Why Leaves Change Color?

hy Leaves Change Color?
image of leaf
The Splendor of Autumn

Every autumn we revel in the beauty of the fall colors. The mixture of red, purple, orange and yellow is the result of chemical processes that take place in the tree as the seasons change from summer to winter.

During the spring and summer the leaves have served as factories where most of the foods necessary for the tree’s growth are manufactured. This food-making process takes place in the leaf in numerous cells containing chlorophyll, which gives the leaf its green color. This extraordinary chemical absorbs from sunlight the energy that is used in transforming carbon dioxide and water to carbohydrates, such as sugars and starch.

Along with the green pigment are yellow to orange pigments, carotenes and xanthophyll pigments which, for example, give the orange color to a carrot. Most of the year these colors are masked by great amounts of green coloring.
Chlorophyll Breaks Down

But in the fall, because of changes in the length of daylight and changes in temperature, the leaves stop their food-making process. The chlorophyll breaks down, the green color disappears, and the yellow to orange colors become visible and give the leaves part of their fall splendor.

At the same time other chemical changes may occur, which form additional colors through the development of red anthocyanin pigments. Some mixtures give rise to the reddish and purplish fall colors of trees such as dogwoods and sumacs, while others give the sugar maple its brilliant orange.

The autumn foliage of some trees show only yellow colors. Others, like many oaks, display mostly browns. All these colors are due to the mixing of varying amounts of the chlorophyll residue and other pigments in the leaf during the fall season.
Other Changes Take Place

As the fall colors appear, other changes are taking place. At the point where the stem of the leaf is attached to the tree, a special layer of cells develops and gradually severs the tissues that support the leaf. At the same time, the tree seals the cut, so that when the leaf is finally blown off by the wind or falls from its own weight, it leaves behind a leaf scar.

Image of trees changing colors in the fall

Most of the broad-leaved trees in the North shed their leaves in the fall. However, the dead brown leaves of the oaks and a few other species may stay on the tree until growth starts again in the spring. In the South, where the winters are mild, some of the broad-leaved trees are evergreen; that is, the leaves stay on the trees during winter and keep their green color.
Only Some Trees Lose Leaves

Most of the conifers – pines, spruces, firs, hemlocks, cedars, etc. – are evergreen in both the North and South. The needle- or scale-like leaves remain green or greenish the year round, and individual leaves may stay on for two to four or more years.
Weather Affects Color Intensity

Temperature, light, and water supply have an influence on the degree and the duration of fall color. Low temperatures above freezing will favor anthocyanin formation producing bright reds in maples. However, early frost will weaken the brilliant red color. Rainy and/or overcast days tend to increase the intensity of fall colors. The best time to enjoy the autumn color would be on a clear, dry, and cool (not freezing) day.

Enjoy the color, it only occurs for a brief period each fall.

Life Cycle of A Mosquito (Practical IX Class Biology)

Objective

Our objective is to study the life cycle of a mosquito.

The Theory

The mosquitoes are a family of small, midge-like flies. Like all flies, mosquitoes go through four stages in their life – egg, larva, pupa, and adult. We call this as the life cycle.  Each of these stages is morphologically different from the other, with even the habitat of each stage differing. The first three stages – egg, larva and pupa are largely aquatic, whereas the adult stage is aerial.

Mosquito Life cycle

We will now look at the four distinct stages of development in the life cycle of a mosquito.

Stage 1 – Egg

The eggs are laid one at a time and they float on the surface of the water. Normally the eggs are white when first deposited, then darken to near black within a day. They hatch in one to three days depending on the temperature. Eggs left on moist soil can last for up to a year, until the ground is flooded again, before hatching.

In the case of Culex and Culiseta species, 200-300 eggs are stuck together in rafts. Anopheles and Aedes species do not make egg rafts but lay their eggs separately. Culex, Culiseta, and Anopheles lay their eggs on water while Aedes lay their eggs on damp mud. The eggs generally do not hatch until the place is flooded. Most eggs hatch into larvae within 48 hours. When the larvae are ready to hatch, they use a small temporary ‘tooth’ on their head to break open the egg along a suture that was made by it.

