6.5 Nerves, Hormones and Homeostasis
View more presentations from Stephen Taylor.
miércoles, 20 de octubre de 2010
Water properties for IB one
Water Properties
States of Water
Adhesion and Cohesion
Surface Tension
Capillary Action
The States of Water
Water has three states. Below freezing water is a solid (ice or snowflakes), between freezing and boiling water is a liquid, and above its boiling point water is a gas. There are words scientists use to describe water changing from one state to another. Water changing from solid to liquid is said to be melting. When it changes from liquid to gas it is evaporating. Water changing from gas to liquid is called condensation (An example is the 'dew' that forms on the outside of a glass of cold soda). Frost formation is when water changes from gas directly to solid form. When water changes directly from solid to gas the process is called sublimation.
Gas
Liquid
Solid
Most liquids contract (get smaller) when they get colder. Water is different. Water contracts until it reaches 4 C then it expands until it is solid. Solid water is less dense that liquid water because of this. If water worked like other liquids, then there would be no such thing as an ice berg, the ice in your soft drink would sink to the bottom of the glass, and ponds would freeze from the bottom up!
Water is found on Earth in all three forms. This is because Earth is a very special planet with just the right range of temperatures and air pressures. Earth is said to be at the triple point for water.
Adhesion and Cohesion
Water is attracted to other water. This is called cohesion. Water can also be attracted to other materials. This is called adhesion.
The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is what gives water its cohesive and adhesive properties.
Surface Tension
Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. Try this at home: place a drop of water onto a piece of wax paper. Look closely at the drop. What shape is it? Why do you think it is this shape?
What is happening? Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules in the drop. This causes the water to pull itself into a shape with the smallest amount of surface area, a bead (sphere). All the water molecules on the surface of the bead are 'holding' each other together or creating surface tension.
Surface tension allows water striders to 'skate' across the top of a pond. You can experiment with surface tension. Try floating a pin or a paperclip on the top if a glass of water. A metal pin or paper clip is heavier than water, but because of the surface tension the water is able to hold up the metal.
Surface tension is not the force that keeps boats floating. If you want to know why a boat floats look here: Why do boats float?
Capillary Action
Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water (Can you make up an experiment to test this?).
Plants take advantage of capillary action to pull water from the into themselves. From the roots water is drawn through the plant by another force, transpiration. Click here for more information about transpiration.
States of Water
Adhesion and Cohesion
Surface Tension
Capillary Action
The States of Water
Water has three states. Below freezing water is a solid (ice or snowflakes), between freezing and boiling water is a liquid, and above its boiling point water is a gas. There are words scientists use to describe water changing from one state to another. Water changing from solid to liquid is said to be melting. When it changes from liquid to gas it is evaporating. Water changing from gas to liquid is called condensation (An example is the 'dew' that forms on the outside of a glass of cold soda). Frost formation is when water changes from gas directly to solid form. When water changes directly from solid to gas the process is called sublimation.
Gas
Liquid
Solid
Most liquids contract (get smaller) when they get colder. Water is different. Water contracts until it reaches 4 C then it expands until it is solid. Solid water is less dense that liquid water because of this. If water worked like other liquids, then there would be no such thing as an ice berg, the ice in your soft drink would sink to the bottom of the glass, and ponds would freeze from the bottom up!
Water is found on Earth in all three forms. This is because Earth is a very special planet with just the right range of temperatures and air pressures. Earth is said to be at the triple point for water.
Adhesion and Cohesion
Water is attracted to other water. This is called cohesion. Water can also be attracted to other materials. This is called adhesion.
The oxygen end of water has a negative charge and the hydrogen end has a positive charge. The hydrogens of one water molecule are attracted to the oxygen from other water molecules. This attractive force is what gives water its cohesive and adhesive properties.
Surface Tension
Surface tension is the name we give to the cohesion of water molecules at the surface of a body of water. Try this at home: place a drop of water onto a piece of wax paper. Look closely at the drop. What shape is it? Why do you think it is this shape?
What is happening? Water is not attracted to wax paper (there is no adhesion between the drop and the wax paper). Each molecule in the water drop is attracted to the other water molecules in the drop. This causes the water to pull itself into a shape with the smallest amount of surface area, a bead (sphere). All the water molecules on the surface of the bead are 'holding' each other together or creating surface tension.
