Biology B3

Plants & photosynthesis

photosynthesis - Water + carbon dioxide --> glucose + oxygen

Sunlight and chlorophyll is needed. Chlorophyll is found in chloroplasts. Temperature affects rate of photosynthesis because of enzymes. Minerals are abosrbed into root haris by active transport and water by osmosis. Water is carried through the plant in the xylem. water is drawn up the plant by evaporation and out of the leaves by transpiration.

Transpiration is the water loss from leaves. As temperature increases more water evaporates as the particles gain energy so the rate is higher.  When it's not humid and it's windy there is a bigger difference in the amount of water outside the plant so the water moves down the concentration gradient out of the plant. (Diffusion). The bigger the surface area of the plant the higher the rate of transpiration because there are more stomata for the water to escaoe out of.

Structure of a leaf (top to bottom): cuticle - waxy layer to prevent evaporation, upper epidermis - transparent to allow sunlight through, palisde cells - vertical cells containing lots of chloroplasts - where most photosynthesis occurs, spongy mesophyll - lots of air spaces - gas exchange, vascular bundle - stiff for support, xylem - water, phloem - sugar, lower epidermis, guard cells, stoma - allows carbon dioxide to diffuse in, can be closed to stop water loss.

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Plant minerals

Nitrates - for growth, produce amino acids that combine to make proteins. Lack of nitrates causes poor growth and yellow leaves.

Phosphates - Make DNA, involved in respiration and growth. deficiency causes poor root growth and discoloured leaves.

potassium - involved in respiration and photosyntheis, helps enzyme action. Lack of potassium causes poor flower and root growth, discoloured leaves.

Magnesium - makes chlorophyll, essential for photosynthesis. Lack of magneisum causes yellow leaves.

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Blood and vessels

Red blood cells - contain haemoglobin to carry oxygen. They combine to form oxyhaemoglobin and split to release oxygen to cells. They are dougnut shaped to haev a large surface area to carry more oxygen and don't have a nucleus.

White blood cells - fight off disease. phagocytes can changes shape to engulf microorganisms. They do have a nucleus.

platelets - clot the blood.small fragments of cell, no nucleus.

Plasma carries everything - red blood cells, white blood cells, platelets, carbon dioxide, glucose, urea, hormones, antibodies, antitoxins, amino acids.

Arteries - thick, muscular walls to cope with high pressure.

Veins - thinner walls as lower pressure, valves to stop backflow of blood.

Capillaries - one cell thick, permeable to allow exchange of materials e.g oxygen into cells.

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Circulatory system and heart problems

Humans have a double ciruclatory system. Involving one to the lungs and one for the rest of the body.

Deoxygenated blood flows through the Vena Cava (vein) into the right atrium. It then flows through the tricuspid valve into the right ventricle and is pumped out of the pumlonary artery to the lungs. Oxygenated blood returns to the heart in the pulmonary vein and flows into the left atrium. It is pusehd through the bicuspid valve into the left ventricle and then pumped out of the aorta (artery) around the body.

The heart has its own blood supply in the coronary vessels.

Coronary heart disease is when there is a build up of fatty deposits. The arteries then get blocked and oxygen and glucose can't get to the heart. The muscle dies and causes a heart attack.

A stent can be used to keep the arteries open. It's a piece of metal that expands once inside and widens the artery.

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Nervous system

Reflexes are fast, automatic and protective.

The CNS (central nervous system) consists of brain and spinal cord.

Stimuli - sound, light, pressure, temperature, dissolved chemicals, evaporated chemicals,

Reflex arc -

Stimulus - receptor - sensory neurone - synapse - CNS - synapse - motor neurone - effector - response

A synapse is a junction between two neurones. When a impulse reaches the synapse a chemical transmitter is released which diffuses across the gap and triggers an impulse in the next neurone.

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The Eye

The sclera is a white protective layer.

cornea - clear window at front, does most the refracting

pupil - controls how much light reaches retina

iris - controls size of pupil

Lens - refract light to retina to focus it, suspended by muscles and ligaments.

Choroid - stops refelction of light inside eyes, blood supply to keep eye alive

Retina - turns light to impulse. light sensitive contains rods and cones, mianly rods so is senstive to dim light and black and white

Forvea - sensitive to colour, contains more cones.

Blind spot, in front of optic nerve, lack of rods and cones, not sensitive to light.

optic nerve- transports impulses from retina to brain

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Role of the Kidneys

Kidneys have 3 main functions; excretion, control of water balance and control of ion balance -salts.

Excretion is the removal of wastes - carbon dioxide made during respiration is removed via the lungs when we breathe out, urea made in the liver by the breakdown of excess amino acids leaves the body in urine.

Kidneys filter the blood and reabsorb what the body needs. All glucose is reabsorbed and some salts and water is reabsorbed. The excess makes urea.

Nephrons are the filtration units in the kidneys. A high pressure is built up which squeezes water, urea, ions and sugar out of the blood into Bowman's capsule. The membranes between the blood vessels and bowman's capsule act as filters so big molecules like blood cells remain in the blood. As the liquid flows along the nephron, useful substances are reabsorbed back into the blood. All glucose, some ions and enough water is reabsorbed. The waste including urea travels down the collecting duct to the ureter. The urine is stored in the bladder before leaving the body through the urethra.

Renal arteries supply the kidneys and renal veins carry blood away from the kidneys.

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Regulating urine content/ Kidney failure

Regulating urine concentration – if there is too much water in the blood it will become dilute. This is sensed by receptors and less anti-diuretic hormone is made. This changes how permeable the collecting duct is and less water is reabsorbed. As more water is excreted as waste, there will be a bigger volume of urine and it will be more dilute.  If there isn’t enough water in the blood it is concentrated. The receptors in the hypothalamus detect this and more ADH is released from the pituitary gland. More water is reabsorbed and the urine is concentrated and a smaller volume of it.

