Wednesday 16 December 2015
Prepare a concept map on photosynthesis after reading the content given below (Class X) kindly complete the worksheets
PHOTOSYNTHESIS
Plants may be viewed as
carbon sinks,
removing carbon dioxide from the atmosphere and oceans by fixing it into
organic chemicals. Plants also produce some carbon dioxide by their
respiration, but this is quickly used by photosynthesis. Plants also convert
energy from light into chemical energy of C-C covalent bonds. Animals are
carbon dioxide producers that derive their energy from carbohydrates and other
chemicals produced by plants by the process of photosynthesis.
The balance between the
plant carbon dioxide removal and animal carbon dioxide generation is equalized
also by the formation of carbonates in the oceans. This removes excess carbon dioxide
from the air and water (both of which are in equilibrium with regard to carbon
dioxide).
Photosynthesis is
the process by which plants, some bacteria, and some protistans use the energy
from sunlight to produce sugar, which cellular
respiration converts into ATP, the
"fuel" used by all living things. The conversion of unusable sunlight
energy into usable chemical energy, is associated with the actions of the green
pigment chlorophyll. Most of
the time, the photosynthetic process uses water and releases the oxygen that we
absolutely must have to stay alive. Oh yes, we need the food as well!
We can write the overall
reaction of this process as:
6H2O + 6CO2 ---------->
C6H12O6+ 6O2
Diagram
of a typical plant, showing the inputs and outputs of the photosynthetic
process.
Plants are the only
photosynthetic organisms to have leaves (and
not all plants have leaves). A leaf may be viewed as a solar collector crammed
full of photosynthetic cells.
The raw materials of
photosynthesis, water and carbon dioxide, enter the cells of the leaf, and the
products of photosynthesis, sugar and oxygen, leave the leaf.
Cross
section of a leaf, showing the anatomical features important to the study of
photosynthesis: stoma, guard cell, mesophyll cells, and vein.
Water enters the root and
is transported up to the leaves through specialized plant cells known as xylem (pronounces
zigh-lem). Land plants must guard against drying out (desiccation) and so have
evolved specialized structures known as stomata to allow gas to enter and leave
the leaf. Carbon dioxide cannot pass through the protective waxy layer covering
the leaf (cuticle), but it can enter the leaf through an opening (the stoma;
plural = stomata; Greek for hole) flanked by two guard cells. Likewise, oxygen
produced during photosynthesis can only pass out of the leaf through the opened
stomata. Unfortunately for the plant, while these gases are moving between the
inside and outside of the leaf, a great deal water is also lost. Cottonwood
trees, for example, will lose 100 gallons of water per hour during hot desert
days. Carbon dioxide enters single-celled and aquatic autotrophs through no
specialized structures.
White light is separated
into the different colors (=wavelengths) of light by passing it through a
prism.The order of colors is determined by the wavelength of light. Visible
light is one small part of the electromagnetic spectrum. The longer the
wavelength of visible light, the more red the color. Likewise the shorter
wavelengths are towards the violet side of the spectrum. Wavelengths longer
than red are referred to as infrared, while those shorter than violet are
ultraviolet.
Chlorophyll
and Accessory Pigment
A pigment is any substance
that absorbs light. The color of the pigment comes from the wavelengths of
light reflected (in other words, those not absorbed). Chlorophyll, the
green pigment common to all photosynthetic cells, absorbs all wavelengths of
visible light except green, which it reflects to be detected by our eyes. Black
pigments absorb all of the wavelengths that strike them. White pigments/lighter
colors reflect all or almost all of the energy striking them. Pigments have
their own characteristic absorption spectra, the absorption pattern of a given
pigment.
The thylakoid is the structural unit of
photosynthesis. Both photosynthetic prokaryotes and eukaryotes have these
flattened sacs/vesicles containing photosynthetic chemicals. Only eukaryotes
have chloroplasts with a surrounding membrane.
Thylakoids are stacked like
pancakes in stacks known collectively as grana. The areas between grana are referred to
as stroma. While the mitochondrion has two membrane
systems, the chloroplast has three, forming three compartments.
