PLANT NUTRITION PART 14: WATER CULTURE EXPERIMENT

The water culture experiment is used to find out whether nitrogen, phosphorus and magnesium are essential for plant growth.


HOW TO MAKE A COMPLETE CULTURE SOLUTION?

• 1000cc distilled water
• 0.25g potassium nitrate
• 0.25g magnesium sulphate
• 0.25g potassium acid phosphate
• 1g calcium nitrate
• 2 drops iron(III) chloride solution

(Important: The chemicals should be added to the water in the order shown above)

To investigate whether Nitrogen is really needed for plant growth, omit the nitrates and use potassium chloride and calcium sulphate.

To investigate whether Magnesium is really needed for plant growth, omit magnesium sulphate and use potassium sulphate.

PRECAUTIONS

• Before setting up the experiment, all apparatus are to be sterilize to ensure that the apparatus is free from micro-organisms which might interfere with the growth of the seedlings.
• The outside of the gas jars are to be covered completely with black papers to prevent light from entering the gas jars. This prevents algae from growing around the roots and hinder their normal functioning.
• The gas jars are to be placed in such a way that they receive enough sunlight but be very careful not to place the gas jars in direct sunlight as it may caused the leaves of the seedlings to scorch and heat up the culture solutions.
• Keep the cotton wool around the seedling dry to prevent the stem from rotting.
• Renew the culture solution every 2 weeks (Remember: Depletion).
• Aerate the solution by blowing air through the delivery tube to supply oxygen for root respiration.
  

PLANT NUTRITION PART 13: MINERAL NUTRITION

And you think photosynthesis is enough for plants to make food right? Nope.... there is more to it actually. After carbohydrate (glucose) is synthesized, some of them need to be converted into amino acids and later from amino acids, proteins are synthesized. For this to occur, plants need minerals. The minerals needed by plants are divided into two groups: Macronutrients and Micronutrients.

MACRONUTRIENTS: Needed in large amount. Examples are Nitrogen, Phosphorus, Sulphur, Magnesium, Potassium and Calcium.

MICRONUTRIENTS: Needed in small amount. Examples are Iron, Manganese, Boron, Cobalt, Zinc, Copper and Molybdenum.

THE ROLE OF MACRONUTRIENTS IN PLANT GROWTH
Do you need to know all these? Hold your horses. In the Biology syllabus, you are required to know the functions and deficiency symptoms of Nitrogen and Magnesium only.


NITROGEN

• Plants generally dependent on nitrogen in the form of nitrate ions or ammonium ions.
• Symptom of deficiency: Chlorosis and stunted growth (Why? Nitrogen is a component of chlorophyll and amino acids and hence proteins are needed for growth. Therefore if plants lack Nitrogen, chlorophyll formation will be affected and there will be insufficient proteins for growth, hence stunted growth)

MAGNESIUM

• Magnesium is also a component of chlorophyll.
• Deficiency symptoms: Chlorosis develops upward from the base of the plant. Unlike in Nitrogen deficiency, yellowing is only in-between the veins (the veins remain green). Chlorosis is accompanied by death of the entire leaf or portions of it.

PLANT NUTRITION PART 12: RATE OF PHOTOSYNTHESIS

The following set up can be used to investigate the effect of different light intensities, different temperatures and different carbon dioxide concentrations on the RATE of photosynthesis.
MODIFICATIONS

• For investigating the effect of different light intensities on the rate of photosynthesis, the distance of the light source should be altered. For example, 50cm, 40cm, 30cm, 20cm and 10cm away from the plant. Air bubbles are given out from the cut end of the plant. Allow some time for the plant to adapt to the conditions provided before taking readings. When they are coming at a regular rate, count the number of air bubbles over a period of time, say five minutes. Repeat this a few times to obtain the average rate (Note: the bubbles produced are oxygen gas released as a result of photosynthesis). The readings may be tabulated like the one shown in the following figure (The heat from the light source may affect the temperature of the water bath, so throughout the investigation, the temperature should be monitored so that it is always constant)

• To investigate the effect of different temperature on the rate of photosynthesis, the temperature of the water bath may be altered by using hot water and ice cubes.
• To investigate the effect of different carbon dioxide concentrations, sodium hydrogen carbonate solutions of different concentrations may be used. For example, 0.01M, 0.02M, 0.03M up to 0.1M.

EXPECTED OBSERVATIONS:

• Effect of different light intensities: The closer the light source to the plant, the higher the light intensity and the more bubbles will be produced and this means that the higher the rate of photosynthesis. Likewise, the further the light source away from the plant, the lower the light intensity and the less bubbles will be produced and this means that the lower the rate of photosynthesis.
• Effect of different temperatures: The lower the temperature the less bubbles will be produced and this means that the lower the rate of photosynthesis. As the temperature is increased, more and more bubbles will be produced and this indicates that the rate of photosynthesis increases with the increase in temperature. WHAT DO YOU THINK HAPPENED IF THE TEMPERATURE IS ABOVE 40 DEGREE CELSIUS? WILL THE RATE INCREASE? OR DECREASE?
• Effect of different carbon dioxide concentrations: The lower the carbon dioxide concentration, the less bubbles will be produced and this means that the lower the rate of photosynthesis. The higher the concentration of carbon dioxide, the more bubbles will be produced and this means that the higher the rate of photosynthesis.
  

