1. List the environmental conditions needed to sustain life
2. Contrast the different types of living organisms based on their cellular structure and the way
they acquire energy and nutrients
3. Classify marine organisms based on their habitat and lifestyle.
WHY DO WE NEED C, N, P, H2O?
Carbon, Nitrogen, Phosphate and Water are all essential nutrients for all living cells on the planet, they
are the building blocks of the cells such as proteins and lipids, etc. but they are needed to build the DNA
Living organisms need two things – a source of energy and a source of raw materials to build living
tissues and skeletons or shells. Life on Earth is water based, but in addition to this, organisms need a
wide range of other elements. Besides carbon and water – the top two are nitrogen and phosphorus.
- Nitrogen is needed to produce proteins
- Phosphorus is a major constituent of DNA.
Other elements are essential – but in trace amounts. Many metals for example are constituents of
important enzymes that regulate a wide range of body functions such as respiration, digestion, growth,
etc. Once these basic needs are met, then an organism is able to:
- Grow and maintain itself for a period of time
- Reproduce to perpetuate its species
- Mutate to evolve into better adapted life forms.
Maintaining life on Earth also requires efficient recycling of dead organisms and the waste produced by
living organisms to regenerate the raw materials and keep the life support system on the planet
sustainable. Water isn’t just an essential ingredient; it is also an essential medium to bring reacting
chemicals together. Liquid water can only exist under restricted conditions of temperature and pressure
thus is a relative commodity in the universe and so it determines whether or not a planet can harbour
life as we know it.
There is a lot of water on Earth and life is very versatile and diverse, as a result there is a large number
of species living continuously. Although most of them are very small – roughly 99% of all species are
smaller than bees. Also, many species that have existed on Earth have gone Extinct as such is the
eventually path of all life on Earth.
THE LINNAEAN CLASSIFICATION SYSTEM: Since life on Earth is so diverse, we have a classification system that groups living organisms into
categories according to their similarities. These similarities are called Taxonomic Categories. The most
widely used mode of classification is based on the work of a Swedish botanist, Karl von Linné.
- The highest category in the Linnean Classification System is the kingdom. There are five
kingdoms, Monera, Protista, Fungi, Planta (Metaphyta), and Animalia (Metazoa). The organisms
in each kingdom are different on the basis of their structural organization and their method of
o Structural organisation: all living organisms consist of cells; some organisms consist of
just on cell (bacteria) whereas others consist of many cells with distinct functions
▪ There are two types of cells. Prokaryotes and Eukaryotes.
• Prokaryote cells evolved first. They have a simpler and more primitive
o Membrane (cell wall) that separates the inside and outside of
o The material inside the cell wall is the cytoplasm in which all the
molecules needed for the cell function are dispersed.
• Eukaryote cells evolved later and are more structured.
o They have a LARGE nucleus consisting of a membrane enclosing
the DNA which contains the genetic instructions for the
development and functioning of the cell (the lack of a distinct
nucleus is one of the main characteristics of the prokaryote
o The cytoplasm also contains cell organelles
o Method of nutrition: there are two basis methods modes: autotrophy and heterotrophy
▪ Autotrophs are organisms able to synthesize their food. They produce organic
matter from inorganic molecules such as CO 2 nitrate, phosphate, etc. that is
obtained from their environment.
• They need energy to complete this task:
o If they use energy derived from light, they are photoautotroph
o If they use energy derived from chemical reactions, they are
called Chemoautotrophs. NOTE THAT NO EUKARYOTE CELLS
▪ Heterotrophs are organisms unable to synthesize their own good and they need
to ingest or absorb organic matter produced by other organism.
• Heterotrophs oxidize the ingested organic matter during respiration to
produce the energy that they need.
• Heterotrophs can either be herbivores, carnivores, and decomposers.
The kingdom of Monera consists of single cell prokaryotes. This kingdom includes all organism made of
primitive prokaryote cells. The method of nutrition within this kingdom is diverse. Some monera are
autotrophs while others are heterotrophs. In this kingdom, you’d find all bacteria and blue-green algae.
2 The kingdom of Protisa consists mostly of single celled organisms, but the cells are eukaryotes. There are
a few examples of colonial members – all the cells are the same and have similar generalized functions,
whereas in truly multicellular species, the body of the organism consists of a variety of types of cells.
