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biology unit 6(nitrogen cyle) new The Nitrogen Cycle Higher Tier Only Nitrogen is present as N2 gas in the atmosphere and within biological molecules, e.g. proteins, in the tissues of living organisms Nitrogen is cycled through ecosystems by the processes of the nitrogen cycle Uptake of nitrogen by living organisms N2 in the atmosphere is made available to living organisms by the process of nitrogen fixation Nitrogen fixation is carried out by nitrogen-fixing bacteria which convert N2 gas into ammonium compounds; these compounds are converted into nitrates in the soil Nitrogen-fixing bacteria can be free-living in the soil or they can live within root nodules of legume plants, e.g. peas, beans and clover Nitrogen gas can also be fixed by lightning when it strikes the earth, or during the production of chemical fertilisers After nitrogen fixation has occurred plants absorb the nitrates in the soil and use the nitrogen to build plant proteins Transfer of nitrogen between living organisms Animals feed on plants and digest the proteins in the plant tissues, providing nitrogen to build animal proteins Nitrogen may then be passed from one consumer to another up the food chain in the same way Release of nitrogen from living tissues Nitrogen from living organisms is returned to the soil in the form of ammonia by the action of decomposers such as bacteria and fungi When animals and plants die the proteins inside their tissues are broken down by the action of decomposers and returned to the soil in the form of ammonia Waste, i.e. urine and faeces, from animals contains urea, which is converted into ammonia by the action of the bacterial enzyme urease The plants can’t absorb ammonia so nitrifying bacteria convert the ammonia to nitrates which can then be taken up again by plants The conversion of ammonium compounds to nitrates is known as nitrification Returning nitrogen to the atmosphere Nitrates in the soil can be converted back into nitrogen gas (N2) by the action of denitrifying bacteria This process is known as denitrification Denitrifying bacteria are active in anaerobic conditions, e.g. in waterlogged or compacted soil Farmers can decrease the activity of denitrifying bacteria by ploughing the soil to increase aeration Nitrogen cycle diagram nitrogen-cycle-gcse The nitrogen cycle involves nitrogen fixation, decomposition, nitrification and denitrification Factors affecting the nitrogen cycle Because so many processes within the nitrogen cycle are carried out by microorganisms the cycle can be affected by factors that affect microorganism activity, e.g. Temperature This affects the rate at which enzyme-controlled reactions can occur Oxygen availability Aerobic bacteria rely on oxygen for respiration Low oxygen availability may lead to an increase in the activity of anaerobic bacteria, e.g. denitrifying bacteria pH This affects the rate of enzyme-controlled reactions as extreme pH levels can cause denaturation Water Water is needed by living organisms, so the rate of microbial activity increases in soil where moisture is present The presence of heavy metals in the soil Heavy metals, e.g. mercury and lead, can be toxic to the metabolism of microorganisms These factors are known to influence the rate at which decomposition occurs in compost heaps and landfill sites

2: Causes of Lameness

Understand the Basic Principles of Haircutting Good haircuts begin with an understanding of the shape of the head, referred to as the head form, also known as head shape. Hair responds differently on various areas of the head depending on the length and the cutting technique used. Being aware of where the head form curves, turns, and changes will help you achieve the look that you and your client are seeking. Reference Points Reference points on the head mark where the surface of the head changes, such as the ears, jawline, occipital bone, or apex. These points are used to establish design lines (figure 16-1). An understanding of head shape and reference points will help you in the following ways: Finding balance within the design, so that both sides of the haircut turn out the same. Developing the ability to create the same haircut consistently. Showing where and when it is necessary to change technique to make up for irregularities (such as a flat crown) in the head form. Standard reference points are defined below: Parietal ridge (puh-RY-ate-ul RIJ). This is the widest area of the head, starting at the temples and ending at the bottom of the crown. This area is easily found by placing a comb flat on the side of the head: The parietal ridge is found where the head starts to curve away from the comb. The parietal ridge is also referred to as the crest area (figure 16-2). Occipital bone (ahk-SIP-ih-tul BOHN). The bone that protrudes at the base of the skull is the occipital bone. To find the occipital bone, simply feel the back of the skull or place a comb flat against the nape and find where the comb leaves the head (figure 16-3). Apex (AY-peks). This is the highest point on the top of the head. This area is easily located by placing a comb flat on the top of the head. The comb will rest on that highest point (figure 16-4). Four corners. These may be located in one of two ways. One is by placing two combs flat against the side and back, and then locating the back corner at the point where the two combs meet (figure 16-5). The second is by making two diagonal lines crossing the apex of the head, which then point directly to the front and back corners (figure 16-6). You will not necessarily use every reference point for every haircut, but it is important to know where they are. The location of the four corners, for example, signals a change in the shape of the head from flat to round and vice versa. This change in the surface can have a significant effect on the outcome of the haircut. For example, the two front corners represent the widest points in the bang area. Cutting past these points can cause the bang to end up on the sides of the haircut once it is dry, creating an undesirable result. Areas of the Head The areas of the head are described below (figure 16-7): Top. By locating the parietal ridge, you can find the hair that grows on the top of the head. This hair lies on the head shape. Hair that grows below the parietal ridge, or crest, hangs because of gravity. You can locate the top by parting the hair at the parietal ridge, and continuing all the way around the head. Front. By making a parting, or drawing a line from the apex to the back of the ear, you can separate the hair that naturally falls in front of the ear from the hair behind the ear. Everything that falls in front of the ear is considered the front. Sides. The sides are easy to locate. They include all hair from the back of the ear forward, below the parietal ridge. Crown. The crown is the area between the apex and the back of the parietal ridge. On many people, the crown is flat and is the site of cowlicks or whorls. Because of this, it is extremely important to pay special attention to this area when haircutting. Nape. The nape is the area at the back part of the neck and consists of the hair below the occipital bone. The nape can be located by taking a horizontal parting, or by making a horizontal line across the back of the head at the occipital bone. Back. By making a parting or drawing a line from the apex to the back of the ear, you can locate the back of the head, which consists of all the hair that falls naturally behind the ear. When you have identified the front, you have also identified the back. Bang area. also known as fringe area. The bang area is a triangular section that begins at the apex and ends at the front corners (figure 16-8). This area can be located by placing a comb on top of the head so that the middle of the comb is balanced on the apex. The spot where the comb leaves the head in front of the apex is where the bang area begins. Note that the bang area, when combed into a natural falling position, falls no farther than the outer corners of the eyes