THE HUMAN EYES

1. PARTS AND FUNCTIONS

• Sclera - Tough white outer coating (the white part of your eye is actually the sclera. The main function of the sclera is to protect the eyeball.
• Cornea - This is actually the front part of the sclera but unlike the sclera it is transparent. The function of the cornea is to refract light rays into the eye.
• Conjunctiva - This is a thin epithelium which protect the cornea.
• Vitreous humour and aqueous humour - The liquid behind the lens is jelly-like and is called vitreous humour while the aqueous humour in front of the lens is watery. The function of both the vitreous humour and the aqueous humour is to keep the spherical shape of the eyeball. In addition, the aqueous humour also functions in providing nourishment to the non-vascularised lens and cornea.
• Lens - Transparent structure (flexible and can change its shape during accomodation) which refract light rays on to the retina.
• Suspensory ligament - To hold the lens in place. Plays a very important role in accomodation.
  
• Iris - Iris gives colour to your eyes. It consists of the radial and the circular muscles. The iris controls the size of the pupil, thus controlling the amount of light entering the eyes. These muscles of the iris work antagonistically.
• Pupil - Pupil is a hole at the centre of the iris. The function is to allow light to enter the eye.
• Choroid - The second layer of the eye. It is highly vascularised to provide nourishment to the eye. It is also pigmented black (absorbs light) so as to prevent internal reflection in the eye.
• Ciliary body - It produces aqueous humour. It contains circular muscles which helps to alter the size of the lens during accomodation.
• Retina - The internal lining at the back of the eye is the retina. It contains light sensitive cells (the cones and the rods) which respond to light.
• Fovea (yellow spot) - The part of the retina which is very sensitive to light since rods and cones are highly concentrated here. When you focus on an object, the image of the object will fall on to this region.
• Blind spot - This region of the retina contains no light sensitive cells so object will not be seen here if light falls on to this region.
• Optic nerve - This contains nerve fibres which transmit electrical impulses to the brain.
• Tear glands - These are glands present under the top of the eyelid. The function is to produce tear fluid which helps to prevent friction when blinking. The tear fluid also wash away any dust particles or foreign bodies. It contains lysozyme which kills bacteria.

2. ACCOMODATION

• Viewing distant image - Ciliary muscles relax, the suspensory ligaments become taut pulling the lens outwards. As a result the lens becomes thinner. This will in turn, increased the focal length hence enable you to view distant object.
• Viewing near object - Ciliary muscles contract, the suspensory ligaments become slacken. Hence there is no pulling force to pull the lens outwards. As a result the lens becomes thicker and this will decrease the focal length. Hence you are able to focus at near object.
  

3. PUPIL REFLEX

The following figure shows the iris which control the size of the pupil thus controlling the amount of light entering the eye.

In Bright Light AND In Dim Light

• The retina (due to the presence of rods and cones) is very sensitive to light. When light falls on to the retina, the light (stimulus) will stimulates the retina. An electrical impulse will then be transmitted to the brain along the sensory nerve fibres in the optic nerve which contains sensory neurones. At the synapse between the sensory neurones and the relay neurones, acetylcholine will be released which stimulates the relay neurones in the brain to produce an electrical impulse. The electrical impulse is then transmitted along the relay neurones. Again at the synapse between the relay neurones and the motor neurones, acetylcholine will be released which stimulates the motor neurones to produce an electrical impulse. The electrical impulse is then transmitted along the motor neurones to the effector (which in this case are the radial and circular muscles of the iris).
• In dim light, the radial muscles contract and the circular muscles relax. This causes the pupil to dilate and hence allows more light to enter the eye.
• In bright light, the radial muscles relax and the circular muscles contract. This causes the pupil to constrict and hence allows less light to enter the eye (thus protects the delicate light sensitive cells in the retina)

Note: TIME WAITS FOR NO MAN

SKELETON

FUNCTIONS OF THE SKELETON:

• Support - The skeleton holds the body off the ground and keeps its shape even when muscles are contracting to produce movement.
• Protection - The brain is protected from injury by being enclosed in the skull. The heart, lungs and liver are protected by the rib cage and the spinal cord is enclosed inside the backbone.
• Movement and Locomotion - Many bones of the skeleton acts as levers. When muscles pull on these bones, they produce movements such as the raising of the ribs during breathing or the chewing action of the jaws. For a skeletal muscle to produce movement, both its ends need to have a firm attachment. The skeleton provides suitable points of attachment for the ends of muscles. The skeleton with the help of muscles also helps to move the body from one place to another. This is called locomotion.
• Production of blood cells - The red bone marrow of some bones produce both red and white blood cells.

