Biology - EDEXCEL IGCSE - Gaseous Exchange

Gaseous Exchange

Lungs:

 

During inhalation the external intercostal muscles contracts and the internal relaxes which pushes the ribs up and out. Apart from this, the diaphragm contracts, puling the diaphragm down and flat. All this creates a high volume in the chest (thorax) and therefore low pressure. This causes air to be pulled into the lungs as there is higher pressure outside. During exhalation, the opposite happens meaning the ribs are pulled down and in and the diaphragm goes back to a dome shape. This creates high pressure which pulls the air out of the lungs.

Adaptations of alveoli	Advantages
Large surface area	This allows for faster diffusion as more particles can diffuse across the membrane at one time.
Good blood supply	Maintains a steep concentration gradient between alveoli and the blood capillaries.
Walls one cell thick	Creates a short diffusion pathway.
Moist	Increases the rate of oxygen diffusion as it dissolves.

Diseases from smoking:

1.    Emphysema - chemicals from cigarettes damage the elastic tissue in the lungs, reducing the surface area of the alveoli and therefore the speed and mount of oxygen it absorbs.

2.    Lung cancer - carcinogenic chemicals in cigarette tar causes cancer.

3.    Bronchitis - cigarette smoke paralyses cilia in the trachea meaning phlegm and microbes enter the lungs, this can cause infections.

4.    Heart disease - nicotine in the cigarettes leads to the hardening and narrowing of blood vessels. This can lead to heart attacks.

5.    Lethargy - cigarette smoke contains carbon monoxide which means less oxygen are carried around the body.

6.    Nervousness - cigarettes contain nicotine which is addictive so withdrawal symptoms occur when one is not smoking.

Investigating the effects of exercise on breathing:

1.    Breath into a double bubbler with limewater or bicarbonate indicator for twenty seconds.

2.    Do vigorous exercise for three minutes.

3.    Repeat step one with new double bubbler.

After exercise the limewater is usually cloudier and the indicator should be more yellow. This is because your breathing is more concentrated in carbon dioxide and also because the breathing rate is high after exercise.

Effects of exercise:

1.    Muscles need more energy so breathing rate increases to supply more oxygen for respiration and to oxidise carbon dioxide.

2.    Heart rate increases to pump more oxygen around the body and faster.

3.    Arterioles widen to stop blood pressure from increasing.

4.    Blood diverted from inactive organs (e.g. stomach/liver) towards muscles through vasodilation and constriction

Biology - EDEXCEL IGCSE - Nutrition

Nutrition:

In Plants:

Photosynthesis occurs in plant chloroplasts and is a process where carbon dioxide and water, when there is light, chemically react to form glucose and oxygen. This occurs as light energy is converted to chemical energy, allowing for the reaction to occur.

Testing a leaf for starch:

If there is starch present in the leaf then the plant has been photosynthesising as one of the products of photosynthesis is glucose which is converted to starch for storage.

1.    Boil leaf in water for 2-3 minutes. This is to stop any more reactions such as photosynthesis by denaturing the enzymes. It also opens up all the cell membranes for starch to come out or iodine to go in.

2.    Switch of bunsen burner. Soak leaf in ethanol for 2-3 minutes. The bunsen burner was switched off as ethanol is highly flammable. Ethanol is used to remove chlorophyll, making the leaf milky white and so easier to see what colour the iodine is.

3.    Soak leaf in warm water for 2-3 minutes. This is to soften the lead to allow it to be spread out. It also removes the ethanol.

4.    Spread leaf on a white surface and add 2-3 drops of iodine. It is spread out on the white surface to make the results easier to see. The iodine will turn from red-orange to blue-black if iodine is present.

Release of oxygen in aquatic plants experiment:

1.    Slit the top of the elodea plant used.

2.    Place under funnel in breaker of sodium hydrogen carbonate aqueous solution.

3.    Place measuring cylinder filled with water over funnel after a few minutes and when the elodea plant starts to bubble.

4.    Wait for 1 minute.

5.    Measure how much water has been displaced.

6.    This will give you a result in cm³ / min

7.    You can change factors such as temperature, light intensity, light wavelength and concentration of CO2 to see how this affects the rate of oxygen production.

Factors affecting the rate of photosynthesis:

1.    Temperature - this is related to enzymes. If the temperature is closer to optimum temperature then the rate pf photosynthesis will be higher.

2.    Light intensity - this relates to the light energy that is provided.

3.    Light wavelength - chlorophyll is green so green light will be reflected.

4.    CO2 concentration - this is a requirement for photosynthesis.

5.    Number of chloroplasts - the more chloroplasts available the more light can be absorbed.

Leaf structure and their adaptations:

•    Cuticle - a waxy surface that means water does not congregate on a leaf and therefore means it does not block the light.