Stage 2 – Larva

Mosquito larvae, commonly called ‘wigglers’ or ‘wrigglers’, live in water from 7 to 14 days depending on the water temperature. Larvae swim either through propulsion with their mouth brushes, or by jerky movements of their entire bodies, giving them the common name of ‘wigglers’. The larva begins to feed on bacteria and decaying organic matter on the water surface, soon after they hatch out of eggs. They spend most of their time hanging upside down at the surface, sucking in oxygen through the siphon. The siphon is located at the base of their abdomen and is similar to a snorkel. Brushes that are located in front of their mouths collect the food. Anopheles larvae do not have a siphon and they lay parallel to the water surface. The larval stage lasts for a few days to a few weeks, during which the larvae shed several layers of their outer skin, called moulting. This allows further growth.

Stage 3 – Pupa

After the larvae have completed moulting, they become pupae. This is the stage in which they undergo metamorphosis to become an adult mosquito. The pupal stage is a resting, non-feeding stage. Mosquito pupae are commonly called ‘tumblers’. The pupa is lighter than water and therefore floats at the surface. The mosquito pupa is comma-shaped. The head and thorax are merged into a cephalothorax, with the abdomen curving around underneath. At one end of these curved bodies is the large head and at the other end is the flippers used for swimming. They must take in oxygen from time to time through two breathing tubes known as ‘trumpets’. After a few days or longer, depending on the temperature and other circumstances, the pupa rises to the water surface, the dorsal surface of its cephalothorax splits, and the adult mosquito emerges.

Stage 4 – Adult

The newly emerged adult rests on the surface of the water for a short time to allow itself to dry and harden its parts. Also, the wings have to spread out and dry properly before it can fly.

Adult mosquitoes have a head with two large compound eyes, a thorax, a pair of scaled wings and six jointed legs. They also have antennae and a proboscis. Adult mosquitoes mate within the first few days after emerging from the pupal stage.

It is the carbon dioxide that we exhale, and the lactic acid from our sweat that combine to make us smell like a mosquito buffet. Mosquitoes can pick up these smells from 100 feet, and they can also feel our body heat and notice movements.

Only female mosquitoes have the mouth parts necessary for sucking blood. When biting with their proboscis, they stab two tubes into the skin, one is an anti-coagulant to keep the blood flowing and is a mild painkiller that helps them escape detection, the other helps to suck blood. They use the blood not for their own nourishment but as a source of protein for their eggs. For food, both males and females eat nectar and other plant sugars.

Some interesting mosquito facts

  • There are over 2500 different species of mosquitoes.
  • The feeding habits of mosquitoes are quite unique in that it is only the adult females that feed on blood. The male mosquitoes feed only on plant juices.
  • Mosquitoes must have water in which to complete their life cycle.
  • Most female mosquitoes need to feed on animal blood before they can develop eggs.
  • A female can produce up to 500 eggs before she finally dies.
  • Mosquitoes don’t travel more than a mile from the place where they were hatched.
  • The length of life of the adult mosquito usually depends on factors like – temperature, humidity, sex of the mosquito and time of the year.
  • Once mosquitoes emerge from their pupal cocoons and take flight, male mosquitoes last less than a week and the females’ maybe a couple of months.

Learning Outcomes

  1. Students understand the different stages of a Mosquito life cycle.
  2. Students get to know different types of Mosquitoes and the diseases spread by them.
  3. Students understand the differences in each stage of the mosquito life cycle through the animated demonstrations.

Stress Mastery

What is the “fight or flight response?”

This fundamental physiologic response forms the foundation of modern day stress medicine. The “fight or flight response” is our body’s primitive, automatic, inborn response that prepares the body to “fight” or “flee” from perceived attack, harm or threat to our survival.

What happens to us when we are under excessive stress?

When we experience excessive stress—whether from internal worry or external circumstance—a bodily reaction is triggered, called the “fight or flight” response. Originally discovered by the great Harvard physiologist Walter Cannon, this response is hard-wired into our brains and represents a genetic wisdom designed to protect us from bodily harm. This response actually corresponds to an area of our brain called the hypothalamus, which—when stimulated—initiates a sequence of nerve cell firing and chemical release that prepares our body for running or fighting.

What are the signs that our fight or flight response has been stimulated (activated)?

