Chapter 3: Multicellular Diversity
From Algae to Terrestrial Plants
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ALGAE: are unicellular or multicellular photosynthetic, aquatic protists.
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Multicellular algae are called seaweed.
They are classified into three phyla based on their colour: brown, red, or green.
A) Brown Algae (Phylum Phaeophyta)
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Are the largest and most complex protists.
They are abundant and key components of marine and tidal environments.
Some species of kelp can grow to be 60 meters in height, and can form underwater forests.
They provide shelter for over 800 marine species of animals, plants, and protists.
Brown algae do not have true leaves or roots. They have specialized tissues. These tissues
anchor the algae to a rock or other hard structure (called a holdfast). Then, a long, stem-like
structure (called a stipe) extends from the holdfast. Finally, the stipe grow flat, leaf-like blades
that are used to collect light, take in carbon dioxide, and give off oxygen.
B) Red Algae (Phylum Rhodphyta)
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Red algae appear to have been the first multicellular organisms on Earth (over 1.2 billion years
ago!).
There are about 6000 living species of red algae.
It can grow to a meter in length.
It is most abundant in the warm coastal waters of tropical oceans.
Red algae have chlorophyll. They also have an additional pigment, called phycoerythrin. This
pigment is sensitive to light waves that reach greater ocean depths.
Red algae are commonly used as a food in the food-processing industry. Nori (the seaweed
used to wrap suchi). As well, carrageenan (a gel-like substance) is used to help ingredients stay
mixed together; it is often used in milkshakes and ice cream.
C) Green Algae (Phylum Chlorophyta)
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Most green algae are aquatic. Most are commonly found in fresh water.
They can also be found in other ecosystems, including sea ice, attached to the surface of trees,
or even in the fur of sloths (a mammal found in tropical rainforests).
Green algae are structurally diverse.
Green algae are the most plant-like of the algae. They have the same type of chlorophyll and
the same colour as most land plants. As well, their cell walls contain cellulose, and store food
reserves in the form of starch.
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Brown Algae
Red Algae
Green Algae
The Shift to Land
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PLANTS are multicellular photosynthetic eukaryotes with cellulose-based cell walls.
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The hypothesis that green algae are the closest evolutionary relatives of a land plant is based on several
structures within the cell.
o Plants and green algae have chlorophylls a and b in their cells.
o Plants and green algae have cellulose cells walls.
o Plants and green algae store food energy in the form of starch (whereas bacteria, fungi , and animals
store food as glycogen).
o Analysis of the DNA of plants and green algae show similar sequences.
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However, despite the similarities to green algae, plants have some important distinctions.
o One key distinction is the environment – the move from aquatic to terrestrial ecosystems.
o Plants reproduce using EMBRYOS (an organism’s early pre-birth stage of development).
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Vascular plants have two types of vascular tissue: xylem and phloem.
o Xylem carries water and minerals from the roots to the rest of the plant. Water only moves upward
through the xylem. Xylem consists of dead tube-shaped cells that contain a tough material called lignin.
o Phloem tissue is made of living cells that are also arranged in tubular form. It is used for transporting
larger molecules, including sugars. Sugar molecules move in any direction through the phloem.
o Vascular tissue allowed for the evolution of roots. Roots provide strong anchoring ability and cells
specializing in absorbing and transporting water and minerals.
o Leaves increased the surface area of the plant above ground. Leaves allow for a better exchange of
gases in photosynthesis, and a larger surface for capturing sunlight.
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Plants and some green algae use SPORIC REPRODUCTION which is sexual reproduction that alternates
between a gamete-making individual and a spore-making individual. This is also known as alternation of
generations. This means that are 2 multicellular stages in the life cycle of plants.
o The haploid version of the organism, called the GAMETOPHYTE, is the haploid plant in sporic
reproduction that produces gametes by mitosis. The haploid cells contains only 1 set of chromosomes.
o When the gametes fuse, they develop into the diploid version of the organism, called the SPOROPHYTE
(the diploid plant in sporic reproduction that produces spores by meiosis). A dipoid cell contains 2 sets
of chromosomes. The sporophyte produces spores, by meiosis, which develops into the haploid
gametophyte.
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THE PLANT KINGDOM
1) Non-Vascular Plants: Bryophytes
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BRYOPHYTE is a small, non-vascular land plant. It includes 3 phyla of plants: mosses, liverworts, and
hornworts.
These plants do not have vascular tissue, and they are dependent on the processes of diffusion and osmosis to
transport nutrients.
They tend to grow in mats of low, tangled vegetation that can hold water like a sponge. This allows them to
survive cold and dry periods.
