Biology 30S

Wellness & HomeostasisUnit One

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Introduction

The study of life and living organisms, including their structure, function, growth, evolution, distribution, and taxonomy.

Some of the major fields of biological study are: Zoology – the study of animals Botany – the study of plants Microbiology – the study of microorganisms Cytology – the study of cells Histology – the study of tissues Ecology – the study of living things in their environments Genetics – the study of genes and heredity

What is life?

A Story: Is Sammy Alive?

Sammy was a normal, healthy boy. There was nothing in his life to indicate that he was anything different from anyone else. When he completed high school, he obtained a job in a factory, operating a machine press. On this job he had an accident and lost his hand. It was replaced with an artificial hand that looked and operated almost like a real one.

Is Sammy Alive?

Soon afterward, Sammy developed a severe intestinal difficulty, and a large portion of his lower intestine had to be removed. It was replaced with an elastic silicon tube.

Is Sammy Alive?

Everything looked good for Sammy until he was involved in a serious car accident. Both of his legs and his good arm were crushed and had to be amputated. He also lost an ear. Artificial legs enabled Sammy to walk again, and an artificial arm replaced the real arm. Plastic surgery enabled doctors to rebuild the ear.

Is Sammy Alive?

Over the next several years, Sammy was plagued with internal disorders. First, he had to have an operation to remove his aorta and replace it with a synthetic vessel. Next, he developed a kidney malfunction, and the only way he could survive was to use a kidney dialysis machine (no donor was found for a kidney transplant). Later, his digestive system became cancerous and was removed. He received nourishment intravenously. Finally, his heart failed. Luckily for Sammy, a donor heart was available, and he had a heart transplant.

Is Sammy Alive?

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It was now obvious that Sammy had become a medical phenomenon. He had artificial limbs, nourishment was supplied to him through his veins; therefore he had no solid wastes. The kidney dialysis machine removed all waste material. The heart that pumped his blood to carry oxygen and food to his cells was not his original heart. But Sammy's transplanted heart began to fail. He was immediately placed on a heart-lung machine. This supplied oxygen and removed carbon dioxide from his blood, and it circulated blood through his body.

Is Sammy Alive?

The doctors consulted bioengineers about Sammy. Because almost all of his life-sustaining functions were being carried on by machine, it might be possible to compress all of these machines into one mobile unit, which would be controlled by electrical impulses from Sammy's brain. This unit would be equipped with mechanical arms to enable him to perform manipulative tasks. A mechanism to create a flow of air over his vocal cords might enable him to speak. To do all this, they would have to amputate at the neck and attach his head to the machine, which would then supply all nutrients to his brain. Sammy consented, and the operation was successfully performed.

Is Sammy Alive?

Sammy functioned well for a few years. However, a slow deterioration of his brain cells was observed and was diagnosed as terminal. So the medical team that had developed around Sammy began to program his brain. A miniature computer was developed: it could be housed in a machine that was humanlike in appearance, movement, and mannerisms. As the computer was installed, Sammy's brain cells completely deteriorated. Sammy was once again able to leave the hospital with complete assurance that he would not return with biological illness.

Is Sammy Alive?

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Criteria used to classify something is living:

Reproduction - Organisms make new organisms

Genetic Material - Features carried by complex molecule (DNA) passed through reproduction

Cell - Collection of living matter enclosed in a barrier. Smallest units of life.

Grow and Develop - Grow means increase in size. Develop means organism changes over the course of its life (cells differentiate)

Metabolism - Require materials (matter) and energy to function

Response to Stimuli - React to changes in environment (temperature, humidity, light, gravity ect.)

Homeostasis - Maintaining an internal balance (body temp., water levels, Ph levels ect.)

Evolution - Change of a closely related group of organisms over time (individuals do not evolve they develop).

What Is Life? Is Death Real?

https://www.youtube.com/watch?v=QOCaacO8wus

Health and Wellness

Health refers to the physical well-being of an individual.

Wellness refers to the multidimensional interrelationship between the physical, emotional, spiritual, intellectual, interpersonal or social, and environmental aspects of life.

