher than that of the surrounding water.
Turtles are classified as amniotes, along with other reptiles, birds, and mammals. Like other amniotes, turtles breathe air and do not lay eggs underwater, although many species live in or around water.
1 Turtle, tortoise or terrapin
2 Anatomy and morphology
2.1 Neck withdrawral
2.4 Skin and molting
4 Ecology and life history
5 Systematics and evolution
5.1 Classification of turtles
6 Fossil record
8 In captivity
9 As food, traditional medicine, and cosmetics
10 Conservation status
11 See also
14 Further reading
15 External links
Turtle, tortoise or terrapin
Turtle, tortoise and terrapin
Green sea turtle
African spurred tortoise
Red-eared slider turtle (terrapin)
The word chelonian is popular among veterinarians, scientists, and conservationists working with these animals as a catch-all name for any member of the superorder Chelonia, which includes all turtles living and extinct, as well as their immediate ancestors. Chelonia is based on the Greek word χελώνη chelone "tortoise", "turtle" (another relevant word is χέλυς chelys "tortoise"), also denoting armor or interlocking shields; testudines on the other hand, is based on the Latin word testudo "tortoise". "Turtle" may either refer to the order as a whole, or to particular turtles which make up a form taxon that is not monophyletic.
The meaning of the word turtle differs from region to region. In North America, all chelonians are commonly called turtles, including terrapins and tortoises. In Great Britain, the word turtle is used for sea-dwelling species, but not for tortoises.
The term tortoise usually refers to any land-dwelling, non-swimming chelonian. Most land-dwelling chelonians are in the Testudinidae family, only one of the 14 extant turtle families.
Terrapin is used to describe several species of small, edible, hard-shell turtles, typically those found in brackish waters, and is an Algonquian word for turtle.
Some languages do not have this problem, as all of these are referred to by the same name. For example, in Spanish, the word tortuga is used for turtles, tortoises, and terrapins. A sea-dwelling turtle is tortuga marina, a freshwater species tortuga de río, and a tortoise tortuga terrestre.
Anatomy and morphology
The largest living chelonian is the leatherback sea turtle (Dermochelys coriacea), which reaches a shell length of 200 cm (6.6 ft) and can reach a weight of over 900 kg (2,000 lb). Freshwater turtles are generally smaller, but with the largest species, the Asian softshell turtle Pelochelys cantorii, a few individuals have been reported up to 200 cm (6.6 ft). This dwarfs even the better-known alligator snapping turtle, the largest chelonian in North America, which attains a shell length of up to 80 cm (2.6 ft) and weighs as much as 113.4 kg (250 lb). Giant tortoises of the genera Geochelone, Meiolania, and others were relatively widely distributed around the world into prehistoric times, and are known to have existed in North and South America, Australia, and Africa. They became extinct at the same time as the appearance of man, and it is assumed humans hunted them for food. The only surviving giant tortoises are on the Seychelles and Galápagos Islands, and can grow to over 130 cm (51 in) in length, and weigh about 300 kg (660 lb).
The largest ever chelonian was Archelon ischyros, a Late Cretaceous sea turtle known to have been up to 4.6 m (15 ft) long.
The smallest turtle is the speckled padloper tortoise of South Africa. It measures no more than 8 cm (3.1 in) in length and weighs about 140 g (4.9 oz). Two other species of small turtles are the American mud turtles and musk turtles that live in an area that ranges from Canada to South America. The shell length of many species in this group is less than 13 cm (5.1 in) in length.
Neck withdrawral in turtles
Pleurodires withdraw their neck sideways
Cryptodiree withdraw their neck backwards
Turtles are divided into two groups according to how they withdraw their necks into their shells (something the ancestral Proganochelys could not do). The Cryptodira withdraw their necks backwards while contracting it under their spine, whereas the Pleurodira contract their necks to the side.
