Study of Cells

Historical Development of the Cell Theory

Many scientist working during the past 300 years have contributed to the cell theory. A historical development of the cell theory is briefly given below.

In 1665, Robert Hooke, an English scientist, examined a thin sliced of cork under a microscope. Hooke could see that the cork was composed of many small compartments. Because the compartments resembled the little rooms, or cells, of a monastery, Hooke named these compartments cells. The cells that Hooke observed were not living. Hooke did not pursue his discovery by investigating the structure or function of living cells.

Almost 200 years passed before biologists came to understand the importance of calls. In 1835, the French biologists Felix Dujardin determined that many microorganisms are composed of a single cell. Dujardin also observed that the internal substance of all living cells was similar.

Three years later, Matthias Schleiden and Schwann concluded that all animals are composed of cells. Schleiden and Schwann then suggested that cells are the basic living components of all organisms.

Twenty years later, Rudolf Virchow, another German biologist, wrote that the body is “a state in which every cell is a citizen.” From his observation of dividing cells, Virchow concluded that cells can arise only from other cells.

The observations of these and other scientists formed the basis of cell theory. The cell theory states that

a. The cell is the basic unit structure of living things. All living things are composed of cells or the products of cells.

b. The cell is the basic unit of function of living things.

c. All cells come from other cells by the process of cell division.

Since Hooke’s discovery of cells, scientists have developed a wide variety of techniques to study cells. The earliest tool used was the light microscope. Scientists discovered that treating cells with various chemicals, or stains, would color certain parts so they could be distinguished under the microscope. This allow the biologists to investigate the internal structure of cells.

More recently, the electron microscope and other tools have been used to study cells. Modern tools and techniques have allowed biologists to increase greatly their knowledge of cells. All current findings continue to support the cell theory

Differences between Prokaryotes and Euakaryotes

Parts of a Euakaryotic Cell

A. The Cell or Plasma Membrane

Surrounding a cell is a thin layer called the plasma membrane. The plasma membrane is more than just a boundary between the inside and outside of the cell. Among other functions the plasma membrane determines which molecules may enter or leave the cell.

Plasma membrane is made up of a double layer of phospholipid molecules. Each phospholipid is composed of a lipid and a phosphate group. Embedded in the phospholipids are protein molecules.

B. The Nucleus

The nucleus is a spherical structure that is usually located near the center of the cell. The nucleus directs the activity of the cell. Within the nucleus is a material called chromatin. Chromatin is readily stained than the rest of the nucleus. The chromatin contains the hereditary information of the cell. When a cell reproduces, the chromatin becomes visible as long strands called chromosomes.

1. Nuclear membrane - enclosed the nucleus and it contains pores through which only certain substances can pass. It also keeps the contents of the nucleus separate from the rest of the cell.

2. Nucleolus - is a chromatin condensed into a darker area. The nucleolus is involved in the production of ribosomes, which are organelles involved in protein synthesis.

C. Protoplasm and Its Organelles

The plasma membrane enclose a mass of jellylike material called protoplasm. The protoplasm is a colorless or somewhat grayish, translucent, viscous substance that is colorless or somewhat grayish that is capable of flowing.

Among them are:

a. Mitochondria - contain an enzymes that release the energy stored in food in the process of cellular respiration. For this reason, mitochondria are sometimes called powerhouse of the cell. It is surrounded by two membranes. The inner membrane is highly folded, forming cristae, which are sites of many enzymes of the respiratory processes of the cell.

b. Ribosomes - are small granules found within a specialized region of the nucleus called nucleolus and in the outer lining of the rough endoplasmic reticulum. Ribosomes are composed of nucleic acids and proteins. The synthesis of proteins occurs on the ribosomes.

c. Endoplasmic Reticulum - consists of a system of canals which form a continuous network throughout the cytoplasm. The canals serve as a path for the transport of materials throughout the cell. The canals are enclosed by membranes which have structure similar to the cell membrane and nuclear membrane. There is evidence that rough endoplasmic reticulum is involved both in producing proteins and preparing them for shipment out of the cell. Golgi bodies serve as packaging and distribution centers, especially for substances formed on the endoplasmic reticulum.

d. Golgi Bodies - are believed to prepare proteins for secretion after they are released from the endoplasmic reticulum.

e. Vacuoles - are fluid-filled “bubbles” in the cytoplasm. They are bordered by a unit membrane that is identical to the cell membrane. They serve as storage center of the cell.

f. Lysosomes - are also membrane-bound organelles. They contain enzymes that are capable of digesting the cell’s proteins.

g. Cytoskeleton - is a miniature internal support system is made up of microtubules and other tiny protein structures. Together these structural elements give the cell its shape.

h. Centrioles - consists of microtubules which is seldom found in plants. Near the nucleus of the animal cell is a pair of centrioles which are involved in cell replication where they function as centers for organization of the spindle. They also serve as template for the organization and development of cilia and flagella.

