Feb 28, 2011


Simple Ways to Fight Depression

If you feel depressed, it's best to do something about it — depression doesn't just go away on its own. In addition to getting help from a doctor or therapist, here are few things you can do to feel better.

Exercise. Take a 15- to 30-minute brisk walk every day — or dance, jog, or bike if you prefer. People who are depressed may not feel much like being active. But make yourself do it anyway (ask a friend to exercise with you if you need to be motivated). Once you get in the exercise habit, it won't take long to notice a difference in your mood.

Nurture yourself with good nutrition. Depression can affect appetite. One person may not feel like eating at all, but another might overeat. If depression has affected your eating, you'll need to be extra mindful of getting the right nourishment. Proper nutrition can influence a person's mood and energy. So eat plenty of fruits and vegetables and get regular meals (even if you don't feel hungry, try to eat something light, like a piece of fruit, to keep you going).

Identify troubles, but don't dwell on them. Try to identify any situations that have contributed to your depression. When you know what's got you feeling blue and why, talk about it with a caring friend. Talking is a way to release the feelings and to receive some understanding. If there's no one to tell, pouring your heart out to a journal works just as well.

Once you air out these thoughts and feelings, turn your attention to something positive. Take action to solve problems. Ask for help if you need it. Feeling connected to friends and family can help relieve depression. (It may also help them feel there's something they can do instead of just watching you hurt.)

Express yourself. With depression, a person's creativity and sense of fun may seem blocked. Exercise your imagination (painting, drawing, doodling, sewing, writing, dancing, composing music, etc.) and you not only get those creative juices flowing, you also loosen up some positive emotions. Take time to play with a friend or a pet, or do something fun for yourself. Find something to laugh about — a funny movie, perhaps. Laughter helps lighten your mood.

Look on the bright side. Depression affects a person's thoughts, making everything seem dismal, negative, and hopeless. If depression has you noticing only the negative, make an effort to notice the good things in life. Try to notice one thing, then try to think of one more. Consider your strengths, gifts, or blessings. Most of all, don't forget to be patient with yourself. Depression takes time to heal.

IN and OUT

Plasma membranes help organisms maintain homeostasis by controlling what substances may enter or leave cells. Some substances can cross the plasma membrane without any input of energy by the cell. The movement of such substances across the membrane is known as passive transport.
The activities of a cell depend on the materials that enter and leave the cell.
To stay alive, a cell must exchange materials such as food, oxygen and wastes with its surroundings.
These materials must cross the plasma membrane.
Small molecules like water, oxygen and carbon dioxide can move in and out freely, since they can squeeze between the molecules of the membrane.
Large or charged molecules like proteins, sugars and ions cannot.
The plasma membrane is thus said to be partially permeable.
A selectively permeable membrane only allows certain molecules to pass through.

The simplest type of passive transport, diffusion does not require the cell to use energy. Only small molecules can cross the plasma membrane by simple diffusion.
Diffusion is the movement of molecules from an area of high concentration to one of low concentration.
This difference in the concentration of molecules across a space is called the concentration gradient.
Diffusion is driven by the kinetic energy of the molecules. Because of their KE, molecules are in constant motion. Diffusion occurs when molecules move randomly away from each other in a liquid or gas.
The rate of diffusion depends on the temperature, size and the type of molecules that are diffusing.
Molecules diffuse faster at higher temperatures than at lower temperatures, and smaller molecules diffuse faster than large molecules.
Most transport of materials into and out of cells occurs by diffusion.
The concentration gradient is the difference between the concentration of a solute in one place and its concentration in an adjacent area.

Diffusion always occurs down a concentration gradient, i.e. from the area of higher concentration to the area of lower concentration.
When molecules are dispersed evenly, there is no longer any diffusion because there is no longer a concentration gradient.
Diffusion will eventually cause the concentration of molecules to be the same throughout the space the molecules occupy, when they will be in equilibrium.