Photosynthesis is a two
stage process. The first process is the Light Dependent Process (Light
Reactions), requires the direct energy of light to make energy
carrier molecules that are used in the second process. The Light Independent
Process (or Dark
Reactions) occurs when the products of the Light Reaction are used to
form C-C covalent bonds of carbohydrates. The Dark Reactions can usually occur
in the dark, if the energy carriers from the light process are present. Recent
evidence suggests that a major enzyme of the Dark Reaction is indirectly
stimulated by light, thus the term Dark Reaction is somewhat of a misnomer. The
Light Reactions occur in the grana and the Dark Reactions take place in
the stroma of the chloroplasts.
In the Light Dependent
Processes (Light Reactions) light strikes chlorophyll a in such a way as to
excite electrons to a higher energy state. In a series of reactions the energy
is converted (along an electron
transport process) into ATP and NADPH. Water
is split in the process, releasing oxygen as a by-product of the reaction. The
ATP and NADPH are used to make C-C bonds in the Light Independent Process (Dark
Reactions).
In the Light Independent
Process, carbon dioxide from the atmosphere (or water for aquatic/marine
organisms) is captured and modified by the addition of Hydrogen to form
carbohydrates (general formula of carbohydrates is [CH2O]n).
The incorporation of carbon dioxide into organic compounds is known as carbon
fixation. The energy for this comes from the first phase of the photosynthetic
process. Living systems cannot directly utilize light energy, but can, through
a complicated series of reactions, convert it into C-C bond energy that can be
released by glycolysis and other metabolic processes.
Carbon-Fixing Reactions are
also known as the Dark Reactions (or Light Independent Reactions). Carbon
dioxide enters single-celled and aquatic autotrophs through no specialized
structures, diffusing into the cells. Land plants must guard against drying out
(desiccation) and so have evolved specialized structures known as stomata to
allow gas to enter and leave the leaf. The Calvin
Cycle occurs in the stroma of chloroplasts (where would it
occur in a prokaryote?). Carbon dioxide is captured by the chemical ribulose biphosphate (RuBP). RuBP is a 5-C
chemical. Six molecules of carbon dioxide enter the Calvin Cycle, eventually
producing one molecule of glucose. .
The first stable product of
the Calvin Cycle is phosphoglycerate (PGA), a 3-C chemical. The
energy from ATP and NADPH energy
carriers generated by the photosystems is used to attach phosphates to (phosphorylate) the PGA. Eventually there are 12
molecules of glyceraldehyde phosphate (also known as phosphoglyceraldehyde or PGAL, a 3-C), two of
which are removed from the cycle to make a glucose. The
remaining PGAL molecules are converted by ATP energy to reform 6 RuBP molecules, and thus start the cycle
again. Remember the complexity of life, each reaction in this process, as in
Kreb's Cycle, is catalyzed by a different reaction-specific enzyme.
Photosynthesis is a crucial energy-converting process by
which plants produce molecular oxygen and carbohydrates by the use of photons
present in the light. The natural source of light, the sun, helps the green
colored plants to fix the atmospheric carbon dioxide in to usable molecular
oxygen, that we humans happen to breathe.
They help in maintaining a balanced level of oxygen and
carbon dioxide in the atmosphere. Almost all the oxygen present in the
atmosphere can be attributed to the process of photosynthesis, which also means
that respiration and photosynthesis go together. Also, the chemical energy
stored in plants is transferred to animal and humans when they consume plant
matter. Photosynthesis can therefore be considered the ultimate source of life
for nearly all plants and animals by providing the source of energy that drives
all their metabolic processes.
In a nutshell, the process of photosynthesis benefits us in the following ways:
1. Photosynthesis converts inorganic raw
materials into food, that provides our ecosystem with energy.
2. Green plants provide organic food to all the
animals and humans.
3. Rare fossil fuels like coal, petroleum and
natural gas are formed through the degradation of the past plant and animal parts, which were
originally formed by photosynthesis.
4. Plant products like timber, rubber, herbs,
medicines resin and oils are derived from photosynthesis.