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Components of Wellness:

Physical Wellness:

The physical needs of our body must be met before we can try to balance the other areas of need. If we are hungry, cold, or tired, it is difficult to deal with the emotional, social, intellectual or spiritual issues. Physical balance includes eating properly, getting adequate exercise, and sufficient rest. Only after meeting the physical demands of our body can we move on to the other areas.

Questions to ask yourself: Do I know important health numbers, like my cholesterol, weight, blood pressure, and blood

sugar levels? Do I get annual physical exams? Do I avoid using tobacco products? Do I get sufficient amount of sleep? Do I have an established exercise routine?

Emotional Wellness:

Emotional needs involve our relationships with other people. Most of us need to have interactions with a variety of different people. Emotional balance includes relationships with close family and friends and the less intense personal contacts with other acquaintances. Emotional balance also involves how we deal with the human emotions such as anger, guilt, love, fear and happiness. It is important that we find balance and try to keep a positive attitude rather than allowing negative emotions to build.

Questions to ask yourself: Be aware of and accept our feelings, rather than deny them Have an optimistic approach to live Express feelings freely and manage feelings effectively Express emotions appropriately Adjust to change Cope with stress in a healthy way Enjoy life despite its occasional disappointments and frustrations

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Spiritual Wellness:

Spirituality is an essential need of human nature. Our feelings, thoughts, choices, and questions are related to our spirituality. Some think of spirituality including all of our efforts to gain insight into the underlying, overriding forces of life. For many, it is the justification for our moral and ethical standards. Research studies in recent years have found that the influence of religion or spirituality appears to be highly related to a sense of well-being in elderly persons. Ideas for helping achieve spiritual balance might include taking time for quiet reflection, maintaining a personal journal, incorporating meditation and/or prayer into your life, becoming more aware of the world around you and the lessons it teaches, and practicing an open attitude.

Questions to ask yourself: It is better to ponder the meaning of life for ourselves and to be

tolerant of the beliefs of others than to close our minds and become intolerant.

It is better to live each day in a way that is consistent with our values and beliefs than to do otherwise and feel untrue to ourselves.

Intellectual Wellness:

People need intellectual growth and stimulation to help keep balance in their lives. This involves continually finding ways to challenge our minds and continue learning. Learning is crucial in adapting to life’s changes. Intellectual development helps improve our skills and expands the potential for sharing with others.

Questions to ask yourself: Cherishes mental growth and stimulation Is involved in intellectual and cultural activities Is engaged in the exploration of new ideas and understandings

Social Wellness:

Social balance includes taking the time to give to others. What contributions are you making to your family and community? It is important to contribute to one’s own community and environment. Interdependence with others, with nature and within the family is an important aspect of living a balanced life. Examples include, volunteering in your community or performing acts of kindness.

Questions to ask yourself: It is better to contribute to the common welfare of our community than to think only of

ourselves. It is better to live in harmony with others and our environment than to live in conflict with

them.

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Environmental Wellness:

Environmental well-being includes trying to live in harmony with the Earth by understanding the impact of your interaction with nature and your personal environment, and taking action to protect the world around you. Protecting yourself from environmental hazards and minimizing the negative impact of your behavior on the environment are also central elements.

Leading a lifestyle that is respectful to our environment and minimizes any harm done to it is a critical part of environmental wellness. Examples of environmental threats include air pollution, ultraviolet radiation in the sunlight, chemicals, noise, water pollution, and second-hand smoke.

Questions to ask yourself: Are you engaged in the process of environmental wellness? Do I recycle? If I see a safety hazard, do I take the steps to fix the problem? Do I volunteer time to worthy causes? Am I aware of my surroundings at all times?

Occupational Wellness:

Occupational Wellness is the ability to achieve a balance between work and leisure time, addressing workplace stress and building relationships with co-workers. It focuses on our search for a calling and involves exploring various career options and finding where you fit. Because what we do for a living encompasses so much of our time, it's important for our overall well-being to do what we love and love what we do. When people are doing what they were meant to do, they deepen their sense of meaning and purpose.

Questions to ask yourself: Do I enjoy going to work most days? Do I have a manageable workload at work? Do I feel that I can talk to my boss and co-workers about problems that may arise?

What is my current level of wellness or health?

