Before Islam

Muslim Scientists and Thinkers (700 - 1400 C.E.)

CONSOLIDATED ADVERTISEMENT NO 16/2011

Muslim Scientists 2

Muslim Scientists

Abu Bakr Muhammad-ibn-zakariyya-al-razi

Ali ibn Abbas al Majusi

Ali ibn Abbas al-Majusi

Abu Bakr Muhammad ibn Zakariyya al-Razi

Abbasid Caliphs

Umayyad Caliphs

If This Had Happened Before By Dr Abdul Qadeer Khan

Muslim Scientists

Plants

Cells are the Starting Point

All living organisms on Earth are divided in pieces called cells. There are smaller pieces to cells that include proteins andorganelles. There are also larger pieces called tissues andsystems. Cells are small compartments that hold all of the biological equipment necessary to keep an organism alive and successful on Earth. 

A main purpose of a cell is to organize. Cells hold a variety of pieces and each cell has a different set of functions. It is easier for an organism to grow and survive when cells are present. If you were only made of one cell, you would only be able to grow to a certain size. You don't find single cells that are as large as a cow. Also, if you were only one cell you couldn't have a nervous system, no muscles for movement, and using the internet would be out of the question. The trillions of cells in your body make your life possible. 

One Name, Many Types

There are many types of cells. In biology class, you will usually work with plant-likecells and animal-like cells. We say animal-like because an animal type of cell could be anything from a tiny microorganism to a nerve cell in your brain. Plant cells are easier to identify because they have a protective structure called a cell wall made of cellulose. Plants have the wall; animals do not. Plants also have organelles like the chloroplast(the things that make them green) or large water-filled vacuoles. 

We said that there are many types of cells. Cells are unique to each type of organism.Humans may have hundreds of types of cells. Some cells are used to carry oxygen (O₂) through the blood (red blood cells) and others might be specific to the heart. If you look at very simple organisms, you will discover cells that have no defined nucleus (prokaryotes) and other cells that have hundreds of nuclei (multinucleated). The thing they all have in common is that they are compartments surrounded by some type ofmembrane. 

Plant Basics

If you're not a microbe and you're not an animal, chances are you are a plant. There are loads of species of plants on Earth. Just as there is a system of classification for animals, there is also a system of classification for plants. Because plants adapt so well to any climate, scientists need a way to organize the hundreds of thousands of species. 

What Makes a Plant?

What do they all have in common? The big thing that connects plants is photosynthesis.Photosynthesis is the process that allows plants to take energy from the Sun and create sugars. Not all plants go through the process of photosynthesis. As with all of biology, there are exceptions and you may learn about plant species that are parasites. Plants also have cell walls. In the cells tutorials we explained that all cells have a membrane. Only plants have an additional cell wall made from cellulose. 

Let's look at photosynthesis. Plants are able to turn sunlight into energy but not directly. Plants are actually able to store energy in some chemical bonds that can be used later. Before we get into details, we'll explain that there are two processes on Earth: Photosynthesis and Respiration. Photosynthesis stores the energy and respiration releases that energy. It all starts with the Sun. Check out the tutorial on photosynthesis. 

Learning from Plants

Not only do you see plants everywhere in the real world, but they are also all over the scientific world. Scientists use them for studies in genetics. A guy named Gregor Mendel used pea pods and their flowers to come up with some of the first ideas on how traits are passed from one generation of organism to another (genetics). We also use plants for food. Scientists are constantly developing new plants that are more resistant to disease and insects. Scientists also help create plants that grow faster and make more food. 
PHOTOSYNTHESIS -
PART I: THE SUN AND LIGHT

Not all of the light from the Sun makes it to the surface of the Earth. Even the light that does make it here is reflected and spread out. The little light that does make it here is enough for the plants of the world to survive and go through the process of photosynthesis. Light is actually energy, electromagnetic energy to be exact. When that energy gets to a green plant, all sorts of reactions can take place to store energy in the form of sugar molecules. 

Remember we said that not all the energy from the Sun makes it to plants? Even when light gets to a plant, the plant doesn't use all of it. It actually uses only certain colors to make photosynthesis happen. Plants mostly absorb red and blue wavelengths. When you see a color, it is actually a color that the object does NOT absorb. In the case of green plants, they do not absorb light from the green range. 

PART II: THE CHLOROPLAST

We already spoke about the structure of chloroplasts in the cells tutorials. We want to reinforce that photosynthesis happens in the chloroplast. Within this cell organelle is the chlorophyll that captures the light from the Sun. We'll talk about it in a bit, but the chloroplasts are working night and day with different jobs. The molecules are moved and converted in the area called the stroma. 

PART III: THE MOLECULES

Chlorophyll is the magic compound that can grab that sunlight and start the whole process. Chlorophyll is actually quite a varied compound. There are four (4) types: a, b, c, and d. Chlorophyll can also be found in many microorganisms and even some prokaryotic cells. However, as far as plants are concerned, the chlorophyll is found in the chloroplasts. The other big molecules are water (H₂O), carbon dioxide (CO₂), oxygen (O₂) and glucose (C₆H₁₂O₆). Carbon dioxide and water combine with light to create oxygen and glucose. That glucose is used in various forms by every creature on the planet. Animal cells require oxygen to survive. Animal cells need an aerobic environment (one with oxygen). 