Head of African spurred tortoise
Most turtles that spend most of their lives on land have their eyes looking down at objects in front of them. Some aquatic turtles, such as snapping turtles and soft-shelled turtles, have eyes closer to the top of the head. These species of turtles can hide from predators in shallow water, where they lie entirely submerged except for their eyes and nostrils. Near their eyes, sea turtles possess glands that produce salty tears that rid their body of excess salt taken in from the water they drink.
Turtles have rigid beaks, and use their jaws to cut and chew food. Instead of having teeth, which they appear to have lost about 150-200 million years ago, the upper and lower jaws of the turtle are covered by horny ridges. Carnivorous turtles usually have knife-sharp ridges for slicing through their prey. Herbivorous turtles have serrated-edged ridges that help them cut through tough plants. They use their tongues to swallow food, but unlike most reptiles, they cannot stick out their tongues to catch food.
Main article: Turtle shell
The upper shell of the turtle is called the carapace. The lower shell that encases the belly is called the plastron. The carapace and plastron are joined together on the turtle's sides by bony structures called bridges. The inner layer of a turtle's shell is made up of about 60 bones that include portions of the backbone and the ribs, meaning the turtle cannot crawl out of its shell. In most turtles, the outer layer of the shell is covered by horny scales called scutes that are part of its outer skin, or epidermis. Scutes are made up of the fibrous protein keratin that also makes up the scales of other reptiles. These scutes overlap the seams between the shell bones and add strength to the shell. Some turtles do not have horny scutes. For example, the leatherback sea turtle and the soft-shelled turtles have shells covered with leathery skin, instead.
The rigid shell means turtles cannot breathe as other reptiles do, by changing the volume of their chest cavities via expansion and contraction of the ribs. Instead, they breathe in two ways. First, they employ buccal pumping, pulling air into their mouths, then pushing it into their lungs via oscillations of the floor of the throat. Secondly, when the abdominal muscles that cover the posterior opening of the shell contract, the internal volume of the shell increases, drawing air into the lungs, allowing these muscles to function in much the same way as the mammalian diaphragm.
The shape of the shell gives helpful clues about how a turtle lives. Most tortoises have a large, dome-shaped shell that makes it difficult for predators to crush the shell between their jaws. One of the few exceptions is the African pancake tortoise, which has a flat, flexible shell that allows it to hide in rock crevices. Most aquatic turtles have flat, streamlined shells which aid in swimming and diving. American snapping turtles and musk turtles have small, cross-shaped plastrons that give them more efficient leg movement for walking along the bottom of ponds and streams.
The color of a turtle's shell may vary. Shells are commonly colored brown, black, or olive green. In some species, shells may have red, orange, yellow, or grey markings, often spots, lines, or irregular blotches. One of the most colorful turtles is the eastern painted turtle, which includes a yellow plastron and a black or olive shell with red markings around the rim.
Tortoises, being land-based, have rather heavy shells. In contrast, aquatic and soft-shelled turtles have lighter shells that help them avoid sinking in water and swim faster with more agility. These lighter shells have large spaces called fontanelles between the shell bones. The shells of leatherback sea turtles are extremely light because they lack scutes and contain many fontanelles.
It has been suggested by Jackson (2002) that the turtle shell can function as pH buffer. To endure through anoxic conditions, such as winter periods trapped beneath ice or within anoxic mud at the bottom of ponds, turtles utilize two general physiological mechanisms. In the case of prolonged periods of anoxia, it has been shown that the turtle shell both releases carbonate buffers and uptakes lactic acid.
Skin and molting
Tail of a snapping turtle
As mentioned above, the outer layer of the shell is part of the skin; each scute (or plate) on the shell corresponds to a single modified scale. The remainder of the skin is composed of skin with much smaller scales, similar to the skin of other reptiles. Turtles do not molt their skins all at once, as snakes do, but continuously, in small pieces. When turtles are kept in aquaria, small sheets of dead skin can be seen in the water (often appearing to be a thin piece of plastic) having been sloughed off when the animals deliberately rub themselves against a piece of wood or stone. Tortoises also shed skin, but dead skin is allowed to accumulate into thick knobs and plates that provide protection to parts of the body outside the shell.