CHROMOSOMES

Chromosomes consist of one DNA molecule. Each somatic cell of your body has 23 pairs of chromosomes, one member of each pair contributed by your mother and the other by your father. (In egg and sperm cells - there are 23 individual chromosomes, not chromosome pairs.) One pair are the sex chromosomes, which can come in two forms, X and Y. A pair of X's gives a female, and an XY results in a male.

CELL DIVISION

Cell divides!!! Yes, cell divides constantly. This is important for growth, replacing dead cells and gamete formation. Cell divides in two ways: MITOSIS and MEIOSIS. The following figure shows the difference between mitosis and meiosis.

NOTICE ANY DIFFERENCES? WHICH TYPE INVOLVES IN GROWTH? WHICH TYPE INVOLVES IN GAMETE FORMATION?

BIOLOGICAL DRAWING OF BANANA (CROSS SECTION)

In the past practical papers, there used to be a question asking candidates to draw a cross section (or transverse section) of a banana. The following figures should help.

Real Specimen

Biological Drawing of a Cross Section of a Banana
NOTE:
During that time, food tests were also conducted on the banana slice. What type of food nutrients do you think are present in it?

MONOCOT LEAF

The following figures show transverse sections of monocot leaves.

NOTICE HOW THE STOMATA ARE DISTRIBUTED (COMPARED TO DICOT LEAVES)?
YOU CAN ALSO SEE STOMATA ON THE UPPER SURFACE, RIGHT?
EVER WONDER WHY?
(TRY TO FIGURE OUT WHY?)

XEROPHYTE, MESOPHYTE AND HYDROPHYTE

XEROPHYTE
Plants that live in conditions where water is scare (for example in the desert)

MESOPHYTE
Land plants living in environment with moderate amount of moisture.

HYDROPHYTE
A plant adapted to grow in water.

Transverse Section of a Mesophyte Leaf

Transverse Section of a Xerophyte Leaf

Transverse Section of a Hydrophyte Leaf

Notice the adaptations of the Xerophyte and the Hydrophyte leaves?

• Xerophyte leaf needs to conserve as much water as possible so it tends to curl so as not to expose the stomata. So the stomata is hidden inside the curl inner side of the leaf. Apart from this, it has a very thick waxy cuticle and some may even have leaf hairs. Generally leaves of the xerophyte are succulent to store water as much as possible.
• Hydrophyte leaf needs to be able to float so that it can trap as much light energy from the sun as possible. To enable it to float the leaf has unusually large intercellular air spaces for storing air which in turn provides BUOYANCY. Apart from this, the stomata can be found on the upper surface (unlike the mesophyte - the stomata are found on the lower surface of the leaf).
  

ONION BULB

DO YOU KNOW THAT AN ONION BULB ACTUALLY CONSISTS OF LEAVES (SCALE LEAVES)?

DO YOU KNOW THAT AN ONION PLANT IS AN EXAMPLE OF A MONOCOT?
NOTE: BE AWARE THAT THERE MAY BE QUESTIONS IN THE PRACTICAL PAPER ASKING YOU TO MAKE A FULLY LABELLED DRAWING OF AN ONION BULB. NOTE THE LEAVES AND THE STEM TISSUE.
FOOD TEST MAY ALSO BE ASKED AND DO NOT BE SURPRISE THAT AN ONION BULB CONTAINS REDUCING SUGAR!!! (NOTE: WHEN COOKING ONION, THE DARK BROWN CARAMEL IS ACTUALLY THE SUGAR!!!)


The following figure shows how an onion bulb is to be drawn (Longitudinal Section!!!)

CHLOROPLAST

CHLOROPLAST AS CAN BE SEEN UNDER A MICROSCOPE

A FIGURE SHOWING THE INTERNAL STRUCTURE OF A CHLOROPLAST

NOTE: CHLOROPLAST - SITE WHERE PHOTOSYNTHESIS TAKES PLACE

PLANT NUTRITION PART 11: ADAPTATION OF LEAVES FOR PHOTOSYNTHESIS

The term ADAPTATION means - the way in which a particular structure suits to perform a particular function.

