Kingdom Monera
The smallest and most common microorganisms are prokaryotes, which are unicellular
organisms that lack a nucleus but have a cell wall.
Prokaryotes are heterotrophs – they must obtain their energy
by consuming other organisms. Bacteria can move using
flagella while others will use cilia.
Prokaryotes release energy by both cellular respiration
and fermentation. They perform gas exchange (take in
oxygen and gets rid of carbon dioxide waste) through
diffusion across their cell
membrane. This is also how
bacteria get rid of wastes.
When a bacterium has grown so that it has nearly
doubled in size, it makes a copy of its DNA and divides in
half, producing two identical “daughter” cells. This type of
asexual reproduction is called binary fission.
Bacteria are vital to maintaining the living world.
Some bacteria are decomposers that break down dead
matter. Some soil bacteria convert natural nitrogen gas
into a form plants can use through a process called
nitrogen fixation.
Kingdom Protista
The kingdom Protista is a diverse group. Protists are eukaryotes that are not members
of the kingdoms plantae, animalia, or fungi. Most protists are unicellular. The first eukaryotic
organisms on Earth were protists. Protists can reproduce sexually or asexually and will grow
throughout their lifespan using the process of mitosis.
Because protists are such a diverse group,
scientists don’t always agree on how to classify them.
One way to classify protists is according to the way
they move. Some protists will use flagella (tail that whips
around to allow the organism to move), pseudopods
(“false foot” – projections of cytoplasm), or cilia (short
hair-like projections similar to flagella) to move and
feed. Another interesting structure is called the eyespot.
This is a special organelle that allows the protists to
sense light
and either
move toward or away from it depending on the
needs of the organism.
Some protists cause serious disease.
Plasmodium causes malaria. Trypanosoma
causes African sleeping sickness. Trichonympha
lives within the digestive system of termites and
helps termites digest wood.
Some plant-like protists are commonly
called algae. Algae are unique because they contain photosynthetic pigments and can
make their own food (autotrophs). Other protists are heterotrophs and absorb or digest their
own food. Protists will transport important molecules and gases across their membranes by
diffusion. They also have a special structure called a contractile vacuole that allows them to
get rid of excess water. In order to get rid of wastes, some protists have an anal pore –
essentially a microscopic anus.
Kingdom Fungi
Fungi are eukaryotic heterotrophs that have cell walls. The cell walls of fungi are made
up of chitin, a complex carbohydrate. Fungi do not ingest their food, as animals do. Instead,
fungi digest food outside their bodies and then absorb it. Many fungi feed by absorbing
nutrients from decaying matter. Some fungi are parasites.
All fungi except for yeasts are
multicellular. Most fungi reproduce
both sexually and asexually. Asexual
reproduction can occur when cells
break off and begin to grow on their
own. Some fungi also produce spores.
Spores of fungi are found in almost
every environment. Many fungi
produce dry, almost weightless spores
that are easily scattered in the wind.
Sexual reproduction in fungi usually
involves two different mating types.
All fungi are heterotrophs. Many are decomposers, some are parasites, and others live
in symbiosis with other species. Fungi play an essential role in maintaining equilibrium in nearly
every ecosystem. They do this by recycling nutrients as they break down the bodies and
wastes of other organisms. Fungi will transport important molecules and gases across their
membranes by diffusion. Much like plants and animals, fungi will regulate themselves through
the use of simple hormones to signal events such as growth which is done through mitosis.
Kingdom Plantae
Plants provide the base for food chains on land. They also provide shade, shelter, and
oxygen for animals. Plants are multicellular organisms with cell walls made of cellulose. They
make their own food in the process of photosynthesis using green pigments.
In order to survive, all plants need sunlight,
water, minerals, oxygen, carbon dioxide, and a way
to move water and nutrients to their cells. Excess
water is lost through a process known as
transpiration. The water simply evaporates away!