Chemistry of Life

Atoms

Smallest particles that retain properties of an element.

Made up of subatomic particles.

Protons (+)

Electrons (-)

Neutrons (no charge)

Elements

Fundamental forms of matter

Can't be broken by normal means

92 occur naturally on Earth

The most common elements in living organisms are Oxygen, Carbon, Nitrgoen and Hydrogen.

Molecules

A molecule is a group of atoms held together by energy

The holding force is called a chemical bond.

There are 3 kinds of chemical bonds

1. Ionic bonds

2. Covalent bonds

3. Hydrogen bonds

Ionic Bonds

An ion is a charged atom or molecule.Ions of opposite charge may form an ionic bond.

Covalent Bonds

Molecules are groups of atoms linked by covalent bonds.

Hydrogen Bonds

Hydrogen bonding occurs between polar molecules.

Water makes up a large portion of living organisms. It has several unusual properties that make it essential for life. Hydrogen bonds lie behind these important properties.

Specific heat capacity – 1 calorie is required to elevate temperature of 1 gram of water 1°C. Moderates environmental changes.

High heat of vaporization – more than 500 calories are required to convert 1 g of liquid water to water vapor.

Cooling produced by evaporation of water is important for expelling excess heat.

Unique density behavior - while most liquids become denser with increasing temperature, water's maximum density is at 4 degrees C.

Water has high surface tension. Because of the hydrogen bonds between water molecules at the water-air interface, the water molecules cling together. Water has low viscosity.

Water acts as a solvent – salts dissolve more in water than in any other solvent.Result of the dipolar nature of water.

Acids and Bases

Acids increase the hydrogen ion concentration of a solution.

Bases decrease the hydrogen ion concentration of a solution.

pH scale measures the strength of acids and bases.

Neutral solution with a pH of 7: [H+] = [OH-]

Basic solution with a pH above 7: [H+] < [OH-]

Acidic solution with a pH below 7: [H+] > [OH-]

Buffer: Molecules that prevent dramatic changes in the pH of fluids. lRemove H+ and OH- in solution and transfers them to other molecules. Example: Bicarbonate Ion (HCO3-)

Recall the four major categories of biological macromolecules:

1. Carbohydrates
2. Lipids
3. Proteins

4. Nucleic Acids

Carbohydrates are compounds of carbon (C), hydrogen (H) and oxygen (O). Usually found 1C:2H:1O. Usually grouped as H-C-OH.

Function as structural elements and as a source of chemical energy (ex. glucose)

Plants use water (H2O) and carbon dioxide (CO2) along with solar energy to manufacture carbohydrates in the process of photosynthesis. 6CO2 +6H2O ----> light

---->C6H12O6 + 6O2

Life depends on this reaction – it is the starting point for the formation of food.

3 classes of carbohydrates

• Monosaccharide: Glucose, Fructose and ribose
• Disaccharide: Maltose (Glucose + Glucose) and Sucrose (Glucose + Fructose)
• Polysaccharide: Starch (made of glucose subunits) and
• Glycogen (made of glucose subunits, but linked differently from starch). (Plants use mostly starch, humans use mostly glycogen)
• Also note that most polysaccharides are insoluble.

State one function of a monosaccharide and one function of a polysaccharide.

Glucose, a monosaccharide has many important functions.

Glucose molecules are used in respiration.

Glucose is builidng blocs larger carbohydrates such as starch, glycogen, and cellulose.

Starch, a storage polysaccharide for plants.Cellulose and Chitin, are polysaccharides important for structure.

Advantages of Carbohydrates

1. More easily digested, so energy is releases more easily from them.

2. Carbohydrates are soluble in water, so easier to transport.

Lipids are fatty substances

Nonpolar - insoluble in water

Neutral fats

Phospholipids

Steroids

lNeutral fats are the major fuel of animals.

lTriglycerides – glycerol and 3 fatty acids

lSaturated fatty acids occur when every carbon holds two hydrogen atoms.

lUnsaturated fatty acids have two or more carbon atoms joined by double bonds.

Phospholipids are important components of cell membranes.

lThey resemble triglycerides, except one fatty acid is replaced by phosphoric acid and an organic base.

lThe phosphate group is charged (polar)..

lSteroids are complex alcohols with fatlike properties.lCholesterol

lVitamin D

lAdrenocortical hormones

lSex hormones

Proteins are large complex molecules composed of amino acids.