Surface tension allows water striders to 'skate' across the top of a pond. You can experiment with surface tension. Try floating a pin or a paperclip on the top if a glass of water. A metal pin or paper clip is heavier than water, but because of the surface tension the water is able to hold up the metal.
Surface tension is not the force that keeps boats floating. If you want to know why a boat floats look here: Why do boats float?
Capillary Action
Surface tension is related to the cohesive properties of water. Capillary action however, is related to the adhesive properties of water. You can see capillary action 'in action' by placing a straw into a glass of water. The water 'climbs' up the straw. What is happening is that the water molecules are attracted to the straw molecules. When one water molecule moves closer to a the straw molecules the other water molecules (which are cohesively attracted to that water molecule) also move up into the straw. Capillary action is limited by gravity and the size of the straw. The thinner the straw or tube the higher up capillary action will pull the water (Can you make up an experiment to test this?).
Plants take advantage of capillary action to pull water from the into themselves. From the roots water is drawn through the plant by another force, transpiration. Click here for more information about transpiration.
viernes, 15 de octubre de 2010
jueves, 14 de octubre de 2010
Defence against infectious diseases
6.3.1 Define pathogen.
Pathogen: an organism or virus that causes a disease.
6.3.2 Explain why antibiotics are effective against bacteria but not against viruses.
Antibiotics are produced by microorganisms to kill or control the growth of other microorganisms by blocking specific metabolic pathways within the cell. Since bacteria are so different to human cells, antibiotics can be taken by humans to kill bacteria without harming the human cells. Viruses on the other hand are different as they do not carry out many metabolic processes themselves. Instead they rely on a host cell (a human cell) to carry out these processes for them. Therefore viruses cannot be treated with antibiotics as it is impossible to harm the virus without harming the human cells.
Summary:
Antibiotics block specific metabolic pathways in bacteria.
Bacteria are very different to human cells so human cells are not affected.
Viruses require host cell to carry metabolic processes for them and so antibiotics cannot be used to treat viruses.
Harming the virus would harm the human cells.
6.3.3 Outline the role of skin and mucous membranes in the defence against pathogens.
The skin forms a physical barrier that prevents pathogens from entering the body as the outer layer is very tough. In addition the skin contains sebaceous glands which secret lactic acid and fatty acids which creates an acidic environment on the surface of the skin preventing the growth of pathogens.
Mucous membranes form another type of barrier against pathogens. Mucous membranes are soft and moist areas of skin found in the trachea, nose, vagina and urethra. These membranes are not strong enough to create a physical barrier but they do have mucus which contain lysozyme enzymes that digest the phagocytes. Also, the mucus can be sticky such as in the trachea, and trap the pathogens which are then expelled up the trachea and out of the body by muscles within the trachea.
Summary:
Skin:
Forms a physical barrier.
Sebaceous glands secret lactic acid and fatty acids.
Mucous membranes:
Mucous contains lysozyme enzymes.
Mucous can be sticky and trap pathogens.
6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and body tissues.
Phagocytes are found in the blood and ingest pathogens. They do so by recognising pathogens and engulfing them by endocytosis. Enzymes within the phagocytes called lysosomes then digest the pathogens. Phagocytes can ingest pathogens in the blood but also within body tissue as they can pass through the pores of capillaries and into these tissues.
6.3.5 Distinguish between antigens and antibodies.
Antibodies are proteins that defend the body against pathogens by binding to antigens on the surface of these pathogens and stimulating their destruction. Antigens are foreign substances which stimulate the production of antibodies. Antibodies usually only bind to one specific antigen.
6.3.6 Explain antibody production.
Lymphocytes are a type of leukocyte which make antibodies. Each lymphocyte makes only one specific antibody. A large amount of different lymphocytes are needed so that the body can produce different types of antibodies. The antibodies are found on the surface of the plasma membrane of these lymphocytes with the antigen-combining site projecting outwards. Pathogens have antigens on their surface which bind to the antigen-combining site of the antibodies of a specific lymphocyte. When this happens the lymphocyte becomes active and starts to make clones of itself by dividing by mitosis. These clones then start to make more of this specific antibody needed to defend the body against the pathogen.