There are special holes on the underside of leaves
called stomata. This is where the water evaporates
from. This is also where CO2 ENTERS the plant and
where O2 LEAVES the plant (remember
photosynthesis!).
There are four different plant groups based
on their water-carrying tissues, seeds, and flowers.
Mosses: Mosses and their relatives do not have tubes to move
water and nutrients through the plant. Water simply moves from cell
to cell by osmosis. These types of plants reproduce sexually and
asexually. They can produce sperm that swim through water to
fertilize egg cells. This is why mosses must live in moist and wet
environments.
Ferns: Ferns and their relatives were the first plants to have
special tissues that carry water and food throughout a plant. These
tissues are called vascular tissues and there are two types: Xylem
and Phloem. Xylem moves water from the roots to all areas of the
plant. Phloem carries nutrients and food throughout the plant.
These plants have leaves to make food through photosynthesis,
roots to absorb water and minerals, and s tems to support and
connect the plant. Ferns and their relatives can reproduce sexually
(with sperm and egg cells) or asexually (using spores).
Gymnosperms: cone-bearing plants. Think of the pine
cones outside on the ground. These cones produce seeds
directly on the surface of cones. The cone does not cover the
seeds. This is why gymnosperms are called “naked seed plants”.
These plants reproduce sexually using pollen (plant sperm) and
female reproductive structures in the plant. Pollen can be carried
by the wind, birds, mammals, or insects. This process is called
pollination. They create a zygote (fertilized egg) that is protected
by a seed.
Angiosperms: flowering plants. Flowers attract animals which carry
pollen from flower to flower. This is a more efficient way of pollination than
the wind pollination of most gymnosperms. The seeds of angiosperms are
not naked like in gymnosperms, instead, they are protected by a fruit. We
(humans) often eat this fruit – think about how apples and oranges have
seeds at their core. That’s because the fruit is protected those precious
seeds!
Kingdom Animalia
Animals are multicellular, eukaryotic heterotrophs whose cells lack cell walls. The
bodies of most animals contain tissues. Invertebrates are animals that do not have a
backbone, or vertebral column. Vertebrates are animals that do have a backbone.
Animals that reproduce sexually begin life as zygotes after a sperm fertilizes an egg.
They can produce zygotes through either internal or external
fertilization. This means that some animals fertilize the eggs outside
of the female’s body (external) and some animals fertilize the eggs
inside of the female’s body (internal).
Mammals are special types of animals that have hair and
mammary glands (produce milk in females to nourish the young).
Marsupials are mammals that give birth to live young that complete
their development in an external pouch on their mother. Placental
mammals are the most familiar. They are named for the placenta –
an internal structure that allows nutrients, oxygen, carbon dioxide, and wastes to pass
between the embryo and the mother.
Animals have either an open circulatory system or a closed
circulatory system. The circulatory system is the transport system
throughout their body. Animals with closed circulatory systems pump
blood through blood vessels (arteries and veins). Animals with open
circulatory systems pump blood through blood vessels and sinuses in
their body – open areas without blood vessels.
All cells of animals require a
constant supply of oxygen and
nutrients and cells must also
remove wastes. Some animals can
perform gas exchange (bring in
oxygen and get rid of carbon dioxide waste) through
lungs, their skin, or gills. To get rid of wastes, animals
have an anus at the end of their digestive system to
get rid of solid food waste.
Some animals such as frogs and some
insects (butterflies and beetles) undergo a
process called metamorphosis. This process
allows them to grow and change throughout
their lifetime.
In order to regulate their bodies, most
animals have hormones (chemical messengers)
and nervous systems (brain & nerves) to keep
their bodies working properly. Some animals are
able to control their own body temperature by
themselves and they are called endotherms
(humans are endotherms!). Other animals
cannot directly control their body temperature
and they are called ectotherms (reptiles like
snakes and lizards are good examples). They
must lie in the sun to warm up or go into the shade to cool down.