When our fight or flight response is activated, sequences of nerve cell firing occur and chemicals like adrenaline, noradrenaline and cortisol are released into our bloodstream. These patterns of nerve cell firing and chemical release cause our body to undergo a series of very dramatic changes. Our respiratory rate increases. Blood is shunted away from our digestive tract and directed into our muscles and limbs, which require extra energy and fuel for running and fighting. Our pupils dilate. Our awareness intensifies. Our sight sharpens. Our impulses quicken. Our perception of pain diminishes. Our immune system mobilizes with increased activation. We become prepared—physically and psychologically—for fight or flight. We scan and search our environment, “looking for the enemy.”

When our fight or flight system is activated, we tend to perceive everything in our environment as a possible threat to our survival. By its very nature, the fight or flight system bypasses our rational mind—where our more well thought out beliefs exist—and moves us into “attack” mode. This state of alert causes us to perceive almost everything in our world as a possible threat to our survival. As such, we tend to see everyone and everything as a possible enemy. Like airport security during a terrorist threat, we are on the look out for every possible danger. We may overreact to the slightest comment. Our fear is exaggerated. Our thinking is distorted. We see everything through the filter of possible danger. We narrow our focus to those things that can harm us. Fear becomes the lens through which we see the world.

We can begin to see how it is almost impossible to cultivate positive attitudes and beliefs when we are stuck in survival mode. Our heart is not open. Our rational mind is disengaged. Our consciousness is focused on fear, not love. Making clear choices and recognizing the consequences of those choices is unfeasible. We are focused on short-term survival, not the long-term consequences of our beliefs and choices. When we are overwhelmed with excessive stress, our life becomes a series of short-term emergencies. We lose the ability to relax and enjoy the moment. We live from crisis to crisis, with no relief in sight. Burnout is inevitable. This burnout is what usually provides the motivation to change our lives for the better. We are propelled to step back and look at the big picture of our lives—forcing us to examine our beliefs, our values and our goals.

What is our fight or flight system designed to protect us from?

Our fight or flight response is designed to protect us from the proverbial saber tooth tigers that once lurked in the woods and fields around us, threatening our physical survival. At times when our actual physical survival is threatened, there is no greater response to have on our side. When activated, the fight or flight response causes a surge of adrenaline and other stress hormones to pump through our body. This surge is the force responsible for mothers lifting cars off their trapped children and for firemen heroically running into blazing houses to save endangered victims. The surge of adrenaline imbues us with heroism and courage at times when we are called upon to protect and defend the lives and values we cherish.

What are the saber tooth tigers of today and why are they so dangerous?

When we face very real dangers to our physical survival, the fight or flight response is invaluable. Today, however, most of the saber tooth tigers we encounter are not a threat to our physical survival. Today’s saber tooth tigers consist of rush hour traffic, missing a deadline, bouncing a check or having an argument with our boss or spouse. Nonetheless, these modern day, saber tooth tigers trigger the activation of our fight or flight system as if our physical survival was threatened. On a daily basis, toxic stress hormones flow into our bodies for events that pose no real threat to our physical survival.

Once it has been triggered, what is the natural conclusion of our fight or flight response?

By its very design, the fight or flight response leads us to fight or to flee—both creating immense amounts of muscle movement and physical exertion. This physical activity effectively metabolizes the stress hormones released as a result of the activation of our fight or flight response. Once the fighting is over, and the threat—which triggered the response—has been eliminated, our body and mind return to a state of calm.

Has the fight or flight response become counterproductive?

In most cases today, once our fight or flight response is activated, we cannot flee. We cannot fight. We cannot physically run from our perceived threats. When we are faced with modern day, saber tooth tigers, we have to sit in our office and “control ourselves.” We have to sit in traffic and “deal with it.” We have to wait until the bank opens to “handle” the bounced check. In short, many of the major stresses today trigger the full activation of our fight or flight response, causing us to become aggressive, hypervigilant and over-reactive. This aggressiveness, over-reactivity and hypervigilance cause us to act or respond in ways that are actually counter-productive to our survival. Consider road rage in Los Angeles and other major cities.

It is counterproductive to punch out the boss (the fight response) when s/he activates our fight or flight response. (Even though it might bring temporary relief to our tension!) It is counterproductive to run away from the boss (the flight response) when s/he activates our fight or flight response. This all leads to a difficult situation in which our automatic, predictable and unconscious fight or flight response causes behavior that can actually be self-defeating and work against our emotional, psychological and spiritual survival.

Is there a cumulative danger from over-activation of our fight or flight response?

