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Monday, 6 August 2012

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:

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

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

Saturday, 4 August 2012

The advantages and disadvantages of sexual and asexual reproduction

The advantages and disadvantages of sexual and asexual reproduction

Sexual reproduction involves the fusion of two gametes. The advantages of sexual reproduction are that the offspring may inherit beneficial qualities from both parents, and that there is greater genetic variation among the offspring. Genetic variation increases the chances of a species’ survival as some individual organisms will be better adapted to changes in the environment. The disadvantages of sexual reproduction is that two parents are required, so it will be disadvantageous in a very competitive environment.

Asexual reproduction, on the other hand, does not involve gametes as the offspring arise from the parent through cell division. Thus the advantages of asexual reproduction are that only one parent is required, and that beneficial qualities are more likely to be passed on to the offspring since all offspring are genetically identical to the parent. However, the disadvantage of having genetically identical offspring is that there is less variation, so the organism will be less adapted to changes in the environment.

  • Reproduction is the production of new organisms. Reproduction is necessary to ensure the continuity of species.
  • Asexual reproduction produces genetically identical offspring from one parent by mitosis. Genetically identical offspring are called clones.
  • Sexual reproduction involves the fusion of two gametes to form a zygote, producing genetically dissimilar offspring from two parents. Gametes are special reproductive cells produced by meiosis
  • The process by which the nucleus of the male gamete fuses with the nucleus of the female gamete to form a zygote is called fertilisation. 

Wednesday, 9 May 2012


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:
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. :)

Sunday, 6 May 2012

Planning an experiment

So I was taught to use CORMS. Basically  when you plan an experiment, do it logically and make sure what you're measuring is relevant to your investigation. 

Have some repetition in it so that you can have comparison, and to reduce risk of errors and anomalies. If you were to only take one measurement, and it's wrong, you would not have any valid data. 

What factor are you investigating? Will you have a range of values? (You should always have a minimum of 5 values in a range) Or will you have two groups, one with the factor and one without? What is your control?
What species/size/age/gender will you use? Note if you were planning an investigation into enzyme activity, you would identify the enzyme and the substrate.
You MUST take more than one reading- you should take a minimum of 3 readings and repeat the whole experiment.
What will you be measuring, how often and what are the units? You should describe how you will take the measurement, and with what equipment.
You must say what factors you will keep the same to make sure you have carried out a fair test, e.g. temperature/light intensity/volume of water etc.

Effect drinking tea has on heart rate

Change- 2 groups: one group with tea, the other with water

Organism- human, same gender + same age

Repetition- how many people in each group

Measurement- heart rate in beats per minute, describe how you would do this, and when

Same- temperature of tea/water, volume of tea/water, level of exercise before drinking tea, same room/temperature of room

After considering these factors you should then write your description in full.

Thursday, 26 April 2012

Keywords Glossary

Somebody asked for a glossary, well here's all I have. There's so many bio words out there so obviously I can't include everything, so anything not here, just you know, Google it. :P


Active transport: The process in which energy is used to move the particles of a substance against a concentration gradient, that is, from a region where they are of lower concentration to a region where they are of higher concentration.

Adaptation: Any characteristic of an organism that improves its chances of surviving in its environment.

Aerobic respiration: Respiration with oxygen. It’s the oxidation of food substances in the presence of oxygen with the release of a large amount of energy. Carbon dioxide and water are released as waste products.

AIDS: An abbreviation for Acquired Immune Deficiency Syndrome.

Alleles: Different forms of a gene which occupy the same relative positions on a pair of homologous chromosomes.

Anaerobic respiration: Respiration without oxygen. It’s the oxidation of food substances in the absence of oxygen. Anaerobic respiration releases less energy than aerobic respiration.

Anaesthetics: Drugs that make the body unable to feel pain.

Arteries: Blood vessels which carry blood away from the heart.

Artificial selection: A method used by human beings to produce plants and animals with desired qualities.

Asexual reproduction: The process resulting in the production of genetically identical offspring from one parent, without the fusion of gametes.