Amino acids linked by peptide bonds

Two amino acids joined – dipeptide

Many amino acids – polypeptide chain

lProteins are complex molecules organized on many levels.

lPrimary structure – sequence of amino acids.

lSecondary structure – helix or pleated sheet. Stabilized with H-bonds.

lTertiary structure – 3-dimensional structure of folded chains. Eg. Disulfide bond is a covalent bond between sulfur atoms in two cysteine amino acids that are near each other.

lQuaternary structure describes proteins with more than one polypeptide chain. Hemoglobin has four subunits.

Proteins serve many functions.

Structural framework.

Enzymes that serve as catalysts

Enzymes are protein catalysts that accelerate certain chemical reactions by providing alternative mechanism in which energy-of-activation bariers are lower than in the original reaction mechanim.

Nucleic acids are complex molecules with particular sequences of nitrogenous bases that encode genetic information.

lThe only molecules that can replicate themselves – with help from enzymes.

lDeoxyribonucleic acid (DNA)

lRibonucleic acid (RNA)

lThe repeated units, called nucleotides, each contain a sugar, a nitrogenous base, and a phosphate group.

Hierarchial Levels of Organization

The Levels of Biological Organization are EVERYTHING!!! The definition of Biological Organization are the levels that make up all of life. Its difficult to explain which levels are most important personally I think that they all have there own importance. Its almost like a chain, you need one for all the rest to work. There are eight levels that are agreed upon and have classification's under them.

Knowing these levels is important, Its good to know what makes up of certain aspects of life.

The first level, and smallest is the molecular level. This includes DNA. Molecular level also includes cells, the smallest unit of life capable of carrying out the functions of living things. This could also be the chemical level.

Tissue level is what comes next. This is a group of similar cells that perform a certain function.

Organ level, next in line. This is several different types of tissues that function together to do a certain job. This is like your blood and vessels.

Organ system level, are several different organs working together for a specific function. This could include your digestive system or circulatory an etc.

Population level, the actions of individual organisms and there interactions together. This is an area defined by one species.

Community level, which is opposite of the population because this level is an area defined by all loving things. Like you have your grass community; which would be all the living things that are in that place like the grass, weeds, insects, an etc.

Ecosystem level, an this includes the community plus all the non-living factors as well.

Biosphere level is all the ecosystems together.

So each level ties into the next you cant have one without having the other. Knowing how to tell the difference helps because you should be able to tell what falls under each category each one. This will help further your knowledge and understanding of science.

Characteristics of Living Things

1. Living things are highly organized, from the smallest part to the largest.

On the chemical level: atoms make up elements. Each element has a specific number of electrons that orbit the nucleus. In the center of the element, the nucleus has protons and neutrons. The number of protons in an element is always equal to the number the electrons. The number of neutrons may vary to make isotopes of that element. Elements come together to give up, accept or equally share electrons to make molecules.

The smallest part of an organism is a cell.

Some single-celled organisms are free-living and contain structures, called organelles, that allow them to be self-sufficient.

More complex organisms are multicellular. In the case of a human, cells are organized into tissues. These have a common function like a muscle.

Tissues are organized into organs like the heart.

Organs are organized into organ systems, like the cardiovascular system. Organ systems functioning together make up a living organism.

A population is an organization of more than one individual. This is generally all of one species in a particular area. We could talk about the population of squirrels in our area or dogs or cats.

Enlarging our view, next comes a community. An example of a community is the town or place we live. A more accurate biological description would include all the living things in that area. A community is composed of many species, including plants and animals

An ecosystem not only considers the living things in an area, but also the physical environment and the interrelated flow of energy. You may live in a desert ecosystem, a forest ecosystem, or another kind of ecosystem.

Most complex of all is the biosphere. In our case, this includes the all the areas of our planet where living things are found.

2. All living things have an ability to acquire materials and energy.

Most of us call this eating! Then we have to be able to convert our food, a form of energy, to chemicals our cells can use through metabolism. Some organisms like plants, algae, and some microorganisms are autotrophs. The autotrophs we are most familiar with are the green plants that usephotosynthesis to make their own "food." Some bacteria usechemosynthesis for their energy source. Animals and fungi areheterotrophs and capture their food in a variety of ways.

The ability to acquire and use energy is extremely important. Without a constant input of usable energy, organisms would quickly become "disorganized" and die.