By counting the rings formed by the stack of smaller, older scutes on top of the larger, newer ones, it is possible to estimate the age of a turtle, if one knows how many scutes are produced in a year. This method is not very accurate, partly because growth rate is not constant, but also because some of the scutes eventually fall away from the shell.
Terrestrial tortoises have short, sturdy feet. Tortoises are famous for moving slowly, in part because of their heavy, cumbersome shells, which restrict stride length.
Skeleton of snapping turtle (Chelydra serpentina)
Amphibious turtles normally have limbs similar to those of tortoises, except the feet are webbed and often have long claws. These turtles swim using all four feet in a way similar to the dog paddle, with the feet on the left and right side of the body alternately providing thrust. Large turtles tend to swim less than smaller ones, and the very big species, such as alligator snapping turtles, hardly swim at all, preferring to walk along the bottom of the river or lake. As well as webbed feet, turtles have very long claws, used to help them clamber onto riverbanks and floating logs upon which they bask. Male turtles tend to have particularly long claws, and these appear to be used to stimulate the female while mating. While most turtles have webbed feet, some, such as the pig-nosed turtle, have true flippers, with the digits being fused into paddles and the claws being relatively small. These species swim in the same way as sea turtles do (see below).
Sea turtles are almost entirely aquatic and have flippers instead of feet. Sea turtles fly through the water, using the up-and-down motion of the front flippers to generate thrust; the back feet are not used for propulsion, but may be used as rudders for steering. Compared with freshwater turtles, sea turtles have very limited mobility on land, and apart from the dash from the nest to the sea as hatchlings, male sea turtles normally never leave the sea. Females must come back onto land to lay eggs. They move very slowly and laboriously, dragging themselves forwards with their flippers.
Turtles are thought to have exceptional night vision due to the unusually large number of rod cells in their retinas. Turtles have color vision with a wealth of cone subtypes with sensitivities ranging from the near ultraviolet (UV A) to red. Some land turtles have very poor pursuit movement abilities, which are normally found only in predators that hunt quick-moving prey, but carnivorous turtles are able to move their heads quickly to snap.
See also: Animal cognition
It has been reported that wood turtles are better than white rats at learning to navigate mazes. Case studies exist of turtles playing. They do however have a very low encephalization quotient (relative brain to body mass), their hard shell enable them to live without fast reflexes and elaborate predator avoidance strategies. In the laboratory, turtles (Pseudemys nelsoni) can learn novel operant tasks and have demonstrated a long-term memory of at least 7.5 months.
Ecology and life history
File:Turtle in Indonesia.ogvPlay media
Sea turtle swimming
Although many turtles spend large amounts of their lives underwater, all turtles and tortoises breathe air, and must surface at regular intervals to refill their lungs. They can also spend much or all of their lives on dry land. Aquatic respiration in Australian freshwater turtles is currently being studied. Some species have large cloacal cavities that are lined with many finger-like projections. These projections, called papillae, have a rich blood supply, and increase the surface area of the cloaca. The turtles can take up dissolved oxygen from the water using these papillae, in much the same way that fish use gills to respire.
Like other reptiles, turtles lay eggs which are slightly soft and leathery. The eggs of the largest species are spherical, while the eggs of the rest are elongated. Their albumen is white and contains a different protein from bird eggs, such that it will not coagulate when cooked. Turtle eggs prepared to eat consist mainly of yolk. In some species, temperature determines whether an egg develops into a male or a female: a higher temperature causes a female, a lower temperature causes a male. Large numbers of eggs are deposited in holes dug into mud or sand. They are then covered and left to incubate by themselves. Depending on the species, the eggs will typically take 70–120 days to hatch. When the turtles hatch, they squirm their way to the surface and head toward the water. There are no known species in which the mother cares for her young.
Sea turtles lay their eggs on dry, sandy beaches. Immature sea turtles are not cared for by the adults. Turtles can take many years to reach breeding age, and in many cases breed every few years rather than annually.
