Name: ____________________________ Homework/class-work Unit#7 photosynthesis and cellular respiration(25 points)
Think and try every question. There is no reason for a blank response or an I don’t know. Any blanks will receive a zero.
Every assignment must be done on a separate piece of paper. Each assignment must be complete, neat, in complete sentences
and done on time for full credit. Any assignment may be used as a take home or pop quiz at any time. One missing or late
assignment will lose 5 points, 2 will lose 15 points, 3 will be considered incomplete and given a zero.
1. Photosynthesis and cellular respiration reading:
Date:______________________
Photosynthesis
A great variety of living things on Earth, including all green plants,
synthesize their food from simple molecules, such as carbon dioxide
and water. For this process, the organisms require energy, and that
energy is derived from sunlight.
The figure shows the energy relationships in living cells. Light energy
is captured in the chloroplasts of plant cells and used to synthesize
glucose molecules. In the process, oxygen (O2) is released as a waste
product. The glucose and oxygen are then used in the mitochondria
of the plant and animal cell, and the energy is released and used to fuel
the synthesis of ATP from ADP and P. In the reaction, CO2 and
water are released in the mitochondria to be reused in photosynthesis
in the chloroplasts.
The process of utilizing energy to synthesize carbohydrate molecules
is referred to as photosynthesis. Photosynthesis is actually two
separate processes. In the first process, energy-rich electrons flow
through a series of coenzymes and other molecules. This electron
energy is trapped. During the trapping process, adenosine
triphosphate (ATP) molecules and molecules of nicotinamide
adenine dinucleotide phosphate hydrogen (NADPH) are formed.
Both ATP and NADPH are rich in energy. These molecules are used
in the second half of the process, where carbon dioxide molecules are
bound into carbohydrates to form organic substances such as glucose.
Chloroplasts
The organelle in which photosynthesis occurs (in the leaves and stems of plants) is
called the chloroplast. Chloroplasts are relatively large organelles, containing a
watery, protein-rich fluid called stroma. The stroma contains many small
structures composed of membranes that resemble stacks of coins. Each stack is a
granum (the plural form is grana). Each membrane in the stack is a thylakoid.
Within the thylakoid membranes of the granum, many of the reactions of
photosynthesis take place.
Chlorophyll
Pigment molecules capture sunlight in the chloroplasts. In the reaction center there
are about 200 molecules of a green pigment called chlorophyll and about 50
molecules of another family of pigments called carotenoids. In the reaction
center, the energy of sunlight is converted to chemical energy. The center is
sometimes called a light-harvesting antenna. The energy captured in the reaction
centers drive the production of ATP in the chloroplasts.
The process of photosynthesis
The process of photosynthesis is conveniently divided into two parts: the energy-fixing reaction (also called the light reactions) and
the carbon-fixing reaction (also called the light-independent reaction or the Calvin cycle)
Light reactions (energy-fixing reactions)
The light reactions of photosynthesis begin when light is absorbed in the thylakoid membranes. The energy of the sunlight captured
in the reaction center, activates electrons to jump out of the chlorophyll molecules. These electrons pass through a series of
cytochromes in the nearby electron-transport system.
After passing through the electron transport system, the energy-rich electrons eventually reduce NADP. This reduction occurs as two
electrons join NADP and energize the molecule. Because NADP acquires two negatively charged electrons, it attracts two positively
charged protons to balance the charges. Consequently, the NADP molecule is reduced to NADPH, a molecule that contains much
energy.
Electrons that are lost during the reduction of NADP
into NADPH are replaced by taking them from the
water molecules. Each split water molecule releases
two electrons that enter the chlorophyll molecules to
replace those lost. Another product of the split water
molecules is oxygen. Two oxygen atoms combine with
one another to form molecular oxygen, which is given
off as the byproduct of photosynthesis. Oxygen fills
the atmosphere and is used by all oxygen breathing
organisms, including plant and animal cells.
The ATP production in the energy-fixing reactions of
photosynthesis occurs by the process of chemiosmosis.
Essentially, this process consists of a rush of protons
across a membrane (the thylakoid membrane, in this
case), accompanied by the synthesis of ATP molecules.
Biochemists have calculated that the proton
concentration on one side of the thylakoid is 10,000
time that on the opposite side of the membrane. ATP is
formed in the energy-fixing reactions along with the
NADPH formed in the main reactions. Both ATP and
NADPH provide the energy necessary for the synthesis of carbohydrates that occurs in the second major set of events in
photosynthesis.