LEAVES' ADAPTATION FOR MAXIMIZING THE RATE OF PHOTOSYNTHESIS

• Leaves are generally horizontally positioned on the plants so that more sunlight can be absorbed.
• Leaves are generally broad which offers a large surface area which enable the leaves to absorb as much sunlight as possible. Having broad shape also enables more carbon dioxide to diffuse in into the leaves. (Some plants having small leaves compensated this by having numerous of these small leaves)
  
• Most leaves are thin and carbon dioxide has to diffuse across only short distances to reach the inner cells.
• Some leaves have thick waxy cuticle on the upper surface of the leaves to prevent evaporation of water (Remember, water is one of the requirements for photosynthesis. So it must be conserved).
• More chloroplasts containing chlorophyll are located on the upper surface of the leaves (mainly in the palisade mesophyll cells) to maximize absorption of energy from sunlight by the chlorophyll (Remember, the upper surface of the leaves are more exposed to sunlight, so only right that there should be more chloroplasts on the upper surface of the leaves).
• The palisade mesophyll cells are vertically arranged ends-on so that more cells are exposed to sunlight and hence more sunlight can be absorbed by the chlorophyll in these cells.
• Lots of stomata are generally found in the lower surface of the leaves. Being on the lower surface reduces transpiration hence conserving water. Being numerous in number allow more carbon dioxide to diffuse in into the leaves.
• There are lots of intercellular air spaces in the spongy mesophyll layer. This enables carbon dioxide to be stored for use in photosynthesis. Apart from this, it allows gaseous exchange to take place.
• The presence of branching network of veins provides a good water supply to the photosynthesizing cells. The veins also help to remove the products of photosynthesis to other parts of the plants.
  

PLANT NUTRITION PART 10: IMPORTANCE OF PHOTOSYNTHESIS

WHY IS PHOTOSYNTHESIS IMPORTANT TO LIFE ON EARTH?

• Plants play an important role in maintaining the percentage of carbon dioxide at 0.03% in the atmosphere.
• There has been a gradual increase in carbon dioxide output globally.
• This increase is attributed to large scale deforestation, forest fires and the burning of fossil fuels.
• The carbon dioxide in the atmosphere traps heat. This heat-trapping effect of carbon dioxide is called the GREENHOUSE EFFECT which may lead to global warming which would increase the atmospheric temperature of the earth.
• So the importance of photosynthesis is that it helps to remove carbon dioxide from the atmosphere - this helps to greatly reduce the dangers of global warming.
• Apart from maintaining the percentage of carbon dioxide in the atmosphere, photosynthesis also helps to give out oxygen which is useful for other living organisms (for cellular respiration).
  

PLANT NUTRITION PART 9: FATE OF GLUCOSE

WHAT HAPPENS TO THE GLUCOSE PRODUCED DURING PHOTOSYNTHESIS?

• Glucose is used up by actively respiring cells during respiration to release energy.

• In the actively growing root tips and shoot tips, glucose is converted into cellulose to be used for making the cell wall needed for growth of the newly divided cells.

• Together with nitrates, sulphates and phosphates, glucose are used in the synthesis of amino acids which combined to form proteins which are converted into new protoplasm within the cells. Some of these newly synthesized proteins may be used to synthesize enzymes (Some of these proteins are also send to the storage organs for storage).

• Some of the glucose may be converted to sucrose in the storage organs like the seeds and fruits as well as the bulbs and tubers (like onion bulbs and potato tubers). Some of the glucose combined to form starch and this starch is then stored in the storage organs (Note: the potato tuber stores starch)
  

Onion Bulb

Potato Tuber

PLANT NUTRITION PART 8: IS OXYGEN PRODUCED DURING PHOTOSYNTHESIS?

Let us recall back the equation:


From the equation, it can be concluded that oxygen is produced as a by product of photosynthesis. Now, how do we know that oxygen is really produced? OK, here's the procedure:

• Set up the apparatus as shown in the following figure and make sure that the test tube is completely full of water.
• Place the apparatus in bright sunlight for a few days.
• Carefully remove the test tube from the top of the funnel, allowing the water to run out but not allowing the gas to escape.
• Light a wooden splint and then blow it out so that it is just glowing. Carefully put it into the gas in the test tube. If it relights the glowing splint, then the gas is oxygen.
  

CONTROLS
When setting up an experiment and a control, which of the two procedures constitutes the CONTROL depends on the way the prediction is worded. For example, if the prediction is that "in the absence of light, the pondweed will not produce oxygen", then the control is the plant in the light. If the prediction is that "the pondweed in the light will produce oxygen", then the control is the plant in darkness.

MUSCLE CRAMP

What is cramp?

A cramp is an involuntary and forcibly contracted muscle that does not relax. If you haven't experienced it, count yourself lucky. Try clenching your thigh muscles. Then imagine squeezing them so hard it hurts and holding them like that for a minute. Cramp locks up your leg in a painful grip, you certainly can't pedal. Sometimes, you'll get a small cramp where you can soft pedal but if you're racing, the chances are it's game over as you're not going to be able to force the pace much and often this small tension is a sign that you're going to cramp up a lot.

What causes cramp?

• Dehydration
• Accumulation of Lactic Acid
• Electrolyte imbalance
  

PLANT NUTRITION PART 7: IS CHLOROPHYLL NEEDED?

This experiment makes use of plants having variegated leaves (leaves in which in some parts chlorophyll is absent). The following figure shows an example of such plants.



PROCEDURE

• Destarch a potted plant with variegated leaves.
• Choose a leaf and make a simple drawing of the leaf showing clearly the regions which are green in colour as well as the regions which are not green in colour.
• Expose the plant to bright sunlight for 2 hours.
• After 2 hours removed the pre-chosen leaf and test it for the presence of starch using Iodine solution.