They do not have any roots. Instead, they have small root-like structures called rhizoids, which develop from
their lower surfaces.
Bryophyte
Mosses
Description
-Has short, vertical stems with leaf-like
structures that are usually only one cell thick.
-Can grow in bogs, tundra, and shaded areas.
-Are the 2nd most diverse group of plants.
Importance
-Sphagnum moss is an important biomass in the
bogs of boreal Canada. The peat that is
harvested from the bogs is used in gardens.
-Some Aboriginal people use Sphagnum moss to
make diapers, to mark trails, and as a cleaning
agent.
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Liverworts
-Appear as leafy steams, or as small, flattened
blades that are typically one cell thick.
-Grow more horizontally than vertically.
-Most grow in moist, shady places on rocks,
trees, rotten wood, and soil.
-Help reduce soil erosion.
-Serve as food for animals.
-Are useful as a study organism in the evolution
of plants, since their DNA suggests that they are
the land plants most like green algae.
Hornworts
-Similar to liverworts, but they have just one
chloroplast per cell.
-The sporophyte grows out of the
gametophyte as a long horn-like extension.
-Lives on tree trunks, riverbanks, and other
damp locations.
-They play an important role in nutrient cycling
within ecosystems.
-They have small diversity – only about 100
species.
-Have pharmaceutical potential.
2) Seedless Vascular Plants
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They developed the vascular tissue that allows them to grow tall, but the sporophyte generation is the
dominant stage in their life cycle.
Their gametophytes are reduced to tiny, short-lived structures that still depend on moisture to carry out
sexual reproduction.
Seedless vascular plants include: whisk ferns, club mosses, horsetails, and ferns.
Ferns are the most popular, and are common inhabitants of the floor of temperate forests throughout
Canada.
Seedless Vascular
Plants
Whisk Ferns
Club Mosses
Horsetails
Key Features
-Grow in moist, tropical environments.
-Do not have leaves or roots
-Photosynthesis is carried out in the stem.
-Produce spores that are dispersed by wind.
-Only 3 known species.
-Common in moist, woodland environments – mainly tropical environments.
-Have small, needle-like leaves
-Produce wind-dispersed spores that form in compact clusters of leaves at the end of the
steam.
-About 100 species.
-They are the oldest group of vascular plants.
-Common in moist tropical and temperate environments.
-Have hollow stems with scale-like leaves that grow from nodes along the stems.
-The ends of their stems produce spores.
-About 50 species.
-Commonly called scouring rushes because the tough, rigid stems are abrasive (making
them useful for scrubbing pots and polishing wood).
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Ferns
-Common in warm, moist environments; but also inhabit cooler, drier habitats.
-Have root stems, and leaves. The leaves are quite prominent in many species.
-There are approximately 10,000 species worldwide.
-Used extensively by florists and gardeners as an ornamental plant.
3) Seed-Producing Vascular Plants: Gymnosperms and Angiosperms
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There are 2 groups of plants that disperse by means of seeds: gymnosperms and angiosperms.
Seeds allow plants to reproduce sexually without needing water. As well, seeds provide protection against harsh
environmental conditions.
GYMNOSPERMS: A vascular plants with non-enclosed seeds
o Gymnosperm Diversity:
o Gymnosperms have seeds that are exposed on the surface of cone scales.
o This group includes cone-bearing trees (conifers) such as pines, firs, yew, spruce, cedars, and
redwood.
o In Canada (in cool boreal and alpine ecosystems) conifers are often the dominant woody
vegetation.
o Most are evergreen, which allows them to photosynthesize whenever conditions are suitable.
o Gymnosperm Reproduction: Cones and Pollen
o Conifer reproductive structures are called CONES (a gymnosperm structure that contains male
or female reproductive parts).
o Male cones are soft and short-lived. Female cones are hard and long-lasting. The female cones
are made up of scales on which the eggs develop.
o Sexual reproduction in seed plants requires the transport of sperm from the male cone to the
unfertilized eggs in the female cones. For this to occur, seed plants use pollen grains.
o Pollen grains are tiny, reduced gametophytes that do not form a free-living plant.
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ANGIOSPERMS: A vascular plant with seeds enclosed in protective tissue.
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Angiosperm Diversity:
o Angiosperms are commonly known as flowering plants. They are vascular seed plants.
o They reproduce using flowers, and their seeds are contained in a fruit.
o This group includes flowers such as roses and trilliums; to grasses and trees such as, oaks,
maples, and birches.
o About 90% of all plants are angiosperms, meaning there are more than 250 000 species of
angiosperms on Earth.
