B2 Key Cards


Principles of Organisation

A tissue is a group of similar cells that work together to perform a function e.g muscle tissue is a group of cells that work together to move things.

An organ is a group of tissues that work together to perform a function e.g the heart is a group of tissues that pumps blood.

An organ system is a group of organs that work together to perform a function e.g the circulatory system is made up of the heart and blood vessels - it moves blood around the body.

The order from smallest to largest is cell, tissue, organ, organ system.

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Enzymes Pt. 1

Enzymes are proteins that catalyse chemical reactions in an organism. A catalyst is a substance that speeds up a chemical reaction but isn't changed by the reaction - it can be used over and over again.

The active site is the part of an enzyme that a substrate binds with. A substrate is a thing that an enzyme interacts with - it's a substance in the chemical reaction that the enzyme catalyses.

An enzyme's active site is a specific shape. Only certain substrates fit the active site, so an enzyme can only catalyse specific reactions.

Lock and key model of enzyme action: only a substrate that exactly fits an enzyme's active site can bind to the enzyme. Once a substrate binds, the enzyme catalyses the reaction.

An alternative model is the induced fit model - the active site changes shape to tightly bind to a substrate that's roughly the right shape.

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Enzymes Pt. 2

When an enzyme is denatured, its active site changes shape. This means the substrate won't fit the active site any more, so the enzyme can't catalyse any more reactions. The rate of an enzyme-catalysed reaction decreases if the enzymes denature.

As temperature increases, the rate of an enzyme-catalysed reaction increases. If the temperature gets too high, enzymes denature and the rate of reaction increases.

Particles have more kinetic energy at higher temperatures. So at higher temperatures, particles collide more frequently and with more force, making reactions more likely to happen - this increases the rate of reaction.

The temperature and pH at which an enzyme works best are the enzyme's optimum temperature and optimum pH. The rate of an enzyme-catalysed reaction is highest at the enzyme's optimum temperature and pH.

Enzymes are denatured by high temperatures and a pH value that's too high or too low.

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Enzymes Pt. 3

The effect of pH on amylase activity can be investigated by comparing how long it takes amylase to fully break down a sample of starch solution at different pH levels.

In the presence of starch, iodine solution changes from orangey to blue-black. Continually sampling the reaction and testing with iodine solution will show when there's no starch left (i.e when the iodine solution stays orangey).

Method for investigating the effect of pH on amylase activity: put a drop of iodine solution in each well of a spotting tile. Add 2cm cubed of starch solution and 2cm cubed of pH 5 buffer solution to a test tube in a water bath at 35 degrees. After 10 minutes, stir in 2cm cubed of amylase solution and start timing. Take a drop from the test tube every 20 seconds and put it in a well - repeat until the iodine solution stays orangey and record the time passed.

Repeat the experiment with a range of pH buffer solutions.

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Digestion & Enzymes Pt. 1

Organs in the digestive system include the oesophagus, salivary glands, liver, gall bladder, small intestine, stomach, pancreas and large intestine.

Digestive enzymes break down large food molecules into smaller, soluble molecules that can be absorbed into the blood. The products of digestion are used to make new proteins, carbohydrates and lipids, Some of the glucose made in digestion is used in respiration.

Carbohydrases are digestive enzymes that catalyse the breakdown of carbohydrates into simple sugars e.g amylase.

Amylase catalyses the breakdown of starch into simple sugars such as glucose and maltose.

Amylase is produced in the salivary glands, the small intestine and the pancreas.

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Digestion & Enzymes Pt. 2

Proteases catalyse the breakdown of proteins into amino acids.

Proteases are produced in the stomach (called pepsin) and in the pancreas.

Lipases catalyse the breakdown of lipids (fats) into fatty acids and glycerol.

Lipases are produced in the mouth, the stomach and the pancreas.

Bile is produced in the liver and it's stored in the gall bladder. Bile is released from the gall bladder into the small intestine during digestion.

During digestion, food that's mixed with hydrochloric acid passes from the stomach into the small intestine. Bile is an alkaline substance that neutralises the acid so the digestive enzymes in the small intestine can function at their optimum pH.

Bile emulsifies fats. This means it turns fats into very small droplets. This creates a large surface area for lipase to act on, increasing the rate of lipid breakdown by lipase.

