Levels of Organization

Tissue

Multicellular (large) organisms function more efficiently if cells become specialized for specific functions.
A tissue is composed of cells that function together in a specialized activity.
There are four types of tissues found in animals: epithelial, connective, nerve, and muscle tissue.
Sponges do not have tissues.

Organs

Organs are composed of two or more tissues which function together to perform a common task. For example, the heart contains all 4 types of tissues.
Sponges and cnidarians do not have organs.

Organ systems

An organ system consists of two or more organs which perform a specific task.
Some organ systems are: the integumentary, nervous, sensory, endocrine, skeletal, muscular, circulatory, immune, digestive, respiratory, excretory, and reproductive systems.

Embryonic Tissues

Ectoderm, mesoderm, and endoderm are embryonic tissues that give rise to all of the tissues, organs, and organ systems in the body.

Ectoderm forms the outer layer of skin and nervous system.

Mesoderm forms the muscles, connective tissues, skeleton, kidneys, and circulatory and reproductive organs.

Endoderm forms the lining of the gut, respiratory tract, and urinary bladder. It also forms the glands associated with the gut and respiratory tract.

Junctions

Cells are joined to each other by proteins. The point of connection between two cells is called a junction.
Junctions bind cells together. Some kinds of junctions prevent the passage of molecules between cells. Other kinds of junctions allow molecules to pass from one cell to another.

Epithelial Tissue

Epithelial tissue covers external surfaces and internal cavities and organs. Glands are also composed of epithelial tissue.
Epithelia forms boundaries. Most substances that move into or out of the body must pass through epithelial tissue.
One surface of the tissue is free and the other adheres to a basement membrane.

The photograph below shows kidney tubules. The cells lining the tubules are epithelial tissue. One surface is attached (the basal surface) and the other surface is free.

The apical surface of epithelial cells may have tiny projections called microvilli. These function to increase surface area. For example, microvilli on intestinal cells increase the surface area available for absorption.
Eipthelial cells may have cilia. Cilia can be seen on the cells lining the trachea in the photograph below. They function to move mucus and trapped particles upward toward the mouth where it will be swallowed, thus keeping the trachea clear of foreign particles.

Function of Epithelial Tissue

Protection

Epithelial tissue forms the skin of many animals.
Terrestrial vertebrates have keratin in their skin cells making them resistant to water loss.
Ciliated epithelium lines the respiratory tract. Numerous cilia on these cells sweep impurities toward the throat.

Absorption

Absorption is an important function of epithelial tissue. For example, the gut is lined with epithelial tissue and it functions to absorb nutrients from food. The lungs are also lined with epithelial tissue and it functions to absorb oxygen.

Secretion

Glandular epithelium secretes chemicals.
Endocrine glands secrete hormones directly into the extracellular space.
Exocrine glands often secrete through DUCTS; they secrete mucus, saliva, wax, milk, etc.

Layers

Simple epithelium is one cell thick.
Example: Respiratory surfaces such as the lining of the lungs or the skin of a frog (below) are only one cell thick so that gasses can pass through quickly.

Squamous Epithelium - Frog Skin Flat Mount Click the photograph to view a larger photograph.

Stratified epithelium has more than one layer. It is found in areas of high abrasion such as the skin or the lining of the mouth.
Cell division occurs in cells near the basement membrane, pushing older cells toward the surface. Cells lost by abrasion at the surface are replaced by cells underneath.
Example: the human skin shown below contains stratified epithelium.

Stratified Squamous Epithelium, Human sec. X 100

Pseudostratified epithelium appears to be layered but each cell touches the same basement membrane. Some cells are elongate; they extend from the basement membrane to the free surface. Other cells are smaller, causing the tissue to appear stratified. The nuclei in the cells shown below appear to form multiple layers but the cells are all attached to the same basement membrane.

Pseudostratified Ciliated Columnar Epithelium

Shape

Epithelial cells are flat (squamous), cube-shaped (cuboidal), or elongated (columnar).

The words that describe layers (previous slides) can be used with words that describe shape. For example, simple squamous epithelium is one layer of flat cells.
Squamous

Simple Squamous Epithelium

Simple squamous epithelium is a single layer of flat cells. It is found in the walls of small blood vessels (capillaries) and in the air sacs of the lungs (alveoli). Because it is thin, it permits diffusion of substances from one side to the other. For example, materials can diffuse out of the capillaries. In the lungs, oxygen can diffuse across the alveoli and into the blood.
Below: The skin of a frog is used for gas exchange. The outer layer of skin is simple squamous epithelium. The thin, flattened cells promote rapid diffusion of gasses between the air and the blood vessels underneath the epithelium.