Angiosperm Characteristics:
o The FLOWER is a collection of structures in angiosperms used for sexual reproduction.
o The male gametophyte in a flowering plant is a pollen grain containing sperm nuclei.
o They use wind to transport pollen.
o Other species with large and colourful flowers have features, such as attractive odours, to
attract animal visitors that will transport the pollen.
o Few angiosperms have separate male and female plants. However, it is more common for
individual flowering plants to be both male and female. These plants have flowers that are both
male and female. Example) The Lily
Angiosperm Classification
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Angiosperms are typically divided into 2 main groups based on a structure called a seed leaf or cotyledon.
A COTYLEDON is a structure in the embryo that helps to nourish the plants as it first starts to grow.
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Angiosperms that have 1 cotyledon are called MONOCOTS. Examples) corn, orchids, and onions.
o Monocots tend to have flowers and fruits that are divided into 3’s (or multiples of 3’s).
o Monocot leaves usually have parallel veins.
Angiosperms that have 2 cotyledons are called DICOTS. Examples) dandelions, crap apples, and maple trees.
o Dicots usually have flowers and fruit parts in 4’s or 5’s.
o Dicot leaves tend to be in a netted pattern.
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THE FUNGUS KINGDOM
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FUNGI are stationary, heterotrophic eukaryotic organisms whose cell walls contain chitin. They feed by
releasing digestive enzymes into their surroundings, and then absorbing the digested nutrients into their cells.
There are more than 100 000 species of fungi. They feed by releasing digestive enzymes into their surroundings,
and then absorbing the digested nutrients into their cells.
o Structure of Fungi:
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Yeasts are unicellular – they are individual oval or cylindrical cells.
Most fungi are multicellular – they are structurally diverse. However, their body forms are generalized.
 They basic structural unit that makes up the body is called the HYPHAE.
 The bulk of the organism is in the form of a branching network called a MYCELIUM. This is the
part that lives in the soil and on other nutritious substances (such as living, dying, or dead wood
and animal bodies).
 The part of the fungus you see above the ground is the reproductive structure called the
FRUITING BODY.
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o Fungal Nutrition:
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Most animals consume food and then digest it. Fungi do the opposite.
Fungi release enzymes that break down food externally. Then, the fungi absorb nutrients from the food
through their cell membranes.
There are 4 ways in which fungi obtain their nutrients:
Type of Nutrition
Parasitic
Predatory
Mutualistic
Saprobial
Description
-Parasitic fungi absorb nutrients from the living cells of a host organism.
-They usually live inside the host organism.
-Predatory fungi are soil fungi whose mycelia have specialized structures for trapping
prey.
-Mutualistic fungi have partnerships with other organisms, often plants or protists.
-Usually, the mycelia cover the roots of a plant. The mycelia increase the absorptive
surface of the plant roots, allowing the plants to take up more nutrients. Then, the
fungus receives sugar from the plant.
-A saprobe is an organism that feeds on dead organisms or organic wastes.
-Saprobial fungi are decomposers whose mycelia absorb nutrients from dead or
decaying organic matter.
-These fungi play a big role in recycling nutrients in ecosystems.
o Fungal Reproduction:
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Most fungi have both asexual and sexual methods of reproduction.
Asexual and sexual life cycles in fungi can be by SPORE PRODUCTION (which involves the production
of trillions of single-celled spores from fruiting bodies).
As well, some unicellular yeasts use BUDDING (a smaller cell that develops while attached to the parent
cell, and eventually is pinched off).
Finally, asexual fungi can reproduce by FRAGMENTATION (a piece of mycelium breaks and forms a
new individual).
o Lichens
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LICHEN are an organism that results from a mutualistic relationship between a fungus and a
photosynthetic plant or algae. It is called a composite organism.
They are an important source of food for many animals, including deer, elk, and caribou.
They can survive in very harsh conditions and temperatures.
Are used to make litmus paper.
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THE ANIMAL KINGDOM
o What is an Animal?
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They are eukaryotic, multicellular organisms. Their cells do not have cell walls.
They are heterotrophs that usually ingest and then digest their food.
They are usually mobile, or have the ability to move, in at least one stage of their lives.
They reproduce sexually and produce an embryo that undergoes stages of development.
o Characteristics Used to Classify Animals:
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One of the main characteristics used to classify animals is the presence of a backbone.
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Animals without a backbone are called INVERTEBRATES. They make up 95% of animals.
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Animals with an internal skeleton and a backbone are called VERTEBRATES.
a) Levels of Organization:
o Animals are classified on the basis of differences in their structure, tissues, and organ systems.
o The cells of animals are organized into tissues (a tissue is a group of similar cells that is specialized to
perform specific tasks).
o For example) In the human body, muscle tissue generates the force needed to move the body.
o Tissues are organized into organs and organ systems, with particular functions.
b) Number of Body Layers:
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Most animals have 3 layers of cells: The ectoderm is the outer layer; the mesoderm is the middle layer;
and the endoderm is the inner layer.