5. Photosynthesis helps in providing oxygen in
the atmosphere required by all living organisms.
6.
Photosynthesis
decreases the concentration of carbon dioxide and other harmful industrial
wastes that lead to respiration problems in living beings.
1
WORKSHEET (HOTS)
Q1.Study
the general equation for photosynthesis and be able to indicate in which
process each reactant is used and each product is produced.
Q2.List
the two major processes of photosynthesis and state what occurs in those sets
of reactions.
Q3.Distinguish
between organisms known as autotrophs and those known as heterotrophs as
pertains to their modes of nutrition.
Q4.Explain
the significance of the ATP/ADP cycle.
Q5.Describe
the nature of light and how it is associated with the release of electrons from
a photosystem.
Q6.Describe
how the pigments found on thylakoid membranes are organized into photosystems
and how they relate to photon light energy.
Q7.Describe
the role that chlorophylls and the other pigments found in chloroplasts play to
initiate the light-dependent reactions.
Q8.Describe
the function of electron transport systems in the thylakoid membrane.
Q9.Explain
the role of the two energy-carrying molecules produced in the light-dependent
reactions (ATP and NADPH) in the light-independent reactions.
Q10.Describe
the Calvin-Benson cycle in terms of its reactants and products.
Q11.How
photosynthesis relates to acid rain and the carbon cycle..
MCQ Based
Worksheet.
1. The organic molecule
produced directly by photosynthesis is:
a) lipids; b) sugar; c)
amino acids; d) DNA
2. The photosynthetic
process removes ___ from the environment.
a) water; b) sugar; c) oxygen; d) chlorophyll;
e) carbon dioxide
3. The process of splitting
water to release hydrogens and electrons occurs during the _____ process.
a) light dependent b) light independent; c) carbon fixation;
d) carbon photophosphorylation;
4. The process of fixing
carbon dioxide into carbohydrates occurs in the ____ process. a) light
dependent; b) light independent; c) ATP synthesis; d) carbon
photophosphorylation;
5. Carbon dioxide enters
the leaf through ____.
a) chloroplasts; b) stomata: c) cuticle; d)
mesophyll cells; e) leaf veins
6. The cellular transport
process by which carbon dioxide enters a leaf (and by which water vapor and
oxygen exit) is ___
. a) osmosis; b) active
transport; c. co- transport; d) diffusion; e) bulk flow
7. Which of the following
creatures would not be an autotroph?
a) cactus; b) cyanobacteria; c) fish; d) palm
tree; e) phytoplankton
8. The process by which
most of the world's autotrophs make their food is known as ____
. a) glycolysis; b)
photosynthesis; c) chemosynthesis; d) herbivory; e) C-4 cycle
9. The process of ___ is
how ADP + P are converted into ATP during the Light dependent process.
a) glycolysis; b) Calvin
Cycle; c) chemiosmosis; d) substrate-level phosphorylation; e)
Kreb's Cycle
10. Once ATP is converted
into ADP + P, it must be ____.
a) disassembled into
components (sugar, base, phosphates) and then ressembled; b) recharged by
chemiosmosis; c) converted into NADPH; d) processed by the glycolysis process;
e) converted from matter into energy.
11. Generally speaking, the
longer the wavelenght of light, the ___ the available energy of that light.
a) smaller; b) greater; c)
same
12. The section of the
electromagnetic spectrum used for photosynthesis is ___.
a) infrared; b) ultraviolet;
c) x-ray; d) visible light; e) none of the above
13. The colors of light in
the visible range (from longest wavelength to shortest) is ___.
a) ROYGBIV; b) VIBGYOR; c) GRBIYV; d)
ROYROGERS; e) EBGDF
14. The photosynthetic
pigment that is essential for the process to occur is ___.
a) chlorophyll a; b)
chlorophyll b; c) beta
carotene; d) xanthocyanin; e) fucoxanthin
15. When a pigment reflects
red light, _____.
a) all colors of light are absorbed; b) all
col;ors of light are reflected; c) green light is reflected, all others are
absorbed; d) red light is reflected, all others are absorbed; e) red light is
absorbed after it is reflected into the internal pigment molecules.