Squamous Epithelium - Frog Skin

Cuboidal
The cells that line the tubules of the kidneys are cuboidal. They function in secretion and absorption.
The ducts of some glands contain simple cuboidal epithelium.

Simple Cuboidal Epithelium

Simple Columnar
Simple columnar epithelium is a single layer of elongate cells. It is found in the lining of the gut and parts of the respiratory tract. It functions in secretion and absorption. The photograph below is a cross section of the small intestine.

Small Intestine (Jejunum) X 200

Connective Tissue

The cells of connective tissue are separated by non-living material.
Connective tissue binds and supports body parts, protects, fills spaces, stores fat (for energy), and transports materials.

Structure of Loose and Dense Connective Tissue

Loose connective tissue and dense connective tissue contain three kinds of fibers. Collagen fibers provide strength and flexibility. Collagen is the most abundant protein in animal bodies. Elastic fibers provide elasticity. When stretched, they return to their original shape. Reticular fibers are small and branched. They provide a support framework for organs such as the liver and lymph nodes.
The cells of loose and dense connective tissue are called fibroblasts. They produce the fibers and nonliving matrix material. Macrophages are cells specialized for phagocytizing foreign materials, bacteria, and cleaning up debris. Macrophages will be discussed in the chapter on the immune system.

Loose Connective Tissue

Loose connective tissue includes areolar, adipose, and reticular connective tissue.

Areolar Connective Tissue

The fibroblasts (cells) of areolar connective tissue are separated by a nonliving, jellylike matrix. The tissue contains collagen fibers for flexibility and strength, and numerous elastic fibers that enable it to be stretched.

Areolar connective tissue X 200

Areolar connective tissue is found in the skin and in most internal organs of vertebrates, where it allows the organs to expand; it also forms a protective covering for muscles, blood vessels, and nerves.
Adipose tissue is a type of loose connective tissue. It has reduced matrix material and contains enlarged fibroblasts (cells) that store fat. Adipose tissue functions to store energy, insulate, and provide padding, especially in the skin and around the kidneys and heart.

Adipose Tissue Human sec X 200

Reticular Connective Tissue

Reticular connective tissue contains an abundance of reticular fibers. It provides a supporting framework for organs such as the lymph nodes, spleen, and liver.

Dense (Fibrous) Connective Tissue

The collagen fibers of dense connective tissue are more closely packed than those of loose connective tissue.

White Fibrous Connective Tissue X 200

Regular dense connective tissue contains collagen fibers oriented in one direction to provide strength in that direction. It is found in tendons and ligaments. Tendons connect muscle to bone; ligaments connect bone to bone.
Irregular dense connective tissue (not shown) contains collagen fibers oriented in many different directions. It is found in the deep layers of the skin (dermis) and the tough capsules that surround many of the organs such as the kidneys, adrenal glands, nerves, bones, and the covering of muscles. It provides support and strength.

Cartilage

The cells of cartilage are embedded in a protein-containing matrix that is strong but flexible.
It contains collagen and elastic fibers.

Hyaline Cartilage X 200

It is resilient; it does not stretch and can resist compression. It is also flexible but maintains its shape.
It is found in the ends of bones where it prevents friction within the joints. In the nose, external ear, and the walls of the trachea it functions to support the softer tissues.
The intervertebral disks function as shock pads.
The fetal skeleton of vertebrate animals is composed of cartilage before bone forms. The skeleton of cartilaginous fish is composed of cartilage.

Bone

Bone forms when calcium salts are deposited around protein fibers. The calcium salts provide rigidity while the fibers provide elasticity and strength.

Bone, dry ground human c.s. X 100

Blood

Blood is a connective tissue. Like other kinds of connective tissues, it contains cells that are separated by a non-living material. In this case, the nonliving material is the plasma.

Human Blood, Wright Stain X 1000

Muscle Tissue

Muscle tissue contracts in response to stimulation. It cannot lengthen by itself but is lengthened by the contraction of other muscles..
Muscle tissue is used for locomotion, food movement in gut, and heat production.