Assimilation: The process whereby some of the absorbed food materials are converted into new protoplasm or used to provide energy.

Axon: A nerve fibre that transmits impulses away from the cell body of a neurone.

Bioaccumulation: The process by which substances collect in all parts or part of a living organism.

Breathing: The process that brings about an exchange of gases between an organism and its environment.

Capillaries: Microscopic thin-walled (one cell thick) blood vessels which carry blood from a small artery (arteriole) to a small vein (venule).

Codominance: A condition where both alleles express themselves in a hybrid, as they are both either dominant or recessive to one another. (Roughly equal expression.)

Community: Populations of organisms living together and interacting with one another under the same environmental conditions.

Conservation: The protection and preservation of natural resources of the environment.

Consumers: Organisms which obtain their energy by feeding on other organisms.

Continuous variation: Traits with phenotypes ranging from one extreme to the other. It is brought about by combined (or additive) effects of many genes. It is affected by environmental conditions, e.g. intelligence, height and skin colour in human beings.

Cross-pollination: The transfer of pollen grains from one plant to the stigma of a flower in another plant of the same species.

Decomposers: Saprotrophs and detritivores. Organisms which obtain energy by breaking down dead organisms, faeces and excretory products.

Dendron: A nerve fibre that transmits impulses towards the cell body of a neurone.

Desertification: The destruction of land leading to desert-like conditions.

Detoxification: The process of converting harmful substances into harmless ones in the body.

Differentiation: The process by which a cell becomes specialized for a specific function.

Diffusion: The net movement of particles (atoms, ions or molecules) from a region of higher concentration to a region of lower concentration, that is, down a concentration gradient.

Digestion: The process by which large food molecules are broken down into small, soluble and diffusible molecules that can be absorbed by the body cells.

Diploid: Cells that contain the full number of chromosomes.

Discontinuous variation: Traits that show limited variation in their phenotypes which are easily distinguishable. It is usually controlled by only one or a few genes. It is not affected by the environment. E.g. detached earlobes-it’s either yes or no.

Dominant: A form of a gene that is expressed and masks the recessive gene. It gives the same phenotype in both homozygous and heterozygous conditions as it expresses itself.

Ecology: The study of the relationships between living organisms and the natural environment.

Ecosystem: An ecological system formed by the interaction of living organisms (biotic) and their non-living (abiotic) environments.

Egestion: The removal of undigested matter from the body. Egestion would be like pooing-you’re egesting faeces which are basically undigested food. [Different to excretion! See excretion.]

Endocrine glands: Ductless glands that secrete hormones into the bloodstream.

Enzymes: Biological catalysts made of protein. They alter the rate of (mostly catalyse) chemical reactions without themselves being chemically changed at the end of the reactions.

Eutrophication: The profuse growth and multiplication of algae and green plants as a result of the enrichment of nutrients in the water. Often leads to depletion of oxygen levels.

Excretion: The process by which metabolic waste products and toxic materials are removed from the body of an organism. E.g. sweating, sweat is a metabolic waste product. [Different to egestion! See egestion.]

Fertilisation: The process by which the male gamete fuses with the female gamete to form a zygote.

Focusing/accommodation: The adjustment of the lens of the eye so that clear images of objects at different distances are formed on the retina.

Food chain: A series of organisms through which energy is transferred in the form of food.

Food web: Two or more food chains interlinked together.

Gamete: A reproductive cell containing the haploid number of chromosomes.

Gene: A hereditary factor found on a particular locus in a chromosome. It controls a particular characteristic and codes for a specific protein.

Genetic engineering: A technique used to transfer genes from one organism to another.

Genotype: The combination of genes in an individual.

Gland: A cell, tissue or an organ that secretes chemical substances.

Habitat: The place where an organism lives.

Haploid: Cells that contain half the number of chromosomes as the parent cells which produced them.

Heterozygous: A condition where you have different alleles for a particular trait. E.g. if B codes for brown eyes (dominant allele is always upper case) and the recessive allele is b (always the lower case of the dominant alleles’ letter), then a person with a Bb genotype for eye colour is heterozygous dominant, so will have brown eyes.