Summary:
Each lymphocyte makes one type of antibody.
Antibodies are found on the surface of the lymphocyte.
Pathogen have antigens on their surface.
The antigens bind to the antibodies.
Lymphocyte becomes active and makes clones of itself.
The clones make more of the specific antibody.
6.3.7 Outline the effects of HIV on the immune system.
The HIV virus (which causes AIDS) destroys a type of lymphocyte which has a vital role in antibody production. Over the years this results in a reduced amount of active lymphocytes. Therefore, less antibodies are produced which makes the body very vulnerable to pathogens. A pathogen that could easily be controlled by the body in a healthy individual can cause serious consequences and eventually lead to death for patients affected by HIV.
6.3.8 Discuss the cause, transmission and social implications of AIDS.
Cause: HIV causes AIDS (acquired immunodeficiency syndrome). A syndrome is a group of symptoms that are found together. HIV destroys a type of lymphocyte which is vital for antibody production. Over the years, less active lymphocytes are produced which leads to a fall in the amount of antibodies. Pathogens that would normally be easily controlled by the body in healthy individuals can cause serious consequences and eventually lead to death for patients affected by HIV. The immune system is considerably weakened.
Transmission: HIV is transmitted through body fluids from an infected person to an uninfected one. This can occur through vaginal and anal intercourse as well as oral sex if there are cuts or tears in the vagina, penis, mouth or intestine. It can also be transmitted by hypodermic needles that are shared by intravenous drug abusers. The small amount of blood present on these needles after their use may contain the virus and is enough to infect another person. Another way of transmission is through the placenta from mother to child, or through cuts during childbirth or in milk during breast feeding. Finally there is a risk of transmission in transfused blood or with blood products such as Factor VIII used to treat hemophiliacs.
Social implications: Relatives and friends suffer grief. Families can also suffer from a loss of income as the person infected by HIV can lose their wage if they are unable to work and are refused life insurance. Also, HIV patients may find it hard to find partners, employment and even housing. Finally, AIDS can cause fear in a population and reduce sexual activity.
Summary:
Cause:
HIV causes AIDS.
HIV destroys a type of lymphocyte vital for antibody production.
Overtime there are less active lymphocytes.
The body becomes very vulnerable to pathogens.
Transmission:
Through vaginal and anal intercourse as well as oral sex if cuts or tears are present.
Through hypodermic needles shared by drug users.
Through placenta from mother to child.
Through cuts during child birth or in milk during breast feeding.
Through transfused blood.
Through blood factors such as Factor VIII used to treat hemophiliacs.
Social Implications:
Grief suffered by relatives and friends.
Families can get poorer.
Can be hard to find a partner, employment and housing.
Can reduce sexual activity in a population.
Pathogen: an organism or virus that causes a disease.
6.3.2 Explain why antibiotics are effective against bacteria but not against viruses.
Antibiotics are produced by microorganisms to kill or control the growth of other microorganisms by blocking specific metabolic pathways within the cell. Since bacteria are so different to human cells, antibiotics can be taken by humans to kill bacteria without harming the human cells. Viruses on the other hand are different as they do not carry out many metabolic processes themselves. Instead they rely on a host cell (a human cell) to carry out these processes for them. Therefore viruses cannot be treated with antibiotics as it is impossible to harm the virus without harming the human cells.
Summary:
Antibiotics block specific metabolic pathways in bacteria.
Bacteria are very different to human cells so human cells are not affected.
Viruses require host cell to carry metabolic processes for them and so antibiotics cannot be used to treat viruses.
Harming the virus would harm the human cells.
6.3.3 Outline the role of skin and mucous membranes in the defence against pathogens.
The skin forms a physical barrier that prevents pathogens from entering the body as the outer layer is very tough. In addition the skin contains sebaceous glands which secret lactic acid and fatty acids which creates an acidic environment on the surface of the skin preventing the growth of pathogens.
Mucous membranes form another type of barrier against pathogens. Mucous membranes are soft and moist areas of skin found in the trachea, nose, vagina and urethra. These membranes are not strong enough to create a physical barrier but they do have mucus which contain lysozyme enzymes that digest the phagocytes. Also, the mucus can be sticky such as in the trachea, and trap the pathogens which are then expelled up the trachea and out of the body by muscles within the trachea.