Smooth Muscle

Smooth muscle is involuntary.
It surrounds the gut and moves food through the digestive tract.
It surrounds the blood vessels where it controls the distribution of blood. There is not enough blood in the body to fill all of the blood vessels so some must be contracted while others are filled. For example, after meals, the blood vessels of the gut are opened while many of those in the skeletal muscles contract.
The ends of the cells are tapered.

Smooth Muscle, Human X 200

Skeletal Muscle

Skeletal muscle is voluntary.
The cells are very long, extending the length of the muscle. They are multinucleate, and striated (striped).

Skeletal Muscle Teased X 200

Cardiac Muscle

Cardiac muscle is found in the heart.
It is striated and branched.

Cardiac Muscle X 200

Muscle tissue will be discussed in more detail in the chapter on motor systems.

Nervous Tissue

Nervous tissue responds to stimuli and transmits impulses from one body part to another.

Motor Neuron X 200

Nervous tissue will be discussed in more detail in these two chapters: 1) neurons, 2) nervous systems.

Skin

The skin is the largest organ in the body. It protects the tissues underneath, prevents invasion by foreign organisms, prevents dehydration, helps regulate body temperature, and contains receptors that provide information about the external environment.

Epidermis

The outer layer, the epidermis, is composed of stratified squamous epithelium. These cells prevent dehydration because they are filled with a waterproof protein called keratin.
The lower layers of the epidermis are basal cells that continuously divide to replace the layers above. The basal layer also contains melanocytes which produce melanin, the pigment that darkens skin and protects from ultraviolet radiation in sunlight.

Dermis

The dermis lies underneath the epidermis and is composed of dense connective tissue.
Hair of mammals originates in hair follicles, which are embedded in the dermis. A smooth muscle called the arrector pili is attached to the hair follicle. When it contracts, the hair becomes erect. Sebaceous glands secrete an oily substance (sebum) into the follicle to lubricate the hair and skin.
Sweat glands are found in the dermis and subcutaneous layer. They secrete water to the surface, which cools the body when it evaporates.
The dermis contains blood vessels and neurons that control the flow of blood through the skin in order to regulate body temperature. When the body temperature is high, blood flow to these vessels increases. The increased blood flow to the surface helps the body lose excess heat. When the body temperature is low, blood flow to the dermis decreases. Shivering occurs as a mechanism to produce heat when the body temperature is low.
The dermis contains receptors for pressure, touch, temperature, vibration, and pain.

Subcutaneous layer

The subcutaneous layer is the deepest layer and is composed of loose connective tissue.
This layer is actually not part of the skin.
Adipose tissue in this layer insulates and stores energy in the form of fat.

Phagocytosis in amoeba



In cell biology, Phagocytosis is the process of engulfing a solid particle by a phagocyte or a protist to form an internal phagosome (from Ancient Greek φαγεῖν (phagein) , meaning "to devour", κύτος, (kytos) , meaning "cell", and -oais’, meaning "process"). Phagocytosis was revealed by Élie Metchnikoff in 1882. Phagocytosis is a specific form of endocytosis involving the vesicular internalization of solids such as bacteria, and is, therefore, distinct from other forms of endocytosis such as the vesicular internalization of various liquids. Phagocytosis is involved in the acquisition of nutrients for some cells, and, in the immune system, it is a major mechanism used to remove pathogens and cell debris. Bacteria, dead tissue cells, and small mineral particles are all examples of objects that may be phagocytized.
The process is homologous to eating only at the level of single-celled organisms; in multicellular animals, the process has been adapted to eliminate debris and pathogens, as opposed to taking in fuel for cellular processes, except in the case of the animal Trichoplax.

In immune system

Phagocytosis in mammalian immune cells is activated by attachment to Pathogen-associated molecular patterns (PAMPS), which leads to NF-κB activation. Opsonins such as C3b and antibodies can act as attachment sites and aid phagocytosis of pathogens.

Engulfment of material is facilitated by the actin-myosin contractile system. The phagosome of ingested material is then fused with the lysosome, leading to degradation.

Degradation can be oxygen-dependent or oxygen-independent.

• Oxygen-dependent degradation depends on NADPH and the production of reactive oxygen species. Hydrogen peroxide and myeloperoxidase activate a halogenating system, which leads to the creation of hypochlorite and the destruction of bacteria
• Oxygen-independent degradation depends on the release of granules, containing proteolytic enzymes such as defensins, lysozyme, and cationic proteins. Other antimicrobial peptides are present in these granules, including lactoferrin, which sequesters iron to provide unfavourable growth conditions for bacteria.