PART IV: LIGHT AND DARK REACTIONS

The whole process doesn't happen all at one time. The process of photosynthesis is divided into two main parts. The first part is called the light dependent reaction. This reaction happens when the light energy is captured and pushed into a chemical called ATP. The second part of the process happens when the ATP is used to make glucose (the Calvin Cycle). That second part is called the light independent reaction. 


A GENERAL PLANT STRUCTURE

We're going to look at plant structure in this section. The plants we discuss will be vascular plants that have systems of tubes (xylem and phloem) for the transport of nutrients and water. Remember that there is a wide variety of plants on Earth and even a whole group that doesn't havevascular systems. Mosses and liverworts may still have photosynthesis, but they do not have that 'classic' plant structure. Then you will find species such as cacti that don't have leaves. They conductphotosynthesis in their stems. Anyway, just remember that there are many other possibilities in the plant kingdom. 

ALIKE BUT DIFFERENT

We just told you about the many exceptions to the basic plant structure, so let's look at some similarities. An easy similarity is on a cellular level. Plants conduct photosynthesis. This process of converting the Sun's energy into molecular energy happens in chloroplasts with the help of chlorophyll molecules and a variety of enzymes. Vascular plants share a similar set of structures called roots, stems, and leaves. Many plants have specialized versions, but the basics are there. One specialization might be the petals of a flower. Those flower petals are specialized leaves that surround the reproductive structures of the plant. 

THE ROOTS BELOW GROUND

We'll start at the bottom with the roots. These structures are designed to pull water and minerals from whatever material the plant sits on. For water plants, the roots may be in the water. For traditional trees, the roots go deep into the soil. There are even plants called epiphytes that live in trees and their root system clings to branches. Humans often capitalize on the roots of plants for food. Carrots are just one big orange root. 

Root systems also provide support for plants in the form of an anchor in the soil. If the wind blows hard, those roots keep the plant from falling over. Some plant species have roots above ground that provide support for the entire plant. Roots are further broken down into the primary root and lateral roots that each has apical meristem at their tips. Root hairs are also a common structure on roots. They make the roots look fuzzy and help in the absorption of water and nutrients. 

SHOOTS ABOVE GROUND

Sure we said that there are some roots above the surface, but the majority of the plant you see is made up of stems and leaves. Think about a tree. The stems are the trunks and branches. Leaves are self-explanatory. Stems are all about transporting food and water and acting as support structures. Leaves are all about photosynthesis, creating food molecules and absorbing carbon dioxide for the plant. These parts are connected by the vascular system of xylem and phloem that spreads through the entire plant. 

The tip (terminal bud) of the main stem has a specialized structure that is the source of new growth for plants. You will find the apical meristem that develops into young leaves (primodium). There are other points of growth at each node where leaves and branches develop on the stems. Those branching points are home to axillary budsthat can also develop into new branches. 

PLANTS VASCULAR SYSTEMS

Xylem and phloem make up the big transportation system of vascular plants. As you get bigger, it is more difficult to transport nutrients, water, and sugars around your body. You have a circulatory system if you want to keep growing. As plants evolved to be larger, they also developed their own kind of circulatory systems. The main parts you will hear a lot about are called xylem and phloem. 

It all starts with a top and a bottom. Logically, it makes sense. Trees and other vascular plantshave a top and a bottom. The top has a trunk, branches, leaves, or needles. The bottom is a system of roots. Each needs the other to survive. The roots hold the plant steady and grab moisture and nutrients from the soil. The top is in the light, conducting photosynthesis and helping the plant reproduce. You have to connect the two parts. That's where xylem and phloem come in. 

ZIPPY XYLEM

The xylem of a plant is the system of tubes and transport cells that circulates water and dissolved minerals. As a plant, you have roots to help you absorb water. If your leaves need water and they are 100 feet above the ground, it is time to put the xylem into action! Xylem is made of vessels that are connected end to end for the maximum speed to move water around. They also have a secondary function of support. When someone cuts an old tree down, they reveal a set of rings. Those rings are the remains of old xylem tissue, one ring for every year the tree was alive. 

PHLOEM FUN

The fun never stops in the plant's circulatory system. Most plants have green leaves, where the photosynthesis happens. When those sugars are made, they need to be given to every cell in the plant for energy. Enter phloem. The phloem cells are laid out end-to-end throughout the entire plant, transporting the sugars and other molecules created by the plant. Phloem is always alive. Xylem tissue dies after one year and then develops anew (rings in the tree trunk). What is the best way to think about phloem? Think about sap coming out of a tree. That dripping sap usually comes from the phloem. 

PLANT REPRODUCTION - THEY'LL MAKE MORE

If you are an organism, you will need to reproduce. Otherwise, there will be no more of your species and the species will die off. You may have heard of endangered animals. There are also endangered plants. These endangered species have very few individuals left and scientists/naturalists are working together to make sure the species don't become extinct. 

We talked a little about reproduction when we discussed meiosis in the cells tutorials. Reproduction is one of two things. 

(1) One cell can split into two, giving you two identical cells. That type is asexual reproduction. 
(2) The second type is when two cells, each with half of the DNA needed, combine and create a living cell. That type is sexual reproduction. 

When plants hit a point in evolution, the second is the one that occurs more often. 

