Part 1: Photosynthesis Activity
Leaves are like small factories that produce food for the plant. Different parts
of the leaf have different jobs. The veins in a leaf are bundles of tiny tubes that
carry water and minerals to the leaf and return food from the leaf to the rest of
the plant. Veins also help to support the leaf.
On the underside of the leaf are small openings or pores called the stomata.
The stomata serve as the lungs of the leaf allowing air to enter. The stomata
allow the evaporation of water and the release of oxygen during the night.
The outer layers of the leaf are covered with a waxy layer which prevents the
leaf from drying out.
Leaves are green because they contain small bodies in the cells called
chloroplasts. The chloroplasts contain a green pigment called chlorophyll.
This green material gives the leaf its color.
With the help of chlorophyll and energy from the sun, a leaf can change
lifeless substances into food. This process is called photosynthesis. Plants
need water (H2O) and carbon dioxide (CO2) to make food through the
process of photosynthesis. The water is gathered by the plant's roots.
Carbon dioxide is gathered from the air through the stomata.
The leaf uses chlorophyll and sunlight to change the water and carbon
dioxide into oxygen and glucose (sugar). This sugar is mixed with water and
sent to other parts of the plant to be used by the plant as food. The oxygen is
released into the air through the stomata. This is usually written as:
This is usually read as carbon dioxide plus water in the presence of light
and chlorophyll produces oxygen and sugar glucose.
Activity 1: Use the following terms to draw your own photosynthesis diagram.
Draw the parts you need (a leaf, sun, etc.). Use arrows to show what the
reactants (substances coming in) and products (substances going out) are.
Make sure your diagram is fully labeled with words and arrows. Write the
chemical equation for photosynthesis at the bottom of your diagram.
Carbon dioxide (CO2)
Water (H2O)
Carbohydrates (sugars, glucose, C6H12O6)
Sunlight
Oxygen (O2)
Leaf
ATP
chloroplast
Part 2: Respiration Activity
The overall reaction of cellular respiration:
C6H12O6 + 6O2 + 6H2O -----> 6CO2 + 12H2O + energy
...which is the opposite of photosynthesis!
This is done in a series of enzyme reactions to allow gradual release of the energy
stored in sugar. The entire process is known as CELLULAR RESPIRATION.
Cellular respiration can be
a. aerobic (done in the presence of oxygen) or
b. anaerobic (done in the absence of oxygen).
aerobic is far more efficient (i.e., more ATP's can be made per sugar
molecule) at extracting the energy stored in sugar!
There are two basic steps to the aerobic cycle:
1. Glycolysis - the splitting of glycogen/glucose into smaller sugars yields two
ATP's
-occurs in the cytoplasm of a cell
2. The smaller sugars are broken down further with the use of oxygen which
releases water and carbon dioxide as waste. As long as oxygen is present, 32
ATP’s are created from this step.
-occurs in the mitochondria (as long as O2 is present)
If no oxygen is present (anaerobic), (which all occurs in the cytoplasm)
1. Glycolysis
2. Fermentation
a. NO additional ATP’s are made.
Part 2: Use the following terms to make a diagram of respiration. Again, make sure
the diagram is fully labeled with arrows showing reactants and products. Write the
equation for respiration at the bottom of the diagram.
Sugar (glucose)(C6H12O6)
oxygen (O2)
ATP
Glycolysis
carbon dioxide (CO2)
lots of ATP
Aerobic respiration
fermentation
cytoplasm
Anaerobic respiration
mitochondria
water (H2O)
Part 3: Energy Cycles
WHY DO PLANTS MAKE SUGAR?
FOR YOU?
Yeah. Right.
NO. Plants make sugar for their own use! As they collect solar energy and store it as sugar,
they are also *burning* that sugar and using the energy to run their own chemical
reactions.
Fortunately for the consumers (heterotrophs), plants usually have some energy left over
after photosynthesis. This is what becomes the BIOMASS (dry weight) of the plant, and it's
what the heterotrophs eat, stealing the plant's hard-won energy! Energy and matter cycle
among the organisms via photosynthesis, cellular respiration and other processes.
All organisms interact with one another in ECOSYSTEMS (the living and non-living
components of a habitat, considered collectively) and one of the most fundamental ways in
which they interact is by eating and being eaten.
Different levels of feeding, or TROPHIC LEVELS ("trophism" - from the Greek word
troph, meaning "to eat") are named on the basis of how many levels they are from the first
level, plants
The source of all food is the activity of autotrophs, mainly photosynthesis by plants.
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They are called producers because only they can manufacture food from inorganic raw materials.
This food feeds herbivores, called primary consumers.
Carnivores that feed on herbivores are called secondary consumers.
Carnivores that feed on other carnivores are tertiary (or higher) consumers.
DECOMPOSERS - digest organic molecules and break them down into their inorganic
components. Depending on what dead thing they're eating, their trophic levels can be just about
anywhere above primary producer.
Such a path of food consumption is called a food chain.
Each level of consumption in a food chain is called a trophic level.
The table gives one example of a food chain and the trophic levels represented in it.
Grass
Grasshopper
Toad
Snake
Hawk
→
→
→
→
→
Bacteria of
decay
In general,
Autotrophs
Herbivores
(Producers) (Primary Consumers)
→
→
Carnivores
(Secondary, tertiary, etc. consumers)
→
Decomposers
As you might guess, most organisms eat more than one kind of food, and a
particular species isn't always eating at the same trophic level (Can you think
of an example of this, using yourself?).
This means that the trophic levels do not form a straight line, or "chain" from
one level to the next. Rather, they interlace to form more of a WEB. Ecologists
call these complex feeding relationships the FOOD WEB, and every ecosystem
is characterized by a specific type of food web.
The Pyramid of Energy
Conversions efficiencies are always much less than 100%. At each link in a food chain, a
substantial portion of the sun's energy — originally trapped by a photosynthesizing autotroph —
is dissipated back to the environment (ultimately as heat).
Thus it follows that the total amount of energy stored in the bodies of a given population is
dependent on its trophic level.
For example, the total amount of energy in a population of toads must necessarily be far less than
that in the insects on which they feed.
The insects, in turn, have only a fraction of the energy stored in the plants on which they feed.
This decrease in the total available energy at each higher trophic level is called the pyramid of
energy.
Food chain example: grass rabbitfox (read like: grass is eaten by rabbit which
is eaten by fox.)
Part 3: Create a food web consisting of at least 3 food chains. Make sure each
chain has at least 3 trophic levels and no more than 4 plus a decomposer. Draw
arrows to show what “is eaten by” what. Circle the organisms in the food web
that have the greatest biomass. Leave room on the sides to write additional
information discussed in class.