Gas exchange in Humans

2.38 understand the role of diffusion in gas exchange

In humans, gas exchange happens all the time in the lungs. The oxygen diffuses from the alveoli into the blood and carbon dioxide from the blood into the alveoli-the carbon dioxide is then exhaled.  This is actually a form of excretion would you believe it, as carbon dioxide is a metabolic waste product from respiration. 

2.44 describe the structure of the thorax, including the ribs, intercostal muscles, diaphragm, trachea, bronchi, bronchioles, alveoli and pleural membranes

So your thorax is the part of your body that lies between your neck and your abdomen (around your stomach), and it includes all of the above. They are vital for gas exchange.

So air usually enters your body through your nose-through your two external nostrils whose walls bear a fringe of hairs. The nostrils lead into two nasal passages which are lined with moist mucous membrane. Breathing through the nose has the following advantages:

• Dust and foreign particles, including bacteria in the air, are trapped by the hairs in the nostrils as well as by the mucus on the mucous membrane.
• As air passes through the nasal passages, it is warmed and moistened before it enters the lungs.
• Harmful chemicals may be detected by small sensory cells in the mucous membrane.

The air in your nasal passages enters the pharynx, then to the larynx, and then into your trachea. The trachea lies in front of your oesophagus. It extends downwards from the larynx into the chest cavity. The lower end of the trachea divides into two tubes, the bronchi (singular: bronchus), one to each lung. Each bronchus divides repeatedly and ends in very small, fine bronchioles. Each bronchiole ends in a cluster of air sacs called alveoli. 

Each lung lies in the pleural cavity, within which the lung expands. The pleural cavity is lined by two transparent elastic membranes called the pleura (singular: pleuron) or pleural membranes. The inner pleuron covers the lung. The outer pleuron is in contact with the walls of the thorax and the diaphragm. A thin layer of lubricating fluid between the pleura allows the membranes to glide over each other easily when the lungs expand and contract during breathing. 

Within the lungs, the bronchial tubes divide repeatedly, giving rise to smaller tubes called bronchioles as mentioned earlier. They each end in a cluster of air sacs or alveoli (singular: alveolus). Thousands of alveoli are found in the lungs, providing a very large surface area for gas exchange. 

Fun fact! 

The total surface area of the alveoli in both lungs has been estimated to be equal to the surface area of a tennis court! That is 50 times more than the whole area of the skin. 

Your chest wall is supported by the ribs. They are attached dorsally to the backbone in such a way that they can move up and down. The ribs are attached ventrally to the chest bone or sternum. Two sets of muscles, the external and internal intercostal muscles, can be found between the ribs. They are antagonistic muscles. When the external intercostal muscles contract, the internal intercostal muscles relax and vice versa.

The diaphragm, which is a dome-shaped sheet of muscle and elastic tissue, separates the thorax from the abdomen. When the diaphragm muscles contract, the diaphragm flattens downwards and whey they relax, the diaphragm arches upwards again. 

2.45 understand the role of intercostal muscles and the diaphragm in ventilation

During inhalation/inspiration:

• Your diaphragm contracts and flattens.
• Your external intercostal muscles contract while your internal intercostal muscles relax.
• Your ribs move upwards and outwards. Your sternum also moves up and forward.
• The volume of your thoracic cavity increases.
• Air pressure in your lungs causes them to expand to fill up the enlarged space in your thorax.
• Expansion of your lungs causes the air pressure inside them to decrease. 
• Atmospheric pressure (pressure of air outside) is now higher than the pressure within your lungs. This causes air to rush into your lungs from outside.

During exhalation/expiration:

• Your diaphragm relaxes and arches upwards. 
• Your internal intercostal muscles contract while your external intercostal muscles relax.
• Your ribs move downwards and inwards. Your sternum also moves down to its original position.
• The volume of your thoracic cavity decreases.
• Your lungs are compressed and air pressure inside them increases as the volume decreases. 
• Air pressure within the lungs is now higher than atmospheric pressure. The air is forced out of your lungs to the exterior. 

Here's my easy way of remembering what happens to your intercostal muscles when you are breathing:

RICE and ERIC

When you inhale, you...

Relax your 

Internal intercostal muscles and

Contract your 

External intercostal muscles

When you exhale, your...

External intercostal muscles

Relax and your 

Internal intercostal muscles

Contract

2.46 explain how alveoli are adapted for gas exchange by diffusion between air in the lungs and b

Respiration

2.33 recall that the process of respiration releases energy in living organisms

Just recall this. Energy is locked up in food molecules such as glucose. Living organisms release energy by breaking these molecules down. Without respiration, you wouldn’t have energy to do all your physical activities and survive. 