Osmosis is “The process by which water molecules diffuse across a partially permeable membrane from a region of higher water potential/higher water concentration to a region of lower water potential/concentration”
Water moves by diffusion, like any other molecule, from a region of high concentration to one of low concentration, i.e. down its concentration gradient. Confusion occurs because ‘concentration’ normally refers to the solute concentration, whereas, in this case, we are referring to the solvent concentration.
For this reason, the use of the term ‘water potential/water concentration' is essential; water then simply moves ‘down the water potential gradient’ – easy!
The water potential of pure water is zero (0), so, since a solution must always be less than 100% pure water, all solutions (and cells) have a negative (-) water potential.
Insoluble molecules do not affect the solute potential (obviously), so have no osmotic effect. Such molecules are used for storage – starch, lipids, and very large proteins (albumin).
Water potential is actually a pressure, and is measured in Pascals (Pa), but since these are so small the normal unit is the kilo Pascal (kPa). Typical plant values are -200 to -2000kPa.
Plants have a cell wall which normally presses on the cell membrane, giving us the pressure potential (Ψp). Since this opposes the tendency of the cell to expand due to osmosis, it therefore follows that the pressure potential (Ψp) is always positive.
Since animals have no cell wall, and so no pressure potential, the solute potential and the water potential must be the same:
Similar logic shows that the water potential of every cell in an animals’ body must be the same, since they are all in contact with blood, and thus in equilibrium (‘two values that are equal to a third value, must be equal to each other’)
When a plant cell is turgid (its normal state), the net movement of water into and out of the cell is zero. Thus:
Note that calculations on this will not be set in the exam.
The net direction of osmosis depends on the relative concentration of solutes on the two sides of the cell membrane.
In a hypertonic solution, the concentration of solutes in the solution is higher and so it has a lower (i.e. more negative) water potential (Ψw). Therefore, when placed in a hypertonic solution, water leaves the cell by osmosis, until equilibrium is established.
If the cell loses too much water, the cell will shrivel and shrink. Eventually they die, as their metabolism is disrupted i.e. badly wilted plants never recover fully.

Conversely, cells in a hypotonic (or weaker) solution will absorb water by osmosis until equilibrium is reached, since the cell has the lower water potential, and water ‘flows downhill’.
This flow of water into a cell causes it to swell:
a. Animal cells placed in a hypotonic solution will swell and often burst because of osmosis. N.B. The bursting of cells is called cytolysis.
b. Plant, fungal and bacterial cells do not burst because of their cell wall. The pressure that the cell exerts against the cell wall is its pressure potential Ψp. These cells are normally in this state, i.e. turgid.

In an isotonic solution, the concentration of solutes on both sides of the membrane is the same and so the net movement of water is zero. This is the normal position inside an animal’s body.


Cells that are exposed to an isotonic environment have no difficulty keeping the movement of water across the cell membrane in balance. This includes all land and most marine animals.
However, cells functioning in a hypotonic environment, such as Protoctista living in fresh water have a problem, as water will constantly enter them, down the water potential gradient, from their surroundings.
Since they cannot lower their water potential to near-zero, such organisms must rid themselves of the excess water.
Some (e.g. Paramecium sp. – see above) have contractile vacuoles, which actively pump water out of the cell.
This pumping action requires energy – so is a form of active transport. Up to 30% of the cell’s energy may be used in this way.
Plant root cells also live in hypotonic environment, so water (only!) normally moves by osmosis into the root hair cells, until they are turgid. Water then moves from these cells into the xylem down the water potential gradient.
In a hypertonic environment, water leaves the cells by osmosis, the cell membrane shrinks away from the cell wall, and turgor is lost. This condition is called plasmolysis, and is the reason plants wilt.

Passive transport across a membrane requires no energy input from the cell and always goes down the concentration gradient. Simple diffusion and osmosis are examples of passive transport.
However, most molecules cannot cross the membrane by simple diffusion; to do so, the molecule must either be very small (H2O, CO2) or be soluble in both water and lipid (ethanol).
Some molecules are carried across the membrane by carrier proteins which are embedded in the cell membrane.