Researchers have recently discovered a turtle’s organs do not gradually break down or become less efficient over time, unlike most other animals. It was found that the liver, lungs, and kidneys of a centenarian turtle are virtually indistinguishable from those of its immature counterpart. This has inspired genetic researchers to begin examining the turtle genome for longevity genes.
A group of turtles is known as a bale.
A green sea turtle grazing on seagrass
A turtle's diet varies greatly depending on the environment in which it lives. Adult turtles typically eat aquatic plants; invertebrates such as insects, snails and worms; and have been reported to occasionally eat dead marine animals. Several small freshwater species are carnivorous, eating small fish and a wide range of aquatic life. However, protein is essential to turtle growth and juvenile turtles are purely carnivorous.
Sea turtles typically feed on jellyfish, sponge and other soft-bodied organisms. Some species of sea turtle with stronger jaws have been observed to eat shellfish while some species, such as the green sea turtle do not eat any meat at all and, instead, have a diet largely made up of algae.
Systematics and evolution
Main article: Turtle classification
See also: List of Testudines families
Life restoration of Odontochelys semitestacea, the oldest known turtle relative with a partial shell
"Chelonia" from Ernst Haeckel's Kunstformen der Natur, 1904
The first proto-turtles are believed to have existed in the late Triassic Period of the Mesozoic era, about 220 million years ago, and their shell, which has remained a remarkably stable body plan, is thought to have evolved from bony extensions of their backbones and broad ribs that expanded and grew together to form a complete shell that offered protection at every stage of its evolution, even when the bony component of the shell was not complete. This is supported by fossils of the freshwater Odontochelys semitestacea or "half-shelled turtle with teeth", from the late Triassic, which have been found near Guangling in southwest China. Odontochelys displays a complete bony plastron and an incomplete carapace, similar to an early stage of turtle embryonic development. Prior to this discovery, the earliest-known fossil turtle ancestors, like Proganochelys, were terrestrial and had a complete shell, offering no clue to the evolution of this remarkable anatomical feature. By the late Jurassic, turtles had radiated widely, and their fossil history becomes easier to read.
Their exact ancestry has been disputed. It was believed they are the only surviving branch of the ancient evolutionary grade Anapsida, which includes groups such as procolophonids, millerettids, protorothyrids, and pareiasaurs. All anapsid skulls lack a temporal opening, while all other extant amniotes have temporal openings (although in mammals the hole has become the zygomatic arch). The millerettids, protorothyrids, and pareiasaurs became extinct in the late Permian period, and the procolophonoids during the Triassic.
However, it was later suggested the anapsid-like turtle skull may be due to reversion rather than to anapsid descent. More recent morphological phylogenetic studies with this in mind placed turtles firmly within diapsids, slightly closer to Squamata than to Archosauria. All molecular studies have strongly upheld the placement of turtles within diapsids; some place turtles within Archosauria, or, more commonly, as a sister group to extant archosaurs, though an analysis conducted by Lyson et al. (2012) recovered turtles as the sister group of lepidosaurs instead. Reanalysis of prior phylogenies suggests they classified turtles as anapsids both because they assumed this classification (most of them studying what sort of anapsid turtles are) and because they did not sample fossil and extant taxa broadly enough for constructing the cladogram. Testudines were suggested to have diverged from other diapsids between 200 and 279 million years ago, though the debate is far from settled. Even the traditional placement of turtles outside Diapsida cannot be ruled out at this point. A combined analysis of morphological and molecular data conducted by Lee (2001) found turtles to be anapsids (though a relationship with archosaurs couldn't be statistically rejected). Similarly, a morphological study conducted by Lyson et al. (2010) recovered them as anapsids most closely related to Eunotosaurus. A molecular analysis of 248 nuclear genes from 16 vertebrate taxa suggests that turtles are a sister group to birds and crocodiles (the Archosauria). The date of separation of turtles and birds and crocodiles was estimated to be 255 million years ago. The most recent common ancestor of living turtles, corresponding to the split between Pleurodira and Cryptodira, was estimated to have occurred around 157 million years ago. The oldest definitive crown-group turtle (member of the modern clade Testudines) is the species Caribemys oxfordiensis from the late Jurassic period (Oxfordian stage). Through utilizing the first genomic-scale phylogenetic analysis of ultraconserved elements (UCEs) to investigate the placement of turtles within reptiles, Crawford et al. (2012) also suggest that turtles are a sister group to birds and crocodiles (the Archosauria).