•    Upper epidermis - they contain no chloroplasts meaning they are transparent and so allow light to pass through. They are also thin.

•    Palisade cells (mesophyll) - they are long to provide more space for chloroplasts and a large surface area. They are also arranged vertically to stop light refraction away from the chloroplasts.

•    Spongy cells (mesophyll) - they contain air spaces to keep gases and to allow circulation of gases. They also have a circular shape, meaning a large surface area.

•    Xylem, Phloem tubes - there are many of these so that they’re always close to bring water and minerals and to take away sugars.

•    Lower epidermis - contain stomata and guard cells to allow a controlled intake and removal of gases.

A stoma is controlled by 2 guard cells which open and close it. It allows for CO2 to diffuse in and oxygen and water vapour to diffuse out. Stomata is used to get rid of carbon dioxide and oxygen which are created as waste products from metabolism.

When respiration > photosynthesis:

•    CO2 outtake > CO2 intake

•    oxygen intake > oxygen outtake

When photosynthesis > respiration:

•    CO2 intake > CO2 outtake

•    oxygen outtake > oxygen intake

Effects of light intensity of gas exchange:

1.    Wash some pondweed to get rid of small organisms that might respire such as snails.

2.    Place then in 3 test tubes.

3.    Add some equalibrated hydrogen carbonate solution. It was equalibrated to show the surrounding air had normal CO2 concentration.

4.    Place 2 test tube in bright light, 1 in dim and 1 in the dark.

5.    A fourth test tube without the pondweed should be placed in bright light.

6.    After 10 minutes, see what colour the hydrogen carbonate solution is.

Colours of hydrogen carbonate solution:

•    Orange - normal CO2

•    Yellow - Extra CO2

•    Purple - Less CO2

In Humans:

Balanced Diet: eating foods on a regular basis that provide all the right nutrients (carbs, lipids, protein, minerals, vitamins, water and fibre) in the right amount and proportion for the person to remain healthy.

Your diet will change according to your age, whether you’re pregnant, climate and occupation. Your energy requirement will also change according to your activity, age and whether you’re pregnant.

Digestive System:

1.    Mouth - food is ingested, and broken down by the teeth and tongue. Saliva is secreted by the salivary glands which begins the digestion of starch.

2.    Oesophagus - helps food move to the stomach through peristalsis.

3.    Stomach - a muscular bag where food is mixed with hydrochloric acid and pepsin. The acid is used to sterilise the food and create the optimum pH for pepsin to break down protein.

4.    Pancreas - produces pancreatic juices which contains digestive enzymes and hydrogen carbonate which is used to neutralise stomach acids to create the optimum pH for these enzymes to work.

5.    Small Intestine - contains the duodenum where food is mixed with bile and pancreatic juices and the ileum where enzymes complete digestion and digested food is absorbed.

6.    Large Intestine - contains the colon where water and also some vitamins and minerals is absorbed from undigested food. Also contains the rectum which stores undigested faeces.

Nutrient	Where from	Function	Illnesses
Carbohydrates	dessert, table sugar	Needed for respiration to supply energy for cells.	Dental caries such as toothache
Protein	red meats, nuts	Growth, repair and maintenance of cell issue.	Kwashiorkor which causes weakness and tiredness and also a swollen abdomen.
Lipids	butter, eggs	Long term stored energy and insulation.	Coronary heart disease such as angina and heart attacks.
Vitamin A	butter, carrots	Needed for rod and cone cells in the retina.	Nyctalopia - night blindness
Vitamin C	fruit, vegetables (e.g. broccoli)	To make connective tissue that bonds cells together.	Scurvy - bleeding gums
Vitamin D	sunlight, fish liver oil	Needed to take in calcium.	Rickets - deformation of bones
Calcium	dairy, bread	Needed to make teeth and bones.	Rickets - deformation of bones
Iron	eggs, spinach	Helps carry oxygen in haemoglobin.	Anaemia - pale and tired
Fibre	bread, cereal	Allows for the muscles in the gut to have something to push against.	Constipation - infrequent and painful bowel movements
Water	water, fruit	Transports materials and maintains the turgidity of cells.	Dehydration

Bile: produced in the liver, stored in the gall bladder and released into the duodenum. It is used to emulsify/breakdown fats from globules into an emulsion of tiny droplets, giving a larger surface area to volume ratio for lipase to act on. It also neutralises the food.

