Plant Divisions: Lycopodiophyta

Clubmoss Selaginella kraussiana

Plants within the division Lycopodiophyta are small, green, leafy and have spores but no flowers. They are a little like mosses, and many contain the word ‘moss’ in their common names. However, Lycopodiophyta evolved later than plants in the Bryophyta division and have a fully formed vascular system, with phloem and xylem, they are the earliest vascular plants to have evolved. There are about 2,000 species in total, and although they are more numerous in the tropics, they grow throughout the world.

There are, broadly speaking, four different types of plant within the Lycopodiophyta Division: clubmosses, firmosses, spikemosses and quillworts. The following diagram shows how they fit together in the plant kingdom. (click to enlarge)

Lycopodiophyta Family Tree

• Class – all end with ‘opsida’
• Order – all end with ‘ales’
• Family – all end with ‘aceae’

Of the four families within the Lycopodiophyta Division, Lycopodiaceae, the clubmoss family, is the largest and most diverse, containing between 13 and 19 genera. The spikemoss (Selaginellaceae) and quillwort (Isoetaceae) families contain only one genus each, although within those genera are many species.

Note: Lycophyte is a general term for plants in the Lycopodiophyta Division.

What makes lycophytes different from other plants?

Leaves

Lycophytes are distinct from most other plants, by having microphylls, a primitive form of leaf. Microphylls are a few evolutionary steps on from the leaves of BAMs (Bryophyta, Anthocerophyta and Marchantiophyta– see previous blog) which are mostly one cell thick and without specialization. Microphylls can be many cells thick, with special cells for the epidermis and vascular tissue. They are not necessarily small – extinct Lepidodendron had microphylls over a metre long – but they are simpler than normal leaves, which are called megaphylls. Whereas megaphylls have a complex network of veins, or a number of veins running from base to tip, microphylls have a single, unbranched vein.

Horsetails (a type of fern) also have microphylls, but from the fossil record it looks as if they evolved megaphylls and then reverted to microphylls later.

Reproduction

See previous blog Plant Divisions: Mosses, Liverworts and Hornworts for more information about gametophytes and sporophytes.

Like BAMs (Bryophyta, Anthocerophyta and Marchantiophyta), lycophytes have alternating generations. The sporophyte stage produces spores and these grow into the gametophyte stages which produce sperm and eggs which then fuse to form a new sporophyte. However, there are a few important differences.

One difference occurs only in spikemosses and quillworts. BAMs, clubmosses and firmosses are homosporous, which means that all spores produced look identical and only become apparently male or female when the spores become gametophytes. Spikemosses and quillworts  are heteropsorous, meaning they produce two types of spores that look very different: large megaspores (female) and small microspores (male).

Heterosporous Reproduction

Selaginella – Heterosporous Reproduction

A fertile cone grows out from the sporophyte (the sporophyte is the main body of the plant, the part that has leaves), from this grow sporangia that contain spores, some the male microspores, others the large female megaspores.  When these spores are released they become separate, tiny plants, the gametophytes. The male gametophyte releases sperm, the female contains eggs. The sperm find and fertilise the egg by swimming to it after it has rained. The new sporophyte then grows out of the female gametophyte, putting down roots and growing leaves, becoming a whole new plant.

Other Differences in Reproduction

• The female gametophyte generation has rhizoids, the more primitive form of root, while the sporophyte generation has roots
• The sporophyte generation is the larger, longer lasting stage; in BAMs it is the gametophyte stage
• Unlike BAMs, the gametophyte generation is completely removed from the sporophyte generation. In some lycophyte species gametophytes grow on the surface of the ground, others grow in water.

Different Types of Lycophytes

Spikemoss, Quillwort, Clubmoss, Firmoss

Pictures taken from here:

• Spikemoss: Wikipedia
• Quillwort: Wikimedia
• Clubmoss: Saluda Shoals Parke Rangers Blog
• Firmoss: Wikimedia

Clubmoss

Some clubmoss shapes

Clubmosses are in the Lycopodiaceae family, they have needle-like or scale-like leaves, a few of the different leaf shapes can be seen above. They are the most varied within the Lycopodiophyta Division, descibed as having between 13 and 19 genera and somewhere between 400 and a thousand species. Although most clubmosses are only a few centimetres high, and green, there are a few exceptions, for example Lycopodium deuterodensum, that grows in Australasia, can reach a metre high and Lycopodium fastigiatum, native to New Zealand, is orange in colour.

Clubmosses usually have a creeping or epiphytic habit (grow on other plants, or sometimes inanimate objects, high up). Most grow in tropical mountains, but they are found throughout the world, including in the UK. Clubmosses are homosporous and although their reproductive lifecycle is similar to the one shown above, the male and female spores are the same size and shape.

Firmoss

Firmoss

Firmosses are in the Huperziaceae family. They are mostly epiphytic and grow throughout the world. There are over 400 hundred different species of firmoss, although their appearance does not change much from one to another. They are more upright than clubmosses tend to grow in clusters, looking like a small fir tree forest. They are also homosporous.