In order to survive, organisms must be able to achieve homeostasis. Each type of organism has a specialized way to stay in balance with its outside and inside environments. A paramecium has a contractile vacuole that pumps excess water out of its cell in order to survive in a fresh water environment. You and I have an internal "thermostat" that helps us maintain a body temperature of about 98.6 degrees Fahrenheit.

3. All living things have an ability to respond to their environment.

This often results in movement of the individual toward safety. This helps to ensure survival of the organism. For example, as young children we learned to avoid hot stoves and busy streets.

Plants also have some limited ability to move. They grow up toward the sun, and some have leaves able to turn to follow the sun, allowing them to photosynthesize better. Their roots grow down to search for water and minerals. If a plant doesn't get enough sunlight, water or minerals it will die.

4. All living things have an ability to reproduce.

All living things, even the smallest bacteria, have a chromosomecontaining DNA. Prokaryotes like bacteria only have one circular chromosome, called a plasmid. Eukaryotes, multicellular organisms like plants and humans, have a species-specific number of chromosomes. As humans, we have 46 chromosomes, in 23 pairs. Genes on chromosomes contain the instructions for the organism's structure and function.

However, the amazing diversity of organisms on earth have resulted because most organisms reproduce sexually. Some, like earthworms arehermaphrodites. Most others have separate sexes, male and female, like marijuana plants, fish, birds, cattle and humans.

In order for two organisms to combine their genetic information without doubling the number of chromosomes given to offspring, Mother Nature came up with a way to reduce the number of chromosomes. Without it, each new generation would have double the number of its parents' chromosomes. This halving is done by meiosis in the sex organs. In the female, the ovary produces haploid eggs and in the male the testesproduces haploid sperm. Each of these gametes contains only one chromosome from each of the pairs of chromosomes.

During fertilization, the sperm and egg unite to form a zygote, a diploid individual. This new individual is different from either parent, although it contains characteristics from both. This is what gives us the great diversity of life. In living things, we call this genetic biodiversity.

5. All living things have an ability to adapt.

Modifications enable an organism to survive in its environment. Natural selection allows individuals with better adaptations to survive better and reproduce more. Thus, their characteristics are passed into future generations and that makes the species stronger. However, it is important to note that individuals can only adapt to their environment, and species don’t adapt, they evolve.

All living things:

1. Are comprised of one or more units called cells

2. Reproduce (sexually or asexually)

3. Grow and develop

4. Obtain and use energy

5. Respond to their environment

1) All living things are comprised of cells.

Cell- a collection of living matter enclosed by a barrier that protects it from its surroundings.

Unicellular organism- a one-celled organism (e.g. bacteria)

Multicellular organism-an organism made of more than one cell, starfish, turtle)

2) All living things reproduce

…that is, they produce new individuals similar to themselves. Why is reproduction necessary?

To replace the dead ones.

Two Kinds of Reproduction:

Asexual Reproduction:

· The prefix a- means without, so without sex.

· A single organism reproduces without the aid of another.

- Common among bacteria and other microscopic organisms

- Splitting (bacterial cells) or budding (plants)

Sexual Reproduction:

· two cells from different individuals unite to produce the first cell of a new organism.

· Union of a sperm cell

from male united with

egg cell from female.

* Some organisms are capable of sexual and asexual reproduction.

3) All living things grow and develop

· Life does not necessarily mean continuous growth

· During growth organisms undergo a cycle of changes called development.

· Bodily maintenance occurs throughout life (requires energy). Aging occurs when an organism loses its ability to maintain itself.

4) All living things obtain and use energy · Energy required for growth and maintenance

· Energy (usually sugars) obtained from the environment

· Anabolism - a process (such as tissue growth) that involves synthesizing, or putting together, complex substances from simpler substances (sugars) (REQUIRES ENERGY)

· Catabolism- final breakdown (digestion) of complex substances into simpler ones, (RELEASES ENERGY)

· Metabolism- total sum of all chemical reactions in the body, or the balance between anabolism and catabolism

5) All living things respond to their environment Stimulus (plural stimuli)- anything that causes an organism to react

Irritability- the ability to react

Can plants respond to stimuli? Yes, but normally not as quickly as animals.

Homeostasis- (homeo- similar, -stasis standing) an organism’s ability to maintain the constant or stable conditions necessary for life.

Just as the thermostat automatically cools or warms a room if it deviates from a desired temperature, your body maintains a constant temperature, 98.6 F or 37 C, at which it functions optimally.

1) Living things are highly ordered.

2) Living things are organized into units called cells.

3) Living things use energy from their environment

4) Living organisms respond to stimuli -

5) Living things develop.

6) Living things reproduce themselves

7) Living things contain genetic information