What things do people do to promote wellness?

What other things could I do to improve my own health?

How do my personal choices relate to my own health?

How do they affect others around me (e.g., family, community)?

Something we often forget about is... Sleep

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Think about the following in regards to sleep:

1. What is it?

2. Why is it important?

3. How does sleep affect our health and wellness?

4. On average how many hours of sleep do you get a night?

5. How do you feel after you get a good night’s sleep?

6. What time do you go to sleep at night?

7. Do you sleep without getting up during the night?

Here is what research shows about the average amount of sleep needed for different age groups:

Age Average Sleep NeedsNewborn to 2 months old 12 – 18 hrs3 months to 1 year old 14 – 15 hrs1 to 3 years old 12 – 14 hrs3 to 5 years old 11 – 13 hrs5-12 years old 10 – 11 hrs12-18 years old 8.5 – 10 hrsAdults (18 +) 7.5 – 9 years old

Let’s talk about Sleep

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Survey: You may be sleep deprived if you... (Place a checkmark is the statement applies to you!)

YES NO1. Need an alarm clock in order to wake up on time

2. Rely on the snooze button

3. Have a hard time getting out of bed in the morning

4. Feel sluggish in the afternoon

5. Get sleepy in meetings, lectures, or warm rooms

6. Get drowsy after heavy meals or when driving

7. Need to nap to get through the day

8. Fall asleep while watching TV or relaxing in the evening

9. Feel the need to sleep in on weekends

10. Fall asleep within five minutes of going to bed

While it may seem like losing sleep isn't such a big deal, sleep deprivation has a wide range of negative effects that go way beyond daytime drowsiness. Lack of sleep affects your judgment, coordination, and reaction times. In fact, sleep deprivation can affect you just as much as being drunk.

The effects of sleep deprivation include:

Fatigue, lethargy, and lack of motivation

Moodiness and irritability

Reduced creativity and problem-solving skills

Inability to cope with stress

Reduced immunity; frequent colds and infections

Concentration and memory problems

Weight gain

Impaired motor skills and increased risk of accidents

Difficulty making decisions

Increased risk of diabetes, heart disease, and other health problems

Homeostasis

What is the temperature in the room right now?10

How does this temperature compare to your body temperature?

If your body temperature doesn’t stay within the relatively narrow range of 35°C to 41.7°C the results can be dangerous and lead to death.

Our bodies, as all living organisms, depend on a set of balanced systems. We have systems that keep our internal temperature pretty constant. Our breathing rate matches our activity level to make sure that our cells get enough oxygen. Heart rate speeds up and slows down as necessary. We keep the correct fluid balance by taking in more fluids and expelling excess.

One of the most important concepts in biology is homeostasis:

Homeostasis is the maintenance of a constant internal environment in response to changes in the conditions of the external environment.

Homeostasis is a self-adjusting mechanism involving feedback where the response to a stimulus alters the internal conditions.

To maintain cells, tissues and entire organisms within their biological tolerance limits, various mechanisms have evolved. These mechanisms may be:

A. Structural - the animal or plant has particular physical features which help its survival in an otherwise hostile environment.

B. Functional - the metabolism of the animal or plant is able to adjust to changes in conditions as they are detected.

C. Behavioral - the actions and interactions of the individual, either alone or with others, help it to survive in its particular environment.

Homeostasis is really the combined result of all of these, a failure of any one of them can result in the death of an individual.

In order to function properly, homeostatic mechanisms must allow the body to: regulate respiratory gases maintain water and salt balance regulate energy and nutrient supply maintain constant body temperature protect against pathogens make repairs when injured

Maintaining Homeostasis

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Biological systems like those of your body are constantly being pushed away from their balance points.

Ex) What happens when you exercise?

Homeostasis depends on the ability of your body to detect and oppose these changes. Because the external environment is constantly changing and homeostatic reactions respond to the change and bring the body back to a given set point, it is often referred to as a dynamic equilibrium.

Dynamic equilibrium - Is a condition that remains stable within fluctuating limits.

How does this work?

