Life+Science

= Study Mate = = Characteristics of Life =

Not all scientists agree exactly about what makes up life. Many characteristics describe most living things. However, with most of the characteristics listed below we can think of one or more examples that would seem to break the rule, with something non-living being classified as living or something living being classified as non-living.

There is not just one distinguishing feature that separates a living thing from a non-living thing. A cat moves but so does a car. A tree grows bigger, but so does a cloud. A cell has structure, but so does a crystal. Biologists define life by listing characteristics that living things share.

An individual living creature is called an organism. There are many characteristics that living organisms share. All organisms are made up of cells. Cells are the smallest units of an organism (a living thing).
 * Unicellular: organisms made up of only one cell
 * Multicellular: organisms made up of many cells.

These cells must be able to carry out the following life activities:

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 * respond to their environment
 * grow and change
 * reproduce and have offspring
 * produce energy through metabolism while maintaining homeostasis

Response to Stimulus One of the most important characteristics of living things is that they respond to the environment around them. This one single characteristic makes them very different from non-living things, which do not respond to the environment, but instead just let whatever happens to them happen. Your own body responds to its environment in order to keep you healthy. You might sneeze to keep dust and germs from entering through your nose, your immune system responds to invaders by producing antibodies, etc. Now consider a non-living thing. If a bear invades a cave, can the cave sneeze to get it out? Does the cave produce antibodies to attack the bear? You can see why this ability is so unique and important to living things.

Growth and Development Almost all living things start their lives as smaller infant-like creatures. Over a period of time, they grow and develop into adults. Some lifeforms, such as frogs, start their life in a completely different form, and then change dramatically as they grow. A frog begins its life as a tadpole, then turns into an adult frog. A butterfly starts its life as a caterpillar before maturing into a full grown beautiful butterfly.

Reproduction All living organisms must have the ability to reproduce. Living things make more organisms like themselves. Whether the organism is a rabbit, or a tree, or a bacterium, life will create more life. If a species cannot create the next generation, the species will go extinct. Reproduction is the process of making the next generation and may be a sexual or an asexual process. Sexual reproduction involves two parents and produces offspring that are genetically unique and increases genetic variation within a species. Asexual reproduction involves only one parent. It produces offspring that are all genetically identical to the parent.

Energy Living things take in energy and use it for maintenance and growth. Autotrophs are organisms that can produce their own food from the substances available in their surroundings using light (photosynthesis) or chemical energy (chemosynthesis). Heterotrophs cannot synthesize their own food and rely on other organisms — both plants and animals — for nutrition.

A human body has a temperature of 37 degrees Celsius, (about 98.6 degrees Fahrenheit). If you step outside on a cold morning, the temperature might be below freezing. Nevertheless, you do not become an ice cube. You shiver and the movement in your arms and legs allows you to stay warm. Eating food also gives your body the energy it needs to keep warm. Living organisms keep their internal environments within a certain range (they maintain a stable internal condition), despite changes in their external environment. This process is called homeostasis, and is an important characteristic of all living organisms. Temperature regulation is an important bodily function for warm-blooded animals, because it allows them to live in any climate and to survive in places where the climate fluctuates seasonally. Homeostasis is important not only in regulating temperature but in performing tasks, such as digestion and elimination of waste. When an animal's kidneys filter its liquid intake and triggers the elimination of waste in the form of urine, that animal's body is performing a natural, involuntary function that helps regulate the amount of potentially toxic or otherwise harmful materials in the body. Homeostasis is important all the way down to the cellular level; without proper homeostasis, cells cannot perform essential tasks such as osmosis, which is a process of water passing through a cell's membrane.

= Big Idea: All organisms are made up of one or more cells. = toc

** Essential Question: What are living things made of? **
//biotic, abiotic, spontaneous generation, biogenesis//

Origin of Life
//Students will be able to trace the ideas that lead to our current scientific understanding about how life began.// []

Amino acids are the building blocks of life as we know it. They can be formed from abiotic (non-biological) chemical reactions (in a jar with electricity for example). It’s been known for a while that amino acids can be found on comets and asteroids, but now this fascinating article suggests that a lot of the chemical reactions that created these precursors to life happened on the asteroids themselves. Then when the asteroids bombarded the Earth, the seeds of life were delivered.

