MY E MAIL.....

For the benefits of visitors who are not my students, thank you for visiting this blog.... Hopefully it helps.... If you are still interested.... e-mail me at adidarwish@yahoo.co.uk........

OSMOSIS AND THE OPENING AND CLOSING OF STOMATA

The figure above shows the guard cells with a stoma in between them. The guard cells are actually an example of specialized cells or modified cells. Modified in such a way that they can perform their function well. Their function is to allow the stoma to open or to close.

In what way are they specialized?
They are specialized in such a way that their cell wall around the stoma is much thicker. This allows the cells to bend on one side when they become turgid. Hence causing the stoma to open.

Opening:
Stoma opens when the guard cells are turgid. They become turgid when the water potential of the cells adjacent to the guard cells are higher than that in the cell sap of the guard cells. This result in water molecules from the adjacent cells to move into the guard cells by osmosis. When water molecules enter, the vacuoles increase in size causing osmotic pressure to build up and this in turn causes the guard cells to become turgid. When the guard cells become turgid, they bend inwards causing the stoma to open. The opening of the stoma is an advantage because it allows gaseous exchange to take place.

Closing:
When the water potential of the adjacent cells is lower than that in the cell sap of the guard cells, water molecules move out of the guard cells into the adjacent cells by osmosis. When this happens, the guard cells become plasmolysed which in turn causes the stoma to close.

THE IMPORTANCE OF ACTIVE SITES OF ENZYMES

Have a look at the following figure:


A particular enzyme molecule has an active site which is usually complimentary to the shape of the substrate on which it acts on. Hence enzyme's specificity. Meaning, a particular enzyme can only act on a particular substrate but not with other substrates.

At temperature higher than the optimum temperature, the shape of the active site of an enzyme starts to become distorted making it difficult for the substrate molecule to fit in into it. We say that after the optimum temperature, the enzyme starts to denature. Because of this chances for the enzyme molecules and the substrate molecules to collide to form enzyme-substrate complexes are now becoming lower and lower despite the availability of more kinetic energy at higher temperature. This in turn, causes less products to be formed. Hence the rate of reaction becomes lower and lower at temperatures higher than the optimum temperature.

At extremely high temperature the active site of an enzyme is said to be totally DENATURED. This means that the active site is actually totally distorted. As a result, substrate molecule finds it difficult to fit in into the active site. No enzyme-substrate complexes formed. Meaning, no products formed. This in turn means no reaction occurs. Hence the rate of reaction is actually NIL at this temperature.

Is this REVERSIBLE?
Absolutely NOT reversible. Once an enzyme is denatured, it is actually damaged and cannot be used again even if one tries to lower back the temperature to the optimum temperature.

How about at extremely low temperature?
Enzyme is not DENATURED at a very low temperature. It is simply INACTIVATED. This means there is no kinetic energy available at this temperature to activate the enzyme. Once the temperature is increased, kinetic energy will start to become available and the enzyme and substrate molecules will start to collide with each other to form enzyme-substrate complexes which will eventually break/combine to form products. [Break if the reaction is a CATABOLIC reaction (as shown in the figure above)and Combine if the reaction is an ANABOLIC reaction]

HAPPY READING PEOPLE!!!

ENZYMES AND pH

pH is also a factor which affects the rate of an enzyme catalyzed reaction. The following graph shows how three different enzymes are affected by pH.

From the graph above, it can be seen that Enzyme #1 works well at pH 4. It means that the optimum pH of this particular enzyme is 4. Above or below this pH, the rate of the reaction slows down. The optimum pH for enzymes #2 and #3 are 6 and 9 respectively. This means that below or above these pH, the reactions catalyzed by these enzymes will slow down.

ENZYMES AND TEMPERATURE

One of the characteristics of enzymes is that they are very sensitive to temperature. The following graph shows how the rate of an enzyme catalyzed reaction is affected by temperature.

The graph above tells you that as the temperature is increased, the rate of the enzyme activity increases. As you can see from the graph, the rate of reaction doubles as the temperature is increased by 10 degree Celsius. The rate is at its optimum at the optimum temperature of about 40 degree Celsius. If the temperature is increased further the rate will decrease. This is due to the effect of high temperature on the active sites of the enzymes. At a very high temperature, the shape of the active sites changed. When this happened, the substrate molecules will not be able to fit in into the active site. As a result, the reaction stops. At this stage, the enzymes are said to be denatured and this is irreversible. Unlike at a very low temperature, though the enzymes are not active, they still can be activated if the temperature is increased.

MOVEMENT OF FOOD IN THE PHLOEM

This process is called translocation and involves the movement of organic substances around the plant. It requires energy to create a pressure difference and so is considered an active process.

