Life Science Study Guide
Unit 1: Life Cycles
Key Concepts
- Organisms
undergo observable changes during their life cycles including birth,
growth, development, reproduction, and death.
- We
can compare the life cycles of various plants and animals.
- Some
animals, such as frogs and lady bugs, pass through distinctly different
life stages with very different appearances. Most plants, such as tomato
plants, develop from seeds into small plants that resemble the adult form.
Key
Concept 1: Organisms undergo observable changes during their life cycles,
including birth, growth and development, reproduction, and death.
An organism’s life cycle refers to each stage of its life;
birth, life, and death. By reproducing, a species’ life cycle is repeated over
and over with the main goal is to continue to survive in its environment.
Key
Concept 2: We can compare the life cycles of various plants and animals.
Most organisms change their appearance from birth to the adult
stage. However, those changes can be simple, like the life cycle of tomato
plants, or complicated, like the life cycle of ladybugs and frogs. Emerging
from a seed or an egg, life begins small and fragile. A seedling or young
animal must be nurtured to continue growth into the adult stage of life.
Students can find examples of the various stages in the life cycle of plants
and animals in the library, on the Internet, outside at home or school, or in
local fields.
Remind students to respect the environment and protect the plants
and animals they are observing. Students can record observations on digital
cameras, in sketchbooks, or make descriptions on a tape recorder. They must
have permission of property owners if they collect specimens. Also, discuss
safe and proper collection methods and what type of specimens are appropriate
to collect.
Key
Concept 3: Some animals, such as frogs and lady bugs, pass through distinctly
different life stages with very different appearances, while most plants, such
as tomato plants, develop from seeds into small plants that resemble the adult
form.
Plants demonstrate a relatively simple process of life. Beginning
with the seed of the plant placed in the ground through an act of nature or by
human hand, eventually it will begin to grow and break through the crust of the
ground to become a seedling, which is just a small plant. Young plants
(seedlings), such as tomato plants usually resemble their parents,
though smaller in size. Their leaves, color, and shape will copy their parents.
As a seedling becomes an adult plant, the general appearance will not change;
it will only be larger with more limbs, branches, and leaves. Once a plant
reaches the adult stage, it prepares for reproduction by creating seeds. A
plant sometimes protects its seed by either encasing it in a hard shell, such as
a walnut, or a soft, fleshy covering, such as a tomato. When the tomato falls
from the vine, this protection gives the seeds a chance to begin to grow. Some
plants use flowers to attract insects to carry their seeds to other plants for
fertilization. When the seed falls to the ground, and if is fortunate enough to
settle into good soil and receives water, it will begin to grow into a seedling
and the life cycle will be repeated.
Many animals, including fish, mammals, reptiles, and birds have
relatively simple life cycles: they are born (either alive from their mothers
or hatched from eggs), grow up, and become adults. Most young
animals are similar to their parents, just smaller, and slowly
grow into adulthood. This form of life process is called direct development.
Amphibians, such as frogs, have completely different
life cycles.
Frogs change their appearances from childhood to adulthood. This is called
complete metamorphosis. (Third grade students are not responsible for this
term). Frogs lay floating clumps of soft, jellylike eggs in water. The eggs
hatch into a water breathing, fishlike tadpole with gills and no limbs. Slowly,
legs develop, and the tadpole tail shortens. Adult frogs become air breathing,
land animals, with fully-grown legs and lungs.
Insects also experience a complete change in their appearances during their
life cycle. For example, butterflies and ladybugs have four stages of life:
(1) Egg, or unborn stage
(2) Larva, the young stage when most feeding is done
and the insects look like worms
(3) Pupa, the no-feeding stage when the insect is
camouflaged insides a sac and changes from a worm shape to a full grown insect
(4) Adult, the stage when the insect leaves the pupa,
usually has wings, and is ready for reproduction
Unit 2: Adaptations and Traits
Key Concepts
· The structures of plants and
animals are adapted to particular environments.
· Structures of some animals, such
as the blubber of seals or the fur of rabbits, help some animals survive in
cold weather conditions.
