Double Biology

These cards provide a brief overview of most of the main topics in B2, with the key words highlighted. I hope they're helpfull :)

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Controling glucose levels

Glucose is carried around the body in the blood. It is carried to all the cells – where it is used for respiration. If the concentration falls too low, the central nervous system wouldn’t work properly. The pancreas is an organ in the abdomen which monitors glucose levels in the blood. Soon after eating a meal the glucose levels increase and the hormone insulin is made. This causes the liver to remove insulin from the blood. Any excess glucose in transformed into glycogen by the liver. If the glucose levels then fall beneath what is required another hormone called glucagon is produced by the pancreas and this ensures that the liver transforms glycogen back into glucose. A normal glucose concentration in the blood is about 90mg per 100cm cubed.

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Diabetics are people that can’t produce enough of their own natural insulin. This causes glucose to be lost in the urine. This means that the glucose has not been able to enter the sufferer’s blood, leaving them feeling tired. The long term effect is that cells start to respire protein and fats, causing the sufferer to lose weight. The 2 main forms of diabetes are mild and severe. Sufferers of mild diabetes may just have to monitor their diet, making sure they don’t take in too much carbohydrates, therefore keeping their blood glucose levels low. Sufferers of severe diabetes have to take an injection of insulin before a meal. Insulin can’t be taken orally because it would be digested before it could reach the blood.

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The process of decay begins as soon as a substance dies. The first organisms that consume the materials are the detritivores. These can be things like worms and maggots. They are then further broken down by the decomposers – which are usually bacteria or fungi. These ensure that carbon dioxide, water and minerals are returned into the soil. The process can be speeded up with the right temperature and moist conditions. Compost heaps shouldn’t get too wet because it excludes oxygen, which the microorganisms need for respiration. A good compost will contain lots of mineral nutrients and will act as a fertiliser.

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The carbon cycle

Carbon is absorbed from the air by plants to use for photosynthesis. Animals eat the plants and so the carbon is passed along the food chain. Respiration from plants and animals will return carbon dioxide to the atmosphere. When the animals/plants die, their bodies are invaded by decomposers (like fungi and bacteria). When these decomposers respire the carbon will be released back into the atmosphere. A lot of carbon is locked up in fossil fuels from when plants were photosynthesising millions of years ago. When the fossil fuels are burnt this carbon is released into the atmosphere. This is called combustion. As we started to burn more fossil fuels because of the bigger demand for power, there has been more carbon in the atmosphere which has started to contribute to global warming.

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Animal and plant cells

All animals and plants are made up of many cells and are said to be multicellular. Organisms, such as bacteria, only consist of one cell and are called unicellular. You need a microscope to see cells. School microscopes only magnify things by about 100 times. To properly see cells you need an electron microscope. The nucleus controls the cells activities and stores the instructions of how to make new cells. In the cytoplasm there are also the mitochondria where most of the energy is released during respiration. All cells have ribosomes which are involved in protein synthesis. Plants have a sap filled vacuole which helps to keep the cell rigid. Enzymes are made of proteins. Enzymes control the reactions in the cell. Root hair cells are always close to xylem tissue which speeds the water along the root to the leaves where it can evaporate.

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Osmosis and diffution

Movement of particles from where there is a high gradient to where there is a lower gradient is called diffusion. The rate of movement depends on the size of the particles (the smaller the faster) and the concentration gradient (the higher the faster) and temperature (the higher the faster) Diffusion does not use any energy. Which makes it a passive process. Osmosis is the same as diffusion but only involves water molecules. A dilute solution is one that contains a high level of water molecules. So, water molecules will move from a dilute solution to a more concentrated solution. Osmosis does not use energy to work either. Animal’s cells can burst if too much water enters them by osmosis. If the cell is placed in a more concentrated solution the water may leave, causing the cell to shrink

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The test for starch involves the use of Iodine solution. It starts brown in colour and turns blue/black if starch is present. To find out whether chlorophyll is necessary a variegated leaf can be used. This is a leaf which has pale and green parts. The lower surface of a leaf has pairs of guard cells on either side of a stomata which can control water loss from the plant. Oxygen and carbon dioxide can also leave the plant through these gaps. The spongy layer of the leaf has lots of air spaces for gas exchange. You can test the rate of photosynthesis by counting the number of bubbles coming off a water plant. The enzymes that control photosynthesis can be destroyed if the temperature is over 45-50 degrees centigrade. The atmosphere only contains 0.04% carbon dioxide which can limit the rate of photosynthesis, especially on warm summer days. Cellulose (used in cell walls) is made from starch. Sugars and mineral ions travel in the phloem.

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Plant minerals

Plants need nitrogen to make proteins which are formed from amino acids. Most minerals are dissolved in water so can be absorbed by the root hair cells. When a plant dies it decays and most of the minerals it contained will be recycled back into the soil. Plants need magnesium to make chlorophyll. Crop rotation is making sure you don’t grow the same plants in the same place too long, because if you do the soil will run out of the mineral that certain plant needs. A modern approach is to grow plants in water rather than soil. These are called hydroponic crops. The positive of this technique is that you can add whatever minerals you need. However it is a lot more expensive than growing plants normally.

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