Sucrose is loaded into the phloem at a source, usually a photosynthesizing leaf. For this to occur, hydrogen ions are pumped out of the companion cell using ATP. This creates a high concentration of hydrogen ions outside the companion cell. Sucrose is loaded (moved into companion cells) by active transport, against the concentration gradient.

However, the protein carrier involved in the loading, has two sites, one for sucrose and one for a hydrogen ion. When it is used to pump sucrose into the companion cell, hydrogen will move in the opposite direction, back down its concentration gradient. This is why a high concentration of ions is needed outside the cell.

The sucrose can then diffuse down the concentration gradient into the sieve tube element via the plasmodesmata that connects the companion cell with the sieve tube element. This lowers the water potential of the sieve element so water enters by osmosis.

At another point sucrose will be unloaded from the phloem into a sink (e.g. root). It is likely that the sucrose moves out by diffusion and is then converted into another substance to maintain a concentration gradient. Again, water will follow by osmosis.

This loading and unloading results in the mass flow of substances in the phloem. There is evidence to support this theory; the rate of flow in the phloem is about 10,000 times faster than it would be if it was due only to diffusion, the pH of the phloem sap is around 8 (it is alkaline due to loss of hydrogen ions), and there is an electrical potential difference across the cell surface (negative inside due presumably to the loss of positively charged ions).

MOVEMENT OF WATER IN THE XYLEM

Water evaporates from the mesophyll cells into air spaces in the leaf. If the air surrounding the leaf has less water vapour than the air in the intercellular spaces, water vapour will leave the leaf through stomata.

This process is called transpiration and will continue as long as the stomata are open and the air outside is not too humid. On dry, windy days when water vapour is continually diffusing out and being removed, transpiration will increase in rate.

Although this loss of water can cool the plant, it is essential that the plant does not lose too much water. Therefore water must be continuously supplied to the leaves. The xylem ensures that this happens.

Water is removed from the top of xylem vessels into the mesophyll cells down the water potential gradient. This removal of water from the xylem reduces the hydrostatic pressure exerted by the liquid so the pressure at the top is less than at the bottom. This pushes the water up the tube. The surface tension of the water molecules, the thin lumen of the xylem vessels and the attraction of the water molecules for the xylem vessel wall (adhesion), helps to keep the water flowing all the time and to keep the water column intact.

Pressure to push water up can also be increased from the bottom. By actively pumping minerals from cells surrounding the xylem into the xylem itself, more water is drawn into the xylem by osmosis.

This increase in water pressure, called root pressure, certainly helps in the process but is less important than the simple movement of water down the water potential gradient, ultimately from the soil at the bottom, to the air at the top. This is because moving water this way does not require energy (it is passive).

TUITION

UPON REQUEST, MY WIFE AND I ARE OFFERING TUITION EXCLUSIVELY FOR BIOLOGY 'O' AND 'A' LEVELS.....

• $50 FOR 'O' LEVEL AND $60 FOR 'A' LEVEL
• A MAXIMUM OF 6 STUDENTS PER CLASS
• 2 HOURS PER SESSION
  
• SUNDAYS ONLY
  

BIOLOGY O LEVEL RESULTS

33 As (OF WHICH 7 OBTAINED ALL GRADE 1 IN PAPERS 1, 2 AND 3)

44 Bs (OF WHICH 38 OBTAINED B3)

9 Cs (OF WHICH 7 OBTAINED C5)

3 Ds

3 Us

WELL DONE EVERYONE!!!..... IT'S BEYOND MY EXPECTATION.... MOST OBTAINED 2 OR 3 GRADES BETTER THAN THE QUALIFYING EXAMINATION!!!

PLASMOLYSED PLANT CELL

Question: Focus on the plasmolysed cell in the following figure... especially the space in between the cell wall and the cytoplasm....... What's in it?

The answer is: concentrated solution.....

Why?
Because cell wall if FULLY PERMEABLE... therefore it allows the concentrated solution to enter the cell..... so the space in between the cell wall and the cytoplasm is actually filled with the concentrated solution.....

ASEXUAL REPRODUCTION VERSUS SEXUAL REPRODUCTION

ASEXUAL REPRODUCTION (AR)
This is a type of reproduction resulting in the production of genetically identical offspring from one parent.

SEXUAL REPRODUCTION (SR)
This is the formation of new individuals by a process which involves the fusion of nuclei in the sex cells called gametes to form a zygote. In sexual reproduction, the offspring are genetically different from their parents.