Note: You should be able to identify the humerus, ulna, radius, femur, tibia, fibula, pelvic girdle, pectoral girdle and of course the skull, ribs and rib cage, sternum and skull.JOINTS:

• Where two bones meet they form a joint.
• In the syllabus, you only have to know the hinge and the ball and socket joints.

THE HINGE JOINT

THE BALL AND SOCKET JOINT

• Where can these joints be found? Hinge joints are found at your elbows and your knees whereas the ball and socket joint are usually found at your shoulder and your hip.
• The differences between these two types of joints are: hinge joints only allow movement in one direction only (for example bending your knee and your arm) whereas the ball and socket joints allow movement in all direction.

THE CARTILAGE, LIGAMENT, SYNOVIAL MEMBRANE AND SYNOVIAL FLUID

• The cartilage functions in reducing friction between two bones as shown in the figure above.
• Friction is further reduced by the synovial fluid which is produced by the synovial membrane.
• The function of the ligaments is to hold bones in position thus preventing dislocation. Dislocation may occurs if the ligaments are torn.
  

ANTAGONISTIC ACTION OF THE BICEPS AND TRICEPS IN THE ARM

• You need to know the role the biceps and triceps (these are known as skeletal muscles) in your arm which helps in bringing about movement such as when you are flexing or stretching your arm.
• Arm flexing - Biceps contracts while triceps relaxes.
• Arm stretching - Biceps relaxes while triceps contracts.

TRANSPORT IN MAMMALS PART 7: ORGAN TRANSPLANT AND TISSUE REJECTION

Organ or tissue transplant is when a damaged or diseased organ or tissue is replaced by a healthy or functional one. This healthy or functional organ or tissue may come from another person or the patient himself.

PROBLEM:
If the healthy organ or tissue to be donated comes from another person (donor), the organ or tissue may be treated by the patient's (recipient's) immune system as foreign body. As a result the lymphocytes may respond to this transplanted organ or tissue by producing antibodies which destroy the transplanted tissue or organ. This results in TISSUE/ORGAN REJECTION.



Tissue or organ rejection may not be a problem if the tissue or organ to be transplanted comes from the patient himself. For example, a blocked coronary artery may be replaced by an artery form another part of the patient's body.

PREVENTION OF TISSUE REJECTION:

• Tissue match: the tissue of both the donor and recipient must be genetically as close as possible. Therefore the likely candidate should be the brother, sister, parents and close relatives of the patient.
• Using immuno-suppressive drugs: this drug inhibits the activity of the recipient's immune system. Problem: the patient is prone to many kind of infection and he has to continue treatment of this drug for the rest of his life.
• X-ray radiation of the bone marrow and lymphoid tissue: this method inhibits the production of blood cells which slows down the rejection process.
  

TRANSPORT IN MAMMALS PART 6: THE FUNCTION OF BLOOD

The blood has two important functions: the transport function and the protective function.

THE TRANSPORT FUNCTION OF BLOOD
Blood acts as a transport medium carrying various substances from one part of the body to another. The blood transport the following:

• Digested food nutrients from the ileum to all parts of the body (via plasma).
• Excretory products from the tissues to the excretory organs for removal (via plasma).
• Hormones, from the endocrine glands to the target organs (via plasma).
• Heat, from the respiring tissues to other parts of the body, hence maintaining constant body temperature (via plasma).
• Oxygen, from the lungs to all parts of the body (via the red blood cells).