Homeostatic control involved three main components:

- Receptor (aka Sensor)- Control Center- Effector

The receptor is responsible for detecting changes and will that information to the control center. The control center will compare the change to the set point at which the variable is to be maintained and then send a message to a specific effector to bring the body back to the set point.

Examples:

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What happens when a bright light shines in your eye? What happens to your eye when in darkness?

What happens when your body heats up? Cools down?

What happens when you consume a sugary beverage?

These examples illustrate types of negative feedback mechanisms. Almost all homeostatic control mechanisms are negative feedback mechanisms. Negative feedback acts to reduce the original stimulus.

Positive feedback mechanisms are very rare in the human body. Positive feedback mechanisms enhance the original stimulus. Childbirth is a good example.

Homeostatic Systems

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Three important homeostatic systems in the human body that depend upon negative feedback mechanisms to maintain equilibrium are: thermoregulation (the maintenance of body temperature), osmoregulation (water balance) and waste management.

Thermoregulation

Is the ability to maintain a constant body temperature. The constant body temperature for humans is 37 degrees Celsius. Humans are able to maintain a constant body temperature despite changes in the external environmental temperature (endotherm). The hypothalamus, a part of the human brain, is the coordinating centre for body’s temperature regulation. When there is a change in the external temperature the hypothalamus will release hormones that target specific effectors such as sweat glands.

Osmoregulation

Is the ability to maintain a constant water balance. For the body to maintain water balance, humans must consume fluids daily. A drop in fluid intake by as little as 1 % of your body mass will cause thirst, a decrease of 5 % will result in extreme pain and collapse, while a decrease of 10% often results in death. The hypothalamus is the coordinating centre for water balance and can detect changes in the fluid concentrations of the blood. When the fluid concentration of the blood decreases (dehydration), the hypothalamus will trigger the release of a hormone to increase water absorption.

Waste management

The ability of the body to rid itself of harmful wastes, is essential for the maintenance of homeostasis. One example of a harmful waste product is the ammonia produced during the breakdown of proteins. Ammonia is extremely toxic to the body. The liver is most important organ involved in the elimination of ammonia. Various organs, such as the kidneys, lungs, skin and stomach, as well as the liver, are involved in the elimination of various other waste products.

A look at Homeostatic Mechanisms at work: The Swimming Race

65 kg Debra was sitting quietly along the side of the pool. She was anticipating the swimming race that she would be competing in shortly. Four-hundred metres of intense physical activity, pushing

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her body to the very limits of its capabilities. She was calm and relaxed, mentally willing her heart and respiratory rate down. She had done some stretching and warm-up exercises, but her heart rate was just 65 beats per minute and she was breathing 12 breaths per minute. Her body temperature was 37° C. She was well hydrated.

That was an hour ago. Now, she was standing on the lane four starting block ready to go. She could see two swimmers to her left and three to her right. The swimmers all looked bigger than her, but then they always did. The starter on the pool deck was saying something over the loudspeaker but Debra wasn't paying attention. These last few seconds before the race were the most stressful--you could feel the tension in the air. She was sweating although the air was cool. Her heart rate was now 85 beats per minute and she was breathing 18 breaths per minute. She felt a nervous excitement.

“Take your mark,” the starter announced and with the sound of the horn the swimmers dove into the water.

After a short glide through the water Debra surfaced stroking at maximum power. She was putting all of her strength into each stroke.

Thirty seconds later, she had traveled just over 50 meters. Debra was completely focused, shutting out external distractions and concentrating on keeping the power up. She was giving each stroke about 80% of her maximum power. Her heart rate was 201. Her respiratory rate was also up slightly. Her body temperature was 37.5° C.

At the end of that first minute, Debra’s heart rate was 180 beats per minute. She was taking breaths every 6 strokes, fast and forced. Her body temperature was 38° C.

With 100 meters to go to the finish line, Debra had been swimming for just over 3 minutes. Debra could see she was even with the swimmer in lane 2. Debra knew she needed to push herself if she wanted to win. She focused completely on the placement and pull of each stroke. She was breathing faster, one breath every 3 strokes. Her heart rate was 195 beats per minute and her body temperature was 38.5° C.