ASEXUAL REPRODUCTION VERSUS SEXUAL REPRODUCTION

• AR involves one parent whereas SR involves two parents.
• No gametes involved in AR but haploid male and female gametes are involved in SR.
• No zygote formed in AR but a diploid zygote is formed by fertilization in SR.
• No genetic variation occurs in AR as offspring are identical to parent but in SR, genetic variation occurs as offspring are different from the parents.
• AR is very rapid under favourable conditions whereas SR takes a longer time.
• Population number increases rapidly in AR but slowly in SR.

MENSTRUATION AND THE DEVELOPMENT OF THE EMBRYO

MENSTRUATION
Monthly discharge of blood from the vagina. The blood is normally referred to as MENSES and it contains blood, broken uterine lining and unfertilized egg. Normally menstruation takes about five days.

SUMMARY: ROLES OF HORMONES IN MENSTRUATION

• Onset of menstruation (starting from day one): The pituitary gland secretes follicle stimulating hormone (FSH) into the bloodstream and from here it is then transported to the Target organ (Ovary)
• In the ovary FSH stimulates one primary follicle to ripen (mature) into Graafian follicle
• FSH also stimulates the follicles in the ovary to secrete oestrogen
• Oestrogen causes the repair and growth of the uterine lining (after menstruation)
• Oestrogen (in high concentration) also inhibits FSH production (therefore preventing ripening of more follicles)
• Oestrogen also stimulates the pituitary gland to secrete luteinising hormone (LH)
• LH causes ovulation
• LH also causes the formation of corpus luteum
• Corpus luteum secretes progesterone
• Progesterone keeps the uterine lining thick to prepare itself for implantation if there is fertilization
• Progesterone inhibits both FSH and LH production
• If there is no fertilization, the corpus luteum breaks; Progesterone production stops; Uterine lining breaks; MENSTRUATION occurs

DEVELOPMENT OF THE EMBRYO

• After fertilization, the zygote passes along the oviduct to the uterus and as it does so, it begins to divide (by mitosis) to form a ball of cells which later develops into an embryo
• It takes about five days for the embryo to reach the uterus and upon reaching the uterus, it will eventually sinks in or embeds itself in the uterine lining, hence IMPLANTATION takes place
• The embedded embryo will then develop into a foetus
• Function of amniotic fluid: to enclose the foetus in a fluid-filled space known as the amniotic cavity
• The amnion/amniotic cavity functions in supporting and cushioning the foetus, thus preventing it from mechanical damage
• The amniotic fluid also acts as a shock absorber
• During birth, the amniotic fluid lubricates and reduces friction in the vagina
• The amniotic fluid also buoys the foetus and allows it to move freely during growth
• Generally the umbilical cord functions in supplying the foetus with oxygen and dissolved food nutrients as well as removing waste products (carbon dioxide and urea) from the foetus
• Inside the umbilical cord, there are three blood vessels. Two of these blood vessels are the umbilical arteries whereas one is an umbilical vein
• The umbilical arteries function in carrying deoxygenated blood from the foetus to the placenta
• The umbilical vein functions in carrying oxygenated blood (rich in oxygen and food substances as well as antibodies) from the placenta to the foetus

FUNCTIONS OF PLACENTA

• Allows dissolved food substances (e.g. glucose, amino acids, mineral salts) and oxygen to diffuse from the mother’s blood into that of the embryo
• Allows metabolic waste products (e.g. urea and carbon dioxide) to diffuse from the foetus’ blood into the mother’s blood
• Allows antibodies to diffuse from the mother’s blood into the foetus’ blood (antibodies protect the foetus against diseases)
• Produces progesterone which maintains uterine lining in healthy state during pregnancy
  

NOTE: MOTHER'S BLOOD AND FOETUS' BLOOD DO NOT MIX AND MOTHER'S BLOOD DO NOT DIFFUSE INTO THE PLACENTA NOR DOES FOETUS' BLOOD DIFFUSE OUT OF THE PLACENTA INTO THE MOTHER'S BLOOD

MALE AND FEMALE REPRODUCTIVE SYSTEMS

MALE REPRODUCTIVE SYSTEM

• Testes: These are compact structures, each consists of hundreds of tiny sperm (seminiferous) tubules which produce sperms cells (male gametes). Apart from producing sperm cells, the testes also produce male sex hormone, testosterone.
• Scrotum: This is a pouch of skin containing the testes which are located outside the body at a temperature slightly lower than the body temperature which is an optimum temperature for sperm production.
• Epididymis: It stores sperms temporarily.
• Sperm duct (vas deferens): Carries sperms from the epididymis to the urethra during ejaculation.
• Prostate gland and seminal vesicles: Secrete seminal fluid which provides nourishment and oxygen to the sperms and also provides medium for the sperms to swim towards the oviduct in the female reproductive system. (Seminal fluid combines with the sperms to form semen)
• Urethra: To convey the semen out.
• Penis: To deposit semen into the vagina.
• Erectile tissue: Spongy tissue containing blood spaces and blood vessels. It causes erection during sexual intercourse.
  