THE PROTECTIVE FUNCTION OF BLOOD

• Phagocytosis by the phagocytes: The phagocytes engulf and ingest foreign particles (mainly bacteria) at the site of the wound or cut. Some of the phagocytes are killed in the process. These dead phagocytes at wound, together with the dead foreign particles, form pus.
• Production of antibodies by the lymphocytes: The production is triggered when foreign particles produce toxins. The antibodies neutralise the poisonous effect of the toxins. The antibodies can also kill the foreign particles by causing the foreign particles to clump together (agglutination). The agglutinated bacteria are then ingested by the phagocytes.
• Blood clotting: This seals wound, prevents entry of foreign particles and prevents excessive loss of blood.

IMPORTANT:

• In the lungs, haemoglobin in the red blood cell combines loosely with oxygen to form oxyhaemoglobin.
• The blood containing oxyhaemoglobin is called OXYGENATED BLOOD.
• The oxyhaemoglobin is then transported to all body tissues.
• The oxyhaemoglobin then releases its oxygen as the blood passes through tissues containing very little oxygen.
• The blood containing little oxygen is called DEOXYGENATED BLOOD.
• The deoxygenated blood is then transported back to the lungs

OXYGENATED BLOOD TENDS TO BE BRIGHT RED IN COLOUR WHEREAS DEOXYGENATED BLOOD TENDS TO BE BLUISH. HENCE ARTERIES WHICH GENERALLY TRANSPORT OXYGENATED BLOOD IS RED IN COLOUR WHILE THE VEINS WHICH GENERALLY TRANSPORT DEOXYGENATED BLOOD IS BLUISH IN COLOUR.

TRANSPORT IN MAMMALS PART 5: PLATELETS (THROMOBOCYTES)

Thrombocytes are actually not true cells. They are fragments of cytoplasm from certain bone marrow cells. Together with fibrin, they play a very important role in BLOOD CLOTTING. Blood clotting is very important because it helps to seal wound and cut, thus preventing excessive loss of blood. Apart from this it also stops foreign particles like bacteria from entering the blood stream.

The following figure shows how blood clot clogged wound thus preventing blood loss.
MECHANISM OF BLOOD CLOTTING

• At cut or wound, an enzyme called thrombokinase is released by the damaged tissues and blood platelets.
• The thrombokinase together with calcium ions, then convert the (inactive) protein prothrombin to thrombin (Calcium ions as well as vitamin K must be present, otherwise blood clotting will not take place - hence one of the importance role of calcium in your diet).
• The thrombin (which is also an enzyme) then catalyses the conversion of soluble protein fibrinogen to a meshwork of insoluble threads of fibrin.
• The fibrin threads formed entangle the red blood cells which results in the formation of BLOOD CLOT. White blood cells can also be found together with the blood clot to fight against foreign particles like bacteria at the cut or wound.
  

The following figures show how the fibrin entangle the red blood cells to form BLOOD CLOT.

The following figure summarises the mechanism of blood clotting. It heps a lot if you remember the flow.


Vitamin K? Where is Vitamin coming from? It is actually produced by bacteria (NOT HARMFUL!!!) in your intestines.

TRANSPORT IN MAMMALS PART 4: WHITE BLOOD CELLS (LEUCOCYTES)

Characteristics of white blood cells:

• Colourless
• Irregular in shape
• Contains nucleus
• Contains no haemoglobin
• Larger in size than red blood cells
• Fewer in number than red blood cells
• The ratio of red to white blood cells is 700:1

There are two main kinds of white blood cells

• Lymphocytes
• Phagocytes

LYMPHOCYTES

• Produced by the lymph glands or the lymph nodes.
• Has large rounded nucleus with small amount of non-granular cytoplasm.
• Nearly round in shape.
• Show limited movement.
• Function: to produce antibodies which fight against micro-organisms other than bacteria (mainly viruses).

A Lymphocyte

PHAGOCYTES

• Produced by the bone marrow.
• Has lobed nucleus with granular cytoplasm.
• Irregular shape.
• Able to move.
• Function: to fight against foreign particles (mainly bacteria) by means of phagocytosis.
  

