Science 24 Tutorial – November 25th, 2003-11-24
Go over assignments due this week.
-Continue from tutorial last week.
In U3L6, you learned about how your body fights disease.
What are the three lines of defence that your body has?
1. Physical Defences (pg 194…look at diagram figure 11.1)
Did You Know? (p. 194)
Find and use a visual of cilia to show students how they trap pathogens. Cilia are tiny,
hair-like projections that line all air passages. They are covered with mucus to trap dust,
bacteria, and other particles that enter the body when you breathe. Particles that get
trapped are either coughed out of the body or swallowed and destroyed during digestion.
Mention that smoker’s cough is due to the toxins in cigarette smoke killing the
cilia in the throat. Without cilia, the cough is the only way to remove debris.
Extend the discussion by talking about how chemicals such as nicotine and tar
from cigarettes line the lungs and prevent easy absorption of oxygen.
2. Inflammatory Response – Body sends white blood cells to repel the invader. If you
damage yourself with a bruise or cut, the inflammatory response also kicks in as the
specialized white blood cells called macrophages engulf damaged cells and cell parts in
order to clean up and heal the area. This response also occurs with any type of infection.
(Refer to pg. 195, figure 11.2 and 11.3)
3. Immune System – antibodies. The best way for you to gain an understanding of the
immune response is to refer to figure 11.5. You were asked to draw this diagram in your
science binder for U3L6. (Go over it). Next, ask the students questions about it and see
if they know the answer).
Slide 1 – Different types of immunity. See figure 11.6 on page 199 to differentiate
between naturally acquired and artificially acquired.
Inherited Immunity — Humans have inherited immunity to most diseases of plants and
animals. For example, the pathogens that cause runny eyes in cats do not cause runny
eyes in humans because the pathogens cannot live in humans. Two exceptions are
rabies and tuberculosis, diseases that affect animals and humans.
• Acquired Immunity — There are two types of acquired immunity — active and
passive. In active immunity, the body produces its own antibodies to defend against a
specific antigen. Active immunity takes several weeks before it can provide protection.
In passive immunity, the recipient is given antibodies, which were produced during an
active response in another animal, to defend against a specific antigen. Passive
immunity lasts for only a short time because the body destroys the borrowed antibodies.
Passive immunity provides immediate protection. In active and passive immunity,
resistance may be acquired by natural means or by artificial means such as
vaccinations.
• Naturally Acquired Active Immunity — After getting an infectious disease such as
chicken pox, the body produces memory cells. Memory cells prevent a re-occurrence of
the infection.
• Artificially Acquired Active Immunity — Although the pathogens in a vaccine are
too weak to cause a specific disease, the B lymphocytes will recognize the antigens and
produce memory cells.
• Naturally Acquired Passive Immunity — Breast milk will protect infants from some
diseases, but is not a substitute for vaccinations since it cannot protect a baby from all
of the illnesses that vaccines can prevent.
• Artificially Acquired Passive Immunity — Antitoxins are administered for potentially
fatal conditions (e.g., tetanus, snake venom). These provide instant protection for a
short time since the antibodies are not the recipient’s own and memory cells are not
created. Memory cells are produced only in active immunity.
How does immunization work?
Ans. A vaccine consists of weakened or dead disease pathogens. Once a vaccination is
inside your body, your body begins to produce antibodies against the antigens in the
vaccine. The disease is weaker than usual because of the weakened or dead pathogens.
As a result, you get few or no symptoms. After your body produces antibodies, you have
lasting protection against the real disease.
Some people think that since the diseases for which there are vaccines have been
almost eliminated, there is no longer any need for vaccinations. Tell students that these
diseases still exist in other countries that may not have immunization programs. Ease of
travel makes exposure to these diseases only an air flight away.
Explain that diseases thought to be eliminated can re-occur. For example,
recurrence of polio does exist in isolated areas. There is also a disorder called Post-polio
syndrome (PPS), in which people who had polio as children suffer a recurrence.
As a class, make a list on the chalkboard of benefits and concerns about vaccines.
What are allergies?
Ans. They develop when the immune system overreacts and becomes sensitive to
substances such as pollen, dust, or mould. These substances are called allergens.
Allergens cause the body to release a substance called histamine which causes an allergic
reaction.