It is possible for cells other than dedicated phagocytes (such as dendritic cells) to engage in phagocytosis.

In apoptosis

Following apoptosis, the dying cells need to be taken up into the surrounding tissues by macrophages in a process called efferocytosis. One of the features of an apoptotic cell is the presentation of a variety of intracellular molecules on the cell surface, such as calreticulin, phosphatidylserine (From the inner layer of the plasma membrane), annexin A1, and oxidised LDL. These molecules are recognised by receptors on the cell surface of the macrophage such as the phosphatidylserine receptor or by soluble (free floating) receptors such as thrombospondin 1, Gas-6, and MFG-E8, which themselves then bind to other receptors on the macrophage such as CD36 and alpha-v beta-3 integrin. Defects in apoptotic cell clearance are usually associated with impaired phagocytosis of macropghages. Accumulation of apoptotic cell remnants often causes autoimmune disorders, thus pharmacological potentiation of phagocytosis has a medical potential in treatment of certain forms of autoimmune disorders.
Additional information on phagocytosis of apoptotic cells could be found in the book: “Phagocytosis of dying cells: from molecular mechanisms to human diseases” (Eds DV Krysko and P Vandenabeele, 2009, Springer).

In protists

Trophozoites of Entamoeba histolytica with ingested erythrocytes

In many protists, phagocytosis is used as a means of feeding, providing part or all of their nourishment. This is called phagotrophic nutrition, as distinguished from osmotrophic nutrition, which takes place by absorption.

• In some, such as amoeba, phagocytosis takes place by surrounding the target object with pseudopods, as in animal phagocytes. In humans, Entamoeba histolytica can phagocytose red blood cells. This process is known as "erythrophagocystosis", and is considered the only reliable way to distinguish Entamoeba histolytica from noninvasive species such as Entamoeba dispar.

• Ciliates also engage in phagocytosis. In ciliates there is a specialized groove or chamber in the cell where phagocytosis takes place, called the cytostome or mouth.

The resulting phagosome may be merged with lysosomes containing digestive enz

ymes, forming a phagolysosome. The food particles will then be digested, and the released nutrients are diffused or transported into the cytosol for use in other metabolic processes.

Mixotrophy can involve phagotrophic nutrition and phototrophic nutrition. 

BUILD YOUR OWN PERSONAL FOG TORNADO!

A copier paper box A small 12 volt computer fan from a computer or electronics store. It should be at least 3x3 inches (8cm X 8cm). A piece of clear plastic 10 X 17 inches (25cm X43cm) If your really in a hurry, you can test your fog tornado with clear plastic food wrap. A small plastic food container Dry ice (or other source of fog - see below) Black paint 9-volt battery (if your fan doesn't plug in) Optional (but cool) battery-powered tap light Adult help Parts of the cardboard will need to be cut out using an exact-o blade.This part is definitely for an adult - kids hurt themselves every year trying to cut foam core and cardboard - don't let that be you - know when to ask for help. Follow the diagrams below, cutting away the areas marked in gray. IMPORTANT: Pay special attention to the placement of the slots. In order for the tornado to work, the slots will need to be in the correct place. The opening at the top should be just a bit smaller than your fan. The opening at the bottom should be bigger than the plastic food container. Paint the inside of the box with flat black poster paint and allow it to dry. Tape (or hot glue) the clear piece of plastic into the large window on the front. Be sure to keep the nearby slot open so air can flow through it. Attach the tap-light to the inside of the top of the tornado box near the fan opening. That’s it! Your Tornado Chamber is ready. A note about the fog. I have found 3 decent sources of fog: DRY ICE - Dry ice makes the best looking tornado, in my opinion, which is why I give the directions for it here. Dry ice should only be handled by adults. It can cause instant frostbite. Never handle dry ice without thick gloves and always wear safety goggles. Only someone familiar with dry ice and its dangers should handle it. HUMIDIFIER - Many small humidifiers create a continuous source of mist that works well for the tornado chamber. You will need to find a way to mount the tornado chamber above your humidifier. FOUNTAIN MISTERS - A fountain mister uses ultrasonic vibrations to create a light mist. They can often be found in stores that sell small fountains and in some pet shops. FOG TORNADO TIME! Turn on the battery powered light if you have one, and power up the fan. (red wire goes on the skinnier lead of the 9 volt battery) and place it on the top of the chamber with the breeze blowing up. Place some small chunks of dry ice into your food container and add some warm water to create fog. Put your tornado chamber over the container and watch the wonders of vortex currents at work! As the fan forces air out of the chamber, air from outside the box is forced in through the slots on the sides. The position of the slots causes the incoming air to create a VORTEX (spiral) of air as it is drawn up and out of the box. Real tornados form in a similar way using updrafts and wind-shear (wind from different directions at different altitudes)