MAKING MORE MOSSES

Sporophytes are the reproductive structures you will find in mosses. They are actually a phase of the moss life cycle that feeds off the green parent plant (the gametophyte). The sporophyte is a stalk that grows after the haploid sperm of one moss plant is able to mix with the haploid egg of a female moss plant. The resulting diploid cell grows into the sporophyte stalk. When ready, spores stored in the sporophyte are released and they grow into new moss plants. 

CONFIERS AND THEIR CONES

While there are male and female mosses, conifers produce two types of cones on the same tree. One of the cone types gives off pollen (thestaminate cone). The other type of cone catches the pollen if the wind is moving in the right direction. Better yet, the wind blows the pollen to another conifer of the same species, and a cone (called the ovulate cone) catches the pollen. Again, the pollen and megaspore (receiving haploid cell) are haploid and combine to form a diploid cell. That diploid cell grows into a zygote (baby conifer) that eventually lives in a seed. 

FLOWERS AND POLLEN

The most advanced of the plants have their own way of sexually reproducing. It is a very fancy and very complex process. Plants that rely on flowersfor reproduction are also very dependent on outside help such as insects and animals. While conifers have the two structures on one tree, flowering plants went one step further and put the devices that make and receive pollen in the same structure. 

How does that help? A bee might go to one flower and get a little pollen on its back. If it goes to another flower of the same species, that pollencan land on the stigma. From that point, one haploid male nucleus combines with a female nucleus and the other haploid male nucleus combines with a polar nucleus. If successful, an embryo and seed/fruitdevelop respectively. 

DIFFERENT PARTS = DIFFERENT ADVANTAGES

Obviously, not all plants look the same. They have different flowers, stems, and even root structures. Extreme examples have given some plants big advantages. These advantages have let them settle in new environments and become more successful. 

SPECIALIZED LEAVES

What kinds of leaves are there? What kinds aren't there? There are thick ones for storing water as in succulents. There are long twisting vine-likeleaves that can wrap around and dig in for support as in grapes. There are also thorns. Nothing says, "Don't eat me" like a bunch of sharp thorns on your branches. 

FLOWERS

Flowers have developed such a wide variety. That variety is often dependent on what kind of creature helps out with the pollination. If I am a big insect, I will be looking at plants with big flowers. If I am a tiny little bug, I might live my whole life inside a flower. There are also a variety of colors that attract different insects and animals. 

STEMS

Stems are a good place to store water. It's very efficient to develop a big protected area. Think about a barrel in hot areas where water is scarce. Enter a cactus. All stem and trunk. No leaves. Having no leaves means very little evaporationon hot days. Other extremes are plants with no stem. They could grow one, being vascular plants, but they have found it to be an advantage to stay near the ground. Vines are another extreme. 

The bark of a tree or plant can also perform a specific function. Corks in wine bottles are actually from the bark of a tree (cork tree). Some bark has been designed to peel away as the tree grows. Other types of bark are very thick to protect the plant from animals and insects. 

EPIPHYTES - SPECIALIZED ROOTS

Not all plants even live in the ground. Some specialized plants called epiphytes actually live on the side of other trees or on rocks. They are able to collect water themselves but do not use roots to gather it up. Their roots have been specialized to dig in or grab on to the larger object. They don't always hurt the trees; they just hang out on the outside. Epiphytes can include some seedless species, bromeliads, and orchids. There are also epiphyte species that can grow very large and even break tree limbs. They can suck nutrients away from the tree and weaken it over time. Several ficus species are killer parasitic epiphytes. 
MOSSES AND LIVERWORTS

These are the little ones. The most important feature of mosses and liverworts is that they haveno vascular system. A vascular system in plants is a series of tubes that can transport water and nutrients over a distance. That vascular system of xylem and phloem allows redwood and sequoia trees to grow to over one hundred feet tall. 

LIMITED IN SIZE

Without a vascular system, mosses, and liverworts cannot grow very large. If you have seen mosses, you know that they are actually carpets of individual plants. They are rarely taller than one inch high. Another important characteristic of these little guys is that they require water to reproduce. It's another characteristic of their low place in plant evolution. While all plants need water, mosses and bryophytes need droplets of water to enable their haploid reproductive cells to combine. They are all known as the bryophytes. 

MOSSES

Let's start with mosses. These are waxy little plants with no leaves and no stem that use each other to stay upright. Their inability to stay up is why you never see one little moss plant; it's always a group. That grouping also helps them retain water in the area. A waxy covering across their bodies helps keep water from evaporating. You will usually find them in moist areas out of the direct sunlight. 

GOOD WORTS

We'll cover liverworts and hornworts together. If you can believe it, the worts are even simpler than mosses. These are considered to be the simplest of all plants and often grow flat along the ground in large leaf-like structures. None of the bryophytes have roots. They all have rhizoids (little hairs), and the worts are no exception. Like mosses, they are found in very moist areas, and some species even spend their whole lives in the water. 

FERNS AND HORSETAILS -
FIRST PLANTS WITH PIPES

These are the first of the vascular plants you will study. Mosses and worts are non-vascular. The ferns were the first plant species to develop a circulatory system that lets them grow larger. They have roots, leaves, stems, and trunks. With their new vascular system, the sky was the limit for plants. 

THEY LIKE WATER

Ferns are often used in landscaping. There's a good chance you've seen them. They are also able to live in a variety of climates as long as it is moist. You will find ferns in Canadian rain forests just as easily as you will find them near the equator. They are similar to mosses in that they need liquid to reproduce. When water is around, they are able to have baby ferns called zygotes. Ferns have some neat structural features. Some have large stems, several feet in length. Scientists call those bad boys the tree ferns. Ferns also have specialized leaves called fronds. They unroll as they mature and spread out in a fan shape. 