In humans – the ectoderm produces the skin, nerve tissue and some sense organs; the mesoderm
produces the muscles, blood, kidneys, and reproductive organs; and the endoderm produces the lungs,
liver, pancreas, bladder, and stomach lining.
c) Symmetry and Body Plans:
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Some animals have an asymmetrical body plan, which means that their body shape is irregular.
RADIAL SYMMETRY is a body plan that can be divided along any plane, through a central axis, into
roughly equal halves. This includes corals and jellyfish.
BILATERAL SYMMETRY is a body plan that can be divided along one plane, through the central axis,
into equal halves. This includes worms, insects, and vertebrates.
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d) Body Cavity:
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Some animals have their digestive tract and other organs suspended in a fluid-filled body cavity
called the COELOM. This includes some worms, insects, and vertebrates called coelomates.
Animals without a coelom, such as corals, jellyfish, and flatworms, are called acoelomates.
e) Segmentation:
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SEGMENTATION is the division of the body into repetitive sections, or segments.
An advantage to segmentation is that a single segment can be damaged, and the other
segments will continue to function properly. Secondly, mobility is more effective because
segments move independently.
Example) worms and scorpions.
f) Movement:
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Some animals, such as sponges and sea anemones, are sessile (stationary) as adults.
The evolution of nerve and muscle tissue in animals has allowed the development of both
complex and fast movements.
g) Reproduction:
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Most animals reproduce sexually using gametic reproduction. In gametic reproduction, a zygote
develops into a diploid organism, and the only haploid cells are eggs and sperm.
Zygotes are produced by either external or internal fertilization.
External fertilization occurs when gametes combine outside the body. It is common among
animals that live in aquatic environments, such as fish and amphibians.
Internal fertilization occurs when the egg and sperm combine inside the female body.
o Invertebrate Animals:
o Sponges and Cnidarians:
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Sponges have an asymmetrical body plant and they have no tissues.
Their body consists of 2 layers of cells.
They are sessile as adults.
They feed by trapping food particles in water.
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Cnidarians include freshwater hydras, marine jellyfish, and corals. They do have tissues and a
simple nervous system. They swim and capture prey using stinging tentacles.
o Worms:
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Flatworms are the least complex worms – they are acoelomates with 3 layers of cells.
They have a simple nervous system, including an eyespot at the head end.
It has a segmented body.
o Molluscs:
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It is the 2nd most diverse animal phylum, with about 100,000 species.
They all have bilateral symmetry, 3 layers of cells, a coelom, and 2 body openings.
Examples) Clams, mussels, oysters, scallops, octopuses, and squids.
They all have similar body plans – A MANTLE surrounds the internal organs and secretes
calcium carbonate for the shell. The Mollusc’s body contains organ systems. They also have a
muscular foot for movement.
o Echinoderms:
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Includes sea stars, sea urchins, sea cucumbers, and sand dollars.
They are marine animals with radial symmetry, spiny endoskeletons, and tube feet.
The endoskeleton is an internal skeleton that protects organs and provides support for muscle
attachment.
Tube feet are small, muscular, fluid-filled tubes that work as suction cups for movement.
o Arthropods:
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It is the largest animal phylum. It includes spiders, scorpions, crustaceans, and insects.
Arthropod means jointed foot – they have legs that are made up of movable sections,
connected by joints.
They also have a body divided by segments and a hard EXOSKELETON (an external skeleton
that protects organs, provides support for muscle attachment, and protects against water loss
and predation). The exoskeleton is composed of protein and chitin, and is periodically shed as
the animal grows.
o Vertebrate Animals:
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Vertebrate animals have several important features in common. One significant feature is a
NOTOCHORD (a rod-shaped structure that extends the length of the body, used for the attachment of
movement muscles). The second significant feature is a dorsal nerve cord (a tube-shaped cord that
extends along the back of the body).
o Fish:
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Half of all vertebrate species are fish. They occupy freshwater and saltwater habitats.
Fish are divided into 2 groups:
 The first group is sharks and rays. They have a skeleton of CARTILAGE (the flexible,
non-bony tough material found in vertebrate endoskeletons).
 The second group is the bony fish. This includes guppies, tuna, and salmon. These bony
fish have a skeleton made up of bone. They usually have an air sac called a swim
bladder (which they fill with oxygen and then empty it).