The response to an allergy can range from mild discomfort to more serious
physiological effects that are life threatening. For example, in hay fever, pollen allergens
can cause continuous sneezing, itching, swollen tissues, and blocked nasal passages.
Food allergies often result in cramps, diarrhea, or eczema.
When many cells all over the body react at the same time to an allergen such as
bee venom, the body goes into anaphylactic shock. Symptoms may include hives, itching
all over the body, lung spasms, a sudden drop in blood pressure, and swelling in the
airways which, if not immediately treated, can cause death.
Someone suffering from anaphylactic shock must be treated quickly — usually
with a shot of adrenaline (also called epinephrine) and an antihistamine. Adrenaline, a
hormone found in the body, causes blood pressure to rise. The antihistamine neutralizes
or slows down the effects of histamine.
During spring and fall, someone sensitive to pollen (e.g., trees, weeds such as
ragweed, grasses) might stay indoors and keep windows closed. During the winter, when
air movement in homes and buildings is minimal, someone allergic to pets, dust, or
moulds may need to rid the space of the allergen, take medications, or do a combination
of both.
Who Gets Allergies? — Some people are born with a greater chance of getting allergies.
For example, children have a greater chance of having allergies if one parent has
allergies. Some children outgrow these allergies, but scientists do not yet know how.
Some people develop allergies over time. Coming in contact with certain
allergens over many years may build up an allergic reaction in an individual.
What are Hypoallergenic Products? — A hypoallergenic product implies that it is less
likely to cause allergic reactions than competing products. However, manufacturers can
label and advertise their products as hypoallergenic without any supporting evidence.
Health Canada states that no scientific studies have proven that hypoallergenic
products produce fewer allergic reactions than products that do not make such claims.
The same is true for products labelled dermatologist-tested, allergy tested, and nonirritating. Almost any cosmetic could cause an allergic reaction in some individuals.
In Canada, ingredient listings are not yet mandatory on cosmetic labels. Such
information may help consumers who know they are allergic to certain ingredients to
protect themselves.
Since many teens buy cosmetic products (e.g., perfumes, colognes, skin care
products, soaps, shampoos, lipsticks, sunscreens, lotions), tell them that according to the
Food and Drug Administration in the United States, fragrance is the number one cause of
allergic reactions in cosmetics. There are more than 5000 fragrances used in cosmetic
products. Products that are labelled as unscented may contain fragrances that camouflage
the smell of other ingredients in the product.
Preservatives are another common trigger for allergic reactions in cosmetic
products.
In U3L6, we begin our study of genetics.
What is genetics?
Ans. Genetics is the study of how characteristics or traits are passed from parents to
offspring.
Go over figure 12.1 on page 121.
The human body cells contain 46 chromosomes arranged in 23 pairs that hold all the
genetic information. One chromosome of each pair comes from the mother and the other
chromosome of each pair comes from the father. Human sex cells (egg or sperm) contain
half the number of chromosomes (23). Females have two X chromosomes in their cells,
while males have one x or one y chromosome. When an egg is fertilized with an X-
containing sperm, the offspring is XX (girl), when an egg is fertilized by a y-containing
sperm, the offspring is XY, a male.
In lesson 6, you will be learning about Gregor Mendel’s work with pea plants and how he
learned about how traits can be passed on from one generation to the next.
Mendel determined that each organism contains two factors for each trait (eg. height,
colour, pod shape etc.)
Geneticists tend to use capital and lower-case letters to name the factors for any trait. The
actual letter can change, depending on what is being recorded, but the use of capital and
lower-case letters is consistent. For any trait, an individual likely has one of the following
pairs:
• DD — two dominant factors.
• dd — two recessive factors.
• Dd — one dominant gene and one recessive gene for a trait. This is called a hybrid.
Inheritance of Factors— When gametes form during reproduction, the factors segregate
so that each gamete carries only one member of the gene pair. During fertilization, the
new organism inherits two factors— one from each parent.
Geneticists use something called a Punnett square to predict the probability of offspring
inheriting certain traits.
A Punnett Square is a tool used to predict the inheritance of specific traits.
Go over the Punnett Squares for Slides 2-4.
Finish with a Punnet Square for the sex of offspring.