The winner of this race was going to be whoever touched the wall first. As Debra touched the edge of the pool, four minutes and 15 seconds after starting and one-tenth of a second behind the swimmer from lane two, her heart rate was 208 beats per minute. She slumped over the lane marker, breathing nearly 60 times per minute but still not feeling like she could get enough air. It felt like her arms and legs were on fire. She felt light-headed. Her body temperature was 39° C.

Ten minutes later after a cool down, Debra’s heart rate and respiratory rate were almost back to normal. She weighed 64 kgs. Her body temperature was still half a degree above normal. She felt drained of energy. She was thirsty. She had allowed herself only small sips of water during the cool down.

Fill in the above chart with as much information about each system as you can. Feel free to talk with your neighbours.

Respiratory Cardiovascular Excretory System

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System SystemTemperature

Starting Block

30 Seconds In

60 Seconds In

3 MinutesIn

Finish

After Cool Down

Questions:

At the start……

1. What is responsible for raising Debra’s heart and respiratory rate and stimulating sweating before the race at the starting block?

30 Seconds In……

2. Swimming hard is putting new demands on Debra's body. What are these new demands and how does the body respond to them?

At the finish……..

3. Debra has stopped swimming and her muscles are now at rest. Why are her heart and breathing rates still so high?

After the Cool Down…….

4. What changes have occurred in the last 10 minutes to allow Debra’s heart and respiratory rates to come down?

Feedback Mechanisms Practice

Each following statement describes a feedback loop. For each determine if it is negative or positive feedback and justify your answer by illustrating the loop.

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Problem #1: When you become dehydrated, and the osmolality of the blood increases (meaning your blood has more salt and less water), osmoreceptors in the hypothalamus cause the posterior pituitary to secrete anti-diuretic hormone (ADH). ADH acts on the kidney to increase the reabsorption of water, and put the water back into your bloodstream. This helps prevent the osmolality of the blood from increasing even further. If you drink lots of water, ADH production decreases, and the kidneys remove water from the blood, again maintaining the osmolality of the blood. Is this a positive or negative feedback loop?

Problem #2: During childbirth, the fetus is pushed against the uterine opening, causing it to stretch. Receptors that detect the stretching send signals to the brain. The brain sends both neural and hormonal signals which increase both the contraction force and the contraction frequency in the smooth muscles of the uterus. This continues until the baby is delivered through the birth canal. Is this a positive or negative feedback loop?

Problem #3: An increase of carbon dioxide in the blood leads to a decrease in blood pH. The drop in blood pH is detected by chemoreceptors in the aorta and carotid artery. These receptors send nerve impulses to the respiratory center in the medulla oblongata in the brain, which then stimulates increased breathing. Increased breathing helps remove carbon dioxide from the blood, returning blood pH to normal levels. Is this a positive or negative feedback loop?

Problem #4: After eating a meal, your blood glucose level increases. Islet cells in your pancreas detect the rise in blood sugar, and release insulin into the bloodstream. Insulin binds to receptors on cells throughout the body, allowing the cells to take up glucose from the blood. This lowers blood glucose levels back to a normal level. Is this a positive or negative feedback loop?

Problem #5: During sexual intercourse, stimulation leads to an increase in arousal and sexual behavior. This in turn leads to increased stimulation, until climax is reached and orgasm takes place. Is this a positive or negative feedback loop?

Problem #6: As a follicle develops in the female ovary, it releases estradiol into the blood. Estradiol stimulates the anterior pituitary to secrete luteinizing hormone (LH), which further stimulates the developing follicle and therefore the production of estradiol. This cycle continues until the follicle ruptures, releasing the egg into the fallopian tube. Is this a positive or negative feedback loop?

Problem #7: When thyroxine levels in the body are low, the hypothalamus secretes thyrotropin-releasing hormone (TRH). TRH acts on the anterior pituitary causing the secretion of thyroid-stimulating hormone (TSH). TSH, in turn, acts on the thyroid gland, causing secretion of thyroxine. Increased levels of thyroxine act on both the hypothalamus and anterior pituitary, decreasing the release of both TRH and TSH. Is this a positive or negative feedback loop?