Until the 1600's, most people believed in spontaneous generation. This theory maintained that life could start from non-living matter. People believed that mice came from straw and that frogs and turtles came from rotting wood and mud at the bottom of a pond. For example, many people know that if you left meat out to rot that maggots would often appear within a few days. They thought that the meat turned into little worms, which would eventually turn into flies.

**Francesco Redi**
An Italian doctor, Francesco Redi, did not believe in this idea. Like many educated people of his time, he was interested in how life developed. He decided to test the common idea that maggots could come from rotting meat that was exposed to air. In 1668~ he disproved the theory of spontaneous generation using the scientific method. Redi thought that if spontaneous generation was possible, maggots would be found even in meat that was sealed in jars. So Redi placed pieces of meat into several jars. Some jars he sealed tightly. Some he covered with a fine cloth. Some he left open to the air. No maggots appeared in the sealed jars. The meat in the open jars attracted flies and soon maggots appeared on the meat. Flies were attracted to the cloth covered jars too. But the maggots laid eggs on the top of the cloth. Since the flies could not reach the meat, eggs could not develop into maggots without food and moisture. = = If maggots could come from meat alone, they would have appeared in all of the jars. If maggots could come from meat and air, they would have appeared in the jars covered by the cloth. Redi had shown that maggots did not arise from meat, whether air was present or not. The maggots had to come from some other source.
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**Lazaro Spallanzani**
In 1768~ an Italian biologist boiled a broth in glass bottles. Boiling killed any organisms in the broth. He sealed the bottles so that air could not enter. The broth stayed clear. Finally he opened the bottles and allowed the air to enter. Small organisms floating in the air got into the broth. The broth quickly began to spoil. = = Spallanzani's results supported Redi's. But Spallanzani had not tested the effect of the presence or the absence of air. Some people thought that if there had been air in the sealed bottles, the results would have been different. About 100 years later, a French scientist changed the format of Spallanzani's experiment in order to make it more scientific. = =

**Louis Pasteur**
Louis Pasteur believed that bacteria existed in the air as spores that were in a resting state. He thought these spores were attached to dust particles in the air. When the spores landed on a place where there was food and water, they would begin to grow and reproduce. Pasteur modified Spallanzani' s experiment by using special long necked flasks to hold the broth. The necks were curved and very thin, but they were open. Air could enter the flasks, but dust carried in the air became trapped in the curved necks. Pasteur found that nothing grew in the flasks until he broke off the necks. Then dust from the air could enter, carrying small organisms with it. Soon the broth became cloudy and bubbly, and organisms in the broth were visible under the microscope. He showed that organisms could not appear in the broth unless the broth first came in contact with living organisms. Scientists have not believed in spontaneous generation since the results of this experiment became known. Today there is no doubt that living things can come only from other living things. Scientists finally were convinced that living things, no matter how small, do NOT come from nonliving things. The present theory of where living things come from is called Biogenesis. This theory states that living things come only from other living things. For example, mice come only from mice, and microorganisms such as bacteria can only come from other bacteria.

So if living things can only come from other living things, then where did the first living things come from? = =

**Stanley Miller**
In 1953, a graduate student named Stanley Miller set out to verify the Oparin-Haldane ­Urey hypothesis with a simple, but elegant experiment. The results of this experiment have been taught to every high school and college biology student for nearly four decades. He reproduced the early atmosphere of Earth that Urey proposed by creating a chamber with only hydrogen, water, methane, and ammonia. To speed up "geologic time" in his experiment, he boiled the water and instead of exposing the mix to ultraviolet light he used an electric discharge something like lightning. After just a week, Miller had a residue of compounds settled in his system. He analyzed them and the results were electrifying: Organic compounds had been formed, most notably some of the "building blocks of life," amino acids. Amino acids are necessary to form proteins which themselves form the structure of cells and play important roles in the biochemical reactions life requires.