Homeostasis: The maintenance of a constant internal environment.

Homologous pairs: Chromosomes which have the same genes, shape and length. 

Homozygous: Having identical alleles for a particular trait. E.g. BB-homozygous dominant, or bb-homozygous recessive.

Hormone: A chemical substance produced in minute quantities by an endocrine gland. It is transported in the bloodstream to target organ(s) where it exerts its effects.

Irritability/sensitivity: The ability of an organism to respond to a stimulus.

Meiosis: A form of cell division such that the daughter cells contain half the number of chromosomes as the parent cell. –will be haploid, e.g. to form sex cells/gametes (Chromosomes are in the nucleus.)

Mitosis: Cell division such that the daughter cell produced contains the same number of chromosomes as the parent cell. –will be diploid, e.g. to form somatic (body) cells

Mutation: The sudden or spontaneous change in gene structure or a chromosome, or even the chromosome number, and may be inheritable.

Nerve: A collection of nerve fibres.

Nerve fibre: A long cytoplasmic extension of the cell body of a neurone. It serves to transmit impulses.

Neurone: A nerve cell.

Nutrition: The intake of food and the processes that convert food substances into living matter.

Osmoregulation: The control of water and solute levels in the blood to maintain a constant water potential in the body. Basically to maintain blood water levels.

Osmosis: The net movement of water molecules from a solution of higher water potential to a solution of lower water potential, through a partially permeable membrane, i.e. down a water potential gradient.  Or, from a region of high concentration to a region of low concentration, through a partially permeable membrane, i.e. down a concentration gradient.

Oxygen debt: The amount of oxygen required to oxidize the lactic acid produced in muscles during anaerobic respiration and convert it into harmless substances.

Partially/selectively permeable membrane: A membrane that allows selected substances to pass through.

Peristalsis: The rhythmic wave-like contractions of the walls of the gut.

Phagocytosis: The process of engulfing and ingesting foreign particles, such as bacteria, by phagocytes such as the white blood cells.

Phenotype: The physically expressed trait in an individual, e.g. outward appearances such as height and eye colour.

Photosynthesis: The process in which light energy absorbed by chlorophyll is transformed into chemical energy.

Pollination: The transfer of pollen grains from an anther to a stigma.

Pollution: The addition of substances to the environment that damage it, making it unfit for life.

Population: A group of organisms of the same species living together in the same habitat.

Producers: Organisms which convert energy from the sun, or light energy, into chemical energy and store it as food during photosynthesis. They are the start of the food chain.

Recessive:  A form of a gene that expresses itself only in the homozygous condition. E.g. Bb, it won’t be expressed because the dominant ‘B’ allele masks it and is expressed instead. But in ‘bb’, this is homozygous recessive, so it will be expressed.

Reducing sugars: Sugars that produce a red precipitate when boiled with Benedict’s solution. E.g. glucose, maltose, fructose, lactose.

Reflex action: An immediate response to a specific stimulus without conscious control.
Reflex arc: The shortest pathway by which impulses travel from the receptor to the effector in a reflex action.

Respiration: The oxidation of food substances with the release of energy in living cells.

Self-pollination: The transfer of pollen grains from the anther the stigma of the same flower or of a different flower on the same plant.

Sexual reproduction: The process involving the fusion of two gametes to form a zygote, resulting in the production of genetically dissimilar offspring-as in there will be variation.

Species: A group of similar organisms. Organisms within a species can breed. They produce healthy offspring that are able to grow, develop and reproduce normally.

Synapse: A junction between two neurones.

Tissue: A group of similar cells which work together to perform a specific function.

Tissue respiration: The process in living cells by which food substances are oxidized with energy released for the vital activities of the cells. Basically: C6H12O6 + 6O2 à 6CO2 + 6H2O + energy (ATP)

Translocation: The transport of manufactured food substances such as sugar and amino acids in plants (in phloem.)

Transpiration: The loss of water vapour from aerial parts of a plant, especially through the stomata of the leaves.

Transpirational pull: The suction force caused by transpiration that is the main factor causing water movement up the xylem.

