Biology Notes Life on Earth Essay Example

tongue and lips which are all depended on to take food into mouth- mouth of a cat contains a variety of different teeth: Canines– grab, hold & tear prey Incisors– scrape meat off bones Molars and premolars– crush meat so it is easier to swallow See picture 1- only a few, tiny teeth - incisors and canines are narrow and pointed - cheek teeth flat with round tips - lack of strong teeth because of no need to bite or crush food See picture 6

Esophagus- tube-like passageway from mouth to the stomach - opens into the stomach at the point where rumen and reticulum meet - helps transport both gases and cud- begins at end of pharynx, continues down neck next to the trachea, through the diaphragm, finally connecting with the stomach - first passageway in the digestive system, so often exposed to rough food which has not been fully chewed i. e. pieces of bone - surface, therefore, has to be resistant to damage, so is lined with stratified squamous epithelium.

See picture 2- the simple tube that moves food from mouth to stomach - At entry from the esophagus to stomach the lining of the esophagus changes from stratified squamous  to tall column-shaped cells StomachGoat’s stomach has four compartments:

1.  rumen: largest compartment. Here food is moistened and churned around to break down into smaller pieces Capacity: 11 -22 liters depending on food eaten
2.  honey-combed reticulum: located just below the entrance from the esophagus into the stomach.Part of the rumen, only separated by a thin fold. Bacterial cellulases act on food here and food is made into round balls called cud which is
   

regurgitated into the mouth and chewed into small particles. Capacity: 1-2 L

Capacity: approx. 4L- stomach of a cat is designed to store large amounts of food and begin the digestive process - esophagus carries food into the stomach, where it enters through a valve called the cardiac sphincter - the lining of the stomach has many folds called gastric folds, which elp crush and grind food - stomach lining also secretes acids and enzymes which break down the food - Once stomach digestive process is done, the partly digested food exits the stomach through the pyloric sphincter area and then enters first part of the small intestine

Most food leaves the cat’s stomach within 12 hours after entering- two chambers: the main chamber and the diverticulum (the smaller chamber) - stomach wall is lined with ridges and also epithelial cells which produce mucus, but no pepsinogen is secreted so no protein is digested in the stomach - stomach merely acts as a storage place for nectar and pollen Small intestine- as partly digested food enters the first part of the small intestine (duodenum), enzymes produced and secreted by the pancreas break down nutrients from food into simple compounds

These compounds are absorbed mainly from the jejunum and ileum (2nd and 3rd part of small intestine), into the blood stream

- the lining of the wall is covered in many small fingerlike projections called villi see picture 4, which increase surface area for absorption- small intestine is lined with villi (for larger surface area for absorption) see picture 4 - has blood vessels which take nutrients to other parts of the body - three sections: duodenum, jejunum and ileum Duodenum – a section where Jejunum – the largest part of small intestine, section where most of the absorption takes place Ileum – the final section of small intestine, where absorption process ends- Honey-Possum lacks a Caecum, which makes it difficult to identify where small intestine finishes and where large intestine starts - we do know that pollen is digested in both the small and large intestines.

Caecum- located at the point where small and large intestines meet - Digestion in caecum is done by microorganisms that break down the cellulose fibers in plant material. - caecum of a goat can hold up to 1 litre! the small, comma-shaped pouch which hangs just below the point where the ileum meets the large intestine - compared to most carnivores, the caecum of a cat is very small, and its function is unknown- Honey-Possum does not actually have a caecum Large intestine- Undigested food and unabsorbed nutrients leaving small intestine move into the large intestine - functions include water absorption and further digestion of food by microorganisms - large intestine of a goat is made up of the colon and rectum- large intestine connects the small intestine to the anus - larger in diameter than the small intestine, but shorter in length - made up of the caecum, rectum

and colon (longest section)

Main functions are water absorption, keeping the body’s hydration level constant, and to store feces waiting to leave the body- Honey-Possum has no Caecum, which makes it hard to tell where the small intestine finishes and the large intestine starts - we do know that pollen is digested in both small and large intestines - feces waiting to leave the body is stored at the end of the large intestine Digestive juices and Enzymes- Enzymes secreted by pancreas are important in the digestion of carbohydrates, proteins and fats - Bile produced by the liver and stored and secreted by gall bladder helps soften the fat particles in preparation for digestion - stomach contains bacteria and protozoa which break down cellulose walls, as well as hydrochloric acid, pepsin and lipase which break down plant proteins and fats-