OBSERVATION

• Iodine solution changed to blue-black only in the green regions of the leaf whereas the Iodine solution remain unchanged in the non-green regions.
  

CONCLUSION

• Chlorophyll (in the green regions) is needed by green plants to photosynthesize.
  

PLANT NUTRITION PART 6: IS CARBON DIOXIDE NEEDED?

Carbon dioxide is one of the four requirements for photosynthesis to take place. Again, since it is a requirement, photosynthesis will not take place without it.

PROCEDURE:

• Set up two destarched potted plants as shown in the following figure.
• In set up X, a container containing saturated sodium hydrogen carbonate is placed (This is to provide the plant with carbon dioxide) whereas in set up Y, soda lime is used instead (This is to absorb the carbon dioxide inside the polythene bag as well as the carbon dioxide given off by microorganisms in the soil).
• Expose bot set ups to bright sunlight for two hours.
• After 2 hours, remove one leaf from each set up and test each leaf for the presence of starch using Iodine solution.
  

OBSERVATION

• The Iodine solution in the leaf taken from set up X turns blue black whereas the Iodine solution in the leaf taken from set up Y remain unchanged.
  

CONCLUSION

• The outcome of the experiment shows that carbon-dioxide must be present for plants to photosynthesize.
  

PLANT NUTRITION PART 5: IS LIGHT NEEDED?

The objective of this experiment is to investigate if light is one of the requirements for plants to photosynthesize.

PROCEDURE

• Destarch a potted plant.
• Cover one leaf of this destarched plant with a black paper with patterns cut in it (See the following figure).
• Expose the plant to bright sunlight for two hours.
• After 2 hours, test the leaf for the presence of starch using Iodine solution (Remember the procedure outlined in the previous post)
  

OBSERVATION

• The Iodine solution will change colour to Blue-black in the uncovered region whereas in the regions which is covered with black paper, the Iodine solution remain unchanged.

CONCLUSION

• Light is unable to penetrate in the region which is covered with the black paper, so no photosynthesis and therefore no starch is produced.
• Light penetrates in the uncovered region, so photosynthesis takes place and therefore starch is produced and detected when the leaf is tested with Iodine solution.
• The experiment shows that light from the sun is necessary for photosynthesis to take place.
  

PLANT NUTRITION PART 4: DESTARCHING AND TEST FOR STARCH IN LEAF

In the next part (part 5) of this chapter, practical investigations to prove whether chlorophyll, light and carbon dioxide are really needed for green plants to photosynthesize will be discussed. Before these practical investigations can be discussed, it is SOOOOO necessary for you to know HOW and WHY destarching is necessary.

First thing first. In investigating these three requirements, we need to ask ourselves - How do we know whether photosynthesis is really taking place or not? And then ask further - How do we know whether these requirements are responsible or involved in any ways, in photosynthesis? Well, the answer to the first one - If photosynthesis is really taking place, starch must have been produced, right? And the second question - By conducting an investigation where one requirement is deprived from the photosynthesizing plants. OK, enough about this. Lets move on to the real objective of this part of the chapter.

WHAT IS DESTARCHING?

• Removal of starch from the leaves.

WHY DESTARCHING?

• To ensure that at the beginning of the above mentioned investigations, there are no starch in the leaves of the plants to be used in the investigations. We really need to ensure that starch is really produced or not as a result of photosynthesis in the presence or absence of the above mentioned requirements.
  

HOW IS IT CONDUCTED?

• By placing the plants to be used in the investigations in a dark place, for example a dark cupboard for 24 to 48 hours (Darkness will stop photosynthesis in these plants and as a result all starch stored in the leaves will be used as a source of energy)
  

HOW DO WE KNOW IF DESTARCHING IS SUCCESSFUL?

• If we want to know whether the destarching is successful or not, we may take one of the leaf and test it for the presence of starch using Iodine solution.
• SUCCESSFUL??? It means, the outcome of the starch test must be NEGATIVE, the brown Iodine should not change. This means that starch is absent in the tested leaf - meaning, the DESTARCHING IS SUCCESSFUL.

IODINE TEST ON LEAF FOR THE PRESENCE OF STARCH
Starch test using Iodine solution? Hmm... peculiar right? You must be thinking about the same test like the one you did in your food test practical classes? Well....not that easy missy or mister. Here's the procedures:

Procedures:

• Heat some water to boiling point in a beaker and then TURN OUT the Bunsen flame.
• Use forceps to dip a leaf in the hot water for about 30 seconds (This kills the cytoplasm, denatures the enzymes and makes the leaf more permeable to Iodine solution)
• Push the leaf to the bottom of a test tube and pour in some alcohol (ethanol) into the test tube (The alcohol will boil and dissolve out most of the chlorophyll. This makes colour changes with Iodine easier to see)
  

• Pour the green alcohol into a spare beaker.
• Remove the leaf (brittle at this stage) and dip it once more into the hot water to soften it.
• Spread the decolourized leaf flat on a white tile and place a few drops of Iodine solution on to it.
• If the Iodine solution changed colour to Blue black, it means that starch is still present and it means that the destarching is not successful.
• If the Iodine solution does not changed colour, it means that starch is absent in the leaf and it means that the destarching is successful

Once you get the successful outcome, then you can start to investigate!!!