Light independent reactions (carbon-fixing reactions)
Glucose and other carbohydrates are synthesized in the carbon-fixing reaction of photosynthesis, often called the Calvin cycle for
Melvin Calvin, who performed much of the biochemical research. This phase of photosynthesis occurs in the stroma of the plant cell.
In the carbon-fixing reaction, an essential material is carbon dioxide, which is obtained from the atmosphere. The carbon dioxide is
attached to a five-carbon compound called ribulose diphosphate. A series of reaction convert the newly formed six-carbon
compound into glucose by using the energy in ATP and NADPH made during the light dependent reactions.
Glucose can be stored in plants in many ways. In some plants, the glucose molecules are joined to one another to form starch
molecules. Potato plants, for example, store starch in tubers (underground stems). In some plants, glucose converts to fructose (fruit
sugar), and the energy is stored in this form. In still other plants, fructose combines with glucose to form sucrose, commonly known
as table sugar. Plant cells obtain energy for their activities from these molecules. Animals use the same forms of glucose by
consuming plants and delivering the molecules to their cells. All living things on Earth depend in some way on photosynthesis. It is
the main mechanism for bringing the energy of sunlight into living systems and making that energy available for the chemical
reactions taking place in cells.
Cellular respiration
Organisms, such as plants, can
trap the energy in sunlight
through photosynthesis and
store it in the chemical bonds
or carbohydrates molecules.
The principle carbohydrate
formed through photosynthesis
is glucose. Other organisms,
such as animals, fungi,
protozoa, and a large portion of
bacteria, are unable to perform
this process. Therefore, these
organisms must rely on the
carbohydrates formed in plants
to obtain the energy necessary for their metabolic processes.
Animals and other organisms obtain the energy available in carbohydrates through the process of cellular respiration. Cells take the
carbohydrates into their cytoplasm, and though a complex series of metabolic processes, they break down the carbohydrates and
release the energy. The energy is generally not needed immediately; rather it is used to combine adenosine diphosphate (ADP) with
phosphate ions to form adenosine triphosphate (ATP) molecules. The ATP can then be used for processes in the cells that require
energy, much as a battery powers a mechanical device.
During the process of cellular respiration, carbon dioxide is given off. This carbon dioxide can be used by plant cells during
photosynthesis to form new carbohydrates. Also in the process of cellular respiration, oxygen gas is required to serve as an acceptor
of electrons. This oxygen is identical to oxygen gas given off during photosynthesis. Thus, there is an interrelationship between the
process of photosynthesis and cellular respiration, namely the entrapment of energy available in sunlight and the provision of the
energy for cellular processes in the form of ATP.
Reading Questions:
1. Do plants and animals both go through photosynthesis? Why or why not? Do both plants and animals go through cellular
respiration? Why or why not?
6. Briefly describe what occurs during the light dependent reaction?
8. What is NADPH? What is its role in the process of photosynthesis?
9. Where does photosynthesis take place? What molecules absorb sunlight?
10. Describe the physical structure of the chloroplast.
11. Briefly describe what happens in the light independent reactions?
14. Do plants produce oxygen? Explain.
4. Photosynthesis and advanced questions:
Date: ____________________
1. How do plants get energy from their environment?
2. When animals shiver in the cold, muscles move almost uncontrollably. Suggest how shivering helps as animal survive in cold.
3. Elodea springs were under white light, and the rate of photosynthesis was measured by counting the number of oxygen bubbles per
minute for ten minutes. Predict the rate of photosynthesis if a piece of red cellophane were placed over the white light.
4. A window plant native to the desert of South Africa has leaves that grow almost entirely under ground with only the transparent tip
of the leaf protruding above the soil surface. Suggest how this adaptation aids the survival of this plant.
5. Why would you not expect to find mitochondria in anaerobic organisms?
6. Cells of an onion are clear (white) why? The cells of an onion do not go through photosynthesis. Why? Only some cells in a plant
have chloroplast but all cells in a plant have mitochondria. Why?
7. Write the chemical equation for photosynthesis:
A.
Tell where each molecule is used or made.
B.
Briefly explain how each is used or made.
8. Which process do you think plants carry out faster, photosynthesis or respiration? Why?
5. Review:
Date: _______________
1. An organism that makes it’s own food.
2. What does ATP stand for?
3. Does ATP or ADP have more energy?
4. What does ROY G. BIV stand for?
5. Plants have light-absorbing substances called.
16. Where does the Calvin cycle take place?
17. What are the two starting materials for the Calvin cycle?
18. What two compounds made in the light reactions are used during the Calvin cycle?