Yes. The evidence is overwhelming that there is a cumulative buildup of stress hormones. If not properly metabolized over time, excessive stress can lead to disorders of our autonomic nervous system (causing headache, irritable bowel syndrome, high blood pressure and the like) and disorders of our hormonal and immune systems (creating susceptibility to infection, chronic fatigue, depression, and autoimmune diseases like rheumatoid arthritis, lupus, and allergies.)

To protect ourselves today, we must consciously pay attention to the signals of fight or flight.

To protect ourselves in a world of psychological—rather than physical—danger, we must consciously pay attention to unique signals telling us whether we are actually in fight or flight. Some of us may experience these signals as physical symptoms like tension in our muscles, headache, upset stomach, racing heartbeat, deep sighing or shallow breathing. Others may experience them as emotional or psychological symptoms such as anxiety, poor concentration, depression, hopelessness, frustration, anger, sadness or fear.

Excess stress does not always show up as the “feeling” of being stressed. Many stresses go directly into our physical body and may only be recognized by the physical symptoms we manifest. Two excellent examples of stress induced conditions are “eye twitching” and “teeth-grinding.” Conversely, we may “feel” lots of emotional stress in our emotional body and have very few physical symptoms or signs in our body.

By recognizing the symptoms and signs of being in fight or flight, we can begin to take steps to handle the stress overload. There are benefits to being in fight or flight—even when the threat is only psychological rather than physical. For example, in times of emotional jeopardy, the fight or flight response can sharpen our mental acuity, thereby helping us deal decisively with issues, moving us to action. But it can also make us hypervigilant and over-reactive during times when a state of calm awareness is more productive. By learning to recognize the signals of fight or flight activation, we can avoid reacting excessively to events and fears that are not life threatening. In so doing, we can play “emotional judo” with our fight or flight response, “using” its energy to help us rather than harm us. We can borrow the beneficial effects (heightened awareness, mental acuity and the ability to tolerate excess pain) in order to change our emotional environment and deal productively with our fears, thoughts and potential dangers.

A public health agency in Finland is using an interesting approach to shock teens into not smoking

The Tobacco Body website features an interactive image of a man and a woman. Users zoom in and out of their body parts to observe the effects smoking has on a male and female body.

This is a new campaign by the Cancer Society of Finland, whose objective, according to the website of their ad agency, is to use this as a tool to show teenagers “to think critically about smoking.” The idea is to move beyond the black lungs, gooey tar and damaged livers, and use technology to “make the shock effect more shocking.”

And pretty shocking it is. Before-lady and Before-man are indeed much better-looking than After-lady and the After-man.

The strategy employed is clear: teens today don’t care about lungs, livers and cancer, or if they do, the constant exposure to such warnings has rendered them ineffective. What they do care about is appearances. So let’s show them how ugly smoking makes them.

On one hand you can’t argue with facts: smoking does give you spots, increase your testosterone levels, give you bad breath and unhealthy hair, yellow your teeth and nails, etc. Fact-wise there’s not much to dispute in the Tobacco Body website. But how advisable is it to resort to telling teenagers what is beautiful/popular/acceptable and what is not, even if it is towards the noble cause of telling them to not smoke?

Sample these snippets taken from the website:

[Man & Woman] “Dear Smoker, we’re sorry to inform you that according to nail fashion experts, nicotine yellow is not this season’s colour.”

[Woman] “Hey non-smoking girl, you are on a wonder-diet and you don’t even know it! Your body shape is closer to the average, whereas research shows that smokers weigh more and are rounder around the abdominal area.”

[Woman] “The non-smoking woman is less-likely to have as much hair growing on her arms as a smoker.”

[Woman] “The non-smoking woman usually has no additional hairs growing under her nose… No need for a five-bladed special razor.”

[Man & Woman] “Smokers have bad breath. As many as 20 per cent of people have ended relationships because of smoking. In Burn Magazine’s interviews several celebrities reveal they prefer kissing non-smokers.”

[Man & Woman] “A weary face is not a popular one: out of the 100 most popular profile pictures in a dating service only 2 were pictures of smokers.”

Basically, the Cancer Society of Finland is telling youngsters that smoking makes you hairy, fat, yellow-toothed and gives you bad breath. I found it slightly bothersome how features that are quite normal in several healthy teenagers, like rounded abdomens and hair on arms (for women), was being grouped with those which are blatantly undesirable and unhealthy, like yellowing teeth, bad breath and damaged lungs.