Cell Theory //(page 8 in your text)//
//Students will be able to explain the components of the scientific theory of cells.//


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While observing dead cork samples with a crude lens, **Robert Hooke** identified and named “cells.” He was able to see the minute, boxlike units of which the cork was made up. Hooke called these structures cells because he thought the boxes looked like monastery cells.

Years later, as microscopes improved, other biologists were able to continue the work of Hooke and Leeuwenhoek, learning more about cells. Van Leeuwenhoek is probably best known for his refinement of the microscope. While your high school biology textbook may have identified him as the inventor of the instrument, Zacharias Jansen actually developed the first primitive **microscope**. However, Van Leeuwenhoek was the first person to develop lens of such superior quality. His technological contributions include increasing the magnification capacity of the microscope from 20x-30x to 270x. Anton Van Leeuwenhoek's single most important discovery was the existence of **single-cell organisms**. While using a microscope to examine pond water in 1674, he observed dozens of **protists**, which he called '**animalcules**,' as well as **spirogyra**, or green alga. The term 'animalcules' was used for a long time; eventually scientists began using the word 'microorganisms.' The existence of single-celled organisms not only opened an entirely new unseen world for biologists, but also established the field of **microbiology**. Leeuwenhoek's discovery helped to form the basis of cell theory and discredit the idea of spontaneous generation.

German biologist **Matthias Schleiden** discovered that every part of a plant he looked at was made of cells. Another German scientist by the name of **Theodor Schwann** discovered that every part of an animal he looked at through a microscope was made of cells. Later in 1855, a German physician named Rudolph Virchow was doing experiments with diseases when he found that all cells come from other existing cells.

While Virchow, in Germany, was developing the new science of cellular pathology, Louis Pasteur, in France, was developing the new science of bacteriology. Virchow fought the germ theory of Pasteur. He believed that a diseased tissue was caused by a breakdown of order within cells and not from an invasion of a foreign organism. We know today that Virchow and Pasteur were both correct in their theories on the causality of disease.

Today scientists have developed what we call the **Cell Theory**. This theory states the following:
 * All living things are made of cells.
 * Cells are the basic units of structure and function in living things.
 * Living cells come only from other living cells.

Essential Question: What are the different types of cells?
//prokaryote, eukaryote//

** Types of Cells ** (page 11 in your text)
// Students will learn that different cells vary in size and shape. //

Cells are the building blocks of life – all living organisms are made up of them.There are lots of different types of cells. Each type of cell is different and performs a different function. In the human body, we have nerve cells which can be as long as from our feet to our spinal cord. Nerve cells help to transport messages around the body. We also have billions of tiny little brain cells and muscle cells which help us move around. There are many more cells in our body that help us to function and stay alive.

Although there are lots of different cells, most of them can be divided into two main categories: prokaryotic and eukaryotic.


 * Prokaryotic Cells ** - The prokaryotic cell is a simple, small cell with no nucleus. Most bacteria are prokaryotic. There are three main parts to the prokaryotic cell: 1) the outside of the cell called the cell wall 2) the flagella which is like an appendage and can help the cell to move 3) the inside of the cell called the cytoplasm.


 * Eukaryotic Cells ** - these cells are a lot bigger and have a cell nucleus which houses the cell's DNA. These are the types of cells we find in plants and animals.

Textbooks often show a single ‘typical’ example of a plant cell or an animal cell, but in reality, the shapes of cells can vary widely. Animal cells in particular come in all kinds of shapes and sizes. Plant cell shapes tend to be quite similar to each other because of their rigid cell wall. We can learn a lot about what a cell does by looking at its shape and size, and microscopes are the ideal tool for this.

Cells have different shapes because they do different things. Each cell type has its own role to play in helping our bodies to work properly, and their shapes help them carry out these roles effectively. The following cell types all have unusual shapes that are important for their function. 
 * Shaped for the task**

Neurons are cells in the brain and nervous system. Their job is to carry electrical messages all the way from the brain to the rest of the body and back (almost like electrical wire), so they are very long, thin cells. They also need to connect with other neurons to form communication networks, so they have many long branches. You can learn more about neurons elsewhere in this context and in the context Uniquely Me.