Spikemoss

Some spikemoss shapes

Spikemosses are contained in one genus, Selaginella, but there are still a number of different leaf shapes within the 700 or so species. In the US it is sometimes grown as a houseplant or as ground cover. It is heterosporous having both micro and megaspores.

.

Spikemoss diagram

Quillwort

Quillwort

Quillworts are in the order Isoetales, which, like the spikemoss order, has only one family and genus, but about 150 species. Most are aquatic or semi-aquatic plants. Some species have been found off the coast of Scotland. The leaves are narrow and grasslike and it is difficult to distinguish from grass without a microscope. It is heterosporous.

A website tracking lycophytes in the UK is here http://www.ferns.rogergolding.co.uk/ferngenus/isoetes/echinospora.html

Extinct Species

Sigillaria and Lepidodendron Trees

Originally Lycopodiophyta contained three other orders: Lepidodendrales, Pleuromeiales in the Isoetopsida class and Drepanophycales in the Lycopodiopsida class. Plants in these three orders grew metres high, some up to 30m high, and formed forests in the Carboniferous Period 300-350mya. Tree ferns and early conifers also grew in Carboniferous forests. Coal formed from the decaying plant matter in these forests.

Plant Divisions: Mosses, Liverworts and Hornworts

Bryophytes used to be a general term for mosses, liverworts and hornworts, and these three were grouped together into a single division due to their similarity. It is now known that they are not closely related and they have been split into three separate divisions.

• Bryophyta Division – mosses

• Anthocerophyta Division – hornworts

• Marchantiophyta Division – liverworts

Although the term bryophyte is still used to mean plants in all three divisions, including Bryophyta, I think that is confusing, so instead I will use “BAMs” (Bryophyta, Anthocerophyta and Marchantiophyta) to refer to the three divisions, and the plants within them.

Moss

Introduction

BAMs (Bryophyta, Anthocerophyta and Marchantiophyta) were some of the earliest plants to evolve, as a result they are primitive when compared to later, vascular plants. Their leaves, stems, and the rhizoids they have in the place of roots, are all simpler and less effective. BAMs are non-vascular, although they do have a simple, conducting system for transporting water and nutrients, it does not contain the xylem and phloem vessels found in vascular plants and is not nearly so efficient. As a result, BAMs do not grow large, because they cannot transport water a long distance, and are limited to damp shady areas, because in the sun  they dry out. They reproduce by spores, rather than seeds and their reproductive cycle involves two distinct, external stages, (essentially two different plants) which does not happen in plants with seeds.

Mosses can be divided into two different groups:

• Acrocarp – upright
• Pleurocarp – creeping

Leafy and Thallose

And Liverworts:

• Thallose – larger rubbery leaves and flower-like capsules containing spores (sporophytes). Thallose means the tissue is undifferentiated.
• Leafy – smaller leaves arranged along a short stem, small globe capsules. Most liverworts are leafy.

The Hornwort Division is much smaller and does not split readily into types.

Note: Plants in the Ceratophyllum genus are also referred to as hornworts, these are very different plants and they are aquatic and flowering.

Moss with Sporophytes (capsules and seta)

What makes BAMs different from other plants?

Click for close up

Roots and rhizoids: BAMs do not have roots, they have rhizoids, these are also found on horsetails and ferns (Pteridophyta), club mosses and quillworts (Lycopodiophyta). Some fungi and algae also have rhizoids. Rhizoids are similar to roots, in that they transport water and nutrients, and anchor the plant to the soil or substrate, but are much simpler in form, often only one cell thick.

Click for close up

Simple and Complex Leaves: Leaves on BAMs are single celled, apart from the midrib. They contain chloroplasts for photosynthesis, but otherwise the cells are not specialised as they are in other plants.

Reproduction

To explain how sexual reproduction is different in BAMs, it’s necessary to first explain sexual reproduction as it is in all organisms.

Diploid and Haploid Cells

There are two types of cell:

• Diploid cell (2n) –  a cell with two sets of DNA, most cells in an organism are diploid.
• Haploid Cell (n) –  cell with one set of DNA, cells are only haploid when an organism is reproducing or preparing to reproduce.

And two types of cell division:

• Mitosis – a cell replicates its DNA and splits in two so that each new cell has the same amount of DNA as the original. This type of cell division is used when an organism grows. Can occur in both haploid and diploid cells.
• Meiosis – the DNA does not replicate and when the cell splits in two each new cell has half the DNA of the original. This type of cell division is used only for sexual reproduction. Occurs only in diploid cells and results only in haploid cells.*

Diagram Showing Mitosis

Diagram Showing Meiosis

Example: Daisy

Inside the flower of a daisy, some cells are dividing by meiosis in order to create haploid cells, called the male gamete. These haploid cells form pollen (each pollen grain contains one gamete) which are picked up by bees and deposited onto another daisy flower that will contain the female gamete. The two haploid gamete cells fuse to form a single diploid cell (one strand of DNA from each gamete), called the zygote. The zygote grows by mitosis in the flower until it forms a slightly larger and more complex embryo daisy. This embryo is contained within a seed which falls (or is blown) away from the mother plant to land and grow, by mitosis, into a new daisy, similar but not identical to the two parents.