HORSETAILS

Horsetails are related to ferns in that they have a vascular system. They never developed the ability to reproduce with seeds. They might be a little hard for you to see because many of them are extinct. Because they are better able to survive in various environments, you can find them from very northern and southern latitudes to the equator. Unlike ferns, these are tough plants. While ferns are soft, horsetails are rough plants and even have silica (silicon-based compound) in theirepidermal cells. Ouch! 
GYMNOSPERMS - FIRST PLANTS WITH SEEDS

So you've got a vascular system. What comes next? Seeds. Seeds let you send your offspring out into the world. Seeds provide a protective coat so that the embryo plant can develop when it finds a nice piece of soil. But remember this: gymnosperms have not developed the ability to make flowers. Flowers are an evolutionary advancement after seeds. So if you have a vascular system, seeds, and no flowers, what are you? A gymnosperm! 

Seeds are a protective structure that lets a plant embryo survive for long periods of time before it germinates. Seeds have food sources pre-packaged for plant embryos to provide for an embryo's needs in early growth. Seeds let plants spread their embryos over large areas. Some are even so lightweight that they are carried across the planet by strong winds. Seeds are an advantage if you want to be a plant that can grow anywhere. Seeds are da bom'! 

CYCADS IN THE TROPICS

Looking like a fern. Looking like a palm tree. It's actually neither! It's a cycad. These are another favorite of landscape designers. These are sturdy little plants that can survive in harsh conditions. You won't find them in cold areas like the conifers. Cycadsneed warmer weather to survive. They have cone-like structures for reproduction. Instead of being on branches, their cones are in the center of the plant and can get really large. They also have big waxy fronds, and when it's time to reproduce, the female plants have a great fruit that grows in the middle of their stem. 

CONIFERS IN THE FORESTS

Pine, cedar, redwood, and spruce. Sounds like we're at a hardware store buying lumber. Not so. We are listing off a bunch of trees that are called conifers. If you've ever gone skiing or to northern latitudes you have seen loads of conifers. The conifers most people think of are pine trees. Every year millions of trees are grown for Christmas and they are all conifers. They usually have needles and cones (thus the name CONifer). 

They are also evergreens: even in cold winter months they are able to keep their needles. That ability is one reason they do so well in northern latitudes. The ever-present needles allow conifers to take advantage of the Sun whenever it is around. They are also some of the tallest plants in the world. They are able to get very tall and strong because of heavy-duty xylem that hardens and makes them sturdy. That sturdiness is why these kinds of trees make good lumber - hard and strong wood. 

GINKGOES ON YOUR STREET

Not every plant made it to the modern day. Fossil evidence shows what plants used to be alive in other geological eras. The Ginkgo is one of the ones that made it. Some people call it a "Maidenhair Tree". It's the last one of its kind. It has needles that have combined to form very sturdy leaf-like structures. You need to remember they are not like leaves in the traditional sense. You've probably seen these all over. Landscape designers love to use them because they look very nice and are very resistant to pollution. They are great for cities. Being able to resist insects and disease has let this species survive beyond all of its close relatives. 
ANGIOSPERMS - FIRST PLANTS WITH FLOWERS

We asked it before. What would give you an advantage if you were a plant? You have a vascular system to transport nutrients. You have seeds for reproduction that allow your babies to spread out in new areas. What next? Flowers! Flowers are the most recent evolutionary advantage for plants. 

LOOKING GOOD FOR THE BIRDS AND BUGS

When we talked about gymnosperms, we spoke of seeds. That was a big advantage. The angiosperms took it one step further. They not only have seeds, but they also have flowers. What kind of an advantage is that? Many angiosperm species use wind for pollination the way that gymnosperms do. What if you didn't need to rely on the wind to spread your pollen around anymore? What if another creature could do it for you? Maybe an insect? Sounds like a new advantage. 

Those specialized flowers are able to attract organisms to help pollinate and distribute seeds. Another cool advantage is the fruit/seed packaging. Would you rather eat a pine cone or an apple? A lot of animals would go for the apple. When they do, they are able to spread the seeds across wide areas after the animal poops out the seeds. 

SOME WITH ONE COTYLEDON

There are two kinds of seeds in the angiosperms,monocots and dicots. Monocot is short for monocotyledon. A cotyledon is the seed leaf. When you are a monocot, your seed only has one package of food. "Mono" means one or a single cotyledon. Monocots are made up of simple flowering plants like grasses, corn, palm trees, and lilies. Two of the characteristics of monocots are that their flowers have petals in numbers of three and their leaves are made of long strands. Think of the leaves of grass or a palm frond. 

AND SOME WITH TWO

The other kind of plant in the flowering plant world is called a dicot. Dicot is short for dicotyledon. "Di" means two or a double cotyledon. These plants have seeds that have two cotyledons, two seed leaves of food for the embryo. Most of the flowers you see every day are dicots. They have flowers with petals in numbers of four and five. They also have really complex leaves with veins all over, not long like monocots. Some examples of dicots are roses, sunflowers, cacti, apple, and cherry plants. 