Turgor pressure: The pressure exerted outwards on the cell wall due to the water in the cell-hence the cell becomes turgid.

Variation: The differences that can be observed within a species.

Veins: Blood vessels which carry blood towards the heart.

Voluntary action: An action that is under the control of the will, requires thinking so it’s obviously slower than involuntary/reflex actions. 

Monday, 16 April 2012

Movement of substances into and out of cells

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

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

Biological molecules

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
  • 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

Wednesday, 11 April 2012

GM Food

5.15 evaluate the potential for using genetically modified plants to improve food production (illustrated by plants with improved resistance to pests)

Genetically modifying plants can have some advantages and disadvantages. Despite the fact that the world produces enough food to feed the whole world many times over, some people are still starving. Others are suffering from malnutrition and many are hungry. Genetic modification has great potential; it can allow certain crops to survive in harsher conditions so that for example, people in Africa can grow crops despite the harsh conditions there. Scientists can even genetically modify foods so that they are more nutritious, for instance they genetically modified rice plants to produce 'Golden Rice' which has a higher vitamin A content. So here you see that GM foods can help address certain nutrient deficiencies too. Not all of a crop planted will be harvested; a percentage will be lost to disease, some to pests, others to weeds. So GM plants can be designed to have resistance to not only harsher conditions, but to pests too. This way crop yield is increased. But of course, there are disadvantages too. I'll just list a few of each, and then include a table for some benefits of genetic engineering applications to society.
Advantages, GM crops:
  • Need fewer chemical sprays
  • Could give bigger yields
  • Could grow in harsher conditions
  • Could result in cheaper food (if there were higher crop yields, supplies increase and with the same demand, prices are lowered)
  • Could be more nutritious
Adv. -Research into the genetic modification of plants hopes to provide (or provides already) plants with:
  • Increased resistance to a range of pests
  • Resistance to pathogens so they don't contract diseases
  • Increased heat and drought tolerance
  • Increased salt tolerance
  • A better balance of proteins, carbohydrates, lipids, vitamins and minerals-more nutritious crop plants
  • Accidental transfer of new genes to other wild plants-unpredictable
  • GM crops could reduce biodiversity
  • The new proteins in GM crops could cause allergies
  • GM seeds are expensive, but the costs of production are lower as sometimes less water is needed, or expensive chemicals such as herbicides and pesticides are not needed if the crops are resistant towards diseases and pests and weeds

Applications of genetic engineering
Benefits to society
Low-cost production of medicines
Genetic engineering of important drugs such as human insulin has dramatically reduced the cost of these medicines. This makes it more affordable and therefore more accessible to people who need them, so they can be treated.
Production of crops that grow in extreme conditions (e.g. high-salt environments)
Examples of such crops include:
  • Drough-resistant crops;
  • Salt-tolerant crops; and
  • Crops that make more efficient use of nitrogen and other nutrients.

This allows farmers to grow crops even when the soil conditions are not suitable for cultivating most crops.
Development of:
  • Crops that produce toxins that kill insect pests; and
  •  Pesticide-resistant crops

The use of costly pesticides that may damage the environment is reduced. For example, the Bt gene from t

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. 

Animal Cell
Plant Cell
Cell Membrane

Wednesday, 4 April 2012

Nature and Variety

The specification for section 1 pretty much says it all, I didn't really add anything: 

a) Characteristics of living organisms

1.1 recall that living organisms share the following basic characteristics: 

  • they require nutrition
  • they respire
  • they excrete their waste
  • they respond to their surroundings
  • they move
  • they control their internal conditions
  • they reproduce
  • they grow and develop
b) Variety of living organisms

1.2 describe the common features shared by organisms within the following main groups, plants, animals, fungi, bacteria, protoctists and viruses, and for each group describe examples and their features as follows (details of life cycle and economic importance are not required).

Plants: These are multicellular organisms; they contain chloroplasts and are able to carry out photosynthesis; they have cellulose cell walls; and they store carbohydrates as starch or sucrose.

Examples include flowering plants, such as a cereal (for example maize) and a herbaceous legume (for example peas or beans). 