Plants and most animals, including humans, respire aerobically. These complex organisms need a lot of energy to survive. Some examples of energy-consuming processes in organisms are:

• The synthesis of proteins from amino acids
• Cell division
• Muscular contractions such as heartbeats and respiratory movements
• Active transport in the absorption of food substances by the small intestine
• Transmission of nerve impulses or messages

2.34 describe the differences between aerobic and anaerobic respiration

Aerobic respiration is with oxygen, anaerobic respiration is without. Basically, your muscle cells can respire anaerobically for short periods of time when there is a shortage of oxygen.

Aerobic respiration is actually a multi-step reaction that is catalysed by enzymes in the mitochondria. 

And aerobic respiration releases more energy, but the good thing with anaerobic respiration is that it’s almost instant, it’s quick-which is why events such as a 100m sprint  which requires a quick burst of energy is anaerobic.

But anaerobic respiration leads to the production of lactic acid-a poison, which builds up in your muscles. The lactic acid concentrations build up slowly in the muscles and may eventually become high enough to cause fatigue, muscular pains and cramps to stop you from continuing.

This is why you continue to breathe hard after anaerobic exercise for a while, as you are repaying your oxygen debt, which is the oxygen required to oxidize and convert the harmful lactic acid into harmless products like carbon dioxide and water.

2.35 recall the word equation and the balanced chemical symbol equation for aerobic respiration in living organisms

Glucose + oxygen à carbon dioxide + water + energy (ATP)

My class likes to use ‘ATP’ in place of energy, and it stands for adenosine triphosphate. It's like the 'currency' of energy. I'll let this link do the explaining of what it is:
http://wiki.answers.com/Q/What_is_ATP
The explanation in the link may be confusing, as we don't need that kind of depth yet. In very basic terms, ATP is like small packets of energy. They store energy temporarily and provide energy for all the reactions taking place in the cell.

C₆H₁₂O₆ + 6O₂ à 6CO₂ + 6H₂O + ATP

2.36 recall the word equation for anaerobic respiration in plants and in animals

Glucose à lactic acid + ATP (smaller amount!)

C₆H₁₂O₆ à 2C₃H₆O₃ + ATP

The small amount of energy released in anaerobic respiration, together with that produced in aerobic respiration, is sufficient to keep the muscles contracting.

Keep in mind that this equation is different for alcoholic fermentation where yeast respires anaerobically. This is used in the production of bread to make bread rise, as the carbon dioxide produced raises the bread.

Glucose à ethanol + carbon dioxide + small amount of energy

Note that the glucose molecule is only partially broken down in anaerobic respiration. The ethanol produced still contains much energy, hence explaining why only a small amount of energy is set free in anaerobic respiration. 

As you can see, anaerobic respiration and removing lactic acid is much more complex than what I've described, but you don't need to concern yourself with glycolysis for now. Just know the equations I've stated above and all the general stuff. :)

Movement of substances into and out of cells

Specification:

2.12 recall simple definitions of diffusion, osmosis and active transport

2.13 understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport

2.15 understand the factors that affect the rate of movement of substances into and out of cells to include the effects of surface area to volume ratio, temperature and concentration gradient

2.16 describe simple experiments on diffusion and osmosis using living and non-living systems

Specification:

2.12 recall simple definitions of diffusion, osmosis and active transport 

Diffusion: this is the net movement of fluid molecules from a region of high concentration to a region of low concentration. i.e down a concentration gradient. The steeper the gradient, as in the bigger the difference in concentration, the faster diffusion will occur. Examples include if you spray perfume in a corner of the room, it will slowly spread out until you can smell it from the opposite side of the room. This is because the particles move randomly and continuously collide with each other until they spread out evenly. In our body, diffusion occurs when oxygen from the alveolus in the lungs diffuses into the red blood cells which have a lower concentration of oxygen, since it transports it to body cells and 'gives it away'.

Osmosis: this is like diffusion, except it involves water molecules. So again, water molecules move via osmosis from a region of high concentration to a region of low concentration, through a partially permeable membrane. In our body cells, the cell surface membrane is partially permeable, its function is to control what is allowed to enter the cell.

Sometimes you read a definition on osmosis regarding water potential. And this confuses a lot of people. People think that it's from a region of low water potential to high water potential, since a region without much water should have water going to it right? Wrong.