MEDICINES

One of the good examples of plants giving medicine to man is an aloe plant. Inside the leaves of an aloe plant are compounds that soothe burns on our skin. Man also gets something called digitalis from plants. The truly exciting discoveries are in the future. Scientists are analyzing plants every day to find out if they have any compounds that can help humans survive and lead a better life. 

MITOSIS - WHEN CELLS SPLIT APART

Eventually cells need to duplicate. There are two main methods of replication, mitosis and meiosis. This tutorial will talk about mitosis. 

The big idea to remember is that mitosis is the simple duplication of a cell and all of its parts. It duplicates its DNA and the two new cells (daughter cells) have the same pieces and genetic code. Two identical copies come from one original. Start with one; get two that are the same. You get the idea. 

Beyond the idea that two identical cells are created, there are certain steps in the process. There are five (5) basic phases in the life-cycle of a cell. You should remember the term PMATI (pronounced PeeMahtEee). PMATI is the acronym for the phases of a cell's existence. It breaks down to. 

PROPHASE - METAPHASE - ANAPHASE - TELOPHASE - INTERPHASE

We suppose it would be good to know what happens during those phases. Always remember - PMATI! 

THE PHASES

Prophase: A cell gets the idea that it is time to divide. First, it has to get everything ready. You need to duplicate DNA, get certain pieces in the right position (centrioles), and generally prepare the cell for the process of mitotic division. 

Metaphase: Now all of the pieces are aligning themselves for the big split. The DNAlines up along a central axis and the centrioles send out specialized tubules that connect to the DNA. The DNA (chromatin) has now condensed into chromosomes. Two strands of a chromosome are connected at the center with something called a centromere. The tubules actually connect to the centromere, not the DNA. 

Anaphase: Here we go! The separation begins. Half of the chromosomes are pulled to one side of the cell; half go the other way. When the chromosomes get to the side of the cell, it's time to move on to telophase. 

Telophase: Now the division is finishing up. This is the time when the cell membrane closes in and splits the cell into two pieces. You have two separate cells each with half of the original DNA. 

Interphase: This is the normal state of a cell. We suppose that when it comes to cell division, you could call this the resting state. It's just going about its daily business of surviving and making sure it has all of the nutrients and energy it needs. It is also getting ready for another division that will happen one day. It is duplicating its nucleic acids, so when it's time for prophase again, all the pieces are there. 

MEIOSIS - IT'S FOR SEXUAL REPRODUCTION

What are the big ideas here? There are two cell divisions. Mitosis has one division and meiosis has two divisions. You still have to remember PMATI, but now you do it twice. You also need to remember that four cells are created where there was originally one. That's four (4) cells with half of the amount of DNA needed by a cell. When a cell goes through meiosis, it's not concerned about creating another working cell. 

Meiosis happens when it's time to reproduce an organism. The steps of meiosis are very simple. When you break it down it's just two PMATI's in a row. Scientists say Meiosis I and Meiosis II, but it's just two PMATIs. The interphase that happens between the two processes is very short and the DNA is not duplicated. 

As we said, meiosis happens when it's time to reproduce. Meiosis is the great process that shuffles the cell's genes around. Plants do it, animals do it, and evenfungi do it (sometimes). Instead of creating two new cells with equal numbers of chromosomes (like mitosis), the cell does a second division soon after the first. 

That second division divides the number of chromosomes in half. When you have half the number of chromosomes, you are called a haploid cell. Haploid means half the regular number. Diploid is the opposite (two strands). Normal cells are considered to be diploid cells. 

STEP ONE

MEIOSIS I: This is basically like the PMATI of a regular mitosis. Pairs of chromosomes are lined up at the center of the cell and then pulled to each side. Meiosis is a bit different because there something called crossing-over happens with the DNA. 

This crossing over is an exchange of genes. The genes are mixed up, not resulting in a perfect duplicate like mitosis. The cell divides, leaving two new cells with a pair of chromosomes each. Normally the cell would begin to go about its business of living and slowly duplicate the chromosomes for another mitotic division. Since this is meiosis, there is a very short interphase and division begins again. 

STEP TWO

MEIOSIS II: In Prophase II the DNA that remains in the cell begins to condense and form short chromosomes. Each chromosome pair has a centromere. The centrioles also begin their journey to opposite sides of the cell. In Metaphase II all of the chromosomes line up along the center of the cell and the centrioles are in position for the duplication. Anaphase II shows the chromosomes split and move to opposite sides of the cell. Each one splits into two pieces. They don't divide up the DNA between the new cells; they split the DNA that exists. Each daughter cell will get one-half of the DNA needed to make a functioning cell. 

Telophase II shows the DNA completely pulled to the sides and the cell membrane begins to pinch. When it's all over, you are left with four haploid cells that are called gametes. The eventual purpose of the gametes will be to find other gametes with which they can combine. When they do, they will form a new organism.

 Chromosomes - Pull up Those Genes

Chromosomes are the things that make organisms what they are. They carry all of the information used to help a cell grow, thrive, and reproduce. Chromosomes are made up of DNA. Segments of DNA in specific patterns are called genes. Your genes make you who you are. You will find the chromosomes and genetic material in the nucleus of a cell. In prokaryotes, DNA floats in the cytoplasm in an area called the nucleoid. 

Loose and Tight

Chromosomes are not always visible. They usually sit around uncoiled and as loose strands called chromatin. When it is time for the cell to reproduce, they condense and wrap up very tightly. The tightly wound DNA is the chromosome. Chromosomes look kind of like long, limp, white hot dogs. They are usually found in pairs. 