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o Amphibians:
 TETRAPODS are vertebrates with 2 pairs of limbs – including amphibians, reptiles, birds, and
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mammals. The first limbs were modified fins. The structural diversity of limbs has increased
with time – leading to legs in frogs, the wings of birds, and the arms of humans.
Most amphibians use their moist skin to assist in gas exchange.
Most amphibians reproduce using external reproduction.
o Reptiles:
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There are 4 major groups, placed in 3 orders: lizards and snakes; turtles; and crocodilians.
Reptiles have body scales that create a waterproof barrier that helps prevent dehydration in dry
air. Reptiles use only their lungs for gas exchange since they lack the moist skin of amphibians.
Fertilization in reptiles is internal. Once the egg and sperm join inside the female, several layers
of membranes develop around the egg prior to the secretion of the shell. The egg is called an
amniotic egg.
o Birds:
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Evidence suggests that birds are related to at least one group of dinosaurs. This makes them
highly modified reptiles.
However, reptiles are ECTOTHERMIC (rely on environmental heat for determining internal body
temperature) and have a 3-chambered heart. Birds are ENDOTHERMIC (use metabolic heat to
maintain a high, constant body temperature) and have a 4-chambered heart.
Birds also have a high body temperature and a unique respiratory system (it promotes one-way
movement of air through the use of air sacs connected to the lungs).
Most birds can fly (since they have feathered wings, hollow bones, and a toothless skull)
o Mammals:
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The most distinctive feature of mammals is the MAMMARY GLANDS (a mammalian gland that
produces and secretes milk for nourishing developing young) in females.
Mammals are also distinguished by having hair. Hair is used for insulation, camouflage,
waterproofing, and communication.
Mammals are endothermic, have a 4-chambered heart, and have highly developed brains.
Mammals are divided into 3 main groups:
Mammal Group
Monotremes
Marsupials
Placental Mammals
Distinguishing Feature
-Egg laying mammals
-Found only in Australia and New Guinea
-Only living examples are the duck-billed platypus and the echidna.
-Pouched mammals
-Have a short gestation period
-Mostly found in Australia
-Include koala bears, and kangaroos.
-Opossum is the only North American marsupial
-Have a PLACENTA (an organ in the pregnant uterus that exchanges nutrients and
oxygen between the mother and the developing offspring).
-Includes: bears, bats, whales, primates, and humans.
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THE BIODIVERSITY CRISIS
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MASS EXTINCTION is a large-scale dying out of a large percentage of all living organisms within an area over a
short time.
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BIODIVERSITY CRISIS is the current decline in genetic, species, and ecosystem diversity that may represent a
mass extinction.
o Climate Change and Food Sources:
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For example) The population of caribou and reindeer populations have decreased by 60% over the last
3 decades – mainly due to changes in climate. Since the climate has become warmer, the warmer
summers favour plant growth instead of lichen growth, resulting in less winter forages. And, since there
is now more snow and freezing rain at times, further reducing the ability of the caribou to access the
lichens that remain.
o Climate Change and Habitat:
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Temperatures decrease with increasing altitudes, producing different vegetation zones. Plant
communities that thrive in warmer temperatures are found at low elevations; and cold-tolerant plant
communities are found at higher altitudes.
The problem is that as the climate changes, mountainous regions are experiencing long-term warming in
an upward direction. The communities at the top of mountains are very vulnerable to the upward shift
in vegetation zones. This is because warming results in habitat loss, since it reduces the amount of
suitable land area on which these plants can grow. As well, the remaining area becomes more
fragmented. This leads to isolated plant populations and a lack of genetic diversity.
o Climate Change and Reproduction:
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In many reptiles, the temperature at which the eggs are incubated determines the sex of the offspring.
Warmer temperatures create females, while cooler temperatures create males. With warmer
temperatures, more females are being created without enough males, making reproduction a problem.
o Climate Change, Plants, and Animal Pollinators:
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A plant and its pollinator (such as an insect, bird, or bat) are dependent on each other. The pollinator
needs the plant for food, and the plant needs the pollinator to move pollen from one flower to another.
A big part of the success of the relationship depends on timing – the pollinator must be in the right stage
of its life cycle or migration cycle to be present when the plant flowers.
Warmer temperatures have made plants flower earlier than usual. It can also bring insect pollinators
emerging from winter conditions too early.
o Climate Change and Aquatic Ecosystems:
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As the temperature increases in aquatic ecosystems, invertebrate growth rates increase. Also, adult
insects emerge earlier, and the male to female sex ratio can be altered.
Changes in temperatures can also alter the appetite of fish. Overall, the growth of the fish is reduced,
and their consumption of oxygen is increased.
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