Humans for example are multicellular – the cells in the brain and the cells in the liver have different
functions. Examples of Protisa include Protozoa (heterotrophs) which are animal like single cell
organisms such as amoebas and ciliates. Microalgae (photoautotrophs) which are plant like single cell
organisms such as diatoms, dinoflagellates.
The kingdom of Fungi consists mostly of multicellular organisms. There are all heterotrophs – some
examples being mushrooms, molds, yeast, mildew. Organisms belonging to the kingdom of Fungi play an
important role in the decomposition of dead organic matter and the recycling of nutrients in terrestrial
The kingdom of Plantae/metaphyta consists uniquely of multicellular organisms made up eukaryotic
cells that are all photoautotrophs. Another characteristics of the organisms belonging to the kingdom is
that they do not have their own means of locomotion – examples include: mosses, ferns, trees,
flowering plants, etc. which mostly grow on land and account for about half the organic matter
produced by photosynthesis.
The kingdom of Animalia/Metazoa includes all multicellular, eukaryotic, heterotroph cells that have
their own means of locomotion. This kingdom includes organisms ranging from insects, frogs, lizards,
Photoautotrophs are found in three of the five kingdoms: Plantae (Metaphyta), Protisa, and Monera.
Single celled photoautotrophs belong to either the kingdom of Protisa or Monera, whereas multicellular
photoautotrophs mostly belong to the kingdom of metaphyta (trees) although seaweed are multicellular
The division that occurs after a kingdom is as such, we will do the example for humans.
- Kingdom: Animalia – we consist of eukaryotic cells, are multicellular and heterootropic
o Phylum: Chordata – all animals with a notochord (supporting rod running most of the
length of animals, in our case, the spinal cord)
▪ Class: Mammalia – we have mammary glands, are warm-blooded, bear life
• Order: Primates – we have colar bones, eyes facing forward, grasping
hands with fingers, two types of teeth, incisions and molars.
o Family: Hominidae - we have an upright posture, large brain,
stereoscopic vision, a flat face, hands and feet with different
▪ Genus: Homo: we have a s-curved spine.
• Species: Homo sapiens – high foreheads, well-
developed chins, thin skull bones.
3 Recently, we’ve sequenced the genetic code of many organism and thus have a basis for refining the
classification of organisms on Earth. Based on similarities and differences of the geneti codes between
organisms, the kingdom of Monera has been divided into two separate domains:
- The domain of the bacteria
- The domain of the archaea
Although both groups contain prokaryotic cells, the genetic sequencing seems to suggest that they
evolved independently from an ancient common ancestor very early in the evolution of life as they are
very different. On the other hand, the genetic codes of all organism made up eukaryotes cells are much
closer, hence grouping them into one single domain.
- Based on the similarities and differences of the genetic codes between organisms, we can draw
a tree with three main branches or domains: Bacteria, Archaea, Eucarya.
o The three domains emerge and branch from a common ancestor to all living organisms
on Earth. Organisms that have arisen from it are placed at the ends of the tree’s
branches – each node on each branch represents the most recent common ancestor of
the descendants. The distance of one group from the other groups indicates the degree
o All these different organisms are not living in isolation but interact with each other:
▪ Some feed on others, producing food chains or food webs.
▪ They compete for resources and living space within the environment
o They also interact with and modify their physical surroundings, forming the
▪ We distinguish a large number of ecosystems on land and in the ocean
The surface of the continents can be broadly divided between different ecosystems, which we also
sometimes call biomes such as rain forests, coniferous forests, deserts, tundra’s, grasslands, etc.
- From space, you can see that on land, there are lush rain forests and dry deserts. The oceans are
blue water and the productive regions indicating high concentrations of marine plankton.
o This colour depends on the amount of chlorophyll present (chlorophyll is the green
pigment that plants use to capture energy from the sun)
o Blue = low chlorophyll concentration
o The different regions – even in the ocean – are characterized by different ecosystems.
- On land, photoautotrophs are mainly multicellular organisms part of the metaphyta kingdom,
on the sea photoautotrophs are mostly single cell organism belonging to the kingdom of protisa
are called phytoplankton.
Plankton involves small organisms drifting in surface water. Phytoplankton are plant-like whereas
zooplankton is animal life. Marine phytoplankton contribute about half the organic carbon produced by
photosynthesis on Earth.