PLANT NUTRITION PART 3: PHOTOSYNTHESIS

Autotrophs such as green plants contain green pigments called chlorophyll (in the chloroplasts). A pigment absorbs certain wavelengths of light and reflects other. A chlorophyll pigment absorbs blue and red light and reflects green light. Therefore the leaves appear to be green.



When light is absorbed by green plants, the light energy is used to synthesize organic compounds such as sugars from inorganic compounds, water (absorbed by the roots of the plants from the soil) and carbon dioxide (obtained from the atmosphere and enters the plants through the stomata of the leaves by diffusion). This process is known as photosynthesis and can be summarized by the following equation.



The GLUCOSE produced during photosynthesis can be converted into other forms of carbohydrates such as starch (for storage) and other complex sugars (sucrose). Notice in the equation, oxygen is also produced as a by product. This oxygen is useful and can be used by other organisms and the plants themselves for respiration.

REQUIREMENTS (CONDITIONS) FOR PHOTOSYNTHESIS:

• Carbon dioxide
• Water
• Chlorophyll
• Light energy

These requirements must be present for plants to photosynthesize. Without one, plants will not be able to photosynthesize.

WHERE IN THE LEAF DOES PHOTOSYNTHESIS TAKING PLACE?
CHLOROPLASTS...... CHLOROPLASTS..... CHLOROPLASTS.... *Hitting the white screen with my purple broom stick*

NOTE: SINCE THE STUDENTS' PRESENTATIONS, I LONGED FOR MY PURPLE BROOM STICK!!!

PLANT NUTRITION PART 2: MODES OF NUTRITION

Living things may be classified according to their modes of nutrition. They may be HETEROTROPHS or AUTOTROPHS.

AUTOTROPHS

• These are organisms that can synthesize their organic materials from inorganic materials in the environment (OR in other words, they are able to make their own food).
• GREEN PLANTS must have come to you mind at this moment right? You are right. Yes green plants are examples of autotrophs but there are other organisms which can be considered as autotrophs like some bacteria.
• BUT for some bacteria, they are using chemical energy instead of light energy so for these bacteria we say that they are chemo-synthesizing instead of photosynthesizing (Remember, since green plants are using light energy from the sun, we say that they are photosynthesizing)
• An autotroph can be a multicellular organism or unicellular organism such as Euglena (Notice the chloroplasts containing chlorophyll?)

HETEROTROPHS

• These are organisms which cannot make their own food.
  
• A heterotroph obtains its food (hence source of energy) from the organic molecules that have already been produced by the autotrophs.
  

PLANT NUTRITION PART 1:THE LEAF

This chapter covers the ways in which plants make use of the carbon dioxide from the atmosphere and water from the soil to make food (carbohydrate) with the help of energy from sunlight which is trapped by chlorophyll in the chloroplasts. This is photosynthesis. Apart from this process, this chapter also covers the way in which plants convert this carbohydrate into proteins and other materials by using minerals absorbed from the soil. Before photosynthesis is to be discussed further, we must first pay tribute to the important organ of the plants in which this process occurs, THE LEAF.

The following figure shows the whole structure of a simple dicotyledonous leaf:


Note: Being able to draw a leaf accurately (based on observing a real specimen) is very important and commonly asked in the practical paper. Students should not take the proportion and the number of veins lightly when drawing a leaf. However drawing the vein network is usually not required but if you are asked specifically in the question to draw the vein network, drawing some (at least covering 10% of the leaf) should suffice. AND mind your labelling. By now, you should be able to identify and label the petiole, midrib, veins, lamina, leaf apex and axil

The following figure shows the internal structure of a dicotyledonous leaf (transverse section):


Can you identify the upper and lower epidermal layers, the palisade mesophyll layer, the spongy mesophyll layer and the intercellular air spaces?

The following figure shows the internal structure of a dicotyledonous leaf (3-Dimensional):


Note: Notice the positions of the xylem and the phloem in the vascular bundle. In a leaf the xylem is always above the phloem (And just for comparison: the phloem is on the outer side while the xylem is in the inner side of the stem). Can you visualise how the vascular bundles in the stem are connected to those in the leaves?

MONOCOTS VERSUS DICOTS

Monocotyledonous plants and dicotyledonous plants are different in many ways. Knowing their differences is very important in your practical paper. The following figure shows five ways in which they are different:

They are different in terms of:

• The number of cotyledons in their seeds - A monocot has one cotyledon in their seeds whereas a dicot has two cotyeldons in their seeds.
• The arrangement of the veins in their leaves - The veins in the leaves of a monocot are usually parallel whereas those in the leaves of a dicot are netlike or branching (reticulated venation).
• The arrangement of the vascular bundles in their stems - In a monocot, the vascular bundles are usually randomly arranged whereas in a dicot, they are arranged in ring.
• The root systems - A monocot has fibrous root system whereas a dicot has a tap root system.
• The number of flower parts - The flower parts in a monocot are usually in a multiple of three whereas those in a dicot are in a multiple of four or five.
• The stomata in the leaves of a dicot leaf are mostly found on the lower surface of the leaf whereas those in the leaves of a monocot are evenly distributed on the lower and upper surfaces of the leaves.
  