A Phagocyte

The following figure shows phagocytosis. In phagocytosis, first the phagocyte moves with the help of its pseudopodia towards the foreign particles (bacteria). Upon reaching the foreign particles, it will then engulf the foreign particles by surrounding them using the pseudopodia. A vacuole is formed as a result. Digestive enzyme is then secreted into the vacuole which digests the foreign particles. The products of digestion is then absorbed into the cytoplasm and when the phagocyte died, pus will be formed at the infected area.

TRANSPORT IN MAMMALS PART 3: RED BLOOD CELLS (ERYTHROCYTES)

The following are the characteristics of a mammalian red blood cell:

• Shape: biconcave (provides large surface area for more absorption of oxygen).
• No nucleus (this enables the red blood cell to accommodate more haemoglobin so that more oxygen molecules can be transported and to make the red blood cell more flexible so that it can squeeze itself through the blood capillaries).
• Produced by the bone marrow as shown below.

• Lifespan: 3 to 4 months (when they are worn out, they are destroyed in the liver).
• Contains haemoglobin (a speial kind of protein containing iron): this pigment enables red blood cell to transport oxygen from the lungs to all cells in the body (mind you carbon monoxide combines readily with haemoglobin than oxygen).
• When haemoglobin is broken down in the liver, the iron is released and stored in the liver (hence liver is very rich source of iron). Bile pigments are also produced during the breakdown of haemoglobin (bile pigments are excreted into the colon and gives faeces its colour - brownish and sometimes greenish depending on the amount of bile pigments being excreted).

BLOOD APPEARS RED IN COLOUR BECAUSE OF THE RED BLOOD CELLS

TRANSPORT IN MAMMALS PART 2: THE BLOOD

The average person has about 5.5 litres of blood. Although blood is liquid, about 45% of it is made up of solid particles held in suspension. The remaining 55% is a straw-coloured fluid called PLASMA. The solid matter in blood consists of:

• Red blood cells (erythrocytes)
• White blood cells (leucocytes)
• Platelets (thrombocytes)

THE PLASMA
The plasma is a pale yellowish liquid. About 90% of plasma is water in which a complex mixture of various substances is dissolved. These substances are:

• Soluble proteins: serum albumin, serum globulin, fibrinogen, prothrombin and antibodies (fibrinogen and pro-thrombin play an important role in blood clotting whereas antibodies are involved in fighting diseases).
• Dissolved mineral salts: chlorides, bicarbonates, and sulphates and phosphates of sodium and potassium. All these occur as ions in the plasma. CALCIUM SALTS are also present which are essential for blood clotting.
• Food substances such as glucose, amino acids, fats and vitamins.
• Excretory products such as urea, uric acid and carbon dioxide.
• Hormones such as Insulin, Glucagon, Adrenaline and Anti-Diuretic Hormone.
  

TRANSPORT IN MAMMALS PART 1: WHY DO WE NEED ONE?

WHY DO WE NEED A TRANSPORT SYSTEM?

• To distribute the absorbed useful substances like oxygen and food substances (particularly products of digestion - simple sugars, amino acids and fats) throughout the body of the animal (example: glucose is distributed to all respiring cells to generate energy).
• To remove waste products such as carbon dioxide and urea from the body of the animal before these waste products accumulate to harmful levels.

TRANSPORT SYSTEM IN MAMMALS
In mammals, the transport system consists of the:

• Blood system for transporting blood
• Lymphatic system for transporting lymph

(Note: Both blood and lymph are fluids in which substances are distributed all over the body)

The main transport system in mammals is its Blood System (also called the Vascular System). It consists of three important components:

• The Blood
• The Blood Vessels
• The Heart (a pump which keep the blood flowing through the blood vessels)

The following figure shows the general layout of the transport system (blood system) of a human as seen from the front.

Notice that the figures above show that the human transport system consists of the SYSTEMIC CIRCULATION and the PULMONARY CIRCULATION. The systemic circulation transports blood all over the body (except the lungs) whilst the pulmonary circulation transports blood only to the lungs.

If you follow the arrows, beginning at the lungs, you can see that the blood flows into the left-hand side of the heart, and then out to the rest of the body. It is brought back to the right hand side of the heart, before going back to the lungs again. This is called a DOUBLE CIRCULATORY SYSTEM because the blood travels through the heart TWICE on one complete journey around the body.