Summary:
Skin:
Forms a physical barrier.
Sebaceous glands secret lactic acid and fatty acids.
Mucous membranes:
Mucous contains lysozyme enzymes.
Mucous can be sticky and trap pathogens.
6.3.4 Outline how phagocytic leucocytes ingest pathogens in the blood and body tissues.
Phagocytes are found in the blood and ingest pathogens. They do so by recognising pathogens and engulfing them by endocytosis. Enzymes within the phagocytes called lysosomes then digest the pathogens. Phagocytes can ingest pathogens in the blood but also within body tissue as they can pass through the pores of capillaries and into these tissues.
6.3.5 Distinguish between antigens and antibodies.
Antibodies are proteins that defend the body against pathogens by binding to antigens on the surface of these pathogens and stimulating their destruction. Antigens are foreign substances which stimulate the production of antibodies. Antibodies usually only bind to one specific antigen.
6.3.6 Explain antibody production.
Lymphocytes are a type of leukocyte which make antibodies. Each lymphocyte makes only one specific antibody. A large amount of different lymphocytes are needed so that the body can produce different types of antibodies. The antibodies are found on the surface of the plasma membrane of these lymphocytes with the antigen-combining site projecting outwards. Pathogens have antigens on their surface which bind to the antigen-combining site of the antibodies of a specific lymphocyte. When this happens the lymphocyte becomes active and starts to make clones of itself by dividing by mitosis. These clones then start to make more of this specific antibody needed to defend the body against the pathogen.
Summary:
Each lymphocyte makes one type of antibody.
Antibodies are found on the surface of the lymphocyte.
Pathogen have antigens on their surface.
The antigens bind to the antibodies.
Lymphocyte becomes active and makes clones of itself.
The clones make more of the specific antibody.
6.3.7 Outline the effects of HIV on the immune system.
The HIV virus (which causes AIDS) destroys a type of lymphocyte which has a vital role in antibody production. Over the years this results in a reduced amount of active lymphocytes. Therefore, less antibodies are produced which makes the body very vulnerable to pathogens. A pathogen that could easily be controlled by the body in a healthy individual can cause serious consequences and eventually lead to death for patients affected by HIV.
6.3.8 Discuss the cause, transmission and social implications of AIDS.
Cause: HIV causes AIDS (acquired immunodeficiency syndrome). A syndrome is a group of symptoms that are found together. HIV destroys a type of lymphocyte which is vital for antibody production. Over the years, less active lymphocytes are produced which leads to a fall in the amount of antibodies. Pathogens that would normally be easily controlled by the body in healthy individuals can cause serious consequences and eventually lead to death for patients affected by HIV. The immune system is considerably weakened.
Transmission: HIV is transmitted through body fluids from an infected person to an uninfected one. This can occur through vaginal and anal intercourse as well as oral sex if there are cuts or tears in the vagina, penis, mouth or intestine. It can also be transmitted by hypodermic needles that are shared by intravenous drug abusers. The small amount of blood present on these needles after their use may contain the virus and is enough to infect another person. Another way of transmission is through the placenta from mother to child, or through cuts during childbirth or in milk during breast feeding. Finally there is a risk of transmission in transfused blood or with blood products such as Factor VIII used to treat hemophiliacs.
Social implications: Relatives and friends suffer grief. Families can also suffer from a loss of income as the person infected by HIV can lose their wage if they are unable to work and are refused life insurance. Also, HIV patients may find it hard to find partners, employment and even housing. Finally, AIDS can cause fear in a population and reduce sexual activity.
Summary:
Cause:
HIV causes AIDS.
HIV destroys a type of lymphocyte vital for antibody production.
Overtime there are less active lymphocytes.
The body becomes very vulnerable to pathogens.
Transmission:
Through vaginal and anal intercourse as well as oral sex if cuts or tears are present.
Through hypodermic needles shared by drug users.
Through placenta from mother to child.
Through cuts during child birth or in milk during breast feeding.
Through transfused blood.
Through blood factors such as Factor VIII used to treat hemophiliacs.
Social Implications:
Grief suffered by relatives and friends.
Families can get poorer.
Can be hard to find a partner, employment and housing.
Can reduce sexual activity in a population.
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