This process is fairly similar in animals with the same use of meiosis and haploid cells to reproduce, the main difference is in how the male gamete finds the female gamete (eg by mating) and instead of falling as a seed the embryo is released as an egg, a pupa or forms inside the adult.

Diagram of Moss

BAMs do not reproduce in quite the same way. Although they too create haploid cells by meiosis (called spores), these haploid cells form a plant called a gametophyte. The gametophyte is made of haploid cells and creates more haploid cells, the gametes, by mitosis. Some gametes are male, some female (although some species produce only male or female gametes and these gametes will need to find a gamete of the opposite gender to fuse with). A female gamete fuses with a male gamete to create a new diploid plant, called a sporophyte. Often the sporophyte grows out of the gametophyte (seen right). The sporophyte produces spores, these are haploid and each will potentially grow into a new gametophyte and so the cycle starts again.

This alternation of diploid and haploid plants, sporophyte and gametophyte, is called Alternation of Generations. It is often described as happening in all plants, but only plants, never animals (although it can also be said to happen in fungi). However, animals do have a diploid and haploid phase, the only real difference is that plant gametes, such as pollen can divide, whereas haploid gamete cells in animals cannot. Otherwise the process is very similar: diploid cells divide by meiosis to become haploid gametes and two gametes of different genders fuse to become a diploid zygote which then divides by mitosis to get bigger and become a whole new organism. Thank you to Walter Hintz at this website for helping me understand this http://www.allexperts.com/user.cgi?m=4&expID=48818&catID=664

Here are my question and his answer.

http://en.allexperts.com/q/Biology-664/2013/3/alternating-generations.htm

What makes BAMs different from each other?

Yellow Moss

All BAMs like moist shady areas, but mosses are a little hardier than liverworts and cope better with dry weather.

There are 12,000 species of moss, 6,000-8,000 species of liverwort but only 100 species of hornwort. Mosses are abundant in England, liverworts are a little harder to find and hornworts are not common here, preferring tropical climates.

Liverwort and Pencil Tip

I took a recent trip to Highgate Cemetery to find mosses and liverworts. I found a few liverworts in the really boggy areas, growing on soil, although liverworts can grow on stone. I was surprised at how small the liverworts were and the photo above shows some with a pencil tip to show size. Moss covered everything, but at first it was difficult to see any more than one kind – partly because I wasn’t used to looking and partly because certain mosses are much more successful than others and tend to take over. In the end I did spot a few different kinds, the photos throughout this blog are ones I took on the trip, but here are some close up photos of the different types of moss I discovered.

Mosses Found In Highgate Cemetery

Differences in Appearance

Liverwort

Mosses are soft and leafy, with many tiny leaves, and the sporophytes are small capsules on the end of long thin seta (seen in diagrams above). Liverworts have slightly larger, flat rubbery leaves usually growing much closer to the ground, their sporophytes are either like rubbery, green flowers (seen on the drawing at the top of this page) or globes on a stem (seen below). Some liverworts have round gemma cups (seen at the top of this photo) containing fragments of liverwort that can break away and form new gametophytes, this is a form of asexual reproduction. Gemmae can also be found in mosses. Hornworts look fairly similar to liverworts in the gametophyte stage, but the sporophyte is a distinctive long, thin, needle-like protuberance.

Liverwort with Sporophytes

Differences in Biology

The biological differences are a little detailed for the purposes of this blog, so I will only list a few briefly: Hornworts produce slime in between the cells. Most hornwort species have a single chloroplast in each cell, unlike liverworts, mosses and all other plants, only algae have this same feature. The rhizoids in mosses are multicellular, but unicellular in hornworts and liverworts. Mosses and hornworts have true stomata (breathing holes) on their sporophytes, but liverworts do not.

Bizarre bryophytes and not-bryophytes

Spanish Moss

Spanish moss or beard lichen is often thought to be a parasitic, but it merely grows in abundance on trees. However, it is NOT actually a moss, or a lichen, but a flowering plant in the bromeliad family. Ball moss is similar, a flowering plant rather than a moss. Reindeer moss is also not a moss, but a lichen.

This picture was taken from the following website http://www.learnnc.org/lp/multimedia/6540

Mosses are not parasitic, but some liverworts are. Aneura mirabilis, Cryptothallus mirabilis and Cryptothallus hirsutus are all parasitic liverworts. They are pale because they have no chlorophyll and therefore cannot photosynthesize. Instead they gain their nutrients from fungi that are working symbiotically with a tree, ie the fungus and tree are aiding one another, the tree provides carbohydrate for the fungus, the fungus extracts nutrients from the soil for the tree and then the Aneura sneaks in and takes nutrients from the fungus without giving anything back.

Luminous Moss

Luminous moss (Schistostega pennata), also known as Elfin Gold, glows green in the dark. It can take light, no matter how faint, and reflect it, leading to the luminescence. For this reason it is able to grow in places too dark for other mosses. It is native to the Northern Hemisphere and is found growing in caves or between rocks. This picture is taken from http://www.botanic.jp/plants-ha/higoke.htm and there are other pictures of the moss on that site.