Completing the Sets

Scientists count individual strands of chromosomes. They count individuals not every organism has pairs. You probably have 46 chromosomes (23 pairs). Peas only have 12. A dog has 78. The number of chromosomes is NOT related to the intelligence or complexity of the creature. There is a crayfish with 200 chromosomes. Does that make a crayfish five times smarter or more complex than you are? No. There are even organisms of the same species with different numbers of chromosomes. You will often find plants of the same species with multiple sets of chromosomes. 

Chromosomes work with other nucleic acids in the cell to build proteins and help in cell division. You will most likely find mRNA in the nucleus with the DNA. tRNA is found outside of the nucleus in the cytosol. When the chromosomes are visible, cells with two complete sets of chromosomes are called diploids (46 in a human). Most cells are diploid. Cells with only one set (23 in a human) are called haploid cells. Haploids are most often found in cells involved in sexual reproduction such as a sperm or an egg. Haploid cells are created in cell division termed meiosis. 

THE TOP FOUR KINGDOMS

Now we get down to details. We already explained that kingdom is the general way that organisms are described. It is the broadest category for normal classification. Don't forget about the domain grouping, but we aren't talking about the subtle differences between prokaryotic species here. The top four kingdoms are... 

PROTISTA

The protists are usually single celled organisms. They have a distinct nucleus. Some form colonies (or groups of single cells), some act more like animals (they move around and have large cells), and some are even like plants (algae, have chlorophyll and do photosynthesis). 

FUNGI

This kingdom is made up of the decomposers (they absorb nutrients). Some of the members of this kingdom are fungi, slime molds, yeast, mold, and mushrooms. 

PLANTAE

Plantae, hmmm... maybe these are plants? The characteristics of plants are that they have chlorophyll, cell walls (cellulose), and vacuoles. This kingdom also includes red, brown, and green algae. 

ANIMALIA

Last, but certainly not least, are the animals. These are the most complex organisms on the planet. One big thing about animals is that they must eat other organisms to survive. They cannot create their own food because they do not contain chlorophyll. They are able to move around, and most have sense organs of some type. Because they have those sense organs, they have nervous systems. Animals include species such as anemone, insects, lizards, and mammals. 
KINGDOMS=GROUP... SPECIES=INDIVIDUALS

Scientists have all these complex ways of organizing living things. They look at your physical traits, how you develop as a fetus, or in an egg. They look to see if you are a plant. 

MUST MAKE MORE

But there is one big thing that helps them determine whether you are in the same species as another animal or plant. You are the same species as another being if you can do a really important thing. You can reproduce and have babies. Also, those babies have to be able to have more babies. They have to be fertile. 

If you are a type of fern, scientists would know that another fern is the probably the same species if the two ferns can create a similar fern that is fertile. The same rules apply if you are a mouse. Not all mice can have fertile babies together. They can't have babies because there are different types of mice. And of course there is you. You can't have babies with a dog. You can't have babies with a horse. You can't have babies with a monkey that looks a lot like your brother or sister. You can only have offspring(babies) with other humans. You two would be the same species. 

NO BEGINNING AND ENDING

So remember, everything we talked about here describes a living system. Scientists are always re-evaluating and developing the classification system. Science will always change and evolve as new facts are discovered. Even the idea of a species is difficult. 

There is no sure fire way to say, "Here is where one species ends and another begins." Some species are so closely related that they can have fertile offspring. Species are defined by man, and it is often difficult to make clear definitions when two organisms are incredibly similar. If those organisms reproduce and create a completely new line of creatures, those parents actually were not that different when it came time to mix up the genes. 

IT'S NEVER BLACK AND WHITE

In all of biology and the world, there is overlap. Coming up with definite black and white answers that always work rarely happens. You can get definite answers in math. You can even get definite answers in physics. Biology has many gray areas. Scientists will always debate and try to improve ideas and explanations. You may learn about ligers. Ligers are the offspring of lions and tigers but they are not fertile offspring. Those two organisms are incredibly similar, genetically, but their differences are enough to make them separate species. 

PROKARYOTES - MISSING A NUCLEUS

If you're looking to learn about cells with a nucleus, this is the wrong place. Prokaryotes do not have an organized nucleus. Their DNA is kind of floating around the cell. It's clumped up, but not inside of a nucleus. If you want to learn about cells with a nucleus, look for information on eukaryotes. And, once again, a prokaryote is a single cell or organisms that does NOT have organized nuclei. 

CAN YOU EXIST WITHOUT A NUCLEUS

You can't, but they can. What can you do without a nucleus? You can do a whole lot. Most prokaryotes are bacteria and bacteria can do amazing things. Although they are very simple organisms, they are found everywhere on the planet. Some scientists even think that they may be found on other planets (maybe even Mars). Some places you can find bacteria every day are in your intestines, a cup of natural yogurt, or a bakery. Prokaryotes are the simplest of simple organisms. Here's the checklist. 

(1) Prokaryotes have no organized nucleus. Like we said, the DNA is clumped in an area but there is no organized nucleus with a membrane. 

(2) Prokaryotes do not usually have any organelles. They will probably have ribosomes inside of their cells, but ribosomes are not technically considered organelles. No chloroplasts. No mitochondria. No nucleus. Not much at all. 