Photoreceptor cells (rods and cones) are cells in the eye that detect light. They’re actually a very specialized form of neuron. Photoreceptors need to collect light as efficiently as possible, so they have a specialized protrusion from the cell (called the outer segment) that is full of the molecules that absorb light. Rods, which are especially good at detecting light, have a bigger protrusion. The outer segment is now known to be a highly modified kind of primary cilium, a recently discovered organelle. You can read more about the primary cilium elsewhere in this context.

Immune cells are cells that respond when the body is infected (by a bacterium, for instance). To do their job, they need to be able to change shape. For instance, lymphocytes may need to move through body tissue to get to the site of infection, so they change their shape to squeeze past tightly packed tissue cells. Some immune cells engulf bacteria and viruses, so they need to change their shape to ‘swallow’ them. You can learn more about the different kinds of immune cells in the context Fighting Infection.

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= Essential Question: What are the different parts of a cell? = //mitochondrion, ribosome, endoplasmic reticulum, Golgi body, cell wall, vacuole, chloroplast, lysosome, cytoplasm, cell membrane, nucleus//

https://play.kahoot.it/#/k/bfcfae89-138a-49c5-bca0-66d256a3e873

** Parts of a Cell ** ( pages 27-32 in your text)
//Students will learn that different parts help the cell to carry out all the tasks needed for life.//

Cells have many different organelles that help it function. There is sometimes a cell wall that supports the cell membrane, a endoplasmic reticulum that creates lipids (fats). Chloroplasts give plant color and energy.Mitochondria gives a cell protein while a golgi complex ships content around the cell. Vesicles form when cell membrane covers something outside and a vacuole that stores water for a plant. Finally, lysosomes that eat used up things and dissolve cells.


 * Cell Parts **


 * **Nucleus** - the "brain" of the cell. DNA.
 * **Ribosomes** - these organelles make new proteins for the cell
 * **Endoplasmic Reticulum** - this organelle acts as a delivery system of the proteins made by the ribosomes.
 * **Golgi Body**- prepares the proteins for delivery
 * **Mitochondria** - this is the "energy station" for the cell.
 * **Chloroplast -** converts energy from the sun into food for autotrophs
 * **Lysosomes** - digests food
 * **Vacuole** - cell sap, water, salts (calcium), inorganic ions (K+ and Cl-), enzymes, toxic byproducts.
 * **Cell Wall** - cellulose, cell shape, protection, filtering mechanism, found in plants, bacteria, Archaea, fungi, and algae.
 * **Cytoplasm** - cytosol. This is the semi-liquid materials in which organelle float.
 * **Cytoskeleton** - microfilaments, microtubules / centrioles. This provides support to the structure of the cell.
 * **Cell Membrane** - phospholipid bi-layer that surrounds the cell. It controls what can go in and out of the cell because it is semi-permeable.

Cell Membrane - Holding It All Together
 * All cells have an outer covering that separates the inside of the cell from the outside
 * The job of the cell membrane is to keep all the cytoplasm, allow nutrients in and waste out, and to interact with things outside the cell
 * The cell wall is only found in the cells of plant and algae
 * The cell wall is a layer that surrounds and provide strength and support to the cell membrane
 * The cell wall keeps the cell membrane from ripping when too much water enters the cell
 * Cell walls in plants are made of cellulose fiber that crosses over each other
 * The strength of a cell wall can defy gravity

Nucleus - The Cell's Library
 * The largest and most visible organelle is the nucleus
 * Nucleus is the control center and contains DNA
 * The dark spot in the nucleus is the nucleolus
 * The nucleolus stores materials that will be used later to make ribosomes in the cytoplasm

Ribosomes - Protein Factories
 * Proteins are the building blocks of all cells
 * Proteins are made of amino acids
 * Amino cells are hooked together to make proteins at an organelle called ribosomes
 * Ribosomes are the smallest organelle
 * Ribosomes are the only organelles that have no membrane
 * Every cell needs ribosomes to live

Endoplasmic Reticulum - The Cell's Delivery System
 * The endoplasmic reticulum, or ER, is a membrane covered compartment that makes lipids and other materials to be used inside and outside the cell
 * The ER breaks down drugs and other harmful materials in the cell
 * The internal delivery system of a cell
 * The ER gathers the protein from the ribosomes and release it for use elsewhere