MYOGLOBIN VERSUS HAEMOGLOBIN

Another respiratory pigment in vertebrates is MYOGLOBIN. It contains a single haem group rather than the four found in the HAEMOGLOBIN. Myoglobin has a greater affinity for oxygen than haemoglobin. Myoglobin occurs in the muscles of all vertebrates where it acts as a store of oxygen. In periods of extreme exertion, when the supply of oxygen by the blood is insufficient to keep pace with the demand, the oxygen stored in the muscles is used instead.

MYOGLOBIN HAS A GREATER AFFINITY FOR OXYGEN MEANS THAT IT COMBINES WITH OXYGEN MORE READILY THAN HAEMOGLOBIN.

ADENOSINE TRIPHOSPHATE (ATP)

During catabolism, useful energy is temporarily conserved in the "high energy bond" of ATP - adenosine triphosphate. No matter what form of energy a cell uses as its primary source, the energy is ultimately transformed and conserved as ATP. ATP is the universal currency of energy exchange in biological systems. When energy is required during anabolism, it may be spent as the high energy bond of ATP which has a value of about 8 kcal per mole. Hence, the conversion of ADP to ATP requires 8 kcal of energy, and the hydrolysis of ATP to ADP releases 8 kcal.

HUMAN NUTRITION PART 10: TRIBUTE TO THE LIVER

FUNCTIONS OF THE LIVER
A. METABOLISM OF GLUCOSE

• Excess glucose is converted with the help of insulin into glycogen and stored in the liver cells and the muscle tissues.
• When there is a decrease in the blood sugar level, the glycogen is converted back to glucose with the help of a hormone, glucagon and released into the bloodstream.
• With the help of the hormones, insulin and glucagon, the liver actually helps to regulate the amount of glucose in the blood.
  

B. METABOLISM OF AMINO ACIDS

• Amino acids are transported to all parts of the body for the synthesis of proteins, enzymes, hormones and the replacement of damaged tissues.
• Since excess amino acids cannot be stored by the body, they are DEAMINATED into two parts: the amino part and the carbohydrate part. The carbohydrate part is converted into glycogen and stored in the liver cells and muscle tissues whereas the amino part is converted into urea and transported to the kidneys for excretion.
  

C. PRODUCTION OF BILE

• The liver produces bile which helps to emulsify fats globules into tiny fat droplets.
• Note: Emulsification occurs in the duodenum.
  

D. STORAGE OF IRON

• The iron from the breakdown of haemoglobin is stored in the liver.
• It is used for the synthesis of new haemoglobin molecules.
  

E. EXCRETION OF BILE PIGMENTS

• The breakdown of haemoglobin produces bile pigments (called bilirubin and biliverdin).
• Both pigments are excreted into the duodenum as bile pigments (The colour of the faeces is actually due to these bile pigments).
  

F. SYNTHESIS OF PLASMA PROTEINS

• Plasma proteins such a s fibrinogen, serum globulin and serum albumin are synthesized by the liver from amino acids.
• Fibrinogen together with other proteins plays a very important role in blood clotting.
  

G. DETOXIFICATION

• The liver removes 95% of the alcohol from the blood. The other 5% of the alcohol in the blood leaves the body in perspiration, in the urine and in the breath.
• The alcohol contains sugar and this sugar can be oxidised in the liver to release energy.
• Overconsumption of alcohol may lead to obesity since the surplus sugar in the alcoholic drinks cannot be oxidised. So, instead the surplus is converted into fats and stored in the body.
  

H. STORAGE OF VITAMINS

• Vitamins A and D are stored in the liver.
  

I. RESERVOIR FOR BLOOD

• The blood spaces and network of blood capillaries in the liver hold a large volume of blood.
  

J. SOURCE OF HEAT ENERGY

• The liver is metabolically active. Hence it produces a large amount of heat energy.
• The heat energy is distributed to all parts of the body by the bloodstream and helps in maintaining the body temperature.
  

HUMAN NUTRITION PART 9: ASSIMILATION AND EGESTION

ASSIMILATION
Blood transports the digested food products round the body after they are being absorbed by the villi in the ileum. They are then taken up by cells. The UPTAKE and USE of the products of digestion is called ASSIMILATION.

A. ASSIMILATION OF GLUCOSE

• Glucose is used as fuel by all respiring cells. Energy is produced as a result of respiration and used in various cellular activities.
• Excess glucose is converted into glycogen with the help of Insulin and stored in the liver cells and muscle tissues in the form of glycogen granules. When the body needs energy or when the blood sugar level decreases, the glycogen in the liver will be converted back to glucose and released into the blood circulatory system.
• If the stored glycogen is not used for more than 6 hours, it may be converted to fats and stored in the adipose tissues.
  