*Note to meiosis: Occasionally, or with some specific species, the process of meiosis and mitosis do not occur as described above, and instead a cell, a tissue, or an entire organism can end up having more than two sets of DNA. For example if a diploid cell does not split by meiosis as usual and then fuses with a haploid cell, the result is a cell with three sets of chromosomes. This state is called polyploidy, it can have a function, both biologically and commercially.

Plant Divisions

The kingdom Plantae is split into ten divisions:

• Anthocerotophyta
• Marchantiophyta
• Bryophyta
• Lycopodiophyta
• Pteridophyta
• Gnetophyta
• Cycadophyta
• Ginkgophyta
• Pinophyta
• Magnoliophyta

Occasionally algae are included as a further two divisions Charophyta and Chlorophyta, but recent research classifies these as too primitive to be called plants. See Kingdom blog for more information.

Another division is Pteridospermatophyta, these are seed ferns dating from the Devonian period, and have died out.

Plant Divisions

Non vascular – plants without a proper system for transporting water through the plant, as a result these are small plants that need damp shady areas to live in. These were the earliest plants to evolve.

Vascular – plants that have a proper system for transporting water and sugars around the plant. The vascular system itself has continued to evolve, with Gnetophyta having a more evolved system than other Gymnosperms and Magnoliphyta having the most evolved system.

Spores – spores are a primitive form of reproduction.

Gymnosperms – seed producing, but the seeds are not contained in an ovary and there are no flowers . All are woody.

Flowering plants – no plants outside of the Magnoliophyta Division flower and this was the latest plant organ to evolve. Flowering plants account for most plants in existence (about 80-90%).

Timeline of Earth and Plant Evolution

Timeline of Earth

Earth’s Timeline

Note: No date from prehistoric Earth can be completely definite. I have done my best to choose reliable dates, but there is much contention with conflicting evidence. Hopefully these diagrams will give a sense of the changes and events occurring within our planet’s history, but I cannot guarantee complete and long lasting accuracy.

The above image is a timeline of Earth’s history, from its formation 4,540 million years ago (mya) to now. The first Eon, Hadean, was a tumultuous one, the planet was still very hot and volcanic and the air was mostly made of carbon dioxide. Although oceans formed about 4,300 MYA ago, they were vapourised by a meteor bombardment that lasted until the Archean Eon.

The Archean Eon saw the first microscopic life, with Bacteria and Archaea evolving, plus the process of photosynthesis started to occur. The Oxygen Catastrophe, a massive increase in oxygen that killed most of the planet’s anaerobic bacteria, occurred in the Proterozoic Eon and was caused by photosynthesizing Cyanobacteria. This also led to the longest period of glaciation (shown by the white edges of the timeline). Acritarch and Grypania are fossils from this time and are thought to be evidence of the first Eukaryotic cells (it is not definite whether either or both are Eukaryots, so I have included both). The multicellular Bangiomorpha is the the first organism to reproduce sexually, and this was a very important development. Without sexual reproduction there could be no mixing of DNA from two parents, which meant that natural selection and consequently evolution, were extremely slow. After Bangiomorpha the change from multicelled, but very simple organisms, to the wide and complex variety of living things we have today, is comparatively fast.

800mya the first multicelled organisms evolved, algae – Cladophora, and around this time another glaciation occurred. The first fungi arrived 700mya, the first animals 665mya. All these organisms lived only in the sea.

The Cambrian Explosion, 530mya, was when many animals appeared, they were arthropods and many of these were crustaceans (see previous blog for more information), here is a great animation of some of those animals. The first big extinction event happened about 50 million years later, in the Phanerozoic Eon (shown on the diagram with a vertical line of crosses), and led to the loss of many animals, especially Trilobites, one of the first Arthropods to have existed. It is interesting to note that while there have been a number of animal extinctions (six can be seen on the diagram) there have been no known plant extinctions and I could find no record of fungi extinctions. This is probably because both plants and fungi are able to survive extreme trauma, regenerating from small portions of root or mycelium. Animals, however, tend die quite easily, the more sophisticated the animal, the more vulnerable it tends to be. Hit an animal on the head or set fire to it and it will probably be dead, but do the same to a plant or fungus and, given a bit of time, they will flourish again.

The Phanerozoic Eon, 542-0mya (we are still in this Eon today) also saw the move onto land by animals, algae and fungi. Whereas animals and fungi had evolved into sophisticated enough forms to be classified in the Fungi and Animal Kingdoms, plants hadn’t appeared at that stage, there was only algae from the Protista Kingdom (see previous blog). Once on land, plants evolved quickly in order to prevent dessication and make use of the greater access to sunlight; seashores played an important part in this transition due to the shifting back and forth from dry to wet. 200mya was the Age of Reptiles, a time of dinosaurs, and their extinction was followed by the Age of Mammals.

Plant Evolution

Plant Evolution

Note:

• All pictures of plants are symbolic representations only, for example the first orchids were unlikely to have looked like the Phalaenopsis that I have drawn.
• A slightly more accurate, but less clear version of this diagram, with smaller pictures of the plants can be seen by clicking on this thumbnail. The picture of the plant, rather than the writing, marks the time when it is believed to have first appeared.