Problem #8: Here are some examples related to ecosystems and global climate change. Ice caps at the north and south poles are very reflective -- the ice reflects light and heat rather than absorbing it. If global warming occurs, then the increase in temperature will cause polar ice to melt, and the bare dark ground will absorb rather than reflect heat. This additional absorption of heat will further boost the temperature of the earth. Is this a positive or negative feedback loop?

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Problem #9: Carbon dioxide is considered a "greenhouse gas" since it absorbs heat that would otherwise dissipate out into space. If there is more carbon dioxide in the atmosphere, global temperatures are likely to increase. It is possible that plants will respond to the increased carbon dioxide and increased temperatures with an increase in photosynthesis. Since carbon dioxide is needed for photosynthesis, this could reduce the amount of carbon dioxide in the atmosphere, leading to cooler temperatures. Is this a positive or negative feedback loop?

Problem #10: We know that warm water holds less dissolved gas -- that's why a soda pop goes flat when it gets warm. Normally, there is a great deal of dissolved carbon dioxide in cold ocean water. If global warming occurs and global temperatures increase, warmer ocean water will hold less dissolved carbon dioxide. Less dissolved carbon dioxide in the ocean means more carbon dioxide in the atmosphere. Since carbon dioxide is a "greenhouse gas," the increase in atmospheric carbon dioxide will further boost global temperatures, making it even warmer. Is this a positive or negative feedback loop?

Biological Levels of Organization

Cell – Most basic unit of all living things

Tissue - A group of similar cells that performs a specific function.

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Organ - Formed of two or more tissues and carries out a specific function.

Organ System - A group of organs that work together to perform a vital body function

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Cell Theory

Is a universally accepted scientific theory and one of the basic principles of Biology.

Cell Theory States:

1. All living organisms are composed of cells. They may be unicellular or multicellular.

2. The cell is the basic unit of life.

3. Cells arise from pre-existing cells.

Two main types of cells:

Prokaryotes – bacteria and archaea

Eukaryotes – animal, plant, and fungal cells

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The Plasma Membrane

There must be ways to transport materials into and out of the cell. Vital processes such as exchanging gases (usually CO2 and O2), taking in water, minerals, and food, and eliminating wastes require that molecules move through the membrane that surrounds the cell. This membrane is a complex structure that is a barrier separating the contents of the cell from its surroundings, for controlling the movement of materials into and out of the cell, and for interacting with the environment surrounding the cell.

The plasma membrane is a phospholipid bilayer with protein molecules embedded in it. It is said to be selectively permeable, allowing only certain substances such as nutrients and other essential molecules to enter the cell and allowing waste materials to leave the cell.

The phospholipid bilayer is made up of single units called phospholipids.

A phospholipid is made up of a polar hydrophilic head (polar head - phosphate group and glycerol) and a non-polar hydrophobic tail (2 chains of fatty acids)

The non-polar, hydrophobic tails position themselves in the middle region of the bilayer. The polar, hydrophilic heads positions facing outwards and interacts with the water.

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Fluid Mosaic Model

The fluid mosaic model describes the plasma membrane of animal cells, in which the membrane is a fluid structure with a “mosaic” of various proteins, carbohydrates, and lipids embedded or attached.

Cholesterol – makes the membrane less fluid. Used to regulate membrane fluidity.

Carbohydrates – forms the glycocalyx, a matrix that surrounds the cell and contributes to cell-cell recognition, communication, and intercellular adhesion. Integral proteins – are protein structures that completely spans the hydrophobic region of the plasma membrane.

Peripheral proteins – are protein structures that are attached to the surface of the plasma membrane and not embedded in the lipid bilayer.

These proteins have many roles, like identifying harmful pathogens, communicating with other cells, receiving hormonal signals, adhering to other cells, and transporting substances across the membrane.

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Passive and Active Transport

Cells must maintain an internal balance of substances, and requires the ability to eliminate toxins and waste products produced within the cell.

This can be done in two ways:- Passive Transport- Active Transport

Passive Transport

Does not require energy for transport of materials into and out of the cell.

Examples: - Simple Diffusion- Facilitated diffusion- Osmosis

Solutes will move in the direction of higher concentration to lower concentration of a particular solute. This movement is bi-directional.