FEMALE REPRODUCTIVE SYSTEM

• Ovaries: These are compact structures attached to the dorsal wall of the abdomen. Each consists of primary follicles (one develops into Graafian follicle containing mature ovum each month). The ovary also produces female sex hormones, oestrogen and progesterone.
• Oviduct: This is the site at which fertilization (fusion of the sperm nucleus with the ovum nucleus to form a zygote) takes place.
• Uterus: It receives, accomodates, nourishes and protects the embryo and foetus during pregnancy. Being muscular, it helps to expel the foetus out during birth.
• Cervix: This is the narrow region where uterus meets the vagina. It prevents infection from entering the uterus.
• Vagina: It receives the penis during sexual intercourse and at the end of pregnancy, it acts as a birth canal.
  

MALE AND FEMALE GAMETES

SPERMS	OVA (EGG CELLS)
Released in millions (300 to 400 millions) per ejaculation.	Only one ovum is released in every 28 days.
The sperms are able to move (swim) towards the egg cell due to the presence of the tail.	Unable to move on its own.
Very small (0.05mm – of which around 80% is tail).	Comparatively large (0.1mm in diameter).
Very little cytoplasm with large nucleus and large number of mitochondria in the middle piece (This is necessary since energy is required for the sperms to move or swim).	A lot of cytoplasm which contains nourishment for the zygote if the ovum is fertilized.
The nucleus contains either an X or a Y chromosome.	The nucleus always contains an X chromosome.

SEXUALLY TRANSMITTED DISEASES

DISEASES TRANSMITTED FROM ONE PERSON TO ANOTHER DURING A SEXUAL ACT

SYPHILIS

CAUSED BY A CORKSCREW- SHAPED BACTERIA CALLED SPIROCHAETE

Signs and symptoms of syphilis

Stage 1

THREE WEEKS AFTER INFECTION: PAINLESS SORE (CHANCRE) ON PENIS/VAGINA

EVENTUALLY DISAPPEAR EVEN WITHOUT TREATMENT

Stage 2

2 TO 6 MONTHS AFTER INFECTION:

NON-ITCHY SKIN RASHES

SORES ON MOUTH, THROAT & GENITALS

BALD PATCHES ON HEAD

SWOLLEN LYMPH GLANDS

MAY DISAPPEAR BUT BACTERIA REMAIN DORMANT UNTIL THE THIRD STAGE

Stage 3

HEART FAILURE

BLINDNESS

BRAIN/SPINAL CORD DAMAGED (MAY LEAD TO PARALYSIS, INSANITY AND EVEN DEATH)

Prevention and control

ANTIBIOTIC

REFRAIN SEXUAL INTERCOURSE

CONDOMS GUYS!!!

NO PROMISCUOUS SEXUAL BEHAVIOUR

ONE SEX PARTNER PLEASE!!!

AIDS

IT MEANS ACQUIRED IMMUNE DEFICIENCY SYNDROME

CAUSED BY HIV (HUMAN IMMUNODEFICIENCY VIRUS)

HIV DESTROYS IMMUNE SYSTEM ( MEANING, WHITE BLOOD CELLS ARE DESTROYED)

BODY NOT PRODUCING ENOUGH ANTIBODIES; BODY NOT PROTECTED; DISEASE CAUSING ORGANISMS CAN ENTER BODY EASILY; VARIOUS DISEASES AT THE SAME TIME

SYNDROME MEANS: DISEASE IN WHICH MANY SIGNS OCCURRING AT THE SAME TIME

Signs and symptoms

CHRONIC FEVER

SEVERE DIARRHOEA

PNEUMONIA

BLOOD VESSELS CANCER

BRAIN INFECTION

TUBERCULOSIS

Mode of transmission

SEXUAL INTERCOURSE WITH INFECTED PERSON

SHARING HYPODERMIC NEEDLES

UNSTERILIZED NEEDLES USED FOR TATTOOING, ACUPUNCTURE & EAR- PIERCING

BLOOD TRANSFUSION

PREGNANCY: VIRUS MAY PASS FROM INFECTED MOTHER TO FETUS

Prevention and control

KEEP TO ONE SEX PARTNER

AVOID PROMISCUOUS SEXUAL BEHAVIOUR

CONDOMS GUYS!

AVOID DRUG ABUSE

AVOID SHARING INSTRUMENTS WHICH ARE LIKELY TO BREAK SKIN AND CONTAMINATE BLOOD

ENSURE STERILIZED NEEDLES FOR ACUPUNCTURE, EAR PIERCING AND TATTOOING