(3) Prokaryotes are very small. Because they don't have all of the normal cell machinery, they are limited in size. As always in biology, there are exceptions, but generally, prokaryotes are very small (compared to other cells). Mind you, compared to a virus they are big, but next to an amoeba, tiny. 

(4) Prokaryotes don't have mitosis or meiosis like other cells. Scientists don't really have a good way of describing how they duplicate, but it's not through normal means. Check out the bacteria tutorial to get an idea. 
EUKARYOTES - CELLS WITH PARTS

This is the place to learn about cells with a nucleus and all sorts of organelles. Eukaryotes are what you think of when you think of a classic "cell." There are cells without organized nuclei or organelles that are called prokaryotes, but not on this page. 

The possibilities are endless. Eukaryotes are cells that can do anything. They are the cells that have helped organisms advance to new levels of specialization beyond imagination. You wouldn't be here if eukaryotic cells did not exist. What makes a eukaryotic cell? Let's watch. 

(1) Eukaryotic cells have an organized nucleuswith a nuclear envelope. They have a "brain" for the cell. They have a discreet area where they keep their DNA. It is also said that they have a "true nucleus." Can we say it any other way? 

(2) Eukaryotic cells usually have organelles. They might have mitochondria, maybe a chloroplast, or some endoplasmic reticulum. They have parts that work to make the cell a self-sufficient organism. 

(3) Although limited in size by the physics of diffusion, eukaryotic cells can get very large. There are even some extreme examples called plasmodial slime molds that can be a meter wide. The cell is multinucleated (many nuclei) and it gets huge. Generally, eukaryotic cells are a couple hundred times the size of a prokaryotic cell. 

(4) Eukaryotic cells have extra stuff going on and extra parts attached. Since they have organelles and organized DNA they are able to create parts. One example is theflagellum (a tail-like structure to help it move). They could also create cilia (little hairs that help scoot the cell through the water). In the invertebrate section, we talk about nematocysts that are cells with little harpoons for catching prey. The list is endless. 

GOOD MICROBES...

With such a variety of microscopic organisms, it's bound to happen that there are some that help the world. There will also be some that hurt the world. We will cover those in another section. We're going to cover a few of the good ones here. 

FIXING NITROGEN IN SOIL

There are bacteria that go through a process called fixing nitrogen. These bacteria, living in the roots of plants, actually help them absorb nitrogen from the surrounding soil. The nitrogen is very important for the growth of the plant, and these little bacteria give them an advantage for survival. 

HELPING COWS EAT GRASS

As we said, not all protists are bad for the world. In the bacteria section we already told you about a species that lives in the digestive system in cows. These bacteria help cows break down thecellulose in plants. Similar bacteria live in all sorts of grazing animals, helping them survive off plant material. Many ecosystems are based on creatures that are called herbivores. 

ANTIBIOTICS

Scientists have even discovered fungi that will help you battle bacterial diseases. So you get sick, the doctor looks at you and says you have a bacterial infection, maybe bronchitis. He prescribes an antibiotic to help you get better. Antibiotics are drugs designed to destroy bacteria by weakening their cell walls. When the bacterial cell walls are weak, your immune cells can go in and destroy the bacteria. Although there are many types now, one of the first antibiotics was calledpenicillin. It was developed from a fungus (a fungus named Penicillium found on an orange, to be exact). 

AND BAD MICROBES

With such a variety of microscopic organisms, it's bound to happen that some do not help anything in the world. Some also help the world. We cover those in another section. We're going to cover a few of the bad ones here. 

DISEASES

Many species of bacteria cause disease in humans, animals, and even plants. Humans worry about bacteria that cause botulism (bacteria living in spaces without oxygen, such as cans), tetanus and E. coli. You should know that there are also some good forms of E. Coli living in your intestines. They help break down food and live a simple life (and yes, they make it smell down there). There are also E. Coli that can be passed to you from undercooked meat. These bad bacteria can make you very sick and even kill you. 

A ROLE IN NATURAL SELECTION

We don't know of any viruses that are good for the world. They are an important piece of evolution and natural selection. Weaker and older animals are more easily infected. Those organisms are removed from the population so that healthier animals can survive. But the virus life cycle, that of a parasite, only hurts the organisms. Some even destroy cells in order to reproduce. And don't think you are the only one to get sick. Viruses attack plants and even bacteria. No organism is safe from damage. Examples of viruses include Rabies, Pneumonia, and Meningitis. 

SORRY ABOUT THAT (AGAIN)

Humans are actually creating stronger bacteria and viruses by accident. The idea of natural selection is that weaker organisms are killed off and stronger ones survive and duplicate. Think about a bacterium for a moment. If you take antibiotics that kill bacteria, you get better. 

However, because of variety, some bacteria may survive your medicine. Not enough bacteria survive to hurt you now, but they are there. If they eventually get someone sick, there is a chance that the antibiotics will not work again. You have incubated super bacteria! It's happening all the time in hospitals. We are killing off the easy diseases but some mutant strains are surviving. We might not be able to cure people next time a bad disease infects people. 

MAN AND MICROBES

As with many things in life, humans need more than nature provides, not only to battle hazards in nature but also to battle things we have created ourselves. You're asking, "What are these guys talking about?" Biotechnology! Scientists all over the world are experimenting with viruses, bacteria, and fungi for hundreds of reasons. Why mess around with these little creatures? They are the simplest of all organisms. They can also be the most deadly. That is reason enough to study them. 