As food passes into the stomach, the stomach lining secretes acids and enzymes needed to break down food - pancreas and liver supply enzymes needed to break down fats and proteins so they can enter into the bloodstream - Bile that is stored in the gall bladder is mixed with the food in the duodenum to chemically break down food even further- honey possum’s stomach produces mucus from the epithelial cells that cover the lining of the stomach wall. However, this mucus contains no protein-digesting enzyme (pepsinogen) Faeces- Goat faeces are formed in end part of the colon - comes out as small, dry pellets. See picture 5- feces of a cat is stored in the end section of the large intestine called the rectum - colour and texture varies depending on cat’s diet- Almost all pollen

grains that are excreted in faeces are empty, as the content of the pollen is digested in stomach and intestines Why are they different? Mouth + Teeth The main difference in the mouths of the mammals’ digestive systems are the teeth.

The teeth differ according to the diet of the animals.

The grazing herbivore only eats plants, so their teeth are designed to grind the food to increase the surface area, whereas the carnivore eats meat, so the main function if its teeth is to grab, hold and tear the prey, scrape meat off bones, and then finally crush the meat before swallowing. Lastly, the nectar-feeding mammal barely uses its tiny teeth, as the tongue collects the pollen and scrapes it against the roof of the mouth, so no chewing or tearing is involved. Esophagus The esophagus of the different types of mammals acts quite similarly, mainly just functioning as the passageway from the mouth to the stomach. Stomach

A grazing herbivore eats only plants, in which cellulose is very difficult to break down, so they, therefore, have a four-chambered stomach so that the food can be partly digested and then regurgitated and moved into the next stomach so that the cellulose can be properly broken down.

The carnivore only has one stomach which begins the chemical breakdown process of the meat. Meat is not as complex to digest as plant matter, which is why only one stomach is needed. The nectar-feeding mammal has a two-chambered stomach, which produces mucus, but the stomach mainly acts as a storage place for nectar and pollen, with most of the digestion being done in the small intestine. Small intestine The

small intestine of the grazing herbivore and the carnivore are quite similar.

Both of these small intestines take nutrients into the body through the bloodstream and are both lined with villi to increase surface area for absorption. Also, they both have three sections called the Duodenum, Jejunum and Ileum. The nectar-feeding mammal’s small intestine also absorbs nutrients into the bloodstream, but as they lack a caecum, it is difficult to tell where the small intestine ends and the large intestine starts. Caecum The caecum in a grazing herbivore is quite large, and is very important in the digestive process, as cellulose fibres are broken down here. This is very different to the caecum of a carnivore, which is very small and has an unknown function.

A nectar-feeding mammal lacks a caecum altogether, as there is no need for it in the digestion process. Large intestine

Water absorption and further digestion is common in the large intestines of both the grazing herbivore and the carnivore, whereas almost all of the digestion of pollen and nectar is done in the small and large intestines of the nectar-feeding mammal. In all three mammal types, the end of the large intestine is used to store the faeces before it leaves the body. Digestive juices and Enzymes The digestive juices of the three types of mammals are different because of their different diets. Grazing herbivores eat plants, therefore their stomachs contain bacteria and protozoa to break down the cellulose walls, as well as acids and enzymes to break down the plant proteins and fats.

Their pancreas also secretes enzymes to break down carbohydrates, proteins and fats.

The carnivore’s pancreas and liver supply

the enzymes to break down fats and proteins of the meat they eat. Their stomach lining also secretes acids and enzymes needed to break down the meat. The nectar-feeding mammal’s stomach produces digestive mucus, however, this mucus contains no pepsinogen, as most of the digestion of protein from the pollen is done in the intestines.

Faeces of the different types of mammals are stored in the rectum but are all very different due to the different diets. Faeces of a grazing herbivore come out as small, dry pellets, due to their diet of plant matter and all the water absorption that takes place in the large intestine.