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Food Tests

Testing a food sample for sugars: heat a water bath to 80 degrees. Put the food sample in a test tube and add a few drops of Benedict's solution. Put the test tube in the water bath for around 5 minutes. If sugars are present, the solution changes from blue to green (some sugar), yellow, or brick red (lots of sugar).

Testing a food sample for starch: put the food sample in a test tube. Add a few drops of iodine solution to the test tube. If starch is present, the solution changes from orangey to blue-black.

Testing a food sample for protein: put the food sample in a test tube. Add 2cm cubed of Biuret solution. Gently shake the test tube. If protein is present, the solution changes from blue to violet or purple.

Testing a food sample for lipids: put the sample in a test tube with some distilled water. Add a few drops of ethanol OR a few drops of Sudan III stain to the test tube. Gently shake the test tube. If lipids are present, a cloudy emulsion forms (ethanol) OR a separate red layer forms at the top (Sudan III).

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The Lungs

The thorax is the top part of your body, separated from the lower part by the diaphragm.

The lungs are like big pink sponges and are protected by the ribcage.

The air you breathe goes through the trachea.

This splits into two tubes called bronchi (the individual is a bronchus), with one bronchus going to each lung.

The bronchi split into progressively smaller tubes called bronchioles.

The bronchioles finally end at small bags called alveoli, where gas exchange takes place.

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The Heart Pt. 1

Parts of the heart include the right and left ventricle, the right and left atrium, the pulmonary artery and vein, the vena cava and the aorta.

There are four valves in the heart. Valves stop blood from flowing in the wrong direction.

Circuits of a double circulatory system: deoxygenated blood is pumped by the heart to the lungs where it gains oxygen and loses carbon dioxide - oxygenated blood flows back to the heart. Oxygenated blood is pumped by the heart to the rest of the body where it loses oxygen and gains carbon dioxide - deoxygenated blood flows back to the heart.

The vena cava carries deoxygenated blood from the body to the heart. Deoxygenated blood from the body contains little oxygen but lots of carbon dioxide.

The right ventricle contracts to pump deoxygenated blood to the lungs via the pulmonary artery. Pulmonary just means 'relating to the lungs'.

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The Heart Pt. 2

When deoxygenated blood is pumped to the lungs it flows through the capillary network around the alveoli and gas exchange happens; oxygen diffuses out of the alveoli into the blood, and carbon dioxide diffuses out of the blood into the alveoli. Breathing in fills alveoli with oxygen-rich air, and breathing out expels air with lots of carbon dioxide.

The pulmonary vein carries oxygenated blood from the lungs to the heart.

The left ventricle contracts to pump oxygenated blood to the body via the aorta.

The coronary arteries supply the heart muscle with oxygenated blood. The coronary arteries branch off from the aorta.

A group of cells in the right atrium act as a pacemaker and control a person's resting heart rate. The pacemaker cells generate electrical impulses that cause heart muscle cells to contract.

An irregular heart rate can be corrected with an artificial pacemaker. An artificial pacemaker is a device that generates electrical impulses to regulate a person's heart rate.

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The main components of blood are red and white blood cells, platelets and plasma. Blood is a tissue - it's a group of similar cells that work together.

Red blood cells carry oxygen around the body. They contain haemoglobin, a protein that binds oxygen. They don't have a nucleus so more haemoglobin can fit in. Their biconcave shape gives a large surface area for oxygen absorption and flexibility for fitting in tiny capillaries.

White blood cells help to protect the body against infection. Different types of white blood cell deal with pathogens in different ways - some ingest pathogens, some produce antibodies or antitoxins.

Platelets are just small cells. They prevent bleeding by helping blood to clot.

Plasma is a liquid that carries everything found in blood.

Things carried by plasma in blood: red blood cells, white blood cells, platelets, carbon dioxide, proteins, hormones, urea and dissolved nutrients (e.g glucose and amino acids).

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Blood Vessels

Arteries carry high pressure blood away from the heart. They have thick muscular walls to withstand high pressure. They have elastic fibres so they can stretch under pressure then recoil to push blood along. They have a narrow lumen to maintain a high pressure.

Capillaries carry blood close to cells so substances can be exchanged. They have very thin walls so substances diffuse over a short distance, improving the rate of diffusion. They have permeable walls that let substances in and out.

Veins carry low pressure blood to the heart. They have valves to stop blood flowing in the wrong direction. They have a large lumen to allow blood to flow easily.

The walls of veins are thinner than the walls of arteries - veins don't have to withstand high pressure.