Carrier proteins often change shape when molecules attach to them, and this change in shape enables the molecule to cross the membrane.
Because the carrier protein has to fit around the molecule, it is specific to one molecule, or related class of molecules.
This use of carrier proteins to cross the membrane is known as facilitated diffusion, and can be used by those molecules to cross the membrane in either direction – into or out of the cell.
Like simple diffusion, facilitated diffusion always goes down the concentration gradient, and therefore continues until equilibrium is reached, for that molecule.
A good example of facilitated diffusion is the transport of glucose into the cell. Once inside the cell, the glucose is immediately turned into glucose phosphate, for which no carrier protein exists. Glucose will thus continue to enter the cell, since equilibrium can never be reached!
Facilitated diffusion is therefore another form of passive transport, since it requires no energy input from the cell.
Some molecules, mainly ions (e.g. Na+, K+) cross the membrane through tunnels made of protein called ion channels.
Some ion channels are always open, but others (e.g. in neurones) have ‘gates’ that open to allow ions to pass or close to stop their passage.
Gates open and close in response to conditions in the external environment, or in the cell. It is the opening and closing of the sodium and potassium gates that allows a nerve impulse to be formed and passed along a neurone.
Cells often move molecules across the membrane against the concentration gradient, i.e. from an area of low concentration to an area of high concentration.
This requires energy (uses ATP), and is known as active transport.
Active transport involves the use of carrier proteins, similar to those of facilitated diffusion, but these carrier proteins act as pumps, using the energy from splitting ATP to pump specific molecules against the concentration gradient.
These carrier proteins are known as membrane pumps, and are particularly important in maintaining the Na+ /K+ ion balance between Eukaryotic cells and their external environment.
The sodium/potassium (Na+ /K+) pump maintains a high concentration of Na+ ions outside the cell, and a high concentration of K+ ions inside the cell. This is particularly important in muscle contractions, nerve impulses and the absorption of nutrients from the gut.
The Na+/K+ ion pump moves Na+ ions out of the cell, and K+ ions into the cell, against their concentration gradient, using ATP to supply the energy needed.

In plants, active transport enables roots to absorb mineral ions from the soil, which are therefore more concentrated inside plant cells than in the soil.
This requires ATP energy from aerobic respiration, and therefore roots need oxygen to allow mineral uptake and a waterlogged (thus anaerobic) soil will kill most roots.

Feb 27, 2011

Osmosis using osmometer

Feb 23, 2011

Fluid Mosaic Model

Feb 15, 2011

A Frog's Fate

Feb 8, 2011

What is AIDS?

What does AIDS mean?
AIDS stands for Acquired Immune Deficiency Syndrome:
Acquired means you can get infected with it;
Immune Deficiency means a weakness in the body's system that fights diseases.
Syndrome means a group of health problems that make up a disease.

AIDS is caused by a virus called HIV, the Human Immunodeficiency Virus. If you get infected with HIV, your body will try to fight the infection. It will make "antibodies," special molecules to fight HIV.

A blood test for HIV looks for these antibodies. If you have them in your blood, it means that you have HIV infection. People who have the HIV antibodies are called "HIV-Positive.

Being HIV-positive, or having HIV disease, is not the same as having AIDS. Many people are HIV-positive but don't get sick for many years. As HIV disease continues, it slowly wears down the immune system. Viruses, parasites, fungi and bacteria that usually don't cause any problems can make you very sick if your immune system is damaged. These are called "opportunistic infections."

How do you get AIDS?
You don't actually "get" AIDS. You might get infected with HIV, and later you might develop AIDS. You can get infected with HIV from anyone who's infected, even if they don't look sick and even if they haven't tested HIV-positive yet. The blood, vaginal fluid, semen, and breast milk of people infected with HIV has enough of the virus in it to infect other people. Most people get the HIV virus by:
* having sex with an infected person
* sharing a needle (shooting drugs) with someone who's infected
* being born when their mother is infected, or drinking the breast milk of an infected woman

Getting a transfusion of infected blood used to be a way people got AIDS, but now the blood supply is screened very carefully and the risk is extremely low.
There are no documented cases of HIV being transmitted by tears or saliva, but it is possible to be infected with HIV through oral sex or in rare cases through deep kissing, especially if you have open sores in your mouth or bleeding gums.

What happens if I'm HIV positive?
You might not know if you get infected by HIV. Some people get fever, headache, sore muscles and joints, stomach ache, swollen lymph glands, or a skin rash for one or two weeks. Most people think it's the flu. Some people have no symptoms.

The virus will multiply in your body for a few weeks or even months before your immune system responds. During this time, you won't test positive for HIV, but you can infect other people.

When your immune system responds, it starts to make antibodies. When this happens, you will test positive for HIV.

After the first flu-like symptoms, some people with HIV stay healthy for ten years or longer. But during this time, HIV is damaging your immune system.