Peristalsis: a series of muscle contractions that occurs in the gut. When the circular muscle contracts and the longitudinal muscles relaxes the gut narrows. A rhythmic series of narrowing and widening of the gut wall causes the food to be pushed along. Peristalsis needs fibre to work efficiently as this gives the gut something to push against in order to move the food along.

Digestive Enzymes:

Amylase - breaks down starch into maltose. Created in the salivary glands, pancreas and the wall of the gut.

Maltase - breaks down maltose into glucose. Created in the salivary glands, pancreas and the wall of the gut.

Proteases - pepsin and trypsin breaks down proteins into peptides. Peptidases breaks down peptides into amino acids. Both are produced in the stomach wall, pancreas and gut wall.

Lipase - this breaks down lipids into glycerol and fatty acids. Produced in the pancreas.

Feature of the villus	Advantage
Has microvilli	Increases surface area to volume ratio, thereby increasing the rate of diffusion, allowing food to be absorbed quickly.
Circular shape	Again increases surface area to volume ratio.
Steady supply of blood	Maintains a steep concentration gradient.
Epithelium cell only one cell thick	Creates a short diffusion pathway, thereby creating a faster diffusion rate.

Experiment to find energy content of food:

1.    Clamp test tube with 20ml of water and record the temperature.

2.    Set the food alight with a bunsen burner and place the food under the water, relight it if it goes out.

3.    When the food cannot be relit, record the new temperature of the water.

Energy content = (mass of water * temperature change * 4.2) / mass of food

Respiration:

The process of respiration is used to release energy in living organisms. Without respiration energy would not be supplied and therefore many vital functions such as muscle contraction could not occur.

Aerobic respiration - is the respiration which occurs in the presence of oxygen

Anaerobic respiration -  is the respiration which occurs not in the presence of oxygen.

Biology - EDEXCEL IGCSE - Living Organisms

The Biology course is very similar to the Human Biology course we have already covered. Because of this the notes I post will be very similar.

The Nature and Variety of Living Organisms:

Characteristics of living organisms:

•    Require nutrition

•    Respire

•    Excrete their waste

•    Respond to external stimuli

•    Move

•    Control their internal conditions

•    Reproduce

•    Grow and develop

Features of plants:

•    Multicellular organisms

•    Their cells contain chloroplasts and therefore they photosynthesise

•    Have cellulose cell walls

•    Store carbohydrates such as starch or sucrose

•    Examples include maize, peas, beans etc…

Features of animals:

•    Multicellular organisms

•    Their cells don’t contain chloroplasts and so don’t photosynthesise

•    Have no cell walls

•    Usually have nervous coordination

•    Are able to move from one place to another

•    Often store carbohydrates such as glycogen

•    Examples include humans, houseflies and mosquitos

Features of Fungi:

•    Cannot photosynthesise

•    Organised into mycelium made from thread like structures called hyphae which contain many nuclei.

•    Some are single celled.

•    Cell walls made of chitin

•    Fed by extracellular secretions of digestive enzymes on to food material and absorption of the organic product.

•    May store carbohydrates and glucagon

•    Examples include yeast.

Features of Bacteria:

•    Microscopic single celled organisms

•    Lack a nucleus but contain circular chromosomes of DNA called plasmids. Also has cell wall, membrane and cytoplasm.

•    Most feed of other organisms. Some photosynthesise.

•    Examples include pneumococcus, lactobacillus bulgaricus etc…

Features of Protoctists:

•    Microscopic single celled organisms

•    Examples include amoeba, chlorella and plasmodium.

Features of Viruses:

•    Smaller than bacteria; parasitic; only reproduce inside living cells.

•    Wide variety of shapes and sizes; no cellular structure.

•    Have a protein coat and contain one type of nucleic acid, DNA or RNA.

•    Examples include influenza, HIV and tobacco mosaic.

Features of pathogens:

•    Something that causes diseases.

•    Can be fungi, bacteria, protoctist, or virus.

Structures and functions in living organisms:

Levels of organisation:

Specialised cells that perform similar functions are grouped together as tissues:

There are many types of tissues:

1.    Bones - collection of cells that secrete calcium salts.

2.    Muscle - these can be voluntary, involuntary or also cardiac.

3.    Blood - collection of red and white blood cells.

4.    Nervous tissue - makes up the brain, nerves and spinal cord.

5.    Epithelium - these are tissues that line organs. They can be both squamous or ciliated.

Tissues that perform the same function are grouped together to form organs. e.g. Heart.

Organs that perform the same function are grouped together to form organ systems. e.g. The circulation system

Organ systems are grouped together to form organisms. e.g. Humans.