Plant Evolution

Plant evolution happened, like most evolution, in spurts. The first spurt happened during the Silurian and Devonian Period (Periods are subdivisions of Eons, or to be more accurate, Eons are subdivided into Eras which are further subdivided into Periods which are further divided into Ages or Stages, but not until the Phanerozoic Eon. See thumbnail at end of blog.) and involved two important changes, first, soils were created and second, proto-plants developed a cuticle, a waxy covering that stopped them drying out. These two alterations led to the first plants able to grow on land around 475mya, these were probably small non-vascular plants such as mosses or liverworts, sometimes described as bryophytes. Bryophytes do not have properly formed leaves, roots or stems and were, and are, still very reliant on water, this is why they can only be found growing in moist, often shady areas.

Shortly afterwards, vascular plants evolved, Cooksonia, a plant that no longer exists, was one of these and first appeared around 428mya. Plants in the Division Lycopodiophyta were the first vascular plants that still live now. The vascular system is made up of two tubes that travel to all parts of the plant, these are called the phloem and xylem. The xylem carries water from the roots to all parts of the plant and the phloem transports sugars that are made by photosynthesis in the leaves. This system enabled the plants to grow tall and in fact horsetails were part of the first forests (occurring around 350mya) and grew to 30m tall, nowadays they rarely grow more than 150cm tall. Ferns, horsetails and bryophytes all reproduce by spores, a method that requires water.

The next leap forward was conifers in the Carboniferous Period (299-352mya), these had a more developed vascular system than the ferns, and could, and can, grow in drier areas. They also evolved pollen and seeds, rather than spores. Seeds were useful because they were tougher than spores, able to survive for long periods, and relied less on water. Gnetophytes and Ginkgos evolved in the Permian period (252-298mya). These three divisions (Cycadophyta, Gnetophyta and Ginkgophyta) do not contain many species still in existence. Cycadophyta has only three living families, one of which is Cycadaceae which contains palm-like plants (although palm trees are actually flowering plants and only evolved 90mya). Gnetophyta has only three genera and they are odd looking plants, such as Welwitschia mirabilis. Finally Ginkgo which now has only one species, Ginkgo biloba.

Flowering plants the Angiosperms, did not evolve until the Cretaceous Period about 140mya. In the following 100 million years there was another spurt, monocotyledons evolved and orchids (80mya), lilies (60mya) and grasses (50mya) followed, all of which are monocots. Cacti also evolved around this time, about 30mya.

Note: I haven’t shown humans on either timeline, this is because we are such a recent addition that there is not enough detail on the diagrams to be able to mark our appearance. Both timelines mark out every 50 million years, but the genus Homo only evolved 2 million years ago, and the species Homo sapiens 200,000 thousand years ago. Agriculture probably first occurred 12,000 years ago.

Eons, Eras and Periods

Note: On researching further I realised I had made a few errors in this blog, hopefully they are all now corrected.

Kingdom

The Four Kingdom System

There are four kingdoms found in the Eukaryota Domain, they are Fungi, Plantae, Animalia and Protista. Plants and animals are familiar to most people, although there are specific criteria for each that may not be so familiar and a few very odd exceptions. Fungi were once included with plants, but are now known to be very different, and in some ways more similar to animals. Protista is a bit of a hodge podge as kingdoms go, it is unlikely to last much longer as one kingdom, and indeed many scientists have already rejected it because it doesn’t make much sense in evolutionary terms, however, the reordering is still in flux, so I will include Protista as one kingdom.

A clear to understand website about the Protista Kingdom and one from which I got the photo of Giardia lamblia below. http://www.uic.edu/classes/bios/bios104/mike/bacteria01.htm

A website that talks about a possible Seven Kingdom system http://www.fossilmuseum.net/Tree_of_Life/Domain_Eukaryota.htm

Animal

Drosophila

What makes an animal, an animal? Animals are heterotrophs, they cannot make their own food. They can move, are multicellular and reproduce sexually.

Evolutionary history: The earliest animal fossils that have been found are from sponges, dated 665mya, however, animals may have originated 1000mya. Most animals appeared around 542mya and relations of millipedes are the first animals proved to have made it on land 428mya.

Common examples: Crabs, coral, flies, birds and humans.

Number of phyla and species: 35 phyla, this includes 13 phyla for different worm-like creatures. The most familiar phyla are:

• Chordata  – contains mammals, but also fish and reptiles, about 60,000 species
• Arthropoda  – thought to contain 80% of all living animal species, includes insects, spiders and crustaceans. About a million species have been named, but there are many times that number not yet discovered or classified.

In total it is believed there are between 3 and 30 million species of animal.

Habitats: Polar to desert, temperate to tropical, oceans to mountains.

 

Animal Cell

Cellular and structural description: Animal cells do not have cell walls or chloroplasts and are often a round shape. Animals contain tissues and organs of a complex nature, for example the tympanal organ for hearing in insects and brain tissue in humans.

Abilities and behaviour: Most animals move at some point in their life-cycle, they breathe out carbon dioxide and breathe in oxygen. They eat food for energy – fungi, plants, bacteria, other animals. Most reproduce using sperm and an egg, although some animals are hermaphrodite or reproduce asexually.