Animals: These are multicellular organisms; they do not have chloroplasts and are not able to carry out photosynthesis; they have no cell walls; they usually have nervous coordination and are able to move from one place to another; they often store carbohydrates as glycogen.

Examples include mammals (for example humans) and insects (for example housefly and mosquito).

Fungi: These are organisms that are not able to carry out photosynthesis; their body is usually organised into a mycelium made from thread-like structures called hyphae, which contain many nuclei; some examples are single-celled; they have cell walls made of chitin; they feed by extracellular secretion of digestive enzymes onto food material and absorption of the organic products; this is known as saprotrophic nutrition; they may store carbohydrates as glycogen.

Examples include Mucor, which has the typical fungal hyphal structure, and yeast which is single-celled. 

Bacteria: These are microscopic single-celled organisms; they have a cell wall, cell membrane, cytoplasm and plasmids; they lack a nucleus but contain a circular chromosome of DNA; some bacteria can carry out photosynthesis but most feed off other living or dead organisms.

Examples include Lactobacillus bulgaricus, a rod-shaped bacterium used in the production of yoghurt from milk, and Pneumococcus, a spherical bacterium that acts as the pathogen causing pneumonia. 

Protoctists: These are microscopic single-celled organisms. Some, like Amoeba, that live in pond water, have features like an animal cell, while others, like Chlorella, have chloroplasts and are more like plants. A pathogenic example is Plasmodium, responsible for causing malaria. 

Viruses: These are small particles, smaller than bacteria; they are parasitic and can reproduce only inside living cells; they infect every type of living organism. They have a wide variety of shapes and sizes; they have no cellular structure but have a protein coat and contain one type of nucleic acid, either DNA or RNA. 

Examples include tobacco mosaic virus that causes discolouring of the leaves of tobacco plants by preventing the formation of chloroplasts, the influenza virus that causes 'flu' and the HIV virus that causes AIDS. 

1.3 Recall the term 'pathogen' and know that pathogens may be fungi, bacteria, protoctists or viruses. 

Monday, 26 March 2012

Cell Division

  • Understand that division of a diploid cell by mitosis produces two cells which contain identical sets of chromosomes
  • Understand that mitosis occurs during growth, repair, cloning and asexual reproduction
  • Understand that division of a cell by meiosis produces four cells, each with half the number of chromosomes, and that this results in the formation of genetically different haploid gametes

  • A cell nucleus divides into two identical 'daughter' nuclei.
  • The daughter cells produced by mitosis are genetically identical to the parent cell.
  • Mitosis is important for the growth of an organism, for repair of worn-out parts of the body and for asexual reproduction in plants.

    Stages in mitosis:
  1. A pair of chromosomes in the nucleus.
  2. Each chromosome makes an identical copy of itself.
  3. Cell starts to divide into two. each daughter cell has a complete set of chromosomes.
  4. Two new daughter cells, each identical to the parent cell they divided from.

  • 2 cell divisions, producing 4 sex cells, daughter nuclei are haploid (contains half the number of chromosomes as the parent nucleus).
  • Meiosis produces haploid gametes.
  • Meiosis results in variations in the gametes produced.
  • Variations occur due to crossing over and also due to independent assortment of chromosomes.
  • Independent assortment of chromosomes means one chromosome from each pair can combine with either chromosome of the other pair. This results in four different gametes being produced from two pairs of chromosomes. --since fertilisation is random (any sperm fuses with any egg), such variations in the gametes produce variations in the offspring. 

Daughter cells contain same number of chromosomes as parent cellDaughter cells contain half the number of chromosomes as parent cell
Pairing of homologous chromosomes doesn't occurHomologous chromosomes pair at prophase I
No crossing overCrossing over may occur
Daughter cells are identical to parent cellVariations occur in daughter cells
Two daughter cells are produced from one parent cellFour daughter cells are produced from one parent cell
Involves only one nuclear divisionInvolves two nuclear divisions
Occurs in normal body cells (somatic cells) during growth or repair of body partsOccurs in the gonads (Sex organs) during gamete formation