Cell Structure:

The main differences between a plant cell and an animal one is the lack of certain organelles such as a permanent vacuole, cell wall and chloroplasts. Apart from this plant cells also have a more regular structure.

The Functions of the parts of the cell:

Nucleus: contains chromosomes (46 in humans) which carry the genetic information. It controls the activity of the cell by controlling which proteins the cell will synthesise.

Cytoplasm: this is where chemical reactions occur.

Cell membrane: this controls what substances can pass in and out of the cell. It is selectively permeable.

Cell wall: this protects the cell and helps support itself.

Chloroplasts: these are needed for photosynthesis to take place in plants.

Mitochondria: this carries out some of the reactions in respiration.

Vacuole: filled with cell sap which contains nutrients. It is also used for cell structure and support.

Biological Molecules:

Carbohydrates:

1.    Contain the elements Carbon, Hydrogen and Oxygen.

2.    Are split into groups polysaccharides (e.g. starch), disaccharide (e.g. sucrose) and monosaccharides (e.g. glucose).

3.    The test for starch involves iodine. If it changes colour from red-orange to blue-black then starch is present.

4.    The test for glucose involves Benedict's Reagent. If, when placed in heat, the solution turns from blue to brick-red then glucose is present.

Protein:

1.    Contain the elements Carbon, Hydrogen, Oxygen and sometimes Sulfur.

2.    Made of subunits called amino acids.

3.    The test for protein involves the use of a biuret solution (Sodium Hydroxide and Copper Sulphate). If the solution goes from blue to pink-purple then protein is present.

Lipids:

1.    Contain the elements Carbon, Hydrogen and Oxygen.

2.    Made of a molecule of Glycerol and three fatty acids.

3.    The test for lipids involves the use of ethanol. If when mixed the solution goes cloudy then lipid is present.

Enzymes are biological catalysts meaning that they are organic molecules that speed up reactions but remain unchanged. The lock and key model is used to describe the actions of enzymes. Enzymes have an active site which the substrate (reagent) fits into. After the enzymes catalyses the reaction it's then free to go elsewhere. Because of the varying shapes of the enzymes and substrates, only one type of enzyme can "fit" a substrate, they are, therefore, specific. Enzymes are used to catalyse metabolic reactions.

Enzymes are affected by temperature. The rate of reaction increases as temperature increases as there is more kinetic energy supplied which means more collisions occur between the enzymes and substrates. However, after the optimum temperature the rate of reaction falls as the enzymes are being denatured which means the active site is changed. Enzymes are also affected by pH. If the optimum pH is not reached the active site is once again changed.

Experiment to show enzyme activity with temperature:

1.    Place test tubes of amylase and another with starch in a water bath.

2.    After five minutes mix.

3.    Take sample and test with iodine.

4.    Do this every thirty seconds until the iodine turns blue-black.

5.    Repeat the experiment changing the temperature of the water bath to 20, 30, 40, 50, 60 °C

The movement of substances into and out of cells:

Diffusion - the next movement of particles from an area of high concentration to low concentration down a concentration gradient.

Osmosis - the movement of water molecules from an area of high water potential to an area of low water potential through a partially permeable membrane.

Active transport - the movement of particles against a concentration gradient using energy from respiration and carrier proteins.

The movement of substances into and out of cells can be through diffusion, osmosis and/or active transport.

The movement of substances in plants is essential to create turgid (firm) cells which are needed for support. Without turgid cells, the plants would wilt.

Factors affecting rate of movement:

1.    A high concentration gradient will increase the rate of movement.

2.    A high temperature will increase the rate of movement as there is more energy meaning more kinetic energy is present. This means the particles move faster.

3.    A large surface area to volume ratio will increase the rate of movement as there is more area for the particles to move across.

Experiment for diffusion:

1.    Cut potassium permanganate agar jelly cubes into cubes of length 0.5, 1, and 2 cm.

2.    Place cubes of jelly at the same time into three beakers containing 75ml hydrochloric.

3.    Record the amount of time it takes for the jelly to go from the dyed purple colour to colourless.

Experiment for osmosis:

1.    In three test tubes, pour in one 10ml of distilled water, one 10ml 0.85% salt solution and one 10ml 3% salt solution.

2.    Add 1ml of fresh blood to each test tube and shake.

3.    Look at the sample of each under a microscope.

4.    No red blood cells should be seen in test tube one as lysis has occurred. Normal red blood cells should be shown in test tube two and shrunken red bloods cells should be present in test tube three (flaccid and plasmolysed).

Experiment for both diffusion and osmosis:

1.    Fill visking tubing with a substance.

2.    Place in beaker containing the substance but in different concentrations.

3.    The amount of substance in each should change.