Water potential is a measure of the tendency of water to move from one place to another. So a place without much water would have a low water potential, it's not going anywhere. So the definition is still the same, just switch 'concentration' for 'water potential'.

So osmosis is the movement of water molecules from high to low water potential i.e. down a water potential gradient, through a partially permeable membrane.

So a high concentration of water would be a dilute salt solution, and a low concentration of water would be a concentrated salt solution.

Likewise, a dilute salt solution has a higher water potential, and a concentrated salt solution has a lower water potential.

Active transport: This is the active uptake of molecules against a concentration gradient using ATP (adenosine triphosphate) or if you don't think you can remember this, just say using energy. Against a concentration gradient just means from a region of low concentration to a region of high concentration-unlike diffusion/osmosis. Carrier proteins transport the molecules from one side of the membrane to the other side .

This occurs in root hair cells when they actively uptake mineral ions from the soil even though there is a greater concentration in the root hair cells.

2.13 understand that movement of substances into and out of cells can be by diffusion, osmosis and active transport

Diffusion: e.g. oxygen diffusing into red blood cells, or carbon dioxide diffusing into leaves for photosynthesis

Osmosis: e.g. when water diffuses into plant cells it makes the cells turgid, which provides the plant with support so it can stand upright. If water diffuses out of the cell, it becomes flaccid and wilts. The cell is turgid because the water entering the cell makes the cytoplasm and the vacuole push against the cell wall, exerting turgor pressure. In animal cells, there isn't a cell wall so if too much water enters the cell, it may burst-called lysis. 

Active transport: e.g. root hair cells actively uptaking mineral ions such as magnesium for chlorophyll. In humans, in our kidneys, salts are actively uptaken into the blood.

2.15 understand the factors that affect the rate of movement of substances into and out of cells to include the effects of surface area to volume ratio, temperature and concentration gradient

Surface area to volume ratio: root hair cells have a high surface area to volume ratio, so it increases the rate of diffusion/osmosis.

Temperature: temperature increases the kinetic energy of the particles, so diffusion occurs quicker.

Concentration gradient: The steeper it is, i.e. the greater the difference in concentration between 2 regions, the faster the rate of diffusion/osmosis.

2.16 describe simple experiments on diffusion and osmosis using living and non-living systems

BlogThis!

Biological molecules

Specification:

2.5 recall the chemical elements present in carbohydrates, proteins and lipids (fats and oils)

2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up of smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol

2.7 describe the tests for glucose and starch

2.8 understand the role of enzymes as biological catalysts in metabolic reactions

2.9 understand how the functioning of enzymes can be affected by changes in temperatures

2.11 describe how to carry out simple controlled experiments to illustrate how enzyme activity can be affected by changes in temperature

2.5 recall the chemical elements present in carbohydrates, proteins and lipids (fats and oils)

Carbs and lipids: carbon, hydrogen, oxygen

Protein:

• Carbon
• Hydrogen
• Oxygen
• Sulphur
• Phosphorous
• Nitrogen 

2.6 describe the structure of carbohydrates, proteins and lipids as large molecules made up of smaller basic units: starch and glycogen from simple sugar; protein from amino acids; lipid from fatty acids and glycerol 

Simple sugars e.g. glucose, maltose, galactose Starch, glycogen

Amino acids Protein

Fatty acids + glycerol Lipids

      2.7 describe the tests for glucose and starch

Test for glucose

Benedict's solution-blue solution containing copper (II) sulphate.

Reducing sugars such as glucose, maltose, fructose and lactose can reduce the copper (II) in Benedict's solution to copper (I).

-produce a brick-red precipitate of copper (I) oxide when boiled with Benedict's solution.

Benedict's test:

1. Add 2 cm³ of Benedict's solution to 2 cm³ of glucose solution in a test tube and shake the mixture. Leave the test tube in a beaker of boiling water for five minutes.
2. As a control experiment, repeat step 1 using 2 cm³ of distilled water in place of glucose solution.
3. What do you observe after five minutes for both experiments? Is glucose a reducing sugar?
4. Yes, we already know that, but this test just proves it. The colour change seen is the blue Benedict's solution turning brick-red or orange-red precipitate.
   Test for starch
   Iodine test:
   Starch can be detected by the iodine test. A few drops of iodine solution added to any substance containing starch will produce a blue-black colour.
5. Add a few drops of iodine solution to a piece of potato on a white tile.
6. What do you observe?
   Plants store glucose in the form of starch. For example, starch is abundant in vegetable such as potato and tapioca.