Some exceptional animals: Coral are colonies of genetically identical animals that don’t move. Sponges also don’t move and lack true tissues or organs. Green sea slugs use chloroplasts from algae they eat to then photosynthesize like plants. One species of hornet, Vespa orientalis, may derive energy from the sun. (For some other unusual animals see the Odds and Ends of Nature tab)

Plant

What makes a plant, a plant? Plants are autotrophs, producers, they make food (carbohydrate), by photosynthesis. Plants can’t usually move and their reaction to their environment is slow. They are multicellular and have complex organs and tissues.

Evolutionary history: Although plants originated in the sea, unlike animals and fungi, they did not evolve much there. Green algae (a primitive prototype plant and member of the Protist Kingdom) lived in the sea, but in order to make the move to land, where they could access more sunlight for photosynthesis, they needed to adapt to different, drier conditions. The first plant to grow on land was the now extinct Cooksonia (433-393mya), it had a waxy cuticle to stop the leaves drying out and roots to anchor it to the ground and absorb water. From Cooksonia evolved mosses, liverworts and hornworts (475mya), plants with a very basic ability to transport water. Ferns, followed by conifers and finally all flowering plants, evolved later.

Common examples: Sycamore tree, fern, sunflower, moss and box hedge.

Number of phyla and species: 10 divisions, 270,000 species.

• Anthocerotophyta – hornworts
• Marchantiophyta – liverworts
• Bryophyta – mosses
• Lycopodiophyta – club and spike-mosses
• Pteridophyta – ferns and horsetails
• Gnetophyta – 3 extant genera of woody plants
• Cycadophyta – cycads
• Ginkgophyta – Ginkgo
• Pinophyta/Coniferophyta – conifers
• Magnoliophyta – flowering plants

More on Divisions and plant evolutionary history in future blogs.

Habitats: Diverse, just about anywhere with air and sunlight.

 

Plant Cell

Cellular and structural description: Plants cells have cell walls made of cellulose and chloroplasts. They have a very rudimentary circulatory system and the ability to sense their environment, but only simply – they can detect sunlight, but not see images, they can react to touch but it is mostly a slow process. They have organs and tissues, for example, the leaf is an organ and on its surface is photosynthetic tissue.

Abilities and behaviour: Plants are generally rooted in one place and do not move on their own, however they can grow in response to their environment. They give off oxygen and take in carbon dioxide through photosynthesis, a process which uses sunlight to make carbohydrate, which is then broken down by the plant for energy, however it is often consumed by fungi or animals instead. Plants reproduce sexually by fusing egg and sperm, but being unable to move they need different methods to transport the sperm to where the egg is, for example using wind or insects.

Some exceptional plants: Mimosa pudica can move, responding instantly to touch by collapsing its leaves against the stem, this is a defensive measure that hides the leaves from animals that might eat them. Ivy broom rape does not photosynthesize, but parasitizes ivy, growing from its roots in a similar manner to fungi. Some plants trap insects and digest them for nutrients, but not for energy in the way that animals do, these plants often move also, for example Venus Fly Trap. The Socratea exorrhiza is a tree described as being able to walk, but this is not walking in the way an animal would; it involves having above ground roots that move towards the sunlight by growing more roots on one side and allowing those on the shady side of the plant to die, so that in time the plant shifts both over- and underground.

Fungi

Fungus

What makes fungi, fungi? Fungi are heterotrophs, decomposers that cannot make food so they grow on living or dead organisms, breaking them down.

Evolutionary history: The first fungi were in the sea probably dating from 760-1060mya, fungi colonised the land long before animals or plants, probably 542-488mya.

Common examples: Athlete’s foot, coral spot (bright orange dots sometimes seen on leaves), white mushrooms, truffles, penicillin, bread mould.

 

 

Number of phyla and species: 6 phyla (although a seventh has been proposed). They are:

• Chytridiomycota
• Zygomycota
• Ascomycota
• Basidiomycota
• Glomeromycota
• Blastocladiomycota

10,000 species of fungus have been described, but there are thought to be at least a million. Fungi are more varied in the tropics than in areas closer to the North or South pole. For example in Britain and Ireland fungi outnumber plants 6:1, in Southeast Asia the ratio is 33:1.

Habitats: Fungi need plants, animals or other fungi to grow on or with. Most live on land, but a few live in water. Plenty live inside other organisms.

 

Fungal Cell

Cellular and structural description: Fungi have cell walls like plants, but made of chitin, the substance found in the hard exoskeletons of insects, rather than cellulose. The main part of a fungus is the mycelium, small threads that attach to other organisms to obtain food, these mycelium can grow for several km. Most fungi produce fruiting bodies these are what we think of as mushrooms, but are only a fraction of the actual fungus. Fungi have a simpler structure than plants or animals, but the fruiting body is an organ and it is made of tissue.