Hybrid plants:

Hybrid plants are derived from matings between genetically distinct parents. Such matings are called crosses. Crosses often occur between plants classified as distinct species. Many hybrids are sterile, but many others are merely of reduced fertility and can, in fact, produce offspring. The level of fertility seen in the hybrids varies both with the cross in question and, for a given type of cross, from one individual hybrid to another. Some crosses produce hybrids apparently just as fertile as their parents. 

Typically, hybrids combine the traits of their parents. Often, too, a given trait in a hybrid, say flower color, will be intermediate (for example, the hybrid's flowers might be orange, whereas the flowers of one of its parents are red and those of the other, yellow). Sometimes, however, a new trait not seen in either of its parents will arise in a hybrid. 

Plant breeders commonly start with variable plant hybrids and then apply selection to produce new crops, trees, and flowers with desirable properties. Soliman (1992: 199) says no other factor has had a greater impact on agricultural production. 

New breeds produced by hybridization in the proportion of their genetic from the other (natural processes of this sort are sometimes called introgression ). At the other end of the spectrum are breeds that derive their traits in equal number from both parents. In the former case, one can think of the new hybrid as a slightly altered version of one of the parents, in the latter as a distinct, new composite.                                      Beach Stgaria chirawberry Fraloensis
A complete list of all the new crops derived from the production of plant hybrids, followed by selection, would be both tedious and beyond the scope of this article, but the reader is referred to a summary paper on this topic by Kalloo (1992).

 An inventory of the cultivated flowers derivedfrom hybridization would probably be even more lengthy. Here we will mention a only one example of the many new breeds of plants derived from hybridization: The modern commercial strawberry is derived from hybridization of the Virginia strawberry (Fragaria virginiana) and the beach strawberry (F. chiloensis), both of which are shown at right. Virginia Strawberry Fragaria virginiana

Bacteria:

Use petri dishes and agar to grow bacteria.

• What effect do household cleaners have on a bacteria culture? What about temperature? What is the best or worst environment in your house for bacteria growth?
• Are there substances in your kitchen (garlic, red pepper, curry, tea tree oil, etc.) that have natural antibacterial properties?
• Use the Gram stain method for testing whether Gram-positive or Gram-negative bacteria is more common in your house. Do common antibiotics interact differently with Gram-positive and Gram-negative bacteria?
• Studying mold growth conditions also makes an interesting experiment. What types of food mold the quickest? How does temperature affect mold growth? Are there some practical ways to slow down the growth of mold? Experiment with different types of preservatives to see how they prevent mold growth.
• Does bacteria grow in a predictable pattern? Try an experiment by making thumbprint, fingerprint, or handprint bacteria cultures using agar and petri dishes.
• How much bacteria grows in the mouth and what effects do common cleaning techniques have on bacteria growth? Consider brushing with a dry toothbrush, comparing different toothpastes, mouthwashes, and flossing as well as time spent cleaning teeth to find which methods work best to keep the mouth clean.
• Is a dog's mouth really cleaner than a human's?
• Use GloGerms to simulate the behavior of germs. Experiment to find the best ways to eliminate germs from hands and surfaces. (Test water temperature, soaps, length of time spent washing, etc.)

What has a human achieved today in astronomical sciences ?

-How might we decide what qualifies as “the ultimate human achievement” in different areas of knowledge? How might we go about deciding? Would expert opinion necessarily influence what we think?

 In what ways might our cultural paradigms shape our response?

According to Professor Brian Cox, presenter of the BBC’s excellent 3-part series Stargazing: LIVE the International Space Station is the ‘ultimate human achievement’. If you watch this episode from 36:25 minutes into the programme, Prof Brian Cox speaks to 3 of the astronauts on board.

More information regarding it:

·         It is the largest artificial satellite that has ever orbited our planet.

·         It travels around the earth at 28,000km per hour and 400km above the earth.

·         There are 6 astronauts currently living on the spaceship; they are the only people currently in space.

·         Astronauts from around the world have been living in zero gravity for the last 10 years and some stay for more than 6 months.

·         It functions as an observatory, laboratory and workshop.