The following figure shows the lymphatic system:


(Note: there is no "pump" in the lymphatic system as in the blood system)


Now, because there is no pump in this system, lymph is prevented from flowing backward by having VALVES along the lymph vessels. The following figure shows the valves in the lymph vessels.



The following figure shows the relationship between the BLOOD SYSTEM and the LYMPHATIC SYSTEM:

PLANT NUTRITION PART 16: MORE ON THE RATE OF PHOTOSYNTHESIS

As mentioned in the previous post, any factor that directly affects a process if its quantity is changed is called the LIMITING FACTOR.



By looking at graph 1, we can see that the rate of photosynthesis increases as the light intensity increases (0 to A). We say that light intensity is the LIMITING FACTOR. Beyond point A, light intensity is no longer the LIMITING FACTOR since the rate remains constant even though the light intensity increases. In this case we have to consider other factors that could cause the rate to become constant (A to B).

Graph 2 shows that the rate does not increase so much despite the temperature being increased from 20 to 30 degree celsius (with the carbon dioxide being kept constant). This means that temperature is not the actual LIMITING FACTOR. But if the conditions are reversed, the temperature being constant and the carbon dioxide being increased from 0.03% to 0.13%, the rate increases (Look at graph 3). Both of these indicate that carbon dioxide concentration is the LIMITING FACTOR in A to B (Graph 1).

The LIMITING FACTOR in E to F (Graph 3) is the temperature. Increasing the temperature from 20 to 30 degree celsius causes an increase in the rate of photosynthesis (Look at graph 4) though the carbon dioxide concentration remains constant at 0.13%.

END OF CHAPTER 6

PLANT NUTRITION PART 15: FACTORS AFFECTING PHOTOSYNTHESIS

The rate of photosynthesis is affected by the following factors:

• LIGHT INTENSITY

• CONCENTRATION OF CARBON DIOXIDE

• TEMPERATURE

When we consider light intensity, immediately we would think that, the higher the light intensity, the higher would the rate of photosynthesis be, right? That's right actually. But at certain point even if the light intensity is increased, the rate will not increase any further. This is because, the chlorophyll in the chloroplasts can only absorb so much energy from sunlight. It's just like pouring water into a glass. The more you pour in water the higher will the water level be in the glass but if the level is already reaching the brim of the glass, no matter how much water you pour in, the water level will not increase any further. UNDERSTAND?

In the above analogy, when the water level reaches the brim of the glass, we can say that the glass is the LIMITING FACTOR because despite the availability of water, the glass can only take so much. Now, lets consider light intensity which is a factor affecting the rate of photosynthesis. In this case, the LIMITING FACTOR is the chlorophyll right? Right you are, if you consider the absorption of light at a point at which the chlorophyll can no longer absorb more than it should. Because, no matter how much light energy there is available, the chlorophyll can only absorb so much. So at this point, increasing the light intensity will not increase the rate of photosynthesis any further.

But mind you, before reaching that particular point where the graph levels off, light intensity is actually the LIMITING FACTOR because the rate of photosynthesis depends on it. Meaning, before this particular point (where the graph levels off), the rate of photosynthesis will only increase, when the light intensity is increased.


Now, lets consider the effect of carbon dioxide concentration. By looking at the graph below, the rate of photosynthesis increases as the concentration (%) of carbon dioxide is increased. We say that carbon dioxide is the LIMITING FACTOR since the rate depends on it. But at certain point, even after increasing the concentration of carbon dioxide, the rate remain constant. After this point, carbon dioxide concentration is no longer the LIMITING FACTOR.



Temperature may also affect the rate of photosynthesis. Since photosynthesis is an enzyme-controlled reaction, the rate depends on the temperature at which the reaction takes place. As can be seen from the graph, as the temperature is increased, the rate will also increased. We say that the temperature is the LIMITING FACTOR since the rate really depends on it. But at the optimum temperature, the reaction decreased and eventually stops at 45 degree celsius because at high temperature the enzyme catalysing photosynthesis is denatured. So, after the optimum temperature, temperature is no longer the LIMITING FACTOR.

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