A carnivore’s feces vary in colour and texture, as their diet often changes between different species and breeds. When a nectar-feeding mammal’s faeces is excreted, the pollen grains are empty, as the content of the pollen has been digested in the stomach and intestine to provide the nutrients needed for the animal to survive. Topic: life on Earth Describe the experiments of Urey and Miller and use available evidence to analyse the: a)Reason for their experiment(s) b)Result of their experiment(s) c)Importance of their experiment(s) in illustrating the nature and practice of science

In 1953 Professor Harold C. Urey of the University of Chicago and his graduate student Stanley L. Miller created an experiment to test the hypothesis made by Oparin and Haldane which stated that ‘organic chemicals were produced from non-living matter on the early Earth’ – Biology in Context.

Miller set up a series of glass tubes and flasks connected in a loop with a lower chamber of water representing oceans and an upper chamber representing the atmosphere. The

liquid was heated to make evaporation occur and electric currents were passed through the atmosphere chamber to simulate energy such as lightning that is thought to be common in the early atmosphere.

The atmosphere was then cooled so that the water could condense and slowly return back into the first flask and the cycle would begin again. The tests were carried out for one week and at the end of the week Miller and Urey observed that 10-15% of the carbon had formed organic compounds and 2% of the carbon had formed amino acids (including glycine and alanine) that are used to make proteins.

Sugars, lipids, and some of the building blocks for nucleic acids were also formed. Reason for their experiment(s) The purpose of Urey and Miller’s experiment was to investigate whether it would be possible for non-living matter to create organic chemicals under the conditions thought to be present in the early Earth.

They essentially designed their experiment to test the hypothesis made by Oparin and Haldane. The experiment was designed to simulate conditions of the unstable early Earth and to test for biological chemicals.

The result of their experiment Urey and Miller’s experiment proves that certain organic compounds such as amino acids could be made under the conditions that scientists considered to be present on early Earth. However, the experiment does not prove that this is how life began or that this is the way those particular compounds were created either. It also does not prove that early Earth was how Oparin and Haldane suggested it. c)Importance of their experiment(s) in illustrating the nature and practice of science

The scientific method is a process used

when designing and carrying out an experiment. The first step is to ask a question about something that you observe, then to do background research on the topic. After this you must construct a hypothesis, test it with an experiment and record your results. You must then draw a conclusion and state whether your hypothesis is true or not.

Urey and Miller’s experiment illustrates the nature and practice of science through their thorough use of the scientific method. They took the hypothesis of Oparin and Haldane and developed a controlled experiment to test whether this hypothesis could be correct.

After researching their idea they came up with the best way to experiment to get the most reliable results. After performing their experiment, they clearly recorded the data that they came up with without changing it. Their experiment was reproducible so that others can try it and come up with the same results.

Although the results of their experiment are often argued over by different scientists around the world, Urey and Miller have created a stable base for further research into the origins of the Earth. d)Contribution to hypotheses about the origin of life (supported? Refuted? ) There are many theories about the origin of life. One theory – Spontaneous Generation – supports the idea that life spontaneously arises from non-living matter.

This theory was accepted as ‘fact’ until it was scientifically tested by Francesco Redi in 1668, who discovered that maggots came from eggs laid by flies and did not just spontaneously arise. But it was not until 1862 that people stopped believing in a spontaneous generation when Louis Pasteur convinced them that it does not occur.

Another theory is that our DNA and RNA come from outer space and arrived here during the time of early Earth.

A third theory is that life came from non-living matter on early Earth. This theory began from a hypothesis made by two scientists, Oparin and Haldane, but was not actually tested until 1953 by Miller and Urey.

Urey and Miller contributed greatly to Oparin and Haldane’s hypothesis of the origin of life, as they were the first to actually test it. Their experiment half supported the hypothesis, as it proved that it is possible for non-living matter to produce organic chemicals under specific conditions. But it did not completely support the hypothesis, as their experiment did not prove that this was how life on Earth began, or that early Earth was how Oparin and Haldane suggested it. Urey and Miller’s experiment significantly contributed to Oparin and Haldane’s hypothesis of the origin of life, and provided a base for further investigation of this theory.