The first genome-wide phylogenetic analysis was completed by Wang et al. (2013). Using the draft genomes of Chelonia mydas and Pelodiscus sinensis, the team used the largest turtle data set to date in their analysis and concluded that turtles are likely a sister group of crocodilians and birds (Archosauria). This placement within the diapsids suggests that the turtle lineage lost diapsid skull characteristics as it now possesses an anapsid skull.
The earliest known fully shelled member of the turtle lineage is the late Triassic Proganochelys. This genus already possessed many advanced turtle traits, and thus probably indicates many millions of years of preceding turtle evolution. It lacked the ability to pull its head into its shell, had a long neck, and had a long, spiked tail ending in a club. While this body form is similar to that of ankylosaurs, it resulted from convergent evolution.
Turtles are divided into two extant suborders: the Cryptodira and the Pleurodira. The Cryptodira is the larger of the two groups and includes all the marine turtles, the terrestrial tortoises, and many of the freshwater turtles. The Pleurodira are sometimes known as the side-necked turtles, a reference to the way they withdraw their heads into their shells. This smaller group consists primarily of various freshwater turtles.
A two-month-old hypomelantistic snapping turtle.
Chart of the two extant suborders, extinct groups that existed within these two suborders are shown as well
Classification of turtles
Family Pelomedusidae (African sideneck turtles)
Family Podocnemididae (Madagascan big-headed and American sideneck river turtles)
Basal and incertae sedis
Family Chelydridae (snapping turtles)
Superfamily Chelonioidea (sea turtles)
Sea turtle at Henry Doorly Zoo, Omaha NE
Family Cheloniidae (green sea turtles and relatives)
Family Dermochelyidae (leatherback sea turtles)
Family Emydidae (pond, box, and water turtles)
Family Geoemydidae (Asian river turtles, Asian leaf turtles, Asian box turtles, and roofed turtles)
Family Testudinidae (true tortoises)
Family Carettochelyidae (pignose turtles)
Family Dermatemydidae (river turtles)
Family Kinosternidae (mud turtles)
Family Trionychidae (softshell turtles)
Turtle fossils of hatchling and nestling size have been documented in the scientific literature. Paleontologists from North Carolina State University have found the fossilized remains of the world's largest turtle in a coal mine in Colombia. The specimen named as Carbonemys cofrinii is around 60 million years old and nearly 8 ft long.
On a few rare occasions, paleontologists have succeeded in unearthing large numbers of Jurassic or Cretaceous turtle skeletons accumulated in a single area (the Nemegt Formation in Mongolia, the Turtle Graveyard in North Dakota, or the Black Mountain Turtle Layer in Wyoming). The most spectacular find of this kind to date occurred in 2009 in Shanshan County in Xinjiang, where over a thousand ancient freshwater turtles apparently died after the last water hole in an area dried out during a major drought.Last edited by Puddles the Monkey; 13-05-2015 at 09:44.
- 13-05-2015 08:45
what was the answer about heart attacks and why they occur when there is less oxygen in the body?
- 13-05-2015 09:07
essentially the cardiac muscles need oxygen to respire, if they don't get it they can't really respire, so they have no energy and can't contract anymore
- 13-05-2015 09:15
- 13-05-2015 09:20
What about the question with pollution of water by phosphate? It was something like why this conclusion may not be accurate with two answers. Also the question about why it's more common to cut tube B instead of oviduct.