Mitochondria - The Cell's Power Plants
 * Cells need energy to function
 * Food molecules are burned to release energy
 * The burned/broken down molecules are transferred a special molecule called ATP
 * Mitochondria produce ATP
 * Mitochondria need oxygen to make ATP, and that is the reason we need to breathe
 * Plant and algae have an organelle called chloroplast
 * Chloroplast looks like stack of coins and contains a chemical called chlorophyll
 * Chlorophyll makes the plant green and traps sunlight to create sugar, this is the process of photosynthesis
 * The sugar is used by the mitochondria to make ATP
 * The mitochondria and the chloroplast are as small as a bacteria and have two cell membranes
 * They divide like a bacteria and known to be originated from prokaryotic cells

Golgi Body - The Cell's Packaging Center
 * The golgi complex is the organelle that ships and processes proteins and other materials out of the eukaryotic cells
 * Named after the Italian scientist, Camillo Golgi
 * Golgi complex looks like a ER, but closer to the cell membrane
 * Lipids and proteins from the ER is delivered to the golgi complex to be modified for different function
 * The final product is enclosed in a piece of the golgi complex's membrane that pinches off to form a compartment where materials are put in to be shipped
 * also call the Golgi apparatus or the Golgi complex

Vacoule - The Cell's Storage Center
 * All eukaryotic cells have membrane covered compartment called vesicles
 * Vesicles cover objects outside the cell
 * Vacuole is a large membrane covered chamber that contains the plant's water
 * Vacuoles can change the color of a plant and contain the juice of a plant
 * Some unicelluar organisms that live in water has a special vacuole called contractile vacuole that squeeze out water when there is too much

Lysosomes - Packages of Destruction
 * Lysosomes are special vesicles that contain enzymes
 * Lysosomes pour enzymes on a particle that is enclosed in a vesicle
 * Lysosomes destroy worn out or damaged cells
 * They protect the cell from waste materials and foreign invaders
 * Sometimes the lysosome break and spill the enzymes that destroys the cell

Essential Question: How are living things organized?
//organism, tissue, organ, organ system, structure, function//

We know it all starts with the cell. And for some species it ends with the cell. But for others, the cells come together to form tissues, tissues form organs, organs form organ systems, and organ systems combine to form an organism.
 * //Organization of Living Things.//** **What does this mean?**

Levels of Organization
The living world can be organized into different levels. For example, many individual organisms can be organized into the following levels:
 * **Cell**: Basic unit of structure and function of all living things.
 * **Tissue **: Group of cells of the same kind.
 * **Organ**: Structure composed of one or more types of tissues. The tissues of an organ work together to perfume a specific function. Human organs include the brain, stomach, kidney, and liver. Plant organs include roots, stems, and leaves.
 * **Organ system **: Group of organs that work together to perform a certain function. Examples of organ systems in a human include the skeletal, nervous, and reproductive systems.
 * **Organism**: Individual living thing that may be made up of one or more organ systems.

There are also levels of organization above the individual organism.
 * Organisms of the same species that live in the same area make up a **population **. For example, all of the goldfish living in the same area make up a goldfish population.
 * All of the populations that live in the same area make up a **community**. The community that includes the goldfish population also includes the populations of other fish, coral, and other organisms.
 * An **ecosystem** consists of all the living things (**biotic factors**) in a given area, together with the nonliving environment (**abiotic factors**). The nonliving environment includes water, sunlight, soil, and other physical factors.
 * A group of similar ecosystems with the same general type of physical environment is called a **biome**.
 * The **biosphere ** is the part of Earth where all life exists, including all the land, water, and air where living things can be found. The biosphere consists of many different biomes.