When kidneys fail, there is three big problems; accumulation of urea, no control of water levels, and no control of salt levels.

Treatment - Dialysis or transplant.     Dialysis machines take blood out of the person's body and filter against dialysing membrane. The urea and other waste (excess salt and water) diffuses out of the blood into the dialysis fluid. The concentration of glucose most be the same as in the blood so it doesn't diffuse down a concentration gradient into the fluid. It is inconvenient as the person has to go to hospital a lot and there is a risk of infection from the needles. Transplant - the donor organ can be attacked by the immune system. To prevent rejection, a donor kidney with the same tissue type of the recipient is used. Immunosupressant drugs are sometimes used but leave the individual immunocompromised and less able to fight off disease. It it a better long term solution.

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Types of microorgansims

Bacteria - cell wall, no nucleus, flagellum for movement./ different shapes - spherical, rod shaped, spiral, curved rods/ Reproduce asexually by splitting into two (binary fission) / cause the spread of disease and food to spoil / Can be used for making yoghurt - lactobasillius makes lactase which breaks down lactose into lactic acid.

Viruses - protein case with some genetic material ( RNA or DNA ) / only reproduce inside a host cell - they attatch themselves, make componenets of the new virus inside, and kill the host releasing the new viruses

Fungi - (yeast) - cell wall, nucleus, yeast is a single celled fungus/ reproduce by budding, used in fermentation to brew alcohol and used in bread making.

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Microorganisms and disease

There are two types of disease; infectious – diseases you can catch caused by pathogens (bacteria and viruses) & non-infectious – cannot catch/ caused by other factors (lifestyle – smoking, your genes or getting older.    Diseases caused by bacteria – food poisoning, cholera, typhoid, leprosy. Diseases caused by viruses – HIV/AIDS, influenza, colds, chicken pox.  Pathogens have antigens on them. These are markers so the immune system recognises different pathogens. Once a pathogen is identified for the first time, the body will have to make new antibodies. Lymphocytes (white blood cells) make these antibodies that attach to the pathogen and destroy it.  Another type of white blood cell is the phagocyte. These engulf the pathogen and destroy them. Some white blood cells released anti-toxins to neutralise toxins released by pathogens.

Vaccines prepare the immune system. When the body meets a disease for the first time it won’t have any antibodies for that disease. A vaccine contains dead or weakened pathogens and stimulates the immune system to make antibodies. Some parents won’t let their children have vaccinations because there was a rumour about autism and the MMR vaccine. Also there could be side effects; however the vaccines are safe for most people and save lives. When the body comes into contact with the same disease again, antibodies will be ready because we have memory cells. These save antibodies for if you have the same disease again and the immune system can fight off the disease quicker, without you developing symptoms.  This is why most people only have chicken pox once in their lifetime. However viruses that cause colds have different antigens as there are lots of different strains so people get colds quite often. Antibiotics are used to kill bacteria. E.g. penicillin.  However some bacteria have become resistant to antibiotics because of over use. It has a mutation making it resistant and breeds. The bacterium that has become resistant survives through natural selection and more bacteria become resistant. MRSA is a bacterium that has become resistant and is called a superbug.  

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Uses of microorganisms

Fermenters are used to grow penicillium from which penicillin is extracted by filtration. Bacteria are used to make yoghurt. Lactobacillus makes lactase which breaks down lactose into lactic acid. The milk is pasteurised by heating it to 78°c and cooled. It is then incubated with a culture of bacteria and flavours and colours added before it’s packaged. Bacteria grow quicker at its optimum temperature of 37°c. Below this temperature the rate of growth is slower and above this temperature, enzymes will be denatured.  Yeast (fungi) is used in the process of fermentation involving anaerobic respiration.  Glucose --> ethanol + carbon dioxide.  It is used to brew alcohol. Frist sugar is extracted by crushing grapes or from barley grains. Then yeast is added. It is kept warm to allow it to ferment and then the wine or beer is clarified before pasteurisation.  The concentration of alcohol made is limited because high concentrations will kill the yeast so distillation is used to increase the concentration for drinks like brandy and whisky.

Food storage – freezing foods will kill some bacteria and stop the growth of others because they won’t have any kinetic energy and won’t be able to move. Chilling foods slows the growth for the same reason. In canning, foods are heated to kill bacteria and then sealed in a vacuum to prevent oxygen and bacteria entering. Drying foods removes water so bacteria can’t feed and grow. Adding salt or sugar uses osmosis to remove water from the bacteria and adding vinegar produces acidic conditions that will kill most bacteria. Microorganisms have an important role in decay. Detritivores (maggots, woodlice and earthworms) feed on decaying matter which increases the rate of decay because there is a bigger surface area for microbial breakdown. Bacteria and fungi cause decay to happen. This is why bacteria can spoil food and spread disease quickly as they reproduce quickly. Saprophytes are fungi that produce enzymes to digest food outside of their cells. They reabsorb simple soluble substances. This is called extracellular digestion.

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Safe microbiology techniques

Everything must be sterilised before use.

An autoclave is sometimes used – a high temperature, pressure cooker.

All work is done near a naked flame so convection currents are set up to carry away bacteria.

Flame metal hoops before taking a sample to sterilise them.

Flame the opening of containers to get rid of bacteria from entrance.

Don’t fully open petri dishes to minimise contamination.

Store petri dishes upside down so if condensation drips, nothing harmful comes out.

Never re-open a petri dish – could have grown something harmful.

Don’t incubate over 25°c because could grow bacteria harmful to humans at 37°c.

Sterilise everything after use.

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