Abilities and behaviour: Fungi cannot photosynthesize and must consume food, they do this by attaching to other organisms (plants, animals or other fungi) by filaments and then take food from their host – sometimes this is a parasitic relationship, sometimes symbiotic (mutually beneficial, eg the fungi provides a means of extracting nutrients from the soil for its host plant) and sometimes saprophytic (consuming dead material, this is an essential part of the process whereby dead organisms break down, without these fungi the planet would be filled with dead bodies.)

Xanthoria Lichen

Some exceptional fungi: Lichens are composite organisms, made up of fungi and algae working together. The alga can photosynthesize and so provides food for the fungus and the fungus protects the alga from desiccation in harsh environments. Lichens can grow in environments that neither algae or fungi could survive in alone. Along with bryophytes, lichens were probably some of the first organisms on land. Some lichens also contain Cyanobacteria (a bacteria).

Protist

Giardia lamblia

What makes a protist, a protist? Essentially any organism that cannot be classified as a fungi, plant, animal, bacteria or archaea is classified as a protist, most protists are prototype fungi, plants and animals.

Evolutionary history: Algae were probably the first protists to appear, 1600-1700mya.

Common examples: Kelp, amoebas (Protozoa), seaweed, algae, the cause of malaria and sleeping sickness (NB: cyanobacteria are sometimes referred to as blue-green algae, but they are in the

Protozoa

Bacteria Domain), slime molds, diatoms (type of  algae). Volvox is a genus of single celled protists that live in colonies (see Odds and Ends of Nature tab for more about these and slime molds).

Number of phyla and species: 200,000 species. Usually ten phyla, although these often change.

Habitats: Protists live mostly in wet places, the sea, a damp corner, or an animal intestine.

Algae

Cellular and Structural description: Most are unicellular and invisibleto the naked eye. They are more complex than bacteria and have their nuclei wrapped in a membrane, but simpler than other eukaryotes having no specialised tissues, they do, however, have organelles in their cells such as mitochondria and chloroplasts.

Abilities and behaviour: Some protists are autotrophs, some are heterotrophs, some photosynthesize and expire oxygen, others consume and breathe in oxygen. The protists that move do so by a number of means such as pseudopodia or flagella.  Most Protists reproduce asexually, a few reproduce sexually and some alternate between the two.

Some exceptional protists: All protists are exceptions really.

Note: I recently received an email from someone helpfully pointing out that cells have only one Golgi apparatus, rather than the several that I had drawn. I have since altered these diagrams, sorry for the misinformation and thank you to the informer.

Life and Domain

Life –  The Three Domains:

1. Bacteria

2. Archaea

3. Eukaryota – The Four Kingdoms:

1. Fungi

2. Plantae

3. Animalae

4. Protista

Blog notes

MYA = Million years ago

All living things are divided into groups that are subdivided into smaller groups that are subdivided and so on. The Groups (largest first) are:

• Life
• Domain
• Kingdom
• Phyla/ Division
• Class
• Order
• Family
• Genus
• Species

In the Plant Kingdom, phyla are referred to as divisions (also in the Fungus Kingdom sometimes) and with plants, species are further split into varieties (naturally occurring changes) and cultivars (specially bred changes). An organism’s Latin name is made up of its genus and species, for example Helianthus annuus (a sunflower) is in the genus Helianthus and is of the species annuus.

In order to write a blog that doesn’t stretch on forever, I have chosen a specific classification system, The Three Domain System, there are others and there are constant changes within those systems arising from scientific discovery. Scientists (and humans in general) attempt to make clear distinctions between one group of organisms and another, but evolution is a slow, gradual, complex process and any classification system we impose on nature will be a simplification. I have found it is necessary to be aware of this when trying to learn about classification, because the closer I looked, the more jumbled it became.

The Definition of Life

The differences between a living thing and a non-living thing may seem obvious, but Life has specific criteria. A living organism is one that possesses the capacity to grow, respond to stimuli and reproduce, they also have the ability to regulate their internal environment (homeostasis), and are made up of cells.

The Virus Dispute: There has been some debate as to whether viruses can be classified as living or not – they are not made up of cells, but are just strips of  DNA; they can reproduce, but only by inserting themselves into the cells of other organisms that then carry out the replication process for them. When humans get a cold it is the result of a strip of virus DNA getting into our cells and using the ability of those cells to replicate its DNA and multiply.

Three Domains

There are three domains, two of which consist of microscopic, simple cells that can’t reproduce sexually, Archaea and Bacteria (prokaryotes) and then the third domain (Eukaryota) contains everything else, from mushrooms to mould to antelopes to humans to oak trees. At first glance, this seems odd, surely the differences between Archaea and Bacteria are small, yet the variety within the Eukaryota Domain is enormous? However, it is the smallness of the differences that is important; while the shapes and behaviour of organisms made of eukaryotic cells is varied and even the cells differ from one kingdom to another, the amino acids, the building blocks of DNA, are the same. However, within the Bacteria and Archaea Domains, these building blocks are different and that is such a fundamental change that the two groups cannot be classified together.