· Structures, such as the waxy
coating of a cactus or the presence of spines instead of leaves, help some
plants survive in hot, dry conditions.
- Some
characteristics are inherited while others are learned in response to the
environment.
- Inherited
characteristics include mainly physical characteristics such as fins on a
fish, stripes on a tiger, and the yellow color of a daffodil.
- Learned
behaviors include using tools, such as a chimp’s use of sticks to retrieve
termites from mounds or a sea otter’s use of rocks to open shellfish.
Key
Concept 1: The structures of plants and animals are adapted to particular
environments.
Over 150 years ago, Charles Darwin, the English Naturalist,
observed that species of animals and plants that were able to survive and
reproduce had adapted to the challenges of their environments. An adaptation is a physical or behavioral
characteristic that helps an animal or plant survive in its environment. Some
organisms are better suited for some environments than others, and for any
organism in any environment, it must adapt to survive. Adaptations do not
happen rapidly; they are processes of change that takes generations and
generations.
For example, in the rainforest with lots of plant life, the
competition is for sunlight. As a result, plants in rainforests grow taller and
faster than neighboring plants to reach the sunlight. Several types of plants
in rainforests have adapted to the tall canopy of trees by simply growing as
vines straight up tree trunks to reach the sunlight, whereas, trees and plants
in cold tundra regions must adapt instead to the constantly blowing, freezing
wind in an unprotected landscape. As a result, tundra trees grow only a few
inches tall and stay near the ground to avoid the howling wind. Plants are also
smaller in this frigid environment to conserve energy for their short growing
season.
Key
Concept 2: Structures of some animals, such as the blubber of seals or the fur
of rabbits, help some animals survive in cold weather conditions.
Structures are how the parts are put
together on a plant or animal. Because mammals living in cold climates have to
conserve body heat, they need structures that will keep their bodies warm.
Seals, whales, and polar bears have blubber as an extra layer of fat under
their skin that helps them insulate their bodies to adapt to freezing water
temperatures. The double-layered fur on Arctic hares and polar bears are
examples of cold climate adaptations that help animals insulate warm air
trapped among the dense hairs in their fur.
Other cold weather adaptations include large bodies with short
legs and tails to conserve body heat, large padded feet to walk on snow, and
short snouts (noses). All of these structures have the function or purpose of
keeping an animal warm. These adaptations are inherited traits that have been
passed down through the generations to help an organism survive in its
surroundings. Organisms also learn behaviors that help them adapt to their
environment.
Key
Concept 3: Structures, such as the waxy coating of a cactus or the presence of
spines instead of leaves, help these plants survive in hot, dry conditions.
Generally, evaporation occurs on plants’ leaves due to the release
of moisture here. However, water is scarce in the desert so plants, like cacti,
have leaves known as spines that are adapted for only allowing a bare minimum
of evaporation to be able to occur due to their shape. The spines also protect
against predators looking for a water source inside the cactus. The thick areas
of a cactus are actually enlarged stems coated in a waxy substance that
prevents water evaporation. These stems also function as photosynthesis sites,
but in a different way than most plants. Instead of opening their pores to
absorb carbon dioxide during the day, which would evaporate water, the cactus
waits until night when temperatures are cooler to open their pores and store
carbon dioxide. During the day with pores closed, cactus use the stored carbon
dioxide, combined with sunlight and water, to begin photosynthesis, thereby
conserving water. Cacti can store gallons of water in their trunks for use when
rain is scarce. Their root systems spread far and wide across the surface of
the ground to help catch every drop of water. Every part of a plant is adapted
to respond to the environment around it.
Key
Concept 4: Some characteristics are inherited, while others are learned in
response to the environment.