4 - Blue-green algae are important contributors to marine plankton in large areas of the ocean
- Copepods are tiny shrimp-like organism, are also common members of marine plankton are also
common members of marine plankton (they belong to the kingdom of Animalia).
In the productive waters in the Southern Ocean, phytoplankton is dominated by relatively large chain-
forming diatoms. These relatively large phytoplankton cells support relatively large zooplankton which
directly feed fish, mammals and birds resulting in relatively short food chain. In contrast to this, in low
productivity regions phytoplankton is dominated by very small flagellates and cyanobacteria which can
only be eaten by small micro zooplankton species which then feed larger zooplankton, thus supporting
longer and more complex food chain which ends up with large predatory fishes.
- The pelagic province is the water column environment, the benthic province is the seafloor
- Phytoplankton can only grow in the presence of light and light can only penetrate a few tens of
meters in the water column. As a result, the ocean is subdivided into two groups based upon the
depth of light penetration:
o Photic zone which occupies the depth range where light penetration is sufficient for
photosynthesis. It extends from the atmosphere-water interface downwards to a depth
where light intensity falls to 1% of that at the surface. THIS is where phytoplankton
▪ The depth of this zone varies about 10m on the shelf to about 100m in the open
ocean depending on the clarity of the water.
o The aphotic zone which is situated below and receives essentially no light because is all
absorbed by the water above.
o Since the mean water depth is 5000m, most of the water is aphotic and the euphotic
zone only included a small fraction of the total volume of the ocean.
Organisms living in the sea can also be classified based on lifestyle.
1. Plankton are the organisms which float and drift freely in the water with the currents. They
sometimes have limited swimming ability.
a. They are divided into phytoplankton and zooplankton
2. Nekton are active swimmers that can move independently of ocean currents. They include fish,
reptiles, mammals, birds and others.
3. Benthos are the organisms which live on the surface or within bottom sediments. Organisms
living on the surface of sediment are called epibenthic and animals living without sediment are
called infauna. Benthic plants need light and thus are restricted to sediment shallow enough to
within the photic zone.
1. Explain how organisms interact with each other to create food webs and sustainable ecosystems
2. Describe the chemical transformations that occur during photosynthesis, chemosynthesis,
nitrogen fixation and respiration
3. Contrast food chains and trophic pyramids in different ecosystems
5 Organisms do not live in isolation but interact with each other and their environment to form
ecosystems and any ecosystem can be represented using a diagram. Energy is continuously added and
dissipated – the energy for nearly all ecosystems on Earth is provided by the sun and dissipates into the
environment as heat produced by the metabolism and movement of organisms. Materials are routinely
recycled in food webs/chains.
- Plants produce organic matter from inorganic nutrients by photosynthesis
- Plants are eaten by herbivores
- Herbivores are eaten by carnivores
- All of these are decomposed after their death by decompress. As a result of this, carbon and
inorganic nutrients are regenerated and released back into the environment.
- Regenerated carbon and nutrients are then again taken up by the plants to start the cycle over
Step one in the food chain is done by the autotrophs (organisms able to produce organic matter from
inorganic chemical found in the environment). Due to this, they are called “primary producers”. These
organisms need energy to produce the organic matter though, if their energy comes from the sunlight,
they are called photoautotrophs; if it comes from exothermic chemical reactions they care called
- Photosynthesis converts solar energy into chemical energy stored in the chemical bonds of
organic matter. 6 molecules of CO are forced to combine with 6 molecules with 6 molecules of
water to produce one molecule of organic matter called carbohydrate. 6 molecules of O are 2
also creates as a by-product of this process.
o Not just carbohydrates, there are other things such as proteins, molecules containing
nitrogen and DNA containing phosphorus. So plants take these molecules in to meet
their needs in N and P.
- Chemoautotrophs are bacteria or archaea that are found in environment such as deep seat
vents, sediments, mid, hot springs, etc. for most ecosystems the external source of energy is
sunlight and the primary producers are photoautotrophs.
Since plants are found on land and sea – some of the phytoplankton that is found in the sea, dubbed
cyanobacteria, is particular important because they are the most numerous organisms on earth and
account for half the total primary production in the marine environment.
- Many phytoplankton species also produce biominerals – the two most common ones being
calcium carbonate and silica (opal). To produce these biominerals, the phytoplankton must also
take up dissolved calcium ions (Ca ) to make calcium carbonat