B. ASSIMILATION OF FATS

• A portion of the absorbed fats are stored in the adipose tissues as fat droplets.
• Some are used in the synthesis of cell membrane and the rest are used for energy (only if the body is in short of carbohydrate as a source of energy).
  

C. ASSIMILATION OF AMINO ACIDS

• Amino acids serve as the basic units in the synthesis of large protein molecules. The proteins may be used for growth and development.
• Enzymes and hormones are also synthesized from amino acids.
• Excess amino acids cannot be stored. They are broken down in the liver into the amino part and the carbohydrate part. The amino part will then be transported to the kidney in the form of UREA for excretion whereas the carbohydrate part will be converted into glycogen and stored in the liver cells and muscle tissues.
• The process in which EXCESS AMINO ACIDS are broken down in the liver is called DEAMINATION.
  

EGESTION
The residues of food that cannot be digested or absorbed leave the small intestine and pass into the large intestine. There, water and vitamins (synthesised by bacteria) are absorbed and waste material is compacted into faeces. The faeces is propelled along the colon and rectum. When the anal sphincter is relaxed, the faeces is expelled. This process is called defaecation or egestion.

HUMAN NUTRITION PART 8: ABSORPTION IN THE ILEUM

Remember in the duodenum? The food is fully digested in the duodenum. The molecules (SIMPLE SUGARS (LIKE GLUCOSE, FRUCTOSE and GALACTOSE), AMINO ACIDS, and FATTY ACIDS and GLYCEROL) are small enough already to be absorbed in the ileum. Lets focus first on the structure of the ileum. In what ways is the ileum efficient in absorbing the products of the digested food?

The following figure shows the structure of some parts of the ileum:
ADAPTATIONS TO FUNCTION:

• It is fairly long and presents a large absorbing surface to the digested food.
• Its internal surface is greatly increased by circular folds bearing thousands of tiny projections called VILLI (singular = VILLUS).
• The lining epithelium is very thin and the fluids can pass rapidly through it. The outer membrane of each epithelial cell has microvilli which increase the exposed surface of the cell.
• There is a dense network of blood capillaries in each villus.

ABSORPTION!!!

• Simple sugars (glucose mainly, galactose and fructose) and amino acids pass through the walls of the villi into the blood capillaries by ACTIVE TRANSPORT.
• Mineral salts and vitamins also pass into the blood capillaries of the villi by active transport.
• Fatty acids and glycerol diffuse into the epithelium and RECOMBINE to form minute fat globules which later diffuse into the lacteal.
• The absorbed simple sugars, amino acids, mineral salts and vitamins are then transported to the liver by the HEPATIC PORTAL VEINS.
• The minute fat globules which absorbed into the lacteal are then transported into the lymphatic vessels that eventually empty into the blood circulation in the neck.
  

HUMAN NUTRITION PART 7: DIGESTION IN THE DUODENUM

The duodenum is the first few feet of the small intestine. We can say that it is the most active part of the digestive system since all types of food are digested here. The liver and the pancreas are playing very important role here. Before we discuss digestion in the duodenum, lets discuss the liver and the pancreas briefly.
THE LIVER

• The role of the liver in digestion is to manufacture BILE.
• Bile is a green watery fluid containing NO ENZYMES. It contains BILE PIGMENTS (hence the green colour) formed from the breakdown of haemoglobin in the liver. It also contains BILE SALTS which helps to emulsify fats.
• What is EMULSIFICATION? The breakdown of fat globules into smaller fat droplets (to increase the surface area so as to facilitate enzyme action). Note that, emulsification only breaks the fats physically but it does not change the fats chemically.
• After the bile is manufactured it is then stored in the GALL BLADDER. The presence of food in the duodenum triggers the secretion of bile from the gall bladder into the duodenum through the bile duct.
• EMULSIFICATION IS JUST LIKE CUTTING A BIG CHUNK OF BUTTER INTO SMALLER CUBES. THEY ARE ONLY DIFFERENT PHYSICALLY BUT STILL THE SAME CHEMICALLY. AND THINK! WHICH WILL MELT DOWN FASTER, THE CHUNK OR THE CUBES? OF COURSE THE CUBES RIGHT? SIMILAR TO FAT GLOBULES AND FAT DROPLETS, ENZYME REACTION WILL BE FASTER ON THE DROPLETS RATHER THAN ON THE GLOBULES.
  

THE PANCREAS

• The important role of the pancreas in digestion is to produce PANCREATIC JUICE.
• Pancreatic juice contains SODIUM HYDROGEN CARBONATE, PANCREATIC AMYLASE, LIPASE and TRYPSINOGEN.
• The sodium hydrogen carbonate helps to neutralise the acidic chyme once it enters the duodenum
  

WHAT HAPPENS IN THE DUODENUM?

• As mentioned earlier, the duodenum is very active since all types of food are digested here.
  
• Apart from the BILE and the PANCREATIC JUICE, the duodenum itself secretes the INTESTINAL JUICE produced by the intestinal glands in the wall of the duodenum itself.
• The intestinal juice contains ENTEROKINASE, EREPSIN, MALTASE, SUCRASE, LACTASE and LIPASE.
  