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Coronary heart disease is when layers of fatty material build up in coronary arteries and narrow them, reducing blood flow through them and so reducing the supply of oxygen to heart muscle. It can cause heart attacks.

Stents are used to hold open the coronary arteries of people with coronary heart disease. This improves blood flow in the coronary arteries and so improves the supply of oxygen to heart muscle, reducing the risk of a heart attack.

Advantages of stents: short recovery time after surgery, can quickly have a positive effect and they can stay in place and work for a long time.

Disadvantages of stents: surgery comes with a risk of infection, surgery complications (e.g heart attack) and blood clots can form inside stents and cause heart attacks.

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Statins are drugs that can reduce the level of cholesterol in the blood, which slows the build-up of fatty materials in arteries.

Statins are used to help prevent coronary heart disease and reduce the risk of a heart attack in people with coronary heart disease.

Advantages of using statins: they're taken as pills (no surgery) and they can reduce the risk of strokes and heart attacks as well as coronary heart disease.

Disadvantages of using statins: they take weeks to lower blood cholesterol, you have to remember to take them regularly for the rest of your life and there are possible side effects (e.g aching muscles).

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Heart Valves

Heart valve faults: valve doesn't open fully (the heart works harder to pump blood through the faulty valve) or the valve becomes leaky (blood can flow in the wrong direction, so the heart works harder to maintain blood flow.

Faulty heart valves can be replaced with biological valves made from animal tissue or mechanical valves made from synthetic materials.

Blood clots are less likely to form on biological replacement heart valves than mechanical ones.

People with mechanical valves take drugs to stop their blood clotting for the rest of their life. This reduces the risk of clots forming and causing heart attacks and strokes, but it also means they can bleed a lot from cuts and other injuries.

Mechanical replacement heart valves usually last longer than biological ones, so they don't need replacing as often. Replacing a valve requires surgery, which has risks.

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Artificial Hearts

An artificial heart might be given to someone if they're waiting for a heart transplant (it could help to keep them alive until a donor's heart becomes available) or if their heart needs to rest and heal (e.g recover after heart failure).

Advantages of artificial hearts: they can help improve a patient's general health, making a heart transplant more likely to succeed, and they give patients more time to do things like spend time with family.

Disadvantages of artificial hearts: they're not a permanent solution, there is a risk of blood clots forming in an artificial heart which could cause a stroke and surgery is needed to fit an artificial heart which risks infection and complications.

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Health & Disease

Health is the state of physical and mental wellbeing. Factors that can cause ill health: disease, poor diet, stress and life situations. Life situations that can have a negative impact on physical and mental health are things like poor education, low income and a lack of support. Communicable diseases can spread between organisms, e.g HIV. Non-communicable diseases can't spread between organisms, e.g coronary heart disease.

Ways that diseases can interact: people with weaker immune systems are more likely to get communicable diseases, some viruses can trigger some types of cancer, severe physical health issues can cause mental health issues and immune responses to pathogens can trigger rashes and asthma.

Human costs of con-communicable diseases: millions of people die from them, they can reduce people's lifespan, and they can lower your quality of life.

Health organisations all over the world spend vast amounts of money diagnosing and treating non-communicable diseases. They can cause people to miss work or give it up completely.

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Risk Factors

Risk factors are things that are linked to an increased chance of a person developing a certain disease. They are aspects of lifestyle or substances in the body or environment.

Some risk factors cause diseases, but not all do (e.g smoking is a risk factor for lung cancer that has been proven to cause disease, while a lack of exercise is a risk factor for coronary heart disease but not a direct cause).

Risk factors for coronary heart disease: smoking, a lack of exercise, and a high-fat diet.

Obesity is a risk factor for type 2 diabetes. Someone is classed as obese if they are very overweight and have a lot of body fat.

Drinking alcohol is a risk factor for liver disease, lowered brain function and health problems in unborn babies.

Smoking is a risk factor for lung cancer, lung disease (e.g emphysema), coronary heart disease and health problems in unborn babies.

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Cancer Pt. 1

Carcinogens are things that cause cancer. They can be substances (e.g asbestos) or ionising radiation (e.g UV rays and X-rays).

Tumours are masses of cells formed when cells grow and divide uncontrollably. Not all tumours are cancers. Cells can grow and divide uncontrollably if they're changed in some way (e.g if they are damaged by ionising radiation).