2.8 understand the role of enzymes as biological catalysts in metabolic reactions

Enzymes are biological catalysts made of proteins that speed up chemical reactions without being used up/chemically altered. They lower activation energy-which is the energy needed to start a chemical reaction.

2.9 understand how the functioning of enzymes can be affected by changes in temperatures

High temperatures denature enzymes so they do not function anymore.

To explain this in more detail:

The chains of amino acids are coiled/folded up to give the protein a three-dimensional shape. The coils are held in place by weak bonds (hydrogen bonds).

An increase in temperature increases vibrations in the atoms of the enzyme. At high temperatures (Above 65°C for many human proteins), the vibrations are so violent that they break the hydrogen bonds in the enzyme, causing it to lose its shape.

When the active site changes shape, the substrate

2.11 describe how to carry out simple controlled experiments to illustrate how enzyme activity can be affected by changes in temperature

http://askmichellebiology.blogspot.com/2012/04/effect-of-temperature-on-amylase.html

Cell Structure

a) Levels of Organisation
2.1 describe the levels of organisation within organisms: organelles, cells, tissues, organs and systems

b) Cell Structure
2.2 recognise cell structures, including the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

2.3 describe the functions of the nucleus, cytoplasm, cell membrane, cell wall, chloroplast and vacuole

2.4 describe the differences between plant and animal cells

Animal cell

1. A cell membrane is like a sieve, it controls what goes in and out of the cell. 
2. The cytoplasm is where the chemical reactions take place, the mitochondria in the cytoplasm is where respiration takes place to release energy. The cytoplasm also contains enzymes that control the chemical reactions. 
3. The nucleus is like the 'brain' of the cell, it controls the cell, telling it what to do. It also contains DNA which is important when the cell reproduces. 

Plant cell

Plant cells have extra features:

1. They have a cell wall, this is made of cellulose. It gives the cell shape and structure and provides support. It also means the cell can't burst, it becomes turgid when it is full of water. (The cell walls are actually impermeable to water, which is why they have small gaps in them called plasmodesmata which allow water to enter via osmosis..)
2. They have chloroplasts which contain chlorophyll-the green pigment that allows it to absorb light energy and convert it to chemical energy during photosynthesis. Plants are autotrophs-they can make their own food. 
3. Plant cells have a permanent vacuole that contains cell sap, it provides support. It is also basically a storage and removes waste, and provides/maintains the cell structure. 