Inherited characteristics are passed from
parent to offspring through reproduction. Offspring are the children, or
offshoots, from a parent. The number of limbs, the color of fur, and the shape
of a beak are examples of traits (internal or external characteristic or
feature) that are inherited from the parent organism. These characteristics are
not received after birth, but are part of the genetic code passed on to
offspring during reproduction and determine internal and external structures.Behaviors, on the other hand, are movements or
actions that are taught or learned after birth. Riding a bicycle, knowing where
to find prey, and rolling over for a treat are examples of behaviors that are
not inherited, but must be learned.
Key
Concept 5: Inherited characteristics include mainly physical characteristics,
such as fins on a fish, stripes on a tiger, or the yellow color of a daffodil.
Every structure, size, whether it be big or small, color, shape,
and the number of parts in every plant or animal is inherited through traits
passed down from parent to offspring. Every physical characteristic a living thing is born with represents an inherited trait.
Although general characteristics among the same species are similar and passed
on to each generation, such as all spiders have eight legs, the individual
variations that make each plant or animal unique result from the random
combination of genes passed down from the parents.
Key
Concept 6: Learned behaviors include using tools, such as a chimp’s use of
sticks to retrieve termites from mounds or a sea otter’s use of pebbles to open
shellfish.
Although students have seen dogs and circus animals learn tricks,
a surprising number of learned behaviors exist in the animal kingdom where
rocks and sticks become useful tools.
Unit 3: Environments
Key Concepts
· Environments have specific
physical characteristics that provide food, water, air, and protection to
populations and communities in an ecosystem.
· Changes to an environment can
affect whether certain organisms can survive in that ecosystem.
· Environmental changes such as
floods, droughts, or fires will cause some organisms to perish or move while
permitting other organisms to thrive.
Key
Concept 1: Environments have specific physical characteristics that provide
food, water, air, or protection to populations and communities in an ecosystem.
Every environment (an
organism’s surroundings) is a result of a delicate balance of living elements
(organisms) and nonliving elements (objects, landforms, weather, and climate).
An ecosystem is
a community of living and nonliving things in their natural environment. In
order for any population (living things that belong to the same group in the
same area) or a community (group of different populations sharing an
environment) to survive (stay alive), the living and nonliving elements must provide basic needs:
food, water, air, and protection. Any adjustment to any of these factors can
result in a dramatic change in an environment’s appearance or composition. Many
influences on an environment can come from nature itself. Plants and animals
must respond to changes in the ecosystem, or they can perish (die).
Key
Concept 2: Changes to an environment can affect whether certain organisms can
survive in that ecosystem.
Plants and animals respond to changes from very different sets of
living and nonliving elements depending on the ecosystem in which they live.
For example, winter and summer months look very different in the far north
tundra of North America. In July, it is common to see lots of greenery and
animals roaming and grazing for food. However, in January, the ecosystem is
frozen and quiet as many animals migrate to warmer locations. In forest
ecosystems, summer brings warmth (nonliving element), greenery, and an
abundance of insects (living element), and winter produces chilly weather
(nonliving element), and the grass and plants become brown and dormant.
Temperature changes can have powerful effects on living organisms in
ecosystems. It is common for some animals to react to the sudden changes in
temperature by hibernating after finding a safe place to hide from predators
and the harsh weather.
Nature is not the only thing to cause changes to an ecosystem.
Living organisms can also be responsible for changes within an environment. For
example, when a population of beavers builds a dam, it can create a body of
water like a pond or lake. This body of water then attracts other species of
animals because of the increase in availability of freshwater. Also, the
species that typically thrive in a pond of lake begin to grow in numbers and
thrive in this newfound body of water.
The physical characteristics of an environment (nonliving element)
can also determine the suitability for life of organisms. The high, craggy
mountains of forest ecosystems in the northwestern United States are ideal
habitats (animal homes) for mountain goats, whereas grassland ecosystems of the
prairies are the environment of choice for the pronghorn antelope.
Key
Concept 3: Environmental changes, such as floods, droughts, or fires, will
cause some organisms to perish or move, while permitting other organisms to
thrive.