I wondered if this ad could be sending negative body image messages to kids who are naturally fat or hairy – are they implying that these kids are not as desirable?

But the more I thought about it the harder I realised it was to completely buy into that line of reasoning. Because, as a friend pointed out, this may be a case where the end could perhaps justify the means.

It was different in the case of the Dove ‘You’re more beautiful than you think you are’ campaign which also used a similar strategy to sell their product. They too inadvertently (?) went about setting definitions for beauty. The glaring difference of course was that Dove, at the end of the day, was trying to sell us soap under the guise of the noble motive of wanting women to feel good about themselves.

In the case of Tobacco Body, there’s no such deception. As questionable as their strategy might be, we can probably be sure that all this campaign wants is for teenagers to say no to smoking. They are, after all, the Cancer Society of Finland.

ScreenHunter_15 Oct. 18 13.27

http://tobaccobody.fi/

Life Cycle of the Malaria Parasite

lifecycleWeb

  1. A female Anopheles mosquito carrying malaria-causing parasites feeds on a human and injects the parasites in the form of sporozoites into the bloodstream. The sporozoites travel to the liver and invade liver cells.
  2. Over 5-16 days*, the sporozoites grow, divide, and produce tens of thousands of haploid forms, called merozoites, per liver cell. Some malaria parasite species remain dormant for extended periods in the liver, causing relapses weeks or months later.
  3. The merozoites exit the liver cells and re-enter the bloodstream, beginning a cycle of invasion of red blood cells, asexual replication, and release of newly formed merozoites from the red blood cells repeatedly over 1-3 days*. This multiplication can result in thousands of parasite-infected cells in the host bloodstream, leading to illness and complications of malaria that can last for months if not treated.
  4. Some of the merozoite-infected blood cells leave the cycle of asexual multiplication. Instead of replicating, the merozoites in these cells develop into sexual forms of the parasite, called male and female gametocytes, that circulate in the bloodstream.
  5. When a mosquito bites an infected human, it ingests the gametocytes. In the mosquito gut, the infected human blood cells burst, releasing the gametocytes, which develop further into mature sex cells called gametes. Male and female gametes fuse to form diploid zygotes, which develop into actively moving ookinetes that burrow into the mosquito midgut wall and form oocysts.
  6. Growth and division of each oocyst produces thousands of active haploid forms called sporozoites. After 8-15 days*, the oocyst bursts, releasing sporozoites into the body cavity of the mosquito, from which they travel to and invade the mosquito salivary glands. The cycle of human infection re-starts when the mosquito takes a blood meal, injecting the sporozoites from its salivary glands into the human bloodstream .

The Mechanism of Muscle Contraction

1) The sequence of events leading to contraction is initiated somewhere in the central nervous system, either as voluntary activity from the brain or as reflex activity from the spinal cord.

(2) A motor neuron in the ventral horn of the spinal cord is activated, and an action potential passes outward in a ventral root of the spinal cord.

(3) The axon branches to supply a number of muscle fibers called a motor unit, and the action potential is conveyed to a motor end plate on each muscle fiber.

(4) At the motor end plate, the action potential causes the release of packets or quanta of acetylcholine into the synaptic clefts on the surface of the muscle fiber.

(5) Acetylcholine causes the electrical resting potential under the motor end plate to change, and this then initiates an action potential which passes in both directions along the surface of the muscle fiber.

(6) At the opening of each transverse tubule onto the muscle fiber surface, the action potential spreads inside the muscle fiber.

(7) At each point where a transverse tubule touches part of the sarcoplasmic reticulum, it causes the sarcoplasmic reticulum to release Ca++ ions.

(8) The calcium ions result in movement of troponin and tropomyosin on their thin filaments, and this enables the myosin molecule heads to “grab and swivel” their way along the thin filament. This is the driving force of muscle contraction.

Contraction is turned off by the following sequence of events:

(9) Acetylcholine at the neuromuscular junction is broken down by acetylcholinesterase, and this terminates the stream of action potentials along the muscle fiber surface.

(10) The sarcoplasmic reticulum ceases to release calcium ions, and immediately starts to resequester all the calcium ions that have been released.

(11) In the absence of calcium ions, a change in the configuration of troponin and tropomyosin then blocks the action of the myosin molecule heads, and contraction ceases.

(12) In the living animal, an external stretching force, such as gravity or an antagonistic muscle, pulls the muscle back to its original length.