Feature	Animal Cell	Plant Cell
Nucleus	Yes	Yes
Cytoplasm	Yes	Yes
Cell Membrane	Yes	Yes
Mitochondria	Yes	BlogThis! Saturday, 24 March 2012 Nutrition and Transport in Plants etc. 2.17 describe the process of photosynthesis and understand its importance in the conversion of light energy to chemical energy 2.18 recall the word equation and the balanced chemical symbol equation for photosynthesis  Overall equation for photosynthesis: *Ignore the second equation!! It is unbalanced, and is there just to illustrate the thought process as you convert from a word equation to a symbol equation.* What conditions are essential for photosynthesis? · sunlight · carbon dioxide · chlorophyll · a suitable temperature · water Photosynthesis depends on enzyme reactions in the chloroplasts. Remember the effect of temperature on enzyme activity-enzymes have optimum temperatures that vary between different organisms. (Optimum temperature=this is the temperature at which the enzyme is most active, catalysing the largest number of reactions per second.) --Certain enzymes in plants have a high optimum temperature. E.g. the optimum temperature of the enzyme papain found in papaya is about 65°C. How do guard cells control the size of stomata? In sunlight: ·         The concentration of potassium ions (K+) increases in the guard cells ·         Chloroplasts in the guard cells photosynthesise. The light energy is converted into chemical energy used to pump potassium ions into the guard cells from neighbouring epidermal cells. This lowers the water potential in the guard cells. ·         Water from neighbouring epidermal cells enters guard cells by osmosis so that they swell and become turgid. ·         The guard cells have a thicker cellulose wall on one side of the cell (the side around the stomatal pore). Hence, the swollen guard cells become more curved and pull the stoma open. At night: ·         The potassium ions accumulated in the guard cells during the day diffuse out of the guard cells. ·         This increases the water potential in the guard cells and water leaves them by osmosis. ·BlogThis! Wednesday, 7 March 2012 The Eye Updated: 20/03/13 Note: According to an anonymous comment (see below), knowledge of the fovea and optic disc is now required so please beware of that. I did this blog according to the 2009 syllabus, which was what I did, so I am unaware of the differences in the new syllabus. And plus I've finished IGCSEs... so yeah. Thanks to the anonymous tipper!! :)  This section focuses on the eye-its structure and function. I'll do things according to the syllabus, so it's WHAT YOU NEED TO KNOW. (for DOUBLE AWARD) Specification 2.87 describe the structure and function of the eye as a receptor Tip: Know about the cornea, iris, lens, pupil, retina and optic nerve mainly. You may be asked to label a diagram and possibly answer a few 1-2 mark questions on the functions of these parts. You should know the positions of the rest, but they aren't the main important bits you need to know..  .  1. Sclera: the tough outer coat of the eye, which is the visible, white part of the eye. It protects the eyeball from mechanical damage.  2. Cornea: at the front of the eye the sclera becomes a transparent 'window' which is the cornea-this lets light into the eye, refracting or bending the light rays into the eye. This plays a key part in the focusing of an image on the retina.  3. Choroid: this is the middle layer of the eye (between the sclera and the retina), it is black, preventing reflection of light in the interior of the eyeball. (It also contains blood vessel that bring oxygen and nutrients to the eyeball and remove metabolic waste products.) 4. Ciliary body: this contains a circular ciliary muscle (just call it ciliary muscle) which is attached to the lens with the suspensory ligaments. These play a huge role in accomodation-which is basically changing the shape of the lens to focus light onto the retina so an image may be formed.  5.Iris: this is in front of the lens, it is a circular diaphragm controlling the amount of light entering the eye. 6. Pupil: this is basically a hole/opening in the iris to let light through. 7. Retina: this is inside the choroid layer, it is a light-sensitive membrane with neurones and photoreceptor cells. There are 2 types of photoreceptor cells: rods and cones. Cones enables us to see colours in bright light while rods enable us to see in black and white in dim light. The photoreceptors are connected to the nerve-endings from the optic nerve.  8. Macula: NOT NEEDED. Fyi, the fovea is in the centre of the macula. Basically, this is where visual perception is most acute. 9. Optic nerve: A nerve that transmits nerve impulses to the brain when the photoreceptors in the retina are stimulated.  10. Optic disc: NOT NEEDED. Fyi, this connects the retina to the optic nerve.  11. Vitreous humour: A transparent, jelly-like substance. This keeps the eyeball firm and helps to refract light onto the retina too.  12. Aqueous humour: A transparent, watery fluid. This keeps the front of the eyeball firm and helps to refract light into the pupil.  13. Canal of Schlemm: NOT NEEDED. Fyi, this is basically just a channel in the eye that collects aqueous humour and moves it into the bloodstream. 14. Lens: A transparent, circular, biconvex structure. It is elastic and changes it shape or thickness to refract light onto the retina.  15. Conjunctiva: this is a thin transparent membrane covering the sclera in front. It is a mucous membrane, it secretes mucus, thus keeping the front of the eyeball moist.  Subscribe to: Posts (Atom) Community Service JSFA CAS (a football team I help manage for CAS) Sekolah Bisa (A school CAS students built and manage) About Me Hi I'm Michelle. I've finished IGCSEs and the IB but I hope these blogs help people with their IGCSEs anyway!! :) Note: That's why these blogs are no longer updated, what's there is all I had time for back then so I'm sorry that they're not fully complete with the whole syllabus and all. Hope what's there helps anyway.. :) I do actually have more notes than is posted, and these can be purchased by buying my IGCSE Notes sets. Contact me at: michelle.lim205@gmail.com Total Pageviews Content: Sections Humans (2) Reproduction (2) Section 1: The nature and variety of living organisms (1) Section 2: Structures and functions in living organisms (7) Section 3: Reproduction and inheritance (5) Section 5: Use of biological resources (1) Blog Archive ▼  2014 (1) ▼  May (1) IGCSE / IB Notes for Sale! ►  2012 (16) ►  August (2) ►  May (2) ►  April (6) ►  March (6) Hi! Note: This blog will no longer be updated, but I will read emails. So, I've finished IGCSEs but I'm leaving my blogs open in hopes that they help people. It would be great if you can tick a box at the bottom of each post to show me what you think, and please feel free to leave comments! A Google+1 below would be awesome too. Thank you so much, hope they help. :) Btw, I did take information out of textbooks. But I've reworded what I can. About Me Michelle Lim Hi I'm Michelle, I've finished the IB (May 2014) and was a Biological Natural Sciences undergraduate student at the University of Cambridge (Class of 2017). You can contact me via michelle.lim205@gmail.com :) View my complete profile Is this blog useful? Ethereal theme. Theme images by konradlew. Powered by Blogger.