Benign tumours are masses of cells that stay in one part of the body - they don't invade tissues around them or spread to other parts of the body. Benign tumours are not cancers. They are usually contained within a membrane.

Malignant tumours are masses of cells that can invade tissues around them and spread to other parts of the body. Malignant tumours are cancers.

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Cancer Pt. 2

Cells can break off from malignant tumours and enter the bloodstream, spreading them around the body - these cells can then form secondary tumours.

A secondary tumour is a new cancer growth away from the original malignant tumour. Cancers become more dangerous if tumours spread around the body.

Example lifestyle risk factors for cancers: obesity (breast and bowel cancer), smoking (lung cancer) and exposure to UV rays (skin cancer).

There are genetic risk factors for some cancers - people with certain genes are more likely to develop breast or ovarian cancer.

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Plant Leaves & Tissues

A plant leaf is an organ - a leaf is made up of several tissues that work together. Parts of a leaf include upper and lower epidermal tissue, palisade mesophyll tissue, spongy mesophyll tissue, phloem, xylem, and guard cells surrounding the stomata.

Plant epidermal tissue has tightly packed cells to form a protective layer over the plant. It is transparent to let light reach the tissues where photosynthesis occurs and it has a waxy cuticle to reduce water loss.

Palisade mesophyll tissue is tightly packed with cells containing lots of chloroplasts so it can host photosynthesis when it occurs. Spongy mesophyll tissue has loosely packed cells surrounded by air spaces to allow gases to diffuse in and out of cells for photosynthesis.

Xylem is made up of hollow tubes to transport water and mineral ions from the roots to the leaves, and it's strengthened with lignin for support. Phloem is made up of elongated cells with pores in the end walls, to transport dissolved sugars from the leaves to the rest of the plant for use or storage.

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Transpiration & Translocation

Transpiration is the loss of water vapour from a plant's surface by evaporation and diffusion. It mostly happens at a plant's leaves.

Translocation is the movement of food (dissolved sugars) and other substances through a plant's phloem tissue.

Transpiration at a plant's leaf: water evaporates from spongy mesophyll cells into the air spaces that surround the cells. The water vapour diffuses through open stomata into the air around the leaf.

Transpiration stream is the continuous movement of water into a plant through its roots, through its xylem tissue and out of its leaves.

The transpiration stream: water is lost at the leaves by transpiration. To replace the lost water, water is drawn out of the xylem into the leaves. Root hair cells draw in water from the soil by osmosis to replace the water in the xylem. Each step happens continuously.

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Transpiration Pt. 2

As light intensity increases, the rate of transpiration increases. This is because stomata open as the light intensity rises, increasing the amount of water lost by transpiration. Photosynthesis can't happen without light, so plants don't need carbon dioxide at night - plants close their stomata at night to prevent losing water for no benefit. 

As temperature increases, the rate of transpiration increases. This is because water molecules have more kinetic energy at higher temperatures, so more water molecules evaporate and diffuse out of a plant in a given time compared to at lower temperatures.

As humidity decreases, the rate of transpiration increases. This is because at low humidity the concentration gradient of water between a plant and the air around it is greater than at high humidity - so the rate of diffusion is higher.

As air flow increases, the rate of transpiration increases. This is because when more air flows around a plant, more water vapour is carried away from around the plant. This keeps a concentration gradient of water between a plant and the air around it, so the rate of diffusion is higher than if the air was still.

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Stomata & Guard Cells

Stomata are little openings in a plant's epidermal tissue (usually lower layer). Plants have stomata so they can exchange gases with their environment for photosynthesis. Air with lots of carbon dioxide diffuses through the stomata into a plant's spongy mesophyll tissues - the carbon dioxide is used to make glucose via photosynthesis. Air with lots of oxygen diffuses out through the stomata into the environment. 

Guard cells are cells that surround the stomata in a plant's epidermal tissue. A pair of guard cells surround each stoma. A plant's guard cells open and close the stomata to control gas exchange and water loss from the plant. A plant needs to open its stomata so it can exchange gases during photosynthesis, but water vapour is lost through the stomata at the same time. If the stomata were always open, the plant would lose too much water to survive - so the guard cells open and close them as needed.

To open a plant's stomata, guard cells fill with water and become turgid, which makes them bend apart. To close a plant's stomata, guard cells lose water and become flaccid, which makes them come together. The amount of water in guard cells is affected by things like light intensity and how much water and carbon dioxide is in the plant.

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