Rapid changes to an environment
are those that happen quickly. Some examples of rapid changes include
hurricanes, floods, earthquakes, a volcano erupting, etc. Hurricanes bring high
winds and huge amounts of water. When water from the ocean crashes onto land,
the living organisms that typically survive in freshwater are threatened and
may not survive. Living organisms have two outcomes that face them when they
are hit by a rapid change to their ecosystem. First, if they are capable, they
can migrate to escape the harmful conditions. If that is not an option for the
organism, it may die. Nature often finds a balance when environments change;
some organisms may die, while others find an opportunity to survive
Unit 4: Food Chains
Key Concepts
· Energy that moves through a food
chain originally comes from the Sun.
· Plants get their energy from the
Sun, and animals get their energy from plants and other organisms.
· Removal of an organism from a
food chain can affect other organisms.
Key
Concept 1: Energy that moves through a food chain originally comes from the
Sun.
Most students realize that they have to eat food in order to have
energy to run and play. All organisms, from the smallest plant to the largest
elephant, must have food to give them energy to live and grow. A food chain
is the path of food energy that
comes from the Sun is and passed on to organisms in an ecosystem. The energy
that is transferred in the food chain begins with the Sun, which gives off heat
and light energy. Green plants have special cells that can absorb sunlight and
combine that energy with water and carbon dioxide to produce glucose, a sugar
that plants use for food. That process is called photosynthesis. The original
energy from the Sun is stored in plants, which are at the bottom of the food
chain in an ecosystem. An ecosystem consists of all the living and nonliving
things surrounding an organism. When food chains are illustrated to show the
path of energy that is transferred from one organism to another, the Sun should
be part of that image to show where the energy started. Food chain
arrows should
always flow from the beginning (the Sun) to the end of the food chain (the last
organism). The amount of energy that is transferred becomes smaller and smaller
along the food chain because much of the energy is used by each organism for
growth, movement, and cellular activity before that organism is eaten.
Key
Concept 2: Plants get their energy from the Sun and animals get their energy
from plants and other organisms.
Plants get their energy from the Sun through the process of
photosynthesis. All food chains begin with the energy from the Sun transferring
energy to plant producers. In the illustration below, the energy that plants
absorb from the Sun is passed on to plant-eating animals, such as the
grasshopper. Some of the energy stored in the grasshopper is passed on to
meat-eating animals, such as the frog. Then, the snake eats the frog. Finally,
the small amount of energy left is passed on to the last meat-eating animal
when the hawk eats the snake. The amount of energy that is transferred becomes
smaller and smaller along the food chain because much of the energy is used up
by each organism along the way for growth, movement, and cellular activity
before that organism is eaten. Plants are called producers because they make
their own food for energy. Animals, not able to produce their own food, are
required to eat plants or other animals to gain energy and are called
consumers. In other words, a food chain will always begin with the Sun’s energy
passed on to a plant producer, then usually to a plant-eating consumer, then to
one or more meat-eating consumers like the frog, snake, and eagle.
Key
Concept 3: Removal of an organism from a food chain can affect other organisms.
In order to ensure a successful, interactive ecosystem, there must
be a proper balance in the populations of organisms. Any change in the
population of any organism in a food chain will affect other organisms.
For example, imagine a food chain in which all the snakes in an
area are killed or removed. There will be fewer predators eating the field mice
and the field mice population will increase. If there are no snakes, the eagles
might have a smaller food supply and the number of eagles may dwindle. If a
fire destroys the shrubs, there will be fewer insects in the shrubs for the
frogs to eat and so on. If any population of organisms changes in some way,
either increasing or decreasing, it will affect other organisms in the community.
If frogs are removed from a pond, the insect population will
increase due to lack of insect predators. However, the plants that the insects
eat will begin to decrease due to an increased number of insects. The animals
that feed on the frogs, such as snakes or other meat eaters, will be
endangered.
In another example, if field bees suddenly decline, there will be
fewer insects pollinating flowers, so the flowering plant population will
decrease, thereby, providing less food for plant eaters who will also dwindle
in population. The effects on ecosystems are never simple when a member of the
food chain changes. Changes in a food chain impact the whole ecosystem.