• So all three juices are actually working together in the duodenum to digest all types of food present in the chyme. To make our life easier, lets discuss the roles of the contents of the juices by the types of food they work on.
  

CARBOHYDRATE DIGESTION IN THE DUODENUM

• The remaining undigested starch from the mouth is digested by the pancreatic amylase into maltose and the maltose is further digested into glucose by maltase.
• Lactose is digested into glucose and galactose by lactase.
• Sucrose is digested into glucose and fructose by sucrase.
  

PROTEIN DIGESTION IN THE DUODENUM

• Trypsinogen is first activated into trypsin by enterokinase.
• Trypsin then digests proteins into polypeptides.
• Polypeptides are then digested further by erepsin into amino acids.
  

FATS DIGESTION IN THE DUODENUM

• Bile first emulsify fat globules into fat droplets (SURFACE AREA!!!).
• The fat droplets are then digested chemically by lipase into FATTY ACIDS and GLYCEROL.
  

END PRODUCTS OF DIGESTION

• Carbohydrates --> GLUCOSE, FRUCTOSE and GALACTOSE
  
• Proteins --> AMINO ACIDS
• Fats --> FATTY ACIDS and GLYCEROL

NOW, THE MOLECULES ARE SMALL ENOUGH TO BE ABSORBED BY THE VILLI IN THE ILEUM!!!

HUMAN NUTRITION PART 6: DIGESTION IN THE STOMACH

• The stomach has a strong muscular walls. The muscles contract and relax to churn the food an mix it with the enzymes and mucus. The mixture is called CHYME.
• The presence of food in the stomach, triggers the gastric glands (in the wall of the stomach) to secrete GASTRIC JUICE.

• The gastric juice contains PEPSINOGEN (inactive form of pepsin), HYDROCHLORIC ACID and MUCUS.
• The function of the hydrochloric acid is to provide acidic medium for the pepsin to function well (Pepsin works well at pH 2). Apart from this, it also kills any bacteria coming along with the food and activates the inactive pepsinogen into PEPSIN (REMEMBER these three functions of the hydrochloric acid). (Note: The salivary amylase from the mouth is denatured in the stomach? WONDER WHY?)
  
• The mucus protects the stomach wall from being attacked by the acid (REMEMBER the nature of an acid? CORROSIVE!!!)
• Any proteins present in the chyme is digested by the pepsin into POLYPEPTIDES.

NOTE: IN THE STOMACH, ONLY PROTEINS ARE DIGESTED CHEMICALLY (ALSO PHYSICALLY DUE TO THE STOMACH MUSCLE CONTRACTION). STARCH AND FATS ARE NOT DIGESTED CHEMICALLY IN THE STOMACH AS THE STOMACH DO NOT PRODUCE ENZYMES THAT CAN WORK ON STARCH AND FATS!!!

HUMAN NUTRITION PART 5: DIGESTION IN THE MOUTH AND OESOPHAGUS

DIGESTION IN THE MOUTH

• Once ingested, the food is first broken down into smaller pieces (physical digestion - chewing action with the help of the teeth) so as to increase the surface area and this in turn facilitates chemical digestion.
• The presence of food in the mouth triggers the salivary glands to secrete saliva.
• Saliva contains water, mucus and the enzyme, amylase.
• The water helps to soften the food whereas the mucus lubricates the food (bolus) so that the bolus can be swallowed into the oesophagus.
• The enzyme, amylase digests starch in the food into maltose. Since the bolus is not kept in the mouth for a very long time, some of the starch is still remain undigested.
• REMEMBER: Only starch is digested in the mouth (though not all) whereas proteins and fats are not, since there are no enzymes in the saliva that can digest them.
• The bolus is then swallowed into the oesophagus through the pharynx.
• Swallowing action causes the epiglottis to close the mouth of the trachea. This prevents food from entering the trachea during swallowing.
  

DIGESTION IN THE OESOPHAGUS

• No chemical digestion occurs in the oesophagus because there are no enzymes produced by the oesophagus. However starch digestion from the mouth continues as the bolus moves down the oesophagus. But not all the starch is digested as the bolus only stays in the oesophagus very briefly.
  
• Physical digestion continues as the circular and longitudinal muscles contract and relax alternately. This breaks the bolus further physically and at the same time helps to move the bolus down into the stomach.
  

HUMAN NUTRITION PART 4: THE ALIMENTARY CANAL

Before discussing chemical digestion along the digestive tract, it is better to know the parts in your digestive system first (Actually it helps, if you can memorize the figure and draw it freely).

From the following figure, it can be seen clearly that your digestive system consists of two main parts:

• The ALIMENTARY CANAL. This is the muscular tube (consisting of the circular and longitudinal muscles) in which digestion takes place. It is about 8 metres long, running from your mouth to your anus and has several distinct parts each one fulfilling an important role in digestion.
• The ASSOCIATED ORGANS. These associated organs consist of the salivary glands, liver, gall bladder, gastric glands (in the stomach), and pancreas. No digestion takes place in these associated organs except the stomach. These organs however play a very important role in chemical digestion since they produce enzymes and chemicals which help to facilitate chemical digestion.