MICROBES TO MAKE MEDICINE

Scientists are working with microbes and the compounds they create to make new medicines to save our lives. You might be vaccinated for pox or the flu. Scientists have studied those viruses to see how they act. Then they came up with a way to teach your immune system to do battle. If you get sick at all, you will be able to fight off the infection. Labs are also developing drugs that help you fight infections after you get the disease. We already spoke about antibiotics. Labs are creating new and stronger antibiotics every day. 

MICROBES IN WAR

Although nobody likes to talk about it, humans have a history of using disease and compounds created by microbes in warfare. Labs were built to create chemical compounds that would kill people. They also isolate diseases (viruses) that could be released to infect entire populations of people. Most of the world has chosen not to develop diseases for use in war. They realized how dangerous and uncontrollable these diseases are. Once they are out, they might not be able to be stopped. 

CLEANING THE ENVIRONMENT

Let's finish on a good note. Scientists are also working with microbes to help the environment. In reality, the environment did not need help; we're just trying to lower the negative impact we have on the environment. Good examples are the bacteria that have developed to break down oil in the water. If a tanker leaked and oil began to get into the water, these bacteria could be released to break down the oil. The resulting compounds would not hurt the environment. Scientists are also working with bacteria and fungi to help breakdown garbage. 

ARE VIRUSES EVEN ALIVE?

We're starting with the smallest of the small here. Some scientists argue that viruses are not even living things. We suppose it's easier to give you a list of what they can't do as opposed to what they can. What viruses can't do: 
(1) They can't reproduce on their own. They need to infect or invade a host cell. That host cell will do all the work to duplicate the virus. 
(2) They don't respond to anything. You can poke them or set up barriers, it doesn't matter. They either function or they are destroyed. 
(3) They don't really have any working parts. While there some advanced viruses that seem fancy, viruses don't have any of the parts you would normally think of when you think of a cell. They have no nuclei, mitochondria, or ribosomes. Some viruses do not even have cytoplasm. 

We've already established what viruses aren't. Let's talk about what they are. Every virus has a few basic parts. The most important part is a small piece of DNA or RNA(never both). That strand of nucleic acid is considered the core of the virus. The second big part is a protein coat to protect the nucleic acid. That coat is called thecapsid. The capsid protects the core but also helps the virus infect new cells. Some viruses have another coat or shell called the envelope. The envelope is made of lipids and proteins in the way a regular cell membrane is structured. The envelope can help a virus get into systems unnoticed and help them invade new host cells. 

TYPES OF VIRUSES

As you go on to study more biology, you'll see many virus types. There are three basic shapes. 
1) First there are helical virions. They are set up like a tube. The protein coat winds up like a garden hose around the core. 
2) Next comes the polyhedral shape. This shape group includes the classic virus shape that looks like a dodecahedron. A dodecahedron is a geometric shape with twelve (12) sides. These viruses have many facets and a seemingly hard shell of capsomeres (pieces of a capsid). There is a variation of the polyhedral called globular. Globular shapes are basically polyhedral virions inside of a spherical (like a ball) envelope. 
3) Last is the complex virus shape. You may have seen this one in books with thegeometric head and long legs. 

SMALLER THAN VIRUSES?

There are things out there even smaller than viruses. The two that scientists have discovered are called prions and viroids. A prion is (as far as we know) just a protein. Prions are proteins that can invade cells and somehow direct their own duplication, making more of the isolated proteins. Viroids are a little different in that they are just RNA. Scientists have even discovered that they are responsible for some diseases. 

BACTERIA BASICS - THEY ARE ALIVE!

Bacteria are the simplest of creatures that are considered alive. Bacteria are everywhere. They are in the bread you eat, the soil that plants grow in, and even inside of you. They are very simple cells that fall under the heading prokaryotic. That word means they do not have an organized nucleus. Bacteria are small single cells whose whole purpose in life is to replicate. 

Okay. So we've told you they don't have an organized nucleus. True. They do have DNA. It is grouped in an area called the nucleoid. They have cell membranes like other cells and even a protective cell wall. Mind you, their cell wall is not like the one in a plant. It's a special kind that bacteria have for protection. They don't have any organelles, just ribosomes. (These are all characteristics of prokaryotes if you remember.) 

WHAT DO THEY LOOK LIKE?

Very small. Very, very small. You might have seen pictures of some bacteria. Since we don't know what you have seen, we'll tell you there are three basic shapes. Sphericalbacteria are in the shape of little spheres or balls. They usually form chains of cells like a row of circles. Rod shaped bacteria are look like the E. coli living in your intestine. You can imagine a bunch of bacteria that look like hot dogs. They can make chains like a set of linked sausages. Spiral shaped bacteria twist a little. Think about balloon animals for these shapes. It's like a balloon animal in the shape of a corkscrew. 

WHAT DO THEY DO?

All sorts of things. Sorry to be so vague, but they do just about everything. Some help plants absorb nitrogen (N) from the soil. Some cause diseases like botulism. Some bacteria even live inside the stomachs of cows to help them break down cellulose. Cows on their own can digest grass and plants about as well as we do. They don't get many nutrients out of the plants and can't break down the cellulose. With those super bacteria, the cellulose can be broken down into sugars and then release all of the energy they need. Imagine if scientists could develop bacteria to live inside of us that would break down plants. That would be something. We could eat grass and leaves all day long.