= Essential Question: How do organisms maintain homeostasis? = //homeostasis, diffusion, active transport, photosynthesis, osmosis, endocytosis, cellular respiration, passive transport, exocytosis, mitosis//

Living cells can function only within a narrow range of such conditions as temperature, **pH**, **ion** concentrations, and nutrient availability, yet living organisms must survive in an environment where these and other conditions vary from hour to hour, day to day, and season to season. Organisms therefore require mechanisms for maintaining internal stability in spite of environmental change. American physiologist Walter Cannon (1871–1945) named this ability homeostasis ( //homeo// means "the same" and //stasis// means "standing or staying"). Homeostasis has become one of the most important concepts of physiology, physiological ecology, and medicine. Most bodily functions are aimed at maintaining homeostasis, and an inability to maintain it leads to disease and often death.

The human body, for example, maintains blood pH within the very narrow range of 7.35 to 7.45. A pH below this range is called acidosis and a pH above this range is alkalosis. Either condition can be life-threatening. One can live only a few hours with a blood pH below 7.0 or above 7.7, and a pH below 6.8 or above 8.0 is quickly fatal. Yet the body's metabolism constantly produces a variety of acidic waste products that challenge its ability to maintain pH in a safe range.

Body temperature also requires careful homeostatic control. On a spring or fall day in a temperate climate, the outdoor Fahrenheit temperature may range from the thirties or forties at night to the eighties in the afternoon (a range of perhaps 4 to 27 degrees Celsius). In spite of this environmental fluctuation, our core body temperature is normally 37.2 to 37.6 degrees Celsius (99.0 to 99.7 degrees Fahrenheit) and fluctuates by only 1 degree or so over the course of 24 hours. Indeed, if core body temperatures goes below 33 degrees Celsius (91 degrees Fahrenheit) a person is likely to die of **hypothermia**, and if it goes above 42 degrees Celsius (108 degrees Fahrenheit), death from hyperthermia is likely.

Internal conditions are not absolutely stable but fluctuate within a narrow range around an average called the set point. The set point for core body temperature, for example, is about 37.4 degrees Celsius, but the temperature fluctuates within about ( 0.5 degrees Celsius. Thus, it is more accurate to say the body maintains an internal dynamic equilibrium than to say it maintains absolute stability.

Negative Feedback and Stability
The usual means of maintaining homeostasis is a general mechanism called a negative **feedback** loop. The body senses an internal change and activates mechanisms that reverse, or negate, that change.

An example of negative feedback is body temperature regulation. If blood temperature rises too high, this is sensed by specialized neurons in the hypothalamus of the brain. They signal other nerve centers, which in turn send signals to the blood vessels of the skin. As these blood vessels dilate, more blood flows close to the body surface and excess heat radiates from the body. If this is not enough to cool the body back to its set point, the brain activates sweating. Evaporation of sweat from the skin has a strong cooling effect, as we feel when we are sweaty and stand in front of a fan. If the blood temperature falls too low, on the other hand, this is also sensed by the hypothalamus and signals are sent to the cutaneous arteries (those supplying the skin) to constrict them. Warm blood is then retained deeper in the body and less heat is lost from the surface. If this is inadequate, then the brain activates shivering. Each muscle tremor in shivering releases heat energy and helps warm the body back toward its 37 degrees Celsius set point.

In both cases, specialized neurons sense the abnormal body temperature and activate corrective negative feedback loops that return the temperature to normal. As a result, body temperature seldom goes more than0 .5 degrees Celsius above or below its set point. Other negative feedback loops regulate blood sugar concentration, water balance, pH, and countless other variables. Many such loops are regulated by the nervous system, and others by the hormones of the endocrine system.

Positive Feedback and Rapid Change
The counterpart to negative feedback is the positive feedback loop, a process in which the body senses a change and activates mechanisms that accelerate or increase that change. This can also aid homeostasis, but in many cases it produces the opposite effect and can be life-threatening. An example of its beneficial effect is seen in blood clotting. Part of the complex biochemical pathway of clotting is the production of an **enzyme** that forms the matrix of the blood clot, but also speeds up the production of still more thrombin. That is, it has a self- **catalytic**, self-accelerating effect, so that once the clotting process begins, it runs faster and faster until, ideally, bleeding stops. Thus, this positive feedback loop is part of a larger negative feedback loop, one that is activated by bleeding and ultimately works to stop the bleeding. 

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