Simple Diffusion:

Process by which a substance passes through a membrane without the aid of an intermediary such as a transport protein.

Only water, small molecules, and non-polar molecules can readily pass. Example: Oxygen diffusing into a cell and carbon dioxide diffusing out.

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Facilitated Diffusion:

Utilized imbedded membrane proteins to aid in the transport of larger molecules and polar molecules. Example: Glucose or amino acids moving from blood and into a cell

Osmosis:

Diffusion of water across the plasma membrane down its concentration gradient. Moves from HIGH water potential (low solute) to LOW water potential (high solute)

Aquaporins

Water channel proteins that increase the rate diffusion during osmosis. These porins are highly specific.

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Definitions: The osmotic conditions of the solutions surrounding a cell are given special names.

Hypertonic

Hypotonic

Isotonic

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Active Transport

Moves materials from low concentration to high concentration, i.e. against its concentration gradient.

This process requires energy (ATP)

Example: Sodium-Potassium pump which creates the nervous membran potential

Bulk Transport

When an animal cell comes in contact with required substances that are too large to pass through the cell membrane, the cell can form a pocket or infolding of the membrane which transports the needed substance into the cell. This process is known as Endocytosis.

There are three types of endocytosis:

Phagocytosis (cellular eating) - membrane extends to wrap around a large particle (food, bacteria, ect.) bringing it into the cell in a membrane enclosed sack called a vesicle. The vesicle fuses with a lysosome to digest the particle.

Pinocytosis (cellular drinking) – random sampling of environment to bring in bulk dissolved materials. Pinocytotic vesicles are very small and can be seen only with an electron microscope.

Receptor mediated endocytosis - Some integral membrane proteins have receptors on their surface to recognize, bind, and take in specific metabolites, hormones, or proteins.

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Exocytosis is the opposite of endocytosis, transporting materials out of the cell.

Cells use exocytosis to expel waste materials and to secrete important macromolecules, such as enzymes and hormones.

During exocytosis intracellular vesicles in the cytoplasm fuse with the plasma membrane and release or "secrete" their contents into the extracellular space.

**Both endocytosis and exocytosis require energy and are forms of active transport.

The Role of Energy in Maintaining Homeostasis

Living cells require a constant source of energy to do three kinds of work:

1. Chemical - includes constructing and breaking down large complex molecules such as proteins and nucleic acids.

2. Transportation - involves the movement and concentration of raw materials or nutrients for building complex molecules or growth of cellular structures.

3. Mechanical - involves movement such as muscle contractions. Without a constant source of

energy, living systems would not survive.

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Glucose is the energy currency of the body. However, it cannot be utilized directly to perform work. Glucose must be converted first to ATP through a process called Cellular Respiration.

C6H12O6 + 6O2 6CO2 + 6H2O + Energy (ATP)Glucose + oxygen carbon dioxide + water + Energy (ATP)

What is ATP?

Adenosine triphosphate (ATP) is a molecule composed of three components.

a) At the centre is a sugar molecule, ribose (the same sugar that forms the basis of DNA). b) Attached to one side of this is a base; in this case the base is adenine. c) The other side of the sugar is attached to a string of phosphate groups. These phosphates

are the key to the activity of ATP. The energy of ATP is due to these bonds as they are highly unstable.

The energy in ATP can be released as heat or can be used in the cell as a power source to drive various types of chemical and mechanical activities.

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ATP works by losing the endmost phosphate group when instructed to do so by an enzyme. The reaction product is adenosine diphosphate (ADP) and inorganic phosphate (Pi). When the inorganic phosphate forms a new bond, energy is released.

The regeneration of ATP from ADP requires energy, which is obtained in the process of oxidation. The energy released in the oxidation of carbohydrates, proteins, and fats initiates a complex series of chemical reactions that ultimately regenerate ATP molecules from ADP molecules.

When your parents said “go outside and burn some energy” little did they know they were being scientifically accurate.

Remember: The energy in an ATP molecule is stored in the bonds between the phosphate groups. As energy is required, the ATP loses one phosphate group, releasing energy to fuel a process such as contracting a muscle. Once the cell has used the energy required, ATP can be "recharged" by providing an energy source.

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