16. Chlorophyll a absorbs
light energy in the ____color range.
a) yellow-green; b)
red-organge; c) blue violet; d) a and b; e) b and c.
17. A photosystem is ___.
a) a collection of
hydrogen-pumping proteins; b) a collection of photosynthetic
pigments arranged in a thylakjoid membrane; c) a series of electron-accepting
proteins arranged in the thylakoid membrane; d. found only in prokaryotic
organisms; e) multiple copies of chlorophyll a located
in the stroma of the chloroplast.
18. The individual
flattened stacks of membrane material inside the chloroplast are known as ___.
a) grana; b) stroma; c)
thylakoids; d) cristae; e) matrix
19. The fluid-filled area
of the chloroplast is the ___.
a) grana; b) stroma; c)
thylakoids; d) cristae; e) matrix
20. The chloroplast
contains all of these except ___.
a) grana; b) stroma; c) DNA;
d) membranes; e) endoplasmic reticulum
21. The chloroplasts of
plants are most close in size to __.
a) unfertilized human eggs; b) human cheek
cells; c) human nerve cells; d) bacteria in the human mouth; e) viruses
22. Which of these
photosynthetic organisms does not have a chloroplast?
a) plants; b) red algae; c)
cyanobacteria; d) diatoms; e) dinoflagellates
23. The photoelectric
effect refers to ____.
a) emission of electrons
from a metal when energy of a critical wavelength strikes the metal; b) absorbtion
of electrons from the surrounding environment when energy of a critical
wavelength is nearby; c) emission of electrons from a metal when struck by any
wavelength of light; d) emission of electrons stored in the daytime when
stomata are open at night; e) release of NADPH and ATP energy during the Calvin
Cycvle when light iof a specific wavelength strikes the cell.
24. Light of the green
wavelengths is commonly absorbed by which accessory pigment?
a) chlorophyll a; b) chlorophyll b; c)
phycocyanin; d) beta carotene
25. The function of the
electron transport proteins in the thyakoid membranes is ___. a) production of
ADP by chemiosmosis; b) production of NADPH by substrate-level phosphorylation;
c) pumping of hydrogens into the thylakoid space for later generation of ATP by
chemiosmosis; d) pumping of hydrogens into the inner cristae space for later
generation of ATP by chemiosmosis; e) preparation of water for eventual
incorporation into glucose
26. ATP is known as the
energy currency of the cell because ____.
a) ATP is the most readily
usable form of energy for cells; b) ATP passes energy along in an electron
transport chain; c) ATP energy is passed to NADPH; d) ATP traps more energy
than is produced in its formation; e) only eukaryotic cells use this energy
currency.
27. Both cyclic and
noncyclic photophosphorylation produce ATP. We can infer that the purpose of
ATP in photosynthesis is to ____.
a) supply hydrogen to the
carbohydrate; b) supply carbon to the carbohydrate; c) supply
energy that can be used to form a carbohydrate; d) transfer oxygens from the
third phosphate group to the carbohydrate molecule; e) convert RuBP into PGA
28. The role of NADPH in
oxygen-producing photosynthesis is to ____.
a) supply hydrogen to
the carbohydrate; b) supply carbon to the carbohydrate; c) supply energy that
can be used to form a carbohydrate; d) transfer oxygens from the third
phosphate group to the carbohydrate molecule; e) convert RuBP into PGA.
29. The dark reactions
require all of these chemicals to proceed except ___.
a) ATP; b) NADPH; c) carbon
dioxide; d) RUBP; e) oxygen
30. The first stable
chemical formed by the Calvin Cycle is _____.
a) RUBP; b) RU/18; c) PGA;
d) PGAL; e) Rubisco
31. The hydrogen in the
carbohydrate produced by the Calvin Cycle comes from ___ a.) ATP; b) NADPH; c)
the environment if the pH is very acidic; d) a and b; e) a and c
32. The carbon incorporated
into the carbohydrate comes from ___.
a) ATP; b) NADPH; c) carbon
dioxide; d) glucose; e) organic molecules
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