Archaea

• What makes archaea, archaea? They are microscopic and single celled, with DNA not contained within a nucleus, same as for the Bacteria Domain, however they are genetically distinct from Bacteria, and their amino acids and chemical components are different.
• Evolutionary history: Thought to first have evolved 3800mya and some of those archaea species probably still exist now. Their ability to survive extreme conditions is part of what places them at the start of life, when temperatures were high, oxygen was low and most gases were toxic. Archaea have changed little throughout their existence because they reproduce asexually, this means there is no mixing of DNA, changes can only occur due to mutation and so there is little natural selection. Archaea is believed to be an older Domain than Bacteria, however it is thought that Eukaryotes evolved from Archaea rather than Bacteria, because Eukaryotes and Archaea have more genes in common.
• Number of phyla and species: 5-23, less than 9000 species have been classified for both Archaea and Bacteria, but many, many more exist.
• Habitats: Can survive extremes of temperature, acidity and salinity, or without oxygen (most are anaerobic), as well as less diverse environments such as soil and seas. Examples of habitats are salt lakes, hot springs, oceans and the human colon.
• Cellular description: Consist of a cell membrane, cytoplasm, some DNA and a cell wall, no nucleus
• Shapes and sizes: Quite similar in size to bacteria, microscopic, unicellular with various different shapes. However, one Archaea genus has square shaped cells, which is not seen in any other Domain.
• Abilities and behaviour: Their basic actions are consuming (or absorbing), growing and dividing. Rarely parasitic (one parasitic example may have been found), they either work in harmony with other organisms (some archaea in animals aid digestion) or within them, but without affecting them. They reproduce asexually or by fission. This means offspring have identical genetic code to parent. Archaea use a great variety of different energy sources such as sugar, gases and sunlight. Many archaea can move using various different methods such as flagellum tails.

Bacteria

• What makes bacteria, bacteria? They are single celled with DNA not contained within a nucleus, same as for the Archaea Domain, however they are genetically distinct from archaea and and their amino acids and chemical components are different.
• Evolutionary history – Thought to have evolved after archaea, not known exactly when, but probably before 3500mya.
• Common examples Include cyanobacteria which photosynthesise, but not in the same way plants do (ie they do not have chloroplasts). Cholera and Bubonic Plague. Stromatolites.
• Number of phyla and species – 29-52, less than 9000 species classified for both Archaea and Bacteria, but many, many more exist.
• Habitats – soil, water, inside other organisms. Usually in less extreme environments than archaea.
• Cellular description Consist of a cell membrane, cytoplasm, some DNA and a cell wall, no nucleus. .
• Shapes and sizes – A few micrometres long, a tenth the size of a eukaryotic cell (although there are some exceptions, some are even visible to the naked eye). Many shapes including spirals and spiky shapes, although most are round or rod shaped. There are approximately five nonillion bacteria and archaea on Earth, many more than Organisms in the Eukaryota Domain, however, bacteria and archaea are so small, the biomass is thought to be similar. There are ten times as many bacteria cells as human cells in the human body.
• Abilities and behaviour – Their basic actions are consuming, growing and dividing. Parasitic or symbiotic, they can be damaging to their host. They reproduce asexually or by fission, some make endospores – these are reproductive bodies, a little like seeds, but with no genetic variation. Bacteria use a great variety of different energy sources such as sugar, gases (including ammonia) and sunlight. Many bacteria can move using various different methods such as flagellum tails.

 Eukaryota

*

• What makes eukaryotes, eukaryotes? Their cells have a nucleus which contains the DNA. Most cells also contain organelles and many eukaryotes are multicellular complex organisms.
• Evolutionary history – Thought to have evolved from Archaea at some point between 1600-2100mya.
• Common examples – Monkeys, roses, toadstools, dragonflies, slime molds and humans.
• Number of kingdoms, phyla and species – Contains four different kingdoms – Plant, Fungi, Animal and Protist. About sixty phyla in total and several million species.
• Habitats – Varied, although not quite to the extent that Archaea is. Deserts to the poles, deep sea to mountain tops, all contain some kind of Eukaryota.
• Cellular description – Have a nucleus (the DNA contained in a membrane) and organelles, such as mitochondria or chloroplasts
• Shapes and sizes – Pretty much any shape or size from Honey Fungus, one of the largest organisms in the world, to amoeba. Although there are far fewer Eukaryotes than there are Archaea or Bacteria, the much larger size of Eukaryotes mean that their biomass is thought to be about the same.
• Abilities and behaviour – Again, massive variety, some move (animals) some don’t (plants), some are big and complex, some are small and simple. All are capable of sexual reproduction, which is important because it explains the diversity – sexual reproduction leads to a mixing of DNA, which leads to genetic variation and evolution.

*Note: Picture of Protist above is from

http://www.uic.edu/classes/bios/bios104/mike/bacteria01.htm

 Table Comparing Domains

	Bacteria	Archaea	Eukaryota
No of species	Less than 9000 archea and bacteria classified, no idea how many	See left	Several million
No of phyla	29-52	5-23	60
First arrived in	3500mya	3800mya	1600-2100mya
Reproduction	asexual	asexual	Sexual and asexual
Can move?	Yes, many can move via different means – eg flagella	Same as Bacteria	Mixed (animals can and some protists)
Make food (photosynthesize)	Mixed	None photosynthesize, some use sunlight	Mixed (plants can, some protists)