One way to measure the damage to your immune system is to count your CD4 cells you have. These cells, also called "T-helper" cells, are an important part of the immune system. Healthy people have between 500 and 1,500 CD4 cells in a milliliter of blood.

Without treatment, your CD4 cell count will most likely go down. You might start having signs of HIV disease like fevers, night sweats, diarrhea, or swollen lymph nodes. If you have HIV disease, these problems will last more than a few days, and probably continue for several weeks.

How do I know if I have AIDS?
HIV disease becomes AIDS when your immune system is seriously damaged. If you have less than 200 CD4 cells or if your CD4 percentage is less than 14%, you have AIDS. See If you get an opportunistic infection, you have AIDS. There is an "official" list of these opportunistic infections put out by the Centers for Disease Control (CDC). The most common ones are:
* PCP (Pneumocystis pneumonia), a lung infection;
* KS (Karposi's sarcoma), a skin cancer;
* CMV (Cytomegalovirus), an infection that usually affects the eyes
* Candida, a fungal infection that can cause thrush (a white film in your mouth) or infections in your throat or vagina

AIDS-related diseases also includes serious weight loss, brain tumours, and other health problems. Without treatment, these opportunistic infections can kill you.

AIDS is different in every infected person. Some people die a few months after getting infected, while others live fairly normal lives for many years, even after they "officially" have AIDS. A few HIV-positive people stay healthy for many years even without taking antiretroviral medications (ARVs).

Is there a cure for AIDS?
There is no cure for AIDS. There are drugs that can slow down the HIV virus, and slow down the damage to your immune system. There is no way to "clear" the HIV out of your body.

Other drugs can prevent or treat opportunistic infections (OIs). In most cases, these drugs work very well. The newer, stronger ARVs have also helped reduce the rates of most OIs. A few OIs, however, are still very difficult to treat.

Movement of water from soil to leaves

i) from soil to roots
- water diffuse into the cell of root hairs by osmosis
- concentration of water in the cell is lower than outside the cell/soil
- cell becomes hypotonic to the adjacent cells by osmosis
- osmosis goes on until water molecules reach the xylem vessels

ii) roots up the stem
- transpirational pull draws water upwards
- cohesive forces between water molecules
- adhesive forces between water molecules and the wall of xylem vessels
- generates capillary action

iii) from the leaves to the atmosphere
- water evaporates from the surface of the mesophyll cells into the air spaces/surrounding
- water which is lost, is replaced by water in the xylem by osmosis
- water vapour diffuses out/evaporates into the atmosphere through the stomata

Feb 1, 2011

Analogy of the cell

Nucleus (a cell's information center) would be the school's general office where all information about the student , school etc are.
Nucleolus would be the principal who is "located" inside the nucleus controlling the running of the school.
Like how important the nucleus & the nucleolus is to the cell, the principal & the school's general office are very important to the school too & they both control the running of the cell & school.

Plasma membrane (regulates the movement of water, nutrients and wastes into and out of the cell.) would be like the school's security guard.
Like the plasma membrane, the school's security guard prevents students from leaving the school during school hours & prevents strangers from entering the school.

Mitochondria (the power generators) would be the school's canteen where all types of food are & where all students and teachers get their food .
Like the mitochondria, the school canteen provides food for the students & teachers giving them energy to last for the day.

Rough Endoplasmic Reticulum (moves materials around the cell) would be like the teachers in the school.
Like the rough endoplasmic reticulum, the teachers teach the students thus providing them with information, circulating their knowledge around the school.

Ribosomes (make proteins) would be like the students in the school.
Like the ribosomes , students would produce good results for the school like how ribosomes make proteins for the cell .

Lysosomes (chemicals used to digest waste) would be like the cleaners we have in the school.
Like the lysosomes , the cleaners in the school help to clear all rubbish and help clean the school in turn making the school a clean environment to study in. Like the importance of the lysosomes, the cleaners are important in a school too.

Golgi apparatus (packing & secreting of energy) would be like the Head of the panel (Ketua Panitia).
Like the golgi apparatus, the Head of the panel,decides  in what way should the teachers be teaching the students . Like how the golgi apparatus and the rough endoplasmic reticulum work closely together, the Head of each panels work closely with the teachers too.

Tata.....my cell analogy of school